Fracture strength of drilled wafers: study of the stress concentration factor and determination of the weibull distribution of the fracture stress

In the photovoltaic field, the back contact solar cells technology has appeared as an alternative to the traditional silicon modules. This new type of cells places both positive and negative contacts on the back side of the cells maximizing the exposed surface to the light and making easier the interconnection of the cells in the module. The Emitter Wrap-Through solar cell structure presents thousands of tiny holes to wrap the emitter from the front surface to the rear surface. These holes are made in a first step over the silicon wafers by means of a laser drilling process. This step is quite harmful from a mechanical point of view since holes act as stress concentrators leading to a reduction in the strength of these wafers. This paper presents the results of the strength characterization of drilled wafers. The study is carried out testing the samples with the ring on ring device. Finite Element models are developed to simulate the tests. The stress concentration factor of the drilled wafers under this load conditions is determined from the FE analysis. Moreover, the material strength is characterized fitting the fracture stress of the samples to a three-parameter Weibull cumulative distribution function. The parameters obtained are compared with the ones obtained in the analysis of a set of samples without holes to validate the method employed for the study of the strength of silicon drilled wafers.

The strength distribution of brittle materials with a high-concentration of cavities

The maximum stress concentration factor in brittle materials with a high concentration of cavities is obtained. The interaction between the nearest cavities, in addition to the far field interactions, is taken into account to evaluate the strength distribution based on the statistical analysis of the nearest distance distribution. Through this investigation, it is found that the interaction between the nearest neighbors is much more important than the far field interactions, and one has to consider it in calculating the strength of brittle materials even if the volume fraction of cavities it contains is small. The other important conclusion is that the maximum stress concentration factor has a wide scattered distribution.

On-line concentration of neutral and charged species in capillary electrochromatography with a methacrylate-based monolithic stationary phase

A method involving self-concentration, on-column enrichment and field-amplified sample stacking for on-line concentration in capillary electrochromatography with a polymer monolithic column is presented. Since monolithic columns eliminate the frit fabrication and the problems associated with frits, the experimental conditions could be more flexibly adjusted to obtain higher concentration factor in comparison with conventional particulate packed columns. With self-concentration effect, the detection sensitivity of benzene and hexylbenzene is improved by a factor of 4 and 8, respectively. With on-column enrichment and ultralong injection, improvement as high as 22 000 times in detection sensitivity of benzoin is achieved. Furthermore, a combination of the three above-mentioned methods yields up to a 24000-fold improvement in detection sensitivity for caffeine, a charged compound. Parameters affecting the efficiency of on-line concentration are investigated systematically. In addition, equations describing on-line concentration process are deduced.

Study on the concentration and seasonal variation of inorganic elements in 35 species of marine algae

The concentrations of five major and 28 trace elements in 35 marine algae collected along the coast of China were determined by instrumental neutron activation analysis. The concentrations of halogens, rare earth elements and many transition metal elements in marine algae are remarkably higher than those in terrestrial plants. The concentration factors for 31 elements in all collected algae were calculated, those for tri- and tetra-valent elements were higher than those of the mono- and di-valent elements in marine algae. The biogeochemical characteristics of inorganic elements in marine algae were investigated. In addition, the seasonal variation of inorganic elements in Sargassum kjellmanianum was also studied. (C) 1998 Elsevier Science B.V. All rights reserved.

Cassava root husks as a sorbent material for the uptake and pre-concentration of cadmium(II) from aqueous media

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Caractérisation de l'impact des conditions opératoires sur l'efficience d'un procédé de concentration du lait par ultrafiltration

