Elektronendichteverteilung in Forimaten, Chloraten und Thiosulfaten

Ohne Zusammenfassung

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Electron density distribution in formates, chlorates and thiosulphates

     

Elution strength and selectivity of the mobile phase in reverse phase high performance liquid chromatography (HPLC)

Ohne ZusammenfassungComplete data (chromatograms and tables) can be provided by the editor upon request.     

Information theory applied to qualitative analysis

Summary Fundamental aspects of information theory and its usefulness for qualitative analysis are discussed in view of the applications described so far in the literature. General expressions for the uncertainty, information, equivocation and information content are described and related to the more commonly used expressions of the information parameters.It is shown that the information content (or equivocation) can serve — with certain restrictions — as an important criterion for the evaluation, selection or optimization of analytical procedures.The information theoretical concepts are easy to apply to one-channel identification or classification procedures. However, when multi-channel procedures (combinations of one-channel procedures) are involved, a straightforward use of information theory is to a large extent restricted by the excessive computations. Therefore, the further development of simple methods for the calculation of reliable estimates of information contents and of optimization strategies enabling the calculation of only small numbers of information contents, is of great importance for the future use of information theory in qualitative analysis.

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Anwendung der Informationstheorie in der qualitativen Analyse

Zusammenfassung Grundlegende Aspekte der Informationstheorie und ihre Anwendbarkeit für die qualitative Analyse werden unter Berücksichtigung der bisher in der Literatur beschriebenen Anwendungen besprochen. Allgemeine Ausdrücke für Unsicherheit, Information, Äquivokation und Informationsgehalt werden beschrieben und ihre Beziehung zu den gebräuchlicheren Ausdrücken für die Informationsparameter wird angegeben.Es wird gezeigt, daß der Informationsgehalt (oder die Äquivokation) — unter bestimmten Bedingungen — als ein wichtiges Kriterium für die Auswertung, Selektion oder Optimierung von analytischen Verfahren dienen kann.Die Grundlagen der Informationstheorie können auf einfache Weise für einkanalige Identifizierungsoder Klassifizierungsverfahren angewendet werden. Wenn es sich jedoch um mehrkanalige Verfahren (Kombinationen von Einkanal-Verfahren) handelt, wird die Anwendung der Informationstheorie in hohem Maße durch übermäßige Berechnungen begrenzt.Die weitere Entwicklung von einfachen Verfahren für die Berechnung zuverlässiger Schätzungen von Informationsgehalten und von Optimierungsstrategien, die die Berechnung einer beschränkten Anzahl von Informationsgehalten erfordern, ist deshalb von großer Wichtigkeit für die künftige Anwendung der Informationstheorie in der qualitativen Analyse.

     

A brief remark on van der Waerden spaces

We demonstrate that Martin's axiom for -centered notions of forcing implies the existence of a van der Waerden space that is not a Hindman space. Our proof is an adaptation of the one given by M. Kojman and S. Shelah that such a space exists if one assumes the continuum hypothesis to be true.

     

Nuclear hyperfine coupling interactions in the rotational spectra of the linear and bent isomers of HF-N2O

The rotational spectra of six isotopomers of the linear and bent isomers of HF-N₂O have been collected in the 7-18 GHz region with a Fourier transform microwave spectrometer. The nuclear hyperfine structure in the spectra produced by HF spin-spin coupling interaction and nuclear quadrupole coupling interactions due to the D nucleus of DF and the nuclei of N₂O have been resolved and analyzed. In the linear isomer, H in HF is bonded to the terminal N in N₂O. The NF bond lengths are 2.9808(2) Å for the HF-containing isotopomers and 2.9732(2) Å for the DF-containing isotopomers. The zero point angles are 23.1° for HF and 31-34° for N₂O. The hyperfine constants suggest that the HF bond is lengthened by 0.0105 Å upon complexation and that the electric field gradients of the two nitrogen nuclei in N₂O are perturbed differently in the complex. In the bent isomer, the hydrogen bond is formed between HF and O in N₂O. The intermolecular distances are 3.4942(2) Å for the HF-containing isotopomers and 3.4436(2) Å for the DF-containing isotopomers, with HF and N₂O forming angles of 34° and 46°, respectively, with the intermolecular axis. The nuclear quadrupole coupling constants of the two nitrogen nuclei do not indicate electric field gradient perturbation in this isomer.     

Cooling efficiency in collisions between Pd and He,Ne, Ar and Kr

The cooling of the metal cluster Pd₁₃ in an atmosphere of rare gas has been studied by means of computer simulation. By simulation, the average energy transfer in collisions between one cluster and one gas atom has been obtained. Emphasis has been placed on conditions when the temperatures of the colliding species are almost equal. All modes of motion, inclusive the translation, must be considered in order to obtain vanishing energy transfer at equilibrium. A simulation scheme is presented by which the energy transfer is zero to the cluster when the gas and the cluster temperatures are equal. At equilibrium the energy transfer does however not vanish for all impact parameters. In the collisions with Pd₁₃, the cluster is heated by collisions with a small impact parameter but equally cooled by collisions with a large impact parameter. Argon and krypton are found to cool Pd₁₃ equally efficiently while neon and helium are less efficient cooling agents. Received 28 September 2001 / Received in final form 8 August 2002 Published online 12 November 2002 RID="a" ID="a"e-mail: JanW@phc.gu.se     

Experimental determination of spin-rotation and spin-spin magnetic interactions in by nuclear spin conversion

When a gas sample of ¹³CH₃F is prepared with a population of isomers (ortho and para forms) far from the equilibrium given by nuclear spin statistics, it relaxes towards this equilibrium with an exponential decay rate. This phenomenon called nuclear spin conversion is mainly governed by intramolecular spin-spin and spin-rotation interactions. In the quantum relaxation model [P.L. Chapovsky, Phys. Rev. A 43, 3624 (1991)], two pairs of ortho-para levels (J = 9, K = 3; J' = 11, K' = 1) and (J = 20, K = 3; J' = 21, K' = 1) are principally responsible for the conversion. The levels of the second pair are coupled by both spin-spin and spin-rotation interactions. The application of an electric field (up to 10 kV/cm) induces a crossing of the Stark components of this pair, which is observed for the first time. A specific experimental set-up based on an electric field of alternating triangular shape is used, which allows the determination of the strength of both interactions via the measurement of the spin conversion decay rates. This work yields the first experimental value for the electronic contribution to the spin-rotation interaction in ¹³CH₃F. Received 23 May 2002 / Received in final form 18 September 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: Patrice.Cacciani@univ-lille1.fr     

随机Bonhoeffer-Van der Pol系统的随机混沌控制

讨论了具有有界随机参数的随机Bonhoeffer-Van der Pol系统的随机混沌现象，并利用噪声对其进行控制.首先运用Chebyshev多项式逼近的方法，将随机Bonhoeffer-Van der Pol系统转化为等价的确定性系统，使原系统的随机混沌控制问题转换为等价的确定性系统的确定性混沌控制问题，继而可用Lyapunov指数指标来研究等价确定性系统的确定性混沌现象和控制问题.数值结果表明，随机Bonhoeffer-Van der Pol系统的随机混沌现象与相应的确定性Bonhoeffer-Van der Pol系统极为相似.利用噪声控制法可将混沌控制到周期轨道，但是在随机参数及其强度的影响下也呈现出一些特点.