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Groundwater flow processes and mixing in active volcanic systems: the case of Guadalajara (Mexico)
Get PDF"Groundwater chemistry and isotopic data from 40 production wells in the Atemajac and Toluquilla valleys, located in and around the Guadalajara metropolitan area, were determined to develop a conceptual model of groundwater flow processes and mixing. Stable water isotopes (delta H-2, delta O-18) were used to trace hydrological processes and tritium (H-3) to evaluate the relative contribution of modern water in samples. Multivariate analysis including cluster analysis and principal component analysis were used to elucidate distribution patterns of constituents and factors controlling groundwater chemistry. Based on this analysis, groundwater was classified into four groups: cold groundwater, hydrothermal groundwater, polluted groundwater and mixed groundwater. Cold groundwater is characterized by low temperature, salinity, and Cl and Na concentrations and is predominantly of Na-HCO3-type. It originates as recharge at "La Primavera" caldera and is found predominantly in wells in the upper Atemajac Valley. Hydrothermal groundwater is characterized by high salinity, temperature, Cl, Na and HCO3, and the presence of minor elements such as Li, Mn and F. It is a mixed-HCO3 type found in wells from Toluquilla Valley and represents regional flow circulation through basaltic and andesitic rocks. Polluted groundwater is characterized by elevated nitrate and sulfate concentrations and is usually derived from urban water cycling and subordinately from agricultural return flow. Mixed groundwaters between cold and hydrothermal components are predominantly found in the lower Atemajac Valley. Twenty-seven groundwater samples contain at least a small fraction of modern water. The application of a multivariate mixing model allowed the mixing proportions of hydrothermal fluids, polluted waters and cold groundwater in sampled water to be evaluated. This study will help local water authorities to identify and dimension groundwater contamination, and act accordingly. It may be broadly applicable to other active volcanic systems on Earth.
Estrategias de control conmutado robusto para mitigar volcadura y derrape en vehículos con ruedas
Get PDF"En esta tesis se estudian los problemas de volcadura no lanzada, derrape lateral, así como un tipo de volcadura lanzada inducida por derrape lateral, bajo un enfoque de estabilidad robusta entrada-salida que utiliza una representación conmutada para la dinámica de un vehículo de 4 ruedas. Se introduce un criterio de medición del riesgo de derrape y de volcadura que se utiliza como la salida del sistema conmutado para propósitos de control. La conmutación se obtiene en función de la existencia del riesgo en la maniobra del conductor; si el riesgo es inminente se aplican acciones de frenado y tracción/propulsión diferenciales para mitigar el riesgo, por lo que el control no es invasivo. El problema de control se formula como el diseño de acciones de frenado y aceleración que garanticen que el vehículo se encuentra en un régimen seguro de manejo. El objetivo de control se complica por la presencia de incertidumbre de modelado en el sistema, la cual depende del tipo de terreno, de la suspensión, del tipo de llanta y del tipo de vehículo entre los más relevantes. La ley de control que se acciona bajo riesgo inminente, se modifica con el uso de un sistema predictivo de riesgo para mejorar el desempeño y se establecen las condiciones suficientes para garantizar la estabilidad del sistema. En resumen, esta tesis se enfoca en el estudio de condiciones de estabilidad y en el diseño de estrategias de conmutación estabilizantes para los casos en donde existe o no predicción del riesgo de la maniobra.""This Thesis studies the tripped rollover and lateral skid problems as well as a kind of nontripped rollover induced by lateral skid. The input-output robust stability of the system is established using a piecewise linear description of the wheeled vehicle and the definition of a rollover and skid indexes. The skid index is proposed based on the well-known friction ellipse along with some considerations regarding vertical dynamics of the system. The rollover and skid risks are evaluated continuously using measurements of vehicle’s side slip, yaw and roll angles and they are used to define the switching criterion to guarantee the stability of the system. The proposed control is not invasive since braking and traction/propulsion actions are only performed if an imminent risk is detected. The control problem is formulated as the synthesis of braking and accelerating actions that guarantee stability in spite of model uncertainty, parameter variations, fast switching actions and bounded control inputs. The model uncertainty arises from an imperfect description of the vehicle dynamics, and estimation mismatches of the vehicle parameters depending on the type of terrain, the type of tire, the vehicle suspension among others. In order to further improve the performance of the control, predictive actions on drivers maneuvering is included using a first order linear model. The resulted predictive switched robust linear controller proves to be sufficient to mitigate both rollover and skid and displays less conservative control actions since the control is performed only if a risk is foreseen within a designer-fixed time horizon.
