Hydrogen in porous Vycor glass ͑pore radius R p ϭ3.0 nm͒ has been investigated with a torsional oscillator technique at 7.5 K рTр 22 K. H 2 molecules which are adsorbed in Vycor at TϾT 3 (T 3 , triple point of bulk H 2 ) leave the Vycor when decreasing the temperature to below a characteristic value T c рT 3 ; T c depends on the amount of H 2 in the Vycor. This interpretation of the data is supported by simultaneous measurements of the H 2 vapor pressure. A similar phenomenon is observed with a capacitor filled with Vycor into which H 2 is condensed. We conclude that the free energy of solid H 2 in the Vycor is larger than that of bulk solid H 2 . Information on the free energy of H 2 confined in the Vycor is important to understand the depression of its freezing temperature in restricted geometries. We also discuss the properties of solids and the depression of their freezing temperature in restricted geometries.

Naturally occurring gas hydrates contain significant amounts of natural gas that might be produced as an energy resource in the foreseeable future. Thus, it is necessary to understand the pore‐space characteristics of hydrate reservoirs, particularly the pore‐scale distribution of the hydrate and its interaction with the sediment. Four end‐member models for hydrate distribution in the pore space are pore filling, sediment‐frame component, envelope cementing, and contact cementing. The goal of this study is to compare the models with pore‐scale hydrate distributions obtained in laboratory‐formed hydrates. Our results verify hydrate pore‐scale distributions by direct, visual observations that were previously implied by indirect, elastic property measurements. Laboratory measurements were conducted using tetrahydrofuran as a guest molecule since tetrahydrofuran hydrate can be used as a proxy for naturally occurring hydrates. We performed micro X‐ray computed tomography to obtain information about the distribution of hydrate in the pore space of synthetic sediment (glass beads). We also made ultrasonic velocity measurements on the same samples. Micro X‐ray computed tomography images and ultrasonic velocity measurements both indicate that the tetrahydrofuran hydrate forms in the pore space with a part of the hydrate bridging the grains without touching the grain surfaces. These hydrate‐bearing sediments appear to follow a pore‐filling model with a portion of the hydrate becoming a load‐bearing part of the sediment frame.

IUE spectra of the slowly rotating mild barium star 56 Peg (HD 218356; KO Up) show excess continuum emission from 1300 to 2000 Â, a broad Lya absorption feature, and emission lines usually associated with a 10 4-(2 x 10 5) K plasma. The best fit blackbody curve to the dereddened continuum gives a temperature of 32,000 ± 4000 K and a radius for the object of (2.7 ± 1.0) x 10 9 cm, consistent with that of a white dwarf. Einstein IPC observations of this system yield L x ae 3 x 10 31 ergs s-1 , which is as bright as the RS CVn binary systems. The X-rays can be fitted to a bremsstrahlung spectrum with kT = 0.45 ± 0.3 keV, or a blackbody spectrum with kT ae 0.2 keV. Since bright X-ray and high temperature emission lines are unusual for single stars in this region of the H-R diagram, we do not believe that the 56 Peg primary has a hot corona and transition region. Instead, we propose that the observed X-ray luminosity is due to accretion onto the white dwarf of ~0.1 % of the wind from the primary, which we assume has a reasonable mass loss rate of 2 x 10~7 to 4 x 10" 9 M 0 yr-1. The ultraviolet emission lines likely result from reprocessed X-radiation absorbed by the wind. The Mg n K line exhibits a time-varying emission core, that may be explained by ionization of Mg + in the wind by X-rays from the white dwarf.

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We have investigated the dielectric properties of a porous glass ͑Vycor 7930, typical pore radius: Ϸ3 nm͒ with submonolayer coverages of H 2 , HD, or D 2 on the pore surface by means of a capacitive technique between 5 and 20 K. The adsorption of hydrogen influences, depending on the hydrogen species as well as on the coverage, the dielectric glass properties. We discuss our observations in terms of the thermally activated dynamics of atoms in the combined glass/hydrogen system, where atoms denote atoms which build the porous glass as well as adsorbed hydrogen molecules.

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