Cooperació i teoria de jocs, el programari lliure o el #15m, dos exemples per l'universitat

Xerrada de cloenda de la Setmana internacional d'accés obert 2011 a la UOC, a càrrec de l'advocat Josep Jover. Per què les estratègies altruistes guanyen les egoistes en el programari lliure i en el #15m? El moviment #15m, igual que el programari, a diferència dels béns materials, no es pot posseir, ja que en pot gaudir (formant-ne part) un nombre indeterminat de persones sense que per això hagi de privar ningú de tenir-lo al seu torn. I això porta a girar com un mitjó la manera com manegen la informació les universitats, i quina és la missió de la universitat en la nova societat. En el futur immediat, valorarem les universitats no per la informació que guarden, que fora sempre serà millor i més extensa, sinó per la capacitat de crear masses crítiques, sia de recerca de coneixement, de capacitació humana, d'enllaç entre iguals... Les universitats hauran d'implantar el model o quedaran relegades.

Linear and nonlinear terrain deformation maps from a reduced set of interferometric SAR images

In this paper, an advanced technique for the generation of deformation maps using synthetic aperture radar (SAR) data is presented. The algorithm estimates the linear and nonlinear components of the displacement, the error of the digital elevation model (DEM) used to cancel the topographic terms, and the atmospheric artifacts from a reduced set of low spatial resolution interferograms. The pixel candidates are selected from those presenting a good coherence level in the whole set of interferograms and the resulting nonuniform mesh tessellated with the Delauney triangulation to establish connections among them. The linear component of movement and DEM error are estimated adjusting a linear model to the data only on the connections. Later on, this information, once unwrapped to retrieve the absolute values, is used to calculate the nonlinear component of movement and atmospheric artifacts with alternate filtering techniques in both the temporal and spatial domains. The method presents high flexibility with respect to the required number of images and the baselines length. However, better results are obtained with large datasets of short baseline interferograms. The technique has been tested with European Remote Sensing SAR data from an area of Catalonia (Spain) and validated with on-field precise leveling measurements.

Sea state effect on the sea surface emissivity at L-band

In May 1999, the European Space Agency (ESA) selected the Earth Explorer Opportunity Soil Moisture and Ocean Salinity (SMOS) mission to obtain global and frequent soil moisture and ocean salinity maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L-band two-dimensional aperture synthesis radiometer with multiangular observation capabilities. At L-band, the brightness temperature sensitivity to the sea surface salinity (SSS) is low, approximately 0.5 K/psu at 20/spl deg/C, decreasing to 0.25 K/psu at 0/spl deg/C, comparable to that to the wind speed /spl sim/0.2 K/(m/s) at nadir. However, at a given time, the sea state does not depend only on local winds, but on the local wind history and the presence of waves traveling from far distances. The Wind and Salinity Experiment (WISE) 2000 and 2001 campaigns were sponsored by ESA to determine the impact of oceanographic and atmospheric variables on the L-band brightness temperature at vertical and horizontal polarizations. This paper presents the results of the analysis of three nonstationary sea state conditions: growing and decreasing sea, and the presence of swell. Measured sea surface spectra are compared with the theoretical ones, computed using the instantaneous wind speed. Differences can be minimized using an "effective wind speed" that makes the theoretical spectrum best match the measured one. The impact on the predicted brightness temperatures is then assessed using the small slope approximation/small perturbation method (SSA/SPM).

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.

A model of the wind direction signature in the Stokes emission vector from the ocean surface at microwave frequencies

This paper presents a model of the Stokes emission vector from the ocean surface. The ocean surface is described as an ensemble of facets with Cox and Munk's (1954) Gram-Charlier slope distribution. The study discusses the impact of different up-wind and cross-wind rms slopes, skewness, peakedness, foam cover models and atmospheric effects on the azimuthal variation of the Stokes vector, as well as the limitations of the model. Simulation results compare favorably, both in mean value and azimuthal dependence, with SSM/I data at 53° incidence angle and with JPL's WINDRAD measurements at incidence angles from 30° to 65°, and at wind speeds from 2.5 to 11 m/s.

