A gated single-photon avalanche diode array fabricated in a conventional CMOS process for triggered systems

A bidimensional array based on single-photon avalanche diodes for triggered imaging systems is presented. The diodes are operated in the gated mode of acquisition to reduce the probability to detect noise counts interfering with photon arrival events. In addition, low reverse bias overvoltages are used to lessen the dark count rate. Experimental results demonstrate that the prototype fabricated with a standard HV-CMOS process gets rid of afterpulses and offers a reduced dark count probability by applying the proposed modes of operation. The detector exhibits a dynamic range of 15 bits with short gated"on" periods of 10ns and a reverse bias overvoltage of 1.0V.

Gated Geiger mode avalanche photodiode pixels with integrated readout electronics for low noise photon detection

Avalanche photodiodes operated in the Geiger mode offer a high intrinsic gain as well as an excellent timing accuracy. These qualities make the sensor specially suitable for those applications where detectors with high sensitivity and low timing uncertainty are required. Moreover, they are compatible with standard CMOS technologies, allowing sensor and front-end electronics integration within the pixel cell. However, the sensor suffers from high levels of intrinsic noise, which may lead to erroneous results and limit the range of detectable signals. They also increase the amount of data that has to be stored. In this work, we present a pixel based on a Geiger-mode avalanche photodiode operated in the gated mode to reduce the probability to detect noise counts interfering with photon arrival events. The readout circuit is based on a two grounds scheme to enable low reverse bias overvoltages and consequently lessen the dark count rate. Experimental characterization of the fabricated pixel with the HV-AMS 0.35µm standard technology is also presented in this article.

El significado de las ocupaciones en las personas mayores-jóvenes: algunas tendencias

Con la llegada del nuevo paradigma del “envejecimiento activo” planteado por la Organización Mundial de la Salud (OMS, 2002), estamos asistiendo a una nueva manera de enfocar el progresivo envejecimiento de la población. Este enfoque trata de fomentar la consecución de una esperanza de vida saludable y libre de discapacidad, gracias a la promoción de políticas y programas cuyos objetivos principales se centran en la independencia y en la autonomía a lo largo del proceso de envejecimiento. Acorde con este enfoque pensamos que las ocupaciones significativas son una buena herramienta para mantener la autonomía de estas personas al fomentar la prevención y la promoción de su salud, motivo por el cual desarrollamos este estudio. Los objetivos principales del presente estudio son conocer y comprender que ocupaciones adquieren un significado y satisfacción personal en las personas mayores-jóvenes, que han concluido su etapa laboral, que cuentan con buena salud y condiciones psicofísicas favorables y que viven de manera autónoma en la comunidad, así como explorar también si se establece en estas personas alguna vinculación entre las actividades que eligen desarrollar en la actualidad con su perfil e historia ocupacional previa. Por último, este estudio pretende conocer el tipo de gestión que cada persona prefiere para llevar a cabo las actividades cotidianas que les son más significativas, a partir de los contextos en los que se inscribe. El marco teórico se desarrolla a partir de la conceptualización aportada por diversos autores sobre el envejecimiento activo y la ciencia de la ocupación. La metodología utilizada es de carácter cualitativo, enfocado desde un paradigma constructivista. Los resultados del estudio muestran que se inicia tímidamente un cambio de tendencias en la elección y el significado que las personas mayores-jóvenes atribuyen a sus ocupaciones. Muestran también que las ocupaciones elegidas como más significativas por estas personas mantienen una vinculación con las que ya realizaban con anterioridad a la jubilación, con su historia o perfil 6 ocupacional previo. Y finalmente demuestran que el tipo de gestión que eligen para efectuarlas influye en la elección del entorno donde las llevan a término.

Els jueus de Puigcerdà a l'Edat Mitjana (1260-1493)

Aquest treball és un recull de tot el que s'ha trobat documentat sobre els jueus que van habitar Puigcerdà entre els anys 1260 i 1493. S'estructura a partir d'una introducció sobre la cultura jueva, l'arribada a Puigcerdà dels jueus, per què, com i quan s'hi instal·len, el Call puigcerdanès, on trobem tot el que fa referència a l'espai físic, l'humà i el material, i finalment la seva expulsió.

