Using spatially distributed parameters and multi-response objective functions to solve parameterization of complex applications of semi-distributed hydrological models

Application of semi-distributed hydrological models to large, heterogeneous watersheds deals with several problems. On one hand, the spatial and temporal variability in catchment features should be adequately represented in the model parameterization, while maintaining the model complexity in an acceptable level to take advantage of state-of-the-art calibration techniques. On the other hand, model complexity enhances uncertainty in adjusted model parameter values, therefore increasing uncertainty in the water routing across the watershed. This is critical for water quality applications, where not only streamflow, but also a reliable estimation of the surface versus subsurface contributions to the runoff is needed. In this study, we show how a regularized inversion procedure combined with a multiobjective function calibration strategy successfully solves the parameterization of a complex application of a water quality-oriented hydrological model. The final value of several optimized parameters showed significant and consistentdifferences across geological and landscape features. Although the number of optimized parameters was significantly increased by the spatial and temporal discretization of adjustable parameters, the uncertainty in water routing results remained at reasonable values. In addition, a stepwise numerical analysis showed that the effects on calibration performance due to inclusion of different data types in the objective function could be inextricably linked. Thus caution should be taken when adding or removing data from an aggregated objective function.

Frontshear and backshear instabilities of the mean longshore current

An analytical model based on Bowen and Holman [1989] is used to prove the existence of instabilities due to the presence of a second extremum of the background vorticity at the front side of the longshore current. The growth rate of the so-called frontshear waves depends primarily upon the frontshear but also upon the backshear and the maximum and the width of the current. Depending on the values of these parameters, either the frontshear or the backshear instabilities may dominate. Both types of waves have a cross-shore extension of the order of the width of the current, but the frontshear modes are localized closer to the coast than are the backshear modes. Moreover, under certain conditions both unstable waves have similar growth rates with close wave numbers and angular frequencies, leading to the possibility of having modulated shear waves in the alongshore direction. Numerical analysis performed on realistic current profiles confirm the behavior anticipated by the analytical model. The theory has been applied to a current profile fitted to data measured during the 1980 Nearshore Sediment Transport Studies experiment at Leadbetter Beach that has an extremum of background vorticity at the front side of the current. In this case and in agreement with field observations, the model predicts instability, whereas the theory based only on backshear instability fai led to do so.

On the approximation of the subgrid scale for systems of equations

Postprint (published version)

Trust region versus line search for computing the optical flow

We consider the numerical treatment of the optical flow problem by evaluating the performance of the trust region method versus the line search method. To the best of our knowledge, the trust region method is studied here for the first time for variational optical flow computation. Four different optical flow models are used to test the performance of the proposed algorithm combining linear and nonlinear data terms with quadratic and TV regularization. We show that trust region often performs better than line search; especially in the presence of non-linearity and non-convexity in the model.

Minimal requirements for parameters to be used for the development of predictive models for microbial source tracking. The example of the pair somatic coliphages and phages infecting Bacteroides

Several methods and approaches for measuring parameters to determine fecal sources of pollution in water have been developed in recent years. No single microbial or chemical parameter has proved sufficient to determine the source of fecal pollution. Combinations of parameters involving at least one discriminating indicator and one universal fecal indicator offer the most promising solutions for qualitative and quantitative analyses. The universal (nondiscriminating) fecal indicator provides quantitative information regarding the fecal load. The discriminating indicator contributes to the identification of a specific source. The relative values of the parameters derived from both kinds of indicators could provide information regarding the contribution to the total fecal load from each origin. It is also essential that both parameters characteristically persist in the environment for similar periods. Numerical analysis, such as inductive learning methods, could be used to select the most suitable and the lowest number of parameters to develop predictive models. These combinations of parameters provide information on factors affecting the models, such as dilution, specific types of animal source, persistence of microbial tracers, and complex mixtures from different sources. The combined use of the enumeration of somatic coliphages and the enumeration of Bacteroides-phages using different host specific strains (one from humans and another from pigs), both selected using the suggested approach, provides a feasible model for quantitative and qualitative analyses of fecal source identification.

