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Detección electroquímica de cadmio mediante electrodos de pasta de carbón modificados con hidrogeles de poli(ácido acrílico)/ácido itacónico/nanotubos de carbono multipared tipo bambú dopados con nitrógeno
Get PDFTesis (Maestría en Ciencias Ambientales)"El cadmio es un elemento tóxico que puede estar presente en agua, aire y suelo debido a procesos naturales y antropogénicos, por tan razón, la EPA recomienda 0.005 mgL-1 como límite máximo permisible en agua para uso y consumo humano. Entre las técnicas que se han empleado para detectarlo o cuantificarlo, se encuentran las electroanalíticas que, permiten efectuar diagnósticos en campo ya que su aplicación se fundamenta en la utilización de dispositivos portátiles acoplados a sensores electroquímicos. Recientemente, en la fabricación de sensores electroquímicos se han empleado nanotubos de carbono pues no sólo sirven como agentes pre-concentradores sino también como amplificadores de señal eléctrica. Un tipo especial de nanotubos de carbono son los tipo bambú (BMWCNT), éstos se han empleado en la construcción de biosensores para la detección de biomoléculas; sin embargo, no se han usado en la detección electroquímica de Cd(II) pero si para su remoción. Por otro lado, se sabe que hidrogeles de poli(ácido acrílico)/ácido itacónico (PAA/IA) sirven como agentes pre-concentradores de cadmio pues poseen grupos funcionales carboxilo capaces de formar compuestos de coordinación con Cd(II) en solución. En este trabajo se construyó un sensor electroquímico capaz de detectar Cd(II), a partir de un pasta de carbón modificada con composito de PAA/IA/B-MWCNT, para el cual se obtuvo un LOD de 19.24 μgL-1 y una sensibilidad de 0.15 μC ppb-1.""Cadmium is a toxic element present in water, air and soil because of natural and anthropogenic processes, for that reason, EPA recommends 0.005 mgL-1 as maximum permitted level in water for human use and consumption. Between techniques that have been used for its detection and quantification are the electroanalytical ones that, permit diagnostics ex situ due to their application is based on the use of portable devices coupled to electrochemical sensors. Recently, in the making of electrochemical sensors, carbon nanotubes have not only been used as pre-concentration agents but also as electrical signal amplifiers. A special kind of carbon nanotubes is the bamboo-type (B-MWCNT), these have been used in biosensors construction for biomolecules detection; however, they have not been used in electrochemical detection of Cd(II) but they have been applied for its removal. On the other hand, it has been known poly(acrylic acid)/itaconic acid hydrogels serve as cadmium pre-concentration agents because they have carboxyl functional groups that are able to form coordination compounds with Cd(II) in solution. In this work it was built an electrochemical sensor capable of detecting Cd(II), from a carbon paste modified with PAA/IA/B-MWCNT composite, it was obtained a LOD of de 19.24 μgL-1 and a sensitivity of 0.15 μC ppb-1.
Nonlinear and robust control strategy based on chemotherapy to minimize the HIV concentration in blood plasma
Get PDF"A nonlinear PI-type control strategy is designed in order to minimize the HIV concentration in blood plasma, via medical drug injection, under the framework of bounded uncertain input disturbances. For control design it is considered a simplified mathematical model of the virus infection as a benchmark. The model is based on mass balances of healthy cells, infected cells, and the virus concentrations. The proposed controller contains a nonlinear feedback PI structure of bounded functions of the regulation error. The closed-loop stability of the system is analyzed via Lyapunov technique, in which robustness against system disturbances is demonstrated. Numerical experiments show a satisfactory performance of the proposed methodology as a HIV therapy, in which the virion particles and the infected CD4+T cells are minimized and, as an interesting result, the drug dosage can be suspended, thus avoiding drug resistance from the virus. Finally, the proposed controller is compared to a standard sliding-mode and hyperbolic tangent controllers showing better performance.
