858 research outputs found
On the Correlated X-ray and Optical Evolution of SS Cygni
We have analyzed the variability and spectral evolution of the prototype
dwarf nova system SS Cygni using RXTE data and AAVSO observations. A series of
pointed RXTE/PCA observations allow us to trace the evolution of the X-ray
spectrum of SS Cygni in unprecedented detail, while 6 years of optical AAVSO
and RXTE/ASM light curves show long-term patterns. Employing a technique in
which we stack the X-ray flux over multiple outbursts, phased according to the
optical light curve, we investigate the outburst morphology. We find that the
3-12 keV X-ray flux is suppressed during optical outbursts, a behavior seen
previously, but only in a handful of cycles. The several outbursts of SS Cygni
observed with the more sensitive RXTE/PCA also show a depression of the X-rays
during optical outburst. We quantify the time lags between the optical and
X-ray outbursts, and the timescales of the X-ray recovery from outburst. The
optical light curve of SS Cygni exhibits brief anomalous outbursts. During
these events the hard X-rays and optical flux increase together. The long-term
data suggest that the X-rays decline between outburst. Our results are in
general agreement with modified disk instability models (DIM), which invoke a
two-component accretion flow consisting of a cool optically thick accretion
disk truncated at an inner radius, and a quasi-spherical hot corona-like flow
extending to the surface of the white dwarf. We discuss our results in the
framework of one such model, involving the evaporation of the inner part of the
optically thick accretion disk, proposed by Meyer & Meyer-Hofmeister (1994).Comment: 24 pages, 8 figures, 2 tables, accepted for publication in Ap
Feasibility of sensor-based technology for monitoring health in developing countries - cost analysis and user perception aspects
Understanding the financial burden of chronic diseases in developing regions still remains an important economical factor which influences the successful implementation of sensor based applications for continuous monitoring of chronic conditions. Our research focused on a comparison of literature-based data with real costs of the management and treatment of chronic diseases in a developing country, and we are using Kosovo as an example here. The results reveal that the actual living costs exceed the minimum expenses that chronic diseases impose. Following the potential of a positive economic impact of sensor based platforms for monitoring chronic conditions, we further examined the users perception of digital technology. The purpose of this paper is to present the varying cost levels of treating chronic diseases, identify the users concerns and requirements towards digital technology and discuss issues and challenges that the application of sensor based platforms imply in low and middle income countries
Extreme Variability in the Be-Type, Periodic Recurrent X-Ray Transient A0538 - 66: A Highly Eccentric Interacting Binary
We present optical spectroscopy and photometry and IUE spectroscopy of the counterpart of the extremely powerful LMC recurrent X-ray transient A0538 â 66. During one 16.6 day outburst cycle at the end of 1980 December the optical spectra show steadily increasing Balmer and He I emission (indicative of an expanding envelope) superposed on a B2 IIIâIV spectrum. There is a substantial optical brightness increase of 2 mag at the peak, accompanied by the sudden turn-on of He IIλ 4686. These and other optical spectra show significant radial velocity changes but we can find no clear correlation with the 16.6 day cycle. Further optical and IUE spectra were obtained at the peak of subsequent outbursts, and these show very strong and broad (⌠5000 km sâ1) emission lines. We interpret the system as a ⌠1 Mâ compact object in a highly eccentric (e ⌠0.7) orbit about the ⌠12 Mâ B star with a binary period equal to the flare period. Continuum measurements indicate that the emitting region at outburst is several times the size of the B star thus implying that at periastron passage the envelope of the primary is tidally expanded by the neutron star. Although this is now the best example of a growing group of recurrent X-ray transients, A0538 â 66 is unique in its optical behaviour and peak Lx when compared with other galactic X-ray transients and shell/Be stars
Disk Diffusion Propagation Model for the Outburst of XTE J1118+480
We present a linear diffusion model for the evolution of the double-peaked
outburst in the transient source XTEJ1118+480. The model treats the two
outbursts as episodic mass deposition at the outer radius of the disk followed
by evolution of disk structure according to a diffusion process. We demonstrate
that light curves with fast-rise, exponential decay profile are a general
consequence of the diffusion process. Deconvolution of the light curve proves
to be feasible and gives an input function specifying mass deposition at the
outer disk edge as well as the total mass of the disk, both as functions of
time. The derived evolution of total disk mass can be correlated with the
observed evolution of the ~0.1 Hz QPO in the source reported in Wood et al.
