Scipedia: Documents published in 2010

Optimizing the reliability of pipelined applications under throughput constraints

Scipedia content — Wed, 03 Feb 2021 20:15:40 +0100

Mapping a pipelined application onto a distributed and parallel platform is a challenging problem. The problem becomes even more difficult when multiple optimization criteria are involved, and when the target resources are heterogeneous (processors and communication links) and subject to failures. This report investigates the problem of mapping pipelined applications, consisting of a linear chain of stages executed in a pipeline way, onto such platforms. The objective is to optimize the reliability under a performance constraint, i.e., while guaranteeing a threshold throughput. In order to increase reliability, we replicate the execution of stages on multiple processors. We present complexity results, proving that this bi-criteria optimization problem is NP-hard. We then propose some heuristics, and present extensive experiments evaluating their performance.

Tactical Conflict Detection in Terminal Airspace

Scipedia content — Wed, 03 Feb 2021 20:05:39 +0100

traffic systems have long relied on automated short-term conflict prediction algorithms to warn controllers of impending conflicts (losses of separation). The complexity of terminal airspace has proven difficult for such systems as it often leads to excessive false alerts. Thus, the legacy system, called Conflict Alert, which provides short-term alerts in both en-route and terminal airspace currently, is often inhibited or degraded in areas where frequent false alerts occur, even though the alerts are provided only when an aircraft is in dangerous proximity of other aircraft. This research investigates how a minimal level of flight intent information may be used to improve short-term conflict detection in terminal airspace such that it can be used by the controller to maintain legal aircraft separation. The flight intent information includes a site-specific nominal arrival route and inferred altitude clearances in addition to the flight plan that includes the RNAV (Area Navigation) departure route. A new tactical conflict detection algorithm is proposed, which uses a single analytic trajectory, determined by the flight intent and the current state information of the aircraft, and includes a complex set of current, dynamic separation standards for terminal airspace to define losses of separation. The new algorithm is compared with an algorithm that imitates a known en-route algorithm and another that imitates Conflict Alert by analysis of false-alert rate and alert lead time with recent real-world data of arrival and departure operations and a large set of operational error cases from Dallas/Fort Worth TRACON (Terminal Radar Approach Control). The new algorithm yielded a false-alert rate of two per hour and an average alert lead time of 38 seconds.

An effective Lagrangian relaxation approach for multiple-mode crude oil transportation optimization

Scipedia content — Wed, 03 Feb 2021 20:02:54 +0100

International audience; In this paper, an crude oil transportation planning problem for an oil distributor is studied, in which crude oil is transported by tankers and pipelines from an unlimited supply center to a set of customer harbors to satisfy their dynamic demands over multiple periods. In the problem, inventory level and shortage level of crude oil at each customer are limited; both fully loaded and partially loaded tankers are allowed in the transportation of crude oil, and part of the tankers may be rented from a third party. The objective is to determine in each period the schedule of tankers and pipelines and the number of tankers of each type to be rented/returned at the supply center in order to minimize the total logistics cost. After formulating the problem as a mixed integer programming problem, we generalize an existing Lagrangian relaxation approach that only allows fully loaded tanks to one that allows both fully loaded and partially loaded tankers of the problem. Numerical experiments show that the new approach can find a near optimal solution of the problem of large size in a reasonable computation time.

Joint Integrity of Plastic Pressure Pipes in Municipal Service

Scipedia content — Wed, 03 Feb 2021 20:00:03 +0100

Plastic pressure pipes have been in use in North America for at least 40 years. Thermosetting plastics and thermoplastics commonly utilized in municipal pressure applications include fiberglass reinforced plastic pipes (FRP), polyvinyl chloride (PVC), high density polyethylene (HDPE), and more recently, fusible polyvinyl chloride (FPVC). Typically, these materials undergo hydrostatic pressure testing first in the manufacturing facility, then a second time in the field following installation. For field hydrostatic leakage testing, most pipe materials have an associated “allowable makeup water” or “allowable leakage” to accommodate the unique characteristics of the material as well as other irregularities during testing such as air in the line, temperature variations, and even instrument inaccuracies. Test methods and formulas for calculating makeup water usually vary based on the pipe material-specific standards. The wide discrepancies that exist for makeup water between different pipe materials do not place them on a level playing field for a given application. This paper is a review of both in-plant and in-field hydrostatic pressure testing and the topic of makeup water as outlined in AWWA standards for plastic materials. Quality control and qualification tests for joints of each pipe material standard are also reviewed. Recommendations are made for consideration by the Specification Engineering community for future revisions of standards pertaining to the field testing of plastic pipelines.

Evaluating skylines in the presence of equijoins

Scipedia content — Wed, 03 Feb 2021 19:57:36 +0100

When a database system is extended with the skyline operator, it is important to determine the most efficient way to execute a skyline query across tables with join operations. This paper describes a framework for evaluating skylines in the presence of equijoins, including: (1) the development of algorithms to answer such queries over large input tables in a non-blocking, pipeline fashion, which significantly speeds up the entire query evaluation time. These algorithms are built on top of the traditional relational Nested-Loop and the Sort-Merge join algorithms, which allows easy implementation of these methods in existing relational systems; (2) a novel method for estimating the skyline selectivity of the joined table; (3) evaluation of skyline computation based on the estimation method and the proposed evaluation techniques; and (4) a systematic experimental evaluation to validate our skyline evaluation framework.

Optimization of Trailer Transport

Scipedia content — Wed, 03 Feb 2021 19:56:24 +0100

20% of Europe's GHG emissions come from road transportation. Freight transport energy consumption, and thus emission levels, is tightly coupled to GDP. So if Europe seeks to dramatically reduce emissions without sacrificing wealth, it is crucial to address the issue of energy efficiency within the road transportation sector. Today, empty journeys comprise 25%-40% of all road haulage. To address that issue the goal of this project is to describe and solve an optimization program that utilizes the opportunity for trailer-haulers to exchange trailers mid-way. If successful, this will allow haulers to reduce their amount of empty journeys, benefiting the environment.

Effect of Proactive Braking on Traffic Flow and Road Throughput

Scipedia content — Wed, 03 Feb 2021 19:51:49 +0100

With the emergence of pervasive computing technologiesinto vehicles, driving has moved from an active task of steering towards an interaction or adaptation task withrespect to the driver-vehicle feedback loop. Up to now vehicular interfaces have mostly been evaluated from a single-driver single-car viewpoint, however, driving is a more complex task involving – beside the local interaction – the interrelationship between all the cars in a certain community of interest.The question investigated in this research work is how avehicle’s local parameters in a bulk of cars (e. g. vehicle speed, braking parameters) affect the global behavior of this system (traffic congestion, driving speed variation, throughput). To explore this, two traffic models have been developed and simulated using the NetLogo simulation environment.Simulation results have shown that the intercar distance hasa direct impact on both the throughput and the mean triptime. The proactive driving approach using vibro-tactile driver notification followed in the second, advanced model achieved much better results regarding these parameters compared to the simple manual-driven case. Finally, the outcomes legitimate the implementation of a prototype, and the installation of such a technology into a large number of cars in order to provide evidence for the improved traffic flow and decreased probability of traffic accidents in real driving scenarios.

Optimizing multi-layered networks towards a transparently optical internet

Scipedia content — Wed, 03 Feb 2021 19:51:15 +0100

Data transported on the Internet is handled by various technologies at different layers. The move towards an optically transparent internet will accelerate when it is justified by the cost structure of the various technologies. In this paper we describe a unified optimization framework for multiple technologies that interwork together based on the following assumptions: (i) every layer is associated with a unique technology, (ii) traffic can be modeled as a Poisson stream of flows, (iii) a flow will be served by a layer (technology) on a least-cost basis. This way traffic is split between the layers and if, under a given cost structure, a layer (e.g. IP) is found to have no "customers" (flows) because it is too costly relative to other layers (e.g. WDM), it will be excluded. In addition to technology choices we also optimize link dimensioning and virtual topology.

A Concept and Implementation of Optimized Operations of Airport Surface Traffic

Scipedia content — Wed, 03 Feb 2021 19:50:53 +0100

This paper presents a new concept of optimized surface operations at busy airports to improve the efficiency of taxi operations, as well as reduce environmental impacts. The suggested system architecture consists of the integration of two decoupled optimization algorithms. The Spot Release Planner provides sequence and timing advisories to tower controllers for releasing departure aircraft into the movement area to reduce taxi delay while achieving maximum throughput. The Runway Scheduler provides take-off sequence and arrival runway crossing sequence to the controllers to maximize the runway usage. The description of a prototype implementation of this integrated decision support tool for the airport control tower controllers is also provided. The prototype decision support tool was evaluated through a human-in-the-loop experiment, where both the Spot Release Planner and Runway Scheduler provided advisories to the Ground and Local Controllers. Initial results indicate the average number of stops made by each departure aircraft in the departure runway queue was reduced by more than half when the controllers were using the advisories, which resulted in reduced taxi times in the departure queue.

Safer systems: A NextGen Aviation Safety Strategic goal

Scipedia content — Wed, 03 Feb 2021 19:47:33 +0100

The Joint Planning and Development Office (JPDO), is charged by Congress with developing the concepts and plans for the Next Generation Air Transportation System (NextGen). The national aviation safety strategic plan (NASSP), developed by the Safety Working Group of the JPDO, focuses on establishing the goals, objectives, and strategies needed to realize the safety objectives of the NextGen integrated plan. The three goal areas of the NASSP are safer practices, safer systems, and safer worldwide. Safer practices emphasizes an integrated, systematic approach to safety risk management through implementation of formalized safety management systems (SMS) that incorporate safety data analysis processes, and the enhancement of methods for ensuring safety is an inherent characteristic of NextGen. Safer systems emphasizes implementation of safety-enhancing technologies, which will improve safety for human-centered interfaces and enhance the safety of airborne and ground-based systems. Safer worldwide encourages coordinating the adoption of the safer practices and safer systems technologies, policies and procedures worldwide, such that the maximum level of safety is achieved across air transportation system boundaries. This paper introduces the NASSP and its development, and focuses on the Safer systems elements of the NASSP, which incorporates three objectives for NextGen systems: (1) provide risk reducing system interfaces, (2) provide safety enhancements for airborne systems, and (3) provide safety enhancements for ground-based systems. The goal of this paper is to expose avionics and air traffic management system developers to NASSP objectives and safer systems strategies.

Analysis of a Real-Time Separation Assurance System with Integrated Time-in-Trail Spacing

Scipedia content — Wed, 03 Feb 2021 19:43:23 +0100

This paper describes the implementation and analysis of an integrated ground-based separation assurance and time-based metering prototype system into the Center-TRACON Automation System. The integration of this new capability accommodates constraints in four dimensions: position (x-y), altitude, and meter-fix crossing time. Experiments were conducted to evaluate the performance of the integrated system and its ability to handle traffic levels up to twice that of today. Results suggest that the integrated system reduces the number and magnitude of time-in-trail spacing violations. This benefit was achieved without adversely affecting the resolution success rate of the system. Also, the data suggest that the integrated system is relatively insensitive to an increase in traffic of twice the current levels.

A method to optimise train energy consumption combining manual energy efficient driving and scheduling

Scipedia content — Wed, 03 Feb 2021 19:41:54 +0100

This article presents a combined simulation and optimisation technique to optimise the energy consumption of a single manual-driving train service with inter-stations along a High Speed Line. For this purpose, the best energy efficient driving strategies along every stretch between two stations will be simulated with an accurate and detailed train simulator to obtain the run time and energy consumption Pareto curves of each stretch. Afterwards, an optimisation tool will distribute the available slack time for the service among the stretches, which will minimise the overall energy consumption of the service. The potential of the method will be shown with a case study at the end of the article.

Speech systems for autonomous unmanned aircraft: Enabling autonomous unmanned aircraft to communicate in civil airspace

Scipedia content — Wed, 03 Feb 2021 19:40:24 +0100

ce control is currently based largely on the exchange of speech between aircraft and Air Traffic Service Units, or between aircraft themselves. ICAO regulatory guidelines make no distinction between unmanned and manned aircraft, implying that unmanned aircraft will have to comply with requirements for radio communication in certain airspaces. The availability of speech capability is therefore imperative for autonomous operations in civil airspace. The paper assesses the feasibility of automated speech in unmanned aircraft given the current state of the art. CSIR Meraka Institute, Pretoria, South Africa Multilingual Speech Technologies, Northwest University, Vanderbijlpark, South Africa Department of Electrical and Electronic Engineering, Stellenbosch University, Matieland, South Afric

Variable interactions and exploring parameter space in an expensive optimisation problem: Optimising Short Term Conflict Alert

Scipedia content — Wed, 03 Feb 2021 19:33:05 +0100

Short Term Conflict Alert (STCA) systems provide warnings to air traffic controllers if aircraft are in danger of becoming too close. They are complex software programs, with many inter-dependent parameters that must be adjusted to achieve the best trade-off between wanted and nuisance alerts. We describe a multi-archive evolutionary algorithm for optimising regional parameter subsets in parallel, reducing the number of evaluations required to generate an estimated Pareto optimal Receiver Operating Characteristic (ROC), showing that it provides superior results to traditional single-archived algorithms. A method of ‘aggressive’ optimisation, designed to explore unknown parameter ranges in a ‘safe’ manner, is shown to yield more extensive and better converged estimated Pareto fronts.

