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排序方式: 共有61条查询结果,搜索用时 31 毫秒
21.
M. Dülk ST. Fischer M. Bitter M. Caraccia W. Vogt E. Gini H. Melchior W. Hunziker A. Buxens H.N. Poulsen A.T. Clausen 《Optical and Quantum Electronics》2001,33(7-10):899-906
A monolithically integrated and fully packaged Mach–Zehnder interferometer with semiconductor optical amplifiers (MZI-SOA) is demonstrated as polarisation-independent high-speed demultiplexer for up to 160 Gbit/s optical time division multiplexed (OTDM) data streams. 相似文献
22.
A theoretical study of the 21Ag ← 11Ag two-photon transition and its vibronic band in trans-stilbene
JONNA STÅLRING LAURA GAGLIARDI PER-ÅKE MALMQVIST ROLAND LINDH 《Molecular physics》2013,111(11):1791-1796
The two-photon spectrum of the 21Ag ← 11Ag transition in trans-stilbene has been calculated at the complete active space self-consistent field (CASSCF) level of theory. Energies were obtained at the complete active space second-order perturbation (CASPT2) level of theory, while the geometries of both the initial and final states were optimized at the CASSCF level. The energy and the geometry optimizations were performed using an active space of 14 electrons in 14 active π orbitals. The vibrational frequencies of both states and the two-photon transition (TPT) cross-section were calculated with a smaller active space where the two lowest π orbitals were kept inactive. A newly implemented algorithm, in the quantum chemical package Molcas was used to determine the two-photon transition intensity. This method requires only the linear response of the CASSCF wavefunction. Furthermore, the vibronic structure of this TPT was studied. The Franck-Condon factors were obtained by calculating the overlap between the vibrational states involved, which were determined from the force fields of both the initial and final states, at the CASSCF level of theory. The results are in agreement with experiment. 相似文献
23.
JONNA STÅLRING MARTIN SCHÜTZ ROLAND LINDH GUNNAR KARLSTRÖM PER-OLOF WIDMARK 《Molecular physics》2013,111(21):3389-3399
The low-energy region of the intermolecular potential energy hypersurface (PES) of the ammonia dimer was studied at the level of second-order Moller-Plesset perturbation theory (MP2) using a very large basis set. Individual minima were located on the PES employing the counterpoise (CP) correction to account for the basis set superposition error (BSSE). Apart from these canonical MP2 calculations local MP2 (LMP2) calculations were performed. For the latter the BSSE at the correlated level is inherently absent by virtue of the local truncation of the virtual space. Results from canonical and local MP2 calculations are compared and the reliability of the LMP2 method for intermolecular complexes and clusters is discussed. The canonical MP2 calculations predicted five minimum structures, the four most stable ones lying energetically very close. For these four structures single point MP2 energy calculations with a further extended basis set (1024 functions for the ammonia dimer) were performed. The equilibrium dissociation energies so obtained are close to the one-particle basis set limit, as illustrated by a remaining BSSE of less than 0.2 kJ mol?1. The geometry optimizations at the LMP2 level, using the three most stable canonical MP2 structures as initial geometries, all collapsed to a single minimum corresponding to an asymmetric structural arrangement. A canonical MP2 single point calculation, at that geometry, revealed that the LMP2 minimum structure is virtually as stable as the lowest minima on the canonical MP2 PES. Based on these calculations the global minimum of the ammonia dimer was assigned to a part of the PES represented by an asymmetric structure with an equilibrium dissociation energy of 13.5±0.3 kJ mol?1 相似文献
24.
Edwin JaoStephane Bogen Anil K SaksenaViyyoor Girijavallabhan 《Tetrahedron letters》2003,44(27):5033-5035
Unsaturated lactam derived from (S)-pyroglutaminol undergoes a totally stereoselective cycloaddition reaction with (2-(acetoxymethyl)-3-allyl)trimethylsilane in the presence of Pd(P(OiPr)3)4 in refluxing toluene. This step was efficiently used to introduced the 5,5-fused framework desired for the preparation of novel proline surrogates. 相似文献
25.
An experimental arrangement is described which allows the detection of low gas densities by resonance fluorescence in the
vacuum ultraviolet. As a light source a capillary discharge through helium was used. Fluorescence signals as a function of
density have been measured in krypton, deuterium, and hydrogen, and the results have been compared with calculations. Detection
limits of 3·109 atoms/cm3 have been obtained. 相似文献
26.
Qun Dang Zhibo Zhang Yunfeng Bai Ruijun Sun Jie Yin Tongqian Chen Stephane Bogen Vinay Girijavallabhan David B. Olsen Peter T. Meinke 《Tetrahedron letters》2014
To discover novel nucleosides as potential anti-HCV agents, nucleosides with a 1′,2′-β-lactam moiety were designed as a hybrid scaffold of MK-608 and GS-6620. Synthetic strategies were successfully developed to prepare two series of C-nucleosides with a 1′,2′-β-lactam moiety: a 7-deaza-purine C-nucleoside analog 11 was prepared in 10 steps with an overall yield of 3.7%; a purine C-nucleoside analog 22 was prepared in 9 steps with an overall yield of 9.7%. 相似文献
27.
A comparison has been made of the morphology of fibrillar polyethylene crystals prepared by shear-induced crystallization and heterogeneous Ziegler-Natta catalysis under similar solvent and temperature conditions. Both specimens had a shish-kebab superstructure consisting of lamellar overgrowths on a filamentary backbone. For polyethylenes stirrer-crystallized at small supercoolings, the overgrown lamallae were removed by nitric acid oxidation followed by selective dissolution, leaving naked filamentary ribbons. Thermal analysis of these specimens suggested a dual molecular conformation of both folded and extended chains. The fact that these fibrils did not deform easily under uniaxial stress conforms with a core of extended chains. Thermal and oxidative behavior of polyethylenes prepared at lower crystallization temperatures suggested a greater content of chain folds in the central thread as the degree of supercooling increased. The Ziegler-Natta fibrils were degraded into lamellar fragments on oxidation and their thermal behavior suggested a predominantly folded-chain conformation. Uniaxial deformation occurred on stretching the Ziegler-Natta specimens in harmony with a core of folded chains. Molecular models have been proposed to account for the observed phenomena. 相似文献
28.
D. C. Bogen C. A. Henkel C. G. C. White G. A. Welford 《Journal of Radioanalytical and Nuclear Chemistry》1973,13(2):335-341
A method for the determination of the tritium distribution in environmental and biological samples is described. Tritium as
HTO is removed by freeze-drying and the residue is combusted to obtain organically bound tritium. Each tritium fraction is
electrolytically enriched and determined by liquid scintillation spectrometry. Enrichment and large sample sizes are required
due to the low environmental tritium levels. During the analyses of more than 600 samples over a two-year period all aspects
of the method (freeze-drying, combustion, enrichment and counting) have provided reproducible and precise results. 相似文献
29.
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