244 research outputs found
The Spatial Structure of An Accretion Disk
Based on the microlensing variability of the two-image gravitational lens
HE1104-1805 observed between 0.4 and 8 microns, we have measured the size and
wavelength-dependent structure of the quasar accretion disk. Modeled as a power
law in temperature, T proportional to R^-beta, we measure a B-band (0.13
microns in the rest frame) half-light radius of R_{1/2,B} = 6.7 (+6.2 -3.2) x
10^15 cm (68% CL) and a logarithmic slope of beta=0.61 (+0.21 -0.17) for our
standard model with a logarithmic prior on the disk size. Both the scale and
the slope are consistent with simple thin disk models where beta=3/4 and
R_{1/2,B} = 5.9 x 10^15 cm for a Shakura-Sunyaev disk radiating at the
Eddington limit with 10% efficiency. The observed fluxes favor a slightly
shallower slope, beta=0.55 (+0.03 -0.02), and a significantly smaller size for
beta=3/4.Comment: 5 pages, 4 figures, submitted to Ap
Electronic correlations in vanadium chalcogenides: BaVSe3 versus BaVS3
Albeit structurally and electronically very similar, at low temperature the
quasi-one-dimensional vanadium sulfide BaVS3 shows a metal-to-insulator
transition via the appearance of a charge-density-wave state, while BaVSe3
apparently remains metallic down to zero temperature. This different behavior
upon cooling is studied by means of density functional theory and its
combination with the dynamical mean-field theory and the rotationally-invariant
slave-boson method. We reveal several subtle differences between these
chalcogenides that provide indications for the deviant behavior of BaVSe3 at
low temperature. In this regard, a smaller Hubbard U in line with an increased
relevance of the Hund's exchange J plays a vital role.Comment: 16 pages, 11 figures, published versio
Asymptotic Expansions and Amplification of a Gravitational Lens Near a Fold Caustic
We propose two methods that enable us to obtain approximate solutions of the
lens equation near a fold caustic with an arbitrary degree of accuracy. We
obtain "post-linear" corrections to the well-known formula in the linear
caustic approximation for the total amplification of two critical images of a
point source. In this case, in order to obtain the nontrivial corrections we
had to go beyond the approximation orders earlier used by Keeton et al. and to
take into account the Taylor expansion of the lens equation near caustic up to
the fourth order. Corresponding analytical expressions are derived for the
amplification in cases of the Gaussian and power-law extended source models;
the amplifications depend on three additional fitting parameters. Conditions of
neglecting the correction terms are analysed. The modified formula for the
amplification is applied to the fitting of light curves of the Q2237+0305
gravitational lens system in a vicinity of the high amplification events
(HAEs). We show that the introduction of some "post-linear" corrections reduces
chi^2 by 30% in the case of known HAE on the light curve of image C (1999).
These corrections can be important for a precise comparison of different source
models with regard for observational data. Key words: gravitational lensing:
micro - quasars: individual (Q2237+0305) - gravitational lensing: strong -
methods: analyticalComment: 16 pages, 3 figure
Q2237+0305 in X-rays: spectra and variability with XMM-Newton
X-ray observations of gravitationally lensed quasars may allow us to probe
the inner structure of the central engine of a quasar. Observations of
Q2237+0305 (Einstein Cross) in X-rays may be used to constrain the inner
structure of the X-ray emitting source. Here we analyze the XMM-Newton
observation of the quasar in the gravitational lens system Q2237+0305 taken
during 2002. Combined spectra of the four images of the quasar in this system
were extracted and modelled with a power-law model. Statistical analysis was
used to test the variability of the total flux. The total X-ray flux from all
the images of this quadruple gravitational lens system is 6 x 10^{-13}
erg/cm2/s in the range 0.2-10 keV, showing no significant X-ray spectral
variability during almost 42 ks of the observation time. Fitting of the cleaned
source spectrum yields a photon power-law index of Gamma=1.82+0.07/-0.08. The
X-ray lightcurves obtained after background subtraction are compatible with the
hypothesis of a stationary flux from the source.Comment: 6 pages, 7 figures, 4 tables, accepted by A&
Assessment of Novel Semen Evaluation Technologies and Breed Comparisons in Yearling Beef Bulls
Objective: The objectives were 1) to evaluate the iSperm, when conducting breeding soundness exams (BSE) on bulls by comparing sperm motility to a technician’s assessment and 2) to evaluate correlations between sperm response to reactive oxygen species (ROS) and functional sperm measurements.
Study Description: Ejaculates were collected via electroejaculation from yearling bulls as part of a BSE. All BSE were conducted by one veterinarian and ejaculates were evaluated by a single technician. Additional sperm motility analysis was conducted with the iSperm analyzer. Ejaculates meeting minimum thresholds for passing a BSE were diluted and sent overnight for flow cytometry evaluation. Data were analyzed using Pearson’s correlation coefficients in SAS.
