2,076 research outputs found
The disk-halo connection and the nature of the interstellar medium
Some results on the nature of the interstellar medium that are specifically concerned with the disk-halo interaction are discussed. Over the last five years or so it has become clear that the supernovae rate in our Galaxy is spatially clumped and the consequences of such clumping are superbubbles and supershells fed by tens or hundreds of supernovae per shell. These objects evolve and expand rapidly and soon break out of the disk of the Galaxy, feeding the halo with very significant mass, energy, and momentum. As cooling occurs, gas will rain down onto the disk of the Galaxy completing the cycle. The basic flow of physical quantities from disk to halo and vice versa are discussed. Some of the many implications are noted including aspects of dynamo theory, quasar absorption lines, the theory of galactic coronae, and the nature of the x ray background. The essential difference here with the McKee-Ostriker (1977) theory is that the filling factor of the hot gas in the disk is significantly less than unity
Supersymmetric extension of Moyal algebra and its application to the matrix model
We construct operator representation of Moyal algebra in the presence of
fermionic fields. The result is used to describe the matrix model in Moyal
formalism, that treat gauge degrees of freedom and outer degrees of freedom
equally.Comment: to appear in Mod.Phys.Let
Scanning SQUID Microscope Study of Vortex Polygons and Shells in Weak Pinning Disks of an Amorphous Superconducting Film
Direct observation of vortices by the scanning SQUID microscopy was made on
large mesoscopic disks of an amorphous MoGe thin film. Owing to the weak
pinning nature of the amorphous film, vortices are able to form geometry
induced, (quasi-)symmetric configurations of polygons and concentric shells in
the large disks. Systematic measurements made on selected disks allow us to
trace not only how the vortex pattern evolves with magnetic field, but also how
the vortex polygons change in size and rotate with respect to the disk center.
The results are in good agreement with theoretical considerations for
mesoscopic disks with sufficiently large diameter. A series of vortex images
obtained in a disk with a pinning site reveals a unique line symmetry in vortex
configurations, resulting in modifications of the shell filling rule and the
magic number.Comment: 8 pages, 5 figures. Phys Rev B 82 014501 (2010
Carrier doping to a partially disordered state in the periodic Anderson model on a triangular lattice
We investigate the effect of hole and electron doping to half-filling in the
periodic Anderson model on a triangular lattice by the Hartree-Fock
approximation at zero temperature. At half-filling, the system exhibits a
partially disordered insulating state, in which a collinear antiferromagnetic
order on an unfrustrated honeycomb subnetwork coexists with nonmagnetic state
at the remaining sites. We find that the carrier doping destabilizes the
partially disordered state, resulting in a phase separation to a doped metallic
state with different magnetic order. The partially disordered state is
restricted to the half-filled insulating case, while its metallic counterpart
is obtained as a metastable state in a narrow electron doped region.Comment: 4 pages, 2 figure
Magnetic quantum tunnelling in Fe8 with excited nuclei
We investigate the effect of dynamic nuclear spin fluctuation on quantum
tunneling of the magnetization (QTM) in the molecular magnet Fe8 by increasing
the nuclei temperature using radio frequency (RF) pulses before the hysteresis
loop measurements. The RF pulses do not change the electrons spin temperature.
Independently we show that the nuclear spin-spin relaxation time T2 has strong
temperature dependence. Nevertheless, we found no effect of the nuclear spin
temperature on the tunneling probability. This suggests that in our
experimental conditions only the hyperfine field strength is relevant for QTM.
We demonstrate theoretically how this can occur.Comment: 4 pages, 4 figure
Effective Sampling in the Configurational Space by the Multicanonical-Multioverlap Algorithm
We propose a new generalized-ensemble algorithm, which we refer to as the
multicanonical-multioverlap algorithm. By utilizing a non-Boltzmann weight
factor, this method realizes a random walk in the multi-dimensional,
energy-overlap space and explores widely in the configurational space including
specific configurations, where the overlap of a configuration with respect to a
reference state is a measure for structural similarity. We apply the
multicanonical-multioverlap molecular dynamics method to a penta peptide,
Met-enkephalin, in vacuum as a test system. We also apply the multicanonical
and multioverlap molecular dynamics methods to this system for the purpose of
comparisons. We see that the multicanonical-multioverlap molecular dynamics
method realizes effective sampling in the configurational space including
specific configurations more than the other two methods. From the results of
the multicanonical-multioverlap molecular dynamics simulation, furthermore, we
obtain a new local-minimum state of the Met-enkephalin system.Comment: 15 pages, (Revtex4), 9 figure
Self-written waveguides in photopolymerizable resins
We study the optically-induced growth and interaction of self-written
waveguides in a photopolymerizable resin. We investigate experimentally how the
interaction depends on the mutual coherence and relative power of the input
beams, and suggest an improved analytical model that describes the growth of
single self-written waveguides and the main features of their interaction in
photosensitive materials.Comment: 3 pages, 3 figure
eta' meson under partial restoration of chiral symmetry in nuclear medium
We shed light upon the eta' mass in nuclear matter in the context of partial
restoration of chiral symmetry, pointing out that the U_{A}(1) anomaly effects
causes the eta'-eta mass difference necessarily through the chiral symmetry
breaking. As a consequence, it is expected that the eta' mass is reduced by
order of 100 MeV in nuclear matter where partial restoration of chiral symmetry
takes place. The discussion given here is based on Ref. [1].Comment: 3 pages, 2 figures. Contribution to Meson201
Matroids on convex geometries (cg-matroids)
AbstractWe consider matroidal structures on convex geometries, which we call cg-matroids. The concept of a cg-matroid is closely related to but different from that of a supermatroid introduced by Dunstan, Ingleton, and Welsh in 1972. Distributive supermatroids or poset matroids are supermatroids defined on distributive lattices or sets of order ideals of posets. The class of cg-matroids includes distributive supermatroids (or poset matroids). We also introduce the concept of a strict cg-matroid, which turns out to be exactly a cg-matroid that is also a supermatroid. We show characterizations of cg-matroids and strict cg-matroids by means of the exchange property for bases and the augmentation property for independent sets. We also examine submodularity structures of strict cg-matroids
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