Factors associated with successful answering of clinical questions using an information retrieval system*

Objectives: Despite the growing use of online databases by clinicians, there has been very little research documenting how effectively they are used. This study assessed the ability of medical and nurse-practitioner students to answer clinical questions using an information retrieval system. It also attempted to identify the demographic, experience, cognitive, personality, search mechanics, and user-satisfaction factors associated with successful use of a retrieval system.

An endogenous rate of time preference, the Penrose effect, and dynamic optimality of environmental quality.

In the present paper, the endogenous theory of time preference is extended to analyze those processes of capital accumulation and changes in environmental quality that are dynamically optimum with respect to the intertemporal preference ordering of the representative individual of the society in question. The analysis is carried out within the conceptual framework of the dynamic analysis of environmental quality, as has been developed by a number of economists for specific cases of the fisheries and forestry commons. The duality principles on intertemporal preference ordering and capital accumulation are extended to the situation where processes of capital accumulation are subject to the Penrose effect, which exhibit the marginal decrease in the effect of investment in private and social overhead capital upon the rate at which capital is accumulated. The dynamically optimum time-path of economic activities is characterized by the proportionality of two systems of imputed, or efficient, prices, one associated with the given intertemporal ordering and another associated with processes of accumulation of private and social overhead capital. It is particularly shown that the dynamically optimality of the processes of capital accumulation involving both private and social overhead capital is characterized by the conditions that are identical with those involving private capital, with the role of social overhead capital only indirectly exhibited.

N2 fixation in marine heterotrophic bacteria: dynamics of environmental and molecular regulation.

Molecular and immunological techniques were used to examine N2 fixation in a ubiquitous heterotrophic marine bacterium, the facultative anaerobic Vibrio natriegens. When batch cultures were shifted from aerobic N-replete to anaerobic N-deplete conditions, transcriptional and post-translational regulation of N2 fixation was observed. Levels of nifHDK mRNA encoding the nitrogenase enzyme were highest at 140 min postshift and undetectable between 6 and 9 h later. Immunologically determined levels of nitrogenase enzyme (Fe protein) were highest between 6 and 15 h postshift, and nitrogenase activity peaked between 6 and 9 h postshift, declining by a factor of 2 after 12-15 h. Unlike their regulation in cyanobacteria, Fe protein and nitrogenase activity were present when nifHDK mRNA was absent in V. natriegens, indicating that nitrogenase is stored and stable under anaerobic conditions. Both nifHDK mRNA and Fe protein disappeared within 40 min after cultures were shifted from N2-fixing conditions (anaerobic, N-deplete) to non- N2-fixing conditions (aerobic, N-enriched) but reappeared when shifted to conditions favoring N2 fixation. Thus, unlike other N2-fixing heterotrophic bacteria, nitrogenase must be resynthesized after aerobic exposure in V. natriegens. Immunological detection based on immunoblot (Western) analysis and immunogold labeling correlated positively with nitrogenase activity; no localization of nitrogenase was observed. Because V. natriegens continues to fix N2 for many hours after anaerobic induction, this species may play an important role in providing "new" nitrogen in marine ecosystems.