In-use measurement of the activity, fuel use, and emissions of eight cement mixer trucks operated on each of petroleum diesel and soy-based B20 biodiesel

In-use micro-scale fuel use and emission rates were measured for eight cement mixer trucks using a portable emission measurement system. Each vehicle was tested on petroleum diesel and B20 biodiesel. Average fuel use and emission rates increase monotonically versus engine manifold absolute pressure. A typical duty cycle includes loading at a cement plant, transit while loaded from the cement plant to work site, creeping in a queue of vehicles at the worksite, unloading, and transit without load from the site to the plant. For B20 versus petroleum diesel, there is no significant change in the rate of fuel use, CO₂ emissions, and NO emissions, and significant decreases in emissions for CO, hydrocarbons, and particulate matter. For loaded versus unloaded onroad travel, fuel use and CO₂ emissions rates are approximately 60% higher and the rates for other pollutants are approximately 30–50% higher. A substantial portion of cycle emissions occurred at the work site. Inter-vehicle and intra-cycle variability are also quantified using the micro-scale methodology.     

A model of the travel to work limits of parents

This paper considers the length of time that parents are willing to travel to an existing or new job. Using data for over 12,000 parents it finds that many characteristics were associated with being less likely to be willing to travel to work for at least an hour (roundtrip). These include: being a women, those out of work, having children under 5, being a lone parent and using formal childcare. Professionals and associate professions were more willing to travel for longer periods. In terms of location, those in accessible small towns and rural areas were willing to travel more than those in larger urban areas and those in remote rural areas willing to travel most. Policy implications are also set out.     

Maintenance optimization for transportation systems with demand responsiveness

We present a quadratic programming framework to address the problem of finding optimal maintenance policies for multifacility transportation systems. The proposed model provides a computationally-appealing framework to support decision making, while accounting for functional interdependencies that link the facilities that comprise these systems. In particular, the formulation explicitly captures the bidirectional relationship between demand and deterioration. That is, the state of a facility, i.e., its condition or capacity, impacts the demand/traffic; while simultaneously, demand determines a facility’s deterioration rate. The elements that comprise transportation systems are linked because the state of a facility can impact demand at other facilities. We provide a series of numerical examples to illustrate the advantages of the proposed framework. Specifically, we analyze simple network topologies and traffic patterns where it is optimal to coordinate (synchronize or alternate) interventions for clusters of facilities in transportation systems.     

Satellite remote sensing of the Polar Oceans

The advent of satellite remote sensing has opened doors for detailed monitoring of the polar regions at a relatively high temporal resolution. Several sensors have been developed over the years, the most noteworthy of which are the visible, the infrared and the microwave systems. The visible and infrared systems are most intelligible to the human eye and provide images that have good spatial resolution. However, because of persistent cloudiness and several months of darkness in the polar regions the most promising sensors appear to be the microwave systems, both passive and active. The passive microwave sensors have been the source of consistently derived ice cover and ice extent data and have provided about fifteen years of global data sets. The Synthetic Aperture Radar (SAR), on the other hand, is noted for very high resolution and a wide range of applications including ice dynamics and ice/wave interaction studies. Nevertheless, there are applications which require the use of the visible and infrared channels, such as the mapping of chlorophyll pigment concentrations in the marginal ice zones which require an ocean color scanner. Also, the infrared sensors are most effective for detecting physical temperatures over cloud-free ice and open water surfaces. Furthermore, altimeters could play an important role in mapping ice surface topography and in evaluating ridge and lead statistics. A review of past, present and future satellite systems, methods and techniques of interpretation and potential applications to the study of the polar oceans is presented.     

Factors affecting tanker safety

The major factors influencing tanker safety are discussed. For the discussion information has been gleaned from maritime labour officials, industry experts and a recent United States Coast Guard study on tanker safety. Results of other tanker safety studies and/or accident reports are also utilized. Some of the factors analysed are the size and age of vessel, licence qualifications for mates and engineers and manning levels. Other factors are those related to or attributed to flags of convenience and the pressure to maintain shipping schedules.     

Nutrient cycling and primary production in the marine systems of the Arctic and Antarctic

Primary production events in both the Arctic and the Antarctic are highly localized. Carbon-14 incubations that did not account for this caused antarctic primary production estimates to be revised too far downwards from the historic view of high productivity. The primary production regime in the Arctic is even more heterogeneous than in the Antarctic. Arctic primary production rates are in the process of being revised upwards because of a better spatial and temporal distribution of incubation experiments and a re-awakening of interest in estimating new production from the distribution of chemical variables. Similarly, recent examination of temporal changes in nitrate concentrations and recognition of the importance of ice-edge blooms has caused antarctic primary productivity to be revised upwards. In both the Arctic and the Antarctic, the ratio of “new” to total primary production is high, and neglect of this fact can lead to an underestimation of the potential that these regions have for influencing global cycles of bioactive chemicals. Some recent data on temporal changes in nitrate from Fram Strait emphasize the poor state of our knowledge by suggesting an unexpectedly high “new” production rate of 1 g C m⁻² d⁻¹ for a 35 day experiment that encountered an early Phaeocystis bloom. Chemical distributions suggest that new production over the shelf seas that border the Polar Basin is about 50 g Cm⁻² yr⁻¹.The shelves in the Arctic Ocean's marginal and adjacent seas comprise 25% of the total global continental shelf. These extensive shallow regions have much higher rates of primary production than the Polar Basin and may be globally significant sites of denitrification. Globally significant silica deposition could occur on these shelves or on the adjacent slopes.Because of the differences in geomorphology and stratification, global warming is likely to increase primary production in the Arctic and will probably decrease antarctic primary production.In addition to sharing high ratios of “new” to total primary production, high ammonium concentrations occur in the Arctic and Antarctic. It is possible that these accumulations arise from a strong repression of nitrification at low temperatures.     

机车轮对装配应力的数值分析

提出了一套模拟车轮装配全过程的数值分析程序，分析轮对配合面内的接触应力分布，在轴对称模型基础上，模拟分析了整体直辐板车轮与车轴之间的过盈配合接触现象，详细地讨论了过盈配公差和加工精度对配合面内的接触应力分面和摩擦滑动的影响；在三维模型基础上，模拟分析了论心－轮箍型斜辐板车轮与车轴的两个过盈配合面内的接触压力分布，研究了不同过盈配合量，轮箍厚度和垂向外载荷对接触压应力分布的影响。     

美国拉臂钩技术发展及应用现状

我叫大卫·泽洛斯特里克,是斯泰勒工业有限公司的董事长.斯泰勒工业有限公司是美国第一家拉臂钩制造商,成立于1990年,座落于美国爱荷华州的加纳区.     

编者的话

2008年重卡各车型的销量格局比较稳定，牵引车仍旧是重卡市场中份额最大的车型。而载货车和自卸车的市场份额也势均力敌。重卡各吨位销量还是以总质量19～26t为主，但份额稍有下滑，而1～19t和26～32t的市场份额各有一个百分点的增长。今年1—5月是近年来重卡车型格局变化最大的一次，自卸车市场迅速扩张，牵引车市场的萎缩，使原来三足鼎立的格局发生了翻天覆地的变化。目前，我国正处于大规模基础设施建设中。新开工项目比较集中，形成了自卸车的销售高峰。在前5个月销售的重卡中，自卸车占到了相当大的比重，市场份额几乎翻倍。部分企业自卸车的销量占到总销量的近一半甚至更多。预计这种势头还将持续一段时期。