Modelling comminution patterns within a pilot scale AG/SAG mill

The patterns of rock comminution within tumbling mills, as well as the nature of forces, are of significant practical importance. Discrete element modelling (DEM) has been used to analyse the pattern of specific energy applied to rock, in terms of spatial distribution within a pilot AG/SAG mill. We also analysed in some detail the nature of the forces, which may result in rock comminution.In order to examine the distribution of energy applied within the mill, the DEM models were compared with measured particle mass losses, in small scale AG and SAG mill experiments. The intensity of contact stresses was estimated using the Hertz theory of elastic contacts. The results indicate that in the case of the AG mill, the highest intensity stresses and strains are likely to occur deep within the charge, and close to the base. This effect is probably more pronounced for large AG mills. In the SAG mill case, the impacts of the steel balls on the surface of the charge are likely to be the most potent. In both cases, the spatial pattern of medium-to-high energy collisions is affected by the rotational speed of the mill.Based on an assumed damage threshold for rock, in terms of specific energy introduced per single collision, the spatial pattern of productive collisions within each charge was estimated and compared with rates of mass loss. We also investigated the nature of the comminution process within AG vs. SAG mill, in order to explain the observed differences in energy utilisation efficiency, between two types of milling. All experiments were performed using a laboratory scale mill of 1.19 m diameter and 0.31 m length, equipped with 14 square section lifters of height 40 mm.     

Toolbox for exchanging constituent fatty acids in lecithins

Since the compositional variety of phospholipids in native lecithins is limited, and structurally diverse synthetic phospholipids are expensive, the aim of this work was to develop a lecithin modification toolbox capable of modifying the fatty acid composition of native lecithins at a convenient lab‐scale of 10‐100 g. Starting with the native phospholipids of soybean lecithin, two types of fatty acid modification were carried out using either phospholipase A2 from porcine pancreas or a lipase from Rhizopus oryzae. The former was immobilised onto celite and used to selectively hydrolyse the sn‐2 positioned fatty acid and the latter, commercially available in an immobilised form, was used to transesterify novel fatty acids onto the sn‐1 position. The degree of phospholipid hydrolysis could be controlled between 5 and 95% by varying the contact time with the biocatalyst. A key parameter was the water concentration. By avoiding the presence of a bulk phase of water, emulsion formation was prevented and so simple product recovery was possible. However, sufficient water was required in order to maintain the water activity above 0.2, and because phospholipids increased the polarity of the solvent (hexane), it was necessary to add water in proportion to the lecithin concentration. During transesterification with methyllaurate, up to 43% lauric acid could be incorporated and although the recovery of fully acylated phospholipids was only 28%, due to the formation of hydrolysis products, they were isolated using solvent partitioning in hexane/isopropanol/water. The temperature was important in determining the relative rates of hydrolysis and transesterification and a lower temperature (40 °C) was favourable as the rate of hydrolysis was lowered without affecting the rate of transesterification.     

The role of telencephalic NMDA receptors in avoidance learning in goldfish (Carassius auratus).

Studies with goldfish (Carassius auratus) have suggested that N-methyl-D-aspartate (NMDA) receptors are concentrated most densely in the telencephalon, a simple structure homologous to the limbic stricture of higher vertebrates. The present study investigated the amnestic effects of microinjections of the NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) to the goldfish telencephalon on avoidance conditioning. Results showed that microinjections of D-AP5 before training impaired avoidance learning at doses that did not impair performance processes. High-performance liquid chromatography measurements showed that D-AP5 was detected only in the telencephalon following microinjections. Thus, D-AP5 impaired avoidance learning through its interaction with telencephalic NMDA receptors in goldfish. Furthermore, microinjections of D-AP5 to the goldfish telencephalon immediately following training did not impair memory consolidation of avoidance conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rapid loss of Paraguay's Atlantic forest and the status of protected areas — A Landsat assessment

Using Landsat images acquired since early 1970s, we have mapped the forest cover and change between 1989 and 2000, and estimated forest area in 1973 in Paraguay's Atlantic Forest Ecoregion (PAFE). The results revealed that as of 1973, 73.4% of the PAFE region was covered by forest. Since then, the proportion of forested area was quickly reduced to 40.7% by 1989 and further down to 24.9% by 2000. Two competing deforestation processes contributed to this rapid forest loss, with the first being driven by settlers and the second by large private land owners. During the 1989-2000 period, 80% of deforested areas were cleared by private land owners and 20% by the settlers. Protected areas slowed down forest loss within their boundaries, but not in their surrounding areas. The average percent forest loss in the area within 5 km from the boundary of Paraguay's major forested protected areas was 39% during the 1989-2000 period, which was essentially the same as that for the entire PAFE region during the same period. The high rates of forest loss in the areas surrounding the protected areas not only left the protected areas highly isolated as ecological “islands”, they may also be precursors to rapid forest loss within the protected areas. These protected areas are critical to the conservation of many species endemic or limited to the PAFE region and surrounding areas, and should be continuously monitored using recent and future satellite observations.     

