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231.
232.
The opacity and emission performance of two “identical” cold-side precipitators at a power plant utilizing a Western coal source was investigated through an extensive test program. The test program included establishment of outlet emission versus opacity correlations for the two “identical” units, correlation of rapper strategy (frequency and amplitude) with opacity, and correlation of power-off rapping strategy with opacity. Analysis of the test program data demonstrates that the opacity-emission correlations from the two “identical” units can be significantly different. The potential reasons for the differences between the two units are identified and examined in light of the test program data. Strong correlation of opacity with rapping strategy was developed from the test program. Results demonstrate that an automatic power-off rapping technique can significantly enhance precipitator performance on ash from Western coal. 相似文献
233.
It is well established that older drivers' fragility is an important factor associated with higher levels of fatal crash involvement for older drivers. There has been less research on age-related fragility with respect to the sort of minor injuries that are more common in injury crashes. This study estimates a quantity that is related to injury fragility: the probability that a driver or a passenger of that driver will be injured in crashes involving two cars. The effects of other factors apart from drivers' fragility are included in this measure, including the fragility of the passengers, the crashworthiness of cars driven, seatbelt use by the occupants, and characteristics of crashes (including configuration and impact speed). The car occupant injury liability estimates appropriately includes these factors to adjust risk curves by age, gender, and speed limit accounting for overrepresentation in crashes associated with fragility and these other factors. 相似文献
234.
From May 1999, a new system for licensing older drivers was introduced in New Zealand. It included a practical on-road driving test with expanded scope, to be completed every two years from the time the driver turns 80. The relationship between crashes and test performance needed to be studied to inform the debate regarding the testing system. The population studied was all drivers who entered this licensing system during its first three years of operation. They were defined as crash involved if they were involved in an injury crash during the two years following their first licensure under the new system. Logistic regression was used to describe the risk of crash involvement in terms of driving test performance and other driver characteristics. Each driving test failure was associated with a 33% increase in the odds of crash involvement (95% CI 14% to 55%), controlling for age, gender, minor traffic violations, and whether the older driver lived with another licensed driver or not. Minor traffic violations in the two years following the driving test were associated with twice the odds of crash involvement. These results suggest that the new on-road driving test does identify older driver behaviors or limitations that are related to crash liability. It is anticipated that the results presented here will provide essential information for discussing older driver licensing systems, whose impact will grow in importance as the population of drivers ages. 相似文献
235.
Because organic sorption in soil may never reach equilibrium, a thin-disc flow nonequilibrium method may be helpful in understanding herbicide-soil interactions. This research was conducted to (i) determine the influence of incubation time on imazaquin [2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid] desorption from soil, (ii) examine the influence of solution flow velocities on desorption, and (iii) elucidate the most appropriate kinetic model to describe imazaquin leaching. Soil at 7.5% moisture w/w was treated with imazaquin and incubated for 24, 72, and 168 h. Treated soil was sealed in an in-line filter apparatus and rinsed with 5.0 mM CaCl2 at 0.33, 0.67, or 1.0 mL min(-1). Effluent was collected as 1.0-mL fractions for a total of 50 mL. Flow was stopped for 24 h. When flow resumed, fractions were collected for an additional 15 mL. After the initial desorption, 79% of the imazaquin incubated for 24 h was leached. Increasing incubation time beyond 24 h reduced imazaquin leaching. After both desorption events, 13% of the initially applied imazaquin remained in the soil incubated for 168 h, compared with 7% with soil incubated for 24 h. Elovich and Freundlich kinetics accounted for 98% of the variance observed in the imazaquin desorption curves. First-order and diffusion kinetics accounted for 91% of the variance. Incubating soil for 72 h before desorption reduced the rate of imazaquin desorption by approximately 12%, compared with the 24-h incubation treatment. Imazaquin desorption was not affected by wash solution flow rate. These data suggest that the kinetics of desorption in prolonged desorption events are limited by transport phenomena (i.e., particle and film diffusion). 相似文献
236.
