245,828 research outputs found
A model of a dual-core matter-wave soliton laser
We propose a system which can generate a periodic array of solitary-wave
pulses from a finite reservoir of coherent Bose-Einstein condensate (BEC). The
system is built as a set of two parallel quasi-one-dimensional traps (the
reservoir proper and a pulse-generating cavity), which are linearly coupled by
the tunneling of atoms. The scattering length is tuned to be negative and small
in the absolute value in the cavity, and still smaller but positive in the
reservoir. Additionally, a parabolic potential profile is created around the
center of the cavity. Both edges of the reservoir and one edge of the cavity
are impenetrable. Solitons are released through the other cavity's edge, which
is semi-transparent. Two different regimes of the intrinsic operation of the
laser are identified: circulations of a narrow wave-function pulse in the
cavity, and oscillations of a broad standing pulse. The latter regime is
stable, readily providing for the generation of an array containing up to
10,000 permanent-shape pulses. The circulation regime provides for no more than
40 cycles, and then it transforms into the oscillation mode. The dependence of
the dynamical regime on parameters of the system is investigated in detail.Comment: Journal of Physics B, in pres
Stable circulation modes in a dual-core matter-wave soliton laser
We consider a model of a matter-wave laser generating a periodic array of
solitary-wave pulses. The system, a general version of which was recently
proposed in Ref. [5], is composed of two parallel tunnel-coupled cigar-shaped
traps (a reservoir and a lasing cavity), solitons being released through a
valve at one edge of the cavity. We report a stable lasing mode accounted for
by circulations of a narrow soliton in the cavity, which generates an array of
strong pulses (with 1,000 - 10,000 atoms in each, the array's duty cycle ~ 30%)
when the soliton periodically hits the valve.Comment: J. of Physics B: At. Mol. Opt. Physics, in pres
The Angular Momentum Distribution within Halos in Different Dark Matter Models
We study the angular momentum profile of dark matter halos for a statistical
sample drawn from a set of high-resolution cosmological simulations of
particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and
the halos are selected to have at least particles in order to
reliably measure the angular momentum profile. In contrast with the recent
claims of Bullock et al., we find that the degree of misalignment of angular
momentum within a halo is very high. About 50 percent of halos have more than
10 percent of halo mass in the mass of negative angular momentum . After the
mass of negative is excluded, the cumulative mass function follows
approximately the universal function proposed by Bullock et al., though we
still find a significant fraction of halos () which exhibit
systematic deviations from the universal function. Our results, however, are
broadly in good agreement with a recent work of van den Bosch et al.. We also
study the angular momentum profile of halos in a Warm Dark Matter (WDM) model
and a Self-Interacting Dark Matter (SIDM) model. We find that the angular
momentum profile of halos in the WDM is statistically indistinguishable from
that in the CDM model, but the angular momentum of halos in the SIDM is reduced
by the self-interaction of dark matter.Comment: 23 pages, 10 figures, 2 tables. Revised version, added a new table,
accepted for publication in MNRA
Study on the spectrum of the injected relativistic protons
About 10TeV gamma-ray emission within 10 pc region from the Galactic Center
had been reported by 4 independent groups. Considering that this TeV gamma-ray
emission is produced via a hadronic model, and the relativistic protons came
from the tidal disruption of stars by massive black holes, we investigate the
spectral nature of the injected relativistic protons required by the hadronic
model. The calculation was carried on the tidal disruption of the different
types of stars and the different propagation mechanisms of protons in the
interstellar medium. Compared with the observation data from HESS, we find for
the best fitting that the power-law index of the spectrum of the injected
protons is about -1.9, when a red giant star is tidally disrupted, and the
effective confinement of protons diffusion mechanism is adopted.Comment: 2 pages, IAU Symposium 25
Engineering the accurate distortion of an object's temperature-distribution signature
It is up to now a challenge to control the conduction of heat. Here we
develop a method to distort the temperature distribution signature of an object
at will. As a result, the object accurately exhibits the same temperature
distribution signature as another object that is predetermined, but actually
does not exist in the system. Our finite element simulations confirm the
desired effect for different objects with various geometries and compositions.
The underlying mechanism lies in the effects of thermal metamaterials designed
by using this method. Our work is of value for applications in thermal
engineering.Comment: 11 pages, 4 figure
Can one identify the intrinsic structure of the yrast states in Cr after the backbending?
The backbending phenomenon in Cr has been investigated using the
recently developed Projected Configuration Interaction (PCI) method, in which
the deformed intrinsic states are directly associated with shell model (SM)
wavefunctions. Two previous explanations, (i) band crossing, and (ii)
band crossing have been reinvestigated using PCI, and it was found that
both explanations can successfully reproduce the experimental backbending. The
PCI wavefunctions in the pictures of band crossing and band
crossing are highly overlapped. We conclude that there are no unique intrinsic
states associated with the yrast states after backbending in Cr.Comment: 5 pages, 5 figure
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