490 research outputs found
On a semiclassical formula for non-diagonal matrix elements
Let be a Schr\"odinger operator on the real
line, be a bounded observable depending only on the coordinate and
be a fixed integer. Suppose that an energy level intersects the potential
in exactly two turning points and lies below
. We consider the semiclassical limit
, and where is the th
eigen-energy of . An asymptotic formula for , the
non-diagonal matrix elements of in the eigenbasis of , has
been known in the theoretical physics for a long time. Here it is proved in a
mathematically rigorous manner.Comment: LaTeX2
Severe Loss of Tritan Color Discrimination in RPE65 Associated Leber Congenital Amaurosis
Purpose: RPE65-associated Leber congenital amaurosis (RPE65-LCA) is a progressive severe retinal dystrophy with early profound dysfunction of rod photoreceptors followed by progressive cone photoreceptor degeneration. We aim to provide detailed information about how cone dysfunction affects color discrimination. Methods: Seven adults (aged 16-21) with RPE65-LCA underwent monocular color discrimination assessment using the Trivector and Ellipse versions of three computerized tests: Cambridge Colour Test (CCT), low vision version of the Cambridge Colour Test (lvvCCT), and the Universal Colour Discrimination Test (UCDT). For comparison, subjects were also tested using the American Optical Hardy Rand Rittler (AO-HRR) plates. Each assessment was repeated three times. Results: The Trivector version of the tests demonstrated that color discrimination along the tritan axis was undetectable in four subjects, and severely reduced in three subjects. These findings were confirmed by the Ellipse version of the tests. Color discrimination along the protan and deutan axes was evident but reduced in six of seven subjects. Four of seven subjects were unable to read any of the HRR plates. Conclusions: The computerized color vision tests adopted in this study provide detailed information about color discrimination in adult RPE65-LCA patients. The condition is associated with severe impairment of color discrimination, particularly along the tritan axis indicating possible early involvement of S-cones, with additional protan and deutan loss to a lesser extent. This psychophysical assessment strategy is likely to be valuable in measuring the impact of therapeutic intervention on cone function
Bismuth vanadate photoanodes for water splitting deposited by radio frequency plasma reactive co-sputtering
Photoactive bismuth vanadate (BiVO4) thin coatings were deposited on fluorine-doped tin oxide glass by plasma reactive sputtering from Bi2O3 and vanadium (V) radio frequency (RF) powered targets. The films were characterized by x-ray diffraction, scanning electron microscopy, energy dispersion spectroscopy, and UV-vis spectroscopy. The effects that the power density supplied to the Bi2O3 target, the post-annealing treatment, and the film thickness have on the structural features and on the photoelectrochemical (PEC) performances of the so obtained BiVO4 film-based photoelectrodes were investigated. Their PEC performance in water splitting was evaluated in a three-electrode cell by both incident photon to current efficiency (IPCE) and linear sweep voltammetry measurements under AM 1.5 G simulated solar light irradiation. A monoclinic phase of BiVO4, which is more photoactive than the tetragonal BiVO4 phase, was obtained by optimizing the power density supplied to the Bi2O3 target, i.e., by tuning the Bi:V:O atomic ratio. The best PEC performance was obtained for a stoichiometric 1:1 Bi:V atomic ratio, attained with 20 W power supplied at the Bi2O3 target and 300 W power supplied at the vanadium target, and an optimal 200 nm thickness of the BiVO4 film, with a 0.65 mA/cm2 photocurrent density attained at 1.23 V vs. standard calomel electrode, under simulated solar light. These results show the suitability of plasma reactive sputtering with two RF powered electrodes for the deposition of BiVO4 photoanodes for water splitting
Low-Mass Relics of Early Star Formation
The earliest stars to form in the Universe were the first sources of light,
heat and metals after the Big Bang. The products of their evolution will have
had a profound impact on subsequent generations of stars. Recent studies of
primordial star formation have shown that, in the absence of metals (elements
heavier than helium), the formation of stars with masses 100 times that of the
Sun would have been strongly favoured, and that low-mass stars could not have
formed before a minimum level of metal enrichment had been reached. The value
of this minimum level is very uncertain, but is likely to be between 10^{-6}
and 10^{-4} that of the Sun. Here we show that the recent discovery of the most
iron-poor star known indicates the presence of dust in extremely
low-metallicity gas, and that this dust is crucial for the formation of
lower-mass second-generation stars that could survive until today. The dust
provides a pathway for cooling the gas that leads to fragmentation of the
precursor molecular cloud into smaller clumps, which become the lower-mass
stars.Comment: Offprint of Nature 422 (2003), 869-871 (issue 24 April 2003
Dark Stars and Boosted Dark Matter Annihilation Rates
Dark Stars (DS) may constitute the first phase of stellar evolution, powered
by dark matter (DM) annihilation. We will investigate here the properties of DS
assuming the DM particle has the required properties to explain the excess
positron and elec- tron signals in the cosmic rays detected by the PAMELA and
FERMI satellites. Any possible DM interpretation of these signals requires
exotic DM candidates, with an- nihilation cross sections a few orders of
magnitude higher than the canonical value required for correct thermal relic
abundance for Weakly Interacting Dark Matter can- didates; additionally in most
models the annihilation must be preferentially to lep- tons. Secondly, we study
the dependence of DS properties on the concentration pa- rameter of the initial
DM density profile of the halos where the first stars are formed. We restrict
our study to the DM in the star due to simple (vs. extended) adiabatic
contraction and minimal (vs. extended) capture; this simple study is sufficient
to illustrate dependence on the cross section and concentration parameter. Our
