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The ammonia molecule is known to be useful as a probe for studying conditions inside interstellar clouds and planetary atmospheres. Correct interpretation of interstellar and planetary spectra need to be supported by adequate laboratory measurements. in the present studies we report the high resolution Fourier transform spectra of ammonia recorded with a pathlength of 192m at the Kitt Peak National Observatory. Transitions with intensities that are two orders of magnitude weaker than those that have been reported earlier, have been observed and assigned. These include high J transitions, hot bands and forbidden transitions. These transitions are not saturated under long paths such as those available in planetary atmospheres and are therefore useful in the estimation of temperatures. The forbidden transitions have been processed with other relevant data to provide complete information on the energy levels. Such information is required for the calculation of equilibrium population of energy levels and partition functions, which go into the estimation of spectral intensities and abundances in terrestrial, interstellar and planetary atmospheres.
The GALLEX collaboration aims at the detection of solar neutrinos in a radiochemical experiment employing 30 tons of Gallium in form of concentrated aqueous Gallium-chloride solution. The detector is primarily sensitive to the otherwise inaccessible pp-neutrinos. Details of the experiment have been repeatedly described before [1-7]. Here we report the present status of implementation in the Laboratori Nazionali del Gran Sasso (Italy). So far, 12.2 tons of Gallium are at hand. The present status of development allows to start the first full scale run at the time when 30 tons of Gallium become available. This date is expected to be January, 1990.
The Full-sky Astrometric Mapping Explorer (FAME) is designed to perform an all-sky, astrometric survey with unprecedented accuracy. It will create a rigid astrometric catalog of 4 × 107 stars with 5 < mV < 15. For bright stars, 5 < mV < 9, FAME will determine positions and parallaxes accurate to < 50 μas, with proper motion errors < 50 μas/yr. For fainter stars, 9 < mV < 15, FAME will determine positions and parallaxes accurate to < 500 μas, with proper motion errors < 500 μas/yr. It will also collect photometric data on these 4 × 107 stars in four Sloan Digital Sky Survey colors. NASA selected FAME to be one of five MIDEX missions funded for a concept study. In October 1999, NASA selected FAME for launch in 2004 as the MIDEX-4 mission in its Explorer program.
Solidification microstructures of Mg rich Mg-Zn-Y alloys were studied by using optical microscopy, scanning electron microscopy and transmission electron microscopy. Pseudo eutectic reaction (Liquid→α-Mg + icosahedral phase) takes place during solidification. Alloys containing high Mg content solidifies by primary crystallization ofα-Mg followed by the eutectic reaction at interdendritic region. Mg68Zn28Y4 alloy solidifies by primary crystallization of I-phase followed by theeutectic reaction into a mixture of α-Mg and I-phase. Occasionally D-phase and Mg4Zn7 phases were observed to form with orientation relationships with previously formed I-phase and D-phase, respectively. Thestrength of the alloys increased with increasing the volume fraction of I-phase.
An experimental comparison has been made between the properties of the surfaces of an Al70Pd21Mn9 quasicrystal and its Al48Pd42Mn10 approximant. The Al70Pd21Mn9 sample was a single grain icosahedral quasicrystal cut to expose its five-fold symmetric (000001) surface. The approximant was polycrystalline β-phase Al48Pd42Mn10, which has a CsCl-type cubic structure. Surfaces of both were prepared under ultra-high vacuum (UHV) conditions and then used for comparative measurements of their frictional properties and oxidation rates. Both materials are oxidized by reaction with O2 to form a thin film of aluminum oxide that ultimately passivates their surfaces. The interesting difference between the two is that the rate of oxidation of the approximant is significantly higher than that of the quasicrystal in spite of the fact that the bulk Al concentration of the approximant is lower than that of the quasicrystal. Friction measurements were made under UHV conditions between pairs of quasicrystals and pairs of approximants whose surfaces were either clean or oxidized to varying degrees. The friction between pairs of the approximant surfaces is significantly higher than that measured between the quasicrystal surfaces under all conditions of surface oxidation.
