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131.
O. Anwar Bég J. Zueco H.S. Takhar T.A. Bég A. Sajid 《Communications in Nonlinear Science & Numerical Simulation》2009,14(11):3856-3866
A boundary-layer model is described for the two-dimensional nonlinear transient thermal convection heat and mass transfer in an optically-thick fluid in a Darcian porous medium adjacent to an impulsively started vertical surface, in the presence of significant thermal radiation and buoyancy forces in an (X1,Y1,t1) coordinate system. An algebraic approximation is employed to simplify the integro-differential equation of radiative transfer for unidirectional flux normal to the plate into the boundary-layer regime, by incorporating this flux term in the energy conservation equation. The conservation equations are non-dimensionalized into an (X,Y,T) coordinate system and solved using the Network Simulation Method (NSM), a robust numerical technique which demonstrates high efficiency and accuracy. The transient variation of non-dimensional streamwise velocity component (u) and temperature (T) and concentration (C) functions is computed for various selected values of Stark number (radiation–conduction interaction parameter) and Darcy number. Transient velocity (u) and steady-state local skin friction (τX) are also studied for various thermal Grashof number (Gr), species Grashof number (Gm), Schmidt number (Sc) and Stark number (N) values. These computations for the infinite permeability case (Da → ∞) are compared with previous finite difference solutions [Prasad et al. Int J Therm Sci 2007;46(12):1251–8] and shown to be in excellent agreement. An increase in Darcy number is seen to accelerate the flow and boost velocity. A decrease in Stark number (corresponding to an increase in thermal radiation heat transfer contribution) is shown to increase the velocity values. Temperature function is observed to fall in value with a rise in Da and increase with decrease in N (corresponding to an increase in thermal radiation heat transfer contribution). Applications of the study include rocket combustion chambers, astrophysical flows, spacecraft thermal fluid dynamics in debris-laden environments (cosmic dust), heat transfer in forest fire spread, geochemical contamination and ceramic materials processing. 相似文献
132.
The present article investigates the dual nature of the solution of the magneto- hydrodynamic (MHD) stagnation-point flow of a Prandtl fluid model towards a shrinking surface. The self-similar nonlinear ordinary differential equations are solved numerically by the shooting: method. It is found that the dual solutions of the flow exist for cer- tain values of tile velocity ratio parameter. The special case of the first branch solutions (the classical Newtonian fluid model) is compared with the present numerical results of stretching flow. The results are found to be in good agreement. It is also shown that the boundary layer thickness for the second solution is thicker than that for the first solution. 相似文献
133.
Anwar Gavili Taghi Dallali Isfahani Fatemeh Zabihi Iraj Hadi 《Heat and Mass Transfer》2013,49(10):1433-1445
The heat transfer and fluid flow behavior of water based Al2O3 nanofluids are numerically investigated inside a two-sided lid-driven differentially heated rectangular cavity. Physical properties which have major effects on the heat transfer of nanofluids such as viscosity and thermal conductivity are experimentally investigated and correlated and subsequently used as input data in the numerical simulation. Transport equations are numerically solved with finite volume approach using SIMPLEC algorithm. It was found that not only the thermal conductivity but also the viscosity of nanofluids has a key role in the heat transfer of nanofluids. The results show that at low Reynolds number, increasing the volume fraction of nanoparticles increases the viscosity and has a deteriorating effect on the heat transfer of nanofluids. At high Reynolds number, the increase in the viscosity is compensated by force convection and the increase in the volume fraction of nanoparticles which results in an increase in heat transfer is in coincidence with experimental results. 相似文献
134.
We present a methodology to analyze the stationary states and stability of complex fluid flows by using hybrid, discrete, and/or continuum multi-scale simulations. Building on existing theories, our scheme extracts dynamical and equilibrium characteristics from carefully chosen time integrations of these multi-scale evolution equations. Two canonical problems are presented to demonstrate the ability and accuracy of the formalism. The first is an investigation of flow-induced transitions seen in homogeneous, hard- rod liquid crystal suspensions subjected to a linear shear flow. In the second problem, we study the phenomenon of draw resonance, a dynamical instability in an isothermal fiber-spinning process, by using a multi-scale hybrid simulation that incorporates both stochastic and continuum models. 相似文献
135.
Azra ulovi Franko Bur
ul Vedrana ike uli Mirko Ru
i Petra Brzovi Sabine Montaut Patrick Rollin Ivica Blaevi 《Molecules (Basel, Switzerland)》2021,26(17)
Glucosinolates (GSLs) from Lepidium graminifolium L. were analyzed qualitatively and quantitatively by their desulfo-counterparts using UHPLC-DAD-MS/MS technique and by their volatile breakdown products-isothiocyanates (ITCs) using GC-MS analysis. Thirteen GSLs were identified with arylaliphatic as the major ones in the following order: 3-hydroxybenzyl GSL (glucolepigramin, 7), benzyl GSL (glucotropaeolin, 9), 3,4,5-trimethoxybenzyl GSL (11), 3-methoxybenzyl GSL (glucolimnanthin, 12), 4-hydroxy-3,5-dimethoxybenzyl GSL (3,5-dimethoxysinalbin, 8), 4-hydroxybenzyl GSL (glucosinalbin, 6), 3,4-dimethoxybenzyl GSL (10) and 2-phenylethyl GSL (gluconasturtiin, 13). GSL breakdown products obtained by hydrodistillation (HD) and CH2Cl2 extraction after hydrolysis by myrosinase for 24 h (EXT) as well as benzyl ITC were tested for their cytotoxic activity using MTT assay. Generally, EXT showed noticeable antiproliferative activity against human bladder cancer cell line UM-UC-3 and human glioblastoma cell line LN229, and can be considered as moderately active, while IC50 of benzyl ITC was 12.3 μg/mL, which can be considered as highly active. 相似文献
136.
