Repositorio IPICYT
Not a member yet
1534 research outputs found
Sort by
Tropical coral reef system hydrodynamics in the western Gulf of Mexico
Get PDF"The acoustic Doppler current profiler, temperature, salinity and density data set were recorded monthly over the course of a year in a tropical coral reef system to elucidate the effects of abrupt bathymetric changes on current variability and surface temperature over time. A minimum of five transect repetitions were performed during one diurnal tidal cycle each month during the year 2008. According to the empirical orthogonal functions, the dominant terms were advection and friction due to the shallowness of the system and the relatively short continental shelf located in front of the Port of Veracruz (Mexico). The data showed the dominance of the northwest-southeast current velocity components (parallel to the coast) attributed to the winds. The southeastward current velocity was the dominant component throughout the year, followed by the northwestward current velocity component. The data suggested that coral reefs produce current rectification near the shallow reef areas (1 m depth). No correlation existed between surface temperature and the chlorophyll-a levels throughout the year. Residual current velocities throughout the year never reached more than 50 cm s–1 during the sampling periods, and the surface temperature varied from 21 to 30°C, with the highest temperature being observed near the coast and reefs. Finally there was a direct correlation of the northeasterly and strong northwesterly winds with the well-mixed cold-salty water column in the reef area.""Las corrientes marinas, la temperatura del agua, la salinidad y densidad del mar fueron registradas mensualmente a lo largo de un año, en un sistema de arrecifes coralinos del Golfo de México, para obtener los efectos de los cambios batimétricos sobre la variabilidad de las corrientes marinas y de la temperatura superficial. Se realizó un mínimo de cinco repeticiones, para cada transecto durante un ciclo de marea diurna, de forma mensual durante el 2008. De acuerdo con las Funciones Ortogonales Empíricas (EOF), los términos dominantes fueron la advección y la fricción. Esto se debió a la poca profundidad del sistema (<45 m) y a la plataforma continental, relativamente corta, situada frente al puerto de Veracruz (México). Los datos mostraron que la componente de velocidad dominante en el sistema es paralela a la costa (sureste-noroeste) principalmente debido al régimen de vientos. La dirección de la velocidad de la corriente dominante fue hacia el sureste seguida por el componente noroeste. Los datos sugieren que los arrecifes de coral producen una rectificación de la corriente cerca de las zonas de arrecifes poco profundas (1 m de profundidad). No se encontró en este estudio una correlación entre la temperatura de la superficie y los niveles de clorofila-a lo largo del año. Las velocidades de las corriente residual a lo largo del año no rebasaron los 50 cm s–1 durante los períodos de muestreo, y la temperatura superficial variaron de 21 a 30°C. La temperatura más alta se observó cerca de la costa y los arrecifes. Por último, existe una correlación directa entre los vientos del noroeste con la columna de agua mezclada (fría y salada) en el área muestreada.
Cobalt double-ring and double-dot structures: Magnetic properties
Get PDF"The magnetization reversal mechanism of nanostructures of cobalt double-rings (D-rings) and double-dots (D-dots) is investigated in the framework of micromagnetic simulations. The arrays contain two identical coupled rings (wide and narrow) or dots with outer diameter of 200 nm and thicknesses ranging from 2–20 nm. Hysteresis loops, dipole–dipole and exchange energies are systematically calculated for the cases of the structures touching and the structures with a 50-nm inter-magnet separation; moreover, magnetization states along the hysteresis curve are analyzed. The results of both dot and ring D-magnets are compared with the corresponding individual magnets. Our results reveal that all D-ring (in contact and separated) arrays containing narrow rings exhibit non-null remanent magnetization; furthermore, higher coercive fields are promoted when the magnet thickness is increased. It is observed that the magnetization reversal is driven mainly by a clockwise rotation of onion-states, followed by states of frustrated vortices. Our results could help improve the understanding of the magnetic interactions in nanomagnet arrays.
