10,635 research outputs found
Horizontal Structures of Velocity and Temperature Boundary Layers in 2D Numerical Turbulent Rayleigh-B\'{e}nard Convection
We investigate the structures of the near-plate velocity and temperature
profiles at different horizontal positions along the conducting bottom (and
top) plate of a Rayleigh-B\'{e}nard convection cell, using two-dimensional (2D)
numerical data obtained at the Rayleigh number Ra=10^8 and the Prandtl number
Pr=4.4 of an Oberbeck-Boussinesq flow with constant material parameters. The
results show that most of the time, and for both velocity and temperature, the
instantaneous profiles scaled by the dynamical frame method [Q. Zhou and K.-Q.
Xia, Phys. Rev. Lett. 104, 104301 (2010) agree well with the classical
Prandtl-Blasius laminar boundary layer (BL) profiles. Therefore, when averaging
in the dynamical reference frames, which fluctuate with the respective
instantaneous kinematic and thermal BL thicknesses, the obtained mean velocity
and temperature profiles are also of Prandtl-Blasius type for nearly all
horizontal positions. We further show that in certain situations the
traditional definitions based on the time-averaged profiles can lead to
unphysical BL thicknesses, while the dynamical method also in such cases can
provide a well-defined BL thickness for both the kinematic and the thermal BLs.Comment: 16 pages, 16 figure
Evolution of pairing from weak to strong coupling on a honeycomb lattice
We study the evolution of the pairing from weak to strong coupling on a
honeycomb lattice by Quantum Monte Carlo. We show numerical evidence of the
BCS-BEC crossover as the coupling strength increases on a honeycomb lattice
with small fermi surface by measuring a wide range of observables: double
occupancy, spin susceptibility, local pair correlation, and kinetic energy.
Although at low energy, the model sustains Dirac fermions, we do not find
significant qualitative difference in the BCS-BEC crossover as compared to
those with an extended Fermi surface, except at weak coupling, BCS regime.Comment: 5 page
Testing quantum adiabaticity with quench echo
Adiabaticity of quantum evolution is important in many settings. One example
is the adiabatic quantum computation. Nevertheless, up to now, there is no
effective method to test the adiabaticity of the evolution when the
eigenenergies of the driven Hamiltonian are not known. We propose a simple
method to check adiabaticity of a quantum process for an arbitrary quantum
system. We further propose a operational method for finding a uniformly
adiabatic quench scheme based on Kibble-Zurek mechanism for the case when the
initial and the final Hamiltonians are given. This method should help in
implementing adiabatic quantum computation.Comment: This is a new version. Some typos in the New Journal of Physics
version have been correcte
Constraints on Holographic Dark Energy from Latest Supernovae, Galaxy Clustering, and Cosmic Microwave Background Anisotropy Observations
The holographic dark energy model is proposed by Li as an attempt for probing
the nature of dark energy within the framework of quantum gravity. The main
characteristic of holographic dark energy is governed by a numerical parameter
in the model. The parameter can only be determined by observations.
Thus, in order to characterize the evolving feature of dark energy and to
predict the fate of the universe, it is of extraordinary importance to
constrain the parameter by using the currently available observational
data. In this paper, we derive constraints on the holographic dark energy model
from the latest observational data including the gold sample of 182 Type Ia
supernovae (SNIa), the shift parameter of the cosmic microwave background (CMB)
given by the three-year {\it Wilkinson Microwave Anisotropy Probe} ({\it WMAP})
observations, and the baryon acoustic oscillation (BAO) measurement from the
Sloan Digital Sky Survey (SDSS). The joint analysis gives the fit results in
1-: and . That
is to say, though the possibility of is more favored, the possibility of
can not be excluded in one-sigma error range, which is somewhat different
from the result derived from previous investigations using earlier data. So,
according to the new data, the evidence for the quintom feature in the
holographic dark energy model is not as strong as before.Comment: 22 pages, 8 figures; accepted for publication in Phys. Rev.
