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1.
Extending to r > 1 a formula of the authors, we compute the expected reflection distance of a product of t random reflections in the complex reflection group G(r, 1, n). The result relies on an explicit decomposition of the reflection distance function into irreducible G(r, 1, n)-characters and on the eigenvalues of certain adjacency matrices.Received December 8, 2003 相似文献
2.
Earlier measurements in large synchronous generators indicate the existence of backward whirling motion, and also relatively large deviations of shape in both the rotor and the stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called unbalanced magnetic pull (UMP). The target of this paper is to analyse the whirling frequencies and amplitude of the response for large synchronous generators with a high number of poles, due to deviations of shape in the rotor and stator. A mathematical model is developed to describe the shapes of the rotor and stator, and the corresponding UMP is obtained by using the law of energy conservation. The UMP is analysed due to different deviations of shape. The result gives the average angular frequency and the magnitude of the UMP for certain deviations of shape. From this result, the whirling frequency and the amplitude of the corresponding response can be approximated. Simulations of the response of a Jeffcott rotor model show good agreement with the theoretical results of the UMP for some generator geometries. The conclusion is that different whirling frequencies, both backward and forward whirling, can occur in these machines due to deviations in shape of the generator. Therefore, the shape of the generator can excite resonance vibrations on several other frequencies than the rotation frequency. During maintenance of hydropower generators the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and to explain the existence of complicated whirling motion. 相似文献
3.
The strain energies and through-space distances between the two bridgehead E atoms of a selection of 1,3-dimethyl-1,3-ditetrelbicyclo[1.1.1]pentanes
(tetrel E = Si, Ge or Sn) were examined by quantum chemical calculations at MP2 and B3LYP levels. The aim is to identify which
bridges lead to short through-space E,E distances, and simultaneously, to as low strain as possible. A short E,E distance
should improve through-space interaction, and a low strain should promote the thermal stability and possibly also facilitate
their synthesis. The bridges examined included CH2, CMe2, CtBu2, C(CH2)n (n = 2–4), O, NMe, S, PMe, SiMe2, GeMe2, and SnMe2. The calculations indicate that the phospha bridge is a good compromise providing reasonably low strain as well as E,E through-space
distances which are only longer than normal E–E single bonds by factors of 1.06–1.10.
This paper is dedicated to Professor Mitsuo Kira in recognition of his stimulating Si chemistry and his 2005 Wacker Award. 相似文献
4.
Kato H Brink M Möllerstedt H Piqueras MC Crespo R Ottosson H 《The Journal of organic chemistry》2005,70(23):9495-9504
[Figure: see text]. A quantum chemical study has been performed to assess changes in aromaticity along the T1 state Z/E-isomerization pathways of annulenyl-substituted olefins. It is argued that the point on the T1 energy surface with highest substituent aromaticity corresponds to the minimum. According to Baird (J. Am. Chem. Soc. 1972, 94, 4941), aromaticity and antiaromaticity are interchanged when going from S0 to T1. Thus, olefins with S0 aromatic substituents (set A olefins) will be partially antiaromatic in T1 and vice versa for olefins with S0 antiaromatic substituents (set B olefins). Twist of the C=C bond to a structure with a perpendicular orientation of the 2p(C) orbitals (3p*) in T1 should lead to regaining substituent aromaticity in set A and loss of aromaticity in set B olefins. This hypothesis is verified through quantum chemical calculations of T1 energies, geometries (bond lengths and harmonic oscillator measure of aromaticity), spin densities, and nucleus independent chemical shifts whose differences along the T1 PES display zigzag dependencies on the number of -electrons in the annulenyl substituent of the olefin. Aromaticity changes are reflected in the profiles of the T1 potential energy surfaces (T1 PESs) for Z/E-isomerizations because olefins in set A have minima at 3p* whereas those in set B have maxima at such structures. The proper combination (fusion) of the substituents of set A and B olefins could allow for design of novel optical switch compounds that isomerize adiabatically with high isomerization quantum yields. 相似文献
5.