Modelos neuronales memresistivos
Get PDF"El memresistor ha sido llamado el cuarto elemento básico de circuitos eléctricos y desde la implementación en estado sólido, ha surgido un remarcable interés por desarrollar aplicaciones que aprovechen la naturaleza del dispositivo, en específico su capacidad de funcionamiento como memoria no volátil de donde surge su nombre (resistencia con memoria). En este trabajo se muestra que los canales iónicos de potasio y de sodio que se distribuyen sobre el axón de las neuronas pueden ser representados desde el punto de vista eléctrico como memresistores genéricos de primer y segundo orden respectivamente. En particular, dichos memresistores se caracterizaron para mostrar bajo entrada periódica la histéresis pinchada en el plano voltaje-corriente y la dependencia del área de histéresis a la frecuencia de la señal de entrada periódica las cuales son características propias del comportamiento memresistivo y específicas para cada memresistor genérico. Lo cual permite obtener circuitos eléctricos que contienen memresistores genéricos, derivados de los modelos de Hodgkin-Huxley y Morris-Lecar y se muestra la ausencia de estos dispositivos en los modelos de FitzHugh-Nagumo y Hindmarsh-Rose. Asímismo, al no existir memresistores comerciales con las características específicas mostradas en el presente trabajo, se propone una emulación digital para cada memresistor genérico de los canales iónicos, donde las respuestas de spike y bursting típicas de los modelos de neurona son también obtenidas mediante simulaciones numéricas con el emulador propuesto.""The memristor has been named the fourth basic element of electric circuits and since the solid state implementation has emerged an remarkable interest for develop applications that take advantages of the nature of the device, in specifically its ability to work as non-volatile memory hence its name (memory resistor). This work shows that the potassium ionic channels and sodium ionic channels that are distributed over the entire length of the neural axon can be represented from the electric point of view as generic memristors of first and second order, respectively. In particular, the memristors has been characterized to show under periodic entry signal the pinched hysteresis loop in the voltage-current plane and the dependency of the hysteresis area to the frequency of the periodic entry signal, which are the fingerprints of memristors and specific for each generic memristor. The previous result allows to obtain electric circuits that contain generic memristors originated from the Hodgkin-Huxley and Morris-Lecar models and shows the absence of this devices in the FitzHugh-Nagumo and Hindmarsh-Rose models. The absence of commercial memristors with the specific characteristics showed in the present work brings to the proposal of a digital emulator for each generic memristor of the ionic channels. The typical response of spikes and bursting of the neural models are also preserved in the numerical simulations of the proposed emulator.
Military macaw ( Ara militaris ) in Sierra Gorda, Guanajuato, Mexico
Get PDF"I report a new displacement route of the Military macaw (Ara militaris) population located in Sotano del Barro (Querétaro) to the northeastern Guanajuato. This record suggests that Military macaw perform seasonal movements in search of foraging areas between the Sotano del Barro in Xichú (Guanajuato), my study area. Therefore, the presence of Military macaw in the region would have direct implications for policy change in land use, which directly affects the land management of the Sierra Gorda Biosphere Reserve.
Geoecohydrological mechanisms in semiarid tropical forests: spatial and temporal use of water of two coexisting forest tree species
Get PDF"Las regiones semiáridas ya enfrentan un fuerte estrés hídrico y es probable que
aumente, ya que los cambios en los patrones de lluvia, asociados al cambio
climático, son cada vez más variables. El Centro-Norte de México representa una
de las regiones más expuestas a sequía para los bosques semiáridos, a lo largo
del gradiente de precipitación estacional que va de Norte-Sur, siendo un excelente
sistema para estudiar las interacciones ecohidrológicas, incluyendo; las relaciones
hídricas de la planta, la dinámica de la humedad del suelo y los patrones de
distribución de raíces. Llevamos a cabo un estudio para identificar los mecanismos
y estrategias que permiten la coexistencia de las especies de bosques semiáridos
mixtos en temporada de sequía. Este estudio se realizó en tres diferentes tipos de
rodales, que incluyen: rodales monoespecíficos de pino, rodales moespecíficos de
encino y rodales mixtos de pino-encino. Con la utilización de herramientas
geofísicas, identificamos que el bosque se encuentra establecido sobre un suelo
rocoso poco profundo de material volcánico impermeable, con un alto grado de
fracturamiento y fisuras, y una muy delgada capa de suelo (15 – 30 cm). Con los
valores de 18O y 2H de las lluvias provenientes de las cuencas oceánicas del
Pacífico y Atlántico, y manantiales, trazamos nuestra Línea Meteórica Local de
Agua, la cual se comparó con las 2,800 muestras de abundancias naturales de
agua en el xilema. Confirmamos que las especies utilizan diferentes fuentes de
agua durante todo el año, lo que nos ha permitido identificar nichos y rasgos
funcionales de las especies. Quercus potosina utiliza el agua de la roca volcánica
fracturada, particularmente durante la estación seca, moviéndola a través del perfil
del sustrato, cuando está en asociación con Pinus cembroides, evitando así la
exclusión competitiva. En contraste, P. cembroides, no muestra adaptaciones para
