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排序方式: 共有409条查询结果,搜索用时 15 毫秒
121.
122.
Mustapha Benmouna Thomas A. Vilgis Henri Benoit 《Macromolecular theory and simulations》1992,1(6):333-358
Theoretical models describing the dynamics of multicomponent polymer mixtures are reviewed. Some detailed derivations are shown to make the basic assumptions clear and to ease the comparison between these models. The effects of random noise and memory functions on the time evolution of dynamical correlation functions are examined. The long-range hydrodynamic interactions or mode-coupling effects are also included. A possible extension of these models to the kinetics of spinodal decomposition in solutions of polymer mixtures is briefly discussed. 相似文献
123.
Thermal and dielectric loss properties of Na3PO4-Pb3(PO4BiPO4 (Na2O-PbO-Bi2O3-P2O5) phosphate glasses, have been studied by the differential scanning calorimetry (DSC) and electrical factor loss (tgδ) measurements. Experiments have been carried out from ambient temperature to 500°C and show a strong influence of sodium ions on Tg and tgδ. 相似文献
124.
Maha Benzarti-GhédiraHaikel Hrichi Nejmeddine JaballahRafik Ben Chaâbane Mustapha MajdoubHafedh Ben Ouada 《Physica B: Condensed Matter》2012,407(7):1051-1054
The opto-electronic properties of native poly(p-phenylene vinylene) (PPV) were tuned by the confinement of the π-conjugation and the incorporation of a sulphur group as a spacer in order to obtain a blue-green emitting polymer (PPVS). The energy band gap of the PPVS thin film has been measured by UV-vis absorption spectroscopy and evaluated to 2.87 eV. Current-voltage characteristics and impedance spectroscopy measurements performed on sandwich structures [ITO/PPVS/Al] are used to elucidate the conduction mechanisms. The static electrical characterisations showed a space charge limited conduction (SCLC) and a conductivity with low power frequency behaviour characteristic of a hopping transport in disordered materials. The impedance spectra can be discussed in terms of an equivalent circuit model designed as a parallel resistor RP and capacitor CP network in series with a resistor RS. We extract numerical values of these parameters by fitting experimental data. Their evolution with bias voltages has shown that the SCLC mechanism is characterised by an exponential trap distribution. 相似文献
125.
This work deals with spectral mapping theorems for neutron transport semigroups
in unbounded geometries and L1 setting. The mathematical analysis relies on harmonic analysis of certain measure valued mappings related to
Dyson-Phillips expansions and on some functional analytic results on the
critical spectrum. 相似文献
126.
Mustapha Mokhtar-Kharroubi 《Positivity》2006,10(2):231-249
We deal with a general streaming semigroup arising in transport theory. We show that in general such a semigroup has a direct
decomposition into three simpler semigroups one of which extends to a group. A general spectral theory of them is given and
is partly derived from that of a class of positive semigroups on Banach lattices. 相似文献
127.
Mustapha Mokhtar-Kharroubi 《Journal of Functional Analysis》2009,256(6):1998-2025
This paper deals with two related subjects. In the first part, we give generation theorems, relying on (weak) compactness arguments, for perturbed positive semigroups in general ordered Banach spaces with additive norm on the positive cone. The second part provides new functional analytic developments on semigroup theory for Schrödinger operators in Lp spaces with (L1) Δ-bounded potentials without restriction on the (L1) Δ-bound. In particular, our formalism enlarges a priori the classical Kato class and its subsequent refinements. The connection with form-perturbation theory is also dealt with. 相似文献
128.
Intermolecular radical addition to C=N bonds with acyclic stereocontrol offers excellent potential as a mild, nonbasic carbon-carbon bond construction approach to chiral amines. Here, complete details of the first radical additions to chiral N-acylhydrazones as an approach to asymmetric amine synthesis are disclosed. Novel N-acylhydrazones were designed as chiral C=N radical acceptors with Lewis acid activation, restriction of conformational mobility, and commercial availability of precursors. Amination of 4-alkyl-2-oxazolidinones with O-(mesitylenesulfonyl)hydroxylamine or O-(p-nitrobenzoyl)hydroxylamine afforded N-aminooxazolidinones which were condensed with aldehydes to afford N-acylhydrazones 3-8. Three synthetic methods were developed, implementing these N-acylhydrazones in Lewis acid-promoted intermolecular radical additions to C=N bonds. First, additions of various secondary and tertiary alkyl iodides to propionaldehyde and benzaldehyde hydrazones (3 and 7) under tin hydride radical chain conditions in the presence of ZnCl2 gave N-acylhydrazine adducts with diastereomeric ratios ranging from 93:7 to 99:1. Radical additions to a series of N-acylhydrazones with different substituents on the oxazolidinone revealed that benzyl and diphenylmethyl were more effective stereocontrol elements than those with the aromatic ring directly attached to the oxazolidinone. Second, a tin-free method, exploiting dual functions of triethylborane for both initiation and chain propagation, enabled improved yields in addition of secondary alkyl iodides. Third, under photolytic conditions with hexamethylditin, primary radical addition could be achieved with ethyl iodide in the presence of diethyl ether as cosolvent; the 1-ethoxyethyl adduct was observed as a minor product. Chloromethyl addition was achieved under both the tin-free and photolytic conditions; in this case, the adduct bears alkyl chloride functionality with potential for further elaboration. 相似文献
129.
Redouane Khaoulaf Mustapha Ezzaafrani Abdelaziz Ennaciri Mohammed Harcharras Francesco Capitelli 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):1367-1376
Abstract Infrared and Raman spectra of dipotassium zinc bis(dihydrogendiphosphate) dihydrate, K2Zn(H2P2O7)2 .2H2O have been collected and interpreted using factor group analysis. Noncoincidence of the Raman and infrared spectra bands confirms a centrosymmetric structure for K2Zn(H2P2O7)2 .2H2O previously investigated by X-ray structural study, as well as the joint appearance of νas POP and νs POP point to a bent POP configuration. 相似文献
130.
Hilbert transform and continuous wavelet transform are combined to form an algorithm for the analysis of a single fringe pattern with open or closed fringes. Only one recorded fringe pattern is needed to extract the phase information. A second π/2 phase shifted fringe pattern should first be generated from the other using Hilbert transform to superpose numerically the spatial carrier. Several phase extraction techniques are conceived to demodulate fringe patterns. In this paper, the wavelet technique is used to obtain the required phase distribution. The algorithm offers an advantage that it is appropriate when the spatial carrier is impossible to be added experimentally. Finally, a simulation was carried out to validate the algorithm, giving good results. 相似文献