Repositorio IPICYT
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On the broadening of the magnetic entropy change due to Curie temperature distribution
Get PDF"We have studied the correlation between the broadening of the isothermal magnetic entropy change and the Curie temperature (T-C) distribution in nanostructured Pr2Fe17 and Nd2Fe17 alloys produced by high-energy ball-milling after milling times of 10, 20, and 40 h. The changes in the microstructure affect the Fe local environments and as a consequence the magnetic interactions, giving rise to T-C distributions centered around 285K and 330K for the Pr2Fe17 and Nd2Fe17 alloys, respectively. The width of the distributions enlarges (up to 60K) as the milling-time increases, and consequently, the isothermal magnetic entropy change curves show an extended full width at half maximum.
Analysis of Ostwald ripening in Ni-rich Ni–Ti alloys by diffusion couples
Get PDF"The coarsening kinetics of gamma' precipitates in Ni-rich Ni-Ti alloys are studied using a Ni-11-5 wt% Ti and pure Ni diffusion couple. The formed concentration gradient allowed to study the aging process at 1023 K (750 degrees C) in Ni-rich Ni Ti alloys with Ti content from 8-62 to 11-15 wt% Ti. In general, during the coarsening of gamma' precipitates, the experimental coarsening kinetics do not fit well to the LSW or TIDC theoretical models and anomalous behaviour of coarsening rate constant (k(r)) associated with gamma' volume-fraction is confirmed at high values.
Ermakov-Lewis invariants and Reid systems
Get PDF"Reid´s mth-order generalized Ermakov systems of nonlinear coupling constant ? are equivalent to an integrable Emden-Fowler equation. The standard Ermakov-Lewis invariant is discussed from this perspective, and a closed formula for the invariant is obtained for the higher-order Reid systems (m ? 3). We also discuss the parametric solutions of these systems of equations through the integration of the Emden-Fowler equation and present an example of a dynamical system for which the invariant is equivalent to the total energy.
The separation between the 5′-3′ ends in long RNA molecules is short and nearly constant
Get PDF"RNA molecules play different roles in coding, decoding and gene expression regulation. Such roles are often associated to the RNA secondary or tertiary structures. The folding dynamics lead to multiple secondary structures of long RNA molecules, since an RNA molecule might fold into multiple distinct native states. Despite an ensemble of different structures, it has been theoretically proposed that the separation between the 5 ' and 3 ' ends of long single-stranded RNA molecules (ssRNA) remains constant, independent of their base content and length. Here, we present the first experimental measurements of the end-to-end separation in long ssRNA molecules. To determine this separation, we use single molecule Fluorescence Resonance Energy Transfer of fluorescently end-labeled ssRNA molecules ranging from 500 to 5500 nucleotides in length, obtained from two viruses and a fungus. We found that the end-to-end separation is indeed short, within 5-9 nm. It is remarkable that the separation of the ends of all RNA molecules studied remains small and similar, despite the origin, length and differences in their secondary structure. This implies that the ssRNA molecules are 'effectively circularized' something that might be a general feature of RNAs, and could result in finetuning for translation and gene expression regulation.
