Graphene and carbon black filled conductive nanocomposite films for heating element applications

Graphene has ultra-high electrical and thermal conductivity, which makes graphene as the most encouraging fillers for thermally conductive composites. Graphene and/or carbon black filled conductive polymer composite (CPC) films used as heating element are smarter than the traditional heating elements due to less environmental pollution, ease of application on many surfaces and possess the merits of lightweight. In this study, we investigated mainly the production, characterization and industrial application of graphene/carbon black reinforced styrene acrylic copolymer emulsion matrix composite films deposited on polyvinyl chloride for flexible heating element. After that, the films were dried at room temperature for 24 h in air. Structural and surface properties of the CPC films were characterized by X-ray diffraction and scanning electron microscopy. Temperature, time and voltage relation of the produced composite films were investigated. Heating and electrical properties of the CPC films were determined by using a thermal camera and 4-point probe measurement system, respectively. The electrical resistivity of the CPC films decreases from ~?10⁸ to 10¹ Ω cm with increasing the filler content or using a combination of two fillers. Graphene and carbon black filled conductive polymer composites to be considered as candidates for flexible heating element applications exhibited good electrical and heating properties thanks to synergistic effect of fillers.     

Tracer Particles for Application to PIV Studies of Liquid Helium

Material selection and methods for introduction of tracer particles into liquid helium are reviewed for application in particle image velocimetry experiments. The combination of low temperature environment and low-density fluid place unique requirements on particle selection. Options discussed include a variety of commercially available solid particles of different size and density as well as solid particles generated by freezing liquids or gases. Recommendations are presented based on the dynamic behavior of the particles. Also, methods for introducing the particles into liquid helium are discussed.     

A simplified model based on clearness index for estimating yearly performance of hybrid PV energy systems

A simplified model for estimating the energy contribution of PV converter in a hybrid PV–wind system is presented. The simplified model determines the yearly solar fraction, that is the fraction of energy demand provided by PV, and the remaining loss of load (LOL) is assumed to be provided by wind turbines. The novel model is based on simulation results derived from 8 years of measured hour‐by‐hour solar irradiation data from five different locations in the world. The system performance is simulated by the PV–wind energy simulation program of the Cardiff School of Engineering (ARES). An hourly constant load profile is assumed. The performance of a PV system is primarily dependent on the solar irradiation distribution in a given location for the period of time in question. The new model correlates the location dependence observed in the yearly solar fraction curves of different data sets with one of the most characteristic solar irradiation distribution parameters, the yearly clearness index of the respective solar irradiation data. The new model requires the yearly clearness index value, which is commonly available for most locations throughout the world, as input. As the novel model is validated with solar irradiation data from different locations in the world, it could be used for predicting the solar fraction in a hybrid PV system with a very high level of accuracy, for a wide range of climates. Copyright © 2002 John Wiley & Sons, Ltd.     

A Set Theoretic Framework for Watermarking and Its Application to Semifragile Tamper Detection

We introduce a set theoretic framework for watermarking. Multiple requirements, such as watermark embedding strength, imperceptibility, robustness to benign signal processing, and fragility under malicious attacks are described as constraint sets and a watermarked image is determined as a feasible solution satisfying these constraints. We illustrate that several constraints can be formulated as convex sets and develop a watermarking algorithm based on the method of projections onto convex sets. The framework allows flexible incorporation of different constraints, including embedding strength requirements for multiple watermarks that share the same spatial context and different imperceptibility requirements based on frequency-weighted error and local texture perceptual models. We illustrate the effectiveness of the framework by designing a hierarchical semifragile watermark that is tolerant to mild compression, allows tamper localization, and is fragile under aggressive compression. Using a quad-tree representation, a spatial resolution hierarchy is established on the image and a watermark is embedded corresponding to each node of the hierarchy. The spatial hierarchy of watermarks provides a graceful tradeoff between robustness and localization under mild JPEG compression, where watermarks at coarser levels demonstrate progressively higher immunity to JPEG compression. Under aggressive compression, watermarks at all hierarchy levels vanish, indicating a lack of trust in the image data. The constraints implicitly partition watermark power in the resolution hierarchy as well as among image regions based on robustness and invisibility requirements. Experimental results illustrate the flexibility and effectiveness of the method     

Seasonal changes in the proximate chemical compositions and fatty acids of chub mackerel (Scomber japonicus) and horse mackerel (Trachurus trachurus) from the north eastern Mediterranean Sea

The effects of seasonal variations on the proximate chemical compositions and fatty acid profiles of chub mackerel (Scomber japonicus) and horse mackerel (Trachurus trachurus) captured in the north‐eastern Mediterranean Sea were investigated. Protein fluctuations were observed in two species for all seasons. The lipid content of both species was lower in winter than in autumn and spring. In all seasons, the major fatty acids in both species were observed to be palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1 ω9), eicosapentaenoic acid (20:5 ω3) and docosahexaenoic acid (20:6 ω3). Chub mackerel and horse mackerel exhibited seasonal fluctuations in their fatty acid contents. The fatty acid profile of the two species had a higher degree of unsaturation during winter. The levels of EPA in chub mackerel in winter, spring and autumn were 5.96%, 4.86% and 4.33%, respectively, while those of DHA were 24.94%, 18.75% and 17.12%, respectively. The levels of EPA in horse mackerel in winter, spring and autumn were 5.42%, 5.03% and 4.86%, respectively, while those of DHA were 14.96%, 13.31% and 11.10%, respectively. The PUFA (polyunsaturated fatty acids) values and ω3/ω6 ratios in the two species were highest in winter. The results indicate that chub mackerel and horse mackerel captured in the north‐eastern Mediterranean Sea, which are among the most important fish in Turkey and of international commercial value, are a good source of nutrition for human consumption in terms of their proximate chemical composition and fatty acids.     

