11,370 research outputs found
Inversion of polarimetric data from eclipsing binaries
We describe a method for determining the limb polarization and limb darkening
of stars in eclipsing binary systems, by inverting photometric and polarimetric
light curves.
Because of the ill-conditioning of the problem, we use the Backus-Gilbert
method to control the resolution and stability of the recovered solution, and
to make quantitative estimates of the maximum accuracy possible. Using this
method we confirm that the limb polarization can indeed be recovered, and
demonstrate this with simulated data, thus determining the level of
observational accuracy required to achieve a given accuracy of reconstruction.
This allows us to set out an optimal observational strategy, and to critcally
assess the claimed detection of limb polarization in the Algol system.
The use of polarization in stars has been proposed as a diagnostic tool in
microlensing surveys by Simmons et al. (1995), and we discuss the extension of
this work to the case of microlensing of extended sources.Comment: 10pp, 5 figures. To appear in A&
Polarimetric variations of binary stars. II. Numerical simulations for circular and eccentric binaries in Mie scattering envelopes
We present numerical simulations of the periodic polarimetric variations
produced by a binary star placed at the center of an empty spherical cavity
inside a circumbinary ellipsoidal and optically thin envelope made of dust
grains. Mie single-scattering is considered along with pre- and post-scattering
extinction factors which produce a time-varying optical depth and affect the
morphology of the periodic variations. We are interested in the effects that
various parameters will have on the average polarization, the amplitude of the
polarimetric variations, and the morphology of the variability. We show that
the absolute amplitudes of the variations are smaller for Mie scattering than
for Thomson scattering. Among the four grain types that we have studied, the
highest polarizations are produced by grains with sizes in the range 0.1-0.2
micron. In general, the variations are seen twice per orbit. In some cases,
because spherical dust grains have an asymmetric scattering function, the
polarimetric curves produced also show variations seen once per orbit.
Circumstellar disks produce polarimetric variations of greater amplitude than
circumbinary envelopes.
Another goal of these simulations is to see if the 1978 BME (Brown, McLean, &
Emslie, ApJ, 68, 415) formalism, which uses a Fourier analysis of the
polarimetric variations to find the orbital inclination for Thomson-scattering
envelopes, can still be used for Mie scattering. We find that this is the case,
if the amplitude of the variations is sufficient and the true inclinations is
i_true > 45 deg. For eccentric orbits, the first-order coefficients of the
Fourier fit, instead of second-order ones, can be used to find almost all
inclinations.Comment: 23 pages, 5 figures, to be published in Astronomical Journa
Microlensing of Extended Stellar Sources
We investigate the feasibility of reconstructing the radial intensity profile
of extended stellar sources by inverting their microlensed light curves. Using
a simple, linear, limb darkening law as an illustration, we show that the
intensity profile can be accurately determined, at least over the outer part of
the stellar disc, with realistic light curve sampling and photometric errors.
The principal requirement is that the impact parameter of the lens be less than
or equal to the stellar radius. Thus, the analysis of microlensing events
provides a powerful method for testing stellar atmosphere models.Comment: 4 pages LaTeX, to appear in New Astronomy Reviews - proceedings of
the Oxford Workshop `Gravitational Lensing: Nature's Own Weighing Scales'.
