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排序方式: 共有476条查询结果,搜索用时 15 毫秒
91.
By using asymptotic methods recurrence relations are found that rule weakly CML evolution, with both global and diffusive coupling. The solutions obtained from these relations are very general because they do not hold restrictions about boundary conditions, initial conditions and number of oscilators in the CML. Furthermore, oscillators are ruled by an arbitraty C2 function. 相似文献
92.
Diego A. Manjarrs William J. Herrera Shirley Gmez 《Physica B: Condensed Matter》2009,404(18):2799-2801
In order to consider the Dirac-like spectrum of graphene we employ the Bogoliubov de Gennes–Dirac formalism to determine the quasiparticle Andreev levels in an NS surface (normal–superconductor). The normal region is characterized by a width L while the superconducting region is semi-infinite and both regions are made of doped graphene. The quasiparticle energy spectrum is originated by the Andreev reflections that occur in the NS interface. It is shown that this spectrum depends on the width of the normal region and the Fermi energy in each region. When the Fermi energy in the normal metal is lower than the gap of the superconductor region, the spectrum is affected by specular Andreev reflections. The equation that is obtained to find the spectrum is very general and we solve it for some particular cases. We find that the energy spectrum oscillates when the Fermi energy in graphene is changed. Finally we obtain under some approximations an equation for the energy spectrum which is similar in structure as those obtained for an INS conventional junction. 相似文献
93.
L.K. Herrera S. Montalbani M. Cotte V.A. Solé A. Duran J.L. Perez-Rodriguez 《Talanta》2009,80(1):71-8428
The process of investigating paintings includes the identification of materials to solve technical and historical art questions, to aid in the deduction of the original appearance, and in the establishment of the chemical and physical conditions for adequate restoration and conservation. In particular, we have focused on the identification of several samples taken from six famous canvases painted by Pedro Atanasio Bocanegra, who created a very special collection depicting the life of San Ignacio, which is located in the church of San Justo y Pastor of Granada, Spain. The characterization of the inorganic and organic compounds of the textiles, preparation layers, and pictorial layers have been carried out using an XRD diffractometer, SEM observations, EDX spectrometry, FT-IR spectrometry (both in reflection and transmission mode), pyrolysis/gas chromatography/mass spectrometry and synchrotron-based μ-X-ray techniques. In this work, the advantages over conventional X-ray diffraction of using combined synchrotron-based μ-X-ray diffraction and μ-X-ray fluorescence in the identification of multi-layer paintings is demonstrated. 相似文献
94.
Study by grazing incident diffraction and surface spectroscopy of amalgams from ancient mirrors 总被引:1,自引:0,他引:1
L. K. Herrera A. Duran M. L. Franquelo A. R. González-Elipe J. P. Espinós J. Rubio-Zuazo G. R. Castro A. Justo J. L. Perez-Rodriguez 《Central European Journal of Chemistry》2009,7(1):47-53
Characterization of four amalgam surfaces, with different alteration degrees from Andalusia historical mirrors, has been carried
out by grazing-incidence X-ray diffraction (GIXRD), and other spectroscopic techniques (SEM/EDX, XPS, and REELS). The combination
of all these techniques allows determining the corrosion state of the amalgams. The results show that the amalgams are composed
in all cases of a binary alloy of tin and mercury. As mercury has high vapour pressure at RT, it slowly segregates and eventually
evaporates, it leaves finely divided particles of tin that easily can be oxidize, forming tin monoxide (SnO) and tin dioxide
(SnO2). In one of the samples, most of the amalgam remains unoxidized, since Hg0.1Sn0.9 and metallic Sn phases are the major components; in two other samples, Hg0.1Sn0.9 and Sn phases are not detected while SnO2 and SnO phases appear. Finally, in the last studied sample, only SnO2 phase is detected. The surface analyses of these samples by XPS show that, for most of them an unique chemical species (Sn4+) is found.
相似文献
95.
Vanessa R. Landaeta Maurizio Peruzzini Verónica Herrera Roberto A. Sánchez-Delgado Andrés E. Goeta 《Journal of organometallic chemistry》2006,691(5):1039-1050
New rhodium and iridium complexes, with the formula [MCl(PBz3)(cod)] [M = Rh (1), Ir (2)] and [M(PBz3)2(cod)]PF6 [M = Rh (3), Ir (4)] (cod = 1,5-cyclooctadiene), stabilized by the tribenzylphosphine ligand (PBz3) were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. The addition of pyridine to a methanol solution of 1or 2, followed by metathetical reaction with NH4PF6, gave the corresponding derivatives [M(py)(PBz3)(cod)]PF6 [M = Rh (5), Ir (6)]. At room temperature in CHCl3 solution, 4 converted spontaneously to the ortho-metallated complex [IrH(PBz3)(cod){η2-P,C-(C6H4CH2)PBz2}]PF6 (7) as a mixture of cis/trans isomers via intramolecular C-H activation of a benzylic phenyl ring. The reaction of 3 or 4 with hydrogen in coordinating solvents gave the dihydrido bis(solvento) derivative [M(H)2(S)2(PBz3)2]PF6 (M = Rh, Ir; S = acetone, acetonitrile, THF), that transformed into the corresponding dicarbonyls [M(H)2(CO)2(PBz3)2]PF6 by treatment with CO. Analogous cis-dihydrido complexes [M(H)2(THF)2(py)(PBz3)2]PF6 (M = Rh, Ir) were observed by reaction of the py derivatives 5 and 6 with H2. 相似文献
96.