basic results are that the final stellar properties, once the star enters the
main sequence, are always roughly the same, regardless of the value of boosted
annihilation or concentration parameter in the range between c=2 and c=5:
stellar mass ~ 1000M\odot, luminosity ~ 10^7 L\odot, lifetime ~ 10^6 yrs (for
the minimal DM models considered here; additional DM would lead to more massive
dark stars). However, the lifetime, final mass, and final luminosity of the DS
show some dependence on boost factor and concentration parameter as discussed
in the paper.Comment: 37 pages, 11 figure
A metal rich molecular cloud surrounds GRB 050904 at redshift 6.3
GRB050904 is the gamma-ray burst with the highest measured redshift. We
performed time resolved X-ray spectroscopy of the late GRB and early afterglow
emission. We find robust evidence for a decrease with time of the soft X-ray
absorbing column. We model the evolution of the column density due to the flash
ionization of the GRB and early afterglow photons. This allows us to constrain
the metallicity and geometry of the absorbing cloud. We conclude that the
progenitor of GRB050904 was a massive star embedded in a dense metal enriched
molecular cloud with Z~0.03 Z_solar. This is the first local measurement of
metallicity in the close environment of a GRB and one of the highest redshift
metallicity measurements. We also find that the dust associated with the cloud
cannot be similar to that of our Galaxy but must be either sizably depleted or
dominated by silicate grains. We discuss the implications of these results for
GRB progenitors and high redshift star formation.Comment: 4 pages, 2 figures. Accepted for publication on Astrophysical Journal
Letter
Galactic neutron stars I. Space and velocity distributions in the disk and in the halo
Aims. Neutron stars (NSs) produced in the Milky Way are supposedly ten to the
eighth - ten to the ninth, of which only are observed.
Constraining the phase space distribution of NSs may help to characterize the
yet undetected population of stellar remnants. Methods. We perform Monte Carlo
simulations of NS orbits, under different assumptions concerning the Galactic
potential and the distribution of progenitors and birth velocities. We study
the resulting phase space distributions, focusing on the statistical properties
of the NS populations in the disk and in the solar neighbourhood. Results. It
is shown that percent of NSs are in bound orbits. The fraction of NSs
located in a disk of radius 20 kpc and width 0.4 kpc is percent.
Therefore the majority of NSs populate the halo. Fits for the surface density
of the disk, the distribution of heights on the Galactic plane and the velocity
distribution of the disk, are given. We also provide sky maps of the projected
number density in heliocentric Galactic coordinates (l, b). Our results are
compared with previous ones reported in the literature. Conclusions. Obvious
applications of our modelling are in the revisiting of accretion luminosities
of old isolated NSs, the issue of the observability of the nearest NS and the
NS optical depth for microlensing events. These will be the scope of further
studies.Comment: 11 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
Prognostic evaluation in patients with advanced cancer in the last months of life:ESMO Clinical Practice Guideline
: âą This ESMO Clinical Practice Guideline provides key recommendations for using prognostic estimates in advanced cancer. âą The guideline covers recommendations for patients with cancer and an expected survival of months or less. âą An algorithm for use of clinical predictions, prognostic factors and multivariable risk prediction models is presented. âą The author group encompasses a multidisciplinary group of experts from different institutions in Europe, USA and Asia. âą Recommendations are based on available scientific data and the authorsâ collective expert opinion
Total hip arthroplasty in an inveterate femoral neck fracture in a patient with congenital insensitivity to pain with anhidrosis
Congenital insensitivity to pain with anhidrosis (CIPA) is an extremely rare disorder characterized by autonomic and sensory nerves malfunction with insensitivity to both deep and superficial painful stimuli, inability to sweat and produce tears, and mild to moderate mental retardation with self-mutilating behavior. Related consequences of inveterate musculoskeletal injuries represent a major issue for these patients, since pain cannot act as a protectionmechanism. For the same reason, the patients are at risk during postoperative rehabilitation, which should be taken into account when selecting an orthopaedic implant. To our knowledge, only one case of total hip arthroplasty has been reported in the literature to date. A 21-year-old Caucasian male patient affected with CIPA arrived at our attention complaining about a functional limitation of the left hip. No history of trauma was reported. The X-rays showed an inveterate femoral neck fracture with a severe necrosis and resorption of the femoral head. We decided to performa total hip arthroplasty with a cemented stem and a cemented dual mobility cup. The postoperative course and rehabilitation were satisfactory, with excellent clinical results, measured with the Harris Hip Score at 1 year
Observational Manifestations of the First Protogalaxies in the 21 cm Line
The absorption properties of the first low-mass protogalaxies (mini-halos)
forming at high redshifts in the 21-cm line of atomic hydrogen are considered.
The absorption properties of these protogalaxies are shown to depend strongly
on both their mass and evolutionary status. The optical depths in the line
reach 0.1-0.2 for small impact parameters of the line of sight. When a
protogalaxy being compressed, the influence of gas accretion can be seen
manifested in a non-monotonic frequency dependence of the optical depth. The
absorption characteristics in the 21-cm line are determined by the thermal and
dynamical evolution of the gas in protogalaxies. Since the theoretical line
width in the observer's reference frame is 1-6 kHz and the expected separation
between lines 8.4 kHz, the lines from low mass protogalaxies can be resolved
using ongoing and future low frequency interferometers.Comment: 12 pages, 5 figure
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