1,389 research outputs found
Self-organized Criticality on Small World Networks
We study the BTW-height model of self-organized criticality on a square
lattice with some long range connections giving to the lattice the character of
small world network. We find that as function of the fraction of long
ranged bonds the power law of the avalanche size and lifetime distribution
changes following a crossover scaling law with crossover exponents 2/3 and 1
for size and lifetime respectively.Comment: 7 figure
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
Improvement of the high-temperature oxidation resistance of Zr alloy cladding by surface modification with aluminium-containing ternary carbide coatings
Alumina-forming MAX phase ternary carbides are being considered as protective coatings on zirconium alloys as occident tolerant fuel (ATF) cladding because of their resistivity against high-temperature steam oxidation during occident scenarios. This study attempted to synthesize three types of Al-containing MAX phase carbides (Ti2AlC, Cr2AlC and Zr2AlC) as coatings on Zircaloy-4 substrates via deposition of elemental nanoscale multilayer thin films
using magnetron sputtering, and subsequent thermal annealing in argon. Formation of Ti2AlC and Cr2AlC MAX hases was confirmed after annealing at 800°C and 550°C, respectively, while growth of Zr(Al)C carbide rather than Zr2AlC AX phase was observed in the Zr-C-Al system. Oxidation of the three coated samples at 1000°C in steam for 1 hour evealed no protective effect of the Ti2AlC and Zr(Al)C coatings with significant spallation and cracking. The Cr2AlC oatings possess superior oxidation resistance and self-healing capability with a thin and
dense α-Al2O3 layer growth on the surface, which shows good promise as a candidate for coated ATF claddings
Depinning of elastic manifolds
We compute roughness exponents of elastic d-dimensional manifolds in
(d+1)-dimensional embedding spaces at the depinning transition for d=1,...,4.
Our numerical method is rigorously based on a Hamiltonian formulation; it
allows to determine the critical manifold in finite samples for an arbitrary
convex elastic energy. For a harmonic elastic energy, we find values of the
roughness exponent between the one-loop and the two-loop functional
renormalization group result, in good agreement with earlier cellular automata
simulations. We find that the harmonic model is unstable with respect both to
slight stiffening and to weakening of the elastic potential. Anharmonic
corrections to the elastic energy allow us to obtain the critical exponents of
the quenched KPZ class.Comment: 4 pages, 4 figure
Quantum disorder in the two-dimensional pyrochlore Heisenberg antiferromagnet
We present the results of an exact diagonalization study of the spin-1/2
Heisenberg antiferromagnet on a two-dimensional version of the pyrochlore
lattice, also known as the square lattice with crossings or the checkerboard
lattice. Examining the low energy spectra for systems of up to 24 spins, we
find that all clusters studied have non-degenerate ground states with total
spin zero, and big energy gaps to states with higher total spin. We also find a
large number of non-magnetic excitations at energies within this spin gap.
Spin-spin and spin-Peierls correlation functions appear to be short-ranged, and
we suggest that the ground state is a spin liquid.Comment: 7 pages, 11 figures, RevTeX minor changes made, Figure 6 correcte
Real space renormalization group approach to the 2d antiferromagnetic Heisenberg model
The low energy behaviour of the 2d antiferromagnetic Heisenberg model is
studied in the sector with total spins by means of a renormalization
group procedure, which generates a recursion formula for the interaction matrix
of 4 neighbouring " clusters" of size ,
from the corresponding quantities . Conservation
of total spin is implemented explicitly and plays an important role. It is
shown, how the ground state energies , approach each
other for increasing , i.e. system size. The most relevant couplings in the
interaction matrices are generated by the transitions
between the ground states
() on an -cluster of size , mediated
by the staggered spin operator Comment: 18 pages, 8 figures, RevTe
Path Integral Description of a Semiclassical Su-Schrieffer-Heeger Model
The electron motion along a chain is described by a continuum version of the
Su-Schrieffer-Heeger Hamiltonian in which phonon fields and electronic
coordinates are mapped onto the time scale. The path integral formalism allows
us to derive the non local source action for the particle interacting with the
oscillators bath. The method can be applied for any value of the {\it e-ph}
coupling. The path integral dependence on the model parameters has been
analysed by computing the partition function and some thermodynamical
properties from up to room temperature. A peculiar upturn in the low
temperature {\it heat capacity over temperature} ratio (pointing to a glassy
like behavior) has been ascribed to the time dependent electronic hopping along
the chain
Interface Depinning in the Absence of External Driving Force
We study the pinning-depinning phase transition of interfaces in the quenched
Kardar-Parisi-Zhang model as the external driving force goes towards zero.
For a fixed value of the driving force we induce depinning by increasing the
nonlinear term coefficient , which is related to lateral growth, up to
a critical threshold. We focus on the case in which there is no external force
applied (F=0) and find that, contrary to a simple scaling prediction, there is
a finite value of that makes the interface to become depinned. The
critical exponents at the transition are consistent with directed percolation
depinning. Our results are relevant for paper wetting experiments, in which an
interface gets moving with no external driving force.Comment: 4 pages, 3 figures included, uses epsf. Submitted to PR
A Monte Carlo generator of nucleon configurations in complex nuclei including Nucleon-Nucleon correlations
We developed a Monte Carlo event generator for production of nucleon
configurations in complex nuclei consistently including effects of
Nucleon-Nucleon (NN) correlations. Our approach is based on the Metropolis
search for configurations satisfying essential constraints imposed by short-
and long-range NN correlations, guided by the findings of realistic
calculations of one- and two-body densities for medium-heavy nuclei. The
produced event generator can be used for Monte Carlo (MC) studies of pA and AA
collisions. We perform several tests of consistency of the code and comparison
with previous models, in the case of high energy proton-nucleus scattering on
an event-by-event basis, using nucleus configurations produced by our code and
Glauber multiple scattering theory both for the uncorrelated and the correlated
configurations; fluctuations of the average number of collisions are shown to
be affected considerably by the introduction of NN correlations in the target
nucleus. We also use the generator to estimate maximal possible gluon nuclear
shadowing in a simple geometric model.Comment: 7 pages, 8 figures; removed one figure, reduced length; to be
published in Phys. Lett.
Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers
A vector spin model is used to show how frustrations within a multisublattice
antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting
on an exchange coupled ferromagnetic film. Possibilities for the existence of
exchange bias are examined and shown to exist for the case of weak chemical
disorder at the interface in an otherwise perfect structure. A sensitive
dependence on interlayer exchange is found for anisotropies acting on the
ferromagnet through the exchange coupling, and we show that a wide range of
anisotropies can appear even for a perfect crystalline structure with an
ideally flat interface.Comment: 7 pages, 7 figure
- …