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Multilocus coalescent species delimitation to evaluate traditionally defined morphotypes in Hydrangea sect. Asperae (Hydrangeaceae)
Get PDF"The number of species recognized in section Asperae of the flowering plant genus Hydrangea differs widely between subsequent revisions. This variation is largely centered around the H. aspera species complex, with numbers of recognized species varying from one to nearly a dozen. Despite indications of molecular variation in this complex, no sequence-based species delimitation methods have been employed to evaluate the primarily morphology-based species boundaries. In the present study, a multi-locus coalescent-based approach to species delimitation is employed in order to identify separate evolutionary lines within H. sect. Asperae, using four chloroplast and four nuclear molecular markers. Eight lineages were recovered within the focal group, of which five correspond with named morphotypes. The other three lineages illustrate types of conflict between molecular species delimitation and traditional morphology-based taxonomy. One molecular lineage comprises two named morphotypes, which possibly diverged recently enough to not have developed sufficient molecular divergence. A second conflict is found in H. strigosa. This morphotype is recovered as a separate lineage when occurring in geographic isolation, but when occurring in sympatry with two other morphotypes (H. aspera and H. robusta), the coalescent species delimitation lumps these taxa into a single putative species.
Transformation process dependent magnetocaloric properties of annealed Ni50Mn18Cu7Ga25 ribbons
Get PDF"The properties related to magnetocaloric effect (MCE) of annealed Ni50Mn18Cu7Ga25 ribbons were studied in connection with their microstructural features and magnetostructural transformations. The differences in magnetic entropy change between the reverse and direct austenite-to-martensite transformation processes lie in the magnetic field induced martensitic transformation. It occurs uniquely during the direct transformation but not reciprocal in the reverse transformation, which results in the relatively lower value of maximum ΔSM but higher δTFWHM of the ΔSM curve for the direct transformation (ΔSM = 17.8 Jkg−1K−1, δTFWHM = 6 K) with respect to those of the reverse transformation (ΔSM = −32.1 Jkg−1K−1, δTFWHM = 3 K) under magnetic field change μoΔH of 5 T. These transformation singularities have a deep connection with the microstructural configurations of the parent and product phases. The present study provides fundamental information necessary to understand the transformation dependent MCE of ferromagnetic functional alloys.
Timing of speleogenesis of Las Karmidas Cave (Mexico): first description of pseudokarst developed in ignimbrite
Get PDF"Las Karmidas Cave (Puebla State, Mexico) is an unusual type of pseudokarstic cavity generated by piping and erosive processes within the contact of a diamicton and an overlying Quaternary ignimbrite. Morphological evidence suggests that the cave was developed in two stages: a phreatic stage and a vadose stage. The latter was characterized by the formation of carbonate speleothems. The absolute upper-age limit for the cave (168 +7.1/-7.5 ka) was established by U-Th dating of zircons grains extracted from the overlying ignimbrite, whilst a minimum age for the transition from a phreatic to vadose regime (95.6 ± 2.1 ka) was constrained by U-Th dating of carbonate speleothems within the cave. The geochronological results indicate a very rapid evolution of this pseudokarstic system, and suggest that similar systems might evolve and degrade at a very fast pace; consequently, making them hard to be preserved. Despite this, and considering the rather common geological context in which this system was developed, it is likely that similar pseudokarstic systems are yet to be detected worldwide.
Full vector magnetic dating of some pyroclastic rocks associated to the Colima volcano, western Mexico
Get PDF"Se presentan los resultados de un estudio paleomagnético y de magnetismo de rocas realizado en rocas de flujos piroclásticos y algunos fragmentos de cerámica pre-Colombina asociados al complejo Volcánico de Colima. Con la finalidad de estimar la mineralogía magnética y determinar tanto la magnetización remanente característica, así como la intensidad absoluta, se realizó un conjunto de experimentos y mediciones magnéticas. Se reporta una edad absoluta determinada mediante el fechamiento magnético de dos erupciones volcánicas asociadas al volcán Colima (volcán de Fuego). Esta es la primera vez que el modelo de predicción de campo magnético SHADIF.14K, basado en el vector completo (declinación, inclinación y paleointensidad absoluta), es utilizado en depósitos de flujos piroclásticos intercalados con cerámicas. Los resultados obtenidos concuerdan con las edades radiométricas (C14) disponibles y constituyen una determinación más precisa de la edad del momento de enfriamiento de los flujos de lava.""A combined rock-magnetic and paleomagnetic researches were carried out on some pyroclastic rocks and pre-Columbian pottery fragments associated to the Colima Volcanic Complex. A full battery of magnetic measurements was performed in order to estimate magnetic mineralogy and to determine both the directions and absolute intensities of the characteristic remanent magnetization. In this paper we report absolute age determination using magnetic dating for two volcanic eruptions associated to the Colima volcano (Volcán de Fuego). The geomagnetic field prediction model SHA.DIF.14K, based on full vector (declination, inclination and absolute paleointensity), was used for first time in pyroclastic flows deposits and intercalated potteries. The results obtained agree reasonably well with available radiometric (C14) data, them provide a more accurate age determination of the cooling moment for the lava flows.