Dibenzothiophene adsorption at boron doped carbon nanoribbons studied within density functional theory
Get PDF"The adsorption of dibenzothiophene (DBT) on bare and boron-doped armchair carbon nanoribbons (ACNRs) is being investigated in the framework of the density functional theory by implementing periodic boundary conditions that include corrections from dispersion interactions. The reactivity of the ACNRs is characterized by using the Fukui functions as well as the electrostatic potential as local descriptors. Non-covalent adsorption mechanism is found when using the local Perdew-Becke-Ernzerhof functional, regardless of the DBT orientation and adsorption location. The dispersion interactions addition is a milestone to describe the adsorption process. The charge defects introduced in small number (i.e., by doping with B atoms), within the ACNRs increases the selectivity towards sulfur mainly due to the charge depletion at B sites. The DBT magnitude in the adsorption energy shows non-covalent interactions. As a consequence, the configurations where the DBT is adsorbed on a BC3 island increase the adsorption energy compared to random B arrangements. The stability of these configurations can be explained satisfactorily in terms of dipole interactions. Nevertheless, from the charge-density difference analysis and the weak Bader charge-distribution interactions cannot be ruled out completely. This is why the electronic properties of the ribbons are analyzed in order to elucidate the key role played by the B and DBT states in the adsorbed configurations.
Laboratory synthesis of goethite and ferrihydrite of controlled particle sizes
Get PDF"Iron oxyhydroxides, such as goethite and ferrihydrite, are highly abundant and ubiquitous minerals in geochemical environments. Because of their small particle sizes, their surface reactivity is high towards adsorption of anions and cations of environmental relevance. For this reason these minerals are extensively studied in environmental geochemistry, and also are very important for environmental and industrial applications. In the present work, we report the synthesis and characterization of goethite and ferrihydrite of controlled particle sizes. It has been shown that surface reactivity of these minerals is highly dependent on crystal sizes, even after normalizing by specific surface area. In order to investigate the reasons for this changing reactivity it is necessary to work with reproducible particle sizes of these minerals. We investigated here the experimental conditions to synthesize goethite samples of four different specific surface areas: ca. 40, 60, 80 and 100 m2 g-1, through the controlled speed of hydroxide addition during hydrolysis of acid Fe(III) solutions. In the case of 2-line ferrihydrite, samples with two different particle sizes were prepared by changing the aging time under the pH conditions of synthesis (pH = 7.5). The synthesized minerals were identified and characterized by: X-ray diffraction, N2adsorption BET specific surface area, transmission electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and maximum Cr(VI) adsorption.""Los oxihidróxidos de hierro, como la goetita y ferrihidrita, son minerales altamente abundantes y ubicuos en ambientes geoquímicos. Su reactividad superficial es alta hacia la adsorción de aniones y cationes de relevancia ambiental dados sus pequeños tamaños de partícula. Por esta razón estos minerales son estudiados extensamente en geoquímica ambiental, y también son muy importantes en aplicaciones ambientales e industriales. En el presente trabajo reportamos la síntesis y caracterización de goetitas y ferrihidritas de tamaño de partícula controlado dado que se ha demostrado que su reactividad superficial es altamente dependiente de sus tamaños cristalinos, aún después de normalizar por su área superficial específica. Para investigar las razones de estos cambios de reactividad es necesario trabajar con tamaños de partícula reproducibles de estos minerales. Aquí presentamos las condiciones experimentales para sintetizar muestras de goetita de cuatro diferentes áreas superficiales específicas: ca. 40, 60, 80 y 100 m2 g-1, a través de la velocidad controlada de adición de hidróxido durante la hidrólisis de soluciones ácidas de Fe(III). En el caso de ferrihidrita de 2 líneas, se prepararon muestras con dos tamaños diferentes de partícula cambiando el tiempo de añejamiento bajo las condiciones de pH de síntesis (pH=7.5). Los minerales sintetizados se identificaron y caracterizaron por: difracción de rayos X, área superficial específica por adsorción de N2 BET, microscopía de transmisión electrónica, espectroscopía de infrarrojo de transformada de Fourier con reflectancia total atenuada, y adsorción de Cr(VI) máxima.
