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61.
We study the infinitesimal generator of the Poisson semigroup in L p associated with homogeneous, second-order, strongly elliptic systems with constant complex coefficients in the upper-half space, which is proved to be the Dirichlet-to-Normal mapping in this setting. Also, its domain is identified as the linear subspace of the L p -based Sobolev space of order one on the boundary of the upper-half space consisting of functions for which the Regularity problem is solvable. Moreover, for a class of systems containing the Lamé system, as well as all second-order, scalar elliptic operators, with constant complex coefficients, the action of the infinitesimal generator is explicitly described in terms of singular integral operators whose kernels involve first-order derivatives of the canonical fundamental solution of the given system. Furthermore, arbitrary powers of the infinitesimal generator of the said Poisson semigroup are also described in terms of higher order Sobolev spaces and a higher order Regularity problem for the system in question. Finally, we indicate how our techniques may be adapted to treat the case of higher order systems in graph Lipschitz domains. 相似文献
62.
Dorina?Modra Gabriela?Vlase Paul?Albu Constantin?Bolcu Titus?VlaseEmail author 《Journal of Thermal Analysis and Calorimetry》2015,121(3):1021-1030
This study presents the synthesis of polyesters obtained from phthalic anhydride as acidic components and one mixture of monoethylene glycol and monohydric alcohol (in ratio 1.1:0.15). Molar ratio of the acid component and alcohol component was 1:1.25. n-Propanol, n-butanol, n-octanol and isoamyl alcohol were used as monohydric alcohol. Physicochemical characterization was performed by elemental analysis, FTIR/UATR spectroscopy of polyesters and char, EGA (evolved gas analysis), thermal analysis in synthetic air and in nitrogen atmosphere. 相似文献
63.
64.
Tasnádi G Winkler CK Clay D Sultana N Fabian WM Hall M Ditrich K Faber K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(33):10362-10367
The degree of C?C bond activation in the asymmetric bioreduction of α,β-unsaturated carboxylic esters by ene-reductases was studied, and general recommendations to render these "borderline-substrates" more reactive towards enzymatic reduction are proposed. The concept of "supported substrate activation" was developed. In general, an additional α-halogenated substituent proved to be beneficial for enzymatic activity, whereas β-alkyl or β-aryl substituents were detrimental for the reactivity of nonhalogenated substrates, and α-cyano groups showed little effect. The alcohol moiety of the ester functionality was found to have a strong influence on the reaction rate. Overall, activities were determined by both steric and electronic effects. 相似文献
65.
A comparative study, ultrasound (US) versus microwave (MW) versus conventional thermal heating (TH), for synthesis of isoindolo-1,2-diazine is described. The reaction pathway is fast, efficient and straight applicable, involving a Huisgen [3+2] dipolar cycloaddition of cycloimmonium ylides to 1,4-naphthoquinone. A feasible reaction mechanism for the obtaining of the fully aromatized tetra- and penta- cyclic isoindolo-1,2-diazine is presented. Under US irradiation the yields are much higher (sometimes substantially, by almost double), the reaction time decreases substantially, the reaction conditions are milder. The use of a generator with a higher nominal power induces higher yields and short reaction times. Overall the use of US it proved to be more efficient than MW or TH. A feasible explication for US efficiency is presented. 相似文献
66.
Dorina Mantu Costel Moldoveanu Alina Nicolescu Calin Deleanu Ionel I. Mangalagiu 《Ultrasonics sonochemistry》2009,16(4):452-454
A new, efficient and general method for preparation of N-substituted-pyridazinones using ultrasound irradiation is reported. Under ultrasound the reaction time decreases substantially, the yields are high and the reaction conditions are mild. It was noticed that substituents at the 3-(6)-position of pyridazone heterocycle have a substantial influence on the reactivity, while the effect of the substituents at the 1-(2)-position seems to be of minor importance. A comparative study of the reactions performed under ultrasound conditions versus at room temperature has been done. 相似文献
67.
Dorina Strugaru Eleonora Trif V. Cristea Gabriela Gheorghe R. Russu 《Radiation Physics and Chemistry》1995,45(6):917-922
The EPR spectroscopy has been used to study the interaction of vanadium pentoxide with H-ZSM-5 zeolite, supplied by ICITPR-Ploiesti, Romania, occurring at the calcination of the mixture at temperatures from 100 to 1000°C, in air, followed by evacuation at 20°C, as well as for those rehydrated at room temperature. The EPR method is also used to follow the thermal stability of the investigated zeolite, the framework alteration and the nature of VO2+ complexes formed during solid phase reaction. At least two types VO2+ centres were identified in H-ZSM-5 zeolite. One of them being ascribed to dehydrated VO2+ complexes in cationic sites, with C4v ligand field symmetry and the second one corresponding to the hydrated complex with a square bipyramidal symmetry, D4h. Increasing covalent character, for the in-plane σ-bond and increasing ionic character for the out-of-plane π bond, have been found on rehydrated samples. For a low content of oxide ( 5% wt V2O5) in a mixture the thermal stability, T = 1070°C, of the zeolite phase is not affected by the presence of the reaction products. 相似文献
68.
