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21.
Gert Brandl Fritz Kastner Rainer Fritsch Herbert Zinner Albrecht Mannschreck 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):1059-1069
Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke. 相似文献
22.
Anton Meller Walter Maringgele Rainer Oesterle 《Monatshefte für Chemie / Chemical Monthly》1980,111(5):1087-1096
The reaction of galliumtrichloride and galliumtribomide resp. with 2,6-dimethyl- and 2,4,6-trimethyl-N-trimethylsilyl-trifluoroacetanilide leads to the trifluoracetanilidodihalogenogallanes1–3. The 2,6,9-trioxa-4,8-diaza-1,5-digalla-bicyclo-[3.3.1]-nonadiene derivatives1 a–3 a are formed probably as by products.N-Trimethylsilyltrifluoroacetamide reacts with galliumtrichloride to yield the trifluoroacetamido-dichlorogallane4.N-Trimethylsilyl-N,N,N-triorganyl-thioureas react with galliumtrichloride under elimination of chlorotrimethylsilane to give the thio-ureido-gallanes5 and6. IfN,N-diorganylureas andN,N-diorganyl-thio-ureas resp. are reacted with galliumtrichloride and methyl-gallium-dichloride resp., the thio-ureido- and ureido-gallanes7–9 are obtained by elimination of hydrogenchloride. The compounds are characterized by analysis and spectral data (NMR:1H,19F; MS; IR). The substances are monomeric in the gas phase, obviously due to internal coordination.
30. Mitt.:W. Maringgele undA. Meller, J. Organomet. Chem., im Druck. 相似文献
23.
Ivar Ugi Johannes Bauer Klemens Bley Alf Dengler Andreas Dietz Eric Fontain Bernhard Gruber Rainer Herges Michael Knauer Klaus Reitsam Natalie Stein 《Angewandte Chemie (International ed. in English)》1993,32(2):201-227
The topic of this article is the development and the present state of the art of computer chemistry, the computer-assisted solution of chemical problems. Initially the problems in computer chemistry were confined to structure elucidation on the basis of spectroscopic data, then programs for synthesis design based on libraries of reaction data for relatively narrow classes of target compounds were developed, and now computer programs for the solution of a great variety of chemical problems are available or are under development. Previously it was an achievement when any solution of a chemical problem could be generated by computer assistance. Today, the main task is the efficient, transparent, and non-arbitrary selection of meaningful results from the immense set of potential solutions—that also may contain innovative proposals. Chemistry has two aspects, constitutional chemistry and stereochemistry, which are interrelated, but still require different approaches. As a result, about twenty years ago, an algebraic model of the logical structure of chemistry was presented that consisted of two parts: the constitution-oriented algebra of be- and r-matrices, and the theory of the stereochemistry of the chemical identity group. New chemical definitions, concepts, and perspectives are characteristic of this logic-oriented model, as well as the direct mathematical representation of chemical processes. This model enables the implementation of formal reaction generators that can produce conceivable solutions to chemical problems—including unprecedented solutions—without detailed empirical chemical information. New formal selection procedures for computer-generated chemical information are also possible through the above model. It is expedient to combine these with interactive methods of selection. In this review, the Munich project is presented and discussed in detail. It encompasses the further development and implementation of the mathematical model of the logical structure of chemistry as well as the experimental verification of the computer-generated results. The article concludes with a review of new reactions, reagents, and reaction mechanisms that have been found with the PC-programs IGOR and RAIN. 相似文献
24.
25.
A method for fast in situ measurement of adsorption kinetics based on a finite bath was developed. We modified the conventional finite bath by replacing the external loop by a dip probe which enables in situ measurement of the concentration change in the contactor. Deposition of adsorbent particles on the reflection surface of the dip probe compromised measurements. Different membranes, a polyamide, a polypropylene and a nylon membrane were tested to protect the internal reflection surface of the dip probe from fouling with adsorbent particles. The nylon membrane provided efficient protection and high mass transfer evaluated by response time experiments. Unspecific adsorption of the model protein on the membrane could also be excluded. To corroborate the measurements of the dip probe the results were compared to a conventional finite bath and to a shallow-bed. The uptake curves for human polyclonal IgG at different concentrationes (0.1-3 g/l) on rProtein A Sepharose FF and MabSelect were used as model system. The effective diffusion coefficients were determined using a pore diffusion model. These values were in good agreement for all methods. 相似文献
26.
