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Rangeland systems in developing nations: conceptual advances and societal implications
Get PDF"Developing-country rangelands are vast and diverse. They are home to millions who are often poor, politically marginalized, and dependent on livestock for survival. Here we summarize our experiences from six case-study sites in sub-Saharan Africa, central Asia, and Latin America generally covering the past 25 years. We examine issues pertaining to population, natural resource management, climate, land use, livestock marketing, social conflict, and pastoral livelihoods. The six study sites differ with respect to human and livestock population dynamics and the resulting pressures on natural resources. Environmental degradation, however, has been commonly observed. Climate change is also having diverse systemic effects often related to increasing aridity. As rangelands become more economically developed pastoral livelihoods may diversify, food security can improve, and commercial livestock production expands, but wealth stratification widens. Some significant upgrades in rural infrastructure and public service delivery have occurred; telecommunications are markedly improved overall due to widespread adoption of mobile phones. Pressures from grazing, farming, mining, and other land uses-combined with drought-can ignite local conflicts over resources, although the intensity and scope of conflicts markedly varies across our case-study sites. Pastoralists and their herds have become more sedentary overall due to many factors, and this can undermine traditional risk-management tactics based on mobility. Remote rangelands still offer safe havens for insurgents, warlords, and criminals especially in countries where policing remains weak; the resulting civil strife can undermine commerce and public safety. There has been tremendous growth in knowledge concerning developing-country rangelands since 1990, but this has not often translated into improved environmental stewardship or an enhanced wellbeing for rangeland dwellers. Some examples of demonstrable impact are described, and these typically have involved longer-term investments in capacity building for pastoralists, local professionals, and other stakeholders. Research is shifting from ecologically centered to more human-centered issues; traditional academic approaches are often being augmented with participatory, community-based engagement. Building human or social capital in ways that are integrated with improved natural resource stewardship offers the greatest returns on research investment. Our future research and outreach priorities include work that fortifies pastoral governance, enhances livelihoods for a diverse array of rangeland residents, and improves land and livestock management in a comprehensive social-ecological systems approach.
Mathematical modeling of a composting process in a small-scale tubular bioreactor
Get PDF"A mathematical model is presented to describe a composting process occurring in a tubular bioreactor. The mathematical model is based on heat and mass transfer phenomena under the continuum approximation. The bioreactor is divided into two phases: a gas phase and a solid–liquid phase. Between these phases, oxygen and heat are interchanged. In the solid–liquid phase, biomass growth occurs causing a change in substrate concentration as well as a change in temperature due to heat release from microbial activity. Thus the mathematical model is able to describe temperature and oxygen concentration profiles in the gas phase and temperature and biomass and substrate concentration profiles in the solid–liquid phase as a function of time and axial and radial positions. Useful information obtained from the model solution are the highest temperature that can be attained within the bioreactor and the length of high temperature conditions, which are important if sludge sanitization is the purpose of the composting process. Also a theoretical calculation of the logarithmic decimal reduction of Salmonella is presented. Using the model, a design analysis was performed to determine the effect of the main design variables in the temperature of the solid–liquid phase and the oxygen concentration in the gas phase.
Geochronological and geochemical evidences for extension-related Neoarchean granitoids in the southern São Francisco Craton, Brazil
Get PDF"New LA-SF-ICP-MS U-Pb zircon dating of high-K granitoids from the Campo Belo metamorphic complex, southern Sao Francisco Craton (Brazil), reveals a long period (ca. 100 My) of Neoarchean granitic magmatism that post-date the TTG magmatism. The oldest studied pluton is a highly porphyritic biotite orthogneiss emplaced at 2748 +/- 5 Ma, followed by a hornblende-biotite orthogneiss (2727 +/- 7 Ma). Both granitic bodies were affected by a deformation event prior to the emplacement of the Rio do Amparo, Bom Sucesso and Lavras granitoid plutons at 2716 +/- 6 Ma, 2696 +/- 6 Ma and 2646 +/- 5 Ma, respectively. The Neoarchean granitic magmatism ended with the intrusion of peraluminous leucogranitic dikes at 2631 +/- 4 Ma.
