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101.
T. S. LEE LIAO WEI H. T. LOW 《International Journal of Computational Fluid Dynamics》2013,27(3):197-208
A numerical method has been developed to solve the steady and unsteady incompressible Navier-Stokes equations in a two-dimensional, curvilinear coordinate system. The solution procedure is based on the method of artificial compressibility and uses a third-order flux-difference splitting upwind differencing scheme for convective terms and second-order center difference for viscous terms. A time-accurate scheme for unsteady incompressible flows is achieved by using an implicit real time discretization and a dual-time approach, which introduces pseudo-unsteady terms into both the mass conservation equation and momentum equations. An efficient fully implicit algorithm LU-SGS, which was originally derived for the compressible Eulur and Navier-Stokes equations by Jameson and Toon [1], is developed for the pseudo-compressibility formulation of the two dimensional incompressible Navier-Stokes equations for both steady and unsteady flows. A variety of computed results are presented to validate the present scheme. Numerical solutions for steady flow in a square lid-driven cavity and over a backward facing step and for unsteady flow in a square driven cavity with an oscillating lid and in a circular tube with a smooth expansion are respectively presented and compared with experimental data or other numerical results. 相似文献
102.
YANG Zunhua KIM Kyung Ran PARK Ah-Young LEE Hyung-Rock KANG Jin-Ah KIM Won Hee CHUN Pusoon GONG Ping LEE Boeun JEONG Lak Shin MOON Hyung Ryong 《中国化学》2009,27(12):2405-2412
Synthesis of north‐5'‐methylbicyclo[3.1.0]hexyl purine and pyrimidine nucleosides with an ethynyl group at C‐3' position has been successfully accomplished by a facile method. Methylbicyclo[3.1.0]hexanone (±)‐ 5 having three contiguous chiral centers was remarkably simply constructed only by four steps containing a carbenoid insertion reaction in the presence of rhodium(II) acetate dimer and CuSO4, giving a correct relative stereochemistry of the generated three chiral centers. Upon Grignard reaction of (±)‐ 5 with ethynylmagnesium bromide, exclusive diastereoselectivity was observed. Condensation of glycosyl donor (±)‐ 9 with purine nucleobase afforded only the desired N9‐alkylated nucleoside, while condensation with pyrimidine, N3‐benzoylated uracil gave the desired N1‐alkylated nucleoside (±)‐ 13 with the undesired O2‐alkylated nucleoside (±)‐ 14 . Probably, (±)‐ 14 would be formed due to steric hindrance caused upon approaching for N1‐alkylation. 相似文献
103.
104.
Pulsatile flows in the vicinity of mechanical ring-type constrictions in pipes were studied for transitional turbulent flow with a Reynolds number (Re) of the order of 104. The Womersley number (Nw) is in the range 30–50, with a corresponding Strouhal number (St) range of 0·0143–0·0398. The pulsatile flows considered are a pure sinusoidal flow, a physiological flow and an experimental pulsatile flow profile for mechanical aortic valve flow simulations. Transitional laminar and turbulent flow characteristics in an alternating manner within the pulsatile flow fields were studied numerically. It was observed that fluid accelerations tend to suppress the development of flow disturbances. All the instantaneous maximum values of turbulent kinetic energy, turbulent viscosity and turbulent shear stress are smaller during the acceleration phase than during the deceleration period. Various parametric equations have been formulated through numerical experimentation to better describe the relationships between the instantaneous flow rate (Q), the pressure loss (ΔP), the maximum velocity (Vmax), the maximum vorticity (ζmax), the maximum wall vorticity (ζw,max), the maximum shear stress (τmax) and the maximum wall shear stress (τw,max) for turbulent pulsatile flow in the vicinity of constrictions in the vascular tube. An elliptic relationship has been found to exist between the instantaneous flow rate and the instantaneous pressure gradient. Other linear and quadratic relations between various flow parameters were also obtained. 相似文献
105.
