12,504 research outputs found
Stochastic algorithms for discontinuous multiplicative white noise
Stochastic differential equations with multiplicative noise need a mathematical prescription due to different interpretations of the stochastic integral. This fact implies specific algorithms to perform numerical integrations or simulations of the stochastic trajectories. Moreover, if the multiplicative noise function is not continuous then the standard algorithms cannot be used. We present an explicit algorithm to avoid this problem and we apply it to a well controlled example. Finally, we discuss on the existence of higher-order algorithms for this specific situation
Lattice Boltzmann methods for global linear instability analysis
Modal global linear instability analysis is performed using, for the first time ever, the lattice Boltzmann method (LBM) to analyze incompressible flows with two and three inhomogeneous spatial directions. Four linearization models have been implemented in order to recover the linearized Navier–Stokes equations in the incompressible limit. Two of those models employ the single relaxation time and have been proposed previously in the literature as linearization of the collision operator of the lattice Boltzmann equation. Two additional models are derived herein for the first time by linearizing the local equilibrium probability distribution function. Instability analysis results are obtained in three benchmark problems, two in closed geometries and one in open flow, namely the square and cubic lid-driven cavity flow and flow in the wake of the circular cylinder. Comparisons with results delivered by classic spectral element methods verify the accuracy of the proposed new methodologies and point potential limitations particular to the LBM approach. The known issue of appearance of numerical instabilities when the SRT model is used in direct numerical simulations employing the LBM is shown to be reflected in a spurious global eigenmode when the SRT model is used in the instability analysis. Although this mode is absent in the multiple relaxation times model, other spurious instabilities can also arise and are documented herein. Areas of potential improvements in order to make the proposed methodology competitive with established approaches for global instability analysis are discussed
Government transparency measurement through prioritized distance operators
© 2018 - IOS Press and the authors. All rights reserved. The prioritized induced probabilistic ordered weighted average distance (PIPOWAD) has been developed. This new operator is an extension of the ordered weighted average (OWA) operator that can be used in cases where we have two sets of data that want to be compared. Some of the main characteristics of this new operator are: 1) Not all the decision makers are equally important, so the information needs to be prioritized, 2) The information has a probability to occur and 3) The decision makers can change the importance of the information based in an induced variable. Additionally, characteristics and families of the PIPOWAD operator are presented. Finally, an application of the PIPOWAD operator in order to measure government transparency in Mexico is presented
Implementation of Cali's food system profile as a pedagogical tool for environmental awareness raising
Education in schools can be a key driver for the rescue of the planet and its sustainability, without sacrificing progress. Education that teaches students to understand their active role in these processes, a sustainable use of natural resources, healthy food habits and critical and responsible consumption.
This is a pilot test that takes food as a central theme, generating different cross-cutting activities to generate applied knowledge in students, greater awareness of its environmental, socioeconomic and health impacts, and the development of a critical and vindicating spirit in the face of ecological and social problems and the promotion of responsibility and collaboration for their solution
Time domain reconstruction of sound speed and attenuation in ultrasound computed tomography using full wave inversion
Ultrasound computed tomography (USCT) is a non-invasive imaging technique that provides information
about the acoustic properties of soft tissues in the body, such as the speed of sound (SS) and
acoustic attenuation (AA). Knowledge of these properties can improve the discrimination between
benign and malignant masses, especially in breast cancer studies. Full wave inversion (FWI) methods
for image reconstruction in USCT provide the best image quality compared to more approximate
methods. Using FWI, the SS is usually recovered in the time domain, and the AA is usually
recovered in the frequency domain. Nevertheless, as both properties can be obtained from the same
data, it is desirable to have a common framework to reconstruct both distributions. In this work, an
algorithm is proposed to reconstruct both the SS and AA distributions using a time domain FWI
methodology based on the fractional Laplacian wave equation, an adjoint field formulation, and a
gradient-descent method. The optimization code employs a Compute Unified Device Architecture
version of the software k-Wave, which provides high computational efficiency. The performance of
the method was evaluated using simulated noisy data from numerical breast phantoms. Errors were
less than 0.5% in the recovered SS and 10% in the AA. V
New Symmetries in Crystals and Handed Structures
For over a century, the structure of materials has been described by a
combination of rotations, rotation-inversions and translational symmetries. By
recognizing the reversal of static structural rotations between clockwise and
counterclockwise directions as a distinct symmetry operation, here we show that
there are many more structural symmetries than are currently recognized in
right- or left-handed handed helices, spirals, and in antidistorted structures
composed equally of rotations of both handedness. For example, though a helix
or spiral cannot possess conventional mirror or inversion symmetries, they can
possess them in combination with the rotation reversal symmetry. Similarly, we
show that many antidistorted perovskites possess twice the number of symmetry
elements as conventionally identified. These new symmetries predict new forms
for "roto" properties that relate to static rotations, such as rotoelectricity,
piezorotation, and rotomagnetism. They also enable symmetry-based search for
new phenomena, such as multiferroicity involving a coupling of spins, electric
polarization and static rotations. This work is relevant to structure-property
relationships in all material structures with static rotations such as
minerals, polymers, proteins, and engineered structures.Comment: 15 Pages, 4 figures, 3 Tables; Fig. 2b has error
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