Results: Both gross and progressive motilities were significantly (r = 0.30; 0.38; P \u3c 0.001) correlated to the technician’s assessment of progressive motility. Percentage of live spermatozoa with positive ROS status was correlated (r = 0.53; P \u3c 0.001) with percentage progressive motility. Percentage of live spermatozoa with negative ROS status was moderately correlated with percentage spermatozoa exhibiting secondary abnormalities (r = 0.33; P = 0.02). Percentage live spermatozoa that had disrupted acrosomes was strongly correlated with percentage live spermatozoa with negative ROS (r = 0.66; P \u3c 0.001) and moderately negatively correlated with percentage live spermatozoa with positive ROS (r = -0.31; P = 0.04). Percentage of live spermatozoa with positive ROS status was correlated (r = 0.58; P \u3c 0.001) with percentage of spermatozoa with active mitochondrial membranes. Percentage of live spermatozoa with positive ROS status was strongly correlated (r = 0.92; P \u3c 0.001) with percentage of live spermatozoa with intact acrosomes.
The Bottom Line: The iSperm can be used to produce semen assessments similar to those of a trained technician and may offer a useful tool for producers to perform on-farm semen analysis. Sperm health and function continue to be related to negative ROS status
The nature and size of the optical continuum source in QSO 2237+0305
From the peak of a gravitational microlensing high-magnification event in the
A component of QSO 2237+0305, which was accurately monitored by the GLITP
collaboration, we derived new information on the nature and size of the optical
V-band and R-band sources in the far quasar. If the microlensing peak is caused
by a microcaustic crossing, we firstly obtained that the standard accretion
disk is a scenario more reliable/feasible than other usual axially symmetric
models. Moreover, the standard scenario fits both the V-band and R-band
observations with reduced chi-square values very close to one. Taking into
account all these results, a standard accretion disk around a supermassive
black hole is a good candidate to be the optical continuum main source in QSO
2237+0305. Secondly, using the standard source model and a robust upper limit
on the transverse galactic velocity, we inferred that 90 per cent of the V-band
and R-band luminosities are emitted from a region with radial size less than
1.2 10^{-2} pc (= 3.7 10^{16} cm, at 2*sigma confidence level).Comment: ApJ, in press (LaTeX, 28 pages, 6 eps figures
Redefining risk research priorities for nanomaterials
Chemical-based risk assessment underpins the current approach to responsible development of nanomaterials (NM). It is now recognised, however, that this process may take decades, leaving decision makers with little support in the near term. Despite this, current and near future research efforts are largely directed at establishing (eco)toxicological and exposure data for NM, and comparatively little research has been undertaken on tools or approaches that may facilitate near-term decisions, some of which we briefly outline in this analysis. We propose a reprioritisation of NM risk research efforts to redress this imbalance, including the development of more adaptive risk governance frameworks, alternative/complementary tools to risk assessment, and health and environment surveillance
Neutron flux and spectrum in the Dresden Felsenkeller underground facility studied by moderated He counters
Ambient neutrons may cause significant background for underground
experiments. Therefore, it is necessary to investigate their flux and energy
spectrum in order to devise a proper shielding. Here, two sets of altogether
ten moderated He neutron counters are used for a detailed study of the
ambient neutron background in tunnel IV of the Felsenkeller facility,
underground below 45 meters of rock in Dresden/Germany. One of the moderators
is lined with lead and thus sensitive to neutrons of energies higher than 10
MeV. For each He counter-moderator assembly, the energy dependent neutron
sensitivity was calculated with the FLUKA code. The count rates of the ten
detectors were then fitted with the MAXED and GRAVEL packages. As a result,
both the neutron energy spectrum from 10 MeV to 300 MeV and the flux
integrated over the same energy range were determined experimentally.
The data show that at a given depth, both the flux and the spectrum vary
significantly depending on local conditions. Energy integrated fluxes of , , and cm
s, respectively, are measured for three sites within Felsenkeller tunnel
IV which have similar muon flux but different shielding wall configurations.
The integrated neutron flux data and the obtained spectra for the three sites
are matched reasonably well by FLUKA Monte Carlo calculations that are based on
the known muon flux and composition of the measurement room walls.Comment: 10 figures, 4 tables; to be published in Phys. Rev.
Long-term evolution of the neutron rate at the Canfranc Underground Laboratory
We report results on the long-term variation of the neutron counting rate at
the Canfranc Underground Laboratory, of importance for several low-background
experiments installed there, including rare-event searches. The measurement
campaign was performed employing the High Efficiency Neutron Spectrometry Array
(HENSA) mounted in Hall A and lasted 412 live days. The present study is the
first long-term measurement of the neutron rate with sensitivity over a wide
range of neutron energies (from thermal up to 0.1 GeV and beyond) performed in
any underground laboratory so far. Data on the environmental variables inside
the experimental hall (radon concentration, air temperature, air pressure and
humidity) were also acquired during all the measurement campaign. We have
investigated for the first time the evolution of the neutron rate for different
energies of the neutrons and its correlation with the ambient variables.Comment: 12 pages, 5 figures, 2 table
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