2,157 research outputs found
Modeling incompressible thermal flows using a central-moment-based lattice Boltzmann method
In this paper, a central-moment-based lattice Boltzmann (CLB) method for
incompressible thermal flows is proposed. In the method, the incompressible
Navier-Stokes equations and the convection-diffusion equation for the
temperature field are sloved separately by two different CLB equations. Through
the Chapman-Enskog analysis, the macroscopic governing equations for
incompressible thermal flows can be reproduced. For the flow field, the tedious
implementation for CLB method is simplified by using the shift matrix with a
simplified central-moment set, and the consistent forcing scheme is adopted to
incorporate forcing effects. Compared with several D2Q5
multiple-relaxation-time (MRT) lattice Boltzmann methods for the temperature
equation, the proposed method is shown to be better Galilean invariant through
measuring the thermal diffusivities on a moving reference frame. Thus a higher
Mach number can be used for convection flows, which decreases the computational
load significantly. Numerical simulations for several typical problems confirm
the accuracy, efficiency, and stability of the present method. The grid
convergence tests indicate that the proposed CLB method for incompressible
thermal flows is of second-order accuracy in space
Block-block entanglement and quantum phase transitions in one-dimensional extended Hubbard model
In this paper, we study block-block entanglement in the ground state of
one-dimensional extended Hubbard model. Our results show that the phase diagram
derived from the block-block entanglement manifests richer structure than that
of the local (single site) entanglement because it comprises nonlocal
correlation. Besides phases characterized by the charge-density-wave, the
spin-density-wave, and phase-separation, which can be sketched out by the local
entanglement, singlet superconductivity phase could be identified on the
contour map of the block-block entanglement. Scaling analysis shows that behavior of the block-block entanglement may exist in both
non-critical and the critical regions, while some local extremum are induced by
the finite-size effect. We also study the block-block entanglement defined in
the momentum space and discuss its relation to the phase transition from
singlet superconducting state to the charge-density-wave state.Comment: 8 pages, 9 figure
The ground state entanglement in the model
In this paper, we investigate spin entanglement in the model defined on
a -dimensional bipartite lattice. The concurrence, a measure of the
entanglement between two spins, is analyzed. We prove rigorously that the
ground state concurrence reaches maximum at the isotropic point. For
dimensionality , the concurrence develops a cusp at the isotropic
point and we attribute it to the existence of magnetic long-range order.Comment: 5 pages, 2 figure
Entanglement and quantum phase transition in the extended Hubbard model
We study quantum entanglement in one-dimensional correlated fermionic system.
Our results show, for the first time, that entanglement can be used to identify
quantum phase transitions in fermionic systems.Comment: 5 pages, 4 figure
Nodeless energy gaps of single-crystalline Ba0.68K0.32Fe2As2 as seen via 75As NMR
We report As nuclear magnetic resonance studies on a very clean
hole-doped single-crystal BaKFeAs ( K). The spin-lattice relaxation rate shows an exponential
decrease below down to ,
which indicates a fully opened energy gap. From the ratio , where and denote the crystal directions, we find that the
antiferromagnetic spin fluctuation is anisotropic in the spin space above
. The anisotropy decreases below and disappears at . We argue that the anisotropy stems from spin-orbit coupling
whose effect vanishes when spin-singlet electron pairs form with a nodeless
gap.Comment: 10 pages, 6 figure
Ground-state properties of the two-site Hubbard-Holstein model: an exact solution
We revisit the two-site Hubbard-Holstein model by using extended phonon
coherent states. The nontrivial singlet bipolaron is studied exactly in the
whole coupling regime. The ground-state (GS) energy and the double occupancy
probability are calculated. The linear entropy is exploited successfully to
quantify bipartite entanglement between electrons and their environment
phonons, displaying a maximum entanglement of the singlet-bipolaron in strong
coupling regime. A dramatic drop in the crossover regime is observed in the GS
fidelity and its susceptibility. The bipolaron properties is also characterized
classically by correlation functions. It is found that the crossover from a
two-site to single-site bipolaron is more abrupt and shifts to a larger
electron-phonon coupling strength as electron-electron Coulomb repulsion
increases.Comment: 6 pages, 6 figure
Solutions to the Jaynes-Cummings model without the rotating-wave approximation
By using extended bosonic coherent states, the solution to the
Jaynes-Cummings model without the rotating-wave approximation can be mapped to
that of a polynomial equation with a single variable. The solutions to this
polynomial equation can give all eigenvalues and eigenfunctions of this model
with all values of the coupling strength and the detuning exactly, which can be
readily applied to recent circuit quantum electrodynamic systems operating in
the ultra-strong coupling regime.Comment: 6 pages,3 figure
Enhanced cell-permeant Cre protein for site-specific recombination in cultured cells
BACKGROUND: Cell-permeant Cre DNA site-specific recombinases provide an easily controlled means to regulate gene structure and function in living cells. Since recombination provides a stable and unambiguous record of protein uptake, the enzyme may also be used for quantitative studies of cis- and trans-acting factors that influence the delivery of proteins into cells. RESULTS: In the present study, 11 recombinant fusion proteins were analyzed to characterize sequences and conditions that affect protein uptake and/or activity and to develop more active cell-permeant enzymes. We report that the native enzyme has a low, but intrinsic ability to enter cells. The most active Cre proteins tested contained either an N-terminal 6xHis tag and a nuclear localization sequence from SV40 large T antigen (HNC) or the HIV Tat transduction sequence and a C-terminal 6xHis tag (TCH(6)). The NLS and 6xHis elements separately enhanced the delivery of the HNC protein into cells; moreover, transduction sequences from fibroblast growth factor 4, HIV Tat or consisting of the (KFF)(3)K sequence were not required for efficient protein transduction and adversely affected enzyme solubility. Transduction of the HNC protein required 10 to 15 min for half-maximum uptake, was greatly decreased at 4°C and was inhibited by serum. Efficient recombination was observed in all cell types tested (a T-cell line, NIH3T3, Cos7, murine ES cells, and primary splenocytes), and did not require localization of the enzyme to the nucleus. CONCLUSIONS: The effects of different sequences on the delivery and/or activity of Cre in cultured cells could not be predicted in advance. Consequently, the process of developing more active cell-permeant recombinases was largely empirical. The HNC protein, with an excellent combination of activity, solubility and yield, will enhance the use of cell-permeant Cre proteins to regulate gene structure and function in living cells
Experimental Decoy Quantum Key Distribution Up To 130KM Fiber
Decoy State Quantum Key Distribution (QKD), being capable of beating PNS
attack and uncon- ditionally secure, have become an attractive one recently.
But, in many QKD systems, disturbances of transmission channel make quantum bit
error rate (QBER) increase which limits both security distance and key bit rate
of real-life decoy state QKD systems. We demonstrate the two-intensity decoy
QKD with one-way Faraday-Michelson phase modulation system, which is free of
channel dis- turbance and keeps interference fringe visibility (99%) long
period, near 130KM single mode optical fiber in telecom (1550 nm) wavelength.
This is longest distance fiber decoy state QKD system based on two intensity
protocol.Comment: 4 pages, 2figure
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