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Cryogenic Temperatures (cryogenic + temperature)
Selected AbstractsTechnical Cost Modeling for the Mechanical Milling at Cryogenic Temperature (Cryomilling),ADVANCED ENGINEERING MATERIALS, Issue 8 2004J. Ye Cryomilling is one of the few technologies available to fabricate a large quantity of nanostructured materials. No matter how exciting and promising a technology is, its ultimate realization is invariably dependent on economic success. Technical cost modeling was employed in this paper to analyze the processing cost of cryomilling. The results demonstrated that cryomilling has the potential to be commercially economical to fabricate nanostructured materials. [source] Chemistry on Single Atoms: Spontaneous Hydrogen Production from Reactions of Transition-Metal Atoms with Methanol at Cryogenic Temperatures,ANGEWANDTE CHEMIE, Issue 7 2010Guanjun Wang Wichtig für Methanol-Brennstoffzellen: Bei der Reaktion von Atomen früher Übergangsmetalle im Grundzustand mit Methanol in einer Argonmatrix entstehen spontan Diwasserstoff und Methoxidsalze M(OMe)2 (M=Sc, Ti, V, Nb). Die Befunde belegen, dass selbst bei tiefen Temperaturen Wasserstoff direkt durch die Umsetzung von Metallatomen im Grundzustand mit Methanol produziert werden kann. [source] Simultaneously improved toughness and dielectric properties of epoxy/core-shell particle blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Weitao Wan Abstract Epoxy/core-shell particle blends were prepared using a diglycidylether of bisphenol A epoxy and acrylics-type core-shell particles. The impact strength of the blends was tested, and the result showed that the epoxy was greatly toughened with optimum core-shell particle content. Meanwhile, the dielectric properties of both epoxy and its blends were investigated using a broadband dielectric analyzer. It was found that the dielectric constant of the epoxy blends with lower core-shell particle content were less than that of the epoxy in the investigated frequency range, while the dielectric loss was less than that of the neat epoxy over a low frequency range, even for the epoxy blends with the optimum core-shell particle content. The dielectric breakdown strength of the epoxy blends at room and cryogenic temperature were also investigated. To identify the primary relationship of the above properties and structure of the epoxy blends, the microstructure of the core-shell particle and the morphology of the samples were observed by transmission electron microscopy and scanning electron microscopy. It was considered that these epoxy/core-shell particle blends with improved toughness and desirable dielectric properties could have a potential application in the insulation of electronic packaging system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Three-dimensionally structured silicon as a substrate for the MOVPE growth of GaN nanoLEDsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Sönke Fündling Abstract Three-dimensionally patterned Si(111) substrates are used to grow GaN based heterostructures by metalorganic vapour phase epitaxy, with the goal of fabricating well controlled, defect reduced GaN-based nanoLEDs. In contrast to other approaches to achieve GaN nanorods, we employed silicon substrates with deep etched nanopillars to control the GaN nanorods growth by varying the size and distance of the Si pillars. The small footprint of GaN nanorods grown on Si pillars minimise the influence of the lattice mismatched substrate and improve the material quality. For the Si pillars an inductively coupled plasma dry-etching process at cryogenic temperature has been developed. An InGaN/GaN multi quantum well (MQW) structure has been incorporated into the GaN nanorods. We found GaN nanostructures grown on top of the silicon pillars with a pyramidal shape. This shape results from a competitive growth on different facets as well as from surface diffusion of the growth species. Spatially resolved optical properties of the structures are analysed by cathodoluminescence. Strongly spatial-dependent MQW emission spectra indicate the growth rate differences on top of the rods. