459 research outputs found
Statistical properties of one dimensional attractive Bose gas
Using classical field approximation we present the first study of statistical
properties of one dimensional Bose gas with attractive interaction. The
canonical probability distribution is generated with the help of a Monte Carlo
method. This way we obtain not only the depletion of the condensate with
growing temperature but also its fluctuations. The most important is our
discovery of a reduced coherence length, the phenomenon observed earlier only
for the repulsive gas, known as quasicondensation.Comment: 4 pages, 4 figure
Classical fields approximation for cold weakly interacting bosons without free parameters
Classical fields approximation to cold weakly interacting bosons allows for a
unified treatment of condensed and uncondensed parts of the system. Until now,
however, the quantitative predictions were limited by a dependence of the
results on a grid chosen for numerical implementation of the method. In this
paper we propose replacing this unphysical ambiguity by an additional
postulate: the temperature of the gas at thermal equilibrium should be the same
as that of an ideal Bose gas with the same fraction of condensed atoms. As it
turns-out, with this additional assumption, nearly all atoms are within the
classical fields, thus the method applies to the whole system
On the stability of Bose-Fermi mixtures
We consider the stability of a mixture of degenerate Bose and Fermi gases.
Even though the bosons effectively repel each other the mixture can still
collapse provided the Bose and Fermi gases attract each other strongly enough.
For a given number of atoms and the strengths of the interactions between them
we find the geometry of a maximally compact trap that supports the stable
mixture. We compare a simple analytical estimation for the critical axial
frequency of the trap with results based on the numerical solution of
hydrodynamic equations for Bose-Fermi mixture.Comment: 4 pages, 3 figure
Application of lightning location systems for fault detection on transmission and distribution lines
The lightning location systems were installed in many countries during last twenty years. The paper presents the SAFIR system called PERUN, which was built in Poland in 2002. The lightning location systems are used for different purposes including among other things meteorology, weather forecasting and aviation. A brief review of fault detection on transmission and distribution lines made abroad and the first experience of the Polish National Grid PSE was shown
Soliton trains in Bose-Fermi mixtures
We theoretically consider the formation of bright solitons in a mixture of
Bose and Fermi degenerate gases. While we assume the forces between atoms in a
pure Bose component to be effectively repulsive, their character can be changed
from repulsive to attractive in the presence of fermions provided the Bose and
Fermi gases attract each other strongly enough. In such a regime the Bose
component becomes a gas of effectively attractive atoms. Hence, generating
bright solitons in the bosonic gas is possible. Indeed, after a sudden increase
of the strength of attraction between bosons and fermions (realized by using a
Feshbach resonance technique or by firm radial squeezing of both samples)
soliton trains appear in the Bose-Fermi mixture.Comment: 4 pages, 4 figure
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Inter-granular effects at high magnetic fields of cuprate and iron chalcogenide superconducting materials
The weak links effects are one of the main challenges for effective power applications of high temperature superconducting materials. Studies of these effects help for their better understanding and subsequent improvement. An overview analysis of the intergranular properties of cuprate (Y0.8Ca0.2Ba2Cu3O7-δ) and iron-based chalcogenide (FeSe0.5Te0.5) polycrystalline samples was carried out, by means of series of electro-transport experiments at different magnetic fields. The temperature evolution of the Josephson coupling and intrinsic superconductivity effects for the both systems was constructed. The FeSe0.5Te0.5 compound shows very stable and superior behavior compared to Y0.8Ca0.2BCO up to the highest magnetic fields (14T) used. We have explored FeSe0.5Te0.5 Josephson weak links influence (as a non-linear process) over the resistive transition using different AC current amplitudes and applying the sensitive AC transport third harmonics technique
Adventures of a tidally induced bar
Using N-body simulations, we study the properties of a bar induced in a discy dwarf galaxy as a result of tidal interaction with the Milky Way. The bar forms at the first pericentre passage and survives until the end of the evolution at 10 Gyr. Fourier decomposition of the bar reveals that only even modes are significant and preserve a hierarchy so that the bar mode is always the strongest. They show a characteristic profile with a maximum, similar to simulated bars forming in isolated galaxies and observed bars in real galaxies. We adopt the maximum of the bar mode as a measure of the bar strength and we estimate the bar length by comparing the density profiles along the bar and perpendicular to it. The bar strength and the bar length decrease with time, mainly at pericentres, as a result of tidal torques acting at those times and not to secular evolution. The pattern speed of the bar varies significantly on a time-scale of 1 Gyr and is controlled by the orientation of the tidal torque from the Milky Way. The bar is never tidally locked, but we discover a hint of a 5/2 orbital resonance between the third and fourth pericentre passage. The speed of the bar decreases in the long run so that the bar changes from initially rather fast to slow in the later stages. The boxy/peanut shape is present for some time and its occurrence is preceded by a short period of buckling instability
Choosing the best yielding wheat and barley variety under high crown rot
This paper reports on a three year series (2014-2016) of Western region based trials to provide WA grain growers experimental field evidence of the effect of crown rot on barley and wheat variety yields in local environmental conditions
Superfluidity of the BEC at finite temperature
We use the classical fields approximation to study a translational flow of
the condensate with respect to the thermal cloud in a weakly interacting Bose
gas. We study both, subcritical and supercritical relative velocity cases and
analyze in detail a state of stationary flow which is reached in the dynamics.
This state corresponds to the thermal equilibrium, which is characterized by
the relative velocity of the condensate and the thermal cloud. The
superfluidity manifests itself in the existence of many thermal equilibria
varying in (the value of this velocity) the relative velocity between the
condensate and the thermal cloud. We pay a particular attention to excitation
spectra in a phonon as well as in a particle regime. Finally, we introduce a
measure of the amount of the superfluid fraction in a weakly interacting Bose
gas, allowing for the precise distinction between the superfluid and the
condensed fractions in a single and consistent framework.Comment: 8 pages, 5 figure
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