53,542 research outputs found
Large-scale low-energy excitations in 3-d spin glasses
We numerically extract large-scale excitations above the ground state in the
3-dimensional Edwards-Anderson spin glass with Gaussian couplings. We find that
associated energies are O(1), in agreement with the mean field picture. Of
further interest are the position-space properties of these excitations. First,
our study of their topological properties show that the majority of the
large-scale excitations are sponge-like. Second, when probing their geometrical
properties, we find that the excitations coarsen when the system size is
increased. We conclude that either finite size effects are very large even when
the spin overlap q is close to zero, or the mean field picture of homogeneous
excitations has to be modified.Comment: 11 pages, typos corrected, added reference
Anticoherence of spin states with point group symmetries
We investigate multiqubit permutation-symmetric states with maximal entropy
of entanglement. Such states can be viewed as particular spin states, namely
anticoherent spin states. Using the Majorana representation of spin states in
terms of points on the unit sphere, we analyze the consequences of a
point-group symmetry in their arrangement on the quantum properties of the
corresponding state. We focus on the identification of anticoherent states (for
which all reduced density matrices in the symmetric subspace are maximally
mixed) associated with point-group symmetric sets of points. We provide three
different characterizations of anticoherence, and establish a link between
point symmetries, anticoherence and classes of states equivalent through
stochastic local operations with classical communication (SLOCC). We then
investigate in detail the case of small numbers of qubits, and construct
infinite families of anticoherent states with point-group symmetry of their
Majorana points, showing that anticoherent states do exist to arbitrary order.Comment: 15 pages, 5 figure
Energy exponents and corrections to scaling in Ising spin glasses
We study the probability distribution P(E) of the ground state energy E in
various Ising spin glasses. In most models, P(E) seems to become Gaussian with
a variance growing as the system's volume V. Exceptions include the
Sherrington-Kirkpatrick model (where the variance grows more slowly, perhaps as
the square root of the volume), and mean field diluted spin glasses having +/-J
couplings. We also find that the corrections to the extensive part of the
disorder averaged energy grow as a power of the system size; for finite
dimensional lattices, this exponent is equal, within numerical precision, to
the domain-wall exponent theta_DW. We also show how a systematic expansion of
theta_DW in powers of exp(-d) can be obtained for Migdal-Kadanoff lattices.
Some physical arguments are given to rationalize our findings.Comment: 12 pages, RevTex, 9 figure
Multifractality and intermediate statistics in quantum maps
We study multifractal properties of wave functions for a one-parameter family
of quantum maps displaying the whole range of spectral statistics intermediate
between integrable and chaotic statistics. We perform extensive numerical
computations and provide analytical arguments showing that the generalized
fractal dimensions are directly related to the parameter of the underlying
classical map, and thus to other properties such as spectral statistics. Our
results could be relevant for Anderson and quantum Hall transitions, where wave
functions also show multifractality.Comment: 4 pages, 4 figure
Magnetic exponents of two-dimensional Ising spin glasses
The magnetic critical properties of two-dimensional Ising spin glasses are
controversial. Using exact ground state determination, we extract the
properties of clusters flipped when increasing continuously a uniform field. We
show that these clusters have many holes but otherwise have statistical
properties similar to those of zero-field droplets. A detailed analysis gives
for the magnetization exponent delta = 1.30 +/- 0.02 using lattice sizes up to
80x80; this is compatible with the droplet model prediction delta = 1.282. The
reason for previous disagreements stems from the need to analyze both singular
and analytic contributions in the low-field regime.Comment: 4 pages, 4 figures, title now includes "Ising
Transient behavior of surface plasmon polaritons scattered at a subwavelength groove
We present a numerical study and analytical model of the optical near-field
diffracted in the vicinity of subwavelength grooves milled in silver surfaces.