The study of urban track transportation environmental noise and vibration prevention: floating slab track of Taipei MRT

Scipedia content — Wed, 03 Feb 2021 19:27:00 +0100

This paper will discuss how population density and traffic jams are common phenomena in modern society. Although roadway areas increase every year, traffic congestion still cannot be solved effectively. Land transportation is now turning to track transportation. Track transportation has many advantages, but the noise and vibration induced from the wheel/rail contact are sensitive issues to the neighboring residents along the line in the urban areas. Much complaint about noise and vibration arose from the residents along the Taipei MRT lines where the MRT tunnels were underneath the buildings, so Floating Slab Track (FST), one of the best solutions of noise and vibration prevention in the track engineering, was applied to the Taipei MRT. This paper studies the overall issues of the FST based on the localized consideration in the planning, design, construction, final noise and vibration performance measurement stages, including the mode of structure analyses, vibration isolating component, material, localize geotechnical parameters, type of structure, rail fastener, elastic coefficient, vibration isolating component, the actually performance of noise and vibration deduction, etc. The authors hope to share practical experience of the noise and vibration prevention/environmental pollution prevention in urban transportation to other railway systems or with academics in the environment and railway fields in other part of the world.

EScience in the cloud: A MODIS satellite data reprojection and reduction pipeline in the Windows Azure platform

Scipedia content — Wed, 03 Feb 2021 19:11:25 +0100

The combination of low-cost sensors, low-cost commodity computing, and the Internet is enabling a new era of data-intensive science. The dramatic increase in this data availability has created a new challenge for scientists: how to process the data. Scientists today are envisioning scientific computations on large scale data but are having difficulty designing software architectures to accommodate the large volume of the often heterogeneous and inconsistent data. In this paper, we introduce a particular instance of this challenge, and present our design and implementation of a MODIS satellite data reprojection and reduction pipeline in the Windows Azure cloud computing platform. This cloud-based pipeline is designed with a goal of hiding data complexities and subsequent data processing and transformation from end users. This pipeline is highly flexible and extensible to accommodate different science data processing tasks, and can be dynamically scaled to fulfill scientists' various computational requirements in a cost-efficient way. Experiments show that by running a practical large-scale science data processing job in the pipeline using 150 moderately-sized Azure virtual machine instances, we were able to produce analytical results in nearly 90× less time than was possible with a high-end desktop machine. To our knowledge, this is one of the first eScience applications to use the Windows Azure platform.

Adaptive online testing for efficient hard fault detection

Scipedia content — Wed, 03 Feb 2021 19:10:58 +0100

With growing semiconductor integration, the reliability of individual transistors is expected to rapidly decline in future technology generations. In such a scenario, processors would need to be equipped with fault tolerance mechanisms to tolerate in-field silicon defects. Periodic online testing is a popular technique to detect such failures; however, it tends to impose a heavy testing penalty. In this paper, we propose an adaptive online testing framework to significantly reduce the testing overhead. The proposed approach is unique in its ability to assess the hardware health and apply suitably detailed tests. Thus, a significant chunk of the testing time can be saved for the healthy components. We further extend the framework to work with the StageNet CMP fabric, which provides the flexibility to group together pipeline stages with similar health conditions, thereby reducing the overall testing burden. For a modest 2.6% sensor area overhead, the proposed scheme was able to achieve an 80% reduction in software test instructions over the lifetime of a 16-core CMP.

Assessment of CO2 storage potential in turkey, modeling and a prefeasibility study for injection into an oil field

Scipedia content — Wed, 03 Feb 2021 19:07:01 +0100

The large amount of CO 2 that can be mitigated by geologic storage had gained interest during the last 15 years. Acceptance of CCS under CDM is still under discussion(IEA, 2008) however there are several pilot or field scale projects and monitoring surveys that are underway which will make the technology better known and resolve the risks involved. This study involves assessment of possible geologic sites for CO 2 storage and calculation of CO 2 emissions from thermal power plants with capacities "500 MWe, cement factories, steel industry, sugar factories and refineries in Turkey. In emission calculations IPCC methodology is used. Coupling of sources and sinks resulted in a decision to use the emissions from a cement factory which is about 130 km from the selected oil field, Caylarbasi. The cement factory does not have capture facilities yet, but during modelling it was assumed that CO 2 is available at the factory site. According to the results of the model study, during the project life of 20 years, enhanced oil recovery effect of CO 2 lasts 8 years and 2 million barrels of oil will be produced and the remaining 12 years are modelled as CO 2 storage phase which shows 220 million Sm 3 of CO 2 can be stored.The transportation phase was designed with two alternatives, pipeline transport and transport by tankers. Economic evaluation at 100$/barrel of oil value, it will be possible to produce for 6 years. For the following years during CO 2 storage, incentives are necessary to cover operating costs so that project will continue for 20 years. Since the initial investment is already made, only the operational costs must be financed. Natural CO 2 field in Dodan is another possibility for geologic storage, the field has already produced 7 billion Sm 3 of CO 2 for the BatiRaman EOR project. Total capacity is about 10 billion Sm 3 . Other possible storage sites are deep saline aquifers, which were encountered in Thrace region, Central Anatolia and South Eastern Turkey and salt caverns of the soda mines. The experience of the Turkish oil industry for use of CO 2 in EOR application in BatiRaman field will be utilized if and when such an application is required.

Empirical Study of a National-Scale Distributed Intrusion Detection System: Backbone-Level Filtering of HTML Responses in China

Scipedia content — Wed, 03 Feb 2021 18:53:04 +0100

We present results from measurements of the filtering of HTTP HTML responses in China, which is based on string matching and TCP reset injection by backbone-level routers. This system, intended mainly for Internet censorship, is a national-scale filter based on intrusion detection system (IDS) technologies. Our results indicate that the Chinese censors discontinued this HTML response filtering for the majority of routes some time between August 2008 and January 2009 (other forms of censorship, including backbone-level GET request filtering, are still in place). In this paper, we give evidence to show that the distributed nature of this filtering system and the problems inherent to distributed filtering are likely among the reasons it was discontinued, in addition to potential traffic load problems. When the censor successfully detected a keyword in our measurements and attempted to reset the connection, their attempt to reset the connection was successful less than 51% of the time, due to late or out-of-sequence resets. In addition to shedding light on why HTML response filtering may have been discontinued by the censors, we document potential sources of uncertainty, which are due to routing and protocol dynamics, that could affect measurements of any form of censorship in any country. Between a single client IP address in China and several contiguous server IP addresses outside China, measurement results can be radically different. This is probably due to either traffic engineering or one node from a bank of IDS systems being chosen based on source IP address. Our data provides a unique opportunity to study a national-scale, distributed filtering system.

En route charges for ANSP revenue maximization

Scipedia content — Wed, 03 Feb 2021 18:51:13 +0100

In Europe, all Air Navigation Service Providers (ANSPs) finance their activities by charging airlines using their airspace. These ‘en route charges’ usually account for a significant part of the cost of a flight, and they can therefore influence the route choice: airlines may decide to fly longer routes to avoid countries with higher charges. If ANSPs want to maximize their revenues, they must choose the optimal charge to impose on their airspace. We show that this optimal charge can be identified through a Network Pricing Problem (NPP) formulation in the form of Bilevel Programming where the leader (i.e. the ANSP) owns a set of arcs (the airways in its national airspace) and charges the commodities (i.e. the flights) passing through them. As the en route charges are proportional to a Unit Rate value fixed by the ANSP, we are able to apply a similar methodology as in the case of a single toll arc for the NPP. By exploiting the structure of the problem, we propose an exact algorithm to compute the optimal Unit Rate and apply it to a case study relying on real air traffic data and realistic flight cost figures.

Abstract disponible à l'adresse suivante :http://www.icrat.org/downloads/bookofabstract.pdf

info:eu-repo/semantics/published

Intercontinental freight transport impacts: modeling and measuring choice effects

Scipedia content — Wed, 03 Feb 2021 18:37:12 +0100

This paper brings to the topic of world shipments an investigation of more efficient multimodal routes from the commercial (time and consumption costs) and environmental (impacts) points of view. In particular, the freight relations existing between Asia and Europe, through the Suez Canal, have been investigated because of the constant growth of these relations, despite the Europe-America ones. European destinations are reached by alternative paths, which use road or railway connections starting from the main Mediterranean (Genova, Venezia, Trieste) or North European (Antwerp, Rotterdam, Hamburg, Bremerhaven) ports. Environmental and commercial index values, evaluated for each possible route through an original software (written in the APL code), allow a comparison in order to identify which is the most sustainable transport chain relating to the different destinations. These results could be useful to re-organize a freight network in terms of managing and adjusting the existing infrastructures in order to obtain lower environmental impacts.

Tire/road friction coefficient estimation applied to road safety

Scipedia content — Wed, 03 Feb 2021 18:25:03 +0100

International audience; Recent statistics show that a large number of traffic accidents occur due to a loss of control on vehicle by the driver. This is mainly due to a loss of friction between tire and road. Many of these accidents could be avoided by introducing ADAS (Advanced Driver Assistance Systems) based on the detection of loss of tire/road friction. Friction (more specifically the maximum coefficient of friction) which is a parameter of tire/road interaction, mainly depends on the state of the road (dry, wet, snow, ice) and is closely related to the efforts at the tire level. In this paper, we propose, a new method for the estimation of the maximum tire/road friction coefficient, to automatically detect possible state of loss of friction which result in an abrupt change on the road state. This method is based on an iterative quadratic minimization of the error between the developed lateral force and the model of tire/road interaction. Results validate the application of the method.

A robust pipeline for rapid feature-based pre-alignment of dense range scans

Scipedia content — Wed, 03 Feb 2021 18:01:52 +0100

ming at reaching an interactive and simplified usage of high-resolution 3D acquisition systems, this paper presents a fast and automated technique for pre-alignment of dense range images. Starting from a multi-scale feature point extraction and description, a processing chain composed by feature matching and correspondence searching, ranking grouping and skimming is performed to select the most reliable correspondences over which the correct alignment is estimated. Pre-alignment is obtained in few seconds per million point images on a off-the-shelf PC architecture. The experimental setup aimed to demonstrate the system behavior with respect to a set of concurrent requirements and the obtained performance are significant in the perspective of a fast, robust and unconstrained 3D object reconstruction.

High throughput and low power dissipation in QCA pipelines using Bennett clocking

Scipedia content — Wed, 03 Feb 2021 17:54:45 +0100

This paper presents a detailed analysis of an architectural pipeline scheme for Quantum-dot Cellular Automata (QCA); this scheme utilizes the so-called Bennett clocking for attaining high throughput and low power dissipation. In this arrangement, computation stages (utilizing Bennett clocking) and memory stages combine the low power dissipation of reversible computing with the high throughput feature of a pipeline. An example of the application of the proposed scheme to an XOR tree circuit (parity generator) is presented; a detailed analysis of throughput and power consumption is provided to show the effectiveness of the proposed architectural solution for QCA.

Investigation of Practical Flight Envelope Protection Systems for Small Aircraft

Scipedia content — Wed, 03 Feb 2021 17:48:47 +0100

Personal air transportation utilizing small aircraft is a market that is expected to grow significantly in the future. For this segment, “stick and rudder” related accidents should be mitigated to guide this process in a safe manner. Instead of downscaling advanced and expensive fly-by-wire platforms that incorporate flight envelope protection found in commercial aircraft, a low cost solution should be considered. This paper focuses on a flight envelope protection system for small aircraft, to allow carefree maneuvering for the less experienced pilot. Preliminary results are obtained from an empirical comparison study in the time domain, between a PID based control limiting approach, a command limiting approach and a constrained Flight Control Law (FCL) approach using Model-based Predictive Control (MPC), with and without parametric model uncertainties. Investigation of the results reveals that, for this study, command limiting and MPC should be preferred over control limiting and that the practicality of command limiting outweighs the small performance increase of MPC.

