65 research outputs found
Two-scale convergence for locally-periodic microstructures and homogenization of plywood structures
The introduced notion of locally-periodic two-scale convergence allows to
average a wider range of microstructures, compared to the periodic one. The
compactness theorem for the locally-periodic two-scale convergence and the
characterisation of the limit for a sequence bounded in are
proven. The underlying analysis comprises the approximation of functions, which
periodicity with respect to the fast variable depends on the slow variable, by
locally-periodic functions, periodic in subdomains smaller than the considered
domain, but larger than the size of microscopic structures. The developed
theory is applied to derive macroscopic equations for a linear elasticity
problem defined in domains with plywood structures.Comment: 22 pages, 4 figure
Locally periodic unfolding method and two-scale convergence on surfaces of locally periodic microstructures
In this paper we generalize the periodic unfolding method and the notion of
two-scale convergence on surfaces of periodic microstructures to locally
periodic situations. The methods that we introduce allow us to consider a wide
range of non-periodic microstructures, especially to derive macroscopic
equations for problems posed in domains with perforations distributed
non-periodically. Using the methods of locally periodic two-scale convergence
(l-t-s) on oscillating surfaces and the locally periodic (l-p) boundary
unfolding operator, we are able to analyze differential equations defined on
boundaries of non-periodic microstructures and consider non-homogeneous Neumann
conditions on the boundaries of perforations, distributed non-periodically
Interior Regularity Estimates in High Conductivity Homogenization and Application
In this paper, uniform pointwise regularity estimates for the solutions of
conductivity equations are obtained in a unit conductivity medium reinforced by
a epsilon-periodic lattice of highly conducting thin rods. The estimates are
derived only at a distance epsilon^{1+tau} (for some tau>0) away from the
fibres. This distance constraint is rather sharp since the gradients of the
solutions are shown to be unbounded locally in L^p as soon as p>2. One key
ingredient is the derivation in dimension two of regularity estimates to the
solutions of the equations deduced from a Fourier series expansion with respect
to the fibres direction, and weighted by the high-contrast conductivity. The
dependence on powers of epsilon of these two-dimensional estimates is shown to
be sharp. The initial motivation for this work comes from imaging, and enhanced
resolution phenomena observed experimentally in the presence of
micro-structures. We use these regularity estimates to characterize the
signature of low volume fraction heterogeneities in the fibred reinforced
medium assuming that the heterogeneities stay at a distance epsilon^{1+tau}
away from the fibres
Effective macroscopic dynamics of stochastic partial differential equations in perforated domains
An effective macroscopic model for a stochastic microscopic system is
derived. The original microscopic system is modeled by a stochastic partial
differential equation defined on a domain perforated with small holes or
heterogeneities. The homogenized effective model is still a stochastic partial
differential equation but defined on a unified domain without holes. The
solutions of the microscopic model is shown to converge to those of the
effective macroscopic model in probability distribution, as the size of holes
diminishes to zero. Moreover, the long time effectivity of the macroscopic
system in the sense of \emph{convergence in probability distribution}, and the
effectivity of the macroscopic system in the sense of \emph{convergence in
energy} are also proved
Bounds on strong field magneto-transport in three-dimensional composites
This paper deals with bounds satisfied by the effective non-symmetric
conductivity of three-dimensional composites in the presence of a strong
magnetic field. On the one hand, it is shown that for general composites the
antisymmetric part of the effective conductivity cannot be bounded solely in
terms of the antisymmetric part of the local conductivity, contrary to the
columnar case. So, a suitable rank-two laminate the conductivity of which has a
bounded antisymmetric part together with a high-contrast symmetric part, may
generate an arbitrarily large antisymmetric part of the effective conductivity.
