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921.
Mara C. Diguez Claudia P. Queimalios Sergio Ribeiro Guevar Mark Marvin-DiPasquale Carolina Soto Crdenas Mara A. Arribre 《环境科学学报(英文版)》2013,25(10):1980-1991
Ligands present in dissolved organic matter (DOM) form complexes with inorganic divalent mercury (Hg^2+) affecting its bioavailability in pelagic food webs. This investigation addresses the influence of a natural gradient of DOM present in Patagonian lakes on the bioaccumulation of Hg^2+ (the prevailing mercury species in the water column of these lakes) by the algae Cryptomonas erosa and the zooplankters Brachionus calyciflorus and Boeckella antiqua. Hg^2+ accumulation was studied through laboratory experiments using natural water of four oligotrophic Patagonian lakes amended with^197Hg^2+. The bioavailability of Hg^2+ was affected by the concentration and character of DOM. The entrance of Hg^2+ into pelagic food webs occurs mostly through passive and active accumulation. The incorporation of Hg^2+ by Cryptomonas, up to 27% of the Hg^2+ amended, was found to be rapid and dominated by passive adsorption, and was greatest when low molecular weight compounds with protein-like or small phenolic signatures prevailed in the DOM. Conversely, high molecular weight compounds with a humic or fulvic signature kept Hg^2+ in the dissolved phase, resulting in the lowest Hg^2+ accumulation in this algae. In Brachionus and Boeckella the direct incorporation of Hg from the aqueous phase was up to 3% of the Hg^2+ amended. The dietary incorporation of Hg^2+ by Boeckella exceeded the direct absorption of this metal in natural water, and was remarkably similar to the Hg^2+ adsorbed in their prey. Overall, DOM concentration and character affected the adsorption of Hg^2+ by algae through competitive binding, while the incorporation of Hg^2+ into the zooplankton was dominated by trophic or dietary transfer. 相似文献
922.
Rakesh Kumar Pathak A. Ravi Kumar G.K. Ananthasuresh 《Journal of Manufacturing Processes》2013,15(1):108-114
This work demonstrates the feasibility of meso-scale (100 μm to mm) punching of multiple holes of intricate shapes in metals. Analytical modeling, finite element (FE) simulation, and experimentation are used in this work. Two-dimensional FE simulations in ABAQUS were done with an assumed material modeling and plane-strain condition. A known analytical model was used and compared with the ABAQUS simulation results to understand the effects of clearance between the punch and the die. FE simulation in ABAQUS was done for different clearances and corner radii of the punch, die, and holder. To complement modeling with real experiments and for the purpose of comparison, a set of punches and dies were made to punch out a miniature spring-steel gripper. Comparison of compliant grippers made by wire-cut electro discharge machining (EDM) and punching shows that realizing sharp interior and re-entrant corners by punching is not easy to achieve. However, the promise of realizing meso-scale parts with complicated shapes through punching is demonstrated in this work; and further work is identified and some strategies are suggested for improvement. The main contribution of this paper is in adapting the well-established punching and blanking operations to the meso-scale as a viable alternative to making miniature devices currently dominated by lithography-based techniques. 相似文献
923.
Finite element analysis (FEA) has become an invaluable tool in the design of sheet metal stamping dies and processes. FEA has gained widespread acceptance as the best method of optimizing dies for conventional stamping processes. More recently, FEA has been shown to be an effective method of designing tooling for sheet forming processes. In this work, an FEA based approach is applied to the warm stamping (warm forming) process. This work introduces a new thermal finite element analysis software called PASSAGE®/Forming (PASSAGE) that enables the up-front design of the thermal management of warm forming dies. This thermal finite element analysis software is designed to specifically handle the forming and optimization scenarios related to the heating of a stamping die while minimizing user interface time. In this work, PASSAGE has been applied to a simple block of steel embedded with cartridge heaters to validate the prediction capability of this software under two different heating conditions. The results show that PASSAGE is capable of predicting the actual steady-state temperature distribution within the block with an acceptable level of accuracy while yielding notable information to the user with respect to specifying power requirements. A finite element software package like PASSAGE is a valuable tool that will aid greatly in the implementation of warm forming as a manufacturing process beyond the scope of the laboratory and into production. 相似文献
924.
Joseph F. Wilson Brad L. Kinsey Yannis P. Korkolis 《Journal of Manufacturing Processes》2013,15(4):580-585
Characterization of the evolving yield loci and forming limit diagrams for sheet materials under biaxial loading is necessary for the development of accurate sheet metal forming process simulations. Biaxial tension testing has been shown to have significant advantages over the current computational and experimental methods for such material characterization; however, the few commercially available loading frames are far too large and expensive to be practical for most metal forming research laboratories. In this paper, the design of a practical servohydraulic biaxial loading frame is presented. The design, control, and operation of the loading frame are discussed in detail, and experimental data is provided to validate the effectiveness of the control system with respect to specimen center shifting. 相似文献
925.
