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61.
Fabio RD Alvaro G Bertani B Donati D Giacobbe S Marchioro C Palma C Lynn SM 《The Journal of organic chemistry》2002,67(21):7319-7328
To prepare in multigram scale new antagonists of the glycine binding site associated to the NMDA receptor, an efficient distereoselective route was set up. The addition of suitable allyltin reagents to chiral N-aryl alpha-imino esters (R-(+)-tert-butyl lactate used as chiral auxiliary), gave the corresponding alpha amino acid-type derivative in high chemical yield and optical purity. This allylation reaction represents a novel example of efficient long-range stereodifferentiation process. In the last part of the synthesis, a regioselective Heck-type cyclization reaction enabled preparation of the target tetrasubstituted exocycle and trisubtituted endocycle double bond derivatives. 相似文献
62.
Enzo Giannetti Giuseppe Martino Nicoletti Romano Mazzocchi 《Journal of polymer science. Part A, Polymer chemistry》1985,23(8):2117-2134
Homogeneous Ziegler-Natta systems for the ethylene polymerization, deriving from R2R2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ-alkyl and the π-cyclo-pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ-alkyl derivatives of IVB transition metals, such as Zr(CH2C6H5)4, are also able to polymerize ethylene with a fairly high productivity. Active species containing Zr? O? Al bonds have been postulated. 相似文献
63.
Ruggero Ferro 《Annali dell'Universita di Ferrara》1973,18(1):55-57
Sommario In un'algebra di Boole si considerano le funzioni simmetriche rispetto al coniugio su un sottoinsieme delle variabili. Si
danno delle rappresentazioni di tali funzioni in funzione delle funzioni simmetriche elementari.
Il presente lavoro è stato eseguito mentre l'autore era teaching assistant presso l'University of California at Los Angeles (UCLA). 相似文献
Summary In a Boolean Algebra, the functions which are symmetric with respect to conjugation on a subset of the variables are considered. A representation of such functions by means of the elementary symmetric functions is given.
Il presente lavoro è stato eseguito mentre l'autore era teaching assistant presso l'University of California at Los Angeles (UCLA). 相似文献
64.
In the PrBi system the heats of formation were measured using a direct isoperibol calorimeter. The composition and equilibrium state of the samples have been checked by chemical, metallographic and X-ray analyses. The following values were found for the two known compounds (reaction in the solid state, 300 K): The results obtained, compared with those already achieved in other REBi systems, are briefly discussed. 相似文献
65.
G. Coremans-Bertrand J. Sacton A. Breslin S. McMahon A. Montwill D.H. Davis D.N. Tovee F.R. Stannard G. Baroni S. Di Liberto A. Manfredini S. Petrera G. Romano M. Jung N. Kurtz M. Paty T. Pniewski 《Physics letters. [Part B]》1976,65(5):480-482
The associated production of charmed particles by the interactions of 300 GeV/c protons with complex nuclei has been sought using nuclear emulsions. The failure to observe any candidates for this process among some 60,000 interactions investigated implies, provided charmed particles lifetimes are in the range 10?12 to 10?14 s, a cross section for their associated production by the interactions of 300 GeV/c protons with nucleons of less than 1.5 microbarns at a 90% confidence level. 相似文献
66.
If Nuo is the Nusselt Number for a temperature-independent Prandtl number Pr, and Nu the Nusselt number for a temperature dependent Prandtl number, it is usual to define the correction factor Nu/Nuo=C. A correction factor which has been defined in this form has, up to now, only been expressed as a function of two characteristic Pr numbers. Thus it was simply assumed that the Pr number was a linear function of the temperature. Fluids with very large Pr numbers show a (T;Pr) relationship which deviates considerably from a linear one. This leads to a very large difference (up to 70%) between the calculated and the measured values of the Nusselt number. In the following study we shall determine a so-called curvature parameter of the (T;Pr) curve and obtain a semi-empirical formula for C. This formula has a deviation from the actual relationship many times smaller than that of the formulae for a linear (T;Pr) relationship.
