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排序方式: 共有456条查询结果,搜索用时 15 毫秒
1.
Eduard Feireisl Antonín Novotný Hana Petzeltov 《Mathematical Methods in the Applied Sciences》2002,25(12):1045-1073
We prove a general compactness result for the solution set of the compressible Navier–Stokes equations with respect to the variation of the underlying spatial domain. Among various corollaries, we then prove a general existence theorem for the system in question with no restrictions on smoothness of the spatial domain. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
Hana Macková Daniela Králová Daniel Horák 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5884-5898
The aim of this study was to develop novel thermally responsive polymer microspheres with magnetic properties. Dispersion and inverse emulsion copolymerization of N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm) was investigated in the presence of γ‐Fe2O3 nanoparticles. The resulting microspheres were characterized in terms of morphology, size, polydispersity, iron content, and temperature‐dependent swelling using optical microscopy, transmission electron microscopy, scanning electron microscopy, QELS, and AAS. The effects of several variables, such as the concentration of γ‐Fe2O3, MBAAm crosslinking agent, Span 80 surfactant, 2,2′‐azobis(2‐methyloctanenitrile) (AMON) initiator, and polymerization temperature on the properties of the microspheres were studied. Swelling and thermoresponsive behavior of the microspheres containing γ‐Fe2O3 nanoparticles were also investigated. The microspheres contained about 8 wt % of iron. The presence of magnetic nanoparticles and their concentration changes did not have any significant effect on the temperature sensitivity of the composites. The particles gradually shrink into an increasingly collapsed state when the temperature is raised to 40 °C since the increase in temperature weakens the hydration and PNIPAAm chains gradually become more hydrophobic, which leads to the collapse of the particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5884–5898, 2007 相似文献
3.
We study algebraic geometric codes obtained from rational normal scrolls. We determine the complete weight hierarchy and spectrum
of these codes.
相似文献
4.
A simple microscopic model of charge ordering in the NaxCoO2 system is presented. The model takes into account the interplane interactions between the ordered Na ions and d electrons from the CoO2 layers as well as the nearest-neighbor intraplane Coulomb interactions between d electrons. It is shown that a driving force of charge ordering in the CoO2 layers is the interplane interaction that alone is able to describe various types of inhomogeneous charge ordering (e.g., the striped phases) as well as to predict correctly the conducting properties of the system. 相似文献
5.
In this contribution, the on-line coupling of solid phase extraction (SPE), based on a restricted-access material (RAM), with sequential injection technique (SIA) for the analysis of biological samples, is described. The SIA-RAM system was tested with a new potential antileucotrienic drug (VUFB-19363 (Quinlukast)) for serum analysis. The method is based on SPE with the novel internal-surface reversed-phase column packing material-alkyl-diol silica (ADS). The supports tolerate direct and repetitive injection of proteinaceous fluids (plasma, serum) and allow reversed-phase partitioning at the internal surface. A column packed with a 25 microm C18 alkyl-diol support was used for direct serum injection. Using a 6-port selection valve and the system of three mobile phases, the polar matrix compounds and metabolites are removed by sequentially aspirated mobile phases with lower content of the organic part (methanol-water (2:98) and following acetonitrile-water (20:80)) to the waste, and then, the analyte enriched on the column is eluted by a strong mobile phase (acetonitrile-methanol-water (40:20:40)) to the UV detector without transfer loss. With the fully automated SIA system, a total analysis time of less than 10 min was achieved. The only off-line sample pre-treatment step required to remove particulate matter was centrifugation. The studies showed a range of linearity (2-40 microg ml(-1)) and a high recovery (93.6-96.8%) of drug from the biological matrix with coefficients of variation (RSD) less than 5.0% (n = 6). This paper introduces a new, simple and robust analytical technique suitable for screening determination and direct analysis of drugs in biological materials. 相似文献
6.
Bernatkova M Dvorakova H Andrioletti B Kral V Bour P 《The journal of physical chemistry. A》2005,109(24):5518-5526
Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and transitions studied with temperature-dependent NMR spectroscopy. On the basis of density functional computations, several conformer species could be identified and observed changes in chemical shifts explained. In some compounds, the aryl group rotation and porphyrin ring flipping could be monitored independently, as their NMR coalescence temperatures were well-separated. Calculated relative conformer energies, transition barriers, and isotropic shieldings agree well with the experimental data. In the meso-substituted porhyrins (calixphyrins) the sp3 carbon atoms perturb their pi-electron system and significantly modify the molecular shape and the flexibility. Even when the conjugation of the pi-electron system was destroyed by the nonplanarity, far-range electronic induction effects still exist and influence chemical shielding and molecular geometry. The aryl functional groups moderately modify the structure of the calixphyrin ring and thus can be used for fine-tuning of the mechanical and chemical properties of these compounds. 相似文献
7.
The method of capillary isotachophoresis with conductivity detection was applied for the determination of the physico-chemical characteristics (conditional stability constants log beta') of holmium and yttrium complexes with DTPA (diethylenetriaminepentaacetic acid) and DOTA (1,4,7,10-tetraazadodecane-N,N',N',N'-tetraacetic acid). The log beta' determination is based on the linear relation between the stability constants of lanthanide-DTPA (lanthanide-DOTA) complexes and the reduction of the zone of the complex owing to the bleeding phenomena (liberating free metal ion). The stability constants calculated using this relationship are comparable with the literary data obtained by other methods for both holmium (log beta'(Ho-DTPA)=21.9, log beta'(Ho-DOTA)=24.5) and yttrium complexes (log beta'(Y-DTPA)=21.2, log beta'(Y-DOTA)=24.4). Capillary isotachophoresis was applied for the determination of the optimum composition of the reaction mixture (metal:ligand ratio) as well. 相似文献
8.
The preparation of an array of benzimidazoles and benzothiazoles from polymer-bound esters is described. Polymer-bound esters were treated with 2-aminothiophenols or 1,2-phenylenediamines in the presence of a Lewis acid to afford the corresponding benzothiazole or benzimidazole cleavage products. The reaction of 2-aminophenols with the polymer-bound esters failed to give the desired benzoxazole products using this procedure. 相似文献
9.
An electrochemical method for the determination of the ionophores monensin and lasalocid was developed, based on the polarization of an agar gel/nitrobenzene electrolyte interface. The measured current corresponding to the facilitated ion transfer across this interface is directly proportional to the concentration of an ionophore dissolved in the organic phase. Using cyclic voltammetry in a three-electrode system the detection limit for both ionophores is about 3 × 10?5 M. 相似文献
10.
Pavel Jano Hana Chromá Vlastimil Kubá 《Fresenius' Journal of Analytical Chemistry》1996,355(2):135-140
Separations of metal cations on a column packed with the strongly acidic cation exchanger Separon SGX CX were investigated in the presence of -hydroxyisobutyric acid (HIBA) in the mobile phase. A retention model based on the general theory of side equilibria was elaborated and relations describing dependences of capacity factors of analytes on the compositon of the mobile phase were derived. Effects of HIBA concentration and pH of the mobile phase on the analyte retention were studied in detail. Stability constants of divalent metal cations (Cd2+, Co2+, Mn2+, Ni2+ and Zn2+) with HIBA were calculated from the experimental dependences of the reciprocal values of capacity factors on the ligand concentration. 相似文献