Computation and evaluation of scheduled waiting time for railway networks

Scipedia content — Wed, 03 Feb 2021 17:37:15 +0100

This paper on the computation and evaluation of scheduled waiting time for railway networks is from the proceedings of the 12th International Conference on Computer System Design and Operation in Railways and Other Transit Systems, held in Beijing, China, in 2010. The authors contend that timetables are affected by the scheduled waiting time (SWT), which prolongs the travel times for trains and thereby passengers. SWT occurs when a train prevents another train from running at the necessary speed. The passengers may be further affected due to longer transfer times to other trains. SWT can be estimated analytically for a given timetable or by simulation of timetables and/or plans of operation. The simulation of SWT has the benefit of making it is possible to examine the entire network and thus improve the future timetable by analyzing different timetables and/or plans of operation. The authors review methods to examine SWT by simulation for both trains and passengers in entire railway networks. These simulations can be used to evaluate the consequences of different scenarios, including cases of disrupted operation.

Performance study of a Green Light Optimized Speed Advisory (GLOSA) application using an integrated cooperative ITS simulation platform

Scipedia content — Wed, 03 Feb 2021 17:36:40 +0100

This paper proposes a Green Light Optimized Speed Advisory (GLOSA) application implementation in a typical reference area, and presents the results of its performance analysis using an integrated cooperative ITS simulation platform. Our interest was to monitor the impacts of GLOSA on fuel and traffic efficiency by introducing metrics for average fuel consumption and average stop time behind a traffic light, respectively. For gathering the results we implemented a traffic scenario defining a single route through an urban area including two traffic lights. The simulations are varied for different penetration rates of GLOSA-equipped vehicles and traffic density. Our results indicate that GLOSA systems could improve fuel consumption and reduce traffic congestion in junctions. © 2011 IEEE.

The Trajectory Synthesizer Generalized Profile Interface

Scipedia content — Wed, 03 Feb 2021 17:34:50 +0100

The Trajectory Synthesizer is a software program that generates aircraft predictions for Air Traffic Management decision support tools. The Trajectory Synthesizer being used by researchers at NASA Ames Research Center was restricted in the number of trajectory types that could be generated. This limitation restricted its ability to support the evolving NextGen research requirements. The Generalized Profile Interface was developed to address this issue. It provides a flexible approach to describe the constraints applied to trajectory generation and may provide a method for interoperability between trajectory generators. It also supports the request and generation of new types of trajectory profiles not possible with the previous interface to the Trajectory Synthesizer. Other enhancements allow the Trajectory Synthesizer to meet the current and future needs of Air Traffic Management research.

Accelerated Monte Carlo Simulation for Safety Analysis of the Advanced Airspace Concept

Scipedia content — Wed, 03 Feb 2021 17:21:27 +0100

Safe separation of aircraft is a primary objective of any air traffic control system. An accelerated Monte Carlo approach was developed to assess the level of safety provided by a proposed next-generation air traffic control system. It combines features of fault tree and standard Monte Carlo methods. It runs more than one order of magnitude faster than the standard Monte Carlo method while providing risk estimates that only differ by about 10%. It also preserves component-level model fidelity that is difficult to maintain using the standard fault tree method. This balance of speed and fidelity allows sensitivity analysis to be completed in days instead of weeks or months with the standard Monte Carlo method. Results indicate that risk estimates are sensitive to transponder, pilot visual avoidance, and conflict detection failure probabilities.

VAN: Vehicle-assisted shortest-time path navigation

Scipedia content — Wed, 03 Feb 2021 17:13:14 +0100

Traffic congestion is a very serious problem in large cities. With the number of vehicles increasing rapidly, especially in cities whose economy is booming, the situation is getting even worse. In this paper, by leveraging the techniques of Vehicular Ad hoc Networks (VANETs) we present a dynamic navigation protocol called VAN for individual vehicles to find the shortest-time paths toward their given destinations. Specifically, a vehicle initiates a number of queries, which are routed by VANETs along different paths toward its destination. During query forwarding, the real-time road traffic information in each road segment is aggregated from multiple participating vehicles and returned to the source after the query reaches the destination. This information enables the source to calculate the shortest-time path. We also propose two forwarding optimization methods to reduce communication costs and an error handling mechanism to deal with abnormal circumstances. To evaluate its performance, we use the real traffic data of Beijing, including 2,308 road segments at two different times. Our simulation results demonstrate that our protocol, on average, could save around 30% driving time, compared to traveling along the shortest distance paths.

Safety Analysis of the Advanced Airspace Concept using Monte Carlo Simulation

Scipedia content — Wed, 03 Feb 2021 17:13:00 +0100

Safe separation of aircraft is a primary objective of all air traffic control systems. A probabilistic risk analysis of a next-generation air traffic control operational concept was conducted using Monte Carlo simulation. Results indicate that this safety-critical system would have a mean time between mid-air collisions of about 281 years in enroute airspace, which is around the desired target for an automated separation assurance function. Among the simulation trials that ended with mid-air collision, most involved failure to locate and track aircraft through radar or satellite positioning systems with the remainder due to conflict detection failure.

Moving towards Sustainability: New York State Department of Transportation's GreenLITES Story

Scipedia content — Wed, 03 Feb 2021 17:09:28 +0100

Transportation is an essential component of a sustainable society, and its benefits and costs are well studied at the project level. However, while methodologies for assessing environmental impacts are well developed, commensurate tools for assessing how transportation investments contribute to a sustainable society and what the mechanisms are for adjusting transportation programs to support a sustainable society are lacking. Under the current construct, transportation agencies avoid impacts but find it difficult to quantify benefits and align transportation programs with the greater needs of a sustainable society. The New York State Department of Transportation’s (NYSDOT’s) GreenLITES (Green Leadership In Transportation and Environmental Sustainability) program is a tool to advance the Department’s efforts to better align sustainability efforts in planning, design, construction, and maintenance operations with long term needs. Though the Department has been incorporating sustainable elements into its transportation projects for years, GreenLITES promotes increased awareness and best practices across program areas to enhance sustainability. GreenLITES also gives the Department a way to measure our performance, recognize best practices, and identify needed partnerships. GreenLITES was initially designed to assess capital project environmental sustainability elements. However, as GreenLITES was put into use, its potential to address transportation investments across a range of program areas became apparent, and a more holistic approach to the “triple bottom line” of economy, society, and environment has been adopted. As a result, the GreenLITES program expanded to include a growing collection of tools (rating systems, spreadsheets, and other metrics) to assess projects, plans, operations and maintenance programs, and regional programs. This paper describes NYSDOT’s GreenLITES program evolution from its environmentally based beginnings to a more comprehensive approach in support of a more sustainable society. The paper covers program vision, goals, benefits, management, and evolving next steps.

Gas Field Deliverability Forecasting: A Coupled Reservoir Simulator And Surface Facilities Model

Scipedia content — Wed, 03 Feb 2021 17:09:15 +0100

To determine if a gas contract can be satisified now and in the future, it is necessary to forecast the performance of the gas reservoir, the gas inflow into the sandface, the multiphase pressure losses in the wellbore and gathering system and the field facilities. Surface production models which rigorously model from the sandface to the plant gate are available. However, these surface packages model reservoirs simply, in most cases as tank-type reservoirs. Comprehensive 3 dimensional reservoir simulators are available, but typically only include simple surface networks which don`t adequately model multiphase flow in complex gathering systems. This paper describes the procedures used in a joint venture by two software vendors to combine an existing reservoir simulator and an existing surface facilities model into a single forecasting tool. Relatively small changes were made to each program. In the new model, the black oil reservoir simulator provides the formation pressure and water to gas ratio for each well. The surface facilities model then calculates the multiphase flow pressure losses in the wellbore and gathering system, plus the corresponding flow rates for each well. The actual production required from each well to satisfy the pipeline contractual requirements, over each time step, ismore » computed by the surface facilities model and relayed back to the reservoir simulator. The time step is determined dynamically according to the requirements of each program. The performance and results from the coupled model are compared to that of running each model separately for a gas storage field in the USA and for a gas production field with bottom-water. It is shown that running each model separately does not account for all the factors affecting the forecast.« le

Automated Microarchitectural Exploration for Achieving Throughput Targets in Pipelined Asynchronous Systems

Scipedia content — Wed, 03 Feb 2021 17:08:01 +0100

This paper presents a systematic approach for microarchitectural exploration in pipelined asynchronous systems, with the goal of achieving a specified throughput target while minimizing a given cost function (based on energy, area, etc.). The method includes a general framework that (i) allows for a rich extensible set of microarchitectural transformations for improving throughput; and (ii) can handle a variety of cost functions, such as area, energy, $E\\tau^2$ and the energy-area product.In general, the space of transformations that can be applied to a given circuit is potentially infinite because an arbitrarily long sequence of transformations may be applicable. To compound the challenge, the value of the given cost function can change non-monotonically as successive transformations are applied (e.g., some transformations increase area, while others decrease area), thereby making it difficult to apply a typical branch-and-bound approach to prune the search space. Our method employs simple but effective heuristic search strategies (including greedy, look ahead, and breadth-first). A key contribution is to identify commutativity of certain transformations, thereby pruning the design space significantly. The approach was automated and applied to a number of examples. Various throughput targets were assumed: from 50\\% to 20x throughput improvement. In each example, the approach was successful in meeting the throughput target.

Implementation of multi-layer techniques using FEDERICA, PASITO and OneLab network infrastructures

Scipedia content — Wed, 03 Feb 2021 17:03:56 +0100

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. V. López, J. L. Añamuro, V. Moreno, J. E. L. De Vergara, J. Aracil, C. García, J. P. Fernández-Palacios, and M. Izal, "Implementation of multi-layer techniques using FEDERICA, PASITO and OneLab network infrastructures", in 17th IEEE International Conference on Networks, ICON 2011, p. 89-94 This paper describes an implementation of multilayer techniques using the network infrastructure provided by FEDERICA, PASITO and OneLab projects. FEDERICA project provides a network infrastructure, based on virtualization capabilities in both network and computing resources, which creates custom-made virtual environments. PASITO is a layer- 2 network that connects universities and research centers in Spain. OneLab measurements tools allow carrying out highaccuracy active network measurements. Thanks to FEDERICA and PASITO, we have a multi-layer architecture where the traffic is routed based on the measurements of OneLab equipment. To carry out this experiment, we have developed a Multi-layer Traffic Engineering manager and an implementation of the Path Computation Element Protocol to solve the lack of a control plane in IP oriented networks. This work shows the feasibility of multilayer techniques as a convenient solution for network operators and it validates our Path Computation Element implementation. This work has been partially funded by the Spanish Ministry of Education and Science under project ANFORA (TEC2009-13385), by the Spanish Ministry of Industry, Tourism and Trade under PASITO project, and by the European Union under project OneLab2 (FP7-224263). Authors would like to thank Mauro Campanella (GARR, the project coordinator of FEDERICA) and Miguel Angel Sotos (RedIris) for their support to carry out this work.

Power Allocation Problem in Charging Electric Vehicles with Photovoltaic Production

Scipedia content — Wed, 03 Feb 2021 17:00:44 +0100

International audience; Power Allocation Problem in Charging Electric Vehicles with Photovoltaic Production

Emergency Landing Automation Aids: An Evaluation Inspired by US Airways Flight 1549

Scipedia content — Wed, 03 Feb 2021 16:56:33 +0100

The Hudson River emergency landing of US Airways Flight 1549 inspired aviation enthusiasts and citizens alike. The pilot's skill and composure were exceptional, clearly contributing to one of the most successful aircraft water ditchings possible. As we prepare for transition to a next-generation air transportation system, we are developing new technologies both to increase system capacity and efficiency and improve safety levels. This paper describes the practical application of an adaptive flight planning automation aid to the specific US Airways loss-of-thrust situation, demonstrating how this technology, if available, could have enabled a safe return to a LaGuardia runway. First, the adaptive flight planning architecture and its evolution are summarized, followed by an analysis of the Flight 1549 cockpit data recording time histories to identify pertinent features for our analysis. The adaptive flight planner was tasked with identifying emergency no-thrust landing plans for the A320 at a series of different delay times after the dual bird strike incident occurred. Our results show that LaGuardia airport runways were reachable so long as the approach is initiated within approximately sixteen seconds after the dual bird strike incident. This result is consistent with accident docket data published by the NTSB. Our results further illustrate how chances of a safe runway landing decrease as a function of delay, in this case due to being forced to land on a runway with suboptimal wind conditions, or ultimately being forced into a water ditch situation that may not always have the positive result of Flight 1549. Our adaptive flight planning software, written in C, computes landing flight plans in under a second on a single-core PC with no changes in this work from a pre-2009 implementation beyond A320 glide parameters. With sub-second real-time response, an emergency landing plan can be presented to the pilot just as he/she is beginning to consider options, maximizing the efficiency with which the plan can be executed. Further, with datalink capability, emergency flight plan information can be disseminated throughout the local air traffic network to maximize coordination efficiency.

