Child poverty in rural America: new data shows increases in 41 states

A study by the Carsey Institute, based on U.S. Census Bureau data, found that in forty-one states, a higher percentage of rural children live in poverty than did in 2000. While the poverty level in 2006 was relatively stagnant compared to 2005\u27s poverty level, the situation is clearly becoming worse for rural kids

Child poverty high in rural America

On August 28, 2007, new data from the U.S. Census Bureau\u27s American Community Survey show that 22 percent of rural children are living in poverty, up from 19 percent in 2000. On average, rates are highest in the nonmetropolitan South (27 percent) and have climbed the most in the nonmetropolitan Midwest (by 3.9 percentage points)

Developing an Action Concept Inventory

We report on progress towards the development of an Action Concept Inventory (ACI), a test that measures student understanding of action principles in introductory mechanics and optics. The ACI also covers key concepts of many-paths quantum mechanics, from which classical action physics arises. We used a multi-stage iterative development cycle for incorporating expert and student feedback into successive revisions of the ACI. The student feedback, including think-aloud interviews, enabled us to identify their misconceptions about action physics.Comment: 6 pages. This paper started out as arXiv:1507.06075v1, then split into arXiv:1507.06075v2 and this paper as a result of feedback from referees and an editor. arXiv:1507.06075v2 presents the case for teaching action physics, while this paper presents an evaluation too

Flexibility effects on tooth contact location in spiral bevel gear transmissions

An analytical method to predict the shift of the contact ellipse between the meshing teeth in a spiral bevel gear set is presented in this report. The contact ellipse shift of interest is the motion of the nominal tooth contact location on each tooth from the ideal pitch point to the point of contact between the two teeth considering the elastic motions of the gears and their supporting shafts. This is the shift of the pitch point from the ideal, unloaded position on each tooth to the nominal contact location on the tooth when the gears are fully loaded. It is assumed that the major contributors of this motion are the elastic deflections of the gear shafts, the slopes of the shafts under load and the radial deflections of the four gear shaft bearings. The motions of the two pitch point locations on the pinion and the gear tooth surfaces are calculated in a FORTRAN program which also calculates the size and orientation of the Hertzian contact ellipse on the tooth faces. Based on the curvatures of the two spiral bevel gear teeth and the size of the contact ellipse, the program also predicts the basic dynamic capacity of the tooth pair. A complete numerical example is given to illustrate the use of the program

The optimal design of standard gearsets

A design procedure for sizing standard involute spur gearsets is presented. The procedure is applied to find the optimal design for two examples - an external gear mesh with a ratio of 5:1 and an internal gear mesh with a ratio of 5:1. In the procedure, the gear mesh is designed to minimize the center distance for a given gear ratio, pressure angle, pinion torque, and allowable tooth strengths. From the methodology presented, a design space may be formulated for either external gear contact or for internal contact. The design space includes kinematics considerations of involute interference, tip fouling, and contact ratio. Also included are design constraints based on bending fatigue in the pinion fillet and Hertzian contact pressure in the full load region and at the gear tip where scoring is possible. This design space is two dimensional, giving the gear mesh center distance as a function of diametral pitch and the number of pinion teeth. The constraint equations were identified for kinematic interference, fillet bending fatigue, pitting fatigue, and scoring pressure, which define the optimal design space for a given gear design. The locus of equal size optimum designs was identified as the straight line through the origin which has the least slope in the design region

First-principles quantum simulations of dissociation of molecular condensates: Atom correlations in momentum space

We investigate the quantum many-body dynamics of dissociation of a Bose-Einstein condensate of molecular dimers into pairs of constituent bosonic atoms and analyze the resulting atom-atom correlations. The quantum fields of both the molecules and atoms are simulated from first principles in three dimensions using the positive-P representation method. This allows us to provide an exact treatment of the molecular field depletion and s-wave scattering interactions between the particles, as well as to extend the analysis to nonuniform systems. In the simplest uniform case, we find that the major source of atom-atom decorrelation is atom-atom recombination which produces molecules outside the initially occupied condensate mode. The unwanted molecules are formed from dissociated atom pairs with non-opposite momenta. The net effect of this process -- which becomes increasingly significant for dissociation durations corresponding to more than about 40% conversion -- is to reduce the atom-atom correlations. In addition, for nonuniform systems we find that mode-mixing due to inhomogeneity can result in further degradation of the correlation signal. We characterize the correlation strength via the degree of squeezing of particle number-difference fluctuations in a certain momentum-space volume and show that the correlation strength can be increased if the signals are binned into larger counting volumes.Comment: Final published version, with updated references and minor modification