307 research outputs found
Accretion physics of AM Herculis binaries, I. Results from one-dimensional stationary radiation hydrodynamics
We have solved the one-dimensional stationary two-fluid hydrodynamic
equations for post-shock flows on accreting magnetic white dwarfs simultaneous
with the fully frequency and angle-dependent radiative transfer for cyclotron
radiation and bremsstrahlung. Magnetic field strengths B = 10 to 100 MG are
considered. At given B, this theory relates the properties of the emission
region to a single physical parameter, the mass flow density (or accretion rate
per unit area). We present the normalized temperature profiles and fit formulae
for the peak electron temperature, the geometrical shock height, and the column
density of the post-shock flow. The results apply to pillbox-shaped emission
regions. With a first-order temperature correction they can also be used for
narrower columns provided they are not too tall.Comment: 10 pages with 10 Postscript figures, accepted for publication in
Astronomy & Astrophysics. The source file contains Table 1a/b in ASCII forma
System and market failures: the unavailability of magnesium sulphate for the treatment of eclampsia and pre-eclampsia in Mozambique and Zimbabwe.
Low cost and effective drugs, such as magnesium sulphate, need to be included in initiatives to improve access to essential medicines in Afric
Factors associated with access to HIV care and treatment in a prevention of mother to child transmission programme in urban Zimbabwe
<p>Abstract</p> <p>Background</p> <p>This cross-sectional study assessed factors affecting access to antiretroviral therapy (ART) among HIV-positive women from the prevention of mother to child transmission HIV programme in Chitungwiza, Zimbabwe.</p> <p>Methods</p> <p>Data were collected between June and August 2008. HIV-positive women attending antenatal clinics who had been referred to the national ART programme from January 2006 until December 2007 were surveyed. The questionnaire collected socio-demographic data, treatment-seeking behaviours, and positive or negative factors that affect access to HIV care and treatment.</p> <p>Results</p> <p>Of the 147 HIV-positive women interviewed, 95 (65%) had registered with the ART programme. However, documentation of the referral was noted in only 23 (16%) of cases. Of the 95 registered women, 35 (37%) were receiving ART; 17 (18%) had not undergone CD4 testing. Multivariate analysis revealed that participants who understood the referral process were three times more likely to access HIV care and treatment (OR = 3.21, 95% CI 1.89-11.65) and participants enrolled in an HIV support group were twice as likely to access care and treatment (OR = 2.34, 95% CI 1.13-4.88). Those living with a male partner were 60% less likely to access care and treatment (OR = 0.40, 95% CI 0.16-0.99). Participants who accessed HIV care and treatment faced several challenges, including long waiting times (46%), unreliable access to laboratory testing (35%) and high transport costs (12%). Of the 147 clients surveyed, 52 (35%) women did not access HIV care and treatment. Barriers included perceived long queues (50%), competing life priorities, such as seeking food or shelter (33%) and inadequate referral information (15%).</p> <p>Conclusions</p> <p>Despite many challenges, the majority of participants accessed HIV care. Development of referral tools and decentralization of CD4 testing to clinics will improve access to ART. Psychosocial support can be a successful entry point to encourage client referral to care and treatment programmes.</p
EUVE J0425.6-5714: A Newly Discovered AM Herculis Star
We detected a new AM Her star serendipitously in a 25 day observation with
the EUVE satellite. A coherent period of 85.82 min is present in the EUVE Deep
Survey imager light curve of this source. A spectroscopic identification is
made with a 19th magnitude blue star that has H and He emission lines, and
broad cyclotron humps typical of a magnetic cataclysmic variable. A lower limit
to the polar magnetic field of 46 MG is estimated from the spacing of the
cyclotron harmonics. EUVE J0425.6-5714 is also detected in archival ROSAT HRI
observations spanning two months, and its stable and highly structured light
curve permits us to fit a coherent ephemeris linking the ROSAT and EUVE data
over a 1.3 yr gap. The derived period is 85.82107 +/- 0.00020 min, and the
ephemeris should be accurate to 0.1 cycles until the year 2005. A narrow but
partial X-ray eclipse suggests that this object belongs to the group of Am Her
stars whose viewing geometry is such that the accretion stream periodically
occults the soft X-ray emitting accretion spot on the surface of the white
dwarf. A non-detection of hard X-rays from ASCA observations that are
contemporaneous with the ROSAT HRI shows that the soft X-rays must dominate by
