沥青混合料抗剪强度影响因素评价指标研究

较高的抗剪强度可以保证沥青混合料在高温下具有良好的抵抗永久变形的能力。主要采用单轴贯入试验,就如何选择高性能沥青混合料的材料设计参数指标进行了研究。研究结果表明,除了沥青的性能外,粗集料、特别是细集料的性能对沥青混合料抗剪性能也有极大的影响。在进行沥青混合料设计时,采用高棱角性指标的粗、细集料以及高粘度的沥青来提高沥青混合料的整体抗剪强度。并且在施工时控制混合料的压实度以确保沥青路面的长期性能。     

沥青混凝土抗剪强度及抗压回弹模量试验研究

对高模量沥青混凝土、SBS改性沥青和70#普通沥青混凝土进行了15,20,40,60℃条件下的单轴贯入及抗压回弹模量试验,并结合单轴无侧限抗压强度试验结果对黏聚力c值进行计算,结果表明:高模量沥青混凝土在各温度下均具有相对较高的抗剪强度、黏聚力和抗压回弹模量,尤其在高温时仍然优势明显.通过指标相关性分析,得到了由抗剪强度换算成抗压强度、黏聚力c值及抗压回弹模量的回归方程.     

A Study on Xinjiang Asphaltite as an Asphalt Modifier. Part II: Rheological Evaluation of Modified Asphalt Binders

Modified asphalt binders with varying Xinjiang asphaltite contents between 4% and 16% were prepared in laboratory. Dynamic shear rheometer temperature sweep and time sweep tests, bending beam rheometer tests, some conventional tests including penetration and softening point were performed to analyze the rheological properties of these asphalt binders and evaluate Xinjiang asphaltite potential as asphalt modifier. Test results showed with the Xinjiang asphaltite content increasing, complex shear modulus increased and phase angle decreased, which indicated Xinjiang asphaltite could improve the elasticity and deformation resisting of binders. Fatigue failure life of asphalt binders grew exponentially with Xinjiang asphaltite content. Moreover, Xinjiang asphaltite had an adverse effect on the low temperature performances of asphalt binders based on measured creep stiffness and m-value. Based on these test results modification mechanism of Xinjiang asphaltite was analyzed. It is thus suggested that Xinjiang asphaltite is better suitable as a high temperature resistant and anti-fatigue asphalt modifier material.     

Adapting materialized views after redefinitions: techniques and a performance study

We consider a variant of the view maintenance problem: How does one keep a materialized view up-to-date when the view definition itself changes? Can one do better than recomputing the view from the base relations? Traditional view maintenance tries to maintain the materialized view in response to modifications to the base relations; we try to “adapt” the view in response to changes in the view definition.Such techniques are needed for applications where the user can change queries dynamically and wants to see the changes in the results fast. Data archaeology, data visualization, and dynamic queries are examples of such applications. Views defined over the Internet tend to evolve and our technique can be useful for adapting such views.We consider all possible redefinitions of SQL SELECT-FROM-WHERE-GROUP-BY-HAVING, UNION, and EXCEPT views, and show how these views can be adapted using the old materialization for the cases where it is possible to do so. We identify extra information that can be kept with a materialization to facilitate redefinition. Multiple simultaneous changes to a view can be handled without necessarily materializing intermediate results. We identify guidelines for users and database administrators that can be used to facilitate efficient view adaptation.We perform a systematic experimental evaluation of our proposed techniques. Our evaluation indicates that adaptation is much more efficient than rematerialization in most cases. In-place adaptation methods are better than the non-in-place methods when the change is small. We also point out some important factors that can impact the efficiency of adaptation.     

基于正交法的水泥稳定碎石试验及抗裂性能研究

采用正交法设计研究了水泥稳定碎石的配合比;通过极差和均方差分析确定了水泥含量、碎石含量和碎石级配等因素对水泥稳定碎石7 d无侧限抗压强度影响的主次关系,选择了各因素的最优组合;对骨架密度型水泥稳定碎石和悬浮密实型水泥稳定碎石抗裂性能进行了研究,结果表明骨架密实型水泥稳定碎石具有较好的力学性能和抗裂性能.     

