Ontologies: a review

En aquest paper, analitzem les principals ontologies amb la finalitat de dibuixar un panorama general d'una de les eines més utilitzades en l'estructuració del coneixement. En primer lloc, presentem una àmplia descripció de les cinc ontologies més difoses entre la comunitat científica dedicada a la gestió de la informació. Seguidament, repassem breument algunes de les eines de gestió que s'utilitzen per crear i actualitzar ontologies. I, finalment, presentem algunes conclusions en relació a la selecció d'una ontologia i d'un sistema de gestió per a la seva utilització en el marc dels projectes vigents del grup IULATERM.

Sistemes d'extracció automàtica de (candidats a) termes: estat de la qüestió

Des de l'aparició de TERMINO l'any 1990 fins avui dia s'han portat a terme una sèrie de projectes per dissenyar diferents tipus d'extractors automàtics de terminologia, però malgrat la gran quantitat d'estudis que s'estan realitzant en aquesta línia, els resultats no són del tot satisfactoris. Aquest article presenta una anàlisi dels principals sistemes d'extracció automàtica de terminologia amb la finalitat de dibuixar un panorama general de l'estat de la qüestió. L'estudi comença amb la descripció de diversos sistemes d'extracció de terminologia; en el segon apartat, es comparen els diferents sistemes. L'informe finalitza amb unes conclusions sobre els sistemes analitzats i sobre els criteris que podrien guiar una proposta d'un sistema integrador d'extracció de terminologia.

10 anys del Corpus de l'IULA

En aquest paper, es presenten els criteris de treball que s'han seguit durant els 10 anys en què s'ha anat constituint el corpus de l'IULA. S'exposa l'estat de les dades del corpus, els recursos lèxics utilitzats per al tractament de les dades (diccionaris i etiquetaris) i les eines constituïdes o adaptades. Es dedica especial atenció a la documentació de la cadena de treball de processament del corpus, des de l'adquisició dels textos en format electrònic fins a la seva incorporació definitiva al corpus.

El Corpus de l'IULA: descripció

El principal projecte de recerca desenvolupat a l'Institut Universitari de Lingüística Aplicada (IULA) de la Universitat Pompeu Fabra és el projecte de Llenguatges especialitzats, sota el qual s'aglutina la totalitat dels investigadors pertanyents a aquest centre. És en aquest marc de recerca on es duu a terme la constitució d'un corpus plurilingüe (català, castellà, francès, anglès i alemany), especialitzat en les àrees del dret, l'economia, la informàtica, el medi ambient i la medicina. En aquest article es descriuen els criteris que s'han tingut en compte per al disseny d'aquest recurs lingüístic i cada una de les fases de desenvolupament que s'han seguit. El resultat de diferents estadis en el procés d'elaboració del corpus es mostra en un conjunt d'annexos al final de l'article, on s'incorpora, a més, una síntesi de l'estat actual del projecte, periòdicament actualitzada.

Marcatge estructural i morfosintàctic del Corpus Tècnic amb l'estàndard SGML

L'edició de textos fent ús de mitjans informàtics ha comportat avantatges i inconvenients. Mentre que ha fet molt accessible l'edició acurada de textos també ha provocat tot un seguit de problemes, un del quals és la dificultat de compartir recursos.Per altra banda, la lingüística necessita emprar corpus voluminosos per conèixer amb més precisió i fonament el comportament real del llenguatge. És evident que l'obtenció i consegüent preparació d'un corpus per a la seva explotació esdevé un procés costós en temps i recursos, motiu pel qual és força atractiu i gairebé necessari compartir aquest material de recerca amb altres organitzacions. En aquest treball s'examinen les diferents propostes d'aplicació de l'estàndard SGML (Standard Generalized Markup Language) en la constitució de corpus textuals per a la recerca lingüística, amb èmfasi especial en les solucions proposades a l'Institut Universitari de Lingüística Aplicada de la Universitat Pompeu Fabra.

La Cantata a Europa a l’entorn del segle XVIII : música da camera italiana del Barroc tardà

La cantata da camera italiana va tenir el seu màxim esplendor durant el segle XVII i principis del XVIII. A partir de l’anàlisi d’obres de quatre compositors (Albinoni, Scarlatti, Caldara i Vivaldi) s’estudia l’evolució d’aquesta forma, els seus orígens i la seva interpretació, fent especial atenció al text i a l’ornamentació.