Heat shock effect in breaking physical dormancy in seeds of Lupinus elegans and L. rotundiflorus from Jalisco, Mexico
Get PDF"Most Lupinus spp. (Fabaceae) grow in pine and pine-oak forests with natural and induced fires, and their seeds have physical dormancy, which could be broken in response to appropriate environmental signals, such as high temperatures, humidity and fire. We applied heat treatments to break seed dormancy of L. elegans and L. rotundiflorus from the State of Jalisco, México, with different storage times (0, 1 and 2 yr for L. elegans and 0, 1, 2, 3 and 4 yr for L. rotundiflorus). Seeds were immersed in boiling water for 5, 10, and 15 s and incubated in wet and dry sand at 100 °C, 120 °C, and 150 °C during 60 min and 90 min. Germination trials were set at 25 °C with 12 h of irradiance per day. For both species, no germination resulted after incubation at 120 °C and 150 °C. For L. rontundiflorus, germination was higher for seeds incubated in wet sand for 60 m than for those incubated for 90 m. After scarification with boiling water, fresh seeds of L. elegans, germinated more than those stored for 1 and 2 yr, whereas incubation in wet and dry sand resulted in higher germination for 1 and 2 yr old seeds than for fresh seeds. Fresh seeds of L. rotundiflorus showed higher germination than stored seeds across treatments. Our results may be useful for further studies to understand and predict ecological plant responses in Mexican forests.""La mayoría de las especies silvestres de Lupinus (Fabaceae) crecen en bosques de pino y pino-encino, en donde se presentan incendios naturales e inducidos. Sus semillas tienen latencia física, la cual puede ser rota en respuesta a señales ambientales como altas temperaturas, humedad y fuego. En esta investigación, se aplicaron tratamientos de calor para romper la latencia de semillas de L. elegans y L. rotundiflorus del estado de Jalisco, México, con diferentes tiempos de almacenamiento (0, 1 y 2 años para L. elegans y 0, 1, 2, 3 y 4 años para L. rotundiflorus). Un grupo de semillas fue sumergido en agua hirviendo por 5, 10 y 15 segundos, otro grupo fue incubado en arena húmeda o seca a 100, 120 y 150 °C durante 60 y 90 minutos. Las semillas se pusieron a germinar a 25 °C con fotoperíodo de 12 horas. Para ambas especies, no hubo germinación en semillas incubadas a 120 y 150 °C. Para L. rotundiflorus, la germinación fue más alta en semillas incubadas en arena húmeda por 60 minutos que por 90 minutos. Las semillas frescas de L. rotundiflorus mostraron mayor germinación que las almacenadas, en los distintos tratamientos. Después de la escariicación con agua hirviendo, las semillas frescas de L. elegans germinaron más que las almacenadas por 1 y 2 años, mientras que para las semillas almacenadas por 1 y 2 años la incubación en arena húmeda y seca resultó en mayor germinación que para las semillas frescas. Estos resultados podrían ser útiles para entender y predecir respuestas ecológicas de las plantas en bosques mexicanos.
Global finite-time stability characterized through a local notion of homogeneity
Get PDF"In this work, a notion of local homogeneity is formally defined. Important results involving homogeneous functions or vector fields are reformulated in the consequent local context. In particular, global finite-time stability is characterized through the proposed notion of local homogeneity. As an application of the developed analytical setting, a global finite-time stabilization scheme for robot manipulators with bounded inputs is presented. The developed framework and results prove to be useful to relax analytical and synthesis constraints imposed or generated by homogeneity requirements.
Synthesis, characterization and photocatalytic performance of zinc oxide structured nanocomposites for the treatment of endocrine disrupting compounds in water
Get PDFTesis (Doctorado en Ciencias Ambientales)"El ZnO es un material no tóxico de bajo costo con un interesante potencial fotocatalítico en la degradación de contaminantes en medio acuoso. Sin embargo, su aplicación se encuentra limitada por su baja eficiencia, fotocorrosión y el costo energético de su recuperación. Este trabajo tiene como objetivo incrementar la actividad fotocatalítica en la degradación de compuestos disruptores endócrinos a través de la funcionalización de ZnO con nanopartículas de plata. Además el desarrollo de un método para la inmovilización del fotocatalizador modificado, Ag/ZnO, en una matriz polimérica proyectando su uso en sistemas de tratamiento continuo de agua. Los resultados demuestran que el método de fotodeposición