Seasonal priority effects: Implications for invasion and restoration in California coastal sage scrub

Competition from exotic annual grasses (EAGs) threatens native plant communities in California. Coastal sage scrub communities have substantially diminished in area over the last century, in some instances by greater than 90%, while EAGs continue to proliferate. Several mechanisms may explain the success of EAGs, including the suppression of native seedlings by accumulated litter, exhaustion of soil moisture, and low seed production or dispersal of natives. 
The timing and magnitude of rainfall plays a significant role in determining the survival and reproduction of plant species in Mediterranean ecosystems. Populations of annuals fluctuate greatly from year to year, corresponding with variability in autumn precipitation. EAGs in California germinate quickly following small threshold rain events, whereas native species have more complex germination cues, such that exotic annual grasses become active earlier in the growing season. In this way, EAGs may exhibit a priority effect over native plant species with respect to establishment; however, they may have reduced success if their germination is induced at a time followed by a substantial drought (for instance, in the summer) so that they will not persist. 
The goal of this investigation is 1) to evaluate whether seasonal priority effects contribute to community-level patterns of abundance, and 2) whether late summer watering could be a feasible restoration technique for suppression of exotic annual grasses and weeds in Mediterranean ecosystems

Gas diffusion liquid storage bag and method of use for storing blood

The shelf life of stored whole blood may be doubled by adding a buffer which maintains a desired pH level. However, this buffer causes the generation of CO2 which, if not removed at a controlled rate, causes the pH value of the blood to decrease, which shortens the useful life of the blood. A blood storage bag is described which permits the CO2 to be diffused out at a controlled rate into the atmosphere, thereby maintaining the desired pH value and providing a bag strong enough to permit handling

Evaluation of the effects of a freeze/thaw environment on cellular glass

Using the evaluation criteria of water vapor permeability and conformability, a protective butylrubber/silicone conformal coating system was selected for use on Foamglas substrates in a freeze/thaw environment. The selection of a specific freeze/thaw cycle which closely models field conditions is discussed. A sampling plan is described which allows independent evaluation of the effects of conformal coatings, cycle number and location within the environmental chamber. The results of visual examination, measurement of density, modulus of rupture and Young's modulus are reported. Based upon statistical evaluation of the experimental results, it is concluded that no degradation in mechanical properties of either coated or uncoated Foamglas occurred within the duration of the test (53 freeze/thaw cycles)

Polymers for spacecraft hardware - Materials characterization, part I Interim report, Mar. - Dec. 1966

Environmental testing of polymeric materials for spacecraft hardwar

Religious affiliation and extramarital sex among men in Brazil.

CONTEXT: Since 1990, HIV infection in Brazil has spread among the heterosexual population, particularly in the north. Containment of the epidemic can be informed by a better understanding of men's sexual risk behavior. METHODS: Logistic, Poisson and multilevel logit models were applied to data on married and cohabiting men who had participated in the 1996 Brazilian Demographic and Health Survey. RESULTS: Twelve percent of married or cohabiting men reported having had at least one extramarital partner in the previous 12 months; half of these had had two or more. The majority (77%) of partners were described as friends or lovers; 4% had been prostitutes and 15% strangers. Among men who had had sex with an extramarital partner in the last year, 40% reported having used condoms during last extramarital sex. Compared with members of evangelical religions, other men were significantly more likely to report having had an extramarital partner (odds ratios, 3.0-4.7) and unprotected extramarital sex in the last 12 months (3.4-7.9). Region of residence was also strongly correlated with extramarital sex: Compared with men in southern or central Brazil, those in the north had more than three times the odds of having had extramarital sex and unprotected extramarital sex in the last year (3.1-3.8). CONCLUSION: In Brazil, religious affiliation and region of residence exert a major influence on risk behavior

Clinical trials with endothelin receptor antagonists: What went wrong and where can we improve?

In the early 1990s, within three years of cloning of endothelin receptors, orally active endothelin receptor antagonists (ERAs) were tested in humans and the first clinical trial of ERA therapy in humans was published in 1995. ERAs were subsequently tested in clinical trials involving heart failure, pulmonary arterial hypertension, resistant arterial hypertension, stroke/subarachnoid hemorrhage and various forms of cancer. The results of most of these trials – except those for pulmonary arterial hypertension and scleroderma-related digital ulcers – were either negative or neutral. Problems with study design, patient selection, drug toxicity, and drug dosing have been used to explain or excuse failures. Currently, a number of pharmaceutical companies who had developed ERAs as drug candidates have discontinued clinical trials or further drug development. Given the problems with using ERAs in clinical medicine, at the Twelfth International Conference on Endothelin in Cambridge, UK, a panel discussion was held by clinicians actively involved in clinical development of ERA therapy in renal disease, systemic and pulmonary arterial hypertension, heart failure, and cancer. This article provides summaries from the panel discussion as well as personal perspectives of the panelists on how to proceed with further clinical testing of ERAs and guidance for researchers and decision makers in clinical drug development on where future research efforts might best be focused

Performance of silicon solar cell assemblies

Solar cell assembly current-voltage characteristics, thermal-optical properties, and power performance were determined. Solar cell cover glass thermal radiation, optical properties, confidence limits, and temperature intensity effects on maximum power were discussed

Metastability and the Casimir Effect in Micromechanical Systems

Electrostatic and Casimir interactions limit the range of positional stability of electrostatically-actuated or capacitively-coupled mechanical devices. We investigate this range experimentally for a generic system consisting of a doubly-clamped Au suspended beam, capacitively-coupled to an adjacent stationary electrode. The mechanical properties of the beam, both in the linear and nonlinear regimes, are monitored as the attractive forces are increased to the point of instability. There "pull-in" occurs, resulting in permanent adhesion between the electrodes. We investigate, experimentally and theoretically, the position-dependent lifetimes of the free state (existing prior to pull-in). We find that the data cannot be accounted for by simple theory; the discrepancy may be reflective of internal structural instabilities within the metal electrodes.Comment: RevTex, 4 pages, 4 figure