Some arithmetic properties of Pólya’s urn

Following Hales (2018), the evolution of Pólya’s urn may be interpreted as a walk, a Pólya walk, on the integer lattice N2 . We study the visibility properties of Pólya’s walk or, equivalently, the divisibility properties of the composition of the urn. In particular, we are interested in the asymptotic average time that a Pólya walk is visible from the origin, or, alternatively, in the asymptotic proportion of draws so that the resulting composition of the urn is coprime. Via de Finetti’s exchangeability theorem, Pólya’s walk appears as a mixture of standard random walks. This paper is a follow-up of Cilleruelo–Fernández–Fernández (2019), where similar questions were studied for standard random walk

La convergencia de las series de Fourier y su conexión con la Cristalografía

Tesis doctoral inédita de la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Matemáticas. Fecha de lectura: 15-12-199

Characterization of Ultra-Nonlinear SOA in a heterodyne detector configuration with remote photonic local oscillator distribution

A heterodyne receiver scheme based on electro-optical (EO) downconversion is introduced. The local oscillator (LO) and the retrieved intermediate frequency (IF) signals are remotely distributed over fiber to/from a single ultra-nonlinear semiconductor optical amplifier (SOA) device that acts as a highly nonlinear mixer device, enhancing the downconversion performance of the system. The photonic LO is generated modulating a DFB under gain switching (GS), eliminating the need of external elements and the polarization dependency. We evaluate the performance of the downconversion up to frequencies much higher than the bandwidth of the devices (15 GHz). Results show broadband heterodyne detection performance of the system. The presented scheme offers advantages in terms of compactness and cost efficiency and can be easily scaled to remotely reach multiple receivers in scalable detection arrays.The work by A.R. Criado has been supported by the Spanish Ministry of Science and Technology under the FPI Program, Grant# BES2010-030290.Publicad

The use of negation in rhetorical questions and persuasion

El presente trabajo examinó el efecto que posee la presencia de una negación dentro de una pregunta retórica (pr) sobre el cambio de actitudes. La investigación previa ha mostrado que el formato retórico afecta las evaluaciones, pero no ha estudiado el efecto del formato de las preguntas sobre el cambio de actitudes. Con el objetivo de abordar experimentalmente este problema, un grupo de participantes recibió una PR con o sin negación después de haber tenido que generar pensamientos a favor o en contra de una propuesta persuasiva. Los resultados mostraron que, manteniendo el formato retórico constante, la presencia de una negación en la pr redujo el uso de los pensamientos previamente generados ante la propuestaTh is article examines the eff ect of the presence of a negation within a rhetorical question (rq) on attitude change. Previous research has shown that a rhetorical format can aff ect people’s evaluations, but has not examined to what extent the format within the rq can change attitudes. With the main goal of addressing this gap, participants in this experiment received a rq with or without a negation after having generated thoughts for or against a persuasive proposal. Th e results showed that, keeping the rhetorical format constant, the presence of a negation in the rq reduced the use of previously generated thoughts in subsequent attitudes toward the proposalEste trabajo fue realizado gracias a los aportes de la Dirección de Investigación de la Universidad de Talca, Chile, y del proyecto psi 2011-26212 del Ministerio de Innovación y Ciencia, España, otorgados al primer y tercer autor, respectivament

Mid-infrared heterodyne phase-sensitive dispersion spectroscopy using difference frequency generation

This article is part of the topical collection "Mid-infrared and THz Laser Sources and Applications" guest edited by Wei Ren, Paolo De Natale and Gerard Wysocki.Difference frequency generation is a flexible method for the generation of mid-infrared light. It allows downshifting a near-infrared optical signal to the mid-infrared region by means of a nonlinear process, enabling to take full advantage of the availability of optical communications components for the generation of the multi-tone signals that are characteristic of molecular dispersion spectroscopic methods. In this way, it is possible to avoid several issues associated with optical instruments in which directly modulated mid-infrared quantum cascade lasers are employed. In this paper, we take full advantage of this benefit to implement the first heterodyne phase sensitive dispersion spectroscopy gas sensor based on a difference frequency generation source. The performance of the instrument is validated by detecting with high sensitivity methane in the 3.4 mum mid-infrared band.The authors would like to thank the Spanish Ministry of Economy and Competitiveness for supporting the project under the Grant TEC-2014-52147-R (MOSSI). The work by Borja Jerez has been performed in the frame of a FPU Program, #FPU014/06338, granted by the Spanish Ministry of Education, Culture and Sports

Hyperspectral terahertz imaging with electro-optic dual combs and a FET-based detector