Design and Simulation Methodology to Improve the Performance of Airspace Tube Networks

Scipedia content — Wed, 03 Feb 2021 16:55:38 +0100

The concept of high-traffic corridors and tube networks has been proposed to meet air traffic demand in the future. Several airspace tube network designs are available using different approaches. The utility of any transcontinental air traffic tube network is limited by the hub and spoke nature of air traffic in the US and the existence of over 50% of commercial flights with ranges less than 500 miles. Therefore, this paper describes an improved design methodology that accounts for the nature of the domestic air traffic that utilizes this network, characterizes the utility of a given tube network, and demonstrates possible limits in the efficacy of any tube network with current air traffic. Simulation results show that the number of aircraft flying within the redesigned tube network is comparable to the number flying through the other tube networks; however, since the length of the redesigned tube network is roughly half the length of the next-shortest tube network, the instantaneous occupancies are approximately twice that of the other tube designs.

Prediction and Use of Contrail Frequency Index for Contrail Reduction Strategies

Scipedia content — Wed, 03 Feb 2021 16:54:54 +0100

Methods have been proposed to reduce aircraft-induced contrails by on-board sensing and strategic planning. This paper describes a class of indices that predict potential aircraft-induced contrail formations one to six hours in advance. The indices can be used to identify air traffic control centers and altitudes with high potential for contrail formation. The results show that the index is affected more by the changing atmospheric conditions than by small daily variations in the nominal traffic. The analysis shows that the one-hour predicted contrail frequency index is highly correlated with the actual contrail frequency, with an average correlation coefficient of 0.85. The correlation coefficient is lower with longer prediction time, down to 0.52 for six-hour prediction. The average success rates for identifying air traffic control centers and altitudes with high contrail frequency are as high as 83.47% for one-hour prediction.

Private car transport and the 10% RES-T target - quantifying the contribution of EVs and biofuels

Scipedia content — Wed, 03 Feb 2021 16:45:23 +0100

In 2008, renewable energy accounted for less than 1% of final energy consumption in the Irish transport sector. In order to increase this share to 10% by 2020 as required under EU directive 2009/28/EC, the Irish government has introduced two specific measures: 10% of the transport fleet is to be powered by electricity by 2020, and an obligation on road transport fuel suppliers that biofuels account for a certain portion of their fuel sales. This study forecasts the impact of these existing measures towards meeting the 10% RES-T target by 2020, focussing on private car transport. The methodology presented is derived from a forecast of private car fuel demand based on a technological stock model of Ireland’s fleet. This paper demonstrates the use of this as a tool firstly as an energy forecasting technique and secondly as a method for evaluating the effects of policy measures on the technological composition and consequent renewable energy demand and related CO2emissions of private cars. Technological scenarios examined in this light are electric vehicles, compressed natural gas vehicles and biofuel blending

Headway generation with ROBERTO

Scipedia content — Wed, 03 Feb 2021 16:29:10 +0100

This paper on the use of the computer program ROBERTO for generating headway times is from the proceedings of the 12th International Conference on Computer System Design and Operation in Railways and Other Transit Systems, held in Beijing, China, in 2010. Rather than use the traditional solution for congestion in a railway network (the building of new infrastructure), the author reports on the search for alternative ways to solve capacity and quality bottlenecks on the Dutch rail service. The Dutch rail manager, ProRail, wants to evaluate and improve the timetable development process. By applying design principles and by other conditions, buffer times can be used in different timetable construction phases. An important design principle is the use of headway times to separate two trains in the timetable safely. To improve the knowledge and application of headway times, ProRail started the development of ROBERTO, a tool that can generate a large number of headway times. The aim is to compute headway times for specific situations and also to determine general headway times for use on a more global level. The input for ROBERTO is generated by simulating train characteristics, block section occupation times and signaling aspects. ROBERTO then combines possible conflicting train pairs and calculates the headway times. The authors conclude that the results and the calculation performance of ROBERTO are promising.

Complexity Analysis of Traffic in Corridors-in-the-Sky

Scipedia content — Wed, 03 Feb 2021 16:28:18 +0100

The corridors-in-the-sky concept imitates the highway system in ground transportation. The benefit expected from a corridor relies on its capability of handling high density traffic with negligible controller workload, the acceptance of extra fuel or distance, and the complexity reduction in underlying sectors. This work evaluates a selected corridor from these perspectives through simulations. To examine traffic inside the corridor, a corridor traffic simulation tool that can resolve conflicts is developed using C language. Prescribed conflict resolution maneuvers mimic corridor users’ behaviors and conflict resolution counts measure complexity. Different lane options and operational policies are proposed to examine their impacts on complexity. Fuel consumption is calculated and compared for corridor traffic. On the other hand, to investigate the complexity of non-corridor traffic in underlying sectors, the existing Airspace Concept Evaluation System tool is utilized along with the Automated Airspace Concept tool. The number of conflict resolutions is examined and treated as the complexity measurement. The results show heavy traffic can be managed with low complexity for a historical traffic schedule simulated with appropriate operational policies and lane options. For instance, with 608 flights and peak aircraft count of 100, only 84 actions need to be taken in a 24-hour period to resolve the conflicts for an 8-lane corridor. Compared with the fuel consumptions with great circle trajectories, the simulation of corridor traffic shows that the total extra fuel for corridor flights is 26,373 gallons, or 2.76%, which is 0.38% less than flying filed flight plans. Without taking climb and descent portions of corridor traffic, the complexity of underlying sectors is reduced by 17.71%. However the climb and descent portions will eliminate the reduction and the overall complexity of sectors is actually increased by 9.14%.

Buck-boost converter with fractional control for electric vehicles

Scipedia content — Wed, 03 Feb 2021 16:27:22 +0100

In this paper, non-integer order control is applied to improve the performance of a buck-boost dc-dc power converter with ultracapacitor based on state feedback techniques. The approach is based on stabilization in the Lyapunov's sense for linear rational-order systems. The ultracapacitor can overcome the classical problems of energy losses due to the use of batteries, giving more accuracy, autonomy and efficiency to the electrical vehicles.

Peer Reviewed

Semantics-based, strategic planning and composition of intermodal freight transport services in sea port hinterlands

Scipedia content — Wed, 03 Feb 2021 16:25:37 +0100

The modular logistic transport of goods on streets, railroads, inland water and sea is a complex and versatile process. It requires exact knowledge of geographic information, available logistical service providers and communication channels. This application paper describes IMOTRIS, an automated Intermodal Transport Routing Information System which is developed as a state-aided collaborative project that benefits from practical experience by contributions from different ports and transport service providers. We present a novel approach which combines service-oriented multi-modal route planning with semantic web technologies for the selection and ranking of transport and turnover services to create suitable and optimized complex logistic service chains. We utilize committed semantic descriptions of logistic services and their relationships with regard to the application context.

Simulation Of Highly Heterogeneous Traffic Flow Characteristics

Scipedia content — Wed, 03 Feb 2021 16:22:12 +0100

Simulation models are mathematical/logical representations of real-world systems. Microscopic traffic simulation models have been playing an important role in traffic engineering and particularly in cases, in which field studies, involving extensive data collection, over a wide range, is difficult or expensive to conduct. As the available simulation models can only replicate homogeneous traffic flow, a model of heterogeneous traffic flow, named, HETEROSIM was developed to simulate heterogeneous traffic flow. In this model, a dynamic stochastic type discrete event simulation is adopted in which the aspects of interest are analysed numerically with the aid of a computer program. The model was validated using field observed data of traffic flow. Then, the model was applied to measure one of the fundamental charactertistics of traffic flow, namely concentration. It is a broader term encompassing both density and occupancy. Occupancy takes into account the traffic composition and speed, and hence, occupancy is more meaningful than density. The concept of occupancy can not be directly applied under heterogeneous traffic conditions, as the traffic has no lane discipline. In this paper, a new concept named, ‘area-occupancy’ is proposed to measure traffic concentration.

Camera-based bidirectional reflectance measurement for road surface reflectivity classification

Scipedia content — Wed, 03 Feb 2021 16:16:45 +0100

In this paper we propose a novel framework for road reflectivity classification in cluttered traffic scenarios by measuring the bidirectional reflectance distribution function of road surfaces from inside a moving vehicle. The predominant restrictions in our application are a strongly limited field of observations and a weakly defined illumination environment. To overcome these problems, we estimate the parameters of an extended Oren-Nayar model that considers the diffuse and specular behavior of real-world surfaces and extrapolate the surface reflectivity measurements to unobservable angle combinations. Model ambiguities are decreased by utilizing standardized as well as customized reflection characteristics. In contrast to existing approaches that require special measurement setups, our approach can be implemented in vision-based driver assistance systems using radiometrically uncalibrated gray value cameras and GPS information. The effectiveness of our approach is demonstrated by a successful classification of the road surface reflectance of expressway scenes with low error rates.

An active approach to guaranteed arrival times based on traffic shaping

Scipedia content — Wed, 03 Feb 2021 16:16:06 +0100

To address the goal of providing drivers on highways with guaranteed arrival times, we propose a traffic management system that combines virtual slots with semi-autonomous driving to shape traffic and prevent congestion. Two algorithms that address aligning vehicles into slots and efficient merging from three to two lanes are proposed. Furthermore, an implementation and evaluation of these algorithms using the VISSIM traffic simulator is presented. Our initial results indicate that a slot-based system has the potential to be used to guarantee arrival times and provide a significant overall increase in efficiency when compared against a human driving model.

Motorway traffic surveillance and control

Scipedia content — Wed, 03 Feb 2021 16:12:42 +0100

Summarization: The available capacity of motorway networks is degraded in presence of traffic congestion, leading to reduced throughput, increased pollution and higher accident risk. The traffic flow efficiency may be increased via suitable application of several control measures, such as ramp metering, driver information, route guidance, variable speed limits and further link control measures. This paper presents a macroscopic traffic flow model along with selected validation results, followed by an overview of some generic traffic surveillance methods and control strategies for motorway networks. Limited simulation and field results demonstrating the efficiency of the presented methods are also provided. Παρουσιάστηκε στο: Dynamic Systems and Simulation Laboratory

Incorporating Active Runway Crossings in Airport Departure Scheduling

Scipedia content — Wed, 03 Feb 2021 16:10:07 +0100

mixed integer linear program is presented for deterministically scheduling departure and arrival aircraft at airport runways. This method addresses different schemes of managing the departure queuing area by treating it as first-in-first-out queues or as a simple par king area where any available aircraft can take-off ir respective of its relative sequence with others. In addition, this method explicitly considers separation criteria between successive aircraft and also incorporates an optional prioritization scheme using time windows. Multiple objectives pertaining to throughput and system delay are used independently. Results indicate improvement over a basic first-come-first-serve rule in both system delay and throughput. Minimizing system delay results in small deviations from optimal throughput, whereas minimizing throughput results in large deviations in system delay. Enhancements for computational efficiency are also presented in the form of reformulating certain constraints and defining additional inequalities for better bounds.

An innovative technique for water leak detection stemming from radio astronomy: A potential university technology transfer

Scipedia content — Wed, 03 Feb 2021 16:09:54 +0100

There have been many documented cases of technology transfer from astronomy to other disciplines such as medicine, for example, a system for diagnosing breast cancer utilising software originally developed to mosaic planetary images. The approach taken in this research will involve using a technology originally developed for radio astronomy to detect water leaks in pipes that are part of water networks in various infrastructure systems. This is innovative research as it involves an interdisciplinary approach to explore a technology and evaluate its commercial potential. Experiments are underway in which signals from an acoustic phased array are amplified and digitized using a multichannel analogue-to-digital (ADC) converter and analysed using a software correlation technique to identify leak signatures. Therefore, the chosen technology's commercialisibility will be tested for alternate applications which can be applied to infrastructures such as water networks. In addition, the importance of interdisciplinary research will also be reflected through this research.

A power-aware hybrid RAM-CAM renaming mechanism for fast recovery

Scipedia content — Wed, 03 Feb 2021 15:49:25 +0100

Modern superscalar processors implement register renaming by using either RAM or CAM tables. The design of these structures should address their access time and misprediction recovery penalty. While direct-mapped RAMs provide faster access times, CAMs are more appropriate to avoid recovery penalties. Although they are more complex and slower, CAMs usually match the processor cycle in current designs. However, they do not scale with the number of physical registers and the pipeline width. In this paper we present a new hybrid RAM-CAM register renaming scheme, which combines the best of both approaches. In a steady state, a RAM provides the current mappings quickly; on mispeculation, a low-complexity CAM enables immediate recovery and further register renaming. Compared to an ideal CAM in a 4-way state-of-the-art superscalar microprocessor, and for almost the same performance (1% slowdown) and area (95% of the ideal CAM size), the proposed scheme consumes about 90% less dynamic energy.