Estudio experimental de nanotubos de carbono dopados con nitrógeno y de óxido de grafeno
Get PDFTesis (Maestría en Nanociencias y Materiales)"En esta tesis se presentan la segunda parte del estudio sistemático de síntesis y caracterización de nanotubos de carbono dopados con nitrógeno (CNx) mediante la técnica de deposición química de vapores (CVD). Partimos de los análisis referentes a la morfología de los CNx discutidos en la sección de Antecedentes del trabajo, posteriormente con la misma metodología de análisis de resultados dependientes de la posición de la muestra dentro del reactor, se indaga y amplia las caracterizaciones de los nanotubos de carbono dopados con nitrógeno mediante las técnicas de espectroscopía (Raman, XPS, FTIR), cálculos computacionales (teoría del funcional de la densidad), magnética (curvas de histéresis), térmica (análisis termogravimétrico) y electroquímica (voltamperometría cíclica).
Los análisis de resultados espectroscópicos muestran como los nanotubos de carbono dopados con nitrógeno tienen propiedades diferentes dependiendo de la posición de síntesis dentro del reactor como en el caso de la capacitancia, remanencia magnética o grupos funcionales las cuales son de interés en el caso de aplicaciones como celdas para baterías y transporte de fármacos en los nanotubos de carbono dopados con nitrógeno.
Una de los beneficios de este estudio sistemático donde se colectan y estudian las muestras de CNx centímetro por centímetro a lo largo del reactor es que asimilaría a obtener muchas síntesis de CNx por separado con variaciones en pequeñas cantidades de sus especies. Esto significó que además de obtener y concatenar información del sistema por múltiples técnicas de caracterización teniendo de común denominador la posición de la muestra dentro del reactor, nos permitió distinguir a detalle la interacción, efecto y evolución que provocan los cambios de las especies de carbono, nitrógeno, oxígeno y hierro en un material nanoestructurado 1D el cual tiene propiedades diferentes de los nanotubos de carbono sin dopar.
Otra de las ventajas es que en posteriores síntesis de CNx con las mismas condiciones experimentales la reproducibilidad del perfil temperatura-posición-peso se mantiene, por lo que los resultados estudiados en esta tesis son válidos en futuros experimentos donde se requiera CNx sintetizados de alguna región en específico dentro del reactor.
De manera alteran se desarrolla el tema sobre desalinización de agua a través de membranas de óxido de grafeno, se describen los parámetros utilizados en la síntesis de óxido de grafeno y su variación respecto al rechazo de la solución salina con concentración de 0.2 wt. % dentro del rango de filtración por ósmosis inversa.""This thesis presents the second part of the systematic study of synthesis and
characterization of nitrogen doped carbon nanotubes (CNx) by chemical vapor
deposition (CVD). We start from morphology analyzes of the CNx discussed in the
background section, then we follow the same analysis methodology results depending on the position of the sample inside reactor, some others characterizations have been upgrade to understand the physicochemical properties: (Raman, XPS, FTIR), computational calculations (density functional theory), magnetic (hysteresis curves), thermal (thermogravimetric analysis) and electrochemistry (cyclic voltammetry). Analyzes of spectroscopic results show how nitrogen-doped carbon nanotubes have different properties depending where the samples take place inside the reactor. We present the results in terms of capacitance, magnetic remanence or functional groups which are of interest in the case of applications as cells for batteries and drug transport in nitrogen-doped carbon nanotubes.One of the benefits of this systematic study where samples of CNx centimeter per centimeter throughout the reactor are collected and studied is that it would assimilate to obtain many CNx synthesis separately with variations in small quantities of its species. This has sense if in addition to obtaining and concatenating system information by multiple characterization techniques having a common denominator the position of the sample inside the reactor, allowed us to distinguish in detail the interaction, effect and evolution caused by changes in carbon species, nitrogen, oxygen and iron in a nanostructured material 1D which has properties different from the nondoped carbon nanotubes. Another advantage is that in subsequent CNx syntheses with the same experimental conditions the reproducibility of the temperature-position-weight profile is maintained, so the results studied in this thesis are valid in future experiments where CNx synthesized from some region inside reactor. Alternately, water desalination by graphene oxide membranes study has been developed, we focus in the parameters used in the synthesis of graphene oxide and its variation with respect to the rejection of saline solution.
