2,580 research outputs found
Reduction criterion for separability
We introduce a separability criterion based on the positive map Î:Ïâ(Tr Ï)-Ï, where Ï is a trace-class Hermitian operator. Any separable state is mapped by the tensor product of Î and the identity into a non-negative operator, which provides a simple necessary condition for separability. This condition is generally not sufficient because it is vulnerable to the dilution of entanglement. In the special case where one subsystem is a quantum bit, Î reduces to time reversal, so that this separability condition is equivalent to partial transposition. It is therefore also sufficient for 2Ă2 and 2Ă3 systems. Finally, a simple connection between this map for two qubits and complex conjugation in the âmagicâ basis [Phys. Rev. Lett. 78, 5022 (1997)] is displayed
Photometric redshifts as a tool to study the Coma cluster galaxy populations
We investigate the Coma cluster galaxy luminosity function (GLF) at faint
magnitudes, in particular in the u* band by applying photometric redshift
techniques applied to deep u*, B, V, R, I images covering a region of ~1deg2 (R
24). Global and local GLFs in the B, V, R and I bands obtained with photometric
redshift selection are consistent with our previous results based on a
statistical background subtraction.
In the area covered only by the u* image, the GLF was also derived after
applying a statistical background subtraction. The GLF in the u* band shows an
increase of the faint end slope towards the outer regions of the cluster (from
alpha~1 in the cluster center to alpha~2 in the cluster periphery). This could
be explained assuming a short burst of star formation in these galaxies when
entering the cluster.
The analysis of the multicolor type spatial distribution reveals that late
type galaxies are distributed in clumps in the cluster outskirts, where X-ray
substructures are also detected and where the GLF in the u* band is steeper.Comment: 14 pages, 2 figures in jpeg format, accepted in A&
On the nature of faint Low Surface Brightness galaxies in the Coma cluster
This project is the continuation of our study of faint Low Surface Brightness
Galaxies (fLSBs) in one of the densest nearby galaxy regions known, the Coma
cluster. Our goal is to improve our understanding of the nature of these
objects by comparing the broad band spectral energy distribution with
population synthesis models. The data were obtained with the MEGACAM and CFH12K
cameras at the CFHT. We used the resulting photometry in 5 broad band filters
(u*, B, V, R, and I), that included new u*-band data, to fit spectral models.
With these spectral fits we inferred a cluster membership criterium, as well as
the ages, dust extinctions, and photometric types of these fLSBs. We show that
about half of the Coma cluster fLSBs have a spectral energy distribution well
represented in our template library while the other half present a flux deficit
at ultraviolet wavelengths. Among the well represented, ~80% are probably part
of the Coma cluster based on their spectral energy distribution. They are
relatively young (younger than 2.3 Gyrs for 90% of the sample) non-starburst
objects. The later their type, the younger fLSBs are. A significant part of the
fLSBs are quite dusty objects. fLSBs are low stellar mass objects (the later
their type the less massive they are), with stellar masses comparable to
globular clusters for the faintest ones. Their characteristics are correlated
with infall directions, confirming the disruptive origin for part of them.Comment: Accepted for publication in A&A, 10 pages, 10 figure
A Possible Case of Neurogenic Pulmonary Edema in a Sheep following Intracranial Surgery
A 3-year-old female crossbred sheep weighing 64 kg was anaesthetized for intracranial surgery as a part of a research project. Premedication and induction of anesthesia were uneventful as well as tracheal intubation. Anesthesia was maintained with isoflurane in a 50% mixture of oxygen and air, fentanyl (5-15 ”g kg-1h-1) and lidocaine (1.8 mg kg-1h-1). During anesthesia, an increased alveolar-arterial oxygen gradient was calculated on the basis of arterial blood gas analysis: inspiratory fraction of oxygen was increased and a recruitment manoeuvre was performed. After 210 minutes of anesthesia, the sheep was let recover with oxygen supplementation under monitoring of pulse-oxymetry, capnography, inspired and expired oxygen, temperature and invasive blood pressure. At tracheal extubation no signs of regurgitation or aspiration were noticed. Twenty-five minutes later, the sheep showed deterioration of neurological status and clonic seizure responsive to diazepam. After transient tachycardia, blood pressure rose acutely and sinus bradycardia followed. Severe tachypnea started in few minutes accompanied by loud respiratory noises and harsh diffuse crackles on both sides of the thorax. Foamy blood nasal exudates discharged from the nostrils. Neurogenic pulmonary edema as a sequel of increased intracranial pressure was suspected and treated with intravenous mannitol (0.5 gkg-1) and furosemide (4 mgKg-1). Hypoxemia was successfully managed with oxygen supplementation. Motor and cognitive functions improved progressively and were deemed normal within 12 hours from the episode, when arterial partial pressure of oxygen was 11.7 kPa (88 mmHg) at room air