A preemptive goal programming method for aggregating OWA operator weights in group decision making

This paper reveals that OWA operator weights cannot be aggregated by the weighted arithmetic or geometric average method in group decision making. A preemptive goal programming method (PGPM) is proposed for aggregating OWA operator weights, which is an extension of the minimax disparity approach developed earlier by the same authors. The effectiveness of PGPM is illustrated with a numerical example.     

A Computer Aided Investigation on Strain Movements in Compacts Under Constant Stress Within the Die

A 2.54cm diameter punch and die set has been used in conjunction with a Mayes Hydraulic Machine to examine strain movements within the die of compacts maintained at constant stress. These were prepared from the bases Avicel PH 101 (AV), Sta-Rx 1500 (ST), Paracetamol DC (PC), Emdex (ED) and Eacompress (EC).

Compression force and punch movements were simultaneously monitored using a CBM nicroconputer with disk storage of data.

All compacts showed time dependent consolidation under constar. stress when held at 'holding time' of up to 60s. PC, AV and ST exhibited comparable movements but that of ED and EC ware less.

Elastic recovery on sudden release of load was followed using machine code logging over a period of 90ms. Large recoveries were recorded for AV, PC and ST. If load release was immediate (zero holding time) then the recovery was greater when compared with recovery after holding tines of 30 and 60s, suggesting that some elastic energy was dissipated during the holding time. Elastic recovery of ED and EC was about half that of the other bases. Although these bases also showed reduced recovery with holding tine, percentage reduction was smaller than for the other bases.

Following elastic recovery, a much slower viscoelastic movement could be demonstrated. It was difficult to clearly demarcate the division between viscoelastic and elastic movement but it appeared that the movement on viscoelastic consolidation was comparable to that en recovery when the load was removed.

There are many references to tine dependent effects during tablet compression to be found in the literature. One of the earliest was due to Rees and Shotton (1) who found that the crushing strength of sodium chloride tablets could double after the lapse of one hour from ejection. This has recently been shown by Rue and Barkworth (2) to be due to the existence of a work hardened outer shell which inhibits relaxation by viscoelastic flow.

Several authors (3,4,5) have investigated the stress decay that occurs when a tablet is held at a nominally constant force. Thus Wells and Langridge (5) monitored the fall from a peak pressure of 332MN/m²on a tablet prepared in a single punch machine turned by hand. Similar techniques have been described by Rees and Rue (3), Kiestand and others (4) and Shlanta and Milosovich (6). However as Rees and Rue have pointed out, these methods measure stress relaxation under constant strain conditions. Their results and conclusions differed from those of David and Augsburger (7) who compressed the same direct compression bases on a rotary tablet machine. In a rotary machine compression takes place under virtually constant, stress conditions because of the buffer effect of the powerful springs fitted to the compression wheels.

This paper describes some techniques and observations on the compression of some direct compression bases using a Mayes Hydraulic Testing Machine (WH Mayes (Windsor) Ltd) which is capable of maintaining constant stress conditions on a compact formed in a punch and die set mounted between the platens.     

Sorption of acid red 57 from aqueous solution onto sepiolite

Sepiolite, a highly porous mineral, is becoming widely used as an alternative material in areas where sorptive, catalytic and rheological applications are required. High ion exchange capacity and high surface area and more importantly its relatively cheap price make it an attractive adsorbent. In this study, the adsorption of acid red 57 by natural mesoporous sepiolite has been examined in order to measure the ability of this mineral to remove coloured textile dyes from wastewater. For this purpose, a series of batch adsorption tests of acid red 57 from aqueous sepiolite solutions have been systematically investigated as a function of parameters such as pH, ionic strength and temperature. Adsorption equilibrium was reached within 1h. The removal of acid red 57 decreases with pH from 3 to 9 and temperature from 25 to 55 degrees C, whereas it increases with ionic strength from 0 to 0.5 mol L(-1). Adsorption isotherms of acid red on sepiolite were determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to fit the isotherm data better than the Freundlich model. The physical properties of this adsorbent were consistent with the parameters obtained from the isotherm equations. Approximately, 21.49% weight loss was observed. The surface area value of sepiolite was 342 m2 g(-1) at 105 degrees C, and it increased to 357 m2 g(-1) at 200 degrees C. Further increase in temperature caused channel plugging and crystal structure deformation, as a result the surface area values showed a decrease with temperature. The data obtained from adsorption isotherms at different temperatures have been used to calculate some thermodynamic quantities such as the Gibbs energy, heat and entropy of adsorption. The thermodynamic data indicate that acid red 57 adsorption onto sepiolite is characterized by physical adsorption. The dimensionless separation factor (RL) have shown that sepiolite can be used for removal of acid red 57 from aqueous solutions. The sorption capacity of the sepiolite is comparable to the other available adsorbents, and it is quite cheaper.     

Artificial neural network modelling and experimental verification of the operating current of mono-crystalline photovoltaic modules

This article presents the artificial neural network modelling of the operating current of a 120 Wp of mono-crystalline photovoltaic module. As an alternative method to analytical modelling approaches, this study uses the advantages of neural networks such as no required knowledge of internal system parameters, less computational effort and a compact solution for multivariable problems. Generalised regression neural network model is used in the present article to predict the operating current of the photovoltaic module. To show its merit, the current predicted from the artificial neural network modelling is compared to that from the analytical model. The five-parameter analytical model is drawn from the equivalent electrical circuit that includes light-generated current, diode reverse saturation current, and series and shunt resistances. The operating current predicted from both the neural and analytical models are compared to the measured current. Results have shown that the artificial neural network modelling provides a better prediction of the current than the five-parameter analytical model.