12,004 research outputs found
Apparent finite-size effects in the dynamics of supercooled liquids
Molecular dynamics simulations are performed for a supercooled simple liquid
with changing the system size from N=108 to to examine possible
finite-size effects. Although almost no systematic deviation is detected in the
static pair correlation functions, it is demonstrated that the structural
relaxation in a small system becomes considerably slower than that in
larger systems for temperatures below at which the size of the
cooperative particle motions becomes comparable to the unit cell length of the
small system. The discrepancy increases with decreasing temperature.Comment: 4 pages 5 figure
Simulating (electro)hydrodynamic effects in colloidal dispersions: smoothed profile method
Previously, we have proposed a direct simulation scheme for colloidal
dispersions in a Newtonian solvent [Phys.Rev.E 71,036707 (2005)]. An improved
formulation called the ``Smoothed Profile (SP) method'' is presented here in
which simultaneous time-marching is used for the host fluid and colloids. The
SP method is a direct numerical simulation of particulate flows and provides a
coupling scheme between the continuum fluid dynamics and rigid-body dynamics
through utilization of a smoothed profile for the colloidal particles.
Moreover, the improved formulation includes an extension to incorporate
multi-component fluids, allowing systems such as charged colloids in
electrolyte solutions to be studied. The dynamics of the colloidal dispersions
are solved with the same computational cost as required for solving
non-particulate flows. Numerical results which assess the hydrodynamic
interactions of colloidal dispersions are presented to validate the SP method.
The SP method is not restricted to particular constitutive models of the host
fluids and can hence be applied to colloidal dispersions in complex fluids
A Smooth Interface Method for Simulating Liquid Crystal Colloid Dispersions
A new method is presented for mesoscopic simulations of particle dispersions
in liquid crystal solvents. It allows efficient first-principle simulations of
the dispersions involving many particles with many-body interactions mediated
by the solvents. Demonstrations have been performed for the aggregation of
colloid dispersions in two-dimensional nematic and smectic-C* solvents
neglecting hydrodynamic effects, which will be taken into account in the near
future.Comment: 13 pages, 4 figure
Mechanical Responses and Stress Fluctuations of a Supercooled Liquid in a Sheared Non-Equilibrium State
A steady shear flow can drive supercooled liquids into a non-equilibrium
state. Using molecular dynamics simulations under steady shear flow
superimposed with oscillatory shear strain for a probe, non-equilibrium
mechanical responses are studied for a model supercooled liquid composed of
binary soft spheres. We found that even in the strongly sheared situation, the
supercooled liquid exhibits surprisingly isotropic responses to oscillating
shear strains applied in three different components of the strain tensor. Based
on this isotropic feature, we successfully constructed a simple two-mode
Maxwell model that can capture the key features of the storage and loss moduli,
even for highly non-equilibrium state. Furthermore, we examined the correlation
functions of the shear stress fluctuations, which also exhibit isotropic
relaxation behaviors in the sheared non-equilibrium situation. In contrast to
the isotropic features, the supercooled liquid additionally demonstrates
anisotropies in both its responses and its correlations to the shear stress
fluctuations. Using the constitutive equation (a two-mode Maxwell model), we
demonstrated that the anisotropic responses are caused by the coupling between
the oscillating strain and the driving shear flow. We measured the magnitude of
this violation in terms of the effective temperature. It was demonstrated that
the effective temperature is notably different between different components,
which indicates that a simple scalar mapping, such as the concept of an
effective temperature, oversimplifies the true nature of supercooled liquids
under shear flow. An understanding of the mechanism of isotropies and
anisotropies in the responses and fluctuations will lead to a better
appreciation of these violations of the FDT, as well as certain consequent
modifications to the concept of an effective temperature.Comment: 15pages, 17figure
Requirement of RIZ1 for cancer prevention by methyl-balanced diet
The typical Western diet is not balanced in methyl nutrients that regulate the level of the methyl donor S-adenosylmethionine (SAM) and its derivative metabolite S-adenosylhomocysteine (SAH), which in turn may control the activity of certain methyltransferases. Feeding rodents with amino acid defined and methyl-imbalanced diet decreases hepatic SAM and causes liver cancers. RIZ1 (PRDM2 or KMT8) is a tumor suppressor and functions in transcriptional repression by methylating histone H3 lysine 9. Here we show that a methyl-balanced diet conferred additional survival benefits compared to a tumor-inducing methyl-imbalanced diet only in mice with wild type RIZ1 but not in mice deficient in RIZ1. While absence of RIZ1 was tumorigenic in mice fed the balanced diet, its presence did not prevent tumor formation in mice fed the imbalanced diet. Unlike most of its related enzymes, RIZ1 was upregulated by methyl-balanced diet. Methyl-balanced diet did not fully repress oncogenes such as c-Jun in the absence of RIZ1. The data identify RIZ1 as a critical target of methyl-balanced diet in cancer prevention. The molecular understanding of dietary carcinogenesis may help people make informed choices on diet, which may greatly reduce the incidence of cancer
Measurement of the cosmic-ray antiproton spectrum at solar minimum with a long-duration balloon flight over Antarctica
The energy spectrum of cosmic-ray antiprotons from 0.17 to 3.5 GeV has been
measured using 7886 antiprotons detected by BESS-Polar II during a
long-duration flight over Antarctica near solar minimum in December 2007 and
January 2008. This shows good consistency with secondary antiproton
calculations. Cosmologically primary antiprotons have been investigated by
comparing measured and calculated antiproton spectra. BESS-Polar II data show
no evidence of primary antiprotons from evaporation of primordial black holes.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
One-way quantum computing in a decoherence-free subspace
We introduce a novel scheme for one-way quantum computing (QC) based on the
use of information encoded qubits in an effective cluster state resource. With
the correct encoding structure, we show that it is possible to protect the
entangled resource from phase damping decoherence, where the effective cluster
state can be described as residing in a Decoherence-Free Subspace (DFS) of its
supporting quantum system. One-way QC then requires either single or two-qubit
adaptive measurements. As an example where this proposal can be realized, we
describe an optical lattice setup where the scheme provides robust quantum
information processing. We also outline how one can adapt the model to provide
protection from other types of decoherence.Comment: 9 pages, 4 figures, RevTeX
Measurement of cosmic-ray low-energy antiproton spectrum with the first BESS-Polar Antarctic flight
The BESS-Polar spectrometer had its first successful balloon flight over
Antarctica in December 2004. During the 8.5-day long-duration flight, almost
0.9 billion events were recorded and 1,520 antiprotons were detected in the
energy range 0.1-4.2 GeV. In this paper, we report the antiproton spectrum
obtained, discuss the origin of cosmic-ray antiprotons, and use antiprotons to
probe the effect of charge sign dependent drift in the solar modulation.Comment: 18 pages, 1 table, 5 figures, submitted to Physics Letters
Semiclassical approach to the thermodynamics of spin chains
Using the PQSCHA semiclassical method, we evaluate thermodynamic quantities
of one-dimensional Heisenberg ferro- and antiferromagnets. Since the PQSCHA
reduces their evaluation to classical-like calculations, we take advantage of
Fisher's exact solution to get all results in an almost fully analytical way.
Explicitly considered here are the specific heat, the correlations length and
susceptibility. Good agreement with Monte Carlo simulations is found for S>1
antiferromagnets, showing that the relevance of the topological terms and of
the Haldane gap is significant only for the lowest spin values and
temperatures.Comment: 4 pages, 7 figure
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