Voltammetric method using a lead film electrode for the determination of caffeic acid in a plant material

This paper deals with development of an adsorptive stripping voltammetric method for determination of caffeic acid (CA) at a lead film electrode (PbFE). The working electrode was prepared in situ on a glassy carbon substrate as a “mercury-free” electrochemical sensor. The method is based on the accumulation by adsorption of caffeic acid on PbFE and then the oxidation of CA during the stripping step. In a acetate buffer based supporting medium the oxidation signal for caffeic acid was found to be proportional to the CA concentration in the range from 1 × 10⁻⁸ to 5 × 10⁻⁷ mol/L with the limit of detection equal to 4 × 10⁻⁹ mol/L (with preconcentration for 30 s). The method, operated in the square-wave voltammetric mode, was successfully applied to the determination of CA in a plant material (herbs of Plantago lanceolata). The content of caffeic acid received by the proposed method was in close agreement with that obtained by high performance thin-layer chromatography (HPTLC) combined with densitometry. This appears to be the first application of a lead film electrode to the determination of an organic compound in such complicated matrix.     

New conductive thick-film paste based on silver nanopowder for high power and high temperature applications

A new thick-film material for screen-printing technology, based on nanoscale silver powders with the particle size distribution 5-55 nm is presented. Silver nanopowder used for paste preparation was elaborated by the authors. The compatibility of investigated paste was proven with alumina, silicon, Kapton foil and glass. The main advantage of this paste is sinterability at much lower temperatures (around 300 °C) compared to pastes obtained from micro-powders (650-850 °C). The thicknesses of obtained layers are 2-3 μm. The elaborated layers are dense and well sintered, exhibit good adhesion to all above mentioned substrates and low resistivity as well as very good resistance to high power and elevated temperatures. The results of loading the layers deposited on alumina substrates with high current and exposed to high temperature are presented as well.     

Investigation on electrical and microstructural properties of Thick Film Lead-Free resistor series under various firing conditions

The paper presents investigation of four lead free thick film resistor pastes, developed at ITME, denoted R-100, R-1k, R-10k and R-100k with sheet resistivities of 0.1, 1, 10 and 100 kΩ/□, respectively. The resistors were based on RuO₂ as the conductive phase. The aim of the work was to evaluate the influence of firing conditions of the resistive pastes on a sintering process. The pastes were screen printed onto alumina substrate with prefired AgPd lead-free terminations. They were fired at several temperatures from 750 to 950 °C for 10 min at peak temperature, as well as fired at the highest temperature for 6 h, in order to bring the sintering process into the equilibrium. The properties of the resistors, i.e , sheet resistivity and temperature coefficient of resistance (TCR), microstructure changes, glass crystallization upon firing, etc., were examined. Dried and fired resistor samples were evaluated by X-Ray diffraction analysis and by the scanning electron microscopy. The RuO₂ conductive phase maintained the same crystal structure regardless of the firing conditions. No devitrification was observed in lead-free resistors glasses. The lattice constants of RuO₂ were uniform after firing at temperatures over 800 °C. The resistors matched the desired resistivity and the TCR was the least temperature dependent at the firing temperatures around 850 °C.     

Investigation on a new silver photoimageable conductor

A new thick film photoimageable silver paste of improved properties has been elaborated. The paste is less sensitive to the visible light. Certain disadvantages of most commercially available materials, such as necessity of operating with the paste in the room illuminating with yellow, green or red light has been eliminated. Further improvement of conductive silver pastes to enable reducing lines width down to 10 μm has been done.     

