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Different Gases (different + gase)
Selected AbstractsA computational study of gas flow in a De-Laval micronozzle at different throat diametersINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2009C. X. Lin Abstract A numerical study has been carried out to investigate the gas flows in a micronozzle using a continuum model under both slip and no-slip boundary conditions. The governing equations were solved with a finite volume method. The numerical model was validated with available experimental data. Numerical results of exit thrust showed good agreement with experimental data except at very low Reynolds numbers. For parametric studies on the effect of geometric scaling, the nozzle throat diameter was varied from 10 to 0.1,mm, whereas throat Reynolds number was varied from 5 to 2000. A correlation has also been developed to calculate the specific impulse at specified throat diameter and Reynolds number. The effect of different gases on the specific impulse of the nozzle, such as helium, nitrogen, argon and carbon dioxide, was also examined. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance analysis of gas liquefaction cyclesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2008Mehmet Kanoglu Abstract Relations are developed for first- and second-law analyses of the simple Linde,Hampson cycle used in gas liquefaction systems. An expression for the minimum work requirement, which is applicable to any gas liquefaction system, is developed with the help of a Carnot refrigerator. It is shown that the minimum work depends only on the properties of the incoming and outgoing gas streams and the environment temperature. Numerical calculations are performed to obtain the performance parameters of different gases while parametric studies are done to investigate the effects of liquefaction and inlet gas temperatures on various first- and second-law performance parameters. As the liquefaction temperature increases and the inlet gas temperature decreases, the liquefied mass fraction, the coefficient of performance (COP) and the exergy efficiency increase while actual and reversible work consumptions decrease. The exergy efficiency values appear to be low, indicating significant potential exists for improving efficiency and thus decreasing the required work consumption for a specified amount of liquefaction. Copyright © 2007 John Wiley & Sons, Ltd. [source] Peak capacity of ion mobility mass spectrometry: the utility of varying drift gas polarizability for the separation of tryptic peptidesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2004Brandon T. Ruotolo Abstract Ion mobility mass spectrometry (IM-MS) peptide mass mapping experiments were performed using a variety of drift gases (He, N2, Ar and CH4). The drift gases studied cover a range of polarizabilities ((0.2,2.6) × 10,24 cm3) and the peak capacities obtained for tryptic peptides in each gas are compared. Although the different gases exhibit similar peak capacities (5430 (Ar) to 7580 (N2)) in some cases separation selectivity presumably based on peptide conformers (or conformer populations), is observed. For example the drift time profiles observed for some tryptic peptide ions from aldolase (rabbit muscle) show a dependence on drift gas. The transmission of high-mass ions (m/z > 2000) is also influenced by increased scattering cross-section of the more massive drift gases. Consequently the practical peak capacity for IM-MS separation cannot be assumed to be solely a function of resolution and the ability of a gas to distribute signals in two-dimensional space; rather, peak capacity estimates must account for the transmission losses experienced for peptide ions as the drift gas mass increases. Copyright © 2004 John Wiley & Sons, Ltd. [source] High-output-power AlGaN/GaN ultraviolet-light-emitting diodes by activation of Mg-doped p-type AlGaN in oxygen ambientPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Kengo Nagata Abstract We demonstrated activation annealing of Mg-doped p-type Al0.17Ga0.83N in different gases. The hole concentration of Al0.17Ga0.83N annealed in oxygen is higher than that annealed in nitrogen or air. A hole concentration of 1.3,×,1016,cm,3 at room temperature was achieved by annealing in oxygen flow at 900,°C. Secondary ion mass spectroscopy shows that hydrogen dissociation from Mg-doped Al0.17Ga0.83N is found to be enhanced by annealing in a flow of oxygen, compared with annealing in a flow of nitrogen. We confirmed the effect of activation annealing in oxygen flow on the performance of UV light-emitting diode (LED). At a DC current of 100,mA, the output power of the LED annealed in oxygen flow at 900,°C is four times higher than that of the LED annealed in nitrogen flow at 800,°C. [source] Cathodoluminescence evaluation of subsurface damage in GaN substrate after polishingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009K. Y. Lai Abstract The surface of HVPE grown GaN substrates were treated with two different polishing procedures. Both procedures were successful in producing highly smooth and featureless surfaces. However, subsurface damage was observed in the sample treated by one of the procedures. The subsurface damage was revealed by cathodoluminescence (CL) spectroscopy imaging but was not visible by scanning electron microscopy (SEM) or Atomic force microscopy (AFM). Thermal annealing at 950 °C with different gases was performed in an attempt to remove subsurface damages. Annealing in gas mixtures containing H2 increased both the presence of surface scratches and overall surface roughness. On the other hand, annealing in mixtures of NH3 and N2 (with no H2) led to the surfaces with significantly reduced subsurface damage. The surface roughness and optical properties of the sample after the annealing with such gas mixtures were slightly sacrificed. In order to evaluate subsurface damage depth, CL images were taken from the annealed surface for different acceleration voltages. The results suggest that the observed subsurface damages were within 1.48 ,m of the surface. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sulfur hexafluoride (SF6) versus perfluoropropane (C3F8) gas tamponade for macular hole surgeryACTA OPHTHALMOLOGICA, Issue 2009M STEFANIOTOU Purpose In Macular Hole surgery gas tamponade is hypothesized to enhance macular hole closure after removal of tangential force. Sulfur hexafluoride (SF6) was described in the initial report of Macular Hole surgery (MHS). Long lasting gas (such as C3F8) may offer more extensive tamponade . To compare outcomes of Macular Hole Surgery using SF6 gas versus C3F8 gas for idiopathic macular hole repair. Methods A consecutive group of patients undergoing MHS with SF6 group A (24 eyes of 24 patients) and a consecutive comparison group B with S3F8 was used (19 eyes of 19 patients). All patients had PP Vitrectomy, ILM peeling, using Kenacort or Blue and two different gases for internal tamponade. Results The macular hole closure rate was similar in both groups. Conclusion Macular Hole surgery using SF6 gas yields similar results as with C3F8 gas and may be a good option. [source] | |||||||||||||