On the Perturbations of Viscous Rotating Newtonian Fluids

The perturbations of weakly-viscous, barotropic, non-self-gravitating, Newtonian rotating fluids are analyzed via a single partial differential equation. The results are then used to find an expression for the viscosity-induced normal-mode complex eigenfrequency shift, with respect to the case of adiabatic perturbations. However, the effects of viscosity are assumed to have been incorporated in the unperturbed (equilibrium) model. This paper is an extension of the normal-mode formalism developed by Ipser & Lindblom for adiabatic pulsations of purely-rotating perfect fluids. The formulas derived are readily applicable to the perturbations of thin and thick accretion disks. We provide explicit expressions for thin disks, employing results from previous relativistic analyses of adiabatic normal modes of oscillation. In this case, we find that viscosity causes the fundamental p- and g- modes to grow while the fundamental c-mode could have either sign of the damping rate.Comment: Accepted for publication by The Astrophysical Journal. 11 pages, no figure

Interface Dynamics in Semilinear Wave Equations

We consider the wave equation epsilon(2)(-partial derivative(2)(t) + Delta)u + f(u) = 0 for 0 = 1, and that is close to a timelike hypersurface of vanishing Minkowskian mean curvature. This provides a Minkowskian analog of the numerous results that connect the Euclidean Allen-Cahn equation and minimal surfaces or the parabolic Allen-Cahn equation and motion by mean curvature. Compared to earlier results of the same character, we develop a new constructive approach that applies to a larger class of nonlinearities and yields much more precise information about the solutions under consideration.UK Royal Society Research Professorship Natural Sciences and Engineering Research Council of Canada Natural Sciences and Engineering Research Council of Canada 261955 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1160135 PAI AFB-17000

Strain-Induced Conduction Band Spin Splitting in GaAs from First Principles Calculations

We use a recently developed self-consistent GW approximation to present first principles calculations of the conduction band spin splitting in GaAs under [110] strain. The spin orbit interaction is taken into account as a perturbation to the scalar relativistic hamiltonian. These are the first calculations of conduction band spin splitting under deformation based on a quasiparticle approach; and because the self-consistent GW scheme accurately reproduces the relevant band parameters, it is expected to be a reliable predictor of spin splittings. We also discuss the spin relaxation time under [110] strain and show that it exhibits an in-plane anisotropy, which can be exploited to obtain the magnitude and sign of the conduction band spin splitting experimentally.Comment: 8 pages, 4 figures, 1 tabl

A search for thermal gyro-synchrotron emission from hot stellar coronae

We searched for thermal gyro-synchrotron radio emission from a sample of five radio-loud stars whose X-ray coronae contain a hot ($T_e>10^7$ K) thermal component. We used the JVLA to measure Stokes I and V/I spectral energy distributions (SEDs) over the frequency range 15--45 GHz, determining the best-fitting model parameters using power-law and thermal gyro-synchrotron emission models. The SEDs of the three chromospherically active binaries (Algol, UX Arietis, HR 1099) were well-fit by a power-law gyro-synchrotron model, with no evidence for a thermal component. However, the SEDs of the two weak-lined T Tauri stars (V410 Tau, HD 283572) had a circularly polarized enhancement above 30 GHz that was inconsistent with a pure power-law distribution. These spectra were well-fit by summing the emission from an extended coronal volume of power-law gyro-synchrotron emission and a smaller region with thermal plasma and a much stronger magnetic field emitting thermal gyro-synchrotron radiation. We used Bayesian inference to estimate the physical plasma parameters of the emission regions (characteristic size, electron density, temperature, power-law index, and magnetic field strength and direction) using independently measured radio sizes, X-ray luminosities, and magnetic field strengths as priors, where available. The derived parameters were well-constrained but somewhat degenerate. The power-law and thermal volumes in the pre-main-sequence stars are probably not co-spatial, and we speculate they may arise from two distinct regions: a tangled-field magnetosphere where reconnection occurs and a recently discovered axisymmetric toroidal magnetic field, respectively.Comment: Submitted to MNRAS; 18 pages, 10 figure

Evaluation of an epigenetic assay for predicting repeat prostate biopsy outcome in African American men

OBJECTIVE: To evaluate an epigenetic assay performed on tissue from negative prostate biopsies in a group of African American (AA) men undergoing repeat biopsy, and to compare accuracy for predicting repeat biopsy outcome to prior studies conducted in predominantly Caucasian populations. MATERIALS AND METHODS: The study population consisted of 211 AA men from 7 urology centers across the United States; all of whom were undergoing 12-core transrectal ultrasound-guided repeat biopsy within 30 months from a negative index biopsy. All biopsy cores from the negative index biopsy were profiled for the epigenetic biomarkers GSTP1, APC, and RASSF1 using ConfirmMDx for Prostate Cancer (MDxHealth, Irvine, CA). RESULTS: Upon repeat biopsy, 130 of 211 subjects (62%) had no prostate cancer (PCa) detected and 81 of 211 (38%) were diagnosed with PCa. Of the subjects with PCa, 54 (67%) were diagnosed with Gleason score (GS) = 7 disease. For detection of PCa at repeat biopsy, ConfirmMDx sensitivity was 74.1% and specificity was 60.0%, equivalent to prior studies (P = .235 and .697, respectively). For detection of GS >= 7 PCa, sensitivity was 78% and specificity was 53%. The negative predictive values for detection of all PCa and GS >= 7 PCa were 78.8% and 94.2%, respectively. CONCLUSION: In this group of AA men, we successfully validated an epigenetic assay to assess the need for repeat biopsy. Results were consistent with previous studies from predominantly Caucasian populations. Therefore, the ConfirmMDx assay is a useful tool for risk stratification of AA men who had an initial negative biopsy