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Specific aspects on crack advance during J -test method for structural materials at cryogenic temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2006K. WEISS ABSTRACT Cryogenic elastic plastic, J -integral investigations on metallic materials often show negative crack extension values with respect to resistance curve J - R. According to the present ASTM standard, the use of unloading compliance technique relies on the estimation procedure of the crack lengths during the unloading sequences of the test. The current standard, however, does not give any specific procedure for treating such negative data. To date, the applied procedure uses the shifting of the negative crack extension values either to the onset of the blunting line or to the offset of the resistance curve. The present paper represents a solution of the negative crack length problem on the basis of a mechanical evaluation procedure of the unloading slopes. The achieved progress using this evaluation technique is demonstrated on different materials such as cryogenic high toughness stainless steels, low carbon ferritic steel and aluminum alloys from the series of 7000 and 5000. In addition, this work deals with the crack tunnelling phenomenon, observed for high toughness materials, and shows the reduction of this crack extension appearance by using electro discharge machining (EDM) side groove technique. The differences between EDM processed side grooves and standard V-notch machining have been investigated within these test series. [source] High-cycle fatigue properties in Ti,5% Al,2.5% Sn ELI alloy with large grain size at cryogenic temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2004Y. ONO ABSTRACT High-cycle fatigue properties were investigated for Ti,5% Al,2.5% Sn ELI alloy with a mean , grain size of 80 ,m, which had been used for liquid hydrogen turbo-pumps of Japanese-built launch vehicles. At cryogenic temperatures, the fatigue strength in high-cycle region did not increase in proportion to increments of the ultimate tensile strength and the fatigue strengths at around 106 cycles were about 300 MPa independent of test temperatures. Fatigue cracks initiated in the specimen interior independent of the test temperatures of 4 K, 77 K and 293 K. At 4 K and 77 K, several crystallographic facet-like structures were formed at crack initiation sites. On the other hand, there were no facet-like structures that could be clearly identified at the crack initiation sites at 293 K. Low fatigue strengths in longer-life region at cryogenic temperatures could be attributable to the formation of large sub-surface crack initiation sites, where large facet-like structure are formed. [source] Microporous Metal,Organic Frameworks with High Gas Sorption and Separation Capacity,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2007Y. Lee Abstract The design, synthesis, and structural characterization of two microporous metal,organic framework structures, [M(bdc)(ted)0.5]·2,DMF·0.2,H2O (M,=,Zn (1), Cu (2); H2bdc,=,1,4-benzenedicarboxylic acid; ted,=,triethylenediamine; DMF: N,N -dimethylformamide) is reported. The pore characteristics and gas sorption properties of these compounds are investigated at cryogenic temperatures, room temperature, and higher temperatures by experimentally measuring argon, hydrogen, and selected hydrocarbon adsorption/desorption isotherms. These studies show that both compounds are highly porous with a pore volume of 0.65 (1) and 0.52,cm3,g,,1 (2). The amount of the hydrogen uptake, 2.1,wt,% (1) and 1.8,wt,% (2) at 77,K (1,atm; 1,atm,=,101,325,Pa), places them among the group of metal,organic frameworks (MOFs) having the highest H2 sorption capacity. [Zn(bdc)(ted)0.5]·2,DMF·0.2,H2O adsorbs a very large amount of hydrocarbons, including methanol, ethanol, dimethylether (DME), n -hexane, cyclohexane, and benzene, giving the highest sorption values among all metal,organic based porous materials reported to date. In addition, these materials hold great promise for gas separation. [source] Tracking reflections through cryogenic cooling with topographyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2006Jeffrey J. Lovelace The mosaic structure of a single protein crystal was analyzed by reflection profiling and topography using highly parallel and monochromatic synchrotron radiation. Fine-,-sliced diffraction images (0.002° stills) were collected using a conventional large-area CCD detector in order to calculate reflection profiles. Fine-,-sliced topographic data (0.002°) stills were collected with a digital topography system for three reflections in a region where the Lorentz effect was minimized. At room temperature, several different mosaic domains were clearly visible within the crystal. Without altering the crystal orientation, the crystal was cryogenically frozen (cryocooled) and the experiment was repeated for the same three