Scott A. Anderson

We present a catalog of 9316 spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey Data Release 4. We have selected the stars through photometric cuts and spectroscopic modeling, backed up by a set of visual inspections. Roughly 6000 of the stars are new discoveries, roughly doubling the number of spectroscopically confirmed white dwarfs. We analyze the stars by performing temperature and surface gravity fits to grids of pure hydrogen and helium atmospheres. Among the rare outliers are a set of presumed helium-core DA white dwarfs with estimated masses below 0.3 Msun, including two candidates that may be the lowest masses yet found. We also present a list of 928 hot subdwarfs.

OBJECTIVE: To present evidence-based recommendations that promote optimized fluid-maintenance practices for physically active individuals. BACKGROUND: Both a lack of adequate fluid replacement (hypohydration) and excessive intake (hyperhydration) can compromise athletic performance and increase health risks. Athletes need access to water to prevent hypohydration during physical activity but must be aware of the risks of overdrinking and hyponatremia. Drinking behavior can be modified by education, accessibility, experience, and palatability. This statement updates practical recommendations regarding fluid-replacement strategies for physically active individuals. RECOMMENDATIONS: Educate physically active people regarding the benefits of fluid replacement to promote performance and safety and the potential risks of both hypohydration and hyperhydration on health and physical performance. Quantify sweat rates for physically active individuals during exercise in various environments. Work with individuals to develop fluid-replacement practices that promote sufficient but not excessive hydration before, during, and after physical activity.

Rainfall-induced debris flows are flow failures in residual and colluvial soils initiated by a reduction of confining stress as a result of pore-water pressure rise during or following periods of intense rainfall. To establish appropriate stability analysis procedures, the behavior of soil from a debris flow source area is investigated. Constant-shear-drained triaxial tests, tests that mimic the field stress path, and anisotropically consolidated undrained triaxial tests performed at the in-situ stress level indicate that undrained loading is a prerequisite for flow failure. Mechanisms of stress transfer are proposed to explain how the initially drained deformation that occurs along the field stress path can lead to undrained mobilization. Because a debris flow involves both drained initiation and undrained mobilization, a complete stability analysis includes an effective stress analysis with constant-shear-drained parameters to determine the potential for failure initiation, and an undrained strength analysis using undrained residual strength to determine the potential for debris flow mobilization.

OBJECTIVE: To present recommendations for the prevention and screening, recognition, and treatment of the most common conditions resulting in sudden death in organized sports. BACKGROUND: Cardiac conditions, head injuries, neck injuries, exertional heat stroke, exertional sickling, asthma, and other factors (eg, lightning, diabetes) are the most common causes of death in athletes. RECOMMENDATIONS: These guidelines are intended to provide relevant information on preventing sudden death in sports and to give specific recommendations for certified athletic trainers and others participating in athletic health care.

OBJECTIVE: To compare the frequency and magnitude of head impacts between National Collegiate Athletic Association Division I and American high school football players. The long-term goal is to correlate impact forces with injury patterns, leading to improvements in protective headgear. METHODS: The helmets of football players at the University of Oklahoma (n = 40) and Casady High School (n = 16) were instrumented with the Head Impact Telemetry System (Simbex, Lebanon, NH). Data were collected for practices and games for the 2005 football season and were analyzed by player position and school. Player positions were separated into two groups (skill and line) for analysis. Two case studies of athletes who sustained a concussion are also presented. RESULTS: A total of 54,154 impacts were recorded at the University of Oklahoma and 8326 at Casady High School. College players sustained high-level impacts greater than 98 g more frequently than high school players. The mean linear accelerations for the top 1, 2, and 5% of all impacts were also higher for college players (P < 0.02). Skill position players received 24.6% of all impacts and sustained an impact greater than 98 g once every 70 impacts. In contrast, linemen sustained the highest number of impacts, but most were relatively low-magnitude (20-30 g). Linemen sustained an impact greater than 98 g once every 125 impacts. CONCLUSION: Differences in the frequency and magnitude of head acceleration after impact exist between a Division I college team and a high school team. Compared with linemen, skill position players typically sustain the highest-level impacts. Additional data collection and analysis are required to correlate concussion diagnosis with acceleration magnitude and impact location.