6,907 research outputs found
Dynamical Properties of Multi-Armed Global Spirals in Rayleigh-Benard Convection
Explicit formulas for the rotation frequency and the long-wavenumber
diffusion coefficients of global spirals with arms in Rayleigh-Benard
convection are obtained. Global spirals and parallel rolls share exactly the
same Eckhaus, zigzag and skewed-varicose instability boundaries. Global spirals
seem not to have a characteristic frequency or a typical size ,
but their product is a constant under given experimental
conditions. The ratio of the radii of any two dislocations (,
) inside a multi-armed spiral is also predicted to be constant. Some of
these results have been tested by our numerical work.Comment: To appear in Phys. Rev. E as Rapid Communication
Use of Devolved Controllers in Data Center Networks
In a data center network, for example, it is quite often to use controllers
to manage resources in a centralized man- ner. Centralized control, however,
imposes a scalability problem. In this paper, we investigate the use of
multiple independent controllers instead of a single omniscient controller to
manage resources. Each controller looks after a portion of the network only,
but they together cover the whole network. This therefore solves the
scalability problem. We use flow allocation as an example to see how this
approach can manage the bandwidth use in a distributed manner. The focus is on
how to assign components of a network to the controllers so that (1) each
controller only need to look after a small part of the network but (2) there is
at least one controller that can answer any request. We outline a way to
configure the controllers to fulfill these requirements as a proof that the use
of devolved controllers is possible. We also discuss several issues related to
such implementation.Comment: Appears in INFOCOM 2011 Cloud Computing Worksho
Transient energy excitation in shortcuts to adiabaticity for the time dependent harmonic oscillator
There is recently a surge of interest to cut down the time it takes to change
the state of a quantum system adiabatically. We study for the time-dependent
harmonic oscillator the transient energy excitation in speed-up processes
designed to reproduce the initial populations at some predetermined final
frequency and time, providing lower bounds and examples. Implications for the
limits imposed to the process times and for the principle of unattainability of
the absolute zero, in a single expansion or in quantum refrigerator cycles, are
drawn.Comment: 7 pages, 6 figure
Microscopic Modeling of the Growth of Order in an Alloy: Nucleated and Continuous Ordering
We study the early-stages of ordering in using a model Hamiltonian
derived from the effective medium theory of cohesion in metals: an approach
providing a microscopic description of interatomic interactions in alloys. Our
simulations show a crossover from a nucleated growth regime to a region where
the ordering does not follow any simple growth laws. This mirrors the
experimental observations in . The kinetics of growth, obtained from
the simulations, is in semi-quantitative agreement with experiments. The
real-space structures observed in our simulations offer some insight into the
nature of early-stage kineticsComment: 13 pages, Revtex, 3 postscript figures in a second file
Hole Doping Dependence of the Coherence Length in Thin Films
By measuring the field and temperature dependence of magnetization on
systematically doped thin films, the critical current
density and the collective pinning energy are determined in
single vortex creep regime. Together with the published data of superfluid
density, condensation energy and anisotropy, for the first time we derive the
doping dependence of the coherence length or vortex core size in wide doping
regime directly from the low temperature data. It is found that the coherence
length drops in the underdoped region and increases in the overdoped side with
the increase of hole concentration. The result in underdoped region clearly
deviates from what expected by the pre-formed pairing model if one simply
associates the pseudogap with the upper-critical field.Comment: 4 pages, 4 figure
Enhanced squeezing with parity kicks
Using exponential quadratic operators, we present a general framework for
studying the exact dynamics of system-bath interaction in which the Hamiltonian
is described by the quadratic form of bosonic operators. To demonstrate the
versatility of the approach, we study how the environment affects the squeezing
of quadrature components of the system. We further propose that the squeezing
can be enhanced when parity kicks are applied to the system.Comment: 4 pages, 2 figure
Spin waves in the block checkerboard antiferromagnetic phase
Motivated by the discovery of new family 122 iron-based superconductors, we
present the theoretical results on the ground state phase diagram, spin wave
and dynamic structure factor of the extended Heisenberg model. In
the reasonable physical parameter region of , we fi{}nd the
block checkerboard antiferromagnetic order phase is stable. There are two
acoustic branches and six optical branches spin wave in the block checkerboard
antiferromagnetic phase, which has analytic expression in the high symmetry
points. To compare the further neutron scattering experiments, we discuss the
saddlepoint structure in the magnetic excitation spectrum and calculate the
predicted inelastic neutron scattering pattern based on linear spin wave
theory
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