Ultrasound, as an efficient, clean, and safe processing technology, is widely used in industries. Grain refiners are widely used in the refinement of cast alloys. In this study, ultrasonic technology ...(UT) and Al–5Ti–1B refiner prepared by continuous rheological extrusion (CRE Al–5Ti–1B) were used to modify the recycled Al–Mg–Si-based alloy, and the microstructure and mechanical properties of the recycled Al–Mg–Si-based alloy were studied. The differences in porosity and grain refinement caused by ultrasonic power were discussed. Results showed that, increasing the ultrasonic power can effectively reduce the porosity of the recycled Al–Mg–Si-based alloy. The synergistic effect of UT and CRE Al–5Ti–1B refiner significantly refined α-Al grains and second phases. The increase of ultrasonic power can effectively cause deagglomeration while reducing the nucleation undercooling of α-Al, which promotes the refinement of the recycled Al–Mg–Si-based alloy and significantly improves the mechanical properties. The yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of the recycled Al–Mg–Si-based alloy were 106 MPa, 210 MPa and 9.4%, respectively. When 0.2 wt% CRE Al–5Ti–1B refiner was added and the ultrasonic power was 150 W, the YS, UTS, and EL were improved by 12.8%, 28.8% and 228.4%, respectively.
Amorphous and crystalline cobalt tungstate (CoWO sub(4)) particles, synthesized by solution co-precipitation and subsequent heat treatment, were examined on rotating disk electrodes as water ...oxidation catalysts. In close to neutral electrolyte (0.2 M Na sub(2)WO sub(4), pH 8.0), amorphous CoWO sub(4) exhibited much higher catalytic activity than its crystalline counterpart over an overpotential range of 0.25 to 0.45 V. Calculated Tafel slopes are similar to 60 mV per decade for amorphous and similar to 110 mV per decade for crystalline electrodes, while the exchange current density of crystalline catalysts is two orders of magnitude higher than that of amorphous. Elemental analysis did not identify substantial composition changes in either amorphous or crystalline films on indium tin oxide (ITO) electrodes, after being used for multiple cyclic voltammetry and bulk electrolysis tests. However, X-ray photoelectron spectroscopy (XPS) revealed that the oxidation state of the surface Co atoms on amorphous catalyst film changed from +2 to +3, although no difference was found in crystalline CoWO sub(4) . The characteristics of the amorphous catalyst closely resemble the well known self-repairing cobalt phosphate catalytic film (Co-Pi), in which the cooperative interaction of adsorbants on neighboring Co sites plays an important role in its high activity. In the case of crystalline CoWO sub(4), density functional theory (DFT) calculations showed that its most stable surface should be along the (010) plane, featuring Co atoms located at least 4.69 Aa apart, which is significantly larger than the reported 2.82 Aa in the cubane structure of Co-Pi. We believe this longer interatomic span hinders the adsorbant interaction and thus results in a different mechanism for oxygen evolution on the surface of crystalline CoWO sub(4).
In recent decades, grain refiners had not only improved the properties on cast aluminum alloy, but also changed the application field of cast aluminum alloys, which had attracted widespread ...attention. However, there were few reports on microstructure evolution of A356/CRE Al-X-Ce(Ti, C) system by combining traditional grain refiners with element Ce. In this study, refined A356 alloys with excellent strength and plasticity were obtained by adding CRE Al-X-Ce(Ti, C) (0, 0.4, 0.8, 1.2, 1.6 and 2.0 wt%, respectively). Using XRD, SEM and TEM, the morphology of phases in the refined A356 alloy and phases of grain refiner were identified. The microstructure evolution of α-Al grains and eutectic Si with the introduction of TiC and Ce was analyzed. The results showed that the novel CRE Al-X-Ce(Ti, C) could not only effectively refine α-Al grains, but also modify Si microstructure of the alloy. The refined A356 alloys with excellent strength and plasticity were obtained with 2.0 and 1.6 wt% grain refiner (CRE) additions, respectively. TiC as nucleation particle and Ce as the surfactant refined the α-Al grains. Also, Ce modified eutectic Si by changing the way it grows. When the CRE Al-X-Ce(Ti, C) content researched 2.0 wt%, the long plate-like Al–Si–Ce phase was formed which can easily caused cracks and reduced the elongation of alloy.
Autonomous vehicles (AVs) have the potential to improve safety, traffic capacity, and energy efficiency, but these advantages can only be realized when the AV market penetration is sufficiently high. ...To promote the adoption of AVs, it would be crucial for the government to take policy measures. This paper develops a two-stage model to explore the effects of subsidy and AV lanes’ policies on AV adoption. In the first stage, given the subsidy policy, the vehicle manufacturer sets AV price to pursue maximum profit while anticipating the choice of consumers for AVs or conventional vehicles (CVs), from which the AV market penetration can be accessed. Subsequently, based on the AV market penetration acquired from the first stage model, an optimization model integrating the mixed traffic assignment is developed in the second stage to determine the time-dependent progressive AV lanes’ deployment plan. The first and second stage models are solved using the simulation-optimization and genetic-algorithm-based approaches, respectively. Due to the mutual influence of the two models, an iterative optimization approach is applied to solve the whole model. Two numerical experiments are conducted, and the results demonstrate the positive effects of subsidy and AV lane policies on increasing AV market penetration. The analysis provides significant managerial insights for policymakers to promote the development of AVs.
