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排序方式: 共有108条查询结果,搜索用时 31 毫秒
71.
Keith N. Eshleman Robert H. Gardner Steven W. Seagle Nancy M. Castro Daniel A. Fiscus James R. Webb James N. Galloway Frank A. Deviney Alan T. Herlihy 《Environmental monitoring and assessment》2000,63(1):187-197
The objective of this research project is to develop, test, validate, and demonstrate an analytical framework for assessing regional-scale forest disturbance in the mid-Atlantic region by linking forest disturbance and forest nitrogen export to surface waters at multiple spatial scales. It is hypothesized that excessive nitrogen (N) leakage (export) from forested watersheds is a potentially useful, integrative "indicator" of a negative change in forest function which occurs in synchrony with changes in forest structure and species composition. Our research focuses mainly on forest disturbance associated with recent defoliations by the gypsy moth larva (Lymantria dispar) at spatial scales ranging from small watersheds to the entire Chesapeake Bay watershed. An approach for assessing the magnitude of forest disturbance and its impact on surface water quality will be based on an empirical model relating forest N leakage and gypsy moth defoliation that will be calibrated using data from 25 intensively-monitored forested watersheds in the region and tested using data from more than 60 other forested watersheds in Virginia. Ultimately, the model will be extended to the region using spatially-extensive data describing: 1) the spatial distribution of dominant forest types in the mid-Atlantic region based on both remote sensing imagery and plot-scale vegetation data; 2) the spatial pattern of gypsy moth defoliation of forested areas from aerial mapping; and 3) measurements of dissolved N concentrations in streams from synoptic water quality surveys. 相似文献
72.
73.
A widespread distrust in the significance of the observation of trisomy 20 mosaicism in amniotic fluid cultures has led to an increasing belief that this particular type of aneuploidy is of extra foetal origin and is clinically incosequential. The report presents an example of amnoitic fluid cell mosaicism for trisomy 20 which was ultimately confirmed in the foetus, and proposes that, in spite of the absence of obvious congenital malformation from the foetus, trisomy 20 mosaicism in amnoitic fluid cultures should be regarded with the same deference as mosaicism for any other autosome of unknown effect. 相似文献
74.
Gardner C. Bent Bruce F Goff Kim G. Rightmire Roy C. Sidle 《Journal of the American Water Resources Association》1999,35(2):441-455
ABSTRACT: Control of runoff (reducing infiltration) and erosion at shallow land burials is necessary in order to assure environmentally safe disposal of low-level radioactive-waste and other waste products. This study evaluated the runoff and erosion response of two perennial grass species on simulated waste burial covers at Idaho National Engineering and Environmental Laboratory (INEEL). Rainfall simulations were applied to three plots covered by crested wheatgrass [Agropyron desertorum(Fischer ex Link) Shultes], three plots covered by streambank wheatgrass [Elymus lanceolatus(Scribner and Smith) Gould spp. lanceolaus], and one bare plot. Average total runoff for rainfall simulations in 1987, 1989, and 1990 was 42 percent greater on streambank wheatgrass plots than on crested wheatgrass plots. Average total soil loss for rainfall simulations in 1987 and 1990 was 105 percent greater on streambank wheatgrass plots than on crested wheatgrass plots. Total runoff and soil loss from natural rainfall and snowmelt events during 1987 were 25 and 105 percent greater, respectively, on streambank wheatgrass plots than on crested wheatgrass plots. Thus, crested wheatgrass appears to be better suited in revegetation of waste burial covers at INEEL than streambank wheatgrass due to its much lower erosion rate and only slightly higher infiltration rate (lower runoff rate). 相似文献
75.
Why Economics Matters for Endangered Species Protection 总被引:3,自引:0,他引:3
Jason F. Shogren ‡‡‡ John Tschirhart Terry Anderson † Amy Whritenour Ando ‡ Steven R. Beissinger § David Brookshire Gardner M. Brown JR. †† Don Coursey ‡‡ Robert Innes §§ Stephen M. Meyer and Stephan Polasky††† 《Conservation biology》1999,13(6):1257-1261
Abstract: We offer three reasons why economics matters more to species protection than many people think and what this implies for the ongoing debate over the reauthorization of the Endangered Species Act of 1973. Economics matters because (1) human behavior generally, and economic parameters in particular, help determine the degree of risk to a species; (2) in a world of scarce resources, the opportunity cost of species protection—the costs of reduced resources for other worthwhile causes—must be taken into account in decision making; and (3) economic incentives are critical in shaping human behavior, and consequently the recovery of species. Endangered species protection that explicitly addresses these basic principles can avoid wasting valuable resources that yield no gain in species protection. 相似文献
76.
Janie L. Gittleman Author Vitae Paige C. Gardner Author Vitae Author Vitae Julie M. Sampson Author Vitae Author Vitae Erica D. Ermann Author Vitae Author Vitae Peter Y. Chen Author Vitae 《Journal of Safety Research》2010,41(3):263-281
Problem
The present study describes a response to eight tragic deaths over an eighteen month times span on a fast track construction project on the largest commercial development project in U.S. history.Methods
Four versions of a survey were distributed to workers, foremen, superintendents, and senior management. In addition to standard Likert-scale safety climate scale items, an open-ended item was included at the end of the survey.Results
Safety climate perceptions differed by job level. Specifically, management perceived a more positive safety climate as compared to workers. Content analysis of the open-ended item was used to identify important safety and health concerns which might have been overlooked with the qualitative portion of the survey.Discussion
The surveys were conducted to understand workforce issues of concern with the aim of improving site safety conditions. Such efforts can require minimal investment of resources and time and result in critical feedback for developing interventions affecting organizational structure, management processes, and communication.Summary
The most important lesson learned was that gauging differences in perception about site safety can provide critical feedback at all levels of a construction organization.Impact on the Industry
Implementation of multi-level organizational perception surveys can identify major safety issues of concern. Feedback, if acted upon, can potentially result in fewer injuries and fatal events. 相似文献77.
