151 research outputs found
Variational approach in dislocation theory
A variational approach is presented to calculate the stress field generated
by a system of dislocations. It is shown that in the simplest case, when the
material containing the dislocations obeys Hooke's law the variational
framework gives the same field equations as Kr\"oner's theory. However, the
variational method proposed allows to study many other problems like
dislocation core regularisation, role of elastic anharmonicity and
dislocation--solute atom interaction. The aim of the paper is to demonstrate
that these problems can be handled on a systematic manner.Comment: 16 pages, 4 figures. Minor changes in the text and few numerical
corrections. Few references also adde
Disclination vortices in elastic media
The vortex-like solutions are studied in the framework of the gauge model of
disclinations in elastic continuum. A complete set of model equations with
disclination driven dislocations taken into account is considered. Within the
linear approximation an exact solution for a low-angle wedge disclination is
found to be independent from the coupling constants of the theory. As a result,
no additional dimensional characteristics (like the core radius of the defect)
are involved. The situation changes drastically for 2\pi vortices where two
characteristic lengths, l_\phi and l_W, become of importance. The asymptotical
behaviour of the solutions for both singular and nonsingular 2\pi vortices is
studied. Forces between pairs of vortices are calculated.Comment: 13 pages, published versio
An elastoplastic theory of dislocations as a physical field theory with torsion
We consider a static theory of dislocations with moment stress in an
anisotropic or isotropic elastoplastical material as a T(3)-gauge theory. We
obtain Yang-Mills type field equations which express the force and the moment
equilibrium. Additionally, we discuss several constitutive laws between the
dislocation density and the moment stress. For a straight screw dislocation, we
find the stress field which is modified near the dislocation core due to the
appearance of moment stress. For the first time, we calculate the localized
moment stress, the Nye tensor, the elastoplastic energy and the modified
Peach-Koehler force of a screw dislocation in this framework. Moreover, we
discuss the straightforward analogy between a screw dislocation and a magnetic
vortex. The dislocation theory in solids is also considered as a
three-dimensional effective theory of gravity.Comment: 38 pages, 6 figures, RevTe
Regge Calculus in Teleparallel Gravity
In the context of the teleparallel equivalent of general relativity, the
Weitzenbock manifold is considered as the limit of a suitable sequence of
discrete lattices composed of an increasing number of smaller an smaller
simplices, where the interior of each simplex (Delaunay lattice) is assumed to
be flat. The link lengths between any pair of vertices serve as independent
variables, so that torsion turns out to be localized in the two dimensional
hypersurfaces (dislocation triangle, or hinge) of the lattice. Assuming that a
vector undergoes a dislocation in relation to its initial position as it is
parallel transported along the perimeter of the dual lattice (Voronoi polygon),
we obtain the discrete analogue of the teleparallel action, as well as the
corresponding simplicial vacuum field equations.Comment: Latex, 10 pages, 2 eps figures, to appear in Class. Quant. Gra
The Einsteinian T(3)-Gauge Approach and the Stress Tensor of the Screw Dislocation in the Second Order: Avoiding the Cut-off at the Core
A translational gauge approach of the Einstein type is proposed for obtaining
the stresses that are due to non-singular screw dislocation. The stress
distribution of second order around the screw dislocation is classically known
for the hollow circular cylinder with traction-free external and internal
boundaries. The inner boundary surrounds the dislocation's core, which is not
captured by the conventional solution. The present gauge approach enables us to
continue the classically known quadratic stresses inside the core. The gauge
equation is chosen in the Hilbert--Einstein form, and it plays the role of
non-conventional incompatibility law. The stress function method is used, and
it leads to the modified stress potential given by two constituents: the
conventional one, say, the `background' and a short-ranged gauge contribution.