Preferences in multi-objective evolutionary optimisation of electric motor speed control with hardware in the loop

This paper presents the design of a robust Pareto-optimal controller with the designer preference articulation for a Permanent Magnet Synchronous Motor (PMSM). An evolutionary multi-objective optimisation (EMOO) algorithm is used to tune the proportional integral (PI) speed regulator in the Direct Torque Control drive system.Approximation of the Pareto front with hardware in the loop (HiL) is chosen as an alternative to the time-consuming software simulation studies. Thanks to this approach problems of un-modelled plant dynamics are alleviated and additional manual tuning on-line is not required. The weak point of the HiL approach is caused by disruptive presence of noise which affects the performance of EMOO. This influence is strongly problem-dependent; therefore no generalized results have yet been presented in the literature. In this paper the robustness features of the proposed design approach are verified using the state-of-the-art multi-objective evolutionary Non-dominated Sorting Genetic Algorithm (NSGA-II; Deb, 2001 [1]).The on-line optimised motor drive speed controller is shown to be effective, possessing good dynamic characteristics, demonstrating applicability of the a priori preference articulation technique to the controller design. The final Pareto-optimal solution is selected according to the designer's preference articulation before the Pareto front is approximated by EMOO.     

Vertex reconstruction using a single layer silicon detector

Typical vertex finding algorithms use reconstructed tracks, registered in a multi-layer detector, which directly point to the common point of origin. A detector with a single layer of silicon sensors registers the passage of primary particles only in one place. Nevertheless, the information available from these hits can also be used to estimate the vertex position, when the geometrical properties of silicon sensors and the measured ionization energy losses of the particles are fully exploited. In this paper, the algorithm used for this purpose in the PHOBOS experiment is described. The vertex reconstruction performance is studied using simulations and compared with results obtained from real data. The very large acceptance of a single-layered multiplicity detector permits vertex reconstruction for low multiplicity events where other methods, using small acceptance subdetectors, fail because of insufficient number of registered primary tracks.     

Effect of cultivar and fruit storage on basic composition of clear and cloudy pear juices

BackgroundPears due to low acidity are a suitable raw material for the production of multifruit nectars thus it is justified to determine the chemical composition and investigate the effect of cultivar and fruit maturity on juices quality.MethodsJuices from ‘Alexander Lucas’ and ‘Conference’ cultivars were produced after harvest and after 3 months of pears storage.ResultsAverage yield of clear juices was 76.4% for ‘Conference’ cultivar and 74.3% for ‘Alexander Lucas’. In the case of cloudy juices, the yield was lower by about 3%. Processing of ‘Conference’ cv. from stored fruit resulted in yield decrease compared to fruits after harvest; this was not in case of ‘Alexander Lucas’ in 2008, where juices produced from stored fruits were characterized by a higher yield compared to fresh fruit.Total solids content in clear juices was 125–135 g/L and 135–141 g/L for cloudy juices. ABTS^●+ and total phenolics analysis showed that cloudy juices were characterized by a higher antioxidant activity and phenolics content than the clear ones.ConclusionPear storage, on the contrary to apples, does not decrease their suitability for cloudy juice production. Cloudy juices as a rule have higher antioxidant activity than the clear ones.     

Impact of enzyme on quality of blackcurrant and plum juices

The aim of work was optimization of technology of cloudy blackcurrant and plum juices production. The major concern was the increase of product cloudiness and its stability. Red fruit were processed with commercial pectinolytic preparations (Pectinex BE Colour, Pectinex BE XXL, and mixture of Rohapect PTE with Rohament PL). The effect of enzyme dose, maceration time and addition of ascorbic acid (in case of plum) on juices quality was investigated. Using single enzyme, either polygalacturonase or pectin lyase did not allow obtaining juices with high enough turbidity, however appropriate enzyme mixture allowed to obtain cloudy juice with the turbidity of at least 230 NTU for blackcurrant and above 500 NTU for plum juice. The best pressing-yield for blackcurrant was achieved with polygalacturonase and pectin lyase, 65 g/100 g after 1 h and 74 g/100 g after 4 h of pectinolysis. The macerating mixture gave about 58÷59 g/100 g yield, irrespectively of enzymation time. Pressing-yield of plum juices was in the range of 94÷97 g/100 g due to the fact that practically only skins were retained on pressing cloth. Addition of ascorbic acid (AA) during plum juice processing in quantity of 500 mg/kg had protective effect on anthocyanins. In control plum juices range of anthocyanins contents were 12.1÷16.5 mg/100 ml while in juice with AA addition even 21.4÷24.5 mg/100 ml.