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51.
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Summary A method for pesticide residue analysis applying the technique of two-dimensional gas chromatography with effluent splitting to three selective detectors in parallel is described. Screening and confirmation procedures are combined in one single instrument. The column combination used allows the separation and identification of more than three hundred pesticides on the basis of the resulting retention times and detector signals. Critical pairs of pesticides are distinguished by using the response ratio of the selective detectors characteristic for each substance. An example is given to demonstrate the merits of the described GC-system using the multimethod S19 of the DFG Pesticide Commission for clean-up.Part of this paper was presented at the Seventh International Congress of Pesticide Chemistry, Hamburg, August 5–10, 1990 相似文献
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Conclusion Might there be a chance of proving in a simple way thatx/π(x) is asymptotic to an increasing function, thus getting another proof of PNT? This is probably wishful thinking. However,
there is a natural candidate for the increasing function. LetL(x) be the upper convex hull of the full graph ofxπ(x) (precise definition to follow). The piecewise linear functionL(x) is increasing becausex/π(x) → ∞ asx → ∞. Moreover, using PNT, we can give a proof thatL(x) is indeed asymptotic tox/π(x). But the point of our work in this article is that for someone who wishes to understand why the growth of primes is governed
by natural logarithms, a reasonable approach is to convince oneself via computation that the convex hull just mentioned satisfies
the hypothesis of our theorem, and then use the relatively simple proof to show that this hypothesis rigorously implies the
prime number theorem. 相似文献
55.
The paper discusses the existence of positive solutions, dead core solutions and pseudodead core solutions of the singular
Dirichlet problem (ϕ(u′))′ = λf(t, u, u′), u(0) = u(T) = A. Here λ is the positive parameter, A > 0, f is singular at the value 0 of its first phase variable and may be singular at the value A of its first and at the value 0 of its second phase variable.
This work was supported by grant no. A100190703 of the Grant Agency of the Academy of Sciences of the Czech Republic and by
the Council of Czech Government MSM 6198959214. 相似文献
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The Mathematical Intelligencer - 相似文献
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The possibility to employ external magnetic field for acceleration of plasma clusters is discussed in this paper both theoretically and experimentally. The optimum value of the magnetic field has been found for the “snow plough” model, in which case there is the maximum cluster acceleration. The obtained results show a real possibility of further increasing the plasma cluster velocity in the electromagnetic shock tube. 相似文献
60.
H. -J. Stan 《Fresenius' Journal of Analytical Chemistry》1982,311(4):333