Natural and anthropogenic enrichments of molybdenum, thorium, and uranium in a complete peat bog profile, Jura Mountains, Switzerland 总被引:1,自引:0,他引:1
A core from an ombrotrophic Swiss bog representing 12 370 (14)C years of peat accumulation was evaluated as a possible archive of atmospheric deposition of Mo, Th and U. Calcium, Sr, and Ba were also determined to quantify weathering inputs, Mn to follow possible redox transformations, and Rb to identify plant uptake. Each of these elements was determined using ICP-MS, following digestion in a microwave heated autoclave using 3 ml HNO(3) and 0.1 ml HBF(4). Calcium and Sr clearly identify the thickness of the ombrotrophic zone because they are enriched in the minerogenic zone relative to the concentration of mineral matter. The concentration of Ba, however, is proportional to the concentration of mineral matter in all samples, and is not added to peat column by weathering reactions at the peat-sediment interface. The lowest element concentrations are found during the Holocene climate optimum (5320 to 8030 (14)C year BP) with the following natural background values (n= 18): Mo 0.08 +/- 0.02 microg g(-1), U 0.029 +/- 0.008 microg g(-1), Ba 5.2 +/- 2.6 microg g(-1), Th 0.070 +/- 0.022 microg g(-1) and Rb 0.63 +/- 0.09 microg g(-1). By far the highest concentrations of Ba, Mn, Rb and Th were found during the Younger Dryas cold climate event (10 590 (14)C year BP) when the flux of atmospheric soil dust was at its post-glacial maximum. Molybdenum and U are elevated in concentration throughout the minerogenic zone because of sediment weathering and this masks the atmospheric signal in samples older than ca. 8000 (14)C year BP (ca. 9000 calendar years). Enrichment factors (EF) calculated using Sc as a conservative, lithogenic element shows that minerogenic peats are enriched in Mo up to 18x and U 26x, relative to the natural "background" values. During the two millennia prior to industrialisation, the accumulation rate of atmospheric Mo averaged 0.23 +/- 0.13 microg m(-2) year(-1). With the onset of the Industrial Revolution, Mo accumulation rates rapidly and continuously increased to approximately 10 microg m(-2) year(-1) in the late 1980s. These data suggest that Mo in atmospheric aerosols today is derived predominately from anthropogenic emissions. Uranium does not show the same enrichment pattern which suggests that steel-making rather than coal combustion is the primary source of atmospheric Mo contamination at this site. 相似文献
237.
The southern Africa crisis represents the first widespread emergency in a region with a mature HIV/AIDS epidemic. It provides a steep learning curve for the international humanitarian system in understanding and responding to the complex interactions between the epidemic and the causes and the effects of this crisis. It also provoked much debate about the severity and causes of this emergency, and the appropriateness of the response by the humanitarian community. The authors argue that the over-emphasis on food aid delivery occurred at the expense of other public health interventions, particularly preventative and curative health services. Health service needs were not sufficiently addressed despite the early recognition that ill-health related to HIV/AIDS was a major vulnerability factor. This neglect occurred because analytical frameworks were too narrowly focused on food security, and large-scale support to health service delivery was seen as a long-term developmental issue that could not easily be dealt with by short-term humanitarian action. Furthermore, there were insufficient countrywide data on acute malnutrition, mortality rates and performance of the public health system to make better-balanced evidence-based decisions. In this crisis, humanitarian organisations providing health services could not assume their traditional roles of short-term assistance in a limited geographical area until the governing authorities resume their responsibilities. However, relegating health service delivery as a long-term developmental issue is not acceptable. Improved multisectoral analytical frameworks that include a multidisciplinary team are needed to ensure all aspects of public health are dealt with in similar future emergencies. Humanitarian organisations must advocate for improved delivery and access to health services in this region. They can target limited geographical areas with high mortality and acute malnutrition rates to deliver their services. Finally, to address the underlying problem of the health sector gap, a long-term strategy to ensure improved and sustainable health sector performance can only be accomplished with truly adequate resources. This will require renewed efforts on part of governments, donors and the international community. Public health interventions, complementing those addressing food insecurity, were and are still needed to reduce the impact of the crisis, and to allow people to re-establish their livelihoods. These will increase the population's resilience to prevent or mitigate future disasters. 相似文献
238.
