1,208 research outputs found
Interatomic Fe-H potential for irradiation and embrittlement simulations
The behavior of hydrogen in iron and iron alloys is of interest in many
fields of physics and materials science. To enable large-scale molecular
dynamics simulations of systems with Fe-H interactions, we develop, based on
density-functional theory calculations, an interatomic Fe-H potential in the
Tersoff-Brenner formalism. The obtained analytical potential is suitable for
simulations of H in bulk Fe as well as for modeling small FeH molecules, and it
can be directly combined with our previously constructed potential for the
stainless steel Fe-Cr-C system. This will allow simulations of, e.g.,
hydrocarbon molecule chemistry on steel surfaces. In the current work, we apply
the potential to simulating hydrogen-induced embrittlement in monocrystalline
bulk Fe and in an Fe bicrystal with a grain boundary. In both cases, hydrogen
is found to soften the material.Comment: 23 pages, 4 color figures; identical in content to the published
articl
Localization and Mobility Gap in Topological Anderson Insulator
It has been proposed that disorder may lead to a new type of topological
insulator, called topological Anderson insulator (TAI). Here we examine the
physical origin of this phenomenon. We calculate the topological invariants and
density of states of disordered model in a super-cell of 2-dimensional
HgTe/CdTe quantum well. The topologically non-trivial phase is triggered by a
band touching as the disorder strength increases. The TAI is protected by a
mobility gap, in contrast to the band gap in conventional quantum spin Hall
systems. The mobility gap in the TAI consists of a cluster of non-trivial
subgaps separated by almost flat and localized bands.Comment: 8 pages, 7 figure
Molecular dynamics study of the fragmentation of silicon doped fullerenes
Tight binding molecular dynamics simulations, with a non orthogonal basis
set, are performed to study the fragmentation of carbon fullerenes doped with
up to six silicon atoms. Both substitutional and adsorbed cases are considered.
The fragmentation process is simulated starting from the equilibrium
configuration in each case and imposing a high initial temperature to the
atoms. Kinetic energy quickly converts into potential energy, so that the
system oscillates for some picoseconds and eventually breaks up. The most
probable first event for substituted fullerenes is the ejection of a C2
molecule, another very frequent event being that one Si atom goes to an
adsorbed position. Adsorbed Si clusters tend to desorb as a whole when they
have four or more atoms, while the smaller ones tend to dissociate and
sometimes interchange positions with the C atoms. These results are compared
with experimental information from mass abundance spectroscopy and the products
of photofragmentation.Comment: Seven two-column pages, six postscript figures. To be published in
Physical Review
First principles calculations in iron: structure and mobility of defect clusters and defect complexes for kinetic modelling
Helping Schools Select and Implement Empirically Supported Practices in Prevention
This poster was presented at the American Psychological Association Conference, Boston, MA, in August 2008.School districts are inundated with innovation. Ongoing developments in academic and social-emotional curriculum, combined with external pressures to improve student outcomes, create challenges for districts to make informed decisions about programs to implement in their schools. In particular, efforts to identify and implement best practices in mental health programming and services are complicated by constantly evolving initiatives, strategies, and delivery systems. Our poster presents a rationale and model for helping school districts select and implement best practices in prevention and mental health promotion programming
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Suppression of Exosomal PD-L1 Induces Systemic Anti-tumor Immunity and Memory.
PD-L1 on the surface of tumor cells binds its receptor PD-1 on effector T cells, thereby suppressing their activity. Antibody blockade of PD-L1 can activate an anti-tumor immune response leading to durable remissions in a subset of cancer patients. Here, we describe an alternative mechanism of PD-L1 activity involving its secretion in tumor-derived exosomes. Removal of exosomal PD-L1 inhibits tumor growth, even in models resistant to anti-PD-L1 antibodies. Exosomal PD-L1 from the tumor suppresses T cell activation in the draining lymph node. Systemically introduced exosomal PD-L1 rescues growth of tumors unable to secrete their own. Exposure to exosomal PD-L1-deficient tumor cells suppresses growth of wild-type tumor cells injected at a distant site, simultaneously or months later. Anti-PD-L1 antibodies work additively, not redundantly, with exosomal PD-L1 blockade to suppress tumor growth. Together, these findings show that exosomal PD-L1 represents an unexplored therapeutic target, which could overcome resistance to current antibody approaches
Simulation of thermodynamic properties of magnetic transition metals from an efficient tight-binding model
Atomic scale simulations at finite temperature are an ideal approach to study
the thermodynamic properties of magnetic transition metals. However, the
development of interatomic potentials explicitly taking into account magnetic
variables is a delicate task. In this context, we present a tight-binding model
for magnetic transition metals in the Stoner approximation. This potential is
integrated into a Monte Carlo structural relaxations code where trials of
atomic displacements as well as fluctuations of local magnetic moments are
performed to determine the thermodynamic equilibrium state of the considered
systems. As an example, the Curie temperature of cobalt is investigated while
showing the important role of atomic relaxations. Furthermore, our model is
generalized to other transition metals highlighting a local magnetic moment
distribution that varies with the gradual filling of the d states.
Consequently, the successful validation of the potential for different magnetic
configurations indicates its great transferability makes it a good choice for
atomistic simulations sampling a large configuration space
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