Spectral sparsification

We survey recent literature focused on the following spectral sparsification question: Given an integer n and > 0, does there exist a function N(n; ) such that for every collection of C1; : : : ;Cm of n n real symmetric positive semidefinite matrices whose sum is the identity, there exists a weighted subset of size N(n; ) whose sum has eigenvalues lying between 1 and 1 + ? We present the algorithms for solving this problem given in [4, 8, 10]. These algorithms obtain N(n; ) = O(n= 2), which is optimal up to constant factors, through use of the barrier method, a proof technique involving potential functions which control the locations of the eigenvalues of a matrix under certain matrix updates. We then survey the applications of this sparsification result and its proof techniques to graph sparsification [4, 10], low-rank matrix approximation [8], and estimating the covariance of certain distributions of random matrices [32, 26]. We end our survey by examining a multivariate generalization of the barrier method used in Marcus, Spielman, and Srivastava’s recent proof [19] of the Kadison-Singer conjecture

Long-range correlations and trends in Colombian seismic time series

We study long-range correlations and trends in time series extracted from the data of seismic events occurred from 1973 to 2011 in a rectangular region that contains mainly all the continental part of Colombia. The long-range correlations are detected by the calculation of the Hurst exponents for the time series of interevent intervals, separation distances, depth differences and magnitude differences. By using a modification of the classical $R/S$ method that has been developed to detect short-range correlations in time series, we find the existence of persistence for all the time series considered except for magnitude differences. We find also, by using the $DFA$ until the third order, that the studied time series are not influenced by trends. Additionally, an analysis of the Hurst exponent as a function of the number of events in the time and the maximum window size is presented.Comment: 21 pages, 6 figures, 2 figures added, types corrected, accepted to be published in Physica

Poly-Harmonic Distortion Model Extraction in Charge-Controlled One-Port Devices

A charge-controlled, one-port device is used to describe and discuss the extraction procedure of a Poly-Harmonic Distortion (PHD) model in detail. For this case, both voltage and current waveforms are shown to be enough to fully characterize the PHD model. It is also shown that all the information specifically required for this PHD model definition can be stored in the Fourier coefficients of the incremental conductance and capacitance. The results are validated by comparing them with those obtained using a commercial circuit simulation tool.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Equivalent Circuit Modelling of Non-Symmetric Reciprocal Lossy Electromagnetic Structures

Lattice-network-based equivalent circuits of lossy symmetric reciprocal electromagnetic structures have shown superior performance when compared to other topologies like the T- or PI- networks. This is due to the realizability of their elements and the orthogonal-mode decomposition, which, in most cases, provides a deep physical insight into the behaviour of the modelled structure. The aim of this contribution is to provide a short description of these equivalent circuits and to compare their performances by modelling a misaligned complementary strip-slot element.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Marie Sklodowska-Curie grant agreement No 706334. Spanish Ministerio de Economía y Competitividad and the European Regional Development Funds under Grants TEC2016-76070-CR3-2-R and TEC2016-76070-CR3-3-R (ADDMATE)

On the Phase Response and Radiation Efficiency of the Complementary Strip-Slot as an Array Element

The complementary strip-slot element is a broadlymatched microstrip radiator that has been used to design innovative series-fed arrays. It consists of a microstrip series-fed slot that have its complementary stub on the layer of the microstrip and aligned to the slot. In this contribution, the influence of the strip and slot geometry on its performance is studied through the analysis of four different designs. The obtained results highlight the possibility of controlling the radiation efficiency or the phase response, without compromising the broad matching. Therefore, potential series-fed arrays built with this element can exploit this feature to set the magnitude and phase of the excitations with certain flexibility.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by the Spanish Ministerio de Ciencia e Innovaci ´on (Programa Consolider-Ingenio 2010) under Grant CSD2008-00066, EME

Possibilities and limits of prospective GIS land cover modelling--a compared case study: Garrotxes (France) and Alta Alpujarra Granadina (Spain)

International audienceThis study focuses on the possibilities and the limits of a prospective GIS land cover modelling applied to two case studies (France and Spain). The methodology, based on available GIS tools, consists of using earlier land cover maps and relevant environmental factors (calibration data) to model actual, known land cover to validate the model. The model aggregates Markov chain analysis for time prediction and multi-critera evaluation, multi-objective evaluation and cellular automata to perform spatial contiguity of modelled land cover scores. The first results give an accurate, pixel by pixel prediction rate of approximately 75%. An important issue of this study consists of analysing prediction residues to improve the model

Modelos de simulacion espacio-temporal y teledeteccion : el método de la segmentacion para la cartografia cronologica de usos del suelo

National audienceEl desarrollo de modelos para la simulación de dinámicas ambientales o simulaciones geomáticas, persigue trazar las evoluciones del pasado y actuales, extraer los comportamientos espacio-temporales más característicos y prever los cambios futuros o, al menos, construir los escenarios previsibles a corto y medio plazo. Modelizar dinámicas ambientales contribuye a comprender y prever la evolución futura, y la simulación prospectiva proporciona una herramienta de ayuda a la decisión para la gestión ambiental. Las simulaciones geomáticas se apoyan en bases de datos espacio-temporales en cuyo proceso de elaboración tienen un papel fundamental la Teledetección aérea y de satélite. El método de clasificación por segmentación se está aplicando a ortofotografías aéreas, como método alternativo al clásico de fotointerpretación manual. En este trabajo se muestran los resultados de la construcción de una serie cronológica de usos del suelo en los Pirineos Orientales franceses. Una segmentación puramente espectral ha sido aplicada a la BD Ortho del IGN de 2004 y a la fotografía aérea escaneada y posteriormente ortorectificada más antigua (1980, pancromática). Se explica su puesta en práctica y se discuten los resultados obtenidos. En conclusión, indicamos que la automatización del método permite agilizar la etapa de detección de unidades espaciales homogéneas y su asignación de atributos

Obtaining quasi-static models using a frequency domain extraction methodology

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”This contribution illustrates how a realistic nonlinear quasi-static model for FET-type devices can be extracted using an original frequency domain extraction technique. An ideal ‘made-up’ device is built from the measured bias dependence of a GaN medium power device. This ideal device is excited by two ideal voltage sources and its response (drain current) is used to illustrate how the extraction procedure can separate conduction and displacement current components provided the total current spectrum (or, alternatively, waveform) and control voltages are known.This work has been supported by the Junta de Andalucía under Grant (TIC2012-1237). Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

A Methodological Framework for Evaluating Uncertainty in Hydrodynamic Models

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

From Collapse to Freezing in Random Heteropolymers

We consider a two-letter self-avoiding (square) lattice heteropolymer model of N_H (out ofN) attracting sites. At zero temperature, permanent links are formed leading to collapse structures for any fraction rho_H=N_H/N. The average chain size scales as R = N^{1/d}F(rho_H) (d is space dimension). As rho_H --> 0, F(rho_H) ~ rho_H^z with z={1/d-nu}=-1/4 for d=2. Moreover, for 0 < rho_H < 1, entropy approaches zero as N --> infty (being finite for a homopolymer). An abrupt decrease in entropy occurs at the phase boundary between the swollen (R ~ N^nu) and collapsed region. Scaling arguments predict different regimes depending on the ensemble of crosslinks. Some implications to the protein folding problem are discussed.Comment: 4 pages, Revtex, figs upon request. New interpretation and emphasis. Submitted to Europhys.Let