Efficient and low cost devices for solar energy conversion: Efficiency and stability of some natural-dye-sensitized solar cells

Dye-sensitized solar cells, named by us Dye-Cells, are one of the most promising devices for solar energy conversion due to their reduced production cost and low environmental impact, especially those sensitized by natural dyes. The efficiency and stability of devices based on natural sensitizers such as mulberry (Morus alba Lam), blueberry (Vaccinium myrtillus Lam), and jaboticaba`s skin (Mirtus cauliflora Mart) were investigated. Dye-Cells prepared with aqueous mulberry extract presented the highest P(max) value (1.6 mW cm(-2)) with J(sc) = 6.14 mA cm(-2) and V(oc) = 0.49 V, Photoelectrochemical parameters of 16 cm(2) active area devices sensitized by mulberry dye were constant for 14 weeks of continuous evaluation. Moreover, the cell remained stable even after 36 weeks with a fairly good efficiency. Therefore, mulberry dye opens up a perspective of commercial feasibility for inexpensive and environmentally friendly Dye-Cells. (C) 2009 Elsevier B.V. All rights reserved.

Role of Polyelectrolyte for Layer-by-Layer Compact TiO(2) Films in Efficiency Enhanced Dye-Sensitized Solar Cells

Efficient compact TiO(2) films using different polyeleetrolytes are prepared by the layer-by-layer technique (LbL) and applied as an effective contact and blocking film in dye-sensitized solar cells (DSCs). The polyanion thermal stability plays a major role on the compact layers, which decreases back electron transfer processes and current losses at the FTO/TiO(2) interface. FESEM images show that polyelectrolytes such is sodium sullonated polystyrene (PSS) and sulfonated lignin (SE), in comparison to poly(acrylic acid) (FAA), ensure an adequate morphology for the LbL TiO(2) layer deposited before the mesoporous film, even triter the sintering step at 450 degrees C. The so treated photoanode in DSCs leads to a 30% improvement On the overall conversion efficiency. Electrochemical impedance spectroscopy (EIS) is employed to ascertain the role of die compact films with such polyelectrolytes. The significant increase in V(oc) of the solar cells with adequate polyelectrolytes in the LbL TiO(2) films shows their pivotal role in decreasing the electron recombination at the FTO surface and enhancing the electrical contact of FTO with the mesoporous TiO(2) layer.

Em busca da sustentabilidade: células solares sensibilizadas por extratos naturais

The present work reports the use of anthocyanins extracted from mulberry (Morus Alba L.), raspberry (Rubus Idaeus L.) and blueberry (Vaccinium myrtillus L.) as sensitizers in dye-sensitized solar cells. The conversion efficiency of these devices is dependent on the extracts employed and can be rationalized in terms of their composition and spectral properties. Solar cells sensitized by the mulberry extract showed the highest efficiency among the fruits investigated. Moreover, a 16 cm² active area solar cell with the mulberry extract has presented fair good efficiency of conversion for natural dye-based solar cells, besides stability over twenty weeks, showing perspectives for developing these low cost devices with a commercial viability.

Africanized honey bees more efficiently convert protein diets into hemolymph protein than do Carniolan bees (Apis mellifera carnica)

The superiority of Africanized over European honey bees in tropical and subtropical regions of the New World is both well documented and poorly understood. As part of an effort to try to understand the process by which the displacement of European bees occurred, we examined the ability of these two types of bees and of hybrids between the two to convert natural and artificial diets into usable protein. Newly emerged bees from colonies of tropically adapted Africanized and temperate-origin Carniolan bees and first-generation hybrids between the two were caged and fed artificial and natural protein diets for six days to determine whether there were differences in their ability to use these diets. The Africanized bees developed significantly higher protein levels in the hemolymph than did the Carniolan bees. The difference was 31% when the bees were fed bee bread (37.5 and 28.56 mu g protein/mu L hemolymph, respectively). The hybrids developed protein levels intermediate between the two parental types. These were approximately 10 times the levels found in bees fed with sucrose alone. Superior food conversion efficiency of the Africanized bees may be one of the reasons for their superiority both in the wild and for beekeeping in tropical and subtropical Latin America.

