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441.
This paper reports the feasibility of using surface mount adhesives to produce low temperature microchannel arrays in a wide variety of metals. Sheet metal embossing and chemical etching processes have been used to produce sealing bosses that eliminate channel laminae, resulting in approximately 50% material savings over traditional methods. An assembly process using adhesive dispense and cure is outlined to produce leak-free devices. Optimal fill ratios were determined to be between 1.1 and 1.25. Bond strength investigation reveals robustness to surface conditions and a bond strength of 5.5–8.5 MPa using a 3X safety factor. Dimensional characterization reveals a two sigma (95%) post-bonded channel height tolerance under 10% after bonding. Patterning tolerance and surface roughness of the laminae faying surfaces were found to have a significant influence on the final post-bonded channel height. Leakage and burst pressure testing on several samples has established confidence that adhesive bonding can produce leak-free joints. Operating pressures up to 413 kPa have been satisfied, equating to tensile pressure on bond joints of 1.9 MPa. Higher operating pressures can be accommodated by increasing the bond area of devices. 相似文献
442.
Since 1980, liver neoplasms in brown bullhead and polynuclear aromatic hydrocarbons (PAH) in sediment have been researched in a series of studies on the Black River in Lorain, Ohio. In the early 1980s the liver cancer prevalence in fish of age 3 and older was high, ranging from 22% to 39% of the adult population. These high cancer rates corresponded to high levels of PAHs in the sediment resulting from long-term releases by an upstream coking facility (USX). In 1983 this coking plant was closed, and by 1987 the PAH in sediment had declined by about two orders of magnitude. Coincidentally the tumor prevalence in 1987 was only about one-fourth of that in the early 1980s. In 1990, the most contaminated sediments were dredged. Neoplasm surveys in 1992 and 1993 found liver tumor frequencies in mature bullhead were as high as or higher than in the early 1980s. However liver tumor incidence declined in 1994, especially among age 3 fish, where neoplasm incidence was zero. These age 3 fish were the first group sampled that were not present during the 1990 dredging. These data are consistent with a hypothesis that the increase in tumor prevalence in 1992 and 1993 was caused by exposure to buried PAH-contaminated sediments released by the dredging. This research points out the insight provided by long term effects studies. 相似文献
443.
Production of boundary layer ozone from tropical American Savannah biomass burning emissions 总被引:1,自引:0,他引:1
Eugenio Sanhueza Paul J. Crutzen Enmanuel Fernndez 《Atmospheric environment (Oxford, England : 1994)》1999,33(30):5819
Boundary layer ozone and carbon monoxide were measured at a savannah site in the Orinoco river basin, during the dry and wet seasons. CO and O3 concentrations recorded around noontime show a good linear correlation, suggesting that the higher ozone levels observed during the dry season are photochemically produced during the oxidation of reactive hydrocarbons in the presence of NOx both emitted by biomass burning. The rate of photochemical ozone production in the boundary layer ozone by biomass burning calculated from the production ratio ΔO3/ΔCO (0.17±0.01 v : v) and the amount of CO produced by fires (0.26–1.3 mole m−2 dry season−1), ranges from 0.6 to 2.6 ppbv h−1 for 8 h of daylight. This O3 production rate is in fairly good agreement with the value derived from RO2 radical measurements made in the Venezuelan savannah during the dry season. The net boundary layer production of O3 from all tropical America savannah fires is estimated to range between 0.28 and 0.36 Tmol O3 per year, which is about 3 times higher than the O3 produced from pollution sources in the eastern United States during the summer. An extrapolation to all of the world's savannah would indicate a net boundary layer ozone production of about 1.2 Tmol yr−1. This is discussed in the context of the overall global budget of tropospheric ozone. 相似文献
444.
Paul L. Ringold Barry Mulder Jim Alegria Raymond L. Czaplewski Tim Tolle Kelly Burnett 《Environmental management》1999,23(2):179-192
adaptive monitoring design. Adaptive monitoring design is an iterative process that refines the specifications for monitoring over time as a result of
experience in implementing a monitoring program, assessing results, and interacting with users. An adaptive design therefore
facilitates ecosystem management. We also discuss lessons of temporal and spatial scales raised by the consideration of a
design for ecosystem management. Three additional issues—integration of information from different sources, institutional
infrastructure, and the roles of individuals working in an interagency setting—are also identified, but not developed in detail. 相似文献
445.