at least an order of magnitude, which is consistent with a known trend among AM
Her stars with large magnetic field. This object should not be confused with
the Seyfert galaxy 1H 0419-577 (= LB 1727), another X-ray/EUV source which lies
only 4' away, and was the principal target of these monitoring observations.Comment: 13 pages, 5 figures, to appear in PASP, Dec. 1998 issu
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Nuclear resonance tomography with a toroid cavity detector
A toroid cavity detection system for determining the spectral properties and distance from a fixed point for a sample using Nuclear Magnetic Resonance. The detection system consists of a toroid with a central conductor oriented along the main axis of the toroidal cylinder and perpendicular to a static uniform magnetic field oriented along the main axis of the toroid. An rf signal is inputted to the central conductor to produce a magnetic field perpendicular to the central axis of the toroid and whose field strength varies as the inverse of the radius of the toroid. The toroid cavity detection system can be used to encapsulate a sample, or the detection system can be perforated to allow a sample to flow into the detection device or to place the samples in specified sample tubes. The central conductor can also be coated to determine the spectral property of the coating and the coating thickness. The sample is then subjected to the respective magnetic fields and the responses measured to determine the desired properties
Hypothalamus proteomics from mouse models with obesity and anorexia reveals therapeutic targets of appetite regulation
Objective: This study examined the proteomic profile of the hypothalamus in mice exposed to a high-fat diet (HFD) or with the anorexia of acute illness. This comparison could provide insight on the effects of these two opposite states of energy balance on appetite regulation.Methods: Four to six-week-old male C56BL/6J mice were fed a normal (control 1 group; n=7) or a HFD (HFD group; n=10) for 8 weeks. The control 2 (n=7) and lipopolysaccharide (LPS) groups (n=10) were fed a normal diet for 8 weeks before receiving an injection of saline and LPS, respectively. Hypothalamic regions were analysed using a quantitative proteomics method based on a combination of techniques including iTRAQ stable isotope labeling, orthogonal two-dimensional liquid chromatography hyphenated with nanospray ionization and high-resolution mass spectrometry. Key proteins were validated with quantitative PCR.Results: Quantitative proteomics of the hypothalamous regions profiled a total of 9249 protein groups (q<0.05). Of these, 7718 protein groups were profiled with a minimum of two unique peptides for each. Hierachical clustering of the differentiated proteome revealed distinct proteomic signatures for the hypothalamus under the HFD and LPS nutritional conditions. Literature research with in silico bioinformatics interpretation of the differentiated proteome identified key biological relevant proteins and implicated pathways. Furthermore, the study identified potential pharmacologic targets. In the LPS groups, the anorexigen pro-opiomelanocortin was downregulated. In mice with obesity, nuclear factor-?B, glycine receptor subunit alpha-4 (GlyR) and neuropeptide Y levels were elevated, whereas serotonin receptor 1B levels decreased.Conclusions: High-precision quantitative proteomics revealed that under acute systemic inflammation in the hypothalamus as a response to LPS, homeostatic mechanisms mediating loss of appetite take effect. Conversely, under chronic inflammation in the hypothalamus as a response to HFD, mechanisms mediating a sustained âperpetual cycleâ of appetite enhancement were observed. The GlyR protein may constitute a novel treatment target for the reduction of central orexigenic signals in obesity
New Low Accretion-Rate Magnetic Binary Systems and their Significance for the Evolution of Cataclysmic Variables
Discoveries of two new white dwarf plus M star binaries with striking optical
cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to
six the total number of X-ray faint, magnetic accretion binaries that accrete
at rates < 10^{-13} Msun/yr, or <1% of the values normally encountered in
cataclysmic variables. This fact, coupled with donor stars that underfill their
Roche lobes and very cool white dwarfs, brand the binaries as post
common-envelope systems whose orbits have not yet decayed to the point of
Roche-lobe contact. They are pre-magnetic CVs, or pre-Polars. The systems
exhibit spin/orbit synchronism and apparently accrete by efficient capture of
the stellar wind from the secondary star, a process that has been dubbed a
``magnetic siphon''. Because of this, period evolution of the binaries will
occur solely by gravitational radiation, which is very slow for periods >3 hr.
