11,828 research outputs found
Flux-lattice melting in LaOFFeAs: first-principles prediction
We report the theoretical study of the flux-lattice melting in the novel
iron-based superconductor and
. Using the Hypernetted-Chain closure and an
efficient algorithm, we calculate the two-dimensional one-component plasma pair
distribution functions, static structure factors and direct correlation
functions at various temperatures. The Hansen-Verlet freezing criterion is
shown to be valid for vortex-liquid freezing in type-II superconductors.
Flux-lattice meting lines for and
are predicted through the combination of the density
functional theory and the mean-field substrate approach.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Dimensional crossover of thermal conductance in graphene nanoribbons: A first-principles approach
First-principles density-functional calculations are performed to investigate
the thermal transport properties in graphene nanoribbons (GNRs). The
dimensional crossover of thermal conductance from one to two dimensions (2D) is
clearly demonstrated with increasing ribbon width. The thermal conductance of
GNRs in a few nanometer width already exhibits an approximate low-temperature
dependence of , like that of 2D graphene sheet which is attributed to
the quadratic nature of dispersion relation for the out-of-plane acoustic
phonon modes. Using a zone-folding method, we heuristically derive the
dimensional crossover of thermal conductance with the increase of ribbon width.
Combining our calculations with the experimental phonon mean-free path, some
typical values of thermal conductivity at room temperature are estimated for
GNRs and for 2D graphene sheet, respectively. Our findings clarify the issue of
low-temperature dependence of thermal transport in GNRs and suggest a
calibration range of thermal conductivity for experimental measurements in
graphene-based materials.Comment: 18 pages, 4 figure
Hidden Tree Structure is a Key to the Emergence of Scaling in the World Wide Web
Preferential attachment is the most popular explanation for the emergence of
scaling behavior in the World Wide Web, but this explanation has been
challenged by the global information hypothesis, the existence of linear
preference and the emergence of new big internet companies in the real world.
We notice that most websites have an obvious feature that their pages are
organized as a tree (namely hidden tree) and hence propose a new model that
introduces a hidden tree structure into the Erd\H{o}s-R\'e}yi model by adding a
new rule: when one node connects to another, it should also connect to all
nodes in the path between these two nodes in the hidden tree. The experimental
results show that the degree distribution of the generated graphs would obey
power law distributions and have variable high clustering coefficients and
variable small average lengths of shortest paths. The proposed model provides
an alternative explanation to the emergence of scaling in the World Wide Web
without the above-mentioned difficulties, and also explains the "preferential
attachment" phenomenon.Comment: 4 Pages, 7 Figure
Retardation Terms in The One-Gluon Exchange Potential
It is pointed out that the retardation terms given in the original
Fermi-Breit potential vanish in the center of mass frame. The retarded
one-gluon exchange potential is rederived in this paper from the
three-dimensional one-gluon exchange kernel which appears in the exact
three-dimensional relativistic equation for quark-antiquark bound states. The
retardation part of the potential given in the approximation of order
is shown to be different from those derived in the previous literature. This
part is off-shell and does no longer vanish in the center of mass frame
Re-evaluation of the surface ruptures of the November 1951 earthquake series in eastern Taiwan, and its neotectonic implications
The earthquakes of November 1951 constitute the most destructive seismic episode in the recorded history of the Longitudinal Valley, eastern Taiwan. However, information about their source parameters is sparse. To understand the relationship between the 1951 ruptures and new interpretations of the regional neotectonic architecture of the Longitudinal Valley, we re-evaluated the November 1951 ruptures by analyzing old documents, reports and photographs, and by interviewing local residents who experienced the earthquake. As a result, we have revised significantly the rupture map previously published. We divide the surface ruptures from south to north into the Chihshang, Yuli, and Rueisuei sections. The first shock of the 1951 series probably resulted from the Chihshang rupture, and the second shock probably resulted from the Yuli and Rueisuei ruptures. The lengths of these ruptures indicate that the two shocks had similar magnitudes. The Chihshang and Rueisuei ruptures are along segments of the Longitudinal Valley fault, a left-lateral oblique fault along which the Coastal Range thrusts westward over the Longitudinal Valley. The Yuli rupture, on the other hand, appears to be part of a separate, left-lateral strike-slip Yuli fault, which traverses the middle of the Longitudinal Valley. The complex behavior of these structures and interaction between them are important in understanding the future seismic hazard of the area
Dynamical behavior of interacting dark energy in loop quantum cosmology
The dynamical behaviors of interacting dark energy in loop quantum cosmology
are discussed in this paper. Based on defining three dimensionless variables,
we simplify the equations of the fixed points. The fixed points for interacting
dark energy can be determined by the Friedmann equation coupled with the
dynamical equations {in Einstein cosmology}. But in loop quantum cosmology,
besides the Friedmann equation, the conversation equation also give a constrain
on the fixed points. The difference of stability properties for the fixed
points in loop quantum cosmology and the ones in Einstein cosmology also have
been discussed.Comment: 7 pages, 5 figure
Optical Nondestructive Controlled-NOT Gate without Using Entangled Photons
We present and experimentally demonstrate a novel optical nondestructive
controlled-NOT gate without using entangled ancilla. With much fewer
measurements compared with quantum process tomography, we get a good estimation
of the gate fidelity. The result shows a great improvement compared with
previous experiments. Moreover, we also show that quantum parallelism is
achieved in our gate and the performance of the gate can not be reproduced by
local operations and classical communications.Comment: 5 pages, 3 figures, Slight changes have been made, Journal-ref adde
Non-Markovian finite-temperature two-time correlation functions of system operators: beyond the quantum regression theorem
An extremely useful evolution equation that allows systematically calculating
the two-time correlation functions (CF's) of system operators for non-Markovian
open (dissipative) quantum systems is derived. The derivation is based on
perturbative quantum master equation approach, so non-Markovian open quantum
system models that are not exactly solvable can use our derived evolution
equation to easily obtain their two-time CF's of system operators, valid to
second order in the system-environment interaction. Since the form and nature
of the Hamiltonian are not specified in our derived evolution equation, our
evolution equation is applicable for bosonic and/or fermionic environments and
can be applied to a wide range of system-environment models with any factorized
(separable) system-environment initial states (pure or mixed). When applied to
a general model of a system coupled to a finite-temperature bosonic environment
with a system coupling operator L in the system-environment interaction
Hamiltonian, the resultant evolution equation is valid for both L = L^+ and L
\neq L^+ cases, in contrast to those evolution equations valid only for L = L^+
case in the literature. The derived equation that generalizes the quantum
regression theorem (QRT) to the non-Markovian case will have broad applications
in many different branches of physics. We then give conditions on which the QRT
holds in the weak system-environment coupling case, and apply the derived
evolution equation to a problem of a two-level system (atom) coupled to a
finite-temperature bosonic environment (electromagnetic fields) with L \neq
L^+.Comment: To appear in the Journal of Chemical Physics (12 pages, 1 figure
Deterministic and Efficient Quantum Cryptography Based on Bell's Theorem
We propose a novel double-entanglement-based quantum cryptography protocol
that is both efficient and deterministic. The proposal uses photon pairs with
entanglement both in polarization and in time degrees of freedom; each
measurement in which both of the two communicating parties register a photon
can establish one and only one perfect correlation and thus deterministically
create a key bit. Eavesdropping can be detected by violation of local realism.
A variation of the protocol shows a higher security, similarly to the six-state
protocol, under individual attacks. Our scheme allows a robust implementation
under current technology.Comment: 4 pages, 1 figure; published version with a note adde
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