Zusammenfassung Ist Nuo die Nusseltzahl bei temperaturunabhangiger und Nu die Nusseltzahl bei temperaturabhangiger Prandtlzahl Pr, so ist es üblich, mit Nu/Nuo=C den Korrekturfaktor zu bezeichnen. Ein in dieser Form definierter Faktor C ist bisher als Funktion nur zweier charakteristischer Pr-Zahlen ausgedrückt worden. Es wurde somit nur eine lineare Abhängigkeit von der Pr-Zahl von der Temperatur T vorausgesetzt. Flüssigkeiten mit großen Pr-Zahlen weisen eine (T;Pr)-Charakteristik auf, die sehr stark von der linearen abweicht. Sehr große Abweichungen (bis — 70%) der gerechneten von den gemessenen Nu-Zahlen sind eine Folge davon. In vorliegender Arbeit bilden wir mit einer dritten charakteristischen Pr-Zahl einen sogenannten Krümmungsparameter der Kurve (T;Pr) und leiten eine semiempirische Formel für C ab, die um ein großes Vielfaches kleinere Fehler aufweist, als die Formeln für den linearen (T;Pr)-Verlauf.
Nomenclature
Material constants cp specific heat at constant pressure [J/kgK] - k heat conductivity [W/mK] - density [kg/m3] - a temperature diffusivity, a=k/cp [m2/s] - dynamic viscosity [Ns/m2] - kinematic viscosity [m2/s] Fluid dynamics D inner diameter of the tube [m] - L length of tube [m] - w mean speed of fluid [m/s] Heat transfer h coefficient of heat transfer [W/m2K] - T absolute temperature [K] - Tb bulk temperature (corresponding to the adiabatic mixing temperature) [K] - Tw tube wall temperature [K] - Tf=(Tb+Tw)/2 film temperature [K] - T=Tb-Tw temperature forcing difference of heat transfer [K] Characteristic quantities without dimensions Re=wD/ Reynolds number - Pr=/a Prandtl number - Nu=hD/k Nusselt number - related temperature - related Prandtl number - curvature parameter of the Prandtl number Various - C=Nub/Nuo correction factor according to Eq.(5) - p exponent in Eq.(6), (a), (8) and (16) Indices o corresponding to the quasi-isothermal heat transfer - b,w,f with reference to quantities, including physical properties which correspond to the temperatures Tb, Twor Tf - Pr,k,, for quantities calculated corresponding to the Prandtl number, the thermal conductivity coefficient, the density or the dynamic viscosity - H,C for heating or cooling exp for quantities calculated from experimental data 相似文献67.
Youte JJ Barbier D Al-Mourabit A Gnecco D Marazano C 《The Journal of organic chemistry》2004,69(8):2737-2740
Potassium ferricyanide oxidation of salt 1 gave isoquinolinone 7 whose treatment with Grignard reagents resulted in a high-yield formation of substituted isoquinolinium salts 5. The selectivity of the reduction of these salts to give derivatives 6 has been studied. Particularly good selectivities (82-84%) were observed when R is a benzylic group. On the basis of these results, a practical and enantioselective synthesis of the natural alkaloid (-)-argemonine is presented. 相似文献
68.
In this paper we show that two dynamical invariants, the second order Renyi entropy and the correlation dimension, can be estimated from recurrence plots (RPs) with arbitrary embedding dimension and delay. This fact is interesting as these quantities are even invariant if no embedding is used. This is an important advantage of RPs compared to other techniques of nonlinear data analysis. These estimates for the correlation dimension and entropy are robust and, moreover, can be obtained at a low numerical cost. We exemplify our results for the Rossler system, the funnel attractor and the Mackey-Glass system. In the last part of the paper we estimate dynamical invariants for data from some fluid dynamical experiments and confirm previous evidence for low dimensional chaos in this experimental system. 相似文献
69.
70.
Cotton FA Liu CY Murillo CA Villagrán D Wang X 《Journal of the American Chemical Society》2004,126(45):14822-14831
Very strong electronic communication, manifested in a K(C) value of ca. 10(9), has been found in a system of three compounds separated by one electron oxidation where each compound contains two metal-metal bonded Mo(2)(n+) units linked by a dimethyloxamidate anion, CH(3)N(O)C-C(O)NCH(3)(2)(-). The Mo-Mo distances increase as the oxidation state increases and the bond order decreases, while the diamagnetic, doubly oxidized species becomes essentially planar and resembles a naphthalene molecule. Calculations at the DFT level indicate that a strong transition in the near-IR region, shown by the singly oxidized and paramagnetic species, is best described as a HOMO-1 --> SOMO transition. 相似文献