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排序方式: 共有171条查询结果,搜索用时 15 毫秒
1.
K. Holmåker 《Journal of Optimization Theory and Applications》1991,71(2):205-235
Some optimization problems concerning a substrate in a fluid are considered. The concentration of the substrate is affected by diffusion, convection, and elimination by enzymes, and the problem is to find the optimal distribution of enzymes. In this paper, the rate of elimination and the transmission coefficient are optimized. Mathematically, these problems are optimal control problems, and they are analyzed by means of Pontryagin's maximum principle. 相似文献
2.
Volkmer D Bredenkötter B Tellenbröker J Kögerler P Kurth DG Lehmann P Schnablegger H Schwahn D Piepenbrink M Krebs B 《Journal of the American Chemical Society》2002,124(35):10489-10496
Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins. 相似文献
3.
4.
Janina Möker Ursula Salge-Bartels Joachim Thiem 《Journal of carbohydrate chemistry》2013,32(9):702-710
Syntheses of carbohydrate-functionalized platinum complexes resembling presently employed cytostatics were performed. Mono-allylated sugar substrates obtained in two steps from glucose and galactose were connected with 2-allyl diethyl malonate by cross-metathesis. Following hydrogenation and acidic cleavage of the ester and alkylidene functionalities gave dicarboxylated glycoconjugates, which were transformed into their diammine platinum complexes. The antitumor activities of these platinum complexes were checked by sensitivity testing with 11 lung cancer cell lines. The novel glucose-platinum complex proved to be comparable to the drug carboplatin. 相似文献
5.
Anna Rabe Julia Büker Dr. Soma Salamon Adarsh Koul Dr. Ulrich Hagemann Dr. Joachim Landers Dr. Klaus Friedel Ortega Dr. Baoxiang Peng Prof. Dr. Martin Muhler Prof. Dr. Heiko Wende Prof. Dr. Wolfgang Schuhmann Prof. Dr. Malte Behrens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17038-17048
By using the crystalline precursor decomposition approach and direct co-precipitation the composition and mesostructure of cobalt-based spinels can be controlled. A systematic substitution of cobalt with redox-active iron and redox-inactive magnesium and aluminum in a cobalt spinel with anisotropic particle morphology with a preferred 111 surface termination is presented, resulting in a substitution series including Co3O4, MgCo2O4, Co2FeO4, Co2AlO4 and CoFe2O4. The role of redox pairs in the spinels is investigated in chemical water oxidation by using ceric ammonium nitrate (CAN test), electrochemical oxygen evolution reaction (OER) and H2O2 decomposition. Studying the effect of dominant surface termination, isotropic Co3O4 and CoFe2O4 catalysts with more or less spherical particles are compared to their anisotropic analogues. For CAN-test and OER, Co3+ plays the major role for high activity. In H2O2 decomposition, Co2+ reveals itself to be of major importance. Redox active cations in the structure enhance the catalytic activity in all reactions. A benefit of a predominant 111 surface termination depends on the cobalt oxidation state in the as-prepared catalysts and the investigated reaction. 相似文献
6.
Determination of conditional stability constants for some divalent transition metal ion‐EDTA complexes by electrospray ionization mass spectrometry 下载免费PDF全文
Susanne Boija Ann Almesåker Erik Hedenström Dan Bylund Håkan Edlund Magnus Norgren 《Journal of mass spectrometry : JMS》2014,49(7):550-556
Conditional stability constants of coordination complexes comprising divalent transition metals, Cu2+, Ni2+, Zn2+, Co2+, and ethylenediaminetetraacetic acid (EDTA) were determined utilizing electrospray ionization mass spectrometry. The deviation of signal response of a reference complex was monitored at addition of a second metal ion. The conditional stability constant for the competing metal was then determined through solution equilibria equations. The method showed to be applicable to a system where Co2+ and Zn2+ competed for EDTA at pH 5. When Cu2+ and Ni2+ competed for EDTA, the equilibrium changed over time. This change was shown to be affected in rate and size by the type of organic solvent added. In this work, 30% of either methanol or acetonitrile was used. It was found that if calibration curves are prepared for both metal complexes in solution and the measurements are repeated with sufficient time space, any change in equilibrium of sample solutions will be discovered. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
Böker A Elbs H Hänsel H Knoll A Ludwigs S Zettl H Urban V Abetz V Müller AH Krausch G 《Physical review letters》2002,89(13):135502
We investigate the microscopic mechanisms responsible for microdomain alignment in block copolymer solutions exposed to an electric field. Using time-resolved synchrotron small-angle x-ray scattering, we reveal two distinct processes, i.e., grain boundary migration and rotation of entire grains, as the two dominant microscopic mechanisms. The former dominates in weakly segregating systems, while the latter is predominant in strongly segregated systems. The kinetics of the processes are followed as a function of polymer concentration and temperature and are correlated to the solution viscosity. 相似文献
8.
