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Marked influence of crystal structure on the friction and wear characteristics of cobalt and cobalt-base alloys in vacuum to 10-9 millimeter of mercury. i- polycrystalline and single crystal cobalt
Friction and wear characteristics for polycrystalline cobalt sliding on various materials in high vacuum
Large Tapered Crystal (LTC) Growth Method: A New Single Crystal Silicon Carbide Bulk Growth Technique
No abstract available
Quantifying sensitivities of ice crystal number and sources of ice crystal number variability in CAM 5.1 using the adjoint of a physically based cirrus formation parameterization
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Validating Crystal Plasticity Simulations of Surface Strains Crystal Rotations and Temperature / Strain-Rate Effects in FCC and BCC Metals.
Abstract Not Provided
Crystal efficiency evaluation for 16 keV x-ray bent-crystal radiography with ZPW.
Abstract not provided.
Crystal evaluation for 16 keV x-ray bent-crystal imaging and spectroscopy.
Abstract not provided.
THERMAL CONDUCTIVITY MANIPULATION IN SINGLE CRYSTAL SILICON VIA LITHOGRAPHYCALLY DEFINED PHONONIC CRYSTALS.
Abstract not provided.
Thermal conductivity manipulation in lithographically patterned single crystal silicon phononic crystal structures.
Abstract not provided.
Crystal response measurement of the X-ray transmission crystals used by the Imaging Spectroscopy Snout at the National Ignition Facility
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Understanding the influence of iron on crystallization kinetics of nepheline based glasses - 15472
Hanford site in Washington is home to 55 million US gallons of high level radioactive waste rich in sodium, alumina and iron. The strategy is to vitrify this waste in borosilicate glasses. Crystallization of nepheline/carnegeite (NaAlSiO{sub 4}) in glass melts during vitrification and canister cooling is a big challenge as it severely deteriorates the chemical durability of the glass. As the HLW borosilicate glasses are similar to basalt glass on a borate-free basis and as no borate phase crystallize on the liquidus, the crystallization chemistry of waste glasses can be described by the known phase relations of the geochemical basalt quaternary Na{sub 2}O-Al{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-SiO{sub 2} system. The objective of this study is to understand the influence of iron on the thermal stability and crystallization kinetics of model sodium- and alumina- rich simplified silicate glasses in the Na{sub 2}O-Al{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-SiO{sub 2} system designed in the primary crystallization field of nepheline. The results obtained from this study will form the baseline for understanding the nucleation and crystallization kinetics of multicomponent complex nuclear waste glasses in future. A series of glasses with compositions 25Na{sub 2}O-(25-z) Al{sub 2}O{sub 3}-zFe{sub 2}O{sub 3} -50SiO{sub 2} (mol.%) where z varies between 0 -5% has been prepared by melt-quench technique. Glasses have been labelled in reference to their Fe{sub 2}O{sub 3} content, i.e. Fe-z. We could not obtain amorphous glasses with Fe{sub 2}O{sub 3} > 5 mol.% . Glass batches comprising oxides and carbonates were melted at 1650 deg. C in Pt-Rh crucibles for 2 h. The melts were quenched in cold water to yield ∼90 g of glass. Thermal stability and crystallization kinetics of glasses was studied using differential thermal analysis (DTA). Thermal scans (30-1580 deg. C) were collected on glass particles (particle size: 0.5 mm-1 mm) at four different heating rates: 5, 10, 15 and 20 K min{sup -1} in air and inert (N{sub 2}) atmosphere. Non-isothermal crystallization kinetics of the glasses was studied using the Augis-Bennett method and Ozawa method. In accordance with the crystallization data obtained from DTA, glasses were heated in the crystallization temperature range and air quenched. Glasses were also heated from 30 deg. C to 800, 900 and 1000 deg. C for 1 h, respectively, in air and inert (N{sub 2}) atmospheres, at heating rate of 10 K min{sup -1}. Resulting glass-ceramics were characterized for their crystalline phase evolution by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Conversion of melt -to glass-ceramic during cooling DTA data was also collected for all the glasses during their conversion from melt -to -glass-ceramic during cooling at different cooling rates, in air and inert (N{sub 2}) atmosphere. In accordance with the DTA data, conversion of melt to glass-ceramic during cooling was studied by re-melting the glass frit in Pt-Rh crucibles at 1650 deg. C. The melt was allowed to cool at 10 K min{sup -1} and was air quenched at different temperatures (as per DTA data). The as obtained glass-ceramics were characterized by XRD and SEM Incorporation of Fe{sub 2}O{sub 3} in glasses decreases their crystallization temperature and increases their crystallization tendency. Parent glass (stoichiometric nepheline composition) is prone to surface crystallization. Incorporating 5 mol.