Power and wavelength polarization bistability with very wide hysteresis cycles in a 1550nm-VCSEL subject to orthogonal optical injection

We have measured optical power and wavelength polarization bistability in a 1550nm-Vertical Cavity Surface-Emitting Laser (VCSEL) subject to orthogonally-polarized optical injection into the orthogonal polarization of the fundamental transverse mode. Optical bistability with very wide hysteresis cycles, up to four times wider than previously reported results has been measured for both the optical power and wavelength domain. We also report the experimental observation of three different shapes of polarization bistability, anticlockwise, clockwise and X-Shape bistability, all of them with wide hysteresis cycles. This rich variety of behaviour at the important wavelength of 1550 nm offers promise for the use of VCSELs for all-optical signal processing and optical switching/routing applications. ©2009 Optical Society of America

Optical neuron using polarisation switching in a 1550nm-VCSEL

We report a new approach to mimic basic functionalities of a neuron using a 1550 nm Vertical Cavity Surface Emitting Laser (VCSEL) which is based on the polarisation switching (PS) that can be induced in these devices when subject to polarised optical injection. Positive and negative all-optical threshold operations are demonstrated experimentally using external optical injection into the two orthogonal polarizations of the fundamental transverse mode. The polarisation of the light emitted by the device is used to determine the state of the VCSEL-Neuron, active (orthogonal) or inactive (parallel). This approach forms a new way to reproduce optically the response of a neuron to an excitatory and an inhibitory stimulus. © 2010 Optical Society of America

THE UTILITARIAN FOUNDATIONS OF THE ECONOMIC APPROACH TO HUMAN BEHAVIOR.

The economic approach to the study of human behavior has been presented by its foremost representative as the most effective method of studying social phenomena. Gary Becker´s view supposes that, on the one hand, all social phenomena can be explained as a consequence of individual actions and, on the other, there is a stable pattern of individual behavior economics has been able to understand thoroughly. Hence, economics, according to this view, is no longer limited to the study of a certain domain of human actions or to the understanding of material wealth or the necessary conditions for the material reproduction of society. Economics is a method that gives the social scientist the necessary tools to understand and even transform the world that surrounds him/her. Becker clearly acknowledges the direct link between his approach and Jeremy Bentham´s theory. Beyond the apparent connections regarding their conception of human nature there is one central point that links the two authors: their view of economics as an attitude of the human mind, an inherent capacity to calculate that explains all human actions. This paper argues that Bentham provides the philosophical groundings for Becker´s theory. The application of the principle of utility to every aspect of human behavior justifies economic imperialism by transforming economics into a method of general analysis of human behavior. Indeed, economics is no longer defined according to its subject matter but according to its method, which means an increasing scope explaining Becker´s claim that the economic approach provides a rigorous framework for the analysis of all social phenomena.Gary Becker

On contractible edges in convex decompositions

Let $\Pi$ be a convex decomposition of a set $P$ of $n\geq 3$ points in general position in the plane. If $\Pi$ consists of more than one polygon, then either $\Pi$ contains a deletable edge or $\Pi$ contains a contractible edge

Symmetry and the thermodynamics of currents in open quantum systems

Symmetry is a powerful concept in physics, and its recent application to understand nonequilibrium behavior is providing deep insights and groundbreaking exact results. Here we show how to harness symmetry to control transport and statistics in open quantum systems. Such control is enabled by a first-order-type dynamic phase transition in current statistics and the associated coexistence of different transport channels (or nonequilibrium steady states) classified by symmetry. Microreversibility then ensues, via the Gallavotti-Cohen fluctuation theorem, a twin dynamic phase transition for rare current fluctuations. Interestingly, the symmetry present in the initial state is spontaneously broken at the fluctuating level, where the quantum system selects the symmetry sector that maximally facilitates a given fluctuation. We illustrate these results in a qubit network model motivated by the problem of coherent energy harvesting in photosynthetic complexes, and introduce the concept of a symmetry-controlled quantum thermal switch, suggesting symmetry-based design strategies for quantum devices with controllable transport properties.Comment: 12 pages, 6 figure

Development in Chile 1990-2005: Lessons from a Positive Experience

growth, competitiveness, poverty, inequality, institutions, democratic governance

The acoustic, the digital and the body: a survey on musical instruments

This paper reports on a survey conducted in the autumn of 2006 with the objective to understand people's relationship to their musical tools. The survey focused on the question of embodiment and its different modalities in the fields of acoustic and digital instruments. The questions of control, instrumental entropy, limitations and creativity were addressed in relation to people's activities of playing, creating or modifying their instruments. The approach used in the survey was phenomenological, i.e. we were concerned with the experience of playing, composing for and designing digital or acoustic instruments. At the time of analysis, we had 209 replies from musicians, composers, engineers, designers, artists and others interested in this topic. The survey was mainly aimed at instrumentalists and people who create their own instruments or compositions in flexible audio programming environments such as SuperCollider, Pure Data, ChucK, Max/MSP, CSound, etc