Frictional Phenomena in Dynamical Systemwith Two-Frequency Excitation

The paper deals with investigation of a self-excited vibrating system with dry friction. The system is composed of a mass connected by viscoelastic element with the referring frame and interacting with a moving belt by means of dry friction. An experimentally identified, multi-parametric dry friction model for the pair composed of soft and hard elements like steel–polyester pair, describing both the case of stick-slip and quasi-harmonic vibration, has been applied. Additionally, the system is influenced by external, two-frequency kinematic excitation. The results of computer simulation for different excitation conditions are submitted in the present paper.     

The strong decay to equilibrium for the stochastic dynamics of unbounded spin systems on a lattice

Using a method based on the application of hypercontractivity we prove the strong exponential decay to equilibrium for a stochastic dynamics of unbounded spin system on a lattice.     

Voltammetric studies of diffusional and migrational transport of ferrocene derivative of tripeptide glutathione

The transport of mono- and divalent anions of S-ferrocenylmethyl-L-glutathione (FcCH2SG) was investigated voltammetrically at a microelectrode in solutions of low ionic strength. The electrooxidation reactions of the ferrocenyl group attached to biologically active glutathione neutralized with a strong base in two consecutive steps can be represented as FcCH(2)SG(-) --> Fc(+)CH(2)SG(-) + e and FcCH(2)SG(2-) --> Fc(+)CH(2)SG(2-) + e for the mono- and divalent anions of FcCH(2)SG, respectively. The limiting currents due to these electrode processes were investigated under the conditions of varying content of supporting ions. The results obtained for the electrooxidation of the monovalent anion of FcCH(2)SG deviate significantly from the theoretical predictions derived for the charge cancellation electrode processes (i.e., processes producing uncharged species upon electron transfer). The differences observed are attributed to the specific migrational behavior of the generated dipole-like product which formally bears no net charge but in fact contains two oppositely charged moieties within a molecule. To interpret the data obtained for the divalent anion of FcCH(2)SG, a recent model of the theory of migrational voltammetry has been adapted and extended. The agreement between the experimental data and the theory is obtained only for the ratio of diffusion coefficients of the electrode process product (Fc(+)CH(2)SG(2-)) and the substrate (FcCH(2)SG(2-)) smaller than 1. This leads to a conclusion that upon oxidation this molecule undergoes a conformation change and winds up because of the formation of a coordination bond. The conclusion is supported by molecular-mechanics calculations. The presented methodology allows one to study quantitatively the changes in the concentration distribution of biologically active molecules driven by migration and diffusion and to diagnose their possible structural changes upon reduction/oxidation. Both factors are essential for the proper understanding of the functionality of biologically active systems.     

Determination of adrenolytic drugs by SPME–LC–MS

Five adrenolytic drugs have been analyzed by liquid chromatography–mass spectrometry (LC–MS). Samples were prepared by solid-phase microextraction (SPME) using polypyrrole fibers coated on stainless steel support as an adsorbent for the drugs. Adsorption efficiencies were 95% and were close for all the drugs investigated. Relative standard deviations (RSD), calculated for samples prepared in standard solutions, were in the range 2.5–13%, however RSD values for the drugs in human plasma were 2.5–4.5%. Using LC–MS the limit of detection (LOD) and the limit of quantification (LOQ) were in the ranges 0.11–0.18 and 0.39–0.54 ng mL⁻¹, respectively, for the five drugs.     

The equivalence of the logarithmic Sobolev inequality and the Dobrushin-Shlosman mixing condition

Given a finite range lattice gas with a compact, continuous spin space, it is shown (cf. Theorem 1.2) that a uniform logarithmic Sobolev inequality (cf. 1.4) holds if and only if the Dobrushin-Shlosman mixing condition (cf. 1.5) holds. As a consequence of our considerations, we also show (cf. Theorems 3.2 and 3.6) that these conditions are equivalent to a statement about the uniform rate at which the associated Glauber dynamics tends to equilibrium. In this same direction, we show (cf. Theorem 3.19) that these ideas lead to a surprisingly strong large deviation principle for the occupation time distribution of the Glauber dynamics.During the period of this research, both authors were partially supported by grants DAAL 03-86-K-0171 and DMS-8913328     

Substitution electrophile du ferrocene et du dimethylferrocene par les derives carbonyles protones : II. Influence des effets stériques et conformationnels lors de la synthèse des α-ferrocénylcarbinols

In strongly acidic media ferrocene and dimethylferrocene react with carbonyl compounds to produce α-ferrocenylcarbinols. ¹H NMR studies show that the alcohols are quickly transformed into α-ferrocenylcarbenium ions which after hydrolysis afford the alcohols in high yields. In all cases mono-substitution products are only obtained. With dimethyl ferrocene the ratio of 2-isomer versus 3-isomer indicate a higher reactivity of the α position when small electrophiles are used ; on the contrary condensation of ketones occur preferentially at the β position.     

The electrochemical oxidation of carbon monoxide adsorbed on Pt(111) in aqueous electrolytes as monitored by in situ potential step-second harmonic generation

The dynamics of electrooxidation of adsorbed CO on Pt(111) microfacets was examined in CO-saturated 0.1 M HClO4 aqueous solutions by in situ time resolved second harmonic generation (SHG). Analysis of the temporal dependence of the intensity of the SHG signals recorded for experiments in which the potential was stepped to values high enough for adsorbed CO oxidation to ensue, was found to be consistent with the mean field theory model, yielding rate constants somewhat higher than those reported by Lebedeva et al. (N. P. Lebedeva, M. T. M. Koper, J. M. Feliu and R. A. v. Santen, J. Electroanal. Chem., 2002, 524-525, 242-251) in sulfuric acid solutions. The smaller rates observed by these authors may be ascribed to the presence of anions, ie. in all likelihood bisulfate, which are capable of competing effectively for Pt sites thereby blocking formation of oxygenated species on the surface. Also discussed in this work are the virtues and limitations of in situ SHG for monitoring fast surface processes.     

DIRECTIONAL DO-NOTHING CONDITION FOR THE NAVIER-STOKES EQUATIONS

The numerical solution of flow problems usually requires bounded domains although the physical problem may take place in an unbounded or substantially larger domain. In this case, artificial boundaries are necessary. A well established artificial boundary condition for the Navier-Stokes equations diseretized by finite elements is the “do-nothing” condition. The reason for this is the fact that this condition appears automatically in the variational formulation after partial integration of the viscous term and the pressure gradient. This condition is one of the most established outflow conditions for Navier-Stokes but there are very few analytical insight into this boundary condition. We address the question of existence and stability of weak solutions for the Navier-Stokes equations with a “directional do-nothing” condition. In contrast to the usual “do-nothing” condition this boundary condition has enhanced stability properties. In the case of pure outflow, the condition is equivalent to the original one, whereas in the case of inflow a dissipative effect appears. We show existence of weak solutions and illustrate the effect of this boundary condition by computation of steady and non-steady flows.