Novel optimal temperature profile for acidification process of Lactobacillus bulgaricus and Streptococcus thermophilus in yoghurt fermentation using artificial neural network and genetic algorithm

The acidification behavior of Lactobacillus bulgaricus and Streptococcus thermophilus for yoghurt production was investigated along temperature profiles within the optimal window of 38-44 degrees C. For the optimal acidification temperature profile search, an optimization engine module built on a modular artificial neural network (ANN) and genetic algorithm (GA) was used. Fourteen batches of yoghurt fermentations were evaluated using different temperature profiles in order to train and validate the ANN sub-module. The ANN captured the nonlinear relationship between temperature profiles and acidification patterns on training data after 150 epochs. This served as an evaluation function for the GA. The acidification slope of the temperature profile was the performance index. The GA sub-module iteratively evolved better temperature profiles across generations using GA operations. The stopping criterion was met after 11 generations. The optimal profile showed an acidification slope of 0.06117 compared to an initial value of 0.0127 and at a set point sequence of 43, 38, 44, 43, and 39 degrees C. Laboratory evaluation of three replicates of the GA suggested optimum profile of 43, 38, 44, 43, and 39 degrees C gave an average slope of 0.04132. The optimization engine used (to be published elsewhere) could effectively search for optimal profiles of different physico-chemical parameters of fermentation processes

Progress and Prospect on Stability of Perovskite Photovoltaics

Solar energy has the potential to solve world energy problem as it is pollution- free. It could be enhanced using perovskite material as an absorber in perovskite solar cells. The history and what this material is made up of are emphasized. Different methods of fabrication, improving the power conversion efficiency (PCE) and factors influencing degradation of perovskite-based solar are stated. Because of the fact that this material based solar cells are not yet developed, its stability was reviewed to bring different technology employed in tackling the stability aiming for a better understanding of the material and the devices and facilitates the commercialization of perovskite solar cell

Optoelectronic characterizations of vacuum evaporated Cu2SnS3 thin films for device application..

The search for new materials suitable for application in photovoltaic cell necessitates the growth of non-toxic, cheap earthly abundant, ternary compound of Cu2SnS3 thin film. Thin films of Cu2SnS3 semiconductors were prepared by thermal evaporation and sulphurization techniques in vacuum. The bi-layer of Cu-Sn precursors was deposited on cleaned microscopic glass substrate at controlled thickness of 100nm, 500nm and 1000nm and at different substrate temperatures of 270, 1000C and 2000C.The bi-layer of Cu-Sn was sulphurized in a custom-built reactor for 1hour at 4000C to form Cu2SnS3 ternary films. The structure and morphology characteristics of Cu2SnS3 ternary film were investigated by X-Ray Diffraction and Scanning Electron Microscope. Four point probe and semiconductor characterization system were used to determine the electrical properties of the deposited Cu2SnS3 ternary films. UV –Vis Spectrophotometer measured the optical characteristics of the Cu2SnS3 ternary film. The film samples deposited at 270C and at thickness of 100nm and 500nm yielded Cu2SnS3 ternary film .The grain size of deposited Cu2SnS3 ternary film is about 1μm and the films were rough (Average Roughness, Ra = 3133.50nm and Root Mean Square, Rq = 3942.60nm). The elemental composition of the film as determined by Energy Dispersive X-Ray System (EDS) are Cu (24.89%), Sn (15.82%), S (16.29%) and artefacts such as Na, Si, Mg and O.The surface profiler shows that the deposited Cu2SnS3films are rough. Monoclinic, Cu2SnS3 [-1 3 1] at peak 2Ѳ = 28.40 and Anorthic Cu2SnS3 [-2 0 10 ] at peak 2Ѳ = 47.250 were identified. The electrical resistivity, ρ, of the Cu2SnS3 ternary film is 2.55 x 10-3 Ω-cm. The Energy band gap, Eg, of the deposited Cu2SnS3 film is 1.65eV, Refractive Index, n is 1.14, Extinction Coefficient, K,is 5.27 x 109 and Optical Conductivity , σ0 is 6.74708E+16 Ω-1cm-1. These results clearly show good potentials of deposited Cu2SnS3 ternary film as an abundant, cheap, non-toxic absorber layer of photovoltaic solar cell.Key words: Vacuum Evaporation, Sulphurization, Energy band gap, Absorber layer, solar cells

Silicon Heterojunction Solar Cells with Epitaxial Buffer Layer on Textured Substrates

In the present work we report recent results for silicon heterojunction solar cells deposited by conventional Plasma Enhanced Chemical Vapor Deposition (PECVD) technique on textured Czochralski (CZ) silicon wafers. A new texturing technique was developed using a wet anisotropic chemical etching with a tetramethyl-ammonium hydroxide (TMAH) solution. An increase of the device photogenerated current, with maximum short circuit current of more then 36 mA/cm2 was attained. A study of the first stages of device layer growth is presented with relation to plasma ignition in PECVD systems. An original passivation technique of the amorphous/crystalline interface defects was implemented for textured wafers. Using this scheme a reproducible efficiency in excess of 16% was obtained on CZ textured wafers

Effects of pre-buckling on the bending of organic electronic structures

This paper explores the extent to which pre-buckling of layers (in thin film multilayered structures) can be used to increase the flexibility of organic electronic devices. The deformation of wavy/buckle profiles, with a range of nano- and micro-scale wavelengths, is modeled using finite element simulations. The predictions from the models are then validated using experiments that involve the bending of layered structures that are relevant to flexible organic electronics. The introduction of pre-buckled profiles is shown to increase the range of deformation that is applied to model structures, prior to onset of significant stresses and strains. The implications of the work are discussed for the design of robust flexible organic solar cells

Cold welding of organic light emitting diode: Interfacial and contact models

This paper presents the results of an analytical and computational study of the contacts and interfacial fracture associated with the cold welding of Organic Light Emitting diodes (OLEDs). The effects of impurities (within the possible interfaces) are explored for contacts and interfacial fracture between layers that are relevant to model OLEDs. The models are used to study the effects of adhesion, pressure, thin film layer thickness and dust particle modulus (between the contacting surfaces) on contact profiles around impurities between cold-welded thin films. The lift-off stage of thin films (during cold welding) is then modeled as an interfacial fracture process. A combination of adhesion and interfacial fracture theories is used to provide new insights for the design of improved contact and interfacial separation during cold welding. The implications of the results are discussed for the design and fabrication of cold welded OLED structures

Pressure effects on interfacial surface contacts and performance of organic solar cells

This paper explores the effects of pressure on the interfacial surface contacts and the performance of organic solar cells. A combination of experimental techniques and analytical/computational models is used to study the evolving surface contacts profiles that occur when compliant, semi-rigid and rigid particles are interlocked between adjacent layers in model solar cell structures. The effects of layer surface roughness and interlocked (trapped) particles are also considered along with the effects of surface energy, adhesion energy, and pressure. The results show that increased interfacial contact lengths and decreased void lengths are associated with the application of increased pressure. Increased pressure also results in significant improvements in power conversion efficiency. These improvements in power conversion efficiency are associated with the closure up of micro- and nano-voids due to the application of pressure to layers produced via spin coating and thermal evaporation. The results suggest that pressure-induced contacts can be used to enhance the performance of organic solar cells