The Stellar Winds of Galactic Centre and the Low Accretion Rate of Sgr A*

An attempt is made to reconcile the large wind-loss rates of stars in the Galactic Centre (GC) with the predicted low accretion rate for Sgr A*, the putative blackhole at the heart of the Milky Way. It is found that, independent of the details of the accretion, the bound but unaccreted gas has been accumulating in the potential well of Sgr A* for <1000 yrs and thus is not in equilibrium. Otherwise, the gas flows of the region would be visible in both the IR and X-ray. It appears that the blackhole was more active in the recent past due to the passing of a supernova blast shock but is presently in a short-lived dormant phase. The extended low frequency radio emission from the central parsec should visibily increase over the next few decades, as the shock passes completely in front of the absorbing gas and dust near Sgr A*. The GC may become more active in < 100,000 yrs due to either another supernova or sufficient accumulation of stellar winds in the central arcsecond.Comment: accepted by A&A Letter

Association between risk factors for injurious falls and new benzodiazepine prescribing in elderly persons

<p>Abstract</p> <p>Background</p> <p>Benzodiazepines are frequently prescribed to elderly patients' despite concerns about adverse effects leading to injurious falls. Previous studies have not investigated the extent to which patients with pre-existing risk factors for falls are prescribed benzodiazepines. The objective of this study is to assess if some of the risk factors for falls are associated with new benzodiazepine prescriptions in elderly persons.</p> <p>Methods</p> <p>Using provincial administrative databases, elderly Quebec residents were screened in 1989 for benzodiazepine use and non-users were followed for up to 5 years. Logistic regression models were used to evaluate potential predictors of new benzodiazepine use among patient baseline characteristics.</p> <p>Results</p> <p>In the 252,811 elderly patients who had no benzodiazepine prescription during the baseline year (1989), 174,444 (69%) never filled a benzodiazepine prescription and 78,367 (31%) filled at least one benzodiazepine prescription. In the adjusted analysis, several risk factors for falls were associated with statistically significant increases in the risk of receiving a new benzodiazepine prescription including the number of prescribing physicians seen at baseline (OR: 1.12; 95% CI 1.11–1.13), being female (OR: 1.20; 95% CI 1.18–1.22) or a diagnosis of arthritis (OR: 1.11; 95% CI 1.09–1.14), depression (OR: 1.42; 95% CI 1.35–1.49) or alcohol abuse (OR: 1.24; 95% CI 1.05–1.46). The strongest predictor for starting a benzodiazepine was the use of other medications, particularly anti-depressants (OR: 1.85; 95% CI 1.75–1.95).</p> <p>Conclusion</p> <p>Patients with pre-existing conditions that increase the risk of injurious falls are significantly more likely to receive a new prescription for a benzodiazepine. The strength of the association between previous medication use and new benzodiazepine prescriptions highlights an important medication safety issue.</p

Blueschist from the Mariana forearc records long-lived residence of material in the subduction channel

From ca. 50 Ma to present, the western Pacific plate has been subducting under the Philippine Sea plate, forming the oceanic Izu-Bonin-Mariana (IBM) subduction system. It is the only known location where subduction zone products are presently being transported to the surface by serpentinite-mud volcanoes. A large serpentine mud “volcano” forms the South Chamorro Seamount and was successfully drilled by ODP during Leg 195. This returned mostly partially serpentinized harzburgites enclosed in serpentinite muds. In addition, limited numbers of small (1 mm–1 cm) fragments of rare blueschists were also discovered. U–Pb dating of zircon and rutile from one of these blueschist clasts give ages of 51.1 ± 1.2 Ma and 47.5 ± 2.0 Ma, respectively. These are interpreted to date prograde high-pressure metamorphism. Mineral equilibria modelling of the blueschist clast suggests the mineral assemblage formed at conditions of ∼1.6 GPa and ∼590 °C. We interpret that this high-pressure assemblage formed at a depth of ∼50 km within the subduction channel and was subsequently exhumed and entrained into the South Chamorro serpentinite volcano system at depths of ∼27 km. Consequently, we propose that the material erupted from the South Chamarro Seamount may be sampling far greater depths within the Mariana subduction system than previously thought. The apparent thermal gradient implied by the pressure–temperature modelling (∼370 °C/GPa) is slightly warmer than that predicted by typical subduction channel numerical models and other blueschists worldwide. The age of the blueschist suggests it formed during the arc initiation stages of the proto-Izu-Bonin-Mariana arc, with the P–T conditions recording thermally elevated conditions during initial stages of western Pacific plate subduction. This indicates the blueschist had prolonged residence time in the stable forearc as the system underwent east-directed rollback. The Mariana blueschist shows that subduction products can remain entrained in subduction channels for many millions of years prior to exhumation

Common physical framework explains phase behavior and dynamics of atomic, molecular, and polymeric network formers