Generación de sistemas dinámicos multiestables
Get PDF"El trabajo de investigación que está presente en esta tesis se enfoca en la generación de sistemas dinámicos multiestables. Aquí, la multiestabilidad puede ser vista como un fenómeno a través del cual, un sistema lineal afín en R3 conteniendo una función PWL, origina dos o más cuencas de atracción pertenecientes a atractores caóticos distintos. Ya que la multiestabilidad puede ser encontrada en diversas áreas de la ciencia, en el Capítulo 1 se narra como es percibido tal fenómeno en otras áreas y la importancia de su generación. Para lograr los objetivos planteados, fueron necesarias las bases matemáticas que se encuentran en el Capítulo 2, donde se mencionan algunas definiciones y conceptos relacionados a la teoría de sistemas disipativos con dinámica inestable (que llamaremos sistemas disipativos inestables) y caos. Por su parte, los Capítulos 3, 4 y 5 fueron redactados para mostrar individualmente los resultados que se obtuvieron. Cada uno de estos capítulos puede ser consultado en forma aleatoria, sin la necesidad de leer otro capítulo previamente. En Capítulo 3, se muestra un sistema lineal afín para el cual, la multiestabilidad depende principalmente de una función PWL contenida en la parte afín. En Capítulo 4, se describe como la multiestabilidad puede ser obtenida por medio de la modificación de parámetros de la parte lineal del sistema. En capítulo 5, se corrobora que sistemas basados en UDS’s Tipo II [27], propician sistemas multiestables si tienen una función PWL adecuada. Finalmente, las conclusiones y trabajo a futuro se describen en el Capítulo 6.""The research that is present in this thesis focuses on generating multistable dynamical systems. Here, multistability can be seen as a phenomenon through which, an affine linear system in R3 containing a PWL function is able to originate two or more basins of attraction belonging to different chaotic attractors. Since multistability can be found in various areas of science, in Chapter 1 it is narrated it is narrated how this phenomenon is perceived in other areas and the importance of its generation. To achieve the proposed objectives, it was necessary to present the mathematical bases that can be found in Chapter 2, where some definitions and concepts related to theory about dissipative systems that have unstable dynamic (they will be called unstable dissipative systems) and chaos are mentioned. Meanwhile, Chapters 3, 4 and 5 were written to individually display the results that were obtained. Each of these chapters can be consulted randomly, and previous reading of any other chapter is not required. In Chapter 3, it is shown an affine linear system for which multistability depends mainly on PWL function contained in the affine part. In Chapter 4, it is described how multistability can be obtained by modifying parameters of the linear part of the system. In Chapter 5, it is confirmed that systems based on UDS ’s Type II [27], can propitiate multistable systems if they have an adequate PWL function. Finally, conclusions and future work are presented in Chapter 6.
Cement pastes and mortars containing nitrogen-doped and oxygen-functionalized multiwalled carbon nanotubes
Get PDF"Cement pastes and mortars based on ordinary Portland cement containing nitrogen-doped multiwalled carbon nanotubes (MWCNT-Nx) or oxygen-functionalized multiwalled carbon nanotubes (MWCNT-Ox) are investigated. To incorporate MWCNTs into the cementitious matrix, the as-produced carpets are dispersed over periods of 1 and 2 hours in distilled water at pH levels of 1 and 7. The cement pastes are prepared by adding 0.1 wt% of MWCNTs to cement powder, followed by characterization with SEM and X-ray diffraction (XRD) at an early age (first hours of hydration). The mortars are mechanically characterized during the hydration process for a period of 28 days. SEM characterization of cement pastes revealed that the carbon nanotubes are well incorporated in the cementitious matrix, with the hydrated cement grains interconnected by long carbon nanotubes. XRD characterizations demonstrated that, during the hydration of cement pastes, different peaks emerged that were associated with ettringite, hydrated calcium silicate, and calcium hydroxide, among other structures. Results of the compressive strength measurements for mortars simultaneously mixed with MWCNT-Nx and MWCNT-Ox reached an increment of approximately 30% in compressive strength. In addition, density functional theory calculations were performed in nitrogen-doped and oxygen-functionalized carbon nanotubes interacting with a cement grain.