Monitoring Forest Carbon Sequestration with Remote Sensing and Carbon Cycle Modeling 总被引:1,自引:0,他引:1
Sources and sinks of carbon associated with forests depend strongly on the management regime and spatial patterns in potential productivity. Satellite remote sensing can provide spatially explicit information on land cover, stand-age class, and harvesting. Carbon-cycle process models coupled to regional climate databases can provide information on potential rates of production and related rates of decomposition. The integration of remote sensing and modeling thus produces spatially explicit information on carbon storage and flux. This integrated approach was employed to compare carbon flux for the period 1992–1997 over two 165-km2 areas in western Oregon. The Coast Range study area was predominately private land managed for timber production, whereas the West Cascades study area was predominantly public land that was less productive but experienced little harvesting in the 1990s. In the Coast Range area, 17% of the land base was harvested between 1991 and 2000. Much of the area was in relatively young, productive-age classes that simulations indicate are a carbon sink. Mean annual harvest removals from the Coast Range were greater than mean annual net ecosystem production. On the West Cascades study area, a relatively small proportion (< 1%) of the land was harvested and the area as a whole was accumulating carbon. The spatially and temporally explicit nature of this approach permits identification of mechanisms underlying land base carbon flux.
Published online 相似文献
239.
R. Goodland M. Ismail F. Strum David Walker Lupton Marc Jay Rogoff William Erich Cline David E. Goldenberg James C. Starbuck Lee S. Tesdell Anthony G. White John F. Schnell Richard S. Krannich Nan C. Burg Frederick Frankena Meredith Kirkpatrick U. G. Yermakov V. L. Mote C. ZumBrunnen T. B. Denisova V. L. Rauner P. P. Micklin G. L. Rutilevskiy 《Environmental management》1978,2(5):473-476
240.
Gilbert F. Coahran William S. Butcher 《Journal of the American Water Resources Association》1970,6(3):311-322
The Las Vegas, Nevada area like most semi-arid basins, was developed through exploitation of available ground-water resources. Area growth in this large valley has occurred in a scattered and sporadic manner with development both in incorporated areas and within the County. As a result, today there exist five major water suppliers which are: a water district, three municipalities, and a large corporation, in addition to numerous small water companies and thousands of domestic wells. In the past 20 years the area has grown from a population of less than 50,000 to over 300,000 today. The bulk of the water demand for this growth has been met from the ground-water resource and as a result the basin is being severely mined. Current extractions are over three times the estimated annual replenishment. Rapidly declining water levels are increasing the costs of water and are creating water shortages during periods of peak demand. To meet both the current and anticipated water demands, the Southern Nevada Water Supply Project is being constructed to import additional water from nearby Lake Mead. Agriculture in the area is very limited, and primarily uses reclaimed waste water for irrigation. The chief water demands in the area are thus municipal and industrial, with the former predominating. This study was designed to determine how best the Las Vegas Valley Water District, supplier of 80 percent of the domestic water, might integrate the use of the existing ground water and anticipated imported surface water. Additionally the consequences of application of certain provisions in the Nevada Water Law were examined to determine their effects on the ground-water system and costs of water. To achieve these objectives, a dynamic programming technique was utilized. The problem as formulated consists of a single decision variable, single state variable dynamic programming algorithm evaluated over a fifty-year planning horizon at monthly intervals. Three alternative solutions, with different ground-water law constraints are evaluated. In all solutions certain basic operating rules regarding ground-water pumping distribution and use of surface-water systems are kept constant. The problem is considered as deterministic in all respects. Recharge to ground water is assumed to equal the estimated average annual replenishment evenly distributed over the year and additionally is not considered to be a function of average basin ground water potential. The only surface supply, Lake Mead, is considered to operate at near constant elevation and not be subject to shortage conditions. In light of the size of Lake Mead, the Colorado River flow and the size of Nevada's allotment, 300,000 ac ft, the latter assumption is reasonable. Demand for water is considered as a known function of time. Optimization of conjunctive use for the Water District is based on the objective function of minimizing water production costs. Costs of distributing water are considered to be constant regardless of source, and so are not included. Also, fixed costs of amortizing the pipeline project and well fields are not considered. Results of the study are presented as a series of policy traces under each of the three alternatives considered. These traces describe the ground-water basin response under optimal operating conditions, given an estimate as to the present worth of ground-water pumping rights, and prescribe monthly water-procurement schedules for the operation of the Water District. 相似文献