1,620 research outputs found
Nonclassical Moments and their Measurement
Practically applicable criteria for the nonclassicality of quantum states are
formulated in terms of different types of moments. For this purpose the moments
of the creation and annihilation operators, of two quadratures, and of a
quadrature and the photon number operator turn out to be useful. It is shown
that all the required moments can be determined by homodyne correlation
measurements. An example of a nonclassical effect that is easily characterized
by our methods is amplitude-squared squeezing.Comment: 12 pages, 6 figure
Simulating the formation and evolution of galaxies: Multi-phase description of the interstellar medium, star formation, and energy feedback
We present a multi-phase representation of the ISM in NB-TSPH simulations of
galaxy formation and evolution with particular attention to the case of
early-type galaxies. Cold gas clouds are described by the so-called sticky
particles algorithm. They can freely move throughout the hot ISM medium; stars
form within these clouds and the mass exchange among the three baryonic phases
(hot gas, cold clouds, stars) is governed by radiative and Compton cooling and
energy feedback by supernova (SN) explosions, stellar winds, and UV radiation.
We also consider thermal conduction, cloud-cloud collisions, and chemical
enrichment. Our model agrees with and improves upon previous studies on the
same subject. The results for the star formation rate are very promising and
agree with recent observational data on early-type galaxies. These models lend
further support to the revised monolithic scheme of galaxy formation, which has
recently been also strengthened by high redshift data leading to the so-called
downsizing and top-down scenarios.Comment: 17 pages, 17 figure
A High-Resolution Compton Scattering Study of the Electron Momentum Density in Al
We report high-resolution Compton profiles (CP's) of Al along the three
principal symmetry directions at a photon energy of 59.38 keV, together with
corresponding highly accurate theoretical profiles obtained within the
local-density approximation (LDA) based band-theory framework. A good accord
between theory and experiment is found with respect to the overall shapes of
the CP's, their first and second derivatives, as well as the anisotropies in
the CP's defined as differences between pairs of various CP's. There are
however discrepancies in that, in comparison to the LDA predictions, the
measured profiles are lower at low momenta, show a Fermi cutoff which is
broader, and display a tail which is higher at momenta above the Fermi
momentum. A number of simple model calculations are carried out in order to
gain insight into the nature of the underlying 3D momentum density in Al, and
the role of the Fermi surface in inducing fine structure in the CP's. The
present results when compared with those on Li show clearly that the size of
discrepancies between theoretical and experimental CP's is markedly smaller in
Al than in Li. This indicates that, with increasing electron density, the
conventional picture of the electron gas becomes more representative of the
momentum density and that shortcomings of the LDA framework in describing the
electron correlation effects become less important.Comment: 7 pages, 6 figures, regular articl
Formation and evolution of early-type galaxies. II. Models with quasi-cosmological initial conditions
In this study, with the aid of N-Body simulations based on quasi-cosmological
initial conditions, we have followed the formation and evolution of two models
of early-type galaxies, from their separation from global expansion of the
Universe to their collapse to virialized structures, the formation of stars and
subsequent nearly passive evolution. The cosmological background we have
considered is the Standard CDM. The models have significantly different nitial
total mass. Particular care has been paid to the star formation process,
heating and cooling of gas, and chemical enrichment. In both models star
formation is completed within the first Gyrs of evolution. The structural
properties of the present-day models are in good agreement with current
observations. The chemical properties, mean metallicity and metallicity
gradients also agree with available observational data. Finally, conspicuous
galactic winds are found to occur. The models conform to the so-called revised
monolithic scheme, because mergers of substructures have occurred very early in
the galaxy life. Our results agree with those obtained in other similar recent
studies, thus strengthening the idea that the revised monolithic scheme is the
right trail to follow in the forest of galaxy formation and evolution.Comment: 21 pages, 19 figures, 3 tables. To be published on Astronomy &
Astrophysics (accepted April 12, 2006
Studies of Thermally Unstable Accretion Disks around Black Holes with Adaptive Pseudo-Spectral Domain Decomposition Method I. Limit-Cycle Behavior in the Case of Moderate Viscosity
We present a numerical method for spatially 1.5-dimensional and
time-dependent studies of accretion disks around black holes, that is
originated from a combination of the standard pseudo-spectral method and the
adaptive domain decomposition method existing in the literature, but with a
number of improvements in both the numerical and physical senses. In
particular, we introduce a new treatment for the connection at the interfaces
of decomposed subdomains, construct an adaptive function for the mapping
between the Chebyshev-Gauss-Lobatto collocation points and the physical
collocation points in each subdomain, and modify the over-simplified
1-dimensional basic equations of accretion flows to account for the effects of
viscous stresses in both the azimuthal and radial directions. Our method is
verified by reproducing the best results obtained previously by Szuszkiewicz &
