311 research outputs found
Mott Insulators of Ultracold Fermionic Alkaline Earth Atoms: Underconstrained Magnetism and Chiral Spin Liquid
We study Mott insulators of fermionic alkaline earth atoms, described by
Heisenberg spin models with enhanced SU(N) symmetry. In dramatic contrast to
SU(2) magnetism, more than two spins are required to form a singlet. On the
square lattice, the classical ground state is highly degenerate and magnetic
order is thus unlikely. In a large-N limit, we find a chiral spin liquid ground
state with topological order and Abelian fractional statistics. We discuss its
experimental detection. Chiral spin liquids with non-Abelian anyons may also be
realizable with alkaline earth atoms.Comment: 4 pages, 2 figures, 1 table. Minor changes from v2. Final published
versio
Boundary information inflow enhances correlation in flocking
The most conspicuous trait of collective animal behaviour is the emergence of
highly ordered structures. Less obvious to the eye, but perhaps more profound a
signature of self-organization, is the presence of long-range spatial
correlations. Experimental data on starling flocks in 3d show that the exponent
ruling the decay of the velocity correlation function, C(r) ~ 1/r^\gamma, is
extremely small, \gamma << 1. This result can neither be explained by
equilibrium field theory, nor by off-equilibrium theories and simulations of
active systems. Here, by means of numerical simulations and theoretical
calculations, we show that a dynamical field applied to the boundary of a set
of Heisemberg spins on a 3d lattice, gives rise to a vanishing exponent \gamma,
as in starling flocks. The effect of the dynamical field is to create an
information inflow from border to bulk that triggers long range spin wave
modes, thus giving rise to an anomalously long-ranged correlation. The
biological origin of this phenomenon can be either exogenous - information
produced by environmental perturbations is transferred from boundary to bulk of
the flock - or endogenous - the flock keeps itself in a constant state of
dynamical excitation that is beneficial to correlation and collective response
Pharmacokinetic studies of new antiparkinsonian drug Rapitalam
The aim of this study was to investigate the pharmacokinetic parameters of the mGluR4 receptor blocker Rapitalam on rabbits. There was developed the method of the quantitative determination of Rapitalam in the blood plasma of rabbits using high performance liquid chromatography with tandem mass spectrometric detection. The study was performed on 12 rabbits (males, weighing between 3,300 to 3,500 g). In intragastric dosing of the substance was administered using a gastric tube in the form of suspension in water 0.9 mg/ml, 9 mg/ml, and 90 mg/ml at a dose of 0.3 mg/kg, 3 mg/kg and 30 mg/kg. The main pharmacokinetic parameters of the substance was established on rabbits that allow you to optimize the future use of it's as a potential drug for the treatment of Parkinson's diseas
Fermion Analogy for Layered Superconducting Films in Parallel Magnetic Field
The equivalence between the Lawrence-Doniach model for films of extreme
type-II layered superconductors and a generalization of the back-scattering
model for spin-1/2 electrons in one dimension is demonstrated. This fermion
analogy is then exploited to obtain an anomalous tail for
the parallel equilibrium magnetization of the minimal double layer case in the
limit of high parallel magnetic fields for temperatures in the
critical regime.Comment: 11 pages of plain TeX, 1 postscript figur
Rotating vortex dipoles in ferromagnets
Vortex-antivortex pairs are localized excitations and have been found to be
spontaneously created in magnetic elements. In the case that the vortex and the
antivortex have opposite polarities the pair has a nonzero topological charge,
and it behaves as a rotating vortex dipole. We find theoretically, and confirm
numerically, the form of the energy as a function of the angular momentum of
the system and the associated rotation frequencies. We discuss the process of
annihilation of the pair which changes the topological charge of the system by
unity while its energy is monotonically decreasing. Such a change in the
topological charge affects profoundly the dynamics in the magnetic system. We
finally discuss the connection of our results with Bloch Points (BP) and the
implications for BP dynamics.Comment: 6 pages, 2 figure
Interference Effects in Schwinger Vacuum Pair Production for Time-Dependent Laser Pulses
We present simple new approximate formulas, for both scalar and spinor QED,
for the number of particles produced from vacuum by a time dependent electric
field, incorporating the interference effects that arise from an arbitrary
number of distinct semiclassical turning points. Such interference effects are
important when the temporal profile of the laser pulse has subcycle structure.
We show how the resulting semiclassical intuition may be used to guide the
design of temporal profiles that enhance the momentum spectrum due to
interference effects. The result is easy to implement and generally applicable
to time-dependent tunneling problems, such as appear in many other contexts in
particle and nuclear physics, condensed matter physics, atomic physics,
chemical physics, and gravitational physics.Comment: 19 pages; 21 figures; v2 refs update
The Stokes Phenomenon and Schwinger Vacuum Pair Production in Time-Dependent Laser Pulses
Particle production due to external fields (electric, chromo-electric or
gravitational) requires evolving an initial state through an interaction with a
time-dependent background, with the rate being computed from a Bogoliubov
transformation between the in and out vacua. When the background fields have
temporal profiles with sub-structure, a semiclassical analysis of this problem
confronts the full subtlety of the Stokes phenomenon: WKB solutions are only
local, while the production rate requires global information. Incorporating the
Stokes phenomenon, we give a simple quantitative explanation of the recently
computed [Phys. Rev. Lett. 102, 150404 (2009)] oscillatory momentum spectrum of
e+e- pairs produced from vacuum subjected to a time-dependent electric field
with sub-cycle laser pulse structure. This approach also explains naturally why
for spinor and scalar QED these oscillations are out of phase.Comment: 5 pages, 4 figs.; v2 sign typo corrected, version to appear in PR
Classical and relativistic dynamics of supersolids: variational principle
We present a phenomenological Lagrangian and Poisson brackets for obtaining
nondissipative hydrodynamic theory of supersolids. A Lagrangian is constructed
on the basis of unification of the principles of non-equilibrium thermodynamics
and classical field theory. The Poisson brackets, governing the dynamics of
supersolids, are uniquely determined by the invariance requirement of the
kinematic part of the found Lagrangian. The generalization of Lagrangian is
discussed to include the dynamics of vortices. The obtained equations of motion
do not account for any dynamic symmetry associated with Galilean or Lorentz
invariance. They can be reduced to the original Andreev-Lifshitz equations if
to require Galilean invariance. We also present a relativistic-invariant
supersolid hydrodynamics, which might be useful in astrophysical applications.Comment: 22 pages, changed title and content, added reference
Spin-Torque-Induced Rotational Dynamics of a Magnetic Vortex Dipole
We study, both experimentally and by numerical modeling, the magnetic
dynamics that can be excited in a magnetic thin-film nanopillar device using
the spin torque from a spatially localized current injected via a
10s-of-nm-diameter aperture. The current-driven magnetic dynamics can produce
large amplitude microwave emission at zero magnetic field, with a frequency
well below that of the uniform ferromagnetic resonance mode. Micromagnetic
simulations indicate that the physical origin of this efficient microwave
nano-oscillator is the nucleation and subsequent steady-state rotational
dynamics of a magnetic vortex dipole driven by the localized spin torque. These
results show this novel implementation of a spintronic nano-oscillator is a
promising candidate for microwave technology applications.Comment: 19 pages, 4 figures
Thermal non-equilibrium effects in quantum reflection
We show that the quantum reflection coefficient of ultracold heavy atoms
scattering off a dielectric surface can be tuned in a wide range by suitable
choice of surface and environment temperatures. This effect results from a
temperature dependent long-range repulsive part of the van der
Waals-Casimir-Polder-Lifshitz atom-surface interaction potential
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