Effect of flow on the acoustic reflection coefficient at a duct inlet

The effect of duct Mach number upon the acoustic reflection coefficient at the inlet of a duct with mean flow is investigated. An analysis, which models the duct inlet as a very short, one-dimensional nozzle over which the mean flow is accelerated from rest, gives good agreement with some recent experimental results. Discrepancies between the analysis and the experimental results are discussed in terms of radiation losses at the inlet and real fluid-flow effects within the duct

Predicting Bullying Among High School Students Using Individual and School Factors: Analysis of a National Survey

Being bullied has been recognized as a problem within the U.S. school systems. Individuals who have been bullied physically, verbally, relationally, or electronically typically suffer from mental health problems as a result. As it has been shown that males are more at risk for being bullied, it is important to understand what variables can predict males being bullied in order to design appropriate preventions and interventions to curb bullying in the schools. Four forms of school bullying behaviors among U.S. adolescent males and their association with type of bullying, school environment, and school performance and engagement variables were examined. Data were examined from the National Crime Victimization Survey School Crime Supplement. A sample of 1,636 males ages 14 to 18 was used from the survey. A series of logistic regression analyses were performed for each type of bullying (physical, verbal, relational, and cyber) and school environment (presence of gangs, guns, graffiti, drugs, and number of school safety measures in place) and school performance and engagement predictors (grades, extracurricular activity engagement, truancy, and number of fights). Linear regression analyses were also used to look at all the predictor variables and the frequency of each type of bullying. Results: The R2 values for the logistic regression analyses were quite small. However, trends could be observed from the odds ratios showing that fighting, drug availability, and graffiti were predictive of all four forms of bullying. The linear regression analyses also produced small R2 values. Effect plots were created to identify which significant variables had a greater effect on the frequency of being bullied. Conclusion: Schools should focus on removing graffiti and drugs from the schools. Prevention work should be used to help students find alternative ways to deal with problems other than resorting to fighting. Problems with reliability and validity of the survey are also discussed

Chaotic Orbits in Thermal-Equilibrium Beams: Existence and Dynamical Implications

Phase mixing of chaotic orbits exponentially distributes these orbits through their accessible phase space. This phenomenon, commonly called ``chaotic mixing'', stands in marked contrast to phase mixing of regular orbits which proceeds as a power law in time. It is operationally irreversible; hence, its associated e-folding time scale sets a condition on any process envisioned for emittance compensation. A key question is whether beams can support chaotic orbits, and if so, under what conditions? We numerically investigate the parameter space of three-dimensional thermal-equilibrium beams with space charge, confined by linear external focusing forces, to determine whether the associated potentials support chaotic orbits. We find that a large subset of the parameter space does support chaos and, in turn, chaotic mixing. Details and implications are enumerated.Comment: 39 pages, including 14 figure