Artículos de Investigación

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Banach spaces-based mixed finite element methods for a steady sedimentation-consolidation system
(Springer Science and Business Media LLC, 2026-02-26)
Álvarez, Mario
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Benavides, Gonzalo A.
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Gatica, Gabriel N.
;
Henríquez, Esteban
;
Ruiz-Baier, Ricardo
We introduce and analyze two Banach spaces-based new mixed finite element methods for a flow and transport model commonly encountered in sedimentation-consolidation processes, whose governing equations are given by the Brinkman flow with variable viscosity, coupled with a nonlinear advection–diffusion equation. The first variational formulation is based on a mixed approach for the Brinkman problem (written in terms of Cauchy stress and bulk velocity of the mixture) and the usual primal weak form for the transport equation. In turn, the second variational formulation arises from the introduction of the gradient of the solids volume fraction and the total (diffusive plus advective) flux for the concentration as new unknowns, which yields a momentum-conserving fully–mixed approach as the resulting system of equations. The respective continuous and discrete formulations are equivalently reformulated as fixed-point operator equations, whose solvability is established by combining the Schauder, Banach, and Brouwer theorems, with, among others, the Babuška–Brezzi theory and a recently introduced theory for perturbed saddle-point problems, both in Banach spaces, along with suitable regularity assumptions, Sobolev embeddings, and Rellich–Kondrachov compactness theorems. The mixed–primal and fully-mixed Galerkin schemes employ the classical Raviart–Thomas, piecewise continuous, and piecewise discontinuous polynomial approximations, for their corresponding unknowns. Next, Strang-type inequalities are utilized to rigorously derive optimal error estimates in the natural norms, which, combined with the approximation properties of the chosen finite element spaces yield optimal rates of convergence with respect to the mesh size. Finally, several numerical results illustrating the performance of both schemes and confirming the theoretical convergence rates are presented.
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Maximum electron concentration and total electron content of the ionosphere over Concepción, Chile, prior to the 27 February 2010 earthquake
(2013)
Ovalle, E.M.
;
Bravo M.A.
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Villalobos Núñez, Carlos Ulises
;
Foppiano A.J.
Ionospheric variability observed prior to mayor earthquakes has been studied for decades. In particular, in many such studies the identification of ionospheric precursors of large earthquakes has been regarded as a specific goal. This paper analyses the observations of the maximum electron concentration (NmF2) over Concepción (36.8°S; 73.0°W) and of the total electron content (TEC) for an area covering the rupture zone corresponding to the very large Chile earthquake of 27 February 2010. The analyses used here are similar to those published before for many earthquakes in Taiwan, Japan and Russia. Possible NmF2 and TEC precursors are compared with other precursors proposed for the same earthquake using different TEC determinations and satellite observations of electron/ion concentration, energetic particle bursts and electromagnetic emissions. Some possible precursors derived from the various observations are consistent with each other. However, none can be unambiguously associated to the Chilean earthquake.
