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141.
Addressing the issues of traffic safety in rural areas presents a constant challenge. The mix of light and heavy vehicles and the considerable differences in speed among these traffic participants result in high risks and delays for the faster vehicles. Agricultural vehicles (AVs) in particular have such an impact on traffic, especially when using arterial highways. This paper reviews the problems of safety and delays that AVs cause on arterial highways, and the appropriate mitigation. The concept of 'sustainable safety' in The Netherlands focuses on these problems, because of the proposed construction of parallel roads alongside all arterial highways. However, Dutch accident statistics cannot justify the high costs for the construction of parallel roads alongside 7000 km of arterial highways. Delays experienced by fast traffic are another reason for separating AVs from other road users with parallel roads. Alternative measures alongside the arterial highway, such as passing bays, restricting AVs to travelling at off-peak only and improving the conspicuity of the AVs, may be more cost-effective ways of reducing delays and/or improving traffic safety on arterial highways. Another solution may be to eliminate the need for AVs to use the arterial highway by altering their routes. For this purpose, land reallocation projects (as practised in Holland) can provide a useful tool. 相似文献
142.
Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean 总被引:2,自引:1,他引:1
Catherine Vallires Leira Retamal Patricia Ramlal Christopher L. Osburn Warwick F. Vincent 《Journal of Marine Systems》2008,74(3-4):756
Globally significant quantities of organic carbon are stored in northern permafrost soils, but little is known about how this carbon is processed by microbial communities once it enters rivers and is transported to the coastal Arctic Ocean. As part of the Arctic River-Delta Experiment (ARDEX), we measured environmental and microbiological variables along a 300 km transect in the Mackenzie River and coastal Beaufort Sea, in July–August 2004. Surface bacterial concentrations averaged 6.7 × 105 cells mL− 1 with no significant differences between sampling zones. Picocyanobacteria were abundant in the river, and mostly observed as cell colonies. Their concentrations in the surface waters decreased across the salinity gradient, dropping from 51,000 (river) to 30 (sea) cells mL− 1. There were accompanying shifts in protist community structure, from diatoms, cryptophytes, heterotrophic protists and chrysophytes in the river, to dinoflagellates, prymnesiophytes, chrysophytes, prasinophytes, diatoms and heterotrophic protists in the Beaufort Sea.Size-fractionated bacterial production, as measured by 3H–leucine uptake, varied from 76 to 416 ng C L− 1 h− 1. The contribution of particle-attached bacteria (> 3 µm fraction) to total bacterial production decreased from > 90% at the Mackenzie River stations to < 20% at an offshore marine site, and the relative importance of this particle-based fraction was inversely correlated with salinity and positively correlated with particulate organic carbon concentrations. Glucose enrichment experiments indicated that bacterial metabolism was carbon limited in the Mackenzie River but not in the coastal ocean. Prior exposure of water samples to full sunlight increased the biolability of dissolved organic carbon (DOC) in the Mackenzie River but decreased it in the Beaufort Sea.Estimated depth-integrated bacterial respiration rates in the Mackenzie River were higher than depth-integrated primary production rates, while at the marine stations bacterial respiration rates were near or below the integrated primary production rates. Consistent with these results, PCO2 measurements showed surface water supersaturation in the river (mean of 146% of air equilibrium values) and subsaturation or near-saturation in the coastal sea. These results show a well-developed microbial food web in the Mackenzie River system that will likely convert tundra carbon to atmospheric CO2 at increasing rates as the arctic climate continues to warm. 相似文献
143.
MUHAMMAD F. IBRAHIM 《运输评论》2013,33(2):221-243
A review of the retailing and transportation literature shows that there is an apparently large research gap in the understanding of shoppers’ attitudes towards transport modes for shopping purposes. In particular, not many studies have been done to examine shoppers’ detailed and disaggregated attitudinal image structures of the various transport modes for shopping purposes. Using Singapore as a study area, this paper has attempted to investigate shoppers’ image structure of transport modes and their comparative perception ratings for the various modes of transportation for shopping purposes. Using principal component analysis, the research has unveiled the perceptions of five transport modes for shopping purposes. While some of the factors are unique to certain transport modes, other factors, namely ‘suitability’, ‘practicality’, ‘ease of travel’ and ‘cost’, are common to all modes of transportation. By way of the weighted‐factor rating, the study found that the car recorded the highest overall perception rating while the bus rated the lowest. In addition, the shoppers have reasonably good perception of public transport modes in Singapore. 相似文献
144.
In 1991, the Aquaculture Department of the Southeast Asian Fisheries Development Center launched a community-based fishery resources management project on Malalison Island, in central Philippines, to help conserve the country's marine resources and to help the fisherfolk rise above their poverty. The eight-year project integrated various disciplines in biology, economics, sociology, public administration, and engineering in its study of fishery resources and fishing communities and in evolving intervention strategies for resource conservation and management, and for community development. The project's most important accomplishment was the inculcation among the fisherfolk of the importance of resource conservation and management. The most important lesson learned was that an enlightened and empowered fisherfolk could be effective managers and responsible users of fishery resources. 相似文献
145.