The Hurst exponents of Nitzschia sp. diatom trajectories observed by light microscopy
Get PDF"We present the results of an experiment with light microscopy performed to capture the trajectories of live Nitzschia sp. diatoms. The time series corresponding to the motility of this kind of cells along ninety-five circular-like trajectories have been obtained and analyzed with the scaling statistical method of detrended
Caracterización magnética de polvo urbano y plantas de la Zona Metropolitana del Valle de México
Get PDF"Investigaciones recientes han demostrado que los gases automotores contienen elementos potencialmente tóxicos, los cuales se acumulan sobre las superficies del suelo urbano (asfalto, cemento, empedrado, etc.) y se mezclan con el polvo urbano (PU). En este estudio se determinan los valores de umbrales magnéticos por medio de muestras de PU depositado en calles y hojas de plantas provenientes de zonas con diferentes tipos de usos del suelo de la Zona Metropolitana del Valle de México. Se colectaron 89 muestras de PU y un mismo número de muestras de hojas de Ficus benjamina de zonas con diferentes tipos de uso de suelo (habitacional, equipamiento, habitacional-comercial, espacios abiertos e industria). Los parámetros magnéticos determinados fueron: susceptibilidad magnética específica másica (χlf), porcentaje de la susceptibilidad dependiente de la frecuencia (χdf%), magnetización remanente isotermal a 700 mT (MRI0.7) y adicionalmente la concentración de Pb y Zn. Las curvas de magnetización vs campo magnético presentaron una saturación de la magnetización para campos magnéticos entre 200 a 300 mT y la fracción S-200 (S-200 = MRI-0.2/MRI0.7) presentó valores entre 0.7 a 1.0; este comportamiento es característico de muestras con minerales de baja coercitividad magnética (ferrimagnéticos). Las curvas termomagnéticas (κ vs T) de PU indican que la principal fase magnética es alrededor de 580 °C, lo que sugiere la presencia de titano-magnetita pobre en Ti y magnetita. Las concentraciones de Pb y Zn presentan correlación estadísticamente aceptable con los parámetros magnéticos. Los análisis discriminantes en ambos tipos de muestras (agrupación por tipos de uso del suelo, las variables χlf, χdf%, MRI0.7 y las concentraciones de Pb y Zn) dan un resultado menor al 50% en ambos casos. Por tanto, no es posible establecer diferencias significativas entre los tipos de uso de suelo, los parámetros magnéticos medidos y la concentración de Pb y Zn. La determinación de los valores umbrales magnéticos se obtuvo del polvo urbano con las menores concentraciones de Pb y Zn. Los valores umbrales para el PU fueron: MRI0.7 = 58 mAm2 kg-1 y χlf = 4.5 mm3 kg-1, en tanto que para las plantas fueron: MRI0.7 = 1.6 mAm2 kg-1 y χlf = 0.13 mm3 kg-1. Las representaciones espaciales de los valores umbrales de MRI0.7 de PU y plantas revelaron que las zonas de la parte central y sureste de la Zona Metropolitana del Valle de México son potencialmente peligrosas por su alta concentración de Pb o Zn.""Recent investigations have demonstrated that motor-vehicle gas contains particles with potentially toxic elements. These contaminating particles accumulate on the soil surface or overlying material (asphalt, stone and concrete pavements) and they are usually mixed with urban dust. In this work we determine the magnetic threshold values using urban dust and leave samples collected from different type
of urban land-use soil along the metropolitan area of Mexico City and identify potentially dangerous areas
considering potentially toxic elements. 89 urban dust samples deposited on the streets and same number
of Ficus benjamina leaves were collected from different land-use zones (residential, equipment, residentialcommercial,
open space and industry).
The magnetic parameters determined were: mass especific magnetic susceptibility (χ
lf), percentage frequency
dependent susceptibility (χ
df%), isothermal remanent magnetization at 700 mT (IRM0.7). Additionally the
concentrations of Pb and Zn were also obtained. Isothermal remanence acquisition curves for dust samples
yielded a saturation between 200 and 300 mT and S-200 (S-200= MRI-0.2/MRI0.7) fraction values were found
between 0.7 to 1.0 - characteristic of samples with low magnetic coercivity minerals (ferrimagnetics).
The κ vs T curves indicate the main magnetic phase about 580 °C which attests the presence of Ti-poor
titanomagnetite or almost pure magnetite. The Pb and Zn concentrations show acceptable statistically
correlation with magnetic parameters. Discriminant analyzes in both types of samples gave values low
than 50% in both cases. Therefore, it is not possible to attest the significant differences between measured
magnetic parameters, concentration of Pb and Zn and soil type. The threshold values for urban dust were
MRI0.7 = 58 mAm2 kg-1 and χlf = 4.5 mm3 kg-1 while the plant threshold values were: MRI0.7 = 1.6 mAm2 kg-1
and χlf = 0.13 mm3 kg-1. Spatial representations of these threshold values revealed that zones from central
and southeast of Valle de Mexico Metropolitan Zone are the most potentially dangerous areas considering
their high concentration of Pb and Zn.
Silver nanoparticles loaded on Cu-doped TiO2 for the effective reduction of nitro-aromatic contaminants
Get PDF"The addition of Cu species via copper glycine complexes as a strategy for doping the TiO2 structure during the sol–gel process produces a copper–TiO2-based composite. The combination of the copper–TiO2-based composite with the practical UV functionalization of highly dispersed silver nanoparticles (AgNPs), 3 nm, results in an efficient photocatalyst for eliminating 4-nitrophenol as a model of nitro-aromatic contaminant. This novel Ag/TiO2–Cu composite achieved the effective photoreduction of 4-nitrophenol into the valuable 4-aminophenol in approximately 30 min with high conversion (96%). A possible reduction mechanism of aromatic nitro compounds into amines in aqueous alkaline medium is discussed, considering the interfacial fast charge transfer during the in situ reduction of copper by the presence of hydrazine as a sacrificial electron donor.
