18,796 research outputs found
N-component Bose-Einstein Condensate in an Optical Lattice: Destruction of the Condensate and Quasiparticle Properties
We present a model of N-component hard-core bosons on a lattice. The limit N
to infinity can be solved exactly. A saddle point approximation leads to a 1/N
expansion and allows the calculation of physical quantities like the density of
the condensate, the correlation between the components and the density-density
correlation function and the correlation between different components. We find
a superfluid phase with a tendency towards a Mott insulator at high densities
and finite N.Comment: 8 pages, 3 figures, small changes, error corrected in Appendi
Computer simulator for a mobile telephone system
A software simulator was developed to help in the design of the LMSS. The simulator is used to study the characteristics and implementation requirements of the LMSS' configuration
Computer simulator for a mobile telephone system
A software simulator to help NASA in the design of the LMSS was developed. The simulator will be used to study the characteristics of implementation requirements of the LMSS's configuration with specifications as outlined by NASA
The effect of ram pressure on the star formation, mass distribution and morphology of galaxies
We investigate the dependence of star formation and the distribution of the
components of galaxies on the strength of ram pressure. Several mock
observations in X-ray, H and HI wavelength for different ram-pressure
scenarios are presented. By applying a combined N-body/hydrodynamic description
(GADGET-2) with radiative cooling and a recipe for star formation and stellar
feedback 12 different ram-pressure stripping scenarios for disc galaxies were
calculated. Special emphasis was put on the gas within the disc and in the
surroundings. All gas particles within the computational domain having the same
mass resolution. The relative velocity was varied from 100 km/s to 1000 km/s in
different surrounding gas densities in the range from to
g/cm. The temperature of the surrounding gas was
initially K. The star formation of a galaxy is enhanced by more
than a magnitude in the simulation with a high ram-pressure (
dyn/cm) in comparison to the same system evolving in isolation. The
enhancement of the star formation depends more on the surrounding gas density
than on the relative velocity. Up to 95% of all newly formed stars can be found
in the wake of the galaxy out to distances of more than 350 kpc behind the
stellar disc. Continuously stars fall back to the old stellar disc, building up
a bulge-like structure. Young stars can be found throughout the stripped wake
with surface densities locally comparable to values in the inner stellar disc.
Ram-pressure stripping can shift the location of star formation from the disc
into the wake on very short timescales. (Abridged)Comment: 19 pages, 25 figures, A&A accepted, high resolution version can be
found at http://astro.uibk.ac.at/~wolfgang/kapferer_rps_galaxies.pd
Low level radiation altimeter system study
Low level radiation altimeter for measuring altitude 50 feet above lunar surfac
Cluster induced quenching of galaxies in the massive cluster XMMXCSJ2215.9-1738 at z~1.5 traced by enhanced metallicities inside half R200
(Abridged) We explore the massive cluster XMMXCSJ2215.9-1738 at z~1.5 with
KMOS spectroscopy of Halpha and [NII] covering a region that corresponds to
about one virial radius. Using published spectroscopic redshifts of 108
galaxies in and around the cluster we computed the location of galaxies in the
projected velocity vs. position phase-space to separate our cluster sample into
a virialized region of objects accreted longer ago (roughly inside half R200)
and a region of infalling galaxies. We measured oxygen abundances for ten
cluster galaxies with detected [NII] lines in the individual galaxy spectra and
compared the MZR of the galaxies inside half R200 with the infalling galaxies
and a field sample at similar redshifts. We find that the oxygen abundances of
individual z~1.5 star-forming cluster galaxies inside half R200 are comparable,
at the respective stellar mass, to the higher local SDSS metallicity values. We
find that the [NII]/Halpha line ratios inside half R200 are higher by 0.2 dex
and that the resultant metallicities of the galaxies in the inner part of the
cluster are higher by about 0.1 dex, at a given mass, than the metallicities of
infalling galaxies and of field galaxies at z~1.5. The enhanced metallicities
of cluster galaxies at z~1.5 inside half R200 indicate that the density of the
ICM in this massive cluster becomes high enough toward the cluster center such
that the ram pressure exceeds the restoring pressure of the hot gas reservoir
of cluster galaxies. This can remove the gas reservoir initiating quenching;
although the galaxies continue to form stars, albeit at slightly lower rates,
using the available cold gas in the disk which is not stripped.Comment: Accepted for publication in A&
Interacting bosons in an optical lattice: Bose-Einstein condensates and Mott insulator
A dense Bose gas with hard-core interaction is considered in an optical
lattice. We study the phase diagram in terms of a special mean-field theory
that describes a Bose-Einstein condensate and a Mott insulator with a single
particle per lattice site for zero as well as for non-zero temperatures. We
calculate the densities, the excitation spectrum and the static structure
factor for each of these phases.Comment: 17 pages, 5 figures; 1 figure added, typos remove
SCRIPTKELL : a tool for measuring cognitive effort and time processing in writing and other complex cognitive activities
We present SCRIPTKELL, a computer-assisted experimental tool that makes it possible to measure the time and cognitive effort allocated to the subprocesses of writing and other cognitive activities, SCRIPTKELL was designed to easily use and modulate Kellogg's (1986) triple-task procedure,.which consists of a combination of three tasks: a writing task (or another task), a reaction time task (auditory signal detection), and a directed retrospection task (after each signal detection during writing). We demonstrate how this tool can be used to address several novel empirical and theoretical issues. In sum, SCRIPTKELL should facilitate the flexible realization of experimental designs and the investigation of critical issues concerning the functional characteristics of complex cognitive activities
- …