Effects of coastal submarine canyons on tsunami propagation and impact

We analyse the variations produced on tsunami propagation and impact over a straight coastline because of the presence of a submarine canyon incised in the continental margin. For ease of calculation we assume that the shoreline and the shelf edge are parallel and that the incident wave approaches them normally. A total of 512 synthetic scenarios have been computed by combining the bathymetry of a continental margin incised by a parameterised single canyon and the incident tsunami waves. The margin bathymetry, the canyon and the tsunami waves have been generated using mathematical functions (e.g. Gaussian). Canyon parameters analysed are: (i) incision length into the continental shelf, which for a constant shelf width relates directly to the distance from the canyon head to the coast, (ii) canyon width, and (iii) canyon orientation with respect to the shoreline. Tsunami wave parameters considered are period and sign. The COMCOT tsunami model from Cornell University was applied to propagate the waves across the synthetic bathymetric surfaces. Five simulations of tsunami propagation over a non-canyoned margin were also performed for reference. The analysis of the results reveals a strong variation of tsunami arrival times and amplitudes reaching the coastline when a tsunami wave travels over a submarine canyon, with changing maximum height location and alongshore extension. In general, the presence of a submarine canyon lowers the arrival time to the shoreline but prevents wave build-up just over the canyon axis. This leads to a decrease in tsunami amplitude at the coastal stretch located just shoreward of the canyon head, which results in a lower run-up in comparison with a non-canyoned margin. Contrarily, an increased wave build-up occurs on both sides of the canyon head, generating two coastal stretches with an enhanced run-up. These aggravated or reduced tsunami effects are modified with (i) proximity of the canyon tip to the coast, amplifying the wave height, (ii) canyon width, enlarging the areas with lower and higher maximum height wave along the coastline, and (iii) canyon obliquity with respect to the shoreline and shelf edge, increasing wave height shoreward of the leeward flank of the canyon. Moreover, the presence of a submarine canyon near the coast produces a variation of wave energy along the shore, eventually resulting in edge waves shoreward of the canyon head. Edge waves subsequently spread out alongshore reaching significant amplitudes especially when coupling with tsunami secondary waves occurs. Model results have been groundtruthed using the actual bathymetry of Blanes Canyon area in the North Catalan margin. This paper underlines the effects of the presence, morphology and orientation of submarine canyons as a determining factor on tsunami propagation and impact, which could prevail over other effects deriving from coastal configuration.

The Gaussian assumption in second-order estimation problems in digital communications

This paper deals with the goodness of the Gaussian assumption when designing second-order blind estimationmethods in the context of digital communications. The low- andhigh-signal-to-noise ratio (SNR) asymptotic performance of the maximum likelihood estimator—derived assuming Gaussiantransmitted symbols—is compared with the performance of the optimal second-order estimator, which exploits the actualdistribution of the discrete constellation. The asymptotic study concludes that the Gaussian assumption leads to the optimalsecond-order solution if the SNR is very low or if the symbols belong to a multilevel constellation such as quadrature-amplitudemodulation (QAM) or amplitude-phase-shift keying (APSK). On the other hand, the Gaussian assumption can yield importantlosses at high SNR if the transmitted symbols are drawn from a constant modulus constellation such as phase-shift keying (PSK)or continuous-phase modulations (CPM). These conclusions are illustrated for the problem of direction-of-arrival (DOA) estimation of multiple digitally-modulated signals.

Robust beamforming for interference rejection in mobile communications

The problem of robust beamformer design for mobile communicationsapplications in the presence of moving co-channel sources isaddressed. A generalization of the optimum beamformer based on a statisticalmodel accounting for source movement is proposed. The new methodis easily implemented and is shown to offer dramatic improvements overconventional optimum beamforming for moving sources under a varietyof operating conditions.

Average performance analysis of circular and hyperbolic geolocation

A comparative performance analysis of four geolocation methods in terms of their theoretical root mean square positioning errors is provided. Comparison is established in two different ways: strict and average. In the strict type, methods are examined for a particular geometric configuration of base stations(BSs) with respect to mobile position, which determines a givennoise profile affecting the respective time-of-arrival (TOA) or timedifference-of-arrival (TDOA) estimates. In the average type, methodsare evaluated in terms of the expected covariance matrix ofthe position error over an ensemble of random geometries, so thatcomparison is geometry independent. Exact semianalytical equationsand associated lower bounds (depending solely on the noiseprofile) are obtained for the average covariance matrix of the positionerror in terms of the so-called information matrix specific toeach geolocation method. Statistical channel models inferred fromfield trials are used to define realistic prior probabilities for therandom geometries. A final evaluation provides extensive resultsrelating the expected position error to channel model parametersand the number of base stations.

Second-order parameter estimation

This work provides a general framework for the design of second-order blind estimators without adopting anyapproximation about the observation statistics or the a prioridistribution of the parameters. The proposed solution is obtainedminimizing the estimator variance subject to some constraints onthe estimator bias. The resulting optimal estimator is found todepend on the observation fourth-order moments that can be calculatedanalytically from the known signal model. Unfortunately,in most cases, the performance of this estimator is severely limitedby the residual bias inherent to nonlinear estimation problems.To overcome this limitation, the second-order minimum varianceunbiased estimator is deduced from the general solution by assumingaccurate prior information on the vector of parameters.This small-error approximation is adopted to design iterativeestimators or trackers. It is shown that the associated varianceconstitutes the lower bound for the variance of any unbiasedestimator based on the sample covariance matrix.The paper formulation is then applied to track the angle-of-arrival(AoA) of multiple digitally-modulated sources by means ofa uniform linear array. The optimal second-order tracker is comparedwith the classical maximum likelihood (ML) blind methodsthat are shown to be quadratic in the observed data as well. Simulationshave confirmed that the discrete nature of the transmittedsymbols can be exploited to improve considerably the discriminationof near sources in medium-to-high SNR scenarios.

