Collision rates in the present-day Kuiper Belt and Centaur Regions: Applications to surface activation and modification on Comets, Kuiper Belt Objects, Centaurs, and Pluto-Charon

We extend previous results showing that the surfaces of Edgeworth-Kuiper Belt objects are not primordial and have been moderately to heavily reworked by collisions. Objects smaller than about $r = 2.5$ km have collisional disruption lifetimes less than 3.5 Gyr in the present-day collisional environment and have been heavily damaged in their interiors by large collisions. In the 30--50 AU region, impacts of 1 km radius comets onto individual 100 km radius objects occur on $7\times10^7$--$4\times10^8$ yr timescales, cratering the surfaces of the larger objects with $\sim$8--54 craters 6 km in diameter over 3.5 Gyr. Collision time scales for impacts of 4 meter radius projectiles onto 1 km radius comets range from 3--5 $\times 10^7$ yr. The cumulative fraction of the surface area of 1 and 100 km radius objects cratered by projectiles with radii larger than 4 m ranges from a few to a few tens percent over 3.5 Gyr. The flux of EKO projectiles onto Pluto and Charon is also calculated and is found to be $\sim$3--5 times that of previous estimates. Our impact model is also applied to Centaur objects in the 5--30 AU region. We find the collisional/cratering histories of Centaurs are dominated by the time spent in the Edgeworth-Kuiper Belt rather than the time spent on planet-crossing orbits. Hence, the predominant surface activity of Centaur objects like Chiron is almost certainly not impact-induced.Comment: 17 pages, 8 figures. Icarus, 2000, in pres

Disrupting the Ideology of Settled Expectations: Forging New Social Movements to Dismantle the Educational Racial Contract

This paper draws on the concepts of settled expectations and the educational racial contract to provide an analysis of the current social movements calling for the improvement of teacher salaries and work conditions in K-12 schools. This paper argues that some teacher unions’ lack of centering race in their advocacy to ameliorate educational inequities will not radically transform how teachers are treated in the profession, unless there is an increase in motivation to fully recognize the humanity and educational needs of Students of Color in American society. The author calls for teacher activists to reject the false consciousness of their own settled expectations and work on equal footing with Communities of Color to co-author an emancipatory educational contract on the basis of relational equity, respect, and sympathetic touch

Vitamin D: Newer Concepts of Its Metabolism and Function at the Basic and Clinical Level.

The interest in vitamin D continues unabated with thousands of publications contributing to a vast and growing literature each year. It is widely recognized that the vitamin D receptor (VDR) and the enzymes that metabolize vitamin D are found in many cells, not just those involved with calcium and phosphate homeostasis. In this mini review I have focused primarily on recent studies that provide new insights into vitamin D metabolism, mechanisms of action, and clinical applications. In particular, I examine how mutations in vitamin D metabolizing enzymes-and new information on their regulation-links vitamin D metabolism into areas such as metabolism and diseases outside that of the musculoskeletal system. New information regarding the mechanisms governing the function of the VDR elucidates how this molecule can be so multifunctional in a cell-specific fashion. Clinically, the difficulty in determining vitamin D sufficiency for all groups is addressed, including a discussion of whether the standard measure of vitamin D sufficiency, total 25OHD (25 hydroxyvitamin) levels, may not be the best measure-at least by itself. Finally, several recent large clinical trials exploring the role of vitamin D supplementation in nonskeletal diseases are briefly reviewed, with an eye toward what questions they answered and what new questions they raised

Review of: Sharon M. Friedman et al. eds., Communicating Uncertainty

A review of the book Communicating Uncertainty: Media Coverage of New and Controversial Science (Sharon M. Friedman, Sharon Dunwoody & Carol L. Rogers, eds.; Lawrence Erlbaum Associates 1999). Preface, introduction. ISBN 0-8058-2728-5 [261 pp. $32.50. Paperback, 10 Industrial Avenue, Mahwah, NJ 07430-2262]

The Control of Public Education and School Library Media Programs

published or submitted for publicatio