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101.
This article uses data from the 2001 National Household Travel Survey (NHTS) to compare travel behavior in rural and urban areas of the U.S. As expected, the car is the overwhelmingly dominant mode of travel. Over 97% of rural households own at least one car vs. 92% of urban households; 91% of trips are made by car in rural areas vs. 86% in urban areas. Regardless of age, income, and race, almost everyone in rural areas relies on the private car for most travel needs. Mobility levels in rural areas are generally higher than in urban areas. That results from the more dispersed residences and activity sites in rural areas, which increase trip distances and force reliance on the car. Somewhat surprisingly, the rural elderly and poor are considerably more mobile than their urban counterparts, and their mobility deficit compared to the rural population average is strikingly less than for the urban elderly and poor compared to the urban average. Data limitations prevented a measurement of accessibility, however, and it seems likely that rural areas, by their very nature, are less accessible than urban areas, especially for the small percentage of car-less poor and elderly households. 相似文献
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103.
Francisco?Javier?Amador Rosa?Marina?González Juan?de?Dios?OrtúzarEmail author 《Transportation》2005,32(6):627-647
We examined different model specifications to detect the presence of preference heterogeneity in a mode choice context. The specification that worked best allows for both systematic and random variations in tastes, with parameters obtained at the individual level using Bayesian methods. Subjective values of travel time (SVT) and expected individual compensated variation were derived and aggregated to obtain measures of social welfare. Results suggest that the benefit measures, both at the individual and at the social level, are sensitive to preference heterogeneity assumptions. SVT and welfare changes derived from travel time reductions could be underestimated if the traditional assumption of taste homogeneity is made (we detected differences up to 30% in both types of measures). We also obtained an empirical value for the error made when evaluating changes in social welfare using an approximation of the expected individual compensated variation (expressed as a function of individual SVT) rather than its exact expression. 相似文献
104.
Spectrum sensing is an important part of cognitive radio systems to find spectrum hole for transmission which enables cognitive
radio systems coexist with the authorized radio systems without harmful interference. In this paper, an improved cyclostationary
feature detection method is proposed to reduce computational complexity without loss of good performance based on the optimal
parameter selection strategy for choosing detection parameters of cyclic frequency and lag. Taking binary phase shift keying
(BPSK) and quadrature phase shift keying (QPSK) signals as examples, the theoretical analyses are presented for choosing the
optimal parameters. Simulation results are given to certify the correctness of the proposed parameter selection strategy and
show the performance of the proposed method. 相似文献
105.
Aiming at the limitations of the existing knowledge representations in intelligent detection, a novel extension-based knowledge
representation (EKR) is proposed. The definitions, grammar rules, and formal semantics of EKR are presented. A rhombus solving
strategy (RSS) based on EKR is discussed in detail, including creation of the problem oriented model, extension operator,
the solution formation of contradictions problem and extended inference of matter-element. A knowledge base system based on
EKR and RSS is developed, which is applied in intelligent detection in the Dendrobium huoshanense photosynthesis process (DHPP).
More reasonable results are obtained than traditional rule-based system. The EKR is feasible in intelligent detection to solve
the limitations of traditional knowledge representations. 相似文献
106.
崔利荣 《上海交通大学学报(英文版)》2016,21(4):509-512
Consistent high-quality and defect-free production is the demand of the day. The product recall not only increases engineering and manufacturing cost but also affects the quality and the reliability of the product in the eye of users. The monitoring and improvement of a manufacturing process are the strength of statistical process control. In this article we propose a process monitoring memory-based scheme for continuous data under the assumption of normality to detect small non-random shift patterns in any manufacturing or service process.The control limits for the proposed scheme are constructed. The in-control and out-of-control average run length(AVL) expressions have been derived for the performance evaluation of the proposed scheme. Robustness to non-normality has been tested after simulation study of the run length distribution of the proposed scheme, and the comparisons with Shewhart and exponentially weighted moving average(EWMA) schemes are presented for various gamma and t-distributions. The proposed scheme is effective and attractive as it has one design parameter which differentiates it from the traditional schemes. Finally, some suggestions and recommendations are made for the future work. 相似文献
107.