adquirir agua de la roca, sin embargo, utiliza el agua levantada por los encinos
(levantamiento hidráulico). Durante la estación seca, Q. potosina, puede depender
únicamente del agua almacenada en su tronco proveniente de eventos pasados,
dejando cierta proporción de humedad del suelo disponible a los pinos. Hemos
demostrado que los suelos rocosos también generan un alto grado de variabilidad
en el contenido de agua y grandes desplazamientos en el estado fisiológico de los
árboles. La interacción positiva observada entre el encino y pino, arroja dudas
sobre la capacidad a largo plazo para tener éxito bajo condiciones
geohidrometeorológicas cada vez más limitadas, y proporcionamos evidencia de la
importancia de Q. potosina en el mantenimiento de la estructura y funcionamiento
del ecosistema en este bioma con deficiencias de agua. Estos resultados
modifican significativamente el paradigma actual del uso de agua por las plantas,
donde el agua que ocurre en las rocas no se considera un recurso potencial.""Semiarid regions already facing strong water stress are likely to be exposed to
higher levels as rainfall patterns change and are becoming more variable under
climate change. Central North Mexico represents one of the most drought prone
regions for semiarid forest along the north–south seasonal precipitation gradient,
making it an excellent location to study ecohydrological interactions, including;
plant–water relations, soil moisture dynamics and root distribution patterns. We
conducted a study to identify the type of mechanisms and strategies permitting
species coexistence in a mixed forest during the drought season. This study was
carried in three different stand types including: monospecific P. cembroides stands;
monospecific Q. potosina stands and mixed oak-pine stands. Using geophysical
tools, we identified that the forest is colonizing shallow rocky soils over
impermeable volcanic material with high fracturing and fissuring and an extremely
thin layer of soil (15 - 30 cm). With the 18O and 2H values of all recorded rainfall
events either coming from the Pacific or Atlantic ocean and of water from springs,
we generated our Local Meteoric Water Line and analyzing the natural abundance
of water isotopes of 2,800 samples of water in pine and oak xylem confirmed that
trees used different water sources throughout the year. This confirmed that trees
used different water sources throughout the year, permitting us to identify temporal
and spatial niches and functional traits of species. Quercus potosina used fractured
volcanic rock water, particularly during drought, moving through the substrate
profile when in association with Pinus cembroides, thus avoiding competitive
exclusion. In contrast P. cembroides showed no adaptations to acquire water rock
however it took advantage of water uplifted by oak (hydraulic lift). During the dry
season, Q. potosina rely only on water stored in their trunks from past rain events
leaving available the soil moisture for pines. Here we demonstrated that rocky soils
also generate a high degree of variability in water content and large offsets in the
physiological status of trees. The observed positive interaction between oak and
pine shed doubts on the long-term capacity of P. cembroides to succeed in
monocultures under increasingly limiting geohydrometeorological conditions, and
provided evidence of the importance of Q. potosina to maintain ecosystem
structure and function in this water-limited biome. These results significantly modify
the current paradigm of water use by trees, where water held in the rocks is not
regarded as a potential water source.
Effect of the continuous addition of ozone in a biofilter treating ethyl acetate vapors
Get PDF"En este trabajo se analizaron los efectos de la adición continua de ozono (O3) en un
biofiltro para el tratamiento de Acetato de Etilo (EA). Se operaron tres filtros, un
control abiótico para estimar oxidación química, un biofiltro sin adición de O3 y uno
bajo la adición continúa de O3. El trabajo de tesis se dividió en 4 capítulos. El
capítulo I presenta una visión general sobre la contaminación del aire, datos
estadísticos de los Compuestos Orgánicos Volátiles (COVs) en México y el
problema del taponamiento en biofiltros; el capítulo II evalúa la adición continua de
O3 como un método para el control la biomasa; el capítulo III se enfoca a los efectos
que tuvo la adición continua de O3 sobre los componentes de la biopelícula
microbiana a lo largo de los sistemas de biofiltración; finalmente, el capítulo IV
presenta los efectos de la adición continua de O3 sobre la composición de la
comunidad microbiana. Con el control abiótico se comprobó que más del 94% de la
eliminación del contaminante en los biofiltros fue llevada a cabo por los
microorganismos. La adición continua de O3 ayudó a mantener estable la eficiencia
de remoción en un 100%, y además tuvo un claro efecto sobre la concentración de
la biomasa y la caída de presión. Sin embargo, los resultados de fracción vacía del
lecho indicaron que eventualmente el biofiltro con O3 se obstruirá cuando se
alcancen periodos de operación más largos. Con los análisis de FTIR y sus
componentes, se concluyó, que la adición continúa de O3 solo tiene un efecto sobre
la cantidad de EPS y no en sus componentes. Los análisis de la comunidad
microbiana mostraron, que ambos biofiltros con/sin O3 presentaron una composición
similar. Las principales bacterias identificadas fueron Beijerinckia,
Gluconacetobacter y Acidocella. Los principales hongos identificados fueron
Rhinocladiella similis, Trichosporon veenhuissi, Exophilia oligosperma, entre otros.
