Polynomial neural network for linear and non-linear model selection in quantitative-structure activity relationship studies on the internet

This article presents a self-organising multilayered iterative algorithm that provides linear and non-linear polynomial regression models thus allowing the user to control the number and the power of the terms in the models. The accuracy of the algorithm is compared to the partial least squares (PLS) algorithm using fourteen data sets in quantitative-structure activity relationship studies. The calculated data show that the proposed method is able to select simple models characterized by a high prediction ability and thus provides a considerable interest in quantitative-structure activity relationship studies. The software is developed using client-server protocol (Java and C++ languages) and is available for world-wide users on the Web site of the authors.     

Mit Tellur dotierte Molybdate als Oxydationskatalysatoren

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Study of the base‐catalyzed nitrito–nitro isomerization reaction ([(NH3)5Co‐ONO]2+ → [(NH3)5Co‐NO2]2+) in mixed solvents

The base‐catalyzed linkage isomerization of [Co(NH₃)₅‐ONO]²⁺ to the nitro [(NH₃)₅Co‐NO₂]²⁺ form is studied in various isodielectric water–cosolvent mixtures (methanol, ethanol, tert‐butyl alcohol, and 2‐propanol) at 298 K. In all cases, except for methanol–water mixtures, the rate constants increase with the proportion of cosolvent. Medium effects have been rationalized by using a multiparameter regression of solvent parameters which rationalizes the results obtained, including water–methanol mixtures. The experimental data, k₂, in fact, are well correlated through the following equation: where A, B, and G_exc are the acidity parameter, the basicity parameter, and the excess Gibbs free energy of the mixture, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 410–415, 2004     

Introduction of 4(S)-oxazolidineacetic acid, 2-oxo (D-Oxac) motif in a polypeptide chain: synthesis and conformational analysis

A four step synthesis of 4(S)-oxazolidineacetic acid, 2-oxo benzyl ester (D-Oxac-OBn) from L-Asp-OH in 45% overall yield is reported. The formation of by-products is completely avoided, by microwave irradiation and by the use of caesium carbonate as base. Moreover the synthesis and IR and 1H NMR conformational analysis of the tetramers Boc-L-Val-D-Oxac-L-Ala-OBn and Boc-L-Val-D-Oxac-Aib-L-Ala-OBn in solution is reported.     

A modeling concept of a mechanical system having a piecewise linear spring property for its diagnosis

Machine condition monitoring and fault diagnosis of rotating machinery are very important because of the wide use of rotating machinery in industry. Couplings and gears are used in many mechanical systems to connect elements and transmit power. The system is usually modeled as a single-degree-of-freedom system with a piecewise linear spring property, where the mass of main machine is only considered. In the present study, the dynamic behavior of a system with an unsymmetrical nonlinearity and a significant mass of the connecting part was investigated both experimentally and by numerical simulation. In the experiment, a 1/3 sub-harmonic oscillation was observed, but this oscillation was not found in the simulation using a single-degree-of-freedom system, in which the mass of the connecting part was ignored. However, when a two-degrees-of-freedom system was used that considered both the mass of the connecting part and the impact property, the 1/3 sub-harmonic oscillation was observed. Thus it is recognized that an adequate mathematical model for diagnosis in the early stage of abnormality must be selected on the basis of the mass ratio between the connecting part and the main body.     

Study of the electron transfer reaction between [Co(EDTA)]− and [Ru(NH3)5py]2+ in methanol–water mixtures

The title reaction was studied in different water–cosolvent (methanol) mixtures. The results have been rationalized employing the Marcus–Hush treatment. To apply this treatment, the true, unimolecular, electron‐transfer rate constants (k_et) were obtained from the experimentally measured rate constants after calculation of the equilibrium constant for the processes of formation of the encounter complex. This calculation was carried out using Eigen–Fuoss (EF) and exponential mean spherical (EMSA) approaches employing effective values of the solvent dielectric constant. These effective values were obtained from the measured association constants corresponding to other ion pairs. The results reveal that in these media there is an additional component of reorganization energy, absent in neat solvents. An explanation of the origin of this component is given. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 658–666, 2009