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Alcalá de Henares, Spain

Chen J.,Massachusetts Institute of Technology | Hontz E.,Massachusetts Institute of Technology | Moix J.,Massachusetts Institute of Technology | Welborn M.,Massachusetts Institute of Technology | And 4 more authors.
Physical Review Letters | Year: 2012

Theoretical studies of localization, anomalous diffusion and ergodicity breaking require solving the electronic structure of disordered systems. We use free probability to approximate the ensemble-averaged density of states without exact diagonalization. We present an error analysis that quantifies the accuracy using a generalized moment expansion, allowing us to distinguish between different approximations. We identify an approximation that is accurate to the eighth moment across all noise strengths, and contrast this with perturbation theory and isotropic entanglement theory. © 2012 American Physical Society. Source

Siqueira G.M.,Federal University of Maranhao | da Silva J.S.,University of Pernambuco | Bezerra J.M.,University of Pernambuco | e Silva E.F.F.,University of Pernambuco | And 2 more authors.
Revista Brasileira de Engenharia Agricola e Ambiental | Year: 2015

The intrinsic hypothesis is usually the most utilized because it is less restrictive compared to the other hypotheses of the geostatistics, requires only the existence and stationarity of the semivariogram, without any restriction as to the existence of finite variance. The objective of this study was to evaluate the stationarity of humidity data in a Humiluvic Spodosol. Data were collected on a transect containing 128 points, spaced every 3 m. The soil water content was determined in the layers of 0-0.2 m, 0.2-0.4 m and 0.4-0.6 m. Statistical analysis demonstrated that the data presented lognormal frequency distribution. The moisture values varied with signage variations. There was stationarity of the semivariogram for the three studied depths. The analysis of fragments of the transect had stability of mean and semivariogram, confirming that stationarity is much more exception than rule, because the data as a whole also showed semivariograms well defined and without tendency. © 2015, Departamento de Engenharia Agricola - UFCG/Cnpq. All rights reserved. Source

Oton J.,CSIC - National Center for Biotechnology | Sorzano C.O.S.,CSIC - National Center for Biotechnology | Pereiro E.,ALBA Synchrotron Light Source | Cuenca-Alba J.,CSIC - National Center for Biotechnology | And 3 more authors.
Journal of Structural Biology | Year: 2012

Soft X-ray Tomographic (TomoX) microscopy has become a reality in the last years. The resolution range of this technique nicely fits between confocal and electron microscopies and will play a key role in the elucidation of the organization between the molecular and the organelle levels. In fact, it offers the possibility of imaging three-dimensional structures of hydrated biological specimens near their native state without chemical pre-treatment. Ideally, TomoX reconstructs the specimen absorption coefficients from projections of this specimen, but, unfortunately, X-ray micrographs are only an approximation to projections of the specimen, resulting in inaccuracies if a tomographic reconstruction is performed without explicitly incorporating these approximations. In an attempt to mitigate some of these inaccuracies, we develop in this work an image formation model within the approximation of assuming incoherent illumination. © 2012 Elsevier Inc. Source

Fachinotti V.D.,CONICET | Albanesi A.E.,CONICET | Martinez Valle J.M.,Escuela Polytechnic Superior
Computers and Structures | Year: 2015

The Inverse Finite Element Method (IFEM) for degenerate solid shells is introduced. IFEM allows determining the undeformed shape of a body (in this case, a shell-like body) such that it attains a desired shape after large elastic deformations. The model is based on the degenerate solid approach, which enables the use of the standard constitutive laws of Solid Mechanics. First, IFEM is applied to three popular benchmarks for validation purposes. Then, the capabilities of IFEM for inverse design are demonstrated by means of its application to the design of a microvalve. © 2015 Elsevier Ltd. All rights reserved. Source

Freire E.,Escuela Tecnica Superior de Ingenieria | Ponce E.,Escuela Tecnica Superior de Ingenieria | Torres F.,Escuela Polytechnic Superior
Nonlinear Dynamics | Year: 2014

Discontinuous piecewise linear systems with two zones are considered. A general canonical form that includes all the possible configurations in planar linear systems is introduced and exploited. It is shown that the existence of a focus in one zone is sufficient to get three nested limit cycles, independently on the dynamics of the another linear zone. Perturbing a situation with only one hyperbolic limit cycle, two additional limit cycles are obtained by using an adequate parametric sector of the unfolding of a codimension-two focus-fold singularity. © 2014, Springer Science+Business Media Dordrecht. Source

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