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71.
We construct for the Schrödinger operator in the semi-classical limit compact perturbations of a radial symmetric potential which give rise to resonances associated to arbitrarily high order poles for the meromorphic extension of the resolvent. Our results concern the hamiltonianP
0=–h
2–x
2 in the 2-dimensional case, as well as a fairly large class of radial-symmetric potentials in the 3-dimensional case. We show that the poles of the resolvent for such a potential are necessarily simple, and subsequently the degeneracy is due to a lack of symmetry. 相似文献
72.
Belmadoui N Encinas S Climent MJ Gil S Miranda MA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(2):553-561
Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 in its excited triplet state. The photobiological implications of the above results are discussed with respect to benzophenone-photosensitized damage of thymidine. 相似文献
73.
74.
The influence of six antiferroelectric compounds on the helical pitch of mixture W-1000, which was reported as long pitch orthoconic antiferroelectric liquid crystalline mixture, was checked by spectrophotometry and polarimetry methods. The electro-optical properties for the mixture with the longest pitch were measured. An improvement in electro-optical response due to the long pitch is reported. The novelty in electro-optical properties is the good symmetry response. 相似文献
75.
Amel Bendali-Braham Noureddine Ikhlef-Eschouf Mostafa Blidia 《Comptes Rendus Mathematique》2018,356(2):115-120
The b-chromatic number of a graph G is the largest integer k such that G admits a proper coloring with k colors for which each color class contains a vertex that has at least one neighbor in all the other color classes. A graph G is called -critical if the contraction of any edge e of G decreases the b-chromatic number of G. The purpose of this paper is the characterization of all -critical trees. 相似文献
76.
Amel Dakhlaoui Mouna Jendoubi Leila Samia Smiri Andrei Kanaev Noureddine Jouini 《Journal of Crystal Growth》2009,311(16):3989-3996
Zinc oxide monodispersed nanoparticles were synthesized using a modified polyol process without any requirement to use a catalyst or calcination step at high temperature. The morphology and the size of the resulting oxide particles were adjusted by using several synthesis parameters (temperature, alkaline ratio, hydrolysis ratio, etc.). The increasing of the alkaline ratio results in a great change of the elaborated particles morphology that evolved from irregular and anisotropic forms (conical, nanorod-like and elliptical) to spherical one. A growth mechanism of these particles was proposed on the basis of zincite crystal structure and the morphology evolution as a function of the synthesis parameters. The photoluminescence spectra show UV-excitonic and visible emission bands. The strongest intensity of the visible emission was observed in nanorod-like particles, which implies an increased fraction of oxygen vacancies in this sample. The rod-like particles with 1 μm length show the dominant UV-emission, which evidences their improved stoichiometry. 相似文献
77.
Yahia Harek Lahcène Larabi Leila Boukli Fatima Kadri Noureddine Benali-Cherif Mohsen M. Mostafa 《Transition Metal Chemistry》2005,30(2):121-127
A new NiII complex of 5,6-dihydro-2H-pyran-3-aldehyde thiosemicarbazone (HDPTSC) has been synthesized and characterized by microanalyses, magnetic susceptibility, molar conductance measurements and by spectral methods (i.r., u.v.–vis., 1H-n.m.r.). The structure of [Ni(DPTSC)2] · B DMF has been solved using X-ray diffraction and found to be highly symmetrical with a trans -arrangement of the two bidentate ligands. The thiosemicarbazone coordinates as an anionic ligand via the thiosemicarbazone moietys azomethine nitrogen and thiolate sulfur [on loss of the N2 hydrogen]. The electrochemical behavior of the ligand and its NiII complex, determined by cyclic voltammetry, shows that the redox process of the ligand was highly irreversible, whereas the redox process of the NiII complex was observed as a one electron transfer process in a quasi-reversible and diffusion-controlled reaction. 相似文献
78.
Encinas S Climent MJ Belmadoui N Miranda MA 《Chemical communications (Cambridge, England)》2005,(20):2572-2574
Using two diastereomeric dyads containing naphthalene and thymine units, significant chiral discrimination has been found in the photophysical processes involving the naphthalene excited states: singlet deactivation by hydrogen bonding molecules, singlet-singlet energy transfer from thymine and triplet decay. 相似文献
79.
Khiar N Araujo CS Suárez B Alvarez E Fernández I 《Chemical communications (Cambridge, England)》2004,(6):714-715
Treatment of several C(2) symmetric bis-thioglycosides with Pd(CH(3)CN)(2)Cl(2) always leads to a single diastereomeric Pd(II) complex as a consequence of the exo-anomeric effect. 相似文献
80.
A. Louhadj Mohamed Ghezali F. Badi Noureddine Mehnane Youcef Cherchab Bouhalouane Amrani Hamza Abid Nadir Sekkal 《Superlattices and Microstructures》2009,46(3):435-442
Using the plane wave version of the full potential linear muffin-tin orbital (FPLMTO) method, which enables an accurate treatment of the interstitial regions, the electronic properties of ScN, YN, LaN and GdN rocksalt/rocksalt superlattices are calculated. It is found that apart from YN/ScN, all the other superlattices have negative bandgaps. However, it is shown that these systems can be semiconductors if a correction is made to the local density approximation (LDA). 相似文献