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881.
An analysis of the social context of children’s weekend discretionary activity participation 总被引:3,自引:1,他引:2
This paper examines the discretionary time-use of children, including the social context of children’s participations. Specifically,
the paper examines participation and time investment in in-home leisure as well as five different types of out-of-home discretionary
activities: (1) shopping, (2) social, (3) meals, (4) passive recreation (i.e., physically inactive recreation, such as going
to the movies or a concert), and (5) active recreation (i.e., physically active recreation, such as playing tennis or running).
The social context of children’s activity participation is also examined by focusing on the accompanying individuals in children’s
activity engagement. The accompanying arrangement is classified into one of six categories: (1) alone, (2) with mother and
no one else, (3) with father and no one else, (4) with both mother and father, and no one else, (5) with other individuals,
but no parents, and (6) with other individuals and one or both parents. The utility-theoretic Multiple Discrete-Continuous
Extreme Value (MDCEV) is employed to model time-use in one or more activity purpose–company type combinations. The data used
in the analysis is drawn from the 2002 Child Development Supplement (CDS) to the U.S. Panel Study Income Dynamics (PSID).
The results from the model can be used to examine the time-use choices of children, as well as to assess the potential impacts
of urban and societal policies on children’s activity participation and time-use decisions. Our findings also emphasize the
need to collect, in future travel surveys, more extensive and higher quality data capturing the intra- and inter-household
interactions between individuals (including children). To our knowledge, the research in this paper is the first transportation-related
study to rigorously and comprehensively analyze the social dimension of children’s activity participation.
Ipek Nese Sener is currently a Ph.D. candidate in transportation engineering at The University of Texas at Austin. She received her M.S. degrees in Civil Engineering and in Architecture, and her B.S. degree in Civil Engineering from the Middle East Technical University in Ankara, Turkey. Dr. Chandra R. Bhat has contributed toward the development of advanced econometric techniques for travel behavior analysis, in recognition of which he received the 2004 Walter L. Huber Award and the 2005 James Laurie Prize from the American Society of Civil Engineers (ASCE). 相似文献
Chandra R. Bhat (Corresponding author)Email: |
Ipek Nese Sener is currently a Ph.D. candidate in transportation engineering at The University of Texas at Austin. She received her M.S. degrees in Civil Engineering and in Architecture, and her B.S. degree in Civil Engineering from the Middle East Technical University in Ankara, Turkey. Dr. Chandra R. Bhat has contributed toward the development of advanced econometric techniques for travel behavior analysis, in recognition of which he received the 2004 Walter L. Huber Award and the 2005 James Laurie Prize from the American Society of Civil Engineers (ASCE). 相似文献
882.
[目的]针对计入螺旋桨水动力的舰船轴系校中计算,传统方法通常容易忽略船体伴流场的影响,使得螺旋桨水动力计算的结果与真实值之间存在较大偏差,从而导致轴系校中精度下降。[方法]以某舰船长轴系为对象,建立桨-轴-船一体化有限元模型及其伴流场流域模型,利用CFD数值仿真的叠模方法计算螺旋桨水动力;采用流固耦合法将流体计算结果作用于螺旋桨表面,进行轴系校中计算,并得到螺旋桨水动力对轴系整体挠曲线及各轴承状态参数的影响规律。在此基础上,引入多目标优化算法开展轴系多目标优化校中,来解决轴系末端四套轴承间载荷差值过大的问题。[结果]考虑螺旋桨水动力后,轴系尾部挠度变化减小,越靠近螺旋桨处的轴承其载荷所受影响越大,载荷值随进速系数的增大而减小;对比多目标优化前后的轴系校中状态,轴系各轴承之间的载荷差值明显减小,轴系运行状态得到改善。[结论]所提方法提高了计入螺旋桨水动力的轴系校中计算精度,可为轴系校中质量的提升提供参考。 相似文献
883.
[Objective]This paper aims to suppress the adverse effects of tip clearance flow on the hydrodynamic performance and unsteady excitation force of a pump-jet propulsor. [Method]As for the pre-swirl stator pump-jet propulsor, an annular flexible seal structure closely matched with a rotor tip ring is used to study the validity of suppressing the clearance flow on the rotor tip. The rotor thrust and torque of the propulsor are measured by keeping the shroud approximately rigidly fixed, enabling the rotor open water efficiency to be obtained. In addition, the point of cavitation inception at each design condition is observed and recorded carefully with the help of a high-power stroboscope, and the cavitation inception curves of the propulsor with/without tip clearance are obtained through calculation. Finally, tests of shaft vibration acceleration on the pump-jet propulsor with/without tip clearance are conducted under conditions of cavitation and non-cavitation in order to evaluate the effects of diminishing tip clearance. [Results]The results show that the thrust and torque of the rotor of the pump-jet propulsor with a flexible seal structure are significantly increased, which in turn renders open water efficiency significantly increased at low and medium advance coefficients, unchanged near the design point and slightly decreased at the high advance coefficient. Moreover, the cavitation performance of the pump-jet propulsor without clearance is better at a wide range of advance coefficient, 0.85 相似文献