Formation of regular spatial patterns in ratio-dependent predator-prey model driven by spatial colored-noise
Results are reported concerning the formation of spatial patterns in the
two-species ratio-dependent predator-prey model driven by spatial
colored-noise. The results show that there is a critical value with respect to
the intensity of spatial noise for this system when the parameters are in the
Turing space, above which the regular spatial patterns appear in two
dimensions, but under which there are not regular spatial patterns produced. In
particular, we investigate in two-dimensional space the formation of regular
spatial patterns with the spatial noise added in the side and the center of the
simulation domain, respectively.Comment: 4 pages and 3 figure
Stability and distortions of liquid crystal order in a cell with a heterogeneous substrate
We study stability and distortions of liquid crystal nematic order in a cell
with a random heterogeneous substrate. Modeling this system as a bulk xy model
with quenched disorder confined to a surface, we find that nematic order is
marginally unstable to such surface pinning. We compute the length scale beyond
which nematic distortions become large and calculate orientational correlation
functions using the functional renormalization-group and matching methods,
finding universal logarithmic and double-logarithmic distortions in two and
three dimensions, respectively. We extend these results to a finite-thickness
liquid crystal cell with a second homogeneous substrate, detailing crossovers
as a function of random pinning strength and cell thickness. We conclude with
analysis of experimental signatures of these distortions in a conventional
crossed-polarizer-analyzer light microscopy.Comment: 27 pages, 15 figures, Published in PRE, with minor typos correcte
Mesoscopic circuits with charge discreteness:quantum transmission lines
We propose a quantum Hamiltonian for a transmission line with charge
discreteness. The periodic line is composed of an inductance and a capacitance
per cell. In every cell the charge operator satisfies a nonlinear equation of
motion because of the discreteness of the charge. In the basis of one-energy
per site, the spectrum can be calculated explicitly. We consider briefly the
incorporation of electrical resistance in the line.Comment: 11 pages. 0 figures. Will be published in Phys.Rev.
Quantum secure communication scheme with W state
Recently, Cao et al. proposed a new quantum secure direct communication
scheme using W state. In their scheme, the error rate introduced by an
eavesdropper who takes intercept-resend attack, is only 8.3%. Actually, their
scheme is just a quantum key distribution scheme because the communication
parties first create a shared key and then encrypt the secret message using
one-time pad. We then present a quantum secure communication scheme using
three-qubit W state. In our scheme, the error rate is raised to 25% and it is
not necessary for the present scheme to use alternative measurement or Bell
basis measurement. We also show our scheme is unconditionally secure.Comment: Comments are welcom
Lack of patient involvement in care decisions and not receiving written discharge instructions are associated with unplanned readmissions up to one year
This retrospective, cross-sectional study examined the relationship between aspects of inpatient communication and discharge instructions and unplanned, all-cause readmissions using individual-level data up to one-year post-discharge. Patients completed the Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) telephone survey within 6 weeks of hospital discharge in Alberta, Canada. Survey data were linked to corresponding inpatient records. Independent variables included selected demographic characteristics, clinical variables, and five survey questions: a) patient involvement in care decisions, b) receiving written information at discharge, c) understanding the purpose of taking medications, d) understanding responsibility for one’s health, and e) discussing help needed when returning home. From April 2011 to March 2014, 24,869 patients with a mean age of 52.8±19.8 years (range=18-100) were included. 18.6% of patients (n=4,821) experienced an unplanned hospital readmission within 43 to 365 days post-discharge. In adjusted, logistic regression models, patients who felt they were not involved in care decisions were more likely to be readmitted (OR=1.34; 95%CI: 1.17-1.53), as were patients who reported not receiving written information about signs and symptoms to watch out for post-discharge (OR=1.24; 95%CI: 1.15-1.35). Odds of readmission did not differ according to understanding of medications, understanding responsibility for one’s health, or discussion of help needed when returning home. This study provides objective data, showing that specific hospital actions are associated with unplanned readmissions. It is an example of how patient-reported measures may be linked to administrative data to drive quality improvement initiatives
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