Equidistribution of Fekete Points on the Sphere

Fekete points are the points that maximize a Vandermonde-type determinant that appears in the polynomial Lagrange interpolation formula. They are well suited points for interpolation formulas and numerical integration. We prove the asymptotic equidistribution of Fekete points in the sphere. The way we proceed is by showing their connection to other arrays of points, the so-called Marcinkiewicz-Zygmund arrays and interpolating arrays, that have been studied recently.

Comments on "On the relationship between fractal dimension and the performance of multi-resonant dipole antennas using Koch curves"

Comentaris referits a l'article següent: K. J. Vinoy, J. K. Abraham, and V. K. Varadan, “On the relationshipbetween fractal dimension and the performance of multi-resonant dipoleantennas using Koch curves,” IEEE Transactions on Antennas and Propagation, 2003, vol. 51, p. 2296–2303.

SAR Interferometric phase noise reduction using wavelet transform

The problem of synthetic aperture radar interferometric phase noise reduction is addressed. A new technique based on discrete wavelet transforms is presented. This technique guarantees high resolution phase estimation without using phase image segmentation. Areas containing only noise are hardly processed. Tests with synthetic and real interferograms are reported.

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.

Manipulació geomètrica dels blocs d'AutoCAD

Aquest text és un recull de procediments per inserir els blocs d'AutoCAD de forma més eficient, en la resolució de problemes prèviament tipificats: la PRIMERA PART descriu protocols d'actuació que l'usuari haurà d'aplicar manualment, mentre que la SEGONA PART ofereix rutines programades en AutoLISP i VisualLISP que l'eximiran d'aquesta obligació.Si ho deixéssim aquí, però, podria semblar que els mateixos mètodes manuals presentats en primer lloc són després els que AutoLISP automatitza; per això convé aclarir que la problemàtica de la PRIMERA PART, tot i que pròxima a la de la SEGONA, és diferent i reprodueix el contingut d'una monografia (BLOCS I GEOMETRIA: 5 EXERCICIS COMENTATS) que forma part del material de suport a l'assignatura ELEMENTS DE CAD, impartida per l'autor en l'ETS d'Enginyeria de Telecomunicació de Barcelona i que té per objecte cobrir el buit bibliogràfic que es detectava en el vessant geomètric de la inserció de blocs, a diferència del que s'ocupa de l'estructura de dades més adient en cada context (incrustació de dibuixos amb INSERT versus vinculació mitjançant REFX), més profusament tractat, proposant una sistematització tipològica dels casos on l'escala és funció lineal d'una distància.La SEGONA PART va més enllà i amplia el repertori d'AutoCAD amb les ordres GINSERT, RATREDIT, INSERTOK, INS2D, INS3D, BLOQUEOK, DESCOMPOK, DEF-TRANSF, APL-TRANSF-V i APL-TRANSF-N, de les quals INS2D i INS3D (INSERTOK és una versió simplificada de INS2D, per a blocs sense atributs) són l'aportació més innovadora i que més lluny porta les potencialitats de la inserció de blocs: resumint-ho en una frase, es tracta d’aconseguir que la inserció d’un bloc (que pot ser l’original, un bloc constituït per una inserció de l’original o un de constituït per la inserció del precedent) s’encabeixi en un marc prèviament establert, a semblança de les ordres ESCALA o GIRA, que mitjançant l'opció Referencia apliquen als objectes seleccionats la transformació d'escalat o de rotació necessària per tal que un element de referència assoleixi una determinada grandària o posició. Tot i que, per identificar amb encert el nucli del problema, serà inevitable introduir una reflexió: quan s’ha tingut la precaució de referir un bloc 2D a un quadrat unitari ortogonal, inserir-lo de manera que s’adapti a qualsevol marc rectangular establert en el dibuix és immediat, però ja no ho és tant concatenar insercions de manera que, a més d’una combinació simple de escalat, gir i translació, l’operació dugui implícita una transformació de cisallament. Perquè és clar que si inserim el bloc girat i convertim la inserció en un bloc que al seu torn tornem a inserir, ara però amb escalat no uniforme, el transformat del quadrat de referència primitiu serà un paral·lelogram, però el problema és: dibuixat un marc romboïdal concret, ¿quin gir caldrà donar a la primera inserció, i quin gir i factors d’escala caldrà aplicar a la segona perquè el quadrat de referència s’adapti al marc? El problema es complica si, a més, volem aprofitar el resultat de la primera inserció per a d’altres paral·lelograms, organitzant un sistema no redundant de insercions intermèdies. Doncs bé: INS2D i INS3D donen satisfacció a aquestes qüestions (la segona ja no contempla l'encaix en un paral·lelogram, sinó en un paral·lelepípede) i són aplicables a blocs proveïts d’atributs, no només de tipus convencional (els continguts en el pla de base del bloc, únics de funcionament garantit amb l’ordre INSERT), sinó també dels situats i orientats lliurement.