The 2.73-2.65 Ga Campo Belo granitoids share chemical features of A-type granites, such as high apatite- and zircon-saturation temperatures (mostly > 800 degrees C), relatively high Fe-number, high total alkalis and characteristic enrichment in LREE and HFSE although most samples of the Rio do Amparo granite have lower HFSE and LREE content that typical A-type granites but very high Th. The high Th content of the Rio do Amparo and Bom Sucesso granites may suggest involvement of Th-orthosilicate in their sources. The trace element composition permits to classify the Campo Belo granitoids as A(2)-type granites, suggesting derivation from partial melting of TTG-crustal sources likely in an extensional setting.
Significant reworking of Mesoarchean crust is suggested by mostly negative epsilon Nd-i, values (Rio do Amparo: -2.0 and +3.1; Bom Sucesso: -3.6, -3.1 and +0.9; Lavras: -2.5 and -0.2) and old Nd model ages (T-DM close to 3.1 Ga), although with probable involvement of juvenile material (T-DM of 2.7-2.9 Ga). This contrasts with Neoarchean granites of the northern Sao Francisco and Congo cratons characterized by negligible juvenile imprint.
The 2.75-2.63 Ga Campo Belo granitoids witness the thermal stabilization of the Archean lithosphere through a major episode of high-K granitoid magmatism between 2760 and 2600 Ma, which affected the whole Sao Francisco Craton and the northern Congo Craton. (C) 2017 Elsevier B.V. All rights reserved.
Hydrogen production by tailoring the brookite and Cu2O ratio of sol-gel Cu-TiO2 photocatalysts
Get PDF"Cu-TiO2 photocatalysts were prepared by the sol-gel method. Copper loadings from, 1.0 to 5.0 wt % were used. The materials were annealed at different temperatures (from 400 to 600 °C) to study the formation of brookite and copper ionic species. The photocatalysts were characterized by X-ray diffraction, UV–vis, Raman and XPS spectroscopies, H2-temperature programmed reduction (TPR), N2 physisorption, and SEM–EDS to quantify the actual copper loadings and characterize morphology. The photocatalysts were evaluated during the hydrogen photocatalytic production using an ethanolic solution (50% v/v) under UV and visible radiation. The best hydrogen production was performed by Ti-Cu 1.0 with an overall hydrogen production that was five times higher than that obtained with photolysis. This sample had an optimal thermal treatment at 500 °C, and at this temperature, the Cu2O and brookite/anatase ratio boosted the photocatalytic production of hydrogen. In addition, a deactivation test was carried out for the most active sample (TiO2-Cu 1.0), showing unchanged H2 production for three cycles with negligible Cu lixiviation. The activity of hydrogen-through-copper production reported in this research work is comparable with the one featured by noble metals and that reported in the literature for doped TiO2 materials.
Complex refractive index of InXGa1-XN thin films grown on cubic (100) GaN/MgO
Get PDF"Spectroscopic ellipsometry measurements of InXGa1-XN thin films were carried out in the photon energy range from 0.6 to 4.75 eV. The samples were grown on cubic GaN/MgO (100) template substrates by plasma assisted molecular beam epitaxy. Optical properties as the energy gap, refractive index (η) and extinction coefficient (κ) were obtained from the analysis of experimental data by a parametric dielectric function model. Our results show that the behavior of the optical band gap of cubic InXGa1-XN fits Eg(x) = 1.407x2 − 3.662x + 3.2 eV. The obtained bowing parameter of 1.4 ± 0.1 eV is in good agreement with reported calculated values around 1.37 eV. The complex index of refraction dispersion relations η(ω) and κ(ω) are obtained for the 85–99% mostly cubic InXGa1-XN films for several In concentrations.
