San Diego State University

About: San Diego State University is a education organization based out in San Diego, California, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 12418 authors who have published 27950 publications receiving 1192375 citations. The organization is also known as: SDSU & San Diego State College.

Measuring the Spins of Accreting Black Holes

Abstract: A typical galaxy is thought to contain tens of millions of stellar-mass black holes, the collapsed remnants of once massive stars, and a single nuclear supermassive black hole. Both classes of black holes accrete gas from their environments. The accreting gas forms a flattened orbiting structure known as an accretion disk. During the past several years, it has become possible to obtain measurements of the spins of the two classes of black holes by modeling the X-ray emission from their accretion disks. Two methods are employed, both of which depend upon identifying the inner radius of the accretion disk with the innermost stable circular orbit (ISCO), whose radius depends only on the mass and spin of the black hole. In the Fe K method, which applies to both classes of black holes, one models the profile of the relativistically-broadened iron line with a special focus on the gravitationally redshifted red wing of the line. In the continuum-fitting method, which has so far only been applied to stellar-mass black holes, one models the thermal X-ray continuum spectrum of the accretion disk. We discuss both methods, with a strong emphasis on the continuum-fitting method and its application to stellar-mass black holes. Spin results for eight stellar-mass black holes are summarized. These data are used to argue that the high spins of at least some of these black holes are natal, and that the presence or absence of relativistic jets in accreting black holes is not entirely determined by the spin of the black hole.

Cigarette smoking predicts development of depressive symptoms among U.S. adolescents.

Abstract: To examine whether adolescent cigarette smoking predicts the development of depressive symptoms, we used a longitudinal follow-up survey of 6,863 adolescents ages 12 to 18 in the U.S. who did not report notable depressive symptoms at baseline. This study used a self-report measure of six depressive symptoms experienced within the past twelve months at follow-up as the outcome of interest. Results indicated that 11.5% developed notable depressive symptoms at follow-up. There were marked gender differences with 15.3% of girls developing notable depressive symptoms compared to 8.1% of boys. Gender differences in depressive symptoms were consistent across all age groups and were apparent by the age of twelve. For both genders, smoking status was the most significant predictor of developing notable depressive symptoms. Several other risk factors including involvement in organized athletics, availability of social support, and personality characteristics were also found to be associated with development of depressive symptoms. Adolescent cigarette smoking may have marked health consequences in terms of depressive symptoms. The reduction of cigarette smoking among adolescents should be a focus of depression prevention interventions. In addition, the development of gender-specific components of prevention interventions may be warranted.

SeaWiFS technical report series. Volume 25: Ocean optics protocols for SeaWiFS validation, revision 1

Abstract: This report presents protocols for measuring optical properties, and other environmental variables, to validate the radiometric performance of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and to develop and validate bio-optical algorithms for use with SeaWiFS data. The protocols are intended to establish foundations for a measurement strategy to verify the challenging SeaWiFS uncertainty goals of 5 percent in water-leaving radiances and 35 percent in chlorophyll alpha concentration. The protocols first specify the variables which must be measured, and briefly review the rationale for measuring each variable. Subsequent chapters cover detailed protocols for instrument performance specifications, characterizing and calibrating instruments, methods of making measurements in the field, and methods of data analysis. These protocols were developed at a workshop sponsored by the SeaWiFS Project Office (SPO) and held at the Naval Postgraduate School in Monterey, California (9-12 April 1991). This report began as the proceedings of the workshop, as interpreted and expanded by the authors and reviewed by workshop participants and other members of the bio-optical research community. The protocols are an evolving prescription to allow the research community to approach the unprecedented measurement uncertainties implied by the SeaWiFS goals; research and development are needed to improve the state-of-the-art in specific areas. These protocols should be periodically revised to reflect technical advances during the SeaWiFS Project cycle. The present edition (Revision 1) incorporates new protocols in several areas, including expanded protocol descriptions for Case-2 waters and other improvements, as contributed by several members of the SeaWiFS Science Team.