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91.
Preparation and Spectroscopic Characterization of Carboxylatododecaborates The tetrabutylammonium salt (TBA)2[B12H12]2? reacts with formic, acetic, cyanoacetic, phenylacetic, propionic, butyric, and thioacetic acid at temperatures between 80 and 150°C forming the carboxylatododecaborates [(RC(O)O)n? B12H12? n]2?, n = 1, 2, [CH3C(O)S? B12H11]2?. The isolation of the pure compounds is achieved by ion exchange chromatography on diethylaminoethyl cellulose. In case of the dicarboxylatododecaborates beside the 1,7-isomer predominantly the 1,2-isomer, while 1,2-[(OH)C6H5CH2C(O)O? B12H10]2? is formed exclusively. The alcaline hydrolysis of [RC(O)O? B12H11]2? and 1,2-[(OH)C6H5CH2C(O)O? B12H10]2? results in [(OH)? B12H11]2? and 1,2-[(OH)2? B12H10]2?. All compounds are characterized by their 11B-nmr, 13C-nmr and IR spectra. The 11B-nmr signals are assigned by a sheme allowing to establish expected spectra. 相似文献
92.
研究了利用源内碰撞诱导解离(in-source collision—induced dissociation)的高效液相色谱-大气压化学电离质谱(HPLC—APCI/MS)获取人参和西洋参的化学标志物——人参皂甙Rf和拟人参皂甙F11的特征结构信息及鉴别人参和西洋参的方法。在乙腈-水梯度洗脱反相液相色谱及源内碰撞诱导解离条件下,能获得人参皂甙Rf和拟人参皂甙F11的母核离子及去糖基离子的源内碰撞诱导解离谱,从其差别能清楚区分这对同分异构体。本方法对人参皂甙Rf和拟人参皂甙F11的检出限能达到10^-7g柱上样量,简单、快速,单次质谱实验就能鉴别人参和西洋参。 相似文献
93.
94.
Klaus Hoechsmann 《Rendiconti del Circolo Matematico di Palermo》1995,44(1):5-20
Let ζ be a primitivesp-th root of unity for a primep>2, and consider the group Ω(ζ) of cyclotomic units in the ringR(ζ)=ℒ[ζ+ζ-1]. This paper deals with the image of Ω(ζ) in the unit group ofR(ζ)/qR(ζ), whereq is a prime ≠p. In particular, it obtains criteria for this image to be essentially everything, and a lower bound on the density of primesp (withq fixed) for which it cannot be. These results have a direct bearing on previous work about units in integral group rings for
cyclic groups of orderpq.
Work supported in part by an operating grant from NSERC (Canada). 相似文献
95.
Walter M. Miller 《Set-Valued Analysis》1995,3(2):181-194
A set-valued dynamical systemF on a Borel spaceX induces a set-valued operatorF onM(X) — the set of probability measures onX. We define arepresentation ofF, each of which induces an explicitly defined selection ofF; and use this to extend the notions of invariant measure and Frobenius-Perron operators to set-valued maps. We also extend a method ofS. Ulam to Markov finite approximations of invariant measures to the set-valued case and show how this leads to the approximation ofT-invariant measures for transformations , whereT corresponds to the closure of the graph of . 相似文献
96.
Alessandro D'Aprano Camillo La Mesa Noemi Proietti Bianca Sesta Sonia Tatone 《Journal of solution chemistry》1994,23(12):1331-1346
The interactions between octyl--D-glucoside and glycine in water have been investigated by surface tension, viscosity, and density measurements. The results show that the -amino acid causes an unexpected lowering of the critical micellar concentration of octyl--D-glucoside. Such a finding has been interpreted in temss of dipole-dipole interactions between the hydrophilic site of the surfactant and the peptidic cosluttes. From three to seven amino acid molecules have been estimated to be coordinated with each glucoside unity in the micellar state. The research has been extended to glycine oligopeptides and L-lysine. The latter compound has effects similar to those observed with glycine whereas diglycine and triglycine show weaker effects on the micellization process. 相似文献
97.
X. -D. Cao 《Periodica Mathematica Hungarica》1994,28(1):43-54
Let
, wheref(n) is the characteristic function of square-full integers. A formula is proved that can be used to obtain better upper bound estimate for (x). We get (x)=O(x
5/33+), which improves the exponent 11/72 obtained by R. Blasubramania and K. Ramachandra. 相似文献
98.
J. A. Rush 《Geometriae Dedicata》1994,53(2):217-221
It has long been known that the admissibility of a lattice with respect to a symmetric convex bodyB is equivalent to being a packing lattice for 1/2B. This fact is the basis of the interplay between the classical theory of the arithmetic minima of positive definite quadratic forms, on the one hand, and the dense lattice packing of spheres inR
n
, on the other.We give an indexed set of bounds
L
(B) a
j
, where 0 j n/2, on the lattice packing density ofB. The casej=0 reduces to the aforementioned long-known fact, andj=1 was proved by Elkies, Odlyzko, and Rush, and was used to obtain record high packing densities for various superballs. The new cases make possible the use of smaller primes in the construction of these dense packings.Supported by National Science Foundation grant DMS-9103233. 相似文献
99.
We give a lower bound for the number of vertices of a generald-dimensional polytope with a given numberm ofi-faces for eachi = 0,..., d/2 – 1. The tightness of those bounds is proved using McMullen's conditions. Form greater than a small constant, those lower bounds are attained by simpliciali-neighbourly polytopes. 相似文献
100.
It is the aim of the present work to prove, under appropriate conditions, lower estimates for the dimension of w
1 + ... + w
m
over , wherew
1,...,w
m
are given real numbers. In particular, if this dimension ism, i.e. ifw
1,...,w
m
are linearly independent over , we are also interested in a quantitative version of this fact. Our qualitative theorems generalize a result of Nesterenko. Its formulation is quite similar to the axiomatization of methods for algebraic independence, as it became usual during the last decade. 相似文献