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排序方式: 共有270条查询结果,搜索用时 187 毫秒
1.
Ioana Dumitriu Alan Edelman 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2005,41(6):1083-1099
In this paper we examine the zero and first order eigenvalue fluctuations for the β-Hermite and β-Laguerre ensembles, using tridiagonal matrix models, in the limit as β→∞. We prove that the fluctuations are described by multivariate Gaussians of covariance O(1/β), centered at the roots of a corresponding Hermite (Laguerre) polynomial. The covariance matrix itself is expressed as combinations of Hermite or Laguerre polynomials respectively.We show that the approximations are of real value even for small β; we can use them to approximate the true functions even for the traditional β=1,2,4 values. 相似文献
2.
Carp O. Patron L. Mindru I. Marinescu G. Diamandescu L. Banuta A. 《Journal of Thermal Analysis and Calorimetry》2003,74(3):789-799
The thermal behaviour of three coordination compounds, potential precursors of nickel ferrite [Fe2Ni(C4H4O5)2.5(OH)2]NO3·5H2O,[Fe2Ni(C4H8O3N2)4](NO3)8·24H2O and (NH4)[Fe2Ni(C4H4O5)3(OH)3]·3H2O has been investigated to evaluate their suitability as precursors for nickel ferrite. For a complete and reliable assignment of the thermal transformations, the isolable solid intermediates and end products were characterized by IR, X-ray diffraction and Mössbauer investigations. A decomposition scheme is proposed. 相似文献
3.
A recently proposed perturbational approach to the electron correlation cusp problem 1 is tested in the context of three spherically symmetrical two‐electron systems: helium atom, hydride anion, and a solvable model system. The interelectronic interaction is partitioned into long‐ and short‐range components. The long‐range interaction, lacking the singularities responsible for the electron correlation cusp, is included in the reference Hamiltonian. Accelerated convergence of orbital‐based methods for this smooth reference Hamiltonian is shown by a detailed partial wave analysis. Contracted orbital basis sets constructed from atomic natural orbitals are shown to be significantly better for the new Hamiltonian than standard basis sets of the same size. The short‐range component becomes the perturbation. The low‐order perturbation equations are solved variationally using basis sets of correlated Gaussian geminals. Variational energies and low‐order perturbation wave functions for the model system are shown to be in excellent agreement with highly accurate numerical solutions for that system. Approximations of the reference wave functions, described by fewer basis functions, are tested for use in the perturbation equations and shown to provide significant computational advantages with tolerable loss of accuracy. Lower bounds for the radius of convergence of the resulting perturbation expansions are estimated. The proposed method is capable of achieving sub‐μHartree accuracy for all systems considered here. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
4.
Laura Pop Pierrik Lassalas László Csaba Bencze Monica Ioana Toşa Botond Nagy Florin Dan Irimie Christophe Hoarau 《Tetrahedron: Asymmetry》2012,23(6-7):474-481
Stereoselective preparative enzymatic acylation and hydrolysis/methanolysis of various C-substituted rac-thiazol-2-yl-methanols were achieved for the preparation of enantiopure or enantiomerically enriched, naturally occurring 2-hydroxymethylthiazoles. The absolute configurations of the resulting secondary alcohols were determined by a detailed 1H NMR study of Mosher’s derivatives. 相似文献
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7.
Ioana Konz Beatriz Fernández M. Luisa Fernández Rosario Pereiro Héctor González Lydia Álvarez Miguel Coca-Prados Alfredo Sanz-Medel 《Analytical and bioanalytical chemistry》2013,405(10):3091-3096
Laser ablation coupled to inductively coupled plasma mass spectrometry has been developed for the elemental imaging of Mg, Fe and Cu distribution in histological tissue sections of fixed eyes, embedded in paraffin, from human donors (cadavers). This work presents the development of a novel internal standard correction methodology based on the deposition of a homogeneous thin gold film on the tissue surface and the use of the 197Au+ signal as internal standard. Sample preparation (tissue section thickness) and laser conditions were carefully optimized, and internal normalisation using 197Au+ was compared with 13C+ correction for imaging applications. 24Mg+, 56Fe+ and 63Cu+ distributions were investigated in histological sections of the anterior segment of the eye (including the iris, ciliary body, cornea and trabecular meshwork) and were shown to be heterogeneously distributed along those tissue structures. Reproducibility was assessed by imaging different human eye sections from the same donor and from ten different eyes from adult normal donors, which showed that similar spatial maps were obtained and therefore demonstrate the analytical potential of using 197Au+ as internal standard. The proposed analytical approach could offer a robust tool with great practical interest for clinical studies, e.g. to investigate trace element distribution of metals and their alterations in ocular diseases. Figure
Development of a new internal standard correction methodology for qualitative elemental imaging by LA-ICP-MS 相似文献
8.
