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41.
Supersonic Flow Structure in the Entrance Part of a Mixing Chamber of 2D Model Ejector 总被引:1,自引:0,他引:1
The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail. 相似文献
42.
43.
Vaclav Pouchly Karel Maca Zhijian Shen 《Journal of the European Ceramic Society》2013,33(12):2275-2283
Tetragonal (3 mol% Y2O3) and two cubic zirconia (8 mol% Y2O3) as well as alumina green bodies were used for the construction of the Master Sintering Curve (MSC) created from sets of constant-rate-of-heating (CRH) sintering experiments. The activation energies calculated according to the MSC theory were 770 kJ/mol for Al2O3, 1270 kJ/mol for t-ZrO2, 620 kJ/mol and 750 kJ/mol for c-ZrO2. These values were verified by an alternative approach based on an analysis of the densification rate in the intermediate sintering stage. The MSCs established from the Two-Step Sintering (TSS) experiments showed at high densities a significant deflection from those constructed from the CRH experiments. This deflection was explained by lower sintering activation energy in the closed porosity stage. A new two-stage MSC model was developed to reflect the change in sintering activation energy and to describe TSS. The efficiency of TSS of four materials under investigation was correlated with their activation energies during the final sintering stage. 相似文献
44.
Magdalena Kristiawan Amina Meslem Ilinca Nastase Vaclav Sobolik 《International Journal of Heat and Mass Transfer》2012,55(1-3):282-293
This article presents a study on the wall shear rate and mass transfer of impinging jets on a flat plate. The performance of a cross-shaped orifice nozzle was compared with a reference convergent circular nozzle having similar equivalent diameter. An array of electrodiffusion micro probes inserted into the plate was used for wall shear rates measurements. Mass transfer in the impinging region was calculated from the measured wall shear rates for a Reynolds number around 5500 and over a range of streamwise distances between the nozzle and the impinging plane within 1 to 5 nozzle equivalent diameters. The obtained Sherwood number of the reference convergent nozzle is close to the one given by Chin and Tsang (1978) [5]. The most important observation in the present investigation is that the wall shear rates and the mass transfer in the impingement region of the cross-shaped orifice nozzle are up to 175% and 40%, respectively, higher than that of the convergent nozzle. The performance of the cross-shaped orifice jet is probably related to its particular vortex dynamics characteristic of the near exit region. All the results confirm that the jet passive control enhance the mass transfer. 相似文献
45.
Vaclav Dolezal 《Circuits, Systems, and Signal Processing》1999,18(2):183-187
Necessary and sufficient conditions for the invertibility of a (not necessarily linear) operatorN between normed linear spaces are given. It is shown thatN is invertible precisely if a certain operator associated withN is a contraction. 相似文献
46.
Vaclav Dolezal 《Circuits, Systems, and Signal Processing》1994,13(5):545-570
The estimates derived in this paper strengthen the available results on sensitivity and robust stability of input-output systems.
Two types of estimates are discussed: the “sensitivity type”, which establishes a bound for the output change when the system
is perturbed but the input remains the same, and the “robustness type”, which gives a bound for the output change when the
input changes but the perturbation does not. First, estimates for general systems over abstract extended spaces are derived;
these results are then applied to (1) two frequently used control configurations, and (2) systems governed by vector integral
and differential equations on the time domain [0, ∞). The applications of the estimates are illustrated by several examples.
This research was supported by the National Science Foundation under Grant #DMS-9102910 相似文献
47.
48.
E
2 are presented. The suggested algorithms are based on a technique of coding the line direction together with the end points
of the clipped line segment. They solve all cases more effectively. The algorithms are convenient for clippings lines or line
segments by rectangle. Theoretical considerations and experimental results are also presented. 相似文献
49.
Pavel Ctibor Helene Ageorges Vaclav Stengl Nataliya Murafa Igor Pis Tatiana Zahoranova Vaclav Nehasil Zdenek Pala 《Ceramics International》2011,37(7):2561-2567
Plasma spraying enables the creation of layers with thickness in a millimeter range adhering on various substrates. This paper provides a study of phase composition, optical properties and photocatalytic activity of BaTiO3 coatings prepared by atmospheric plasma spraying. The spraying was carried out by a direct current gas-stabilized plasma gun. BaTiO3 was fed into the plasma jet as a feedstock powder prepared by a reactive sintering of micrometer-sized powders of BaCO3 and TiO2. Microstructure and phase composition are reported and discussed in connection with optical properties and photocatalytic activity. The spraying was carried out by a direct current gas-stabilized plasma gun which normally utilizes spray distance (SD) in frames from 100 to 150 mm. Besides conventional SD 100 mm also extremely high SD 190 mm was used. The color of the sprayed coating is different for each SD and also differs from sintered BaTiO3. X-ray diffraction and also SAD mode of HR-TEM show certain content of amorphous fraction in the coating. The hydrogen content in the coating was found to be higher in the coatings than in the sintered bulk. The diffuse reflectance was measured by UV–VIS spectrophotometry and corresponding band-gap energy was estimated. X-ray photoelectron spectroscopy confirms specific stoichiometric and structural disorder observed also at bang-gap evaluation and by Raman spectroscopy. HR-TEM images for crystalline and amorphous zones are given. Photocatalytic decomposition of acetone was tested and BaTiO3 coatings compared with a sintered bulk. 相似文献
50.
Alena Reznickova Zdenka Novotna Nikola Slepickova Kasalkova Vaclav Svorcik 《Nanoscale research letters》2013,8(1):252
Properties of gold films sputtered under different conditions onto borosilicate glass substrate were studied. Mean thickness of sputtered gold film was measured by gravimetry, and film contact angle was determined by goniometry. Surface morphology was examined by atomic force microscopy, and electrical sheet resistance was determined by two-point technique. The samples were seeded with rat vascular smooth muscle cells, and their adhesion and proliferation were studied. Gold depositions lead to dramatical changes in the surface morphology and roughness in comparison to pristine substrate. For sputtered gold structures, the rapid decline of the sheet resistance appears on structures deposited for the times above 100 s. The thickness of deposited gold nanoparticles/layer is an increasing function of sputtering time and current. AFM images prove the creation of separated gold islands in the initial deposition phase and a continuous gold coverage for longer deposition times. Gold deposition has a positive effect on the proliferation of vascular smooth muscle cells. Largest number of cells was observed on sample sputtered with gold for 20 s and at the discharge current of 40 mA. This sample exhibits lowest contact angle, low relative roughness, and only mild increase of electrical conductivity. 相似文献