Coma cluster object populations down to M_R~-9.5
This study follows a recent analysis of the galaxy luminosity functions and
colour-magnitude red sequences in the Coma cluster (Adami et al. 2007). We
analyze here the distribution of very faint galaxies and globular clusters in
an east-west strip of arcmin crossing the Coma cluster
center (hereafter the CS strip) down to the unprecedented faint absolute
magnitude of M. This work is based on deep images obtained at the
CFHT with the CFH12K camera in the B, R, and I bands. The analysis shows that
the observed properties strongly depend on the environment, and thus on the
cluster history. When the CS is divided into four regions, the westernmost
region appears poorly populated, while the regions around the brightest
galaxies NGC 4874 and NGC 4889 (NGC 4874 and NGC 4889 being masked) are
dominated by faint blue galaxies. They show a faint luminosity function slope
of -2, very significantly different from the field estimates. Results are
discussed in the framework of galaxy destruction (which can explain part of the
very faint galaxy population) and of structures infalling on to Coma.Comment: To be published in A&
Stability and symmetry-breaking bifurcation for the ground states of a NLS with a interaction
We determine and study the ground states of a focusing Schr\"odinger equation
in dimension one with a power nonlinearity and a strong
inhomogeneity represented by a singular point perturbation, the so-called
(attractive) interaction, located at the origin. The
time-dependent problem turns out to be globally well posed in the subcritical
regime, and locally well posed in the supercritical and critical regime in the
appropriate energy space. The set of the (nonlinear) ground states is
completely determined. For any value of the nonlinearity power, it exhibits a
symmetry breaking bifurcation structure as a function of the frequency (i.e.,
the nonlinear eigenvalue) . More precisely, there exists a critical
value \om^* of the nonlinear eigenvalue \om, such that: if \om_0 < \om <
\om^*, then there is a single ground state and it is an odd function; if \om
> \om^* then there exist two non-symmetric ground states. We prove that before
bifurcation (i.e., for \om < \om^*) and for any subcritical power, every
ground state is orbitally stable. After bifurcation (\om =\om^*+0), ground
states are stable if does not exceed a value that lies
between 2 and 2.5, and become unstable for . Finally, for and \om \gg \om^*, all ground states are unstable. The branch of odd
ground states for \om \om^*,
obtaining a family of orbitally unstable stationary states. Existence of ground
states is proved by variational techniques, and the stability properties of
stationary states are investigated by means of the Grillakis-Shatah-Strauss
framework, where some non standard techniques have to be used to establish the
needed properties of linearization operators.Comment: 46 pages, 5 figure
Critical and Near-Critical Branching Processes
Scale-free dynamics in physical and biological systems can arise from a
variety of causes. Here, we explore a branching process which leads to such
dynamics. We find conditions for the appearance of power laws and study
quantitatively what happens to these power laws when such conditions are
violated. From a branching process model, we predict the behavior of two
systems which seem to exhibit near scale-free behavior--rank-frequency
distributions of number of subtaxa in biology, and abundance distributions of
genotypes in an artificial life system. In the light of these, we discuss
distributions of avalanche sizes in the Bak-Tang-Wiesenfeld sandpile model.Comment: 9 pages LaTex with 10 PS figures. v.1 of this paper contains results
from non-critical sandpile simulations that were excised from the published
versio
The CFH Optical PDCS survey (COP) I: The Data
This paper presents and gives the COP (COP: CFHT Optical PDCS; CFHT:
Canada-France-Hawaii Telescope; PDCS: Palomar Distant Cluster Survey) survey
data. We describe our photometric and spectroscopic observations with the MOS
multi-slit spectrograph at the CFH telescope. A comparison of the photometry
from the PDCS (Postman et al. 1996) catalogs and from the new images we have
obtained at the CFH telescope shows that the different magnitude systems can be
cross-calibrated. After identification between the PDCS catalogues and our new
images, we built catalogues with redshift, coordinates and V, I and
Rmagnitudes. We have classified the galaxies along the lines of sight into
field and structure galaxies using a gap technique (Katgert et al. 1996). In
total we have observed 18 significant structures along the 10 lines of sight.Comment: 40 pages, 13 figures, accepted in A
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