Faecal Pellets in Deep Marine Soft Clay Crusts: Implications for Hot-Oil Pipeline Design

Scipedia content — Wed, 03 Feb 2021 15:48:05 +0100

In recent years, the presence of crusts within near surface sediments found in deep water locations off the west coast of Angola has been of interest to hot-oil pipeline designers. The origin for these crusts is considered to be of biological origin, based on the observation of thousands of faecal pellets in natural crust core samples. This paper presents the results of laboratory tests undertaken on natural and faecal pellet-only samples. These tests investigate the role faecal pellets play in modifying the gemechanical behaviour of clayey sediments. It is found that faecal pellets are able to significantly alter both the strength and the average grain-size of natural sediments, and therefore, influence the permeability and stiffness. Hot-oil pipelines self-embed into and subsequent shear on crusts containing faecal pellets. Being able to predict the time required for installed pipelines to consolidate the underlying sediment and thus, how soon after pipe-laying, the interface strength will develop is of great interest to pipeline designers. It is concluded from wet-sieving samples before and after oedometer tests, that the process of pipe laying is unlikely to destroy pellets. They will therefore, be a major constituent of the sediment subject to soil-pipeline shearing behaviour during axial pipe-walking and lateral buckling. Based on the presented results, a discussion highlighting the key implications for pipeline design is therefore provided.Copyright © 2011 by ASME

Relieving road congestion through motorway concessions in Moscow

Scipedia content — Wed, 03 Feb 2021 15:47:32 +0100

Russia has a well-developed and powerful transportation system. However, the entire transpon infrastructure was designed to meet the needs of a closed and centralized economy. It has become clear that the current road network does not fillfill Russia's social and economic needs. The growth of Russia's road network has fallen far behind motorization rates and the growing demand for road transportation. This gap is a result of the low level of investment in road infrastructure, especially during the last decade. The lack of an adequate stock of roads is particularly evident in Moscow, leading to extremely high traffic congestión, with adverse consequences in terms of wasted time, air pollution, noise, climatic effects, etc. Increased investment in road infrastructure is necessary to reduce Moscow's road congestión. To this end, in addition to increasing public investment, it would be helpful to involve the prívate sector by means of public-private partnerships (PPP). This paper analyses the issues surrounding road concessions and the challenges and difficulties of using a PPP model in Russia. First, the study analyses data on the evolution of the road network and of transport demand in Russia over the last decade. These data illustrate the difficulties of maintaining the road network and of responding to the growing transport demand. Then the paper reviews the challenges of PPP projects aimed at improving the road network, focusing on two recently granted motorway concessions near Moscow. Finally, prospects for further development of public-private partnerships to relieve road congestión in the Russian capital are explored.

Document type: Conference object

Toll Plaza Merging Traffic Control for Throughput Maximization

Scipedia content — Wed, 03 Feb 2021 15:40:45 +0100

Summarization: A simple real-time merging traffic control concept is proposed for efficient toll plaza management in cases where the total flow exiting from the toll booths exceeds the capacity of the downstream highway (or bridge, or tunnel), leading to congestion and reduced efficiency due to capacity drop. Merging traffic control aims at maintaining the number of vehicles in the merge area close to a critical value that maximizes throughput; to this end, an algorithm known from local ramp metering operations is proposed (ALINEA). The potential control concept efficiency is demonstrated by use of microscopic simulation applied to a particular toll plaza infrastructure with and without merging traffic control. It is shown that the employed feedback regulator is little sensitive to various settings which indicates easy applicability with low fine-tuning needs in potential field applications. The case of partially uncontrolled lanes (e.g., for high-occupancy vehicles, buses or other vehicles) is also addressed. Παρουσιάστηκε στο: 10th International Conference on Application of Advanced Technologies in Transportation

Three-dimensional ultrasonic imaging in multilayered media

Scipedia content — Wed, 03 Feb 2021 15:38:29 +0100

The synthetic aperture focusing technique is a method for focusing ultrasonic scans used in nondestructive testing. Traditionally, the technique has mainly been used for contact testing, where the speed of sound is constant throughout the whole medium, but a number of recently proposed algorithms have extended the technique to multilayered media. One important application for such multilayer methods is immersion testing, where an object is immersed in water and the transducer is scanned within the water layer. Similarly, a multilayer technique is useful for inline ultrasound inspection of pipelines filled with liquid, for example water or oil. The multilayer methods have so far only been applied to the 2-dimensional line scan case, but in this paper we extend the the focusing procedure to the 3-dimensional surface scan case. The proposed method is based on the frequency-domain Phase Shift Migration algorithm, which is both conceptually simpler and more computationally efficient than similar time-domain methods. The performance of the focusing algorithm is tested on a three-layer structure, consisting of acrylic glass and aluminum blocks immersed in water. Several small flat-bottom holes in each block are used to simulate point scatterers, and the scatterer responses are studied using both B- and C-scan presentation. The lateral resolution of the focused image is shown to be approximately equal to half the transducer diameter, independent of both depth and layer.

Communicating Driver Intents: A Layered Architecture for Cooperative Active Safety Applications

Scipedia content — Wed, 03 Feb 2021 15:33:00 +0100

The great promise of vehicle to vehicle communications includes a reduction or even elimination of collisions and fatalities on roadways, especially of those due to driver error. A major roadblock to the effectiveness of these systems is the market penetration of cooperative Driver Assistance Systems. Many proposed and existing implementations of cooperative systems are only effective if a majority of vehicles are capable of cooperating. We propose the use of a Layered Architecture for Cooperative Active Safety Applications (LACASA) that includes driver behavior or intent prediction as a fundamental building block for cooperative assistance systems. Simulation results show how such information could improve safety even in limited-deployment scenarios, and in wide-scale deployment, unsafe maneuvers are nearly eliminated.

Analysis and Design of an In-Pipe System for Water Leak Detection

Scipedia content — Tue, 02 Feb 2021 08:45:57 +0100

In most cases the deleterious effects associated with the occurrence of leaks may present serious problems and therefore, leaks must be quickly detected, located and repaired. The problem of leakage becomes even more serious when it is concerned with the vital supply of fresh water to the community. In addition to waste of resources, contaminants may infiltrate into the water supply. The possibility of environmental health disasters due to delay in detection of water pipeline leaks has spurred research into the development of methods for pipeline leak and contamination detection. Leaking in water networks has been a very significant problem worldwide, especially in developing countries, where water is sparse. Many different techniques have been developed to detect leaks, either from the inside or from the outside of the pipe; each one of them with their advantages, complexities but also limitations. To overcome those limitations we focus our work on the development of an in-pipe-floating sensor. The present paper discusses the design considerations of a novel autonomous system for in-pipe water leak detection. The system is carefully designed to be minimally invasive to the flow within the pipe and thus not to affect the delicate leak signal. One of its characteristics is the controllable motion inside the pipe. The system is capable of pinpointing leaks in pipes while operating in real network conditions, i.e. pressurized pipes and high water flow rates, which are major challenges.Copyright © 2011 by ASME

Multi-dimensional Uncertainty Analysis in Secure and Dependable Domain

Scipedia content — Tue, 02 Feb 2021 08:39:23 +0100

Most of the critical aspects for secure and dependable systems, such as safety, integrity, availability, are related to uncertainty. Literature proposes many approaches to deal with uncertainty, mainly in the area of risk management and safety and reliability engineering. However, what is still missing is a clear understanding of the nature of uncertainty that very often has produced mistreatments in the design. In this paper, we propose a conceptual model for uncertainty that can be used to deal with systems’ qualities such as security and dependability. Particularly, we will consider the relation between uncertainty risk and how risk affects quality attributes of the system. We use a case study in Air Traffic Management to illustrate our approach.

Examination of Icing Induced Loss of Control and Its Mitigations

Scipedia content — Tue, 02 Feb 2021 08:38:50 +0100

Factors external to the aircraft are often a significant causal factor in loss of control (LOC) accidents. In today s aviation world, very few accidents stem from a single cause and typically have a number of causal factors that culminate in a LOC accident. Very often the 'trigger' that initiates an accident sequence is an external environment factor. In a recent National Aeronautics and Space Administration (NASA) statistical analysis of LOC accidents, aircraft icing was shown to be the most common external environmental LOC causal factor for scheduled operations. When investigating LOC accident or incidents aircraft icing causal factors can be categorized into groups of (1) in-flight encounter with super-cooled liquid water clouds, (2) take-off with ice contamination, or (3) in-flight encounter with high concentrations of ice crystals. As with other flight hazards, icing induced LOC accidents can be prevented through avoidance, detection, and recovery mitigations. For icing hazards, avoidance can take the form of avoiding flight into icing conditions or avoiding the hazard of icing by making the aircraft tolerant to icing conditions. Icing detection mitigations can take the form of detecting icing conditions or detecting early performance degradation caused by icing. Recovery from icing induced LOC requires flight crew or automated systems capable of accounting for reduced aircraft performance and degraded control authority during the recovery maneuvers. In this report we review the icing induced LOC accident mitigations defined in a recent LOC study and for each mitigation describe a research topic required to enable or strengthen the mitigation. Many of these research topics are already included in ongoing or planned NASA icing research activities or are being addressed by members of the icing research community. These research activities are described and the status of the ongoing or planned research to address the technology needs is discussed

Simultaneous Observation of Inputs and State of Wheeled Vehicle Model

Scipedia content — Tue, 02 Feb 2021 08:36:16 +0100

International audience; This paper deals with the problematic of Advanced Driver Assistance systems for active-safety and automatic control of wheeled vehicles. A non-linear high-gain unknown inputs state observer is designed to compute simultaneously longitudinal and transversal tire forces, resultant torques applied to wheels and the vehicle speeds. This kind of software sensors is very useful in defining these new mechatronic systems. Having validated the model of knowledge using a realistic vehicle simulator, the observer is tested under the same conditions and shows good performances for the vehicle state, tire forces and the unknown torques reconstruction.

V2I-Based Architecture for Information Exchange among Vehicles

Scipedia content — Tue, 02 Feb 2021 08:31:28 +0100

International audience; The significant increment in the number of advanced driver assistance systems (ADAS) in mass-produced cars suggest the idea of autonomous or semi-autonomous vehicles driving in roads in a medium-large term. Consequently, a system to allow the communication among this kind of vehicles and manual driven vehicles will have to be used in order to permit the circulation of both of them at the same time. Two communication modes have to be taken into account. First, a vehicle-to-vehicle communication (V2V) to permit the traffic data flow among cars. Second, a vehicle-to-infrastructure communication (V2I) to allow a central station to coordinate the movements of the vehicle in case of a failure in the V2V. In this paper we present an architecture capable of operating either in autonomous vehicles or manual driven vehicles and coordinating their movements based on a V2I communication. Two mass-produced vehicles are used in order to test the behavior of the architecture implementation. Experimental trials to study the response of the system and the information flow have been carried out.

An efficient Associative Processor solution to an Air Traffic Control problem

Scipedia content — Tue, 02 Feb 2021 08:16:49 +0100

This paper proposes a SIMD solution to air traffic control (ATC) using an enhanced SIMD machine model called an Associative Processor (AP). This differs from previous ATC systems that are designed for MIMD computers and have a great deal of difficulty meeting the predictability requirements for ATC, which are critical for meeting the strict certification standards required for safety critical software components. The proposed SIMD solution will support accurate and meaningful predictions of worst case execution times and will guarantee all deadlines are met. Also, the software will be much simpler and smaller in size than the current corresponding ATC software. An important consequence of these features is that the V&V (Validation and Verification) process will be considerably simpler than for current ATC software. Additionally, the associative processor is enhanced SIMD hardware and is considerably cheaper and simpler than the MIMD hardware currently used to support ATC. The ClearSpeed CSX600 accelerator is used to emulate the AP model. A preliminary implementation of the proposed method has been developed and experimental results comparing MIMD and CSX600 approaches are presented. The performance of CSX600 has better scalability, efficiency, and predictability than that of MIMD.

Automated Flight Routing Using Stochastic Dynamic Programming

Scipedia content — Tue, 02 Feb 2021 08:08:18 +0100

ce capacity reduction due to convective weather impedes air traffic flows and causes traffic congestion. This study presents an algorithm that reroutes flights in the presence of winds, enroute convective weather, and congested airspace based on stochastic dynamic programming. A stochastic disturbance model incorporates into the reroute design process the capacity uncertainty. A trajectory-based airspace demand model is employed for calculating current and future airspace demand. The optimal routes minimize the total expected traveling time, weather incursion, and induced congestion costs. They are compared to weather-avoidance routes calculated using deterministic dynamic programming. The stochastic reroutes have smaller deviation probability than the deterministic counterpart when both reroutes have similar total flight distance. The stochastic rerouting algorithm takes into account all convective weather fields with all severity levels while the deterministic algorithm only accounts for convective weather systems exceeding a specified level of severity. When the stochastic reroutes are compared to the actual flight routes, they have similar total flight time, and both have about 1% of travel time crossing congested enroute sectors on average. The actual flight routes induce slightly less traffic congestion than the stochastic reroutes but intercept more severe convective weather.

