Coalitional Game Theoretic Approach for Cooperative Transmission in Vehicular Networks

Cooperative transmission in vehicular networks is studied by using coalitional game and pricing in this paper. There are several vehicles and roadside units (RSUs) in the networks. Each vehicle has a desire to transmit with a certain probability, which represents its data burtiness. The RSUs can enhance the vehicles' transmissions by cooperatively relaying the vehicles' data. We consider two kinds of cooperations: cooperation among the vehicles and cooperation between the vehicle and RSU. First, vehicles cooperate to avoid interfering transmissions by scheduling the transmissions of the vehicles in each coalition. Second, a RSU can join some coalition to cooperate the transmissions of the vehicles in that coalition. Moreover, due to the mobility of the vehicles, we introduce the notion of encounter between the vehicle and RSU to indicate the availability of the relay in space. To stimulate the RSU's cooperative relaying for the vehicles, the pricing mechanism is applied. A non-transferable utility (NTU) game is developed to analyze the behaviors of the vehicles and RSUs. The stability of the formulated game is studied. Finally, we present and discuss the numerical results for the 2-vehicle and 2-RSU scenario, and the numerical results verify the theoretical analysis.Comment: accepted by IEEE ICC'1

A Cross-layer Perspective on Energy Harvesting Aided Green Communications over Fading Channels

We consider the power allocation of the physical layer and the buffer delay of the upper application layer in energy harvesting green networks. The total power required for reliable transmission includes the transmission power and the circuit power. The harvested power (which is stored in a battery) and the grid power constitute the power resource. The uncertainty of data generated from the upper layer, the intermittence of the harvested energy, and the variation of the fading channel are taken into account and described as independent Markov processes. In each transmission, the transmitter decides the transmission rate as well as the allocated power from the battery, and the rest of the required power will be supplied by the power grid. The objective is to find an allocation sequence of transmission rate and battery power to minimize the long-term average buffer delay under the average grid power constraint. A stochastic optimization problem is formulated accordingly to find such transmission rate and battery power sequence. Furthermore, the optimization problem is reformulated as a constrained MDP problem whose policy is a two-dimensional vector with the transmission rate and the power allocation of the battery as its elements. We prove that the optimal policy of the constrained MDP can be obtained by solving the unconstrained MDP. Then we focus on the analysis of the unconstrained average-cost MDP. The structural properties of the average optimal policy are derived. Moreover, we discuss the relations between elements of the two-dimensional policy. Next, based on the theoretical analysis, the algorithm to find the constrained optimal policy is presented for the finite state space scenario. In addition, heuristic policies with low-complexity are given for the general state space. Finally, simulations are performed under these policies to demonstrate the effectiveness

Charging Scheduling of Electric Vehicles with Local Renewable Energy under Uncertain Electric Vehicle Arrival and Grid Power Price

In the paper, we consider delay-optimal charging scheduling of the electric vehicles (EVs) at a charging station with multiple charge points. The charging station is equipped with renewable energy generation devices and can also buy energy from power grid. The uncertainty of the EV arrival, the intermittence of the renewable energy, and the variation of the grid power price are taken into account and described as independent Markov processes. Meanwhile, the charging energy for each EV is random. The goal is to minimize the mean waiting time of EVs under the long term constraint on the cost. We propose queue mapping to convert the EV queue to the charge demand queue and prove the equivalence between the minimization of the two queues' average length. Then we focus on the minimization for the average length of the charge demand queue under long term cost constraint. We propose a framework of Markov decision process (MDP) to investigate this scheduling problem. The system state includes the charge demand queue length, the charge demand arrival, the energy level in the storage battery of the renewable energy, the renewable energy arrival, and the grid power price. Additionally the number of charging demands and the allocated energy from the storage battery compose the two-dimensional policy. We derive two necessary conditions of the optimal policy. Moreover, we discuss the reduction of the two-dimensional policy to be the number of charging demands only. We give the sets of system states for which charging no demand and charging as many demands as possible are optimal, respectively. Finally we investigate the proposed radical policy and conservative policy numerically

