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151.
In a recent paper a generalized potential flow theory and its application to the solution of the Navier–Stokes equation are developed.1 The purpose of this comment is to show that the analysis presented in that paper is in general not correct. We note that the theoretical development of Reference 1 is in fact an extension—although not cited—of some work first done by Hawthorne for steady inviscid flow.2 Hawthorne's solution is correct, and his analysis, which we briefly describe, provides a useful introduction to this note. 相似文献
152.
K. A. Wishah Y. A. Mahmud M. M. Abdul-Gader M. Al-Haj Abdallah R. N. Ahmad-Bitar 《Applied Physics A: Materials Science & Processing》1987,43(1):61-63
The real part of the dielectric constant was studied in the temperature range of 340 to 10 K, and at frequencies that range from 1 to 104 Hz. The dipole contribution to the dielectric constant has been found at temperatures lower than 110 K while the space-charge contribution due to the increase of crystal defects is dominant at temperatures higher than 290K. 相似文献
153.
Various temperature measurements have been carried out in microwave induced plasmas (MIP) generated with a surfatron and inductivcly coupled plasmas (ICP) both with argon and helium as plasma gas. Iron has been used for the determination of excitation temperature, and OH and N+2 for rotational temperatures. In the case of the Ar ICP, equilibrium is attained between the various temperatures (4500 K), as previously described. On the other hand, in the He ICP and the MIPs, iron provides the highest temperature (4500 K) but discrepancies are obtained with results from N+2 and OH. These two species show lower values, especially OH (2000 K). 相似文献
154.
Na2WO4 films have been grown on Si (1 0 0) and glass substrate using ultrasonic spray pyrolysis. The films are prepared from aqueous solution containing Na2WO4·2H2O at 475 °C temperature and characterized by XRD and SEM techniques and the chemical composition of the films have been verified by EDX and PIXE and its formula Na2WO4 is confirmed by XRD. The evolution of the crystallinity was studied as a function of film thickness ranging from 2500 to 4200 nm, which corresponds to a deposition time from 10 to 30 min, respectively. The crystalline quality was found to improve, where the grain size values increased with increasing thickness. Atomic Force Microscopy (AFM) was used to study the morphology evolution with the deposition time, where porous films were found due to the synthesis parameters, and a better sensing response to gases was developed with increasing thickness. Thus, this study demonstrates the possibility of utilizing Na2WO4 thick films as a sensor element for the detection of ethanol vapor at room temperature, where thicker films exhibit excellent ethanol vapor sensing properties with a maximum sensitivity at 25 °C in air atmosphere with fast response time. 相似文献
155.
An electrochemical study of hydroxyzine at a glassy carbon electrode was carried out in the Britton-Robinson universal buffer of pH 2-11. Hydroxyzine was oxidized in a single two-electron irreversible process controlled mainly by adsorption. A simple, sensitive and time-saving square-wave adsorptive anodic stripping voltammetric procedure has been developed for determination of hydroxyzine in its commercial tablets and human serum without prior extraction. The optimized procedural conditions were: frequency=120Hz, scan increment=10mV, pulse-amplitude=25mV, accumulation potential=-0.3V, accumulation time=90-300s and a Britton-Robinson universal buffer of pH 4 as a supporting electrolyte. Mean recoveries of 100.5+/-0.71 and 98.6+/-1.12% (n=5) were achieved for assay of hydroxyzine in Atarax 10 and 25mg dosage forms, respectively. Limit of detection of 1.5x10(-8)molL(-1) (5.624ngmL(-1)) and limit of quantitation of 5.0x10(-8)molL(-1) (18.746ngmL(-1)) were achieved in human serum with a mean recovery of 98.4+/-1.22%, without prior extraction of the drug. Moreover, the described procedure was applied for evaluating the pharmacokinetic parameters of hydroxyzine in plasma of two healthy volunteers after administration of a single oral dose (Atarax)-25mg). 相似文献
156.
PdI2 in DMSO promoted the oxidation of functionalized diarylalkynes into benzil derivatives in excellent yields. This new oxidation reaction was achieved with short reaction times and low loading of palladium catalyst. This efficient catalytic process has been applied successfully to the one-pot construction of a series of nitrogen-containing heterocycles of biological interest according to a tandem oxidation-nitrogen nucleophiles condensation-cyclization. 相似文献
157.