Polarimetric radar interferometry for improved mine detection and surface clutter rejection

A recently developed technique, polarimetric radar interferometry, is applied to tackle the problem of the detection of buried objects embedded in surface clutter. An experiment with a fully polarimetric radar in an anechoic chamber has been carried out using different frequency bands and baselines. The processed results show the ability of this technique to detect buried plastic mines and to measure their depth. This technique enables the detection of plastic mines even if their backscatter response is much lower than that of the surface clutter.

Maakaasun kuumailmapolton teoria ja koelaitteiston suunnittelu

Tässä diplomityössä on tarkasteltu maakaasun kuumailmapolton teoriaa ja suunniteltu koelaitteisto. Työn alkuosassa on käsitelty maakaasun ominaisuuksia kuumailmapolton polttoaineena. Lisäksi on vertailtu kuumailmapolttoa perinteiseen polttoon. Teoreettinen tarkastelu on painottunut kuumailmapolton toiminnallisiin vaatimuksiin, joiden perusteella koelaitteisto on suunniteltu. Uuden koelaitteiston lähtökohtana on ollut Lappeenrannan teknillisen yliopiston voimalaitostekniikan laboratorion polttolaitteisto, johon on suunniteltu ja rakennettu kuumailmapolton edellyttämät muutokset. Koelaitteistolla tehtäviä maakaasun kuumailmapolttokokeita varten on laadittu koesuunnitelma, mutta koepolttoja ei tämän diplomityön puitteissa ole tehty. Laitteiston toiminta-arvoja on tarkasteltu esimerkkilaskulla, jossa käsitellään tyypillistä maakaasun kuumailmapolton koetilannetta.

Capitals, trajectòries i estratègies: la teoria general dels camps de P. Bourdieu

El model de classes de P. Bourdieu articula la dimensió objectiva —l’estructura de classe— i la dimensió subjectiva —l’acció de classe—. Aquesta anàlisi de classe forma part d’un debat al voltant de la naturalesa de la realitat social, en el qual el punt més important és la connexió del camp de la producció i del camp de la reproducció de subjectes. Bourdieu, en enfasitzar la condició relacional de l’àmbit social, defineix l’acció social com a dependent de l’estructura relacional, en existir una connexió lògica necessària entre la localització dels agents en un conjunt de relacions socials i els seus interessos, objectius i estratègies d’acció. Per tant, per a aquest autor, hi ha una eficàcia estructuradora de l’acció dels agents socials per l’estructura de classe, i es constitueix, així, en una matriu d’acció, o millor dit, en una estructura probabilística de l’acció. És, doncs, fonamental, considerar el paper de l’acció en la construcció de les classes en si, ja que les classes teòriques, agrupacions fictícies que només existeixen sobre el paper, estan predisposades a convertir-se en classes en el sentit marxista del terme. I sols es passa de la classe sobre el paper a clase real a costa d’una labor política de movilització. Així, l’existència de classes, tant en la teoria com en la realitat, és una aposta de lluites en existir un espai social, un espai de diferències, en el qual les classes existeixen en estat virtual, no com quelcom donat, sinó com quelcom que es tracta de construir.

Extreme-value distributions and renormalization group

In the classical theorems of extreme value theory the limits of suitably rescaled maxima of sequences of independent, identically distributed random variables are studied. The vast majority of the literature on the subject deals with affine normalization. We argue that more general normalizations are natural from a mathematical and physical point of view and work them out. The problem is approached using the language of renormalization-group transformations in the space of probability densities. The limit distributions are fixed points of the transformation and the study of its differential around them allows a local analysis of the domains of attraction and the computation of finite-size corrections.

La teoria del codis. Una entrevista a Basil Berstein

En el context d'aquesta monografia dedicada a l'obra del professor Bernstein ens va semblar oportú de comptar amb alguna aportació original de l'autor. Estant a punt de publicar-se la seva obra clàssica principal (ja apareguda quan s'editi aquest número de Temps d'educació ), va sorgir la idea d'una entrevista- una entrevista, en aquest cas, 'epistolar'.