Abulencia A Acosta D Adelman J Affolder T Akimoto T Albrow MG Ambrose D Amerio S Amidei D Anastassov A Anikeev K Annovi A Antos J Aoki M Apollinari G Arguin JF Arisawa T Artikov A Ashmanskas W Attal A Azfar F Azzi-Bacchetta P Azzurri P Bacchetta N Bachacou H Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Bartsch V Bauer G Bedeschi F Behari S Belforte S Bellettini G Bellinger J Belloni A Ben-Haim E Benjamin D Beretvas A Beringer J Berry T Bhatti A Binkley M Bisello D Bishai M 《Physical review letters》2005,95(22):221805
We report on a search for B0(s) --> mu+ mu- and B0(d) --> mu + mu- decays in pp collisions at square root(s) = 1.96 TeV using 364 pb(-1) of data collected by the CDF II detector at the Fermilab Tevatron Collider. After applying all selection requirements, we observe no candidates inside the B0(s) or B0(d) mass windows. The resulting upper limits on the branching fractions are B(B0(s) --> mu+ mu-) < 1.5 x 10(-7) and B(B0(d) --> mu+ mu-) < 3.9 x 10(-8) at 90% confidence level. 相似文献
9.
Schlosser M Marzi E Cottet F Büker HH Nibbering NM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(16):3511-3516
The deprotonation energies of benzene, chlorobenzene, all di-, tri-, tetrachlorobenzenes, and pentachlorobenzene have been determined in the gas phase using a Fourier transform ion cyclotron resonance mass spectrometer. The values measured differ only slightly, though significantly, from the corresponding data for oligofluorobenzenes. The heavier halogen acidifies orthopositions slightly less and meta-positions slightly more than fluorine does. Moreover, the contributions of three or more chloro substituents are not perfectly additive. In fact the accumulation attenuates the contributions somewhat. Quantum chemical calculations at the MP2/6-311+G* level reproduce the gas-phase acidities fairly well, but reveal special effects when extended to experimentally not observable benzenides carrying the halogens at anion-remote positions. Competition experiments have been performed to assess the relative reactivity of nine oligochlorobenzenes towards sec-butyllithium in tetrahydrofuran at -100 degrees C. An almost exact linear correlation between logarithmic rates and gas-phase acidities has been found. 相似文献
10.
Cationic polyallylamine (PAH), was adsorbed onto lignocellulosic fibres, and a fluorescent label on the polyelectrolyte enabled
its location to be shown by confocal fluorescence microscopy. The adsorption time and ionic strength were varied to study
their effect on the localisation of the adsorbed PAH. The microscopy showed that a long adsorption time, 24 h, and a high
ionic strength, 10−1 M NaCl + 5 × 10−3 M NaHCO3 or higher, resulted in the adsorption of polyallylamine throughout the fibre walls. Shorter adsorption times and/or lower
ionic strength resulted in adsorption only to the fibre exterior. By preparing sheets from fibres with polyelectrolyte adsorbed
either to the exterior parts or into the fibre cell wall and testing their mechanical behaviour, a link was established between
the localisation of adsorbed polyelectrolyte and the mechanical properties. Adsorption to the fibre exterior led to an increase
in tensile strength and strain at break. The creep deformation at 90%RH was also slightly reduced by the adsorption of low
molecular weight PAH (15 kDa). When polyallylamine was adsorbed throughout the wall of the lignocellulosic fibres, the mechanical
properties were not however improved and the creep deformation at 90%RH actually increased somewhat. 相似文献