Travelling towards and from minor islands through non-conventional air transport: demand and cost analysis

Scipedia content — Tue, 02 Feb 2021 07:48:09 +0100

This research addresses the role of innovative forms of passenger air transport in favouring the mobility of tourists visiting minor islands. In particular, we studied the feasibility of scheduled transport services using a helicopter and a seaplane for rapidly connecting Sicily in the south of Italy to the near and very attractive Eolie Islands. In order to estimate the potential service demand, we allowed for the number of tourists arriving in the Eolie Archipelago during the period 1999-2008. In detail, we considered only the market of visitors with a high willingness-to-pay for time savings (individuals choosing superior hotels) coming from origins at least 300 km away from the Eolie Islands. Furthermore, we excluded a quota of travellers not disposed to flying, determined on the basis of a previous study about air transport demand. We also considered as potential users of the proposed transport services a percentage of the Eolie Isles’ population that was set according to a recent study about the use of air transport by Sicilian residents. The resulting observations were employed to estimate forecasts through an ARIMA model. After a technical analysis to identify the types of helicopter and seaplane suited to implementing regular transport services, we performed a cost analysis concerning the proposed non-conventional air transport services (taking into account fixed, variable, trading and financial costs). In particular, based on the ARIMA model demand forecasts, we determined the service supply (daily frequency and number of aircrafts) in the different cases and evaluated the related total cost per passenger. At the final step, we compared the helicopter and seaplane options with the various existing transport alternatives that can be used to get to the Eolie Island

An Asynchronous FPGA with Two-Phase Enable-Scaled Routing

Scipedia content — Tue, 02 Feb 2021 07:40:24 +0100

The configurable routing in asynchronous FPGAs accounts for 80-90% of the total area and consumes 80-90% of the total power. This paper presents an asynchronous FPGA that applies two techniques to reduce power consumption. First, the routing is altered to use two-phase logic rather than four-phase logic. Second, enable (acknowledge) signals are voltage scaled such that the overall FPGA performance is not affected. The resulting FPGA is evaluated across eight of the MCNC LGSynth93 benchmarks. This FPGA consumes up to 60% less power than a conventional asynchronous FPGA. In addition, the extra slack provided by two-phase routing increases the throughput of some benchmarks by up to 70%. The additional hardware required to implement the low-power techniques increases the total area by only 12%.

Closed-Form Takeoff Weight Estimation Model for Air Transportation Simulation

Scipedia content — Tue, 02 Feb 2021 07:38:46 +0100

Takeoff weight is an important parameter for computing accurate aircraft trajectories. Most systems used for simulating air traffic and for providing air traffic management decision support use takeoff weights that depend only on the aircraft type. This paper proposes a closed-form algorithm for estimating takeoff weights based on flight plan and aircraft performance data. The algorithm is derived by combining the constantaltitude-cruise range equation with the weight estimation procedure commonly used in aircraft design. The model first determines whether the payload is limited by payload capacity, maximum takeoff weight, or fuel tank capacity, and then calculates the takeoff weight accordingly. The model is verified against manufacturer provided payload range diagrams for a jet and a turboprop aircraft. Accurate and fast takeoff weight estimation with negligible computational overhead will enhance large scale air traffic simulations by improving the accuracy of trajectories and fuel burn estimates. Improvement in trajectory and fuel burn estimates will benefit the assessment of noise and emissions as well as improve the accuracy of automated conflict detection and resolution algorithms.

Future strategies for airports

Scipedia content — Tue, 02 Feb 2021 07:17:28 +0100

http://www.icas.org/ICAS_ARCHIVE/ICAS2010/PAPERS/090.PDF; International audience; In air transport, the evolution of traffic depends upon many economic factors, and on the way in which the markets participants respond to those factors. Although airlines are the main actors, the airports are by no means passive, and their strategies will also have an impact on airline behaviour and route development. Our methodology analyzes the potential evolution of airport strategies in the next decade and its impact on the distribution of traffic at airports, using a typology of airports that has been designed for this purpose. It shows in particular that diversification strategies, which are usually reserved for large firms, can also be successfully applied to smaller airports.

Fuzzy observer for state estimation of the METANET traffic model

Scipedia content — Tue, 02 Feb 2021 07:12:46 +0100

Traffic control has proven an effective measure to reduce traffic congestion on freeways. In order to determine appropriate control actions, it is necessary to have information on the current state of the traffic. However, not all traffic states can be measured (such as the traffic density) and so state estimation must be applied in order to obtain state information from the available measurements. Linear state estimation methods are not directly applicable, as traffic models are in general nonlinear. In this paper we propose a nonlinear approach to state estimation that is based on a Takagi-Sugeno (TS) fuzzy model representation of the METANET traffic model. By representing the METANET traffic model as a TS fuzzy system, a structured observer design procedure can be applied, whereby the convergence of the observer is guaranteed. Simulation results are presented to illustrate the quality of the estimate.

Examining the impact of driving style on the predictability and responsiveness of the driver: Real-world and simulator analysis

Scipedia content — Tue, 02 Feb 2021 06:55:10 +0100

Confronted with the broad range of personalities of drivers on the roads today, in-vehicle technology must be able to function either in spite of or in harmony with each driver's style. Individual drivers act and respond in different manners under various conditions, and many Driver Assistance Systems would benefit from some measure of the driver's likely behaviors in these conditions. In this study we present several measures of driving style and show how they correlate with the predictability and responsiveness of the driver in several experimental conditions. In the first two experiments, one simulator and one real-world, we find that “aggressive” drivers are more consistent in behaviors and significantly more predictable than “non-aggressive” drivers. In the third experiment, however, we find that though “non-aggressive” drivers are less predictable, they are also significantly more receptive of feedback from Driver Assistance Systems. These results could affect the design, effectiveness, and feedback mechanisms of future Driver Assistance Systems.

Discrete-Event Simulation of Air Traffic Flow

Scipedia content — Tue, 02 Feb 2021 06:48:06 +0100

discrete-event simulation model of air traffic fl ow is developed to take advantage of the computational efficiency afforded by event-based si mulation. The model is based on a set of reusable library block components that may be used to build models of varying degrees of complexity. The building blocks of discrete-event s imulation are described. To illustrate the modeling technique for air traffic flow management, both small-scale and large-scale models of air traffic flow are developed. Example results are presented to show how event-based simulation may be used to perform air traffic flow management research.

Real time 3D terrain elevation mapping using ants Optimization Algorithm and stereo vision

Scipedia content — Tue, 02 Feb 2021 06:47:24 +0100

Reliable perception of terrain slope and terrain traversability is a key-feature for any off-road unmanned ground vehicle, as well as for any Driver Assistance Systems designed to work in extreme environments, like mining. In this paper we want to present an innovative technique to build a 3D elevation map of the traversable terrain from a world's 3D dense data set, in real time. The 3D points are grouped into lateral and longitudinal equally spaced slices, then they are projected onto the corresponding slices' reference planes. The projections are then analyzed by a biologically inspired Optimization Algorithm able to segment points into terrains inlier and outlier; the resulting 2D terrain slopes represent an optimal terrain approximation along each slice. Finally, the 2D approximations are merged together, to create the overall 3D terrain surface. The algorithm has been successfully tested with 3D data provided by a stereo camera system mounted on a Cat® wheel loader operating in a mining environment.

Use if BEST In-Highways for Green Highway Construction Rating in Wisconsin

Scipedia content — Tue, 02 Feb 2021 06:37:34 +0100

Environmentally and Economically Sustainable Transportation Infrastructure- Highways (BE2ST in-Highways). BE2ST in-Highways employs life cycle analysis techniques to provide a quantitative assessment of the impacts associated with a highway construction project. Energy and water consumption, greenhouse gas emissions, service life, and life cycle cost are evaluated in a quantitative framework that can be used to compare alternative construction strategies from a holistic perspective. The methodology is grounded in quantitative metrics rather than an arbitrary point system so that a transparent linkage exists between the project rating and the sustainable practices employed in design and construction. This transparency reduces the potential for ‘gaming’ of the rating system. Application of the BE2ST in-Highways system to a project in Wisconsin is described. Results of the application indicate that using recycled materials in a pavement can result in reductions in global warming potential (32%), energy consumption (28%), water consumption (29%), and hazardous waste generation (25%) as compared to the reference design using conventional materials, while also extending the service life of the pavement. In addition, using recycled materials in a pavement can result in a life cycle cost savings of 23%. Because of this environmental and economical out-performance of the alternative design using recycled materials compared to the reference design using conventional materials, the maximum total credit (i.e., 12 points) is granted to the project.

Pipe Joint Integrity: Cementitious and Metallic Pressure Pipes

Scipedia content — Tue, 02 Feb 2021 06:24:47 +0100

The ability of a municipal pressure pipeline to prevent leakage at joints is an indicator of the efficiency of that piping system. Cement-based and metallic pipe materials used in pressurized municipal water distribution and transmission systems include high head concrete pressure pipe (CCP), gasket-sealed-joint and welded-joint welded steel pipe (WSP), and ductile iron pipe (DIP). For these materials, hydrostatic pressure testing is typically performed twice, once at the pipe manufacturing plant to confirm structural integrity and proper manufacture, and again after the pipeline has been installed and backfilled to confirm that the pipe, joints, and thrust restraint systems have been properly constructed. For field hydrostatic leakage testing, most pipe materials have an associated “allowable makeup water” or “allowable leakage” to accommodate the unique characteristics of the material as well as other irregularities during testing such as air in the line, temperature variations, and even instrument inaccuracies. Test methods and formulas for calculating makeup water usually vary based on the pipe material-specific standards. The wide discrepancies that exist for makeup water between different pipe materials do not place them on a level playing field for a given application. This paper is a review of both in-plant and in-field hydrostatic pressure testing and the topic of makeup water as outlined in AWWA and ASTM standards for the above-named pipe materials. Quality control and qualification tests for joints of each pipe material standard are also reviewed. Recommendations are made for consideration by the Specification Engineering community for future revisions of standards pertaining to the field testing of pipelines.

Towards Integrating Traffic and Terrain Constraints into a Vertical Situation Display

Scipedia content — Tue, 02 Feb 2021 06:18:53 +0100

Future airspace operations will allow flight crews to plan and fly their own preferred route and time of arrival without much intervention from air traffic control. This implies that pilots become more responsible for planning their own route while maintaining safe separation. This requires a strategic planning tool that support a high level of pilot Situation Awareness. Current aircraft are already equipped with terrain and traffic warning systems to, but these systems only provide short-term conflict resolutions. Recent studies have shown that a constraint-based approach to interface design could be used to support long- and medium-term decision-making and to provide a deeper understanding of the work domain. However, these studies were focused on either terrain or traffic. This paper aims to integrate both by showing the performance, traffic and terrain overlays on an experimental Vertical Situation Display. In a simulator evaluation, in which twelve professional airline pilots participated, this Vertical Situation Display was compared to a baseline Vertical Situation Display that only showed a terrain overlay and intruder aircraft relative to own ship. The experiment results revealed that the performance, traffic and terrain overlays improved pilots’ overall situation awareness and pilots rated their workload lower. Regarding decision-making, however, the results were not significantly better. Regarding safety, there were less traffic conflicts, but more ground proximity intrusions.

On the Limits of Collision Detection Performance of a Sense-and-Avoid System for Non-Cooperative Air Traffic

Scipedia content — Tue, 02 Feb 2021 06:11:29 +0100

Unmanned Aircraft Systems (UAS) face limitations on their utilization in civil airspace because they do not have the ability to Sense and Avoid (SAA) other air traffic. In recent years, there has been growing interest to provide an effective SAA solution for UAS operations. An effective SAA solution must address both cooperative as well as non-cooperative air traffic. A number of different sensor solutions are being evaluated for SAA pertaining to non-cooperative traffic. Examples of such sensors include electro-optical (EO), on-board radar, passive acoustics, laser radar and ground radar. Using one or more such sensing modalities, it is possible to track a non-cooperative aircraft in the vicinity of the own aircraft otherwise known as an intruder. However, an intruder’s future trajectory is never perfectly known and a SAA system’s performance will always be limited by these uncertainties. One of the components of an SAA system is the logic to decide whether a certain aircraft is on a collision course with the own craft. It, therefore, follows that the performance of this collision detection component will also be limited by the uncertainties in the future trajectory of the intruder. In this paper, we investigate the problem of what is the best that a SAA collision detection system can perform in spite of the future uncertainties in the intruder trajectory.

