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141.
142.
Stefania Fioravanti Alberto MorrealeLucio Pellacani Paolo A. Tardella 《Tetrahedron letters》2003,44(15):3031-3034
The synthesis of a new chiral nosyloxycarbamate derived from Helmchen's auxiliary is described. Reactions performed with this aminating reagent successfully give the formation of diastereomeric allylic carbamates or diastereomeric aziridines starting from different kinds of olefins. 相似文献
143.
Simonpietro Agnello Roberto Boscaino Marco Cannas Andrea Cannizzo Franco M. Gelardi Stefania Grandi Maurizio Leone 《Radiation measurements》2004,38(4-6):645-648
We report an experimental investigation of the emission spectra of a 1000 mol ppm sol–gel Ge-doped silica by fine tuning the excitation energy in the ultraviolet (UV) range, around 5 eV, and in the vacuum-UV range, around 7.3 eV, at room temperature and at 10 K. The sample is characterized by a blue (centered at 3.2 eV) and an UV (centered at 4.3 eV) bands. We have found that the ratio between the area of the blue and the UV bands depends on the temperature and on the excitation energy in both the vacuum-UV and the UV range. At both temperatures the spectral features of the blue and the UV bands are weakly affected when the excitation is varied in the vacuum-UV. At variance, under UV excitation the peaks of the bands are shifted and also their widths are changed. These results are interpreted in terms of distinct excitation channels of the luminescence that are influenced in a different way by the structural inhomogeneity of point defects. 相似文献
144.
Summary Linear systems represent the computational kernel of many models that describe problems arising in the field of social, economic
as well as technical and scientific disciplines. Therefore, much effort has been devoted to the development of methods, algorithms
and software for the solution of linear systems. Finite precision computer arithmetics makes rounding error analysis and perturbation
theory a fundamental issue in this framework (Higham 1996). Indeed, Interval Arithmetics was firstly introduced to deal with
the solution of problems with computers (Moore 1979, Rump 1983), since a floating point number actually corresponds to an
interval of real numbers. On the other hand, in many applications data are affected by uncertainty (Jerrell 1995, Marino &
Palumbo 2002), that is, they are only known to lie within certain intervals. Thus, bounding the solution set of interval linear
systems plays a crucial role in many problems. In this work, we focus on the state of the art of theory and methods for bounding
the solution set of interval linear systems. We start from basic properties and main results obtained in the last years, then
we give an overview on existing methods. 相似文献
145.
Euro Solari Stefania De Angelis Mario Latronico Carlo Floriani Angiola Chiesi-Villa Corrado Rizzoli 《Journal of Cluster Science》1996,7(4):553-566
The function of the solvent in the self-assembling mode of [CuCl] with tetrahydrothiophene is reported. Copper(l) chloride has been used in the form of [CuCOCl]
n
, which is slightly soluble in the most common solvents, and to allow an homogeneous phase reaction. The reaction of [CuCOCl]
n
with THT gave [(CuCl)2(THT)3]
x
,1, in CH3OH, [(CuCl)(THT)2]
x
,2 in THF [(CuCl)(THT)]
x
,3, in CH2Cl2, and [(CuCl)3(THT)2]
x
,4, in DME. Compound1 consists of polymeric chains of centrosymmetric Cu2Cl2 dinuclear units bridged by THIT molecules running parallel to the [101] axis. In the structure of2 we found polymeric layers generated from the [(CuCl)(THT)] asymmetric unit by the center of symmetry and by the twofold axis. In compound3 the structure consists of layers generated through the center of symmetry by the [(Cu2Cl2)(THT)2] asymmetric unit, while4 consists of layers generated through the center of symmetry by the [(Cu3Cl3)(THT)2] asymmetric unit. Crystallographic details are as [ollows:2 is monoclinic, space group P21/c.a=9.657(3) A,b=6.441(2) A,c=11.459(3) A,\=111.96(2)°,V=661.0(4) A3. andR=0.075;3 is monoclinic, space group P21/n,a=19.327(7) A,b=6.703(2) A,c=10.116(3) A,ß=103.04(3)°,V=1276.7(7) A3 andR=0.043:4 is triclinic, space group Pl,a=12.513(2) A,b=6.698(1) A,c=9.651(1) A,=91.98(1)°,\=107.86(1)°,=74.59(1)°,V=741.2(2) A3, andR=0.044. 相似文献
146.
Trifluoromethyl aldimines derived from α-amino esters have proven to be very good starting materials to obtain the title compounds. A Ag2O-catalyzed Mannich-type/cyclization cascade reaction starting from suitable α-isocyano acetates leads to enantiopure valuable trans-carboxylic trifluoromethyl substituted 2-imidazolines by a highly stereoselective addition without the need to add organocatalysts. 相似文献
147.
148.
Stefania Marcantognini 《Integral Equations and Operator Theory》1990,13(5):701-727
A model for non-contractive functions is given, according to which every bounded analytic function coincides with the characteristic function of a suitable unitary colligation. In our construction, the function is expressed in terms of a fundamentally reducible unitary dilation of the basic operator of the colligation.The results in this paper first appeared as part of the author's doctoral thesis [13] at the Universidad Central de Venezuela, under the supervision of Mischa Cotlar. The work has been supported by the Consejo Nacional de Investigaciones Cientificas y Techológicas (CONICIT-Venezuela). I am grateful to Professor Aad Dijksma, who read an earlier version of this note and made several helpful criticisms. I also thank Professor Mischa Cotlar for his kind encouragement and Professor Alejandra Cabana for correcting the english text. 相似文献
149.
Maria Zaharescu Maria Crisan Luminita Predoana Mariuca Gartner Dana Cristea Stefania Degeratu Elena Manea 《Journal of Sol-Gel Science and Technology》2004,32(1-3):173-177
In the present work, the influence of substituted Si-alkoxides on the structural and optical properties of films obtained in the SiO2-TiO2 system was studied. Methyltriethoxysilane (MTEOS) and 3-(tri-methoxysilyl)propyl methacrylate (TSPM) were used as SiO2 sources and Ti(OBu)4 was used as TiO2 source. Acetylacetone was added to the Ti(OBu)4 as chelating agent and the synthesis was carried out in acid medium. The films were deposited on oxidized Si-wafers by spin-coating. The films were characterized by XRD, spectro-ellipsometry (SE), and atomic force microscopy (AFM). The results obtained have shown that in the case of hybrid films the desired thickness could be obtained in a single deposition step. The thickness of the films and the optical properties are controlled by the bulkiness of the organic substitute bounded to Si. Among other optical applications, the potential use of such films as optical waveguides is proposed. 相似文献
150.
Bertelli M El-Bastawissy E Knaggs MH Barrett MP Hanau S Gilbert IH 《Journal of computer-aided molecular design》2001,15(5):465-475
A number of triphenylmethane derivatives have been screened against 6-phosphogluconate dehydrogenase from Trypanosoma brucei and sheep liver. Some of these compounds show good inhibition of the enzymes and also selectivity towards the parasite enzyme. Modelling was undertaken to dock the compounds into the active sites of both enzymes. Using a combination of DOCK 3.5 and FLEXIDOCK a correlation was obtained between docking score and both activity for the enzymes and selectivity. Visualisation of the docked structures of the inhibitors in the active sites of the enzymes yielded a possible explanation of the selectivity for the parasite enzyme. 相似文献