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121.
Using CalCOFI data for coastal shallow stations (above 100 m depth), higher than expected nitrate concentrations were detected in near-surface high-temperature waters off of Central Baja California during some El Niño winters. Though recent data are not available for Central Baja California, past El Niño data, though limited, showed nitrate concentrations above 16 μM at temperatures above 16 °C, and nitrate concentrations between 1 and 2 μM at 19 °C, while the previously established relationship of temperature and nitrate for California Current waters predicts nitrate depletion above 14 or 15 °C. The anomalous, high temperature–high nitrate enrichment events documented in Central Baja California were detected as shallow as 9 m and as deep as 73 m, were associated with low-oxygen (between 2 and 4 ml/l) and high-salinity (between 33.8 and 34.3 psu) waters, and occurred during the winter months of an El Niño year. Using recent data for San Diego, CA, similar but weaker enrichment events were detected for the El Niño winter of 1997–1998. The periodic shoaling of a subsurface subtropical water mass of high temperature, high salinity, low oxygen and high nutrients during some El Niño winters is proposed to cause periodic enrichment and to maintain productivity during warming events in this area. Enrichment events were not detected off Ensenada, in Northern Baja California, possibly due to the amplification of the onshore flow during El Niño there, or due to the Ensenada front. The proposed mechanism of periodic enrichment of nutrient-depleted surface waters during some El Niño winters by subsurface waters from the California Undercurrent may explain the following: (1) survival of giant kelp forests at their southern limit in Central Baja California documented during past El Niño events in warm waters, (2) the rapid recovery and high carrying capacity of giant kelp documented after the mass disappearance during El Niño 1997–1998, and (3) the increase in the extent of mesotrophic chlorophyll detected in the area during the 1997–1998 and 1982–1983 El Niño events. 相似文献
122.
Peter B. Marlow 《Maritime Policy and Management》1991,18(4):283-311
This paper concentrates on the determinants of investment and examines both theoretical and empirical work on the investment function. The major determinants are considered and a case study of the United Kingdom shipping industry in the period 1963-1987 is undertaken. The analysis is unable to find any real link between the value of the investment incentives packages available to the UK shipping industry and the size of the UK fleet during this period. The conclusion follows that while financial factors (e.g. favourable credit arrangements) or individual components (e.g. investment grants) of fiscal packages may influence the decision to invest, the total package has not affected the level of shipping investment in the manner expected. 相似文献
123.
Performance estimation model of a torque converter part I: Correlation between the internal flow field and energy loss coefficient 总被引:3,自引:0,他引:3
B. S. Kim S. B. Ha W. S. Lim S. W. Cha 《International Journal of Automotive Technology》2008,9(2):141-148
The objective of this paper is to improve the performance estimation model of the internal flow field of a torque converter.
Compared with performance experiment results, the converter based on the one-dimensional model does not satisfy the performance
requirements demanded in practice. Therefore, we need to develop more predictable and reliable performance estimation models.
In order to obtain shape information on three-dimensional blade geometry, a process of reverse engineering conducts a torque
converter assembly, impeller, turbine and stator. In addition, a CFD simulation including mesh generation and post-processing
was carried out to extract equivalent parameters from the internal flow field. The internal flow field can be explained by
analyze the correlation between a performance estimation model and CFD analysis. The equivalent performance model adopts the
variation of energy loss coefficients for a given operating condition according to the application of a changing energy loss
coefficient by the least mean squares method. The estimated equivalent model improves the agreement in performance between
experiments and the theoretical model. This model can reduce the error to within about 3 percent. Furthermore, this procedure
for predicted performance achieves eminence in the estimation of the capacity factor. 相似文献
124.
This paper establishes the simulation model of a city bus on the basis of the EQ6110 bus prototype and its experimental data.