Reaction of the cyanoruthenate anions [Ru(bpym)(CN)4]2- and [[Ru(CN)4]2(mu-bpym)]4- (bpym = 2,2'-bipyrimidine) with lanthanide(III) salts resulted in the crystallization of coordination networks based on Ru-CN-Ln bridges. Four types of structure were obtained: [Ru(bpym)(CN)4][Ln(NO3)(H2O)5] (Ru-Ln; Ln = Sm, Nd, and Gd) are one-dimensional helical chains; [Ru(bpym)(CN)4]2[Ln(NO3)(H2O)2][Ln(NO3)(0.5)(H2O)(5.5)](NO3)(0.5).5.5H2O (Ru-Ln; Ln = Er and Yb) are two-dimensional sheets containing cross-linked chains based on Ru2Ln2(mu-CN)4 diamond units, which are linked into one-dimensional chains via shared Ru atoms; [[Ru(CN)4]2(mu-bpym)][Ln(NO3)(H2O)5]2.3H2O (Ru2-Ln; Ln = Nd and Sm) are one-dimensional ladders with parallel Ln-NC-Ru-CN-Ln-NC strands connected by the bipyrimidine "cross pieces" acting as rungs on the ladder; and [[Ru(CN)4]2(mu-bpym)][Ln(H2O)6](0.5)[Ln(H2O)4](NO3)(0.5).nH2O (Ru2-Ln; Ln = Eu, Gd, and Yb; n = 8.5, 8.5, and 8, respectively) are three-dimensional networks in which two-dimensional sheets of Ru2Ln2(mu-CN)4 diamonds are connected via cyanide bridges to Ln(III) ions between the layers. Whereas Ru-Gd shows weak triplet metal-to-ligand charge-transfer (3MLCT) luminescence in the solid state from the Ru-bipyrimidine chromophore, in Ru-Nd, Ru-Er, and Ru-Yb, the Ru-based emission is quenched, and all of these show, instead, sensitized lanthanide-based near-IR luminescence following a Ru --> Ln energy transfer. Similarly, Ru2-Nd and Ru2-Yb show lanthanide-based near-IR emission following excitation of the Ru-bipyrimidine chromophore. Time-resolved luminescence measurements suggest that the Ru --> Ln energy-transfer rate is faster (when Ln = Yb and Er) than in related complexes based on the [Ru(bipy)(CN)4]2- chromophore, because the lower energy of the Ru-bpym 3MLCT provides better spectroscopic overlap with the low-energy f-f states of Yb(III) and Er(III). In every case, the lanthanide-based luminescence is relatively short-lived as a result of the CN oscillations in the lattice. 相似文献
97.
Herrera RP Sgarzani V Bernardi L Fini F Pettersen D Ricci A 《The Journal of organic chemistry》2006,71(26):9869-9872
A study into the use of a chiral phase-transfer catalyst in conjunction with acetone cyanohydrin to effect the enantioselective formation of alpha-amino nitriles from alpha-amido sulfones is described. This novel catalytic asymmetric Strecker reaction is analyzed with regard to the possible mechanistic basis. 相似文献
98.
Alberto Guilln Jos Martínez Juan Miguel Carceller Luis Javier Herrera 《Entropy (Basel, Switzerland)》2020,22(11)
The main goal of this work is to adapt a Physics problem to the Machine Learning (ML) domain and to compare several techniques to solve it. The problem consists of how to perform muon count from the signal registered by particle detectors which record a mix of electromagnetic and muonic signals. Finding a good solution could be a building block on future experiments. After proposing an approach to solve the problem, the experiments show a performance comparison of some popular ML models using two different hadronic models for the test data. The results show that the problem is suitable to be solved using ML as well as how critical the feature selection stage is regarding precision and model complexity. 相似文献
99.
Aromatic-solvent-induced 11B NMR shifts (11B ASIS effects), observed for closo-2, 4-C2B5H7 and its 5-chloro and 5, 6-dichloro derivatives, are correlated to ab initio STO-3G derived atom charge densities. A near linear relationship is found upon incorporating nearestneighbor charge density contributions. 相似文献
100.
Ismael Herrera 《Numerical Methods for Partial Differential Equations》1985,1(3):159-186
This is the second in a series of three papers devoted to the presentation of a direct procedure of analysis of numerical methods for partial differential equations. The procedure consists of applying the method of weighted residuals and then interpreting the resulting equations by means of Green's formulas for discontinuous functions. Here, the general Green's formulas for operators defined in discontinuous fields developed in the first article, are applied to formulate the method of weighted residuals for arbitrary linear operators. Finite elements, boundary methods, and general procedures for coupling finite elements and boundary methods are discussed. 相似文献