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461.
Bradley DI Fisher SN Guénault AM Haley RP Kopu J Martin H Pickett GR Roberts JE Tsepelin V 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2008,366(1877):2803-2812
This study presents measurements of the transport of quasiparticle excitations in the B phase of superfluid 3He at temperatures below 0.2Tc. We find that creating and then removing a layer of A-phase superfluid leads to a measurable increase in the thermal impedance of the background B phase. This increase must be due to the survival of defects created as the AB and BA interfaces on either side of the A-phase layer annihilate. We speculate that a new type of defect may have been formed. The highly ordered A-B interface may be a good analogy for branes discussed in current cosmology. If so, these experiments may provide insight into how the annihilation of branes can lead to the formation of topological defects such as cosmic strings. 相似文献
462.
Jouni Puranen Mikko Pihlatie Juha Lagerbom Turkka Salminen Jarmo Laakso Leo Hyvärinen Mikko Kylmälahti Olli Himanen Jari Kiviaho Petri Vuoristo 《International Journal of Hydrogen Energy》2014
Protective coatings based on manganese cobalt oxide spinels are required in solid oxide fuel cells (SOFCs) to prevent the evaporation of volatile Cr(VI)-compounds from the metallic interconnectors and to minimize high temperature corrosion. Atmospheric plasma spraying (APS) was used to manufacture dense manganese cobalt oxide protective coatings on Crofer 22 APU substrates by employing two different spinel powders. The spray powders were MnCo2O4 and Mn2CoO4 + Co (equivalence for Mn1.5Co1.5O4). The Mn2CoO4 + Co powder was prepared by agglomerating the oxide powder with fine metallic cobalt powder. The coated substrates were oxidized at 700 °C in air for 1000 h. During the high temperature oxidation, a four-point on-line measurement technique with a current density of 640 mA/cm2 was simultaneously used for area specific resistance (ASR) studies. The coatings were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), an energy dispersive spectrometer (EDS) and Raman spectroscopy. 相似文献
463.
Peltonen H Kiljunen M Kiviranta H Vuorinen PJ Verta M Karjalainen J 《Environmental science & technology》2007,41(6):1849-1855
The Baltic Sea ecosystem and fish stocks contain high concentrations of environmental chemicals such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs). This study forecasts how changes in fishing or natural mortality would probably influence concentrations of PCDD/F and PCB in the Bothnian Sea (Northern Baltic) herring (Clupea harengus L.). An age-structured simulation model was developed to forecast herring stock dynamics, catches, and weight-at-age under different assumptions about exploitation and natural mortality. The simulated herring weight-at-age estimates were employed in a bioenergetics model capable of simultaneous estimation of bioaccumulation of 17 PCDD/F and 37 PCB congeners. Although the natural variability in recruitment greatly influences the stock dynamics, considerable changes in weight-at-age would ensue changes in exploitation rate or in natural mortality rate. If exploitation rates increase, growth rates would be higher and herring in the weight categories of commercial fisheries would be younger and contain less PCDD/F and PCB. Hence, the average toxicant concentrations in catches would also decline. However, it is likely that only fairly small changes would occur in toxicant concentrations-at-age. On the other hand, a drastic decrease in herring fishing would substantially increase PCDD/F and PCB concentrations in herring. The study indicated that, in spite of the clear influences of fishing on the toxicant concentrations, fishing alone cannot resolve the problems associated with a high concentration of toxicants in herring; further decreases in loading are still required. 相似文献
464.
Cattaneo Zaira; Fantino Micaela; Tinti Carla; Pascual-Leone Alvaro; Silvanto Juha; Vecchi Tomaso 《Canadian Metallurgical Quarterly》2011,37(4):1110
Our representation of peripersonal space does not always accurately reflect the physical world. An example of this is pseudoneglect, a phenomenon in which neurologically normal individuals bisect to the left of the veridical midpoint, reflecting an overrepresentation of the left portion of space compared with the right one. Consistent biases have also been observed in the vertical and radial planes. It is an open question whether these biases depend on normal visual experience for their occurrence. Here we systematically investigated this issue by testing blindfolded sighted and early blind individuals in a haptic line bisection task. Critically, we found a robust leftward bias in all participants. In the vertical and radial planes, sighted participants showed a consistent downward and proximal bias. Conversely, the directional bias in blind participants was dependent on the final movement direction; thus, there was no general bias in either direction. These findings are discussed in terms of different reference frames adopted by sighted and blind participants when encoding space. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
465.