Exploring the high frequency emission of radio loud X-ray binaries

We report millimetre-wave continuum observations of the X-ray binaries Cygnus X-3, SS 433, LSI+61 303, Cygnus X-1 and GRS 1915+105. The observations were carried out with the IRAM 30 m-antenna at 250 GHz (1.25 mm) from 1998 March 14 to March 20. These millimetre measurements are complemented with centimetre observations from the Ryle Telescope, at 15 GHz (2.0 cm) and from the Green Bank Interferometer at 2.25 and 8.3 GHz (13 and 3.6 cm). Both Cygnus X-3 and SS 433 underwent moderate flaring events during our observations, whose main spectral evolution properties are described and interpreted. A significant spectral steepening was observed in both sources during the flare decay, that is likely to be caused by adiabatic expansion, inverse Compton and synchrotron losses. Finally, we also report 250 GHz upper limits for three additional undetected X-ray binary stars: LSI+65 010, LSI+61 235 and X Per.

Statistical analysis and modelling of weather radar beam propagation conditions in the Po Valley (Italy)

Ground clutter caused by anomalous propagation (anaprop) can affect seriously radar rain rate estimates, particularly in fully automatic radar processing systems, and, if not filtered, can produce frequent false alarms. A statistical study of anomalous propagation detected from two operational C-band radars in the northern Italian region of Emilia Romagna is discussed, paying particular attention to its diurnal and seasonal variability. The analysis shows a high incidence of anaprop in summer, mainly in the morning and evening, due to the humid and hot summer climate of the Po Valley, particularly in the coastal zone. Thereafter, a comparison between different techniques and datasets to retrieve the vertical profile of the refractive index gradient in the boundary layer is also presented. In particular, their capability to detect anomalous propagation conditions is compared. Furthermore, beam path trajectories are simulated using a multilayer ray-tracing model and the influence of the propagation conditions on the beam trajectory and shape is examined. High resolution radiosounding data are identified as the best available dataset to reproduce accurately the local propagation conditions, while lower resolution standard TEMP data suffers from interpolation degradation and Numerical Weather Prediction model data (Lokal Model) are able to retrieve a tendency to superrefraction but not to detect ducting conditions. Observing the ray tracing of the centre, lower and upper limits of the radar antenna 3-dB half-power main beam lobe it is concluded that ducting layers produce a change in the measured volume and in the power distribution that can lead to an additional error in the reflectivity estimate and, subsequently, in the estimated rainfall rate.

Enhanced radar precipitation estimates using a combined clutter and beam blockage correction technique

Weather radar observations are currently the most reliable method for remote sensing of precipitation. However, a number of factors affect the quality of radar observations and may limit seriously automated quantitative applications of radar precipitation estimates such as those required in Numerical Weather Prediction (NWP) data assimilation or in hydrological models. In this paper, a technique to correct two different problems typically present in radar data is presented and evaluated. The aspects dealt with are non-precipitating echoes - caused either by permanent ground clutter or by anomalous propagation of the radar beam (anaprop echoes) - and also topographical beam blockage. The correction technique is based in the computation of realistic beam propagation trajectories based upon recent radiosonde observations instead of assuming standard radio propagation conditions. The correction consists of three different steps: 1) calculation of a Dynamic Elevation Map which provides the minimum clutter-free antenna elevation for each pixel within the radar coverage; 2) correction for residual anaprop, checking the vertical reflectivity gradients within the radar volume; and 3) topographical beam blockage estimation and correction using a geometric optics approach. The technique is evaluated with four case studies in the region of the Po Valley (N Italy) using a C-band Doppler radar and a network of raingauges providing hourly precipitation measurements. The case studies cover different seasons, different radio propagation conditions and also stratiform and convective precipitation type events. After applying the proposed correction, a comparison of the radar precipitation estimates with raingauges indicates a general reduction in both the root mean squared error and the fractional error variance indicating the efficiency and robustness of the procedure. Moreover, the technique presented is not computationally expensive so it seems well suited to be implemented in an operational environment.

Proposed gravitational wave observatory based on solid elastic spheres

Spherical gravitational wave (GW) detectors offer a wealth of so far unexplored possibilities to detect gravitational radiation. We find that a sphere can be used as a powerful testbed for any metric theory of gravity, not only general relativity as considered so far, by making use of a deconvolution procedure for all the electric components of the Riemann tensor. We also find that the spheres cross section is large at two frequencies, and advantageous at higher frequencies in the sense that a single antenna constitutes a real xylophone in its own. Proposed GW networks will greatly benefit from this. The main features of a two large sphere observatory are reported.