Widening of the basins of attraction of a multistable switching dynamical system with the location of symmetric equilibria
Get PDF"A switching dynamical system by means of piecewise linear systems in that presents multistability is presented. The flow of the system displays multi-scroll attractors due to the unstable hyperbolic focus-saddle equilibria with stability index of type I, i.e., a negative real eigenvalue and a pair of complex conjugated eigenvalues with positive real part. This class of systems is constructed by a discrete control mode changing the equilibrium point regarding the location of their states. The scrolls appear when the stable and unstable eigenspaces of each adjacent equilibrium point generate the stretching and folding mechanisms needed in chaos, i.e., the unstable manifold in the first subsystem carries the trajectory towards the stable manifold of the immediate adjacent subsystem. The resulting attractors are located around four focus saddle equilibria. If the equilibria are located symmetrically to one of the axes and the distance between each equilibria is properly adjusted to generate two double-scroll chaotic attractors, the system can present from bistable to multistable parallel solutions regarding the position of their initial states. In addition the resulting basin of attraction presents a significatively widening when the distance between the equilibria of the parallel attractors is displaced.
Caracterización mineralógica de suelos impactados por residuos minero-metalúrgicos en una fundición abandonada en Matehuala, San Luis Potosí
Get PDF"En el municipio de Matehuala, San Luis Potosí, se han reportado concentraciones elevadas de arsénico total en suelos localizados en una antigua fundición, a las que se les atribuye la contaminación de arsénico en el acuífero; sin embargo, se desconocen las fases minerales en las que se encuentra presente dicho contaminante. En este trabajo se llevó a cabo una caracterización mineralógica de muestras de sustrato de suelo para identificar las fases de arsénico en las que se encuentra presente el contaminante y generar un modelo conceptual que explique congruentemente la presencia de las mismas en el sitio. Para alcanzar esto se realizaron análisis en bulto por difracción de rayos X, microscopía electrónica de barrido y espectroscopía extendida de estructura fina de absorción de rayos X. Los resultados de este estudio evidenciaron que las muestras se encuentran constituidas mayoritariamente por calcita, yeso y cuarzo. Así como también por minerales de arsénico como farmacosiderita [KFe4(AsO4)3(OH)], bukovskyita [Fe2(AsO4)(SO4)(OH)·9H2O], escorodita (FeAsO4·2H2O), beudantita [PbFe3(OH)6SO4AsO4], clinoclasa [Cu3AsO4(OH)3], arseniato de sodio (Na3AsO4), adamita (Zn2AsO4OH), arsenolita (As2O3), oropimente (As2S3), una mezcla de arseniatos de calcio entre los que se encuentran guerinita [Ca5H2(AsO4)4·9H2O], haidingerita (CaHAsO4·H2O) y farmacolita (CaHAsO4·2H2O); así como arsénico adsorbido sobre ferrihidrita [As≡Fe(OH)3]. De las fases anteriores, clinoclasa, adamita, arsenolita, farmacolita y haidingerita poseen productos de solubilidad altos (-4.79<Log K<10.10) que explican la movilidad del arsénico en el área de estudio a través de procesos de disolución. Los resultados de este estudio aportan al conocimiento de los procesos geoquímicos que sufre el arsénico a lo largo del tiempo cuando se dispone de forma no controlada en suelos de tipo calcisol en donde el principal reservorio de As, los óxidos de Fe, son insuficientes para contener la movilidad del arsénico.""In the municipality of Matehuala, San Luis Potosí, high concentrations of total arsenic have been reported in soils in an old smelter; which are responsible for the contamination of the Matehuala aquifer. However, questions on the mineral phases that host the arsenic remain unresolved. In this work, a mineralogical characterization of soil substrate samples was performed to identify the arsenic phases in which the pollutant is present and to generate a conceptual model that explains logically the presence and potential mobility of arsenic at the study site. To achieve this, X-ray diffraction, scanning electron microscopy and X-ray absorption near edge structure analyses were carried out. The results of this study showed that the samples are mainly composed of calcite, gypsum and quartz as well as pharmacosiderite [KFe4(AsO4)3(OH)], bukovskyite [Fe2(AsO4)(SO4)(OH)·9H2O], scororite (FeAsO4·2H2O), beudantite [PbFe3(OH)6SO4AsO4], clinoclase [Cu3AsO4(OH)3], sodium arsenate (Na3AsO4), adamite (Zn2AsO4OH), arsenolite (As2O3), orpiment (As2S3), calcium arsenates as guerinite [Ca5H2(AsO4)4·9H2O], haidingerite (CaHAsO4·H2O) and pharmacolite (CaHAsO4·2H2O), and arsenic adsorbed on ferrihydrite [As≡Fe(OH)3]. Of these minerals, clinoclase, adamite, arsenolite, pharmacolite and haidingerite have high solubility products (-4.79 <Log K <10.10) which could explain the mobility of arsenic in the study area through dissolution processes. The results of this study contribute to the knowledge of the geochemical processes that undergo arsenic over time in calcareous environments, where the main reservoir of As, Fe oxides, is insufficient to contain the mobility of the contaminant.
