The contact process is a stochastic process which exhibits a continuous, absorbing-state phase transition in the Directed Percolation (DP) universality class. In this work, we consider a contact process with a bias in conjunction with an active wall. This model exhibits waves of activity emanating from the active wall and, when the system is supercritical, propagating indefinitely as travelling (Fisher) waves. In the subcritical phase the activity is localised near the wall. We study the phase transition numerically and show that certain properties of the system, notably the wave velocity, are discontinuous across the transition. Using a modified Fisher equation to model the system we elucidate the mechanism by which the the discontinuity arises. Furthermore we establish relations between properties of the travelling wave and DP critical exponents.
We investigate the conditions under which a moving condensate may exist in a driven mass transport system. Our paradigm is a minimal mass transport model in which n − 1 particles move simultaneously from a site containing n > 1 particles to the neighbouring site in a preferred direction. In the spirit of a Zero-Range process the rate u(n) of this move depends only on the occupation of the departure site. We study a hopping rate u(n) = 1+b/n α numerically and find a moving strong condensate phase for b > b c (α) for all α > 0. This phase is characterised by a condensate that moves through the system and comprises a fraction of the system's mass that tends to unity. The mass lost by the condensate as it moves is constantly replenished from the trailing tail of low occupancy sites that collectively comprise a vanishing fraction of the mass. We formulate an approximate analytical treatment of the model that allows a reasonable estimate of b c (α) to be obtained. We show numerically (for α = 1) that the transition is of mixed order, exhibiting exhibiting a discontinuity in the order parameter as well as a diverging length scale as b b c .
We present WikiSpeech, an ambitious joint project aiming to (1) make open source text-to-speech available through Wikimedia Foundation's server architecture; (2) utilize the large and active Wikipedia user base to achieve continuously improving text-to-speech; (3) improve existing and develop new crowdsourcing methods for text-to-speech; and (4) develop new and adapt current evaluation methods so that they are well suited for the particular use case of reading Wikipedia articles out loud while at the same time capable of harnessing the huge user base made available by Wikipedia. At its inauguration, the project is backed by The Swedish Post and Telecom Authority and headed by Wikimedia Sverige, STTS and KTH, but in the long run, the project aims at broad multinational involvement. The vision of the project is freely available text-to-speech for all Wikipedia languages (currently 293). In this paper, we present the project itself and its first steps: requirements, initial architecture, and initial steps to include crowdsourcing and evaluation. Index Terms: speech synthesis, accessibility, crowdsourcing, multilingual 2 https://meta.wikimedia.org/wiki/Wiki_Project_Med and
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