ML estimator and hybrid beamformer for multipath and interference mitigation in GNSS receivers

This paper addresses the estimation of the code-phase(pseudorange) and the carrier-phase of the direct signal received from a direct-sequence spread-spectrum satellite transmitter. Thesignal is received by an antenna array in a scenario with interferenceand multipath propagation. These two effects are generallythe limiting error sources in most high-precision positioning applications.A new estimator of the code- and carrier-phases is derivedby using a simplified signal model and the maximum likelihood(ML) principle. The simplified model consists essentially ofgathering all signals, except for the direct one, in a component withunknown spatial correlation. The estimator exploits the knowledgeof the direction-of-arrival of the direct signal and is much simplerthan other estimators derived under more detailed signal models.Moreover, we present an iterative algorithm, that is adequate for apractical implementation and explores an interesting link betweenthe ML estimator and a hybrid beamformer. The mean squarederror and bias of the new estimator are computed for a numberof scenarios and compared with those of other methods. The presentedestimator and the hybrid beamforming outperform the existingtechniques of comparable complexity and attains, in manysituations, the Cramér–Rao lower bound of the problem at hand.

La Misión Indígena San Francisco Solano de Tacaaglé en las tierras fiscales de Formosa (1900-1950)

[spa]La Misión Indígena fue inaugurada en el año 1901, en la zona del río Pilcomayo del Territorio Nacional de Formosa, precisamente al costado de la concesión paraguaya otorgada a Elisa (Elizabeth Alicia) Lynch. Desde entonces, fue trasladada, primero a Tacaaglé en 1902, donde adquirió el nombre de Misión San Francisco Solano, y posteriormente, en 1915, al riacho El Porteño. Los misioneros franciscanos asumieron la tarea de formar a “colonos indígenas” tobas y pilagás para la producción de azúcar. Se analiza la evolución de la Misión franciscana y el impacto de la llegada del Ferrocarril de Formosa a Embarcación (F.C.F.E.). La documentación utilizada se encuentra en la Biblioteca y Archivo Históricos de la Provincia Franciscana de San Miguel, del Museo Conventual de San Carlos Borromeo ubicado en San Lorenzo, Provincia de Santa Fe

Perception of acceleration in motion-in-depth with only monocular and both monocular and binocular information

Observers are often required to adjust actions with objects that change their speed. However, no evidence for a direct sense of acceleration has been found so far. Instead, observers seem to detect changes in velocity within a temporal window when confronted with motion in the frontal plane (2D motion). Furthermore, recent studies suggest that motion-in-depth is detected by tracking changes of position in depth. Therefore, in order to sense acceleration in depth a kind of second-order computation would have to be carried out by the visual system. In two experiments, we show that observers misperceive acceleration of head-on approaches at least within the ranges we used [600-800 ms] resulting in an overestimation of arrival time. Regardless of the viewing condition (only monocular or monocular and binocular), the response pattern conformed to a constant velocity strategy. However, when binocular information was available, overestimation was highly reduced.

La Milícia Nacional de Lleida al Trienni Liberal

En aquest treball d'investigació dedicat a la Milícia Nacional de la ciutat de Lleida durant el Trienni Liberal s'ha pretés estudiar la seva implantació, l'evolució, la dinàmica interna i la composició socioprofessional dels seus membres. La Milícia a l'inici del període liberal va tenir dificultats per formar-se. Aquest fet ens va indicar que no hi havia molt individus amb tendència liberal i que la major part de la població treballava en l'àmbit agrari, o sigui, no hi havia gaire comerç i els individus dedicats a les professionals liberals o no eren molts quantitativament o no tenien massa poder polític i econòmic. Tot i que la consolidació i l'actuació del bàndol reialista va potenciar l'organització de la Milícia a la ciutat lleidatana. Per aturar l'avanç dels seguidors absolutistes, l'abril de l'any 1821 es va crear una nova milícia, aquesta vegada de caire voluntari. La Milícia Local va triomfar perquè la seva principal característica residia en el voluntarietat. Les persones que es van apuntar ho van fer per motius derivats de les seves pròpies conviccions polítiques. Finalment apuntar que la Milícia Nacional a Lleida a les darreries del règim liberal va aconseguir mantenir el poder constitucional fins l'arribada dels Cent Mil Fills de Sant Lluis.

La integración del ferrocarril de alta velocidad en el medio urbano. El caso de Segovia-Guiomar

La llegada del tren de alta velocidad genera oportunidades de dinamización que deben de ser ante todo concretadas a escala local. Los lugares suelen reaccionar desplegando medidas de planificación y gestión para garantizar la mejor integración de la nueva infraestructura, procurar su coherencia con el modelo territorial y el mejor aprovechamiento de la accesibilidad que genera el nuevo tren. En este artículo se estudian las medidas desarrolladas en Segovia a raíz de la implantación del tren de alta velocidad con una estación localizada en la periferia, por lo que tuvieron que desplegarse un buen número de acciones de planificación territorial y gestión de la movilidad. A través del planeamiento municipal se trata de integrar la estación y su entorno al conjunto urbano, con el desarrollo de suelo urbanizable y nueva infraestructura viaria. La gestión de la movilidad pasa inicialmente por la articulación de la estación con el centro urbano a través de servicios de autobuses coordinados con los horarios de los trenes.