Discrete Group Actions on Spacetimes: Causality Conditions and the Causal Boundary

Suppose a spacetime $M$ is a quotient of a spacetime $V$ by a discrete group of isometries. It is shown how causality conditions in the two spacetimes are related, and how can one learn about the future causal boundary on $M$ by studying structures in $V$. The relations between the two are particularly simple (the boundary of the quotient is the quotient of the boundary) if both $V$ and $M$ have spacelike future boundaries and if it is known that the quotient of the future completion of $V$ is past-distinguishing. (That last assumption is automatic in the case of $M$ being multi-warped.)Comment: 32 page

Chemical frost weathering of olivine: Experimental study and implications

New experimental results are reported on the frost weathering of olivine. After first weathering, a decrease in Fe sup 2(+)M(2) absorption bands were noted. This decrease is related to the protonation of O(+) in the mineral. It is contented that this reaction may result in the regolith storage of 100 to 1000 m of H(sub 2) over the history of Mars

Stronger instruments and refined covariate balance in an observational study of the effectiveness of prompt admission to intensive care units

Instrumental variable methods, subject to appropriate identification assumptions, enable consistent estimation of causal effects in the presence of unobserved confounding. Near–far matching has been proposed as one analytic method to improve inference by strengthening the effect of the instrument on the exposure and balancing observable characteristics between groups of subjects with low and high values of the instrument. However, in settings with hierarchical data (e.g. patients nested within hospitals), or where several covariate interactions must be balanced, conventional near–far matching algorithms may fail to achieve the requisite covariate balance. We develop a new matching algorithm, that combines near–far matching with refined covariate balance, to balance large numbers of nominal covariates while also strengthening the instrumental variable. This extension of near–far matching is motivated by a case-study that aims to identify the causal effect of prompt admission to an intensive care unit on 7-day and 28-day mortality

Development of an (AlGaAs-Ga As) graded band gap solar cell

The results of an experimental program to develop the epitaxial growth techniques and analytical characterization techniques to fabricate graded bandgap solar cells are reported

Prediction of low frequency and impulsive sound radiation from horizontal axis wind turbines

Theoretical models to predict the radiation of low frequency and impulsive sound from horizontal axis wind turbines due to three sources: (1) steady blade loads; (2) unsteady blade loads due to operation in a ground shear; (3) unsteady loads felt by the blades as they cross the tower wake. These models are then used to predict the acoustic output of MOD-1, the large wind turbine operated near Boone, N.C. Predicted acoustic time signals are compared to those actually measured near MOD-1 and good agreement is obtained

Association of Vitamin D Deficiency with Hypertension in Uninsured Women

Vitamin D deficiency is an epidemic in the United States. Uninsured women are at high risk due to a lower intake of vitamin D and limited sun exposure. We examined the association between vitamin D deficiency and hypertension in 96 uninsured women at a County Free Medical Clinic in urban Michigan. Questionnaires were used to obtain information about demographics, medical history including hypertension, and dietary habits. Measurements including blood pressure and serum 25(OH)D level were also collected. Prevalence of hypertension was higher in subjects with 25(OH)D less than 50nmol/l compared with others (85% vs. 27.3%, p = 0.014). For every 1 nmol/L decrease in serum 25(OH)D, there was an increase in the systolic and diastolic blood pressure by 0.20 (p =0.006) and 0.13 (p =0.003) mm of Hg respectively. These results demonstrate a high prevalence of hypertension in the vitamin D deficient, uninsured female population

On the Formation of Galaxy Halos: Comparing NGC 5128 and the Local Group Members

The metallicity distribution function (MDF) for the old red-giant stars in the halo of NGC 5128, the nearest giant elliptical galaxy, is virtually identical with the MDF for the old-disk stars in the LMC and also strongly resembles the halo MDF in M31. These galaxies all have high mean halo metallicities ( ~ -0.4$) with very small proportions of low-metallicity stars. These observations reinforce the view that metal-rich halos are quite normal for large galaxies of all types. Such systems are unlikely to have built up by accretion of pre-existing, gas-free small satellite galaxies, unless these satellites had an extremely shallow mass distribution (d log N / d log M > -1). We suggest that the halo of NGC 5128 is more likely to have assembled from hierarchical merging of gas-rich lumps in which the bulk of star formation took place during or after the merger stage.Comment: 10 pages, LaTeX, plus 3 figures in separate postscript files; Astronomical Journal, in press for December 200

Invasive Weeds, Wildfire, and Rancher Decision Making in the Great Basin

In this article, a numerical stochastic dynamic programming model (SDP) is developed to characterize the decision problem of a rancher operating on rangelands in northern Nevada that are affected by invasive annual grasses and wildfire. The model incorporates decisions about herd size management of a cow-calf operation and fuels treatment to reduce the size of rangeland wildfires. Currently, high transactions costs to obtain permits to implement land treatments on federally-owned rangelands appear to limit rancher involvement. The results of the model suggest that ranch income motives alone are likely insufficient for private ranchers to adopt preventative land treatments. The current treatment cost ($20 per acre at the minimum) appears to be prohibitively expensive relative to the benefits derived from the treatments under the low-productivity, semi-arid rangeland conditions.stochastic dynamic programming, cow-calf operation, rangeland, ecosystem, Livestock Production/Industries, Resource /Energy Economics and Policy,