(2000).Comment: 26 pages, 6 figures, accepted for publication in Ap
Sensor-based platforms for remote management of chronic diseases in developing regions: A qualitative approach examining the perspectives of healthcare professionals
The continuous monitoring of chronic diseases serves as one of the cornerstones in the efforts to improve the quality of life of patients and maintain the healthcare services provided to them. This study aims to provide an in-depth understanding of the perspectives of healthcare professionals on using sensor-based networks (SBN) used for remote and continuous monitoring of patients with chronic illness in Kosovo, a developing country. A qualitative research method was used to interview 26 healthcare professionals. The study results demonstrate the positive attitudes of participants to using SBN, and considers their concerns on the impact of these platforms on the patientâs life, the number of visits in the medical centre, data privacy concerning interactions between patients and their medical personnel and the costs of the platform. Further to that, the study makes an important contribution to knowledge by identifying the challenges and drawbacks of these platforms and provides recommendations for system designers
ORFEUS II and IUE Spectroscopy of EX Hydrae
Using ORFEUS-SPAS II FUV spectra, IUE UV spectra, and archival EUVE deep
survey photometry, we present a detailed picture of the behavior of the
magnetic cataclysmic variable EX Hydrae. Like HUT spectra of this source, the
FUV and UV spectra reveal broad emission lines of He II, C II-IV, N III and V,
O VI, Si III-IV, and Al III superposed on a continuum which is blue in the UV
and nearly flat in the FUV. Like ORFEUS spectra of AM Her, the O VI doublet is
resolved into broad and narrow emission components. Consistent with its
behavior in the optical, the FUV and UV continuum flux densities, the FUV and
UV broad emission line fluxes, and the radial velocity of the O VI broad
emission component all vary on the spin phase of the white dwarf, with the
maximum of the FUV and UV continuum and broad emission line flux light curves
coincident with maximum blueshift of the broad O VI emission component. On the
binary phase, the broad dip in the EUV light curve is accompanied by strong
eclipses of the UV emission lines and by variations in both the flux and radial
velocity of the O VI narrow emission component. The available data are
consistent with the accretion funnel being the source of the FUV and UV
continuum and the O VI broad emission component, and the white dwarf being the
source of the O VI narrow emission component.Comment: 21 pages, 10 Postscript figures; LaTeX format, uses aaspp4.sty;
table2.tex included separately because it must be printed sideways - see
instructions in the file; accepted on 1999 Feb 20 for publication in The
Astrophysical Journa
Sidebands Due to Quasi-periodic Oscillations in 4U 1626-67
The low-mass X-ray binary pulsar 4U 1626-67 shows 0.048 Hz quasi-periodic
oscillations (QPOs) and red noise variability as well as coherent pulsations at
the 0.130 Hz neutron star spin frequency. Power density spectra of observations
made with the Rossi X-ray Timing Explorer show significant sidebands separated
from the pulsar spin frequency (and its harmonics) by the QPO frequency. These
show that the instantaneous amplitude of the coherent pulsations is modulated
by the amplitude of the QPOs. This phenomenon is expected in models such as the
magnetospheric beat frequency model where the QPOs originate near the polar
caps of the neutron star. In the 4--8 keV energy range, however, the
lower-frequency sidebands are significantly stronger than their
higher-frequency complements; this is inconsistent with the magnetospheric beat
frequency model. We suggest that the 0.048 Hz QPOs are instead produced by a
structure orbiting the neutron star at the QPO frequency. This structure
crosses the line of sight once per orbit and attenuates the pulsar beam,
producing the symmetric (amplitude modulation) sidebands. It also reprocesses
the pulsar beam at the beat frequencies between the neutron star spin frequency
