Electric vehicles and residential parking in an urban environment: Results from a stated preference experiment

This paper presents the results of a preference survey of 1545 respondents’ willingness to purchase electric vehicles (EVs) in Philadelphia. We pay particular attention to respondents’ willingness to pay for convenient charging systems and parking spaces. If the value of dedicated parking substantially outweighs the value of convenient charging systems, residential-based on-street charging systems are unlikely to ever be politically palatable. As expected, respondents are generally willing to pay for longer range, shorter charging times, lower operating costs, and shorter parking search times. For a typical respondent, a $100 per month parking charge decreases the odds of purchasing an EV by around 65%. Across mixed logit and latent class models, we find substantial variation in the willingness to pay for EV range, charge time, and ease of parking. Of note, we find two primary classes of respondents with substantially different EV preferences. The first class tends to live in multifamily housing units in central parts of the city and puts a high value on parking search time and the availability of on-street charging stations. The second class, whose members are likelier to be married, wealthy, conservative, and residing in single-family homes in more distant neighborhoods, are willing to pay more for EV range and charge time, but less for parking than the first group. They are also much likelier to consider purchasing EVs at all. We recommend that future research into EV adoption incorporate neighborhood-level features, like parking availability and average trip distances, which vary by neighborhood and almost certainly influence EV adoption.     

Validation of an extended discrete first-order model with variable speed limits

This paper validates the prediction model embedded in a model predictive controller (MPC) of variable speed limits (VSLs). The MPC controller was designed based on an extended discrete first-order model with a triangular fundamental diagram. In our previous work, the extended discrete first-order model was designed to reproduce the capacity drop and the propagation of jam waves, and it was validated with reasonable accuracy without the presence of VSLs. As VSLs influence traffic dynamics, the dynamics including VSLs needs to be validated, before it can be applied as a prediction model in MPC. For conceptual illustrations, we use two synthetic examples to show how the model reproduces the key mechanisms of VSLs that are applied by existing VSL control approaches. Furthermore, the model is calibrated by use of real traffic data from Dutch freeway A12, where the field test of a speed limit control algorithm (SPECIALIST) was conducted. In the calibration, the original model is extended by using a quadrangular fundamental diagram which keeps the linear feature of the model and represents traffic states at the under-critical branch more accurately. The resulting model is validated using various traffic data sets. The accuracy of the model is compared with a second-order traffic flow model. The performance of two models is comparable: both models reproduce accurate results matching with real data. Flow errors of the calibration and validation are around 10%. The extended discrete first-order model-based MPC controller has been demonstrated to resolve freeway jam waves efficiently by synthetic cases. It has a higher computation speed comparing to the second-order model-based MPC.     

基于UG的混凝土搅拌输送车拌筒螺旋线参数化设计

推导了混凝土搅拌输送车螺旋线的理论公式,并通过UG编程实现了通过拌筒的设计参数进行筒体和螺旋线的一体设计。     

Mixed Logit模型及其在交通方式分担中的应用研究

离散选择模型的典型代表Logit模型简洁易用的特点使其在经济、交通等领域得到了广泛的应用，但同时Logit模型的两个重要缺陷限制了其应用范围。在分析了Logit模型固有的两个缺陷和Mixed Logit模型的良好性质后，比较了Logit模型与Mixed Logit模型的差异，对Mixed Logit模型的算法进行了研究，并借助SAS统计软件提供的仿真算法给出了详细的工程实践应用范例。结果表明，Mixed Logit模型有着更丰富的物理含义，对个人出行交通方式选择行为的描述更符合实际。     

Ordered median hub location problems with capacity constraints

The Single Allocation Ordered Median Hub Location problem is a recent hub model introduced in Puerto et al. (2011) that provides a unifying analysis of a wide class of hub location models. In this paper, we deal with the capacitated version of this problem, presenting two formulations as well as some preprocessing phases for fixing variables. In addition, a strengthening of one of these formulations is also studied through the use of some families of valid inequalities. A battery of test problems with data taken from the AP library are solved where it is shown that the running times have been significantly reduced with the improvements presented in the paper.     