6.
Optimisation and robustness analysis of a hydrophobic interaction chromatography step 总被引:1,自引:0,他引:1
Process development, optimisation and robustness analysis for chromatography separations are often entirely based on experimental work and generic knowledge. The present study proposes a method of gaining process knowledge and assisting in the robustness analysis and optimisation of a hydrophobic interaction chromatography step using a model-based approach. Factorial experimental design is common practice in industry today for robustness analysis. The method presented in this study can be used to find the critical parameter variations and serve as a basis for reducing the experimental work. In addition, the calibrated model obtained with this approach is used to find the optimal operating conditions for the chromatography column. The methodology consists of three consecutive steps. Firstly, screening experiments are performed using a factorial design. Secondly, a kinetic-dispersive model is calibrated using gradient elution and column load experiments. Finally, the model is used to find optimal operating conditions and a robustness analysis is conducted at the optimal point. The process studied in this work is the separation of polyclonal IgG from BSA using hydrophobic interaction chromatography. 相似文献
7.
Optically active C(2)-symmetric (1S,2S,4S,5S)-bicyclo[2.2.2]octane-2,5-diol ((+)-12; 98% ee) and several selectively protected optically active intermediates useful for synthetic transformations were synthesized via a 1,2-carbonyl transposition route starting from the easily available optically active (1R,4S,6S)-6-hydroxybicyclo[2.2.2]octan-2-one ((-)-2). The synthetic route also allowed the preparation of optically active (1S,4S)-bicyclo[2.2.2]octane-2,5-dione ((+)-14; 98% ee). 相似文献
8.
Several highly activated 2,3′-biindolyls were prepared from methyl 5,6-dimethoxyindole-2-carboxylate and oxindoles. The 2,3′-biindolyls were further transformed into a hydroxy indolo[3,2-a]carbazole and a bisindole amide. 相似文献
9.
Holzwarth AR Müller MG Niklas J Lubitz W 《The journal of physical chemistry. B》2005,109(12):5903-5911
The fluorescence kinetics of photosystem I core particles from Chlamydomonas reinhardtii have been measured with picosecond resolution in order to test a previous hypothesis suggesting a charge recombination mechanism for the early electron-transfer steps and the fluorescence kinetics (Müller et al. Biophys. J. 2003, 85, 3899-3922). Performing global target analyses for various kinetic models on the original fluorescence data confirms the "charge recombination" model as the only acceptable one of the models tested while all of the other models can be excluded. The analysis allowed a precise determination of (i) the effective charge separation rate constant from the equilibrated reaction center excited state (438 ns(-1)) confirming our previous assignment based on transient absorption data (Müller et al. Biophys. J. 2003, 85, 3899-3922), (ii) the effective charge recombination rate constant back to the excited state (52 ns(-1)), and (iii) the intrinsic secondary electron-transfer rate constant (80 ns(-1)). The average energy equilibration lifetime core antenna/RC is about 1 ps in the "charge recombination" model, in agreement with previous transient absorption data, vs the 18-20 ps energy transfer lifetime from antenna to RC within "transfer-to-the-trap-limited" models. The apparent charge separation lifetime in the recombination model is about three times faster than in the "transfer-to-the-trap-limited" model. We conclude that the charge separation kinetics is trap-limited in PS I cores devoid of red antenna states such as in C. reinhardtii. 相似文献
10.
Dr. Valentin Radtke Niklas Gebel Denis Priester Andreas Ermantraut Monika Bäuerle Dr. Daniel Himmel Regina Stroh Prof. Thorsten Koslowski Prof. Ivo Leito Prof. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(40):e202200509
Utilizing the “ideal” ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol−1 over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent - and the values that account for the electronating potential of any redox system similar to the value of a medium that accounts for its protonating potential. This scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents′ redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the scale. 相似文献