446.
Local Agenda 21 (LA21) has emerged as the principal means of addressing sustainable development practice at the local government level. In the UK, progressive local authorities have emphasised the need for participatory processes and innovative policy options. This requires commitment and active involvement from a variety of individuals and organisations. Participants in LA21 have been interviewed to determine their motivations and perceptions, and their responses are represented in terms of the storylines of various constituencies of interest. The key themes seem to be those of actively promoting widespread participation, gaining competence in innovative techniques, taking a holistic approach to quality of life concerns, and claiming the legitimacy of local government as a key player in sustainable development. 相似文献
447.
War Zones and Game Sinks in Lewis and Clark's West 总被引:1,自引:0,他引:1
The journals of Lewis and Clark reveal a major difference in the taxa, numbers, and behavior of megafauna on either side of the Rocky Mountains in western North America. Two prior events set the stage for what Lewis and Clark would find. The first was the extinction around 13,000 years ago of two-thirds of the native megafauna of the American West. The second was the effects on Indians of deadly new diseases and new technologies brought by Europeans in the post-Columbian era. Populations of large animals, which were preferred prey for native people, were not immune to European influence. Along the Columbia River corridor west of the Rockies, tens of thousands of people lived in a game sink. Here Lewis and Clark's party found too few animals to live off the land by hunting. They adapted poorly to the local diet of fish and roots offered by the Nez Perce and bought dogs and horses to sustain themselves. To the east, uninhabited lands along the Upper Missouri and the Yellowstone rivers supported an abundance of wild game, especially bison, elk, deer, pronghorn, and wolves. This game source occupied part of a buffer zone of 120,000 km2 probed by various Indian war parties, some of them armed with muskets. William Clark recognized the relationship and near the end of their journey he wrote that they found large numbers of large animals in the land between nations that were at war. Both the abundance of game in buffer or war zones and scarcity of big game in sinks have been misinterpreted as a natural or typical condition. Although efforts to restore ecosystems to what is described in early journals may have merit, they are aimed at a flickering target. Long before these journals were written, the land had been stripped of most of its native megafauna through human influence. In the absence of humans, we predict that much larger populations of bison, elk, deer, and wolves would have ranged the West than were reported in historic documents. 相似文献
448.
449.
Alexandrine Daniel Paul Savary Jean-Christophe Foltête Aurélie Khimoun Bruno Faivre Anthony Ollivier Cyril Éraud Hervé Moal Gilles Vuidel Stéphane Garnier 《Conservation biology》2023,37(3):e14047
Habitat connectivity is a key objective of current conservation policies and is commonly modeled by landscape graphs (i.e., sets of habitat patches [nodes] connected by potential dispersal paths [links]). These graphs are often built based on expert opinion or species distribution models (SDMs) and therefore lack empirical validation from data more closely reflecting functional connectivity. Accordingly, we tested whether landscape graphs reflect how habitat connectivity influences gene flow, which is one of the main ecoevolutionary processes. To that purpose, we modeled the habitat network of a forest bird (plumbeous warbler [Setophaga plumbea]) on Guadeloupe with graphs based on expert opinion, Jacobs’ specialization indices, and an SDM. We used genetic data (712 birds from 27 populations) to compute local genetic indices and pairwise genetic distances. Finally, we assessed the relationships between genetic distances or indices and cost distances or connectivity metrics with maximum-likelihood population-effects distance models and Spearman correlations between metrics. Overall, the landscape graphs reliably reflected the influence of connectivity on population genetic structure; validation R2 was up to 0.30 and correlation coefficients were up to 0.71. Yet, the relationship among graph ecological relevance, data requirements, and construction and analysis methods was not straightforward because the graph based on the most complex construction method (species distribution modeling) sometimes had less ecological relevance than the others. Cross-validation methods and sensitivity analyzes allowed us to make the advantages and limitations of each construction method spatially explicit. We confirmed the relevance of landscape graphs for conservation modeling but recommend a case-specific consideration of the cost-effectiveness of their construction methods. We hope the replication of independent validation approaches across species and landscapes will strengthen the ecological relevance of connectivity models. 相似文献
450.