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81.
Vikram Kestens Gert Roebben Thomas Linsinger 《Accreditation and quality assurance》2010,15(5):269-281
Based on a standard test method for purity by differential scanning calorimetry (DSC), ASTM E 928, a purity determination
method for highly pure polycyclic aromatic hydrocarbons (PAHs) has been developed and validated. The robustness of the developed
method was investigated by determining, under varying measurement conditions, the purity of two PAH certified reference materials
(CRMs), benzo[c]phenanthrene and dibenzo[a,h]anthracene. The repeatability and intermediate precision of the developed method was determined by analysing the purity of
benzo[c]phenanthrene and dibenzo[a,h]anthracene and PAH candidate CRMs indeno[1,2,3-c,d]pyrene, 6-methylchrysene and benzo[a]pyrene. The trueness of the method was studied using the same (candidate) CRMs and a series of 42 other PAH CRMs. For each
of the five (candidate) CRMs, a full measurement uncertainty budget was developed. Also for PAH materials for which the DSC
purity determination method has not been explicitly validated, the relative expanded measurement uncertainty was estimated. 相似文献
82.
Gerd Vanhoenacker Alberto Dos Santos Pereira Takashi Kotsuka Deirdre Cabooter Gert Desmet Pat Sandra 《Journal of chromatography. A》2010,1217(19):3217-3222
The performance of a polymeric stationary phase with reversed-phase properties (ET-RP1) was evaluated for LC separations at elevated temperature. The most significant observation was that the reduced plate height (h) decreased from 3.4 at 25 °C (optimal flow 0.5 mL/min) to 2.4 at 150 °C (optimal flow 2.5 mL/min) which is comparable to the efficiency obtained with silica-based reversed-phase columns of 4.6 mm ID operated at 0.8 mL/min. The phase showed no deterioration after long use at 150 °C within the pH range 1–9. Catalytic activity originating from the stationary phase material, e.g. as experienced on zirconium columns operated at elevated temperature, was absent. The performance of ET-RP1 is illustrated with the analysis of some pharmaceutical samples by LC and LC–MS. Operation at elevated temperature also allows to reduce the amount of organic modifier or to replace acetonitrile and methanol by the biodegradable ethanol. 相似文献
83.
Supervised learning methods are powerful techniques to learn a function from a given set of labeled data, the so-called training data. In this paper the support vector machines approach is applied to an image classification task. Starting with the corresponding Tikhonov regularization problem, reformulated as a convex optimization problem, we introduce a conjugate dual problem to it and prove that, whenever strong duality holds, the function to be learned can be expressed via the dual optimal solutions. Corresponding dual problems are then derived for different loss functions. The theoretical results are applied by numerically solving a classification task using high dimensional real-world data in order to obtain optimal classifiers. The results demonstrate the excellent performance of support vector classification for this particular problem. 相似文献
84.
Bart J. Crielaard Cristianne J. F. Rijcken Lingdong Quan Steffen vanderWal Isil Altintas Martin vanderPot John A. W. Kruijtzer Rob M. J. Liskamp Raymond M. Schiffelers Cornelus F. vanNostrum Wim E. Hennink Dong Wang Twan Lammers Gert Storm 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(29):7366-7370
85.
Gideon Steyl Gert J. Kruger Andreas Roodt 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(10):m473-m475
The molecules of the title complex, [Rh(Trop)(CO)2] (Trop is 2‐hydroxycyclohepta‐2,4,6‐trienonate, C7H5O2), exhibit symmetrical but non‐crystallographic square‐planar molecular geometry, with Rh—C distances of 1.825 (10) and 1.826 (9) Å, Rh—O distances of 2.021 (5) and 2.032 (5) Å, and an O—Rh—O bite angle of 79.4 (2)°. Strong Rh⋯Rh and Rh⋯C intermolecular interactions of 3.683 (3) and 3.650 (5) Å, respectively, are also observed. 相似文献
86.
87.
Given an optimization problem with a composite of a convex and componentwise increasing function with a convex vector function as objective function, by means of the conjugacy approach based on the perturbation theory, we determine a dual to it. Necessary and sufficient optimality conditions are derived using strong duality. Furthermore, as special case of this problem, we consider a location problem, where the “distances” are measured by gauges of closed convex sets. We prove that the geometric characterization of the set of optimal solutions for this location problem given by Hinojosa and Puerto in a recently published paper can be obtained via the presented dual problem. Finally, the Weber and the minmax location problems with gauges are given as applications. 相似文献
88.
The present paper is a continuation of [2] where we deal with the duality for a multiobjective fractional optimization problem. The basic idea in [2] consists in attaching an intermediate multiobjective convex optimization problem to the primal fractional problem, using
an approach due to Dinkelbach ([6]), for which we construct then a dual problem expressed in terms of the conjugates of the functions involved. The weak, strong
and converse duality statements for the intermediate problems allow us to give dual characterizations for the efficient solutions
of the initial fractional problem. The aim of this paper is to compare the intermediate dual problem with other similar dual
problems known from the literature. We completely establish the inclusion relations between the image sets of the duals as
well as between the sets of maximal elements of the image sets.
相似文献
89.
Hans R. Kricheldorf Gert Schwarz Sigrid Bhme Claus‐Ludolf Schultz 《Journal of polymer science. Part A, Polymer chemistry》2003,41(7):890-904
Bisphenol A was polycondensed with diphosgene in a dichloromethane/aqueous NaOH system. Temperature, time, and molar ratios of the reactants were optimized according to a previously elaborated optimization of the hydrolytic polycondensation of bisphenol A bischloroformate. Five of the following catalysts were examined: triethylamine, 4‐(N,N‐dimethylamino)pyridine (DMAP), ethyldiisopropylamine (EDPA), tetrabutylammonium hydrogen sulfate, and triethylbenzylammonium chloride (TEBA‐Cl). Triethylamine and DMAP accelerated the hydrolysis of diphosgene by formation of a hydrophilic acylammonium salt. Therefore, the molecular weights decreased with higher concentration of these tert‐amines. However, the molecular weights increased (weight‐average molecular weight up to 106) with higher concentrations of tetraalkylammonium salts because these catalysts favor chain growth in the organic phase via “naked” phenoxide ions without catalyzing the hydrolysis of diphosgene. EDPA gave poor results under all circumstances. Cyclic polycarbonates were discovered in all samples. Their fraction increased with the average molecular weight of the samples. When samples prepared with triethylamine or TEBA‐Cl were fractionated, cycles having molar masses up to 15,000 Da were detected by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 890–904, 2003 相似文献
90.