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11.
Michael P. Doyle Doina G. Ene Chad S. Peterson Vince Lynch 《Angewandte Chemie (International ed. in English)》1999,38(5):700-702
The intramolecular addition of a diazo ester group to a triple bond in the presence of chiral dirhodium(II ) carboxamidate catalysts gives macrocyclic lactones with a fused cycloproprene ring [Eq. (a)]. This efficient reaction is characterized by high enantiocontrol (up to 98% ee) and chemoselectivity. 相似文献
12.
Nicolae Aldea Rodica Turcu Alexandrina Nan Izabella Craciunescu Ovidiu Pana Xie Yaning Zhonghua Wu Doina Bica Ladislau Vekas Florica Matei 《Journal of nanoparticle research》2009,11(6):1429-1439
In this article, we focus on the structural peculiarities of nanosized Fe3O4 in the core-shell nanocomposites obtained by polymerization of conducting polypyrrole shell around Fe3O4 nanoparticles. The local structure of Fe atoms was determined from the Extended X-ray Absorption Fine Structure analysis
using our own package computer programs. An X-ray diffraction method that is capable to determine average particle size, microstrains,
as the particle size distribution of Fe3O4 nanoparticles is presented. The method is based on the Fourier analysis of a single X-ray diffraction profile using a new
fitting method based on the generalized Fermi function facilities. The crystallites size obtained by X-ray diffraction spectra
analysis was estimated between 3.2 and 10.3 nm. Significant changes in the first and the second Fe coordination shell in comparison
with standard bulk were observed. The global and local structure of the nanosized Fe3O4 are correlated with the synthesis conditions of the core-shell polypyrrole nanocomposites. 相似文献
13.
We theoretically investigated the effects of non-resonant intense laser and magnetic fields on the optical properties of asymmetric GaAs/AlGaAs double quantum dot related to the occurrence of electromagnetically induced transparency, using compact density-matrix formalism and effective mass approximation. The chosen structure has the advantage to present x-lambda(Λ)-configuration or y-ladder(Ξ)-configuration for EIT occurrence, depending on lasers polarization, at low values of the non-resonant laser, and to change the configuration from Λ to Ξ at the increase of the x-polarized non-resonant laser intensity. We discussed in detail the influences of the control laser field intensity, non-resonant laser strength and polarization, and magnetic field intensity on the absorption coefficient, refraction index and group index. It is found that: (i) the control laser or the non-resonant laser at the same control laser intensity influences more the system being in x-Ξ-configuration than in x-Λ-configuration and have intermediate effects on y-Ξ-configuration; (ii) the magnetic field has the greatest influence on the system being in x-Λ-configuration and the lowest for y-Ξ-configuration; (iii) the increment of the non-resonant intense laser or magnetic fields induces a red-shift of the transparency windows and sub (super) luminal frequency intervals for the Λ-configuration but a blue-shift for both Ξ-configurations. 相似文献
14.
15.
Doina Cioranescu 《Applied Mathematics and Optimization》1976,3(2-3):263-282
A constitutive law for a class of non newtonian fluids is considered. The stress-tension is defined as an element in the subgradient of a convex, l.s.c. function: (D);D is the tension of the rate of deformation. We give existence and uniqueness theorems. Some examples (Bingham fluid, pseudo-plastic and dilatant fluids) are also given. 相似文献
16.
17.
