8,141 research outputs found
Pitfalls in the analysis of low-temperature thermal conductivity of high-Tc cuprates
Recently, it was proposed that phonons are specularly reflected below about
0.5 K in ordinary single-crystal samples of high-T_c cuprates, and that the
low-temperature thermal conductivity should be analyzed by fitting the data up
to 0.5 K using an arbitrary power law. Such an analysis yields a result
different from that obtained from the conventional analysis, in which the
fitting is usually restricted to a region below 0.15 K. Here we show that the
proposed new analysis is most likely flawed, because the specular phonon
reflection means that the phonon mean free path \ell gets LONGER than the mean
sample width, while the estimated \ell is actually much SHORTER than the mean
sample width above 0.15 K.Comment: 4 pages, 1 figure; manuscript for the Proceedings of LEHTSC2007 to be
published in Journal of Physics: Conference Serie
Behavioral Phenotyping of Juvenile Long-Evans and Sprague-Dawley Rats: Implications for Preclinical Models of Autism Spectrum Disorders.
The laboratory rat is emerging as an attractive preclinical animal model of autism spectrum disorder (ASD), allowing investigators to explore genetic, environmental and pharmacological manipulations in a species exhibiting complex, reciprocal social behavior. The present study was carried out to compare two commonly used strains of laboratory rats, Sprague-Dawley (SD) and Long-Evans (LE), between the ages of postnatal day (PND) 26-56 using high-throughput behavioral phenotyping tools commonly used in mouse models of ASD that we have adapted for use in rats. We detected few differences between young SD and LE strains on standard assays of exploration, sensorimotor gating, anxiety, repetitive behaviors, and learning. Both SD and LE strains also demonstrated sociability in the 3-chamber social approach test as indexed by spending more time in the social chamber with a constrained age/strain/sex matched novel partner than in an identical chamber without a partner. Pronounced differences between the two strains were, however, detected when the rats were allowed to freely interact with a novel partner in the social dyad paradigm. The SD rats in this particular testing paradigm engaged in play more frequently and for longer durations than the LE rats at both juvenile and young adult developmental time points. Results from this study that are particularly relevant for developing preclinical ASD models in rats are threefold: (i) commonly utilized strains exhibit unique patterns of social interactions, including strain-specific play behaviors, (ii) the testing environment may profoundly influence the expression of strain-specific social behavior and (iii) simple, automated measures of sociability may not capture the complexities of rat social interactions
Avoiding Quantum Chaos in Quantum Computation
We study a one-dimensional chain of nuclear spins in an external
time-dependent magnetic field. This model is considered as a possible candidate
for experimental realization of quantum computation. According to the general
theory of interacting particles, one of the most dangerous effects is quantum
chaos which can destroy the stability of quantum operations. According to the
standard viewpoint, the threshold for the onset of quantum chaos due to an
interaction between spins (qubits) strongly decreases with an increase of the
number of qubits. Contrary to this opinion, we show that the presence of a
magnetic field gradient helps to avoid quantum chaos which turns out to
disappear with an increase of the number of qubits. We give analytical
estimates which explain this effect, together with numerical data supportingComment: RevTex, 5 pages including 3 eps-figure
Dynamical Stability and Quantum Chaos of Ions in a Linear Trap
The realization of a paradigm chaotic system, namely the harmonically driven
oscillator, in the quantum domain using cold trapped ions driven by lasers is
theoretically investigated. The simplest characteristics of regular and chaotic
dynamics are calculated. The possibilities of experimental realization are
discussed.Comment: 24 pages, 17 figures, submitted to Phys. Rev
Simulations of Quantum Logic Operations in Quantum Computer with Large Number of Qubits
We report the first simulations of the dynamics of quantum logic operations
with a large number of qubits (up to 1000). A nuclear spin chain in which
selective excitations of spins is provided by the gradient of the external
magnetic field is considered. The spins interact with their nearest neighbors.
