Students in rural schools have limited access to advanced mathematics courses

This Carsey brief reveals that students in rural areas and small towns have less access to higher-level mathematics courses than students in urban settings, which results in serious educational consequences, including lower scores on assessment tests and fewer qualified students entering science, technology, engineering, and mathematics (STEM) job pipelines

Theoretical study of refraction effects on noise produced by turbulent jets

The transmission of acoustic disturbances from the interior of a jet into the ambient air is studied. The jet is assumed infinitely long with mean velocity profile independent of streamwise location. The noise generator is a sequence of transient sources drifting with the local fluid and confined to a short length of the jet. In Part 1, supersonic jets are considered. Numerical results for mean-square pressure versus angle in the far-field show unexpected peaks which are very sharp. Analysis of simplified models indicates that these are complex quasi-resonant effects which appear to the stationary observer in a high frequency range. The peaks are real for the idealized model, but would be smoothed by mathematical integration over source position, velocity, and frequency. Subsonic jets were considered in part 2, and a preliminary study of the near-field was attempted. Mean-square radial displacements (or mean radial energy flow or space-time correlations of radial pressure gradient) are first found for very simple cases. The most difficult case studied is a sequence of transient sources at the center of a uniform-velocity circular cylindrical jet. Here a numerical triple integration is required and seems feasible although only preliminary results for mean square radial displacement are now available. These preliminary results show disturbances decreasing with increasing radial distance, and with increasing distance upstream and downstream from the source. A trend towards greater downstream disturbances appears even in the near field

Mathematics achievement gaps between suburban students and their rural and urban peers increase over time

In this brief, authors Suzanne Graham and Lauren Provost examine whether attending a school in a rural, urban, or suburban community is related to children’s mathematics achievement in kindergarten, and whether increases in mathematics achievement between kindergarten and eighth grade differ for children in rural, urban, and suburban schools. They also consider whether achievement differs by region of the country and for children of different racial and ethnic groups. Finally, they discuss the impact of a family’s socioeconomic status, and the ways in which place and socioeconomic status together affect both early mathematics achievement levels and change over time. They report that rural and urban kindergarten students have slightly lower average mathematics achievement levels than their suburban peers. In addition, the average increase in mathematics achievement from kindergarten to eighth grade for rural and urban children is smaller than the increase for suburban children, resulting in a widening achievement gap over time

Effect of Gimbal friction modeling technique on control stability and performance for Centaur upper-stage

The powered-phase autopilot for the Centaur upper stage rocket uses an autopilot forward loop gain scheduler that decreases the proportional gain as propellant mass is depleted. Nonlinear time response simulation studies revealed that Centaur vehicles with low-gain autopilots would have large attitude error limit cycles. These limit cycles were due to the assumed presence of Coulomb friction in the engine gimbals. This situation could be corrected through the use of an harmonic dither, programmed into the on-board digital computer and added to the engine command signal. This would introduce impending motion to the engines, allowing control of the engines even under small commands. Control authority was found to be restored when dither was used. A concern arose that the Centaur could be unacceptably excited at resonances near the dither frequency, if the dither amplitude was to be chosen on the basis of friction level present, a test was conducted to measure this level. Dither characteristics were to be based on the test results. The test results showed that the gimbal friction characteristic was actually hysteretic rather than the assumed Coulomb friction. The simulation results showed that, using this new model of gimbal friction, dither would no longer be necessary

Prime divisors of sequences associated to elliptic curves

We consider the primes which divide the denominator of the x-coordinate of a sequence of rational points on an elliptic curve. It is expected that for every sufficiently large value of the index, each term should be divisible by a primitive prime divisor, one that has not appeared in any earlier term. Proofs of this are known in only a few cases. Weaker results in the general direction are given, using a strong form of Siegel's Theorem and some congruence arguments. Our main result is applied to the study of prime divisors of Somos sequences

Reading levels of rural and urban third graders lag behind their suburban peers

This brief examines the complex interplay of family, school, and place factors in the reading achievement levels of third grade students. Third grade reading achievement is critical to later academic and occupational success. Using data from the Early Childhood Longitudinal Study, the authors report that suburban children realize greater gains in reading achievement from kindergarten to Grade 3 than their rural or urban counterparts. Rural students who were struggling readers at the beginning of kindergarten have lower average reading achievement in third grade than both urban and suburban students when children of the same socioeconomic status are compared. The differences in third grade reading achievement between rural and nonrural children who were low achievers in kindergarten most likely reflect different educational opportunities and school resources available to these children. The authors suggest that improved professional development opportunities for rural teachers may help narrow the differences in the third grade reading achievement of rural, urban, and suburban students who were struggling readers in kindergarten