Effects of nonlinear dispersion on squeezed states in two-photon devices

7 págs.; 4 figs.; 1 apémdiceThe deleterious effects of nonlinear dispersion on squeezed light in two-photon devices when absorption losses are included have been analyzed making use of the variables called two-mode quadrature-phase amplitudes. The uncertainties in the quadrature amplitudes have been computed from a generalized Fokker-Planck equation. The dependence of squeezing on the nonlinear coupling, the modulation (including the case of high modulations), the pumping phase (where nonlinear dispersion causes an intensity-dependent shift in the minimum squeezing), and the absorption losses have been studied. © 1989 The American Physical Society.Peer Reviewe

Low-noise properties of squeezed light in transmission chains formed from nonlinear alternating attenuators and amplifiers

4 págs.; 4 figs.An idealized model of an optical communication link in which identical sections of nonlinear attenuating fiber alternate with identical amplifiers is considered. Signal-to-noise ratios of chains of these elements for input squeezed and coherent light have been numerically evaluated. It is found that input squeezed light and nonlinear attenuators improve the signal-to-noise ratios with respect to coherent inputs and linear chains. In the case of three-photon attenuators, the noise and signal-to-noise ratio remain practically constant from certain elements of the chain. Moreover, the influence of the attenuation coefficient and the input mean photon number on the signal-to-noise ratios was considered, as well as chains with nonlinear amplifiers and chains in which the amplifier gain does not exactly compensate for the fiber attenuation. © 1988 The American Physical Society.Peer Reviewe

Efficient procedure for the evaluation of multiple scattering and multiphonon corrections in inelastic neutron-scattering experiments

10 págs.; 7 figs.; 1 tab.We present a full set of procedures to evaluate the experimental corrections needed to derive physically meaningful quantities from the measured neutron intensities in inelastic neutron-scattering experiments. Multiple-scattering corrections are evaluated by means of a Monte Carlo code, in which a combination of experimental data and the Synthetic Model is used to account for neutron-molecule interactions. Multiphonon corrections are treated with an iterative scheme. To illustrate the procedure the densities of vibrational states of deuterated water and ice near room temperature are evaluated from data measured in a chopper spectrometer. ©1998 American Physical SocietyPeer Reviewe

Human Enhancement Technologies and the Arguments for Cosmopolitanism

Según el minimalismo político, un debate es político cuando intenta responder en último término a la pregunta «¿qué hacemos?». Esta posición filosófica explica por qué sería más fructífero contemplar desde una perspectiva política algunas cuestiones relacionadas con las tecnologías de mejora humana que tradicionalmente se han tratado como problemas de ética aplicada. Pero entonces surge la pregunta acerca de quién es el «nosotros» que se interroga, esto es, qué comunidades son las que afrontan los retos políticos provocados por las tecnologías de mejora humana. Defendemos que la comunidad humana global se enfrenta a algunos de esos retos, lo que dando lugar a una perspectiva cosmopolita. Algunos autores han defendido anteriormente la necesidad de una aproximación cosmopolita a asuntos como la pobreza o el cambio climático; sin embargo, al carecer de una diferenciación adecuada entre ética y política, tienden a abogar por el cosmopolitismo con argumentos morales. Defendemos que las tecnologías de mejora humana proporcionan buenas razones en apoyo del cosmopolitismo, entendido como una postura política. En apoyo de esta tesis, examinamos dos casos: el de las píldoras que permitirían comer sin engordar y el de la elección entre diferentes técnicas de mejora cognitiva.According to political minimalism, a debate is considered political when it revolves around the question “What shall we do?” This account suggests that certain issues related to human enhancement technologies (HETs), which have traditionally been addressed in the realm of applied ethics, could be better approached from a political standpoint. However, this raises the question of who constitutes the “we” – the communities that face the political challenges posed by HETs. We argue that there is a global human community that directly faces at least some of these challenges, and this fact underscores the relevance of a cosmopolitan perspective. While some authors have already advocated for a cosmopolitan approach in addressing issues such as poverty or climate change, they often do so from a moral outlook, without adequately distinguishing between ethics and politics. In contrast, we assert that HETs present compelling arguments in favour of cosmopolitanism as a political stance. In support of this claim, we consider two cases: the pills that would allow people to eat at will without gaining weight, and the choice between different types of cognitive enhancers.Ministerio de Ciencia, Innovación y Universidade

