Hoyle-Lyttleton Accretion in Three Dimensions

We investigate the stability of gravitational accretion of an ideal gas onto a compact object moving through a uniform medium at Mach 3. Previous three-dimensional simulations have shown that such accretion is not stable, and that strong rotational 'disk-like' flows are generated and accreted on short time scales. We re-address this problem using overset spherical grids that provide a factor of seven improvement in spatial resolution over previous simulations. With our higher spatial resolution we found these 3D accretion flows remained remarkably axisymmetric. We examined two cases of accretion with different sized accretors. The larger accretor produced very steady flow, with the mass accretion rate varying by less than 0.02% over 30 flow times. The smaller accretor exhibited an axisymmetric breathing mode that modulated the mass accretion rate by a constant 20%. Nonetheless, the flow remained highly axisymmetric with only negligible accretion of angular momentum in both cases.Comment: 6 pages, 6 figures. Submitted to Ap

Estimating time to achieve groundwater protection standards using exponential decline plots

Groundwater concentrations tend to decline exponentially over time and distance due to natural attenuation or remedial actions. Exponential decline plots make use of existing data to empirically predict the time or distance to achieve groundwater protection standards and can be used in lieu of numerical modeling where there is a large amount of historical groundwater monitoring data for the site.Sponsored by: Georgia Environmental Protection Division U.S. Geological Survey, Georgia Water Science Center U.S. Department of Agriculture, Natural Resources Conservation Service Georgia Institute of Technology, Georgia Water Resources Institute The University of Georgia, Water Resources Facult

Employment Concerns of Deaf University Students

In response to a questionnaire distributed at a university-sponsored job fair, 661 students of Gallaudet University responded to questions regarding their employment concerns. Respondents identified employment strengths in two areas-college life and self-efficacy. Students identified three aspects of career preparation- training, resources, and career selection—as problems. The findings emphasize the importance of assisting students with hearing impairments or deafness to address career-related concerns

Interferometric imaging using shared quantum entanglement

Quantum entanglement-based imaging promises significantly increased resolution by extending the spatial separation of optical collection apertures used in very-long-baseline interferometry for astronomy and geodesy. We report a table-top entanglement-based interferometric imaging technique that utilizes two entangled field modes serving as a phase reference between two apertures. The spatial distribution of a simulated thermal light source is determined by interfering light collected at each aperture with one of the entangled fields and performing joint measurements. This experiment demonstrates the ability of entanglement to implement interferometric imaging

Optical Phase-Space-Time-Frequency Tomography

We present a new approach for constructing optical phase-space-time-frequency tomography (OPSTFT) of an optical wave field. This tomography can be measured by using a novel four-window optical imaging system based on two local oscillator fields balanced heterodyne detection. The OPSTFT is a Wigner distribution function of two independent Fourier Transform pairs, i.e., phase-space and time-frequency. From its theoretical and experimental aspects, it can provide information of position, momentum, time and frequency of a spatial light field with precision beyond the uncertainty principle. We simulate the OPSTFT for a light field obscured by a wire and a single-line absorption filter. We believe that the four-window system can provide spatial and temporal properties of a wave field for quantum image processing and biophotonics.Comment: 11 pages, 6 figure

Estructura agraria y dinámica de pobreza rural en el Perú

A partir de un panel provincial para el periodo entre los censos agropecuarios de 1994 y el 2012, este estudio pretende esclarecer el signo de la relación entre estructura agraria y dinámicas de pobreza rural en el Perú. Los resultados descriptivos revelan que las provincias con reducciones importantes en las tasas de pobreza rural son aquellas cuyas unidades agropecuarias tenían, al inicio del periodo, una mayor cantidad de tierra agrícola - en equivalente de riego -, una estructura de propiedad menos fragmentada, una distribución de la tierra más equitativa y una mayor proporción de productores con capacidad de innovación tecnológica. Por otro lado, los resultados econométricos sugieren que un importante determinante de la dinámica de pobreza rural observada es el tamaño de la propiedad, y no la estructura agraria. Asimismo, se muestra que las provincias cuya tasa de emigración es más alta y cuya tasa de inmigración es más baja son las que sufren un mayor aumento de la pobreza rural. Por último, junto con variables que pueden estar determinando un acceso diferenciado a los mercados, persiste un impacto positivo del grado de diversificación de la actividad productiva sobre las posibilidades de generar dinámicas de reducción de la pobreza en áreas rurales

