2,258 research outputs found

    Infinite slabs and other weird plane symmetric space-times with constant positive density

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    We present the exact solution of Einstein's equation corresponding to a static and plane symmetric distribution of matter with constant positive density located below z=0z=0. This solution depends essentially on two constants: the density ρ\rho and a parameter κ\kappa. We show that this space-time finishes down below at an inner singularity at finite depth. We match this solution to the vacuum one and compute the external gravitational field in terms of slab's parameters. Depending on the value of κ\kappa, these slabs can be attractive, repulsive or neutral. In the first case, the space-time also finishes up above at another singularity. In the other cases, they turn out to be semi-infinite and asymptotically flat when zz\to\infty. We also find solutions consisting of joining an attractive slab and a repulsive one, and two neutral ones. We also discuss how to assemble a "gravitational capacitor" by inserting a slice of vacuum between two such slabs.Comment: 8 page

    A Critical Analysis Of Time Allocation In Psychoeducational Evaluations

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    This study provides results form a national survey examining school psychologists’ allocation of time in psycholeducational evaluations. A total of 177 participants with an average of 13.45 years professional experience in school psychology, representing 39 states, participated in the survey. The results indicate that school psychologists spend the majority of their time engaging in test administration and report-writing components of the evaluation process. The data also revealed that the evaluation of students with possible emotional disabilities is most time intensive when compared to evaluations of students with possible learning or intellectual disabilities.  Implications of the results relating to policy and procedures to improve the learning outcomes of students in public school settings are provided

    The Effects Of Training In Timing And Rhythm On Reading Achievement

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    This study investigated the relationship between improvement in students’ timing/rhythmicity and reading achievement. Two hundred eighty high school-age participants completed pre- and post-test measures from the Woodcock-Johnson Tests of Achievement-III (Woodcock, McGrew, & Mather, 2001). Students in the experimental group participated in a timing/rhythm intervention designed to reduce their latency response to a reoccurring metronome beat. Students in the control group participated in traditional classroom activities. The results from the study indicate that after treatment, the experimental group’s post-test Broad Reading and Reading Fluency scores were statistically significantly higher than the non-treatment control group’s post-test scores

    The Exact Geometry of a Kerr-Taub-NUT Solution of String Theory

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    In this paper we study a solution of heterotic string theory corresponding to a rotating Kerr-Taub-NUT spacetime. It has an exact CFT description as a heterotic coset model, and a Lagrangian formulation as a gauged WZNW model. It is a generalisation of a recently discussed stringy Taub-NUT solution, and is interesting as another laboratory for studying the fate of closed timelike curves and cosmological singularities in string theory. We extend the computation of the exact metric and dilaton to this rotating case, and then discuss some properties of the metric, with particular emphasis on the curvature singularities.Comment: 14 pages, 3 figure
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