Determining the number and location of winter road maintenance depots – a case study of the district road network in Serbia

Determining the number and location of depots for winter road maintenance (WRM) represents one of the important strategic decisions while planning WRM activities. However, most organizations dealing with WRM make empirically based decisions. Optimizing the number and location of WRM depots has the potential to achieve considerable cost savings, improve mobility and efficiency, as well as reduce environmental impacts. This paper presents two optimization models. The first model determines the location of WRM depots by minimizing the total distance travelled by maintenance vehicles. The second model determines the optimum number and location of WRM depots by minimizing total transportation costs and capital expenditure and operational expenditure of the depots. The models are then applied to the district road network in Serbia. Results show that their application could lead to significant reductions in WRM costs.     

A reverse causal-effect modeling approach for signal control of an oversaturated intersection

A novel approach is presented in which signalized intersections are treated as normal highway bottlenecks for improved computational efficiency. It is unique in two ways. First, it treats the signalized intersections as common freeway bottlenecks by a reversed cause and effect modeling approach. Both traffic arrivals and departures are modeled by smooth continuous functions of time as if there were no interruptions to traffic flows from signals. The use of smooth continuous functions for departure curves instead of commonly used step functions makes it easy to apply differential calculus in optimization and future extension to a system of intersections. Second, a dynamic linear programming (LP) model is then developed to maximize the total vehicular output from the intersection during the entire period of congestion subject to prevailing capacity and other operational constraints. The continuous optimal departure flow rate (the effect) is then converted to signal timing parameters (the cause) that can be readily implemented. Two numerical examples are presented to demonstrate the properties of the proposed algorithm and examine its performance.     

Evaluation of the effect of cooperative infrastructure-to-vehicle systems on driver behavior

In-vehicle technologies and co-operative services have potential to ease congestion problems and improve traffic safety. This paper investigates the impact of infrastructure-to-vehicle co-operative systems, case of CO-OPerative SystEms for Intelligent Road Safety (COOPERS), on driver behavior. Thirty-five test drivers drove an instrumented vehicle, twice, with and without the system. Data related to driving behavior, physiological measurements, and user acceptance was collected. A macro-level approach was used to evaluate the potential impact of such systems on driver behavior and traffic safety. The results in terms of speeds, following gaps, and physiological measurements indicate a positive impact. Furthermore, drivers’ opinions show that the system is in general acceptable and useful.     

Sensitivity of train stochastic dynamics to long-term evolution of track irregularities

The influence of the track geometry on the dynamic response of the train is of great concern for the railway companies, because they have to guarantee the safety of the train passengers in ensuring the stability of the train. In this paper, the long-term evolution of the dynamic response of the train on a stretch of the railway track is studied with respect to the long-term evolution of the track geometry. The characterisation of the long-term evolution of the train response allows the railway companies to start off maintenance operations of the track at the best moment. The study is performed using measurements of the track geometry, which are carried out very regularly by a measuring train. A stochastic model of the studied stretch of track is created in order to take into account the measurement uncertainties in the track geometry. The dynamic response of the train is simulated with a multibody software. A noise is added in output of the simulation to consider the uncertainties in the computational model of the train dynamics. Indicators on the dynamic response of the train are defined, allowing to visualize the long-term evolution of the stability and the comfort of the train, when the track geometry deteriorates.     

2007年铸造工艺发展新动向

文章介绍了目前常用的真空V法造型、湿砂造型和树脂砂造型的基本原理、工艺过程以及所使用的设备,列举了它们的优缺点和经济的适用范围。针对其各自的特点概述了工艺方法的选择原则以及它们对环境所造成的影响。     

Sizing parking facilities at airports

Established rules-of-thumb and industry guidelines for estimating the supply of parking at airports are based on uncertain quantities such as design year enplanements and number of airport employees, and are independent of cost. In the presence of continued uncertainty and increasing competition for limited space in and around airports, it is important that facilities are sized in relation to cost of providing and using them. A probabilistic model based on the classical “newsboy” problem is proposed to determine the optimal supply of parking in relation to expected total cost while treating demand as a random quantity. Empirical data are used to demonstrate the application of the proposed model for decision making. In addition to construction and maintenance costs, and user costs, decisions are shown to be sensitive to the level of uncertainty of design year enplanements.     

