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51.
M. Clarembeau A. Cravador W. Dumont L. Hevesi A. Krief J. Lucchetti D. Van Ende 《Tetrahedron》1985,41(21):4793-4812
This paper reports our results concerning the syntheses of various bis(alkylseleno)alkanes and some of their arylseleno analogues by different methods. The scope and limitation of each of them are presented. 相似文献
52.
T. Dumont S. Lazare T. Lippert A. Wokaun 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1271-1274
The ablation rates of a polyimide and a triazene polymer were studied gravimetrically by a quartz micro balance for 248-nm and 308-nm irradiation. Special care was taken to examine the dependence of the ablation rate at constant fluences for single pulses and the influence of consecutive pulses at the same position. A clear trend was observed in these measurements, i.e., that the mass loss after the first pulse is always different from values for the following pulses. This implies that it is very difficult to determine true ablation rates, which are the foundation of most ablation models. The differences of the mass loss between the first pulse and the following pulses is most probably due to carbonization of the material, resulting in varying ablation rates for the following pulses. The ablation rates are thus not a real material property but a superposition of the material ablation rates with the ablation rates of carbon and carbonized material. PACS 52.38.Mf; 71.20.Rv; 07.10.Lw 相似文献
53.
The reversible cis-trans photoisomerization of disperse red 1 (DR1) in PMMA thin films has been demonstrated to be strongly polarization sensitive [1]. In this communication two mechanisms are identified: the angular hole burning and the angular redistribution of molecules. It is shown that, in the presence of a DC electric field, the redistribution is not centrosymmetric and produces a poling of the film. The evolution of the second-order nonlinear susceptibility, (2), is monitored by measuring the electro-optic effect by attenuated total reflection and by second-harmonic generation. 相似文献
54.
J. Gleize E. Chikoidze Y. Dumont E. Rzepka O. Gorochov 《Superlattices and Microstructures》2007,42(1-6):242
We report on micro-Raman measurements performed under various visible excitations on wurtzite Zn1−xMnxO thin films grown by MOCVD, for a wide range of Mn content (0<x<0.22). We observe a shift of the frequency of the E2 phonon for increasing Mn content, indicating a substitution of the Mn atoms at the tetrahedral Zn sites of the host matrix. All spectra also reveal a dominant feature related to local vibrations of Mn atoms, as well as the A1 (LO) phonon of the ZnMnO alloy. Both features are resonantly enhanced by the absorption of the incident laser light by internal transitions of the Mn2+ ions. 相似文献
55.
The shift equations iteration (SEI) solves the n-level quantum scattering problem in one dimension, i.e., the close-coupled equations, free from exponential instability arising
from closed channels. SEI provides exponential-instability-free transmission and reflection coefficients, and is well suited
to two-sided scattering problems such as conduction in molecular wires. Our most efficient implementation of SEI utilizes
an adaptation of the log-derivative symplectic integrator described by Manolopoulos and Gray in (J Chem Phys 102:9214, 1995).
The two-level nonadiabatic tunneling system is investigated—in the tunneling regime, above the barrier, and at resonance.
Nonadiabatic components in the upper channel wavefunction (and lower channel wavefunction at resonance energies) are found
to be non-adiabatic, i.e., not describable by WKB functions. Their behavior is characterized in terms of an empirical model
relating these components to adiabatic components in the lower (upper) channel and the potential energy coupling. 相似文献
56.
N. Keller J. Mistrík Š. Višňovský D.S. Schmool Y. Dumont P. Renaudin M. Guyot R. Krishnan 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):67-73
Orthoferrites present, as bulk materials, reorientation transitions of their magnetic moment alignment at temperatures depending
on the rare-earth (RE) ion. In particular, orthoferrites (REFeO3) with RE = Sm, Dy, present this transition at T
SRT = 443 K and 36 K, respectively. The spectra of the complex Kerr and Faraday angle have been measured on orthoferrite thin
films (RE = Sm, Dy, Y), which were prepared by pulsed laser deposition on amorphous quartz substrates. The obtained spectra
exhibit contributions of both surfaces and interfaces. Propagation effects of the polarized light in the magneto-optical medium
which is interpreted in terms of a simplified theoretical formalism, is also observed. For selected photon energies, temperature
dependent Faraday rotation measurements, , on orthoferrite thin films (RE = Sm, Dy, Y) have been performed. A quite different thermal variation compared to the bulk
magnetization has been observed. Curie temperatures are found to be close to the bulk values or slightly larger by 10 K to
20 K as in the case of DyFeO3 and YFeO3. For RE = Sm and Dy, increases with increasing temperature contrary to the saturation magnetization, passes through a maximum at about 460 K and
vanishes with a T
C of 647±18 K, 695 K for RE = Sm and Dy respectively.