J.P.M. Hendrikx T.J.J. Meijlink R.F.C. Kriens 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1996,26(6):449-461
The application of Optimal Control Theory to time-optimal inverse simulation of car handling was investigated. Time-optimal inverse simulation of car handling involves the calculation of driver actions required to perform specified manoeuvres, in as short a time as possible. Driver actions consist of time-histories of front wheel steer rate and longitudinal force. Optimal time-histories of these quantities were calculated using the Gradient method after formulating the problem as one of optimal control. Simulation results are presented for two different cars performing similar lane-changes. These results show significant differences in necessary driver actions for different cars and demonstrate the suitability of the approach taken. 相似文献
146.
P F Stratton D Ho Saxena . BOC Gases European Development Centre Rother Valley Way Holbrook Sheffield S RP UK. . The HOC Group Technical Centre Mountain Avenue Murray Hill New Jersey - USA 《上海交通大学学报(英文版)》2000,(1)
1ntroductionGaswimpfobe,usuallynitrOgen,mandheiumatposuresOfuPtO60barhasbousedinvacmbosfOrSendywtanditScharWshcsforbds-ofCOInNarewe1knOWUIl].More~theuseofgasq-aPPliedtOs~orsinglelayereOfCOmwtthawereheandindsvacuumorCOnwtalatmOSPherbohasboPrOpond(2l.TOathaatetheedtOCOOtheboacestruCtUrasweIIastheCOIntwIkeSechquesOboinvolvethetrareferOftheNttobeqMtoa~allydeaignedcoklchfortsl.6as~of~peinndsngmaybosoaS~the-ofbo'bds-Oha'pesstwfOr'juSb~'manwt.Unlikliquldbased~antS,gaswiiscleannO… 相似文献
147.
A moving bottleneck 总被引:1,自引:0,他引:1
G.F Newell 《Transportation Research Part B: Methodological》1998,32(8):531-537
Suppose that a vehicle or convoy enters a two-lane unidirectional roadway and travels at a velocity v* less than the prevailing traffic. This moving bottleneck may cause a queue to form as vehicles try to pass the obstruction. It is shown that by going to a moving coordinate system traveling at velocity v* the analysis of this can be transformed into a corresponding analysis of flow past a stationary bottleneck. The theory is then extended to investigate possible consequences of trucks on grades. 相似文献
148.
G.F. Newell 《Transportation Research Part B: Methodological》1998,32(8):583-588
—Suppose that in an office building of moderate height (5 to 20 floors) elevator traffic during peak periods is predominantly between a lobby floor and various upper floors. We compare the waiting plus riding time and the average number of passengers carried per trip for various strategies. In particular, if two (or more) elevators serve the same group of floors (a common strategy), the waiting plus riding time would typically be (slightly) less if one split the group into two parts and had each elevator serve separate parts of this group. The latter strategy would have considerably fewer passengers per trip. It may also be advantageous to have a single elevator serve different floors on successive trips. Seldom would it be advantageous for an elevator to serve more than 2 or 3 floors on any trip. If elevator systems used more efficient strategies during peak periods, buildings would not need as many elevators. 相似文献
149.
Short-line railroad managers discuss their industry 总被引:1,自引:0,他引:1
Johnson James C. McClure Diane J. Schneider Kenneth C. Wood Donald F. 《Transportation》2004,31(1):97-123
In the United States, the 1980 Staggers Rail Act created a positive regulatory environment for the creation of new short-line railroads. At present there are about 450 of these railroads that have less than 250 miles of trackage. This study asked managers/owners of these railroads two basic questions. First, what do you believe is the single most important trend that is currently taking place in your industry. The most frequently noted trend was the frustration of working with the larger Class 1 railroads. Five additional trends were also identified by the respondents. The second question asked the respondents if they thought the short-line sector of the rail industry will become more or less important in the next ten years and why. About 70% of the owner/managers believed their industry would become more important in the next decade. The most commonly expressed reason for this position is that the Class 1 railroads will increasingly specialize in mainline service only. Three other rationales were also enumerated. For the managers that thought their industry would become less important, the most noted reason was their trackage would not safely transport the newer very heavy bulk commodity freight cars. 相似文献
150.
A variety of construction problems, such as bad cutting effects of cutters, unreasonable boring parame- ters and blowout, are often encountered during shield tunnelling under unfavorable geological conditions. Aimed at these construction difficulties of high pressure, abundant underground water, fractured rock stratum, long distance and small-radius curves of Fuzhou metro, the mechanical behaviors of cutting tools were analyzed through theoreti- cal calculations of cutter cutting force, then the reasonable cutter configuration, tunneling parameters and the proper time for cutter replacement were presented. Some measures, such as screw conveyor renovation, mucking control and lowering of groundwater, were adopted for controlling blowout based on practice. The stability of excavation face was analyzed by numerical simulation, and the measures for shield boring and posture control in the long distance and small radius curved tunnels were summarized. The conclusions are as follows: 1) when shield machine is driven in fractured stratum, the effect of lateral impact force produced by spalling rock on cutter will be very large and rein- forcement is needed for cutter; 2) cutter replacement should be taken at proper time based on muck samples in con- ditions of increasing of total shield thrust by 4 000-7 000 kN, cutter torque by 1 000-1 500 kN•m and driving speed smaller than 10 mm/min; 3) adopting screw conveyor device with innovative anti-blowout devices and control measures for ground precipitation and mucking, it controls blowout effectively; 4) the maximum axis offset and the height offset of segment meet the requirements of shield construction specifications during shield construction of long distance small-radius curved tunnel. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved. 相似文献