122 research outputs found
Spectroscopy of Infrared Flares from the Microquasar GRS 1915+105
We present near-infrared medium-resolution () spectra of the
microquasar GRS 1915+105 on 1997 August 13-15 UTC from the Hale 200-inch
telescope. The spectra showed broad emission lines of He I (2.058 m) and H
I (2.166 m - Br), consistent with previous work. On August 14 UTC,
we took spectra with -minute time resolution during infrared flaring
events similar to those reported in Eikenberry et al. (1998a), which appear to
reveal plasma ejection from the system. During the flares, the emission line
fluxes varied in approximately linear proportionality to the IR continuum flux,
implying that the lines are radiatively pumped by the flares. We also detected
a weak He II (2.189 m) emission line on August 14 UTC. The nature of the
line variability and the presence of the He II feature indicate that the
emission lines in GRS 1915+105 arise in an accretion disk around the compact
object, rather than in the circumstellar disk of a proposed Oe/Be companion.
The radiative line pumping also implies that the flare emission originates from
ejecta which have moved out of the accretion disk plane.Comment: 13 pages plus 4 figures, to appear in ApJ Letter
The origin of intergalactic thermonuclear supernovae
The population synthesis method is used to study the possibility of
explaining the appreciable fraction (20^+12_15%) of the intergalactic (no-host)
type Ia supernovae observed in galaxy clusters (Gal-Yam ete al. 2003) by binary
whote dwarf merginngs in the cores of globular clusters. In a typical globular
cluster, the number of merging double white dwarfs is fount to be smaller than
10^{-13} per year per average cluster star during the entire evolution of the
cluster, which is a factor of 3 higher than in a Milky-Way-type galaxy. From 5
to 30% of the merging white dwarfs are dynamically expelled from the cluster
with barycenter velocities up to 150 km/s. SN Ia explosions during the mergers
of binary white dwarfs in dense star clusters may account for \sim 1% of the
total rate of SN Ia in the central parts of galaxy clusters if the baryon mass
fraction in such star clusters is \sim 0.3%.Comment: 8 pages, 3 figs. Astronomy Letters (in press
Neighbourhood, Route and Workplace-Related Environmental Characteristics Predict Adults' Mode of Travel to Work
Commuting provides opportunities for regular physical activity which can reduce the risk of chronic disease. Commuters' mode of travel may be shaped by their environment, but understanding of which specific environmental characteristics are most important and might form targets for intervention is limited. This study investigated associations between mode choice and a range of objectively assessed environmental characteristics.Participants in the Commuting and Health in Cambridge study reported where they lived and worked, their usual mode of travel to work and a variety of socio-demographic characteristics. Using geographic information system (GIS) software, 30 exposure variables were produced capturing characteristics of areas around participants' homes and workplaces and their shortest modelled routes to work. Associations between usual mode of travel to work and personal and environmental characteristics were investigated using multinomial logistic regression.Of the 1124 respondents, 50% reported cycling or walking as their usual mode of travel to work. In adjusted analyses, home-work distance was strongly associated with mode choice, particularly for walking. Lower odds of walking or cycling rather than driving were associated with a less frequent bus service (highest versus lowest tertile: walking OR 0.61 [95% CI 0.20–1.85]; cycling OR 0.43 [95% CI 0.23–0.83]), low street connectivity (OR 0.22, [0.07–0.67]; OR 0.48 [0.26–0.90]) and free car parking at work (OR 0.24 [0.10–0.59]; OR 0.55 [0.32–0.95]). Participants were less likely to cycle if they had access to fewer destinations (leisure facilities, shops and schools) close to work (OR 0.36 [0.21–0.62]) and a railway station further from home (OR 0.53 [0.30–0.93]). Covariates strongly predicted travel mode (pseudo r-squared 0.74).Potentially modifiable environmental characteristics, including workplace car parking, street connectivity and access to public transport, are associated with travel mode choice, and could be addressed as part of transport policy and infrastructural interventions to promote active commuting
