No abstract

With the rich set of embedded sensors installed in smartphones and the large number of mobile users, we witness the emergence of many innovative commercial mobile crowdsensing applications that combine the power of mobile technology with crowdsourcing to deliver time-sensitive and locationdependent information to their customers. Motivated by these real-world applications, we consider the task selection problem for heterogeneous users with different initial locations, movement costs, movement speeds, and reputation levels. Computing the social surplus maximization task allocation turns out to be an NP-hard problem. Hence we focus on the distributed case, and propose an asynchronous and distributed task selection (ADTS) algorithm to help the users plan their task selections on their own. We prove the convergence of the algorithm, and further characterize the computation time for users' updates in the algorithm. Simulation results suggest that the ADTS scheme achieves the highest Jain's fairness index and coverage comparing with several benchmark algorithms, while yielding similar user payoff to a greedy centralized benchmark. Finally, we illustrate how mobile users coordinate under the ADTS scheme based on some practical movement time data derived from Google Maps.

This paper examines the stability in viscous liquid of a steady regime in which the temperature decreases with uniform gradient between a lower horizontal surface which is heated and an upper horizontal surface which is cooled. The problem has been treated both experimentally and theoretically by Bénard , Brunt, Jeffreys, Low and Rayleigh , and it is known that in stability will occur at some critical value of gh 3 Ap/pkv, h denoting the thickness of the fluid layer, Ap/p the fractional excess of density in the fluid at the top as compared with the fluid at the bottom surface, k the diffusivity and v the kinematic viscosity. The critical value depends upon the conditions at the top and bottom surfaces, which may be either ‘free ’or constrained by rigid conducting surfaces. The theoretical problem is solved here under three distinct boundary conditions, and greater generality than before is maintained in regard to the ‘cell pattern’ which occurs in plan. In addition an approximate method is described and illustrated, depending on a stationary property akin to that of which Lord Rayleigh made wide application in vibration theory. Within the assumptions of the approximate theory (i.e. with neglect of terms of the second order in respect of the velocities) a particular size is associated with every shape of cell (such that ‘ a 2 ’ takes a preferred value), but no particular shape is more likely than another to occur in a layer of indefinite extent (§ 31'). The explanation of the apparent preference for a hexagonal cell pattern (§5) must presumably be sought in a theory which takes account of second-order terms. This conjecture if correct goes some way towards explaining the rather indefinite nature of observed cell-formations (cf. Low 1930, figure 10).

Abstract-Cognitive radio gives users the ability to switch channels and make use of dynamic spectrum opportunities. However, switching channels takes time, and may affect the quality of a user's transmission. When a cognitive radio user's channel becomes unavailable, sometimes it may be better waiting until its current channel becomes available again. Motivated by the recent FCC ruling on TV white space, we consider the scenario where cognitive radio users are given the foreknowledge of channel availabilities. Using this information, each user must decide when and how to switch channels. The users wish to exploit spectrum opportunities, but they must take account of the cost of switching channels and the congestion that comes from sharing channels with one another. We model the scenario as a game which, as we show, is equivalent to a network congestion game in the literature after proper and non-trivial transformations. This allows us to design a protocol which the users can apply to find Nash equilibria in a distributed manner. We further evaluate how the performance of the proposed schemes depends on switching cost using real channel availability measurements.