567 research outputs found
On the stability problem in the O(N) nonlinear sigma model
The stability problem for the O(N) nonlinear sigma model in the 2+\epsilon
dimensions is considered. We present the results of the 1/N^{2} order
calculations of the critical exponents (in the 2<d<4 dimensions) of the
composite operators relevant for this problem. The arguments in the favor of
the scenario with the conventional fixed point are given.Comment: 9 pages, revtex, 1 Postscript figur
Anomalous Magnetic Properties in Ni50Mn35In15
We present here a comprehensive investigation of the magnetic ordering in
Ni50Mn35In15 composition. A concomitant first order martensitic transition and
the magnetic ordering occurring in this off-stoichiometric Heusler compound at
room temperature signifies the multifunctional character of this magnetic shape
memory alloy. Unusual features are observed in the dependence of the
magnetization on temperature that can be ascribed to a frustrated magnetic
order. It is compelling to ascribe these features to the cluster type
description that may arise due to inhomogeneity in the distribution of magnetic
atoms. However, evidences are presented from our ac susceptibility, electrical
resistivity and dc magnetization studies that there exists a competing
ferromagnetic and antiferromagnetic order within crystal structure of this
system. We show that excess Mn atoms that substitute the In atoms have a
crucial bearing on the magnetic order of this compound. These excess Mn atoms
are antiferromagnetically aligned to the other Mn, which explains the peculiar
dependence of magnetization on temperature.Comment: Accepted in J. Phys. D.:Appl. Physic
O(1/N_f) Corrections to the Thirring Model in 2<d<4
The Thirring model, that is, a relativistic field theory of fermions with a
contact interaction between vector currents, is studied for dimensionalities
2<d<4 using the 1/N_f expansion, where N_f is the number of fermion species.
The model is found to have no ultraviolet divergences at leading order provided
a regularization respecting current conservation is used. Explicit O(1/N_f)
corrections are computed, and the model shown to be renormalizable at this
order in the massless limit; renormalizability appears to hold to all orders
due to a special case of Weinberg's theorem. This implies there is a universal
amplitude for four particle scattering in the asymptotic regime. Comparisons
are made with both the Gross-Neveu model and QED.Comment: 22 pages in plain TeX, with 7 figs included using psfig.tex (Minor
conceptual changes - algebra unaffected
Hybrid heterostructures with superconducting/antiferromagnetic interfaces
We report on structural, DC, X-ray and neutron studies of hybrid
superconducting mesa-heterostructures with a cuprate antiferromagnetic
interlayer Ca1-xSrxCuO2 (CSCO). The upper electrode was bilayer Nb/Au
superconductor and copper oxide superconductor YBa2Cu3O7 (YBCO) was the bottom
electrode. It was experimentally shown that during the epitaxial growth of the
two films YBCO and CSCO a charge carrier doping takes place in the CSCO
interlayer with a depth about 20 nm. The conductivity of the doped part of CSCO
layer is close to the metal type, while the reference CSCO film, deposited
directly on NdGaO3 substrate, behaves as Mott insulator with the hopping
conductivity. The interface Au/CSCO is clearly seen on bright-field image of
the cross-section of heterostructure and gives the main contribution to the
total resistance of mesa-heterostructure.Comment: 16 pages, 9 figure
Integral Transforms for Conformal Field Theories with a Boundary
A new method is developed for solving the conformally invariant integrals
that arise in conformal field theories with a boundary. The presence of a
boundary makes previous techniques for theories without a boundary less
suitable. The method makes essential use of an invertible integral transform,
related to the radon transform, involving integration over planes parallel to
the boundary. For successful application of this method several nontrivial
hypergeometric function relations are also derived.Comment: 20 pagess, LateX fil
INVESTIGATION OF FILTERING AND OBJECTS DETECTION ALGORITHMS FOR A MULTIZONE IMAGE SEQUENCE
The problem of detecting objects on a sequence of images with a complex structure is considered. Optimal and quasi-optimal algorithms for processing multidimensional images have been synthesized and investigated. Improved detection efficiency has been obtained by adequately describing real data using doubly stochastic random fields. The possibility of describing Earth remote sensing data using doubly stochastic models is investigated. The possibility of obtaining significant gains when filtering satellite material and detecting extended objects on it due to the adaptive structure of such models and processing time sequence of multizone images as a single multidimensional dataset is shown. The gains for filtering algorithms in the error variance are about 80% comparing single frame processing, and the gains for detecting algorithms in the signal/noise ratio are about 70% comparing single frame processing
Enhancement of the Thermal Conductivity in gapped Quantum Spin Chains
We study mechanism of magnetic energy transport, motivated by recent
measurements of the thermal conductivity in low dimensional quantum magnets. We
point out a possible mechanism of enhancement of the thermal conductivity in
gapped magnetic system, where the magnetic energy transport plays a crucial
role. This mechanism gives an interpretation for the recent experiment of
CuGeO_3, where the thermal conductivity depends on the crystal direction.Comment: 4 pages, 2 figure
High frequency ESR investigation on dynamical charge disproportionation and spin gap excitation in NaV_2O_5
A significant frequency dependence of the ESR line width is found in NaV_2O_5
between 34-100 K and the line width increases as the resonance frequency is
increased from 95 GHz to 760 GHz. The observed frequency dependence is
qualitatively explained in terms of the dynamical charge disproportionation.
The present results show the essential role of the internal charge degree of
freedom in a V-O-V bond. We have also proposed the existence of the
Dzyaloshinsky-Moriya interaction in the low temperature charge ordered phase
considering the breaking of the selection rule of ESR realized as the direct
observation of the spin gap excitation.Comment: 9 figures submitted to J. Phys.Soc. Jp
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