The latter just causes additional stresses, which are localized. The asymptotic
properties of the resulting stresses are studied. Since the gauge contributions
are short-ranged, the background stress field dominates sufficiently far from
the core. The outer cylinder's boundary is traction-free. At sufficiently
moderate distances, the second order stresses acquire regular continuation
within the core region, and the cut-off at the core does not occur. Expressions
for the asymptotically far stresses provide self-consistently new length scales
dependent on the elastic parameters. These lengths could characterize an
exteriority of the dislocation core region.Comment: 34 pages, LaTe
The effects of second-hand smoke on biological processes important in atherogenesis
BACKGROUND: Atherosclerosis is the leading cause of death in western societies and cigarette smoke is among the factors that strongly contribute to the development of this disease. The early events in atherogenesis are stimulated on the one hand by cytokines that chemoattract leukocytes and on the other hand by decrease in circulating molecules that protect endothelial cells (ECs) from injury. Here we focus our studies on the effects of "second-hand" smoke on atherogenesis. METHODS: To perform these studies, a smoking system that closely simulates exposure of humans to second-hand smoke was developed and a mouse model system transgenic for human apoB(100 )was used. These mice have moderate lipid levels that closely mimic human conditions that lead to atherosclerotic plaque formation. RESULTS: "Second-hand" cigarette smoke decreases plasma high density lipoprotein levels in the blood and also decreases the ratios between high density lipoprotein and low density lipoprotein, high density lipoprotein and triglyceride, and high density lipoprotein and total cholesterol. This change in lipid profiles causes not only more lipid accumulation in the aorta but also lipid deposition in many of the smaller vessels of the heart and in hepatocytes. In addition, mice exposed to smoke have increased levels of Monocyte Chemoattractant Protein–1 in circulation and in the heart/aorta tissue, have increased macrophages in the arterial walls, and have decreased levels of adiponectin, an EC-protective protein. Also, cytokine arrays revealed that mice exposed to smoke do not undergo the switch from the pro-inflammatory cytokine profile (that develops when the mice are initially exposed to second-hand smoke) to the adaptive response. Furthermore, triglyceride levels increase significantly in the liver of smoke-exposed mice. CONCLUSION: Long-term exposure to "second-hand" smoke creates a state of permanent inflammation and an imbalance in the lipid profile that leads to lipid accumulation in the liver and in the blood vessels of the heart and aorta. The former potentially can lead to non-alcoholic fatty liver disease and the latter to heart attacks
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Comparative phylogenetic methods and the cultural evolution of medicinal plant use
Human life depends on plant biodiversity and the ways in which plants are used are culturally determined. Whilst anthropologists have used phylogenetic comparative methods (PCMs) to gain an increasingly sophisticated understanding of the evolution of political, religious, social, and material culture, plant use has been almost entirely neglected. Medicinal plants are of special interest because of their role in maintaining people’s health across the world. PCMs in particular, and cultural evolutionary theory in general, provide a framework in which to study the diversity of medicinal plant applications cross-culturally, and to infer changes in plant use through time. These methods can be applied to single medicinal plants as well as the entire set of plants used by a culture for medicine, and they account for the non-independence of data when testing for floristic, cultural or other drivers of plant use. With cultural, biological, and linguistic diversity under threat, gaining a deeper and broader understanding of the variation of medicinal plant use through time and space is pressing
Nutraceutical therapies for atherosclerosis
Atherosclerosis is a chronic inflammatory disease affecting large and medium arteries and is considered to be a major underlying cause of cardiovascular disease (CVD). Although the development of pharmacotherapies to treat CVD has contributed to a decline in cardiac mortality in the past few decades, CVD is estimated to be the cause of one-third of deaths globally. Nutraceuticals are natural nutritional compounds that are beneficial for the prevention or treatment of disease and, therefore, are a possible therapeutic avenue for the treatment of atherosclerosis. The purpose of this Review is to highlight potential nutraceuticals for use as antiatherogenic therapies with evidence from in vitro and in vivo studies. Furthermore, the current evidence from observational and randomized clinical studies into the role of nutraceuticals in preventing atherosclerosis in humans will also be discussed
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