Miller on the limit-cycle behavior of thermally unstable accretion disks with
moderate viscosity. A new finding is that, according to our computations, the
Bernoulli function of the matter in such disks is always and everywhere
negative, so that outflows are unlikely to originate from these disks. We are
encouraged to study the more difficult case of thermally unstable accretion
disks with strong viscosity, and wish to report our results in a subsequent
paper.Comment: 29 pages, 8 figures, accepted by Ap
Metastatic Malignant Melanoma Presenting as an Appendiceal Mucocele
Melanoma metastatic to the appendix is extremely rare. Here we describe a case of a 31-year-old female from Bolivia with a remote history of metastatic malignant melanoma first diagnosed as a cutaneous malignant melanoma ten years prior to this presentation. The patient was being followed for a mucocele which on resection was found to be metastatic melanoma. âMucoceleâ is a generic diagnosis that warrants further characterization and treatment
Novel approach to a perfect lens
Within the framework of an exact analytical solution of Maxwell equations in
a space domain, it is shown that optical scheme based on a slab with negative
refractive index () (Veselago lens or Pendry lens) does not possess
focusing properties in the usual sense . In fact, the energy in such systems
does not go from object to its "image", but from object and its "image" to an
intersection point inside a metamaterial layer, or vice versa. A possibility of
applying this phenomenon to a creation of entangled states of two atoms is
discussed.Comment: 4 pages, 6 figure
Origin of Two Distinct Populations in Dwarf Spheroidal Galaxies
We study the chemical and kinematic properties of the first galaxies which
formed at a high redshift, using high resolution cosmological numerical
simulations, and compared them with the recent observational results for the
Sculptor dwarf spheroidal galaxy by Tolstoy et al., who found two distinct
stellar populations: the lower metallicity stars are more spatially extended
and possess a higher velocity dispersion than the higher metallicity stars. Our
calculations reproduce these observations as the result of a steep metallicity
gradient, within a single populations, induced by dissipative collapse of the
gas component. We also predict strong [N/O] enhancements in the lowest
metallicity stars in dwarf spheroidals, due to the preferential retention of
ejected gas from intermediate mass stars, compared to Type II supernovae.Comment: 11 pages, 10 figures, accepted for publication in Ap
Cosmological formation and chemical evolution of an elliptical galaxy
We aim at studying the effect of a cosmologically motivated gas infall law
for the formation of a massive elliptical galaxy in order to understand its
impact on the formation of the spheroids. We replace the empirical infall law
of the model by Pipino & Matteucci with a cosmologically derived infall law for
the formation of an elliptical galaxy. We constrast our predictions with
observations. We also compare the obtained results with those of Pipino &
Matteucci. We computed models with and without galactic winds: we found that
models without wind predict a too large current SNIa rate. In particular, the
cosmological model produces a current SNIa which is about ten times higher than
the observed values. Moreover models without wind predict a large current SNII
rate, too large even if compared with the recent GALEX data. The predicted SNII
rate for the model with wind, on the other hand, is too low if compared with
the star formation histories given by GALEX. Last but not least, the mean value
for the [Mg/Fe] ratio in the dominant stellar population of the simulated
galaxy, as predicted by the cosmological model, is too low if compared to
observations. This is, a very important result indicating that the cosmological
infall law is in contrast with the chemical evolution. A cosmologically derived
infall law for an elliptical galaxy cannot reproduce all the chemical
constraints given by the observations. The problem resides in the fact that the
cosmologically derived infall law implies a slow gas accretion with consequent
star formation rate active for a long period. In this situation low [Mg/Fe]
ratios are produced for the dominant stellar population in a typical
elliptical, at variance with observations.Comment: 8 pages, 6 figures, accepted for publication by A&
Simulating the Hot X-ray Emitting Gas in Elliptical Galaxies
We study the chemo-dynamical evolution of elliptical galaxies and their hot
X-ray emitting gas using high-resolution cosmological simulations. Our Tree
N-body/SPH code includes a self-consistent treatment of radiative cooling, star
formation, supernovae feedback, and chemical enrichment. We present a series of
LCDM cosmological simulations which trace the spatial and temporal evolution of
heavy element abundance patterns in both the stellar and gas components of
galaxies. X-ray spectra of the hot gas are constructed via the use of the
vmekal plasma model, and analysed using XSPEC with the XMM EPN response
function. Simulation end-products are quantitatively compared with the
observational data in both the X-ray and optical regime. We find that radiative
cooling is important to interpret the observed X-ray luminosity, temperature,
and metallicity of the interstellar medium of elliptical galaxies. However,
this cooled gas also leads to excessive star formation at low redshift, and
therefore results in underlying galactic stellar populations which are too blue
with respect to observations.Comment: 6 pages, 3 figures, to appear in the proceedings of "The IGM/Galaxy
Connection - The Distribution of Baryons at z=0", ed. M. Putman & J.
Rosenberg; High resolution version is available at
http://astronomy.swin.edu.au/staff/dkawata/research/papers.htm
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