585 research outputs found
Microcomputer array processor system
The microcomputer array system is discussed with specific attention given to its electronic warware applications. Several aspects of the system architecture are described as well as some of its distinctive characteristics
Unveiling hidden structures in the Coma cluster
We have assembled a large data-set of 613 galaxy redshifts in the Coma
cluster, the largest presently available for a cluster of galaxies. We have
defined a sample of cluster members complete to b, using a
membership criterion based on the galaxy velocity, when available, or on the
galaxy magnitude and colour, otherwise. Such a data set allows us to define
nearly complete samples within a region of 1~\Mpc\ radius, with a sufficient
number of galaxies per sample to make statistical analyses possible. Using this
sample and the {\em ROSAT} PSPC X--ray image of the cluster, we have
re-analyzed the structure and kinematics of Coma, by applying the wavelet and
adaptive kernel techniques. A striking coincidence of features is found in the
distributions of galaxies and hot intracluster gas. The two central dominant
galaxies, NGC4874 and NGC4889, are surrounded by two galaxy groups, mostly
populated with galaxies brighter than b and well separated in
velocity space. On the contrary, the fainter galaxies tend to form a single
smooth structure with a central peak coinciding in position with a secondary
peak detected in X--rays, and located between the two dominant galaxies; we
suggest to identify this structure with the main body of the Coma cluster. A
continuous velocity gradient is found in the central distribution of these
faint galaxies, a probable signature of tidal interactions rather than
rotation. There is evidence for a bound population of bright galaxies around
other brightest cluster members. Altogether, the Coma cluster structure seems
to be better traced by the faint galaxy population, the bright galaxies being
located in subclusters. We discuss this evidence in terms of an ongoing
accretion of groups onto the cluster.Comment: to appear in A&A, 19 pages, uuencoded gzipped postscript fil
On the galaxy luminosity function in the central regions of the Coma cluster
We have obtained new redshifts for 265 objects in the central
48~~25~arcmin region of the Coma cluster. When supplemented with
literature data, our redshift sample is 95~\% complete up to a magnitude
b=18.0 (the magnitudes are taken from the photometric sample of Godwin
et al. 1983). Using redshift-confirmed membership for 205 galaxies, and the
location in the colour-magnitude diagram for another 91 galaxies, we have built
a sample of cluster members which is complete up to b=20.0. We show
that the Coma cluster luminosity function cannot be adequately fitted by a
single Schechter (1976) function, because of a dip in the magnitude
distribution at b17. The superposition of an Erlang (or a Gauss)
and a Schechter function provides a significantly better fit. We compare the
luminosity function of Coma to those of other clusters, and of the field.
Luminosity functions for rich clusters look similar, with a maximum at , while the Virgo and the field luminosity
functions show a nearly monotonic behaviour. These differences may be produced
by physical processes related to the environment which affect the luminosities
of a certain class of cluster galaxies.Comment: 7 pages, uuencoded postscript file (figures included) Accepted for
publication on A&
A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory
Compact elliptical galaxies are characterized by small sizes and high stellar
densities. They are thought to form through tidal stripping of massive
progenitors. However, only a handful of them were known, preventing us from
understanding the role played by this mechanism in galaxy evolution. We present
a population of 21 compact elliptical galaxies gathered with the Virtual
Observatory. Follow-up spectroscopy and data mining, using high-resolution
images and large databases, show that all the galaxies exhibit old metal-rich
stellar populations different from those of dwarf elliptical galaxies of
similar masses but similar to those of more massive early-type galaxies,
supporting the tidal stripping scenario. Their internal properties are
reproduced by numerical simulations, which result in compact dynamically hot
remnants resembling the galaxies in our sample.Comment: 26 pages, 5 figures, 2 tables. Science in press, published in Science
Express on 1/Oct/2009. Full resolution figures in the supplementary online
material are available from the Science Magazine web-sit
New Structure In The Shapley Supercluster
We present new radial velocities for 189 galaxies in a 91 sq. deg region of
the Shapley supercluster measured with the FLAIR-II spectrograph on the UK
Schmidt Telescope. The data reveal two sheets of galaxies linking the major
concentrations of the supercluster. The supercluster is not flattened in
Declination as was suggested previously and it may be at least 30 percent
larger than previously thought with a correspondingly larger contribution to
the motion of the Local Group.Comment: LaTex: 2 pages, 1 figure, includes conf_iap.sty style file. To appear
in proceedings of The 14th IAP Colloquium: Wide Field Surveys in Cosmology,
