Efficient gas-phase generation of coherent vacuum ultraviolet radiation

We report the demonstration of a pulsed atomic lead (Pb) vapor-based vacuum ultraviolet frequency converter from 233 to 186 nm with unity photon-conversion efficiency. This conversion is attained without phase matching.     

Physical characterization of the polymorphic variations of magnesium stearate and magnesium palmitate hydrate species

The anhydrate, dihydrate, and trihydrate phases of chemically pure magnesium stearate and magnesium palmitate have been prepared and characterized as to their structural characteristics. The magnesium palmitate materials were obtained as significantly larger crystals than were the magnesium stearate materials, and the crystals of the dihydrate phase of either material were found to be the most fully developed. The crystal structures of all materials were judged to be very similar to each other, differing primarily in the magnitude of the long (001) crystal spacing. Thermal analysis studies revealed that the water of hydration contained within the dihydrate phases of either magnesium stearate or magnesium palmitate was more tightly bound than was the water of hydration within the corresponding trihydrate phases. These findings provide further support for the structural picture where the water contained in these lattice structures is present between the intermolecular planes.     

KINETICS OF THE PHOTO-INDUCED EPR SIGNAL IN WHOLE-CELL RHODOSPIRILLUM RUBRUM: EFFECTS OF LIGHT INTENSITY, DARK ADAPTATION, TEMPERATURE, AND MICROWAVE POWER

Abstract— Kinetics of the bacteriochlorophyll (P870⁺) electron paramagnetic resonance signal photo-induced at room temperature in whole-cell Rhodospirillum rubrum exhibit transients which are strongly dependent upon the light-dark history of the cells. This paper reports a study of these kinetics as a function of actinic light intensity, light-dark history, temperature and applied microwave power. The simplest interpretation of the observed complexities in the kinetic curves is that the rate of formation and the rate of decay of P870⁺ are controlled by slow dark reactions of the electron-transport chain, and that the rate-controlling reaction is variable during the transition from a dark-adapted to a steady state in the light. With this interpretation, it is possible to measure or to infer order-of-magnitude estimates of the lifetimes of some of the slow reactions.     

A new method for quantitation of spin concentration by EPR spectroscopy: application to methemoglobin and metmyoglobin

A new method of EPR spectral analysis is developed to quantitate overlapping signals. The method requires double integration of a number of spectra containing the signals in different proportions and the subsequent solution of a system of linear equations. The result gives the double integral values of the individual lines, which can then be further used to find the concentrations of all the paramagnetic species present. There is no requirement to deconvolute the whole spectrum into its individual components. The method is employed to quantify different heme species in methemoglobin and metmyoglobin preparations. A significantly greater intensity of the high-spin signal in metmyoglobin, compared to methemoglobin at the same heme concentration, is shown to be due to larger amounts of low-spin forms in methemoglobin. Three low-spin types in methemoglobin and two in metmyoglobin are present in these samples. When their calculated concentrations are added to those of the high-spin forms, the results correspond to the total heme concentrations obtained by optical spectroscopy.     

Supercritical hydrogen adsorption in nanostructured solids with hydrogen density variation in pores

Experimental excess isotherms for the adsorption of gases in porous solids may be represented by mathematical models that incorporate the total amount of gas within a pore, a quantity which cannot easily be found experimentally but which is important for calculations for many applications, including adsorptive storage. A model that is currently used for hydrogen adsorption in porous solids has been improved to include a more realistic density profile of the gas within the pore, and allows calculation of the total amount of adsorbent. A comparison has been made between different Type I isotherm equations embedded in the model, by examining the quality of the fits to hydrogen isotherms for six different nanoporous materials. A new Type I isotherm equation which has not previously been reported in the literature, the Unilan-b equation, has been derived and has also been included in this comparison study. These results indicate that while some Type I isotherm equations fit certain types of materials better than others, the T?th equation produces the best overall quality of fit and also provides realistic parameter values when used to analyse hydrogen sorption data for a model carbon adsorbent.     

Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures

A sound understanding of any sorption system requires an accurate determination of the enthalpy of adsorption. This is a fundamental thermodynamic quantity that can be determined from experimental sorption data and its correct calculation is extremely important for heat management in adsorptive gas storage applications. It is especially relevant for hydrogen storage, where porous adsorptive storage is regarded as a competing alternative to more mature storage methods such as liquid hydrogen and compressed gas. Among the most common methods to calculate isosteric enthalpies in the literature are the virial equation and the Clausius–Clapeyron equation. Both methods have drawbacks, for example, the arbitrary number of terms in the virial equation and the assumption of ideal gas behaviour in the Clausius–Clapeyron equation. Although some researchers have calculated isosteric enthalpies of adsorption using excess amounts adsorbed, it is arguably more relevant to applications and may also be more thermodynamically consistent to use absolute amounts adsorbed, since the Gibbs excess is a partition, not a thermodynamic phase. In this paper the isosteric enthalpies of adsorption are calculated using the virial, Clausius–Clapeyron and Clapeyron equations from hydrogen sorption data for two materials—activated carbon AX-21 and metal-organic framework MIL-101. It is shown for these two example materials that the Clausius–Clapeyron equation can only be used at low coverage, since hydrogen’s behaviour deviates from ideal at high pressures. The use of the virial equation for isosteric enthalpies is shown to require care, since it is highly dependent on selecting an appropriate number of parameters. A systematic study on the use of different parameters for the virial was performed and it was shown that, for the AX-21 case, the Clausius–Clapeyron seems to give better approximations to the exact isosteric enthalpies calculated using the Clapeyron equation than the virial equation with 10 variable parameters.