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New results on robust exponential stability of integral delay systems
Get PDF"The robust exponential stability of integral delay systems with exponential kernels is investigated. Sufficient delay-dependent robust conditions expressed in terms of linear matrix inequalities and matrix norms are derived by using the Lyapunov–Krasovskii functional approach. The results are combined with a new result on quadratic stabilisability of the state-feedback synthesis problem in order to derive a new linear matrix inequality methodology of designing a robust non-fragile controller for the finite spectrum assignment of input delay systems that guarantees simultaneously a numerically safe implementation and also the robustness to uncertainty in the system matrices and to perturbation in the feedback gain.
Elastocaloric effect in Ti-Ni shape-memory wires associated with the B2 ↔ B19' and B2 ↔ R structural transitions
Get PDF"We have studied the elastocaloric properties of Ti-Ni shape-memory wires subjected to specific heat treatments to decouple the B2 R transition from the B2 B19' one. The entropy values at moderate stresses (similar to 170 MPa) for the B2 B19' transition are remarkably high (in the range 60-80 J/kg K). However, in spite of the B2 R transition exhibits significantly lower entropy changes (similar to 12 J/kg K), the much smaller hysteresis of this transition gives rise to a larger reversible elastocaloric effect for low applied stresses. Therefore, the reversible elastocaloric strength associated with the B2 R is larger than the elastocaloric strength associated with the B2 B19' transition.
Gold-TiO2-Nickel catalysts for low temperature-driven CO oxidation reaction
Get PDF"Nickel-doped-TiO2 catalysts were prepared by the sol–gel method and surface modified with gold nanoparticles (AuNPs) by the urea-deposition-precipitation technique. The as-synthesized catalysts were characterized by X-ray diffraction, Raman and XPS spectroscopies, N2 physisorption, STEM-HAADF microscopy and TPR hydrogen consumption. The Au/TiO2-Ni catalysts were evaluated catalytically performing CO oxidation reactions. The catalyst with nickel content of 1 wt. % (Au/TiO2-Ni 1) showed the highest CO conversion with respect to the high-nickel-content or bare/commercial TiO2 at 0 °C. In situ DRIFTS showed a strong participation of both nickel due to the presence of surface-nickel-metallic nanoparticles formed during the CO adsorption process at reaction temperatures above 200 °C, and surface-bridged-nickel-CO species. A minor deactivation rate was observed for the Au/TiO2-Ni 1 catalyst in comparison with the Au/TiO2 one. The oxygen vacancies that were created on the sol–gel-doped TiO2 improved the catalytic behavior during the performance of CO oxidation reactions, and inhibited the AuNP sintering.
Facile synthesis and characterization of MnxZn1-xFe2O4/activated carbon composites for biomedical applications
Get PDF"The synthesis of MnxZn1-xFe2O4 ferrites (x = 0.4, 0.5 and 0.6) by means of the co-precipitation method is reported. Furthermore, a composite of Mn0.4Zn0.6Fe2O4/activated carbon was prepared with the mechanosynthesis method. The magnetic, structural, morphological and chemical properties were analyzed by means of VSM, XRD, SEM, FTIR and Boehm's titration. The heating capacity was evaluated under a magnetic field using solid-state induction heating equipment, in addition a hemolysis test was performed using human red blood cells. With regard to the synthesis of manganese-zinc ferrite, the results indicated that Mn0.4Zn0.6Fe2O4 ferrite showed higher saturation magnetization (64.48 emu/g) than the other ferrite obtained, with superparamagnetic behavior. The Mn0.4Zn0.6Fe2O4/activated carbon composite was able to heat in concentrations of 10 mg/ml under a magnetic field (10.2 kAm-1 and frequency 200 kHz), increasing the temperature up to 42.5 °C. The hemolysis test indicated that the presence of activated carbon reduces the hemolytic behavior of the ferrite. Thanks to its heating capacity and non-hemolytic activity, theMn0.4Zn0.6Fe2O4/activated carbon composite is a potential candidate for use in biomedical applications.