Understanding spatio-temporal heterogeneity of bike-sharing and scooter-sharing mobility

The revolution in mobility-sharing services brings disruptive changes to the transportation landscape around the globe. The authorities often rush to regulate the services without a good knowledge of these new options. In Singapore and some other cities, dockless bike-sharing systems rose and fell in just one year and were followed by the booming of docking scooter-sharing systems. This study conducts a comparative analysis of bike-sharing and scooter-sharing activities in Singapore to help understand the phenomenon and inform policy-making. Based on the collected data (i.e., origin-destination pairs enriched with the departure and arrival time and the GPS locations) for one month, this study proposed methods to construct the paths and estimated repositioning trips and the fleet sizes. Hence, the spatio-temporal heterogeneity of the two systems in two discrete urban areas was investigated. It explored the impact of the fleet size, operational regulations (dockless versus docking), and weather conditions on the usages. We found that shared scooters have spatially compact and quantitatively denser distribution compared with shared bikes, and their high demands associate with places such as attractions, metros, and the dormitory. Results suggest that scooter sharing has a better performance than bike sharing in terms of the increased sharing frequency and decreased fleet size; however, the shareability still has potential to be improved. High repositioning rates of shared-scooters indicates high maintenance cost for rebalancing and charging. Rainfall and high temperatures at noon suppress the usages but not conclusively. The study also proposes several initiatives to promote the sustainable development of scooter-sharing services.     

武广高速铁路轨道不平顺谱特征分析

以武广高速铁路轨道不平顺检测数据作为样本,对轨道不平顺谱的特征进行分析.首先,对检测数据进行功率谱分析,并与欧洲高速铁路谱进行比较,结果表明:轨道不平顺谱低于欧洲高速铁路轨道不平顺下限谱,但方向不平顺谱值相对较大;其次,利用相干函数对轨道不平顺和车体垂向和水平振动加速度进行相干分析,得出轨道不平顺不利波长范围;最后计算轨道不平顺的Hilbert时频谱,得出长波不平顺为高低不平顺和水平不平顺能量的主要波长成分,而中长波不平顺为方向不平顺和轨距不平顺的主要波长成分.     

Simulation of bidirectional pedestrian flow in transfer station corridor based on multi forces

A good understanding of pedestrian movement in the transfer corridor is vital for the planning and design of the station, especially for efficiency and safety.A multi-force vector grid model was presented to simulate the movement of bidirectional pedestrian flow based on cellular automata and forces between pedestrians. The model improves rule-based characteristics of cellular automata, details forces between pedestrians and solves pedestrian collisions by a several-step updating method to simulate pedestrian movements. Two general scenarios in corridor were simulated. One is bidirectional pedestrian flow simulation with isolation facility, and the other is bidirectional pedestrian flow simulation without isolation facility, where there exists disturbance in the middle. Through simulation, some facts can be seen that pedestrians in the case with isolation facility have the largest speed and pedestrians in the case without isolation facility have the smallest speed; pedestrians in the case of unidirectional flow have the largest volume and pedestrians in the case of without isolation facility have the smallest volume.     

基于射频技术的油罐车在途状态监测系统设计

针对油罐车罐体温度过高、罐体倾斜、阀门漏油等问题,文章设计了基于射频一体化芯片SI1000的油罐车罐体状态监测系统,车载终端控制单元以S3C2440A为主控制器,SI1000芯片为从控制器,设计了主从结构的片上系统(SOC)方案,提出了各个模块的硬件设计和软件流程;该罐体状态监测系统应用GPRS技术、GPS技术以及温度传感器、倾角传感器、铅封锁能够对车辆位置、罐壁温度、罐体倾角、油阀状态等参数进行远程在线监测;通过实验测试,各个参数的测量误差值在5%以内,且系统运行情况良好,符合系统设计需求。     

AC-13改性沥青混合料劈裂强度的影响因素及其与马歇尔性能指标的相关性

应用正交试验设计和统计分析方法研究了AC-13改性沥青混合料在15℃时的劈裂强度的影响因素和排序,以及与马歇尔性能指标的相关性。结果表明,细集料级配对劈裂强度影响显著,其筛孔通过率的排序为2.36mm筛孔4.75mm筛孔0.075mm筛孔油石比9.5mm筛孔。其中,2.36mm筛孔通过率对劈裂强度影响接近高度显著,而油石比和9.5mm筛孔通过率对劈裂强度影响不显著;劈裂强度与马歇尔性能指标之间存在较为明显的线性相关性,绝对相关系数均大于68%,随空隙率的逐渐增大,劈裂强度衰减近30%。