Ramona Penu Ioana Vasilescu Sandra A. V. Eremia Florentina Gatea Gabriel-Lucian Radu Simona-Carmen Litescu 《Central European Journal of Chemistry》2013,11(6):968-978
The present work describes the development of a nanocomposite system and its application in construction of a new amperometric biosensor applied in the determination of total polyphenolic content from propolis extracts. The nanocomposite system was based on covalent immobilization of laccase on functionalized indium tin oxide nanoparticles and it was morphologically and structural characterized. The casting of the developed nanocomposite system on the surface of a screen-printed electrode was used for biosensor fabrication. The analytical performance characteristics of the settled biosensor were determined for rosmarinic acid, caffeic acid and catechol (as laccase specific substrate). The linearity was obtained in the range of 1.06×10?6 ? 1.50×10?5 mol L?1 for rosmarinic acid, 1.90×10?7 ? 2.80×10?6 mol L?1 for caffeic acid and 1.66×10?6 ? 7.00×10?6 mol L?1 for catechol. A good sensitivity of amperometric biosensor 141.15 nA µmol?1 L?1 and fair detection limit 7.08×10?8 mol L?1 were obtained for caffeic acid. The results obtained for polyphenolic content of propolis extracts were compared with the chromatographic data obtained by liquid-chromatography with diode array detection. 相似文献
9.
Anca Mazare Mirela Dilea Daniela Ionita Ioana Demetrescu 《Surface and interface analysis : SIA》2014,46(3):186-192
The present study is focused on tailoring the morphology of TiO2 nanotubes obtained on Ti6Al7Nb alloy and evaluating their electrochemical behavior in simulated body fluid. The presence of the α and β phases on the Ti6Al7Nb alloy leads to a two‐scale organization of the nanotubes on the samples – which in turn affects the electrochemical stability. Furthermore, five different types of TiO2 nanotubes were obtained in various electrolytes (e.g. Generation I, a mixture of Generation II and Generation III, Generation III). Electrochemical behavior analysis of all obtained nanotubes morphologies was composed of Tafel plots, cyclic voltammetry and electrochemical impedance spectroscopy and was correlated with morphology data obtained from SEM (nanotubes diameters from top‐view and nanotube length from cross‐section view). The electrochemical results showed that morphological modifications of the Ti6Al7Nb alloy's surface by electrochemical anodizing have induced changes to the electrochemical behavior of the material, evident in the corrosion rates. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.
Mariana Prodana Adriana Voiculet Sorina Garea Mihaela Radu Horia Iovu Ioana Demetrescu Anca Dinischiotu 《Central European Journal of Chemistry》2014,12(10):1008-1015
This paper is focused on the synthesis and characterization of a novel hybrid material based on cisplatin and docetaxel-loaded functionalized simultanously carbon nanotubes able to be used in cancer therapy as drug delivery system with controlled toxicity. This material was physico-chemically investigated by determining the structure, as evidenced by Fourier transform infrared (FTIR) spectroscopy, transmission electronmicroscopy (TEM) and its stability was studied with the aid of thermogravimetric analysis (TGA). The amount of platinum ions released into the solution of simulated body fluid (SBF) was highlighted by coupled plasma mass spectrometry (ICP-MS). Toxicology experiments were performed with MDA-MB 231 breast cancer epithelial cells. The performance of the new drug delivery hybrid material was compared with functionalised carbon nanotubes with therapeutic agents functionalized with a single therapeutic agent. 相似文献