Les concentrés de protéines de lait sont couramment utilisés comme ingrédients lors de la standardisation du lait de fromagerie. La concentration des protéines est généralement réalisée par ultrafiltration (UF) à l’aide de membranes polymériques ayant un seuil de coupure de 10 kDa, et ce, jusqu’à un facteur de concentration volumique de 3.5X. Dans l’optique d’améliorer l’efficience du procédé d’UF, l’étude avait pour but de caractériser l’impact du mode opératoire (pression transmembranaire constante (465 et 672 kPa) et flux constant) ainsi que la température (10°C et 50°C) sur la performance du système jusqu’à un facteur de concentration volumique de 3.6X. Le module de filtration à l’échelle pilote comprenait une membrane d’UF en polyéthersulfone de 10 kDa d’une surface de 2,04 m2. La performance du système a été caractérisée sur le flux de perméation, la sélectivité et la consommation énergétique totale. L’étude a montré que le flux de perméation était 1,9 fois plus élevé à une température de 50°C comparativement à 10°C lors de l’UF du lait. Le coefficient de rejet des protéines n’a pas été affecté significativement par la pression transmembranaire et la température (P< 0,05). L’effet de la température a été observé au niveau de la teneur en calcium, laquelle était plus élevée de 12% dans les rétentats générés à 50C. La consommation énergétique totale du système d’UF était plus élevée à 10C comparativement à 50C, représentant 0,32±0,02 et 0,26±0,04 kWh/kg rétentat respectivement. Les résultats montrent que le ratio d’efficience énergétique (rapport entre le flux de perméation et la consommation énergétique) optimal a été obtenu à faible pression transmembranaire constante et à 50C. L’approche développée dans le cadre de ce projet fournira des outils aux industriels laitiers pour améliorer l’éco-efficience de leurs procédés de séparation baromembranaire.

Pesticide bioconcentration factor estimate in apples.

This work objective was to estimate the bioconcentration factor (BCF) of thirty six pesticides used in the Brazilian integrated apple production systems (IAP), in order to select priority pesticides to be monitored in apples. A hypothetical apple orchard was assumed and the model applied was according to Paraíba (2007) [Pesticide bioconcentration modeling for fruit trees. Chemosphere (66:1468-1475)]. The model relates BCF with plant and pesticide characteristics. The octanol-water partition coefficients of pesticides and their degradation rates in the soil were used. The following plant variables were considered: growth rate, total dry biomass, daily water transpiration rate, and total volume of water necessary to produce one kg of fresh fruit per plant. The pesticide stem-water partition coefficient and the transpiration stream concentration factor were calculated using equations that relate each coefficient with the octanol-water partition coefficient. The pesticide BCF in fruits is an important indicator of the pesticide affinity to fruits, and helps to improve the integrated production systems.

Production of microalgal concentrates by flocculation and their assessment as aquaculture feeds

A novel technique was developed for the flocculation of marine microalgae commonly used in aquaculture. The process entailed an adjustment of pH of culture to between 10 and 10.6 using NaOH, followed by addition of a non-ionic polymer Magnafloc LT-25 to a final concentration of 0.5 mg L-1. The ensuing flocculate was harvested, and neutralised giving a final concentration factor of between 200- and 800-fold. This process was successfully applied to harvest cells of Chaetoceros calcitrans, C. muelleri, Thalassiosira pseudonana, Attheya septentrionalis, Nitzschia closterium, Skeletonema sp., Tetraselmis suecica and Rhodomonas salina, with efficiencies >=80%. The process was rapid, simple and inexpensive, and relatively cost neutral with increasing volume (cf. concentration by centrifugation). Harvested material was readily disaggregated to single cell suspensions by dilution in seawater and mild agitation. Microscopic examination of the cells showed them to be indistinguishable from corresponding non-flocculated cells. Chlorophyll analysis of concentrates prepared from cultures of Concentrates of T. pseudonana prepared using pH-induced flocculation gave better growth of juvenile Pacific oysters (Crassostrea gigas) than concentrates prepared by ferric flocculation, or centrifuged concentrates using a cream separator or laboratory centrifuge. In follow up experiments, concentrates prepared from 1000 L Chaetoceros muelleri cultures were effective as supplementary diets to improve the growth of juvenile C. gigas and the scallop Pecten fumatus reared under commercial conditions, though not as effective as the corresponding live algae. The experiments demonstrated a proof-of-concept for a commercial application of concentrates prepared by flocculation, especially for use at a remote nursery without on-site mass-algal culture facilities.

