On relativistic particle creation in Bose-Einstein condensates

We show that particle creation of Bogoliubov modes in a Bose-Einstein condensate due to the accelerated motion of the trap is a genuinely relativistic effect. To this end we show that Bogoliubov modes can be described by a time rescaling of the Minkowski metric. A consequence of this is that Rindler transformations are perceived by the phonons as generalised Rindler transformations where the speed of light is replaced by the speed of sound, enhancing particle creation at small velocities. Since the non-relativistic limit of a Rindler transformation is just a Galilean transformation entailing no length contraction or time dilation, we show that the effect vanishes in the non-relativistic limit.Comment: This work provides further theoretical support to the results in Sci. Rep. 4, 4996 (2014), http://www.nature.com/srep/2014/140521/srep04996/full/srep04996.htm

Hierarchical path-finding for Navigation Meshes (HNA*)

Path-finding can become an important bottleneck as both the size of the virtual environments and the number of agents navigating them increase. It is important to develop techniques that can be efficiently applied to any environment independently of its abstract representation. In this paper we present a hierarchical NavMesh representation to speed up path-finding. Hierarchical path-finding (HPA*) has been successfully applied to regular grids, but there is a need to extend the benefits of this method to polygonal navigation meshes. As opposed to regular grids, navigation meshes offer representations with higher accuracy regarding the underlying geometry, while containing a smaller number of cells. Therefore, we present a bottom-up method to create a hierarchical representation based on a multilevel k-way partitioning algorithm (MLkP), annotated with sub-paths that can be accessed online by our Hierarchical NavMesh Path-finding algorithm (HNA*). The algorithm benefits from searching in graphs with a much smaller number of cells, thus performing up to 7.7 times faster than traditional A¿ over the initial NavMesh. We present results of HNA* over a variety of scenarios and discuss the benefits of the algorithm together with areas for improvement.Peer ReviewedPostprint (author's final draft

Analog quantum simulation of gravitational waves in a Bose-Einstein condensate

We show how to vary the physical properties of a Bose-Einstein condensate (BEC) in order to mimic an effective gravitational-wave spacetime. In particular, we focus in the simulation of the recently discovered creation of particles by real spacetime distortion in box-type traps. We show that, by modulating the speed of sound in the BEC, the phonons experience the effects of a simulated spacetime ripple with experimentally amenable parameters. These results will inform the experimental programme of gravitational wave astronomy with cold atoms.Comment: 9 pages. I. F. previously published as I. Fuentes-Guridi and I.Fuentes-Schuller. v2: minor changes, references adde

Quantum discord in the Dynamical Casimir Effect

We analyse the generation of quantum discord by means of the dynamical Casimir effect in superconducting waveguides modulated by superconducting quantum interferometric devices. We show that for realistic experimental parameters, the conditions for the existence of quantum discord are less demanding than the previously considered for quantum entanglement or non-classicality. The states with non-zero discord and zero entanglement generated by the dynamical Casimir effect are a useful resource for quantum cryptography.Comment: 4 pages, 2 figures. v2: minor changes, published versio

Institutional Arrangements to Determine Loan Repayment in Chile

The major objective of this paper is to investigate institutional arrangements as a determinant of loan repayment in the Chilean financial market. A second aim is to analyze the effects of these arrangements on borrowers’ behavior. Although La Porta et al. (1997, 1998) classify Chile as a French Civil Law country, the law and private arrangements have evolved consistently with the capital market development to protect the rights of the creditors. This is consistent with relatively low rates of bad loans, ranking from 1. 1 to 2. 0 percent in 1993-1997. We examine different variables which may be related to loan repayment: (a) limitations on the access to credit, (b) macroeconomic stability, (c) collection technology, (d) bankruptcy code, (e) information sharing, (f) the judicial system, (g) prescreening techniques and (h) major changes in financial market regulation. Based on the discussion presented in the paper plus regression analyses, we conclude that a satisfactory performance of the Chilean credit market, in terms of loan repayments and credit market development, hinges on a good information sharing system, an advanced collection technology, a good macroeconomic performance, credit market development and major changes in financial market regulation.

Analytical solution of a double-well Bose-Einstein Condensate

We introduce a microscopic computation which shows that the Hamiltonian of a Bose-Einstein Condensate can be analytically solved in the two-mode approximation, in particular, in the case of an asymmetric double-well condensate in the dilute regime. Our model is exactly diagonalisable when the overlap of the quasilocalized modes in each well is small enough with respect to the trap asymmetry. For larger overlaps or highly symmetric traps, our diagonalisable Hamiltonian acquires extra terms that we treat within perturbation theory.Comment: 4 pages, 1 figure. I. F. previously published as I. Fuentes-Guridi and Fuentes-Schulle

Critical Choices at a Critical Age: Youth Emancipation Paths and School Attainment in Latin America

This paper discusses how young people become adults in Latin America and how that process affects educational attainment. An examination of four countries at three levels of development shows that individuals` educational attainment is closely linked to the decisions that young people make regarding adult roles, here referred to as emancipation patterns. The paper documents differences among countries in the age at which young people start working, marry and leave the educational system. Factor and hazard analyses further show how these dimensions vary according to gender and income within countries and how they affect the chances that young people will remain in the educational system. Findings indicate that countries` development levels strongly affect the modal ages at which people become adults, hastening the process in less-developed countries and delaying it at higher stages of development. Second, within countries males and females present distinct risk factors regarding educational attainment; public roles (work) increase the risk of drop-out for men and private roles (marriage) increase this risk for women. In addition, and as expected, lower income groups are more at risk and present earlier adoption of adult values than higher income groups. The interrelation of income and gender operate differently in emancipation patterns and in how public and private adult roles affect the chances of remaining in the educational system. Consequently, in order to increase educational attainment the sequence and timing of adult role adoption have to be factored into policies.

Motion and gravity effects in the precision of quantum clocks

We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions.Comment: 10 pages, 6 figures. I. F. previously published as I. Fuentes-Guridi and I. Fuentes-Schulle

A Pure Soul

CARLOS FUENTES, the distinguished Mexican writer, has published a number of books of fiction, the most recent being Distant Relations, a novel, and Burnt Water, short stories. He has taught at the University of Pennsylvania, Columbia, and Princeton