500 research outputs found
Heterogeneity in structurally arrested hard spheres
When cooled or compressed sufficiently rapidly, a liquid vitrifies into a glassy amorphous state. Vitrification in a dense liquid is associated with jamming of the particles. For hard spheres, the density and degree of order in the final structure depend on the compression rate: simple intuition suggests, and previous computer simulation demonstrates, that slower compression results in states that are both denser and more ordered. In this work, we use the Lubachevsky-Stillinger algorithm to generate a sequence of structurally arrested hard-sphere states by varying the compression rate. We find that while the degree of order, as measured by both bond-orientation and translation order parameters, increases monotonically with decreasing compression rate, the density of the arrested state first increases, then decreases, then increases again, as the compression rate decreases, showing a minimum at an intermediate compression rate. Examination of the distribution of the local order parameters and the distribution of the root-mean-square fluctuation of the particle positions, as well as direct visual inspection of the arrested structures, reveal that they are structurally heterogeneous, consisting of disordered, amorphous regions and locally ordered crystal-like domains. In particular, the low-density arrested states correspond with many interconnected small crystal clusters that form a polycrystalline network interspersed in an amorphous background, suggesting that jamming by the domains may be an important mechanism for these states
Multiphase transport model for heavy ion collisions at RHIC
Using a multiphase transport model (AMPT) with both partonic and hadronic
interactions, we study the multiplicity and transverse momentum distributions
of charged particles such as pions, kaons and protons in central Au+Au
collisions at RHIC energies. Effects due to nuclear shadowing and jet quenching
on these observables are also studied. We further show preliminary results on
the production of multistrange baryons from the strangeness-exchange reactions
during the hadronic stage of heavy ion collisions.Comment: 4 pages, 4 figures, espcrc1.sty included, presented at 15th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(QM2001), Long Island, New York, January 200
Withaferin A promotes proliferation and migration of brain endothelial cells
Purpose: To investigate the effect of withaferin A (WFA) on the proliferation and migration of brain endothelial cells.Methods: BALB-5023 mouse microvascular cells were treated with a range of withaferin A (WFA) concentrations from 10 to 100 ng/mL. Dojindo’s CCK-8 cell proliferation kit was used for the analysis of cell proliferation. Transwell cell culture inserts were used to determine the migration potential of WFAtreated endothelial cells. Absorbance was measured at 450 nm on an enzyme-linked immunosorbent(ELISA) reader.Results: The results revealed a significant increase in the proliferation and migration of endothelial cells following treatment with a low concentration (30 ng/mL) of WFA compared with the higher concentration (> 10 ng/mL). The effect was further enhanced when WFA was used in combination with soluble Fas ligand (sFasL). Autocrine signaling of vascular endothelial growth factor (VEGF) by endothelial cellswas significantly increased following treatment with WFA or in combination with sFasL. WFA increased the expression of Fas on endothelial cells, suggesting the involvement of sFasL in the proliferation and migration of brain endothelial cells.Conclusion: Thus, WFA promotes the proliferation and migration of endothelial cells through increase in the expression of Fas and secretion of VEGF.Keywords: Endothelial cells, Vascular endothelial growth factor, Microvascular, Vascular disease, Withaferin
Unidirectional anisotropy in cubic FeGe with antisymmetric spin-spin-coupling
We report strong unidirectional anisotropy in bulk polycrystalline B20 FeGe
measured by ferromagnetic resonance spectroscopy. Bulk and micron-sized samples
were produced and analytically characterized. FeGe is a B20 compound with
inherent Dzyaloshinskii-Moriya interaction. Lorenz microscopy confirms a
skyrmion lattice at in a magnetic field of 150 mT.
Ferromagnetic resonance was measured at ,
near the Curie temperature. Two resonance modes were observed, both exhibit a
unidirectional anisotropy of in
the primary, and in the secondary
mode, previously unknown in bulk ferromagnets. Additionally, about 25 standing
spin wave modes are observed inside a micron-sized FeGe wedge, measured at room
temperature ( K). These modes also exhibit unidirectional
anisotropy
A Multi-Phase Transport Model for Relativistic Heavy Ion Collisions
We describe in detail how the different components of a multi-phase transport
(AMPT) model, that uses the Heavy Ion Jet Interaction Generator (HIJING) for
generating the initial conditions, Zhang's Parton Cascade (ZPC) for modeling
partonic scatterings, the Lund string fragmentation model or a quark
coalescence model for hadronization, and A Relativistic Transport (ART) model
for treating hadronic scatterings, are improved and combined to give a coherent
description of the dynamics of relativistic heavy ion collisions. We also
explain the way parameters in the model are determined, and discuss the
sensitivity of predicted results to physical input in the model. Comparisons of
these results to experimental data, mainly from heavy ion collisions at the
Relativistic Heavy Ion Collider (RHIC), are then made in order to extract
information on the properties of the hot dense matter formed in these
collisions.Comment: 33 pages, 38 figures, revtex. Added 9 figures, version published in
Phys. Rev. C. The full source code of the AMPT model in the Fortran 77
language and instructions for users are available from the EPAPS ftp site
(ftp://ftp.aip.org/epaps/phys_rev_c/E-PRVCAN-72-781512/) and the OSCAR
website (http://www-cunuke.phys.columbia.edu/OSCAR/
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