2,474 research outputs found
A Potential Energy Landscape Study of the Amorphous-Amorphous Transformation in HO
We study the potential energy landscape explored during a
compression-decompression cycle for the SPC/E (extended simple point charge)
model of water. During the cycle, the system changes from low density amorphous
ice (LDA) to high density amorphous ice (HDA). After the cycle, the system does
not return to the same region of the landscape, supporting the interesting
possibility that more than one significantly different configuration
corresponds to LDA. We find that the regions of the landscape explored during
this transition have properties remarkably different from those explored in
thermal equilibrium in the liquid phase
Density minimum and liquid-liquid phase transition
We present a high-resolution computer simulation study of the equation of
state of ST2 water, evaluating the liquid-state properties at 2718 state
points, and precisely locating the liquid-liquid critical point (LLCP)
occurring in this model. We are thereby able to reveal the interconnected set
of density anomalies, spinodal instabilities and response function extrema that
occur in the vicinity of a LLCP for the case of a realistic, off-lattice model
of a liquid with local tetrahedral order. In particular, we unambiguously
identify a density minimum in the liquid state, define its relationship to
other anomalies, and show that it arises due to the approach of the liquid
structure to a defect-free random tetrahedral network of hydrogen bonds.Comment: 5 pages, 4 figure
Ice XII in its second regime of metastability
We present neutron powder diffraction results which give unambiguous evidence
for the formation of the recently identified new crystalline ice phase[Lobban
et al.,Nature, 391, 268, (1998)], labeled ice XII, at completely different
conditions. Ice XII is produced here by compressing hexagonal ice I_h at T =
77, 100, 140 and 160 K up to 1.8 GPa. It can be maintained at ambient pressure
in the temperature range 1.5 < T < 135 K. High resolution diffraction is
carried out at T = 1.5 K and ambient pressure on ice XII and accurate
structural properties are obtained from Rietveld refinement. At T = 140 and 160
K additionally ice III/IX is formed. The increasing amount of ice III/IX with
increasing temperature gives an upper limit of T ~ 150 K for the successful
formation of ice XII with the presented procedure.Comment: 3 Pages of RevTeX, 3 tables, 3 figures (submitted to Physical Review
Letters
An Analytic Model with Critical Behavior in Black Hole Formation
A simple analytic model is presented which exhibits a critical behavior in
black hole formation, namely, collapse of a thin shell coupled with outgoing
null fluid. It is seen that the critical behavior is caused by the
gravitational nonlinearity near the event horizon. We calculate the value of
the critical exponent analytically and find that it is very dependent on the
coupling constants of the system.Comment: 21pp., ReVTeX, 7 figures (postscript, compressed and uuencoded),
TIT/HEP-266/COSMO-4
Application of the Linux cluster for exhaustive window haplotype analysis using the FBAT and Unphased programs
Background: Genetic association studies have been used to map disease-causing genes. A newly introduced statistical method, called exhaustive haplotype association study, analyzes genetic information consisting of different numbers and combinations of DNA sequence variations along a chromosome. Such studies involve a large number of statistical calculations and subsequently high computing power. It is possible to develop parallel algorithms and codes to perform the calculations on a high performance computing (HPC) system. However, most existing commonly-used statistic packages for genetic studies are non-parallel versions. Alternatively, one may use the cutting-edge technology of grid computing and its packages to conduct non-parallel genetic statistical packages on a centralized HPC system or distributed computing systems. In this paper, we report the utilization of a queuing scheduler built on the Grid Engine and run on a Rocks Linux cluster for our genetic statistical studies.
Results: Analysis of both consecutive and combinational window haplotypes was conducted by the FBAT (Laird et al., 2000) and Unphased (Dudbridge, 2003) programs. The dataset consisted of 26 loci from 277 extended families (1484 persons). Using the Rocks Linux cluster with 22 compute-nodes, FBAT jobs performed about 14.4–15.9 times faster, while Unphased jobs performed 1.1–18.6 times faster compared to the accumulated computation duration.
Conclusion: Execution of exhaustive haplotype analysis using non-parallel software packages on a Linux-based system is an effective and efficient approach in terms of cost and performance
Overnight corneal swelling responses: A comparison of CIBA NewVues vs. Vistakon Acuvue Plus
Two recently marketed disposable soft contact lenses, the CIBA NewVue and the Vistakon Acuvue Plus, were compared for overnight corneal swelling response. After seven hours of sleep, the mean percent central corneal swelling of our fifteen subjects were 7.41% + 3.84 for the CIBA New Vue and 9.28% + 5.69 for the Vistakon Acuvue Plus. There was no statistically significant difference between the mean percent corneal swelling induced by these two contact lenses (
Instability of Myelin Tubes under Dehydration: deswelling of layered cylindrical structures
We report experimental observations of an undulational instability of myelin
figures. Motivated by this, we examine theoretically the deformation and
possible instability of concentric, cylindrical, multi-lamellar membrane
structures. Under conditions of osmotic stress (swelling or dehydration), we
find a stable, deformed state in which the layer deformation is given by \delta
R ~ r^{\sqrt{B_A/(hB)}}, where B_A is the area compression modulus, B is the
inter-layer compression modulus, and h is the repeat distance of layers. Also,
above a finite threshold of dehydration (or osmotic stress), we find that the
system becomes unstable to undulations, first with a characteristic wavelength
of order \sqrt{xi d_0}, where xi is the standard smectic penetration depth and
d_0 is the thickness of dehydrated region.Comment: 5 pages + 3 figures [revtex 4
Structural Order in Glassy Water
We investigate structural order in glassy water by performing classical
molecular dynamics simulations using the extended simple point charge (SPC/E)
model of water. We perform isochoric cooling simulations across the glass
transition temperature at different cooling rates and densities. We quantify
structural order by orientational and translational order metrics. Upon cooling
the liquid into the glassy state, both the orientational order parameter
and translational order parameter increase. At T=0 K, the glasses fall
on a line in the - plane or {\it order map}.
The position of this line depends only on density and coincides with the
location in the order map of the inherent structures (IS) sampled upon cooling.
We evaluate the energy of the IS, , and find that both order
parameters for the IS are proportional to . We also study the
structural order during the transformation of low-density amorphous ice (LDA)
to high-density amorphous ice (HDA) upon isothermal compression and are able to
identify distinct regions in the order map corresponding to these glasses.
Comparison of the order parameters for LDA and HDA with those obtained upon
isochoric cooling indicates major structural differences between glasses
obtained by cooling and glasses obtained by compression. These structural
differences are only weakly reflected in the pair correlation function. We also
characterize the evolution of structural order upon isobaric annealing, leading
at high pressure to very-high density amorphous ice (VHDA).Comment: submitte
Constraints on Hidden Photon Models from Electron g-2 and Hydrogen Spectroscopy
The hidden photon model is one of the simplest models which can explain the
anomaly of the muon anomalous magnetic moment (g-2). The experimental
constraints are studied in detail, which come from the electron g-2 and the
hydrogen transition frequencies. The input parameters are set carefully in
order to take dark photon contributions into account and to prevent the
analysis from being self-inconsistent. It is shown that the new analysis
provides a constraint severer by more than one order of magnitude than the
previous result.Comment: 18 pages, 2 figures, 1 table. v2: minor correction
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