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Choi Y.,Stanford University | Kim H.,Incheon National University | Han S.-W.,UBC | Han Y.,Korea Advanced Institute of Science and Technology
IEEE Transactions on Wireless Communications | Year: 2010

Heterogeneous wireless networks where several systems with different bands coexist for multimedia service are currently in service and will be widely adopted to support various traffic demand. Under heterogeneous networks, a mobile station can transmit over multiple and simultaneous radio access technologies (RATs) such as WLAN, HSPA, and WCDMA LTE. Also, cognitive radio for the efficient use of underutilized/unused frequency band is successfully implemented in some networks. In this letter, we address such operational issues as air interface and band selection for a mobile and power allocation to the chosen links. An optimal solution is sought and analyzed and a distributed joint allocation algorithm is proposed to maximize total system capacity. We investigate the benefit of multiple transmissions by multiple RATs over a single transmission by a single RAT at a time, which can be interpreted as network diversity. Numerical results validate the performance enhancement of our proposed algorithm. © 2010 IEEE. Source

Kinshella M.-L.W.,UBC
Anthropology and Medicine | Year: 2014

Based on ethnographic fieldwork in a coastal village in south-eastern Tanzania, this paper examines how social inequalities and social suffering become embodied in the lived experiences of hunger. The paper explores local meanings of food, fertility and hunger and how these concepts interconnect and materialize on a landscape impacted by two large-scale conservation and development projects, the Mtwara Development Corridor and the Mnazi Bay Ruvuma Estuary Marine Park. Fourteen in-depth interviews Sinde villagers were conducted to elicit narratives about their food experiences in addition to 24 hour food recall and pile sort to explore local taxonomies of food. One focus group discussion with six women was also conducted. The study finds displacement from resources by the conservation and development projects has exacerbated existing food security issues of irregular rains, increasing food prices and malnourished bodies. The downward cycle of food insecurity has local villagers worried about the viability of their community's future, embodied in the health of local children and their performance in school. Increasing food insecurity is internalized within the community as infertility where the health of the landscape is connected to the health of society. © 2014 Taylor & Francis. Source

Ioffe D.,Technion - Israel Institute of Technology | Levit A.,UBC
Journal of Statistical Physics | Year: 2013

We investigate global logarithmic asymptotics of ground states for a family of quantum mean field models in transverse field. Our approach is based on a stochastic representation and a combination of large deviation and weak KAM techniques. We prove that asymptotic ground states are weak KAM (Fathi in C. R. Acad. Sci., Ser. I Math. 324(9):1043-1046, 1997; Fathi, The Weak KAM Theorem in Lagrangian Dynamics 10th Preliminary Version, 2008; Fathi in Nonlinear Differ. Equ. Appl. 14(1):1-27, 2007) and, in particular, viscosity (Capuzzo-Dolcetta and Lions in Trans. Am. Math. Soc. 318(2):643-683, 1990; Fathi, The Weak KAM Theorem in Lagrangian Dynamics 10th Preliminary Version, 2008, Chap. 7) solutions of certain stationary Hamilton-Jacobi equations. In general such solutions are not unique, and additional refined selection criteria are needed. The spin-1/2 model is worked out in more detail. We discuss phase transitions in the ground state as the strength of the transverse field varies. For a class of mean field interaction potentials this transition is of the first order. For all the models in question, asymptotic ground states with multiple wells necessarily develop shocks. A complete description of asymptotic ground states is derived for ferromagnetic p-body interactions. © 2013 Springer Science+Business Media New York. Source

Promislow K.,MSU | St-Pierre J.,University of Hawaii at Manoa | Wetton B.,UBC
Journal of Power Sources | Year: 2011

A simple, analytic model is presented that describes the steady state profile of anode nitrogen concentration in a polymer electrolyte membrane fuel cell operated with anode recirculation. The model is appropriate for fuel cells with straight gas channels and includes the effect of nitrogen crossover from cathode to anode through the membrane. The key analytic simplification in the model is that this crossover rate, when scaled to the gas flows in the channels, is small. This is a good approximation when the device is used at operating power levels. The model shows that the characteristic times for the anode nitrogen profiles to reach steady state are of the order of minutes and that the dilution effect of anode nitrogen is severe for pure recirculation. The model shows additionally that a small anode outlet bleed can significantly reduce the nitrogen dilution effect. Within the framework of the model, the energy efficiency of pure recirculation can be compared to hydrogen venting or partial anode bleeding. An optimal bleed rate is identified. The model and optimization analysis can be adapted to other fuel cell designs and operating conditions. Along with operating conditions, only two key parameters are needed: a nitrogen crossover coefficient and the marginal efficiency loss to compressors for increased anode stoichiometric gas flow. © 2011 Elsevier B.V. All rights reserved. Source

Kim T.,KAIST | Han S.-W.,UBC | Han Y.,KAIST
IEEE Communications Letters | Year: 2010

In future wireless communication networks, seamless handoff either by vertical or horizontal is an important issue in radio resource management. For a vertical handoff (VHO), each candidate network is evaluated as a function of multiple attributes such as available bandwidth, delay, data rate, and cost, etc. However, the variations of these parameters and distributed VHO decisions might cause the instability of VHO decisions, which is inefficient in utilizing network resources due to frequent handoffs. In this letter, we propose a service history-based VHO algorithm to reduce unnecessary handoffs and call dropping probability in addition to QoS parameter considerations. Simulation results show that the proposed VHO algorithm outperforms existing algorithms. © 2010 IEEE. Source

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