Optical surveys for the cyclotron harmonics appear to be the only means of
discovery, so the space density of pre-Polars could rival that of Polars, and
the binaries provide an important channel of progenitors (in addition to the
asynchronous Intermediate Polars). Both physical and SDSS observational
selection effects are identified that may help to explain the clumping of all
six systems in a narrow range of magnetic field strength around 60 MG.Comment: 25 pages, 13 figures, Accepted to Ap
GALEX, Optical and IR Light Curves of MQ Dra: UV Excesses at Low Accretion Rates
Ultraviolet light curves constructed from NUV and FUV detectors on GALEX
reveal large amplitude variations during the orbital period of the Low
Accretion Rate Polar MQ Dra (SDSSJ1553+55). This unexpected variation from a UV
source is similar to that seen and discussed in the Polar EF Eri during its low
state of accretion, even though the accretion rate in MQ Dra is an order of
magnitude lower than even the low state of EF Eri. The similarity in phasing of
the UV and optical light curves in MQ Dra imply a similar location for the
source of light. We explore the possibilities of hot spots and cyclotron
emission with simple models fit to the UV, optical and IR light curves of MQ
Dra. To match the GALEX light curves with a single temperature circular hot
spot requires different sizes of spots for the NUV and FUV, while a cyclotron
model that can produce the optical harmonics with a magnetic field near 60 MG
requires multipoles with fields > 200 MG to match the UV fluxes.Comment: accepted for ApJ; 15 pages, 7 tables, 8 fig
The Cyclotron Fundamental Exposed in the High-Field Magnetic Variable V884 Her
High-quality phase-resolved optical spectropolarimetry is presented for the
magnetic cataclysmic variable V884 Her. The overall circular polarization
during active accretion states is low and only slightly variable in the range
5000-8000A. However, the polarization is highly structured with wavelength,
showing very broad polarization humps, narrow features that are associated with
weak absorption lines in the total spectral flux, and sharp reversals across
each major emission line. The polarization reversals arise from Zeeman
splitting in the funnel gas in a longitudinal magnetic field B~30kG. The set of
narrow, polarized absorption features matches the Zeeman pattern of hydrogen
for a nearly uniform magnetic field of B=150MG, indicating that the features
are "halo" absorption lines formed in a relatively cool reversing layer above
the shock. With this identification, the broad polarization humps centered near
7150A and below 4000A are assigned to cyclotron emission from the fundamental
and first harmonic (n=2), respectively. V884 Her is only the second AM Her
system known with a field exceeding 100MG, and the first case in which the
cyclotron fundamental has been directly observed from a magnetic white dwarf.Comment: 14 pages, 6 figures, LaTeX, to appear in The Astrophysical Journal,
Part
A Detection of an Anti-correlated Hard X-ray Lag in AM Herculis
Context {Earlier cross-correlation studies for AM Her were performed in
various energy range from optical to X-ray and suggested that it mostly shows a
high level of correlation but on occasion it shows a low level of correlation
or uncorrelation.} Aims {To investigate the degree of correlation between soft
(2-4 keV) and hard (9-20 keV) X-rays, we perform the cross-correlation study of
the X-ray data sets of AM Her obtained with {\it RXTE}.}
Methods {We cross-correlate the background-subtracted soft and hard X-ray
light curves using the XRONOS program crosscor and fit a model to the obtained
cross-correlation functions.}
Results {We detect a hard X-ray lag of s in a specific section of
energy-dependent light curve, where the soft X-ray (2-4 keV) intensity
decreases but the hard X-ray (9-20 keV) intensity increases. From a spectral
analysis, we find that the X-ray emission temperature increases during the
anti-correlated intensity variation. In two other observations, the
cross-correlation functions show a low level of correlation, which is
consistent with the earlier results performed in a different energy range.}
Conclusions {We report a detection of an anti-correlated hard X-ray lag of
190 s from the proto-type polar AM Her. The hard X-ray lag is detected
for the first time in the given energy range, and it is the longest lag among
those reported in magnetic cataclysmic variables. We discuss the implications
of our findings regarding the origin of the hard X-ray lag and the
anti-correlated intensity variation.}Comment: Accepted in A&A, 4 page
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