990 research outputs found

    Non-disturbing quantum measurements

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    We consider pairs of quantum observables (POVMs) and analyze the relation between the notions of non-disturbance, joint measurability and commutativity. We specify conditions under which these properties coincide or differ---depending for instance on the interplay between the number of outcomes and the Hilbert space dimension or on algebraic properties of the effect operators. We also show that (non-)disturbance is in general not a symmetric relation and that it can be decided and quantified by means of a semidefinite program.Comment: Minor corrections in v

    Capabilities of Earth-based radar facilities for near-Earth asteroid observations

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    We evaluated the planetary radar capabilities at Arecibo, the Goldstone 70-m DSS-14 and 34-m DSS-13 antennas, the 70-m DSS-43 antenna at Canberra, the Green Bank Telescope, and the Parkes Radio Telescope in terms of their relative sensitivities and the number of known near-Earth asteroids (NEAs) detectable per year in monostatic and bistatic configurations. In the 2015 calendar year, monostatic observations with Arecibo and DSS-14 were capable of detecting 253 and 131 NEAs respectively, with signal-to-noise ratios (SNRs) greater than 30/track. Combined, the two observatories were capable of detecting 276 NEAs. Of these, Arecibo detected 77 and Goldstone detected 32, or 30% and 24% the numbers that were possible. The two observatories detected an additional 18 and 7 NEAs respectively, with SNRs of less than 30/track. This indicates that a substantial number of potential targets are not being observed. The bistatic configuration with DSS-14 transmitting and the Green Bank Telescope receiving was capable of detecting about 195 NEAs, or ~50% more than with monostatic observations at DSS-14. Most of the detectable asteroids were targets of opportunity that were discovered less than 15 days before the end of their observing windows. About 50% of the detectable asteroids have absolute magnitudes > 25, which corresponds diameters < ~30 m.Comment: 12 pages, 7 figures, Accepted to A

    On the Dark Molecular Gas as Revealed by 18CM OH Emission

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    We explore the usage of the 18cm hydroxyl OH lines as a novel tool for observing and characterizing molecular gas on Galactic (kpc) scales. We report the results from a highly sensitive (ΔTmb3\Delta T_{\rm mb} \sim 3 mK) survey for thermal OH emission at 1665 and 1667 MHz over a dense, 9 x 9-pixel grid covering a 1×11^{\circ} \times 1^{\circ} patch of sky in the direction the Perseus spiral arm of our Galaxy. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. Both OH and CO emission disappear at current sensitivity limits below an Av_{\rm v} of 0.2 mag, but the CO emission does not appear until the volume density exceeds 100-200 cm3^{-3}. These results demonstrate that a combination of low column density (Av_{\rm v}) and low volume density (nHn_{\rm H}) can explain the lack of CO emission along sight lines exhibiting OH emission. We then present the serendipitous discovery of an extremely broad (ΔVLSR150\Delta V_{\rm LSR} \sim 150 km s1^{-1}), faint (Tmb8kpc)withtheGreenBankTelescope.ThelongitudevelocitydistributionoftheemissionunambiguouslysuggestslargescaleGalacticstructure.Ourresultsimplytheexistenceofathick(T_{\rm mb} 8 kpc) with the Green Bank Telescope. The longitude-velocity distribution of the emission unambiguously suggests large-scale Galactic structure. Our results imply the existence of a thick (-200< z < 200pc)diskofdiffuse( pc) disk of diffuse (n_{\rm H_{2}} \sim5 5 \times10 10^{-3}cm cm^{-3}$) molecular gas in the Outer Galaxy previously undetected in all-sky CO surveys. Finally, we present the first extragalactic detection of thermal (5:9 LTE ratio), ground-state 18cm (1667 and 1665 MHz) OH emission from the Southern galactic disk of M31. The velocity distribution of the OH emission is found to be similar to the HI distribution. At face value, these results may indicate the ubiquity of abundant `CO-dark` molecular gas at large galactic radii in spiral galaxies. We conclude this thesis with a technical overview of the field of radio observations of 18cm OH as a molecular gas tracer in the future and review upcoming telescopes which may enable large surveys of faint OH emission in the future

