Absolute extrema-seeking procedures †

A universal algorithm is presented in the paper which makes it possible to find out whether a given relative extremum of a scalar-valued function of a vector argument is also the absolute one and, if not, to find a point at which a relative extremum-seeking procedure can be restarted in order that a better relative extremum—i.e. one at which the given function takes a less, alternatively greater, value—may be obtained. Repeated application of the described procedure in combination with an arbitrary relative extremum-seeking procedure leads to determining the absolute extremum. The possibility of application to stochastic and integer programming problems is discussed.     

Molecular photochromic switches based on dihydropyridine

Photochromic behaviour of l-methyl-2,4,4,6-tetraphenyI-l,4-dihydropyridine and the mechanism of the photochromism based on phenyl transfer is described. Formation of polar colour species, changes in optical absorption and in the pi-electron character of the molecular skeleton allow the fabrication of molecular optical memories and switches     

Use of PCM Boards for Solar Cell Cooling

This contribution explains the use of fractal theory to describe thermal properties of materials. The basic idea is rooted in the theory of fractal fields defined in E-dimensional Euclidian space. Generic equations describing heat distribution are then specialized to describe the changes in heat transfer as a response to step-wise increases in the amount of heat added to the system. This model was then applied to the study of properties of a systems consisting of solar cells attached on a phase-change material (PCM) back sheet board. The aim of this study is to evaluate the ability of PCM boards to decrease the working temperature of solar cells and thus to increase the efficiency of the cells. Regression of experimental data was used to obtain model parameters. The parameters obtained this way were the thermal diffusivity, thermal conductivity, and specific heat, as well as parameters of the heat source and parameters related to the heat losses of the system. The method was then verified against parameters of the system based on poly-methyl-methacrylate and then applied to a PCM with a phase-change temperature of 25 °C. The values of the thermal parameters were determined at temperatures where both components of the PCM composite (Micronal^® and gypsum wall) were solid and below the phase-change temperature and then again at temperatures where one of the components (gypsum) was still solid, while the other one was already liquid (wax). The attempt to determine the parameters during the phase change was not made due the physicochemical processes taking place which would alter the measured data.     

Total Hydroxycinnamic Acids Assay: Prevalidation and Application on Lamiaceae Species

In this work, qualitative and quantitative analyses of total hydroxycinnamic acid (THA) derivatives in leaves, flowers and aerial parts of 32 Lamiaceae species were carried out. HPTLC analysis of plant material indicated rosmarinic acid as the main phenolic acid in 22 Lamiaceae plant extracts, while chlorogenic acid predominated in other 10 investigated species. Determination of THA in different medicinal plants was performed by colorimetric methods using chromogenic system of HCl-NaNO₂–Na₂MoO₄–NaOH and two standards: rosmarinic acid (R-THA procedure) and chlorogenic acid (C-THA procedure). Performance characteristics of THA assay were established, and the quality of the analytical procedures was evaluated using valuable prevalidation strategy. Good quality of the measurements at the lower analyte level, excellent resolution of blank and analyte signals, homogenous data material, ideal linear calibration and analytical evaluation functions, very low limit of detection [L _D(R-THA)?=?0.53 μg; L _D(C-THD)?=?1.75 μg] and limit of quantitation [L _Q(R-THD)?=?1.76 μg; L _Q(C-THD)?=?4.21 μg], and high precision and accuracy confirmed the high quality of investigated procedures as valuable tools in THA analysis. Application of these prevalidated, simple and rapid analytical methods revealed that the studied Lamiaceae plants differ greatly in their THA contents, ranging from 1.95 % (Acinos arvensis) to 11.03 % (Satureja subspicata). The results obtained from qualitative and quantitative analysis provided new information regarding phytochemical characterization of Lamiaceae species originating from Croatia and highlighted members of the genus Micromeria, Origanum, Melissa and Satureja as rich sources of hydroxycinnamic acids.     

Estimation of noise covariance matrices for periodic systems

Estimation of the noise covariance matrices for linear time‐variant stochastic dynamic periodic systems is treated. The novel offline method for estimation of the covariance matrices of the state and measurement noises is designed. The method is based on analysis of second‐order statistics of the state estimate produced by the linear multi‐step predictor. The estimates of the noise covariance matrices are unbiased and converge to the true values with increasing number of data. The theoretical results are illustrated in numerical examples. Copyright © 2011 John Wiley & Sons, Ltd.     

NiA and NiX zeolites as bifunctional electrocatalysts for water splitting in alkaline media

NiA and NiX zeolites were prepared and characterised using XRD, FTIR and SEM, and subsequently tested as electrodes for hydrogen (HER) and oxygen (OER) evolution reactions in alkaline media. Linear sweep voltammetry and chronoamperometry techniques showed that NiA has higher catalytic activity for these two reactions, as evidenced by higher current densities, which can be correlated with a higher weight fraction of Ni in this electrocatalyst than in the NiX and with its higher conductivity. HER and OER kinetic parameters, including Tafel slope, exchange current density and apparent activation energy were evaluated. Electrochemical impedance spectroscopy analysis yielded values of the resistance of the solution, charge transfer and mass transfer, as well as double layer capacitance and pseudo-capacitance of the working electrode, at different potentials and temperatures. Unlike the HER, during which the mass transfer resistance of the adsorbed intermediate is dominant in the case of NiA, the OER impedance response is controlled by the charge transfer process itself at the potentials of interest for these process. The overall resistance related to the HER is lower for NiA than for NiX.     

On inter-expressibility of logical connectives in Gödel fuzzy logic

In Gödel fuzzy propositional logic, neither conjunction nor implication is expressible (definable) in terms of the remaining three logical connectives.     

The influence of nanoadditives on surface, permeability and mechanical properties of self-organized organic–inorganic nanocomposite coatings

Transparent and colorless nanocomposite coatings were prepared from a hybrid organic–inorganic matrix and several inorganic nanofillers. The products are characterized by a high degree of self-assembling of the matrix which was prepared from an epoxy-functional organosilicon precursor and an oligomeric diamine. Unmodified and chemically modified montmorillonite, bentonite, laponite, and colloidal silica were used as nanofillers, differing in shape, size, and origin. The nanoadditive concentration in coatings was always 0.5 wt%. Solid-state NMR (¹³C and ²⁹Si CP/MAS) spectroscopy was used for estimation of polyaddition and polycondensation degree in the polymer matrix in order to evaluate its structure changes caused by interaction with the nanoadditives. The influence of the kind of additive on the dynamic mechanical properties, gas permeability, and surface properties (topography, roughness) is discussed.