Abstract

Living biological tissues are complex structures that have the capacity of evolving
in response to external loads and environmental stimuli. The adequate modelling
of soft biological tissue behaviour is a key issue in successfully reproducing
biomechanical problems through computational analysis.
This study presents a general constitutive formulation capable of representing
the behaviour of these tissues through finite element simulation. It is based on
phenomenological models that, used in combination with the generalized mixing
theory, can numerically reproduce a wide range of material behaviours.
First, the passive behaviour of tissues is characterized by means of hyperelastic
and finite-strain damage models. A generalized damage model is proposed,
providing a flexible and versatile formulation that can reproduce a wide range of
tissue behaviour. It can be particularized to any hyperelastic model and requires
identifying only two material parameters. Then, the use of these constitutive
models with generalized mixing theory in a nite strain framework is described
and tools to account for the anisotropic behaviour of tissues are put forth.
The active behaviour of tissues is characterized through constitutive models
capable of reproducing the growth and remodelling phenomena. These are built
on the hyperelastic and damage formulations described above and, thus, represent
the active extension of the passive tissue behaviour. A growth model considering
biological availability is used and extended to include directional growth. In addition,
a novel constitutive model for homeostatic-driven turnover remodelling is
presented and discussed. This model captures the stiffness recovery that occurs
in healing tissues, understood as a recovery or reversal of damage in the tissue,
which is driven by both mechanical and biochemical stimuli.
Finally, the issue of correctly identifying the material parameters for computational
modelling is addressed. An inverse method using optimization techniques
is developed to facilitate the identification of these parameters.

Abstract

Abstract

Some of the key factors that regulate growth and remodeling of tissues are fundamentally mechanical. However, it is important to take into account the role of biological availability to generate new tissue together with the stresses and strains in the processes of natural or pathological growth. In this sense, the model presented in this work is oriented to describe growth of vascular tissue under "stress driven growth" considering biological availability of the organism. The general theoretical framework is given by a kinematic formulation in large strain combined with the thermodynamic basis of open systems. The formulation uses a multiplicative decomposition of deformation gradient, splitting it in a growth part and visco-elastic part. The strains due to growth are incompatible and are controlled by unbalanced stresses related to a homeostatic state. Growth implies a volume change with an increase of mass maintaining constant the density. One of the most interesting features of the proposed model is the generation of new tissue taking into account the contribution of mass to the system controlled through the biological availability. Because soft biological tissues in general have a hierarchical structure with several components (usually a soft matrix reinforced with collagen fibers), the developed growth model is suitable for the growth characterization of each component. This allows considering a different behavior for each of them in the context of a generalized theory of mixtures.

Abstract

Mergers and acquisitions are widely seen as a long-term strategy for resolving financial problems in corporations. This research study that is primarily based on a desk review established that this commercial enterprise approach has given mixed findings, such as failing to establish that the stated factors led to the manner of mergers and acquisitions, nor has it published an increase in profitability of commercial enterprise financial performance due to mergers and acquisitions. However, all mergers and acquisitions are no longer unsuccessful due to some factors like monetary, advertising, and operational problems. Thus, there are other important factors that influence mergers and acquisitions, such as value creation, 'cultural' integration, and profitability. According to the study's findings, mergers and acquisitions have a positive impact on financial institutions' net income in the form of in-creased wealth, decreased effective spending, and increased revenue growth.

Abstract