Tayseer A. Abdallah 《Journal of heterocyclic chemistry》2007,44(4):961-965
2‐Oxo‐3‐(indol‐3‐yl)propanonitrile 2 condensed with dimethylformamide dimethylacetal to yield the enaminonitrile 3 . The latter reacted with 4‐chloroaniline to yield the 4‐chlorophenylaminoacrylonitrile 5 . Reaction of 3 with hydrazine hydrate led to formation of pyrazole‐4‐carbonitrile 6 . Compound 3 reacted with ethyl acetoacetate in refluxing acetic acid and in presence of ammonium acetate to yield the indolylpyridine 10 . Enamine 3 reacted with 5(1H)‐aminotriazole 13 and 3(5)‐aminopyrazole 17 to yield the pyrimidine derivatives 15 and 19 , respectively. 相似文献
158.
Abdallah A. Nahla 《Journal of Difference Equations and Applications》2017,23(6):1003-1016
A stochastic model for the nonlinear point reactor kinetics equations with Newtonian temperature feedback and multi-group of precursor delayed neutrons is presented. This model is a couple of the stiff stochastic nonlinear differential equations. The matrix formula of this stochastic nonlinear model is solved by the analytical exponential technique (AET). This proposed technique is based on the integration factor, Euler’s method and the exponential function of the coefficient matrix. This exponential function is determined via the eigenvalues and corresponding eigenvectors of the coefficient matrix. The mean neutron population of the stochastic nonlinear model in the presence Newtonian temperature feedback and six-groups of delayed neutrons is computed for various cases of the external reactivity. The numerical results of the analytical exponential technique are compared with the results of the Euler–Maruyama method and the deterministic results. This comparison confirms that the AET for stochastic nonlinear model is efficient to study the natural behavior of neutron population in the presence temperature feedback effects and multi-group of precursor delayed neutrons. 相似文献
159.
Rhyman L Abdallah HH Ramasami P 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(1):258-263
The syn- and anti-conformers of 2-tellurophenecarboaldehyde are studied in the gas phase. A transition state is also modelled for the syn-anti isomerisation. Computations are done using different methods namely HF, DFT/B3LYP, MP2 and CCSD(T). The basis set used for all atoms is 6-311++G(d,p) except that LanL2DZ ECP is used for tellurium atom only. The optimised molecular structures and related structural parameters of these conformers are reported. The energy differences between the syn- and anti-conformers, associated rotational barriers and thermodynamic parameters are derived from the computations. The infrared frequencies of these conformers are also reported with appropriate assignments. This study is extended to include solvent effect and the conformers are fully optimised (DFT/B3LYP) using the integral equation formalism in the Polarisable Continuum model. In the gas phase, the theoretical rate constant for the unimolecular conversion, anti conformer to transition state, is reported for the first time; DFT/B3LYP (4.82×10(30) s(-1)) and MP2 (7.81×10(30) s(-1)). It is found that the structures are not much affected by the solvents but energy difference increases and rotational barrier decreases. The results indicate that there is a close agreement with the predictions from the different theoretical methods. The results obtained are critically analysed and compared with the furan, thiophene and selenophene analogues. A major factor affecting conformational preference and the mole fraction is the charge on the chalcogen heteroatom in the ring. An interesting outcome of this work is that in both the gas phase and solutions, the syn conformer is more stable and exists almost exclusively. 相似文献
160.
A systematic investigation on the neutral and anionic digallium tetraoxide, Ga(2)O(4) has been carried out by using density functional theory (DFT), second-order M?ller-Plesset perturbation theory (MP2), and the coupled cluster approach with single and double substitutions and a perturbative treatment of the triple excitations [CCSD(T)]. The geometry of neutral Ga(2)O(4) has been proposed earlier, from an experimental study, to adopt a D(2d) symmetry (J. Phys. Chem. 1979, 83, 656). However, the current research reveals that, out of the several isomers considered for neutral and anionic digallium tetraoxide, the (3)B(1u) and (2)B(3g) of the planar D(2h) geometry (7a-D(2h)) are the lowest-energy states for Ga(2)O(4) and Ga(2)O(4)(-). Our computations rule out the D(2d) geometry (3-D(2d)) as a viable contender for neutral Ga(2)O(4). The (3)B(2) (3-D(2d)) state is located above the (3)B(1u) (7-D(2h)) state by at least 4.26 eV. The energies of the low lying states, geometrical parameters, and energetic features (VEDE, AEDE, and AEA) are reported. The AEA of Ga(2)O(4) is calculated to be 3.94 eV (B3LYP), 3.24 eV (MP2), 3.42 eV [CCSD(T)//B3LYP], and 3.38 eV [CCSD(T)//MP2], respectively. In addition, the dissociation energy, D(e), for the process Ga(2)O(4) ((3)B(1u)) → 2GaO(2) ((2)A(2)) is 3.59 eV (B3LYP), 5.08 eV (MP2), 4.82 eV [CCSD(T)//B3LYP], and 4.80 eV [CCSD(T)//MP2]. The results obtained in this work are critically analyzed, discussed, and compared with those of the analogous metal oxides. 相似文献