5,180 research outputs found
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 AÂż 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
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