The Green's tensor approach permits computation of the phase and amplitude
dependence of the diffracted wave as a function of the groove geometry. It is
shown that the field diffracted along the interface by the groove is equivalent
to replacing the groove by an oscillating dipolar line source. An analytic
expression is derived from the Green's function formalism, that reproduces well
the asymptotic surface plasmon polariton (SPP) wave as well as the transient
surface wave in the near-zone close to the groove. The agreement between this
model and the full simulation is very good, showing that the transient
"near-zone" regime does not depend on the precise shape of the groove. Finally,
it is shown that a composite diffractive evanescent wave model that includes
the asymptotic SPP can describe the wavelength evolution in this transient
near-zone. Such a semi-analytical model may be useful for the design and
optimization of more elaborate photonic circuits whose behavior in large part
will be controlled by surface waves.Comment: 12 pages, 10 figure
A Generic business rules validation system for ORACLE Applications
Picture this : You have just spent the remainder of your IT budget on a new software package for Human Resources. Despite its excellent functionality, it does not perform all of the complex validation that your old in-house-developed system did. How can you improve the standard software package given the following constraints : You cannot afford to pay the vendor for modifications to the package Modifying the package yourself is out of the question. We describe a tool designed to implement the validation of complex business rules for any ORACLE database application - without incurring any modification to the user interface. It enhances your productĂs standard capabilities and improves data quality as soon as data has been entered or modified. . Our initial implementations was for the ORACLE Human Resources package. Our tool consists of four independent components: A description of the data and its location, A set of rules (written in a simple pseudo-code), A generic on-line change detection system, A core engine that checks data consistency by applying the rules to relevant changes. The Validation system makes extensive use of state of the art techniques with database triggers and dynamic PL/SQL
Narrow-band multiresonant plasmon nanostructure for the coherent control of light: An optical analog of the xylophone
We demonstrate that it is possible to combine several small metallic particles in a very compact geometry without loss of their individual modal properties by adding a gold metallic film underneath. This film essentially acts as a "ground plane" which channels the optical field of each particle and decreases the interparticle coupling. The localization of the electric field can then be controlled temporally by illuminating the chain with a chirped pulse. The sign of the chirp controls the excitation sequence of the particles with great flexibility
Molecular hydrogen in the disk of the Herbig Ae star HD97048
We present high-resolution spectroscopic mid-infrared observations of the
circumstellar disk around the Herbig Ae star HD97048 obtained with the VLT
Imager and Spectrometer for the mid-InfraRed (VISIR). We conducted observations
of mid-infrared pure rotational lines of molecular hydrogen (H2) as a tracer of
warm gas in the disk surface layers. In a previous paper, we reported the
detection of the S(1) pure rotational line of H2 at 17.035 microns and argued
it is arising from the inner regions of the disk around the star. We used VISIR
on the VLT for a more comprehensive study based on complementary observations
of the other mid-infrared molecular transitions, namely S(2) and S(4) at 12.278
microns and 8.025 microns respectively, to investigate the physical properties
of the molecular gas in the circumstellar disk around HD97048. We do not detect
neither the S(2) line nor the S(4) H2 line from the disk of HD97048, but we
derive upper limits on the integrated line fluxes which allows us to estimate
an upper limit on the gas excitation temperature, T_ex < 570 K. This limit on
the temperature is consistent with the assumptions previously used in the
analysis of the S(1) line, and allows us to set stronger contraints on the mass
of warm gas in the inner regions of the disk. Indeed, we estimate the mass of
warm gas to be lower than 0.1 M_Jup. We also discuss the probable physical
mechanisms which could be responsible of the excitation of H2 in the disk of
HD97048.Comment: accepted for publication in Ap
Strain analysis of multiferroic BiFeO3-CoFe2O4 nanostructures by Raman scattering
We report a Raman scattering investigation of columnar BiFeO3-CoFe2O4
(BFO-CFO) epitaxial thin film nanostructures, where BFO pillars are embedded in
a CFO matrix. The feasibility of a strain analysis is illustrated through an
investigation of two nanostructures with different BFO-CFO ratios. We show that
the CFO matrix presents the same strain state in both nanostructures, while the
strain state of the BFO pillars depends on the BFO/CFO ratio with an increasing
tensile strain along the out-of-plane direction with decreasing BFO content.
Our results demonstrate that Raman scattering allows monitoring strain states
in complex 3D multiferroic pillar/matrix composites.Comment: revised version submitted to Appl. Phys. Let
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