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71.
A sliced inverse regression approach for data stream 总被引:1,自引:0,他引:1
Marie Chavent Stéphane Girard Vanessa Kuentz-Simonet Benoit Liquet Thi Mong Ngoc Nguyen Jérôme Saracco 《Computational Statistics》2014,29(5):1129-1152
In this article, we focus on data arriving sequentially by blocks in a stream. A semiparametric regression model involving a common effective dimension reduction (EDR) direction \(\beta \) is assumed in each block. Our goal is to estimate this direction at each arrival of a new block. A simple direct approach consists of pooling all the observed blocks and estimating the EDR direction by the sliced inverse regression (SIR) method. But in practice, some disadvantages appear such as the storage of the blocks and the running time for large sample sizes. To overcome these drawbacks, we propose an adaptive SIR estimator of \(\beta \) based on the optimization of a quality measure. The corresponding approach is faster both in terms of computational complexity and running time, and provides data storage benefits. The consistency of our estimator is established and its asymptotic distribution is given. An extension to multiple indices model is proposed. A graphical tool is also provided in order to detect changes in the underlying model, i.e., drift in the EDR direction or aberrant blocks in the data stream. A simulation study illustrates the numerical behavior of our estimator. Finally, an application to real data concerning the estimation of physical properties of the Mars surface is presented. 相似文献
72.
Benoit Carbain 《Tetrahedron letters》2010,51(20):2717-7899
We report an efficient synthetic approach to phospha-isosteres of important intermediates of the shikimic acid pathway by the application of the Hunsdiecker-Barton halodecarboxylation to cyclohexenylcarboxylic acids. As examples, phospha-shikimic acid, its 3-dehydro derivative and the respective monomethyl esters were synthesized. The approach has proven equally useful in the synthesis of isosteres of the antiviral agent oseltamivir. 相似文献
73.
74.
Stefano Caramori Dr. Jérôme Husson Dr. Marc Beley Prof. Carlo A. Bignozzi Prof. Roberto Argazzi Dr. Philippe C. Gros Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(8):2611-2618
Mixtures of polypyridine FeII and CoII complexes are used as electron mediators in Ru–thienyltpy‐sensitised solar cells (tpy=terpyridine). The use of the metalorganic redox couples allows for improved charge‐collection efficiency with respect to the classical iodide/iodine couple which, when associated to Ru–tpy2 dyes, usually produces poor performance. The improved charge collection is explained by a combination of effective dye regeneration and decreased recombination with the oxidised electrolyte on the basis of data obtained by transient spectroscopy and photoelectrochemical measurements. The efficiency of the regeneration cascade is also critically dependent upon the ability of the CoII complex to intercept FeIII centres, as clearly indicated by chronocoulometry experiments. 相似文献
75.
D. Boettle M. Burzio P. Cinato G. Eilenberger J. -B. Jacob T. Martinson F. Masetti A. Mcguire M. Sotom P. Vogel J. Benoit 《Fiber and Integrated Optics》1996,15(4):267-279
The expected traffic growth from new broadband services will require network capacities that can be beneficially provided by optical WDM transport networks. Optical packet techniques are essential for large networks to provide flexibility and granularity. A layered network architecture with a transparent optical layer and optical packet layers has been elaborated. Four switching concept options for large optical ATM switch fabrics in the public network and small access nodes are presented. The technology for the related key functions of space and wavelength switching was developed in the RACE ATMOS project and the feasibility of concepts and technologies was verified in four system demonstrators. 相似文献
76.
Excellent diastereofacial and endo/exo stereoselectivities have been obtained in cycloaddition of the chiral azomethine ylide generated from 4-phenyloxazolidine acetic acid (−)-8-phenylmenthyl ester 1e. 相似文献
77.
78.
A new configuration of distorted homogeneous turbulence is investigated in the domain of rotation-dominated elliptical flows. The experimental results are compared with exact numerical solutions obtained in Fourier space for the linear part of the problem. The inherently periodic character of the flow results in typical oscillatory variations of the anisotropy and the pressure-strain correlations. A new two-point closure approach of the EDQNM type is proposed for the nonlinear problem; it is based on a representation of the spectral tensor by scalar functions expanded in terms of spherical harmonics. 相似文献
79.
α‐Peptide–Oligourea Chimeras: Stabilization of Short α‐Helices by Non‐Peptide Helical Foldamers 下载免费PDF全文
Dr. Juliette Fremaux Laura Mauran Dr. Karolina Pulka‐Ziach Dr. Brice Kauffmann Dr. Benoit Odaert Dr. Gilles Guichard 《Angewandte Chemie (International ed. in English)》2015,54(34):9816-9820
Short α‐peptides with less than 10 residues generally display a low propensity to nucleate stable helical conformations. While various strategies to stabilize peptide helices have been previously reported, the ability of non‐peptide helical foldamers to stabilize α‐helices when fused to short α‐peptide segments has not been investigated. Towards this end, structural investigations into a series of chimeric oligomers obtained by joining aliphatic oligoureas to the C‐ or N‐termini of α‐peptides are described. All chimeras were found to be fully helical, with as few as 2 (or 3) urea units sufficient to propagate an α‐helical conformation in the fused peptide segment. The remarkable compatibility of α‐peptides with oligoureas described here, along with the simplicity of the approach, highlights the potential of interfacing natural and non‐peptide backbones as a means to further control the behavior of α‐peptides. 相似文献
80.
Acid‐Labile Thermoresponsive Copolymers That Combine Fast pH‐Triggered Hydrolysis and High Stability under Neutral Conditions 下载免费PDF全文
Dr. Qilu Zhang Zhanyao Hou Benoit Louage Dr. Dingying Zhou Nane Vanparijs Prof. Dr. Bruno G. De Geest Prof. Dr. Richard Hoogenboom 《Angewandte Chemie (International ed. in English)》2015,54(37):10879-10883
Biodegradable polymeric materials are intensively used in biomedical applications. Of particular interest for drug‐delivery applications are polymers that are stable at pH 7.4, that is, in the blood stream, but rapidly hydrolyze under acidic conditions, such as those encountered in the endo/lysosome or the tumor microenvironment. However, an increase in the acidic‐degradation rate of acid‐labile groups goes hand in hand with higher instability of the polymer at pH 7.4 or during storage, thus posing an intrinsic limitation on fast degradation under acidic conditions. Herein, we report that a combination of acid‐labile dimethyldioxolane side chains and hydroxyethyl side chains leads to acid‐degradable thermoresponsive polymers that are quickly hydrolyzed under slightly acidic conditions but stable at pH 7.4 or during storage. We ascribe these properties to high hydration of the hydroxy‐containing collapsed polymer globules in conjunction with autocatalytic acceleration of the hydrolysis reactions by the hydroxy groups. 相似文献