reflections. Topographs at cryogenic temperatures reveal a significantly increased mosaicity, while the original domain structure is maintained. A model for the observed changes during cryocooling is presented. [source] A beginner's guide to radiation damageJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2009James M. Holton Many advances in the understanding of radiation damage to protein crystals, particularly at cryogenic temperatures, have been made in recent years, but with this comes an expanding literature, and, to the new breed of protein crystallographer who is not really interested in X-ray physics or radiation chemistry but just wants to solve a biologically relevant structure, the technical nature and breadth of this literature can be daunting. The purpose of this paper is to serve as a rough guide to radiation damage issues, and to provide references to the more exacting and detailed work. No attempt has been made to report precise numbers (a factor of two is considered satisfactory), and, since there are aspects of radiation damage that are demonstrably unpredictable, the `worst case scenario' as well as the `average crystal' are discussed in terms of the practicalities of data collection. [source] Radiation damage of protein crystals at cryogenic temperatures between 40,K and 150,KJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2002Tsu-Yi Teng X-ray radiation damage of lysozyme single crystals by an intense monochromatic beam from the Advanced Photon Source is studied at cryogenic temperatures between 40,K and 150,K. The results confirm that primary radiation damage is both linearly dependent on the X-ray dose and independent of temperature. The upper limit for the primary radiation damage observed in our previous study [Teng & Moffat (2000), J. Synchrotron Rad. 7, 313317] holds over the wider temperature range of this study. The X-ray diffraction quality of the data acquired at 40,K is superior to those at 100,K, apparently due to temperature dependence of secondary and tertiary radiation damage and to reduced thermal motion. [source] High pressure structure of Tb2Ti2O7 pyrochlore at cryogenic temperaturesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007Ravhi S. Kumar Abstract The structure of Tb2Ti2O7 pyrochlore was investigated at high pressures up to 24 GPa at cryogenic temperatures down to 6.5 K using angular dispersive X-ray diffraction with synchrotron radiation at HPCAT, Advanced Photon Source. The cell parameters were obtained by performing full profile Rietveld refinements of the diffraction data. The equation of state is obtained at low temperatures by fitting the pressure-volume data to a second order Birch Murnaghan eqation and a bulk modulus value of 168(4) GPa is obtained. The results show persistance of the pyrochlore structure up to the maximum pressure studied in the experiment and further indicate that pressure induces solely magnetic ordering which do not involve crystal symmetry changes. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Carrier recombination processes in 1.3 ,m and 1.5 ,m InGaAs(P)-based lasers at cryogenic temperatures and high pressuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2004S. J. Sweeney Abstract We describe measurements of the threshold current of 1.3 ,m and 1.5 ,m InGaAs(P)-based quantum-well lasers measured at cryogenic temperatures and at high pressures. At low temperatures (,100 K), we find that the threshold current of the devices increases with increasing pressure consistent with the calculated pressure variation of the radiative current. This is in sharp contrast with their pressure dependence at room temperature (RT), where the threshold current decreases with increasing pressure due to the decrease in importance of Auger recombination. These low-temperature, high-pressure results agree well with previous temperature dependence measurements on the same devices, which show a transition from radiative to non-radiative Auger recombination dominated behaviour as the laser temperature is increased from ,100 K to room temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tracking ligand-migration pathways of carbonmonoxy myoglobin in crystals at cryogenic temperaturesACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010Ayana Tomita In order to explore the ligand-migration dynamics in myoglobin induced by photodissociation, cryogenic X-ray crystallographic investigations of carbonmonoxy myoglobin crystals illuminated by continuous wave and pulsed lasers at 1,15,kHz repetition rate have been carried