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排序方式: 共有798条查询结果,搜索用时 31 毫秒
121.
Miguel Perez-Labra Antonio Romero-Serrano Eleazar Salinas-Rodriguez Erika O. Avila-Davila Martin Reyes-Perez 《Metallurgical and Materials Transactions B》2012,43(4):773-780
Rubidium jarosite was synthesized as a single phase by precipitation from aqueous solution. X-ray diffraction and scanning electron microscopy energy-dispersive spectrometry analysis showed that the synthetic product is a solid rubidium jarosite phase formed in spherical particles with an average particle size of about 35???m. The chemical analysis showed an approximate formula of Rb0.9432Fe3(SO4)2.1245(OH)6. The decomposition of jarosite in terms of solution pH was thermodynamically modeled using FACTSage by constructing the potential pH diagram at 298?K (25?°C). The E-pH diagram showed that the decomposition of jarosite leads to a goethite compound (FeO·OH) together with Rb+ and $ {\text{SO}}_{4}^{2 - } $ ions. The experimental Rb-jarosite decomposition was carried out in alkaline solutions with five different Ca(OH)2 concentrations. The decomposition process showed a so-called ??induction period?? followed by a progressive conversion period where Rb+ and $ {\text{SO}}_{4}^{2 - } $ ions formed in the aqueous solutions, whereas calcium was incorporated in the solid residue and iron gave way to goethite. The kinetic analysis showed that this process can be represented by the shrinking core chemically controlled model with a reaction order with respect to Ca(OH)2 equals 0.4342 and the calculated activation energy is 98.70?kJ mol?C1. 相似文献
122.
The influence of neutralizing agents was investigated using strong and weak acids with three different amines. Acidic acrylic latexes were synthesized through free radical emulsion copolymerization of butyl acrylate, methyl methacrylate and methacrylic acid or 2-sulfoethyl methacrylate. Both strong (sulfonic) and weak (carboxylic) acids were neutralized with three amines, N,N-dimethyl-methylamine, N,N-dimethyl-1-butanamine and N-methyl-morpholine. Uncrosslinked neutralized and un-neutralized latex samples were monitored for water loss (drying parameters), pH development and amine evolution during drying. Surface morphology was monitored during the later stages of film coalescence. For the weak acid, amine volatility was the controlling factor for film formation kinetics, and pH reduction. For the strong acid, volatility of the amine was not a factor. The process of deblocking was governed by the acid–base equilibrium. 相似文献
123.
Schiavo S Ebbel E Sharma S Matson W Kristal BS Hersch S Vouros P 《Analytical chemistry》2008,80(15):5912-5923
A novel approach to the parallel coupling of normal-bore high-performance liquid chromatography (LC) with electrochemical-array detection (EC-array) and nanoelectrospray mass spectrometry (MS), based on the use of a nanosplitting interface, is described where both detectors are utilized at their optimal detection mode for parallel configuration. The dual detection platform was shown to maintain full chromatographic integrity with retention times and peak widths at half-height between the EC-array and MS displaying high reproducibility with relative standard deviations of <2%. Detection compatibility between the two detectors at the part per billion level injected on-column was demonstrated using selected metabolites representative of the diversity typically encountered in physiological systems. Metabolites were detected with equal efficiency whether neat or in serum, demonstrating the system's ability to handle biological samples with limited sample cleanup and reduced concern for biological matrix effects. Direct quantification of known analytes from the EC-array signal using Faraday's law can eliminate the need for isotopically labeled internal standards. The system was successfully applied to the detection and characterization of metabolites of phenylbutyrate from serum samples of Huntington's disease patients in an example that illustrates the complementarity of the dual detection nanoelectrospray LC-EC-array-MS system. 相似文献
124.