Timed Implementation Relations for the Distributed Test Architecture

In order to test systems that have physically distributed interfaces, called ports, we might use a distributed approach in which there is a separate tester at each port. If the testers do not synchronise during testing then we cannot always determine the relative order of events observed at different ports and this leads to new notions of correctness that have been described using corresponding implementation relations. We study the situation in which each tester has a local clock and timestamps its observations. If we know nothing about how the local clocks relate then this does not affect the implementation relation while if the local clocks agree exactly then we can reconstruct the sequence of observations made. In practice, however, we are likely to be between these extremes: the local clocks will not agree exactly but we have some information regarding how they can differ. We start by assuming that a local tester interacts synchronously with the corresponding port of the system under test and then extend this to the case where communications can be asynchronous, considering both the first-in-first-out (FIFO) case and the non-FIFO case. The new implementation relations are stronger than implementation relations for distributed testing that do not use timestamps but still reflect the distributed nature of observations. This paper explores these alternatives and derives corresponding implementation relations

Electrodynamic tethers for spacecraft propulsion

Relatively short electrodynamic tethers can use solar power to "push" against a planetary magnetic field to achieve propul sion without expenditure of propellant. The groundwork has been laid for this type of propulsion. Recent important milestones include retrieval of a tether in space (TSS-1, 1992), successful deployment of a 20-km-long tether in space (SEDS-1, 1993), and operation of an electrodynamic tether with tether current driven in both directions (PMG, 1993). The planned Propulsive Small Expendable Deployer System (ProSEDS) experiment will use the flight-proven Small Expendable Deployer System (SEDS) to deploy a 5-km bare copper tether from a Delta II upper stage to achieve -0,4 N drag thrust, thus deorbiting the stage, The experiment will use a predominantly "bare" tether for current collection in lieu of the endmass collector and insulated tether approach used on previous missions, Theory and ground-based plasma chamber testing indicate that the bare tether is a highly efficient current collector. The flight experiment is a precursor to utilization of the technology on the International Space tation (JSS) for reboost and the electrodynamic tether pper stage demonstration misión which will be capable of orbit raising, lowering, and inclination changes—all using electrodynamic thrust. In addition, the use of this type of propulsion may be attractive for future missions to Jupiter

Reversible Transformation of Pt Nanoparticles into Single Atoms inside High-Silica Chabazite Zeolite

[EN] We report the encapsulation of platinum species in highly siliceous chabazite (CHA) crystallized in the presence of N,N,N-trimethyl-1-adamantammonium and a thiol-stabilized Pt complex. When compared to Pt/SiO2 or Pt-containing Al-rich zeolites, the materials in this work show enhanced stability toward metal sintering in a variety of industrial conditions, including H-2, O-2, and H2O. Remarkably, temperatures in the range 650-750 degrees C can be reached without significant sintering of the noble metal. Detailed structural determinations by X-ray absorption spectroscopy and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy demonstrate subtle control of the supported metal structures from similar to 1 nm nanoparticles to site-isolated single Pt atoms via reversible interconversion of one species into another in reducing and oxidizing atmospheres. The combined used of microscopy and spectroscopy is critical to understand these surface-mediated transformations. When tested in hydrogenation reactions, Pt/CHA converts ethylene (similar to 80%) but not propylene under identical conditions, in contrast to Pt/SiO2, which converts both at similar rates. These differences are attributed to the negligible diffusivity of propylene through the small-pore zeolite and provide final evidence of the metal encapsulation.This work has been supported by the European Union through the SYNCATMATCH project (Grant Agreement No. 671093) and the Spanish Government through "Severo Ochoa Program" (SEV 2012-0267) and MAT2015-71261-R. This research used beamline 9-BM of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The Electron Microscopy Service of the UPV is acknowledged for their help in sample characterization. We thank Isabel Millet and Paul Stevens for technical assistance, and Randall Meyer, Aaron Sattler, and Dave Marler for review of the manuscript. We appreciate the support of ExxonMobil Research and Engineering for our efforts in fundamental catalytic research.Moliner Marin, M.; Gabay, JE.; Kliewer, CE.; Carr, RT.; Guzman, J.; Casty, GL.; Serna Merino, PM.... (2016). Reversible Transformation of Pt Nanoparticles into Single Atoms inside High-Silica Chabazite Zeolite. Journal of the American Chemical Society. 138(48):15743-15750. https://doi.org/10.1021/jacs.6b10169S15743157501384