% Fe{sub 2}O{sub 3} in these glasses transforms the crystallization kinetics from surface to volume nucleation. Crystallization kinetics of glass Fe-2.5 is affected by the environment (N{sub 2} vs. Air) while no significant impact of environment could be seen for glass Fe-5. Devitrification in all the glasses begins with the crystallization of carnegeite (NaAlSiO{sub 4}, orthorhombic) (∼1200 deg. C). Prolonged heat treatments leads to the crystallization of nepheline (NaAlSiO{sub 4}, hexagonal) (∼1200 deg. C) as a secondary phase. Fe{sub 2}O{sub 3} promotes the crystallization of nepheline over carnegeite via formation of magnetite as nucleation site. Iron incorporation pre-nucleates the glasses which upon heat treatment result in the formation of magnetite phase as nucleation sites, thus, shifting the mechanism of crystallization from surface to volume. Unlike carnegeite, the crystal structure of nepheline allows partial substitution of Fe{sup 3+}/Al{sup 3+}. This promotes the crystallization of nepheline over carnegeite in iron-containing glasses. Iron incorporation in nepheline-based sodium aluminosilicate glasses shifts crystallization mechanism from surface to bulk. Our results indicate that atmosphere does affect the crystallization kinetics of iron-containing aluminosilicate glasses but only when Fe{sub 2}O{sub 3} concentration is low. Since nepheline crystal structure can easily accommodate iron in comparison to carnegeite, iron seems to promote nepheline formation in these glasses at the expense of carnegeite through formation of Fe{sub 3}O{sub 4} phase as nucleation site. Future work will be focused on adding compositional complexity to these glasses and studying them further for their nucleation and crystallization behavior.
Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields
An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed. The experiment was conducted both in the presence and absence of a magnetic field gradient. The magnet produces a gradient field of approx. 1 Tesla2/cm. Image analysis of the recorded images indicated an enhanced plume velocity that was of the order of the measurement limit. For this experiment, both the gradient and gravity fields are in the same direction resulting in an enhanced effective gravity that tends to accelerate the observed plume velocity. While the results are not conclusive, pending further tests, it clearly points out the inadequacy of the MSFC magnet for conducting protein crystallization experiments and the need for a stronger magnet. In spacebased experiments, however, where the gravitational effects are small, only a weak magnetic field will be required to control or mitigate the effects of convective contamination.
Seeded Lateral Solid-Phase Crystallization of the Perovskite Oxide SrTiO 3
Crystallization from an amorphous precursor presents a new route to control the properties of complex oxides by selecting their nanoscale morphology. A key challenge in crystal growth from the amorphous form is to select the locations of nucleation and the crystallographic orientation of the resulting crystals. Nucleation sites for crystallization of the prototypical perovskite complex oxide SrTiO 3 (STO) from its amorphous form can be reproducibly introduced using nanoscale seed crystals. The results of two seeding strategies are reported here: (i) SrRuO 3 (SRO) (001)-oriented nanomembranes and (ii) STO nanocrystalline seeds. Amorphous STO crystallizes laterally over distances of several microns from the seeds before encountering separately nucleated crystals. The lateral crystallization rates for both types of seeding methods are close to the values measured in solidphase epitaxy (SPE) of STO on single-crystal substrates. The lateral crystallization distances along different crystallographic orientations are equal, indicating that the lateral crystallization rate is isotropic. The isotropic crystallization suggests that the rate-limiting steps for crystallization occur within the amorphous STO away from the amorphous/crystalline interface. In addition to the lateral crystallization, STO crystallizes on top of the planar SRO nanomembrane seeds via SPE, forming partially relaxed [001]-oriented heteroepitaxial STO layers. The in-plane orientation of laterally crystallized STO near the SRO nanomembrane seeds exhibits overall polycrystallinity with regions in which micron-scale grains of laterally crystallized STO share the same in-plane orientation as the SRO nanomembrane seeds. Crystallization from seed crystals provides opportunities to create a wide range of other perovskite oxides in nanoscale geometries.