End-to-End Model Driven Policy Based Network Management

The continued movement towards converged networks changes the focus to building application services that enable customers to move between different types of service providers based on their needs. Policy management becomes paramount for the rapid deployment and management of these application services. This paper presents the concept of a policy continuum and discusses the importance of modelling and natural languages in the presence of the policy continuum, resulting in a novel architecture suitable for autonomic computing

Conceptual and Numerical Analysis of Active Wingtip Vortex Cancellation in Propeller-Driven Electric Aircraft

As battery and electric motor technology continues to advance rapidly, propeller-driven electric aircraft are likely to become a significant part of the aviation market in the near future. One proposed design configuration for electric aircraft involves using large, wingtip- mounted propellers to actively cancel wingtip vortices, a method called active wingtip vortex cancellation (AWVC). By reclaiming part of the kinetic energy that would otherwise be lost to tip vortex formation, drag is decreased. In addition, the induced spanwise flow and upwash from the propeller causes the spanwise lift distribution to remain more uniform at the wingtips, increasing lift. Previous wind tunnel testing of this configuration characterized a significant increase in lift and decrease in drag, particularly in low-aspect-ratio configurations. This paper builds on that research by examining several test cases with a 3D, transient, viscous, sliding mesh CFD analysis in an effort to validate numerical methods for future conceptual design studies. In addition, many practical considerations regarding the implementation of this design are analyzed. Geometry from the aforementioned wind tunnel literature was reconstructed and analyzed. CFD indicated an 18.1% increase in lift and 5.1% increase in net thrust was possible solely through the phenomenon of AWVC. Furthermore, this CFD analysis matched wind tunnel data to within approximately 1%, validating the CFD approach for the analysis of more exotic configurations involving active wingtip vortex cancellation

Biomonitoring of Exposure in Farmworker Studies

Although biomonitoring has been used in many occupational and environmental health and exposure studies, we are only beginning to understand the complexities and uncertainties involved with the biomonitoring process—from study design, to sample collection, to chemical analysis—and with interpreting the resulting data. We present an overview of concepts that should be considered when using biomonitoring or biomonitoring data, assess the current status of biomonitoring, and detail potential advancements in the field that may improve our ability to both collect and interpret biomonitoring data. We discuss issues such as the appropriateness of biomonitoring for a given study, the sampling time frame, temporal variability in biological measurements to nonpersistent chemicals, and the complex issues surrounding data interpretation. In addition, we provide recommendations to improve the utility of biomonitoring in farmworker studies

Association of lower fractional flow reserve values with higher risk of adverse cardiac events for lesions deferred revascularization among patients with acute coronary syndrome

BACKGROUND: The safety of deferring revascularization based on fractional flow reserve (FFR) during acute coronary syndrome (ACS) is unclear. We evaluated the association of FFR and adverse cardiac events among patients with coronary lesions deferred revascularization based on FFR in the setting of ACS versus non-ACS. METHODS AND RESULTS: The study population (674 patients; 816 lesions) was divided into ACS (n=334) and non-ACS (n=340) groups based on the diagnosis when revascularization was deferred based on FFR values >0.80 between October 2002 and July 2010. The association and interaction between FFR and clinical outcomes was evaluated using Cox proportional hazards models within each group (mean follow-up of 4.5±2.1 years). Subsequent revascularization of a deferred lesion was classified as a deferred lesion intervention (DLI), whereas the composite of DLI or myocardial infarction (MI) attributed to a deferred lesion was designated as deferred lesion failure (DLF). In the non-ACS group, lower FFR values were not associated with any increase in adverse cardiac events. In the ACS group, every 0.01 decrease in FFR was associated with a significantly higher rate of cardiovascular death, MI, or DLI (hazard ratio [HR], 1.08; 95% confidence interval [CI], 1.03 to 1.12), MI or DLI (HR, 1.09; 95% CI: 1.04 to 1.14), DLF (HR, 1.12; 95% CI, 1.06 to 1.18), MI (HR, 1.07; 95% CI, 1.00 to 1.14), and DLI (HR, 1.12; 95% CI, 1.06 to 1.18). CONCLUSION: Lower FFR values among ACS patients with coronary lesions deferred revascularization based on FFR are associated with a significantly higher rate of adverse cardiac events. This association was not observed in non-ACS patients