14,470 research outputs found
Geothermal systems simulation: A case study
Geothermal reservoir simulation is a key step for developing sustainable and efficient strategies for the exploitation of geothermal resources. It is applied in the assessment of several areas of reservoir engineering, such as reservoir performance and re-injection programs, pressure decline in depletion, phase transition conditions, and natural evolution of hydrothermal convection systems. Fluid flow and heat transfer in rock masses, fluid-rock chemical interaction and rock mass deformation are some of the processes addressed in reservoir modelling. The case study of the Las Tres Virgenes (LTV) geothermal field (10 MWe), Baja California Sur, Mexico is presented. Three dimensional (3D) natural state simulations were carried out from emplacement and cooling of two spherical magma chambers using a conductive approach. A conceptual model of the volcanic system was developed on a lithostratigraphic and geochronological basis. Magma chamber volumes were established from eruptive volumes estimations. The thermophysical properties of the medium were assumed to correspond to the dominant rock in each lithological unit as an initial value, and further calibration was made considering histograms of experimentally obtained thermophysical properties of rocks. As the boundaries of the model lie far from the thermal anomaly, we assumed specified temperature boundaries. A Finite Volume (FV) numerical scheme was implemented in a Fortran 90 code to solve the heat equation. Static formation temperatures from well logs were used for validation of the numerical results. Good agreement was observed in those geothermal wells dominated by conductive heat transfer. For other wells, however, it is clear that conduction alone cannot explain observed behaviour, three-dimensional convective models are being implemented for future multiphysics simulations
Calculation of renormalized viscosity and resistivity in magnetohydrodynamic turbulence
A self-consistent renormalization (RG) scheme has been applied to nonhelical
magnetohydrodynamic turbulence with normalized cross helicity and
. Kolmogorov's 5/3 powerlaw is assumed in order to compute the
renormalized parameters. It has been shown that the RG fixed point is stable
for . The renormalized viscosity and resistivity
have been calculated, and they are found to be positive for all
parameter regimes. For and large Alfv\'{e}n ratio (ratio of
kinetic and magnetic energies) , and . As
is decreased, increases and decreases, untill where both and are approximately zero. For large ,
both and vary as . The renormalized parameters for
the case are also reported.Comment: 19 pages REVTEX, 3 ps files (Phys. Plasmas, v8, 3945, 2001
Review of the field, analytical and statistical methods used in the determination and handling of rare-earth elements in soil-plant system
El presente artículo es una revisión detallada de estudios científicos publicados que tratan
el tema relacionado con la determinación de los elementos de las tierras raras (REEs) en el
sistema suelo-planta. Los estudios han sido llevados a cabo principalmente en países europeos
y asiáticos. Cabe señalar que la investigación en los países latinoamericanos es muy escasa;
sin embargo, es creciente el interés de analizar la aportación de estos elementos al suelo y la
planta, lo cual se debe a la aplicación de fertilizantes que contienen dosis elevadas de estos
elementos en su composición. Diversas técnicas de muestreo, experimentación y análisis han
sido empleadas para la determinación de los REEs. No obstante, se considera que el manejo de
los datos ha sido incorrecto estadísticamente. El contenido del presente artículo aborda: (i) las
generalidades de los REEs; (ii) el análisis de la bibliografía disponible con el fin de conocer las
metodologías de muestreo y análisis más utilizadas en 37 artículos en total, señalando algunos
puntos que se consideran todavía deficientes; (iii) dos ejemplos de la aplicación de técnicas
estadísticas (intervalo de confianza de la media y pruebas de significancia de la relación F de
Fisher y t de Student) utilizando datos reportados en dos artículos. Los resultados mostraron,
con los datos del primer artículo analizado, que: a) no se aplicó una metodología estadística
para evaluar la calidad de datos; b) al aplicar estadística se encontró que existen diferencias
sistemáticas entre los datos determinados en el laboratorio y los certificados. En el segundo
artículo analizado se demostró, mediante pruebas de significancia, que existen diferencias
significativas en las medias de Ce y Eu (los dos elementos tomados como ejemplos) en las
plantas de un sitio a otro.This study concerns a detailed review of published papers on rare-earth elements (REEs)
in soil-plant system. Such studies have been carried out mainly in Europe and Asia and are
relatively scarse in Latin American countries. Nevertheless, the interest in evaluating the uptake
of REEs in soil-plant system is continually increasing. This is due to the fact that fertilizers contain
high concentrations of these elements. Different techniques have been used for sampling,
experimental work and REE determinations. However, we consider that the data handling has
been rather statistically deficient. This review elaborates on the following points: (i) general
characteristics of the REEs; (ii) bibliographical review of sampling and analytical techniques
actually used in 37 papers with an emphasis on the statistical deficiencies; (iii) examples of
the application of statistical methods (confidence interval of the mean and significance tests
of Fisher F and Student t) based on two of the compiled papers. The first application showed
that the original authors did not apply any statistical methodology to evaluate their data quality
and that there are systematic differences between the data analyzed in their laboratory and the
certified values of the reference material. The application of significance tests to the data from
the second paper demonstrated that there are significant differences in the mean values of Ce
and Eu (only these two elements were exemplified) in plants from different sites.Fil: Hernández-Martínez, J. Lucero.
Universidad Nacional Autónoma de México. Instituto de GeofísicaFil: Verma, Surendra P..
Universidad Nacional Autónoma de México. Centro de Investigación de Energí
Simple Pendulum Revisited
We describe a 8085 microprocessor interface developed to make reliable time
period measurements. The time period of each oscillation of a simple pendulum
was measured using this interface. The variation of the time period with
increasing oscillation was studied for the simple harmonic motion (SHM) and for
large angle initial displacements (non-SHM). The results underlines the
importance of the precautions which the students are asked to take while
performing the pendulum experiment.Comment: 17 pages with 10 figure
Critical Cooperation Range to Improve Spatial Network Robustness
A robust worldwide air-transportation network (WAN) is one that minimizes the
number of stranded passengers under a sequence of airport closures. Building on
top of this realistic example, here we address how spatial network robustness
can profit from cooperation between local actors. We swap a series of links
within a certain distance, a cooperation range, while following typical
constraints of spatially embedded networks. We find that the network robustness
is only improved above a critical cooperation range. Such improvement can be
described in the framework of a continuum transition, where the critical
exponents depend on the spatial correlation of connected nodes. For the WAN we
show that, except for Australia, all continental networks fall into the same
universality class. Practical implications of this result are also discussed
- …