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81.
This is one of two papers designed to test the ability of a theoretical model of productivity measurement [1] with times series empirical data. The analysis was able to identify trends in productivity growth for sailing ships and stcamships. scparating long and short run components . One of the interesting features of the findings is that the long run growth rate is the same for both sailing and steamships. Although sail and steam appear to be two unique technologies, it is found that technologica progress is evolutionary not revolutionary.
The techique using covariance analysis proved useful for times series productivity measurement. 相似文献
The techique using covariance analysis proved useful for times series productivity measurement. 相似文献
82.
Stanley B. Gershwin David M. Orlicki 《Transportation Research Part B: Methodological》1984,18(6):441-458
A new assignment principle for traveler behavior in an urban network is described which is based on empirical findings in the theory of travel budgets. It characterizes the distribution of travelers, demand, and modal split. It treats all travel decisions (whether to travel, where to go, how to get there) and the important costs (time and money) in a single, unified way. A numerical technique is proposed and it is applied to several examples to illustrate qualitative features. 相似文献
83.
To plan new bus routes in suburban areas, expected bus running times on these routes are needed. Using most readily available relevant variables, a regression model is developed for estimating bus running times. The model is conceptually reasonable and it was tested using data other than that used for estimation. 相似文献
84.
85.
John B. Yolland 《Maritime Policy and Management》1979,6(3):175-181
Due to the capital-intensive nature of the modern shipping industry, loan finance plays a major role in vessel-acquisition cost. In this paper, J. B. Yolland discusses government-guaranteed finance, ancillary and commercial new building finance and finance for second-hand tonnage. He also examines a new source of funding found in the Euro-market. 相似文献
86.
87.
A path-based user-equilibrium traffic assignment algorithm that obviates path storage and enumeration 总被引:2,自引:0,他引:2
This paper presents a novel user-equilibrium (UE) traffic assignment algorithm, which under conventional assumptions, promises to compute UE arc flows to acceptable precision, regardless of the network’s topology, size or congestion:
- • The algorithm takes the simple approach of shifting flow from a costliest path to a cheapest path until the costs of all used paths are within a given of the cheapest.
- • Because of being path-based, it avoids tailing.
- • In spite of being path-based, it neither stores nor enumerates paths.
- • These efficiencies derive from decomposing the problem into a sequence of easy single-origin problems on acyclic sub-networks.
88.
G. S. Jung Y. H. Sung B. C. Choi C. W. Lee M. T. Lim 《International Journal of Automotive Technology》2012,13(3):347-353
Although premixed charge compression ignition (PCCI) combustion engines are praised for potentially high efficiency and clean
exhaust, experimental engines built to date emit more hydrocarbons (HCs) and carbon monoxide (CO) than the conventional machines.
These compounds are not only strictly controlled components of the exhaust gas of road vehicles but are also an energy loss
indicator. The prime objective of this study was to investigate the major sources of the HCs formed in the combustion chamber
of an experimental PCCI engine in order to suggest some effective technologies for HC reduction. In this study, to explore
the dominant sources of HC emissions in both operation modes, a single cylinder engine was prepared such that it could operate
using either conventional diesel combustion or PCCI combustion. Specifically, the contributions of the top-ring crevice volume
in the combustion chamber and the bulk quenching of the lean mixture were investigated. To understand the influence of the
shape and magnitude of the crevice on HC emissions, the engine was operated with 12 specially prepared pistons with different
top-ring crevices installed one after another. The engine emitted proportionally more HCs as the depth of the crevice increased
as long as the width remained narrower than the prevailing quench distance. The top-ring-crevice-originated exhaust HCs comprised
approximately 31% of the total HC emissions in the baseline condition. In a series of tests to estimate the effects of bulk
quench on exhaust HC emissions, intake air was heated from 300K to 400K in steps of 25K. With the intake air heated, HC and
CO emissions decreased with a gradually diminishing rate to zero at 375K. In conclusion, the most dominant sources of HC emissions
in PCCI engines were the crevice volumes in the combustion chamber and the bulk quenching of the lean mixtures. The key methods
for reducing HC emissions in PCCI engines are minimizing crevice volume in the combustion chamber and maximizing intake air
temperature allowed based on the permissible NOx level. 相似文献
89.
Tire intelligence is vital in the improvement of the safety of vehicles because the tire supports the car body and is the contact point between the vehicle and the road. To create an intelligent tire, sensors must be installed to measure the behavior of the tire. However, it is difficult to apply a wired sensor system on the wheel of the tire. Hence, it is necessary to implement a self-powering, wireless system (a type of energy harvesting system) that can be mounted inside the tire. The purpose of this study is to convert the strain energy caused by deformation of the tire while driving into useful electrical energy to supply the sensor system. A flexible piezofiber is utilized for the energy conversion. The variation in strain, due to changes in speed, load, and the internal pressure of the tire, was measured along two axial directions to evaluate the amount of available strain energy. The amount of strain changed from 0.15% to 0.8%. To predict the amount of available energy from a tire, we perform an analysis of the relationship between the strain and the voltage. In addition, experiments for impedance matching between piezofiber and related circuits were conducted to optimize the external loads for transferring energy efficiently. Based on the procedure mentioned above, at least 0.58 mJ of electrical energy can be generated by using the laterally oriented strain (1500 to 2500 micro strain). The result of this study is expected to enhance the potential realization of self-generating wireless sensor systems for so-called ??intelligent?? tires. 相似文献
90.
The most important factor in gas strut design is determining an optimized layout. If the layout is not optimized, vehicle operators will have a suboptimal experience when opening and closing the tailgate. A poor layout of the gas struts causes operators to work excessively when they open/close the tailgate, and vehicle owners will incur additional expenses due to deterioration in the body quality of the vehicle. Thus, an optimized gas strut layout is very important, even if it does not seem interesting. This paper describes the tailgate operation process and focuses on determining an optimized gas strut layout for opening/closing the tailgate easily. 相似文献