45,806 research outputs found
Mathematical characterization of mechanical behavior of porous frictional granular media
A new definition of loading and unloading along the yield surface of Roscoe and Burland is introduced. This is achieved by noting that the strain-hardening parameter in the plastic potential function is deduced from the yield locus equation of Roscoe and Burland. The analytical results are compared with the experimental results for plate-bearing and cone-penetrometer problems and close agreements are demonstrated. The wheel-soil interaction is studied under dynamic loading. The rate-dependent plasticity or viscoelastoplastic behavior is considered. This is accomplished by the internal (hidden) variables associated with time-dependent viscous properties directly superimposed with inelastic behavior governed by the yield criteria of Roscoe and Burland. Effects of inertia and energy dissipation are properly accounted for. Example problems are presented
Carrier-mediated antiferromagnetic interlayer exchange coupling in diluted magnetic semiconductor multilayers GaMnAs/GaAs:Be
We use neutron reflectometry to investigate the interlayer exchange coupling
between GaMnAs ferromagnetic semiconductor layers separated
by non-magnetic Be-doped GaAs spacers. Polarized neutron reflectivity measured
below the Curie temperature of GaMnAs reveals a
characteristic splitting at the wave vector corresponding to twice the
multilayer period, indicating that the coupling between the ferromagnetic
layers are antiferromagnetic (AFM). When the applied field is increased to
above the saturation field, this AFM coupling is suppressed. This behavior is
not observed when the spacers are undoped, suggesting that the observed AFM
coupling is mediated by charge carriers introduced via Be doping. The behavior
of magnetization of the multilayers measured by DC magnetometry is consistent
with the neutron reflectometry results.Comment: 4 pages, 4 figure
Fermions out of Dipolar Bosons in the lowest Landau level
In the limit of very fast rotation atomic Bose-Einstein condensates may
reside entirely in the lowest two-dimensional Landau level (LLL). For small
enough filling factor of the LLL, one may have formation of fractional quantum
Hall states. We investigate the case of bosons with dipolar interactions as may
be realized with Chromium-52 atoms. We show that at filling factor equal to
unity the ground state is a Moore-Read (a.k.a Pfaffian) paired state as is the
case of bosons with purely s-wave scattering interactions. This Pfaffian state
is destabilized when the interaction in the s-wave channel is small enough and
the ground state is a stripe phase with unidimensional density modulation. For
filling factor 1/3, we show that there is formation of a Fermi sea of
``composite fermions''. These composites are made of one boson bound with three
vortices. This phase has a wide range of stability and the effective mass of
the fermions depends essentially only of the scattering amplitude in momentum
channels larger or equal to 2. The formation of such a Fermi sea opens up a new
possible route to detection of the quantum Hall correlations.Comment: 12 pages, 5 figures, published versio
Calculation of a Class of Three-Loop Vacuum Diagrams with Two Different Mass Values
We calculate analytically a class of three-loop vacuum diagrams with two
different mass values, one of which is one-third as large as the other, using
the method of Chetyrkin, Misiak, and M\"{u}nz in the dimensional regularization
scheme. All pole terms in \epsilon=4-D (D being the space-time dimensions in a
dimensional regularization scheme) plus finite terms containing the logarithm
of mass are kept in our calculation of each diagram. It is shown that
three-loop effective potential calculated using three-loop integrals obtained
in this paper agrees, in the large-N limit, with the overlap part of
leading-order (in the large-N limit) calculation of Coleman, Jackiw, and
Politzer [Phys. Rev. D {\bf 10}, 2491 (1974)].Comment: RevTex, 15 pages, 4 postscript figures, minor corrections in K(c),
Appendix B removed, typos corrected, acknowledgements change
Extraction of nuclear matter properties from nuclear masses by a model of equation of state
The extraction of nuclear matter properties from measured nuclear masses is
investigated in the energy density functional formalism of nuclei. It is shown
that the volume energy and the nuclear incompressibility depend
essentially on , whereas the symmetry energy
and the density symmetry coefficient as well as symmetry incompressibility
depend essentially on , where
, and are the
neutron and proton chemical potentials respectively, the nuclear energy,
and the Coulomb energy. The obtained symmetry energy is ,
while other coefficients are uncertain within ranges depending on the model of
nuclear equation of state.Comment: 12 pages and 7 figure
Theory of ferromagnetism in (A,Mn)B semiconductors
A brief review of theory of ferromagnetism of dilute magnetic semiconductors
of the form (A,Mn)B based on the double exchange model is first given. A
systematic investigation of the phenomena extending the current theory is
outlined. We begin with an investigation of the regions of instability of the
nonmagnetic towards the ferromagnetic state of a system of Mn-atoms doped in
AB-type semiconductor. A self-consistent many-body theory of the ferromagnetic
state is then developed, going beyond the mean field approaches by including
fluctuations of the Mn-spins and the itinerant hole-gas. A functional theory
suitable for computation of system properties such as Curie temperature as a
function of hole and the Mn-concentration, spin-current, etc. is formulated.Comment: 16 page
Effective nucleon-nucleon interactions and nuclear matter equation of state
Nuclear matter equations of state based on Skyrme, Myers-Swiatecki and
Tondeur interactions are written as polynomials of the cubic root of density,
with coefficients that are functions of the relative neutron excess .
In the extrapolation toward states far away from the standard one, it is shown
that the asymmetry dependence of the critical point ()
depends on the model used. However, when the equations of state are fitted to
the same standard state, the value of is almost the same in Skyrme
and in Myers-Swiatecki interactions, while is much lower in Tondeur
interaction. Furthermore, does not depend sensitively on the choice
of the parameter in Skyrme interaction.Comment: 15 pages, 9 figure
- …