BC Makhubela AM Jardine G Westman GS Smith 《Dalton transactions (Cambridge, England : 2003)》2012,41(35):10715-10723
The synthesis and characterization of low-generation pyridylimine Rh(i) metallodendrimers is described. These metallodendrimers were obtained via a Schiff base condensation of tris-2-(aminoethyl)amine with 2-pyridinecarboxaldehyde to afford the tris-2-(2-pyridylimine ethyl) amine ligand (1). Subsequent complexation reactions with [RhCl(CO)(2)](2) and [RhCl(COD)](2) yielded the corresponding metal-containing dendrimers containing -RhCl(CO) and -Rh(COD) moieties on the periphery. These new rhodium metallodendrimers (2 and 3) and their precursor ligand (1) are thermally stable and have been characterized using (1)H NMR, (13)C NMR, (31)P NMR, FT-IR spectroscopy, elemental analysis as well as mass spectrometry. The Rh(i) metallodendrimers are highly active and chemo- and regioselective in the hydroformylation of 1-octene. Aldehydes were favoured at moderate to high temperatures (95 °C and 75 °C) and pressure (30 bars), while more iso-octenes were formed at low temperature (55 °C) and pressures (5 and 10 bars). The mononuclear analogues (5 and 6) also produced more aldehydes (albeit showing catalyst decomposition at 95 °C and 75 °C, 30 bars) and these aldehydes were mostly branched. 相似文献
137.
Vitex negundo Linn. (Verbenaceae) is used in traditional medical system for respiratory disorders. This study was carried out to investigate its cough-relieving potential. The antitussive effect of the butanolic extract of V. negundo (Vn) on sulphur dioxide (SO(2))-induced cough was examined in mice. Safety profile of Vn was carried out by observing acute neurotoxicity, median lethal dose (LD(50)) and behavioural signs. Vn dose-dependently (250-1000?mg?kg(-1)) inhibited the cough provoked by SO(2) gas in mice and exhibited maximum protection after 60?min of administration. At 1000?mg?kg(-1), Vn caused maximum cough-suppressive effects i.e. cough inhibition at 60?min was 67.4%, as compared to codeine (10?mg?kg(-1)), dextromethorphan (10?mg?kg(-1)) and saline having cough-inhibitory potential 75.7%, 74.7% and 0%, respectively. LD(50) value of V. negundo was found to be greater than 5000?mg?kg(-1). In toxicity tests, no signs of neural impairment and acute behavioural toxicity were observed at antitussive doses and extract has been well tolerated at higher doses. These results indicate that V. negundo exhibits antitussive effect and it was found devoid of toxicity. 相似文献
138.
The kinetics of the homogeneous acylation of microcrystalline cellulose, MCC, with carboxylic acid anhydrides with different
acyl chain-length (Nc; ethanoic to hexanoic) in LiCl/N,N-dimethylacetamide have been studied by conductivity measurements from 65 to 85 °C. We have employed cyclohexylmethanol, CHM,
and trans-1,2-cyclohexanediol, CHD, as model compounds for the hydroxyl groups of the anhydroglucose unit of cellulose. The ratios
of rate constants of acylation of primary (CHM; Prim-OH) and secondary (CHD; Sec-OH) groups have been employed, after correction,
in order to split the overall rate constants of the reaction of MCC into contributions from the discrete OH groups. For the model compounds, we have found
that k(Prim-OH)/k(Sec-OH) > 1, akin to reactions of cellulose under heterogeneous conditions; this ratio increases as a function of increasing Nc. The overall, and partial rate constants of the acylation of MCC decrease from ethanoic- to butanoic-anhydride and then
increase for pentanoic- and hexanoic anhydride, due to subtle changes in- and compensations of the enthalpy and entropy of
activation. 相似文献
139.
Yoshinori Namihira Md. Anwar Hossain Taito Koga Md. Ashraful Islam S. M. Abdur Razzak Shubi F. Kaijage Yuki Hirako Hiroki Higa 《Optical Review》2012,19(2):78-81
In this paper, we propose a highly nonlinear dispersion flattened hexagonal photonic crystal fiber (HNDF-HPCF) with nonlinear
coefficients as large as 57.5W−1 km−1 at 1.31 μm wavelength for dental optical coherence tomography (OCT) applications. This HNDF-HPCF offers not only large nonlinear
coefficient but also very flat dispersion slope and very low confinement losses. Using these characteristics of our proposed
PCF, it is shown through simulations by using finite difference method with an anisotropic perfectly matched boundary layer
that this PCF offers the efficient supercontinuum (SC) generation for dental OCT applications at 1.31 μm wavelength using
a picosecond pulse easily produced by commercially available less expensive laser sources. Coherent length of light source
using SC is found 10 μm and the spatial resolutions in the depth direction for dental applications of OCT are found about
6.1 μm for enamel and 6.5 μm for dentin. 相似文献
140.
Nida Iqbal Rabia NazirAnila Asif Aqif Anwar ChaudhryMuhammad Akram Goh Yi FanAftab Akram Rashid AminSung Ha Park Rafaqat Hussain 《Current Applied Physics》2012,12(3):755-759
Polyvinyl alcohol (PVA) coated hydroxyapatite was deposited onto a 316L stainless steel substrate by electrophoretic deposition. Deposition was carried out in a methanol suspension at pH 5.5 using a graphite rod as an anode. Parameters such as PVA concentration, deposition voltage and time were optimized to achieve a homogeneous, crack-free adhesive coating. Techniques such as X-ray diffraction and Fourier transform infrared spectroscopy were used to study the phase composition of the coated materials and the stability of hydroxyapatite in the presence of PVA. 相似文献