5,830 research outputs found
Computational coarse graining of a randomly forced 1-D Burgers equation
We explore a computational approach to coarse graining the evolution of the
large-scale features of a randomly forced Burgers equation in one spatial
dimension. The long term evolution of the solution energy spectrum appears
self-similar in time. We demonstrate coarse projective integration and coarse
dynamic renormalization as tools that accelerate the extraction of macroscopic
information (integration in time, self-similar shapes, and nontrivial dynamic
exponents) from short bursts of appropriately initialized direct simulation.
These procedures solve numerically an effective evolution equation for the
energy spectrum without ever deriving this equation in closed form.Comment: 21 pages, 7 figure
Using network-flow techniques to solve an optimization problem from surface-physics
The solid-on-solid model provides a commonly used framework for the
description of surfaces. In the last years it has been extended in order to
investigate the effect of defects in the bulk on the roughness of the surface.
The determination of the ground state of this model leads to a combinatorial
problem, which is reduced to an uncapacitated, convex minimum-circulation
problem. We will show that the successive shortest path algorithm solves the
problem in polynomial time.Comment: 8 Pages LaTeX, using Elsevier preprint style (macros included
In vivo terahertz imaging to evaluate scar treatment strategies : silicone gel sheeting
Silicone gel sheeting (SGS) is widely used for scar treatment; however, studies showing its interaction with skin and efficacy of scar treatment are still lacking. THz light is non-ionizing and highly sensitive to changes in water content and thus skin hydration. In this work, we use in-vivo THz imaging to monitor how SGS affects the THz response of human skin during occlusion, and the associated THz reflectivity and refractive index changes are presented. We find that SGS effectively hydrates the skin beneath it, with minimal lateral effects beyond the sheeting. Our work demonstrates that THz imaging is able to detect the subtle hydration changes on the surface of human skin caused by SGS, and it has the potential to be used to evaluate different scar treatment strategies
THz in vivo measurements : the effects of pressure on skin reflectivity
Terahertz (THz) light is non-ionizing and highly sensitive to subtle changes in water concentration which can be indicative of disease. The short THz penetration depth in bio-samples restricts in vivo measurements to be in a reflection geometry and the sample is often placed onto an imaging window. Upon contacting the imaging window, occlusion and compression of the skin affect the THz response. If not appropriately controlled, this could cause misleading results. In this work, we investigate and quantify how the applied pressure affects the THz response of skin and employ a stratified model to help understand the mechanisms at play. This work will enable future THz studies to have a more rigorous experimental protocol, which in turn will facilitate research in various potential biomedical applications under investigation
Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft-X-ray emission spectroscopy
The electronic structures of epitaxially grown films of Ti3AlC2, Ti3SiC2 and
Ti3GeC2 have been investigated by bulk-sensitive soft X-ray emission
spectroscopy. The measured high-resolution Ti L, C K, Al L, Si L and Ge M
emission spectra are compared with ab initio density-functional theory
including core-to-valence dipole matrix elements. A qualitative agreement
between experiment and theory is obtained. A weak covalent Ti-Al bond is
manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2. As Al is
replaced with Si or Ge, the shoulder disappears. For the buried Al and
Si-layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and
Ti3SiC2, respectively. As a result of relaxation of the crystal structure and
the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened.
The differences between the electronic structures are discussed in relation to
the bonding in the nanolaminates and the corresponding change of materials
properties.Comment: 15 pages, 8 figure
Optimal Traffic Networks
Inspired by studies on the airports' network and the physical Internet, we
propose a general model of weighted networks via an optimization principle. The
topology of the optimal network turns out to be a spanning tree that minimizes
a combination of topological and metric quantities. It is characterized by a
strongly heterogeneous traffic, non-trivial correlations between distance and
traffic and a broadly distributed centrality. A clear spatial hierarchical
organization, with local hubs distributing traffic in smaller regions, emerges
as a result of the optimization. Varying the parameters of the cost function,
different classes of trees are recovered, including in particular the minimum
spanning tree and the shortest path tree. These results suggest that a
variational approach represents an alternative and possibly very meaningful
path to the study of the structure of complex weighted networks.Comment: 4 pages, 4 figures, final revised versio
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