Hydrodynamic simulations of shell convection in stellar cores

Shell convection driven by nuclear burning in a stellar core is a common hydrodynamic event in the evolution of many types of stars. We encounter and simulate this convection (i) in the helium core of a low-mass red giant during core helium flash leading to a dredge-down of protons across an entropy barrier, (ii) in a carbon-oxygen core of an intermediate-mass star during core carbon flash, and (iii) in the oxygen and carbon burning shell above the silicon-sulfur rich core of a massive star prior to supernova explosion. Our results, which were obtained with the hydrodynamics code HERAKLES, suggest that both entropy gradients and entropy barriers are less important for stellar structure than commonly assumed. Our simulations further reveal a new dynamic mixing process operating below the base of shell convection zones.Comment: 8 pages, 3 figures .. submitted to a proceedings of conference about "Red Giants as Probes of the Structure and Evolution of the Milky Way" which has taken place between 15-17 November 2010 in Rom

A qualitative study of patients' views on quality of primary care consultations in Hong Kong and comparison with the UK CARE Measure

<b>Background</b> Patients' priorities and views on quality care are well-documented in Western countries but there is a dearth of research in this area in the East. The aim of the present study was to explore Chinese patients' views on quality of primary care consultations in Hong Kong and to compare these with the items in the CARE measure (a process measure of consultation quality widely used in the UK) in order to assess the potential utility of the CARE measure in a Chinese population.<p></p> <b>Methods</b> Individual semi-structured interviews were conducted on 21 adult patients from 3 different primary care clinics (a public primary healthcare clinic, a University health centre, and a private family physician's clinic). Topics discussed included expectations, experiences, and views about quality of medical consultations. Interviews were typed verbatim, and a thematic approach was taken to identify key issues. These identified issues were then compared with the ten CARE measure items, using a CARE framework: Connecting (Care Measure items 1–3), Assessing (item 4), Responding (items 5,6), and Empowering (items 7–10).<p></p> <b>Results</b> Patients judged doctors in terms of both the process of the consultation and the perceived outcomes. Themes identified that related to the interpersonal process of the consultation fitted well under the CARE framework; Connecting and communicating (18/21 patients), Assessing holistically (10/21 patients), Responding (18/21 patients) and Empowering (19/21 patients). Patients from the public clinic, who were generally of lower socio-economic status, were least likely to expect holistic care or empowerment. Two-thirds of patients also judged doctors on whether they performed an adequate physical examination, and three-quarters on the later outcomes of consultation (in terms of relief or cure and/or side-effects of prescribed drugs).<p></p> <b>Conclusion</b> These findings suggest that Chinese patients in Hong Kong value engaged, empathic primary care doctors and judge the quality of consultations largely on these human skills and the attitudes and values that underpin them, as well as on the perceived outcomes of treatment. The match between themes relating to consultation process and the CARE Measure items suggests utility of this measure in this population, but further quantitative validation is required

Dual-encoded magnetization transfer and diffusion imaging and its application to tract-specific microstructure mapping

We present a novel dual-encoded magnetization transfer (MT) and diffusion-weighted sequence and demonstrate its potential to resolve distinct properties of white matter fiber tracts at the sub-voxel level. The sequence was designed and optimized for maximal MT contrast efficiency. The resulting whole brain 2.6 mm isotropic protocol to measure tract-specific MT ratio (MTR) has a scan time under 7 minutes. Ten healthy subjects were scanned twice to assess repeatability. Two different analysis methods were contrasted: a technique to extract tract-specific MTR using Convex Optimization Modeling for Microstructure Informed Tractography (COMMIT), a global optimization technique; and conventional MTR tractometry. The results demonstrate that the tract-specific method can reliably resolve the MT ratios of major white matter fiber pathways and is less affected by partial volume effects than conventional multi-modal tractometry. Dual-encoded MT and diffusion is expected to both increase the sensitivity to microstructure alterations of specific tracts due to disease, ageing or learning, as well as lead to weighted structural connectomes with more anatomical specificity.Comment: 26 pages, 7 figure

Rigorous engineering for hardware security: Formal modelling and proof in the CHERI design and implementation process