Microfiltration in cheese and whey processing

Milk microfiltration (0.05-0.2 um) is a membrane separation technique which divides milk components into casein-enriched and native whey fractions. Hitherto the effect of intensive microfiltration including a diafiltration step for both cheese and whey processing has not been studied. The microfiltration performance of skimmed milk was studied with polymeric and ceramic MF membranes. The changes caused by decreased concentration of milk lactose, whey protein and ash content for cheese milk quality and ripening were studied. The effects of cheese milk modification on the milk coagulation properties, cheese recovery yield, cheese composition, ripening and sensory quality as well as on the whey recovery yield and composition by microfiltration were studied. The functional properties of whey protein concentrate from native whey were studied and the detailed composition of whey protein concentrate powders made from cheese wheys after cheese milk pretreatments such as high temperature heat treatment (HH), microfiltration (MF) and ultrafiltration (UF) were compared. The studied polymeric spiral wound microfiltration membranes had 38.5% lower energy consumption, 30.1% higher retention of whey proteins to milk retentate and 81.9% lower permeate flux values compared to ceramic membranes. All studied microfiltration membranes were able to separate main whey proteins from skimmed milk. The optimal lactose content of Emmental cheese milk exceeded 3.2% and reduction of whey proteins and ash content of cheese milk with high concentration factor (CF) values increased the rate of cheese ripening. Reduction of whey protein content in cheese milk increased the concentration of caseinomacropeptide (CMP) of total proteins in cheese whey. Reduction of milk whey protein, lactose and ash content reduces milk rennet clotting time and increased the firmness of the coagulum. Cheese yield calculated from raw milk to cheese was lower with microfiltrated milks due to native whey production. Amounts of a-lactalbumin (a-LA) and b-lactoglobulin (b-LG) were significantly higher in the reference whey, indicating that HH, MF and UF milk pretreatments decrease the amounts of these valuable whey proteins in whey. Even low CF values in milk microfiltration (CF 1.4) reduced nutritional value of cheese whey. From the point of view of utilization of milk components it would be beneficial if the amount of native whey and the CMP content of cheese whey could be maximized. Whey protein concentrate powders made of native whey had excellent functional properties and their detailed amino acid composition differed from those of cheese whey protein concentrate powders.

Micromechanics of elastic solids weakened by a large number of cracks

This paper presents a micromechanics analysis of the elastic solids weakened by a large number of microcracks in a plane problem. A new cell model is proposed. Each cell is an ellipse subregion and contains a microcrack. The effective moduli and the stress intensity factors for an ellipse cell are obtained. The analytic closed formulas of concentration factor tensor for an isotropic matrix containing an anisotropic inclusion are derived. Based on a self-consistent method, the effective elastic moduli of the solids weakened by randomly oriented microcracks are obtained.

Trace metals in fresh water plankton

The uptake of Cu, Zn, and Cd by fresh water plankton was studied by analyzing samples of water and plankton from six lakes in southern California. Co, Pb, Mn, Fe, Na, K, Mg, Ca, Sr, Ba, and Al were also determined in the plankton samples. Special precautions were taken during sampling and analysis to avoid metal contamination.

The relation between aqueous metal concentrations and the concentrations of metals in plankton was studied by plotting aqueous and plankton metal concentrations vs time and comparing the plots. No plankton metal plot showed the same changes as its corresponding aqueous metal plot, though long-term trends were similar. Thus, passive sorption did not completely explain plankton metal uptake.

The fractions of Cu, Zn, and Cd in lake water which were associated with plankton were calculated and these fractions were less than 1% in every case.

To see whether or not plankton metal uptake could deplete aqueous metal concentrations by measurable amounts (e.g. 20%) in short periods (e.g. less than six days), three integrated rate equations were used as models of plankton metal sorption. Parameters for the equations were taken from actual field measurements. Measurable reductions in concentration within short times were predicted by all three equations when the concentration factor was greater than 10^5. All Cu concentration factors were less than 10^5.

The role of plankton was regulating metal concentrations considered in the context of a model of trace metal chemistry in lakes. The model assumes that all particles can be represented by a single solid phase and that the solid phase controls aqueous metal concentrations. A term for the rate of in situ production of particulate matter is included and primary productivity was used for this parameter. In San Vicente Reservoir, the test case, the rate of in situ production of particulate matter was of the same order of magnitude as the rate of introduction of particulate matter by the influent stream.

Métodos para obtener el coeficiente de concentración de tensiones para fatiga

[ES]Existen diferentes propuestas para obtener el coeficiente de concentración de tensiones para el análisis de fatiga: Neuber, Peterson, distancia crítica, corrección de modelo de elementos finitos, etc. En este trabajo se trata de estudiar los principales y compararlos entre ellos de forma sistemática utilizando como referencia piezas con entallas de geometría sencilla y extrayendo conclusiones útiles para diseño y análisis mecánico.