Saffarzadeh A Shimaoka T Wei Y Gardner KH Musselman CN 《Waste management (New York, N.Y.)》2011,31(12):2440-2454
Natural weathering processes are significant mechanisms that noticeably affect the fundamental nature of incineration ash residues. To provide a greater understanding of these processes, a MSWI (mono)landfill site in the north east of the US was selected as the target for systematic investigation of the natural weathering of bottom ash residues. Samples of various ages were collected from locations A (1 yr), B (10 yrs), C (13-14 yrs) and D (20 yrs) of the landfill in 2009. We investigated the phase transformation of the collected bottom ash particles, neoformation processes as well as the behavior and distribution of certain heavy metals (Cu, Pb, Zn, Ni, and Cr) in the neoformed phases using optical microscopy, SEM-EDX, and bulk examinations. Key findings: at the preliminary stage, the waste metallic particles (Al, Fe, and Cu) and unstable minerals such as lime, portlandite, ettringite and hydrocalumite convert to oxide and hydroxide (hydrate) phases, calcite, alumina gel and gypsum. At the intermediate stage, the decomposition of melt products including magnetite spinels and metallic inclusions is triggered due to the partial dissolution of the melt glass. At the longer time horizon it is possible to track the breakdown of the glass phase, the extensive formation of calcite and anhydrite, Al-hydrates and more stable Fe-hydrates all through the older ash deposits. Among the dominant secondary phases, we propose the following order based on their direct metal uptake capacity: Fe-hydrates>Al-hydrates>calcite. Calcite was found to be the least effective phase for the direct sorption of heavy metals. Based on overall findings, a model is proposed that demonstrates the general trend of ash weathering in the landfill. 相似文献
78.
Three landfill sites that had been closed for 19, 29 and 46 years and had been operated under different management systems were excavated in Sydney. The mean moisture content of the wood samples ranged from 41.6% to 66.8%. The wood products recovered were identified to species, and their carbon, cellulose, hemicellulose and lignin concentration were determined and compared to those of matched samples of the same species. No significant loss of dry mass was measured in wood products buried for 19 and 29 years, but where refuse had been buried for 46 years, the measured loss of carbon (as a percentage of dry biomass) was 8.7% for hardwoods and 9.1% for softwoods, equating to 18% and 17% of their original carbon content, respectively. The results indicate that published decomposition factors based on laboratory research significantly overestimate the decomposition of wood products in landfill. 相似文献
79.
Alper Kiziltas Douglas J. Gardner Yousoo Han Han-Seung Yang 《Journal of Polymers and the Environment》2014,22(3):365-372
In this study, engineering thermoplastic composites were prepared from microcrystalline cellulose (MCC)-filled nylon 6. MCC were added to nylon 6 using melt mixing to produce compounded pellets. The MCC-filled nylon 6 composites with varying concentrations of MCC (from 2.5 to 30 wt%) were prepared by injection molding. The tensile and flexural properties of the nylon 6 composites were increased significantly with the addition of MCC. The maximum strength and modulus of elasticity for the nylon 6 composites were achieved at a MCC weight fraction of 20 %. The Izod impact strength of composites decreased with the incorporation of MCC without any surface treatments and coupling agent. This observation is quite expected for filled polymer systems and has been commonly observed. There was a strong correlation between density and tensile (r = 0.94) and flexural modulus of elasticity (r = 0.9). MCC filled composites manufactured by injection method had highly uniform density distribution through their thickness. The higher mechanical results with lower density demonstrate that MCC can be used as a sufficient reinforcing material for low cost, eco-friendly composites in the automotive industry especially for under-the-hood applications (engine covers, intake manifolds and radiator end tanks) as well as in other applications such as the building and construction industries, packaging, consumer products etc. 相似文献
80.
J.H. Elwood D.J. Robertson D.G. Gardner R.H. Groth 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1158-1162
This paper is directed to people who are involved in the measurement of gas turbine exhaust emissions and as a consequence in the establishment of standard reference gases and attendant analytical procedures. Several problems exist in connection with the establishment of these standards: A number of standard reference gases have been developed by the National Bureau of Standards for use in the automotive industry which are also suitable for gas turbine exhaust measurements. However, there is a need for additional standard reference materials such as NO in nitrogen, intermediate levels of CO2 in air, and higher concentrations of CO in nitrogen and propane in air. There is difficulty in maintaining certain reference materials with confidence in assay, particularly due to instability in the cylinder. Instrumental operational problems with flame ionization detector type units exist. Of particular importance is the difference in response per carbon atom in different organic molecules and the difference in response of a test sample as a function of the oxygen content of the sample. Instrumental method problems such as converter efficiency in chemiluminescence units measuring NO2 and calibration techniques involving CO to CH4 conversion, also must be considered. A number of problems occur in the use of wet chemical reference methods such as the phenoldisulfonic acid method for the determination of NOx. These include both efficiency of collection, conversion of NO to NO2, and subsequent analysis. This paper considers the development of standards for the measurement of NOx, CO, CO2, total hydrocarbons, and O2 and reviews the state-of-the-art with respect to these problems and their resolution. 相似文献