630 research outputs found
Motion of vortices in ferromagnetic spin-1 BEC
The paper investigates dynamics of nonsingular vortices in a ferromagnetic
spin-1 BEC, where spin and mass superfluidity coexist in the presence of
uniaxial anisotropy (linear and quadratic Zeeman effect). The analysis is based
on hydrodynamics following from the Gross-Pitaevskii theory. Cores of
nonsingular vortices are skyrmions with charge, which is tuned by uniaxial
anisotropy and can have any fractal value between 0 and 1. There are
circulations of mass and spin currents around these vortices. The results are
compared with the equation of vortex motion derived earlier in the
Landau-Lifshitz-Gilbert theory for magnetic vortices in easy-plane
ferromagnetic insulators. In the both cases the transverse gyrotropic force
(analog of the Magnus force in superfluid and classical hydrodynamics) is
proportional to the charge of skyrmions in vortex cores.Comment: 19 pages, 2 figures, to be published in the special issue of Fizika
Nizkikh Temperatur dedicated to A.M.Kosevich. arXiv admin note: substantial
text overlap with arXiv:1801.0109
Mechanical measurement of equilibrium spin currents in the Rashba medium
We demonstrate that an equilibrium spin current in a 2D electron gas with
Rashba spin-orbit interaction (Rashba medium) results in a mechanical torque on
a substrate near an edge of the medium. If the substrate is a cantilever, the
mechanical torque displaces the free end of the cantilever. The effect can be
enhanced and tuned by a magnetic field. Observation of this displacement would
be an effective method to prove existence of equilibrium spin currents. The
analysis of edges of the Rashba medium demonstrates the existence of localized
edge states. They form a 1D continuum of states. This suggests a new type of
quantum wire: spin-orbit quantum wire.Comment: 4 pages, 1 figur
Symmetric Case of Locks, Bombs and Testing Model
We present a Defense/Attack resource allocation model, where Defender has
some number of ``locks" to protect vulnerable boxes (sites), and Attacker
is trying to destroy these boxes, having ``bombs" that can be placed into
the boxes. Similar models were studied in game theory - (Colonel) Blotto games,
but our model has a feature absent in the previous literature. Attacker tests
the vulnerability of all sites before allocating her resources, and these tests
are not perfect, i.e., a test can be positive for a box without a lock and
negative for a box with a lock. We describe the optimal strategies for a
special case of a general Locks-Bombs-Testing (LBT) model when all boxes are
identical and the Defender has a fixed number of locks
Vapor condensation on a turbulent liquid interface
An experimental investigation which seeks the fundamental relationship between the interfacial condensation rate and the parameters which control it when the liquid side is turbulent is discussed. The scaling laws for free-surface condensation are discussed for this case. It is argued that the condensation of cryogenic liquids can, in principle, be simulated in experiments using steam and water. Data are presented for the condensation rate in terms of the dimensionless scaling parameters which involve the fluid properties and the liquid-side turbulence velocity and length scales
Three-dimensional quasi-Tonks gas in a harmonic trap
We analyze the macroscopic dynamics of a Bose gas in a harmonic trap with a
superimposed two-dimensional optical lattice, assuming a weak coupling between
different lattice sites. We consider the situation in which the local chemical
potential at each lattice site can be considered as that provided by the
Lieb-Liniger solution. Due to the weak coupling between sites and the form of
the chemical potential, the three-dimensional ground-state density profile and
the excitation spectrum acquire remarkable properties different from both 1D
and 3D gases. We call this system a quasi-Tonks gas. We discuss the range of
applicability of this regime, as well as realistic experimental situations
where it can be observed.Comment: 4 pages, 3 figures, misprints correcte
Equilibrium rotation of a vortex bundle terminating on a lateral wall
The paper investigates possibility of equilibrium solid-body rotation of a
vortex bundle diverging at some height from a cylinder axis and terminating on
a lateral wall of a container. Such a bundle arises when vorticity expands up
from a container bottom eventually filling the whole container. The analysis
starts from a single vortex, then goes to a vortex sheet, and finally addresses
a multi-layered crystal vortex bundle. The equilibrium solid-body rotation of
the vortex bundle requires that the thermodynamic potentials in the
vortex-filled and in the vortex-free parts of the container are equal providing
the absence of a force on the vortex front separating the two parts. The paper
considers also a weakly non-equilibrium state when the bundle and the container
rotate with different angular velocities and the vortex front propagates with
the velocity determined by friction between vortices and the container or the
normal liquid moving together with the container.Comment: 16 pages, 5 figure
Computational Design of Nanoclusters by Property-Based Genetic Algorithms: Tuning the Electronic Properties of (TiO) Clusters
In order to design clusters with desired properties, we have implemented a
suite of genetic algorithms tailored to optimize for low total energy, high
vertical electron affinity (VEA), and low vertical ionization potential (VIP).
Applied to (TiO) clusters, the property-based optimization reveals the
underlying structure-property relations and the structural features that may
serve as active sites for catalysis. High VEA and low VIP are correlated with
the presence of several dangling-O atoms and their proximity, respectively. We
show that the electronic properties of (TiO) up to n=20 correlate more
strongly with the presence of these structural features than with size.Comment: 4 figs, 5 page
Superfluidity in a gas of strongly-interacting bosons
We consider small systems of bosonic atoms rotating in a toroidal trap. Using
the method of exact numerical diagonalization of the many-body Hamiltonian, we
examine the transition from the Bose-Einstein condensed state to the
Tonks-Girardeau state. The system supports persistent currents in a wide range
between the two limits, even in the absence of Bose-Einstein condensation.Comment: 7 pages, 3 figures, revised version, to appear in Europh. Let
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