A Dual-Beam Irradiation Facility for a Novel Hybrid Cancer Therapy
In this paper we present the main ideas and discuss both the feasibility and
the conceptual design of a novel hybrid technique and equipment for an
experimental cancer therapy based on the simultaneous and/or sequential
application of two beams, namely a beam of neutrons and a CW (continuous wave)
or intermittent sub-terahertz wave beam produced by a gyrotron for treatment of
cancerous tumors. The main simulation tools for the development of the computer
aided design (CAD) of the prospective experimental facility for clinical trials
and study of such new medical technology are briefly reviewed. Some tasks for a
further continuation of this feasibility analysis are formulated as well.Comment: 18 pages, 3 tables, 8 figures, 50 reference
The Long-Term Variability of the X-Ray Sources in NGC 6946 and NGC 4485/4490
We analyze data from five Chandra observations of the spiral galaxy NGC 6946
and from three Chandra observations of the irregular/spiral interacting galaxy
pair NGC 4485/4490, with an emphasis on investigating the long-term variability
exhibited by the source populations. We detect 90 point sources coincident with
NGC 6946 down to luminosities of a few times 10^36 erg/s, and 38 sources
coincident with NGC 4485/90 down to a luminosity of ~1x10^37 erg/s. Twenty-five
(15) sources in NGC 6946 (NGC 4485/90) exhibit long-term (i.e., weeks to years)
variability in luminosity; 11 (4) are transient candidates. The single
ultraluminous X-ray source (ULX) in NGC 6946 and all but one of the eight ULXs
in NGC 4485/90 exhibit long-term flux variability. Two of the ULXs in NGC
4485/90 have not been identified before as ultraluminous sources. The
widespread variability in both systems is indicative of the populations being
dominated by X-ray binaries, and this is supported by the X-ray colors of the
sources. The distribution of colors among the sources indicates a large
fraction of high-mass X-ray binaries in both systems. The shapes of the X-ray
luminosity functions of the galaxies do not change significantly between
observations and can be described by power laws with cumulative slopes ~0.6-0.7
(NGC 6946) and ~0.4 (NGC 4485/90).Comment: 26 pages, 9 figures, 15 tables - to appear in the August 2008 issue
of ApJS - new version corrects a few typo
ASASSN-18am/SN 2018gk : An overluminous Type IIb supernova from a massive progenitor
ASASSN-18am/SN 2018gk is a newly discovered member of the rare group of
luminous, hydrogen-rich supernovae (SNe) with a peak absolute magnitude of mag that is in between normal core-collapse SNe and superluminous
SNe. These SNe show no prominent spectroscopic signatures of ejecta interacting
with circumstellar material (CSM), and their powering mechanism is debated.
ASASSN-18am declines extremely rapidly for a Type II SN, with a
photospheric-phase decline rate of . Owing to the
weakening of HI and the appearance of HeI in its later phases, ASASSN-18am is
spectroscopically a Type IIb SN with a partially stripped envelope. However,
its photometric and spectroscopic evolution show significant differences from
typical SNe IIb. Using a radiative diffusion model, we find that the light
curve requires a high synthesised mass and ejecta with high kinetic energy erg. Introducing a magnetar central engine still requires
and erg. The high
mass is consistent with strong iron-group nebular lines in its
spectra, which are also similar to several SNe Ic-BL with high
yields. The earliest spectrum shows "flash ionisation" features, from which we
estimate a mass-loss rate of . This wind density is too low to power the luminous light
curve by ejecta-CSM interaction. We measure expansion velocities as high as km/s for , which is remarkably high compared to other SNe
II. We estimate an oxygen core mass of using the [OI]
luminosity measured from a nebular-phase spectrum, implying a progenitor with a
zero-age main sequence mass of
Urban Biodiversity, City-Dwellers and Conservation: How Does an Outdoor Activity Day Affect the Human-Nature Relationship?
