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1.
An analysis is presented of steady conjugate free convection between two horizontal concentric cylinders filled with a fluid-saturated porous medium; the innermost cylinder surface is maintained at a high temperature and the outermost cylinder surface at a lower one. The velocity-pressure-gradient relation is taken to be nonlinear, with departure from the linear Darcy situation measured by a parameter F0. The investigation is based on the numerical solution, by a finite-difference method, of the full momentum and energy equations. The streamline and isotherm patterns as well as the local and mean Nusselt numbers are plotted for several physical parameters to show some of the flow and heat transfer characteristics. It is found that all parameters play an important role in the flow and heat transfer characteristics. The model can be applied to a variety of engineering problems. 相似文献
2.
Pop D Winter B Freyer W Widdra W Hertel IV 《The journal of physical chemistry. B》2005,109(16):7826-7833
Photoemission measurements were performed on a series of stepwise benzoannelated zinc porphyrazine molecules in thin films. The electronic structure of tert-butyl-substituted zinc tetraazaporphyrin, phthalocyanine, and naphthalocyanine is investigated using mainly EUV synchrotron radiation. A detailed analysis of the zinc satellites in the spectra of the valence region is performed in an attempt to infer the effect of ligand size extension on the metal-ligand interactions. No differences in the character of the bond between zinc and ligand were detected as a function of ligand size. The results are compared with those for the respective metal-free and copper-containing molecules. 相似文献
3.
Vanadium Doped Sol-Gel TiO2 Coatings 总被引:1,自引:0,他引:1
Maria Crisan Maria Zaharescu D. Crisan Rodica Ion Mihaela Manolache 《Journal of Sol-Gel Science and Technology》1998,13(1-3):775-778
A study of the experimental conditions required to obtain vanadium doped sol-gel TiO2 coatings is presented. Tetraethyl orthotitanate was employed as the TiO2 source and VCl3, VOSO4 · H2O and VOSO4 dissolved H2SO4 where employed as vanadium sources.Dip coating has been used to produce coatings on silicon wafers, spectral carbon electrodes and titanium electrodes. Both supported and unsupported films have been studied by UV-Vis spectra, IR spectroscopy and X-ray diffraction (XRD). The measurements have been made on samples as prepared and treated thermally at temperatures between 100°C and 300°C. The thermal treatment temperatures have been established from DTA/TGA measurements.The vanadium doped sol-gel TiO2 coatings have been tested as sensors for redox potential measurements in electrochemical processes. The influence of both the thickness of films and the nature of substrate has been investigated. 相似文献
4.
Dr. Margareta Ruse Rodica Vulcu Iuliana Jepan 《Monatshefte für Chemie / Chemical Monthly》1976,107(4):1007-1010
Phenylpyruvic acid reacts with p-nitroaniline to yield the 3-hydroxypyrrolinone2a, and with anilines bearing+M substituents in the p-position to yield the 3-enaminopyrrolinones1b-1e.
Mit 1 Abbildung
5. Mitt.:M. Ruse, E. Hamburg undM. Petri, Chem. Ber.103, 3727 (1970). 相似文献
Mit 1 Abbildung
5. Mitt.:M. Ruse, E. Hamburg undM. Petri, Chem. Ber.103, 3727 (1970). 相似文献
5.
Emil Pop Marcus E. Brewster J. J. Kaminski Nicholas Bodor 《International journal of quantum chemistry》1989,35(2):315-324
9-Amino-1,2,3,4-tetrahydroacridine (THA ), a potent cholinesterase inhibitor, was recently used in the treatment of Alzheimer's disease. On attempting to prepare a dihydropyridine ? pyridinium salt-based redox chemical delivery system (CDS ) to enhance brain delivery of THA , several of the practical synthetic challenges were examined by using a theoretical MO approach. The structures, reactivities and stability of THA , derivatives of THA and a model compound, 4-aminopyridine, a simple dibasic heterocyclic amine, were studied in the framework of the AM -1 approximation. The study included the possible protonated forms of THA and 4-aminopyridine. The calculated heats of formation showed that ring nitrogen protonated forms are more stable for both THA and 4-aminopyridine. The calculated heats of formation showed that ring nitrogen protonated forms are more stable for both THA and 4-aminopyridine, consistent with experimental results. Electron delocalization is responsible for the remarkable stability of these molecules and for the observed lack of reactivity of the amino group, both in the basic and protonated forms. The site of N-alkylation of the 9-nicotinamide derivative of THA (an intermediate in the synthesis of THA -CDS ) is controlled by electronic, thermodynamic, and steric factors. 相似文献
6.