Análisis local de modelos de tercer y cuarto orden de quimiostatos
No full text"En este trabajo se muestran los resultados del análisis de estabilidad y bifurcaciones locales de tres modelos en ecuaciones diferenciales ordinarias de biorreactores. El análisis de bifurcación se llevó a cabo con respecto del parámetro tasa de dilución, pues es una de las entradas que se manipula con mayor facilidad y es la más usada. Las bifurcaciones que exhiben los puntos de equilibrio son la nodo-silla, la transcrítica y la de Hopf, ésta última de ser del tipo supercrítica implica oscilaciones sin amortiguamiento.
Para el modelo de tercer orden, se determinó una expresión dependiente de los parámetros del sistema que sirve de criterio de estabilidad de los puntos de equilibrio operacionales nones del mismo. En específico, si el signo de dicha expresión es negativo, entonces el punto de equilibrio es estable, en caso contrario cuando el signo es positivo el punto es inestable y resulta no hiperbólico si la expresión es igual a cero. Además se demostró que los puntos de equilibrio pares son inestables y que se pueden suscitar tres tipos de bifurcaciones locales, la transcrítica, la nodo-silla y la de Hopf, dependiendo éstas dos últimas también del criterio de estabilidad. Además se utilizó el criterio para determinar la estabilidad local del máximo de productividad.
El segundo modelo, que es de cuarto orden, tiene a lo más cinco puntos de equilibrio y al menos uno; además, puesto que existen dos especies de microorganismos en el reactor que pueden crecer a distintos ritmos, entonces hay tres modos de operación mutuamente excluyentes: lavado de la biomasa 1, lavado de la biomasa 2 y coexistencia. Los primeros dos modos de operación tienen a lo más dos puntos de equilibrio operacionales, mientras que el tercero hasta cuatro. Del análisis de bifurcaciones locales, se demostró que los puntos de equilibrio presentan bifurcaciones del tipo transcrítica y nodo-silla, pero las condiciones para la bifurcación de Hopf no se cumplen.
Del análisis de bifurcación del tercer sistema, modelo adimensional de cuarto orden estructurado en biomasa, fueron obtenidas expresiones matemáticas para el valor de tasa de dilución al cual el punto de equilibrio operacional es no hiperbólico y para la tasa de cruce por el eje imaginario de los valores propios complejos conjugados con respecto a la tasa de dilución, ambas en función de los parámetros del sistema. Se demostró que sólo existe un punto Hopf y que la tasa de cruce es negativa, por tanto existe una bifurcación de Hopf del punto de equilibrio operacional, el cual pasa de inestable a estable conforme aumenta el valor de la tasa de dilución. Simulaciones numéricas fueron comparadas con datos experimentales colectados en línea de un biorreactor continuo de tanque agitado instrumentado.""In this thesis local stability and bifurcation analysis results of three bioreactor models in ordinary differential equations are shown. The bifurcation analysis was carried out with respect to the dilution rate parameter, since it is a manipulable input and the most commonly used. The bifurcation suffered by the equilibrium points are the transcritical, the saddle-node and the Hopf ones, if this last is supercritical implies undamped oscillations.
For the first model, of third order, it was determined a system parameter dependent expression which serves as a stability criterion for the odd equilibrium points. In specific, if the sign of that expression is negative, then the equilibrium point is stable, being unstable if the sign is positive, and non-hyperbolic if the expression is equal to zero. In addition, it was demonstrated that the even equilibrium points are unstable and that the equilibrium points could suffer three types of local bifurcations: the transcritical, the saddle-node, and the Hopf ones, this two last depending on the stability criterion. Furthermore, that criterion is used to determine the productivity maximum local stability.
