排序方式: 共有43条查询结果,搜索用时 15 毫秒
1.
Yields of eleven fission products with masses A=131 to 135 have been determined for the reactor neutron induced fission of238U by means of radiochemical separation combined with high-precision Ge(Li) -ray spectrometry. The charge distribution in the isobaric chains 131 to 134 and the isotopic distribution of52Te have been studied. 相似文献
2.
3.
Anionic polymerization can produce branches with low molecular weight and narrow molecular weight distributions. Post polymerization linking involving the still active chain ends can then be done to produce branched oligomers with a predetermined number of arms. These species are then excellent model compounds for testing high molecular weight branches. Here we chose the reaction of oligobutadienyllithium with ethyl acetate, dimethyl adipatc, diethyl adipatc, dimethyl phthalatcand epoxidized soyabean oil. For the last linking agent, we compared the result obtained with a high molecular weight poly(styryl-b-butadienyl)lithium. 相似文献
4.
Microscopically visible crystallization in a typical non-crystallizing organic polymer - poly(vinyl chloride) (PVC) is achieved by dissoloving it in an appropriate solvent (cyclohexanone) and inducing the nucleation by introducing various insolube crystallization cores - microcrystals of noble metals (Au, Pd, Pt, Rh, Ir, Ru, Os). It is established that the higher the melting temperature of the metal the higher its activity as a crystallization core in the heterogeneous nucleation of PVC. The reverse process-oriented crystallization of a foreign substance - NaCl crystals on PVC films is also demonstrated. This result gives an indication of precrystalline structures in seemingly amorphous PVC films. 相似文献
5.
Ronald DeVore Guergana Petrova Przemyslaw Wojtaszczyk 《Constructive Approximation》2011,33(1):125-143
Let f be a continuous function defined on Ω:=[0,1]
N
which depends on only ℓ coordinate variables, f(x1,?,xN)=g(xi1,?,xil)f(x_{1},\ldots,x_{N})=g(x_{i_{1}},\ldots,x_{i_{\ell}}). We assume that we are given m and are allowed to ask for the values of f at m points in Ω. If g is in Lip1 and the coordinates i
1,…,i
ℓ
are known to us, then by asking for the values of f at m=L
ℓ
uniformly spaced points, we could recover f to the accuracy |g|Lip1
L
−1 in the norm of C(Ω). This paper studies whether we can obtain similar results when the coordinates i
1,…,i
ℓ
are not known to us. A prototypical result of this paper is that by asking for C(ℓ)L
ℓ
(log 2
N) adaptively chosen point values of f, we can recover f in the uniform norm to accuracy |g|Lip1
L
−1 when g∈Lip1. Similar results are proven for more general smoothness conditions on g. Results are also proven under the assumption that f can be approximated to some tolerance ε (which is not known) by functions of ℓ variables. 相似文献
6.
L. Futekov D. Dobreva und H. Specker 《Fresenius' Journal of Analytical Chemistry》1981,306(5):381-384
Zusammenfassung In einem einfachen Verbundverfahren werden ppm- und ppb-Gehalte von Gold entweder nach Extraktion mit Methacrylsäuremethylester (MME) direkt im ppm-Bereich mittels Flammen-AAS oder im ppb-Bereich nach Absorption an selenorganische Verbindungen in der Graphitküvette bestimmt. Die Nachweisgrenze in der Flammen-AAS ist 0,2 g Au/ml MME; in der Graphitküvette können noch 0.25 ng nachgewiesen werden. Die relative Standardabweichungen für die Goldbestimmungen sind bei Gehalten von 0,064 ppm in Selen 23%, bei 14 ppm 3,5%; in Bleikonzentraten bei 0,41 ppm 10,2%. Das angegebene Verfahren ist auf Erze und andere Metallkonzentrate übertragbar.
AAS Determination of gold in the ppm to ppb range in selenium after enrichment by extraction and adsorption
Summary With a simple method ppm and ppb amounts of gold were determined either after extraction with methyl methacrylate (MME) directly by flame AAS in ppm amounts or after absorption on organoselenium compounds in ppb amounts with flameless AAS. The determination limit by flame AAS is 0.2 g Au/ml MME, by flameless AAS 0.25 ng. The relative standard deviations for the determination of gold are 23% for the determination in selenium in the range of 0.064 ppm, in the range of 14 ppm 3.5%. For lead concentrates with 0.41 ppm the relative standard deviation is 10.2%. This method may be used, too, for the analysis of other metal concentrates and ores.
Für die Gewährung eines Stipendiums (L.F.) danken wir der Alexander von Humboldt-Stiftung. 相似文献
7.
Iodine and tellurium isotopes produced in the fission of 232Th with 30.5 MeV alpha particles were separated using a method of sublimation in an air stream and the independent yields of 130I, 131I, 132m,gI, 133I 134I, 134m,gTe, 133mTe and 134Te (cumulative) were determined by means of high resolution Ge(Li) γ-ray spectrometry. A Gaussian fit to the experimental data was used to obtain the width parameter σz and the most probable charge Zp of the nuclear charge distribution in the isobaric chains 130 – 131. The most probable masses for fission fragments with Z = 52 and Z = 53 were also deduced from the measured fission yields. 相似文献
8.
Pawel Bechler Ronald DeVore Anna Kamont Guergana Petrova Przemyslaw Wojtaszczyk 《Transactions of the American Mathematical Society》2007,359(2):619-635
Let be the space of functions of bounded variation on with . Let , , be a wavelet system of compactly supported functions normalized in , i.e., , . Each has a unique wavelet expansion with convergence in . If is the set of indicies for which are largest (with ties handled in an arbitrary way), then is called a greedy approximation to . It is shown that with a constant independent of . This answers in the affirmative a conjecture of Meyer (2001).
9.
10.
We introduce the concept of a μ-monotone function. It allows us to extend the existing theory for Filippov solutions to ODE, linear transport equations, and conservation laws for a wider range of transport velocities (A1,…,Ad) and fluxes (f1,…,fd). 相似文献