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排序方式: 共有148条查询结果,搜索用时 15 毫秒
1.
Lubomír Kubáček 《Applications of Mathematics》2006,51(6):565-582
Some remarks to problems of point and interval estimation, testing and problems of outliers are presented in the case of multivariate
regression model.
This work was supported by the Council of Czech Government J14/98:153100011. 相似文献
2.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(6):571-588
The multivariate model, where not only parameters of the mean value of the observation matrix, but also some other parameters
occur in constraints, is considered in the paper. Some basic inference is presented under the condition that the covariance
matrix is either unknown, or partially unknown, or known.
Supported by the grant of the Council of Czech Republic MSM 6 198 959 214. 相似文献
3.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(1):59-82
In some situations estimates of unknown parameters must be corrected by additional measurements. It is in principle no problem
to calculate the corrected estimates, however, it is of more interest to find formulae for correction itself. The formulae
enable us to design an additional experiment and to judge its usefulness.
The aim of the paper is to find such formulae for several situations.
Supported by the grant of the Council of Czech Government MSM 6 198 959 214. 相似文献
4.
Lubomír Kubá?ek 《Mathematica Slovaca》2012,62(4):765-774
An uncertainty of an estimated parameter can be, in general, decomposed into two parts, i.e. an uncertainty caused by errors in the actual experiment (the type A uncertainty) and an uncertainty caused by errors in preceding experiment, where some wanted constants were estimated (the type B uncertainty). These constants are necessary for an estimation of the useful parameters. The aim of the paper is to find a condition for elimination of the type B uncertainty. 相似文献
5.
Zbyněk Brůža Dr. Jiří Kratochvíl Prof. Jeremy N. Harvey Dr. Lubomír Rulíšek Dr. Lucie Nováková Jana Maříková Dr. Jiří Kuneš Prof. Pavel Kočovský Prof. Milan Pour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8053-8060
Pyran-2-ones 3 undergo a novel Pd0-catalyzed 1,3-rearrangement to afford isomers 6 . The reaction proceeds via an η2-Pd complex, the pyramidalization of which (confirmed by quantum chemistry calculations) offers a favorable antiperiplanar alignment of the Pd−C and allylic C−O bonds ( C ), thus allowing the formation of an η3-Pd intermediate. Subsequent rotation and rate-limiting recombination with the carboxylate arm then gives isomeric pyran-2-ones 6 . The calculated free energies reproduce the observed kinetics semi-quantitatively. 相似文献
6.
Prof. Dr. Andrei V. Malkov Dr. Sigitas Stončius Dr. Mark Bell Dr. Fabiomassimo Castelluzzo Dr. Pedro Ramírez‐López Dr. Lada Biedermannová Prof. Dr. Vratislav Langer Dr. Lubomír Rulíšek Prof. Dr. Pavel Kočovský 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(28):9167-9185
Detailed kinetic and computational investigation of the enantio‐ and diastereoselective allylation of aldehydes 1 with allyltrichlorosilanes 5 , employing the pyridine N‐oxides METHOX ( 9 ) and QUINOX ( 10 ) as chiral organocatalysts, indicate that the reaction can proceed through a dissociative (cationic) or associative (neutral) mechanism: METHOX apparently favors a pentacoordinate cationic transition state, while the less sterically demanding QUINOX is likely to operate via a hexacoordinate neutral complex. In both pathways, only one molecule of the catalyst is involved in the rate‐ and selectivity‐determining step, which is supported by both experimental and computational data. 相似文献
7.
