4,348 research outputs found
Hund's-Rule Coupling Effect in Itinerant Ferromagnetism
We present a general model which includes the ferromagnetic Kondo lattice and
the Hubbard model as special cases. The stability of the ferromagnetic state is
investigated variationally. We discuss the mechanism of ferromagnetism in
metallic nickel, emphasizing the importance of orbital degeneracy and the
effect of the Hund's-rule coupling.Comment: 19 pages, 10 figures, to appear in Prog.Theor.Phy
Generalization of Gutzwiller Approximation
We derive expressions required in generalizing the Gutzwiller approximation
to models comprising arbitrarily degenerate localized orbitals.Comment: 6 pages, 1 figure, to appear in J.Phys.Soc.Jpn. vol.6
Spin Wave Instability of Itinerant Ferromagnet
We show variationally that instability of the ferromagnetic state in the
Hubbard model is largely controlled by softening of a long-wavelength spin-wave
excitation, except in the over-doped strong-coupling region where the
individual-particle excitation becomes unstable first. A similar conclusion is
drawn also for the double exchange ferromagnet. Generally the spin-wave
instability may be regarded as a precursor of the metal-insulator transition.Comment: 11 pages, 8 figure
Computer simulation of cold sprayed deposition using smoothed particle hydrodynamics
AbstractThe smoothed particle hydrodynamics (SPH) method is applied to simulate the cold spray (CS) process by modeling the impact of a spherical powder particle on substrate.In this work, the adhesive interaction between the contacting surfaces is described by intersurface forces using the cohesive zone model. The application of the SPH method permits simulation of the impact process without the use of mesh and thus avoids the disadvantages of traditional numerical method in handling large deformations and tracing moving interfaces in the highly transient non-linear dynamic CS process. The simulated deformed particle shape evolution and estimated critical velocity from other sources were compared and good agreement was obtained. The analyses demonstrate the feasibility of the presented SPH methodology and the adhesive interaction model for simulating the deformation behavior of CS particles
Weak Lensing Mass Measurements of Substructures in COMA Cluster with Subaru/Suprime-Cam
We obtain the projected mass distributions for two Subaru/Suprime-Cam fields
in the southwest region (r\simlt 60') of the Coma cluster (z=0.0236) by weak
lensing analysis and detect eight subclump candidates. We quantify the
contribution of background large-scale structure (LSS) on the projected mass
distributions using SDSS multi-bands and photometric data, under the assumption
of mass-to-light ratio for field galaxies. We find that one of eight subclump
candidates, which is not associated with any member galaxies, is significantly
affected by LSS lensing. The mean projected mass for seven subclumps extracted
from the main cluster potential is = (5.06\pm1.30)10^12h^-1 M_sun
after a LSS correction. A tangential distortion profile over an ensemble of
subclumps is well described by a truncated singular-isothermal sphere model and
a truncated NFW model. A typical truncated radius of subclumps, r_t\simeq 35
h^-1 kpc, is derived without assuming any relations between mass and light for
member galaxies. The radius coincides well with the tidal radius, \sim42 h^-1
kpc, of the gravitational force of the main cluster. Taking into account the
incompleteness of data area, a projection effect and spurious lensing peaks, it
is expected that mass of cluster substructures account for 19 percent of the
virial mass, with 13 percent statistical error. The mass fraction of cluster
substructures is in rough agreement with numerical simulations.Comment: ApJ, accepted, 16 pages, 10 figures and 4 tables. High-resolution
pictures available at http://www.asiaa.sinica.edu.tw/~okabe/files/comaWL.pd
The Hilbert Action in Regge Calculus
The Hilbert action is derived for a simplicial geometry. I recover the usual
Regge calculus action by way of a decomposition of the simplicial geometry into
4-dimensional cells defined by the simplicial (Delaunay) lattice as well as its
dual (Voronoi) lattice. Within the simplicial geometry, the Riemann scalar
curvature, the proper 4-volume, and hence, the Regge action is shown to be
exact, in the sense that the definition of the action does not require one to
introduce an averaging procedure, or a sequence of continuum metrics which were
common in all previous derivations. It appears that the unity of these two dual
lattice geometries is a salient feature of Regge calculus.Comment: 6 pages, Plain TeX, no figure
Zone Diagrams in Euclidean Spaces and in Other Normed Spaces
Zone diagram is a variation on the classical concept of a Voronoi diagram.
Given n sites in a metric space that compete for territory, the zone diagram is
an equilibrium state in the competition. Formally it is defined as a fixed
point of a certain "dominance" map.
Asano, Matousek, and Tokuyama proved the existence and uniqueness of a zone
diagram for point sites in Euclidean plane, and Reem and Reich showed existence
for two arbitrary sites in an arbitrary metric space. We establish existence
and uniqueness for n disjoint compact sites in a Euclidean space of arbitrary
(finite) dimension, and more generally, in a finite-dimensional normed space
with a smooth and rotund norm. The proof is considerably simpler than that of
Asano et al. We also provide an example of non-uniqueness for a norm that is
rotund but not smooth. Finally, we prove existence and uniqueness for two point
sites in the plane with a smooth (but not necessarily rotund) norm.Comment: Title page + 16 pages, 20 figure
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