On the other hand, bounds are provided which show that the antisymmetric part
of the effective conductivity must go to zero if the upper bound on the
antisymmetric part of the local conductivity goes to zero, and the symmetric
part of the local conductivity remains bounded below and above. Elementary
bounds on the effective moduli are derived assuming the local conductivity and
effective conductivity have transverse isotropy in the plane orthogonal to the
magnetic field. New Hashin-Shtrikman type bounds for two-phase
three-dimensional composites with a non-symmetric conductivity are provided
under geometric isotropy of the microstructure. The derivation of the bounds is
based on a particular variational principle symmetrizing the problem, and the
use of Y-tensors involving the averages of the fields in each phase.Comment: 21 page
Brownfield Action: Dissemination of a SENCER Model Curriculum and the Creation of a Collaborative STEM Education Network
Brownfield Action (BA) is a web-based environmental site assessment (ESA) simulation in which students form geotechnical consulting companies and work together to solve problems in environmental forensics. Developed at Barnard College with the Columbia Center for New Media Teaching and Learning, BA has been disseminated to ten colleges, universities, and high schools, resulting in a collaborative network of educators. The experiences of current users are presented describing how they have incorporated the BA curriculum into their courses, as well as how BA affected teaching and learning. The experiences demonstrate that BA can be used in whole or in part, is applicable to a wide range of student capabilities and has been successfully adapted to a variety of learning goals, from introducing non-science-literate students to basic concepts of environmental science and civic issues of environmental contamination to providing advanced training in ESA and modeling groundwater contamination to future environmental professionals
Homogenized dynamics of stochastic partial differential equations with dynamical boundary conditions
A microscopic heterogeneous system under random influence is considered. The
randomness enters the system at physical boundary of small scale obstacles as
well as at the interior of the physical medium. This system is modeled by a
stochastic partial differential equation defined on a domain perforated with
small holes (obstacles or heterogeneities), together with random dynamical
boundary conditions on the boundaries of these small holes.
A homogenized macroscopic model for this microscopic heterogeneous stochastic
system is derived. This homogenized effective model is a new stochastic partial
differential equation defined on a unified domain without small holes, with
static boundary condition only. In fact, the random dynamical boundary
conditions are homogenized out, but the impact of random forces on the small
holes' boundaries is quantified as an extra stochastic term in the homogenized
stochastic partial differential equation. Moreover, the validity of the
homogenized model is justified by showing that the solutions of the microscopic
model converge to those of the effective macroscopic model in probability
distribution, as the size of small holes diminishes to zero.Comment: Communications in Mathematical Physics, to appear, 200
Radiation Combined With Thermal Injury Induces Immature Myeloid Cells
The continued development of nuclear weapons and the potential for thermonuclear injury necessitates the further understanding of the immune consequences after radiation combined with injury (RCI). We hypothesized that sub-lethal ionization radiation exposure combined with a full thickness thermal injury would result in the production of immature myeloid cells. Mice underwent either a 20% total body surface area (TBSA) full-thickness contact burn or sham procedure followed by a single whole body dose of 5-Gy radiation. Serum, spleen and peripheral lymph nodes were harvested at 3 and 14 days post-injury. Flow cytometry was performed to identify and characterize adaptive and innate cell compartments. Elevated pro- and anti-inflammatory serum cytokines and profound leukopenia were observed after RCI. A population of cells with dual expression of the cell surface markers Gr-1 and CD11b were identified in all experimental groups, but was significantly elevated after burn alone and RCI at 14 days post-injury. In contrast to the T-cell suppressive nature of myeloid-derived suppressor cells (MDSC) found after trauma and sepsis, myeloid cells after RCI augmented T-cell proliferation and were associated with a weak but significant increase in IFN-γ and a decrease in IL-10. This is consistent with previous work in burn injury indicating that a MDSC-like population increases innate immunity. RCI results in the increase of distinct populations of Gr-1+ CD11b+cells within the secondary lymphoid organs, and we propose these immature inflammatory myeloid cells provide innate immunity to the severely injured and immunocompromised host
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