A two-dimensional doppler-radiometer for earth observation

Compared to synthetic aperture radars (SARs), the angular resolution of microwave radiometers is quite poor. Traditionally, it has been limited by the physical size of the antenna. However, the angular resolution can be improved by means of aperture synthesis interferometric techniques. A narrow beam is synthesized during the image formation processing of the cross-correlations measured at zero-lag between pairs of signals collected by an array of antennas. The angular resolution is then determined by the maximum antenna spacing normalized to the wavelength (baseline). The next step in improving the angular resolution is the Doppler-Radiometer, somehow related to the super-synthesis radiometers and the Radiometer-SAR. This paper presents the concept of a three-antenna Doppler-Radiometer for 2D imaging. The performance of this instrument is evaluated in terms of angular/spatial resolution and radiometric sensitivity, and an L-band illustrative example is presented.

High-SNR analytical performance of spatial multiplexing MIMO systems with CSI

In this paper, we investigate the average andoutage performance of spatial multiplexing multiple-input multiple-output (MIMO) systems with channel state information at both sides of the link. Such systems result, for example, from exploiting the channel eigenmodes in multiantenna systems. Dueto the complexity of obtaining the exact expression for the average bit error rate (BER) and the outage probability, we deriveapproximations in the high signal-to-noise ratio (SNR) regime assuming an uncorrelated Rayleigh flat-fading channel. Moreexactly, capitalizing on previous work by Wang and Giannakis, the average BER and outage probability versus SNR curves ofspatial multiplexing MIMO systems are characterized in terms of two key parameters: the array gain and the diversity gain. Finally, these results are applied to analyze the performance of a variety of linear MIMO transceiver designs available in the literature.

Capacity of MIMO Channels: asymptotic evaluation under correlated fading

This paper investigates the asymptotic uniform power allocation capacity of frequency nonselective multiple-inputmultiple-output channels with fading correlation at either thetransmitter or the receiver. We consider the asymptotic situation,where the number of inputs and outputs increase without boundat the same rate. A simple uniparametric model for the fadingcorrelation function is proposed and the asymptotic capacity perantenna is derived in closed form. Although the proposed correlationmodel is introduced only for mathematical convenience, itis shown that its shape is very close to an exponentially decayingcorrelation function. The asymptotic expression obtained providesa simple and yet useful way of relating the actual fadingcorrelation to the asymptotic capacity per antenna from a purelyanalytical point of view. For example, the asymptotic expressionsindicate that fading correlation is more harmful when arising atthe side with less antennas. Moreover, fading correlation does notinfluence the rate of growth of the asymptotic capacity per receiveantenna with high Eb /N0.

The IST METRA Project

This article summarizes the main achievementsof the Multi-Element Transmit andReceive Antennas (METRA) Project, an ISTresearch and technological development project carried out between January 2000 and June 2001 by Universitat Politècnica de Catalunya, the Center for Personkommunikation of Aalborg University, Nokia Networks, Nokia Mobile Phones, and Vodafone Group Research and Development.The main objective of METRA was the performanceevaluation of multi-antenna terminals incombination with adaptive antennas at the basestation in UMTS communication systems. 1 AMIMO channel sounder was developed that providedrealistic multi-antenna channel measurements.Using these measured data, stochasticchannel models were developed and properly validated.These models were also evaluated inorder to estimate their corresponding channelcapacity. Different MIMO configurations andprocessing schemes were developed for both theFDD and TDD modes of UTRA, and their linkperformance was assessed. Performance evaluationwas completed by system simulations thatillustrated the benefits of MIMO configurationsto the network operator. Implementation cost vs.performance improvement was also covered bythe project, including the base station and terminalmanufacturer and network operator viewpoints.Finally, significant standards contributionswere generated by the project and presented to the pertinent 3GPP working groups.

Smart antennas in software radio base stations

The application of adaptive antenna techniques to fixed-architecture base stations has been shown to offer wide-ranging benefits, including interference rejection capabilities or increased coverage and spectral efficiency.Unfortunately, the actual implementation ofthese techniques to mobile communication scenarios has traditionally been set back by two fundamental reasons. On one hand, the lack of flexibility of current transceiver architectures does not allow for the introduction of advanced add-on functionalities. On the other hand, theoften oversimplified models for the spatiotemporal characteristics of the radio communications channel generally give rise toperformance predictions that are, in practice, too optimistic. The advent of software radio architectures represents a big step toward theintroduction of advanced receive/transmitcapabilities. Thanks to their inherent flexibilityand robustness, software radio architecturesare the appropriate enabling technology for theimplementation of array processing techniques.Moreover, given the exponential progression ofcommunication standards in coexistence andtheir constant evolution, software reconfigurabilitywill probably soon become the only costefficientalternative for the transceiverupgrade. This article analyzes the requirementsfor the introduction of software radio techniquesand array processing architectures inmultistandard scenarios. It basically summarizesthe conclusions and results obtained withinthe ACTS project SUNBEAM,1 proposingalgorithms and analyzing the feasibility ofimplementation of innovative and softwarereconfigurablearray processing architectures inmultistandard settings.