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排序方式: 共有159条查询结果,搜索用时 125 毫秒
1.
Richard P. Kent IV 《Geometriae Dedicata》2004,106(1):145-159
We answer a question of J. Anderson's by producing infinitely many commensurability classes of fibered hyperbolic 3-manifolds whose fundamental groups contain subgroups that are locally free and not free. These manifolds are obtained by performing 0–surgery on a collection of knots with the same properties. 相似文献
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The main techniques for the preconcentration of elements on thin-layer filters are considered: sorption on filters with noncovalently immobilized reagents, bonded groups, and mechanically fixed sorbents and the extraction of elements on filters as poorly soluble and polymeric forms previously formed in solution. The matrix of the filters is cellulose, synthetic polymers of the linear and branched structures, synthetic fibers, reversed-phase silica gels, foamed polyurethanes, etc. The variation of the nature of the bonded group or the reagent introduced into the solution, the matrix material, and the technique for the immobilization of groups provides the preconcentration of elements with regard to the peculiarities of test materials and the method for the subsequent determination of elements. Methods for the determination of elements in different samples including preconcentration on filters are considered. 相似文献
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Pisareva A. V. Shilov G. V. Dobrovolsky Yu. A. Karelin A. I. 《Russian Journal of Coordination Chemistry》2004,30(2):137-143
The salt Rb[C6H3(COO)2(–)] · [C6H3(COOH)3] · 2H2O (I) of trimesic acid was synthesized and its thermal stability and conductivity (10–11 ohm–1 cm–1 at 298 K) were measured. Molecular and crystal structures of I were established by X-ray diffraction analysis. Hydrogen bonding system in complex I was detected by IR and Raman spectroscopies. X-ray diffraction data agree with vibration spectroscopy data. 相似文献
7.
A. V. Pisareva R. V. Pisarev A. I. Karelin Yu. A. Dobrovol’skii 《Russian Journal of Electrochemistry》2013,49(8):794-800
The dependence of proton conductivity of 2-sulfobenzoic acid trihydrate on the environmental humidity and temperature is studied. It is shown that trihydrate remains solid when exposed to atmosphere with humidity of up to 65 rel. %. The comparison of 2-sulfobenzoic acid trihydrate with bezoic acid shows that the absence of sulfo group in the benzene ring sharply lowers down the hydrophilic properties of the compound and, correspondingly, its hydration and conductivity. 相似文献
8.
Enrique Castillo Rosa Eva Pruneda MÓnica Esquivel IV 《International Journal of Mathematical Education in Science & Technology》2013,44(2):209-232
The paper presents a method for generating random linear programming problems with a previously selected type of solution. The user can choose a problem whose solution is unbounded, bounded for minima, maxima or both, unique or multiple, with given structure, at wish. Initially, the feasible solution of the LPP is generated as the sum of a linear space, a cone, and a polytope, depending on the desired properties of the solution. With the aim of obtaining a simple set of constraints, the generators of these three structures are selected as random vectors with integer simple components, the range of which can be given. Next, an objective function that satisfies the required conditions, i.e. leads to a solution of the desired type, is obtained. The generating algorithms have been implemented in Mathematica and some illustrative examples are given to clarify the generation process. With this tool, a LPP can be generated, according to the instructor requirements, where this is a human or an expert system. They can control student progress and generate a sequence of problems covering all possible cases, in steps of increasing difficulty. Combining this tool with another (also produced by the same authors) that solves the problems and explains the whole process, step by step, a computer aided module for learning LPP, which is completely autonomous, can be easily obtained. 相似文献
9.
WILLIAM T. SLAVEN IV CHAO-JUN LI YI-PING CHEN VIJAY T. JOHN SUGUNA H. RACHAKONDA 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7-8):971-980
ABSTRACT A high molecular weight poly(aryleneethynylene) (Mw ~ 60,000) is prepared by the palladium catalyzed copolymerization of 3,5-diiodobenzoic acid and acetylene gas in a basic aqueous medium. The polymer has a “zig-zag”, fully conjugated backbone. The polymer has been characterized by a variety of methods and exhibits high thermal stability. Furthermore, the polymer is readily soluble in aqueous base and is reversibly switchable from the solution state to a hydrogel state, in water, by changing the pH of the solvent. 相似文献
10.
L. V. Shmygleva A. V. Pisareva R. V. Pisarev A. E. Ukshe Yu. A. Dobrovol’skii 《Russian Journal of Electrochemistry》2013,49(8):801-806
The proton conductivity of hydrates of calix[4]arene-para-sulfonic acids is studied. The high proton conductivity is observed at ambient temperatures in the wide ranges of environmental humidity and, correspondingly, water content in the hydrate. For the air humidity of 10 rel. %, the conductivity of compounds is 10?4-10?3 S cm?1 and approaches 10?2-10?1 S cm?1 as the humidity increases up to 70 rel. %. 相似文献