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排序方式: 共有1218条查询结果,搜索用时 28 毫秒
121.
Dr. Georgian Melinte Dr. Veselina Georgieva Dr. Marie‐Anne Springuel‐Huet Dr. Andreï Nossov Prof. Ovidiu Ersen Dr. Flavien Guenneau Prof. Antoine Gedeon Dr. Ana Palčić Dr. Krassimir N. Bozhilov Dr. Cuong Pham‐Huu Prof. Shilun Qiu Dr. Svetlana Mintova Dr. Valentin Valtchev 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18316-18327
The principle aspects and constraints of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na‐rich aluminosilicate system. A detailed time‐series EMT‐type zeolite crystallization study in the model hydrogel system was performed to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods was employed to analyze the gel evolution and complement the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core–shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of the gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels. 相似文献
122.
We present an abstract characterization of various types of Menger algebras of n-place functions allowing certain permutations of variables. 相似文献
123.
124.
The enthalpies of solution of dl-α-alanyl-dl-α-asparagine (AlaAsn) were measured in aqueous methanol, ethanol, 1-propanol and 2-propanol with an alcohol mole-fraction content x2 (from 0 to 0.4) at 298.15 K. The experimental results were used to calculate the enthalpies of transfer of AlaAsn from water to these mixtures as well as the enthalpy coefficients of pair-wise interactions (hxy) between AlaAsn and alcohol molecules in water, according to the McMillan–Mayer's model. The hxy values were found to be positive and increasing in a series methanol < ethanol < 1-propanol < 2-propanol. 相似文献
125.
Valentin Goujard Jean-Michel Tatibouët Catherine Batiot-Dupeyrat 《Plasma Chemistry and Plasma Processing》2011,31(2):315-325
The carbon dioxide reforming of methane to synthesis gas was investigated in a dielectric barrier discharge reactor at room
temperature. The influence of dilution of reactants by helium was studied. We showed that, at a fixed contact time, the conversions
of CH4 and CO2 increase when the amount of helium in the gas mixture increases. This result is attributed to the “penning ionization” phenomenon,
which corresponds to an energy transfer from excited He to molecules in ground state (CH4, CO2). The selectivity to products is affected by the dilution factor. As soon as helium is present in a large amount the formation
of products resulting from recombination of methyl radicals (such as C2, C3 and C4) is less favourable due to the lowest probability of collisions to proceed. A kinetic model is proposed based on the assumption
that the reactant molecules CH4 or CO2 are attacked by active species produced by the plasma discharges, and the production of this active species are function
of the plasma power. This model which takes into account the dilution by helium fits particularly well the experimental data
we obtained. 相似文献
126.
Roberts VM Stein V Reiner T Lemonidou A Li X Lercher JA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(21):5939-5948
The products of base-catalyzed liquid-phase hydrolysis of lignin depend markedly on the operating conditions. By varying temperature, pressure, catalyst concentration, and residence time, the yield of monomers and oligomers from depolymerized lignin can be adjusted. It is shown that monomers of phenolic derivatives are the only primary products of base-catalyzed hydrolysis and that oligomers form as secondary products. Oligomerization and polymerization of these highly reactive products, however, limit the amount of obtainable product oil containing low-molecular-weight phenolic products. Therefore, inhibition of concurrent oligomerization and polymerization reactions during hydrothermal lignin depolymerization is important to enhance product yields. Applying boric acid as a capping agent to suppress addition and condensation reactions of initially formed products is presented as a successful approach in this direction. Combination of base-catalyzed lignin hydrolysis with addition of boric acid protecting agent shifts the product distribution to lower molecular weight compounds and increases product yields beyond 85%. 相似文献
127.
Cathodic stripping mechanism of an insoluble salt coupled with a homogenous chemical reaction is considered both theoretically and experimentally under conditions of square‐wave voltammetry. For the mercury electrode in aqueous solution, the electrode reaction is described as L(aq)+Hg(l)=HgL(s)+2e?, where L(aq) is the reactive ligand that forms a sparingly soluble compound HgL(s). The electrode reaction is coupled with a homogenous, first‐order chemical reaction, A(aq)=L(aq). Theoretical predictions are confirmed by experiments with 6‐mercaptopurine‐9‐D‐riboside in the presence of nickel(II) ions. 相似文献
128.
Mani L Petek S Valentin A Chevalley S Folcher E Aalbersberg W Debitus C 《Natural product research》2011,25(20):1923-1930
The compound haliclonacyclamine A was isolated from the Haliclona sponge at Solomon Islands. It acts as a powerful in?vitro and in?vivo anti-plasmodial agent against the chloroquine-resistant Plasmodium falciparum strain FCB1and Plasmodium vinckei petteri-infected mice, respectively. 相似文献
129.
Silvestro L Gheorghe M Iordachescu A Ciuca V Tudoroniu A Rizea Savu S Tarcomnicu I 《Analytical and bioanalytical chemistry》2011,401(3):1023-1034
A new sensitive and fast quantitative analytical method for the simultaneous determination of clopidogrel, its main metabolite
clopidogrel carboxylic acid, and the newly described acyl glucuronide metabolite, in human plasma samples, is presented. The
analytical procedures (plasma storage, handling, and extract storage in the autosampler) were optimized in order to avoid
back-conversion; a known drawback in measurements of clopidogrel. Clopidogrel acyl glucuronide was confirmed as a major source
of back-conversion to the parent drug in the presence of methanol, and thorough stability experiments were carried out to
find the most appropriate conditions for an accurate analysis of clopidogrel and the two metabolites. The method was validated
by assessing selectivity, sensitivity, linearity, accuracy, and precision for all three analytes, in accordance to Food and
Drug Administration guidelines. Spiked quality controls in plasma as well as incurred samples were used to verify back-conversion
in the selected conditions, with results meeting European Medicines Agency acceptance criteria (concentrations within 80–120%
of the first reading). The method was then applied to a pharmacokinetic study, and for the first time, a pharmacokinetic curve
of clopidogrel acyl glucuronide in human plasma is presented. The concentrations ranged up to 1,048.684 ng/mL, with a mean
of 470.268 ng/mL, while clopidogrel had a mean C
max of 1.348 ng/mL; these orders of magnitude show how much the back-conversion of this metabolite may influence clopidogrel
quantification if it is not properly controlled. 相似文献
130.
Consider a multidimensional stochastic differential equation of the form Xt=x+ò0tb(Xs-) ds+ò0tf(Xs-) dZsX_{t}=x+\int_{0}^{t}b(X_{s-})\,ds+\int_{0}^{t}f(X_{s-})\,dZ_{s}, where (Z
s
)
s≥0 is a symmetric stable process. Under suitable assumptions on the coefficients, the unique strong solution of the above equation
admits a density with respect to Lebesgue measure, and so does its Euler scheme. Using a parametrix approach, we derive an
error expansion with respect to the time step for the difference of these densities. 相似文献