Remote Sensing of Crystal Shapes in Ice Clouds
Ice crystals in clouds exist in a virtually limitless variation of geometries. The most basic shapes of ice crystals are columnar or plate-like hexagonal prisms with aspect ratios determined by relative humidity and temperature. However, crystals in ice clouds generally display more complex structures owing to aggregation, riming and growth histories through varying temperature and humidity regimes. Crystal shape is relevant for cloud evolution as it affects microphysical properties such as fall speeds and aggregation efficiency. Furthermore, the scattering properties of ice crystals are affected by their general shape, as well as by microscopic features such as surface roughness, impurities and internal structure. To improve the representation of ice clouds in climate models, increased understanding of the global variation of crystal shape and how it relates to, e.g., location, cloud temperature and atmospheric state is crucial. Here, the remote sensing of ice crystal macroscale and microscale structure from airborne and space-based lidar depolarization observations and multi-directional measurements of total and polarized reflectances is reviewed. In addition, a brief overview is given of in situ and laboratory observations of ice crystal shape as well as the optical properties of ice crystals that serve as foundations for the remote sensing approaches. Lidar depolarization is generally found to increase with increasing cloud height and to vary with latitude. Although this variation is generally linked to the variation of ice crystal shape, the interpretation of the depolarization remains largely qualitative and more research is needed before quantitative conclusions about ice shape can be deduced. The angular variation of total and polarized reflectances of ice clouds has been analyzed by numerous studies in order to infer information about ice crystal shapes from them. From these studies it is apparent that pristine crystals with smooth surfaces are generally inconsistent with the data and thus crystal impurity, distortion or surface roughness is prevalent. However, conclusions about the dominating ice shapes are often inconclusive and contradictory and are highly dependent on the limited selection of shapes included in the investigations. Since ice crystal optical properties are mostly determined by the aspect ratios of the crystal components and their microscale structure, it is advised that remote sensing applications focus on the variation of these ice shape characteristics, rather than on the macroscale shape or habit. Recent studies use databases with nearly continuous ranges of crystal component aspect ratio and-or roughness levels to infer the variation of ice crystal shape from satellite and airborne remote sensing measurements. Here, the rationale and results of varying strategies for the remote sensing of ice crystal shape are reviewed. Observed systematic variations of ice crystal geometry with location, cloud height and atmospheric state suggested by the data are discussed. Finally, a prospective is given on the future of the remote sensing of ice cloud particle shapes.
Large scale crystallization of protein pharmaceuticals in microgravity via temperature change
The major objective of this research effort is the temperature driven growth of protein crystals in large batches in the microgravity environment of space. Pharmaceutical houses are developing protein products for patient care, for example, human insulin, human growth hormone, interferons, and tissue plasminogen activator or TPA, the clot buster for heart attack victims. Except for insulin, these are very high value products; they are extremely potent in small quantities and have a great value per gram of material. It is feasible that microgravity crystallization can be a cost recoverable, economically sound final processing step in their manufacture. Large scale protein crystal growth in microgravity has significant advantages from the basic science and the applied science standpoints. Crystal growth can proceed unhindered due to lack of surface effects. Dynamic control is possible and relatively easy. The method has the potential to yield large quantities of pure crystalline product. Crystallization is a time honored procedure for purifying organic materials and microgravity crystallization could be the final step to remove trace impurities from high value protein pharmaceuticals. In addition, microgravity grown crystals could be the final formulation for those medicines that need to be administered in a timed release fashion. Long lasting insulin, insulin lente, is such a product. Also crystalline protein pharmaceuticals are more stable for long-term storage. Temperature, as the initiation step, has certain advantages. Again, dynamic control of the crystallization process is possible and easy. A temperature step is non-invasive and is the most subtle way to control protein solubility and therefore crystallization. Seeding is not necessary. Changes in protein and precipitant concentrations and pH are not necessary. Finally, this method represents a new way to crystallize proteins in space that takes advantage of the unique microgravity environment. The results from two flights showed that the hardware performed perfectly, many crystals were produced, and they were much larger than their ground grown controls. Morphometric analysis was done on over 4,000 crystals to establish crystal size, size distribution, and relative size. Space grown crystals were remarkably larger than their earth grown counterparts and crystal size was a function of PCF volume. That size distribution for the space grown crystals was a function of PCF volume may indicate that ultimate size was a function of temperature gradient. Since the insulin protein concentration was very low, 0.4 mg/ml, the size distribution could also be following the total amount of protein in each of the PCF's. X-ray analysis showed that the bigger space grown insulin crystals diffracted to higher resolution than their ground grown controls. When the data were normalized for size, they still indicated that the space crystals were better than the ground crystals.