Autonomy, bureaucracy, professionalism and accountability: a transaction cost approach to shipboard controls

In recent years, shipping industry has encountered severe competition, technological change, and environmental and safety concerns. In order to remain competitive, firms need to review and redesign shipboard work. A crucial aspect of these efforts is shipboard controls that define the extent of autonomy and accountability of officers and crew. This study examines four types of controls on board ships. These are monitoring and autonomy, outcome accountability, formalization and professionalization. The study applied trancsaction cost theory to test eight hypotheses on board 16 ships in two companies. The results largely confirm theoretical predictions. Task visibility, complexity and uncertainty show strong relationships to the four types of controls. However, there are also significant gaps in that accountability for outcomes is low, and situation with regard to crew training and autonomy can be improved. Implications for human resource practice and future research are discussed.     

Dissolved organic matter studies in enclosed systems: Application of Hydrophobic fractionation for the assessment of organic nitrogen dynamics

The evolution of dissolved organic matter (DOM) in a non-axenic batch culture of the marine diatom Thalassiosira tumida was studied by hydrophobic fractionation during a three month experiment. DOM was fractionated with XAD-2 resin into hydrophobic (acid and neutral, “humic”) and hydrophilic fractions. The combined amino acid contents of unfractionated filtered seawater, XAD-fractions and particulate material were determined during the growth, stationary and degradation phases of the culture, and variations related to changes in dissolved organic nitrogen (DON) in XAD-fractions, dissolved inorganic nitrogen, algal and bacterial biomass. XAD-fractionation enabled the discrimination of simultaneously ocurring release and uptake of organic nitrogenous compounds: During the diatom growth there was a net increase of tolal DON concentrations, which was mostly accounted for by the hydrophilic fraction. A concurrent heterotrophic uptake of combined amino acids and other non-amino acid organic nitrogen was discernible by the decrease of their concentrations in the hydrophobic fractions. In the stationary phase, during the prevailing net consumption of total DON, the production of algal exudates could be detected in the hydrophobic fractions, while uptake mainly involved non-amino acid organic nitrogen from the hydrophilic fraction. During the degradation phase, after two months part of the particulate amino acid pool was transformed into hydrophilic DON, which in contrast to the stationary phase, was not adequate for supporting sustained bacterial growth. This suggests that the generation of recalcitrant substances may begin in the hydrophilic fraction of DOM. A slight increase of the hydrophobic acid fraction was indicative of the incipient formation of humic substances. XAD-2 was able to adsorb substances from fast changing DOM pools and thus should be a useful tool in studies concerned with phytoplankton and bacterial dynamics.     

基于节气门位置传感器的发动机故障诊断研究

通过在VOLVOB230F型电控汽油喷射发动机上研究节气门位置传感器的全负荷信号对发动机性能的影响．并对节气门位置传感器故障造成的发动机性能变化的对比可分析表明：节气门位置传感器的全负荷信号丢失以后，混合气变稀，功率下降；CO和HC排放降低，NOx排放升高，同时有助于指出了节气门位置传感器在电控发动机故障诊断中的作用。     

Comment: Tankers' modification economics: Is there an arbitrage?

In this paper we address the following question: how much is a ship-owner willing to pay in order to convert his single-hull vessel to a double-hull vessel? Our research is motivated by a recent article in Tradewinds, according to which owners have become reluctant in scrapping their vessels by turning them into double hull from single hull. We apply a structural no-arbitrage condition for deriving and estimating 'good-deal' bounds.