Received 28 July 2000 相似文献
57.
Thomas Criton Dr. Debora Vilona Dr. Guy Jacob Dr. Maurice Médebielle Prof. Elise Dumont Dr. Lionel Joucla Dr. Emmanuel Lacôte 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(11):3670-3674
Polyazanes (i.e., higher nuclearity homologues of hydrazines) with increasing numbers of bound nitrogen atoms (from 3 to 5), including the first pentazane ever described, were prepared by the addition of lower-order polyazanes to diazo reagents. A structure was obtained. It was shown that the polynitrogen chains adopt a helical conformation. DFT modeling shows that the arrangement persists in solution. Although the polyazanes are all reducing agents, they become less so as the number of nitrogens increases. 相似文献
58.
Juan C. López-Realpozo Reinaldo Rodríguez-Ramos Raúl Guinovart-Díaz Julián Bravo-Castillero J.A. Otero Federico J. Sabina F. Lebon Serge Dumont Igor Sevostianov 《International Journal of Solids and Structures》2014
In this contribution, effective elastic moduli are obtained by means of the asymptotic homogenization method, for oblique two-phase fibrous periodic composites with non-uniform imperfect contact conditions at the interface. This work is an extension of previous reported results, where only the perfect contact for elastic or piezoelectric composites under imperfect spring model was considered. The constituents of the composites exhibit transversely isotropic properties. A doubly periodic parallelogram array of cylindrical inclusions under longitudinal shear is considered. The behavior of the shear elastic coefficient for different geometry arrays related to the angle of the cell is studied. As validation of the present method, some numerical examples and comparisons with theoretical results verified that the present model is efficient for the analysis of composites with presence of imperfect interface and parallelogram cell. The effect of the non uniform imperfection on the shear effective property is observed. The present method can provide benchmark results for other numerical and approximate methods. 相似文献
59.
Dumont E Ogra Y Vanhaecke F Suzuki KT Cornelis R 《Analytical and bioanalytical chemistry》2006,384(5):1196-1206
Liquid chromatography (LC) hyphenated with both elemental and molecular mass spectrometry has been used for Se speciation
in Se-enriched garlic. Different species were separated by ion-pair liquid chromatography–inductively coupled plasma mass
spectrometry (LC–ICP–MS) after hot-water extraction. They were identified by on-line reversed-phase liquid chromatography–electrospray
ionization tandem mass spectrometry (RPLC–ESI–MS–MS). Se-methionine and Se-methylselenocysteine were determined by monitoring
their product ions. Another compound, γ-glutamyl-Se-methylselenocysteine, shown to be the most abundant form of Se in the
garlic, was determined without any additional sample pre-treatment after extraction and without the need for a synthesized
standard. Product ions for this dipeptide were detected by LC–ESI–MS–MS for three isotopes of Se—78
Se, 80Se: and 82Se. The method was extended to the species extracted during in-vitro gastrointestinal digestion. Because both Se-methylselenocysteine
and γ-glutamyl-Se-methylselenocysteine have anticarcinogenic properties, their extractability and stability during human digestion
are very important. Garlic was also treated with saliva, to enable detection and analysis of species extracted during mastication.
Detailed information on the extractability of selenium species by both simulated gastric and intestinal fluid are given, and
variation of the distribution of Se among the different species with time is discussed. Although the main species in garlic
is the dipeptide γ-glutamyl-Se-methylselenocysteine, Se-methylselenocysteine is the main compound present in the extracts
after treatment with gastrointestinal fluids. Two more, so far unknown compounds were observed in the chromatogram. The extracted
species and their transformations were analysed by combining LC–ICP–MS and LC–ESI–MS–MS. In both the simulated gastric and
intestinal digests, Se-methionine, Se-methylselenocysteine, and γ-glutamyl-Se-methylselenocysteine could be determined by
LC–ESI–MS–MS by measuring their typical product ions.
相似文献
60.
Especially in the last decade, a vast number of papers on Se and its role in health issues have been published. This review
gives a brief, critical overview of the main analytical findings reported in these papers. Of particular interest is the Se
content in different food sources worldwide and the extent to which their consumption is reflected in the Se content of human
tissues and body fluids. Several food sources, both natural (Brazil nuts, garlic, Brassica juncea) and Se-enriched (yeast-based supplements), are discussed as to origin, characteristics, Se metabolism and impact of their
consumption on the human body. The continuous development of new and improvement of existing analytical techniques has provided
different powerful tools to unravel the Se species and their function. An up-to-date literature study on Se speciation analysis
is given, illustrating how analytical chemistry in its different facets aids in the identification of Se compounds and provides
insight into the complete metabolic pathway of Se throughout the human body. This review includes a detailed image of the
current state-of-the-art of Se speciation analysis in these food sources and in human tissues and body fluids. 相似文献