1,373 research outputs found
Anomalous particle-number fluctuations in a three-dimensional interacting Bose-Einstein condensate
The particle-number fluctuations originated from collective excitations are
investigated for a three-dimensional, repulsively interacting Bose-Einstein
condensate (BEC) confined in a harmonic trap. The contribution due to the
quantum depletion of the condensate is calculated and the explicit expression
of the coefficient in the formulas denoting the particle-number fluctuations is
given. The results show that the particle-number fluctuations of the condensate
follow the law and the fluctuations vanish when
temperature approaches to the BEC critical temperature.Comment: RevTex, 4 page
A Memetic Algorithm for the Multidimensional Assignment Problem
The Multidimensional Assignment Problem (MAP or s-AP in the case of s
dimensions) is an extension of the well-known assignment problem. The most
studied case of MAP is 3-AP, though the problems with larger values of s have
also a number of applications. In this paper we propose a memetic algorithm for
MAP that is a combination of a genetic algorithm with a local search procedure.
The main contribution of the paper is an idea of dynamically adjusted
generation size, that yields an outstanding flexibility of the algorithm to
perform well for both small and large fixed running times. The results of
computational experiments for several instance families show that the proposed
algorithm produces solutions of very high quality in a reasonable time and
outperforms the state-of-the art 3-AP memetic algorithm.Comment: 14 page
Proton-Antiproton Annihilation into a Lambda_c-Antilambda_c Pair
The process p-pbar -> Lambda_c-Antilambda_c is investigated within the
handbag approach. It is shown that the dominant dynamical mechanism,
characterized by the partonic subprocess u-ubar -> c-cbar factorizes in the
sense that only the subprocess contains highly virtual partons, a gluon to
lowest order of perturbative QCD, while the hadronic matrix elements embody
only soft scales and can be parameterized in terms of helicity flip and
non-flip generalized parton distributions. Modelling these parton distributions
by overlaps of light-cone wave functions for the involved baryons we are able
to predict cross sections and spin correlation parameters for the process of
interest.Comment: 39 pages, 7 figures, problems with printout of figures resolved, Ref.
33 and referring sentences in section 4 change
Oscillating flames in open tubes
When a flame passes along a tube that is open at both ends a self induced fluctuating pressure/flow field is created which the flame has to traverse. Here fuel rich (1.1 < Ï < 1.4) propane-air flames have been filmed travelling along a 20 mm internal diameter quartz tube. Fluctuations in the flameâs progression were observed to increase as the flame propagated, achieving a maximum oscillation amplitude of ±10 mm at 220 Hz that decayed as the flame progressed further towards the end of the tube. The impact of the periodic pressure gradients on the flame shape could be discerned with tongues of unburned reactants pushed into the products as well as the corresponding rapid acceleration of the flame into the unburned mixture. The impact of the fluctuations on flame chemistry was monitored by capturing the CHâ and C2 chemiluminescence using a high speed colour camera. The CHâ/C2â ratio was observed to decrease as the flame was pulled back towards the burned mixture; and increased when the flame was pushed forwards. This was consistent throughout the flame progress even when small oscillations in the flame position were measured. This could be a significant feature of flames in this environment
Structural Disorder, Octahedral Coordination, and 2-Dimensional Ferromagnetism in Anhydrous Alums
The crystal structures of the triangular lattice, layered anhydrous alums
KCr(SO4)2, RbCr(SO4)2 and KAl(SO4)2 are characterized by X-ray and neutron
powder diffraction at temperatures between 1.4 and 773 K. The compounds all
crystallize in the space group P-3, with octahedral coordination of the
trivalent cations. In all cases, small amounts of disorder in the stacking of
the triangular layers of corner sharing MO6 octahedra and SO4 tetrahedra is
seen, with the MO6-SO4 network rotated in opposite directions between layers.
