排序方式: 共有28条查询结果,搜索用时 15 毫秒
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Brienne N. Seiner Shannon M. Morley Tere A. Beacham Morgan M. Haney Stephanie Gregory Lori Metz 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(1):673-678
The purpose of this work was to determine polonium losses from a variety of sample types (soil, cotton fiber, and air filter) due to digestion technique, chemical separation, and deposition method for alpha energy analysis. Results demonstrated that yields from a perchloric acid wet-ash (87 ± 5 %) were similar to that from a microwave digestion (100 ± 7 %), but both were greater than the dry-ash procedure (38 ± 5 %). The polonium was separated from an SRM soil using an AG1X8 ion exchange column and deposited on a Ag disk with a recovery of 83 ± 7 % of polonium-209 (Po-209). Deposition yields without chemical separation averaged 90 ± 5 % of Po-209. The polonium-210 content was successfully measured in the three matrix types and quantitated using alpha spectroscopy. 相似文献
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Amadeu Delshams Rafael de la Llave Tere M. Seara 《Communications in Mathematical Physics》2000,209(2):353-392
We give a proof based in geometric perturbation theory of a result proved by J. N. Mather using variational methods. Namely, the existence of orbits with unbounded energy in perturbations of a generic geodesic flow in Ä2 by a generic periodic potential. 相似文献
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Amadeu Delshams Vassili Gelfreich Àngel Jorba Tere M. Seara 《Communications in Mathematical Physics》1997,189(1):35-71
We consider fast quasiperiodic perturbations with two frequencies (1/ɛ,γ/$epsiv;) of a pendulum, where γ is the golden mean
number. The complete system has a two-dimensional invariant torus in a neighbourhood of the saddle point. We study the splitting
of the three-dimensional invariant manifolds associated to this torus. Provided that the perturbation amplitude is small
enough with respect to ɛ, and some of its Fourier coefficients (the ones associated to Fibonacci numbers), are separated from
zero, it is proved that the invariant manifolds split and that the value of the splitting, which turns out to be exponentially
small with respect to ɛ, is correctly predicted by the Melnikov function.
Received: 19 February 1996 / Accepted: 14 February 1997 相似文献
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W. Diemair W. Fresenius H. Serger J. Flater G. Behr J. Koch D. P. Birjukow A. Piegai F. Emanuele L. M. Beacham und W. Friese 《Fresenius' Journal of Analytical Chemistry》1943,125(7-8):310-312
Ohne Zusammenfassung 相似文献
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Exponential separation and invariant bundles for maps in ordered Banach spaces with applications to parabolic equations 总被引:2,自引:0,他引:2
A vector bundle morphism of a vector bundle with strongly ordered Banach spaces as fibers is studied. It is assumed that the fiber maps of this morphism are compact and strongly positive. The existence of two complementary, dimension-one and codimension-one, continuous subbundles invariant under the morphism is established. Each fiber of the first bundle is spanned by a positive vector (that is, a nonzero vector lying in the order cone), while the fibers of the other bundle do not contain a positive vector. Moreover, the ratio between the norms of the components (given by the splitting of the bundle) of iterated images of any vector in the bundle approaches zero exponentially (if the positive component is in the denominator). This is an extension of the Krein-Rutman theorem which deals with one compact strongly positive map only. The existence of invariant bundles with the above properties appears to be very useful in the investigation of asymptotic behavior of trajectories of strongly monotone discrete-time dynamical systems, as demonstrated by Poláik and Tereák (Arch. Ration. Math. Anal.
116, 339–360, 1991) and Hess and Poláik (preprint). The present paper also contains some new results on typical asymptotic behavior in scalar periodic parabolic equations. 相似文献
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The reaction of thymidine with thionyl chloride in HMPA, reported1 to give pure 1-(3,5-dichloro-2,3,5-trideoxy-β-D-threo-pentofuranosyl)thymine, has been found to give a mixture of erythro and threo isomers. Upon reacting thymidine with thionyl chloride, according to the literature procedure,1 a product was isolated which melted 138–141°C [reported1 138–140°C] and gave one spot in CHCl3/ETOH (4:1) on Eastman silica gel sheets at Rf=0.6 [reported1 one spot at Rf=0.7 on Baker silica gel sheets]. However, the TLC of the product in neat ethyl acetate or CHCl3/MeOH (9:1) gave two spots. A sample was separated into pure components by flash chromatography2. 相似文献