32,560 research outputs found

    Effect of the geomagnetic field on the diffusion of meteor trains

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    A solution to the problem of the diffusion of a meteor train in the geomagnetic field from an initial line density may be written in closed form in terms of effective diffusion coefficients depending on direction, enabling detailed calculations across the entire range of angle of train to field and relevant heights. While the effective diffusion coefficient in the plane of train and field then remains close to the zero field ambipolar value right up to 90 deg, the effective coefficient in the direction of the normal to plane of train and field drops steadily to its theta = 0 value at theta = 90 deg. At 95 km this corresponds to a change of almost 5 km, in 'diffusion height', that is, the height of an underdense meteor calculated on the basis of the exponential decay of its radar echo. We have estimated the consequent changes in the expected distribution of diffusion heights for various orientations of radar antenna and find the dependence on azimuth is very marked. The effect of the field is relatively minor for a south pointing beam but very strong if the beam is pointing north

    Music for large orchestra

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    Thesis (M.M.)--Boston University, 1963. A composition presented to the faculty of the School of Fine and Applied Arts, Boston University, in partial fulfillment of the requirements for the degree Master of Music, August 196

    Time is of the Essence: What the past 500 years means for the future of Black Male Achievement

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    This timeline seeks to shed light on how 500 years of slavery, discrimination and disenfranchisement has contributed to the current employment and economic crisis faced by African American men in the United States. In 2012, there were almost 6 million African American men and youth unemployed or not actively seeking work. Of this number, nearly 3.5 million were low income - below 200% of the federal threshold. From the 1960's until today, unemployment rates for black men have been 2 to 2.5 times the white unemployment rate. At the height of the Great Recession, the unemployment rate for black men peaked at 14%, which was nearly double the national average of 6.6% and higher than the national average during the great depression. As of May 2014, there were 717,000 unemployed black youth between the ages of 16-24 in the United States. Recognizing the implications of the historical, social, and political factors and decisions that have contributed to the current employment crisis faced by African American men and youth is critical to shaping future policy

    1991 NCCD Prison Population Forecast: The Impact of Declining Drug Arrests (FOCUS)

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    According to the National Council and Crime and Delinquency (NCCD), prison populations will increase by 35 percent over the next five years under the current criminal justice policies. This rate of growth is significantly lower than NCCD's 1989 estimates of a 60 percent increase over five years. The principal reason for the lower growth rate is a 20 percent reduction in drug arrests, which in turn is reducing projected jail and prison admissions. The declining number of drug arrests are related to the fiscal crisis of state and local governments, drug asset and seizure laws, and lower drug use. However, prison populations will continue to grow despite reductions in admissions due to the passage of mandatory minimum sentencing statutes and lengthier prison terms for certain crimes. Assuming that the 16 states researched are representative of trends that are on-going in other states and the Federal Prison System, the nation's prison population will reach 1 million inmates by 1994

    Low Impact Storm Water Management Projects at the University of New Hampshire

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    The University of New Hampshire has become increasingly concerned with storm water management on the Durham campus. Due to Federal regulations many regional municipalities are feeling pressure to enhance and increase management of storm water to reduce impacts to surface waters. The specific objective of this proposal is to demonstrate reductions in the discharge of storm water runoff from UNH-Durham campus properties. The construction and use of three Low Impact Development (LID) integrated management systems on UNH property will help UNH and the UNH Stormwater Center to champion innovative approaches in the state and region for reducing storm water runoff and improving the health of coastal watershed areas

    Batch means and spectral variance estimators in Markov chain Monte Carlo

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    Calculating a Monte Carlo standard error (MCSE) is an important step in the statistical analysis of the simulation output obtained from a Markov chain Monte Carlo experiment. An MCSE is usually based on an estimate of the variance of the asymptotic normal distribution. We consider spectral and batch means methods for estimating this variance. In particular, we establish conditions which guarantee that these estimators are strongly consistent as the simulation effort increases. In addition, for the batch means and overlapping batch means methods we establish conditions ensuring consistency in the mean-square sense which in turn allows us to calculate the optimal batch size up to a constant of proportionality. Finally, we examine the empirical finite-sample properties of spectral variance and batch means estimators and provide recommendations for practitioners.Comment: Published in at http://dx.doi.org/10.1214/09-AOS735 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org
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