443 research outputs found
Equivalent thermo-mechanical parameters for perfect crystals
Thermo-elastic behavior of perfect single crystal is considered. The crystal
is represented as a set of interacting particles (atoms). The approach for
determination of equivalent continuum values for the discrete system is
proposed. Averaging of equations of particles' motion and long wave
approximation are used in order to make link between the discrete system and
equivalent continuum. Basic balance equations for equivalent continuum are
derived from microscopic equations. Macroscopic values such as Piola and Cauchy
stress tensors and heat flux are represented via microscopic parameters.
Connection between the heat flux and temperature is discussed. Equation of
state in Mie-Gruneisen form connecting Cauchy stress tensor with deformation
gradient and thermal energy is obtained from microscopic considerations.Comment: To be published in proceedings of IUTAM Simposium on "Vibration
Analysis of Structures with Uncertainties", 2009; 14 pages
Forces between elongated particles in a nematic colloid
Using molecular dynamics simulations we study the interactions between elongated colloidal particles (length to breath ratio â«1) in a nematic host. The simulation results are compared to the results of a Landauâde Gennes elastic free energy. We find that depletion forces dominate for the sizes of the colloidal particles studied. The tangential component of the force, however, allows us to resolve the elastic contribution to the total interaction. We find that this contribution differs from the quadrupolar interaction predicted at large separations. The difference is due to the presence of nonlinear effects, namely, the change in the positions and structure of the defects and their annihilation at small separations
SELF-DUAL ANYONS IN UNIFORM BACKGROUND FIELDS
We study relativistic self-dual Chern-Simons-Higgs systems in the presence of
uniform background fields that explicitly break CTP. A rich, but discrete
vacuum structure is found when the gauge symmetry is spontaneously broken,
while the symmetric phase can have an infinite vacuum degeneracy at tree level.
The latter is due to the proliferation of neutral solitonic states that cost
zero energy. Various novel self-dual solitons, such as these, are found in both
the symmetric and the asymmetric phases. Also by considering a similar system
on a two-sphere and the subsequent large sphere limit, we isolate sensible and
finite expressions for the conserved angular and linear momenta, which satisfy
anomalous commutation relations. We conclude with a few remarks on unresolved
issues.Comment: LaTeX, 20 pages, 4 uuencoded figures included
Vortices and extreme black holes: the question of flux expulsion
It has been claimed that extreme black holes exhibit a phenomenon of flux
expulsion for abelian Higgs vortices, irrespective of the relative width of the
vortex to the black hole. Recent work by two of the authors showed a subtlety
in the treatment of the event horizon, which cast doubt on this claim. We
analyse in detail the vortex/extreme black hole system, showing that while flux
expulsion can occur, it does not do so in all cases. We give analytic proofs
for both expulsion and penetration of flux, in each case deriving a bound for
that behaviour. We also present extensive numerical work backing up, and
refining, these claims, and showing in detail how a vortex can end on a black
hole in all situations. We also calculate the backreaction of the vortex on the
geometry, and comment on the more general vortex-black hole system.Comment: 28 pages revtex, 10 figures, minor changes, reference adde
Atomic layering at the liquid silicon surface: a first- principles simulation
We simulate the liquid silicon surface with first-principles molecular
dynamics in a slab geometry. We find that the atom-density profile presents a
pronounced layering, similar to those observed in low-temperature liquid metals
like Ga and Hg. The depth-dependent pair correlation function shows that the
effect originates from directional bonding of Si atoms at the surface, and
propagates into the bulk. The layering has no major effects in the electronic
and dynamical properties of the system, that are very similar to those of bulk
liquid Si. To our knowledge, this is the first study of a liquid surface by
first-principles molecular dynamics.Comment: 4 pages, 4 figures, submitted to PR
Administrative Coding in Electronic Health Care Record-Based Research of NAFLD: An Expert Panel Consensus Statement
cited By 0Background and Aims Electronic health record (EHR)-based research allows the capture of large amounts of data, which is necessary in NAFLD, where the risk of clinical liver outcomes is generally low. The lack of consensus on which International Classification of Diseases (ICD) codes should be used as exposures and outcomes limits comparability and generalizability of results across studies. We aimed to establish consensus among a panel of experts on ICD codes that could become the reference standard and provide guidance around common methodological issues. Approach and Results Researchers with an interest in EHR-based NAFLD research were invited to collectively define which administrative codes are most appropriate for documenting exposures and outcomes. We used a modified Delphi approach to reach consensus on several commonly encountered methodological challenges in the field. After two rounds of revision, a high level of agreement (>67%) was reached on all items considered. Full consensus was achieved on a comprehensive list of administrative codes to be considered for inclusion and exclusion criteria in defining exposures and outcomes in EHR-based NAFLD research. We also provide suggestions on how to approach commonly encountered methodological issues and identify areas for future research. Conclusions This expert panel consensus statement can help harmonize and improve generalizability of EHR-based NAFLD research.Peer reviewe
Argon cluster impacts on layered silicon, silica, and graphite surfaces
Seven structures of covalently bonded materials are used as targets of 6 keV
Ar12 cluster bombardment in classical molecular dynamics
simulations. Energy deposition, cratering and Ar ranges are compared and remarkable
differences are found between the structures. In particular, bombardment of a
thin 2 nm silica layer on top of the Si(111) surface is shown to behave quite
differently from bombardment of pure Si
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
Ripples in a pond: Do social work students need to learn about terrorism?
In the face of heightened awareness of terrorism, however it is defined, the challenges for social work are legion. Social work roles may include working with the military to ensure the well-being of service-men and women and their families when bereaved or injured, as well as being prepared to support the public within the emergency context of an overt act of terrorism. This paper reviews some of the literature concerning how social work responds to confl ict and terrorism before reporting a smallscale qualitative study examining the views of social work students, on a qualifying programme in the UK, of terrorism and the need for knowledge and understanding as part of their education
- âŠ