18,110 research outputs found
Simulations of a classical spin system with competing superexchange and double-exchange interactions
Monte-Carlo simulations and ground-state calculations have been used to map
out the phase diagram of a system of classical spins, on a simple cubic
lattice, where nearest-neighbor pairs of spins are coupled via competing
antiferromagnetic superexchange and ferromagnetic double-exchange interactions.
For a certain range of parameters, this model is relevant for some magnetic
materials, such as doped manganites, which exhibit the remarkable colossal
magnetoresistance effect. The phase diagram includes two regions in which the
two sublattice magnetizations differ in magnitude. Spin-dynamics simulations
have been used to compute the time- and space-displaced spin-spin correlation
functions, and their Fourier transforms, which yield the dynamic structure
factor for this system. Effects of the double-exchange
interaction on the dispersion curves are shown.Comment: Latex, 3 pages, 3 figure
Categorification of quantum symmetric pairs I
We categorify a coideal subalgebra of the quantum group of
by introducing a -category \`a la
Khovanov-Lauda-Rouquier, and show that self-dual indecomposable -morphisms
categorify the canonical basis of this algebra. This allows us to define a
categorical action of this coideal algebra on the categories of modules over
cohomology rings of partial flag varieties and on the BGG category
of type B/C.Comment: final version, to appear in Quantum Topolog
Improved Spin Dynamics Simulations of Magnetic Excitations
Using Suzuki-Trotter decompositions of exponential operators we describe new
algorithms for the numerical integration of the equations of motion for
classical spin systems. These techniques conserve spin length exactly and, in
special cases, also conserve the energy and maintain time reversibility. We
investigate integration schemes of up to eighth order and show that these new
algorithms can be used with much larger time steps than a well established
predictor-corrector method. These methods may lead to a substantial speedup of
spin dynamics simulations, however, the choice of which order method to use is
not always straightforward.Comment: J. Mod. Phys. C (in press
Complex Agent Networks explaining the HIV epidemic among homosexual men in Amsterdam
Simulating the evolution of the Human Immunodeficiency Virus (HIV) epidemic
requires a detailed description of the population network, especially for small
populations in which individuals can be represented in detail and accuracy. In
this paper, we introduce the concept of a Complex Agent Network(CAN) to model
the HIV epidemics by combining agent-based modelling and complex networks, in
which agents represent individuals that have sexual interactions. The
applicability of CANs is demonstrated by constructing and executing a detailed
HIV epidemic model for men who have sex with men (MSM) in Amsterdam, including
a distinction between steady and casual relationships. We focus on MSM contacts
because they play an important role in HIV epidemics and have been tracked in
Amsterdam for a long time. Our experiments show good correspondence between the
historical data of the Amsterdam cohort and the simulation results.Comment: 21 pages, 4 figures, Mathematics and Computers in Simulation, added
reference
Microscopic and self-consistent description for neutron halo in deformed nuclei
A deformed relativistic Hartree-Bogoliubov theory in continuum has been
developed for the study of neutron halos in deformed nuclei and the halo
phenomenon in deformed weakly bound nuclei is investigated. Magnesium and neon
isotopes are studied and some results are presented for the deformed
neutron-rich and weakly bound nuclei 44Mg and 36Ne. The core of the former
nucleus is prolate, but the halo has a slightly oblate shape. This indicates a
decoupling of the halo orbitals from the deformation of the core. The generic
conditions for the existence of halos in deformed nuclei and for the occurrence
of this decoupling effect are discussed.Comment: 7 pages, 2 figures; invited talk at the XXXV Brazilian Workshop on
Nuclear Physics, Sep 2-6, 2012, Maresias, Brazi
Halos in a deformed Relativistic Hartree-Bogoliubov theory in continuum
In this contribution we present some recent results about neutron halos in
deformed nuclei. A deformed relativistic Hartree-Bogoliubov theory in continuum
has been developed and the halo phenomenon in deformed weakly bound nuclei is
investigated. These weakly bound quantum systems present interesting examples
for the study of the interdependence between the deformation of the core and
the particles in the halo. Magnesium and neon isotopes are studied and detailed
results are presented for the deformed neutron-rich and weakly bound nuclei
42Mg. The core of this nucleus is prolate, but the halo has a slightly oblate
shape. This indicates a decoupling of the halo orbitals from the deformation of
the core. The generic conditions for the existence of halos in deformed nuclei
and for the occurrence of this decoupling effect are discussed.Comment: 6 pages, 2 figures; invited talk at the 2nd Int. Conf. on Nuclear
Structure & Dynamics (NSD12), Opatija, Croatia, 9-13 July 201
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