Quasicondensation reexamined

We study in detail the effect of quasicondensation. We show that this effect is strictly related to dimensionality of the system. It is present in one dimensional systems independently of interactions - exists in repulsive, attractive or in non-interacting Bose gas in some range of temperatures below characteristic temperature of the quantum degeneracy. Based on this observation we analyze the quasicondensation in terms of a ratio of the two largest eigenvalues of the single particle density matrix for the ideal gas. We show that in the thermodynamic limit in higher dimensions the second largest eigenvalue vanishes (as compared to the first one) with total number of particles as $\simeq N^{-\gamma}$ whereas goes to zero only logarithmically in one dimension. We also study the effect of quasicondensation for various geometries of the system: from quasi-1D elongated one, through spherically symmetric 3D case to quasi-2D pancake-like geometry

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

Star forming galaxies in the AKARI deep field south : identifications and spectral energy distributions

Aims. We investigate the nature and properties of far-infrared (FIR) sources in the AKARI deep field south (ADF-S). Methods. We performed an extensive search for the counterparts to 1000 ADF-S objects brighter than 0.0301 Jy in the WIDE-S (90 μm) AKARI band in the public databases (NED and SIMBAD). We analyzed the properties of the resulting sample: statistics of the identified objects, quality of position determination of the ADF-S sources, their number counts, redshift distribution, and comparison of morphological types, when the corresponding information was available. We performed a simplifield analysis of the clustering properties of the ADF-S sources and compliled spectral energy distributions (SEDs) of objects with the highest quality photometry, using three different models. Results. Among 1000 investigated ADF-S sources, 545 were identified with sources at other wavelengths in public databases. From them, 518 are known galaxies and 343 of these were previously known as infra-red sources. Among the remaining sources, there are two quasars and both infrared and radio sources of unknown origin. Among six stellar identifications, at least five are probably the effect of contamination. We measured the redshifts of 48 extragalactic objects and determined the morphological types of 77 galaxies. We present SED models of 47 sources with sufficiently good photometric data. Conclusions. We conclude that the bright FIR point sources observed in the ADF-S are mostly nearby galaxies. Their properties are very similar to the properties of the local population of optically bright galaxies, except for unusually high ratio of peculiar or interacting objects and a lower percentage of elliptical galaxies. The percentage of lenticular galaxies is the same as in the optically bright population, which suggests that galaxies of this type may frequently contain a significant amount of cool dust. It is possible that source confusion plays a significant role in more than 34% of measurements. The SEDs correspond to a variety of galaxy types, from very actively star forming to very quiescent. The AKARI long wavelength bands data have enabled us to determine for the first time that these galaxies are objects with very cool dust