12,966 research outputs found

    Tridyne attitude control thruster investigation Final report

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    Experimental results of feasibility Tridyne attitude control thruste

    Flight evaluation of advanced control systems and displays on a general aviation airplane

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    A flight-test program was conducted to determine the effect of advanced flight control systems and displays on the handling qualities of a light twin-engined airplane. A flight-director display and an attitude-command control system, used separately and in combination, transformed a vehicle with poor handling qualities during ILS approaches in turbulent air into a vehicle with good handling qualities. The attitude-command control system also improved the ride qualities of the airplane. A rate-command control system made only small improvements to the airplane's ILS handling qualities in turbulence. Both the rate- and the attitude-command control systems reduced stall warning in the test airplane, increasing the likelihood of inadvertent stalls. The final approach to the point of flare was improved by both the rate- and the attitude-command control systems. However, the small control wheel deflections necessary to flare were unnatural and tended to cause overcontrolling during flare. Airplane handling qualities are summarized for each control-system and display configuration

    Impact and Cost-Effectiveness of Point-Of-Care CD4 Testing on the HIV Epidemic in South Africa.

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    Rapid diagnostic tools have been shown to improve linkage of patients to care. In the context of infectious diseases, assessing the impact and cost-effectiveness of such tools at the population level, accounting for both direct and indirect effects, is key to informing adoption of these tools. Point-of-care (POC) CD4 testing has been shown to be highly effective in increasing the proportion of HIV positive patients who initiate ART. We assess the impact and cost-effectiveness of introducing POC CD4 testing at the population level in South Africa in a range of care contexts, using a dynamic compartmental model of HIV transmission, calibrated to the South African HIV epidemic. We performed a meta-analysis to quantify the differences between POC and laboratory CD4 testing on the proportion linking to care following CD4 testing. Cumulative infections averted and incremental cost-effectiveness ratios (ICERs) were estimated over one and three years. We estimated that POC CD4 testing introduced in the current South African care context can prevent 1.7% (95% CI: 0.4% - 4.3%) of new HIV infections over 1 year. In that context, POC CD4 testing was cost-effective 99.8% of the time after 1 year with a median estimated ICER of US$4,468/DALY averted. In healthcare contexts with expanded HIV testing and improved retention in care, POC CD4 testing only became cost-effective after 3 years. The results were similar when, in addition, ART was offered irrespective of CD4 count, and CD4 testing was used for clinical assessment. Our findings suggest that even if ART is expanded to all HIV positive individuals and HIV testing efforts are increased in the near future, POC CD4 testing is a cost-effective tool, even within a short time horizon. Our study also illustrates the importance of evaluating the potential impact of such diagnostic technologies at the population level, so that indirect benefits and costs can be incorporated into estimations of cost-effectiveness

    The Sound of Sonoluminescence

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    We consider an air bubble in water under conditions of single bubble sonoluminescence (SBSL) and evaluate the emitted sound field nonperturbatively for subsonic gas-liquid interface motion. Sound emission being the dominant damping mechanism, we also implement the nonperturbative sound damping in the Rayleigh-Plesset equation for the interface motion. We evaluate numerically the sound pulse emitted during bubble collapse and compare the nonperturbative and perturbative results, showing that the usual perturbative description leads to an overestimate of the maximal surface velocity and maximal sound pressure. The radius vs. time relation for a full SBSL cycle remains deceptively unaffected.Comment: 25 pages; LaTex and 6 attached ps figure files. Accepted for publication in Physical Review

    Gauge Theories with Cayley-Klein SO(2;j)SO(2;j) and SO(3;j)SO(3;j) Gauge Groups

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    Gauge theories with the orthogonal Cayley-Klein gauge groups SO(2;j)SO(2;j) and SO(3;j)SO(3;{\bf j}) are regarded. For nilpotent values of the contraction parameters j{\bf j} these groups are isomorphic to the non-semisimple Euclid, Newton, Galilei groups and corresponding matter spaces are fiber spaces with degenerate metrics. It is shown that the contracted gauge field theories describe the same set of fields and particle mass as SO(2),SO(3)SO(2), SO(3) gauge theories, if Lagrangians in the base and in the fibers all are taken into account. Such theories based on non-semisimple contracted group provide more simple field interactions as compared with the initial ones.Comment: 14 pages, 5 figure

