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121.
A principal–multiple agent model is used to examine wildlife damage abatement and compensation programs in a setting in which farmers suffer damages and hunters use the wildlife for recreational purposes. In addition to externalities inherent in abatement, abatement/compensation policy confronts the issue of moral hazard. By representing the principal as a wildlife management authority who acts on behalf of hunters, we investigate contracts in which transfers of more or less severe hunting regulations, a public good that aids in dispersing wildlife, and monetary payments from hunting license fees can be used to overcome moral hazard.  相似文献   
122.
Specimens of the abyssal grenadier Coryphaenoides armatus (Hector, 1875), from the western North Atlantic and eastern North Pacific Oceans were compared electrophoretically at 27 presumptive gene loci. At 6 of the 7 polymorphic loci there were only minor differences in allelic frequencies but a nearly fixed difference was found at one locus, phosphogluconate dehydrogenase. Eastern North Pacific grenadiers typically have a narrower interorbital space, a shorter dorsal interspace, more soft rays in the 1st dorsal fin (9–10 versus 8–9) and more pelvic fin rays (21–23 versus 18–21) than grenadiers from the western North Atlantic (as well as grenadiers from the eastern South Pacific, which were included in the biometric analysis). There is an apparent disjunction in the distribution of C. armatus in the eastern Pacific at the Gulf of Panamá which coincides with the change of morphology. It is suggested that North Pacific grenadiers comprise a subspecies, C. armatus variabilis Günther, 1878, which is morphologically distinct from the subspecies C. armatus armatus (Hector, 1875) of the other areas.  相似文献   
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The effects of joint action of SO(2) and HF on the yield and quality of wheat and barley were studied by exposing them to combinations of <13,130 or 267 microg m(-3) SO(2) and 0.03 or 0.38 microg m(-3) HF in open top chambers for 90 days. At the concentrations used, SO(2) had greater effects than HF. All responses were marked by compensatory changes. The treatments had no effect on wheat yield, although SO(2) reduced shoot weight. SO(2) increased the growth and yield of barley, and HF or SO(2) increased the grain protein concentration of barley and wheat. The effects of mixtures of SO(2) and HF were complex, but often antagonistic, as the addition of HF counteracted the effect of SO(2) alone.  相似文献   
126.
Inductively coupled plasma mass spectrometry (ICP-MS) was used to examine trace element concentration in tree-rings over three and half centuries to assess macro-trends of environmental change. Tree-rings of a 350+ year old mammoth ponderosa pine (Pinus ponderosa) were analyzed for element concentration and evaluated versus local and global historical events. The ponderosa pine was located 100 miles south of the Canada/USA border and 180 miles east of the Pacific Ocean, and grew near apple orchards, a public road, and Swakane Creek in western Washington, USA. The elements tested did not all display the same time versus concentration patterns. Copper and chromium displayed cyclic concentration patterns over the last 350+ years, which appear to be associated with local events. Strontium, barium, zinc and cadmium were found to be relatively constant between the mid 1600s and the early 1800s. Strontium, barium, zinc, and cadmium then increased beginning in the early 1800s for approximately 50 years then decreased to present day 2000. Significantly, similar changes seen in Ca, Mg, and Zn in other studies have been attributed to acid rain, whereas, in our study area there is no history of anthropogenic acid rain. Most importantly, our data goes back to the mid-1600s several hundred years further back than most other studies of this nature. This additional time data provides for a better context of trend data not previously available.  相似文献   
127.
Monitoring of particulate matter outdoors   总被引:6,自引:0,他引:6  
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Lipid-containing semipermeable membrane devices are applied to the quantitative determination of the persistence of polynuclear aromatic hydrocarbons (PAH) in an irrigation water canal, a representative waterway. The uniform and reproducible sampling of the USGS design of lipid-containing SPMDs is exploited to measure PAH half-lives without requiring calculation of water concentrations. The trend in calculated PAH half-lives agrees with that expected if volatilization is a significant mechanism for loss from the canal with more volatile PAHs having shorter half-lives. The higher persistence of phenanthrene compared to anthracene is consistent with the greater stability of phenanthrene and suggests, with other physicochemical evidence, that other (reactive) mechanisms may be involved. The results of this study demonstrate the feasibility of the SPMD method for the measurement of residence times in aquatic and other compartments. Such information is essential for quantifying contaminant behavior in the environment and providing insights into contaminant fate.  相似文献   
130.
Assessment of human exposure to ambient particulate matter   总被引:8,自引:0,他引:8  
Recent epidemiological studies have consistently shown that the acute mortality effects of high concentrations of ambient particulate matter (PM), documented in historic air pollution episodes, may also be occurring at the low to moderate concentrations of ambient PM found in modern urban areas. In London in December 1952, the unexpected deaths due to PM exposure could be identified and counted as integers by the coroners. In modern times, the PM-related deaths cannot be as readily identified, and they can only be inferred as fractional average daily increases in mortality rates using sophisticated statistical filtering and analyses of the air quality and mortality data. The causality of the relationship between exposure to ambient PM and acute mortality at these lower modern PM concentrations has been questioned because of a perception that there is little significant correlation in time between the ambient PM concentrations and measured personal exposure to PM from all sources (ambient PM plus indoor-generated PM). This article shows that the critical factor supporting the plausibility of a linear PM mortality relationship is the expected high correlation in time of people's exposure to PM of ambient origin with measured ambient PM concentrations, as used in the epidemiological time series studies. The presence of indoor and personal sources of PM masks this underlying relationship, leading to confusion in the scientific literature about the strong underlying temporal relationship between personal exposure to PM of ambient origin and ambient PM concentration. The authors show that the sources of PM of non-ambient origin operate independently of the ambient PM concentrations, so that the mortality effect of non-ambient PM, if any, must be independent of the effects of the ambient PM exposures.  相似文献   
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