We show that the self-assembly of a diverse collection of building blocks can be understood within a common physical framework. These building blocks, which form periodic honeycomb networks and nonperiodic variants thereof, range in size from atoms to micron-scale polymers and interact through mechanisms as different as hydrogen bonds and covalent forces. A combination of statistical mechanics and quantum mechanics shows that one can capture the physics that governs the assembly of these networks by resolving only the geometry and strength of building-block interactions. The resulting framework reproduces a broad range of phenomena seen experimentally, including periodic and nonperiodic networks in thermal equilibrium, and nonperiodic supercooled and glassy networks away from equilibrium. Our results show how simple “design criteria” control the assembly of a wide variety of networks and suggest that kinetic trapping can be a useful way of making functional assemblies

What differentiates primary care physicians who predominantly prescribe diuretics for treating mild to moderate hypertension from those who do not? A comparative qualitative study

<p>Abstract</p> <p>Background</p> <p>Thiazide diuretics are cost-effective for the treatment of mild to moderate hypertension, but physicians often opt for more expensive treatment options such as angiotensin II receptor blockers or angiotensin converting enzyme inhibitors. With escalating health care costs, there is a need to elucidate the factors influencing physicians' treatment choices for this highly prevalent chronic condition. The purpose of this study was to describe the characteristics of physicians' decision-making process regarding hypertension treatment choices.</p> <p>Methods</p> <p>A comparative qualitative study was conducted in 2009 in the Canadian province of Quebec. Overall, 29 primary care physicians--who are also participating in an electronic health record research program--participated in a semi-structured interview about their prescribing decisions. Physicians were categorized into two groups based on their patterns of prescribing antihypertensive drugs: physicians who predominantly prescribe diuretics, and physicians who predominantly prescribe drug classes other than diuretics. Cases of hypertension that were newly started on antihypertensive therapy were purposely selected from each physician's electronic health record database. Chart stimulated recall interview, a technique utilizing patient charts to probe recall and provide context to physician decision-making during clinical encounters, was used to elucidate reasons for treatment choices. Interview transcripts were synthesized using content analysis techniques, and factors influencing physicians' decision making were inductively generated from the data.</p> <p>Results</p> <p>We identified three themes that differentiated physicians who predominantly prescribe diuretics from those who predominantly prescribe other drug classes for the initial treatment of mild to moderate hypertension: a) perceptions about the efficacy of diuretics, b) preferred approach to hypertension management and, c) perceptions about hypertension guidelines. Specifically, physicians had differences in beliefs about the efficacy, safety and tolerability of diuretics, the most effective approach for managing mild to moderate hypertension, and in aggressiveness to achieve treatment targets. Marketing strategies employed by the pharmaceutical industry and practice experience appear to contribute to these differences in management approach.</p> <p>Conclusions</p> <p>Physicians preferring more expensive treatment options appear to have several misperceptions about the efficacy, safety and tolerability of diuretics. Efforts to increase physicians' prescribing of diuretics may need to be directed at overcoming these misperceptions.</p

External-field-induced tricritical point in a fluctuation-driven nematic-smectic-A transition

We study theoretically the effect of an external field on the nematic-smectic-A (NA) transition close to the tricritical point, where fluctuation effects govern the qualitative behavior of the transition. An external field suppresses nematic director fluctuations, by making them massive. For a fluctuation-driven first-order transition, we show that an external field can drive the transition second-order. In an appropriate liquid crystal system, we predict the required magnetic field to be of order 10 T. The equivalent electric field is of order $1 V/\mu m$.Comment: revtex, 4 pages, 1 figure; revised version, some equations have been modifie

The nature of the Galactic Center source IRS 13 revealed by high spatial resolution in the infrared

High spatial resolution observations in the 1 to 3.5 micron region of the Galactic Center source known historically as IRS 13 are presented. They include ground-based adaptive optics images in the H, Kp (2.12/0.4 micron) and L bands, NICMOS data in filters between 1.1 and 2.2 micron, and integral field spectroscopic data from BEAR, an Imaging FTS, in the HeI 2.06 micron and the Br$\gamma$ line regions. Analysis of all these data provides a completely new picture of the main component, IRS 13E, which appears as a cluster of seven individual stars within a projected diameter of ~0.5'' (0.02 pc). The brightest sources, 13E1, 13E2, 13E3 (a binary), and 13E4, are all massive stars, 13E1 a blue object, with no detected emission line while 13E2 and 13E4 are high-mass emission line stars. 13E2 is at the WR stage and 13E4 a massive O-type star. 13E3A and B are extremely red objects, proposed as other examples of dusty WR stars. All these sources have a common westward proper motion. 13E5, is a red source similar to 13E3A/B. This concentration of comoving massive hot stars, IRS 13E, is proposed as the remaining core of a massive star cluster, which could harbor an intermediate-mass black hole (IMBH) of ~1300 M_sol. This detection plays in favor of a scenario in which the helium stars and the other hot stars in the central pc originate from the stripping of a massive cluster formed several tens of pc from the center. The detection of a discrete X-ray emission (Baganoff et al. 2003) at the IRS~13 position is examined in this context.Comment: 14 pages, 6 figures (3 in color), LaTeX2e, accepted in A&