Repositorio IPICYT
Not a member yet
1534 research outputs found
Sort by
First description of extrafloral nectaries in Opuntia robusta (Cactaceae): Anatomy and ultrastructure
Get PDF"To our knowledge, there are no studies about the structure and ecological function of extrafloral nectaries (EFNs) in Opuntia robusta. This is the first description of EFNs in O. robusta, where young spines have an interesting structure and a secreting function, which are different from EFNs described in other Cactaceae species. We used light, scanning-electron, and transmission-electron microscopy to examine morphology, anatomy, and ultrastructure of the secretory spines in areoles in female and hermaphrodite individuals of O. robusta. Young cladodes develop areoles with modified and secretory spines as EFNs only active during the early growth phase. EFNs are non-vascularized structures, with no stomata, that consist of a basal meristematic tissue, a middle elongation region, and an apical secretory cone formed by large globular epidermal cells, containing nectar and medullar elongated cells. We observed the presence of Golgi apparatus, vesicles and plastids in the medullar and sup-epidermal cells of the spine. We propose that the nectar is stored in the globular cells at the apex of the spine and secreted by breaking through the globular cells or by pores. We recorded a more frequent presence of ants on younger cladode sprouts producing young secreting spines: this result is parallel with the predictions of Optimal Defense Hypothesis, which states that younger plant organs should be better defended than older ones because their loss produces a higher fitness impairment. Although Diaz-Castelazo’s hypothesis states that a more complex structure of EFNs correlates with their lower among-organs dispersion, comparing to less complex EFNs, non-vascularized structure of EFNs in O. robusta is not associated with their higher among-organs dispersion likened to O. stricta, which produces vascularized EFNs. We provide evidence that this characteristic is not a good taxonomic feature of Opuntia genus. Moreover, the comparison of EFNs of O. robusta and O. stricta suggests that the hypothesis of Diaz-Castelazo should be revised: it is rather a rule but not a law.
Regulador de voltaje basado en un convertidor SEPIC con una celda de inductores conmutados
Get PDF"Los convertidores de corriente directa a corriente directa han sido típicamente
usados para elevar o disminuir el voltaje; sin embargo, en algunas aplicaciones
existe la necesidad de mantener un voltaje regulado a partir de fuentes de corriente
directa en donde el voltaje varía por arriba o por debajo de un valor nominal, como
por ejemplo con las baterías de Litio. El convertidor SEPIC es comúnmente usado
en este tipo de aplicaciones ya que funciona como reductor-elevador. Las
principales ventajas de este convertidor son: (a) cuenta con una entrada de corriente
no pulsante con lo cual ayuda a alargar la vida de las baterías, (b) proporciona un
voltaje no invertido, y (c) muestra una gran robustez al ruido. Sin embargo, tiene la
desventaja de usar capacitores más grandes ya que proporcionan una corriente de
salida pulsante. Estructuras de inductores conmutados pueden ser combinadas con
el convertidor SEPIC para mejorar algunas de sus características. Las ventajas son:
usan capacitores más pequeños y la tensión en los dispositivos de conmutación es
más pequeña. En esta tesis se lleva a cabo un estudio completo del convertidor
SEPIC con inductores conmutados. Se establecen las ganancias de voltaje y
corriente, así como los valores promedio de las variables de estado. Se
proporcionan las expresiones para los rizos de corriente de los inductores y de
voltaje en los capacitores que permiten diseñar apropiadamente el convertidor. Se
describe el comportamiento del convertidor a través de modelos: (a) conmutado, (b)
promediado no lineal, y (c) promediado lineal. Usando el último modelo, se
desarrolla una estrategia de control para un regulador de voltaje. Al final, se
muestran resultados experimentales en un prototipo de 120 W que validan los
procedimientos de diseño y control del convertidor.""The DC-DC switching converters have typically been used to step-up or step-down input voltages; however, in some applications there is the need to regulate an output voltage from DC sources where the voltage is above or below a nominal value, for example in applications using Lithium batteries. The SEPIC converter can be used in this application because it can step-up or step-down an input voltage. The most important advantages of this converter are: (a) it has a non-pulsating input current, which can help to increase the lifetime of the batteries, (b) it can provide a non-inverting output voltage, and (c) it shows high robustness against noise perturbations. It has the disadvantage of using capacitors of high value mainly due to the pulsating output current. Switched-inductor cells can be combined with a SEPIC converter, which can provide interesting properties. The resulting converter has the advantages of lower value capacitors and a reduced voltage stress on the switching devices. In this thesis, a complete study of the SEPIC converter with a switched-inductor cell is given with the corresponding relations for the voltage and current gains. The relationships between voltages, currents and duty ratio are given, as well as the corresponding ripples of the inductor currents and capacitor voltages that allow the proper selection of the converter elements. The bilinear switching, nonlinear averaged and linear averaged models are developed such a control strategy can be developed. A control strategy is proposed to regulate the output voltage. Experimental results for a 120 W switching regulator are given to validate the controller design procedure.