    Preparing Social Workers for Practice with LGBT Populations Affected by Substance Use: Perceptions from Students, Alumni and Service Providers

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    Trends in the field of service among those with alcohol and other drug addictions highlight the urgent need for schools of social work to effectively train students to serve clients with substance use disorders, and have cultural humility to effectively serve disproportionately affected LGBT consumers. Online surveys and interviews examined perceptions of graduate social work students and alumni in a certified alcohol and drug counselor program, along with several service providers within an urban setting in the US. Results indicated that students and alumni did not feel adequately prepared through coursework to practice with LGBT populations affected by substance use, while feeling more clinically competent to practice with LGB individuals, than with transgender consumers. Similar findings related to unique differences associated with perceptions of faculty support, along with field preparedness to practice with LGB individuals when compared to transgender individuals. Service providers noted an overall commitment and to serve LGBT consumers as well as positive perceptions of students and alumni to do the same. Implications examine the role of faculty in addressing challenges related to preparation of social work students to practice with LGBT consumers affected by substance use disorders, along with suggestions for curricular changes, and ongoing field trainings

    Aerodynamic Simulation of Runback Ice Accretion

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    This report presents the results of recent investigations into the aerodynamics of simulated runback ice accretion on airfoils. Aerodynamic tests were performed on a full-scale model using a high-fidelity, ice-casting simulation at near-flight Reynolds (Re) number. The ice-casting simulation was attached to the leading edge of a 72-in. (1828.8-mm ) chord NACA 23012 airfoil model. Aerodynamic performance tests were conducted at the ONERA F1 pressurized wind tunnel over a Reynolds number range of 4.7?10(exp 6) to 16.0?10(exp 6) and a Mach (M) number ran ge of 0.10 to 0.28. For Re = 16.0?10(exp 6) and M = 0.20, the simulated runback ice accretion on the airfoil decreased the maximum lift coe fficient from 1.82 to 1.51 and decreased the stalling angle of attack from 18.1deg to 15.0deg. The pitching-moment slope was also increased and the drag coefficient was increased by more than a factor of two. In general, the performance effects were insensitive to Reynolds numb er and Mach number changes over the range tested. Follow-on, subscale aerodynamic tests were conducted on a quarter-scale NACA 23012 model (18-in. (457.2-mm) chord) at Re = 1.8?10(exp 6) and M = 0.18, using low-fidelity, geometrically scaled simulations of the full-scale castin g. It was found that simple, two-dimensional simulations of the upper- and lower-surface runback ridges provided the best representation of the full-scale, high Reynolds number iced-airfoil aerodynamics, whereas higher-fidelity simulations resulted in larger performance degrada tions. The experimental results were used to define a new subclassification of spanwise ridge ice that distinguishes between short and tall ridges. This subclassification is based upon the flow field and resulting aerodynamic characteristics, regardless of the physical size of the ridge and the ice-accretion mechanism

    Comment on "Local accumulation times for source, diffusion, and degradation models in two and three dimensions" [J. Chem. Phys. 138, 104121 (2013)]

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    In a recent paper, Gordon, Muratov, and Shvartsman studied a partial differential equation (PDE) model describing radially symmetric diffusion and degradation in two and three dimensions. They paid particular attention to the local accumulation time (LAT), also known in the literature as the mean action time, which is a spatially dependent timescale that can be used to provide an estimate of the time required for the transient solution to effectively reach steady state. They presented exact results for three-dimensional applications and gave approximate results for the two-dimensional analogue. Here we make two generalizations of Gordon, Muratov, and Shvartsman’s work: (i) we present an exact expression for the LAT in any dimension and (ii) we present an exact expression for the variance of the distribution. The variance provides useful information regarding the spread about the mean that is not captured by the LAT. We conclude by describing further extensions of the model that were not considered by Gordon,Muratov, and Shvartsman. We have found that exact expressions for the LAT can also be derived for these important extensions..