Pop IS Pop V Cobzac S Sarbu C 《Journal of chemical information and computer sciences》2000,40(1):91-98
Weighted least-squares spline functions are discussed and applied for calibration processes in analytical chemistry. Different weighting techniques are also considered, and for the evaluation of the results some quality coefficients are proposed. Depending upon the structure of the data, some weighting procedures may improve the results dramatically. Considering the results obtained in the case of TLC densitometry, it seems that nonlinear weighting procedures based upon the distance to the function are the best ones, with a plus for the y-distance type. It is difficult to give general rules regarding the optimal parameters of the weighted calibration splines-function order (m), number (N) and distribution of knots, and weighting technique. These depend upon the structure of the data. However, higher order splines are not recommended since the result might become extremely unstable. The example used to illustrate the performances of the procedures discussed here involved only a single independent variable. The method is general and extends practically to any number of variables, thus resulting in a multivariate approach. 相似文献
7.
Conformational transformations of the tetraenic nystatin chromophore under the influence of solvents and UV irradiation have been studied by absorption, fluorescence and wide-line NMR spectroscopy. 相似文献
8.
Ionel Haiduc Gellert Mezei Rodica Micu‐Semeniuc Frank T. Edelmann Axel Fischer 《无机化学与普通化学杂志》2006,632(2):295-300
The three (O‐methyl)‐p‐ethoxyphenyldithiophosphonato triphenylphosphine complexes of copper, silver and gold, [(Ph3P)nM{S2P(OMe)C6H4OEt‐p}] (M = Cu, n = 2; M = Ag, Au, n = 1) investigated structurally by X‐ray diffraction exhibit remarkable structural differences. The copper compound is a four‐coordinate chelate monomer with Cu–S 2.4417(6) and 2.5048(6) Å; P–Cu–S 104.24(2)–114.01(2)°; Cu–S–P 82.49(3)° and 80.85(2)°. The silver compound is a cyclic dimer with bridging dithiophosphonato ligands and three‐coordinate silver atoms [Ag–S 2.5371(5) and 2.6867(5) Å; P–Ag–S 122.88(2)° and 122.17(2)°; Ag–S–P 89.32(2)° and 103.56(2)°]. The gold compound is monomeric with linear dicoordinate gold [Au–S 2.3218(6) Å; P–Au–S 177.72(2)°, Au–S–P 100.97(3)°]. 相似文献
9.
Rodica Olar Michaela Badea E. Cristurean C. Parnau D. Marinescu 《Journal of Thermal Analysis and Calorimetry》2006,84(1):53-58
The complexes of the type M(HDMBG)2(CH3COO)2·nH2O ((1)
M:Mn, n=1.5; (2)
M:Ni, n=0; (3)
M:Cu, n=2; (4)
M:Zn, n=2; DMBG: N,N-dimethylbiguanide)
present in vitro antimicrobial activity. The thermal analysis has evidenced
the thermal intervals of stability and also the thermodynamics effects that
accompany them. The different nature of the ligands generates a different
thermal behaviour for the complexes. The thermal transformations are complex
processes according to TG and DTG curves including dehydration, oxidative
condensation of –C=N– units as well as thermolysis processes.
The final products of decomposition are the most stable metal oxides. 相似文献
10.
The aim of this Letter is to show that, the Nusselt number sign might be changed without changing of heat transfer direction at the wall of channels, even for flows without viscous dissipation. 相似文献