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291.
Finite element schemes for hyperbolic systems are applied to the St. Venant equations for one-dimensional, unsteady, open channel flow. The comparative performances of the characteristic-dissipative-Galerkin, Taylor-Galerkin and least squares finite element schemes are assessed by means of linear Fourier analysis and solution of idealized non-linear wave propagation problems. Of particular interest is the behaviour of these schemes for the regressive wave component in both subcritical and supercritical flows. To assess the quality of the basic solution, the methods are compared without any additional artificial diffusion or shock-capturing formulations. The balanced treatment of both wave components in the characteristic-dissipative-Galerkin method is illustrated. Also, the method displays little sensitivity to parameters variations. The Taylor-Galerkin scheme provides good solutions, although oscillations due to wave dispersion and minimal diffusion of the regressive wave are displayed. Also, this method is somewhat sensitive to the time step increment. The least squares method is considered unsuitable for unsteady, open channel flow problems owing to its inability to propagate a regressive wave in a supercritical flow. 相似文献
292.
The variation of the local susceptibility of isolated Fe atoms in Cu with temperature is a problem which has resisted agreement among previous workers. We present additional Mössbauer measurements obtained over the range 4.2 to 126 K and in applied fields of 2.4 to 8.4 T. No anomalous behaviour of the local susceptibility is observed. 相似文献
293.
C. B. Collins F. Davanloo M. C. Iosif R. Dussart J. M. Hicks S. A. Karamian C. A. Ur I. I. Popescu V. I. Kirischuk J. M. Pouvesle P. McDaniel C. E. Crist 《Physics of Atomic Nuclei》2000,63(12):2067-2072
A sample containing 6.3×1014 nuclei of the 16+ isomer of 178Hf having a half-life of 31 yr and an excitation energy of 2.446 MeV was irradiated with x-ray pulses from a device operated at 15 mA to produce bremsstrahlung with an endpoint energy of 90 keV. The gamma spectra of the isomeric target were taken with a Ge detector. The intensity of the 325.5-keV (6+ → 4+) transition in the ground-state band of 178Hf was found to increase by about 2%. Such an enhanced decay of the 178Hf isomer is consistent with an integrated cross section value of 3×10?23 cm2 keV if resonance absorption occurs within energy ranges corresponding to the maxima of the x-ray flux, either near 20 keV or at the energies of the characteristic emission lines of W. 相似文献
294.
Gangyi Chen Dick Cheng Robert F. Hicks Atif M. Noori Sumiko L. Hayashi Mark S. Goorsky Ravi Kanjolia Raj Odedra 《Journal of Crystal Growth》2004,270(3-4):322-328
Indium phosphide, gallium arsenide phosphide, and aluminum indium phosphide have been deposited by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and tertiarybutylarsine. The effects of growth temperature and V/III ratio on the amount of silicon, sulfur, carbon, and oxygen in InP have been determined. Minimum incorporation was observed at 565 °C and a V/III ratio of 32. In this case, the material contained a background carrier concentration of 2.7×1014 cm−3, and the Hall mobilities were 4970 and 135,000 cm2/V s at 300 and 77 K. The oxygen contamination in AlInP was found to be only 9.0×1015 cm−3 for deposition at 650 °C and a V/III ratio of 35. The relative distribution of arsenic to phosphorus in GaAsyP1−y was determined at temperatures between 525 and 575 °C. The distribution coefficient [(NAs/NP)film/(PTBAs/PTBP)gas] ranged from 25.4 to 8.4, and exhibited an Arrhenius relationship with an apparent activation energy of 1.2 eV. 相似文献
295.
