Genetic algorithm optimisation of the maintenance scheduling of generating units in a power system

A new method for optimisation of the maintenance scheduling of generating units in a power system is developed. Maintenance is scheduled to minimise the risk through minimisation of the yearly value of the loss of load expectation (LOLE) taken as a measure of the power system reliability. The proposed method uses genetic algorithm to obtain the best solution resulting in a minimal value of the annual LOLE value for the power system in the analysed period. The operational constraints for generating units are included in the method. The proposed algorithm was tested on a Macedonian power system and the obtained results were compared with the results received from the approximate methodology. The results show the improved reliability of a power system with the maintenance schedule obtained by the new method compared to the results from the approximate methodology.     

Alternating phenylenevinylene and thienylenevinylene copolymers with cyano groups: Synthesis,photophysics and photovoltaics

Two alternating conjugated copolymers TTP and TTT were synthesized by Heck coupling of 2,3-bis-(5-bromothiophene-2-yl)acrylonitrile with 1,4-dihexyloxy-2,5-divinylbenzene and 3-hexyl-2,5-divinylthiophene, respectively. The absorption spectra of the copolymers in THF solution showed three maxima around 270, 370 and 460 nm with optical band gaps of 2.30–2.34 eV. The electrochemically estimated band gaps of copolymers were 2.04–2.10 eV. The thin film absorption spectra were broad and extended about from 250 to 600 nm with a long wavelength maximum near 470 nm. The copolymers emitted yellow-orange light with maximum at 528–551 nm in THF solution and 567–610 nm in thin film. TTP showed the most red shifted emission maximum between the copolymers. The performance of the photovoltaic cells which were fabricated using blends of the copolymers with 6,6-phenyl C61-butyric acid methyl ester (PCBM) (1:1 and 1:4, w/w) as well as pure copolymers was investigated.     

Relationship between effective ionic radii,structure and electro-mechanical properties of zirconia stabilized with rare earth oxides M<Subscript>2</Subscript>O<Subscript>3</Subscript> (M = Yb,Y, Sm)

Zirconia stabilized with various concentrations of rare earth oxides of Yb, Sm and Y with different effective ionic radii ratio between the dopant and host cations was studied. In particular, structure, phase composition, compositional range for existence of cubic solid solutions and their phase transformations, stabilization degree of high-temperature phases and the crystal chemistry and type of solid solutions were investigated. These findings were related to the measured material characteristics, namely the electrical conductivity, microhardness and effective elastic modulus, to elucidate various effects important for practical applications, such as an increase of electrical conductivity due to the pyrochlore phase occurrence or an increase of microhardness arising from the effect of dynamic strain ageing.     

Contribution to the brachistochrone problem with Coulomb friction

This paper formulates and solves in closed form (expressed by elementary functions) the brachistochrone problem with Coulomb friction of a particle which moves down a rough curve in a uniform gravitational field assuming that the initial velocity of the particle is different from zero. The problem is solved by the application of variational calculus. Two variants are considered: first, the initial position and the final position of the particle are given; second, the initial position is given, and the final position lies on a given vertical straight line. The new approach in treating this problem by variational calculus lies in the fact that the projection sign of the normal reaction force of the rough curve onto the normal to the curve is introduced as the additional constraint in the form of an inequality. This inequality is transformed into an equality by introducing a new state variable. Although this is fundamentally a constrained variational problem, by further introducing a new functional with an expanded set of unknown functions, it is transformed into an unconstrained problem where broken extremals appear. Brachistochrone equations in parametric form are obtained for both variants which are examined, with the slope angle of the tangent to the brachistochrone being taken as the parameter. These equations contain a certain number of unknown constants which are determined from the corresponding systems of nonlinear algebraic equations. They are solved by an alternative approach which is based on the application of differential evolution. The obtained brachistochrones are generally two-segment curves with the initial line segment representing a free-fall parabola in nonresistant medium. It is shown that regarding the special values of the parameters the results of the paper coincide with the known results from literature.     

W5O14 Nanowires

We report on the synthesis of quasi‐1D W₅O₁₄ crystals using NiI₂ as a growth promoter. Photoelectron spectroscopy revealed the metallic conductivity of the W₅O₁₄ nanowires, which was also confirmed by direct‐transport measurements on a double‐stranded nanowire. Scanning electron microscopy and transmission electron‐diffraction data are correlated with details of crystal growth revealing the possible mechanism of the formation of this rarely synthesized phase, which was reported as a homogeneous phase only in 1978 by McColm et al., and in the meantime has been declared as a compound that is rare.     

