Hydrodynamical Non-radiative Accretion Flows in Two-Dimensions

Two-dimensional (axially symmetric) numerical hydrodynamical calculations of accretion flows which cannot cool through emission of radiation are presented. The calculations begin from an equilibrium configuration consisting of a thick torus with constant specific angular momentum. Accretion is induced by the addition of a small anomalous azimuthal shear stress which is characterized by a function \nu. We study the flows generated as the amplitude and form of \nu are varied. A spherical polar grid which spans more than two orders of magnitude in radius is used to resolve the flow over a wide range of spatial scales. We find that convection in the inner regions produces significant outward mass motions that carry away both the energy liberated by, and a large fraction of the mass participating in, the accretion flow. Although the instantaneous structure of the flow is complex and dominated by convective eddies, long time averages of the dynamical variables show remarkable correspondence to certain steady-state solutions. Near the equatorial plane, the radial profiles of the time-averaged variables are power-laws with an index that depends on the radial scaling of the shear stress. We find that regardless of the adiabatic index of the gas, or the form or magnitude of the shear stress, the mass inflow rate is a strongly increasing function of radius, and is everywhere nearly exactly balanced by mass outflow. The net mass accretion rate through the disc is only a fraction of the rate at which mass is supplied to the inflow at large radii, and is given by the local, viscous accretion rate associated with the flow properties near the central object.Comment: 33 pages, 12 figures, accepted by MNRA

A Two-Year Longitudinal Study of Bone Mineral Density in Collegiate Distance Runners

Research has shown that weight-bearing physical activity such as running results in osteogenesis; distance runners, however, may experience deficiencies at specific sites. The purpose of this investigation was to examine changes in bone mineral density (BMD) of male and female collegiate cross-country runners over two years. Methods: BMD of 29 collegiate distance runners (16 men and 13 women) were measured five times over 24 months using dual-energy x- ray absorptiometry (DXA) at the anterior-posterior (AP) and lateral (LAT) spine, femoral neck (FN), total hip (TH), whole body (WB), and ultra-distal (UD) forearm. A repeated measures multivariate analysis of covariance, with bone free lean mass (BFLM) as covariate, was used to compare mean BMD values. Results: Adjusted for BFLM, there were no significant differences (p\u3e0.05) in BMD at any site between sexes. There were no significant differences at the AP or LAT spine, or FN across visits for either sex. There was a significant increase in BMD (p=0.044) at the UD forearm over two years in males. However, 56% of the men (n=9) had a z-score \u3c-1 at the UD forearm. Seven of 11 women had z-scores \u3c-1.0 at the LAT spine and four of 13 had z-scores \u3c-1.0 at the AP spine. Conclusion: There were no significant changes in BMD at any site over the two-year time frame, except the men had a significant increase in BMD at the non-dominant forearm. The spine appears to be an area of concern for the women in this study when examining z-score results

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

Elucidating the consequence and cause of microRNA dysregulation in amyotrophic lateral sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a progressive motor neurodegenerative disorder with an average life expectancy of 2-5 years post-diagnosis. Common pathological features associated with ALS are the formation of cytoplasmic inclusions of intermediate filaments and RNA-binding proteins within motor neurons. The formation of intermediate filament cytoplasmic inclusions is believed to be driven by a loss of stochiometric expression between five neuronal intermediate filament proteins—NFL, NFM, NFH, INA and PRPH—where there is a selective suppression of the steady-state levels of NEFL, INA and PRPH mRNA. Further, three RNA-binding proteins—TDP-43, FUS and RGNEF—have been shown to co-aggregate with each other in ALS motor neurons indicating a possible common mechanism that leads to their dysregulation. In the last decade, microRNAs (miRNAs)—small RNA molecules generally responsible for post-transcriptional regulation of gene expression—were observed to be massively dysregulated in the spinal cord tissue of ALS patients, providing a possible explanation for the changes observed in intermediate filament steady-state mRNA levels and RNA-binding protein dysregulation in ALS. Further, TDP-43 and FUS regulate miRNA biogenesis, indicating there may be a regulatory network between RNA-binding proteins and miRNAs that is disrupted in ALS. I hypothesize that a regulatory network between specific RNA-binding proteins and miRNAs is disrupted in ALS leading to changes in miRNA processing which contributes to intermediate filament and RNA-binding protein pathology. In this dissertation, I have examined: 1) whether ALS-linked miRNA(s) contribute to the selective suppression of NEFL, PRPH, and INA; 2) whether ALS-linked miRNAs regulate the expression of NEFM and NEFH; 3) whether ALS-linked miRNAs regulate the expression of RNA-binding proteins whose metabolism is dysregulated in ALS (TDP-43, FUS, and RGNEF); and, 4) whether TDP-43 and FUS are in a regulatory network with ALS-linked miRNAs. Overall, 12 ALS-linked miRNAs were identified to regulate either intermediate filament or RNA-binding protein expression, and further, a novel negative feedback loop between TDP-43 and two miRNAs (miR-27b-3p and miR-181c-5p) was identified. This dissertation highlights that changes to miRNA levels, as seen in ALS, would contribute to overall ALS pathology, making them viable avenues for potential therapeutics

Vortices in Thin, Compressible, Unmagnetized Disks

We consider the formation and evolution of vortices in a hydrodynamic shearing-sheet model. The evolution is done numerically using a version of the ZEUS code. Consistent with earlier results, an injected vorticity field evolves into a set of long-lived vortices, each of which has a radial extent comparable to the local scale height. But we also find that the resulting velocity field has a positive shear stress, . This effect appears only at high resolution. The transport, which decays with time as t^-1/2, arises primarily because the vortices drive compressive motions. This result suggests a possible mechanism for angular momentum transport in low-ionization disks, with two important caveats: a mechanism must be found to inject vorticity into the disk, and the vortices must not decay rapidly due to three-dimensional instabilities.Comment: 8 pages, 10 figures (high resolution figures available in ApJ electronic edition

An evaluation of the implementation of Advanced Nurse Practitioner (ANP) roles in an acute hospital setting.

