Low-complexity computation of plate eigenmodes with Vekua approximations and the Method of Particular Solutions

This paper extends the Method of Particular Solutions (MPS) to the computation of eigenfrequencies and eigenmodes of plates. Specific approximation schemes are developed, with plane waves (MPS-PW) or Fourier-Bessel functions (MPS-FB). This framework also requires a suitable formulation of the boundary conditions. Numerical tests, on two plates with various boundary conditions, demonstrate that the proposed approach provides competitive results with standard numerical schemes such as the Finite Element Method, at reduced complexity, and with large flexibility in the implementation choices

Blind calibration for compressed sensing by convex optimization

We consider the problem of calibrating a compressed sensing measurement system under the assumption that the decalibration consists in unknown gains on each measure. We focus on {\em blind} calibration, using measures performed on a few unknown (but sparse) signals. A naive formulation of this blind calibration problem, using $\ell_{1}$ minimization, is reminiscent of blind source separation and dictionary learning, which are known to be highly non-convex and riddled with local minima. In the considered context, we show that in fact this formulation can be exactly expressed as a convex optimization problem, and can be solved using off-the-shelf algorithms. Numerical simulations demonstrate the effectiveness of the approach even for highly uncalibrated measures, when a sufficient number of (unknown, but sparse) calibrating signals is provided. We observe that the success/failure of the approach seems to obey sharp phase transitions

De potenties voor een duurzame roerdomppopulatie in het Vijvercomplex van Midden-Limburg (België) en het effect op aangrenzende leefgebieden in België en Nederland; voorspellingen met het simulatiemodel METAPHOR

Voor het Vijvercomplex van Midden-Limburg (België) is recentelijk een plan gemaakt om de oorspronkelijke natuurwaarden van dit gebied te gaan herstellen. Een groot aantal diergroepen zal daarvan gaan profiteren, waaronder allerlei moerasvogels. In ditrapport wordt met een modelstudie berekend wat de gevolgen voor de roerdomp zullen zijn wanneer het gebied wordt hersteld volgens verschillende varianten van het herstelplan. Wanneer de optimale situatie wordt uitgevoerd, zullen er jaarlijks gemiddeld zes paren in het Vijvercomplex kunnen broeden. Dit aantal is niet voldoende om van een duurzame populatie te kunnen spreken. Deze situatie zorgt echter wel voor bijna een verdubbeling van het aantal roerdompen in de omliggende moerasgebieden en verhoogt daarmee de levensvatbaarheid van de roerdomp in de gehele regio

A computer mating service established by a cattle herdbook society

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Reasentar un hábitat vulnerable: teoría versus praxis

Given the vulnerability of urban populations exposed to natural threats, Colombian city councils must find solutions through resettlement processes, so that vulnerable communities, from a physical-natural perspective, can acquire new or “used” land in a safe place. By analyzing projects developed up to now, there is a wrong and biased institutional idea of vulnerability, leading to resettlement policies that do not take the whole concept of habitat into consideration, nor are they oriented towards the improvement quality of life of dwellers. Therefore, this article puts forward a reflection on the critical concepts of this kind of processes before presenting and analyzing resettlement experiences that are taking place in Manizales, Colombia.Ante la vulnerabilidad de las poblaciones urbanas expuestas a amenazas naturales, los municipios colombianos tienen la obligación de plantear soluciones, entre otras, a través de procesos de reasentamiento que consisten en la adquisición por parte de la comunidad vulnerable, de un lugar de vida nuevo o “usado” en un sitio seguro desde el punto de vista físico-natural. Al estudiar los proyectos desarrollados hasta el momento, se observa una visión institucional sesgada y errónea del concepto de vulnerabilidad que lleva a unas políticas de reasentamiento que no tienen en cuenta al hábitat en su acepción más amplia, ni tampoco están orientadas hacia el mejoramiento integral de la calidad de vida de los pobladores. Por consiguiente, el presente escrito plantea, primero, una reflexión sobre los conceptos determinantes en este tipo de procesos, antes de presentar y analizar experiencias de reasentamiento llevadas a cabo en la ciudad de Manizales (Colombia)

Nearfield Acoustic Holography using sparsity and compressive sampling principles

Regularization of the inverse problem is a complex issue when using Near-field Acoustic Holography (NAH) techniques to identify the vibrating sources. This paper shows that, for convex homogeneous plates with arbitrary boundary conditions, new regularization schemes can be developed, based on the sparsity of the normal velocity of the plate in a well-designed basis, i.e. the possibility to approximate it as a weighted sum of few elementary basis functions. In particular, these new techniques can handle discontinuities of the velocity field at the boundaries, which can be problematic with standard techniques. This comes at the cost of a higher computational complexity to solve the associated optimization problem, though it remains easily tractable with out-of-the-box software. Furthermore, this sparsity framework allows us to take advantage of the concept of Compressive Sampling: under some conditions on the sampling process (here, the design of a random array, which can be numerically and experimentally validated), it is possible to reconstruct the sparse signals with significantly less measurements (i.e., microphones) than classically required. After introducing the different concepts, this paper presents numerical and experimental results of NAH with two plate geometries, and compares the advantages and limitations of these sparsity-based techniques over standard Tikhonov regularization.Comment: Journal of the Acoustical Society of America (2012