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Modeling Techniques for Coupled,Rotating Beams

Beams are parts of many industrial applications, like robot links, rolls in paper industry and turbo charger. In this work, a rotordynamical problem, the powertrain for a mill stand, is under consideration. Torsional and bending vibrations are used to describe the dynamical behavior. There are several methods for deriving the dynamical equations of motion. In this paper, the Projection Equation, a synthetical method, is used, leading to partial differential equations for the distributed parameter system. A simplification can be done by using the Ritz approximation method. This method requires the fulfillment of the geometric boundary conditions. For our example, a combination of rigid body modes and elastic modes is chosen. Also models for the gear box system and bearings are included. The solutions for the overall example are nonlinear ordinary differential equations which can be integrated numerically. The system is excited by constant torques and forces. Simulation results for this elastic multibody system are presented. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

β-Lactam derivatives as enzyme inhibitors: halogenated β-lactams and related compounds

Different modifications of the imine – acyl chloride reaction were used for the synthesis of 3-mono- and 3,3-dihalogenated 1,4-diaryl substituted β-lactams. Furthermore, these β-lactams were modified by halogen substitution either at the aryl at position 1 or at the aryl substituent at position 4, or at both positions. The influence of the halogen atoms on the reactivity of the β-lactam ring, visible by the carbonyl frequence in their IR spectra, was studied. A selection of compounds was tested as inhibitors of the serin protease porcine pancreatic elastase. No simple correlation between IR frequence and biological activity was found. Finally, the base induced rearrangement of N-benzyl β-lactams was used for the synthesis of 4,5-diaryl substituted pyrrolidinones. Correspondence: Hans-Hartwig Otto, Department of Pharmaceutical/Medicinal Chemistry (PMC), Institute of Pharmacy, Ernst-Moritz-Arndt-University, 17487 Greifswald, Germany.     

A Reactive Molecular Dynamics Study of Chlorinated Organic Compounds. Part II: A ChemTraYzer Study of Chlorinated Dibenzofuran Formation and Decomposition Processes

In our two-paper series, we first present the development of ReaxFF CHOCl parameters using the recently published ParAMS parametrization tool. In this second part, we update the reactive Molecular Dynamics – Quantum Mechanics coupling scheme ChemTraYzer and combine it with our new ReaxFF parameters from Part I to study formation and decomposition processes of chlorinated dibenzofurans. We introduce a self-learning method for recovering failed transition-state searches that improves the overall ChemTraYzer transition-state search success rate by 10 percentage points to a total of 48 %. With ChemTraYzer, we automatically find and quantify more than 500 reactions using transition state theory and DFT. Among the discovered chlorinated dibenzofuran reactions are numerous reactions that are new to the literature. In three case studies, we discuss the set of reactions that are most relevant to the dibenzofuran literature: (i) bimolecular reactions of the chlorinated-dibenzofuran precursors phenoxy radical and 1,3,5-trichlorobenzene, (ii) dibenzofuran chlorination and pyrolysis, and (iii) oxidation of chlorinated dibenzofurans.     

Electric field-induced isomerization of azobenzene by STM

The electric field applied between the tip of a scanning tunneling microscope and a metallic surface is shown to induce the reversible trans-cis isomerization of single azobenzene derivatives adsorbed on a Au(111) surface. The investigated molecule is symmetrically equipped with four tert-butyl groups, which decouple the azobenzene core from the metallic surface, facilitating the formation of highly ordered islands. Due to the spatial extension of the electric field, it is possible to switch many molecules within the same island simultaneously.