6,774 research outputs found
The parity of specular Andreev reflection under mirror operation in zigzag graphene ribbon
It is known that the parity of reflection amplitude can either be even or odd
under the mirror operation. Up to now, all the parities of reflection amplitude
in the one-mode energy region are even under the mirror operation. In this
paper, we give an example of odd parity for Andreev reflection (AR) in a
three-terminal graphene-supercondutor hybrid systems. We found that the parity
is even for the Andreev retroreflection (ARR) and odd for specular Andreev
reflection (SAR). We attribute this remarkable phenomenon to the distinct
topology of the band structure of graphene and the specular Andreev reflection
involving two energy bands with different parity symmetry. As a result of odd
parity of SAR, the SAR probability of a four-terminal system with two
superconducting leads (two reflection interfaces) can be zero even when the
system is asymmetric due to the quantum interference of two ARs.Comment: 11 pages, 3 figure
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Transcriptional regulation of the Nkx3.1 gene in prostate luminal stem cell specification and cancer initiation via its 3' genomic region.
NK3 homeobox 1 (Nkx3.1), a transcription factor expressed in the prostate epithelium, is crucial for maintaining prostate cell fate and suppressing tumor initiation. Nkx3.1 is ubiquitously expressed in luminal cells of hormonally intact prostate but, upon androgen deprivation, exclusively labels a type of luminal stem cells named castration-resistant Nkx3.1-expressing cells (CARNs). During prostate cancer initiation, Nkx3.1 expression is frequently lost in both humans and mouse models. Therefore, investigating how Nkx3.1 expression is regulated in vivo is important for understanding the mechanisms of prostate stem cell specification and cancer initiation. Here, using a transgenic mouse line with destabilized GFP, we identified an 11-kb genomic region 3' of the Nkx3.1 transcription start site to be responsible for alterations in Nkx3.1 expression patterns under various physiological conditions. We found that androgen cell-autonomously activates Nkx3.1 expression through androgen receptor (AR) binding to the 11-kb region in both normal luminal cells and CARNs and discovered new androgen response elements in the Nkx3.1 3' UTR. In contrast, we found that, in Pten-/- prostate tumors, loss of Nkx3.1 expression is mediated at the transcriptional level through the 11-kb region despite functional AR in the nucleus. Importantly, the GFP reporter specifically labeled CARNs in the regressed prostate only in the presence of cell-autonomous AR, supporting a facultative model for CARN specification
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
Controllable Andreev retroreflection and specular Andreev reflection in a four-terminal graphene-superconductor hybrid system
We report the investigation of electron transport through a four-terminal
graphene-superconductor hybrid system. Due to the quantum interference of the
reflected holes from two graphene-superconductor interfaces with phase
difference , it is found that the specular Andreev reflection vanishes
at while the Andreev retroreflection disappears at .
This means that the retroreflection and specular reflection can be easily
controlled and separated in this device. In addition, due to the diffraction
effect in the narrow graphene nanoribbon, the reflected hole can exit from both
graphene terminals. As the width of nanoribbon increases, the diffraction
effect gradually disappears and the reflected hole eventually exits from a
particular graphene terminal depending on the type of Andreev reflection.Comment: 4 pages, 5 figure
Quantum correlations in the collective spin systems
Quantum and classical pairwise correlations in two typical collective spin
systems (i.e., the Dicke model and the Lipkin-Meshkov-Glick model) are
discussed. These correlations in the thermodynamical limit are obtained
analytically and in a finite-size system are calculated numerically. Large-size
scaling behavior for the quantum discord itself is observed, which has never
been reported in another critical system. A logarithmic diverging behavior for
the first derivative of the quantum discord is also found in both models, which
might be universal in the second-order quantum phase transition. It is
suggested that the pronounced maximum or minimum of first derivative of quantum
discord signifies the critical point. Comparisons between the quantum discord
and the scaled concurrence are performed. It is shown that the quantum discord
is very small in one phase and robust in the other phase, while the scaled
concurrence shows maximum at the critical point and decays rapidly when away
from the the critical point.Comment: 8 pages, 4 figure
Effects of Langmuir Kinetics of Two-Lane Totally Asymmetric Exclusion Processes in Protein Traffic
In this paper, we study a two-lane totally asymmetric simple exclusion
process (TASEP) coupled with random attachment and detachment of particles
(Langmuir kinetics) in both lanes under open boundary conditions. Our model can
describe the directed motion of molecular motors, attachment and detachment of
motors, and free inter-lane transition of motors between filaments. In this
paper, we focus on some finite-size effects of the system because normally the
sizes of most real systems are finite and small (e.g., size ). A
special finite-size effect of the two-lane system has been observed, which is
that the density wall moves left first and then move towards the right with the
increase of the lane-changing rate. We called it the jumping effect. We find
that increasing attachment and detachment rates will weaken the jumping effect.
We also confirmed that when the size of the two-lane system is large enough,
the jumping effect disappears, and the two-lane system has a similar density
profile to a single-lane TASEP coupled with Langmuir kinetics. Increasing
lane-changing rates has little effect on density and current after the density
reaches maximum. Also, lane-changing rate has no effect on density profiles of
a two-lane TASEP coupled with Langmuir kinetics at a large
attachment/detachment rate and/or a large system size. Mean-field approximation
is presented and it agrees with our Monte Carlo simulations.Comment: 15 pages, 8 figures. To be published in IJMP
Entanglement dynamics of two independent Jaynes-Cummings atoms without rotating-wave approximation
Entanglement evolution of two independent Jaynes-Cummings atoms without
rotating-wave approximation (RWA) is studied by an numerically exact approach.
The previous results in the RWA are essentially modified in the strong coupling
regime (), which has been reached in the recent experiments on the
flux qubit coupled to the LC resonator. For the initial Bell state with
anti-correlated spins, the entanglement sudden death (ESD) is absent in the
RWA, but does appear in the present numerical calculation without RWA.
Aperiodic entanglement evolution in the strong coupling regime is observed. The
strong atom-cavity coupling facilitates the ESD. The sign of detuning play a
essential role in the entanglement evolution for strong coupling, which is
irrelevant in the RWA. An analytical results based on an unitary transformation
are also given, which could not modify the RWA picture essentially. It is
suggested that the activation of the photons may be the origin of the ESD. The
present theoretical results could be applied to artificial atoms realized in
recent experiments.Comment: 16 pages, 8 figure
Bi- and tri-dentate imino-based iron and cobalt pre-catalysts for ethylene oligo-/polymerization
Recent progress on the use of iron and cobalt complex pre-catalysts for ethylene reactivity is reviewed. The review is organized in terms of the denticity of the chelate ligands employed, with particular reference to the influence of the ligand frameworks and their substituents on the catalytic performance for ethylene oligomerization/polymerization catalysis. The majority of the systems bear tri-dentate ligation at the iron/cobalt centre, though it is clear that bi-dentate iron/cobalt complex pre-catalysts have also attracted significant attention. Such systems produce in most cases highly linear products ranging from oligomeric α-olefins to high molecular weight polyethylene, and as such are promising candidates for both academic and industrial considerations
Laboratory studies of rice bran as a carbon source to stimulate indigenous microorganisms in oil reservoirs
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