The root causes of many security vulnerabilities include a pernicious combination of two problems, often regarded as inescapable aspects of computing. First, the protection mechanisms provided by the mainstream processor architecture and C/C++ language abstractions, dating back to the 1970s and before, provide only coarse-grain virtual-memory-based protection. Second, mainstream system engineering relies almost exclusively on test-and-debug methods, with (at best) prose specifications. These methods have historically sufficed commercially for much of the computer industry, but they fail to prevent large numbers of exploitable bugs, and the security problems that this causes are becoming ever more acute. In this paper we show how more rigorous engineering methods can be applied to the development of a new security-enhanced processor architecture, with its accompanying hardware implementation and software stack. We use formal models of the complete instruction-set architecture (ISA) at the heart of the design and engineering process, both in lightweight ways that support and improve normal engineering practice -- as documentation, in emulators used as a test oracle for hardware and for running software, and for test generation -- and for formal verification. We formalise key intended security properties of the design, and establish that these hold with mechanised proof. This is for the same complete ISA models (complete enough to boot operating systems), without idealisation. We do this for CHERI, an architecture with \emph{hardware capabilities} that supports fine-grained memory protection and scalable secure compartmentalisation, while offering a smooth adoption path for existing software. CHERI is a maturing research architecture, developed since 2010, with work now underway on an Arm industrial prototype to explore its possible adoption in mass-market commercial processors. The rigorous engineering work described here has been an integral part of its development to date, enabling more rapid and confident experimentation, and boosting confidence in the design.This work was supported by EPSRC programme grant EP/K008528/1 (REMS: Rigorous Engineering for Mainstream Systems). This work was supported by a Gates studentship (Nienhuis). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement 789108, ELVER). This work was supported by the Defense Advanced Research Projects Agency (DARPA) and the Air Force Research Laboratory (AFRL), under contracts FA8750-10-C-0237 (CTSRD), HR0011-18-C-0016 (ECATS), and FA8650-18-C-7809 (CIFV)

Optimal control models of the goal-oriented human locomotion

In recent papers it has been suggested that human locomotion may be modeled as an inverse optimal control problem. In this paradigm, the trajectories are assumed to be solutions of an optimal control problem that has to be determined. We discuss the modeling of both the dynamical system and the cost to be minimized, and we analyze the corresponding optimal synthesis. The main results describe the asymptotic behavior of the optimal trajectories as the target point goes to infinity

Testing A (Stringy) Model of Quantum Gravity

I discuss a specific model of space-time foam, inspired by the modern non-perturbative approach to string theory (D-branes). The model views our world as a three brane, intersecting with D-particles that represent stringy quantum gravity effects, which can be real or virtual. In this picture, matter is represented generically by (closed or open) strings on the D3 brane propagating in such a background. Scattering of the (matter) strings off the D-particles causes recoil of the latter, which in turn results in a distortion of the surrounding space-time fluid and the formation of (microscopic, i.e. Planckian size) horizons around the defects. As a mean-field result, the dispersion relation of the various particle excitations is modified, leading to non-trivial optical properties of the space time, for instance a non-trivial refractive index for the case of photons or other massless probes. Such models make falsifiable predictions, that may be tested experimentally in the foreseeable future. I describe a few such tests, ranging from observations of light from distant gamma-ray-bursters and ultra high energy cosmic rays, to tests using gravity-wave interferometric devices and terrestrial particle physics experients involving, for instance, neutral kaons.Comment: 25 pages LATEX, four figures incorporated, uses special proceedings style. Invited talk at the third international conference on Dark Matter in Astro and Particle Physics, DARK2000, Heidelberg, Germany, July 10-15 200

SDSS-II SUPERNOVA SURVEY: AN ANALYSIS of the LARGEST SAMPLE of TYPE IA SUPERNOVAE and CORRELATIONS with HOST-GALAXY SPECTRAL PROPERTIES

This is the author accepted manuscript. The final version is available from the Institute of Physics via http://dx.doi.org/10.3847/0004-637X/821/2/115Using the largest single-survey sample of Type Ia supernovae (SNe Ia) to date, we study the relationship between properties of SNe Ia and those of their host galaxies, focusing primarily on correlations with Hubble residuals (HRs). Our sample consists of 345 photometrically classified or spectroscopically confirmed SNe Ia discovered as part of the SDSS-II Supernova Survey (SDSS-SNS). This analysis utilizes host-galaxy spectroscopy obtained during the SDSS-I/II spectroscopic survey and from an ancillary program on the SDSS-III Baryon Oscillation Spectroscopic Survey that obtained spectra for nearly all host galaxies of SDSS-II SN candidates. In addition, we use photometric host-galaxy properties from the SDSS-SNS data release such as host stellar mass and star formation rate. We confirm the well-known relation between HR and host-galaxy mass and find a 3.6σ significance of a nonzero linear slope. We also recover correlations between HR and host-galaxy gas-phase metallicity and specific star formation rate as they are reported in the literature. With our large data set, we examine correlations between HR and multiple host-galaxy properties simultaneously and find no evidence of a significant correlation. We also independently analyze our spectroscopically confirmed and photometrically classified SNe Ia and comment on the significance of similar combined data sets for future surveys.This material is based on work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1321851. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors(s) and do not necessarily reflect the views of the National Science Foundation. M.S. and J.A.F. are supported by the Department of Energy grant DE-SC-0009890. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England ... Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation ..