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排序方式: 共有1546条查询结果,搜索用时 31 毫秒
21.
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23.
We study a class of quasilinear elliptic equations on the unit ball of ℝ
n
in the divergence form ∑
j=1
n
D
j{G(|x|2,|Du|2)D
j
u} =H(|x|) and get estimates on the boundary by using a modified barrier-function technique of Bernstein. We establish a maximum principle
for the gradients of solutions and get a global gradient estimate. We prove that solutions with constant boundary condition
must be radial. Finally, we apply these results to graphs {(x,u(x)):x∈H
n
} whereu:H
n
→ℝ is a smooth map of then-hyperbolic spaceH
n
=B(0,1) with the metric
to get the existence of graphs with radial prescribed mean curvature. 相似文献
24.
Strachan JD Adler H Alling P Ancher C Anderson H Anderson JL Ashcroft D Barnes CW Barnes G Batha S Bell MG Bell R Bitter M Blanchard W Bretz NL Budny R Bush CE Camp R Caorlin M Cauffman S Chang Z Cheng CZ Collins J Coward G Darrow DS DeLooper J Duong H Dudek L Durst R Efthimion PC Ernst D Fisher R Fonck RJ Fredrickson E Fromm N Fu GY Furth HP Gentile C Gorelenkov N Grek B Grisham LR Hammett G Hanson GR Hawryluk RJ Heidbrink W Herrmann HW Hill KW Hosea J Hsuan H Janos A Jassby DL Jobes FC 《Physical review letters》1994,72(22):3526-3529
25.
掺杂镨的纳米二氧化钛光催化降解2,4-二硝基苯酚的研究 总被引:1,自引:0,他引:1
以钛酸丁酯为原料,用溶胶-凝胶(sol-gel)法制备了掺杂镨的纳米TiO2粉末.采用X光衍射仪对粉体的物相进行了表征.样品经500 ℃焙烧2 h后,0.5%(摩尔分数)Pr3+-TiO2纳米粉末为单一的锐钛型结构.通过粉体对2,4-二硝基苯酚的降解情况对其光催化活性进行了测试,结果表明与纯TiO2相比,Pr3+-TiO2的光催化活性有较大提高,当Pr3+的掺入量为0.5%(摩尔分数)时催化活性最高.以高压汞灯为光源,2,4-二硝基苯酚的初始浓度为50 mg·L-1,催化剂0.5%(摩尔分数)Pr3+-TiO2投加量为1.0 g·L-1时,2,4-二硝基苯酚的光催化降解效果最好. 相似文献
26.
Spectroscopic analysis, thermogravimetric analysis, and crossover experiments performed on a series of imidazolium carboxylates revealed carboxylation was reversible with N-aryl substituted adducts. 相似文献
27.
M. Veber K.N.V. Duong F. Gaudemer A. Gaudemer 《Journal of organometallic chemistry》1979,177(1):231-237
Allylcobaloximes react under very mild conditions with ethyl bromomalonate to yield allyl-substituted ethylmalonates in good yield. In the case of crotyl-, 3,3 dimethyl, allyl- and cinnamyl-cobaloximes, the substitution occurs with total rearrangement of the allyl groups. Similar rearrangements are observed during the reactions of propargyl- and allenylcobaloximes with BrCH(CO2Et)2 yielding allenyl- and propargyl-malonic esters respectively. 相似文献
28.
Zeta-potentials of self-assembled surface micelles of ionic surfactants adsorbed at hydrophobic graphite surfaces 总被引:1,自引:0,他引:1
Vamsi K. Paruchuri Anh V. Nguyen Jan D. Miller 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):519-526
The zeta-potentials of the self-assembled surface ionic surfactants (sodium dodecyl sulfate—SDS and hexadecyltrimethyl ammonium bromide—CTAB) on graphite surfaces were determined both from streaming potential and electrophoretic mobility measurements. The adsorption of the surfactants at graphite–liquid interfaces has been studied using atomic force microscopy (AFM) soft-contact imaging which shows the formation of linear, parallel hemicylinders with headgroups oriented towards the solution. The magnitude of the zeta-potential increased with an increase in surfactant concentration, reaching a constant value at a concentration corresponding to the point of surface micelle formation as confirmed from AFM imaging. The streaming potential and electrophoretic mobility measurements showed that the zeta-potentials of SDS and CTAB surface micelles adsorbed at the graphite surface were about −75 and +70 mV, respectively, well in agreement with the values reported for bulk phase micelles in the literature. 相似文献
29.
S V Dzyadevych T Mai Anh A P Soldatkin N Duc Chien N Jaffrezic-Renault J-M Chovelon 《Bioelectrochemistry (Amsterdam, Netherlands)》2002,55(1-2):79-81
This article describes a biosensor based on pH-sensitive field-effect transistors (pH-FETs) as transducer, and immobilised enzyme tyrosinase as biorecognition element, which was used for the determination of phenolic compounds in water solutions. The biologically active membrane was formed by cross-linking of tyrosinase with bovine serum albumin (BSA) in saturated glutaraldehyde (GA) vapours on the sensitive transducer surface. The main analytical characteristics were studied under different conditions as well as the possibility to optimise these working parameters. Different factors such as the pH of immobilisation, the enzyme loading, the time of exposition to glutaraldehyde vapours were investigated in regards to the influence on sensitivity, limit of detection, dynamic range, and operational and storage stability. 相似文献
30.
Johansson A Abrahamsson M Magnuson A Huang P Mårtensson J Styring S Hammarström L Sun L Akermark B 《Inorganic chemistry》2003,42(23):7502-7511
The preparation of donor (D)-photosensitizer (S) arrays, consisting of a manganese complex as D and a ruthenium tris(bipyridyl) complex as S has been pursued. Two new ruthenium complexes containing coordinating sites for one (2a) and two manganese ions (3a) were prepared in order to provide models for the donor side of photosystem II in green plants. The manganese coordinating site consists of bridging and terminal phenolate as well as terminal pyridyl ligands. The corresponding ruthenium-manganese complexes, a manganese monomer 2b and dimer 3b, were obtained. For the dimer 3b, our data suggest that intramolecular electron transfer from manganese to photogenerated ruthenium(III) is fast, k(ET) > 5 x 10(7) s(-)(1). 相似文献