In this paper, a terahertz hyperspectral imaging architecture based on an electro-optic terahertz dual-comb source is presented and demonstrated. In contrast to single frequency sources, this multiheterodyne system allows for the characterization of the whole spectral response of the sample in parallel for all the frequency points along the spectral range of the system. This hence provides rapid, highly consistent results and minimizes measurement artifacts. The terahertz illumination signal can be tailored (in spectral coverage and resolution) with high fexibility to meet the requirements of any particular application or experimental scenario while maximizing the signal-to-noise ratio of the measurement. Besides this, the system provides absolute frequency accuracy and a very high coherence that allows for direct signal detection without inter-comb synchronization mechanisms, adaptive acquisition, or post-processing. Using a feld-efect transistor-based terahertz resonant 300GHz detector and the raster-scanning method we demonstrate the two-dimensional hyperspectral imaging of samples of diferent kinds to illustrate the remarkable capabilities of this innovative architecture. A proof-of-concept demonstration has been performed in which tree leaves and a complex plastic fragment have been analyzed in the 300 GHz range with a frequency resolution of 10 GHz.This project has received funding from the ATTRACT project funded by the EC under Grant Agreement 777222 and from the Spanish Ministry of Economy and Competitiveness under Project TEC2017-86271-R. The work has also been partially funded by the EU H2020 Celta project under Grant Agreement 675683 and the Foundation for Polish Science under grant IRA CENTERA. Viktor Krozer is thankful for partial financial support in the frame of the Chairs of Excellence program of the Universidad Carlos III, Madrid, Spain

Enhancing the performance of electro-optical heterodyne receivers using gain switched photonic local oscillators

The performance of a Gain Switched (GS) optical source used as a Photonic Local Oscillator (PLO) in an Electro-Optical (EO) heterodyne receiver is experimentally evaluated and compared to the use of a traditional linearly modulated PLO. The EO heterodyne receiver used is based on an Ultra Nonlinear Semiconductor Optical Amplifier (XN-SOA) that provides a compact, cost effective and energy efficient receiver with a remote distribution of both PLO and Intermediate Frequency (IF) signals and a direct 50-ohms input for the Radiofrequency (RF) component. The comparison between both GS and linearly modulated PLO is made in terms of the conversion efficiency (conversion ratio); linearity (1-dB compression point) and noise (integrated RMS timing jitter). The analysis results in a significant improvement of the evaluated figures of merit when using a Gain Switched PLO.This work was supported in part by the Spanish Ministry of Science and Technology through the project TEC2009-14525-C02-02. The work of A. R. Criado has been supported by the Spanish Ministry of Science and Technology under the FPI Program, Grant # BES2010-030290

Introducción a la taxonomía : manual de ejercitaciones

Fil: Fernández, Marta Susana. Cátedra de Introducción a la Taxonomía. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Brusa, Francisco. Cátedra de Introducción a la Taxonomía. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Damborenea, María Cristina. Cátedra de Introducción a la Taxonomía. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Dellapé, Pablo Matias. Cátedra de Introducción a la Taxonomía. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Gallardo, Fabiana Edith. Cátedra de Introducción a la Taxonomía. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

Design of a Multipurpose Photonic Chip Architecture for THz Dual-Comb Spectrometers

This article belongs to the Special Issue Terahertz Sensing and Imaging Technologies.In this work, we present a multipurpose photonic integrated circuit capable of generating multiheterodyne complex Dual-Combs (DC) THz signals. Our work focuses on translating the functionality of an electro-optic tunable DC system into a photonic chip employing standard building blocks to ensure the scalability and cost efficiency of the integrated device. The architecture we analyze for integration is based on three stages: a seed comb, a mode selection stage and a DC stage. This final DC stage includes a frequency shifter, a key element to improve the final detection of the THz signals and obtain real-time operation. This investigation covers three key aspects: (1) a solution for comb line selection on GHz spaced combs using OIL or OPLL on photonic chips is studied and evaluated, (2) a simple and versatile scheme to produce a frequency shift using the double sideband suppressed carrier modulation technique and an asymmetric Mach Zehnder Interferometer to filter one of the sidebands is proposed, and (3) a multipurpose architecture that can offer a versatile effective device, moving from application-specific PICs to general-purpose PICs. Using the building blocks (BBs) available from an InP-based foundry, we obtained simulations that offer a high-quality Dual-Comb frequency shifted signal with a side mode suppression ratio around 21 dB, and 41 dB after photodetection with an intermediate frequency of 1 MHz. We tested our system to generate a Dual-Comb with 10 kHz of frequency spacing and an OOK modulation with 5 Gbps which can be down-converted to the THz range by a square law detector. It is also important to note that the presented architecture is multipurpose and can also be applied to THz communications. This design is a step to enable a commercial THz photonic chip for multiple applications such as THz spectroscopy, THz multispectral imaging and THz telecommunications and offers the possibility of being fabricated in a multi-project wafer.This research was supported by Instituto Tecnológico Metropolitano, Universidad Carlos III de Madrid, the EU H2020 Celta project under Grant Agreement 675683, by the Spanish Ministry of Economy and Competitiveness under Project TEC2017-86271-R and by the ATTRACT project funded by the EC under Grant Agreement 777222

Dual-polarization VCSEL-based optical frequency comb generation

Poster of: 2015 European Conference on Lasers and Electro-Optics/European Quantum Electronics Conference (CLEO/EUROPE-EQEC 2015)Optical Frequency Comb Generators (OFCG) based on Cost of the Shelf (COTS) laser diodes (LDs) are interesting systems for many applications as they offer compactness and cost efficiency. However, the optical frequency span and the coherence of the modes is still a limiting factor when comparing to combs based on other laser technologies. Among LDs, Vertical-Cavity Surface-Emitting Lasers (VCSELs) under Gain Switching (GS) regime [1] produce record combs in terms of energy efficiency and mode coherence. GS is a well-known nonlinear technique to directly generate OFCGs from LDs