718 research outputs found
Graphs with the maximum or minimum number of 1-factors
AbstractRecently Alon and Friedland have shown that graphs which are the union of complete regular bipartite graphs have the maximum number of 1-factors over all graphs with the same degree sequence. We identify two families of graphs that have the maximum number of 1-factors over all graphs with the same number of vertices and edges: the almost regular graphs which are unions of complete regular bipartite graphs, and complete graphs with a matching removed. The first family is determined using the Alon and Friedland bound. For the second family, we show that a graph transformation which is known to increase network reliability also increases the number of 1-factors. In fact, more is true: this graph transformation increases the number of k-factors for all k≥1, and “in reverse” also shows that in general, threshold graphs have the fewest k-factors. We are then able to determine precisely which threshold graphs have the fewest 1-factors. We conjecture that the same graphs have the fewest k-factors for all k≥2 as well
Absorbing systematic effects to obtain a better background model in a search for new physics
This paper presents a novel approach to estimate the Standard Model
backgrounds based on modifying Monte Carlo predictions within their systematic
uncertainties. The improved background model is obtained by altering the
original predictions with successively more complex correction functions in
signal-free control selections. Statistical tests indicate when sufficient
compatibility with data is reached. In this way, systematic effects are
absorbed into the new background model. The same correction is then applied on
the Monte Carlo prediction in the signal region. Comparing this method to other
background estimation techniques shows improvements with respect to statistical
and systematical uncertainties. The proposed method can also be applied in
other fields beyond high energy physics
Comments on "Translation-invariant bipolarons and the problem of high-temperature superconductivity"
We comment on the recent results of Refs. [1, 2] on the bipolaron problem
derived using an approximation of Gross - Tulub. It is proved that, contrary to
the claim made in Refs. [1, 2], the bipolaron ground state energy calculated
there in the strong-coupling approximation has not been shown to constitute a
variational upper bound.Comment: 3 pages, 2 figures, submitted to Solid State Communication
Competition between fluctuations and disorder in frustrated magnets
We investigate the effects of impurities on the nature of the phase
transition in frustrated magnets, in d=4-epsilon dimensions. For sufficiently
small values of the number of spin components, we find no physically relevant
stable fixed point in the deep perturbative region (epsilon << 1), contrarily
to what is to be expected on very general grounds. This signals the onset of
important physical effects.Comment: 4 pages, 3 figures, published versio
On Using High-Definition Body Worn Cameras for Face Recognition from a Distance
Recognition of human faces from a distance is highly desirable for law-enforcement. This paper evaluates the use of low-cost, high-definition (HD) body worn video cameras for face recognition from a distance. A comparison of HD vs. Standard-definition (SD) video for face recognition from a distance is presented. HD and SD videos of 20 subjects were acquired in different conditions and at varying distances. The evaluation uses three benchmark algorithms: Eigenfaces, Fisherfaces and Wavelet Transforms. The study indicates when gallery and probe images consist of faces captured from a distance, HD video result in better recognition accuracy, compared to SD video. This scenario resembles real-life conditions of video surveillance and law-enforcement activities. However, at a close range, face data obtained from SD video result in similar, if not better recognition accuracy than using HD face data of the same range
Gravitation with superposed Gauss--Bonnet terms in higher dimensions: Black hole metrics and maximal extensions
Our starting point is an iterative construction suited to combinatorics in
arbitarary dimensions d, of totally anisymmetrised p-Riemann 2p-forms (2p\le d)
generalising the (1-)Riemann curvature 2-forms. Superposition of p-Ricci
scalars obtained from the p-Riemann forms defines the maximally Gauss--Bonnet
extended gravitational Lagrangian. Metrics, spherically symmetric in the (d-1)
space dimensions are constructed for the general case. The problem is directly
reduced to solving polynomial equations. For some black hole type metrics the
horizons are obtained by solving polynomial equations. Corresponding Kruskal
type maximal extensions are obtained explicitly in complete generality, as is
also the periodicity of time for Euclidean signature. We show how to include a
cosmological constant and a point charge. Possible further developments and
applications are indicated.Comment: 13 pages, REVTEX. References and Note Adde
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
Cluster Monte Carlo study of multi-component fluids of the Stillinger-Helfand and Widom-Rowlinson type
Phase transitions of fluid mixtures of the type introduced by Stillinger and
Helfand are studied using a continuum version of the invaded cluster algorithm.
Particles of the same species do not interact, but particles of different types
interact with each other via a repulsive potential. Examples of interactions
include the Gaussian molecule potential and a repulsive step potential.
Accurate values of the critical density, fugacity and magnetic exponent are
found in two and three dimensions for the two-species model. The effect of
varying the number of species and of introducing quenched impurities is also
investigated. In all the cases studied, mixtures of -species are found to
have properties similar to -state Potts models.Comment: 25 pages, 5 figure
Selection of Wavelet Subbands Using Genetic Algorithm for Face Recognition
Abstract. In this paper, a novel representation called the subband face is proposed for face recognition. The subband face is generated from selected subbands obtained using wavelet decomposition of the original face image. It is surmised that certain subbands contain information that is more significant for discriminating faces than other subbands. The problem of subband selection is cast as a combinatorial optimization problem and genetic algorithm (GA) is used to find the optimum subband combination by maximizing Fisher ratio of the training features. The performance of the GA selected subband face is evaluated using three face databases and compared with other wavelet-based representations.
The Chiral Fermion Meson Model at Finite Temperature
We study the chiral fermion meson model which is the well known linear sigma
model of Gell-Mann-and-Levy at finite temperature.A modified self-consistent
resummation (MSCR) which resums higher order terms in the perturbative
expansion is proposed. It is shown that with the MSCR the problem of tachyonic
masses is solved, the renormalization of the gap equations is carried out and
the Goldstone's theorem is verified. We also apply the method to investigate
another known case at high temperature and compare with results found in the
literature.Comment: 31 pages, 9 EPS figures. Final version with extended Concluding
Remarks section, accepted for publication in Phys. Rev.
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