11,224 research outputs found
A program to evaluate a control system based on feedback of aerodynamic pressure differentials, part 1
The use of pressure differentials in a flight control system was evaluated. The pressure profile around the test surface was determined using two techniques: (1) windtunnel data (actual); and (2) NASA/Langley Single Element Airfoil Computer Program (theoretical). The system designed to evaluate the concept of using pressure differentials is composed of a sensor drive and power amplifiers, actuator, position potentiometer, and a control surface. The characteristics (both desired and actual) of the system and each individual component were analyzed. The desired characteristics of the system as a whole are given. The flight control system developed, the testing procedures and data reduction methods used, and theoretical frequency response analysis are described
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Misbehavior, Suspensions, and Security Measures in High School: Racial/Ethnic and Gender Differences
This study used merged data from three national surveys to address questions about security measures in American high schools, suspension rates, and student misbehavior. First, the study identified the characteristics of schools that implemented the most extreme security measures and those with the highest levels of discipline. Second, the study used data on individual students to examine misbehavior and race and gender disparities in suspensions not attributable to misbehavior. The main findings were: (1) In-school suspensions serve a âgatewayâ function with regard to out-of-school suspensions. They may provide a time and place to address behavior problems before they escalate or disproportionate out-of-school suspensions before they occur; (2) Out-of-school suspensions were more frequent among schools in higher-crime neighborhoods. Thus students suspended may be relegated to an environment not conducive to positive educational or social outcomes; (3) African-American students and Hispanic/Latino students were suspended at higher rates than were non-Hispanic whites, differences in most cases not attributable to different levels of misbehavior; (4) Overall, males were more likely to be suspended than were females, an effect above and beyond that explained by differences in behavior. There was little or no difference in the suspension rates of black males and females, however; (5) High degrees of school security were associated with increased suspension rates and increased black â white disparities in total suspensions. At the same time, most black students were enrolled in schools with high degrees of security; (6) Black males were suspended at higher and higher rates as school size increased.
All of these have implications for school policy and practice. These are discussed in the paper together with limitations of the investigation
On the spin of gravitational bosons
We unearth spacetime structure of massive vector bosons, gravitinos, and
gravitons. While the curvatures associated with these particles carry a
definite spin, the underlying potentials cannot be, and should not be,
interpreted as single spin objects. For instance, we predict that a spin
measurement in the rest frame of a massive gravitino will yield the result 3/2
with probability one half, and 1/2 with probability one half. The simplest
scenario leaves the Riemannian curvature unaltered; thus avoiding conflicts
with classical tests of the theory of general relativity. However, the quantum
structure acquires additional contributions to the propagators, and it gives
rise to additional phases.Comment: Honorable mention, 2002 Gravity Research Foundation Essay
Turning Characteristics of U.S. Coast Guard Icebreaker M-5
http://deepblue.lib.umich.edu/bitstream/2027.42/96616/1/39015087359009.pd
Detecting an association between Ray and Gravitational Wave Bursts
If -ray bursts (GRBs) are accompanied by gravitational wave bursts (GWBs) the correlated output of two gravitational wave detectors evaluated in the moments just prior to a GRB will differ from that evaluated at times not associated with a GRB. We can test for this difference independently of any model of the GWB signal waveform. If we invoke a model for the GRB source population and GWB radiation spectral density we can find a confidence interval or upper limit on the root-mean-square GWB signal amplitude in the detector waveband. To illustrate we adopt a simple, physically motivated model and estimate that initial LIGO detector observations coincident with 1000 GRBs could lead us to exclude, with 95% confidence, associated GWBs with $h_{RMS} be Gaussian or that any inter-detector correlated noise be measured or measurable; it does not require advanced or a priori knowledge of the source waveform; and the limits obtained on the wave-strength improve with the number of observed GRBs
Topological Entropy of Braids on the Torus
A fast method is presented for computing the topological entropy of braids on
the torus. This work is motivated by the need to analyze large braids when
studying two-dimensional flows via the braiding of a large number of particle
trajectories. Our approach is a generalization of Moussafir's technique for
braids on the sphere. Previous methods for computing topological entropies
include the Bestvina--Handel train-track algorithm and matrix representations
of the braid group. However, the Bestvina--Handel algorithm quickly becomes
computationally intractable for large braid words, and matrix methods give only
lower bounds, which are often poor for large braids. Our method is
computationally fast and appears to give exponential convergence towards the
exact entropy. As an illustration we apply our approach to the braiding of both
periodic and aperiodic trajectories in the sine flow. The efficiency of the
method allows us to explore how much extra information about flow entropy is
encoded in the braid as the number of trajectories becomes large.Comment: 19 pages, 44 figures. SIAM journal styl
HMMER web server: interactive sequence similarity searching
HMMER is a software suite for protein sequence similarity searches using probabilistic methods. Previously, HMMER has mainly been available only as a computationally intensive UNIX command-line tool, restricting its use. Recent advances in the software, HMMER3, have resulted in a 100-fold speed gain relative to previous versions. It is now feasible to make efficient profile hidden Markov model (profile HMM) searches via the web. A HMMER web server (http://hmmer.janelia.org) has been designed and implemented such that most protein database searches return within a few seconds. Methods are available for searching either a single protein sequence, multiple protein sequence alignment or profile HMM against a target sequence database, and for searching a protein sequence against Pfam. The web server is designed to cater to a range of different user expertise and accepts batch uploading of multiple queries at once. All search methods are also available as RESTful web services, thereby allowing them to be readily integrated as remotely executed tasks in locally scripted workflows. We have focused on minimizing search times and the ability to rapidly display tabular results, regardless of the number of matches found, developing graphical summaries of the search results to provide quick, intuitive appraisement of them
Psychosocial Correlates of Physical Activity in Children and Adolescents in a Rural Community Setting
The purpose of this study was to evaluate the relationships between selected psychosocial factors and the physical activity behaviors of children (grade 4-8) and adolescents (grades 9-12) in a rural community setting. The Childrenâs Physical Activity Scale (CPAC)was used to measure the psychosocial factors of physical activity, The Physical Activity Questionnaire-Children (PAQ-C), and Physical Activity Questionnaire-Adolescents (PAQ-A) were used to measure the physical activity behaviors of the 167 participants. Results indicated that male and female physical activity behaviors were not significantly different. However, physical activity declined with age [F(8,147) = 5.44, p \u3c 0.05, ES = 0.23]. All psychosocial factors were significantly correlated with physical activity in youth with the single highest correlation for males being âliking of exerciseâ (r = .61) and the highest correlation for females was âliking of games and sportsâ(r = .44). Stepwise regression analyses identified three subscales (liking of games and sport, liking of exercise, and parental support) in a significant prediction model of physical activity in both genders. The results indicate that children\u27s physical activity is associated with a variety of psychosocial variables that represent import predisposing and reinforcing factors
Modeling the Large Scale Structures of Astrophysical Jets in the Magnetically Dominated Limit
We suggest a new approach that could be used for modeling both the large
scale behavior of astrophysical jets and the magnetically dominated explosions
in astrophysics. We describe a method for modeling the injection of magnetic
fields and their subsequent evolution in a regime where the free energy is
magnetically dominated. The injected magnetic fields, along with their
associated currents, have both poloidal and toroidal components, and they are
not force free. The dynamic expansion driven by the Lorentz force of the
injected fields is studied using 3-dimensional ideal magnetohydrodynamic
simulations. The generic behavior of magnetic field expansion, the interactions
with the background medium, and the dependence on various parameters are
investigated.Comment: Accepted to ApJ, May 10, 2006 issue, 12 figures total (3 color
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