held in Paris, 1998 May 26--30, eds. S.Colombi, Y.Mellie
Effects of ultraviolet and visible radiation on the cellular concentrations of dimethylsulfoniopropionate (DMSP) in Emiliania huxleyi (strain L)
Emiliania huxleyi is an important component of the global carbon and sulfur cycles and is known to be sensitive to ultraviolet (UV) radiation. We investigated the influence of radiation intensity and of short-term exposure to UV radiation on the per-cell amount and intracellular concentration of dimethylsulfoniopropionate (DMSP). E. huxleyi (strain L) was exposed to artificial radiation intensities similar to those at 15 in (700 mumol PAR [photosynthetically active radiation] m(-2) s(-1)) and 25 in depth (400 mumol PAR m(-2) s(-1)) in the subtropical Atlantic Ocean. Exposure to UV radiation led to a 10 to 25% increase in the per-cell amount of DMSP as compared to E. huxleyi exposed to only PAR, whereas photosynthetic activity (measured via oxygen production) of UV-exposed E. huxleyi was reduced by 18 to 22%. Furthermore, the intracellular DMSP concentration was always higher in PAR + UV-exposed E. huxleyi than in PAR-exposed E. huxleyi, despite the small but significant increase in cell volume of E. huxleyi after exposure to PAR + UV as compared to PAR exposure only. A shift of the radiation conditions to higher levels resulted in a short-term increase in the per-cell amount and intracellular concentration of DMSP. E. huxleyi cultured in turbidostats under different radiation intensities (ranging from 5.6 to 400 mumol PAR m(-2) s(-1)) revealed a significant monotonical increase in the per-cell amount and the intracellular concentration of DMSP with increasing radiation intensity
Spectral Properties of Holstein and Breathing Polarons
We calculate the spectral properties of the one-dimensional Holstein and
breathing polarons using the self-consistent Born approximation. The Holstein
model electron-phonon coupling is momentum independent while the breathing
coupling increases monotonically with the phonon momentum. We find that for a
linear or tight binding electron dispersion: i) for the same value of the
dimensionless coupling the quasiparticle renormalization at small momentum in
the breathing polaron is much smaller, ii) the quasiparticle renormalization at
small momentum in the breathing polaron increases with phonon frequency unlike
in the Holstein model where it decreases, iii) in the Holstein model the
quasiparticle dispersion displays a kink and a small gap at an excitation
energy equal to the phonon frequency w0 while in the breathing model it
displays two gaps, one at excitation energy w0 and another one at 2w0. These
differences have two reasons: first, the momentum of the relevant scattered
phonons increases with increasing polaron momentum and second, the breathing
bare coupling is an increasing function of the phonon momentum. These result in
an effective electron-phonon coupling for the breathing model which is an
increasing function of the total polaron momentum, such that the small momentum
polaron is in the weak coupling regime while the large momentum one is in the
strong coupling regime. However the first reason does not hold if the free
electron dispersion has low energy states separated by large momentum, as in a
higher dimensional system for example, in which situation the difference
between the two models becomes less significant.Comment: 11 pages, 10 figure
The rich cluster of galaxies ABCG 85.I. X-ray analysis
We present an X-ray analysis of the rich cluster ABCG 85 based on ROSAT PSPC
data. By applying an improved wavelet analysis, we show that our view of this
cluster is notably changed from what was previously believed (a main region and
a south blob). The main emission comes from the central part of the main body
of the cluster on which is superimposed that of a foreground group of galaxies.
The foreground group and the main cluster are separated (if redshifts are
cosmological) by 46 1/h_50 Mpc. The southern blob is clearly not a group: it is
resolved into X-ray emitting galaxies (in particular the second more luminous
galaxy of the main cluster). Several X-ray features are identified with bright
galaxies. We performed a spectral analysis and derived the temperature (T),
metallicity (Z) and hydrogen column density NH. The global quantities are:
T=4keV (in agreement with the velocity dispersion of 760km/s) and
. We cannot derive accurate gradients for these quantities with
our data, but there is strong evidence that the temperature is lower () and the metallicity much higher (Z ) in the very centre
(within about 50 1/h_50 kpc). We present a pixel by pixel method to model the
physical properties of the X-ray gas and derive its density distribution. We
apply classical methods to estimate the dynamical, gas and stellar masses, as
well as the cooling time and cooling flow characteristics. At the limiting
radius of the image (1.4 1/h_50 Mpc), we find _{\odot}M_{gas}/M_{Dyn}\sim 0.18 h_{50}^{-1.5}6.7\ 10^{12}M_{\odot}M/L_{V}\sim 300$.
The cooling time is estimated for different models, leading to a cooling radius
of 30-80 kpc depending on theComment: 14 pages incl 16 postscript figures available, 4 tables, corrected
stellar mass. Accepted for publication in Astronomy & Astrophysic
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