Open problems related to the Hurwitz stability of polynomials segments
Get PDF"In the framework of robust stability analysis of linear systems, the development of techniques and methods that help to obtain necessary and sufficient conditions to determine stability of convex combinations of polynomials is paramount. In this paper, knowing that Hurwitz polynomials set is not a convex set, a brief overview of some results and open problems concerning the stability of the convex combinations of Hurwitz polynomials is then provided.
PRARN. Método alternativo para la prospección de recursos naturales. Aplicaciones hídricas y geotermia.
Get PDF"A nivel mundial, la sociedad requiere de mayor cantidad de recursos naturales que le permitan satisfacer sus necesidades como civilización. Siendo de vital importancia i) el recurso hídrico y ii) los mecanismos empleados para generación de energía eléctrica; imprescindibles para la vida y las actividades diarias. En el primer caso debido a factores como la sobreexplotación y contaminación de acuíferos, el cambio desmedido de uso de suelo (desertificación) entre otros; han provocado que el recurso hídrico sea mermado, po- niendo en riesgo la estabilidad de los ecosistemas y especies que lo habitan. Por otro lado, el uso desmesurado de recursos fósiles como primera opción para la generación de ener- gía eléctrica representa una fuente importante de contaminación, afectando directamente al medio ambiente y a la sociedad. Ante esta problemática es necesario la búsqueda de es- trategias que permitan eficientar el agua disponible y su captación; así como alternativas viables para la producción de energía limpia, destacando la geotermia. En este trabajo, se establece un paradigma asociado al análisis espectral, multitemporal y morfométrico para la prospección de recursos naturales denominado: PRARN, (Percepción Remota Aplicada a prospección de Recursos Naturales). El modelo es capaz de identificar zonas apropiadas de captación de agua en ambientes áridos/semiáridos; así como establecer lugares probables para realizar exploración geotérmica. La estrategia de solución se basa en fusionar capacidades de sensado remoto activo (radar de apertura sintética) y pasivo (multiespectrales) con modelos matemáticos y la inclusión de información geofísica, geológica y estructural dentro de un ambiente de sistemas de información geo-gráfica de código abierto. Se establecieron dos escenarios de prueba y validación, el primero relacionado con la prospección y captación hídrica que se realizó en la cuenca Tierra nueva en San Luis Potosí, la cual es una zona considerada como árida/semiárida con precipitación media anual de 358mm (milímetros) y donde el 28 % de la población no cuenta con agua pota- ble. Las herramientas principales fueron imágenes satelitales adquiridas de la plataforma Landsat 8, datos aeromagnéticos, climatológicos e información geológica. El proceso de identificación se realizó mediante un algoritmo de decisión multi-criterio (Proceso Ana- lítico Jerárquico, AHP) en cuyos resultados obtenidos se identificaron 2 zonas apropiadas para la planeación de obras hidráulicas y el mayor aprovechamiento del recurso hídrico superficial. El segundo escenario planteado corresponde a la Zona Volcánica de Nayarit (ZVN) donde se evaluó las capacidades de la propuesta aplicada a exploración geotérmica. En la ZVN se localizan los volcanes El Ceboruco y Tepetiltic siendo un sitio conocido por su potencial geotérmico y muy adecuado para la validación y calibración de la estrategia PRARN. Se emplearon imágenes de sensores remotos pasivos con los que se obtuvo in- formación de temperatura del terreno haciendo uso de los datos provenientes del satélite Landsat 8 y mediante sensado activo se identificaron modificaciones en la superficie de la ZVN utilizando la técnica DIn-SAR (Interferometría Radar Diferencial). Las imágenes SAR (Radar de Apertura Sintética) que se emplearon fueron obtenidas por la plataforma Sentinel-1. La información satelital fue complementada con los lineamientos estructurales, datos aeromagnéticos y la determinación de zonas de probable acumulación de agua. Los parámetros calculados/estimados fueron suministrados al modelo multicriterio logrando identificar áreas adecuadas para implementar exploración geotérmica in situ. La información obtenida por los sensores remotos se procesó e interpretó dentro de los sistemas de información geográfica GRASS GIS y SNAP.""At a global, society requires more natural resources that allow it to satisfy its
needs as a civilization. The most importat are: i) the water resource and ii) the mechanisms
used to generate electricity; essential for life and daily activities. In the first, case
due to factors such as overexploitation and contamination of aquifers, the excessive change
in land use (desertification) among others, have caused the water resource to be depleted,
putting at risk the stability of the ecosystems and species that inhabit it. On the other hand,
the disproportionate use of fossil resources as the first option for the generation of electric
power represents an important source of pollution, directly aecting
the environment and
society. Faced with this problem, it is necessary to search for strategies that make the water
available and its catchment ecient;
as well as viable alternatives for the production
of clean energy, highlighting geothermal energy.