Dorina Chambree Cornelia Idi?oiu E. Segal A. Ces´ro 《Journal of Thermal Analysis and Calorimetry》2005,82(3):803-811
Summary The thermal behavior under non-isothermal conditions of some low-acidity carboxylic cationites with acrylic-divinylbenzene
(DVB) matrix was investigated in air and nitrogen atmosphere up to 600°C. Thermal analysis (TG/DTG) combined with Mass Spectrometry
(MS) and Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the resins decomposition steps and the degradation
products. Five decomposition steps were observed. The first step is due to elimination of osmotic and bound water. The second
decomposition step is due to dehydration of neighboring (-COOH) groups. The third and fourth mass-loss steps correspond to
decarboxylation of the polyanhydrides and to some depolymerization of the polymeric matrix. The last decomposition step is
associated with total degradation of the polymeric matrix. The shape and the temperature for each decomposition steps depend
on the experimental conditions (heating rate and degradation atmosphere) and on the sample properties (i.e. granulation, cross-linking
degree, porosity and physical form). 相似文献
69.
Margherita Venturi Filippo Marchioni Belén Ferrer Ribera Vincenzo Balzani Dorina M Opris A Dieter Schlüter 《Chemphyschem》2006,7(1):229-239
The PF6- salt of the dinuclear [(bpy)2Ru(1)Os(bpy)2]4+ complex, where 1 is a phenylacetylene macrocycle which incorporates two 2,2'-bipyridine (bpy) chelating units in opposite sites of its shape-persistent structure, was prepared. In acetonitrile solution, the Ru- and Os-based units display their characteristic absorption spectra and electrochemical properties as in the parent homodinuclear compounds. The luminescence spectrum, however, shows that the emission band of the Ru(II) unit is almost completely quenched with concomitant sensitization of the emission of the Os(II) unit. Electronic energy transfer from the Ru(II) to the Os(II) unit takes place by two distinct processes (k(en) = 2.0x10(8) and 2.2x10(7) s(-1) at 298 K). Oxidation of the Os(II) unit of [(bpy)2Ru(1)Os(bpy)2]4+ by Ce(IV) or nitric acid leads quantitatively to the [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ complex which exhibits a bpy-to-Os(III) charge-transfer band at 720 nm (epsilon(max) = 250 M(-1) cm(-1)). Light excitation of the Ru(II) unit of [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ is followed by electron transfer from the Ru(II) to the Os(III) unit (k(el,f) = 1.6x10(8) and 2.7x10(7) s(-1)), resulting in the transient formation of the [(bpy)2Ru(III)(1)Os(II)(bpy)2]5+ complex. The latter species relaxes to the [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ one by back electron transfer (k(el,b) = 9.1x10(7) and 1.2x10(7) s(-1)). The biexponential decays of the [(bpy)2*Ru(II)(1)Os(II)(bpy)2]4+, [(bpy)2*Ru(II)(1)Os(III)(bpy)2]5+, and [(bpy)2Ru(III)(1)Os(II)(bpy)2]5+ species are related to the presence of two conformers, as expected because of the steric hindrance between hydrogen atoms of the pyridine and phenyl rings. Comparison of the results obtained with those previously reported for other Ru-Os polypyridine complexes shows that the macrocyclic ligand 1 is a relatively poor conducting bridge. 相似文献
70.
Alessandro D'Aprano Dorina I. Donato Valeria Agrigento 《Journal of solution chemistry》1981,10(9):673-680
Static dielectric constants, viscosities, densitites and refractive indices of 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-methyl-2-butanol were measured at 15, 25, 35 and 45°C. These results together with the previous data on n-pentanol have been analyzed in terms of the Kirkwood correlation factor g
k
and of the energy of activiation for viscous flow. With the exception of 2-methyl-2-butanol, g
k
was found to be greater than unity. These results show that the monomeric units of isomeric pentanols interact by means of hydrogen bonding to form dynamic structures essentially of two types: linear chains where co-association raises the total polarizability and cyclic dimers with nearly zero net dipole moment. Energies of activation for viscous flow as well as Kirkwood correlation factors correlate with the molecular parameters (i.e. position of OH group in the molecules, steric hindrance of alkyl chain etc.) of the alcohols. The implication of these parameters on the molecular association of the isomeric pentanols are discussed. 相似文献