Andreas Heilmann Dr. Jamie Hicks Dr. Petra Vasko Prof. Jose M. Goicoechea Prof. Simon Aldridge 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4927-4931
Anionic molecular imide complexes of aluminium are accessible via a rational synthetic approach involving the reactions of organo azides with a potassium aluminyl reagent. In the case of K2[( NON )Al(NDipp)]2 ( NON =4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene; Dipp=2,6-diisopropylphenyl) structural characterization by X-ray crystallography reveals a short Al−N distance, which is thought primarily to be due to the low coordinate nature of the nitrogen centre. The Al−N unit is highly polar, and capable of the activation of relatively inert chemical bonds, such as those found in dihydrogen and carbon monoxide. In the case of CO, uptake of two molecules of the substrate leads to C−C coupling and C≡O bond cleavage. Thermodynamically, this is driven, at least in part, by Al−O bond formation. Mechanistically, a combination of quantum chemical and experimental observations suggests that the reaction proceeds via exchange of the NR and O substituents through intermediates featuring an aluminium-bound isocyanate fragment. 相似文献
296.
Gilroy JB McKinnon SD Kennepohl P Zsombor MS Ferguson MJ Thompson LK Hicks RG 《The Journal of organic chemistry》2007,72(21):8062-8069
Two benzene-bridged N,N'-bis(isopropyl)6-oxoverdazyl diradicals 7a (1,4-benzene-bridged) and 7b (1,3-benzene-bridged) were prepared and studied by an array of physicochemical techniques aimed at elucidating the intramolecular electronic and magnetic coupling between verdazyl chromophores. The very high stability of these diradicals permits comprehensive investigations of their properties for the first time. The UV-vis spectra suggest negligible direct conjugative overlap involving the radical SOMOs, although significant differences in higher energy absorptions suggest that radical orbitals other than the SOMO are likely communicating via the central p-phenylene bridge in 7a. The electrochemical features of the two diradicals are nearly identical; in each derivative, both radicals are oxidized essentially independently while the reductions occur in a stepwise manner with differences of approximately 100 mV between the two reductions. EPR and magnetic susceptibility collectively indicate that the para-bridged diradical is weakly antiferromagnetically coupled while the meta analogue is weakly ferromagnetically coupled, in accord with the topology of the substitution pattern on the central benzene ring. 相似文献
297.
Luan L Lippman TM Hicks CW Bert JA Auslaender OM Chu JH Analytis JG Fisher IR Moler KA 《Physical review letters》2011,106(6):067001
We measure the penetration depth λab(T) in Ba(Fe(1-x)Co(x))(2)As(2) using local techniques that do not average over the sample. The superfluid density ρs(T) ≡ 1/λab(T)2 has three main features. First, ρs (T = 0) falls sharply on the underdoped side of the dome. Second, λab(T) is flat at low T at optimal doping, indicating fully gapped superconductivity, but varies more strongly in underdoped and overdoped samples, consistent with either a power law or a small second gap. Third, ρs (T) varies steeply near Tc for optimal and underdoping. These observations are consistent with an interplay between magnetic and superconducting phases. 相似文献
298.
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300.
Michael B. Hicks Keith Mattern Jonathan Fine Shane Grosser Daya Patel Lauren Weisel Pankaj Aggarwal 《Journal of separation science》2023,46(21):2300300
Pharmaceutical development currently relies on quality separation methods from early discovery through to line-of-site manufacturing. There have been significant advancements made regarding the column particle packing, internal diameter, length connectivity, the understanding of the impact key parameters like void volume, flow rate, and temperature all that affects the resultant separation quality, that is, resolution, peak shape, peak width, run time, and signal-to-noise ratio. There is however a strong need to establish better alternatives to large bulky high-performance liquid chromatography racks either for process analytical reaction monitoring or mass spectrometry analysis in establishing product quality. Compact, portable high-pressure liquid chromatography can be a more efficient alternative to traditional ultra-high pressure liquid chromatography and traditional liquid chromatography. The compact versatile instrument evaluated here allows good separation control with either the on-board column with fixed ultra-violet wavelength cartridge or for use with a high-resolution mass spectrometry. Significant space reduction results in greener lab spaces with improved energy efficiency for smaller labs with lower energy demands. In addition, this compact liquid chromatography was used as a portable reaction monitoring solution to compare forced degradation kinetics and assess portable liquid chromatography-mass spectrometry capability for the analyses required for pharmaceutical drug product testing. 相似文献