In this work, a paradigm associated with the spectral, multi-temporal and morphometric
analysis is established for the prospection of natural resources called: PRARN,
(Remote Sensing Applied to Prospecting of Natural Resources). The model is able to identify
appropriate water catchment areas in arid / semi-arid environments; as well as establishing
probable places to perform geothermal exploration. The solution strategy is based on
merging active remote sensing (synthetic aperture radar) and passive (multispectral radar)
sensing capabilities with mathematical models and the inclusion of geophysical, geological
and structural information within an open source geographic information systems
environment.
Two testing and validation scenarios were established, the first one related to water
prospecting and capture was carried out in the Tierra Nueva basin in San Luis Potosí,
which is an arid/semi-arid with average annual rainfall of 358mm (millimeters) and where
28 % of the population does not have drinking water. The main tools were satellite images
acquired from the Landsat 8 platform, aeromagnetic, climatological data and geological
information. The identification process was carried out using a multi-criterion decision algorithm
(Hierarchical Analytical Process, AHP) in which the results obtained identified 2
appropriate zones for the planning of hydraulic works and the greater use of surface water
resources.
The second proposed scenario corresponds to the Volcanic Zone of Nayarit (ZVN)
where the capabilities of the proposal applied to geothermal exploration were evaluated.
In the ZVN wher the Ceboruco and Tepetiltic volcanoes are located, being a site known for its geothermal potential and very suitable for the validation and calibration of the PRARN
strategy. Passive remote sensing images were used to obtain land temperature information
using the data from the Landsat 8 satellite and through active sensing we identified
changes in the surface of the ZVN using the DIn-SAR technique (Dierential
Radar Interferometry).
The SAR (Synthetic Aperture Radar) images that were used were obtained by
the Sentinel-1 platform. The satellite information was complemented with structural guidelines,
aeromagnetic data and the determination of areas of probable water accumulation.
The calculated / estimated parameters were supplied to the multicriteria model, identifying
suitable areas to implement geothermal exploration in situ. The information obtained by
the remote sensors was processed and interpreted within the geographic information systems
GRASS GIS and SNAP.
Anharmonic contribution to the stabilization of Mg(OH)2 from first principles
No full text"Geometrical and vibrational characterization of magnesium hydroxide was performed using density functional theory. Four possible crystal symmetries were explored: P[3 with combining macron] (No. 147, point group −3), C2/m (No. 12, point group 2), P3m1 (No. 156, point group 3m) and P[3 with combining macron]m1 (No. 164, point group −3m) which are the currently accepted geometries found in the literature. While a lot of work has been performed on Mg(OH)2, in particular for the P[3 with combining macron]m1 phase, there is still a debate on the observed ground state crystal structure and the anharmonic effects of the OH vibrations on the stabilization of the crystal structure. In particular, the stable positions of hydrogen are not yet defined precisely, which have implications in the crystal symmetry, the vibrational excitations, and the thermal stability. Previous work has assigned the P[3 with combining macron]m1 polymorph as the low energy phase, but it has also proposed that hydrogens are disordered and they could move from their symmetric position in the P[3 with combining macron]m1 structure towards P[3 with combining macron]. In this paper, we examine the stability of the proposed phases by using different descriptors. We compare the XRD patterns with reported experimental results, and a fair agreement is found. While harmonic vibrational analysis shows that most phases have imaginary modes at 0 K, anharmonic vibrational analysis indicates that at room temperature only the C2/m phase is stabilized, whereas at higher temperatures, other phases become thermally competitive.
Temporal and longitudinal biofilm matrix analysis of a biofilter treating ethyl acetate during ozonation
No full text"The present paper focuses on the biofilm composition and pattern of biomass in gas biofiltration of ethyl acetate working under continuous addition of ozone (O3). Two biofilters were operated for 230 days, one under continuous addition of O3 (90 ppbv) and another one without. Throughout the operation time, the extracellular polymeric substances (EPS), the main components in the extracellular matrix (ECM), were extracted from the biofilm and characterized qualitatively using Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and quantitatively by analyzing its main constituents: carbohydrates, proteins, and glucuronic acid. To date, EPS characterization has been attempted mainly with biofilm aggregates related to water treatment, not air biofiltration. The results of this study may be helpful and provide more information about EPS structure when O3 was added. O3 addition only affected the amount of EPS and not its composition. The greater effect was observed on carbohydrate content since it is the main component in EPS. The EPS/biomass ratio measured was twice lower with O3 addition. Higher removal efficiency (RE) and mineralization rates were obtained with the biofilter subjected to O3 addition, and a smaller volume of a reactor would be necessary to treat all contaminant under this condition. EPS content is only quantitatively reduced by O3 addition, and at the low O3 concentration applied, no structural alteration is noted regarding the composition of the EPS.
