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Stellar evolutionary tracks have been computed for 17 [Fe/H] values from [2.31 to [0.30 assuming, in each case, [a/Fe] \ 0.0, 0.3, and 0.6. The helium abundance was assumed to vary from Y \ 0.2352 at [Fe/H] \ [2.31 to Y \ 0.2550 at [Fe/H] \ [0.30 and held constant for the di †erent choices of [a/Fe] at a Ðxed iron content. Masses in the range in 0.1 steps, were generally considered, 0.5 ¹ M _ ¹ 1.0, M _ though sequences for higher mass values were computed, as necessary, to ensure that isochrones as "" young ÏÏ as 8 Gyr could be generated for each grid. All of the stellar models are based on an equation of state that treats nonideal e †ects, the latest nuclear reaction and neutrino cooling rates, and opacities that were computed speciÐcally for the adopted chemical mixtures. The tracks were extended to the tip of the giant branch or to an age of 30 Gyr, whichever came Ðrst, and zero-age horizontal-branch (ZAHB) loci were constructed using the helium core masses and chemical proÐles from appropriate red giant precursors. Selected models have been compared with those computed by A. V. Sweigart, for the same masses and chemical compositions, to demonstrate that the results obtained from two entirely independent stellar evolution codes agree well with one another when very similar input physics is assumed. In the case of extremely metal-deÐcient stars, an enhancement in the abundance of the aelements causes a single, fairly signiÐcant bump in the opacity at a temperature just above 106 K, which is caused by absorption processes involving the K shell of oxygen. This peak becomes steadily more pronounced as the overall metallicity increases and a second bump, arising from the L edges of Ne, Mg, and Si, eventually appears near log T \ 5.6. As far as the tracks and isochrones are concerned, we Ðnd that, as already reported by others, it is possible to mimic the computations for [a/Fe] [ 0 remarkably well by those for scaled-solar mixes simply by requiring the total mass-fraction abundance of the heavy elements, Z, to be the same. However, this result holds only for metallicities signiÐcantly less than solar. Above tracks and isochrones for enhanced a-element mixtures begin to have systemati-[Fe/H] Z [0.8, cally hotter/bluer turno †s and red giant branches than those for scaled-solar mixtures of the heavy elements. Also addressed is the extent to which our models satisfy the constraints posed by the local subdwarfs, the distances of which are based on Hipparcos parallax measurements. Our analysis suggests that the predicted metallicity dependence of the location of the lower main sequence on the C-M diagram is in good agreement with the observed dependence. In fact, we do not Ðnd any compelling evidence from the local Population II calibrators that the colors of our models require signiÐcant adjustments. In further support of our calculations, we Ðnd that, both in zero point and slope, the computed giant branches on the agree well with those inferred for globular clusters from (M bol , log T eff )-plane observations in th...

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Capsules with beryllium ablators have long been considered as alternatives to plastic for the National Ignition Facility laser ; now the superior performance of beryllium is becoming well substantiated . Beryllium capsules have the advantages of relative insensitivity to instability growth, low opacity, high tensile strength, and high thermal Zimmerman and W. L. h e r , Comments Plasmas Phys. Controlled Thermonucl. Fusion, 2 , 5 1 (2975)l results that particular beryllium capsule designs are several times less sensitive than the CH point design to instability growth from DT ice roughness. These capsule designs contain more ablator mass and leave some beryllium unablated at ignition. By adjusting the level of copper dopant, the unablated mass can increase or decrease, with a corresponding decrease or increase in sensitivity to perturbations . A plastic capsule with the same ablator mass as the beryllium and leaving the same unablated mass also shows this reduced perturbation sensitivity. Beryllium's low opacity permits the creation of 250 eV capsule designs. Its high tensile strength allows it to contain DT fuel at room temperature. Its high thermal conductivity simplifies cryogenic fielding.