The electron diffraction study of KCr(SO4)2 supports this model, which on
average can be taken to imply trigonal prismatic coordination for the M3+ ions;
as was previously reported for the prototype anhydrous alum KAl(SO4)2. The
temperature dependent magnetic susceptibilities for ACr(SO4)2 (A = K,Rb,Cs)
indicate the presence of predominantly ferromagnetic interactions. Low
temperature powder neutron diffraction reveals that the magnetic ordering is
ferromagnetic in-plane, with antiferromagnetic ordering between planes below 3
K.Comment: Accepted to the Journal of Solid State Chemistr
Coupling between electronic and structural degrees of freedom in the triangular lattice conductor NaxCoO2
The determination by powder neutron diffraction of the ambient temperature
crystal structures of compounds in the NaxCoO2 family, for 0.3 < x <= 1.0, is
reported. The structures consist of triangular CoO2 layers with Na ions
distributed in intervening charge reservoir layers. The shapes of the CoO6
octahedra that make up the CoO2 layers are found to be critically dependent on
the electron count and on the distribution of the Na ions in the intervening
layers, where two types of Na sites are available. Correlation of the shapes of
cobalt-oxygen octahedra, the Na ion positions, and the electronic phase diagram
in NaxCoO2 is made, showing how structural and electronic degrees of freedom
can be coupled in electrically conducting triangular lattice systems.Comment: 15 pages, 1 tables, 6 figures Submitted to Physical Review
Explicit Computation of Input Weights in Extreme Learning Machines
We present a closed form expression for initializing the input weights in a
multi-layer perceptron, which can be used as the first step in synthesis of an
Extreme Learning Ma-chine. The expression is based on the standard function for
a separating hyperplane as computed in multilayer perceptrons and linear
Support Vector Machines; that is, as a linear combination of input data
samples. In the absence of supervised training for the input weights, random
linear combinations of training data samples are used to project the input data
to a higher dimensional hidden layer. The hidden layer weights are solved in
the standard ELM fashion by computing the pseudoinverse of the hidden layer
outputs and multiplying by the desired output values. All weights for this
method can be computed in a single pass, and the resulting networks are more
accurate and more consistent on some standard problems than regular ELM
networks of the same size.Comment: In submission for the ELM 2014 Conferenc
One-Loop Helicity Amplitudes for Parton Level Virtual Compton Scattering
We calculate the one-loop QCD virtual corrections to all helicity amplitudes
for parton level virtual Compton scattering processes. We include the
amplitudes both on quark target process and on gluon
target process . The infrared pole structure of the
amplitudes is in agreement with the prediction of Catani's general formalism
for the singularities of one-loop amplitudes, while expressions for the finite
remainder are given in terms of logarithms and dilogarithms that are real in
the physical region.Comment: 16 pages, 2 figures, detailed comparison with DVCS include
Fabrication of Microstructure Arrays on Photosensitive Glass by Femtosecond Laser
A maskless technique for the fabrication of U-shaped microstructure arrays on the surface of photosensitive glass by femtosecond laser-induced modification is developed. This technique is followed by heat treatment to crystallize the modified area, and the specimen is then placed in acid solution for chemical etching. The surface roughness of the microstructures is further improved by a secondary annealing process. The fabricated photosensitive glass is used as a mold template, and replicated plano-convex cylindrical arrays by UV-replica are also presented. The focusing ability of the microlens arrays on the glass mold and replicate is demonstrated. DOI: 10.2961/jlmn.2012.01.002
Role of the Brans-Dicke scalar in the holographic description of dark energy
We study cosmological application of the holographic energy density in the
Brans-Dicke theory. Considering the holographic energy density as a dynamical
cosmological constant, it is more natural to study it in the Brans-Dicke theory
than in general relativity. Solving the Friedmann and Brans-Dicke field
equations numerically, we clarify the role of Brans-Dicke field during
evolution of the universe. When the Hubble horizon is taken as the IR cutoff,
the equation of state (w_{\Lmd}) for the holographic energy density is
determined to be 5/3 when the Brans-Dicke parameter \omg goes infinity. This
means that the Brans-Dicke field plays a crucial role in determining the
equation of state. For the particle horizon IR cutoff, the Brans-Dicke scalar
mediates a transition from w_{\Lmd} = -1/3 (past) to w_{\Lmd} = 1/3
(future). If a dust matter is present, it determines future equation of state.
In the case of future event horizon cutoff, the role of the Brans-Dicke scalar
and dust matter are turned out to be trivial, whereas the holographic energy
density plays an important role as a dark energy candidate with w_{\Lmd} =-1.Comment: 10pages, 3figures, version to appear in PL
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