Minimal requirements for parameters to be used for the development of predictive models for microbial source tracking. The example of the pair somatic coliphages and phages infecting Bacteroides

Several methods and approaches for measuring parameters to determine fecal sources of pollution in water have been developed in recent years. No single microbial or chemical parameter has proved sufficient to determine the source of fecal pollution. Combinations of parameters involving at least one discriminating indicator and one universal fecal indicator offer the most promising solutions for qualitative and quantitative analyses. The universal (nondiscriminating) fecal indicator provides quantitative information regarding the fecal load. The discriminating indicator contributes to the identification of a specific source. The relative values of the parameters derived from both kinds of indicators could provide information regarding the contribution to the total fecal load from each origin. It is also essential that both parameters characteristically persist in the environment for similar periods. Numerical analysis, such as inductive learning methods, could be used to select the most suitable and the lowest number of parameters to develop predictive models. These combinations of parameters provide information on factors affecting the models, such as dilution, specific types of animal source, persistence of microbial tracers, and complex mixtures from different sources. The combined use of the enumeration of somatic coliphages and the enumeration of Bacteroides-phages using different host specific strains (one from humans and another from pigs), both selected using the suggested approach, provides a feasible model for quantitative and qualitative analyses of fecal source identification.

Trust region versus line search for computing the optical flow

We consider the numerical treatment of the optical flow problem by evaluating the performance of the trust region method versus the line search method. To the best of our knowledge, the trust region method is studied here for the first time for variational optical flow computation. Four different optical flow models are used to test the performance of the proposed algorithm combining linear and nonlinear data terms with quadratic and TV regularization. We show that trust region often performs better than line search; especially in the presence of non-linearity and non-convexity in the model.

Bidding support for computational resources

Peer-reviewed

Modelo de comportamiento en sevicio para estructuras reticulares de hormigón. Parte I: Descripción del modelo y ejemplos de aplicación

A general method for instantaneous and time-dependent serviceability analysis of plane concrete frames is presented. The methodology is based in an extension of the classic matrix formulation for bars. The main aspects influencing the behaviour of the structural concrete are considered: cracking, creep, shrinkage or prestress losses. To simulate the effect of cracking a smeared model (developed in Part II) based on the modification of the tensile branch of the concrete stress-strain relationship is adopted. The general approach considered permits the application to different materials and constitutive laws. Sequential construction (sectional and structural), incorporation of reinforcement, consideration of the loads history; placing and removing shores, and restraining or releasing in boundary conditions are considered. Some examples are included to highlight the capabilities of the model

Modelo de comportamiento en sevicio para estructuras reticulares de hormigón. Parte II: Diagrama tensión- deformación para elementos fisurados a flexión

This paper presents a general methodology to adjust the coefficients defining a constitutive law for tensioned concrete to simulate, under serviceability conditions, the behaviour of cracked concrete members subjected to simple and combined bending (with axial compressive forces). Although experimental results could be used to obtain the mentioned objective, in this work the models proposed by the CEB are utilized, in order to obtain more general conclusions not subjected to specific experiments. A numerical parametrical analysis is performed to determine the more significant variables influencing the Tension-Stiffening effect and simplified closed-form solution is derived for rectangular sections. A systematic study has been to verify the ability of the method to simulate long-term effects. The methodology can be implemented as an initial process in a general model of analysis like the one presented in Part I