Václav Navrátil Dr. Vojtěch Klusák Dr. Lubomír Rulíšek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16634-16645
Activation and reaction energies for four model systems capturing the essential physicochemical features of the hydrolysis of the peptide bond have been calculated at various level of theory, including the presumably accurate CCSD(T) calculations. The models studied covered a part of the spectrum encountered in biological systems: the hydrolysis in the absence of metal ions (represented by formamide and Ala–Ala) and the hydrolysis in the presence of one and two zinc(II) ions, mimicking the active sites of mono‐ and dizinc metallopeptidases, respectively (by using thermolysin and glutamate carboxypeptidase II as the model catalytic systems and formamide as the model substrate). The results obtained using CCSD(T)/def2‐TZVP and CCSD(T)/aug‐cc‐pVTZ calculations were used as the benchmark values to which the set of cheaper methods, such as (RI‐)DFT, (RI‐)MP2, and SCS‐MP2, were referenced. It was shown that deviations of 3–5 kcal mol?1 (translating to 2–3 orders in reaction constants) with respect to the reference CCSD(T) barriers are frequently encountered for many correlated methods and most of studied DFT functionals. It has been concluded that from the set of wave‐function methods, both MP2 and SCS‐MP2 methods can be recommended for smaller models (measured by the mean absolute deviation of the activation barriers over the four systems studied), whereas among the popular DFT functionals, B3LYP and especially M06‐2X are likely to be reasonable choices for calculating the activation barriers of zinc metallopeptidases. Finally, with the model of glutamate carboxypeptidase II, issues related to the convergence of the calculated barriers with the size of the model system used as the representative of the enzyme active site were addressed. The intricacies related to system truncation are demonstrated, and suggest that the correlated wave‐function methods may suffer from problems, such as intramolecular BSSE, which make their usage for the larger system questionable. Altogether, the presented data should contribute to efforts to understand enzymatic catalysis more deeply and to gain control of the accuracy and deficiencies of the available theoretical methods and computational approaches. 相似文献
8.
An information system Xemic applicable in analytical chemistry is described and its use in capillary electrophoresis for searching suitable separation conditions is demonstrated. This system is capable to provide suitable separation conditions even for analytes for which no electrophoretic experiments have been published so far. The system works with a database of components of anionic character the analyses of which have been performed, published in reviewed scientific journals, and included into a database created by an expert. Moreover, the system learned to search also in abstracts or complete scientific articles to find articles dealing with the determination of a substance in a given sample matrix. When no experiments have been published so far for a defined substance in a specific matrix, Xemic shows the separation conditions for determination of the substance regardless of the matrix. When no response can be found for the analyte of interest at all, the system Xemic works like an expert in the field and searches chemically similar substances and offers a series of substances the physicochemical properties of which are close to the followed analyte with respect to the behavior in the electric field, and shows working conditions for their analysis. Thus, the analyst puts only the order in the form of a given analyte in a given matrix and obtains a recommendation of a separation system that should enable to perform a successful separation. The system is not rigid and enables the operator to change the importance of individual attributes used in similarity search so as to obtain a broader or narrower group of similar components. With a certain probability the analyte of interest can be successfully analyzed under separation conditions that suited for the analysis of the most similar substances in the given matrix. 相似文献
9.
The mechanism of the decomposition of acryloylcarbamates 7a–b yielding highly reactive isocyanates 3a–b was proposed based on NMR measurements and quantum chemical calculations. A good agreement between the experimental kinetic data and DFT calculations allowed us to demonstrate that the stability of 7a–d depends on the presence of methyl in the acryloyl moiety and the position of the nitro group in the nitrophenolic part of the molecule. Furthermore, the reactivity of 7a–d with weakly nucleophilic and sterically hindered 2,4,6‐tri‐tert‐butylaniline was explored by 1H NMR demonstrating the usefulness of reagents 7a–d offering access to a variety of 1‐N‐substituted uracils and thymines with potentially interesting biological properties. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
The mechanism of the copper-mediated disproportionation of aromatic imine disulfides to benzothiazoles in the gas phase is investigated by experimental and theoretical methods. Application of infrared multiphoton dissociation and hydrogen/deuterium exchange experiments combined with density functional theory (DFT) calculations of the relevant molecular structures and the associated infrared spectra allows the identification of the observed ionic intermediates. The theoretical investigation of the possible reaction pathways supported by collision-induced dissociation experiments provides a consistent mechanistic picture of the reaction catalyzed by a single copper(I) ion. Activation of the substrate proceeds via homolytic sulfur-sulfur bond cleavage, yielding metal complexes in the formal +3 oxidation state; carbon-sulfur coupling and hydrogen-atom transfer complete the transformation to the products. Exploratory studies demonstrate that in the gas phase, the disproportionation of the imine disulfide can also be mediated by other metal ions via different either homo- or heterolytic mechanisms without involving high-valent intermediates. 相似文献