Engineering materials for hydrogen separation

To address the need for enhanced hydrogen separation techniques using metal membranes, a different fabrication technique was utilized that would overcome these concerns. The objectives for the fabrication were: obtaining a highly clean surface on the refractory foil, forming a palladium coating without subsequent surface contamination, and providing a high degree of purity, crystallinity, and crystallographic orientation. To achieve these objectives, the process of physical vapor deposition was used. Within a high vacuum chamber, both sides of a tantalum or vanadium foil were ion milled to remove the surface oxide and, without ever breaking the vacuum, both sides of the cleaned foil were coated with thin palladium layers. The palladium was deposited using either e-beam evaporation or sputtering. Foils produced by this technique have yielded exceptionally high hydrogen flow rates

The stone adze and obsidian assemblage from the Talasiu site, Kingdom of Tonga

Typological and geochemical analyses of stone adzes and other stone tools have played a significant role in identifying directionality of colonisation movements in early migratory events in the Western Pacific. In later phases of Polynesian prehistory, stone adzes are important status goods which show substantial spatial and temporal variation. However, there is a debate when standardisation of form and manufacture appeared, whether it can be seen in earliest populations colonising the Pacific or whether it is a later development. We present in this paper a stone adze and obsidian tool assemblage from an early Ancestral Polynesian Society Talasiu site on Tongatapu, Kingdom of Tonga. The site shows a wide variety of adze types; however, if raw material origin is taken into account, emerging standardisation in adze form might be detected. We also show that Tongatapu was strongly connected in a network of interaction to islands to the North, particularly Samoa, suggesting that these islands had permanent populations

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc

Stomatal responses of Eucalyptus species to elevated CO2 concentration and drought stress

Five species of Eucalyptus (E. grandis, E. urophylla, E. camaldulensis, E. torelliana, and E. phaeotrica), among the ten species most commonly used in large scale plantations, were selected for studies on the effects of elevated CO2 concentration [CO2] and drought stress on stomatal responses of 2.5-month old seedlings. The first three species belong to the subgenus Smphyomyrtus, whereas the fourth species belongs to the subgenus Corymbia and E. phaeotrica is from the subgenus Monocalyptus. Seedlings were grown in four pairs of open-top chambers, arranged to have 2 plants of each species in each chamber, with four replications in each of two CO2 concentrations: 350 ± 30 mumol mol-1 and 700 ± 30 mumol mol-1. After 100 days in the chambers, a series of gas exchange measurements were made. Half the plants in each chamber, one plant per species per chamber, were drought-stressed by withholding irrigation, while the remaining plants continued to be watered daily. Drought stress decreased stomatal conductance, photosynthesis and transpiration rates in all the species. The effect of drought stress on stomatal closure was similar in both [CO2]. The positive effects of elevated [CO2] on photosynthesis and water use efficiency were maintained longer during the stress period than under well-watered conditions. The photosynthetic rate of E. phaeotrica was higher even in the fourth day of the drought stress. Drought stress increased photoinhibition of photosynthesis, as measured by chlorophyll fluorescence, which varied among the species, as well as in relation to [CO2]. The results are in agreement with observed differences in stomatal responses between some eucalyptus species of the subgenera Symphyomyrtus and Monocalyptus

Semiempirical determination of intermolecular anharmonicity in molecular crystals: The case of 1,2,4,5-tetrabromobenzene

The molecular crystal 1,2,4,5-tetrabromobenzene (TBB) has been studied using Brillouin scattering and lattice dynamical calculations. A method for mapping acoustic mode anharmonicity is developed that exhibits substantial directional behavior and correlates well with the directions of the molecular movements associated with the phase transition. It is shown that by comparing the calculated sound velocities with the experimental values, insight can be gained into the displacive phase transition and the lattice dynamics of TBB. The sound velocities are plotted for three crystallographic planes containing the crystal axes. The relationships between sound velocities and lattice dynamics are discussed. The phonon dispersion curves for three directions are also presented. The Journal of Chemical Physics is copyrighted by The American Institute of Physics

Light scattering apparatus for angular dependent studies of anisotropic materials

An improved method for light scattering from acoustic phonons in small, low-symmetry solids is described. This instrumentation greatly facilitates the determination of elastic constants in highly anisotropic materials. Elastic scattering can be greatly reduced so that weaker phonon modes can be observed. Errors associated with the determination of the polarization directions of an anisotropic material are minimized by considering crystal optics. Review of Scientific Instruments is copyrighted by The American Institute of Physics

Advancing the technology base for high-temperature membranes

This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project addresses the major issues confronting the implementation of high-temperature membranes for separations and catalysis. We are pursuing high-temperature membrane systems that can have a large impact for DOE and be industrially relevant. A major obstacle for increased use of membranes is that most applications require the membrane material to withstand temperatures above those acceptable for polymer-based systems. Advances made by this project have helped industry and DOE move toward high-temperature membrane applications to improve overall energy efficiency

Composite metal membranes for hydrogen separation applications

A novel multilayer metal membrane has been developed that can be used for the separation of hydrogen from feed streams with near perfect selectivity. The membrane is comprised of very thin layers of fully dense palladium film deposited on both sides of a thin Group V metal foil, ion-milled prior to sputtering of the palladium. Palladium loading are kept low using the thin film deposition technology: 0.0012 grams of palladium per square centimeter of membrane is typically used, although thinner coatings have been employed. This membrane operates at temperatures on the order of 300 C and is capable of high rates of hydrogen flow. Flows are dependent on the pressure differential applied to the membrane, but flows of 105 sccm/cm{sup 2} and higher are regularly observed with differentials below one atmosphere. Long term testing of the membrane for a period in excess of 775 hours under constant conditions showed stable flows and an 85% hydrogen recovery efficiency. A system has been successfully applied to the hydrogen handling system of a proton exchange membrane fuel cell and was tested using a pseudo-reformate feed stream without any degradation in performance

Pulsed laser deposition of zeolitic membranes

The pulsed laser deposition of zeolites to form zeolitic thin films is described. Films were grown using both mordenite and faujasite targets and were deposited on various substrates. The optimal films were obtained when the target and substrate were separated by 5 cm. These films are comprised of small crystallites embedded in an amorphous matrix. Transmission electron microscopy reveals that the amorphous material is largely porous and that the pores appear to be close to the same size as the parent zeolite. Zeolotic thin films are of interest for sensor, gas separation, and catalytic applications

MOCVD of field emission phosphors using a liquid delivery system

Thin film phosphors for field emission displays show the potential to overcome the life-limiting problems that traditional powders face because of their high surface areas. By depositing a fully dense thin film, the surface area can be dramatically reduced, while the electrical and thermal conductivity is increased. Metal organic chemical vapor deposition offers the ability to deposit high quality, dense films that are crystalline as deposited and at temperatures low enough to allow for inexpensive glass. Deposition has been produced from mixtures of Y(tmhd){sub 3}, TEOS, Tb(tmhd){sub 3}, and O{sub 2} using a liquid delivery system. Coatings were shown to be composed of Y, Si, and Tb by x-ray fluorescence, but x-ray diffraction did not show any crystallinity. Excitation using radioluminescence produced a peak in the visible green at approximately 540 nm, indicative of the excitation of a Tb{sup 3+}. The morphology of the deposition was smooth, with surface features on the order of one micron and below. Some limited microcracking was also observed from the morphology because of the thermal expansion mismatch