Modelación hidrogeoquímica en tres ambientes naturales en México: cárstico, volcánico y cuenca sedimentaria
Get PDF"En el presente trabajo se desarrollan estrategias para la modelación hisrogeoquímica de acuíferos tipo. Para tener un mayor conocimiento del comportamiento del agua subterránea respecto a su origen y evolución. Por medio del desarrollo de una metodología donde se analiza desde un punto de vista de interdisciplinario. La tesis se ha dividido en capítulos; en el primero de ellos se exponen conceptos necesarios para el entendimiento de la hidrogeoquímica. En el segundo se da a conocer la metodología VISHMOD (Virtual Samples in Hydrochemical Modeling) desarrollada, basada principalmente en la geología del sitio, mineralogía, hidrologeologia y la hidrogeoquimica, que dan origen a la evolución del agua subterránea. Esta metodología parte de la hipótesis que el agua una vez que se infiltra inicia su evolución por medio de procesos hidrogeoquimicos los cuales se identifican al aplicar esta metodología. Está conformada por 10 pasos que son: Modelo hidrogeológico conceptual, Caracterización hidrogeoquimica, Modelación Directa, Miembro Extremos, Identificación de Mezclas y Modelo Hidrogeoquímico, Fracciones de mezcla, Obteniendo Concentraciones a partir de las fracciones de mezcla, primera calibración (Comparación de Datos reales vs composición química virtual), Segunda calibración (comparación de composición química reales vs composición química virtual 2) En el capítulo 3 se aplica esta metodología en una zona con rocas carbonatadas donde obtuvimos un modelo con una baja incertidumbre es decir muy similar a lo encontrado en la naturaleza. VISHMOD, resultó ser una efectiva herramienta para identificar y simular los procesos de mezcla con interacción agua roca, precipitación, disolución de minerales que ocurren en los acuíferos de la región. En el capítulo 4 se aplica la metodología VISHMOD a un área kárstica, donde se identificado los procesos hidrogeoquímicos, de forma cualitativas y cuantitativas; obteniendo la evolución hidrogeoquímica del aguas subterráneas. En el capítulo 5 se trabaja con una zona volcánica como parte de la estrategia para el análisis del sistema acuífero, en el que no solo se tienen una mezcla de aguas naturales, también existe una aportación de agua antropizada, con el método se identificó la zona con contaminación.""In this paper it is developed strategies to geochemical modeling of type aquifers for having a better understanding of groundwater behavior regarding its origin and evolution, through the development of a methodology which it is analyzed from an interdisciplinary perspective. The thesis is divided into chapters, in the first one, there are exposed some concepts necessary for the understanding of the hydrogeochemical. In the second chapter, it is given to know the developed methodology VISHMOD (Virtual Samples in Hydrochemical Modeling), based mainly on site geology, mineralogy, hidrologeology and the hydrochemical, which give rise to the evolution of the groundwater. This methodology is based on the hypothesis that when the water, once it infiltrates, begins its evolution through hydrogeochemical processes. It consists of 10 steps: 1) conceptual hydrogeologic model, 2) hydrochemically characterization, 3) geochemical Modeling, 4) Member Extremes 5) Identification of Mixtures and geochiemical modeling , 6) fractions mixture, 7) Getting concentrations from the fractions mixture, 8) first calibration (comparison of actual data vs virtual chemical composition), 9) first calibration (comparison of actual data vs virtual chemical composition), 10) Second calibration (comparison of actual chemical composition vs chemical composition virtual 2) . In chapter 3, this methodology is applied in an area with carbonate rocks; where we got a model with a low uncertainty that is very similar that we found in nature. VISHMOD, turned out to be an effective tool to identify and simulate the processes of interaction rock-water, mix, precipitation, dissolution of minerals that occur in the aquifers in the region. In Chapter 4, the methodology is applied to a karst area where VISHMOD identified evolutionary trends in qualitative and quantitative; as well as groups and hydrogeochemical processes which give the evolution into the groundwater. In Chapter 5, it is applied in a volcanic area as part of the strategy for the analysis of the aquifer system, which not only have a mixture of natural waters, there is also a contribution of water entropized, the method identified this contaminated area.
Electron transport study on functionalized armchair graphene nanoribbons: DFT calculations
No full text"Quantum transport studies are performed on doped and functionalized 8- and 11-armchair graphene nanoribbons (aGNRs) by means of density functional theory. Substitutional doping is performed by introducing boron, nitrogen, oxygen, silicon, phosphorus, and sulfur atoms within the lattice of the aGNRs. Other functional groups such as borane, amine, hydroxyl, thiol, silane, silene, phosphine, and phosphorane groups are also introduced at the nanoribbon's edge. The dopant position and the nanoribbon's width strongly influence the current–voltage characteristics, and generally, the narrow 8-aGNRs and edge-doped 11-aGNRs show deteriorated transport properties, mainly due to the formation of irregular edges that create highly localized states disrupting several conducting bands. On the other hand, the inside-doped 11-aGNRs are barely affected, mainly because these systems preserve the edge's structure, thus edge conduction bands still contribute to the electron transport. Our results suggest that wider graphene nanoribbons could be functionalized at the inner sections without significantly compromising their transport characteristics while retaining the chemical reactivity that characterize doped nanocarbons. Such characteristics are highly desirable in fuel cells where doped graphene is used as a catalyst support or as a metal-free catalyst.