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First Report of an Eclipse From Chilean Ionosonde Observations: Comparison With Total Electron Content Estimations and the Modeled Maximum Electron Concentration and Its Height
(2020)
M. Bravo
;
M. Martínez‐Ledesma
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A. Foppiano
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B. Urra
;
E. Ovalle
<jats:title>Abstract</jats:title><jats:p>The ionospheric responses to the total solar eclipse on 2 July 2019 over low latitudes in southern South America are presented. Ionosonde observations were used within the totality path at La Serena (LS: 29.9°S, 71.3°W) and at Tucumán (TU: 26.9°S, 65.4°W) and Jicamarca (JI: 12.0°S, 76.8°W), with 85% and 52% obscuration, respectively. Total electron content (TEC) estimations over the South American continent were analyzed. The ionospheric impact of the eclipse was simulated using the Sheffield University Plasmasphere‐Ionosphere Model (SUPIM) at the Instituto Nacional de Pesquisas Espaciais (INPE). The significant variability of the diurnal variations of the various ionospheric characteristics over equatorial and low latitudes on geomagnetically quiet days makes it difficult to unambiguously determine the ionospheric responses to the eclipse. Nonetheless, some specific issues can be derived, mainly using simulation results. The <jats:italic>E</jats:italic> and <jats:italic>F</jats:italic>1 layer critical frequencies and densities below 200 km are found to consistently depend on decreasing solar radiation. However, the <jats:italic>F</jats:italic>1 layer stratification observed at both TU and LS cannot be related to the eclipse or other processes. The <jats:italic>F</jats:italic>2 layer does not follow the changes in direct solar radiation during the eclipse. The SUPIM‐INPE‐modeled <jats:italic>F</jats:italic> region critical frequency and TEC are overestimated before the eclipse at LS and particularly at TU. However, these overestimations are within the observed large day‐to‐day variability. When an artificial prereversal enhancement is added, the simulations during the eclipse better reproduce the observations at JI, are qualitatively better for LS, and are out of phase for TU. The simulations are consistent with conjugate location effects.</jats:p>
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SoilTemp: A global database of near‐surface temperature
(2020)
Jonas J. Lembrechts
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Juha Aalto
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Michael B. Ashcroft
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Pieter De Frenne
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Martin Kopecký
<jats:title>Abstract</jats:title><jats:p>Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long‐term average thermal conditions at coarse spatial resolutions only. Hence, many climate‐forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold‐air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free‐air temperatures, microclimatic ground and near‐surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near‐surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes.</jats:p>
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Rotation-Based Mixed Formulations for an Elasticity-Poroelasticity Interface Problem
(2020)
Verónica Anaya
;
Zoa de Wijn
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Bryan Gómez-Vargas
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David Mora
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Ricardo Ruiz-Baier
In this paper we introduce a new formulation for the stationary poroelasticity equations written using the rotation vector and the total fluid-solid pressure as additional unknowns, and we also write an extension to the elasticity-poroelasticity problem. The transmission conditions are imposed naturally in the weak formulation, and the analysis of the effective governing equations is conducted by an application of Fredholm's alternative. We also propose a monolithically coupled mixed finite element method for the numerical solution of the problem. Its convergence properties are rigorously derived and subsequently confirmed by a set of computational tests that include applications to subsurface flow in reservoirs as well as to dentistry-oriented problems.
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Conservative discontinuous finite volume and mixed schemes for a new four-field formulation in poroelasticity
(2020)
Sarvesh Kumar
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Ricardo Oyarzúa
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Ricardo Ruiz-Baier
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Ruchi Sandilya
<jats:p>We introduce a numerical method for the approximation of linear poroelasticity equations, representing the interaction between the non-viscous filtration flow of a fluid and the linear mechanical response of a porous medium. In the proposed formulation, the primary variables in the system are the solid displacement, the fluid pressure, the fluid flux, and the total pressure. A discontinuous finite volume method is designed for the approximation of solid displacement using a dual mesh, whereas a mixed approach is employed to approximate fluid flux and the two pressures. We focus on the stationary case and the resulting discrete problem exhibits a double saddle-point structure. Its solvability and stability are established in terms of bounds (and of norms) that do not depend on the modulus of dilation of the solid. We derive optimal error estimates in suitable norms, for all field variables; and we exemplify the convergence and locking-free properties of this scheme through a series of numerical tests.</jats:p>
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Image recognition of Legacy blueberries in a Chilean smart farm through deep learning
(2020)
Ignacio A. Quiroz
;
Germán H. Alférez
Agriculture is one of the most important pillars of development in Chile. However, it is expected that around the year 2030 there is going to be a gradual decrease in the number of farmers. Therefore, it is necessary to replace this workforce with technology and mechanization. One way to do this is through smart farms to leverage agricultural production. The contribution of this research work is a novel approach for deep-learning image recognition of Legacy blueberries in the rooting stage that can be used in smart farms in Chile. Legacy blueberry is a variety of Southern Highbush blueberry. This species constitutes 80% of the blueberry crops in Chile. Specifically, we propose an image recognition approach based on a convolutional neural network (CNN) to detect the presence of trays with living blueberry plants, the presence of trays without living plants, and the absence of trays. The average results of the evaluation of the predictive model are as follows: accuracy: 86%, precision: 86%, recall: 88%, and F1 score: 86%.