Experiment Analysis of Concrete’s Mechanical Property Deterioration Suffered Sulfate Attack and Drying-Wetting Cycles

The mechanism of concrete deterioration in sodium sulfate solution is investigated. The macroperformance was characterized via its apparent properties, mass loss, and compressive strength. Changes in ions in the solution at different sulfate attack periods were tested by inductively coupled plasma (ICP). The damage evolution law, as well as analysis of the concrete’s meso- and microstructure, was revealed by scanning electron microscope (SEM) and computed tomography (CT) scanning equipment. The results show that the characteristics of concrete differed at each sulfate attack period; the drying-wetting cycles generally accelerated the deterioration process of concrete. In the early sulfate attack period, the pore structure of the concrete was filled with sulfate attack products (e.g., ettringite and gypsum), and its mass and strength increased. The pore size and porosity decreased while the CT number increased. As deterioration progressed, the swelling/expansion force of products and the salt crystallization pressure of sulfate crystals acted on the inner wall of the concrete to accumulate damage and accelerate deterioration. The mass and strength of concrete sharply decreased. The number and volume of pores increased, and the pore grew more quickly resulting in initiation and expansion of microcracks while the CT number decreased

Growth of thrombus core in supersaturated blood

AbstractThis article begins with the mass conservation of blood platelets on the Gibbs interface, and obtains a relation between interfacial curvature and interfacial concentration of a blood–thrombus. A two-dimensional model is established, and the time-dependent inner solution and outer solution are obtained using the perturbation method, the solution characteristics are discussed

Optimal View Angle in Collective Dynamics of Self-propelled Agents

We study a system of self-propelled agents in which each agent has a part of omnidirectional or panoramic view of its sensor disc, the field of vision of the agent in this case is only a sector of a disc bounded by two radii and the included arc. The inclination of these two radii is characterized as the view angle. Contrary to our intuition, we find that, the non-omnidirectional-view for swarm agents with periodic boundary conditions in noiseless Vicsek model can accelerate the transient process of the emergence of the ordered state. One consequent implication is that, there are generally superfluous communications in the Vicsek Model, which may even obstruct the possible fast swarm emergence. This phenomenon may invoke further efforts and attentions to explore the underlying mechanism of the emergence in self-propelled agents.Comment: 4 pages, 6 figure

High capacity group-IV elements (Si, Ge, Sn) based anodes for lithium-ion batteries

AbstractTremendous efforts have been devoted to replace commercial graphite anode (372 mAh g−1) by group IV elements (Si, Ge, Sn) based-materials with high capacities in lithium-ion batteries (LIBs). The use of these materials is hampered by the pulverization of these particles due to the high volumetric change during lithiation and delithiation cycles, which leads to particles pulverization and destabilization of solid electrolyte interphase (SEI) films. These problems result in fast capacity fading and low Coulombic efficiency. Nanostructured materials show significant improvements in rate capability and cyclability due to their high surface-to-volume ratio, reduced Li+ diffusion length, and increased freedom associated with the volume change during cycling. However, the nanostructured active materials with high ratio of surface-to-volume increase the irreversible capacity due to the formation of more SEI films. Although the nanostructured materials active materials keep relatively stable during repeated cycles of lithiation/delithiation process, the SEI film continually breaks/reforms, lowing the Coulombic efficiency. Meanwhile, the high-cost, low Coulombic efficiency and low tapping density limit the commercialization of the nanostructured electrode materials. Therefore, it is urgent to find solutions which could take advantage of both long cycle life of nanomaterials within the group IV elements (Si, Ge, Sn) and high volumetric/gravimetric capacity of micro-materials in the group IV as well as elements (Si, Ge, Sn). This report presents an overview of the recently developed strategies for improving the group IV elements (Si, Ge, Sn)-based anodes performances in LIBs to provide a further insight understanding in designing novel anodes