Variability of carbon fluxes at different time-scales and their biotic and environmental controls on a short-grass steppe in Central Mexico
Get PDFTesis (Doctorado en Ciencias Ambientales)"Los ecosistemas terrestres controlan la dinámica del carbono (C) atmosférico sobre la tierra, removiendo hasta el 25% de las emisiones de C antropogénicas. Sin embargo, la alta variabilidad estacional e interanual de los flujos de C genera gran incertidumbre acerca de su capacidad de captura de C. El entendimiento de los factores que afectan las tasas de captura y liberación de C nos ayudará a mejorar las predicciones de los efectos del cambio climático sobre los procesos ecosistémicos, así como sus efectos de retroalimentación. El objetivo de este trabajo fue determinar los controles bióticos y ambientales sobre el intercambio neto de C a nivel ecosistema (NEE) y sus componentes para entender cuáles condiciones ambientales favorecen la captura de C en el pastizal semiárido, con énfasis en los efectos de “legado” de la precipitación (PPT) y los pulsos de C generados después de los eventos de PPT. Cuatro años continuos de mediciones del NEE con un sistema de covarianza de vórtices (EC) fueron analizados. Los flujos de C mostraron ciclos diarios y estacionales típicos con la temperatura del aire y la densidad de flujo fotónico fotosintético como controles diarios y la humedad del suelo y la dinámica de la vegetación (medida como EVI) controlando el NEE a escala estacional. El pastizal semiárido fue una fuente (16.37 and 93.83 g C m-2 a-1) y un sumidero de C ((-15.85 and -121.02g C m-2 a-1). Se identificaron efecto de legado de la PPT a escala estacional. La PPT invernal afectó positivamente la captura de C durante el verano; mientras que la PPT del verano no tuvo efectos sobre la productividad invernal. Cien mm de PPT invernal y 200 durante el verano fueron necesarios para convertir al pastizal en un sumidero neto de C. Por otra parte, la respiración del ecosistema (ER) respondió pocas horas después del evento de PPT, mientras que pasaron hasta 5 días para observar una respuesta de la productividad del ecosistema (GEE). Eventos de PPT tan bajos como 0.25mm incrementaron ER, pero PPT acumulada mayor a 40mm estimularon GEE. En general, los pulsos de C estuvieron relacionados con la magnitud del estímulo (ej. tamaño del evento de PPT) y las condiciones previas del ecosistema (ej. contenido de humedad del suelo previo al evento de PPT). Los resultados de este estudio demostraron la importancia de la PPT invernal y de los pulsos de C después de los eventos de PPT al balance de C anual en un pastizal semiárido con lluvias durante el verano.""Terrestrial ecosystems control the atmospheric carbon (C) dynamics on Earth, removing~25% of C emissions derived from anthropogenic activities. However, high seasonal and interannual variability generates large uncertainties about their C uptake capacity. Understanding environmental and biotic factors affecting C uptake and C release rates will help us to improve predictions of climate change impacts on ecosystem processes as well as its feedback effects. The aim of this study was to determine biotic and environmental drivers of the net ecosystem C exchange (NEE) and its components to understand which environmental conditions favor uptake or release of C in the semiarid grassland, with emphasis on precipitation (PPT) legacy effects and short term C fluxes following PPT events. Four years of continuous NEE measurements with an eddy covariance (EC) system were analyzed. Carbon fluxes showed typical diurnal and seasonal cycles with air temperature and photosynthetic photon flux density (PPFD) as the main diurnal drivers, whereas soil moisture and vegetation dynamics (the enhanced vegetation index, EVI) controlled NEE at seasonal scale. The semiarid grassland behaved as a source (16.37 and 93.83 g C m-2 y-1), and a sink of C (-15.85 and - 121.02g C m-2 y-1). Precipitation legacy effects on NEE and its components were identified at seasonal scale. Winter precipitation positively affected C uptake of summer, however, summer precipitation did not have effects on winter C fluxes. One hundred mm of winter PPT and 200 mm of summer PPT were needed for turning the ecosystem into a C sink. On the other hand, Ecosystem respiration (ER) responded within few hours following a PPT event whereas it took five days for gross ecosystem exchange (GEE) to respond. Precipitation events as low as 0.25 mm increased ER, but cumulative PPT > 40 mm that infiltrated deeper into the soil profile stimulated GEE. Overall, ER fluxes following PPT events were related with the size of the stimulus (e.g. PPT event size) and previous soil conditions (e.g. previous soil volumetric water content and inter PPT event period).