A novel use for sugarcane bagasse hemicellulosic fraction: Xylitol enzymatic production

The excess of sugarcane bagasse (SCB) from the sugar-alcohol industry is considered a by-product with great potential for many bioproducts production. This work had as objective to verify the performance of sugarcane bagasse hemicellulosic hydrolysate (SCBHH) as source of sugars for enzymatic or in vitro xylitol production. For this purpose, xylitol enzymatic production was evaluated using different concentrations of treated SCBHH in the commercial reaction media. The weak acid hydrolysis of SCB provided a hydrolysate with 18 g L(-1) and 6 g L(-1) of xylose and glucose, respectively. Considering the reactions, changes at xylose xylitol conversion efficiency and volumetric productivity in xylitol were not observed for the control experiment and using 20 and 40% v.v (1) of SCBHH in the reaction media. The conversion efficiency achieved 100% in all the experiments tested. The results showed that treated SCBHH is suitable as xylose and glucose source for the enzymatic xylitol production and that this process has potential as an alternative for traditional xylitol production ways. (C) 2011 Published by Elsevier Ltd.

Contribution of Tris Buffer on Xylitol Enzymatic Production

Xylitol enzymatic production can be an alternative to chemical and microbial processes, because of advantages like higher conversion efficiency. However, for an adequate conversion, it is necessary to investigate the effect of many parameters, such as buffer initial concentration, pH, temperature, agitation, etc. In this context, the objective of this work was to evaluate xylitol enzymatic production under different Tris buffer initial concentrations in order to determine the best condition for this parameter to begin the reaction. The best results were obtained when Tris buffer initial concentration was 0.22 M, reaching 0.31 g L(-1) h(-1) xylitol volumetric productivity with 99% xylose-xylitol conversion efficiency. Although the increase in buffer concentration allowed better pH maintenance, it hindered the catalysis. The results demonstrate that this bioreaction is greatly influenced by involved ions concentrations.

Effective Electromechanical Coupling Coefficients of Piezoelectric Adaptive Structures: Critical Evaluation and Optimization

This work presents a critical analysis of methodologies to evaluate the effective (or generalized) electromechanical coupling coefficient (EMCC) for structures with piezoelectric elements. First, a review of several existing methodologies to evaluate material and effective EMCC is presented. To illustrate the methodologies, a comparison is made between numerical, analytical and experimental results for two simple structures: a cantilever beam with bonded extension piezoelectric patches and a simply-supported sandwich beam with an embedded shear piezoceramic. An analysis of the electric charge cancelation effect on the effective EMCC observed in long piezoelectric patches is performed. It confirms the importance of reinforcing the electrodes equipotentiality condition in the finite element model. Its results indicate also that smaller (segmented) and independent piezoelectric patches could be more interesting for energy conversion efficiency. Then, parametric analyses and optimization are performed for a cantilever sandwich beam with several embedded shear piezoceramic patches. Results indicate that to fully benefit from the higher material coupling of shear piezoceramic patches, attention must be paid to the configuration design so that the shear strains in the patches are maximized. In particular, effective square EMCC values higher than 1% were obtained embedding nine well-spaced short piezoceramic patches in an aluminum/foam/aluminum sandwich beam.

Micro-hardness evaluation of a micro-hybrid composite resin light cured with halogen light, light-emitting diode and argon ion laser

This in vitro study aimed to determine whether the micro-hardness of a composite resin is modified by the light units or by the thickness of the increment. Composite resin disks were divided into 15 groups (n = 5), according to the factors under study: composite resin thickness (0 mm, 1 mm, 2 mm , 3 mm and 4 mm) and light units. The light activation was performed with halogen light (HL) (40 s, 500 mW/cm(2)), argon ion laser (AL) (30 s, 600 mW/cm(2)) or light-emitting diode (LED) (30 s, 400 mW/cm(2)). Vickers micro-hardness tests were performed after 1 week and were carried out on the top surface (0 mm-control) and at different depths of the samples. Analysis of variance (ANOVA) and Tukey tests (P a parts per thousand currency signaEuro parts per thousand 0.05) revealed no statistically significant difference among the light units for the groups of 0 mm and 1 mm thickness. At 2 mm depth, the AL was not statistically different from the HL, but the latter showed higher micro-hardness values than the LED. In groups with 3 mm and 4 mm thickness, the HL also showed higher micro-hardness values than the groups activated by the AL and the LED. Only the HL presented satisfactory polymerization with 3 mm of thickness. With a 4 mm increment no light unit was able to promote satisfactory polymerization.