海洋工程用钢疲劳寿命与CTOD值关系的研究

通过对钻井平台上所用高强钢EQ70进行了韧度和疲劳性能的试验研究,得出了反映其韧度指标的裂纹尖端张开位移(CTOD)值和不同交变载荷下疲劳寿命值呈近似的线性关系.在应力幅值ΔP一定的情况下,疲劳寿命值N随着CTOD值的增大而增大,并且在高应力幅的时候,对数疲劳寿命和CTOD值有比较好的线性关系,最后还从微观意义上解释了产生这种关系的原因.     

船载固体散货流态化数值分析

散货船装载的镍矿、铁矿在运输过程中会发生流态化,流态化导致货物流动性增强,从而降低船舶稳性。当船舶在波浪中航行时,货物的移动会产生一个额外的力矩,该力矩有可能导致船舶倾覆。基于离散元方法,对不同含水率的货物进行了静倾斜、休止角的数值模拟,在全尺度计算中给定了颗粒尺寸和时间步长的选取标准,并采用全尺度货舱模型分析了影响货物稳定性的关键参数。该数值分析方法可为固体散货海上运输过程中船舶稳性预测和安全隐患评估提供参考。     

The multinomial logit model revisited: A semi-parametric approach in discrete choice analysis

The multinomial logit model in discrete choice analysis is widely used in transport research. It has long been known that the Gumbel distribution forms the basis of the multinomial logit model. Although the Gumbel distribution is a good approximation in some applications such as route choice problems, it is chosen mainly for mathematical convenience. This can be restrictive in many other scenarios in practice. In this paper we show that the assumption of the Gumbel distribution can be substantially relaxed to include a large class of distributions that is stable with respect to the minimum operation. The distributions in the class allow heteroscedastic variances. We then seek a transformation that stabilizes the heteroscedastic variances. We show that this leads to a semi-parametric choice model which links the linear combination of travel-related attributes to the choice probabilities via an unknown sensitivity function. This sensitivity function reflects the degree of travelers’ sensitivity to the changes in the combined travel cost. The estimation of the semi-parametric choice model is also investigated and empirical studies are used to illustrate the developed method.     

Carpooling and carpool clubs: Clarifying concepts and assessing value enhancement possibilities through a Stated Preference web survey in Lisbon, Portugal

The increase of urban traffic congestion calls for studying alternative measures for mobility management, and one of these measures is carpooling. In theory, these systems could lead to great reductions in the use of private vehicles; however, in practice they have obtained limited success for two main reasons: the psychological barriers associated with riding with strangers and poor schedule flexibility. To overcome some of the limitations of the traditional schemes, we proposed studying a carpooling club model with two main new features: establishing a base trust level for carpoolers to find compatible matches for traditional groups and at the same time allowing to search for a ride in an alternative group when the pool member has a trip schedule different from the usual one. A web-based survey was developed for the Lisbon Metropolitan Region (Portugal), including a Stated Preference experiment, to test the concept and confirm previous knowledge on these systems’ determinants. It was found through a binary logit Discrete Choice Model calibration that carpooling is still attached with lower income strata and that saving money is still an important reason for participating in it. The club itself does not show promise introducing more flexibility in these systems; however, it should provide a way for persons to interact and trust each other at least to the level of working colleagues.     

一种防欺骗的广义多秘密分享方案

秘密分享是信息安全和密码学的重要研究课题,对通信密钥管理和计算机网络安全具有重要意义。本文针对现有的多秘密分享方案不能有效地防止分发者和分享者的欺骗,以及子秘密恢复时计算复杂量大等问题,在基于离散对数与因式分解难题上,提出一种具有广义接入结构的高效的多秘密分享方案。该方案具有如下特点：可高效地检测秘密管理者与分享者的欺诈行为;秘密管理者只需公开少量数据就可动态地增加一个新子秘密;采用并行算法恢复子秘密;可高效地增加或删除成员,无需重新计算其他成员的秘密份额。该方案可在分布式会议秘密分配、安全分布式计算、电子商务等领域应用。