Antioxidant Characteristics of Hops and Hop Products

The method based on the reaction of stable DPPH radical proved to be the best for the determination of antioxidant characteristics of hops and hop products. Antioxidant activity is expressed as the rate of decline in absorbance of the reaction environment and assessed in relative percents. Differences in the values of antioxidant activity were determined in Czech and foreign hop varieties. The highest antioxidant activities in the scope of 70 to 80% rel. were measured in Saaz and Spalter Select. Antioxidant activity in most of the varieties moved in the scope of 40 to 60% rel. A part of antioxidant activity of hops is irreversibly lost in the course of drying. The loss does not usually exceed 5% of the original RA_DPPH value. Drying also resulted in a decrease of polyphenol compound contents. Drying in belt and chamber kilns is comparable from the point of view of preserving hop antioxidant properties. Results of determination of antioxidant activity in hot water extracts of raw hops and ground hops were comparable and statistically non‐significant. The same held true for pelletizing of ground hops. The antioxidant activity of raw hops declined in the course of long‐term storage in dependence on storage temperature. Storage temperature had no effect on the antioxidant activity of the hop pellets packed in a multi‐layer foil without air access.     

Influence of the chemical composition of 20MoCrS4 and low‐alloyed TRIP steel on the intensity of high temperature corrosion

Material behaviour in a corroding medium varies depending on its properties. These properties are affected by the treatment, alloy elements and last but not least its surface condition. The sensitivity of a material to iron scale formation and decarburisation limits some technological processes, especially those where materials are exposed to a corroding medium at high temperatures for a very long time. A typical example is the heating of semi‐products to forming temperature. Considering that similar materials can react differently under the same heating conditions, it is important to know the characteristic behaviour of a material in certain production processes. A comparison of two kinds of steels during model treatment was carried out in order to be able to determine the influence of different heating parameters. The model treatment consisted of three different heating temperatures at three different time durations. The intensity of the oxidation process was analysed by means of mass increments and the thickness of the oxide layer was detected via metallography. The depth and intensity of the surface layer decarburisation was evaluated from the profile of the microhardness change curve.     

Effect of humic acid on fermentation and ciliate protozoan population in rumen fluid of sheep in vitro

BACKGROUND: Humic acid (HA) as a product of decomposition of animal and plant tissue is used in animal production as a feed supplement, antimicrobial product and growth stimulator. The objective of the present in vitro study was to investigate the effects of dietary humic acid as a commercial Humacid 60 Basic (H60B) feed additive preparation on rumen fermentation and the ciliate protozoan population in the rumen fluid of sheep using a high fibre (HF) and high concentrate (HC) diet in batch cultures and artificial rumen (RUSITEC). RESULTS: Production of total volatile fatty acids (VFAs) was significantly decreased (P < 0.001) for batch cultures by the HF‐H60B diet. The HF‐H60B diet decreased ammonia N in RUSITEC (P < 0.001). An increase in the population of Enoploplastron triloricatum, Isotricha spp. and Ophryoscolex c. tricoronatus with the HF‐H60B diet and Diploplastron affine with the HC‐H60B was observed. The H60B did not affect the total ciliate population and Entodinium spp. CONCLUSION: It can be concluded that dietary humic acid preparations are not effective as dietary antiprotozoal agents. Humic acid might enhance microbial growth and energy efficiency in doses up to 10 g kg^?1 DM of diet. Copyright © 2009 Society of Chemical Industry     

Color rendering properties of light continuously modulated by an electrochromic switchable device

Every chromogenic switchable window gives rise to considerable change of spectral power distribution of the light crossing trough. The filtered light continuously changes during charging/discharging of the device, seen as its coloration/discoloration. As this process occurs continuously, it causes continuous change of colors on an illuminated multicolored scene. The ability of an electrochromic (EC) switchable unit to modulate daylight and different artificial lights passing through it is studied here. The color rendering properties of such a variable light are evaluated. The range of the effect and its consequences on the color of a scene can be adequately described by the change in chroma and hue angle during the modulation of light. These effects were evaluated by different light sources shining through the same EC unit. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 321–329, 2009     

Screening of lactic acid bacteria for antimicrobial properties from mayonnaise-based products and raw materials

A collection of lactic acid bacteria isolated from both mayonnaise-based products and raw materials used to manufacture them was tested for antimicrobial activity. Out of 144 strains (97 lactobacilli, 23 lactococci and 24 enterococci) only three supernatants of Enterococcus spp. strains (EN3, EN14 and EN15) exhibited activity against lactobacilli and lactococci. The supernatant of the strain EN3 exclusively inhibited the growth of Bacillus cereus and Listeria monocytogenes. Enterococcus strains EN3, EN14 and EN15 produced thermostable bacteriocins, which had antibacterial activity.