Florentina L. Chiriac Monica Ili Augustin Madalan Doina Manaila-Maximean Mihail Secu Viorel Cîrcu 《Molecules (Basel, Switzerland)》2021,26(7)
This work focuses on the investigation of the liquid crystalline behavior and luminescence properties of the lanthanide complexes of Eu(III), Sm(III) and Tb(III) with N-biphenyl-alkylated-4-pyridone ligands. The organic ligands having a biphenyl group attached via a long flexible spacer with either 9 or 10 carbon atoms were synthesized by the reaction between 4-hydroxypyridine and the corresponding bromide compounds. The chemical structures of the organic and lanthanide complexes were assigned based on elemental analysis, single-crystal X-ray diffraction, 1H, 13C NMR and IR spectroscopies, and thermogravimetric analysis (TGA). The X-ray diffraction analysis of a parent compound shows that the lanthanide ions are surrounded by three monodentate pyridone ligands and three bidentate nitrate ions, giving a 9-coordinate environment. The mesogenic behavior and the type of liquid crystalline phases exhibited by the new complexes were analyzed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM), and powder X-ray diffraction (XRD) studies. Only the lanthanide complexes with longer spacer (10) display a monotropic SmA phase, typically on a short thermal range (less than 10 °C). The complexes with shorter flexible chains (9) show no liquid crystalline properties with melting temperatures lower than their analogs with longer spacers. The emission spectra recorded in solid state at room temperatures show typical emission bands for each lanthanide ion employed (Eu(III), Tb(III) and Sm(III)). 相似文献
18.
Homogenization in open sets with holes 总被引:1,自引:0,他引:1
Doina Cioranescu Jeannine Saint Jean Paulin 《Journal of Mathematical Analysis and Applications》1979,71(2):590-607
Let Qr be a cylindrical bar with r cylindrical cavities having generators parallel to those of Qr. Let Ω be the cross-section of the bar, Ω1 the cross-section of the domain occupied by the material and the cross- sections of the cavities: . The study of the elastic torsion of this bar leads to the following problem [see 2., 3., 267–320)]: (1) where μ is the shear modulus of the material, α is the angle of twist and represents the stress function. In this paper the problem (1) with an increasing number of holes which are distributed periodically is considered. One would like to know if has a limit , and if so, the equation satisfied by this limit. This is an “homogenization” problem — the heterogeneous bar Qr is replaced by a homogeneous one, the response of which under torsion approximates as closely as possible that of Qr. A more general problem will be studied and the case of elastic torsion will be obtained as an application. The proof uses the energy method [see Lions (Collège de France, 1975–1977), Tartar (Collège de France, 1977)] and extension theorems. A related problem is the homogenization of a perforated plate [cf. Duvaut (to appear)]. 相似文献
19.
Doina Sirbu Barbara Milani Paul S. Pregosin 《Journal of organometallic chemistry》2005,690(9):2254-2262
Two sets of mono- and dicationic palladium complexes (8) and (10), having and as counterions, were synthesised. The interionic structure of the methyl-acetonitrile complexes [Pd((R,S)-Bn-Box)(CH3)(NCCH3)](X) (8) in solution, was investigated by pulsed-gradient spin-echo (PGSE) diffusion measurements and (1H, 19F)-HOESY NMR spectroscopy. A high degree of ion-pairing was found in each complex. The HOESY spectra showed that the and anions take up selective positions, on the side of the complex remote from the benzyl groups, but close to the acetonitrile ligand, while the triflate is, partially, occupying a pseudo fifth coordination position on the side of the cation remote from the two benzyl-groups. The complexes 8 and 10 were used as catalyst precursors for the copolymerisation of styrene with carbon monoxide, producing syndiotactic copolymers, with the exception of complex 10a, that led to isotactic copolymers. 相似文献
20.
Doina Bica Ladislau Vékás Mikhail V. Avdeev Oana Marinică Vlad Socoliuc Maria Bălăsoiu Vasil M. Garamus 《Journal of magnetism and magnetic materials》2007
Magnetic fluids (MFs), prepared by chemical co-precipitation followed by double layer steric and electrostatic (combined) stabilization of magnetite nanoparticles dispersed in water, are presented. Several combinations of surfactants with different chain lengths (lauric acid (LA), myristic acid (MA), oleic acid (OA) and dodecyl-benzene-sulphonic acid (DBS)) were used, such as LA+LA, MA+MA, LA+DBS, MA+DBS, OA+DBS, OA+OA and DBS+DBS. Static light scattering, transmission electron microscopy, small angle neutron scattering, magnetic and magneto-rheological measurements revealed that MFs with MA+MA or LA+LA biocompatible double layer covered magnetite nanoparticles are the most stable colloidal systems among the investigated samples, and thus suitable for biomedical applications. 相似文献