The second model, of fourth order, has at most five equilibrium points and at least one; additionally, since there are two microorganism species into the reactor which could growth at different rates, then there are three operation modes mutually exclusives: biomass 1 washout, biomass 2 washout, and coexistence. The first two operational modes have at most two operational equilibrium points, while the third up to four. With the local bifurcation analysis, it was demonstrated that the equilibrium points suffer transcritical and saddle-node bifurcations, but the Hopf bifurcation conditions are not satisfied.
From the local bifurcation analysis of the third system, a biomass structured dimensionless model of fourth order, a pair of mathematical expressions were obtained, one for the dilution rate value at which the operational equilibrium point is not hyperbolic and another for the imaginary axis cross rate of the complex conjugated eigenvalues with respect to the dilution rate, both in function on the system parameters. It was demonstrated that there is just one Hopf point and the cross rate is negative, thus a Hopf bifurcation on the operational equilibrium point exists, which pass from unstable to stable with the dilution rate value increasing. Numerical simulations were compared with experimental data collected in line from an instrumented continuous stirred tank bioreactor.
Caracterización hidrogeoquímica y vulnerabilidad del acuífero Huichapan-Tecozautla, Estado de Hidalgo
Get PDF"El acuífero Huichapan Tecozautla se encuentra ubicado en los municipios del mismo nombre en el Estado de Hidalgo. La problemática que se tiene es el abastecimiento de agua, debido a que se ha acentuado la escasez en las poblaciones, por lo que con mayor frecuencia, las fuentes de agua, son subterráneas y estas se encuentran sobreexplotadas y de mala calidad, causando conos de abatimiento. El sistema acuífero, está conformado por dos acuíferos, uno superior constituido por materiales volcánicos fracturados, que es el que se encuentra en desarrollo. El acuífero profundo se encuentra constituido por calizas de la Formación El Doctor, no está siendo explotado. En este trabajo se realizó una caracterización hidrogeoquímica de las 45 muestras de agua tomadas de pozos y manantiales, los cuales se representaron a través de diferentes diagramas. Se obtuvo la evaluación de la calidad del agua, en la que se consideraron algunos aspectos de la NOM-127-SSA1-1994 e índices de calidad de agua para consumo humano y uso agrícola. Por último, para el análisis de la vulnerabilidad acuífera se aplicó la metodología “SINTACS”. Los resultados obtenidos de esta investigación, indican que predominan dos tipos de agua, la bicarbonatada sódica (asociada a la zona de descarga) y la bicarbonatada cálcica (asociada a la zona de recarga); el principal proceso hidrogeoquímico es la interacción agua-roca, mezcla y en algunas muestras se presenta el efecto de evaporación. Se identificaron tres tipos de flujo, a) el flujo local asociado a la zona de recarga.; b) el flujo regional en donde se encuentran las aguas más evolucionadas localizadas al norte del área de estudio y c) el flujo intermedio, ubicadas en Tecozautla muy cercanas al flujo regional. La actividad hidrotermal es una componente importante en el funcionamiento para el sistema acuífero Huichapan-Tecozautla, debido a que aporta volúmenes importantes al sistema. El índice de calidad del agua (ICA) para consumo humano, indica que la calidad aceptable y el índice de contaminación (ICON) muestra que no tiene problemas de contaminación, hasta el momento. En general, la calidad para uso agrícola es aceptable. La vulnerabilidad acuífera muestra que las zonas con mayor riesgo a ser vulnerables son: la zona de recarga en Huichapan y en la parte Este de Tecozautla que es donde se encuentran los ríos Tula, San Juan, Tecozautla y San Francisco; así como, la presa de Zimapán con problemas de contaminación.""The Huichapan Tecozautla aquifer is located in the municipalities of the same name in the State of Hidalgo. There is a problem of water supply that is reflected in water scarcity in the human population, so that more frequently the water sources used are underground, with problems of overexploitation and poor water quality, causing cones of dumping. The aquifer system consists of two aquifers, an upper one consisting of fractured volcanic materials that is in development. And the deep aquifer is constituted by limestones of the El Doctor Formation, this aquifer is not being exploited. In this work a hydrogeochemical characterization of the 45 water samples from wells and springs was performed, which were represented by different diagrams. The water quality assessment was performed, in