47,596 research outputs found
Coupled ferro-antiferromagnetic Heisenberg bilayers investigated by many-body Green's function theory
A theory of coupled ferro- and antiferromagnetic Heisenberg layers is
developed within the framework of many-body Green's function theory (GFT) that
allows non-collinear magnetic arrangements by introducing sublattice
structures. As an example, the coupled ferro- antiferromagnetic (FM-AFM)
bilayer is investigated. We compare the results with those of bilayers with
purely ferromagnetic or antiferromagnetic couplings. In each case we also show
the corresponding results of mean field theory (MFT), in which magnon
excitations are completely neglected. There are significant differences between
GFT and MFT. A remarkable finding is that for the coupled FM-AFM bilayer the
critical temperature decreases with increasing interlayer coupling strength for
a simple cubic lattice, whereas the opposite is true for an fcc lattice as well
as for MFT for both lattice types.Comment: 17 pages, 6 figures, accepted for publication in J. Phys. Condens.
Matter, missing fig.5 adde
Strongly interacting Fermi gases with density imbalance
We consider density-imbalanced Fermi gases of atoms in the strongly
interacting, i.e. unitarity, regime. The Bogoliubov-deGennes equations for a
trapped superfluid are solved. They take into account the finite size of the
system, as well as give rise to both phase separation and FFLO type
oscillations in the order parameter. We show how radio-frequency spectroscopy
reflects the phase separation, and can provide direct evidence of the FFLO-type
oscillations via observing the nodes of the order parameter.Comment: Added one reference. Published in PR
Record dynamics and the observed temperature plateau in the magnetic creep rate of type II superconductors
We use Monte Carlo simulations of a coarse grained three dimensional model to
demonstrate that the experimentally observed approximate temperature
independence of the magnetic creep rate for a broad range of temperatures may
be explained in terms of record dynamics, {\it viz.} the dynamical properties
of the times at which a stochastic fluctuating signal establishes records.Comment: 7 pages, 5 figures. Replaced in order to correct the order of the
Bessel function in Eq.
KINETIC RESPONSES DURING LANDINGS OF PLYOMETRIC EXERCISES
The objective of the current study was to compare landing impulse and peak ground reaction force (GRF) during a variety of plyometric exercises. Eight Division-I athletes who routinely trained plyometric exercises performed a single repetition each of countermovement jump (CMJ), drop jumps from 30 and 60 cm (DJ30 and DJ60), cone hop (CH), tuck jump (TJ), single leg CMJ (SLJ), and squat jump with 30% 1 RM dumbbell squat (SJ30). Landing impulses and peak GRF were evaluated on an AMTI force plate.
One-way ANOVA indicated mean and total impulses and peak GRF differed across exercises, with CH and SLJ displaying lower values and DJ30 and SJ30 having higher values. Results indicate that when landing from various plyometric exercises landing impulses and GRF are different across the exercises
Reaction-diffusion processes and non-perturbative renormalisation group
This paper is devoted to investigating non-equilibrium phase transitions to
an absorbing state, which are generically encountered in reaction-diffusion
processes. It is a review, based on [Phys. Rev. Lett. 92, 195703; Phys. Rev.
Lett. 92, 255703; Phys. Rev. Lett. 95, 100601], of recent progress in this
field that has been allowed by a non-perturbative renormalisation group
approach. We mainly focus on branching and annihilating random walks and show
that their critical properties strongly rely on non-perturbative features and
that hence the use of a non-perturbative method turns out to be crucial to get
a correct picture of the physics of these models.Comment: 14 pages, submitted to J. Phys. A for the proceedings of the
conference 'Renormalization Group 2005', Helsink
Interplay between SDW and induced local moments in URu2Si2
Theoretical model for magnetic ordering in the heavy-fermion metal URu2Si2 is
suggested. The 17.5K transition in this material is ascribed to formation of a
spin-density wave, which develops due to a partial nesting between electron and
hole parts of the Fermi surface and has a negligibly small form-factor.
Staggered field in the SDW state induces tiny antiferromagnetic order in the
subsystem of localized singlet-singlet levels. Unlike the other models our
scenario is based on coexistence of two orderings with the same
antiferromagnetic dipole symmetry.The topology of the pressure phase diagram
for such a two order parameter model is studied in the framework of the Landau
theory. The field dependences of the staggered magnetization and the magnon gap
are derived from the microscopic theory and found to be in good quantitative
agreement with experiment.Comment: 11 pages, 2 figure
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