OMG — A new member of the fuel cell community but with a lot of experience

This article reports on progress in catalysts and membrane-electrode assemblies at OM Group, which took over the precious metals businesses of German-based Degussa to become a leading developer of fuel cell components using catalysts. The company’s fuel cell components include the pMembrain? membrane-electrode assembly, the elyst? electrocatalyst, and the protonics? family of fuel processing catalysts.     

Does selecting one visual object from several require inhibition of the actions associated with nonselected objects?

Four experiments are described in which 1 visual object (the target) was selected from another (the distractor) according to its color (Experiments 1, 2, and 4) or its relative location (Experiment 3) and then was classified according to a simple geometric property. Object classification was signaled as fast as possible by a precision or power grip response, and this grip was either compatible or incompatible with either object. When targets were selected by color, target-compatible grip responses were facilitated, but distractor-compatible grip responses were impaired. When targets were selected by location, similar results were obtained for target-compatible grip responses, but not distractor-compatible grip responses. These data are explained in terms of the involvement of action codes in object-level selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contemporary Reviews of Mine Water Studies in Europe,Part 3

Europe was once the most important mining region in the world and nearly every European country has remnants of historic and even pre-historic mining sites. Though the importance of mining activities in most European countries declines, the abandoned sites are still there and can cause environmental dangers as well as technological challenges. On the basis of selected European countries and case studies, these dangers and challenges are described and potential solutions are illustrated.     

能处理宽电压范围的快速稳定的微微安培计电路

对模拟开关、多路复用器、运算放大器和其它IC的评估是对IC测试工程师提出的挑战。典型的测试需要把测试电压或强制电压施加到器件的输入端,并测量导致的任何泄漏电流和偏移电流,这经常是在1pA或更低的级别进行的。图1、图2、图3中的低功耗测量电路与缓慢而昂贵的商品化自动测试仪形成了鲜明对比,这种电路能强制很宽的测试电压范围并提供快速稳定,使器件测试吞吐速度达到最高。表面贴装元件的广泛使用使它的印制电路板空间要求降到了最低,并使多个测量电路的封装能靠近测试夹具。     

His-357 of beta-galactosidase (Escherichia coli) interacts with the C3 hydroxyl in the transition state and helps to mediate catalysis

The His at position 357 of beta-galactosidase (Escherichia coli) was substituted by an Asp, an Asn, a Leu, and a Phe, and studies done with the substituted enzymes showed that the main role of His-357 is to stabilize the transition state by interacting with the C3 hydroxyl. The substituted enzymes were less stable to heat than was wild-type enzyme (40-90% of the activity was lost in 10 min at 52 degreesC compared to wild-type beta-galactosidase which lost no activity), but the gross physical properties of the substituted enzymes at normal temperatures were not changed. There were also no differences in the ability to bind or to be activated by Mg2+. The substitutions (except Asp) did not affect the pKa for binding substrate in the ground state, but the pKa of the kcat was altered as would be expected for a residue important for binding the transition state. Substitution by Asp may cause a conformational change at high pH values. Activation energy differences (Delta DeltaGS), as determined by differences in kcat/Km values, indicated that substitutions for His-357 caused significant destabilizations of the first transition state (for the step in which the galactoside bond is cleaved and the covalent reaction intermediate is formed). This resulted in decreases of up to 900-fold in k2 for the mononitrophenyl substrates. In contrast, the k3 values (which depend on the energy level of the second transition state) were not decreased as much (<90-fold). In some cases, the k3 values even increased (when Asn was substituted for His-357). The importance of His-357 for stabilization of the transition state was confirmed by studies with transition state analogue inhibitors that showed that His-357 forms strong specific interactions with the C3 hydroxyl of the galactose moiety of the transition state. Studies with substrate analogue inhibitors indicated that His-357 is probably not important for the binding of the substrates themselves.