Automatic segmentation and classification of movement trajectories for transportation modes

Scipedia content — Tue, 02 Feb 2021 06:04:29 +0100

Interaction of Airspace Partitions and Traffic Flow Management Delay

Scipedia content — Tue, 02 Feb 2021 05:46:55 +0100

To ensure that air traffic demand does not exceed airport and airspace capacities, traffic management restrictions, such as delaying aircraft on the ground, assigning them different routes and metering them in the airspace, are implemented. To reduce the delays resulting from these restrictions, revising the partitioning of airspace has been proposed to distribute capacity to yield a more efficient airspace configuration. The capacity of an airspace partition, commonly referred to as a sector, is limited by the number of flights that an air traffic controller can safely manage within the sector. Where viable, re-partitioning of the airspace distributes the flights over more efficient sectors and reduces individual sector demand. This increases the overall airspace efficiency, but requires additional resources in some sectors in terms of controllers and equipment, which is undesirable. This study examines the tradeoff of the number of sectors designed for a specified amount of traffic in a clear-weather day and the delays needed for accommodating the traffic demand. Results show that most of the delays are caused by airport arrival and departure capacity constraints. Some delays caused by airspace capacity constraints can be eliminated by re-partitioning the airspace. Analyses show that about 360 high-altitude sectors, which are approximately today s operational number of sectors of 373, are adequate for delays to be driven solely by airport capacity constraints for the current daily air traffic demand. For a marginal increase of 15 seconds of average delay, the number of sectors can be reduced to 283. In addition, simulations of traffic growths of 15% and 20% with forecasted airport capacities in the years 2018 and 2025 show that delays will continue to be governed by airport capacities. In clear-weather days, for small increases in traffic demand, increasing sector capacities will have almost no effect on delays.

A case for dynamic risk assessment in NEC systems of systems

Scipedia content — Tue, 02 Feb 2021 05:33:01 +0100

The level of complexity in Systems of Systems is increasing as more complex functionality emerges from the interaction of individual components. As networks become more complex it becomes more difficult for an individual to identify potential safety risks. We know, from previous accidents, that poor understanding of networks can be dangerous. In this paper, we demonstrate the potential value of incorporating a process to identify risks in a deployed network, focusing on factors concerned with the interaction of this process with a user, and the potential for new hazards.

The Application of an Agent-Based Impact Analysis to a Complex Air Traffic Management System

Scipedia content — Tue, 02 Feb 2021 05:31:19 +0100

It is both costly and time consuming to predict the behavior of complex systems due to their data intensity. They also tend to be dynamic which means they may not lend themselves to a quantitative behavioral analysis. An impact analysis is presented as being a novel qualitative approach with the aim of determining, qualitatively, how a system element deviates from a pre-defined “normal” operational mode due to a change in the operation of another element existing within the same architecture, or due to an interaction with an external environmental condition. Performing such an analysis determines elements in the system that would be affected by the change and aids in system development through identification of relationships and interdependencies prior to modifications. Air Traffic Management (ATM) systems are examples which would benefit from such analyses. This paper presents two impact analyses; one of which encapsulates a complex real world scenario involving the Icelandic Volcanic Eruption in April 2010, the other a series of localized scenarios focused on London Heathrow. The potential and capability of the model and approach to understand more about how the ATM system operates, and how its behavior evolves through scenarios, have been emphasized through these analyses. The agent based impact analysis is shown to identify the elemental relationships and interdependencies in a simple qualitative manner whilst not being data intensive.

Optimal power/performance pipelining for error resilient processors

Scipedia content — Tue, 02 Feb 2021 05:29:45 +0100

Timing speculation has been proposed as a technique for maximizing the energy efficiency of processors with minimal loss in performance. A typical implementation of timing speculation involves speculatively reducing the voltage of a processor to a point where errors are possible but rare, and employing an error recovery mechanism to ensure correct functionality. This allows significant energy savings with a small recovery overhead.

A ground holding model for aircraft deconfliction

Scipedia content — Tue, 02 Feb 2021 05:25:49 +0100

In the SESAR traffic growth predictions, traffic complexity will become an issue that the current Air Traffic Management organization is not able to handle. The 4D trajectory concept offers new perspectives for deconflicting the traffic by ground-holding aircraft before they take-off. This paper studies the possible complexity reduction achievable by optimizing the aircraft take-off times. Therefore a simple model is introduced to detect pairwise 3D possible conflicts and define conflicting take-off time differences. Two resolution algorithms are tested on a real traffic data sample collected in the French airspace. The first one is based on a Constraint Programming model of the problem and ensures the optimality of the maximum delay required to solve every conflict. The second one uses an evolutionary computation algorithm to minimize the mean delay among the aircraft population. A sliding window model is introduced to reduce the size of the problem and to regularly update the current situation. Experimental results performed in the French airspace with fast time simulation show that with perfect 4D trajectory, every conflict over flight level 290 can be solved by delaying less than a quarter of the traffic within a range of delays varying from 1 to 90 minutes and a mean delay of 4 minutes. The Constraint Programming approach gives better results than the evolutionary computation approach. Adding uncertainty around 4D trajectories dramatically degrades the results.

Prediction of Exposure Risk for Buried Pipelines due to Surface Erosion

Scipedia content — Tue, 02 Feb 2021 05:15:22 +0100

Pipeline right-of-way maintenance activities face great challenges that have come from different climates, slopes, soils and other environmental conditions. Control of surface drainage and erosion is an important element in the restoration and maintenance of pipeline right-of-ways, since erosion can result in risk of pipe exposure and its consequences. Evaluation of this risk can be a powerful tool to ensure reliability of buried pipelines. The universal soil loss equation is used as a model to estimate the rates of erosion at sections of rights-of-way of a gas pipeline right-of-way near Vitoria city in southeast of Brazil. The confrontation of these rates to the actual pipe cover depths is used as a basis to derive a probabilistic procedure for determining the time period over which exposure may occur for a given level of uncertainty. Then, risk can be estimate as a product of the probability (or frequency) of product leakage due to pipeline exposure and the associated consequences of this event. Such risk definition is used to estimate results in an effective guideline to engineers, since it leads to the achievement of optimum and safe erosion control and superficial drainage system projects and results in efficient mitigation planning programs. The results obtained are very promising and show relevant correspondence with the erosion process and cover depth reduction identified on the right-of-way.

Integrated Analysis of Airport Capacity and Environmental Constraints

Scipedia content — Tue, 02 Feb 2021 04:58:53 +0100

LMI conducted an integrated analysis of airport capacity and environmental constraints. identifying and ranking the key factors limiting achievement of NextGen capacity goals. The primary metric used was projected throughput, which was estimated for the years 2015 and 2025 based on the unconstrained demand forecast from the Federal Aviation Administration, and planned improvements including those proposed in the NextGen plan. A set of 310 critical airports was identified.. collectively accounting for more than 99 percent of domestic air traffic volume; a one-off analytical approach was used to isolate the constraint being assessed. The study considered three capacity constraints (runway.. taxiway, and gate) and three environmental constraints (fuel, NO(x) emissions, and noise). For the ten busiest airports, runway and noise are the primary and secondary constraints in both 2015 and 2025. For the OEP 35 airports and overall for the remaining airports, the most binding constraint is noise. Six of the 10 busiest airports, will face runway constraints in 2025, and 95 will face gate constraints. Nearly every airport will be subject to constraints due to emissions and NOx. Runway and taxi constraints are more concentrated in the large airports: environmental constraints are present at almost every airport regardless of size.

Fusion of clothoid segments for a more accurate and updated prediction of the road geometry

Scipedia content — Tue, 02 Feb 2021 04:57:54 +0100

basic step in the development of advanced driver assistance systems is the perception and interpretation of information on the vehicle environment. In many cases, the upcoming road geometry in front the own vehicle is of particular interest. Although a prediction of the course of the road can be provided based on map data, the accuracy is not sufficient for most driver assistance systems. The goal of this work is to achieve a more accurate and updated prediction of the road geometry at close range. Therefore, the map data is combined with the information from an existing vision-based lane detection system. Since the shape of detected road lines as well as the map data are represented by clothoid curves, the emphasis of this work is placed on the calculation, combination, and connection of clothoid segments.

Quantifying and coping with parametric variations in 3D-stacked microarchitectures

Scipedia content — Tue, 02 Feb 2021 04:46:52 +0100

Variability in device characteristics, i.e., parametric variations, is an important problem for shrinking process technologies. They manifest themselves as variations in performance, power consumption, and reduction in reliability in the manufactured chips as well as low yield levels. Their implications on performance and yield are particularly profound on 3D architectures: a defect on even a single layer can render the entire stack useless. In this paper, we show that instead of causing increased yield losses, we can actually exploit 3D technology to reduce yield losses by intelligently devising the architectures. We take advantage of the layer-to-layer variations to reduce yield losses by splitting critical components among multiple layers. Our results indicate that our proposed method achieves a 30.6% lower yield loss rate compared to the same pipeline implemented on a 2D architecture.

Assessment and Interpretation of En Route Weather Avoidance Fields from the Convective Weather Avoidance Model

Scipedia content — Tue, 02 Feb 2021 04:36:50 +0100

†‡ This paper presents the results of a study to quantify the performance of Weather Avoidance Fields in predicting the operational impact of convective weather on en route airspace. The Convective Weather Avoidance Model identifies regions of convective weather that pilots are likely to avoid based upon an examination of the planned and actual flight trajectories in regions of weather impact. From this model and a forecast of convective weather from the Corridor Integrated Weather System a probabilistic Weather Avoidance Field can be provided to automated decision support systems of the future impact of weather on the air traffic control system. This paper will present three alternative spatial filters for the Convective Weather Avoidance Model, quantify their performance, address deficiencies in performance, and suggest potential improvements by looking at the ATC environment and common situational awareness between the cockpit and air traffic control.

Automatic multithreaded pipeline synthesis from transactional datapath specifications

Scipedia content — Tue, 02 Feb 2021 04:25:04 +0100

We present a technique to automatically synthesize a multithreaded in-order pipeline from a high-level unpipelined datapath specification. This work extends the previously proposed transactional specification (T-spec) and synthesis technology (T-piper). The technique not only works with instruction processors but also flexible enough to accept any sequential datapath. It maintains previously proposed non-threaded pipeline features and is enhanced with multithreading features. We report a design space exploration study of 32 multithreaded x86 processor pipelines, all synthesized from a single T-spec.

Object Classification from Aerial Visual Imagery

Scipedia content — Tue, 02 Feb 2021 04:16:26 +0100

oil pipeline inspection is a dangerous endeavor in the current practice, where a pilot flying in a general aviation class aircraft flies slowly at low altitudes while concurrently looking at the ground for pipeline hazards with the unaided eye; high pilot workload in a dangerous low-speed, low-altitude environment results in an unacceptable number of accidents and loss of life each year. Automation of image acquisition and threat recognition has the potential to reduce pilot workload, improving the safety of the pilots and increasing efficiency. Towards these goals, this paper describes an image classification architecture and algorithm that utilizes several classifiers on different features extracted from the image to automate the threat detection process. The resulting classifier meets the requirement of greater than 80% accuracy in classification. The results will be discussed, and improvements will be proposed for continued research.

Solving the problem of cascading errors

Scipedia content — Tue, 02 Feb 2021 04:12:40 +0100

The end-to-end performance of natural language processing systems for compound tasks, such as question answering and textual entailment, is often hampered by use of a greedy 1-best pipeline architecture, which causes errors to propagate and compound at each stage. We present a novel architecture, which models these pipelines as Bayesian networks, with each low level task corresponding to a variable in the network, and then we perform approximate inference to find the best labeling. Our approach is extremely simple to apply but gains the benefits of sampling the entire distribution over labels at each stage in the pipeline. We apply our method to two tasks -- semantic role labeling and recognizing textual entailment -- and achieve useful performance gains from the superior pipeline architecture.

Effective Structure-from-Motion for Hybrid Camera Systems

Scipedia content — Tue, 02 Feb 2021 03:47:52 +0100

We describe a pipeline for structure-from-motion with mixed camera types, namely omni directional and perspective cameras. The steps of the pipeline can be summarized as calibration, point matching, pose estimation, triangulation and bundle adjustment. For these steps, we either propose improved methods or modify existing perspective camera methods to make the pipeline more effective and automatic when employed for hybrid camera systems.

A Future Internet Architecture Based on De-Conflated Identities

Scipedia content — Tue, 02 Feb 2021 03:43:07 +0100

We present a new Internet architecture based on de-conflated identities (ADI) that explicitly establishes the separation of ownership of hosts from the underlying infrastructure connectivity. A direct impact of this de-conflated Internet architecture is the ability to express organizational policies separately and thus more naturally, from the underlying infrastructure routing policies. Host or organizational accountability is separated from the infrastructure accountability, laying the foundations of a cleaner security and policy enforcement framework. Also, it addresses the present Internet routing problems of mobility, multihoming, and traffic engineering more naturally by making a clear distinction of host and infrastructure responsibilities and thus defining these functions as a set of primitives governed by individual policies. In this paper, we instantiate the primitive mechanisms related to the issues of end-to-end policy enforcements, mobility, multihoming, traffic engineering, etc., within the context of our architecture to emphasize the relevance of a de-conflated Internet architecture on these functions.