Enhanced refrigerant capacity in Gd-Al-Co microwires with a biphase nanocrystalline/amorphous structure
Get PDF"A class of biphase nanocrystalline/amorphous Gd(50+5x)Al(30-5x)Co20 (x = 0, 1, 2) microwires fabricated directly by melt-extraction is reported. High resolution transmission electron microscopy and Fourier function transform based analysis indicate the presence of a volume fraction (similar to 20%) of similar to 10nm sized nanocrystallities uniformly embedded in an amorphous matrix. The microwires possess excellent magnetocaloric properties, with large values of the isothermal entropy change (-Delta S-M similar to 9.7 J kg(-1) K-1), the adiabatic temperature change (Delta T-ad similar to 5.2K), and the refrigerant capacity (RC similar to 654 J kg(-1)) for a field change of 5 T. The addition of Gd significantly alters T-C while preserving large values of the Delta S-M and RC. The nanocrystallites allow for enhanced RC as well as a broader operating temperature span of a magnetic bed for energy-efficient magnetic refrigeration.
Arabidopsis AtDjA3 null mutant shows increased sensitivity to abscisic acid, salt, and osmotic stress in germination and post-germination stages
Get PDF"DnaJ proteins are essential co-chaperones involved in abiotic and biotic stress responses. Arabidopsis AtDjA3 gene encodes a molecular co-chaperone of 420 amino acids, which belongs to the J-protein family. In this study, we report the functional characterization of the AtDjA3 gene using the Arabidopsis knockout line designated j3 and the 35S::AtDjA3 overexpression lines. Loss of AtDjA3 function was associated with small seed production. In fact, j3 mutant seeds showed a reduction of 24% in seed weight compared to Col-0 seeds. Expression analysis showed that the AtDjA3 gene was modulated in response to NaCl, glucose, and abscisic acid (ABA). The j3 line had increased sensitivity to NaCl and glucose treatments in the germination and cotyledon development in comparison to parental Col-0. Furthermore, the j3 mutant line exhibited higher ABA sensitivity in comparison to parental Col-0 and 35S::AtDjA3 overexpression lines. In addition, we examined the expression of ABI3 gene, which is a central regulator in ABA signaling, in j3 mutant and 35S:rAtDjA3 overexpression lines. Under 5 RNA ABA treatment at 24 h, j3 mutant seedlings displayed higher ABI3 expression, whereas in 35S::AtDjA3 overexpression lines, ABI3 gene expression was repressed. Taken together, these results demonstrate that the AtDjA3 gene is involved in seed development and abiotic stress tolerance.