The simulation is an important means of performance evaluation of the computer architecture. Nowadays, the serial simulation of general purpose graphics processing unit (GPGPU) architecture is the main bottleneck for the simulation speed. To address this issue, we propose the intra-kernel parallelization on a multicore processor and the inter-kernel parallelization on a multiple-machine platform. We apply these two methods to the GPGPU-sim simulator. The intra-kernel parallelization method firstly parallelizes the serial simulation of multiple compute units in one cycle. Then it parallelizes the timing and functional simulation to reduce the performance loss caused by the synchronization between different compute units. The inter-kernel parallelization method divides multiple kernels of a CUDA program into several groups and distributes these groups across multiple simulation hosts to perform the simulation. Experimental results show that the intra-kernel parallelization method achieves a speed-up of up to 12 with a maximum error rate of 0.009 4% on a 32-core machine, and the inter-kernel parallelization method can accelerate the simulation by a factor of up to 3.9 with a maximum error rate of 0.11% on four simulation hosts. The orthogonality between these two methods allows us to combine them together on multiple multi-core hosts to get further performance improvements. 相似文献
108.
To get the accurate wave loads on wharf composite structure, the wave force on small-scale piles and the uplift force on lower
surface of caisson must be considered. Based on the Reynolds averaged Navier-Stokes (RANS) equations, the pore media theory
and the volume of fluid (VoF) method, a three-dimensional numerical model is established. The model has been developed to
simulate wave interaction with a composite structure including caisson, piles and deck. The numerical results agree very well
with the experimental data on total force. The spatial distributions of the non-dimensional wave height and the maximum of
wave pressure on surface of composite structure are presented and discussed. The effects of relative caisson length, relative
wave height and relative caisson height on horizontal wave force are given. The result indicates that the horizontal wave
force achieves maximum value at the relative caisson length of 0.18 and increases linearly with the increase of the relative
caisson and wave height. It is proved that the model is an accurate and efficient numerical tool to investigate different
problems of wave-structure interaction. 相似文献
109.
D.?Savitski V.?IvanovEmail author B.?Shyrokau T.?Pütz J.?De?Smet J.?Theunissen 《International Journal of Automotive Technology》2016,17(2):327-338
Functions of anti-lock braking for full electric vehicles (EV) with individually controlled wheel drive can be realized through conventional brake system actuating friction brakes and regenerative brake system actuating electric motors. To analyze advantages and limitations of both variants of anti-lock braking systems (ABS), the presented study introduces results of experimental investigations obtained from proving ground tests of all-wheel drive EV. The brake performance is assessed for three different configurations: hydraulic ABS; regenerative ABS only on the front axle; blended hydraulic and regenerative ABS on the front axle and hydraulic ABS on the rear axle. The hydraulic ABS is based on a rule-based controller, and the continuous regenerative ABS uses the gain-scheduled proportional-integral direct slip control with feedforward and feedback control parts. The results of tests on low-friction road surface demonstrated that all the ABS configurations guarantee considerable reduction of the brake distance compared to the vehicle without ABS. In addition, braking manoeuvres with the regenerative ABS are characterized by accurate tracking of the reference wheel slip that results in less oscillatory time profile of the vehicle deceleration and, as consequence, in better driving comfort. The results of the presented experimental investigations can be used in the process of selection of ABS architecture for upcoming generations of full electric vehicles with individual wheel drive. 相似文献
110.
Saeed?Abedi Ali?Akbar?Dehghan Ali?SaeidinezhadEmail author Mojtaba?Dehghan?Manshadi 《船舶与海洋工程学报》2016,15(1):8-15
A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found. 相似文献