Microbial sulfate reduction and metal attenuation in pH 4 acid mine water

Sediments recovered from the flooded mine workings of the Penn Mine, a Cu-Zn mine abandoned since the early 1960s, were cultured for anaerobic bacteria over a range of pH (4.0 to 7.5). The molecular biology of sediments and cultures was studied to determine whether sulfate-reducing bacteria (SRB) were active in moderately acidic conditions present in the underground mine workings. Here we document multiple, independent analyses and show evidence that sulfate reduction and associated metal attenuation are occurring in the pH-4 mine environment. Water-chemistry analyses of the mine water reveal: (1) preferential complexation and precipitation by H2S of Cu and Cd, relative to Zn; (2) stable isotope ratios of 34S/32S and 18O/16O in dissolved SO4 that are 2–3 ‰ heavier in the mine water, relative to those in surface waters; (3) reduction/oxidation conditions and dissolved gas concentrations consistent with conditions to support anaerobic processes such as sulfate reduction. Scanning electron microscope (SEM) analyses of sediment show 1.5-micrometer, spherical ZnS precipitates. Phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analyses of Penn Mine sediment show a high biomass level with a moderately diverse community structure composed primarily of iron- and sulfate-reducing bacteria. Cultures of sediment from the mine produced dissolved sulfide at pH values near 7 and near 4, forming precipitates of either iron sulfide or elemental sulfur. DGGE coupled with sequence and phylogenetic analysis of 16S rDNA gene segments showed populations of Desulfosporosinus and Desulfitobacterium in Penn Mine sediment and laboratory cultures

Two instructional aids to optimise processing and learning from instructional explanations

Roelle J, Berthold K, Renkl A. Two instructional aids to optimise processing and learning from instructional explanations. Instructional Science. 2014;42(2):207-228.Although instructional explanations are commonly used to introduce learners to new learning content, previous studies have often shown that their effects on learning outcomes are minimal. This failure might partly be due to mental passivity of the learners while processing introductory explanations and to a lack of opportunity to revise potential misunderstandings after working on introductory explanations. Against this background, we provided learners with two instructional support measures to optimise the introduction of new principles and concepts by providing instructional explanations in the domain of management theory: (a) prompts designed to induce inferences that are focused on the central content of the explanations, and (b) remedial explanations that are adapted to the learners' knowledge gaps. We tested their effects in a 2 x 2 factorial experimental design with the following factors: (a) prompts designed to induce focused processing (with vs. without), and (b) remedial explanations (adapted vs. random). The participants consisted of 80 psychology students. We found that the prompts fostered both the share of deep-oriented processing and the acquisition of conceptual knowledge. The beneficial effect of prompts on conceptual knowledge was mediated by the number of inferences that learners generated in response to the prompts. In addition, we found that prompts also fostered the instructional efficiency of providing instructional explanations. The provision of adapted remedial explanations, however, fostered neither deep-oriented processing nor the acquisition of conceptual knowledge. We conclude that prompts designed to induce focused processing can foster deep-oriented processing as well as both the effectiveness and efficiency of learning from instructional explanations

Effect of carboxymethyl cellulose concentration on physical properties of biodegradable cassava starch-based films

<p>Abstract</p> <p>Background</p> <p>Cassava starch, the economically important agricultural commodity in Thailand, can readily be cast into films. However, the cassava starch film is brittle and weak, leading to inadequate mechanical properties. The properties of starch film can be improved by adding plasticizers and blending with the other biopolymers.</p> <p>Results</p> <p>Cassava starch (5%w/v) based films plasticized with glycerol (30 g/100 g starch) were characterized with respect to the effect of carboxymethyl cellulose (CMC) concentrations (0, 10, 20, 30 and 40%w/w total solid) and relative humidity (34 and 54%RH) on the mechanical properties of the films. Additionally, intermolecular interactions were determined by Fourier transform infrared spectroscopy (FT-IR), melting temperature by differential scanning calorimetry (DSC), and morphology by scanning electron microscopy (SEM). Water solubility of the films was also determined. Increasing concentration of CMC increased tensile strength, reduced elongation at break, and decreased water solubility of the blended films. FT-IR spectra indicated intermolecular interactions between cassava starch and CMC in blended films by shifting of carboxyl (C = O) and OH groups. DSC thermograms and SEM micrographs confirmed homogeneity of cassava starch-CMC films.</p> <p>Conclusion</p> <p>The addition of CMC to the cassava starch films increased tensile strength and reduced elongation at break of the blended films. This was ascribed to the good interaction between cassava starch and CMC. Cassava starch-CMC composite films have the potential to replace conventional packaging, and the films developed in this work are suggested to be suitable for low moisture food and pharmaceutical products.</p