51,392 research outputs found

    Aerodynamic performance of 0.5 meter-diameter, 337 meter-per-second tip speed, 1.5 pressure-ratio, single-stage fan designed for low noise aircraft engines

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    Overall and blade-element aerodynamic performance of a 0.271-scale model of QF-1 are presented, examined, and then compared and evaluated with that from similar low noise fan stage designs. The tests cover a wide range of speeds and weight flows along with variations in stator setting angle and stator axial spacing from the rotor. At design speed with stator at design setting angle and a fixed distance between stage measuring stations, there were no significant effects of increasing the axial spacing between rotor stator from 1.0 to 3.5 rotor chords on stage overall pressure ratio, efficiency or stall margin

    Association between obesity and bacterial vaginosis as assessed by Nugent score

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    Background Bacterial vaginosis is one of the most common vaginal conditions in the U.S. Recent studies have suggested obese women have an abnormal microbiota reminiscent of BV; however, few studies have investigated the prevalence of bacterial vaginosis in overweight and obese populations. Moreover, despite the increased prevalence of obesity and bacterial vaginosis in black women, it is not known whether racial disparities exist in the relationship between obesity and bacterial vaginosis. Objective The objective of this study was to examine the relationship between body mass index and bacterial vaginosis as determined by Nugent score and to determine the influence of race in this context. Study Design We performed a cross-sectional study using patient data and vaginal smears from 5,918 participants of the Contraceptive CHOICE Project. Gram stained vaginal smears were scored using the Nugent method and categorized as BV-negative (Nugent score 0-3), BV-intermediate (Nugent score 4-6), or BV-positive (Nugent score 7-10). Body mass index was determined using Centers for Disease Control and Prevention guidelines and obese individuals were categorized as Class I, II, or III obese based on NIH and World Health Organization body mass index parameters. Linear regression was used to model mean differences in Nugent scores and Poisson regression with robust error variance was used to model prevalence of bacterial vaginosis. Results In our cohort, 50.7% of participants were black, 41.5% were white, and 5.1% were of Hispanic ethnicity with an average age of 25.3 years old. Overall, 28.1% of participants were bacterial vaginosis-positive. Bacterial vaginosis was prevalent in 21.3% of lean, 30.4% of overweight, and 34.5% of obese women (p<0.001). The distribution of bacterial vaginosis-intermediate individuals was similar across all body mass index categories. Compared to lean women, Nugent scores were highest among overweight and obese Class I women (adjusted mean difference; overweight 0.33 [95% CI 0.14, 0.51] and Class I obese 0.51 [95% CI 0.29, 0.72]). Consistent with this, overweight and obese women had a higher frequency of bacterial vaginosis compared to lean women, even after adjusting for variables including race. Among white women, the prevalence of BV was higher for overweight and Class I and Class II/III obese white women compared to lean white women, a phenomenon not observed among black women, suggesting an effect modification. Conclusion Overweight and obese women have higher Nugent scores and a greater occurrence of bacterial vaginosis compared to lean women. Black women have a greater prevalence of bacterial vaginosis independent of their body mass index compared to white women

    Uncovering CDM halo substructure with tidal streams

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    Models for the formation and growth of structure in a cold dark matter dominated universe predict that galaxy halos should contain significant substructure. Studies of the Milky Way, however, have yet to identify the expected few hundred sub-halos with masses greater than about 10^6 Msun. Here we propose a test for the presence of sub-halos in the halos of galaxies. We show that the structure of the tidal tails of ancient globular clusters is very sensitive to heating by repeated close encounters with the massive dark sub-halos. We discuss the detection of such an effect in the context of the next generation of astrometric missions, and conclude that it should be easily detectable with the GAIA dataset. The finding of a single extended cold stellar stream from a globular cluster would support alternative theories, such as self-interacting dark matter, that give rise to smoother halos.Comment: 7 pages, 7 figures, submitted to MNRA

    The perimeter of large planar Voronoi cells: a double-stranded random walk

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    Let p_np\_n be the probability for a planar Poisson-Voronoi cell to have exactly nn sides. We construct the asymptotic expansion of logā”p_n\log p\_n up to terms that vanish as nā†’āˆžn\to\infty. We show that {\it two independent biased random walks} executed by the polar angle determine the trajectory of the cell perimeter. We find the limit distribution of (i) the angle between two successive vertex vectors, and (ii) the one between two successive perimeter segments. We obtain the probability law for the perimeter's long wavelength deviations from circularity. We prove Lewis' law and show that it has coefficient 1/4.Comment: Slightly extended version; journal reference adde