Justifying the Precautionary Principle as a political principle

Our aim is to defend the Precautionary Principle (PP) against the main theoretical and practical criticisms that it has raised by proposing a novel conception and a specific formulation of the principle. We first address the theoretical concerns against the idea of there being a principle of precaution by arguing for a distinctively political conception of the PP as opposed to a moral one. Our claim is that the rationale of the PP is grounded in the fact that contemporary societies wish to avoid morally unacceptable risks while at the same time pursuing other goals, aspirations and values. Following this political conception of the PP, we propose a specific formulation in terms of an argumentation scheme — the Argumentation Scheme for Appealing to Precaution — which is meant to solve, in turn, the main practical concerns that the PP has raised. We explain the advantages of our proposal by analysing appeals to precaution in the cases of (1) the European restrictions on the free movement of persons during the COVID-19 pandemic and (2) the discharge of nuclear wastes into the Irish Sea.Spanish Ministry of Innovation, Science and Universities for funding their research through the project PID2019-107478GB-I0

The Physics of Liquid Para-Hydrogen

Macroscopic systems of hydrogen molecules exhibit a rich thermodynamic phase behavior. Due to the simplicity of the molecular constituents a detailed exploration of the thermal properties of these boson systems at low temperatures is of fundamental interest. Here,we report theoretical and experimental results on various spatial correlation functions and corresponding distributions in momentum space of liquid para-hydrogen close to the triple point. They characterize the structure of the correlated liquid and provide information on quantum effects present in this Bose fluid. Numerical calculations employ Correlated Density-Matrix(CDM)theory and Path-Integral Monte-Carlo(PIMC)simulations. A comparison of these theoretical results demonstrates the accuracy of CDM theory. This algorithm therefore permits a fast and efficient quantitative analysis of the normal phase of liquid para-hydrogen.We compare and discuss the theoretical results with available experimental data.Comment: 14 pages, 7 figure

Molecular dynamics on a realistic model for a strong glass

10 págs.; 9 figs.; 1 tab. ; Erratum Phys. Rev. B 54, 9558 (1996)Thermal motions in a microscopic model for a strong glass (B2O3) are studied by means of computer molecular dynamics simulations. A decomposition of the atomic dynamics in terms of normal modes allows the separation of the truly harmonic components of the generalized frequency distributions. This enables us to discuss a number of magnitudes relevant to current issues on glassy dynamics on quantitative grounds. In particular, the microscopic origin of quantities such as the atomic mean-square displacements, the characterization of mode eigenvectors associated with well-defined spectral features, or the origin of the low-frequency peak appearing in the S(Q,ω) dynamic structure factor, are analyzed in some detail. ©1996 American Physical SocietyThis work has been supported in part by DGICYT Grant No. PB92-0114-C04.Peer Reviewe

Quantum Langevin equations for a two-mode parametric amplifier: Noise squeezing without negative diffusion

13 págs.; 5 figs,; PACS number(s): 42.50.Dv, 42.50.KbThe theory of a two-mode nondegenerate parametric amplifier in a cavity is reformulated in terms of quadrature-phase-amplitude variables. The corrrespondence with a genuine classical stochastic linear process is found (non-negative-definite diffusion matrices) for the case of a cavity device immersed in thermal or ordinary (nonsqueezed) vacuum sources. A special kind of squeezing, i.e., quadrature squeezing [B. L. Schumaker, Phys. Rep. 135, 318 (1986)], is found to be characteristic of the internal steady state for the case of a cavity model subjected to an additional phase-sensitive noise source coupled to one of the two internal modes. Finally, the usual squeezing spectrum of the output field is calculated in both cases by means of an input-output formalism based upon a symmetric ordering scheme of noncommuting operators, well adapted for the quadrature-phase description of the fields involved in the interaction. © 1992 The American Physical Society.Work supported in part by Grants No. TIC90-80, from DGICYT (Spain), and No. A-91002002-15, from U.P.M. (Madrid, Spain).Peer Reviewe

Desarrollo de una plataforma hardware para la Robocup Small Soccer League (SSL)

Este proyecto es un trabajo enfocado al diseño e implementación de un equipo de cinco robots autónomos que juegan al fútbol. Los robots forman parte del proyecto RoboCup del Laboratorio de Sistemas Inteligentes de la UC3M. En la siguiente introducción se describe el problema que el proyecto pretende resolver, se define el objetivo y se acota el alcance del trabajo. Más adelante se expone la justificación que motivó el proyecto y los trabajos relacionados. Finalmente se explica la estructura y el contenido de todo el documento.Ingeniería Técnica en Electrónic