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1.
Two polynuclear complexes, a dimer and a tetramer, involving sulfate and hydroxo bridges and ligating ascorbate were isolated from aqueous solutions. Structural formulae are proposed on the basis of microanalytical and thermal analysis results, i.r., 13C-n.m.r., mass spectral data and magnetic measurements. 相似文献
2.
Lucien Birgé 《Probability Theory and Related Fields》1986,71(2):271-291
Résumé On s'intéresse ici aux possibles vitesses d'estimation d'une densité à support compact dans
m
sous des hypothèses de régularité, lorsque la perte est mesurée par le carré de la distance de Hellinger (on regardera aussi le cas connu des normes
pour 1q2) et le risque est le risque minimax sur la famille. On donne une méthode générale permettant de traiter les problèmes dans le cadre de la théorie de l'approximation sous des conditions concernant l'entropie métrique et l' -capacité des familles à estimer. Les rapports entre régularité et entropie métrique étant bien connus, nous pourrons aussi traiter les cas classiques et d'autres qui le sont moins. Sous des conditions de bornes inférieures les vitesses sont celles observées pour la norme
mais elles diffèrent dans le cas général. On montre aussi que les restrictions sur la compacité du support ou la régularité sont indispensables et que leur absence mène à l'impossibilité d'obtenir une estimation raisonnable en ce sens que n'importe quelle suite d'estimateurs sera arbitrairement mauvaise en un point au moins. Un résultat analogue est vrai sous des conditions de régularité.
This work was carried out during a visit of the author at the Mathematical Sciences Research Institute at Berkeley 相似文献
This work was carried out during a visit of the author at the Mathematical Sciences Research Institute at Berkeley 相似文献
3.
Cu(II) and Zn(II) complexes were synthesized from equimolar amounts of carboxamides; 1,8-bis(2-thiophenecarboxamido)-p-menthane (tkdam) and 1,8-bis(2-furancarboxamido)-p-menthane (furdam). The structure of the carboxamides were determined by elemental analysis; 1H NMR, 13C NMR, FT-IR and LC-MS spectra. The relative energies and the electronic properties (LUMO, HOMO, LUMO-HOMO gap) of the ligands
were investigated theoretically by performing Semi-empirical molecular orbital theory PM3 method in Hyperchem 7 (Release).
Carboxamide complexes having general formula as; monomeric, [ML]Cl2 and dimeric [Cu(tkdam)Cl]2Cl2 · 5H2O were synthesized and characterized by using element analysis; FT-IR, LC-MS spectra; magnetic susceptibility, molar conductivity
and thermal (TGA/DTA curve) studies. It was found that the coordination number of the monomeric complexes is four whereas
dimeric’s is six. The changes in the selected vibration bands in FT-IR indicate that, carboxamides behave as tetradentate
ligands and coordinate to metal ions from acyl ring (through S/O) and amide carbonyl (C=O). Molar conductivity measurements
indicate the 1: 2 ionic nature of the carboxamide complexes. 相似文献
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Mert Umut Ozkaynak Cigdem Atalay-Oral S. Birgül Tantekin-Ersolmaz F. Seniha Güner 《Macromolecular Symposia》2005,228(1):177-184
Polyurethane films based on renewable sources were prepared as an alternative to petroleum-based polyurethane. The effects of the structure and ratio of diisocyanate components on polymer properties were investigated. Hexamethylene diisocyanate (HMDI) and diphenylmethylene diisocyanate (MDI) were chosen as the diisocyanate components in polymer synthesis. Membranes were prepared by casting-evaporation technique and characterized for their gas permeability, film and mechanical properties. The oil-based membranes were found to be suitable for wound dressing applications. 相似文献
7.
