3,253 research outputs found
Microlensing of -Ray Burst Afterglows
The afterglow of a cosmological Gamma-Ray Burst (GRB) should appear on the
sky as a narrow emission ring of radius 3x10^{16}cm(t/day)^{5/8} which expands
faster than light. After a day, the ring radius is comparable to the Einstein
radius of a solar mass lens at a cosmological distance. Thus, microlensing by
an intervening star can modify significantly the lightcurve and polarization
signal from a GRB afterglow. We show that the achromatic amplification signal
of the afterglow flux can be used to determine the impact parameter and
expansion rate of the source in units of the Einstein radius of the lens, and
probe the superluminal nature of the expansion. If the synchrotron emission
from the afterglow photosphere originates from a set of coherent magnetic field
patches, microlensing would induce polarization variability due to the
transient magnification of the patches behind the lens. The microlensing
interpretation of the flux and polarization data can be confirmed by a parallax
experiment which would probe the amplification peak at different times. The
fraction of microlensed afterglows can be used to calibrate the density
parameter of stellar-mass objects in the Universe.Comment: 12 pages, latex, 2 figures, submitted to ApJ
Identifying the Environment and Redshift of GRB Afterglows from the Time-Dependence of Their Absorption Spectra
The discovery of Gamma-Ray Burst (GRB) afterglows revealed a new class of
variable sources at optical and radio wavelengths. At present, the environment
and precise redshift of the detected afterglows are still unknown. We show that
if a GRB source resides in a compact (<100pc) gas-rich environment, the
afterglow spectrum will show time-dependent absorption features due to the
gradual ionization of the surrounding medium by the afterglow radiation.
Detection of this time-dependence can be used to constrain the size and density
of the surrounding gaseous system. For example, the MgII absorption line
detected in GRB970508 should have weakened considerably during the first month
if the absorption occurred in a gas cloud of size <100pc around the source. The
time-dependent HI or metal absorption features provide a precise determination
of the GRB redshift.Comment: 13 pages, 4 figures, submitted to ApJ
Are the therapeutic strategies in anorexia of ageing effective on nutritional status? A systematic review with meta-analysis
BACKGROUND:
Anorexia of ageing (AA) may be considered as a risk factor for frailty and has an important impact on quality of life, morbidity and mortality.
METHODS:
A systematic review and a meta-analysis were performed to summarise the results from several trials on the effectiveness of treatments in AA, as associated with depression, sensory impairment of taste and smell, decreased appetite or early satiety, and disability. Eligible studies were required to report baseline and follow-up values, the mean change (â-change) from baseline, and/or the mean difference among intervention groups versus control group, concerning food intake (kcal/daily) and/or nutritional outcomes, such as body weight, body mass index, albumin and Mini Nutritional Assessment.
RESULTS:
The systematic review included 20 papers based on different therapeutic approaches concerning food intake and/or nutritional outcomes. The results of the meta-analysis indicate that the interventions for AA have an important impact on body weight [+1.59 kg; 95% confidence interval (CI) = 1.48-+1.71 kg; P < 0.001) and on energy intake (+56.09 kcal; 95% CI = -54.05 to +166.25 kcal; P = 0.32). Regarding secondary outcomes, it was not possible to meta-analyse the limited amount of data availab le.
CONCLUSIONS:
The different variants of AA need to be defined because diverse therapeutic approaches are available. A more precise definition of the functional impairments associated with AA may allow a more correct decision about the most appropriate therapy to be prescribed. Moreover, this may allow for a more effective performance of the different therapeutic approaches once they are better targeted to the different scenarios of AA
Population Synthesis of Isolated Neutron Stars with magneto-rotational evolution II: from radio-pulsars to magnetars
Population synthesis studies constitute a powerful method to reconstruct the
birth distribution of periods and magnetic fields of the pulsar population.