    SYSTEM RESPONSE TIME, OPERATOR PRODUCTIVITY AND JOB SATISFACTION

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    This study examines the impact of on-line system response time on CRT operator productivity and job satisfaction. It was predicted that increase in response time would affect total transaction volume and total errors adversely, that is, total transaction volume would decrease with longer response times and total errors would increase. Total productive transactions, the difference between total transactions and total errors, was expected to decrease as response time increased. Operator job satisfaction was also expected to decrease. The study confirmed the prediction with regard to total transactions and productive transactions: both decreased as response time increased. Total errors actually decreased as response time increased, up to times of 12 seconds. When response time exceeded 12 seconds, errors increased. The impact of response time on productivity suggests nearly all transactions should be completed in 12 seconds or less. Beyond this level, the organization in the study suffered severe penalties in lost productivity. A relationship was also found between increased response times and reduced job satisfaction.Information Systems Working Papers Serie

    Complete high-precision entropic sampling

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    Monte Carlo simulations using entropic sampling to estimate the number of configurations of a given energy are a valuable alternative to traditional methods. We introduce {\it tomographic} entropic sampling, a scheme which uses multiple studies, starting from different regions of configuration space, to yield precise estimates of the number of configurations over the {\it full range} of energies, {\it without} dividing the latter into subsets or windows. Applied to the Ising model on the square lattice, the method yields the critical temperature to an accuracy of about 0.01%, and critical exponents to 1% or better. Predictions for systems sizes L=10 - 160, for the temperature of the specific heat maximum, and of the specific heat at the critical temperature, are in very close agreement with exact results. For the Ising model on the simple cubic lattice the critical temperature is given to within 0.003% of the best available estimate; the exponent ratios β/ν\beta/\nu and γ/ν\gamma/\nu are given to within about 0.4% and 1%, respectively, of the literature values. In both two and three dimensions, results for the {\it antiferromagnetic} critical point are fully consistent with those of the ferromagnetic transition. Application to the lattice gas with nearest-neighbor exclusion on the square lattice again yields the critical chemical potential and exponent ratios β/ν\beta/\nu and γ/ν\gamma/\nu to good precision.Comment: For a version with figures go to http://www.fisica.ufmg.br/~dickman/transfers/preprints/entsamp2.pd

    X-Ray Emission from the Warm Hot Intergalactic Medium

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    The number of detected baryons in the Universe at z<0.5 is much smaller than predicted by standard big bang nucleosynthesis and by the detailed observation of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a ``warm-hot'' (10^5-10^7K) filamentary gas, distributed in the intergalactic medium. This gas, if it exists, should be observable only in the soft X-ray and UV bands. Using the predictions of a particular hydrodynamic model, we simulated the expected X-ray flux as a function of energy in the 0.1-2 keV band due to the Warm-Hot Intergalactic Medium (WHIM), and compared it with the flux from local and high red-shift diffuse components. Our results show that as much as 20% of the total diffuse X-ray background (DXB) in the energy range 0.37-0.925keV could be due to X-ray flux from the WHIM, 70% of which comes from filaments at redshift z between 0.1 and 0.6. Simulations done using a FOV of 3', comparable with that of Suzaku and Constellation-X, show that in more than 20% of the observations we expect the WHIM flux to contribute to more than 20% of the DXB. These simulations also show that in about 10% of all the observations a single bright filament in the FOV accounts, alone, for more than 20% of the DXB flux. Red-shifted oxygen lines should be clearly visible in these observations.Comment: 19 pages, 6 figure

    Frequency evaluation of the doubly forbidden 1S0→3P0^1S_0\to ^3P_0 transition in bosonic 174^{174}Yb

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    We report an uncertainty evaluation of an optical lattice clock based on the 1S0↔3P0^1S_0\leftrightarrow^3P_0 transition in the bosonic isotope 174^{174}Yb by use of magnetically induced spectroscopy. The absolute frequency of the 1S0↔3P0^1S_0\leftrightarrow^3P_0 transition has been determined through comparisons with optical and microwave standards at NIST. The weighted mean of the evaluations is ν\nu(174^{174}Yb)=518 294 025 309 217.8(0.9) Hz. The uncertainty due to systematic effects has been reduced to less than 0.8 Hz, which represents 1.5×10−151.5\times10^{-15} in fractional frequency.Comment: 4 pages, 3 figure -Submitted to PRA Rapid Communication

    Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice

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    We report direct single-laser excitation of the strictly forbidden (6s^2)^1S_0 -(6s6p)^3P_0 clock transition in the even 174Yb isotope confined to a 1D optical lattice. A small (~1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FHWM) with high contrast were observed, demonstrating a record neutral-atom resonance quality factor of 2.6x10^13. The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35+/-0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks, and can create new clock possibilities in other alkaline earth-like atoms such as Mg and Ca.Comment: Submitted to Physics Review Letter
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