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981.
Renault M Hadjar Y Blaize S Bruyant A Arnaud L Lerondel G Royer P 《Optics letters》2010,35(19):3303-3305
We report on a concept of compact optical Fourier-transform spectrometer based on bidimensional (2D) spatial sampling of a confined interferogram. The spectrometer consists of a nanostructured glass surface on which two light beams interfere in total internal reflection. Subwavelength spatial sampling of the interferogram near field is achieved by introducing a tilt angle between a 2D array of optical nanoantennas and the interferogram pattern. The intensity distribution of the scattered light is recorded on a 2D CCD camera, and a one-dimensional Fourier transform of the interferogram is used to recover the input light spectrum. Experimental results show a wide spectral bandwidth in the visible range, down to 380 nm, with spectral resolution of 1.6 nm around 780 nm. 相似文献
982.
Effects of ions clustering in Nd3+/Al3+-codoped double-clad fiber laser operating near 930 nm 总被引:1,自引:0,他引:1
C. Bartolacci M. Laroche T. Robin B. Cadier S. Girard H. Gilles 《Applied physics. B, Lasers and optics》2010,98(2-3):317-322
We report experimental and theoretical investigations on the presence and the detrimental effect of neodymium clusters on the three-level transition at near 930 nm in aluminosilicate double-clad fibers. A series of fibers with a W-type refractive index core profile to filter out the competing strong transition at 1060 nm were fabricated to study the impact of clusters on laser efficiency at near 930 nm using different core compositions. Percentage of clustered Nd ions have been evaluated using two methods based either on the saturation of the pump absorption or on laser efficiencies. Laser characterizations and numerical modeling have shown that clustering effect has a strong impact on the laser efficiency at 930 nm and fractions of clustered ions higher than 50% have been found in the most doped fiber. 相似文献
983.
Lakhdar Sibous Embarek Bentouhami Amor Ma?za Gilles M. Bouet Mustayeen Ahmed Khan 《Journal of solution chemistry》2010,39(4):511-521
The condensation of 2-hydroxybenzaldehyde or 2,4-dihydroxybenzaldehyde with 4,4′-diaminobiphenyl in absolute EtOH in a molar
ratio 2:1 gave, respectively, the Schiff base ligands H2L1 or H2L2. The bases served as tetradentate ligands to coordinate CoII, NiII and CdII chlorides, leading to complexes where the metal:ligand ratio is 2:1. All of the compounds were characterized by elemental
analysis, infrared, electronic and mass spectroscopy, 1H-n.m.r. and d.s.c. The cyclic voltammograms of the ligands and their complexes in DMF are discussed. 相似文献
984.
Dolgonos G Lukin O Elstner M Peslherbe GH Leszczynski J 《The journal of physical chemistry. A》2006,110(30):9405-9410
The potential stabilization of normally unstable C20, the smallest fullerene, via its encapsulation inside a tetraureacalix[4]arene dimer has been analyzed using molecular mechanics calculations with different force fields, the self-consistent-charge density-functional tight-binding with dispersion correction (SCC-DFTB-D) model, and standard density-functional-theory (DFT) calculations. The interaction energies obtained for the C20 complex have been compared with analogous values calculated for numerous complexes of the tetraureacalix[4]arene dimer with other guests. Results of the calculations with all force fields and SCC-DFTB-D predict that the binding of C20 occurs with the highest selectivity. On the other hand, standard DFT calculations fail to correctly describe the stabilization of the complexes under study as standard DFT generally does not treat dispersion interactions properly. Predicted relative stabilities of the complexes are discussed in conjunction with available experimental data. Molecular dynamics simulations reveal the instability of the guest-free capsular dimer, which decomposes on a 1-ns time scale, while dimeric complexes with guests remained intact during the 5-ns simulation time, indicating the guest-driven formation of the molecular capsule. 相似文献
985.
Violette A Fournel S Lamour K Chaloin O Frisch B Briand JP Monteil H Guichard G 《Chemistry & biology》2006,13(5):531-538
Unnatural oligomeric scaffolds designed to adopt defined secondary structures (e.g., helices), while retaining the chemical diversity of amino acid side chains, are of practical value to elaborate functional mimetics of bioactive alpha-polypeptides. Enantiopure N,N'-linked oligoureas as short as seven residues long have been previously shown to fold into a stable helical structure, stabilized by 12- and 14-membered H-bonded rings. We now report that eight-residue oligoureas designed to mimic globally amphiphilic alpha-helical host-defense peptides are effective against both gram-negative and gram-positive bacteria (including methicillin-resistant Staphylococcus aureus [MRSA]) and exhibit selectivity for bacterial versus mammalian cells. Circular dichroism (CD) spectroscopy studies suggest enhanced helical propensity of oligoureas in the presence of phospholipid vesicles. The utility of this new class of nonpeptidic foldamers for biological applications is highlighted by high resistance to proteolytic degradation. 相似文献
986.