out. Here it is shown that this novel method, extended pulsed-laser pumping of carbonmonoxy myoglobin, promotes ligand migration in the protein matrix by crossing the glass transition temperature repeatedly, and enables the visualization of the migration pathway of the photodissociated ligands in native Mb at cryogenic temperatures. It has revealed that the migration of the CO molecule into each cavity induces structural changes of the amino-acid residues around the cavity which result in the expansion of the cavity. The sequential motion of the ligand and the cavity suggests a self-opening mechanism of the ligand-migration channel arising by induced fit. [source] Cryoprotection properties of salts of organic acids: a case study for a tetragonal crystal of HEW lysozymeACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Grzegorz Bujacz Currently, the great majority of the data that are used for solving macromolecular structures by X-ray crystallography are collected at cryogenic temperatures. Selection of a suitable cryoprotectant, which ensures crystal stability at low temperatures, is critical for the success of a particular diffraction experiment. The effectiveness of salts of organic acids as potential cryoprotective agents is presented in the following work. Sodium formate, acetate, malonate and citrate were tested, as were sodium potassium tartrate and acetate in the form of potassium and ammonium salts. For each salt investigated, the minimal concentration that was required for successful cryoprotection was determined over the pH range 4.5,9.5. The cryoprotective ability of these organic salts depends upon the number of carboxylic groups; the lowest concentration required for cryoprotection was observed at neutral pH. Case-study experiments conducted using the tetragonal form of hen egg-white lysozyme (HEWL) confirmed that salts of organic acids can successfully act as cryoprotective agents of protein crystals grown from high concentrations of inorganic salts. When crystals are grown from solutions containing a sufficient concentration of organic acid salts no additional cryoprotection is needed as the crystals can safely be frozen directly from the crystallizing buffers. [source] Single Dibenzoterrylene Molecules in an Anthracene Crystal: Spectroscopy and PhotophysicsCHEMPHYSCHEM, Issue 8 2007Aurélien A. L. Nicolet Abstract We study single dibenzoterrylene molecules in an anthracene single crystal at 1.4 K in two insertion sites at 785.1 and 794.3 nm. The single-molecule zero-phonon lines are narrow (about 30 MHz), intense (the detected fluorescence rates at saturation reach 100,000 counts,s,1), and very photostable. The intersystem-crossing yield is extremely low (10,7 or lower). All of these features are hallmarks of an excellent system for high-resolution spectroscopy and nanoscale probing at cryogenic temperatures. [source] Photophysical Properties of a Tetraphenoxy-Substituted Perylene Bisimide Derivative Characterized by Single-Molecule SpectroscopyCHEMPHYSCHEM, Issue 5 2005Erwin Lang Abstract We present a detailed study of the photophysical properties of a tetraphenoxy-substituted perylene bisimide derivative. The probe molecules were immobilized in a Shpol'skii matrix of hexadecane and investigated by single-molecule spectroscopy at cryogenic temperatures. By using single-molecule spectroscopic techniques we reveal the triplet substate kinetics and the fluorescence quantum yield, and we provide an estimate for the S1,S0 transition dipole moment. [source] Gas-chromatographic separation of tri(hetero)halogenomethane enantiomersCHIRALITY, Issue 8 2005Zhengjin Jiang Abstract Five-atomic tri(hetero)halogenomethanes represent the simplest class of non-isotopic small chiral molecules suitable for the study of fundamental aspects of chirality. The analytical gas-chromatographic separation of the enantiomers of bromochlorofluoromethane 1 and of chlorofluoroiodomethane 2 on the immobilized chiral stationary phase octakis(3- O -butanoyl-2,6-di- O - n -pentyl)-,-cyclodextrin 3, chemically linked to polydimethylsiloxane, is described. By temperature-dependent thermodynamic measurements very low isoenantioselective temperatures Tiso are found and for optimum enantiomeric separations cryogenic temperatures are required. The ee values of enantiomerically enriched tri(hetero)halogenomethanes 1 and 2 are determined and relative configurations are correlated with the chromatographic elution order of 1 and 2 on 3. © 2005 Wiley-Liss, Inc. Chirality 17:488,493, 2005. [source] | ||||||||||||||||