This paper develops a distributed cooperative control strategy (DCCS) to plan and optimize the collision‐free trajectory for the connected automated vehicle (CAV) at an isolated roundabout. The ...representation of the trajectories of CAVs is defined within a roundabout. The central angle and lane radius are used to indicate the location of vehicles, and the corresponding angular velocity is used to describe the vehicle's speed through the roundabout. This trajectory definition method simplifies the proposed problem into two parts: the trajectory optimization of each vehicle in a specific lane and the lane change coordination of CAVs in the roundabout. To solve the trajectory optimization problem, a mixed‐integer linear programming (MILP) model is formulated at the vehicle level to minimize the travel time and make the trajectory as smooth as possible. A model predictive control (MPC) framework is designed to coordinate lane‐change conflicts and push CAVs’ trajectories toward global optimization. The proposed framework integrates the vehicles’ trajectory optimization results so that all CAVs reach a consensus. Numerical experiments test the effect of the strategy in terms of traffic efficiency and mobility performance under different demand pattern scenarios. The results show that the proposed RA‐DCCS (Roundabout‐DCCS) can make all CAVs smooth and conflict‐free trajectories and enable vehicles to execute reasonable lane change decisions.
Compared to conventional private vehicles (CPVs), shared autonomous vehicles (SAVs) provide users the potential for the reduced value of time (VoT), improved mobility experience, and less traffic ...congestion. In the presence of the SAV system, numerous studies have mainly concentrated on the strategic planning and operational decision problem separately while ignoring the complicated interaction between them and the distinct features of autonomous vehicles. It is imperative to determine the relocation and pricing strategies at the operational level. In this study, in terms of the pricing strategy, we formalize a logit model to capture the mode choice behavior in a multimodal network, where the reduced VoT is considered simultaneously. A time-space network is employed to capture the daily operation problem based on the elastic demand. The minimum customer service rate is regarded as a constraint to ensure the system’s reliability. Moreover, a mixed-integer nonlinear programming (MINLP) model is formulated to jointly determine the number of stations and parking spaces, fleet size, relocation, and pricing strategies to maximize the total profit. Then, we integrate the Particle Swarm Optimization (PSO) algorithm with the optimization solver Gurobi to address the complex problem. Numerical experiments and comparative analyses are conducted to demonstrate the feasibility and efficiency of the proposed model.
The location problem of logistics park is the basis of logistics network planning. The establishment of conventional logistics park location planning model requires consideration of multiple factors, ...including position relationships between site selection points and demand points, economic cost, service efficiency, and consumer satisfaction. “Green development concept” gradually leads the trend of social and economic development in the contemporary world. The green logistics park emerges as the requirement of era. There are obvious differences between the site selection rules and the location demand of the green logistics park with the conventional logistics park. On the basis of analyzing the evaluation indexes of green logistics park and the factors affecting the site selection, this article builds a single-objective decision model based on the comprehensive cost. The model sets transportation cost and environment cost as the objective function. In addition, according to the constraints of location and quantity of the proposed logistics park, the model is divided into four parts to refine, and the solving process based on hybrid particle algorithm and alternate location allocation heuristic algorithm is given. The model and algorithm are feasible by analyzing the numerical example. Finally, the green logistics park site selection scheme is designed. The location model that considers the single comprehensive cost target provides a simple and feasible decision method for the green logistics park location.
The layout of functional areas has a great impact on the implementing of a logistics park. Existing layout models with multiple planning objectives and influencing factors are too complex to be ...solved. This article puts forward a two-stage layout method for functional areas in logistics parks combining a layer-by-layer analysis process and a multi-objective programming model. Base on the rational setting of functional areas, the optimization of operational processes and the quantification of the interrelations between functional areas, some green logistic goals are achieved in two stages. In the first stage, the method aims at maximizing the comprehensive relationship among functional areas and obtaining the layout structure by the layer-by-layer analysis process. In the second stage, a multi-objective planning model is established to get the location and shape of each functional area, with the goals of minimizing the material handling costs and maximizing the spatial utilization rate. A genetic algorithm is designed to solve the model. Finally, an example is put forward to verify the feasibility of the two-stage layout method, and the comparison with the previous general model is presented. This article provides a new method for the layout planning of function areas in green logistics parks.
The work zone on the urban road network will affect the surrounding road traffic. To represent the influence area of the work zone, the concept of a subnetwork is proposed in this paper. Delineating ...a suitable subnetwork quantitatively is a challenging problem. To address this issue, the node synthesized indexes (NSI) are deployed as a variability measure that captures both the change of link flow and origin-destination (OD) demand. The inertia-based stochastic user equilibrium with the elastic demand (ISUEED) model is proposed to accurately provide the data of link flow and OD demand for the network with the work zone. Correspondingly, the data of the network without a work zone can be obtained by the stochastic user equilibrium (SUE) model. According to the value of NSI, the initial range of the subnetwork is determined. Finally, the connectivity and compactness can be guaranteed by the modified L-shell algorithm. To demonstrate the performance of the method, two case studies and sensitivity analyses are conducted based on the Braess network and the local road network in Changchun, China. The proposed method is beneficial to reduce the complexity of the traffic model by substituting the entire network with a subnetwork.
This paper presents a real-time dynamic path planning method for autonomous driving to avoid collision with crossing pedestrian on branch streets. The velocity obstacle algorithms are introduced to ...pick up the collision-free velocities for vehicles. In this method, the curvilinear lane edges are considered as static obstacle while crossing pedestrians and approaching vehicles are considered as velocity obstacles. The paths planning of vehicles are optimized by considering the delay minimum and comfort of drivers under the constraints of appropriate parameters for veer, throttle, or brake systems. A single vehicle's path planning and multi-vehicles 'coordinated or uncoordinated paths planning with crossing pedestrian collision avoidance are experimentally simulated including the longitudinal and lateral motions planning of vehicles. The simulation results demonstrate the effectiveness of the proposed method and indicate its wide practical application on autonomous driving to improve the traffic safety of branch streets.
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