The formation of high-field magnetic white dwarfs from common envelopes

The origin of highly-magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, such as a planet, brown dwarf, or low-mass star is engulfed by a post-main-sequence giant, the hydrodynamic drag in the envelope of the giant leads to a reduction of the companion's orbit. Sufficiently low-mass companions in-spiral until they are shredded by the strong gravitational tides near the white dwarf core. Subsequent formation of a super-Eddington accretion disk from the disrupted companion inside a common envelope can dramatically amplify magnetic fields via a dynamo. Here, we show that these disk-generated fields are sufficiently strong to explain the observed range of magnetic field strengths for isolated, high-field magnetic white dwarfs. A higher-mass binary analogue may also contribute to the origin of magnetar fields.Comment: Accepted to Proceedings of the National Academy of Sciences. Under PNAS embargo until time of publicatio

Black Male Student-Athletes and Racial Inequities in NCAA Division I College Sports

The purpose of this report is to make transparent racial inequities in NCAA Division I college sports. Specifically, the authors offer a four-year analysis of Black men's representation on football and basketball teams versus their representation in the undergraduate student body on each campus. The report concludes with recommendations for the NCAA and commissioners of the six major sports conferences, college and university leaders, coaches and athletics directors, journalists, and Black male student-athletes and their families

A novel route to Pt-Bi2O3 composite thin films and their application in photo-reduction of water

A novel homoleptic bismuth(III) β-diketonate (dibenzoylmethane – dbm) complex [Bi(dbm)3]2 has been used as a precursor to thin films of crystalline β-Bi2O3, and hexachloroplatinic acid (H2PtCl6·6H2O) has been demonstrated as a suitable precursor for deposition of platinum nanoparticles, both deposited via aerosol-assisted chemical vapour deposition (AACVD). Thin films of Pt–Bi2O3 were co-deposited from a mixture of [Bi(dbm)3]2 and H2PtCl6·6H2O; the introduction of Pt particles into β-Bi2O3 causes hydrogen to be evolved during photolysis of water over the composite material, a property not found for Pt particles or β-Bi2O3 alone

Reconceptualizing Security Strategies For Courts: Developing A Typology For Safer Court Environments

There have been heightened concerns about security in courts in recent years, prompting a strong response that has largely been focused on perimeter security. This paper draws on recent research conducted in Australian on court users' safety needs, to propose a typology for designing safer courtroom environments that moves beyond the entry point to the court, and incorporates consideration of process and design elements

Efficiency at optimal work from finite reservoirs: a probabilistic perspective

We revisit the classic thermodynamic problem of maximum work extraction from two arbitrary sized hot and cold reservoirs, modelled as perfect gases. Assuming ignorance about the extent to which the process has advanced, which implies an ignorance about the final temperatures, we quantify the prior information about the process and assign a prior distribution to the unknown temperature(s). This requires that we also take into account the temperature values which are regarded to be unphysical in the standard theory, as they lead to a contradiction with the physical laws. Instead in our formulation, such values appear to be consistent with the given prior information and hence are included in the inference. We derive estimates of the efficiency at optimal work from the expected values of the final temperatures, and show that these values match with the exact expressions in the limit when any one of the reservoirs is very large compared to the other. For other relative sizes of the reservoirs, we suggest a weighting procedure over the estimates from two valid inference procedures, that generalizes the procedure suggested earlier in [J. Phys. A: Math. Theor. {\bf 46}, 365002 (2013)]. Thus a mean estimate for efficiency is obtained which agrees with the optimal performance to a high accuracy.Comment: 14 pages, 6 figure

Does a novel X-ray imaging technology provide a substantial radiation dose reduction for patients in trans-catheter aortic valve implantation procedures?