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Isothermal drying of plant-based food material: An approach using 2D polydimethylsiloxane (PDMS) micromodels
(2020)
Marco Guzmán-Meza
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João Borges Laurindo
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Marcela Jarpa-Parra
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Luis Segura-Ponce
The aims of this study were to build PDMS micromodels that simulated plant-based food material, and use them to investigate the drying mechanisms at pore-scale, the drying front morphologies and the drying curves during the isothermal drying process. Micromodels were built using a modified photolithographic technique. Three normal pore size distribution functions were developed to simulate the plasmodesma, intercellular space, and cell wall. Micromodels were impregnated with a pyranine aqueous solution and placed on a balance illuminated with ultraviolet light. Isothermal drying was developed by natural convection (20 °C). Drying front morphologies displayed a hierarchical behavior in which pores with the largest diameter dried first. Drainage and surface evaporation sequences and internal evaporation controlled the drying of PDMS micromodels. The micromodels were useful to simulate plant-based food material and study isothermal drying of such porous media. The results led to the proposal of some drying mechanisms that were involved.
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Ionosonde observations at King George Island, Antarctica: 1986-1991
(2019)
Alberto J. Foppiano
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Bravo, Manuel A.
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Villalobos, Carlos U.
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Concha, Guillermo V.
The structure of the thermosphere and ionosphere are particularly interesting along the longitude sector containing South America and the Antarctic Peninsula due to the unique geometry of the geomagnetic field. For these locations, solar associated effects are probably well separated from geomagnetic effects. Modeling of the Thermosphere-Ionosphere-Plasmasphere system has shown that the relation between thermospheric circulation, vertical motions, and composition changes has specific characteristics in this longitude sector. Moreover, the ionospheric phenomena related to tropospheric forcing such as atmospheric gravity waves, are also of significant interest, since the Antarctic Peninsula may be considered as an effective barrier to the prevailing and strong westerly winds, being almost perpendicular to the barrier. To better assess some of the above indicated characteristics and phenomena, a latitudinal extension of available ionospheric observations for many years at Argentine Islands (65°S, 64°W), Port Stanley (52°S, 58°W) and Halley Bay (76°S, 27°W) was needed. Thus an ionospheric station was installed and operated at King George Island (62°S, 59°W), and the present report makes the corresponding data base obtained, available to the scientific community at large. Detailed instructions are given to access the hourly (at 15 min intervals for a few cases) and monthly mean values for the 1986-1991 interval. Also, a routine is provided on request to plot diurnal variations of critical frequencies and virtual heights for the ionospheric E- and F-regions.
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Ionospheric Response to the Space Weather Events of 4-10 September 2017: First Chilean Observations
(2019)
Manuel Bravo
;
Carlos Villalobos
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Rodrigo Leiva Díaz
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Luis Tamblay
;
Pedro Vega-Jorquera
Objective: The diurnal variations of several ionospheric characteristics during the Space Weather Events of 4-10 September 2017, for Chilean latitudes, will be reported. Materials and Methods: Observations were made using a recently installed ionosonde at the Universidad de La Serena field station (29°52'S; 71°15’W). Also, reported is the total electron content determined using the upgraded Chilean network of dual-frequency Global Navigation Satellite Systems (GNSS) receivers. Results: Sudden ionospheric disturbances are described in terms of the minimum reflection frequency determined from ionosonde records. An attempt to derive the extent of the effect on high frequency propagation paths in the region is made using simultaneous ionosonde observations at other locations. The geomagnetic storm ionospheric effects are discussed in detail using the observed diurnal variation of maximum electron concentration (NmF2), virtual height of the F-region (h’F/F2) and Total Electron Content (TEC). These are complemented with the time-latitude variation of TEC for the 70°W meridian. Conclusion: It is found that large increases of NmF2, h’F/F2 and TEC observed during 8 September 2017 storm are well described in terms of the evolution of the Equatorial Ionospheric Anomaly (EIA) over the same time interval. Known physical mechanisms are suggested to explain most of the observations.

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