304,688 research outputs found

    Synchronization transition of heterogeneously coupled oscillators on scale-free networks

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    We investigate the synchronization transition of the modified Kuramoto model where the oscillators form a scale-free network with degree exponent λ\lambda. An oscillator of degree kik_i is coupled to its neighboring oscillators with asymmetric and degree-dependent coupling in the form of \couplingcoeff k_i^{\eta-1}. By invoking the mean-field approach, we determine the synchronization transition point JcJ_c, which is zero (finite) when η>λ2\eta > \lambda-2 (η<λ2\eta < \lambda-2). We find eight different synchronization transition behaviors depending on the values of η\eta and λ\lambda, and derive the critical exponents associated with the order parameter and the finite-size scaling in each case. The synchronization transition is also studied from the perspective of cluster formation of synchronized vertices. The cluster-size distribution and the largest cluster size as a function of the system size are derived for each case using the generating function technique. Our analytic results are confirmed by numerical simulations.Comment: 11 pages, 3 figures and two table

    First passage time for random walks in heterogeneous networks

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    The first passage time (FPT) for random walks is a key indicator of how fast information diffuses in a given system. Despite the role of FPT as a fundamental feature in transport phenomena, its behavior, particularly in heterogeneous networks, is not yet fully understood. Here, we study, both analytically and numerically, the scaling behavior of the FPT distribution to a given target node, averaged over all starting nodes. We find that random walks arrive quickly at a local hub, and therefore, the FPT distribution shows a crossover with respect to time from fast decay behavior (induced from the attractive effect to the hub) to slow decay behavior (caused by the exploring of the entire system). Moreover, the mean FPT is independent of the degree of the target node in the case of compact exploration. These theoretical results justify the necessity of using a random jump protocol (empirically used in search engines) and provide guidelines for designing an effective network to make information quickly accessible.Comment: 5 pages, 3 figure

    Study of component technologies for fuel cell on-site integrated energy system. Volume 2: Appendices

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    This data base catalogue was compiled in order to facilitate the analysis of various on site integrated energy system with fuel cell power plants. The catalogue is divided into two sections. The first characterizes individual components in terms of their performance profiles as a function of design parameters. The second characterizes total heating and cooling systems in terms of energy output as a function of input and control variables. The integrated fuel cell systems diagrams and the computer analysis of systems are included as well as the cash flows series for baseline systems

    Conductance Correlations Near Integer Quantum Hall Transitions

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    In a disordered mesoscopic system, the typical spacing between the peaks and the valleys of the conductance as a function of Fermi energy EFE_F is called the conductance energy correlation range EcE_c. Under the ergodic hypothesis, the latter is determined by the half-width of the ensemble averaged conductance correlation function: F=F= . In ordinary diffusive metals, EcD/L2E_c\sim D/L^2, where DD is the diffusion constant and LL is the linear dimension of the phase-coherent sample. However, near a quantum phase transition driven by the location of the Fermi energy EFE_F, the above picture breaks down. As an example of the latter, we study, for the first time, the conductance correlations near the integer quantum Hall transitions of which EFE_F is a critical coupling constant. We point out that the behavior of FF is determined by the interplay between the static and the dynamic properties of the critical phenomena.Comment: 4 pages, 4 figures, minor corrections, to appear in Phys. Rev. Let

    Study of component technologies for fuel cell on-site integrated energy systems

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    Heating, ventilation and air conditioning equipment are integrated with three types of fuel cells. System design and computer simulations are developed to utilize the thermal energy discharge of the fuel in the most cost effective manner. The fuel provides all of the electric needs and a loss of load probability analysis is used to ensure adequate power plant reliability. Equipment cost is estimated for each of the systems analyzed. A levelized annual cost reflecting owning and operating costs including the cost of money was used to select the most promising integrated system configurations. Cash flows are presented for the most promising 16 systems. Several systems for the 96 unit apartment complex (a retail store was also studied) were cost competitive with both gas and electric based conventional systems. Thermal storage is shown to be beneficial and the optimum absorption chiller sizing (waste heat recovery) in connection with electric chillers are developed. Battery storage was analyzed since the system is not electric grid connected. Advanced absorption chillers were analyzed as well. Recommendations covering financing, technical development, and policy issues are given to accelerate the commercialization of the fuel cell for on-site power generation in buildings