A New Catalytic System for the Photodegradation of Endocrinal Disruptors: Synthesis and Efficiency Modeling and Optimization
No full text"Nowadays, the challenge of understanding relationships between catalysts properties and performance in the context of heterogeneous catalysis is a hot topic. Indeed, catalytic processes are generally affected by many different operational parameters that need to be modeled and optimized. The challenge can be addressed using artificial neural networks due to their flexibility to work without mathematical description of the process. The present work enters within the framework of the photodegradation of water contaminants using ZnObased catalysts. ZnO is a non-toxic cheap material with an interesting photocatalytic potential. However, its application is reduced because of its poor efficiency, photocorrosion and difficulties for recovery. The objective of this work is to improve this efficiency, regarding particularly the photodegradation of an endocrinal disruptor: bisphenol-A (BPA), via the synthesis of a new catalytic system based on ZnO and the modeling of both the synthesis process and photocatalytic performance of this new catalytic system. Modeling and optimization will be carried out using artificial neural network tools coupled to an evolutionary algorithm. The connection between the two artificial neural network models will make it possible to identify the optimal synthesis parameters that lead to the maximum photocatalytic efficiency (within the studied domain), thus shedding light on the association of the system structure with its photocatalytic performance.
Índice de pobreza del agua en zonas subtropicales: el caso de la Huasteca Potosina, México
No full text"Tools are needed in order to evaluate an integrated water resource management, and to encourage the management and coordinated usage of water resources along with the environmental and socioeconomic factors. One of those tools is the Water Poverty Index (WPI), which enables the evaluation of water poverty in terms of the physical and socioeconomic factors related to water availability. The WPI, as calculated in this study, is derived from the weighted sum of six key components -resources, access, usage, capacity, quality and environment- on a scale of 0 to 100. The objective of this work was to calculate the Rio Valles Basin WPI for 2010. This region is a semi-tropical area with abundant water resources, such as large springs. Its annual mean precipitation is 1100 mm. In the Rio Valles Basin, the volume of surface water used per year is 81.33 Mm3, which represents 91 % of the total resource. The volume of groundwater used per year is 8.17 Mm3, representing the remaining 9 %. Usually 45 Mm3/year is stored in La Lajilla dam. These data indicate that surface water is the main source of supply for uses such as agriculture, which is the activity with the largest water demand. A WPi score of 59 was obtained for the Rio Valles Basin.""Para evaluar la gestión integrada de los recursos hídricos se necesitan herramientas para fomentar su administración y uso coordinado con el ambiente y los factores socioeconómicos. Una de estas herramientas es el Índice de Pobreza del Agua (IPA), que permite evaluar la pobreza del agua en términos de los factores físicos y socioeconómicos relacionados con su disponibilidad. El IPA, como se calculó en este estudio, se deriva de la suma ponderada de seis componentes clave: el acceso, el uso, la capacidad, la calidad y el ambiente, en una escala de 0 a 100. El objetivo de este trabajo fue calcular el IPA de la cuenca del Río Valles para el año 2010. Esta región es semitropical, con abundantes recursos hídricos, como grandes manantiales y una precipitación media anual de 1100 mm. En la cuenca del Río Valles el volumen de agua superficial utilizada es de 81.33 Mm3/año, lo que representa el 91 % del total del recurso utilizado. El volumen de agua subterránea utilizada es de 8.17 Mm3/año, lo que representa el 9 % restante, normalmente se almacenan 45 Mm3/año en la presa de La Lajilla. Estos datos indican que el agua superficial es la principal fuente de abasto para diversos usos como la agricultura que es la actividad con la mayor demanda de agua. El IPA que se obtuvo para la cuenca del Río Valles fue de 59 puntos.
Output-feedback proportional-integral- derivative-type control with simple tuning for the global regulation of robot manipulators with input constraints
No full text"An output-feedback proportional-integral-derivative-type control scheme for the global position stabilisation of robot manipulators with bounded inputs is proposed. It guarantees the global regulation objective avoiding input saturation by releasing the feedback not only from the exact knowledge of the system structure and parameter values, but also from velocity measurements. With respect to previous approaches of the kind, the proposed scheme remains simple while increasing design/performance-adjustment flexibility. For instance, it does not impose the use of a specific sigmoidal function to achieve the required boundedness but involves a generalised type of saturation functions. More importantly, it is characterised by a very simple control-gain tuning criterion, the simplest hitherto obtained in the considered analytical context. Experimental tests on a 2-degree-of-freedom direct-drive manipulator corroborate the efficiency of the developed scheme.