promueve la distribución homogénea de nanopartículas de plata. El incremento en los parámetros de red indican la inserción de iones Ag+ en la estructura cristalina del ZnO dando lugar a una fuerte interacción química entre las nanopartículas de plata y ZnO. Adicionalmente, la presencia de grupos hidroxilo, OH-, y el incremento en la absorción de luz visible promovió la degradación fotocatalítica bisfenol A, triclosan y rodamina B de manera más eficiente. Los resultados de degradación del bisfenol A a 302 nm por el fotocatalizador Ag/ZnO muestran una constante de velocidad aparente (kapp) 3.7 veces mayor al valor obtenido por ZnO: kapp =0.01929 min-1 m-2. Además, la degradación de bisfenol A (25%, 3h), triclosan (35%, 2h) y rodamina B (95%, 2h) en condiciones de luz visible se traduce en el potencial del catalizador de ser activado con luz solar. Por otra parte, las nanopartículas de fotocatalizador Ag/ZnO fueron inmovilizadas en una matriz de poli(ácido acrílico) entrecruzado. La superficie de las partículas fue previamente modificada por un agente acoplante (GLYMO®) que permitió (i) la dispersión y anclaje por esterificación de las nanopartículas en la matriz poliacrílica en formación y (ii) promover la cristalización y estabilidad térmica del polímero.""ZnO is a non-toxic catalyst of low cost with interesting photocatalytic potential, particularly for the degradation of water contaminants. However, its application has not been much developed because of its poor efficiency, its photocorrosion and energetic cost of recovery. Therefore, the main objectives of this research was to improve the efficiency of ZnO for the degradation of endocrine disrupting compounds and propose a method for the immobilization of the photocatalyst projecting a continuous water treatment process. The first step consisted in the design of a new photocatalytic system by functionalizing ZnO nanoagglomerates with silver nanoparticles (Ag/ZnO). The results showed that photodeposition method promotes a homogeneous distribution of AgNPs on ZnO surface. Moreover, the increment in lattice parameters suggests the insertion of Ag+ ions into the crystalline structure of ZnO and strong interactions between AgNPs and ZnO. In addition, hydroxyl surface content and the improved absorption under visible light allowed the enhancement in the photodegradation efficiency of bisphenol-A, triclosan and rhodamine-B. The obtained Ag/ZnO photocatalyst showed higher apparent rate constant (kapp) for the degradation of bisphenol-A at 302 nm: kapp=0.01929 min-1 m-2, which is 3.7 times the value for pure ZnO. Degradation of bisphenol-A (25%, 3h), triclosan (35%, 2h) and rhodamine-B (95%, 2h) was successfully carried out under visible light which is an important achievement in case of solar light use. On the other hand, to overcome aggregation problems, Ag/ZnO photocatalyst was immobilized owing to their incorporation in a cross-linked poly(acrylic acid) matrix. The surface of Ag/ZnO was previously modified, using a silane coupling agent: GLYMO® which allowed (i) dispersing and anchoring NPs on the polyacrylic matrix by formation of ester bonds, and (ii) promoting crystallization and thermal stability of the polymer.
Maximizing hydrogen production and substrate consumption by Escherichia coli WDHL in cheese whey fermentation
Get PDF"Fermentative hydrogen production is strongly affected by pH. In order to maximize hydrogen production and substrate consumption in Escherichia coli ΔhycA, ΔlacI (WDHL) cheese whey fermentation, the influence of pH control at values of 5.5, 6, and 6.5 was studied in batch stirred-tank bioreactors. From the conditions evaluated, pH 6.5 was the best condition, at which the highest cumulative hydrogen production and yield (1.78 mol H2/mol lactose) were obtained. Moreover, at this pH, all carbohydrates from the cheese whey were consumed, and a mix of ethanol and organic acids, mainly lactate, were produced from glucose, whereas galactose yielded acetate, ethanol, and succinate. Operating the reactor at pH 5.5 resulted in the highest maximum specific production rate, but smaller hydrogen yield because only glucose was metabolized and galactose was accumulated. At pH 6, not all cheese whey carbohydrates were consumed, and it was not favorable for hydrogen production. Lactose consumption and growth kinetics were not affected by the pH. The results show the importance of controlling pH to maximize hydrogen production and substrate consumption using cheese whey as substrate.
El papel del Glutatión en la respuesta a estrés oxidante del hongo patógeno oportunista Candida glabrata.