The genome of wine yeast Dekkera bruxellensis provides a tool to explore its food-related properties
Piškur J Ling Z Marcet-Houben M Ishchuk OP Aerts A LaButti K Copeland A Lindquist E Barry K Compagno C Bisson L Grigoriev IV Gabaldón T Phister T 《International journal of food microbiology》2012,157(2):202-209
The yeast Dekkera/Brettanomyces bruxellensis can cause enormous economic losses in wine industry due to production of phenolic off-flavor compounds. D. bruxellensis is a distant relative of baker's yeast Saccharomyces cerevisiae. Nevertheless, these two yeasts are often found in the same habitats and share several food-related traits, such as production of high ethanol levels and ability to grow without oxygen. In some food products, like lambic beer, D. bruxellensis can importantly contribute to flavor development. We determined the 13.4 Mb genome sequence of the D. bruxellensis strain Y879 (CBS2499) and deduced the genetic background of several "food-relevant" properties and evolutionary history of this yeast. Surprisingly, we find that this yeast is phylogenetically distant to other food-related yeasts and most related to Pichia (Komagataella) pastoris, which is an aerobic poor ethanol producer. We further show that the D. bruxellensis genome does not contain an excess of lineage specific duplicated genes nor a horizontally transferred URA1 gene, two crucial events that promoted the evolution of the food relevant traits in the S. cerevisiae lineage. However, D. bruxellensis has several independently duplicated ADH and ADH-like genes, which are likely responsible for metabolism of alcohols, including ethanol, and also a range of aromatic compounds. 相似文献
125.
Anne Helbig Erika Silletti Eefjan TimmermanRob J. Hamer Harry Gruppen 《Food Hydrocolloids》2012,28(1):10-19
Developing healthy products requires in-depth knowledge of digestion. This study focuses on lipid digestion in relation to emulsion properties typically followed by pH-stat. Although this is a fast and easy method to follow the overall digestion, it provides no details on lipid digestion products. Thus, the aims of the present study were to use gas chromatography (GC) to determine all products present during lipolysis, i.e. monoglycerides (MG), diglycerides (DG) and triglycerides (TG), and to compare this method with the pH-stat method for free fatty acids (FFA). Fine, medium and coarse emulsions stabilized with two different emulsifiers (whey protein isolate (WPI) or gum arabic) were digested under in vitro intestinal conditions. Although the amount of FFA increased for both methods for WPI stabilized emulsions, the amount of FFA was 2-3 times higher when determined by GC compared with pH-stat. GC analysis showed decreasing amounts of MG and DG with increasing droplet size for both emulsions. Molar ratios of FFA/DG and MG/DG were twofold higher for WPI than for gum arabic stabilized emulsions. This indicates that the total production of lipolytic products (i.e. FFA + MG + DG) depends on the droplet size and the emulsifier but their proportions only depend on the emulsifier. Although pH-stat provides a fast measure of FFA release, it is influenced by the emulsifier type at the oil-water interface and therefore care should be taken when interpreting pH-stat results. We suggest combining this method with GC for accurate FFA determination and further evaluation of all lipolytic products. 相似文献
126.
127.
Erika Madeira Moreira da Silva José Luis Ramírez Ascheri Carlos Wanderlei Piler de Carvalho Cristina Yoshie Takeiti Jose de J. Berrios 《LWT》2014
Extruded products were prepared from a corn flour and dehulled carioca bean (Phaseolus vulgaris, L.) flour blend using a single-screw extruder. A central composite rotate design was used to evaluate the effects of extrusion process variables: screw speed (318.9–392.9 rpm), feed moisture (10.9–21.0 g/100 g) and bean flour level (4.8–55.2 g/100 g) on the specific mechanical energy (SME), sectional expansion index (SEI), longitudinal expansion index (LEI), volumetric expansion index (VEI) and density (D) of the extrudates. The instrumental texture was also analyzed. The independent variables had significant effects on the physical properties (SEI, VEI and density) of extrudates, with the exception of SME and LEI. SEI increased with increasing screw speed, but a higher moisture and bean flour content resulted in decreasing SEI and VEI. The increase of moisture and bean flour increased the density of extrudates. According to texture analysis, some treatments with 30 and 45 g/100 g bean flour did not show significant differences when compared to commercial brand snacks. However, when combined with higher moisture content (≥19 g/100 g) and lower screw speed (≤333 rpm), the results of the expanded product were not satisfactory. 相似文献
128.
