12,191 research outputs found
On the magnon interaction in Haematite. 2: Magnon energy of the acoustical mode and magnetic critical fields
Previous spin wave theories of the antiferromagnet hematite were extended. The behavior of thermodynamic quantities around the Morin transition temperature was studied, and the latent heat of the Morin transition was calculated. The temperature dependence of the antiferromagnetic resonance frequency and the parallel and perpendicular critical spin-flop magnetic fields were calculated. It was found that the theory agrees well with experiment
Geometrical characterization of textures consisting of two or three discrete colorings
Geometrical characterization for discretized contrast textures is realized by computing the Gaussian and mean curvatures relative to the central pixel of a clique and four neighboring pixels, these four neighbors either being first or second order neighbors. Practical formulae for computing these curvatures are presented. Curvatures based on the central pixel depend upon the brightness configuration of the clique pixels. Therefore the cliques are classified into classes by configuration of pixel contrast or coloring. To look at the textures formed by geometrically classified cliques, we create several textures using overlapping tiling of cliques belonging to a single curvature class. Several examples of hyperbolic textures, consisting of repeated hyperbolic cliques surrounded by non-hyperbolic cliques, are presented with the nonhyperbolic textures. We also introduce a system of 81 rotationally and brightness shift invariant geo-cliques that have shared curvatures and show that histograms of these 81 geo-cliques seem to be able to distinguish isotrigon textures
Multiple peak aggregations for the Keller-Segel system
In this paper we derive matched asymptotic expansions for a solution of the
Keller-Segel system in two space dimensions for which the amount of mass
aggregation is , where Previously available asymptotics
had been computed only for the case in which N=1
A New Approach for Simulating Galaxy Cluster Properties
We describe a subgrid model for including galaxies into hydrodynamical
cosmological simulations of galaxy cluster evolution. Each galaxy construct- or
galcon- is modeled as a physically extended object within which star formation,
galactic winds, and ram pressure stripping of gas are modeled analytically.
Galcons are initialized at high redshift (z~3) after galaxy dark matter halos
have formed but before the cluster has virialized. Each galcon moves
self-consistently within the evolving cluster potential and injects mass,
metals, and energy into intracluster (IC) gas through a well-resolved spherical
interface layer. We have implemented galcons into the Enzo adaptive mesh
refinement code and carried out a simulation of cluster formation in a
LambdaCDM universe. With our approach, we are able to economically follow the
impact of a large number of galaxies on IC gas. We compare the results of the
galcon simulation with a second, more standard simulation where star formation
and feedback are treated using a popular heuristic prescription. One advantage
of the galcon approach is explicit control over the star formation history of
cluster galaxies. Using a galactic SFR derived from the cosmic star formation
density, we find the galcon simulation produces a lower stellar fraction, a
larger gas core radius, a more isothermal temperature profile, and a flatter
metallicity gradient than the standard simulation, in better agreement with
observations.Comment: 4 pages, 2 figures, submitted for publication in ApJ
Lattice Gauge Actions for Fixed Topology
We test a set of lattice gauge actions for QCD that suppress small plaquette
values and in this way also suppress transitions between topological sectors.
This is well suited for simulations in the epsilon-regime and it is expected to
help in numerical simulations with dynamical quarks.Comment: 3 pages. Talk presented at Quark Confinement and the Hadron Spectrum
VI, Villasimius, Sardinia, Italy, September 21-25, 2004. References adde
Determination of fragmentation functions and their uncertainties from e+ + e- -> h + X data
Fragmentation functions are determined for pions, kaons, and nucleons by a
global analysis of charged-hadron production data in electron-positron
annihilation. The optimum functions are obtained in both leading order (LO) and
next-to-leading order (NLO) of alpha_s. It is important that uncertainties of
the fragmentation functions are estimated in this work by the Hessian method.
We found that the uncertainties are large at small Q^2 and that they are
generally reduced in the NLO in comparison with the LO ones. We supply a code
for calculating the fragmentation functions and their uncertainties for the
pions, kaons, and nucleons at given z and Q^2.Comment: 4 pages, LaTeX, 5 eps files, to be published in AIP proceedings of
the 17th International Spin Physics Symposium (SPIN2006), Oct. 2-7, 2006,
Kyoto, Japa
ALMA Science Verification Data: Millimeter Continuum Polarimetry of the Bright Radio Quasar 3C 286
We present full-polarization observations of the compact, steep-spectrum
radio quasar 3C~286 made with the ALMA at 1.3~mm. These are the first
full-polarization ALMA observations, which were obtained in the framework of
Science Verification. A bright core and a south-west component are detected in
the total intensity image, similar to previous centimeter images. Polarized
emission is also detected toward both components. The fractional polarization
of the core is about 17\%, this is higher than the fractional polarization at
centimeter wavelengths, suggesting that the magnetic field is even more ordered
in the millimeter radio core than it is further downstream in the jet. The
observed polarization position angle (or EVPA) in the core is
\,, which confirms the trend that the EVPA slowly increases
from centimeter to millimeter wavelengths. With the aid of multi-frequency VLBI
observations, we argue that this EVPA change is associated with the
frequency-dependent core position. We also report a serendipitous detection of
a sub-mJy source in the field of view, which is likely to be a submillimeter
galaxy.Comment: 10 pages, 9 figures, Accepted for publication in the Ap
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