Get PDFTesis (Doctorado en Ciencias en Biologia Molecular)"Candida glabrata es un hongo patógeno oportunista, en EUA se encuentra en el 18 a 26% de las candidiasis sistémicas. C. glabrata tiene una fuerte respuesta a estrés oxidante y en este trabajo caracterizamos el papel del glutatión (GSH), un tiol esencial que se requiere para mantener el equilibrio redox celular y en la eliminación de iones metálicos. El GSH se sintetiza a partir de ácido glutámico, cisteína y glicina mediante dos reacciones secuenciales donde intervienen las enzimas Gsh1 (gama glutamil cisteína sintetasa) y Gsh2 (glutatión sintetasa). En primer lugar hicimos un escrutinio para encontrar mutaciones supresoras que permitieran el crecimiento en ausencia del gen GSH1 (gsh1Δ) y encontramos una única mutación en el gen PRO2 (pro2-4), que codifica para la enzima γ-glutamil fosfato reductasa que cataliza la segunda reacción en la ruta de biosíntesis de la prolina. Encontramos que el GSH es importante en la respuesta a estrés oxidante ya que las mutantes gsh1Δ pro2-4 and gsh2Δ son más sensibles a estrés generado por H2O2 y menadiona. También se requiere para la tolerancia a cadmio. En ausencia de las enzimas Gsh1 y Gsh2 las células mueren rápidamente en fase estacionaria. Además, a pesar de que C. glabrata no contiene el ortólogo al transportador de GSH ScOpt1/Hgt1 nuestros datos genéticos y bioquímicos muestran que las mutantes gsh1Δ pro2-4 and gsh2Δ pueden incorporar GSH del medio. Finalmente, reportamos que los sistemas GSH y tiorredoxina, el segundo sistema redox celular, no son esenciales para la respuesta de adaptación a H2O2 independiente de la catalasa.""Candida glabrata, an opportunistic fungal pathogen, accounts for 18-26% of all Candida systemic infections in the US. C. glabrata has a robust oxidative stress response and in this work we characterized the role of glutathione (GSH), an essential tripeptide-like thiol-containing molecule required to keep the redox homeostasis and in the detoxification of metal ions. GSH is synthesized from glutamate, cysteine and glycine by the sequential action of Gsh1 (gammaglutamyl- cysteine synthetase) and Gsh2 (glutathione synthetase) enzymes. We first screened for suppressor mutations that would allow growth in the absence of GSH1 (gsh1Δ background) and found a single point mutation in PRO2 (pro2-4), a gene that encodes a gamma-glutamyl phosphate reductase and catalyzes the second step in the biosynthesis of proline. We demonstrate that GSH is important in the oxidative stress response since the gsh1Δ pro2-4 and gsh2Δ mutant strains are more sensitive to oxidative stress generated by H2O2 and menadione. GSH is also required for Cadmium (Cd) tolerance. In the absence of both Gsh1 and Gsh2, cells die rapidly in stationary phase. Furthermore, C. glabrata does not contain the Saccharomyces cerevisiae high affinity GSH transporter orthologue, ScOpt1/Hgt1, however our genetic and biochemical experiments show that the gsh1Δ pro2-4 and gsh2Δ mutant strains are able to incorporate GSH from the medium. Finally, GSH and thioredoxin, which is a second redox system in the cell, are not essential for the catalase-independent adaptation response to H2O2.
Multivalued synchronization by Poincar coupling
Get PDF"This work presents multivalued chaotic synchronization via coupling based on the Poincaré plane. The coupling is carried out by an underdamped signal, triggered every crossing event of the trajectory of the master system through a previously defined Poincaré plane. A master–slave system is explored, and the synchronization between the systems is detected via the auxiliary system approach and the maximum conditional Lyapunov exponent. Due to the response to specific conditions two phenomena may be obtained: univalued and multivalued synchronization. Since the Lyapunov exponent is not enough to detect these two phenomena, the distance between the pieces of trajectories of the slave and auxiliary systems with different initial conditions is also used as a tool for the detection of multivalued synchronization. Computer simulations using the benchmark chaotic systems of Lorenz and Rössler are used to exemplify the approach proposed.