    Effect of Multiple Higgs Fields on the Phase Structure of the SU(2)-Higgs Model

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    The SU(2)-Higgs model, with a single Higgs field in the fundamental representation and a quartic self-interaction, has a Higgs region and a confinement region which are analytically connected in the parameter space of the theory; these regions thus represent a single phase. The effect of multiple Higgs fields on this phase structure is examined via Monte Carlo lattice simulations. For the case of N>=2 identical Higgs fields, there is no remaining analytic connection between the Higgs and confinement regions, at least when Lagrangian terms that directly couple different Higgs flavours are omitted. An explanation of this result in terms of enhancement from overlapping phase transitions is explored for N=2 by introducing an asymmetry in the hopping parameters of the Higgs fields. It is found that an enhancement of the phase transitions can still occur for a moderate (10%) asymmetry in the resulting hopping parameters.Comment: 10 pages, 8 figures. References updated and minor typos correcte

    Anomalous isotopic predissociation in the FĀ³Ī u(v=1) state of Oā‚‚

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    Using a tunable, narrow-bandwidth vacuum-ultraviolet source based on third-harmonic generation from excimer-pumped dye-laser radiation, the FĀ³Ī uā†XĀ³Ī£g-(1,0)photoabsorption cross sections of Ā¹ā¶Oā‚‚ and Ā¹āøOā‚‚ have been recorded in high resolution. Rotational analyses have been performed and the resultant F(v=1) term values fitted to the Ā³Ī  Hamiltonian of Brown and Merer [J. Mol. Spectrosc. 74, 488 (1979)]. A large rotationless isotope effect is observed in the F(v=1)predissociation, wherein the Lorentzian linewidth component for Ā¹āøOā‚‚ is a factor of āˆ¼50 smaller than the corresponding Ā¹ā¶Oā‚‚linewidth. This effect, a consequence of the nonadiabatic rotationless predissociation mechanism, is described using a coupled-channel treatment of the strongly Rydberg-valence-mixed 3Ī u states. Significant J, e/f-parity, and sublevel dependencies observed in the isotopic F(v=1) rotational widths are found to derive from an indirect predissociation mechanism involving an accidental degeneracy with the EĀ³Ī£āˆ’u(v=3) level, itself strongly predissociated by Ā³Ī£āˆ’u Rydberg-valence interactions, together with L-uncoupling (rotational) interactions between the Rydberg components of the F and E states. Transitions into the E(v=3) level are observed directly for the first time, specifically in the Ā¹āøOā‚‚ spectrumPartial support was provided by an NSF International Opportunities for Scientists and Engineers Program Grant No. INT-9513350, and Visiting Fellowships for G.S. and J.B.W. at the Australian National University

    Microlensing of Broad Absorption Line Quasars: Polarization Variability

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    Roughly 10% of all quasars exhibit Broad Absorption Line (BAL) features which appear to arise in material outflowing at high velocity from the active galactic nucleus (AGN). The details of this outflow are, however, very poorly constrained and the particular nature of the BAL material is essentially unknown. Recently, new clues have become available through polarimetric studies which have found that BAL troughs are more polarized than the quasar continuum radiation. To explain these observations, models where the BAL material outflows equatorially across the surface of the dusty torus have been developed. In these models, however, several sources of the BAL polarization are possible. Here, we demonstrate how polarimetric monitoring of gravitationally lensed quasars, such as H 1413+117, during microlensing events can not only distinguish between two currently popular models, but can also provide further insight into the structure at the cores of BAL quasars.Comment: 17 pages, 3 figures, accepted to PAS

    Risk, standard deviation, and expected value: when should an individual start social security?

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    In choosing when to start collecting Social Security, the differences in expected net present values (NPVs) are smallā€”but the corresponding standard deviations are not. Starting earlier is less risky. The case analyzed is single individuals in the U.S. system, but the methodology can be applied to couples and to the systems of other nations. Considering risk and return together places Social Security in the same risk/return framework as other capital investments. Behavioral, situational, and qualitative factors that often dominate decisions on when to start are linked with quantitative approaches to longevity risk and mortality risk
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