42,909 research outputs found
Effect of the geomagnetic field on the diffusion of meteor trains
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
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
Evolution of the Quadrantid meteor stream
According to previous orbital calculations, the last close approach of the Quadrantid stream with Jupiter occurred 3200 years ago at which time the parent comet of the stream may have been captured into its present short-period orbit. If this is the case the stream may only be a few thousand years old. We have modeled the evolution of the stream to determine if such a short time scale is consistent with the observed features of the Quadrantid/ delta- Aquarid/Arietid/Ursid complex. A detailed modeling of a stream consisting of 500 test particles released 4000 yr ago and which included the effects of the gravitational perturbations of 6 planets as well as the likely spread in the initial orbital elements resulting from the ejection of the grains from the comet was carried out. Our calculations indicate that an intense shower should be seen a few days before the Quadrantid shower, and that, 4000 yr is too short a period for the branch corresponding to the D-Arietid branch to appear. We have considered the quasi-constants of motion 1/a and J, the Tisserand quantity, and find that the Ursids and the D-Arietids are unlikely to be members of the complex, and that, the complex is probably be less than 4000 yr old
Time is of the Essence: What the past 500 years means for the future of Black Male Achievement
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)
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
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
Changes in heart rate and heart rate variability as a function of age in Thoroughbred horses.
We investigated changes in heart rate (HR) and HR variability as a function of age in newborn foals to old Thoroughbred horses. Experiments were performed on a total of 83 healthy and clinically normal Thoroughbred horses. Resting HR decreased with age from birth. The relationship between age and HR fit the equation Y=48.2X-0.129(R2=0.705); the relationship between age and HR for horses 0-7 years old fit the equation Y=44.1X-0.179(R2=0.882). Seven-day-old horses had the highest HR values (106 ± 10.3 beat/min). The low frequency (LF) and high frequency (HF) powers increased with age in newborn to old horses. These changes in HR and HR variability appear to result from the effects of ageing. Three- to seven-year-old race horses had the lowest HR values (32.9 ± 3.5 beat/min) and the highest LF and HF powers except for the HF powers in the oldest horses. Race training may have contributed to these changes. Horses of ages greater than 25 years old had the highest HF powers and the lowest LF/HF ratios. In individual horses, 8 of the 15 horses over 25 years old had LF/HF ratios of less than 1.0; their HR variability appears to be unique, and they may have a different autonomic balance than horses of younger age
Batch means and spectral variance estimators in Markov chain Monte Carlo
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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