A new electrofluorescent switch was prepared with an electroactive fluorescent tetrazine blend of polymer electrolyte; the cells contain four layers: the tetrazine polymer film, a photocured polymer electrolyte film, and two indium-tin oxide plates as the two contact electrodes. 相似文献
987.
Gré gory Ginot Gilles Halbout 《Proceedings of the American Mathematical Society》2006,134(3):621-630
Let be the Hochschild complex of cochains on and let be the space of multivector fields on . In this paper we prove that given any -structure (i.e. Gerstenhaber algebra up to homotopy structure) on , and any -morphism (i.e. morphism of a commutative, associative algebra up to homotopy) between and , there exists a -morphism between and that restricts to . We also show that any -morphism (i.e. morphism of a Lie algebra up to homotopy), in particular the one constructed by Kontsevich, can be deformed into a -morphism, using Tamarkin's method for any -structure on . We also show that any two of such -morphisms are homotopic.
988.
Terrier F Rodriguez-Dafonte P Le Guével E Moutiers G 《Organic & biomolecular chemistry》2006,4(23):4352-4363
Following a potentiometric determination of the relevant pKa values of the (R1R2)C=NOH functionality, the second order rate constants (k(Ox)) for reaction of a large set of oximate bases with two model organophosphorus esters, i.e. bis-(4-nitrophenyl)phenylphosphonate (BNPPP) and bis-(4-nitrophenyl)methylphosphonate (BNPMP), and three toxic compounds, i.e., sarin (GB), soman (GD) and diisopropylphosphorofluoridate (DFP), in aqueous as well as a 30 : 70 (v/v) H2O-Me2SO mixture have been measured. The corresponding Br?nsted-type nucleophilicity plots of log k(Ox)vs. pKa(Ox) reveal a clear tendency of the reactivity of the oximates to suffer a saturation effect with increasing basicity in aqueous solution. In the case of BNPMP and the three toxic esters, this behaviour is reflected in a levelling off at pKa approximately 9 but a more dramatic situation prevails in the BNPPP system where the attainment of maximum reactivity at pKa approximately 9 is followed by a clear decrease in rate at higher pKa's. Interestingly, a number of data reported previously by different authors for the sarin, soman and DFP systems are found to conform rather well to the curvilinear Br?nsted correlations built with our data. Based on this and previous results obtained for reactions at carbon centers, it can be concluded that the observed saturation effect is the reflection of an intrinsic property of the oximate functionality. An explanation of this behavior in terms of an especially strong requirement for desolvation of the oximates prior to nucleophilic attack which becomes more and more difficult with increasing basicity is suggested. This proposal is supported by the observed changes in pKa(Ox) and k(Ox) brought about by a transfer from H2O to a 30 : 70 H2O-Me2SO mixture. The implications of the saturation effect on the efficiency of oximates as nucleophilic catalysts for smooth decontamination are emphasized. Also discussed is the effect of basicity on the exalted (alpha-effect) reactivity of these bases. 相似文献
989.
990.
Mulligan A Lane I Rousseau GB Johnston SM Lennon D Kadodwala M 《The journal of physical chemistry. B》2006,110(2):1083-1090
Naturally occurring metal surfaces possess planes of mirror symmetry on the nanometer-length scale. This mirror symmetry can be lifted and chirality "physically" conveyed onto a surface by adsorbing a chiral molecule. Until now, it has not been known whether the conveying of chirality is limited to just the physical structure or whether it goes deeper and permeates the electronic structure of the underlying surface. By using optically active second harmonic generation (OA-SHG), it is demonstrated that the adsorption of some, but not all, chiral molecules can reversibly, and without significant structural rearrangement, measurably lift the mirror symmetry of the surface electronic structure of a metal. It is proposed that the ability of a chiral molecule to place a significant "chiral perturbation" on the electronic structure of a surface is correlated to its adsorption geometry. The microscopic origins of the observed optical activity are also discussed in terms of classical models of chirality. The results of the study challenge current models of how chiral adsorbates induce enantioselectivity in the chemical/physical behavior of heterogeneous systems, which are based on geometric/stereochemical arguments, by suggesting that chiral electronic perturbations could play a role. 相似文献