The role of railway stations in increasing transport demand

Scipedia content — Tue, 02 Feb 2021 03:39:37 +0100

The monopoly of the railway companies and rigid railway regulations and carrier tariffs at the majority of the European railways have significantly affected the drastic reduction in the share of railway traffic in the surface transport of the entire Europe. Many years of stagnation and absence of investments into railway transport, particularly regarding railway stations as well as other useful surfaces along the railway lines of a similar or same function, have led to neglect and uselessness of these facilities in the railway system. High maintenance prices affect additional neglect, even destruction of railway stations and other buildings on the railway grounds, and construction of functional roofed platforms for passenger handling. Regardless of the fact that in their past, the construction of railway lines was the stimulator of the development of various regions and towns, today railway stations have become non-attractive places where people stay just for a short time and only in transit, which is much the case in the Republic of Croatia, but it should be pointed out that even the developed countries have similar problems. The approaching and opening of railway companies to the passengers, as well as the local government, is the priority for a serious market competition with the competitive road transport. In order to achieve this a cross-section of the current condition of the basic function of railway companies in the transport of passengers should be made. The introduction and development of integrated transport of passengers is the next step in the creation of competitive supply of the railway companies. The separation of railway carriers from railway infrastructure means also recognition of the important role of infrastructure manager in transforming the railway stations from the neglected and unattractive places to places with multifunctional facilities. In the first step it is necessary to make a cross-section of the current additional facilities at railway stations, and then to design and supply new facilities motivating the existing passengers to stay longer at the station, and also attracting new users towards stations, i.e. passenger trains. In the future, apart from the traffic function, the railway stations, as gates to the cities, need to take over also a part of the economic, commercial, cultural, sport and other social functions of the city.

Assessing the Use of Composite Materials in Reinforcing Offshore Risers and Pipelines

Scipedia content — Tue, 02 Feb 2021 03:39:24 +0100

Composite systems are a generally-accepted method for repairing corroded and mechanically-damaged onshore pipelines. The pipeline industry has arrived at this point after more than 15 years of research and investigation. Because the primary method of loading for onshore pipelines is in the circumferential direction due to internal pressure, most composite systems have been designed and developed to provide hoop strength reinforcement. On the other hand, offshore pipes (especially risers), unlike onshore pipelines, can experience significant tension and bending loads. As a result, there is a need to evaluate the current state of the art in terms of assessing the use of composite materials in repairing offshore pipelines and risers. The paper presents findings from a joint industry effort involving the Minerals Management Service, the Offshore Technology Research Center at Texas A&M University, Stress Engineering Services, Inc., and several composite repair manufacturers was undertaken to assess the state of the art using full-scale testing methods. Loads typical for offshore risers were used in the test program that integrated internal pressure, tension, and bending loads. This program is the first of its kind and likely to contribute significantly to the future of offshore riser repairs. It is anticipated that the findings of this program will foster future investigations involving operators by integrating their insights regarding the need for composite repair based on emerging technology.Copyright © 2011 by ASME

New objectives of the French high-speed rail system within the framework of a highly centralized network: a substitute for the domestic air transport market?

Scipedia content — Tue, 02 Feb 2021 03:38:33 +0100

International audience; Since the beginning of high-speed services in France, the TGV network’s main target has been business traffic using the domestic air transport network. Point-to-point services with the lowest number of intermediate stops have been the preferred solution. SNCF can be considered as an active player in the rail/air transport competition, given that it offers rapid travel times, competitive prices and considerable carrying capacities. Frequencies can be high between the largest towns: 16 round-trip services between Paris and Marseilles (840 km, 190 minutes ), 21 between Paris and Bordeaux (620 km, 190 minutes), etc. ID-TGV, a low-cost subsidiary, has also been created. Operating on selected routes, it provides a good level of on-board services as well as some interesting innovations. The development of high-speed lines has created new competition opportunities between the TGV, Air France and other carriers. This partially explains the relative weakness of competition within the domestic air transport sector: even a low-cost carrier like EasyJet tries to avoid competition on routes where the average travel time of the TGV is lower than 3.5 hours. Air France is now planning to progressively downsize its services on routes where the TGV’s market share is increasing: specific point-to-point services to/from Orly Airport will be closed and, by 2016, only a few feeder lines to/from the CDG-Roissy hub will remain.Our aim is to measure the intensity of the competition in 2010 and, in particular, the shift taking place from a real domestic point-to-point air offer to a stricter hub-feed network with lower frequencies. We have compared the service level provided by the two carriers, basing the comparison on average TGV travel times (which are not related to the real distance covered). Our main hypothesis is that where Air France considers that it has lost in the competition against the TGV, it directs most of its remaining flights towards Roissy-CDG airport, being the carrier’s main hub, in order to focus on connections to long-haul flights. On the other hand, where AF considers that its market share can be consolidated, it then directs most of its flights to Orly Airport which is more convenient for access to and from Paris.

Task superscalar: An out-of-order task pipeline

Scipedia content — Tue, 02 Feb 2021 03:34:09 +0100

We present Task Superscalar, an abstraction of instruction-level out-of-order pipeline that operates at the tasklevel. Like ILP pipelines, which uncover parallelism in a sequential instruction stream, task superscalar uncovers tasklevel parallelism among tasks generated by a sequential thread. Utilizing intuitive programmer annotations of task inputs and outputs, the task superscalar pipeline dynamically detects intertask data dependencies, identifies task-level parallelism, and executes tasks out-of-order. Furthermore, we propose a design for a distributed task superscalar pipeline frontend, that can be embedded into any manycore fabric, and manages cores as functional units. We show that our proposed mechanism is capable of driving hundreds of cores simultaneously with non-speculative tasks, which allows our pipeline to sustain work windows consisting of tens of thousands of tasks. We further show that our pipeline can maintain a decode rate faster than 60ns per task and dynamically uncover data dependencies among as many as ~50,000 in-flight tasks, using 7MB of on-chip eDRAM storage. This configuration achieves speedups of 95–255x (average 183x) over sequential execution for nine scientific benchmarks, running on a simulated CMP with 256 cores. Task superscalar thus enables programmers to exploit manycore systems effectively, while simultaneously simplifying their programming model.

Peer Reviewed

Adaptive post-failure load balancing in fast reroute enabled IP networks

Scipedia content — Tue, 02 Feb 2021 03:32:12 +0100

Fast reroute (FRR) techniques have been designed and standardised in recent years for supporting sub-50-millisecond failure recovery in operational ISP networks. On the other hand, if the provisioning of FRR protection paths does not take into account traffic engineering (TE) requirements, customer traffic may still get disrupted due to post-failure traffic congestion. Such a situation could be more severe in operational networks with highly dynamic traffic patterns. In this paper we propose a distributed technique that enables adaptive control of FRR protection paths against dynamic traffic conditions, resulting in self-optimisation in addition to the self-healing capability. Our approach is based on the Loop-free Alternates (LFA) mechanism that allows non-deterministic provisioning of protection paths. The idea is for repairing routers to periodically re-compute LFA alternative next-hops using a lightweight algorithm for achieving and maintaining optimised post-failure traffic distribution in dynamic network environments. Our experiments based on a real operational network topology and traffic traces across 24 hours have shown that such an approach is able to significantly enhance relevant network performance compared to both TE-agnostic and static TE-aware FRR solutions. © 2011 IEEE.

A Concept for Robust, High Density Terminal Air Traffic Operations

Scipedia content — Tue, 02 Feb 2021 03:28:29 +0100

This paper describes a concept for future high-density, terminal air traffic operations that has been developed by interpreting the Joint Planning and Development Office’s vision for the Next Generation (NextGen) air transportation system and coupling it with emergent National Aeronautics and Space Administration (NASA) and other technologies and procedures during the NextGen timeframe. The concept described in this paper includes five core capabilities: 1) extended terminal area routing, 2) precision scheduling along routes, 3) merging and spacing, 4) tactical separation, and 5) off-nominal recovery. Gradual changes are introduced to the National Airspace System by phased enhancements to the core capabilities in the form of increased levels of automation and decision support as well as targeted task delegation. NASA will be evaluating these conceptual technological enhancements in a series of human-in-the- loop simulations and will accelerate development of the most promising capabilities in cooperation with the Federal Aviation Administration through the Efficient Flows Into Congested Airspace Research Transition Team.

Model of connecting an airport by rail–case study: the city of Zagreb

Scipedia content — Tue, 02 Feb 2021 03:25:43 +0100

Zagreb Airport is at some 15km distance from the City of Zagreb itself. It is connected with the City by road which is congested during the morning and afternoon peak hours of commuting transport thus significantly affecting the travel time to and from the airport. The airport development plan for the next twenty years includes the construction of another runway and a new passenger terminal of higher capacity for passenger handling and of adequate level of equipment. Regarding the planned increase in traffic at Zagreb Airport it is necessary to expand the infrastructure capacities that connect the centre of Zagreb and Zagreb Airport, since already the existing capacities are not sufficient. The current connection of the airport with the city is exclusively by road, more precisely, the main road that connects the city of Velika Gorica with Zagreb, and which is one of the busiest roads in the Republic of Croatia, and already as such cannot meet Zagreb Airport requirements. Since the railway line that connects the cities of Zagreb and Velika Gorica passes in the vicinity of the airport, the plan is to connect Zagreb Airport to the existing railway infrastructure and to construct an underground stop under the passenger terminal. This paper does not focus on the infrastructural solutions but rather on the operator model, i.e. rail carrier that would provide adequate transport of passengers on the Zagreb-Airport-Velika Gorica relation. The paper will analyze the current state regarding the number of passengers and the methods of arriving i.e. leaving the airport. Regarding the expected number of passengers in the future and the construction of an underground railway stop, a railway carrier model will be provided. The model will encompass the dimensions of the mobile capacities, i.e. transport means, the rail carrier trip frequency (headways), and the introduction of integrated transport document for the purpose of more comfortable travelling.

Improving content delivery using provider-aided distance information

Scipedia content — Tue, 02 Feb 2021 03:13:04 +0100

Content delivery systems constitute a major portion of today's Internet traffic. While they are a good source of revenue for Internet Service Providers (ISPs), the huge volume of content delivery traffic also poses a significant burden and traffic engineering challenge for the ISP. The difficulty is due to the immense volume of transfers, while the traffic engineering challenge stems from the fact that most content delivery systems themselves utilize a distributed infrastructure. They perform their own traffic flow optimization and realize this using the DNS system. While content delivery systems may, to some extent, consider the user's performance within their optimization criteria, they currently have no incentive to consider any of the ISP's constraints. As a consequence, the ISP has ``lost control'' over a major part of its traffic. To overcome this impairment, we propose a solution where the ISP offers a Provider-aided Distance Information System (PaDIS). PaDIS uses information available only to the ISP to rank any client-host pair based on distance information, such as delay, bandwidth or number of hops. In this paper we show that the applicability of the system is significant. More than 70% of the HTTP traffic of a major European ISP can be accessed via multiple different locations. Moreover, we show that deploying PaDIS is not only beneficial to ISPs, but also to users. Experiments with different content providers show that improvements in download times of up to a factor of four are possible. Furthermore, we describe a high performance implementation of PaDIS and show how it can be deployed within an ISP.

A Final Approach Trajectory Model for Current Operations

Scipedia content — Tue, 02 Feb 2021 03:03:02 +0100

Predicting accurate trajectories with limited intent information is a challenge faced by air traffic management decision support tools in operation today. One such tool is the FAA's Terminal Proximity Alert system which is intended to assist controllers in maintaining safe separation of arrival aircraft during final approach. In an effort to improve the performance of such tools, two final approach trajectory models are proposed; one based on polynomial interpolation, the other on the Fourier transform. These models were tested against actual traffic data and used to study effects of the key final approach trajectory modeling parameters of wind, aircraft type, and weight class, on trajectory prediction accuracy. Using only the limited intent data available to today's ATM system, both the polynomial interpolation and Fourier transform models showed improved trajectory prediction accuracy over a baseline dead reckoning model. Analysis of actual arrival traffic showed that this improved trajectory prediction accuracy leads to improved inter-arrival separation prediction accuracy for longer look ahead times. The difference in mean inter-arrival separation prediction error between the Fourier transform and dead reckoning models was 0.2 nmi for a look ahead time of 120 sec, a 33 percent improvement, with a corresponding 32 percent improvement in standard deviation.