Determination of bioaccumulation and microscopic survey of LAS pollutant effect on the liver, kidney and gill tissues of Rutilus frisii kutum in Caspian sea

Linear alkylbenzene sulfonate (LAS) are widely used in detergent industry. Due to contaminants entering the water, and the effects of their accumulation in fish, LAS, has a great importance in environmental pollution. In the present study, accumulation of LAS and its histological effects on gill tissue, liver and kidney of Caspian kutum (Rutilus frisii kutum) were studied. Caspian kutum is the most important and most valuable teleosts of the Caspian Sea. Due to releasing Caspian Kutum in rivers and Anzali Lagoon and unlimited entry of wastewater to the aquatic ecosystem, research on the impact of LAS on Caspian kutum is important. In the present study, fish exposed to sublethal concentrations of LAS (0.58, 1.16 and 2.32 mg/l) for 192 hours. Control treatments with three replicates at 0, 24, 48, 72, 96 and 192 hours were done. For assessments of the histological effects of LAS, tissue sections prepared and by using Hematoxylin - Eosin were stained, then the prepared sections, examined by light microscopy. For determination of the bio accumulation of LAS, the soxhlet extraction and solid phase extraction was performed to determine the amount of LAS using HPLC with fluorescence detector. According to results average of bioconcentration factor and LAS concentrations in fish had reached stable levels after approximately 72 h and thus represented steady state BCF values in this species. The value of steady-state bio-concentration factor of total LAS was 33.96 L.Kg- 1 and for each of the homologous C10-n-LAS, C11-n-LAS, C12-n-LAS and C13-n- LAS were 3.84, 6.15, 8.58 and 15.57 L.Kg-1 respectively. According to the results obtained in gills exposed to LAS, histopathological alteration include hypertrophy, lifting of lamella epithelium, edema, clubbing of lamellae hyperplasia, lamellar fusion and aneurysm were seen. In liver tissue exposed to three concentrations of LAS, congestion and dilation of sinusoids, irregular-shaped nuclei and degeneration in the hepatocyte, vacuolar degeneration and necrosis were observed. In kidney exposed to three concentrations of LAS, reduction of the interstitial haematopoietic tissue, degeneration in the epithelial cells of renal tubule, tubular degeneration, necrosis, shrinkage and luminal occlusion were observed. According to the results the most alteration due to exposure to LAS was seen in the gill tissue. None of the control samples showed histological effects of LAS.

Capillary electrophoresis with amperometric detection of curcumin in Chinese herbal medicine pretreated by solid-phase extraction

In the present study, curcumin from Chinese herbal medicine turmeric was determined by capillary electrophoresis with amperometric detection (CE-AD) pretreated by a self-designed, simple, inexpensive solid-phase extraction (SPE) cartridge based on the material of tributyl phosphate resin. An average concentration factor of 9 with the recovery of >80% was achieved when applied to the analysis of curcumin in extracts of turmeric. Under the optimized CE-AD conditions: a running buffer composed of 15 mM phosphate buffer at a pH 9.7, separation voltage at 16 W, injection for 6 s at 9 W and detection at 1.20 V, CE-AD with SPE exhibited low detection limit as 3 - 10(-8) mol/l (SIN = 3), high efficiency of 1.0(.)10(5) N, linear range of 7(.)10(-4) -3(.)10(-6) mol/l (r = 0.9986) for curcumin extracted from light petroleum. The method developed resulted in enhancement of the detection sensitivity and reduction of interference from sample matrix in complicated samples and exhibited the potential application for routine analysis, especially in food, because a relatively complete process of sample treatment and analysis was described.

Detection of non-steroidal anti-inflammatory drugs in aqueous effluents using ionic liquids

Significant improvements in human health have been achieved through the increased consumption of pharmaceutical drugs. However, most of these active pharmaceutical ingredients (APIs) are excreted by mammals (in a metabolized or unchanged form) into the environment. The presence of residual amounts of these contaminants was already confirmed in aqueous streams since treatment processes either wastewater treatment plants (WWTPs) or sewage treatment plants (STPs) are not specifically designed for this type of pollutants. Although they are present in aqueous effluents, they are usually at very low concentrations, most of the times below the detection limits of analytical equipment used for their quantification, hindering their accurate monitoring. Therefore, the development of a pre-concentration technique in order to accurately quantify and monitor these components in aqueous streams is of major relevance. This work addresses the use of liquid-liquid equilibria, applying ionic liquids (ILs), for the extraction and concentration of non-steroidal anti-inflammatory drugs (NSAIDs) from aqueous effluents. Particularly, aqueous biphasic systems (ABSs) composed of ILs and potassium citrate were investigated in the extraction and concentration of naproxen, diclofenac and ketoprofen from aqueous media. Both the extraction efficiency and concentration factor achievable by these systems was determined and evaluated. Within the best conditions, extraction efficiencies of 99.4% and concentration factors up to 13 times were obtained.