Electron Acceleration around the Supermassive Black Hole at the Galactic Center

The recent detection of variable infrared emission from Sagittarius A*, combined with its previously observed flare activity in X-rays, provides compelling evidence that at least a portion of this object's emission is produced by nonthermal electrons. We show here that acceleration of electrons by plasma wave turbulence in hot gases near the black hole's event horizon can account both for Sagittarius A*'s mm and shorter wavelengths emission in the quiescent state, and for the infrared and X-ray flares, induced either via an enhancement of the mass accretion rate onto the black hole or by a reorganization of the magnetic field coupled to the accretion gas. The acceleration model proposed here produces distinct flare spectra that may be compared with future coordinated multi-wavelength observations. We further suggest that the diffusion of high energy electrons away from the acceleration site toward larger radii might be able to account for the observed characteristics of Sagittarius A*'s emission at cm and longer wavelengths.Comment: 13 pages, 2 figures and 1 table, submitted to ApJ

Magnetically Driven Accretion in the Kerr Metric III: Unbound Outflows

We have carried out fully relativistic numerical simulations of accretion disks in the Kerr metric. In this paper we focus on the unbound outflows that emerge self-consistently from the accretion flow. These outflows are found in the axial funnel region and consist of two components: a hot, fast, tenuous outflow in the axial funnel proper, and a colder, slower, denser jet along the funnel wall. Although a rotating black hole is not required to produce these unbound outflows, their strength is enhanced by black hole spin. The funnel-wall jet is excluded from the axial funnel due to elevated angular momentum, and is also pressure-confined by a magnetized corona. The tenuous funnel outflow accounts for a significant fraction of the energy transported to large distances in the higher-spin simulations. We compare the outflows observed in our simulations with those seen in other simulations.Comment: 33 pages, 8 figures, ApJ submitte

What's the point of knowing how?

Why is it useful to talk and think about knowledge-how? Using Edward Craig’s discussion of the function of the concepts of knowledge and knowledge-how as a jumping off point, this paper argues that considering this question can offer us new angles on the debate about knowledge-how. We consider two candidate functions for the concept of knowledge-how: pooling capacities, and mutual reliance. Craig makes the case for pooling capacities, which connects knowledge-how to our need to pool practical capacities. I argue that the evidence is much more equivocal. My suggested diagnosis is that the concept of knowledge-how plays both functions, meaning that the concept of knowledge-how is inconsistent, and that the debate about knowledge-how is at least partly a metalinguistic negotiation. In closing, I suggest a way to revise the philosophical concept of knowledge how

Design Criteria for Zero Leakage Connectors for Launch Vehicles. Mathematical Model of Interface Sealing Phenomenon, Volume 2 Final Report

Mathematical model of interface sealing phenomenon in determining design criteria for zero leakage connectors for launch vehicle

Media coverage and speculation about the impact of the COVID-19 pandemic on suicide: A content analysis of UK news

Objectives: Since the start of the COVID-19 pandemic, there has been much concern and speculation about rises in suicide rates, despite evidence that suicides did not in fact increase in the first year of the pandemic in most countries with real-time suicide data. This public narrative is potentially harmful, as well as misleading, and is likely to be perpetuated by sensational news coverage. Method: Using a bespoke database, we analysed the quality and content of print and online UK news (including opinion pieces) on the impact of COVID-19 on suicidality, based on adherence to international recommendations. Chi-square tests were conducted to examine variability in relation to key characteristics (e.g., type of publication) and to four ‘restriction phases’ (based on UK government official lockdown measures) over the first 14 months of the pandemic. Results: We identified 372 stories about COVID-19 and suicidality in online and print news between the first UK lockdown (March 2020) and May 2021 (when restrictions were significantly eased in the UK). Throughout this period, over a third of articles (39.2%) and headlines (41.4%) claimed or predicted a rise in suicide, often attributed to feelings of entrapment and poor mental health (especially amongst young people), and fueled by expert commentary and speculation. Almost a third of reports were rated as being of negative quality (116, 31.2%), and at least half included no signposting to help and support. However, reporting improved in phases of less stringent COVID-19 restrictions and over time, with later articles and headlines including fewer negative statements and predictions about rises in suicides, and greater reliance on academic evidence. Conclusions: As the longer-term consequences of the pandemic develop, and other national and global events unfold, it is increasingly important that the media, and the wider community of experts shaping its narratives, strive for a positive and evidence-informed approach to news coverage of suicide

