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63.
Bertini I Jiménez B Piccioli M 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,174(1):125-132
To optimize 13C direct detected experiments for the observation of signals close to a paramagnetic center, we have assessed the sensitivity of different sequences based on CO-Cali coherence transfer. Features of CACO experiments were tested for Calbindin D9k, in which one of the two native Ca2+ ions is replaced by the paramagnetic Ce3+ ion. We have studied the comparison of single vs multiple quantum coherence transfer evolution as well as the influence of in-phase vs anti-phase detection of 13CO signals and finally the comparison of a coherence transfer step based on a CyO in plane with respect to a Cy ali in plane. The acquisition of the anti-phase component of the signal, accomplished by the removal of the last refocusing steps, allowed the identification of some signals unobserved with other pathways. The structural dependency of paramagnetism-induced nuclear relaxation is such that the identification of the most suitable coherence transfer pathway is not known "a priori" but it is driven by the relative proximity of Cali and CO to the paramagnetic center. 相似文献
64.
We consider the deterministic generation of entangled multiqubit states by the sequential coupling of an ancillary system to initially uncorrelated qubits. We characterize all achievable states in terms of classes of matrix-product states and give a recipe for the generation on demand of any multiqubit state. The proposed methods are suitable for any sequential generation scheme, though we focus on streams of single-photon time-bin qubits emitted by an atom coupled to an optical cavity. We show, in particular, how to generate familiar quantum information states such as W, Greenberger-Horne-Zeilinger, and cluster states within such a framework. 相似文献
65.
Intermodal dispersion between the supermodes of a directional coupler may induce undesirable pulse breakup in a sufficiently large device. When this happens the device will no longer exchange power between its arms, and the extinction ratio is completely canceled. It is shown that, by carefully designing the coupling area of the directional coupler, one may compensate for intermodal dispersion. The compensating device should accomplish three basic requirements: inverse intermodal dispersion, balanced coupling of each supermode, and maximum power transfer while preserving the sign of the slope of the coupling coefficient with frequency for multiplexing-demultiplexing applications. This structure is designed and optimized with a genetic algorithm. 相似文献
66.
Versatile chelating behavior of benzil bis(thiosemicarbazone) in zinc, cadmium, and nickel complexes
Reactions of benzil bis(thiosemicarbazone), LH(6), with M(NO(3))(2).nH(2)O (M = Zn, Cd, and Ni), in the presence of LiOH.H(2)O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule. Complexes of these metal ions with empirical formula [MLH(4)] were obtained, although they show different molecular structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a 1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as a bridge between the metal ions. However, in the nickel complex LH(6) acts as a N(2)S(2) ligand yielding a planar structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography, microanalysis, mass spectrometry, IR, (1)H, and (13)C NMR spectroscopies and for the cadmium complex by (113)Cd NMR in solution and in the solid state. 相似文献
67.
We introduce and study matrix Christoffel functions for a matrix
weight W.
We find an explicit expression of the matrix Christoffel functions
in terms of any sequence of orthonormal matrix polynomials with
respect to W. An extremal property related to the matrix moment
problem defined by W is established for the matrix Christoffel
functions. We finally find the relative asymptotic behavior of
the matrix Christoffel functions associated to matrix weights in
the matrix Nevai class. 相似文献
68.
Kleij AW Souto B Pastor CJ Prados P de Mendoza J 《The Journal of organic chemistry》2003,68(22):8711-8714
The selective preparation and complete structural characterization of a small series of 1,2-anti-heterodisubstituted calix[4]arenes has been accomplished. These compounds were obtained in two steps from unsubstituted p-tert-butylcalix[4]arene by tribenzoylation and a subsequent one-pot, two-step sequence involving alkylation with simultaneous partial deacylation, resulting in heterodisubstituted calixarenes carrying an alkyl and an aroyl group. The monoalkyl-tribenzoyl intermediate, prior to in situ deprotection, could also be isolated. 相似文献
69.
We propose a scheme for producing large Fock states in cavity QED via the implementation of a highly selective atom-field interaction. It is based on Raman excitation of a three-level atom by a classical field and a quantized field mode. Selectivity appears when one tunes to resonance a specific transition inside a chosen atom-field subspace, while other transitions remain dispersive, as a consequence of the field dependent electronic energy shifts. We show that this scheme can be also employed for reconstructing, in a new and efficient way, the Wigner function of the cavity field state. 相似文献
70.
Hawkes NC Stratton BC Tala T Challis CD Conway G DeAngelis R Giroud C Hobirk J Joffrin E Lomas P Lotte P Mailloux J Mazon D Rachlew E Reyes-Cortes S Solano E Zastrow KD 《Physical review letters》2001,87(11):115001
Simultaneous current ramping and application of lower hybrid heating and current drive (LHCD) have produced a region with zero current density within measurement errors in the core ( r/a< or =0.2) of JET tokamak optimized shear discharges. The reduction of core current density is consistent with a simple physical explanation and numerical simulations of radial current diffusion including the effects of LHCD. However, the core current density is clamped at zero, indicating the existence of a physical mechanism which prevents it from becoming negative. 相似文献