11,537 research outputs found

    Wormholes in the accelerating universe

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    We discuss different arguments that have been raised against the viability of the big trip process, reaching the conclusions that this process can actually occur by accretion of phantom energy onto the wormholes and that it is stable and might occur in the global context of a multiverse model. We finally argue that the big trip does not contradict any holographic bounds on entropy and information.Comment: 2 pages, LaTex, to appear in the Proceedings of the 11th Marcel Grossmann Conference, 200

    Numerical Simulation of III-V Solar Cells Using D-AMPS

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    Numerical simulation of devices plays a crucial role in their design, performance prediction, and comprehension of the fundamental phenomena ruling their operation. Here, we present results obtained using the code D-AMPS-1D, that was conveniently modified to consider the particularities of III-V solar cell devices. This work, that is a continuation of a previous paper regarding solar cells for space applications, is focused on solar cells structures than find application for terrestrial use under concentrated solar illumination. The devices were fabricated at the Solar Energy Institute of the Technical University of Madrid (UPM). The first simulations results on InGaP cells are presented. The influence of band offsets and band bending at the window-emitter interface on the quantum efficiency was studied. A remarkable match of the experimental quantum efficiency was obtained. Finally, numerical simulation of single junction n-p InGaP-Ge solar cells was performed

    Worse than a big rip?

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    We show that a generalised phantom Chaplygin gas can present a future singularity in a finite future cosmic time. Unlike the big rip singularity, this singularity happens for a finite scale factor, but like the big rip singularity, it would also take place at a finite future cosmic time. In addition, we define a dual of the generalised phantom Chaplygin gas which satisfies the null energy condition. Then, in a Randall-Sundrum 1 brane-world scenario, we show that the same kind of singularity at a finite scale factor arises for a brane filled with a dual of the generalised phantom Chaplygin gas.Comment: 6 pages, 4 figures, RevTeX 4. Discussion expanded and references added. Version to appear in PL

    On the origin of the cumulative semantic inhibition effect

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    We report an extension of the cumulative semantic inhibition effect found by Howard, Nickels, Coltheart, and Cole-Virtue (2006). Using more sensitive statistical analyses, we found a significant variation in the magnitude of the effect across categories. This variation cannot be explained by the naming speed of each category. In addition, using a sub-sample of the data, a second cumulative effect arouse for newly-defined supra-categories, over and above the effect of the original ones. We discuss these findings in terms of the representations that drive lexical access, and interpret them as supporting featural or distributed hypotheses

    Two repelling random walks on Z\mathbb Z

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    We consider two interacting random walks on Z\mathbb{Z} such that the transition probability of one walk in one direction decreases exponentially with the number of transitions of the other walk in that direction. The joint process may thus be seen as two random walks reinforced to repel each other. The strength of the repulsion is further modulated in our model by a parameter β≥0\beta \geq 0. When β=0\beta = 0 both processes are independent symmetric random walks on Z\mathbb{Z}, and hence recurrent. We show that both random walks are further recurrent if β∈(0,1]\beta \in (0,1]. We also show that these processes are transient and diverge in opposite directions if β>2\beta > 2. The case β∈(1,2]\beta \in (1,2] remains widely open. Our results are obtained by considering the dynamical system approach to stochastic approximations.Comment: 17 pages. Added references and corrected typos. Revised the argument for the convergence to equilibria of the vector field. Improved the proof for the recurrence when beta belongs to (0,1); leading to the removal of a previous conjectur

    The role of short periodic orbits in quantum maps with continuous openings

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    We apply a recently developed semiclassical theory of short periodic orbits to the continuously open quantum tribaker map. In this paradigmatic system the trajectories are partially bounced back according to continuous reflectivity functions. This is relevant in many situations that include optical microresonators and more complicated boundary conditions. In a perturbative regime, the shortest periodic orbits belonging to the classical repeller of the open map - a cantor set given by a region of exactly zero reflectivity - prove to be extremely robust in supporting a set of long-lived resonances of the continuously open quantum maps. Moreover, for step like functions a significant reduction in the number needed is obtained, similarly to the completely open situation. This happens despite a strong change in the spectral properties when compared to the discontinuous reflectivity case.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with arXiv:1604.0181
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