Simulation assessment of incident detection by cellular phone call-in programs

This research study was designed to assess by simulation the efficacy of incident detection by cellular phone call-in programs. The assessment was conducted by varying the proportion of drivers with cellular phones on the highway so as to mirror the cellular industry statistics that show a continued growth of ownership of cellular phones in the United States. An analytical model, which combined simulation and the limited field data available in the literature, was used to determine measures of effectiveness of the cellular phone-based detection system. The results showed that a cellular phone detection system offers fast incident detection times and higher detection rates for both shoulder and lane blocking incidents. For example, in moderate traffic flow (i.e. 1,550 vehicles per hour per lane), 90 percent of incidents blocking two lanes were detected in 1.5 minutes when the proportion of drivers with cellular phones was one out of 10 drivers, even with only 20 percent of them willing to report incidents. When the current proportion of cellular ownership, i.e. 1 out of 3, was used in the simulation, the detection time improved to 0.8 minutes. The simulation analysis of incident detection by cellular phones also showed that there is a direct relationship between the probability of detection and the detection time; that is, the specification of a higher detection rate resulted in slower detection times. This is in sharp contrast with the results of field study of automatic incident detection (AID) systems which demonstrated an inverse relationship between probability of detection and detection time. This revised version was published online in June 2006 with corrections to the Cover Date.     

Risk management methods for the liner shipping industry: the case of the Bunker Adjustment Factor

Through the implementation of the Bunker Adjustment Factor (BAF), a shipowner is able to transfer the risk of fuel price fluctuation to the shipper. This and other surcharges are generally undesired by shippers who must pay this fee. The research presented provides an alternative method of risk management that is more effective than the current method, while responding to customer service demands for simplified tariffs. By strategic use of commodity futures, the shipowner is able to better reduce his/her risk exposure, transferring it to willing parties at the futures exchanges, thereby eliminating the need for the bunker surcharge.     

One-dimensional modelling of the plankton ecosystem of the north-western Corsican coastal area in relation to meteorological constraints

In order to study the influence of wind mixing on the spring variability of the plankton production of the north western Corsican coastal area, a one-dimensional (1D), vertical, coupled hydrodynamic/biological model (ECOHYDROMV) is used. A hydrodynamic 1D model of the water column with a k–l turbulent closure is applied. The biological model comprises six state variables, representing the plankton ecosystem in the spring period: phytoplankton, copepods, nitrate, ammonium, particulate organic matter of phytoplanktonic origin and particulate organic matter of zooplanktonic origin. The system is influenced by turbulence (expressed by the vertical eddy diffusivity), temperature and irradiance. The model takes into account momentum and heat surface fluxes computed from meteorological data in order to simulate a typical spring atmospheric forcing for the considered area. Results show that primary production vertical structure is characterised by a subsurface maximum which deepens with time and is regulated by the opposite gradients of nitrate concentration and irradiance. Surface plankton productivity is mainly controlled by turbulent vertical transport of nutrients into the mixed layer. The short time scale variability of turbulent mixing generated by the wind appears to be responsible for the plurimodal shape of plankton blooms, observed in the considered area. Furthermore, the model is applied to the study of the spring evolution of the plankton communities off the bay of Calvi (Corsica) for the years 1986 and 1988. In order to initiate and validate the model, time series of hydrological, chemical and biological data have been used. The model reproduces accurately the spring evolution of the phytoplankton biomass measured in situ and illustrates that its strong variability in those years was in close relation to the variability of the wind intensity.     

现代化有轨电车系统在中国城市的发展前景

为什么在中国城市发展现代化有轨电车系统呢？这种交通方式有哪些优点和不足之处呢？通过对现代化有轨电车系统的主要特点的阐述，充分显示了现代有轨电车系统满足中国城市交通需求的独特魅力。     

Valuing road noise for residents in Hong Kong

This study estimates the willingness-to-pay value for a one dB(A) change over a range of initial noise levels for a sample population in Hong Kong. It establishes a protocol for estimating the willingness-to-pay values by first establishing an annoyance–dB relationship. The protocol takes into account the characteristics that the probability of being annoyed at a particular level varied with the initial objective noise level, and the annoyance–dB relationship varied for a range of initial annoyance level. The study shows that household income level and initial annoyance levels exert considerable influences on the individual’s willingness-to-pay values. However, age and educational level were found not to exert any significant influence on individual’s willingness-to-pay values.     

Prediction of tire natural frequency with consideration of the enveloping property

A lumped tire model was developed with consideration of the enveloping property in order to predict the natural tire frequency. Tire stiffness was classified into vertical, sidewall, and enveloping stiffnesses, and the tire characteristics were analyzed in detail experimentally and via finite element analysis. In addition, the effective masses of the tire tread and belt were extracted directly from design specifications taking into account the sizes and material properties of different rubber blocks. Using the design parameters of the tires, natural frequencies were calculated from the derived model and were compared with experimental results. Finally, based on good agreement with experimental results, sensitivity analysis was performed to verify the effect of tire stiffnesses on the natural frequencies.     

Heat transfer enhancement on ventilated brake disk with blade inclination angle variation

Ventilated brake disk is the state of the art technology in automobile braking system. It is well known that the braking capability of brake disk is affected by the rate at which heat is dissipated through forced convection. The rapid increase and decrease of the brake disk temperature could lead to catastrophic failure of the brake disk due to high thermal stress. The objective of the current study is to investigate the potential heat transfer enhancements in ventilated brake disk by varying the geometrical parameters of the blades inside the flow passage. This is done through comparisons of non-dimensional properties for flow and heat transfer in different blade configurations of the ventilated brake disk. The straight blade configuration is used as a baseline reference against the angled blades. The investigations are performed by using both experimental and computational means and the results are compared and discussed. Analysis shows that significant increase in braking performance can be achieved with relatively simple alteration of the ventilated blade angle. The results show a tremendous increase in the heat transfer rate with blade inclination angle configurations as compared to conventional straight blade. The Nusselt number is found to be in a power-law relationship with the Reynolds number. Distinct relationship between laminar and turbulent condition is predicted. An improvement in total convective heat transfer coefficient of 51% was achieved with blade inclination angle of 45° tilting towards clockwise direction.     

Bregman's balancing method

In this paper we observe that most of the independently discovered balancing methods, used in transportation planning and in other fields, are in fact special cases of a method of Bregman. Examples include the usual Kruithof or Furness method, the Evans-Kirby three dimensional balancing procedure, the Murchland multiproportional balancing procedure, the Osborne or Grad method for preconditioning matrices, the Jefferson-Scott procedure for gravity models with inequality constraints, and the method considered by Macgill for partially constrained gravity models. The convergence of all of these methods follows from Bregman's general result.     

Vibrational characteristics of automotive transmission

A mathematical model of an automotive transmission is developed, that considers the flexibility of the shafts, bearings, and gear teeth, and gyroscopic effects of geared rotors. The transverse, torsional, and axial motions are strongly coupled due to helical gearing. The excitation forces acting on the automotive transmission are classified into first, second, and third grades, based on the magnitudes of the forces that are determined by the perturbation method. The excitation forces are caused by the mass imbalances among gears, misalignment of shafts, clearance and non-linear deformation of bearings, transmission errors, and the periodic variation of the gear mesh stiffness. A bench test on loading conditions is carried out for the third speed of the automotive transmission. The experimental results of vibration characteristics are compared with those from theoretical analysis. The results show good agreement, i.e., within a tolerance of 3.3%.