2,181 research outputs found
Early-type galaxies in the Chandra COSMOS Survey
We study a sample of 69 X-ray detected Early Type Galaxies (ETGs), selected
from the Chandra COSMOS survey, to explore the relation between the X-ray
luminosity of hot gaseous halos (L_X, gas) and the integrated stellar
luminosity (L_K) of the galaxies, in a range of redshift extending out to
z=1.5. In the local universe a tight steep relationship has been stablished
between these two quantities (L_X,gas~ L_K^4.5) suggesting the presence of
largely virialized halos in X-ray luminous systems. We use well established
relations from the study of local universe ETGs, together with the expected
evolution of the X-ray emission, to subtract the contribution of low mass X-ray
binary populations (LMXBs) from the X-ray luminosity of our sample. Our
selection minimizes the presence of active galactic nuclei (AGN), yielding a
sample representative of normal passive COSMOS ETGs; therefore the resulting
luminosity should be representative of gaseous halos, although we cannot
exclude other sources such as obscured AGN, or enhanced X-ray emission
connected with embedded star formation in the higher z galaxies. We find that
most of the galaxies with estimated L_X<10^42 erg/s and z<0.55 follow the
L_X,gas- L_K relation of local universe ETGs. For these galaxies, the
gravitational mass can be estimated with a certain degree of confidence from
the local virial relation. However, the more luminous (10^42<L_X<10^43.5 erg/s)
and distant galaxies present significantly larger scatter; these galaxies also
tend to have younger stellar ages. The divergence from the local L_X,gas - L_K
relation in these galaxies implies significantly enhanced X-ray emission, up to
a factor of 100 larger than predicted from the local relation. We discuss the
implications of this result for the presence of hidden AGN, and the evolution
of hot halos, in the presence of nuclear and star formation feedback.Comment: 29 pages, 10 figures, accepted for publication on ApJ on May 27 201
A high-efficiency spin-resolved phototemission spectrometer combining time-of-flight spectroscopy with exchange-scattering polarimetry
We describe a spin-resolved electron spectrometer capable of uniquely
efficient and high energy resolution measurements. Spin analysis is obtained
through polarimetry based on low-energy exchange scattering from a
ferromagnetic thin-film target. This approach can achieve a similar analyzing
power (Sherman function) as state-of-the-art Mott scattering polarimeters, but
with as much as 100 times improved efficiency due to increased reflectivity.
Performance is further enhanced by integrating the polarimeter into a
time-of-flight (TOF) based energy analysis scheme with a precise and flexible
electrostatic lens system. The parallel acquisition of a range of electron
kinetic energies afforded by the TOF approach results in an order of magnitude
(or more) increase in efficiency compared to hemispherical analyzers. The lens
system additionally features a 90{\deg} bandpass filter, which by removing
unwanted parts of the photoelectron distribution allows the TOF technique to be
performed at low electron drift energy and high energy resolution within a wide
range of experimental parameters. The spectrometer is ideally suited for
high-resolution spin- and angle-resolved photoemission spectroscopy
(spin-ARPES), and initial results are shown. The TOF approach makes the
spectrometer especially ideal for time-resolved spin-ARPES experiments.Comment: 16 pages, 11 figure
Self-consistent fragmented excited states of trapped condensates
Self-consistent excited states of condensates are solutions of the
Gross-Pitaevskii (GP) equation and have been amply discussed in the literature
and related to experiments. By introducing a more general mean-field which
includes the GP one as a special case, we find a new class of self-consistent
excited states. In these states macroscopic numbers of bosons reside in
different one-particle functions, i.e., the states are fragmented. Still, a
single chemical potential is associated with the condensate. A numerical
example is presented, illustrating that the energies of the new, fragmented,
states are much lower than those of the GP excited states, and that they are
stable to variations of the particle number and shape of the trap potential.Comment: (11 pages 2 figures, submitted to PRL
Analytical results for a trapped, weakly-interacting Bose-Einstein condensate under rotation
We examine the problem of a repulsive, weakly-interacting and harmonically
trapped Bose-Einstein condensate under rotation. We derive a simple analytic
expression for the energy incorporating the interactions when the angular
momentum per particle is between zero and one and find that the interaction
energy decreases linearly as a function of the angular momentum in agreement
with previous numerical and limiting analytical studies.Comment: 3 pages, RevTe
Single-qubit unitary gates by graph scattering
We consider the effects of plane-wave states scattering off finite graphs, as
an approach to implementing single-qubit unitary operations within the
continuous-time quantum walk framework of universal quantum computation. Four
semi-infinite tails are attached at arbitrary points of a given graph,
representing the input and output registers of a single qubit. For a range of
momentum eigenstates, we enumerate all of the graphs with up to vertices
for which the scattering implements a single-qubit gate. As increases, the
number of new unitary operations increases exponentially, and for the
majority correspond to rotations about axes distributed roughly uniformly
across the Bloch sphere. Rotations by both rational and irrational multiples of
are found.Comment: 8 pages, 7 figure
Distinguishing cancerous from non-cancerous cells through analysis of electrical noise
Since 1984, electric cell-substrate impedance sensing (ECIS) has been used to
monitor cell behavior in tissue culture and has proven sensitive to cell
morphological changes and cell motility. We have taken ECIS measurements on
several cultures of non-cancerous (HOSE) and cancerous (SKOV) human ovarian
surface epithelial cells. By analyzing the noise in real and imaginary
electrical impedance, we demonstrate that it is possible to distinguish the two
cell types purely from signatures of their electrical noise. Our measures
include power-spectral exponents, Hurst and detrended fluctuation analysis, and
estimates of correlation time; principal-component analysis combines all the
measures. The noise from both cancerous and non-cancerous cultures shows
correlations on many time scales, but these correlations are stronger for the
non-cancerous cells.Comment: 8 pages, 4 figures; submitted to PR
spectra in elementary cellular automata and fractal signals
We systematically compute the power spectra of the one-dimensional elementary
cellular automata introduced by Wolfram. On the one hand our analysis reveals
that one automaton displays spectra though considered as trivial, and on
the other hand that various automata classified as chaotic/complex display no
spectra. We model the results generalizing the recently investigated
Sierpinski signal to a class of fractal signals that are tailored to produce
spectra. From the widespread occurrence of (elementary) cellular
automata patterns in chemistry, physics and computer sciences, there are
various candidates to show spectra similar to our results.Comment: 4 pages (3 figs included
Critical scaling in standard biased random walks
The spatial coverage produced by a single discrete-time random walk, with
asymmetric jump probability and non-uniform steps, moving on an
infinite one-dimensional lattice is investigated. Analytical calculations are
complemented with Monte Carlo simulations. We show that, for appropriate step
sizes, the model displays a critical phenomenon, at . Its scaling
properties as well as the main features of the fragmented coverage occurring in
the vicinity of the critical point are shown. In particular, in the limit , the distribution of fragment lengths is scale-free, with nontrivial
exponents. Moreover, the spatial distribution of cracks (unvisited sites)
defines a fractal set over the spanned interval. Thus, from the perspective of
the covered territory, a very rich critical phenomenology is revealed in a
simple one-dimensional standard model.Comment: 4 pages, 4 figure
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