which aspects of NOM-127-SSA1-1994 and water quality indexes for human consumption and agricultural use were considered. Finally, the "SINTACS" methodology was applied for the analysis of the water vulnerability. The results obtained from this research indicate that two types of water predominate: sodium bicarbonate (associated with the discharge zone) and calcium bicarbonate (associated with the recharge zone); the main hydrogeochemical process is the water-rock interaction, mixing and in some samples the evaporation effect is present. Three types of flow were identified: a) the local flow associated with the recharge zone; B) the regional flow where the most evolved waters are located north of the study area and c) the intermediate flow, located in Tecozautla very close to the regional flow. The hydrothermal activity is an important component in the operation for the Huichapan-Tecozautla aquifer system, as it contributes important volumes to the system. The water quality index (ICA) for human consumption indicates acceptable quality and pollution index. (ICON) shows, which for now, has no pollution problems. In general, the quality for agricultural use is acceptable. The aquifer vulnerability shows that the areas at greatest risk to be vulnerable are: the recharge zone in Huichapan and the eastern part of Tecozautla, where the Tula, San Juan, Tecozautla and San Francisco rivers are located; As well as, the dam of Zimapan with pollution problems.
Obtención y caracterización de membranas poliméricas para desalinización de agua.
Get PDFTesis (Maestría en Nanociencias y Materiales)"Cada día es más imperioso buscar nuevas fuentes de agua potable, y una de las alternativas más prometedoras es la desalinización del agua de mar por medio de membranas de ósmosis inversa. La presente investigación pretende realizar una aportación al desarrollo de membranas poliméricas mediante la obtención de éstas por el método de evaporación de solvente y su consecuente caracterización de propiedades, así como su evaluación en el rechazo de sal. Siendo la cuestión central a determinar, el efecto que tienen, el tipo de solvente, el cambio en la temperatura de evaporación y la adición de grafeno, en el tamaño de los poros de las membranas resultantes. Para ello se obtuvieron 10 membranas diferentes, a las cuales se le midieron características como la porosidad, hidrofobicidad, área superficial, resistencia mecánica, entre otras; además, se evaluaron las membranas en un sistema de filtración ad hoc, donde se recolectó el permeado para establecer tanto la permeabilidad de la membrana, como el porcentaje de rechazo de sales. A partir de los resultados obtenidos, se determinó que el factor más importante que influye en el tamaño de poros de las membranas es la volatilidad, es decir, la combinación tanto del tipo de solvente utilizado como de la temperatura de evaporación. Además se encontró que el aditivo tuvo un impacto significativo en la resistencia mecánica de las membranas, al darles mayor dureza y rigidez conforme aumenta el contenido de grafeno. Finalmente, se obtuvo una membrana con características de desempeño similares a las comercializadas actualmente, lo que nos da pauta para seguir avanzando en investigaciones futuras.""Nowadays, it is imperative to look for new sources of drinking water, and one of the most promising alternatives is the reverse osmosis membranes for seawater desalination. The present research aims to contribute to the development of polymeric membranes, obtaining them by the solvent evaporation method, and carrying on its properties characterization, as well as its evaluation for salt rejection. Being the central question to be determined, the effect of the type of solvent, the change in evaporation temperature and the addition of graphene, on the pore size of the resulting membranes. Thus, 10 different membranes were obtained, to which characteristics such as porosity, hydrophobicity, surface area, mechanical resistance, among others were measured; in addition, the membranes were evaluated in ad-hoc filtration system, where the permeate was collected to determine both the permeability of the membrane and the percentage of salt rejection. It was determined that the most important factor influencing the pore size of the membranes is the volatility, i.e. the combination of both the type of solvent used and the evaporation temperature. It was also found that the additive had a significant impact on the mechanical strength of the membranes, giving them greater hardness and rigidity as the graphene content increases. Finally, we obtained a membrane with performance characteristics similar to those currently commercialized, which gives us guidelines for further progress in further research.