Autowave self-organization in heterogeneous natural–anthropogenic ecosystems

This article considers the spatio–temporal model of natural–anthropegenic ecosystems as a conjugated active media that takes the heterogeneity of anthropogenic and natural factors into account. The approach aims to identify the threshold values of the control parameters. The theoretical basis of the system analysis of the sustainability of the ecosystems is synergistic data on autowave self-organization in active media. The mathematical model is based on the modified FitzHugh–Nagumo system of equations.     

Study of the kynurenine pathway of tryptophan metabolism by capillary electrophoresis and mass spectrometry

A procedure has been proposed for the electrophoretic determination of main tryptophan metabolites demonstrating neurotoxic properties, i.e., kynurenine, 3-hydroxykynurenine, and kynurenic acid, with UV detection at 227 nm. The limit of detection at the signal-to-noise ratio equal to 3 makes 0.3 μg/mL. Individuals of fruit flies have been studied as biological objects. The chances for the autooxidation 3-hydroxykynurenine in biological objects are proved by mass spectrometry.     

Estimation of pore size distribution in MCM-41-type silica using a simple desorption technique

A recently developed dynamic desorption technique is used for obtaining vapor isotherms on porous materials. This gravimetric technique does not require any preliminary calibration and is based on analyzing the kinetics of liquid evaporation from a porous sample under quasi-steady state conditions. The crucial feature of the technique is concerned with the fact that no vapor pressure measurements are necessary. The technique is illustrated by desorption of benzene vapors from mesoporous silica MCM-41. To calculate the pore size distribution, the Derjaguin–Broekhoff–de Boer theory in its combination with the Wheeler model for capillary condensation is used. In the calculations, the reference data on benzene adsorption on a nonporous silica gel from two different sources (published by different authors) are applied. The mean mesopore sizes estimated from desorption isotherms are shown to be in a fair agreement with the calculations through the geometrical method based on the X-ray diffraction data. The dynamic desorption technique can serve as an additional tool for the characterization of a porous media.     

An estimation of EDXRF spectrometer properties,based on a two‐layer composite Si‐Ge detector

A mathematical model for the two‐layer composite Si‐Ge energy dispersive X‐ray detector is proposed, based on analyses of radiation and electron transport in the detector, and a mathematical model of an energy dispersive X‐ray fluorescent spectrometer with the detector is considered. The Monte Carlo method is applied to calculate probabilities of photon detection in different parts of the detector's response function. The composite detector with the time anti‐coincidence scheme is proposed; its first layer is Si detector, and the second layer is Ge detector. It is shown that this composite detector has some advantages, such as reduced Ge photo escape peaks intensities and efficiency of detection of high energy photons similar to efficiency of Ge detector. Applying the X‐ray detector for the energy dispersive X‐ray fluorescent spectrometer provides for a lower background level. Copyright © 2012 John Wiley & Sons, Ltd.     

Structure and magnetic properties of metal-carbon nanocomposites based on IR-pyrolized poly(acrylonitrile) and iron

Metal-carbon nanocomposites, namely, IR-pyrolized poly(acrylonitrile)/Fe (IR-PAN/Fe) were produced and studied. The structure and magnetic properties of the composites were studied for various synthesis conditions. Nanosized carbon objects (nanospheres) and iron carbide nanoparticles were revealed in the composite structure. The magnetic properties of the nanocomposites prepared at various IR-annealing temperatures were studied.     

Structural and Electrosurface Properties of Porous Glasses of Various Composition in 1 : 1 Electrolyte Solutions

Complex studies of structural (the specific surface area, the volume porosity, the structural resistance coefficient, and the average pore radius), adsorption and electrokinetic (the electrical conductivity, the ion transport numbers, and the electrokinetic potential) characteristics as functions of pH and the concentration of KCl solution were carried out on porous glasses (PGs) with or without lead oxide and leached under various conditions. It was established that temperature of the leaching solution affects the colloidochemical parameters of PGs, while the addition of salt to the leaching solution exerts practically no influence on the PG behavior. It was shown that the addition of lead oxide results in the formation of membranes with thinner pores and higher surface charge.     

Electrosurface Properties of Microcrystalline Cellulose of Different Origin in 1 : 1 Electrolyte Solutions

Electrosurface characteristics (the exchange capacity and the electrokinetic potential) of the samples of cotton and wood microcrystalline celluloses (MCC) were studied as functions of the pH and the concentration of background electrolyte (10^–3–1M NaCl). It was found that the MCC samples are negatively charged over the studied pH range (3.5–10.0). The results of measuring exchange capacities were used for calculating constants of surface reactions. The values of dissociation constants of the surface groups allow us to state that the charge of the MCC surface within the studied pH range is mainly determined by the dissociation of carboxyl groups. The surface and electrokinetically mobile charges, concentrations of fixed and mobile ions, as well as Donnan's potentials were calculated for the studied samples.     

One-step transformation of the marine alkaloid fascaplysin into homofascaplysins B and B-1. The first syntheses of 3-bromohomofascaplysin B and 3–bromohomofascaplysin B-1

A method for one-step conversion of the marine alkaloid fascaplysin into homofascaplysins B and B-1 was elaborated. It was also used for the first syntheses of the marine alkaloids 3–bromohomofascaplysin B and 3-bromohomofascaplysin B-1. The best results were demonstrated under the action of microwave irradiation in presents of dihydroquinone as a reducing agent.