Bioactive constituents of Iris hybrida (Iridaceae): Processing effect

Iris genus plants are a valuable source of bioactive compounds, which are an important component for pharmaceutical development. The present article shows the potential for mineral nutrition with application of magnesium sulfate, iron chelates and potassium oxide affecting the phenolic compound contents in Iris hybrida ‘Tsikavynka’, I. hybrida ‘Tambo’ and I. hybridа ‘Widecombe Fire’. The effect of mineral processing was specific to plant organs and varied in the component composition. The Iris rhizomes had an increased total phenolic compound content after treatment (up to 10% of the total isoflavonoid content, up to 8% of phenolic acids, up to 5% of γ-pyrones and up to 13% of flavonoids), determined using UV–vis spectroscopy. A positive effect of nutrition on the biosynthesis and content of individual isoflavonoids (tectoridin, nigricin d -glucoside, genistin, iristectorigenin B, nigricin, irigenin and irisolidone) and xanthone mangiferin in Iris rhizomes by HPLC was established. In addition, an increase in the chlorogenic acid amount in Iris leaves was noted. The results demonstrate the sensitivity of Iris phenylpropanoid metabolism to mineral nutrition and can be used to predict medical plant cultivation with increased content of bioactive constituents.     

Comparison characterization of copper selenide thin layers prepared on polyamide 6 films by sorption-diffusion method

Some earlier synthesized copper selenide (Cu _x Se) layers formed on the surface of polyamide 6 by sorption-diffusion method using potassium selenotrithionate (K₂SeS₂O₆) as precursor of selenium were characterized by the XRD, XPS and SEM methods. According to the results of the SEM studies, the most uniform Cu _x Se layers form at the 2.5 h polyamide seleniumized duration at the temperature of 60°C. The thickness of layers, which dependeds on the duration of seleniumization, changed in the range of 0.8–3.2 µm. The XRD patterns of not previously studied Cu _x Se layers showed their phase composition of six copper selenides: Cu₂Se, two phases of CuSe₂, Cu₃Se₂, berzellianite, Cu_2-x Se, and bellidoite Cu₂Se. Analysis of the XRD and XPS data shows that the macrostructure and composition of the Cu_xSe layers depend on the conditions of formation of these layers.      

Stability of difference schemes for two-dimensional parabolic equations with non-local boundary conditions

The stability of difference schemes for one-dimensional and two-dimensional parabolic equations, subject to non-local (Bitsadze-Samarskii type) boundary conditions is dealt with. To analyze the stability of difference schemes, the structure of the spectrum of the matrix that defines the linear system of difference equations for a respective stationary problem is studied. Depending on the values of parameters in non-local conditions, this matrix can have one zero, one negative or complex eigenvalues. The stepwise stability is proved and the domain of stability of difference schemes is found.     

Modeling of electrocatalysis at polyaniline-modified electrodes: autoacceleration of the process by the reaction product

We extend our previous model taking into account a possible autoacceleration mechanism of electrochemical processes. It is supposed that protons generated in an electrochemical oxidation of ascorbate are responsible for an increase of electric conductivity of polyaniline. Accordingly, the current–time profiles have been calculated taking into account a “threshold” value for proton concentration to increase the electric conductivity of polyaniline by one or more orders of magnitude. Different kinds of corresponding profiles, including ones with a sigmoid character and possessing sharp current flashes as well, were obtained and analyzed.     

The Convergence and Stability of Splitting Finite-Difference Schemes for Nonlinear Evolutionary Equations

We consider a splitting finite-difference scheme for an initial-boundary value problem for a two-dimensional nonlinear evolutionary equation. The problem is split into nonlinear and linear parts. The linear part is also split into locally one-dimensional equations. We prove the convergence and stability of the scheme in L ₂ and C norms. Printed in Lietuvos Matematikos Rinkinys, Vol. 45, No. 3, pp. 413–434, July–September, 2005.     

A closer look at the computer modeling and sintering optimization in the preparation of YAG

Recently, we presented a method for estimation of the diffusion and reaction rates of synthesis at high temperatures using limited information, such as synthesis time and dimensions of reactants, from real laboratory experiments (Mackevi?ius et?al. in Central Eur J Chem 10(2):380–385, 2012). There, we restricted ourselves to the one- and two-dimensional models. Having both adapted our computing program to the three-dimensional case and significantly speeded it up, now we are able present the results in the three-dimensional model. Solving an inverse modeling problem, we obtain explicit formulas for the diffusion coefficient and reaction rate as functions of temperature. We calculate the activation energies and other parameters, thus obtaining conditions for occurrence of synthesis. In addition, using the results of the three-dimensional model, we find the optimal temperature for energy consumption in the YAG synthesis.     

Modelling Dynamics of Amperometric Biosensors in Batch and Flow Injection Analysis

A mathematical model of amperometric biosensors has been developed. The model is based on non-stationary diffusion equations containing a non-linear term related to Michaelis–Menten kinetic of the enzymatic reaction. Using digital simulation, the influence of the substrate concentration as well as maximal enzymatic rate on the biosensor response was investigated. The digital simulation was carried out using the finite difference technique. The model describes the biosensor action in batch and flow injection regimes.     

Computational Modelling of the Behaviour of Potentiometric Membrane Biosensors

This paper presents a mathematical model of a potentiometric biosensor based on a potentiometric electrode covered with an enzyme membrane. The model is based on the reaction–diffusion equations containing a non-linear term related to theMichaelis–Menten kinetics of the enzymatic reaction. Using computer simulation the influence of the thickness of the enzyme membrane on the biosensor response was investigated. The digital simulation was performed using the finite difference technique. Results of the numerical simulation were compared with known analytical solutions.      

Comparison of the efficacy of sulfurization agents in decreasing the sheet resistance of polyamide and polyethylene with copper sulfide layers and influence of their compositions

The process of obtaining semiconductive and electrical conductive layers of copper sulfides by the sorption — diffusion method on polymers (polyamide 6 and low density polyethylene) using solutions of potassium pentathionate, K₂S₅O₆, and higher polythionic acids, H₂S _n O₆ (n = 21, 33), was investigated. The layers were characterized for compositional and electrical properties by X-ray diffraction (XRD) analysis and sheet resistance measurements. The thickness of copper sulfides layers on polyamide and polyethylene increased with increasing time of polymer sulfurization and varied from 10 to 43 μm. The variations of the sheet resistance of copper sulfides layers formed on the surface of polymers on sulfurization agent used, the conditions of sulfurization, chemical and phase composition of the obtained layers were established. Sheet resistance of copper sulfides layers decreases with increasing time of the duration of sulfurization and the number of sulfur atoms in the polythionate anion. The sheet resistance values for copper sulfide layers formed on the polyamide surface are much lower than those of Cu _x S formed on the polyethylene surface. XRD showed the predomination of Cu _x S phases with low x values.