Recent directions in automobile demand modeling

We identify seven areas in which recent research on auto demand has made significant progress. We discuss the importance of these areas in understanding and predicting auto demand and describe the methods that researchers have used to address them. Finally, we identify the issues that this research indicates require further investigation.     

Exchange of carbon by an upwelling filament off Cape Ghir (NW Africa)

We have studied the physicochemical and biological structure of a permanent filament off Cape Ghir (31°N) and estimated the transport of organic matter associated with it. The seaward filament exported coastal upwelled water, with low temperature and salinity and high organic matter, to the open ocean even in the absence of upwelling-favorable conditions. The estimated flux of excess organic carbon (the nonrefractory pool) expressed in annual basis yielded a value of 3.1×10⁹ kg C, from which 90% was transported as dissolved organic carbon. This flux represents about 63% of the average annual primary production for the region of study. We conclude that the net-offshore transport may contribute to the enrichment of offshore oligotrophic waters throughout the year, partly explaining the metabolic imbalance found in open ocean waters of the subtropical Northeast Atlantic.     

An overview of the abundance and role of protozooplankton in Antarctic waters

The classic view of the Antarctic pelagic system has suggested that food web dynamics are dominated by the diatom-krill food web link. Recent observations, however, have indicated that this is an oversimplification and that the antarctic food web has a complexity similar to that found in lower latitude systems. More specifically, small particulate feeding protozoans appear to have a much greater importance than was previously assumed.Only a few studies have been sufficiently extensive to characterize the Antarctic pelagic protozoan assemblage. These indicate that heterotrophic flagellates (dinoflagellates and other heterotrophic nanoplankton) and ciliates (mostly non-loricate oligotrichs) dominate the protozooplankton assemblages in surface waters. The combined biomass of protozooplankton has been reported to comprise from < 7 to > 75% of the total nano- and microplankton biomass depending on season and location. Protozoans are also found in sea ice communities where their abundances exceed those typically found in the plankton. Several protozoan species occupy both ice and water habitats, suggesting that seasonally melting sea ice may be the source of ice-edge protozooplankton assemblages.The feeding rates of protozooplankton in Antarctic waters are poorly documented. Consumption estimates based on clearance rates and some preliminary grazing experiments, however, indicate that the protozooplankton should be capable of utilizing a significant proportion of the daily primary and bacterioplankton production. Protozoans may contribute to vertical flux, but present evidence suggests that their contribution will be lower than from other sources.     

FLUXMANCHE radiotracers measurements: A contribution to the dynamics of the English Channel and North Sea

From 1986 to 1992, ¹²⁵Sb released by the nuclear fuel reprocessing plant at La Hague has been used to study the transfer of waters from mid-Channel areas towards the Straits of Dover. Since 1940, these investigations have formed part of the MAST 53 FLUXMANCHE programme and have involved repeated measurements on a Straits of Dover transect. A discussion of the results is presented here which takes into account new information provided by a hydrodynamic model developed in the framework of FLUXMANCHE; it combines knowledge of the monthly fluxes of water trough the Straits of Dover and week-by-week simulation of the ¹²⁵Sb activities of waters flowing in this aera. It is proposed that soluble radionuclides introduced into the central Channel are transferred towards the Straits of Dover over a time which varies from four to seven months depending on the route taken.     

Statistical estimation of the parameters of Daganzo's gap acceptance model

In a recent article in Transportation Research, Daganzo (1981) described a model of gap acceptance that permits the mean of the gap acceptance function to vary among drivers and permits the duration of the shortest acceptable gap for each driver to vary among gaps. The model contains several constant parameters whose values must be estimated statistically from observations of drivers' behavior. The results of numerical experiments reported by Daganzo (1981) suggested that the values of the parameters cannot be estimated by the method of maximum likelihood, which is the most obvious estimation technique, and Daganzo proposed using a sequential estimation method instead. The sequential method appeared to yield reasonable numerical results. In this paper, it is shown that subject to certain reasonable assumptions concerning the true parameter values and the probability distribution of gap durations, the maximum likelihood method does, in fact, yield consistent estimates of the parameters of Daganzo's model, whereas the sequential method does not. Hence, maximum likelihood is the better estimation method for this model.     

Effect of local operational constraints on runway capacity - A case study

The estimation of runway capacity is important in airport planning and operational analysis. Standard procedures for capacity determination typically assume that there is no constraint on aircraft operations and do not provide good estimates when constraints exist. This paper presents a study of runway capacity at Singapore Changi Airport in which local operational constraints are taken into account. In addition, the impacts on capacity due to marine vessel crossings in a shipping channel near the airport, and the timing for implementation of simultaneous, independent instrument approach procedures are also investigated. The levels of annual aviation demand that could be served without excessive delays to aircraft under various operating scenarios are estimated.     

Transit funding: Implications of federal aid strategies

Federal funding strategies greatly affect investment in urban transportation facilities in the United States. This analysis concentrates on the implications of varying federal aid matching requirements, structuring aid programs as categorical or block grants, and allo cating funds on a discretionary basis or according to formula. Toward this end the effects of recent federal transit aid arrangements are assessed.Increased federal matching share broadens program participation, especially among smaller cities. However, when offered a choice, communities' preference for more generous federal aid shares is tempered by their election of discretionary grants (e.g., Urban Mass Transportation Administration - UMTA - Section 3) instead of drawing on formula funds (e.g., UMTA Section 5 or highway fund transfers). Formula funds are easier to administer, distributed quite evenly in the UMTA case, and generally more suitable than discretionary funds except where expenditures are large relative to budgets. Categorical aid programs shift local priorities, and thus should be used with cautionOverall, results suggest that one must begin with established transportation objectives against which to evaluate the effectiveness of funding arrangements. In particular, it is critical to make clear the rationale for federal involvement in funding specific programs. Four such federal funding intents are distinguished: compelling national interest, regional development, stimulation of recipient investment in the given program, or financial relief for the aid recipient. Conclusions are drawn as to the desirability of various funding policies according to such program intent.     

The role of subsidy policies in modernizing the structure of the bus transit industry

Full reliance on conventional forms of bus transit for peak hour needs reduces industry productivity and creates major new subsidy requirements. Restructuring of transit is needed to enable paratransit integration and other innovations than can improve efficiency. This paper discusses the industry's long-term neglect of efficiency and describes subsidy policies that would promote necessary changes.     

临海复杂地质条件下深基坑围护设计和施工技术

通过对地下室深基坑围护的设计方案论证,采用旋喷止水帷幕结合自然放坡和明沟排水的方案成功解决了临海复杂地质条件下深基坑围护施工的问题。     

A Method to Analyse the Dynamic Behavior of a Motorcycle Front Suspension Equipped with Sequential Dampers

This work analyses the dynamic behavior of a motorcycle front suspension equipped with passive sequential hydraulic dampers, in some operative situations. The dampers, with non-linear and asymmetric characteristics, may be regulated in six different ways. Using experimental elasticity and damping data as reference parameters, and a simplified two-degrees-of-freedom model, some dynamic simulations were carried out in order to define damping parameters for optimal comfort and safety.