Joseph Fiksel Bhavik R. Bakshi Anil Baral Erika Guerra Bernhard DeQuervain 《Clean Technologies and Environmental Policy》2011,13(1):19-35
Life cycle assessment is used to determine the most environmentally beneficial alternatives for reuse of scrap tires, based
on the concept of industrial ecology. Unutilized scrap tires can be a major source of pollution, and in the past decade Federal
and state governments in the United States have encouraged the recycling and reuse of scrap tires in a number of applications,
ranging from energy recovery to civil engineering materials to utilization of ground rubber in manufacturing. Life cycle inventory
data are collected from primary industry sources as well as published literature, and life cycle impact analysis is performed
using the TRACI tool. The results indicate that beneficial reuse of scrap tires, particularly in cement plants and artificial
turf, provides reductions in greenhouse gas (GHG) emissions, air toxics, and water consumption. For example, every metric
ton of tire-derived fuel substituted for coal in cement kilns avoids an estimated 543 kg (CO2 equivalent) of direct and indirect GHG emissions. Taking into account the deductible CO2 from natural rubber, the avoided GHG emissions would be 613 CO2 kg eq. per metric ton. The use of scrap tires for fuel in cement plants provides more reductions in most environmental impact
categories compared to other scrap tire applications, excluding application in artificial turf. Although the use of ground
rubber for artificial turf offers the greatest environmental emission reductions, it has limited potential for large-scale
utilization due to the saturated market for artificial turf. Therefore, the use of fuel derived from scrap tires in cement
production appears to be an attractive option in view of its large market capacity and significant potential for environmental
impact reductions. 相似文献
129.
Erika HodúlováMarián Palcut Emil Lechovi?Beáta Šimeková Koloman Ulrich 《Journal of Alloys and Compounds》2011,509(25):7052-7059
The effects of Bi and In additions on intermetallic phase formation in lead-free solder joints of Sn-3.7Ag-0.7Cu; Sn-1.0Ag-0.5Cu-1.0Bi and Sn-1.5Ag-0.7Cu-9.5In (composition given in weight %) with copper substrate are studied. Soldering of copper plate was conducted at 250 °C for 5 s. The joints were subsequently aged at temperatures of 130-170 °C for 2-16 days in a convection oven. The aged interfaces were analyzed by optical microscopy and energy dispersive X-ray spectroscopy (EDX) microanalysis. Two intermetallic layers are observed at the interface - Cu3Sn and Cu6Sn5. Cu6Sn5 is formed during soldering. Cu3Sn is formed during solid state ageing. Bi and In decrease the growth rate of Cu3Sn since they appear to inhibit tin diffusion through the grain boundaries. Furthermore, indium was found to produce a new phase - Cu6(Sn,In)5 instead of Cu6Sn5, with a higher rate constant. The mechanism of the Cu6(Sn,In)5 layer growth is discussed and the conclusions for the optimal solder chemical composition are presented. 相似文献
130.
Aeration accounts for 30% to 75% of the total energy consumption in activated sludge processes (ASPs). This percentage can be significantly reduced since most aeration systems are not optimized for unsteady influent flow rates and oxygen requirements. Reconfiguration, replacement, and the application of optimal dissolved oxygen (DO) control strategies for current aeration systems within the facility and model-based optimization of DO in wastewater treatment plants can lead to impressive increased energy efficiency and savings and improved stability of the system. These measures increase the operational lifetime of the aeration equipment and improve effluent and activated sludge quality. This article provides a review of two critical nonlinear time-varying parameters that characterize the DO concentration dynamics in an ASP: the oxygen uptake rate (OUR), related to microorganism activity, and the volumetric oxygen mass transfer function, represented by the oxygen transfer rate (OTR). Second, the physico-chemical, geometric, and dynamic factors and aerator type affecting the oxygen mass transfer coefficient (K L a) are thoroughly discussed. The article concludes with model-based optimization, explaining the usefulness of accurate DO models in wastewater treatment, and provides examples for plant-wide or water chain cycle–focused optimizations. 相似文献