Purificación, análisis de estabilidad térmica y ensayos de cristalización de la proteína G0S2 de humano
Get PDFTesis (Maestría en Ciencias en Biología Molecular)"G0S2 es una proteína básica de 103 aminoácidos. Hasta la fecha, la función mejor conocida de G0S2 es su capacidad inhibitoria directa sobre la enzima lipolítica triglicérido lipasa de tejido adiposo (ATGL). Aunque también se le han asignado diversas actividades biológicas, incluyendo papeles en el ciclo celular, proliferación celular, apoptosis, inflamación y carcinogénesis. Es por esto que dilucidar la estructura y las funciones con más precisión de G0S2 sería de gran aporte para poder abordar cuestiones específicamente sobre la regulación de ATGL, así como también su participación en aspectos importantes en la lipólisis y otros procesos celulares. Con el objetivo de obtener la estructura tridimensional experimental de G0S2, expresamos G0S2 humana (hG0S2) como proteína de fusión con la proteína SUMO de S. cerevisiae en E.coli mediante el vector de expresión pETSUMO. La proteína de fusión SUMO-hG0S2 y su producto de proteólisis hG0S2 fueron solubles y se purificaron por cromatografías de afinidad, intercambio iónico y exclusión molecular. De estas dos formas de la proteína Obtuvimos concentraciones de proteína de 10 y 5 mg/mL, respectivamente, lo que permitió realizar los primeros ensayos de cristalización. Finalmente, observamos que el uso de glicerol al 10% y pH 6.5 tienen un impacto positivo en la estabilidad térmica de
hG0S2, lo que nos proporciona un buen punto de partida para buscar la optimización de condiciones para su cristalización y poder caracterizar la estructura de hG0S2.""G0S2 is a basic protein of 103 amino acids. To date, the best-known function of G0S2, is the inhibitory effect that it has on the activity of the lipolytic enzyme, adipose triglyceride lipase (ATGL). Although, G0S2 has also been related to various biological activities, including roles in cell cycle, cell proliferation, apoptosis, inflammation and carcinogenesis. That is why, the elucidation of the 3D structure of G0S2 would be a significant contribution to address issues specifically on the regulation of ATGL, as well as their participation in important aspects in lipolysis and other cellular processes. In order to obtain the experimental three-dimensional structure of G0S2, we expressed human G0S2 (hG0S2) as a fusion protein with SUMO protein of S. cerevisiae in E. coli with the expression vector, pETSUMO. The fusion protein SUMO-hG0S2 was found to be soluble and its purification was carried out using IMAC, ion exchange and gel filtration chromatography, the hG0S2 was released by proteolysis with PPS. We obtained protein concentrations of 10 and 5 mg/mL for the SUMO-hG0S2 and hG0S2 proteins, respectively, which allowed us to set the first crystallization trials. Finally, we found by thermofluor approach that the use of 10% glycerol, and pH 6.5 has a positive impact on hG0S2 thermal stability, which provides a good starting point to optimize purification and crystallization conditions that should let us characterize the structure of hG0S2.
Environmental context for the terminal Ediacaran biomineralization of animals
Get PDF"In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel-in-funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high-resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to + 6 parts per thousand) and an increase in the abundance and S-34 composition of pyrite. In contrast, delta S-34 values of carbonate-associated sulfate remain steady throughout the succession, resulting in anomalously large (>70 parts per thousand) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft-bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.
Giant reversible inverse magnetocaloric effects in Ni50Mn35In15 Heusler alloys
Get PDF"The magnetic properties and reversibility of the magnetocaloric effect of Ni50Mn35In15 have been studied in the vicinity of the phase transition using magnetization and direct adiabatic temperature change (?Tad) measurements in magnetic fields up to 14 T. The magnetostructural phase transitions (MSTs) between a martensitic phase (MP) with low magnetization (paramagnetic or antiferromagnetic) and a nearly ferromagnetic austenitic phase were detected from thermomagnetic curves, M(T,H), at the applied magnetic fields up to 5 T. The MST temperature was found to be nearly independent of magnetic field for H < 5 T, and shifted to lower temperature with the further increase of magnetic field to 14 T. A large and nearly reversible inverse magnetocaloric effect (MCE) with ?Tad ? ?11 ? for a magnetic field change of ?H = 14 T was observed in the vicinity of the MST. The irreversibility of ?Tad was found to be 1 K. A direct ?Tad of +7 K for ?H = 14 T was detected at the second order ferromagnetic-paramagnetic phase transition. The obtained results have been discussed in terms of the suppression of antiferromagnetic correlations with the application of a strong magnetic field, and a reversibility of the initial magnetic state of the MP with applied magnetic field when the MST coincides with TC.