Controllable biosynthesis of small silver nanoparticles using fungal extract
Get PDF"The search for reliable and eco-friendly methods for the production of nanoscale materials is an important aspect of nanotechnology. Silver nanoparticles (AgNPs) are of special interest because of their antimicrobial properties, especially those of small size. In this work, AgNPs were produced under different conditions of temperature and pH using the extract from the fungus Neurospora crassa as reducing agent. Mainly quasi-spherical particles were obtained at all incubation conditions. However, optimum conditions to produce small sizes in the range of 2 - 9 nm were at 4°C and pH 3, also particles of 2 - 22 nm were obtained at 25°C with unmodified pH (6.5) and pH 10. Nevertheless, only particles synthesized at 25°C and pH 10 maintained the same size range after storage of 10 months. In summary, optimal incubation conditions for the synthesis of silver nanoparticles of small size range are reported. This improves the storage time of particles without losing its original size and without going into aggregation or agglomeration.
Diseño Top-Down y primeros pasos de fabricación de un chip microfluídico como biosensor para el diagnóstico de virus del papiloma humano: desarrollo del mecanismo de manipulación analito
No full text"Este proyecto de enfoque multidisciplinario e interinstitucional, atiende el problema de la detección e identificación de los tipos predominantes de VPH de alto riesgo, ambas fases necesarias en el diagnóstico de la infección viral y para complementar el tamizaje de las mujeres en riesgo de desarrollar CaCu, por lo que el presente proyecto resulta de relevancia tanto social como científica. En este proyecto de tesis se presenta la integración de los datos recabados durante el proceso de experimentación. Se presentan algunas técnicas empleadas en el desarrollo del dispositivo DMF planteado para lograr la automatización del proceso de sensado de patógenos, se habla de las complicaciones técnicas encontradas durante la fabricación del dispositivo y se menciona el plan de desarrollo del mismo para continuar con su construcción y eventual implementación.""This project of multidisciplinary and inter-institutional focus deals with the problem of detection and identification of predominant HPV viruses kinds, both, necessary phases on diagnosis of viral infections and discrimination of women at risk to develop cervical cancer, due that, this projet results of scientific and social importance.
Human impacts and aridity differentially alter soil N availability in drylands worldwide
No full text"Aims Climate and human impacts are changing the nitrogen (N) inputs and losses in terrestrial ecosystems. However, it is largely unknown how these two major drivers of global change will simultaneously influence the N cycle in drylands, the largest terrestrial biome on the planet. We conducted a global observational study to evaluate how aridity and human impacts, together with biotic and abiotic factors, affect key soil variables of the N cycle.
Location Two hundred and twenty-four dryland sites from all continents except Antarctica widely differing in their environmental conditions and human influence.
Methods Using a standardized field survey, we measured aridity, human impacts (i.e. proxies of land uses and air pollution), key biophysical variables (i.e. soil pH and texture and total plant cover) and six important variables related to N cycling in soils: total N, organic N, ammonium, nitrate, dissolved organic: inorganic N and N mineralization rates. We used structural equation modelling to assess the direct and indirect effects of aridity, human impacts and key biophysical variables on the N cycle.
Results Human impacts increased the concentration of total N, while aridity reduced it. The effects of aridity and human impacts on the N cycle were spatially disconnected, which may favour scarcity of N in the most arid areas and promote its accumulation in the least arid areas.
Main conclusions We found that increasing aridity and anthropogenic pressure are spatially disconnected in drylands. This implies that while places with low aridity and high human impact accumulate N, most arid sites with the lowest human impacts lose N. Our analyses also provide evidence that both increasing aridity and human impacts may enhance the relative dominance of inorganic N in dryland soils, having a negative impact on key functions and services provided by these ecosystems.
Investigating the magnetic entropy change in single-phase Y2Fe17 melt-spun ribbons
Get PDF"The inspection of simplified fabrication and/or processing routes in order to produce materials with attractive magnetocaloric properties is of paramount importance for the development of environmentally friendly magnetic cooling technology. In this work, we have made use of the melt-spinning technique to obtain directly single-phase Y2Fe17 polycrystalline ribbons avoiding any high-temperature annealing for phase consolidation and homogenization. The melt-spun ribbons, with hexagonal Th2Ni17-type crystal structure, exhibit a moderate maximum value of the magnetic entropy change, |?SMpeak| = 2.4(4.4) J kg?1 K?1 under an applied magnetic field change of 2(5) T. Although these values are similar to those for the bulk alloy, the ?SM(T) curves are manifestly broader, thus giving rise to an expansion of the working temperature range and the enhancement of about 15% in the refrigerant capacity. We also show that the magnetic field dependence of |?SMpeak| at T = TC follows a H2/3 power-law.