2,178 research outputs found
On subgroups in division rings of type
Let be a division ring with center . We say that is a {\em
division ring of type } if for every two elements the division
subring is a finite dimensional vector space over . In this paper
we investigate multiplicative subgroups in such a ring.Comment: 10 pages, 0 figure
Block-block entanglement and quantum phase transitions in one-dimensional extended Hubbard model
In this paper, we study block-block entanglement in the ground state of
one-dimensional extended Hubbard model. Our results show that the phase diagram
derived from the block-block entanglement manifests richer structure than that
of the local (single site) entanglement because it comprises nonlocal
correlation. Besides phases characterized by the charge-density-wave, the
spin-density-wave, and phase-separation, which can be sketched out by the local
entanglement, singlet superconductivity phase could be identified on the
contour map of the block-block entanglement. Scaling analysis shows that behavior of the block-block entanglement may exist in both
non-critical and the critical regions, while some local extremum are induced by
the finite-size effect. We also study the block-block entanglement defined in
the momentum space and discuss its relation to the phase transition from
singlet superconducting state to the charge-density-wave state.Comment: 8 pages, 9 figure
Tannaka-Krein duality for Hopf algebroids
We develop the Tannaka-Krein duality for monoidal functors with target in the
categories of bimodules over a ring. The \coend of such a functor turns out
to be a Hopf algebroid over this ring. Using the result of a previous paper we
characterize a small abelian, locally finite rigid monoidal category as the
category of rigid comodules over a transitive Hopf algebroid.Comment: 25 pages, final version, to appear in Israel Journal of Mathematic
The Josephson current in Fe-based superconducting junctions: theory and experiment
We present theory of dc Josephson effect in contacts between Fe-based and
spin-singlet -wave superconductors. The method is based on the calculation
of temperature Green's function in the junction within the tight-binding model.
We calculate the phase dependencies of the Josephson current for different
orientations of the junction relative to the crystallographic axes of Fe-based
superconductor. Further, we consider the dependence of the Josephson current on
the thickness of an insulating layer and on temperature. Experimental data for
PbIn/BaK(FeAs) point-contact Josephson junctions are
consistent with theoretical predictions for symmetry of an order
parameter in this material. The proposed method can be further applied to
calculations of the dc Josephson current in contacts with other new
unconventional multiorbital superconductors, such as and
superconducting topological insulator .Comment: 16 pages, 14 figure
Entanglement and quantum phase transition in the extended Hubbard model
We study quantum entanglement in one-dimensional correlated fermionic system.
Our results show, for the first time, that entanglement can be used to identify
quantum phase transitions in fermionic systems.Comment: 5 pages, 4 figure
Discrete chaotic states of a Bose-Einstein condensate
We find the different spatial chaos in a one-dimensional attractive
Bose-Einstein condensate interacting with a Gaussian-like laser barrier and
perturbed by a weak optical lattice. For the low laser barrier the chaotic
regions of parameters are demonstrated and the chaotic and regular states are
illustrated numerically. In the high barrier case, the bounded perturbed
solutions which describe a set of discrete chaotic states are constructed for
the discrete barrier heights and magic numbers of condensed atoms. The chaotic
density profiles are exhibited numerically for the lowest quantum number, and
the analytically bounded but numerically unbounded Gaussian-like configurations
are confirmed. It is shown that the chaotic wave packets can be controlled
experimentally by adjusting the laser barrier potential.Comment: 7 pages, 5 figure
Two-subband electron transport in nonideal quantum wells
Electron transport in nonideal quantum wells (QW) with large-scale variations
of energy levels is studied when two subbands are occupied. Although the mean
fluctuations of these two levels are screened by the in-plane redistribution of
electrons, the energies of both levels remain nonuniform over the plane. The
effect of random inhomogeneities on the classical transport is studied within
the framework of a local response approach for weak disorder. Both short-range
and small-angle scattering mechanisms are considered. Magnetotransport
characteristics and the modulation of the effective conductivity by transverse
voltage are evaluated for different kinds of confinement potentials (hard wall
QW, parabolic QW, and stepped QW).Comment: 10 pages, 6 figure
Multidimensional Worldline Instantons
We extend the worldline instanton technique to compute the vacuum pair
production rate for spatially inhomogeneous electric background fields, with
the spatial inhomogeneity being genuinely two or three dimensional, both for
the magnitude and direction of the electric field. Other techniques, such as
WKB, have not been applied to such higher dimensional problems. Our method
exploits the instanton dominance of the worldline path integral expression for
the effective action.Comment: 22 pages, 13 figure
ORIGINAL PAPER Sexual Risk and Bridging Behaviors Among Young People
Abstract The risk of the HIV epidemic spreading from high-risk groups to the general population in Vietnam depends on sexual risk and bridging behaviors between highand low-risk individuals. A cross-sectional study was used to describe sexual activities of youth aged 18–29 years. Nearly half (41.4%) were sexually active. Premarital sex was reported by 43.3 % of them; 78.3 % of sexually active males and 13.5 % of sexually active females. Multiple sex partners were reported by 31.0%; 56.7 % of males and 9.2% of females. Almost 27 % of males and 5 % of females engaged in sexual bridging behaviors. Being unmarried was significantly associated with having sex with non-regular partners. Being unmarried and early age at first intercourse were associated with having sex with a sex worker. Consistent condom use was high with commercial sex workers but low with regular partners. Education to delay early sexual debut, increased employment, and strategies to inform young sexually active people to adopt safer behaviors are urgently needed
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