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21.
22.
Carmen Racles Viorica Gaina Mihai Marcu Maria Cazacu Mihaela Simionescu 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):1605-1617
Abstract Organofunctional siloxane oligomers containing maleimide were synthesized by condensation reaction of α. ω-hydroxypropylsiloxane oligomers with n-[4-(chlorocarbonyl)phenyl]maleimide. A model compound [bis(maleimide-ester)disiloxane] was obtained to facilitate the characerization of the oligomers. Then, the heterogeneous catalyzed ring-opening cationic polymerization technique was applied to obtain an oligomer starting from the model compound and octamethylcyclotetrasiloxane. The structures of the resulting oligomers were confirmed by elemental analysis, IR and 1H-NMR spectroscopy. They were characterized by determining softening points, solubility and studying their thermal behavior by thermogravimetric (TGA and differential scanning calorimetry (DSC) measurements. 相似文献
23.
24.
Optimal control of linear stochastic evolution equations in Hilbert spaces and uniform observability
Viorica Mariela Ungureanu 《Czechoslovak Mathematical Journal》2009,59(2):317-342
In this paper we study the existence of the optimal (minimizing) control for a tracking problem, as well as a quadratic cost
problem subject to linear stochastic evolution equations with unbounded coefficients in the drift. The backward differential
Riccati equation (BDRE) associated with these problems (see [2], for finite dimensional stochastic equations or [21], for
infinite dimensional equations with bounded coefficients) is in general different from the conventional BDRE (see [10], [18]).
Under stabilizability and uniform observability conditions and assuming that the control weight-costs are uniformly positive,
we establish that BDRE has a unique, uniformly positive, bounded on ℝ + and stabilizing solution. Using this result we find the optimal control and the optimal cost. It is known [18] that uniform
observability does not imply detectability and consequently our results are different from those obtained under detectability
conditions (see [10]).
相似文献
25.
Pârvulescu VI Pârvulescu V Endruschat U Filoti G Wagner FE Kübel C Richards R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(8):2343-2357
Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au colloids, and pure Pd and Au colloids stabilized with tetraalkylammonium bromide following a modified sol-gel procedure with tetrahydrofuran (THF) as the solvent. Tetraethoxysilicate (TEOS) was used as the precursor for the silica support. The molar composition of the sol was TEOS/THF/H2O/HCl = 1:3.5:4:0.05 for the bimetallic Pd-Au and TEOS/THF/H2O/HCl = 1:4.5:4:0.02 for Pd and Au monometallic systems. After refluxing, the colloid was added as a 4.5 wt % solution in THF for Pd-Au, 10.2 wt % solution in THF for Pd and 8.4 wt % solution in THF for Au at room temperature. The gelation was carried out with vigorous stirring (4 days) under an Ar atmosphere. Following these procedures, bimetallic Pd-Au-SiO2 catalysts with 0.6 and 1 wt % metal, and monometallic Pd- and Au-SiO2 catalysts with 1 wt % metal were prepared. These materials were further treated following four different routes: 1) by simple drying, 2) in which the dried catalysts were calcined in air at 723 K and then reduced at the same temperature, 3) in which they were directly reduced in hydrogen at 723 K, and 4) in which the surfactant was extracted using an ethanol-heptane azeotropic mixture. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption measurements, solid-state 1H, 13C, 29Si-CP/MAS-NMR spectroscopy, powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and 197Au M?ssbauer spectroscopy. The physical characterization by a combination of these techniques has shown that the size and the structural characteristics of the Pd-Au colloid precursor are preserved when embedded in an SiO2 matrix. Catalytic tests were carried out in selective hydrogenation of 3-hexyn-1-ol, cinnamaldehyde, and styrene. These data showed evidence that alloying Pd with Au in bimetallic colloids leads to enhanced activity and most importantly to improved selectivity. Also, the combination of the two metals resulted in catalysts that were very stable against poisoning, as was evidenced for the hydrogenation of styrene in the presence of thiophene. 相似文献
26.
