16,430 research outputs found
Exact solution of Riemann--Hilbert problem for a correlation function of the XY spin chain
A correlation function of the XY spin chain is studied at zero temperature.
This is called the Emptiness Formation Probability (EFP) and is expressed by
the Fredholm determinant in the thermodynamic limit. We formulate the
associated Riemann--Hilbert problem and solve it exactly. The EFP is shown to
decay in Gaussian.Comment: 7 pages, to be published in J. Phys. Soc. Jp
Competing Quantum Orderings in Cuprate Superconductors: A Minimal Model
We present a minimal model for cuprate superconductors. At the unrestricted
mean-field level, the model produces homogeneous superconductivity at large
doping, striped superconductivity in the underdoped regime and various
antiferromagnetic phases at low doping and for high temperatures. On the
underdoped side, the superconductor is intrinsically inhomogeneous and global
phase coherence is achieved through Josephson-like coupling of the
superconducting stripes. The model is applied to calculate experimentally
measurable ARPES spectra.Comment: 5 pages, 4 eps included figure
Dosage compensation in birds
AbstractThe Z and W sex chromosomes of birds have evolved independently from the mammalian X and Y chromosomes [1]. Unlike mammals, female birds are heterogametic (ZW), while males are homogametic (ZZ). Therefore male birds, like female mammals, carry a double dose of sex-linked genes relative to the other sex. Other animals with nonhomologous sex chromosomes possess “dosage compensation” systems to equalize the expression of sex-linked genes. Dosage compensation occurs in animals as diverse as mammals, insects, and nematodes, although the mechanisms involved differ profoundly [2]. In birds, however, it is widely accepted that dosage compensation does not occur [3–5], and the differential expression of Z-linked genes has been suggested to underlie the avian sex-determination mechanism [6]. Here we show equivalent expression of at least six of nine Z chromosome genes in male and female chick embryos by using real-time quantitative PCR [7]. Only the Z-linked ScII gene, whose ortholog in Caenorhabditis elegans plays a crucial role in dosage compensation [8], escapes compensation by this assay. Our results imply that the majority of Z-linked genes in the chicken are dosage compensated
Models of granular ratchets
We study a general model of granular Brownian ratchet consisting of an
asymmetric object moving on a line and surrounded by a two-dimensional granular
gas, which in turn is coupled to an external random driving force. We discuss
the two resulting Boltzmann equations describing the gas and the object in the
dilute limit and obtain a closed system for the first few moments of the system
velocity distributions. Predictions for the net ratchet drift, the variance of
its velocity fluctuations and the transition rates in the Markovian limit, are
compared to numerical simulations and a fair agreement is observed.Comment: 15 pages, 4 figures, to be published on Journal of Statistical
Mechanics: Theory and Experiment
Velocity Slip and Temperature Jump in Hypersonic Aerothermodynamics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76543/1/AIAA-2007-208-226.pd
Electron Dynamics in a Coupled Quantum Point Contact Structure with a Local Magnetic Moment
We develop a theoretical model for the description of electron dynamics in
coupled quantum wires when the local magnetic moment is formed in one of the
wires. We employ a single-particle Hamiltonian that takes account of the
specific geometry of potentials defining the structure as well as electron
scattering on the local magnetic moment. The equations for the wave functions
in both wires are derived and the approach for their solution is discussed. We
determine the transmission coefficient and conductance of the wire having the
local magnetic moment and show that our description reproduces the
experimentally observed features.Comment: Based on work presented at 2004 IEEE NTC Quantum Device Technology
Worksho
Direct simulation for a homogenous gas
A probabilistic analysis of the direct simulation of a homogeneous gas is
given. A hierarchy of equations similar to the BBGKY hierarchy for the reduced
probability densities is derived. By invoking the molecular chaos assumption,
an equation similar to the Boltzmann equation for the single particle
probability density and the corresponding H-theorem is derived
Mechanism of margination in confined flows of blood and other multicomponent suspensions
Flowing blood displays a phenomenon called margination, in which leukocytes
and platelets are preferentially found near blood vessel walls, while
erythrocytes are depleted from these regions. Here margination is investigated
using direct hydrodynamic simulations of a binary suspension of stiff (s) and
floppy (f) capsules, as well as a stochastic model that incorporates the key
particle transport mechanisms in suspensions -- wall-induced hydrodynamic
migration and shear-induced pair collisions. The stochastic model allows the
relative importance of these two mechanisms to be directly evaluated and
thereby indicates that margination, at least in the dilute case, is largely due
to the differential dynamics of homogeneous (e.g. s-s) and heterogeneous (s-f)
collisionsComment: 5 Pages, 4 figure
Structural Relaxation and Mode Coupling in a Simple Liquid: Depolarized Light Scattering in Benzene
We have measured depolarized light scattering in liquid benzene over the
whole accessible temperature range and over four decades in frequency. Between
40 and 180 GHz we find a susceptibility peak due to structural relaxation. This
peak shows stretching and time-temperature scaling as known from
relaxation in glass-forming materials. A simple mode-coupling model provides
consistent fits of the entire data set. We conclude that structural relaxation
in simple liquids and relaxation in glass-forming materials are
physically the same. A deeper understanding of simple liquids is reached by
applying concepts that were originally developed in the context of
glass-transition research.Comment: submitted to New J. Phy
Multi-particle-collision dynamics: Flow around a circular and a square cylinder
A particle-based model for mesoscopic fluid dynamics is used to simulate
steady and unsteady flows around a circular and a square cylinder in a
two-dimensional channel for a range of Reynolds number between 10 and 130.
Numerical results for the recirculation length, the drag coefficient, and the
Strouhal number are reported and compared with previous experimental
measurements and computational fluid dynamics data. The good agreement
demonstrates the potential of this method for the investigation of complex
flows.Comment: 6 pages, separated figures in .jpg format, to be published in
Europhysics Letter
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