El estudio mostro la diversidad y la evolución de comunidad bacteriana y fúngica y
como estas fueron afectadas por la continua adición de O3.""In the present Master thesis, it was analyzed the effects of O3 addition on a biofilter
treating EA (Ethyl Acetate). Three filters were operated, an abiotic control merely to
estimate the chemical oxidation, a biofilter without O3 addition and a biofilter working
under O3 addition. The thesis work was divided into 4 chapters. Chapter I is an
overview of air pollution, statistical data on of VOCs in México and clogging issues,
in Chapter II it was evaluated the biofilter performance with and without continuous
addition of O3 in order to assess the continuous addition of O3 as a biomass control
method, in Chapter III the effects of the continuous O3 addition on the main
components of the biofilm along biofilter systems were discussed, and finally in
Chapter IV microorganisms in biofilters that work with and without O3 addition were
identified in order to study the effect of the O3 treatment on the microbial community
composition by culture-independent molecular approaches. With the abiotic control
was ensured that the removal of the pollutant in the biofilters was merely by microbial
activity. In general, O3 addition helped to keep stable the 100% removal efficiency
of the system with O3 addition, with a clear effect over the biomass concentration
and the pressure drop. However, the results of void fraction indicated that eventually
the biofilter will clog. On the other hand, O3 addition was affecting only the amount
of EPS not the composition with a greater effect on carbohydrate. Regarding the
microbial community of the biofilter investigated, its composition was similar in the
biofilter working with O3 and without, main genus of bacteria identified were
Beijerinckia, Gluconacetobacter and Acidocella, principally; the gene fungal
presented in the biofilters were, Rhinocladiella similis, Trichosporon veenhuissi,
Exophilia oligosperma and others. Thus the study showed the diversity and
development of bacterial and fungal communities and how they were affected by
continuous treatment of O3.
The corn smut-made cholera oral vaccine is thermostable and induces long-lasting immunity in mouse
Get PDF"The use of corn smut for the production of recombinant vaccines has been recently implemented by our group. In this study, the stability and immunogenic properties of the corn smut-based cholera vaccine, based on the cholera toxin B subunit (CTB), were determined in mouse. The immunogenic potential of distinct corn smut CTB doses ranging from 1 to 30 ?g were assessed, with maximum humoral responses at both the systemic (IgG) and intestinal (IgA) levels at a dose of 15 ?g. The humoral response last for up to 70 days after the third boost. Mice were fully protected against a challenge with cholera toxin after receiving three 15 ?g-doses. Remarkably, the corn smut-made vaccine retained its immunogenic activity after storage at room temperature for a period of 1 year and no reduction on CTB was observed following exposure at 50 °C for 2 h. These data support the use of the corn smut-made CTB vaccine as a highly stable and effective immunogen and justify its evaluation in target animal models, such as piglet and sheep, as well as clinical evaluations in humans.
Purificación, caracterización bioquímica y cristalización de la enzima XanA y dos variantes truncas en el extremo N-terminal
Get PDFTesis (Maestría en Ciencias en Biología Molecular)"En el metabolismo de las purinas la degradación de xantina a ácido úrico es mediada por la enzima xantina oxidasa. Sin embargo, en el 2005 se describió una nueva vía de degradación alternativa en Aspergillus nidulans mediada por la enzima xantina dioxigenasa dependiente de Fe2+ y α-cetoglutarato (α-CG, XanA).