The glide resistance of edge dislocations gliding along a two-dimensional quasiperiodic lattice (Burkov II model of the decagonal quasicrystal) has been calculated. The glide resistance consists of τphason and τPeierls components and the τPeierls component depends strongly on the orientation of the dislocation. For the orientation of large τPeierls component, the τphason component is about half of the τPeierls component for individual dislocation glide but becomes negligibly small for glide of a pair of dislocations. The largest τPeierls component is about 0.1G (G: the shear modulus).
Five fold i-AlPdMn surface prepared under UHV by ion bombardment and annealing was so far considered to be bulk terminated. This result was substantially based on a quantitative LEED analyses . Analysis of the specular rod in a X ray diffraction experiment at grazing incidence supported this result . We present a new study of this surface by high resolution X ray diffraction at normal incidence. In this Bragg configuration the diffraction peak 18 – 29 for instance is at a photon energy of 2.873keV, the 72 – 116 reflection at 5.725keV. This results in an analyzed thickness of the sample surface of a few micrometers.
The surface was cleaned by ion bombardment. During annealing (T≅880K), we clearly observed the progressive disappearance of the initial Bragg peak characteristic of the as cast bulk sample. Conversely a new Bragg peak grows at an energy position shifted by 1eV compared to the position of the original Bragg peak. This is a clear signature for an irreversible structural transformation which takes place on at least the micron thickness. On the transformed surface, both, a LEED pattern and a RHEED pattern, characteristic for a five fold surface were easily obtained.
This high resolution experiment (the relative Bragg peak shift is 3ׁ10−4) was reproduced on samples from different initial compositions. This shows that five fold i-AlPdMn surface changes after preparation by ion bombardment and annealing at 900K on a micrometer thickness. This is not consistent with the conclusion that the surface is simply terminated by a cut of the original bulk. We conclude that a reorganization process of the quasicrystalline structure during annealing proceeds in the surface vicinity (probed depth is close to a few microns).
Composite coatings containing quasicrystalline (QC) phases in Al-Cu-Fe alloys were prepared by laser cladding using a mixture of the elemental powders. Two substrates, namely pure aluminum and an Al-Si alloy were used. The clad layers were remelted at different scanning velocities to alter the growth conditions of different phases. The process parameters were optimized to produce quasicrystalline phases. The evolution of the microstructure in the coating layer was characterized by detailed microstructural investigation. The results indicate presence of quasicrystals in the aluminum substrate. However, only approximant phase could be observed in the substrate of Al-Si alloys. It is shown that there is a significant transport of Si atoms from the substrate to the clad layer during the cladding and remelting process. The hardness profiles of coatings on aluminum substrate indicate a very high hardness. The coating on Al-Si alloy, on the other hand, is ductile and soft. The fracture toughness of the hard coating on aluminum was obtained by nano-indentation technique. The K1C value was found to be 1.33 MPa m1/2 which is typical of brittle materials.
The formation of the icosahedral phase, BCC (Body centred cubic) phase and nanocrystals are seen in the as-cast alloy with nominal composition of Mg4Zn94Y2. FCC (face centred cubic) phase and modulated structures are formed in the alloys with higher Y content (10% and 25% Y respectively). These phases are analysed keeping in view their relation to the quasicrystals of the Mg-Zn-Y system.
Icosahedral quasicrystals Al71.5Pd20.3Mn8.2, Al70.7Pd21.34Re7.96, Al62.5Cu25.5Fe12.5, and α-Al68.31Mn21.21Si10.48 1/1- approximant were investigated by using a monoenergetic slow positron beam. The structural vacancy densities in the first three samples were determined to be 5.0×1020, 7.7×1020, and 4.7×1020 cm−3, respectively, by analyzing the measured S-parameter.
Formation of defects during Zn diffusion into undoped and Fe-doped InP single crystals at 700°C has been observed by transmission electron microscopy for various diffusion conditions. The observations are correlated with Zn concentration profiles obtained by electron microprobe measurements and secondary-ion mass spectrometry. The results allow the conclusion that indiffusing interstitial Zn can occupy In sublattice sites via a kick-out reaction. Under appropriate diffusion conditions supersaturations of In self-interstitial atoms result leading to defect formation. Observations in Fe-doped InP suggest that Zn also replaces Fe on In sublattice sites leading to redistribution and to precipitation of Fe.