We simulate the quantum control-not (CN) gate implementation for remote qubits
which provides the long-distance entanglement. Our approach can be applied to
any implementation of quantum logic gates involving a large number of qubits.Comment: 13 pages, 15 figure
Fluctuation superconductivity limited noise in a transition-edge sensor
In order to investigate the origin of the until now unaccounted excess noise
and to minimize the uncontrollable phenomena at the transition in X-ray
microcalorimeters we have developed superconducting transition-edge sensors
into an edgeless geometry, the so-called Corbino disk (CorTES), with
superconducting contacts in the centre and at the outer perimeter. The measured
rms current noise and its spectral density can be modeled as resistance noise
resulting from fluctuations near the equilibrium superconductor-normal metal
boundaryComment: 9 pages, 4 figures.; Corrections to text and equations; replaced the
affected figures. Added reference [12
Total Molecular Gas Masses of Planck - Herschel Selected Strongly Lensed Hyper Luminous Infrared Galaxies
We report the detection of CO(1 - 0) line emission from seven Planck and
Herschel selected hyper luminous (LIR(8-1000um) > 10^13Lsun) infrared galaxies
with the Green Bank Telescope (GBT). CO(1 - 0) measurements are a vital tool to
trace the bulk molecular gas mass across all redshifts. Our results place tight
constraints on the total gas content of these most apparently luminous high-z
star-forming galaxies (apparent IR luminosities of LIR > 10^(13-14) Lsun),
while we confirm their predetermined redshifts measured using the Large
Millimeter Telescope, LMT (zCO = 1.33 - 3.26). The CO(1 - 0) lines show similar
profiles as compared to Jup = 2 -4 transitions previously observed with the
LMT. We report enhanced infrared to CO line luminosity ratios of
= 110 (pm 22) Lsun(K km s^-1 pc^-2)^-1 compared to normal
star-forming galaxies, yet similar to those of well-studied IR-luminous
galaxies at high-z. We find average brightness temperature ratios of =
0.93 (2 sources), = 0.34 (5 sources), and = 0.18 (1 source). The
r31 and r41 values are roughly half the average values for SMGs. We estimate
the total gas mass content as uMH2 = (0.9 - 27.2) x 10^11(alphaCO/0.8)Msun,
where u is the magnification factor and alphaCO is the CO line luminosity to
molecular hydrogen gas mass conversion factor. The rapid gas depletion times
are, on average, tau = 80 Myr, which reveal vigorous starburst activity, and
contrast the Gyr depletion timescales observed in local, normal star-forming
galaxies.Comment: published in MNRAS, 9pages, 5fig
Single-Spin Measurement and Decoherence in Magnetic Resonance Force Microscopy
We consider a simple version of a cyclic adiabatic inversion (CAI) technique
in magnetic resonance force microscopy (MRFM). We study the problem: What
component of the spin is measured in the CAI MRFM? We show that the
non-destructive detection of the cantilever vibrations provides a measurement
of the spin component along the effective magnetic field. This result is based
on numerical simulations of the Hamiltonian dynamics (the Schrodinger equation)
and the numerical solution of the master equation.Comment: 5 pages + 5 figures (PNG format
Quantum Measurement of a Single Spin using Magnetic Resonance Force Microscopy
Single-spin detection is one of the important challenges facing the
development of several new technologies, e.g. single-spin transistors and
solid-state quantum computation. Magnetic resonance force microscopy with a
cyclic adiabatic inversion, which utilizes a cantilever oscillations driven by
a single spin, is a promising technique to solve this problem. We have studied
the quantum dynamics of a single spin interacting with a quasiclassical
cantilever. It was found that in a similar fashion to the Stern-Gerlach
interferometer the quantum dynamics generates a quantum superposition of two
quasiclassical trajectories of the cantilever which are related to the two spin
projections on the direction of the effective magnetic field in the rotating
reference frame. Our results show that quantum jumps will not prevent a
single-spin measurement if the coupling between the cantilever vibrations and
the spin is small in comparison with the amplitude of the radio-frequency
external field.Comment: 16 pages RevTeX including 4 figure
The Fermi-Pasta-Ulam problem: 50 years of progress
A brief review of the Fermi-Pasta-Ulam (FPU) paradox is given, together with
its suggested resolutions and its relation to other physical problems. We focus
on the ideas and concepts that have become the core of modern nonlinear
mechanics, in their historical perspective. Starting from the first numerical
results of FPU, both theoretical and numerical findings are discussed in close
connection with the problems of ergodicity, integrability, chaos and stability
of motion. New directions related to the Bose-Einstein condensation and quantum
systems of interacting Bose-particles are also considered.Comment: 48 pages, no figures, corrected and accepted for publicatio
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