Enzymes are biological catalysts and are very specific, catalyzing either a single chemical reaction or a limited number of closely related reactions. For example, xylanases are enzymes that catalyze the cleavage of polymeric xylan and thereby break down this hemicellulose. The first xylanase enzyme preparations used in the bleaching process of chemical pulp also contained cellulase, which catalyzes the hydrolysis of cellulose. This obviously had an adverse effect on pulp yield and quality. Unfortunately, this setback gave enzyme-assisted pulp bleaching a negative reputation. At a later stage, enzyme producers managed to engineer enzyme production strains that generated cellulase-free xylanase preparations. However, due to the initial negative experiences with the earlier enzyme mixtures, only a limited number of companies in the pulp industry have seriously considered using these so-called second-generation enzymes in their bleach plants. It is apparent that these improved enzyme preparations would bring about significant benefits in terms of chemical cost savings and effluent quality. In addition to xylanase-aided bleaching, it is possible to improve the effectivity further by adding other enzymes, such as lipase and esterase, to create an enzyme cocktail. This may be particularly beneficial in the bleaching of hardwood pulp, such as white birch, which often encounters complex and troublesome problems with wood extractives. By adding different types of enzymes at more than one position in the fiberline, even further improvements are possible. The main objective of this review is to discuss the advantages of incorporating modern enzyme preparations in the bleaching of chemical pulp. 相似文献
466.
Alexander R. Uhl Peter Fuchs Alexandra Rieger Fabian Pianezzi Carolin M. Sutter‐Fella Lukas Kranz Debora Keller Harald Hagendorfer Yaroslav E. Romanyuk Fabio LaMattina Songhak Yoon Lassi Karvonen Theresa Magorian‐Friedlmeier Erik Ahlswede Dirk VanGenechten Fabrice Stassin Ayodhya N. Tiwari 《Progress in Photovoltaics: Research and Applications》2015,23(9):1110-1119
Large‐grained CuInSe2 absorber layers are synthesized using a non‐vacuum process based on nanoparticle ink precursors and selenization by rapid thermal processing (RTP). The use of hydroxide‐based particles in organic solvents allows for the conversion with elemental selenium without the need to employ explosive and/or toxic H2 or H2Se gasses. Lateral grain sizes up to 4 µm are obtained through a novel RTP route, overcoming the inherently high layer porosity for previous nanoparticle processes. Morphological and elemental characterization at interrupted selenization steps suggests that liquid selenium can play a beneficial role in promoting layer densification and grain growth. Long carrier collection lengths in CuInSe2 enable notable conversion efficiencies, despite the low minority carrier lifetimes of below 1 ns. Record efficiencies up to 8.73% highlight the potential of low‐cost, non‐vacuum deposition of chalcopyrite absorber layers with safe and simple precursors and processing routes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
467.
Screening of pulp can be expressed as a process where solid contaminants are removed from a pulp slurry without an excessive loss of fibres of acceptable quality. The impurities originate from the feedstock, or they are generated during the transport, handling, storage, or pulping process. The most typical impurities include bark, fibre bundles or shives, knots, plastic, rubber, and sand. Moreover, there are also other objectives for screening, such as the improvement of the pulp quality, savings in bleaching chemical consumption, and protection of process equipment. In industrial applications, pulp screening is typically carried out with more than one screen for a more beneficial screening result. The pulp screening equipment can be divided into different types by the separation technique employed, such as atmospheric or pressurized screens, centrifugal screens, vibrating screens, etc. In addition, there are other types of related equipment that are common in the pulp screening process, such as knotters, refiners, and hydrocyclones. The main objective of this review is to discuss the advantages and disadvantages of modern screening equipment as well as introduce contemporary screening strategies for chemical pulp mills. 相似文献