The radiation resistance of cylindrical shells

Radiation resistance of cylindrical shells in ideal compressible acoustic mediu

The U.S. economy in 1989 and 1990: walking a fine line

Economic policy ; Forecasting

Alternative computational approaches to inference in the multinomial probit model

This research compares several approaches to inference in the multinomial probit model, based on two Monte Carlo experiments for a seven choice model. The methods compared are the simulated maximum likelihood estimator using the GHK recursive probability simulator, the method of simulated moments estimator using the GHK recursive simulator and kernel-smoothed frequency simulators, and posterior means using a Gibbs sampling-data augmentation algorithm. Overall, the Gibbs sampling algorithm has a slight edge, with the relative performance of MSM and SML based on the GHK simulator being difficult to evaluate. The MSM estimator with the kernel-smoothed frequency simulator is clearly inferior. © 1994

Thermal Equilibration of 26 Al

In astrophysical environments, the long-lived (t1/2 = 0.72 Myr) ground state of 26Al can communicate with its short-lived (t1/2 = 6.35 s) first excited state through thermal excitations. The result is that the astrophysical half-life for 26Al can be much shorter than the laboratory value, which can have an impact on the amount of 26Al produced at high temperatures. We have reexamined the equilibration process using the results of new calculations of some of the key transition rates. In addition, we discuss a simple way of describing the behavior of 26Al in a stellar plasma and use this to better define the conditions where equilibration is expected to be important. Finally, we present a series of network calculations to show how the interplay between the timescale for equilibration versus that for nuclear reactions will govern the evolution of 26Al

Limitations of Animal Models of Parkinson's Disease

Most cases of Parkinson's disease (PD) are sporadic. When choosing an animal model for idiopathic PD, one must consider the extent of similarity or divergence between the physiology, anatomy, behavior, and regulation of gene expression between humans and the animal. Rodents and nonhuman primates are used most frequently in PD research because when a Parkinsonian state is induced, they mimic many aspects of idiopathic PD. These models have been useful in our understanding of the etiology of the disease and provide a means for testing new treatments. However, the current animal models often fall short in replicating the true pathophysiology occurring in idiopathic PD, and thus results from animal models often do not translate to the clinic. In this paper we will explain the limitations of animal models of PD and why their use is inappropriate for the study of some aspects of PD

Direct measurement of the 14N(p,g)15O S-factor

We have measured the 14N(p,g)15O excitation function for energies in the range E_p = 155--524 keV. Fits of these data using R-matrix theory yield a value for the S-factor at zero energy of 1.64(17) keV b, which is significantly smaller than the result of a previous direct measurement. The corresponding reduction in the stellar reaction rate for 14N(p,g)15O has a number of interesting consequences, including an impact on estimates for the age of the Galaxy derived from globular clusters.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Let

Occupational Risks and Pregnancy and Infant Health Outcomes in Florida Farmworkers

The agricultural industry has some of the highest incidence rates and numbers of occupational injuries and illnesses in the United States. Injuries and illnesses in agriculture result from accidents, falls, excessive heat, repetitive motion and adverse pesticide exposure. Women working in agriculture are exposed to the same hazards and risks as their male counterparts, but can face additional adverse impacts on their reproductive health. Yet, few occupational risk assessment studies have considered the reproductive health of female farmworkers. The objective of this community-based participatory research study was to conduct a retrospective, cross-sectional survey to collect information on workplace conditions and behaviors and maternal, pregnancy and infant health outcomes among a sample of female nursery and fernery farmworkers in Central Florida. Survey results showed that nursery workers were more likely to report health symptoms during their pregnancy than fernery workers. We also observed a self-reported increased risk of respiratory illness in the first year of life for infants whose mothers worked in ferneries. Our findings confirm that agricultural work presents potential reproductive hazards for women of childbearing age

Does an NeNa Cycle Exist in Explosive Hydrogen Burning?

According to common assumptions, matter in the mass range A ≥ 20 is processed through the so-called NeNa cycle during hydrogen-burning nucleosynthesis. The existence of such a reaction cycle implies that the (p, α) reaction on 23Na is more likely to occur than the competing (p, γ) reaction. However, recently evaluated thermonuclear rates for both reactions carry relatively large uncertainties and allow for both possibilities, i.e., a "closed" and an "open" NeNa cycle. We measured the 23Na(p, γ)24Mg reaction at the Laboratory for Experimental Nuclear Astrophysics. The present experimental results, obtained with our sensitive γ-ray detection apparatus, reduce the 23Na + p reaction rate uncertainties significantly. We demonstrate that a closed NeNa cycle does not exist at stellar temperatures of T = 0.2-0.4 GK. The new results have important implications for the nucleosynthesis in classical novae, including the amount of 26Al ejected by the thermonuclear explosion, the elemental abundances of Mg and Al observed in nova shells, and observations of Mg and Al isotopic ratios in primitive meteorites

Large-scale synchrony of gap dynamics and the distribution of understory tree species in maple-beech forests

Large-scale synchronous variations in community dynamics are well documented for a vast array of organisms, but are considerably less understood for forest trees. Because of temporal variations in canopy gap dynamics, forest communities—even old-growth ones—are never at equilibrium at the stand scale. This paucity of equilibrium may also be true at the regional scale. Our objectives were to determine (1) if nonequilibrium dynamics caused by temporal variations in the formation of canopy gaps are regionally synchronized, and (2) if spatiotemporal variations in canopy gap formation aVect the relative abundance of tree species in the understory. We examined these questions by analyzing variations in the suppression and release history of Acer saccharum Marsh. and Fagus grandifolia Ehrh. from 481 growth series of understory saplings taken from 34 mature stands. We observed that (1) the proportion of stems in release as a function of time exhibited a U-shaped pattern over the last 35 years, with the lowest levels occurring during 1975–1985, and that (2) the response to this in terms of species composition was that A. saccharum became more abundant at sites that had the highest proportion of stems in release during 1975–1985. We concluded that the understory dynamics, typically thought of as a stand-scale process, may be regionally synchronized