413 research outputs found
Exact results on the dynamics of multi-component Bose-Einstein condensate
We study the time-evolution of the two dimensional multi-component
Bose-Einstein condensate in an external harmonic trap with arbitrary
time-dependent frequency. We show analytically that the time-evolution of the
total mean-square radius of the wave-packet is determined in terms of the same
solvable equation as in the case of a single-component condensate. The dynamics
of the total mean-square radius is also the same for the rotating as well as
the non-rotating multi-component condensate. We determine the criteria for the
collapse of the condensate at a finite time. Generalizing our previous work on
a single-component condensate, we show explosion-implosion duality in the
multi-component condensate.Comment: Two-column 6 pages, RevTeX, no figures(v1); Added an important
reference, version to appear in Physical Review A (v2
Effects of ac-field amplitude on the dielectric susceptibility of relaxors
The thermally activated flips of the local spontaneous polarization in
relaxors were simulated to investigate the effects of the applied-ac-field
amplitude on the dielectric susceptibility. It was observed that the
susceptibility increases with increasing the amplitude at low temperatures. At
high temperatures, the susceptibility experiences a plateau and then drops. The
maximum in the temperature dependence of susceptibility shifts to lower
temperatures when the amplitude increases. A similarity was found between the
effects of the amplitude and frequency on the susceptibility.Comment: 8 pages, 7 figures, Phys. Rev. B (in July 1st
Nonlinear magnetoinductive transmission lines
Power transmission in one-dimensional nonlinear magnetic metamaterials driven
at one end is investigated numerically and analytically in a wide frequency
range. The nonlinear magnetic metamaterials are composed of varactor-loaded
split-ring resonators which are coupled magnetically through their mutual
inductances, forming thus a magnetoiductive transmission line. In the linear
limit, significant power transmission along the array only appears for
frequencies inside the linear magnetoinductive wave band. We present
analytical, closed form solutions for the magnetoinductive waves transmitting
the power in this regime, and their discrete frequency dispersion. When
nonlinearity is important, more frequency bands with significant power
transmission along the array may appear. In the equivalent circuit picture, the
nonlinear magnetoiductive transmission line driven at one end by a relatively
weak electromotive force, can be modeled by coupled
resistive-inductive-capacitive (RLC) circuits with voltage-dependent
capacitance. Extended numerical simulations reveal that power transmission
along the array is also possible in other than the linear frequency bands,
which are located close to the nonlinear resonances of a single nonlinear RLC
circuit. Moreover, the effectiveness of power transmission for driving
frequencies in the nonlinear bands is comparable to that in the linear band.
Power transmission in the nonlinear bands occurs through the linear modes of
the system, and it is closely related to the instability of a mode that is
localized at the driven site.Comment: 11 pages, 11 figures, submitted to International Journal of
Bifurcation and Chao
Detecting community structure in networks using edge prediction methods
Community detection and edge prediction are both forms of link mining: they
are concerned with discovering the relations between vertices in networks. Some
of the vertex similarity measures used in edge prediction are closely related
to the concept of community structure. We use this insight to propose a novel
method for improving existing community detection algorithms by using a simple
vertex similarity measure. We show that this new strategy can be more effective
in detecting communities than the basic community detection algorithms.Comment: 5 pages, 2 figure
Stability of trapped Bose-Einstein condensates
In three-dimensional trapped Bose-Einstein condensate (BEC), described by the
time-dependent Gross-Pitaevskii-Ginzburg equation, we study the effect of
initial conditions on stability using a Gaussian variational approach and exact
numerical simulations. We also discuss the validity of the criterion for
stability suggested by Vakhitov and Kolokolov. The maximum initial chirp
(initial focusing defocusing of cloud) that can lead a stable condensate to
collapse even before the number of atoms reaches its critical limit is obtained
for several specific cases. When we consider two- and three-body nonlinear
terms, with negative cubic and positive quintic terms, we have the conditions
for the existence of two phases in the condensate. In this case, the magnitude
of the oscillations between the two phases are studied considering sufficient
large initial chirps. The occurrence of collapse in a BEC with repulsive
two-body interaction is also shown to be possible.Comment: 15 pages, 11 figure
Nonlocal interactions prevent collapse in negative scattering length Bose-Einstein gases
We study the effect of nonlocality on the collapse properties of a
self-focusing Nonlinear Schr\"odinger system related to Bose-Einstein
condensation problems.
Using a combination of moment techniques, time dependent variational methods
and numerical simulations we present evidences in support of the hypothesis
that nonlocal attractively interacting condensates cannot collapse when the
dominant interaction term is due to finite range interactions. Instead there
apppear oscillations of the wave packet with a localized component whose size
is of the order of the range of interactions.
We discuss the implications of the results to collapse phenomena in negative
scattering length Bose-Einstein condensates
Solutions of Gross-Pitaevskii equations beyond the hydrodynamic approximation: Application to the vortex problem
We develop the multiscale technique to describe excitations of a
Bose-Einstein condensate (BEC) whose characteristic scales are comparable with
the healing length, thus going beyond the conventional hydrodynamical
approximation. As an application of the theory we derive approximate explicit
vortex and other solutions. The dynamical stability of the vortex is discussed
on the basis of the mathematical framework developed here, the result being
that its stability is granted at least up to times of the order of seconds,
which is the condensate lifetime. Our analytical results are confirmed by the
numerical simulations.Comment: To appear in Phys. Rev.
Modulation Instability of Ultrashort Pulses in Quadratic Nonlinear Media beyond the Slowly Varying Envelope Approximation
We report a modulational instability (MI) analysis of a mathematical model
appropriate for ultrashort pulses in cascaded quadratic-cubic nonlinear media
beyond the so-called slowly varying envelope approximation. Theoretically
predicted MI properties are found to be in good agreement with numerical
simulation. The study shows the possibility of controlling the generation of MI
and formation of solitons in a cascaded quadratic-cubic media in the few cycle
regimes. We also find that stable propagation of soliton-like few-cycle pulses
in the medium is subject to the fulfilment of the modulation instability
criteria
OGLE-2013-BLG-0102LA,B: Microlensing binary with components at star/brown-dwarf and brown-dwarf/planet boundaries
We present the analysis of the gravitational microlensing event
OGLE-2013-BLG-0102. The light curve of the event is characterized by a strong
short-term anomaly superposed on a smoothly varying lensing curve with a
moderate magnification . It is found that the event was
produced by a binary lens with a mass ratio between the components of and the anomaly was caused by the passage of the source trajectory over a
caustic located away from the barycenter of the binary. From the analysis of
the effects on the light curve due to the finite size of the source and the
parallactic motion of the Earth, the physical parameters of the lens system are
determined. The measured masses of the lens components are and , which correspond to
near the hydrogen-burning and deuterium-burning mass limits, respectively. The
distance to the lens is and the projected separation
between the lens components is .Comment: 6 figures, 2 tables, ApJ submitte
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