and the QPOs, producing the excess variability observed in the lower-frequency
sidebands. Quite independently, we find no evidence that the red noise
variability modulates the amplitude of the coherent pulsations. This is also in
contrast to the expectations of the magnetospheric beat frequency model and
differs from the behavior in some high-mass X-ray binary pulsars.Comment: 8 pages, 3 figures, AAS macros v4.0. To appear in ApJ Letter
The early X-ray emission from V382 Velorum (=Nova Vel 1999): An internal shock model
We present the results of ASCA and RXTE observations of the early X-ray
emission from the classical nova V382 Velorum. Its ASCA spectrum was hard
(kT~10 keV) with a strong (10**23 cm**-2) intrinsic absorption. In the
subsequent RXTE data, the spectra became softer both due to a declining
temperature and a diminishing column. We argue that this places the X-ray
emission interior to the outermost ejecta produced by V382 Vel in 1999, and
therefore must have been the result of a shock internal to the nova ejecta. The
weakness of the Fe K alpha lines probably indicates that the X-ray emitting
plasmas are not in ionization equilibrium.Comment: 16 pages (including 4 figures), accepted for publication in Ap
Attitudes and perceived social norms towards drug use among gay and bisexual men in Australia
Background: Gay and bisexual men (GBM) report distinctive patterns and contexts of drug use, yet little has been published about their attitudes towards drug use.
Objectives: We developed measures of attitudes and perceived social norms towards drug use, and examined covariates of more accepting attitudes and norms among GBM in Australia.
Methods: We analysed baseline data from the [removed for blinded review] study. This is an online prospective observational study of drug use among Australian GBM. We used principal components factor analysis to generate two attitudinal scales assessing âdrug use for social and sexual enhancementâ and âperceptions of drug riskâ. A third perceived social norms scale examined âacceptability of drug use among gay friendsâ.
Results: Among 2,112 participants, 61% reported illicit drug use in the preceding 6 months. Stronger endorsement of drug use for social and sexual engagement and lower perceptions of drug risk were found among men who were more socially engaged with other gay men and reported regular drug use and drug use for sex. In multivariate analyses, all three scales were associated with recent drug use (any use in the previous six months), but only the drug use for social and sexual enhancement scale was associated with regular (at least monthly) use.
Conclusions: Drug use and sex are difficult to disentangle for some GBM, and health services and policies could benefit from a better understanding of attitudinal and normative factors associated with drug use in gay social networks, while recognising the role of pleasure in substance use
General-relativistic constraints on the equation of state of dense matter implied by kilohertz quasi-periodic oscillations in neutron-star X-ray binaries
If the observed millisecond variability in the X-ray flux of several
neutron-star low-mass X-ray binaries (LMXBs) is interpreted within a
general-relativistic framework (Kluzniak, Michelson \& Wagoner 1990) extant at
the time of discovery, severe constraints can be placed on the equation of
state (e.o.s.) of matter at supranuclear densities. The reported maximum
frequency (1.14 +- 0.01 kHz) of quasiperiodic oscillations observed in sources
as diverse as Sco X-1 and 4U 1728-34 would imply that the neutron star masses
in these LMXBs are M > 1.9 M_solar, and hence many equations of state would be
excluded. Among the very few still viable equations of state are the e.o.s. of
Phandaripande and Smith (1975), and e.o.s. AV14 + UVII of Wiringa, Fiks \&
Fabrocini (1988).Comment: The figures can be found in the references cited in the captions. A
longer version of this paper was submitted to a refereed journal on January
6, 1997 (345 days ago
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