18,643 research outputs found

    Some Constraints On the Effects of Age and Metallicity on the Low Mass X-ray Binary Formation Rate

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    We have studied the low mass X-ray binary (LMXB) populations within and outside globular clusters (GC) in NGC 4365 and NGC 3115. Using published age and metallicity constraints from optical and IR observations of their GCs, we do not find any evidence for an increase in the LMXB formation rate in the intermediate age cluster population of NGC 4365, as has been proposed in some scenarios of dynamical LMXB formation in GCs. The old, metal-rich, red population of GCs in NGC 3115 on the other hand is {\it at least} three times as efficient at creating LMXBs as the old, metal-poor, blue clusters. These data suggest that the higher formation efficiency of LMXBs in the red GC subsystems of many galaxies is largely a consequence of their higher metallicity. A comparison of the densities of field LMXBs in different galaxies does not reveal an obvious correlation with the age of the field stars as predicted by models in which the LMXB formation rate in the field drops monotonically with time after an initial burst. This suggests that either a significant fraction of the field LMXBs are created in GCs and subsequently injected into the field, or the LMXB formation rate has a more complex time evolution pattern.Comment: Accepted for publication in ApJ Letters. 7 pages including 5 figure

    Simultaneous measurement of multiple parameters of a subwavelength structure based on the weak value formalism

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    A mathematical extension of the weak value formalism to the simultaneous measurement of multiple parameters is presented in the context of an optical focused vector beam scatterometry experiment. In this example, preselection and postselection are achieved via spatially-varying polarization control, which can be tailored to optimize the sensitivity to parameter variations. Initial experiments for the two-parameter case demonstrate that this method can be used to measure physical parameters with resolutions at least 1000 times smaller than the wavelength of illumination

    EVALUATION OF ALTERNATIVE RISK SPECIFICATIONS IN FARM PROGRAMMING MODELS

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    The use of alternative probability density functions to specify risk in farm programming models is explored and compared to a traditional specification using historical data. A method is described that compares risk efficient crop mixes using stochastic dominance techniques to examine impacts of different risk specifications on farm plans. Results indicate that a traditional method using historical farm data is as efficient for risk averse producers as two other methods of incorporating risk in farm programming models when evaluated using second degree stochastic dominance. Stochastic dominance with respect to a function further discriminates among the distributions, indicating that a density function based on the historic forecasting accuracy of the futures market results in a more risk-efficient crop mix for highly risk averse producers. Results also illustrate the need to validate alternative risk specifications perceived as improvements to traditional methods.Risk and Uncertainty,
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