Root rot of subterranean clover in W.A

Root rot of subterranean clover has occurred sporadically in the south west of Western Australia for a number of years. In most seasons the disease has affected the clover paddocks of only a few farms, but in 1973 there was widespread pasture decline due to root rot in the South-West and south coastal districts. At present the most promising approaches for minimising the effect of root rot appear to be the use of cultivation techniques and eventually the use of resistant varieties, or other pasture species

Discovery of a New Nearby Star

We report the discovery of a nearby star with a very large proper motion of 5.06 +/- 0.03 arcsec/yr. The star is called SO025300.5+165258 and referred to herein as HPMS (high proper motion star). The discovery came as a result of a search of the SkyMorph database, a sensitive and persistent survey that is well suited for finding stars with high proper motions. There are currently only 7 known stars with proper motions > 5 arcsec/yr. We have determined a preliminary value for the parallax of 0.43 +/- 0.13 arcsec. If this value holds our new star ranks behind only the Alpha Centauri system (including Proxima Centauri) and Barnard's star in the list of our nearest stellar neighbors. The spectrum and measured tangential velocity indicate that HPMS is a main-sequence star with spectral type M6.5. However, if our distance measurement is correct, the HPMS is underluminous by 1.2 +/- 0.7 mag.Comment: 5 pages, 3 figures. Submitted to ApJ Letter

Towards a New Standard Theory for Astrophysical Disk Accretion

We briefly review recent developments in black hole accretion disk theory, placing new emphasis on the vital role played by magnetohydrodynamic (MHD) stresses in transporting angular momentum. The apparent universality of accretion-related outflow phenomena is a strong indicator that vertical transport of angular momentum by large-scale MHD torques is important and may even dominate radial transport by small-scale MHD turbulence. This leads to an enhanced overall rate of angular momentum transport and allows accretion of matter to proceed at an interesting rate. Furthermore, we argue that when vertical transport is important, the radial structure of the accretion disk is modified and this affects the disk emission spectrum. We present a simple model demonstrating that energetic, magnetically-driven outflows give rise to a disk spectrum that is dimmer and redder than a standard accretion disk accreting at the same rate. We briefly discuss the implications of this key result for accreting black holes in different astrophysical systems.Comment: Accepted for publication as brief review in Mod. Phys. Let.

Racial/Ethnic Disparities in Knowledge about Risks and Benefits of Breast Cancer Treatment: Does It Matter Where You Go?

To evaluate the association between provider characteristics and treatment location and racial/ethnic minority patients' knowledge of breast cancer treatment risks and benefits. Data Sources/Data Collection . Survey responses and clinical data from breast cancer patients of Detroit and Los Angeles SEER registries were merged with surgeon survey responses ( N =1,132 patients, 277 surgeons). Study Design . Cross-sectional survey. Multivariable regression was used to identify associations between patient, surgeon, and treatment setting factors and accurate knowledge of the survival benefit and recurrence risk related to mastectomy and breast conserving surgery with radiation. Principal Findings . Half (51 percent) of respondents had survival knowledge, while close to half (47.6 percent) were uncertain regarding recurrence knowledge. Minority patients and those with lower education were less likely to have adequate survival knowledge and more likely to be uncertain regarding recurrence risk than their counterparts ( p <.001). Neither surgeon characteristics nor treatment location attenuated racial/ethnic knowledge disparities. Patient–physician communication was significantly ( p <.001) associated with both types of knowledge, but did not influence racial/ethnic differences in knowledge. Conclusions . Interventions to improve patient understanding of the benefits and risks of breast cancer treatments are needed across surgeons and treatment setting, particularly for racial/ethnic minority women with breast cancer.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71991/1/j.1475-6773.2008.00843.x.pd