Uses elsart.cls. Paper also available at
ftp://info.astro.gla.ac.uk/pub/martin/extended.p
Minimum target prices for production of direct acting antivirals and associated diagnostics to combat Hepatitis C Virus
Combinations of direct-acting antivirals (DAAs) can cure hepatitis C virus (HCV) in the majority of treatment-naïve patients. Mass treatment programs to cure HCV in developing countries are only feasible if the costs of treatment and laboratory diagnostics are very low. This analysis aimed to estimate minimum costs of DAA treatment and associated diagnostic monitoring. Clinical trials of HCV DAAs were reviewed to identify combinations with consistently high rates of sustained virological response across hepatitis C genotypes. For each DAA, molecular structures, doses, treatment duration, and components of retrosynthesis were used to estimate costs of large-scale, generic production. Manufacturing costs per gram of DAA were based upon treating at least 5 million patients per year and a 40% margin for formulation. Costs of diagnostic support were estimated based on published minimum prices of genotyping, HCV antigen tests plus full blood count/clinical chemistry tests. Predicted minimum costs for 12-week courses of combination DAAs with the most consistent efficacy results were: US152 for sofosbuvir+ribavirin; US115 for MK-8742+MK-5172. Diagnostic testing costs were estimated at US34 for two HCV antigen tests and US171-360 per person without genotyping or US$261-450 per person with genotyping. These cost estimates assume that existing large-scale treatment programs can be established. (Hepatology 2015;61:1174–1182
The establishment, maintenance, and use of statistical monitoring programmes for artisanal fisheries: the case of Bermuda
Terahertz photoconductivity and plasmon modes in double-quantum-well field-effect transistors
Double-quantum-well field-effect transistors with a grating gate exhibit a sharply resonant, voltage tuned terahertz photoconductivity. The voltage tuned resonance is determined by the plasma oscillations of the composite structure. The resonant photoconductivity requires a double-quantum well but the mechanism whereby plasma oscillations produce changes in device conductance is not understood. The phenomenon is potentially important for fast, tunable terahertz detectors
Broken particle-hole symmetry at atomically flat a-axis YBa2Cu3O7-d interfaces
We have studied quasiparticle tunneling into atomically flat a-axis films of
YBa2Cu3O7-d and DyBa2Cu3O7-d through epitaxial CaTiO3 barriers. The junction
heterostructures were grown by oxide molecular beam epitaxy and were carefully
optimized using in-situ monitoring techniques, resulting in unprecedented
crystalline perfection of the superconductor/insulator interface. Below Tc, the
tunneling conductance shows the evolution of a large unexpected asymmetrical
feature near zero bias. This is evidence that superconducting YBCO crystals,
atomically truncated along the lobe direction with a titanate layer, have
intrinsically broken particle-hole symmetry over macroscopically large areas.Comment: 15 pages, 4 figures; v2 includes minor changes in concluding
paragraph to match PRL versio
Dual Benefits of a Student-Assisted Interprofessional Men’s Healthy Lifestyle Pilot Program
Reprinted by permission of SAGE PublicationsMen are less willing to seek health professional advice than women and die more often than women from preventable causes. Therefore, it is important to increase male engagement with health initiatives. This study reports the outcomes of a student-assisted, interprofessional, 12-week health program for overweight adult males. The program included weekly health education and structured, supervised group exercise sessions. Thirteen males (participants) and 18 university students (session facilitators) completed the program. Participants were assessed for a range of health and physical activity measures and health and health profession knowledge. Participants demonstrated significant improvement in activity, knowledge, and perceptions of physical and mental function, and appreciated the guided, group sessions. Students completed an interprofessional readiness questionnaire and reported significant improvement in the understanding of the benefits of interprofessional education and of their role in health care. This program provides evidence of the dual benefit that occurs from the delivery of a student-assisted, interprofessional men’s health program to at-risk community members
Identifying single electron charge sensor events using wavelet edge detection
The operation of solid-state qubits often relies on single-shot readout using
a nanoelectronic charge sensor, and the detection of events in a noisy sensor
signal is crucial for high fidelity readout of such qubits. The most common
detection scheme, comparing the signal to a threshold value, is accurate at low
noise levels but is not robust to low-frequency noise and signal drift. We
describe an alternative method for identifying charge sensor events using
wavelet edge detection. The technique is convenient to use and we show that,
with realistic signals and a single tunable parameter, wavelet detection can
outperform thresholding and is significantly more tolerant to 1/f and
low-frequency noise.Comment: 11 pages, 4 figure
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