When this method is applied to populations in different wavelengths, it can
break the degeneracy in the inferred properties of initial distributions that
arises from single-band studies. In this context, we extend previous works to
include -ray thermal emitting pulsars within the same evolutionary model as
radio-pulsars. We find that the cumulative distribution of the number of X-ray
pulsars can be well reproduced by several models that, simultaneously,
reproduce the characteristics of the radio-pulsar distribution. However, even
considering the most favourable magneto-thermal evolution models with fast
field decay, log-normal distributions of the initial magnetic field
over-predict the number of visible sources with periods longer than 12 s. We
then show that the problem can be solved with different distributions of
magnetic field, such as a truncated log-normal distribution, or a binormal
distribution with two distinct populations. We use the observational lack of
isolated NSs with spin periods P>12 s to establish an upper limit to the
fraction of magnetars born with B > 10^{15} G (less than 1\%). As future
detections keep increasing the magnetar and high-B pulsar statistics, our
approach can be used to establish a severe constraint on the maximum magnetic
field at birth of NSs.Comment: 12 pages, 11 figures, 5 table
Multi-Omics Studies Unveil Extraciliary Functions of BBS10 and Show Metabolic Aberrations Underlying Renal Disease in BardetâBiedl Syndrome
Spectral variability on primitive asteroids of the Themis and Beagle families: space weathering effects or parent body heterogeneity?
Themis is an old and statistically robust asteroid family populating the
outer main belt, and resulting from a catastrophic collision that took place
2.51.0 Gyr ago. Within the old Themis family a young sub-family, Beagle,
formed less than 10 Myr ago, has been identified. We present the results of a
spectroscopic survey in the visible and near infrared range of 22 Themis and 8
Beagle families members. The Themis members investigated exhibit a wide range
of spectral behaviors, while the younger Beagle family members look spectrally
bluer with a smaller spectral slope variability. The best meteorite spectral
analogues found for both Themis and Beagle families members are carbonaceous
chondrites having experienced different degrees of aqueous alteration,
prevalently CM2 but also CV3 and CI, and some of them are chondrite samples
being unusual or heated. We extended the spectral analysis including the data
available in the literature on Themis and Beagle families members, and we
looked for correlations between spectral behavior and physical parameters using
the albedo and size values derived from the WISE data. The analysis of this
larger sample confirm the spectral diversity within the Themis family and that
Beagle members tend to be bluer and to have an higher albedo. The differences
between the two family may be partially explained by space weathering
processes, which act on these primitive surfaces in a similar way than on
S-type asteroids, i.e. producing reddening and darkening. However we see
several Themis members having albedos and spectral slopes similar to the young
Beagle members. Alternative scenarios are proposed including heterogeneity in
the parent body having a compositional gradient with depth, and/or the survival
of projectile fragments having a different composition than the parent body.Comment: Manuscript pages: 40; Figures: 15 ; Tables: 4 Icarus (2016),in pres
Extinction properties of the X-ray bright/optically faint afterglow of GRB 020405
We present an optical-to-X-ray spectral analysis of the afterglow of GRB
020405. The optical spectral energy distribution not corrected for the
extragalactic extinction is significantly below the X-ray extrapolation of the
single powerlaw spectral model suggested by multiwavelength studies. We
investigate whether considerable extinction could explain the observed spectral
``mismatch'' by testing several types of extinction curves. For the first time
we test extinction curves computed with time-dependent numerical simulations of
dust grains destruction by the burst radiation. We find that an extinction law
weakly depen dent on wavelength can reconcile the unabsorbed optical and X-ray
data with the expected synchrotron spectrum. A gray extinction law can be
provided by a dust grain size distribution biased toward large grains.Comment: 6 pages, 5 figures, accepted for publication on A&
Photometry of the Oort Cloud comet C/2009 P1(Garradd): pre-perihelion observations at 5.7 and 2.5 AU
The aim of this paper is to contribute to the characterization of the general properties of the Long Period Comets (LPCs) family, and in particular to report on the dust environment of comet C/2009 P1 (Garradd).
The comet was observed at two epochs pre-perihelion, at ~6 AU and at ~2.5 AU: broad-band images have been used to investigate its coma morphology and properties and to model the dust production rate.