On suitable observables for the chaotic Peroxidase-Oxidase autocatalytic reaction
Get PDF"Neurodegenerative diseases such as Alzheimer’s and Parkinson present oxidative damage of neurocytes generally caused by reactive oxygen species (ROS). Heme peroxidases consume and produce ROS thus serving as suppresors and promoters of ROS-related pathology A core reaction network of production and consumption of hydrogen peroxide and superoxide is the Peroxidase-Oxidase (PO). PO reaction was among the first biochemical oscillators to be experimentally and numerically studied, with dynamical scenarios such as multiple steady states, complex oscillations and chaos. In particular, the oxyferrous peroxidase (compound III) and O2 have been used as observable variables in experiments to record the chaotic dynamics. Moreover, PO reaction has been embedded in nanoparticles in order to serve as a sensor for ROS. In this contribution we quantified, using observability coefficients, which chemical species is more suitable to observe and reconstruct the characteristic complex dynamics of the PO reaction.
Coexistence of two-photon absorption and saturable absorption in ion-implanted platinum nanoparticles in silica plates
Get PDF"Platinum nanoparticles were nucleated in a high-purity silica matrix by an ion-implantation method. The third-order nonlinear optical response of the samples was studied using femtosecond pulses at 800 nm with the z-scan technique; picosecond pulses at 532 nm using a self-diffraction approach; and nanosecond pulses at 532 nm employing a vectorial two-wave mixing experiment. Nanosecond and picosecond explorations indicated an important thermal process participating in the optical Kerr effect evaluated. However, femtosecond results allowed us to distinguish a purely electronic response, related exclusively to ultrafast refractive and absorptive nonlinearities. Femtosecond experiments pointed out the possibility to switch the dominant physical mechanism responsible for the nonlinear optical absorption in the sample. This opens the potential for controlling quantum mechanisms of optical nonlinearity by femtosecond interactions.
Biohydrogen production from mixtures of agro-industrial wastes: Chemometric analysis, optimization and scaling up
Get PDF"Cheese whey (CW) and wheat straw hydrolysate (WSH) were used to produce biohydrogen by anaerobic co-digestion of multiple substrates. In this work, the influence of pH, temperature, substrates concentrations on the biohydrogen production was explored with the application of the principal component analysis (PCA) and the hierarchical clustering analysis (HCA), allowing the identification of the main clusters and the uniqueness of some experiments. Response surface methodology (RSM) was used to evaluate the individual and interactive effects of pH, temperature, CW concentration and WSH concentration in the fermentation. Optimal operational conditions obtained by RMS were 5?g?L?1 WSH, 25?g?L?1?CW, 26.6?°C and pH 7.25. With these conditions was expected 5724.5?mL H2 L?1. When optimal conditions were tested using 0.11-L anaerobic serological bottles, 1-L and 4-L bioreactors the results obtained for biohydrogen production were 4554.5?±?105, 3685?±?305 and 4132.3?±?151?mL H2 L?1, respectively; on the other hand, the biohydrogen production rate was improved from 66.6 to 89.5?mL H2 L?1 h?1. Results demonstrate that it is possible to use WSH and CW, both individually and in combination, as a substrate for the production of biohydrogen.
Transformation temperatures and electrochemical behavior of polycrystalline Fe-Doped Ni-Mn-Ga and Co-Ni-Ga Alloys
Get PDF"The effect of Fe addition on martensitic transformation temperatures and electrochemical behavior was studied in polycrystalline Ni51.4Mn24.8-XGa23.8FeX alloys (1<x<2.2) and Co38.3Ni32.1Ga29.6 as alternative to Ni-Mn-Ga alloys which are used as ferromagnetic shape memory alloys. The analysis of corrosion rates was conducted by cyclic polarization curves with potentiostat-galvanostat equipment. The corrosion morphologies were also analyzed by scanning electron microscopy (SEM). The kinetics of corrosion was found to decrease with increasing Fe content in the alloy, while the martensitic transformation temperatures increased with increasing Fe content. The Co38.3Ni32.1Ga29.6 alloy shows i(corr) lower than the Ni-Mn-Ga alloy. From results, the studied alloys exhibited a general dissolution in the anodic branch where a spontaneous passive zone occurred at certain potential and some elements like Co, Mn and also Ni were present in a higher percentage in corrosion deposits.