Purpose: Modern interventional X-ray equipment employs image processing to permit reduction in radiation whilst retaining sufficient image quality. The aim of this study was to investigate whether our recently-installed system (AlluraClarity, Philips Healthcare) which contains advanced real-time image noise reduction algorithms and anatomy-specific X-ray optimization (beam filtering, grid switch, pulse width, spot size, detector and image processing engine), affected patient procedure dose and overall procedure duration in routine trans-catheter aortic valve implantation (TAVI) procedures. Methods: Patient dose for 42 TAVI patients from the AlluraClarity cardiac catheterisation lab and from a reference system (Axiom Artis, Siemens Healthcare) in the same cardiology department was recorded. Median values from the two X-ray systems were compared using the Wilcoxon statistical test. Results: Total patient procedure dose medians were 4016 and 7088 cGy cm2 from the AlluraClarity and reference systems respectively. AlluraClarity median patient doses were 3405 cGy cm2 and 783.5 cGy cm2 from fluoroscopy and digital image acquisition respectively. Reference median patient doses were 4928 cGy cm2 and 2511 cGy cm2 from fluoroscopy and digital image acquisition respectively. All differences in patient dose were significant at the 5% level. Median total fluoroscopy times [min:sec] were 19:57 and 20:20 for the AlluraClarity and reference systems respectively. Conclusion: The AlluraClarity cardiac catheterisation lab had 43% lower total patient procedure dose for TAVI patients than the reference lab; fluoroscopy and digital image acquisition doses were 31% and 69% lower respectively. In terms of total fluoroscopy time, there was no statistically significant difference between the two labs

Current helicity of active regions as a tracer of large-scale solar magnetic helicity

We demonstrate that the current helicity observed in solar active regions traces the magnetic helicity of the large-scale dynamo generated field. We use an advanced 2D mean-field dynamo model with dynamo saturation based on the evolution of the magnetic helicity and algebraic quenching. For comparison, we also studied a more basic 2D mean-field dynamo model with simple algebraic alpha quenching only. Using these numerical models we obtained butterfly diagrams both for the small-scale current helicity and also for the large-scale magnetic helicity, and compared them with the butterfly diagram for the current helicity in active regions obtained from observations. This comparison shows that the current helicity of active regions, as estimated by $-{\bf A \cdot B}$ evaluated at the depth from which the active region arises, resembles the observational data much better than the small-scale current helicity calculated directly from the helicity evolution equation. Here ${\bf B}$ and ${\bf A}$ are respectively the dynamo generated mean magnetic field and its vector potential. A theoretical interpretation of these results is given.Comment: 11 pages, 5 figures, revised versio

Accretion Disks and Dynamos: Toward a Unified Mean Field Theory

Conversion of gravitational energy into radiation in accretion discs and the origin of large scale magnetic fields in astrophysical rotators have often been distinct topics of research. In semi-analytic work on both problems it has been useful to presume large scale symmetries, necessarily resulting in mean field theories. MHD turbulence makes the underlying systems locally asymmetric and nonlinear. Synergy between theory and simulations should aim for the development of practical mean field models that capture essential physics and can be used for observational modeling. Mean field dynamo (MFD) theory and alpha-viscosity accretion theory exemplify such ongoing pursuits. 21st century MFD theory has more nonlinear predictive power compared to 20th century MFD theory, whereas accretion theory is still in a 20th century state. In fact, insights from MFD theory are applicable to accretion theory and the two are artificially separated pieces of what should be a single theory. I discuss pieces of progress that provide clues toward a unified theory. A key concept is that large scale magnetic fields can be sustained via local or global magnetic helicity fluxes or via relaxation of small scale magnetic fluctuations, without the kinetic helicity driver of 20th century textbooks. These concepts may help explain the formation of large scale fields that supply non-local angular momentum transport via coronae and jets in a unified theory of accretion and dynamos. In diagnosing the role of helicities and helicity fluxes in disk simulations, each disk hemisphere should be studied separately to avoid being misled by cancelation that occurs as a result of reflection asymmetry. The fraction of helical field energy in disks is expected to be small compared to the total field in each hemisphere as a result of shear, but can still be essential for large scale dynamo action.Comment: For the Proceedings of the Third International Conference and Advanced School "Turbulent Mixing and Beyond," TMB-2011 held on 21 - 28 August 2011 at the Abdus Salam International Centre for Theoretical Physics, Trieste, http://users.ictp.it/~tmb/index2011.html Italy, To Appear in Physica Scripta (corrected small items to match version in print