Shellfish-Borne Viral Outbreaks: A Systematic Review 总被引:1,自引:0,他引:1
Investigations of disease outbreaks linked to shellfish consumption have been reported in the scientific literature; however, only few countries systematically collate and report such data through a disease surveillance system. We conducted a systematic review to investigate shellfish-borne viral outbreaks and to explore their distribution in different countries, and to determine if different types of shellfish and viruses are implicated. Six databases (Medline, Embase, Scopus, PubMed, Eurosurveillance Journal and Spingerlink electronic Journal) and a global electronic reporting system (ProMED) were searched from 1980 to July 2012. About 359 shellfish-borne viral outbreaks, alongside with nine ProMED reports, involving shellfish consumption, were identified. The majority of the reported outbreaks were located in East Asia, followed by Europe, America, Oceania, Australia and Africa. More than half of the outbreaks (63.6 %) were reported from Japan. The most common viral pathogens involved were norovirus (83.7 %) and hepatitis A virus (12.8 %). The most frequent type of consumed shellfish which was involved in outbreaks was oysters (58.4 %). Outbreaks following shellfish consumption were often attributed to water contamination by sewage and/or undercooking. Differences in reporting of outbreaks were seen between the scientific literature and ProMED. Consumption of contaminated shellfish represents a risk to public health in both developed and developing countries, but impact will be disproportionate and likely to compound existing health disparities. 相似文献
926.
927.
M. M. P. B. Fuentes M. R. Fish J. A. Maynard 《Mitigation and Adaptation Strategies for Global Change》2012,17(1):51-63
Climate change poses a serious threat to sea turtles (Cheloniidae) as their terrestrial reproductive phase is only successful
within a limited range of environmental and physical conditions. These conditions are likely to become less optimal as climate
change progresses. To date, management and conservation of sea turtles has focused almost entirely on non-climatic stressors,
due at least in part to practitioners not knowing what strategies to take and the feasibility and risks of potential strategies.
To aid the management of sea turtles in a changing environment, we identified management strategies via a focus workshop and
surveys to mitigate the impacts of climate change to the terrestrial reproductive phase of sea turtles. The effectiveness,
ecological risks and potential social and logistical constraints associated with implementing each of the identified management
strategies is discussed. Twenty management strategies were identified; strategies varied from habitat protection to more active
and direct manipulation of nests and the nesting environment. Based on our results, we suggest a three-pronged approach to
sea turtle conservation in light of climate change, where managers and researchers should: 1) enhance sea turtle resilience
to climate change by mitigating other threats; 2) prioritise implementing the ‘no regret’ and ‘reversible’ management strategies
identified here; and 3) fill the knowledge gaps identified to aid the trial and implementation of the potential strategies identified here. By combining these three approaches our collective toolkit of sea turtle management strategies
will expand, giving us an array of viable approaches to implement as climate change impacts become more extreme. 相似文献
928.
Chandra Nath Shiv G. Kapoor Richard E. DeVor Anil K. Srivastava Jon Iverson 《Journal of Manufacturing Processes》2012,14(4):452-459
Tool life has been a vital issue in machining titanium alloys. Recently, an atomization-based cutting fluid (ACF) application has been found to be an effective approach for cooling and lubrication in micromachining operations. In this study, an ACF spray system is developed for macro-scale turning of Ti–6Al–4V. The spray system is designed to minimize interaction between the fluid droplets, and the gas nozzle to control the divergence of the fluid droplets. Experiments are conducted to study the effect of five specific ACF spray parameters including fluid flow rate, spray distance, impingement angle, and type and pressure level of the droplet carrier gas on cutting forces, tool life, and chip characteristics. It has been observed that the combination of lower pressure (150 psi) air-mixed CO2 with a higher flow rate (20 ml/min) and a larger spray distance (35 mm) produces a significantly longer tool life and broken chips. The results also reveal that the ACF spray system can extend tool life up to 40–50% over flood cooling. 相似文献
929.
930.
J. S. Rice R. H. Moss P. J. Runci K. L. Anderson E. L. Malone 《Mitigation and Adaptation Strategies for Global Change》2012,17(7):805-819
A new modeling effort exploring the opportunities, constraints, and interactions between mitigation and adaptation at regional scale is utilizing stakeholder engagement in an innovative approach to guide model development and demonstration, including uncertainty characterization, to effectively inform regional decision making. This project, the integrated Regional Earth System Model (iRESM), employs structured stakeholder interactions and literature reviews to identify the most relevant adaptation and mitigation alternatives and decision criteria for each regional application of the framework. The information is used to identify important model capabilities and to provide a focus for numerical experiments. This paper presents the stakeholder research results from the first iRESM pilot region. The pilot region includes the Great Lakes Basin in the Midwest portion of the United States as well as other contiguous states. This geographic area (14 states in total) permits cohesive modeling of hydrologic systems while also providing strong gradients in climate, demography, land cover/land use, and energy supply and demand. The results from the stakeholder research indicate that, for this region, iRESM should prioritize addressing adaptation alternatives in the water resources, urban infrastructure, and agriculture sectors, including water conservation, expanded water quality monitoring, altered reservoir releases, lowered water intakes, urban infrastructure upgrades, increased electric power reserves in urban areas, and land use management/crop selection changes. For mitigation in this region, the stakeholder research implies that iRESM should focus on policies affecting the penetration of renewable energy technologies, and the costs and effectiveness of energy efficiency, bioenergy production, wind energy, and carbon capture and sequestration. 相似文献