Layer-by-layer TiO(2) films as efficient blocking layers in dye-sensitized solar cells

Charge recombination at the conductor substrate/electrolyte interface has been prevented by using efficient blocking layers of TiO(2) compact films in dye-sensitized solar cell photoanodes. Compact blocking layers have been deposited before the mesoporous TiO(2) film by the layer-by-layer technique using titania nanoparticles as cations and sodium sulfonated polystyrene, PSS, as a polyanion. The TiO(2)/PSS blocking layer in a DSC prevents the physical contact of FTO and the electrolyte and leads to a 28% increase in the cell`s overall conversion efficiency, from 5.7% to 7.3%. (C) 2009 Elsevier B.V. All rights reserved.

Influence from the sulfonate group (RSO(3)(-)) on the conversion process and emission efficiency of poly(p-phenylene vinylene)

The discovery of an alternative route to convert poly(xylyliden tetrahydrothiophenium chloride) (PTHT) into poly(p-phenylene vinylene) (PPV) using dodecylbenzenesulfonate (DBS) has allowed the formation of ultrathin films with unprecedented control of architecture and emission properties. In this work, we show that this route may be performed with several sufonated compounds where RSO(3)(-) replaces the counter-ion (Cl(-)) of PTHT, some of which are even more efficient than DBS. Spin-coating films were produced from PTHT and azo-dye molecules, an azo-polymer and organic salts as counter-ions of PTHT. The effects of the thermal annealing step of PTHT/RSO(3)(-) films at 110 and 230 degrees C were monitored by measuring the absorption and emission spectra. The results indicate that the exchange of the counterion Cl(-) of PTHT by a linear long chain with RSO(3)(-) group is a general procedure to obtain PPV polymer at lower conversion temperature (ca. 110 degrees C) with significant increase in the emission efficiency, regardless of the chemical position and the number of sulfonate groups. With the enhanced emission caused by Congo Red and Tinopal as counter-ions, it is demonstrated that the new synthetic route is entirely generic, which may allow accurate control of conversion and emission properties. (C) 2010 Elsevier B.V. All rights reserved.

Substrate/semiconductor interface effects on the emission efficiency of luminescent polymers

The importance of interface effects for organic devices has long been recognized, but getting detailed knowledge of the extent of such effects remains a major challenge because of the difficulty in distinguishing from bulk effects. This paper addresses the interface effects on the emission efficiency of poly(p-phenylene vinylene) (PPV), by producing layer-by-layer (LBL) films of PPV alternated with dodecylbenzenesulfonate. Films with thickness varying from similar to 15 to 225 nm had the structural defects controlled empirically by converting the films at two temperatures, 110 and 230 degrees C, while the optical properties were characterized by using optical absorption, photoluminescence (PL), and photoluminescence excitation spectra. Blueshifts in the absorption and PL spectra for LBL films with less than 25 bilayers (<40-50 nm) pointed to a larger number of PPV segments with low conjugation degree, regardless of the conversion temperature. For these thin films, the mean free-path for diffusion of photoexcited carriers decreased, and energy transfer may have been hampered owing to the low mobility of the excited carriers. The emission efficiency was then found to depend on the concentration of structural defects, i.e., on the conversion temperature. For thick films with more than 25 bilayers, on the other hand, the PL signal did not depend on the PPV conversion temperature. We also checked that the interface effects were not caused by waveguiding properties of the excited light. Overall, the electronic states at the interface were more localized, and this applied to film thickness of up to 40-50 nm. Because this is a typical film thickness in devices, the implication from the findings here is that interface phenomena should be a primary concern for the design of any organic device. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622143]

Utilization of pineapple stem juice to enhance enzyme-hydrolytic efficiency for sugarcane bagasse after an optimized pre-treatment with alkaline peroxide

The enzymatic hydrolysis of sugarcane bagasse was investigated by treating a peroxide-alkaline bagasse with a pineapple stem juice, xylanase and cellulase. Pre-treatment procedures of sugarcane bagasse with alkaline hydrogen peroxide were evaluated and compared. Analyses were performed using 2(4) factorial designs, with pre-treatment time, temperature, magnesium sulfate and hydrogen peroxide concentration as factors. The responses evaluated were the yield of cellobiose and glucose released from pretreated bagasse after enzymatic hydrolysis. The results show that the highest enzymatic conversion was obtained for bagasse using 2% hydrogen peroxide at 60 degrees C for 16 h in the presence of 0.5% magnesium sulfate. Bagasse (5%) was treated with pineapple stem extract, which contains mixtures of protease and esterase, in combination with xylanase and cellulase. It was observed that the amount of glucose and cellobiose released from bagasse increased with the mixture of enzymes. It is believed that the enzymes present in pineapple extracts are capable of hydrolyze specific linkages that would facilitate the action of digesting plant cell walls enzymes. This increases the amount of glucose and other hexoses that are released during the enzymatic treatment and also reduces the amount of cellulase necessary in a typical hydrolysis. (C) 2010 Elsevier Ltd. All rights reserved.