Urban conservation education programs aim to increase knowledge and awareness towards biodiversity and to change attitudes and behaviour towards the environment. However, to date, few urban conservation education studies have evaluated to what extent these programs have managed to achieve their goals. In this study, we experimentally explored the influence of an urban conservation activity day on individual knowledge, awareness and actions towards biodiversity, in both the short and longer term
Search for copy number variants in chromosomes 15q11-q13 and 22q11.2 in obsessive compulsive disorder
<p>Abstract</p> <p>Background</p> <p>Obsessive-compulsive disorder (OCD) is a clinically and etiologically heterogeneous syndrome. The high frequency of obsessive-compulsive symptoms reported in subjects with the 22q11.2 deletion syndrome (DiGeorge/velocardiofacial syndrome) or Prader-Willi syndrome (15q11-13 deletion of the paternally derived chromosome), suggests that gene dosage effects in these chromosomal regions could increase risk for OCD. Therefore, the aim of this study was to search for microrearrangements in these two regions in OCD patients.</p> <p>Methods</p> <p>We screened the 15q11-13 and 22q11.2 chromosomal regions for genomic imbalances in 236 patients with OCD using multiplex ligation-dependent probe amplification (MLPA).</p> <p>Results</p> <p>No deletions or duplications involving 15q11-13 or 22q11.2 were identified in our patients.</p> <p>Conclusions</p> <p>Our results suggest that deletions/duplications of chromosomes 15q11-13 and 22q11.2 are rare in OCD. Despite the negative findings in these two regions, the search for copy number variants in OCD using genome-wide array-based methods is a highly promising approach to identify genes of etiologic importance in the development of OCD.</p
Neutron stars in globular clusters: formation and observational manifestations
Population synthesis is used to model the number of neutron stars in globular
clusters that are observed as LMXBs and millisecond PSRs. The dynamical
interaction between binary and single stars in a GC are assumed to take place
with a permanently replenished "background" of single stars whose density
distribution keeps track with the cluster evolution as a whole and evolution of
single stars. We use the hypothesis (Podsiadlowski et al) that NS forming in
binary systems from components with initial masses \sim 8-12 M_\odot during the
electron-capture collapse of the degenerate O-Ne-Mg core do not acquire a high
space velocities (kicks). The remaining NSs (i.e. from single stars with M>8
M_\odot or binary comonents with M>12 M_\odot) are assumed to be born with high
kicks, as found from obsrevations of single pulsars (Hobbs et al. 2005). Under
this assumption, a sizeable fraction of NSs remain in GCs (about 1000 NSs in a
GC with a mass of 5\times 10^5 M_\odot). The number of ms PSRs formed in the
cluster via accretion spin-up in binaries is then about 10, which is consistent
with observations. Our modelling reproduces the observed shape of the X-ray
luminosity function for accreting NSs in binaries with normal and degenerate
components and the distribution of spin periods of ms PSRs in GCs under the
assumption of accretion-driven magnetic field decay of NSs up to a bottom value
of 10^8 G. The number of LMXBs and ms PSRs dynamically expelling from GCs is
also calculated.Comment: LATEX, 21 pages, 8 gif figures, Astronomy Letters, in pres
Patient-provider interaction from the perspectives of type 2 diabetes patients in Muscat, Oman: a qualitative study
<p>Abstract</p> <p>Background</p> <p>Patients' expectations and perceptions of the medical encounter and interactions are important tools in diabetes management. Some problems regarding the interaction during encounters may be related to a lack of communication skills on the part of either the physician or the patient.</p> <p>This study aimed at exploring the perceptions of type 2 diabetes patients regarding the medical encounters and quality of interactions with their primary health-care providers.</p> <p>Methods</p> <p>Four focus group discussions (two women and two men groups) were conducted among 27 purposively selected patients (13 men and 14 women) from six primary health-care centres in Muscat, Oman. Qualitative content analysis was applied.</p> <p>Results</p> <p>The patients identified some weaknesses regarding the patient-provider communication like: unfriendly welcoming; interrupted consultation privacy; poor attention and eye contact; lack of encouraging the patients to ask questions on the providers' side; and inability to participate in medical dialogue or express concerns on the patients' side. Other barriers and difficulties related to issues of patient-centeredness, organization of diabetes clinics, health education and professional competency regarding diabetes care were also identified.</p> <p>Conclusion</p> <p>The diabetes patients' experiences with the primary health-care providers showed dissatisfaction with the services. We suggest appropriate training for health-care providers with regard to diabetes care and developing of communication skills with emphasis on a patient-centred approach. An efficient use of available resources in diabetes clinics and distributing responsibilities between team members in close collaboration with patients and their families seems necessary. Further exploration of the providers' work situation and barriers to good interaction is needed. Our findings can help the policy makers in Oman, and countries with similar health systems, to improve the quality and organizational efficiency of diabetes care services.</p
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