Sandip?HalderEmail author Theodor?Schneller Rainer?Waser 《Journal of Sol-Gel Science and Technology》2005,33(3):299-306
A new chemical solution deposition (CSD) route for the fabrication of Ba0.7Sr0.3TiO3 (BST) thin films has been developed which completely prevents the formation of an intermediate oxo-carbonate phase. The latter has been reported previously by several authors to be responsible for increased crystallization temperatures. Barium and strontium diaminoethoxides were synthesized starting from pure barium and strontium metal and aminoethanol. These alkoxides were found to be readily soluble in a wide range of solvents and thus were excellent candidates for the CSD process. To prepare a stable precursor solution the aminoalkoxides were dissolved in 2-butoxyethanol and then used for the deposition of BST thin films. We conclude that the minimum crystallization temperature of 600C to be independent of the formation of the oxo-carbonate phase. DTA-TGA were performed on the precursors and their solutions to study their decomposition behaviour. All films annealed at different temperatures were physically characterized by XRD, IR, and SEM. The films prepared by this route at 650C were found to have high dielectric constant and the leakage currents were comparable to BST films prepared by normal carboxylate based routes at 750C. 相似文献
27.
Three valency models for orthorhombic La2-x
Sr
x
CuO4 were investigated for increasing Sr concentrationsx (0x0.21): 1. Cu2+Cu3+, 2. apex O2–O– and 3. in-plane O2–O–. All calculations were done by using structural parameters valid for the temperature range from 10 to 22 K. We thereby calculated the electrostatic interaction energy which, next to ionization potentials and electron affinities, comprises a major of the binding energyE
B
of crystals. Second-order effects were accounted for by calculating the strength of ionic dipole moments induced by crystal electric fields at relevant lattice sites. Their largest strengths are comparable to the dipole moment of the water molecule. Three out of five dipoles in La2-x
Sr
x
CuO4 vanish during the transition from the orthorhombic to the tetragonal phase. The binding energy differences between the different models suggest that the system is in a state of model 1. However, the differences are very small, being in the order of 0.3 to 0.76 eV atx=0.13. 相似文献
28.
The distribution of the likelihood ratio for mixtures of densities from the one-parameter exponential family 总被引:2,自引:0,他引:2
Dankmar Böhning Ekkehart Dietz Rainer Schaub Peter Schlattmann Bruce G. Lindsay 《Annals of the Institute of Statistical Mathematics》1994,46(2):373-388
We here consider testing the hypothesis ofhomogeneity against the alternative of a two-component mixture of densities. The paper focuses on the asymptotic null distribution of 2 log
n
, where
n
is the likelihood ratio statistic. The main result, obtained by simulation, is that its limiting distribution appears pivotal (in the sense of constant percentiles over the unknown parameter), but model specific (differs if the model is changed from Poisson to normal, say), and is not at all well approximated by the conventional
(2)
2
-distribution obtained by counting parameters. In Section 3, the binomial with sample size parameter 2 is considered. Via a simple geometric characterization the case for which the likelihood ratio is 1 can easily be identified and the corresponding probability is found. Closed form expressions for the likelihood ratio
n
are possible and the asymptotic distribution of 2 log
n
is shown to be the mixture giving equal weights to the one point distribution with all its mass equal to zero and the 2-distribution with 1 degree of freedom. A similar result is reached in Section 4 for the Poisson with a small parameter value (0.1), although the geometric characterization is different. In Section 5 we consider the Poisson case in full generality. There is still a positive asymptotic probability that the likelihood ratio is 1. The upper precentiles of the null distribution of 2 log
n
are found by simulation for various populations and shown to be nearly independent of the population parameter, and approximately equal to the (1–2)100 percentiles of
(1)
2
. In Sections 6 and 7, we close with a study of two continuous densities, theexponential and thenormal with known variance. In these models the asymptotic distribution of 2 log
n
is pivotal. Selected (1–) 100 percentiles are presented and shown to differ between the two models. 相似文献
29.
30.
On noise reduction methods for chaotic data 总被引:1,自引:0,他引:1
Recently proposed noise reduction methods for nonlinear chaotic time sequences with additive noise are analyzed and generalized. All these methods have in common that they work iteratively, and that in each step of the iteration the noise is suppressed by requiring locally linear relations among the delay coordinates, i.e., by moving the delay vectors towards some smooth manifold. The different methods can be compared unambiguously in the case of strictly hyperbolic systems corrupted by measurement noise of infinitesimally low level. It was found that all proposed methods converge in this ideal case, but not equally fast. Different problems arise if the system is not hyperbolic, and at higher noise levels. A new scheme which seems to avoid most of these problems is proposed and tested, and seems to give the best noise reduction so far. Moreover, large improvements are possible within the new scheme and the previous schemes if their parameters are not kept fixed during the iteration, and if corrections are included which take into account the curvature of the attracting manifold. Finally, the fact that comparison with simple low-pass filters tends to overestimate the relative achievements of these nonlinear noise reduction schemes is stressed, and it is suggested that they should be compared to Wiener-type filters. 相似文献