According to the actual urban driving cycle, the fuel economy and the traction performance of the EQ6110 city bus have been
simulated, and factors such as the driving cycle, the loss of power to engine accessories, the gear-shifting strategy, the
fuel shut-off strategy of the engine, etc., which influence on the bus’s fuel economy, are also quantitatively analyzed. Some
conclusions are drawn as follows: (1) driving cycles have a great influence on the fuel economy of a city bus; (2) under the
typical urban driving cycle of the public bus in China, the engine fuel shut-off strategy can save about 1 to 1.5 percent
of the fuel consumption; and (3) the optimized gear-shifting rules can save 6.7 percent of the fuel consumption. Experimental
results verify that the fuel economy for the EQ6110 public bus is improved by 7.2 pecent over the actual Wuhan urban driving
cycle of the current public bus in China. 相似文献
125.
This paper presents a steering control method for lane-following in a vehicle using an image sensor. With each image frame
acquired from the sensor, the steering control method determines target position and direction, and constructs a travel path
from the current position to the target position either as an Arc-path or S-path. The steering angle is calculated from the
travel path thus generated, and the vehicle follows the travel path via motor-control. The method was tested using a vehicle
dubbed as KAV (Korea Autonomous Vehicle) along an expressway (Seoul Inner Beltway) trajectory with a variety of radii (50
m ∼ 300 m) while traveling at a speed of 60 km/h to 80 km/h. Compared with an experienced human driver, the method showed
little much difference in performance in terms of lane-center deviation. The proposed method is currently employed for high
speed autonomous driving as well as for stop and go traffic. 相似文献
126.
B. Blanco A. Alonso L. Kari N. Gil-Negrete J. G. Giménez 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2018,56(4):529-552
The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element. The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the ‘pinned–pinned’ vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost. 相似文献
127.
Rural areas generally have lower and more dispersed demands for travel which cannot sustain conventional public transport services and consequently have a greater number of flexible and demand responsive transport services operating. These services usually operate on a stand-alone basis, are often subsidized and are typically only accessible by certain passenger types or for specific trip purposes. This generally results in uncoordinated and inefficient transport provision overall. The Flexible integrated transport services (FITS) system featured in this paper has been designed to address this problem. FITS can be used as a planning tool to assess potential benefits from relaxing operating constraints (e.g., a service's operating boundaries), which can potentially suggest service redesign. It also includes the capacity to assign subsidy payments on a trip by trip basis to increase cost efficiency whilst meeting a greater proportion of transport needs. The case study in the paper focusses on transport to health in the Aberdeenshire and Morayshire areas of Scotland in the UK. Despite flexible transport operators receiving public funds to meet passenger needs, this is currently being supplemented by public bodies paying large amounts in taxi fares in instances where there is a statutory obligation to provide travel but where no other suitable transport service exists. The results demonstrate the potential substantial savings which could be realized by allowing transport operators to redesign their services by relaxing constraints and by the reassignment of subsidies: resulting in more passenger demands being met and a reduction in public spending on taxi fares. 相似文献
128.
Timothy Larson Lars Moseholm David Slater Cyra Cain 《Transportation Research Part A: Policy and Practice》1996,30(6):399-413
The objective of this study was to obtain a better understanding of carbon monoxide (CO) concentrations immediately upwind of urban roadways, the “local background” values, and how these concentrations depend upon the surrounding traffic and the general meteorology. Measurements were made at seven sites in Seattle, WA during the winter of 1993. Local background CO concentrations were characterized by an absence of short term fluctuations, a steady buildup during the 3 p.m. to 11 p.m. period, and a lack of spatial gradients in the 8-h average values. Distinctly different log-normal distributions of the 8-h averages were observed for “trafficked” sites versus “urban park” sites, with mean values of 1.6 and 1.0 ppm respectively. A simple regression model was developed to predict the local background CO that includes distance from roadway, average daily traffic of nearby roadways, and the frequency of occurrence of low wind speeds (R2 = 0.74; F = 170). 相似文献
129.
130.