A High Power Hydrogen Target for Parity Violation Experiments

Parity-violating electron scattering measurements on hydrogen and deuterium, such as those underway at the Bates and CEBAF laboratories, require luminosities exceeding $10^{38}$cm$^{-2}$s$^{-1}$, resulting in large beam power deposition into cryogenic liquid. Such targets must be able to absorb 500 watts or more with minimal change in target density. A 40~cm long liquid hydrogen target, designed to absorb 500~watts of beam power without boiling, has been developed for the SAMPLE experiment at Bates. In recent tests with 40~$\mu$A of incident beam, no evidence was seen for density fluctuations in the target, at a sensitivity level of better than 1\%. A summary of the target design and operational experience will be presented.Comment: 13 pages, 9 postscript figure

Estimating Percent Body Fat in Disabled Individuals with Spinal Cord Injury: A Pilot Study

Accurate and simple to administer field methods that currently exist tend to underestimate values when used to determine percent body fat (%BF) in individuals with spinal cord injury (SCI). This group of people is more prone to obesity and cardiovascular disease (CVD) as well as other secondary conditions. The purpose of this study was to evaluate the accuracy of three methods of measuring body composition as compared to total body dual-energy x-ray absorptiometry (DEXA) scan. These three methods included air displacement plethysmography (Bod Pod), hydrostatic weighing (HW) and seven site skinfold (SKF) measurement as recommended by the American College of Sports Medicine (ACSM). Ten male college students, in the Department of Kinesiology and/or members of the collegiate wheelchair basketball team, participated in the study. Five of the participants were disabled athletes with SCI and five participants were physically active, non-disabled students who served as controls. Of the ten participants, six completed all four of the body composition measures. Both forced vital capacity (FVC), via a flow volume test, and residual volume (RV), via nitrogen washout, were obtained for use in estimating %BF as determined by underwater weighing. The %BF values obtained from the HW using the Siri and Brozek equations had the highest correlation to the DEXA (r=.916). The results of the %BF as measured by the Bod Pod also showed a high correlation (r=.867). Although the SKF method showed a high correlation with the DEXA, (r=.798), it is evident that, with more participants, this method would severely under-predict %BF in the disabled group. In addition, the predicted DEXA from HWSM had a significant relationship (DEXA = 1.342* HWSM -4.795, R2 = .938, SEE = 3.108). These findings suggest that HW and Bod Pod are accurate methods of estimating %BF in both disabled and non-disabled individuals as compared to DEXA

Liquid Hydrogen Target Experience at SLAC

Liquid hydrogen targets have played a vital role in the physics program at SLAC for the past 40 years. These targets have ranged from small "beer can" targets to the 1.5 m long E158 target that was capable of absorbing up to 800 W without any significant density changes. Successful use of these targets has required the development of thin-wall designs, liquid hydrogen pumps, remote positioning and alignment systems, safety systems, control and data acquisition systems, cryogenic cooling circuits and heat exchangers. Detailed operating procedures have been created to ensure safety and operational reliability.This paper surveys the evolution of liquid hydrogen targets at SLAC and discusses advances in several of the enabling technologies that made these targets possible

Highly stable fullerene-based porous molecular crystals with open metal sites

The synthesis of conventional porous crystals involves building a framework using reversible chemical bond formation, which can result in hydrolytic instability. In contrast, porous molecular crystals assemble using only weak intermolecular interactions, which generally do not provide the same environmental stability. Here, we report that the simple co-crystallization of a phthalocyanine derivative and a fullerene (C60 or C70) forms porous molecular crystals with environmental stability towards high temperature and hot aqueous base or acid. Moreover, by using diamond anvil cells and synchrotron single-crystal measurements, stability towards extreme pressure (>4 GPa) is demonstrated, with the stabilizing fullerene held between two phthalocyanines and the hold tightening at high pressure. Access to open metal centres within the porous molecular co-crystal is demonstrated by in situ crystallographic analysis of the chemisorption of pyridine, oxygen and carbon monoxide. This suggests strategies for the formation of highly stable and potentially functional porous materials using only weak van der Waals intermolecular interactions

Usability evaluation of an experimental text summarization system and three search engines: Implications for the reengineering of health care interfaces

This paper describes the comparative evaluation of an experimental automated text summarization system, Centrifuser and three conventional search engines - Google, Yahoo and About.com. Centrifuser provides information to patients and families relevant to their questions about specific health conditions. It then produces a multidocument summary of articles retrieved by a standard search engine, tailored to the user's question. Subjects, consisting of friends or family of hospitalized patients, were asked to "think aloud" as they interacted with the four systems. The evaluation involved audio- and video recording of subject interactions with the interfaces in situ at a hospital. Results of the evaluation show that subjects found Centrifuser's summarization capability useful and easy to understand. In comparing Centrifuser to the three search engines, subjects' ratings varied; however, specific interface features were deemed useful across interfaces. We conclude with a discussion of the implications for engineering Web-based retrieval systems