This paper describes an analytical method for the determination of ceruloplasmin (Cp) in human serum. The method uses immunoaffinity
chromatography and size-exclusion chromatography (SEC) to “purify” the serum sample prior to analysis of 63Cu and 65Cu by inductively-coupled plasma mass spectrometry (ICPMS). By removing the six most abundant proteins from serum with immunoaffinity
chromatography and by using SEC to separate Cu bound by Cp from any free Cu that might be present in the serum sample, we
demonstrated that SEC-ICPMS can accurately and reproducibly measure Cp in the ERM DA470 reference serum. Cp identification
is based on retention time match of the unknown in the serum sample with the Cp external standard and the presence of 63Cu and 65Cu at a ratio of 2.2±0.1. This method was used to analyze a reference serum certified for Cp, 47 serum samples from four different
diseases and a set of normal controls. The reference serum and a serum sample from a patient with myocardial infarction, as
well as a Cp standard, were also analyzed by electrospray mass spectrometry to confirm the presence of Cp in the SEC fraction
known to contain 63Cu. 相似文献
27.
Dumitru Motreanu Viorica V. Motreanu Nikolaos S. Papageorgiou 《Monatshefte für Mathematik》2010,159(1-2):59-80
First we prove the existence of a nontrivial smooth solution for a p-Laplacian equation with a (p ? 1)-linear nonlinearity and a noncoercive Euler functional, under hypotheses including resonant problems with respect to the principal eigenvalue of ${(-{\it \Delta}_p,\,W^{1,p}_0(Z))}$ . Then, for the semilinear problem (i.e., p = 2), assuming nonuniform nonresonance at infinity and zero, we prove a multiplicity theorem which provides the existence of at least three nontrivial solutions, two being of opposite constant sign. Our approach combines minimax techniques with Morse theory and truncation arguments. 相似文献
28.
In the selective process of the syngas conversion to synthetic gasoline a bifunctional catalytic system has to be used. It
was obtained by combination a Fischer-Tropsch catalyst with the HZSM-5 zeolite. The phase compositions of the precursor and
the fresh catalyst were established as well as the optimum thermal treatment. The catalyst was reduced in pure H2 or in a H2+CO mixture. The influence of the reduction and reaction conditions on the catalyst structure was investigated. 相似文献
29.
A method for the determination of total selenium in wheat and wheat flour using graphite furnace atomic absorption spectrometry (GFAAS) with palladium/ascorbic acid as a chemical modifier was studied. The effects of nickel nitrate, palladium/ascorbic acid, and palladium/magnesium nitrate as chemical modifiers on the sensitivity in the determination of selenite, selenate and selenomethionine by GFAAS were compared. The palladium/ascorbic acid modifier was used for the determination of total selenium in wheat and wheat flour, because the oxidation states of the selenium ion are not important in the determination. The detection limit was estimated to be 1 microg L(-1) (calculated as 3sigma of the blank); the calibration curve was linear for the concentration range 5 - 50 microg L(-1) and the recovery range was 96.66 - 101.80%. The optimal ashing and atomizing temperatures were 1300 degrees C and 2250 degrees C, respectively. The proposed method was successfully applied to the determination of total selenium in wheat and wheat flour. 相似文献
30.
Nicusor Fifere Anton Airinei Constantin Gaina Viorica Gaina Mircea Grigoras 《Journal of fluorescence》2014,24(2):345-353
A fluorophore-photochrome system incorporating an aryleneimine type fluorophore and an azobismaleimide photochrome was developed and the photochemical properties of this system were investigated. The photoisomerization of trans-azoaromatic chromophore leads to the increase of the fluorescence intensity of fluorophore. The cis azobismaleimide isomers revert photochemically to the trans form and the emission intensity decreases. The fluorescence intensity of the imine fluorophore can be modulated under irradiation with UV and visible (436 nm) light due to reversible trans-cis-trans photoisomerization of azobismaleimide partner. The photoisomerization kinetics was obeyed a first-order relationship with a rate constant of 1.95?×?10?2 s?1 for azobismaleimide/imine fluorophore system and for polyazothioetherimide/imine derivative the kinetics was described by a biexponential equation. 相似文献