Aim: To evaluate the impact of implementing Advanced Nurse Practitioner roles on patients, staff members and organizational outcomes in an acute hospital. Background: The worldwide development of advanced practice roles in nursing has been influenced by increasing demands and costs of health care. A key issue in the UK has been the reduction in hours junior doctors can work. While there is evidence these roles can have a positive impact in a variety of clinical specialties, little is known about the impact advanced nurses substituting for junior doctors can have on patients, staff members and organizational outcomes in general hospital care settings. Design: Collective case study. Methods: A collective case study in a district general hospital in England was undertaken in 2011–2012. Interviews with strategic stakeholders (n = 13) were followed by three individual case studies. Each case study represented the clinical area in which the roles had been introduced: medicine, surgery and orthopaedics and included interviews (n = 32) and non-participant observation of practice. Findings: The ANPs had a positive impact on patient experience, outcomes and safety. They improved staff knowledge, skills and competence and enhanced quality of working life, distribution of workload and team-working. ANPs contributed to the achievement of organizational priorities and targets and development of policy. Conclusion: ANPs undertaking duties traditionally performed by junior doctors in acute hospital settings can have a positive impact on a range of indicators relating to patients, staff members and organizational outcomes which are highly relevant to nursing

Can phoretic particles swim in two dimensions?

Artificial phoretic particles swim using self-generated gradients in chemical species (self-diffusiophoresis) or charges and currents (self-electrophoresis). These particles can be used to study the physics of collective motion in active matter and might have promising applications in bioengineering. In the case of self-diffusiophoresis, the classical physical model relies on a steady solution of the diffusion equation, from which chemical gradients, phoretic flows, and ultimately the swimming velocity may be derived. Motivated by disk-shaped particles in thin films and under confinement, we examine the extension to two dimensions. Because the two-dimensional diffusion equation lacks a steady state with the correct boundary conditions, Laplace transforms must be used to study the long-time behavior of the problem and determine the swimming velocity. For fixed chemical fluxes on the particle surface, we find that the swimming velocity ultimately always decays logarithmically in time. In the case of finite Péclet numbers, we solve the full advection-diffusion equation numerically and show that this decay can be avoided by the particle moving to regions of unconsumed reactant. Finite advection thus regularizes the two-dimensional phoretic problem.The research was supported by NSF Grants DMS-1109315 and DMS-1147523 (Madison) and by the European Union through a CIG grant (Cambridge)

Theory of Umklapp-assisted recombination of bound excitons in Si:P

We present the calculations for the oscillator strength of the recombination of excitons bound to phosphorous donors in silicon. We show that the direct recombination of the bound exciton cannot account for the experimentally measured oscillator strength of the no-phonon line. Instead, the recombination process is assisted by an umklapp process of the donor electron state. We make use of the empirical pseudopotential method to evaluate the Umklapp-assisted recombination matrix element in second-order perturbation theory. Our result is in excellent agreement with the experiment. We also present two methods to improve the optical resolution of the optical detection of the spin state of a single nucleus in silicon.Comment: 9 pages, 6 EPS figures, Revtex

Enhanced Endurance Performance by Periodization of CHO Intake: "sleep low" strategy

Purpose: We investigated the effect of a chronic dietary periodization strategy on endurance performance in trained athletes. Methods: 21 triathletes (V[Combining Dot Above]O2max: 58.7 +/- 5.7 mL[middle dot]min-1[middle dot]kg-1) were divided into 2 groups: a "sleep-low" (SL, n = 11) and a control group (CON, n = 10) consumed the same daily carbohydrate (CHO) intake (6 g[middle dot]kg-1[middle dot]d-1) but with different timing over the day to manipulate CHO availability before and after training sessions. The "sleep low" strategy consisted of a 3-week training/diet intervention comprising three blocks of diet/exercise manipulations: 1) "train-high" interval training sessions (HIT) in the evening with high-CHO availability; 2) overnight CHO restriction ("sleeping-low"), and 3) "train-low" sessions with low endogenous and exogenous CHO availability. The CON group followed the same training program but with high CHO availability throughout training sessions (no CHO restriction overnight, training sessions with exogenous CHO provision). Results: There was a significant improvement in delta efficiency during submaximal cycling for SL versus CON (CON: +1.4 +/- 9.3 %, SL: +11 +/- 15 %, P<0.05). SL also improved supra-maximal cycling to exhaustion at 150% of peak aerobic power (CON: +1.63 +/- 12.4 %, SL: +12.5 +/- 19.0 %; P = 0.06) and 10 km running performance (CON: -0.10 +/- 2.03 %, SL: -2.9 +/- 2.15 %; P < 0.05). Fat mass was decreased in SL (CON: -2.6 +/- 7.4; SL: -8.5 +/- 7.4 %PRE, P < 0.01), but not lean mass (CON: -0.22 +/- 1.0; SL: -0.16 +/- 1.7 %PRE). Conclusion: Short-term periodization of dietary CHO availability around selected training sessions promoted significant improvements in submaximal cycling economy, as well as supra-maximal cycling capacity and 10 km running time in trained endurance athletes