Discontinuous Transition in a Boundary Driven Contact Process

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.Comment: 14 pages, 9 figure

The synthesis of the light Mo and Ru isotopes: how now, no need for an exotic solution ?

The most detailed calculations of the p-process call for its development in the O/Ne layers of Type II supernovae. In spite of their overall success in reproducing the solar system content of p-nuclides, they suggest a significant underproduction of the light Mo and Ru isotopes. On grounds of a model for the explosion of a 25 solar mass star with solar metallicity, we demonstrate that this failure might just be related to the uncertainties left in the rate of the 22Ne(alpha,n)25Mg neutron producing reaction. The latter indeed have a direct impact on the distribution of the s-process seeds for the p-process.Comment: 4 pages, 4 figures. LaTex2e with aa.cls. A&A Letters, in pres

Structural vulnerability of Nepalese Pagoda temples

Nepal is located in one of the most severe earthquake prone areas of the world, lying between collisions of Indian to the Eurasian plate, moving continuously, resulting in frequent devastating earthquakes within this region. Moreover, different authors refer mention that the accumulated slip deficit (central seismic gap) is likely to produce large earthquakes in the future. Also, the analysis of the available information of previous earthquakes indicates the potential damage that can occurs in unreinforced traditional masonry structures in future earthquakes. Most of the Nepalese pagoda temples were erected following very simple rules and construction details to accomplish with seismic resistance requirement, or even without any consideration for seismic resistance, during the period of Malla dynasty (1200-1768). Presently, conservation and restoration of ancient monuments are one of the major concerns in order to preserve our built heritage, transferring it to the future generations. The present paper is devoted to outline particular structural fragility characteristics in the historic Nepalese pagoda temples which affect their seismic performance. Moreover, based on the parametric analysis identified structural weaknesses/fragilities of pagoda topology, the associated traditional building technology and constructional details

Superlens made of a metamaterial with extreme effective parameters

We propose a superlens formed by an ultra-dense array of crossed metallic wires. It is demonstrated that due to the anomalous interaction between crossed wires, the structured substrate is characterized by an anomalously high index of refraction and supports strongly confined guided modes with very short propagation wavelengths. It is theoretically proven that a planar slab of such structured material makes a superlens that may compensate for the attenuation introduced by free-space propagation and restore the subwavelength details of the source. The bandwidth of the proposed device can be quite significant since the response of the structured substrate is non-resonant. The theoretical results are fully supported by numerical simulations.Comment: Accepted for publication in Phys. Rev. B (in press