激光熔蚀微探针-电感耦合等离子体质谱法--一种快速测定岩石样品中多个元素的新方法 总被引:9,自引:0,他引:9
利用激光探针与等离子体质谱联机技术(LAM-ICPMS)同时测定岩石样品中35个元素.对岩石标样的碱熔玻璃进行了系统的LAM-ICPMS方法研究.结果表明,采用散焦(defocus)激光束扫描法获得了连续稳定的分析信号,并提高了分析灵敏度和分析精密度.该法测定P的检出限为0.1%,Sc、Ti、V、Cr、Mn、Co及Ni的检出限为1.6×10-6~12×10-6,Ga、Rb、Sr及Ba的检出限为0.2×10-6~0.6×10-6,其余21个微量元素的检出限为10-9级;内部精度优于15%,外部精度优于10%.3个岩石标样(NTUG-1、NTUG-2及NTUG-3)的测量结果表明LAM-ICPMS是一种同时测定岩石样品多元素的快速有效方法. 相似文献
106.
107.
DE-CHAO WANG FOO-TIM CHAU EDMOND P. F. LEE ALEXANDER KAI-MAN LEUNG JOHN M. DYKE 《Molecular physics》2013,111(6):995-1005
Geometry optimization and harmonic vibrational frequency calculations at the CASSCF, MP2 and CCSD(T) levels with basis sets up to 6-311G(2df) quality were carried out on the X1Σ+states of FCN and ClCN and the X2Π and A2Σ+ states of their cations. Adiabatic ionization energies were calculated up to the CCSD(T)/6-311G(3df)//CCSD(T)/6-311G(2d) level. Some B3LYP calculations were performed also for the ground states of the neutral molecules and the cations. Franck-Condon simulations were performed for the first two bands in the He I photoelectron spectra of FCN and ClCN by employing the ab initio computed geometries and frequencies. By comparing the observed and the simulated spectra obtained from different CN and CX (X = F or Cl) ionic bond lengths chosen on the basis of the ab initio computed values, the following structural parameters are obtained for the two lowest-lying states of FCN+ and ClCN+ (the method of deriving the uncertainties is described): 相似文献
108.
建立了一种可同时测定锂离子电池电解液中13种有机磷阻燃剂含量的气相色谱-串联质谱分析方法,以乙酸乙酯为萃取溶剂,超声萃取锂离子电池电解液中的有机磷阻燃剂,萃取液经浓缩、定容、过滤后进行气相色谱-串联质谱分析,外标法定量。结果显示,13种有机磷阻燃剂在一定浓度范围内线性良好,相关系数不低于0.999 3,方法的检出限(S/N=3)为0.3~30μg/kg,定量下限(S/N=10)为1~100μg/kg。在低、中、高3个加标水平下的平均回收率为80.4%~94.6%,相对标准偏差(RSD)为3.8%~10%。该方法简单快捷,灵敏度高,定量下限低,可满足锂离子电池电解液中有机磷阻燃剂含量日常检测需要。 相似文献
109.
WANG Yan-hua LI Li CHEN Chia-hung CHENG Shuenn-ren LEE Mu-sheng YU Pu-ping CHANG-CHIEN Guo-ping 《高等学校化学研究》2012,28(2):195-199
Sulfonamide residue in honey existed in a form bonded to sugar via the N-glycosidic bond.It would result in the possible underestimation of concentration of sulfonamide if it is not decomposed by chemi... 相似文献
110.
A dynamically selective multiwavelength cross-connect for wavelength division multiplexed (WDM) networks based on fibre Bragg gratings (FBGs) and optical switches is reported. Dynamically single- or multi-channel cross-connect functionality can be realized according to control of the optical switches and the FBGs' arrangement. Bit-error-rate performance with negligible power penalty is achieved in a 2.5Gbs-1x3 WDM channels over 100km conventional single-mode fibre (SMF) network demonstration. The characteristics of low channel crosstalk, uniform channel loss, high scalability and cascadability, and low cost of this device could provide more reconfiguration flexibility and network survivability for WDM networks. 相似文献