Comet C/2009 P1 (Garradd) is one of the most active and âdust producingâ LPCs ever observed, even at the large heliocentric distance rh~6 AU. Its coma presents a complex morphology, with subtle structures underlying the classical fan-shaped tail, and, at rh~2.5 AU, also jet-like structures and spiralling outflows. In the reference aperture of radius Ï=5°Ă104 km, the R-AfÏ is 3693±156 cm and 6368±412 cm, in August 2010 (rh~6 AU) and July 2011 (rh~2.5 AU), respectively. The application of a first order photometric model, under realistic assumptions on grain geometric albedo, power-law dust size distribution, phase darkening function and grain dust outflow velocity, yielded a measure of the dust production rate for the two epochs of observation of Qd=7.27Ă102 kg/s and Qd=1.37Ă103 kg/s, respectively, for a reference outflow dust velocity of vsmall=25 m/s for small (0.1â10 ”m) grains and vlarge=1 m/s for large (10 ”mâ1 cm) grains.
These results suggest that comet Garradd is one of the most active minor bodies observed in recent years, highly contributing to the continuous replenishment of the Interplanetary Dust Complex also in the outer Solar System, and pose important constraints on the mechanism(s) driving the cometary activity at large heliocentric distances
Probing black hole accretion in quasar pairs at high redshift
Models and observations suggest that luminous quasar activity is triggered by
mergers, so it should preferentially occur in the most massive primordial dark
matter haloes, where the frequency of mergers is expected to be the highest.
Since the importance of galaxy mergers increases with redshift, we identify the
high-redshift Universe as the ideal laboratory for studying dual AGN. Here we
present the X-ray properties of two systems of dual quasars at z=3.0-3.3
selected from the SDSS-DR6 at separations of 6-8 arcsec (43-65kpc) and observed
by Chandra for 65ks each. Both members of each pair are detected with good
photon statistics to allow us to constrain the column density, spectral slope
and intrinsic X-ray luminosity. We also include a recently discovered dual
quasar at z=5 (separation of 21 arcsec, 136kpc) for which XMM-Newton archival
data allow us to detect the two components separately. Using optical spectra we
derived bolometric luminosities, BH masses and Eddington ratios that were
compared to those of luminous SDSS quasars in the same redshift ranges. We find
that the brighter component of both pairs at z=3.0-3.3 has high luminosities
compared to the distribution of SDSS quasars at similar redshift, with J1622A
having an order magnitude higher luminosity than the median. This source lies
at the luminous end of the z~3.3 quasar luminosity function. While we cannot
conclusively state that the unusually high luminosities of our sources are
related to their having a close companion, for J1622A there is only a 3%
probability that it is by chance.Comment: MNRAS, in pres
In vitro phenols bioaccessibility and antioxidant activity of goat milk yogurt fortified with Rhus coriaria leaf powder
Goat yogurt samples fortified with 20% (w/v) Rhus coriaria leaf powder were in vitro digested in order to evaluate the total phenolic content (TPC), antioxidant activity (AA), and bioaccessibility of phenolic compounds in the digestate. After digestion, TPC and AA values of the R. coriaria-fortified yogurts increased compared to the undigested yogurts (P < 0.001). In particular, TPC has increased about twice; whereas, AA values have increased about 10 and 6 times, for ABTS and FRAP assays, respectively. The bioaccessibility index was well above the 100% for all identified phenols; except for (-)-epicatechin (82.04%), rutin (51.51%), and gallic acid (5.42%). This different behavior highlighted that the bioaccessibility was modulated by both the yogurt-polyphenol complexes and phenol stability under digestion system. These findings can contribute to elucidate the influence of in vitro digestion on antioxidant capacity and polyphenols recovery infortified yogurts, and may help in the design of dairy products with better functional quality. Practical Application: Rhus coriaria L. (Sumac) is a polyphenol-rich Mediterranean plant that may be used as functional ingredient to enrich fermented food such as yogurt. However, in fortified yogurts the evaluation of bioaccessibility, that is, the compounds released from the yogurt and stable in the digestive environment, thus able to exert their biological effects on the gastrointestinal system, is more important than the content of these compounds in the corresponding food. This study highlighted the phenolic content, antioxidant activity, and bioaccessibility of phenolic compounds in goat milk yogurt fortified with R. coriaria leaf powder after simulated gastro-pancreatic digestion
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