Peritrophic membrane role in enhancing digestive efficiency Theoretical and experimental models

The pentrophic membrane (PM) is an anatomical structure surrounding the food bolus in most insects. Rejecting the idea that PM has evolved from coating mucus to play the same protective role as it, novel functions were proposed and experimentally tested. The theoretical principles underlying the digestive enzyme recycling mechanism were described and used to develop an algorithm to calculate enzyme distributions along the midgut and to infer secretory and absorptive sites. The activity of a Spodoptera frugiperda microvillar aminopeptidase decreases by 50% if placed in the presence of midgut contents. S. frugiperda trypsin preparations placed into dialysis bags in stirred and unstirred media have activities of 210 and 160%, respectively, over the activities of samples in a test tube. The ectoperitrophic fluid (EF) present in the midgut caeca of Rhynchosciara americana may be collected. If the enzymes restricted to this fluid are assayed in the presence of PM contents (PMC) their activities decrease by at least 58%. The lack of PM caused by calcofluor feeding impairs growth due to an increase in the metabolic cost associated with the conversion of food into body mass. This probably results from an increase in digestive enzyme excretion and useless homeostatic attempt to reestablish destroyed midgut gradients. The experimental models support the view that PM enhances digestive efficiency by: (a) prevention of non-specific binding of undigested material onto cell Surface; (b) prevention of excretion by allowing enzyme recycling powered by an ectoperitrophic counterflux of fluid; (c) removal from inside PM of the oligomeric molecules that may inhibit the enzymes involved in initial digestion; (d) restriction of oligomer hydrolases to ectoperitrophic space (ECS) to avoid probable partial inhibition by non-dispersed undigested food. Finally,PM functions are discussed regarding insects feeding on any diet. (C) 2008 Elsevier Ltd. All rights reserved.

Evaluation of the light polymerization efficiency of copolymers used in dental formulations by differential scanning calorimetry

Different compositions of visible-light-curable triethylene glycol dimethacrylate/bisglycidyl methacrylate copolymers used in dental resin formulations were prepared through copolymerization photoinitiated by a camphorquinone/ethyl 4-dimethylaminobenzoate system irradiated with an Ultrablue IS light-emitting diode. The obtained copolymers were evaluated with differential scanning calorimetry. From the data for the heat of polymerization, before and after light exposure, obtained from exothermic differential scanning calorimetry curves, the light polymerization efficiency or degree of conversion of double bonds was calculated. The glass-transition temperature also was determined before and after photopolymerization. After the photopolymerization, the glass-transi-tion temperature was not well defined because of the breadth of the transition region associated with the properties of the photocured dimethacrylate. The glass-transition temperature after photopolymerization was determined experimentally and compared with the values determined with the Fox equation. In all mixtures, the experimental value was lower than the calculated value. Scanning electron microscopy was used to analyze the morphological differences in the prepared copolymer structures. (C) 2007 Wiley Periodicals, Inc.

Produção de vitelos a partir de bezerros leiteiros mestiços e da raça Holandesa

Neste trabalho foi avaliado o desempenho produtivo de nove animais jovens Zebu × Holandês em comparação a nove animais da raça Holandesa para produção de vitelos. Todos os animais foram mantidos em condições idênticas de ambiente, manejo e alimentação, com acompanhamento individual da ingestão de matéria seca. As medidas de avaliação do desenvolvimento animal, conversão e eficiência alimentar possibilitaram comparações entre os tratamentos, a partir de delineamento inteiramente casualizado. Os bezerros Zebu × Holandês apresentaram maior ganho de perímetro torácico (23,3 cm) e ganho de peso diário (1,45 kg), além de conversão alimentar (2,77 kg de MS/kg de peso corporal), se comparados aos bezerros da raça Holandesa, com, respectivamente, 18,5 cm de perímetro torácico, 1,16 kg de ganho de peso diário e conversão alimentar de 3,48 kg de MS/kg de peso corporal. Não houve diferença na ingestão de matéria seca entre os animais avaliados. Quanto ao estudo econômico da produção de carne de vitelo, os animais mestiços apresentaram o menor custo de produção por quilo de carne produzida e, conseqüentemente, o melhor potencial de produção de vitelos a partir de animais Zebu × Holandês, como atividade complementar à produção de leite.