In univariate Padé approximation we learn from the Froissart phenomenon that Padé approximants to perturbed Taylor series exhibit almost cancelling pole–zero combinations that are unwanted. The location of these pole–zero doublets was recently characterized for rational functions by the so‐called Froissart polynomial. In this paper the occurrence of the Froissart phenomenon is explored for the first time in a multivariate setting. Several obvious questions arise. Which definition of Padé approximant is to be used? Which multivariate rational functions should be investigated? When considering univariate projections of these functions, our analysis confirms the univariate results obtained so far in [13], under the condition that the noise is added after projection. At the same time, it is apparent from section 4 that for the unprojected multivariate Froissart polynomial no conjecture can be formulated yet.
We show that it is possible to efficiently transfer magnetization from 31P to 29Si, using variable amplitude CP MAS experiment. This experiment is demonstrated by using Si5O(PO4)6, the synthesis protocol of which is described. From the obtained results, we show that the experiment allows the spectral edition of 29Si spectra from 31P→29Si CP, enabling the studies of derivatives involving Si–O–P linkages, such as phosphosilicate glasses, microporous silicoaluminophosphates (SAPO) and bioactive phosphosilicates. 相似文献
In this article, we construct a general series for . We indicate that Ramanujan's -series are all special cases of this general series and we end the paper with a new class of -series. Our work is motivated by series recently discovered by Takeshi Sato. 相似文献
While various techniques have been used to demonstrate the classical four squares theorem for the rational integers, the method of modular forms of two variables has been the standard way of dealing with sums of squares problems for integers in quadratic fields. The case of representations by sums of four squares in was resolved by Götzky, while those of and were resolved by Cohn. These efforts utilized modular forms. In previous work, the author was able to demonstrate Götzky's theorem by means of the geometry of numbers. Here Cohn's theorem on representation by the sum of four squares for is proven by a combination of geometry of numbers and quaternionic techniques. 相似文献
Measurements for determining of the path of groundwater migration remain an important tool in the overall assessment of environmental processes and transport of pollutants. This paper examines a multiwavelength laser for the determination of eosin, a groundwater tracer, using capillary electrophoresis/laser-induced fluorescence (CE-LIF) at excitation wavelength 514.5 nm. Eosin was one of four dyes used in a study of adjacent resource conservation and recovery act (RCRA) and Superfund sites (created by the comprehensive environmental response, compensation, and liability act) that routinely relied on spectrofluorimetry for determination as we have previously reported. However, the improved specificity of CE-LIF is further illustrated in this work applied to the analysis of adsorbent pads placed in monitoring wells after dye injection and flushing from injection wells. The multiwavelength laser provided the capability to analyze for several dyes with one laser. The advantages/disadvantages of CE-LIF versus spectrofluorimetry are discussed. Spectrofluorimetry is fast and sensitive and will likely continue to be the primary workhorse technique. CE-LIF could provide confirmation when greater specificity is needed in a regulatory context. 相似文献
Three variants of solid-state ion exchange were studied. Iron exchange was found to proceed in the first case, in theFeCl2+NH4ZSM-5 FeZSM-5 + NH4Cl process, even at low exchange capacity (Si/Al = 25).The second, Fe2O3 (hematite) + HZ direct reaction does not result in any noticeable interaction for eitherZ = Y or ZSM-5. This process can significantly be promoted by introducing CCl4 vapor via forming chlorine-containingmobile species. However, the structure of the Y zeolite largely collapses during this treatment, whereas the crystalline state of ZSM-5is preserved. 相似文献