Risk bounds for model selection via penalization 总被引:11,自引:0,他引:11
Andrew Barron Lucien Birgé Pascal Massart 《Probability Theory and Related Fields》1999,113(3):301-413
Performance bounds for criteria for model selection are developed using recent theory for sieves. The model selection criteria
are based on an empirical loss or contrast function with an added penalty term motivated by empirical process theory and roughly
proportional to the number of parameters needed to describe the model divided by the number of observations. Most of our examples
involve density or regression estimation settings and we focus on the problem of estimating the unknown density or regression
function. We show that the quadratic risk of the minimum penalized empirical contrast estimator is bounded by an index of the accuracy of the sieve. This accuracy index quantifies the trade-off among the candidate models
between the approximation error and parameter dimension relative to sample size.
If we choose a list of models which exhibit good approximation properties with respect to different classes of smoothness,
the estimator can be simultaneously minimax rate optimal in each of those classes. This is what is usually called adaptation. The type of classes of smoothness in which one gets adaptation depends heavily on the list of models. If too many models
are involved in order to get accurate approximation of many wide classes of functions simultaneously, it may happen that the
estimator is only approximately adaptive (typically up to a slowly varying function of the sample size).
We shall provide various illustrations of our method such as penalized maximum likelihood, projection or least squares estimation.
The models will involve commonly used finite dimensional expansions such as piecewise polynomials with fixed or variable knots,
trigonometric polynomials, wavelets, neural nets and related nonlinear expansions defined by superposition of ridge functions.
Received: 7 July 1995 / Revised version: 1 November 1997 相似文献
8.
Matthias Westerhausen Christin Birg Holger Piotrowski Tassilo Habereder Max Suter Heinrich Nth 《无机化学与普通化学杂志》2001,627(5):882-890
Formation of Alkaline Earth Metal‐Arsenic Cages via the Metalation of Triisopropylsilylarsane with Calcium, Strontium, and Barium Bis[bis(trimethylsilyl)amide] in Tetrahydrofuran The metalation of triisopropylsilylarsane with the alkaline earth metal bis[bis(trimethylsilyl)amides] in tetrahydrofuran yields the THF complexes of calcium ( 1 ), strontium ( 2 ), and barium‐bis(triisopropylsilylarsanide) ( 3 ). Dissolving of these compounds in toluene leads to the elimination of triisopropylsilylarsane and the formation of the THF complexes of tetraalkaline earth metal hexakis(triisopropylsilylarsanide)‐triisopropylsilylarsanediide of calcium ( 4 ), strontium ( 5 ), and barium ( 6 ), respectively. The central polyhedron of compound 4 can be described as two trigonal bipyramids with the metal atoms in apical positions, connected via the arsanediide substituent as a common corner. The central moieties of the compounds 5 and 6 consist of four trigonal bipyramids which are connected by common edges as well as common faces. 相似文献
9.
The purpose of this paper is to estimate the intensity of some random measure N on a set ${\mathcal{X}}$ by a piecewise constant function on a finite partition of ${\mathcal{X}}$ . Given a (possibly large) family ${\mathcal{M}}$ of candidate partitions, we build a piecewise constant estimator (histogram) on each of them and then use the data to select one estimator in the family. Choosing the square of a Hellinger-type distance as our loss function, we show that each estimator built on a given partition satisfies an analogue of the classical squared bias plus variance risk bound. Moreover, the selection procedure leads to a final estimator satisfying some oracle-type inequality, with, as usual, a possible loss corresponding to the complexity of the family ${\mathcal{M}}$ . When this complexity is not too high, the selected estimator has a risk bounded, up to a universal constant, by the smallest risk bound obtained for the estimators in the family. For suitable choices of the family of partitions, we deduce uniform risk bounds over various classes of intensities. Our approach applies to the estimation of the intensity of an inhomogenous Poisson process, among other counting processes, or the estimation of the mean of a random vector with nonnegative components. 相似文献
10.
Journal of Solid State Electrochemistry - For Al-air batteries, it is important to develop efficient and economical anodes. In this study, the effect of aluminum anodes treated with copper by... 相似文献