We show that CSD processing can be optimized in order to achieve columnar structured BaTiO3 and SrTiO3 thin films at elevated temperatures. In addition to these, columnar grain growth was also obtained for films of the solid solution (Ba0.7Sr0.3)TiO3 By controlling the film formation process, polycrystalline and columnar grained thin films were grown on Pt coated Si substrates at temperatures between 750° and 800°. The films were analyzed by glancing incidence X-ray diffraction and scanning electron microscopy. Detailed analysis on the thin films’ microstructure was performed by means of transmission electron microscopy. Based on these data, the film formation process is discussed with respect to process control and precursor chemistry. Differences in the crystallization process of BaTiO3 thin films compared to SrTiO3 films are pointed out.
A new cementitious calcium phosphate biomaterial, SuperBone®, was implanted in both a rabbit femoral canal model and a canine humeral plug model. New Zealand White rabbits were implanted with cement through a novel surgical approach where cement was introduced by injection. In the canine model, a uniform gap of 3 mm around a fiber metal porous implant was filled by the cement. Undecalcified light and backscattered electron histological evaluations indicate the cement is highly biocompatible and is replaced by new bone in concert with cell-mediated resorption. Unlike the acrylic bone cement positive controls, no evidence of fibrous tissue was found around the cement.
Konarka Technologies has developed efficient electrolyte compositions based on nonvolatile ionic liquids. The electrolyte compositions were subsequently gelled using a metal ion complexation technique, without compromising the photovoltaic performance of the dye sensitized solar cells (DSSCs). The photovoltaic performance of the gel electrolyte incorporated DSSCs is quite stable for extended period of time even in the absence of sealing. Detailed results on performance and stability of the gel electrolyte incorporated DSSCs are presented.
Numerous applications of electrotextiles and flexible circuits have been identified that can advance systems performance for many commercial, military, and aerospace devices. Several novel uses of electrotextiles have been developed for lab testing, while others have been utilized in products on the commercial market, as well as items that have flown in space. ILC Dover, Inc. has utilized conductive fibers in various inflatable and tensile structures for signal transmission and electrostatic charge protection. Conductive and pressure sensitive textiles have been incorporated in the advanced development space suit (I-Suit) as switch controls for lights and rovers, and as signal transmission cables. Conductive fibers have been used in several stitched applications for electrostatic charge dissipation. These applications include large pharmaceutical containment enclosures where fine potent powders are being captured for transfer between manufacturing facilities, as well as impact attenuation airbags used in landing spacecraft on the surface of Mars. In both cases, conductive threads are uniquely located in seams and panel locations to gather and direct charge through surface fibers and panel interconnects. Conductive fibers have also been utilized in a conformal Sensate Liner garment for the identification of wound locations and medical sensor signal transmission for soldier health monitoring while on the battlefield. The performance challenges of these structures require a careful, systematic application of electrotextiles because of the flexing, straining, and exposure of the materials to harsh environments. ILC has also been developing “gossamer” spacecraft components utilizing unique materials and multi-functional structures to achieve extremely low mass and low launch volumes. Examples of large deployable structures featuring very thin, large flexible circuits for use in space include synthetic aperture radar (SAR) antennas, communications antenna reflectarrays, and active variable reflectance solar sails. Design and materials challenges of electrotextile and large-area flexible circuit membrane structures as demonstrated in engineered applications will be discussed in this paper.
Weaving, knitting or placing electronic circuits within a textile matrix offer exciting possibilities for large-scale conformal circuits where the circuit dimensions can be measured on the scale of yards instead of inches. However, compared with conventional printed circuit board circuits, the textile manufacturing process and the electrical/mechanical properties of the fibers used in making the textile place unusual constraints on the electrical performance of textile circuits. In the case of distributed sensors connected via an electronic fabric, signal attenuation and the ability to form reliable interconnections are major challenges. To explore these challenges we have woven and knitted a variety of electrical transmission lines and optical fibers in fabrics to analyze their performance. The formation of interconnects and disconnects between conductors woven in textiles is also discussed, and a passive acoustic array is described as a possible electronic textile application.