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51.
Momentum and mass transfer at fluid–porous interfaces occur in many technical and natural applications. The vertical extend
below a fluid–porous interface within which the free fluid velocity reduces to a constant Darcy velocity in the porous medium
is known as Brinkman layer. Recently, the Brinkman layer thickness (δ) has been measured for a porous bed of mono-sized spherical
beads, and was found to be in the order of the particle diameter (d). In this study, we investigate a porous medium made of multi-sized spherical beads. The measured averaged interfacial velocity
field clearly indicated that, in the case of multi-sized beads, δ is in the order of a characteristic diameter given by with x
i
and d
i
being the weight fraction and diameter of the component i in the mixture. 相似文献
52.
A high-order immersed boundary method is devised for the compressible Navier-Stokes equations by employing high-order summation-by-parts difference operators. The immersed boundaries are treated as sharp interfaces by enforcing the solid wall boundary conditions via flow variables at ghost points. Two different interpolation schemes are tested to compute values at the ghost points and a hybrid treatment is used. The first method provides the bilinearly interpolated flow variables at the image points of the corresponding ghost points and the second method applies the boundary condition at the immersed boundary by using the weighted least squares method with high-order polynomials. The approach is verified and validated for compressible flow past a circular cylinder at moderate Reynolds numbers. The tonal sound generated by vortex shedding from a circular cylinder is also investigated. In order to demonstrate the capability of the solver to handle complex geometries in practical cases, flow in a cross-section of a human upper airway is simulated. 相似文献
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56.
Shahla Khalili Saied Nouri Khorasani Niloufar Saadatkish Khadije Khoshakhlagh 《Polymer Science Series A》2016,58(3):399-408
Gelatin/cellulose acetate electrospun nanofibers are a good candidates for simulation of extracellular matrix (ECM). Electrospinning of the blend is controlled by many parameters such as applied voltage, gap distance, solvent composition, polymer composition and solution concentration. The individual and interactive effects of these parameters on pH, electrical conductivity (EC) and viscosity of solutions, and diameter and quality of fibers were investigated. Response surface methodology (RSM) and artificial neural networks (ANNs) were considered to model and optimize the responses. EC, pH and viscosity of solutions were dependent on the solution parameters. The solvent composition and solution concentration had an influence on the fiber diameter and quality. The optimum conditions for fabricating qualified nanofibers with minimum diameter were 16.9 kV, 15.3 cm, 77.5 wt % of gelatin, 88.9 vol % of acetic acid and solution concentration of 20 wt %/vol %. Uniform beadless nanofibers with a diameter of 284 nm were attained at this optimum condition. 相似文献
57.
Actinide chloride complexes with pyridinaldazine (PAA), pyrrolaldazine (PyAA-H2), furanaldazine (FAA), and thiophenaldazine (TAA): An(L)Cln·m-H2O, where An = Th, UO2; L = PAA, PyAA-H2, FAA, TAA; n = 2, 4; m = 0, 2, 3, 5 (also, mononuclear with 2L, dinuclear and trinuclear complexes) have been prepared by the reaction of ThCl4, UO2Cl2 or UO2(Ac)2·2H2O with PAA, PyAA-H2, FAA or TAA and characterized by spectral data, electrical conductance, thermal and elemental analysis. 相似文献
58.
A simple and selective spectrophotometric method is proposed for the determination of ultra trace amounts of Tl(III). The reported method is based on the oxidation of 4-(4'-N,N-dimethylaminophenyl)urazole (DAPU) to the corresponding triazolinedione (TAD) by Tl(III) at pH 4.0. The reaction was monitored spectrophotometrically by measuring the increasing color of TAD compound at 514 nm by the fixed-time method. At a given time of 2.0 min at 30 degrees C, the working range of calibration was 5.0 x 10(-8) - 2.0 x 10(-5) M Tl(III) and detection limit of 5.0 x 10(-8) M was obtained. The influences of pH, reagent concentration, ionic strength and temperature were studied. The effect of diverse ions on the determination of Tl(III) by the proposed method was also investigated. Thallium in real samples was determined by this method, with satisfactory results. 相似文献
59.
M. S. Al-Masri H. Mukallati A. Al-Hamwi H. Khalili M. Hassan H. Assaf Y. Amin A. Nashawati 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(2):405-412
More than one hundred different food stuffs (meat, vegetables cereals, seafood,..) have been collected during 1998, 1999 and
2000 and analyzed for radioactivity as part of the National Food Monitoring Program in Syria. Results have shown that most
of the observed concentrations were within the range of the worldwide values with the exception of relatively high levels
of 210Po being observed in fish, vegetables, mushrooms, herbs and flowers. The daily intakes of the radionuclides studied have been
evaluated. Relatively high values, in comparison with some countries, were found for 210Po (1.9 Bq/day). This is due to high content of 210Po in wheat (2.3 Bq/kg) consumed by Syrians, the daily consumption of wheat by Syrians is about 526 g. In addition, natural
and artificial radionuclides in some manufactured food of Syrian infant and their intake rates have been determined. Seventeen
manufactured food and eleven types of canned milk were collected from the local market and their radioactivity analyzed. 210Po activity concentration varied between 0.38 and 2.89 Bq/kg dry wt. in canned milk while the highest concentration in infant
food was found to be 1.69 Bq/kg dry wt. Other radionuclide concentrations were below the limit of detection of 3 Bq/kg dry
wt. and 4 Bq/kg dry wt. for 226Ra and 228Ra, respectively, while uranium concentration varied between 2.2 and 10.5 μg/kg dry wt. in milk samples and 0.78-6.0 μg/kg
dry wt. in other food samples.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
60.
Let G be a finite group, and let N(G) be the set of conjugacy class sizes of G. By Thompson’s conjecture, if L is a finite non-abelian simple group, G is a finite group with a trivial center, and N(G) = N(L), then L and G are isomorphic. Recently, Chen et al. contributed interestingly to Thompson’s conjecture under a weak condition. They only used the group order and one or two special conjugacy class sizes of simple groups and characterized successfully sporadic simple groups (see Li’s PhD dissertation). In this article, we investigate validity of Thompson’s conjecture under a weak condition for the alternating groups of degrees p+1 and p+2, where p is a prime number. This work implies that Thompson’s conjecture holds for the alternating groups of degree p + 1 and p + 2. 相似文献