Esta vía, es exclusiva de hongos como A. clavatus, en algunas levaduras como C. albicans, S. pombe y en los géneros Penicillium y Taleromyces, entre otros. XanA es una enzima de 370 residuos de aminoácidos y 41.3 kDa, que presenta un identidad del 18% con la enzima taurina/ α-CG dioxigenasa (TauD). El
mecanismos catalítico de XanA aún no ha sido descrito y dentro del grupo de las hidroxilasas dependientes de Fe2+ y α-CG, es la única capaz de hidroxilar una purina libre. La estructura tridimensional de la enzima XanA aún no ha sido reportada, por lo tanto el objetivo de este trabajo es caracterizar y cristalizar la
proteína XanA. La proteína fue expresada en la cepa BL21 (DE3) Star de E.coli utilizando 0.4 mM de IPTG. La enzima se purificó en dos etapas, IMAC y filtración en gel, con un rendimiento final de 15 mg/L. Los estudios de cinética enzimática muestran que la enzima XanA silvestre es activa y su cinética se ajusta a la
ecuación de Michaelis-Menten con una Km para el α-CG de 97.9 ± 13.9 μM. Realizamos ensayos de cristalización con XanA silvestre (monomérica), y obtuvimos una aproximación a las condiciones adecuadas para obtener cristales.""In the metabolism of purines, degradation of xanthine to uric acid is mediated by the enzyme xanthine oxidase. However, in 2005, a novel mechanism for xanthine metabolism was discovered, this mechanism is mediated by the enzyme xanthine hydroxylase (XanA), which is Fe2+ and α-ketoglutarate-dependent. This pathway is exclusive of certain fungi as A. clavatus, in some yeast as C. albicans, S. pombe and in the genera Penicillium and Taleromyces, among others. XanA is an enzyme of 370 amino acids and 41.3 kDa, which presents an 18% identity with the enzyme taurine/ α-CG dioxygenase (TauD). The catalytic mechanism has not yet been described and it belongs to the group of the hydroxylases dependent on Fe2+ and α-ketoglutarate, XanA is the first enzyme described of this group that hydroxylates a free purine base .The three-dimensional structure of XanA enzyme has not yet been reported; therefore, the aim of this work was to characterize and crystalize the XanA protein. The protein was expressed in E. coli BL21 (DE3) Star cells using 0.4 mM IPTG. Purification of the wild type enzyme was carried out in two steps, IMAC and size exclusion chromatography, with a final yield of 15 mg/L. Enzyme kinetics studies of XanA wild type enzyme show that the enzyme fits the Michaelis-Menten equation with a Km of 97.9 ± 13.9 μM for α-ketoglutarate. We perform crystallization trials with wild type XanA (monomeric), and obtained an approach to appropriate conditions to obtain crystals
Synthesis, characterization, and sensor applications of spinel ZnCo2O4 nanoparticles
Get PDF"Spinel ZnCo2O4 nanoparticles were synthesized by means of the microwave-assisted colloidal method. A solution containing ethanol, Co-nitrate, Zn-nitrate, and dodecylamine was stirred for 24 h and evaporated by a microwave oven. The resulting solid material was dried at 200 °C and subsequently calcined at 500 °C for 5 h. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, confirming the formation of spinel ZnCo2O4 nanoparticles with average sizes between 49 and 75 nm. It was found that the average particle size decreased when the dodecylamine concentration increased. Pellets containing ZnCo2O4 nanoparticles were fabricated and tested as sensors in carbon monoxide (CO) and propane (C3H8) gases at different concentrations and temperatures. Sensor performance tests revealed an extremely high response to 300 ppm of CO at an operating temperature of 200 °C.
Local-homogeneity-based global continuous control for mechanical systems with constrained inputs: finite-time and exponential stabilisation
Get PDF"A global continuous control scheme for the finite-time or (local) exponential stabilisation of mechanical systems with constrained inputs is proposed. The approach is formally developed within the theoretical framework of local homogeneity. This has permitted to solve the formulated problem not only guaranteeing input saturation avoidance but also giving a wide range of design flexibility. The proposed scheme is characterised by a saturating-proportional-derivative type term with generalised saturating and locally homogeneous structure that permits multiple design choices on both aspects. The work includes a simulation implementation section where the veracity of the so-cited argument claiming that finite-time stabilisers are faster than asymptotical ones is studied. In particular, a way to carry out the design so as to, indeed, guarantee faster stabilisation through finite-time controllers (beyond their finite-time convergence) is shown.