Dynamic nonlinear feedback control applied to improve butanol production by Clostridium acetobutylicum
Get PDF"The goal of this work is to present a closed-loop operational strategy in order to improve the butanol production in an anaerobic continuous bioreactor for the called Acetone-Butanol-Ethanol (ABE) process. The proposed control scheme considers a class of feedback signal which includes a nonlinear bounded function of the regulation error. The control scheme is applied to a phenomenological unstructured kinetic model obtained from an experimental and metabolic study of butanol production by Clostridium acetobutylicum, which allows the proposed structure to predict several operational conditions from batch and continuous regimes. Numerical experiments using the proposed model considering continuous operation were performed in order to find a feasible operating region for maximum butanol production at open-loop regime. The proposed methodology is applied to regulate the product concentration, manipulating the dilution rate to lead to a higher butanol productivity. The closed-loop behaviour of the bioreactor is analysed, finding that the proposed controller minimizes the response time of the system and allows it to achieve a productivity gain of 55 % over open-loop operation. Further numerical experiments show the satisfactory closed-loop performance of the proposed methodology in comparison with a PI controller.
Bioadsorción de plomo (II) presente en solución acuosa sobre residuos de fibras naturales procedentes de la industria ixtlera (Agave lechuguilla Torr. y Yucca carnerosana (TREL.) MCKELVEY)
Get PDF"El plomo ha sido reconocido como uno de los metales más tóxicos por su efecto negativo sobre el ambiente. En el presente trabajo se evaluó el uso potencial de residuos de Agave lechuguilla Torr. (lechuguilla) y Yucca carnerosana (Trel.) McKelvey (yuca) procedentes de la industria ixtlera para remover iones Pb (II) presentes en solución acuosa. Los datos del equilibrio de bioadsorción mostraron que al aumentar el pH de la solución de 2.0 a 5.0, la capacidad de bioadsorción de ambos materiales se incrementa. Este efecto se explicó considerando que la carga superficial negativa de estos materiales es mayor al aumentar el pH y por ello se favorece la remoción de Pb (II). El efecto de la temperatura de la solución en las isotermas de bioadsorción, expuso la naturaleza endotérmica del proceso. La energía libre de Gibbs y la entropía calculada (ΔG° y ΔS°) indicaron la espontaneidad de la bioadsorción y la afinidad del Pb (II) en solución por los bioadsorbentes, respectivamente. La variación de las capacidades de bioadsorción de la lechuguilla y la yuca se atribuyó a la diferencia en el contenido de sitios ácidos y lignina, lo que condujo a la presencia de diversos mecanismos de bioadsorción. En ambos materiales, la bioadsorción de Pb (II) ocurre por los mecanismos de interacciones π-catión, atracciones electrostáticas e intercambio iónico; además en el caso de la lechuguilla se evidenció un proceso de microprecipitación.""Lead has been recognized as one of the most toxic metals due to its negative effect on the environment. In the present work, the potential use of Agave lechuguilla Torr. (lechuguilla) and Yucca carnerosana (Trel.) McKelvey (yucca) residues from the ixtle industry to remove Pb (II) ions in an aqueous solution was evaluated. The adsorption equilibrium data showed that when increasing the pH in the solution from 2.0 to 5.0, the biosorption capacity of both materials increases. This effect might be explained by the negative surface charge of these materials, which is greater at high pH, favoring the removal of Pb (II). The effect of the temperature of the solution on the biosorption isotherms revealed the endothermic nature of the biosorption process. The Gibbs free energy change and the calculated entropy (ΔG° and ΔS°) indicated the spontaneity of biosorption and the affinity of Pb (II) in the solution for biosorbents, respectively. The variation of the biosorption capacities of lechuguilla and yucca was attributed to the different content of acid sites and lignin, which resulted in the presence of different biosorption mechanisms. In both materials, the biosorption of Pb (II) occurs by π-cation interactions, electrostatic attractions and ion exchange; moreover, a microprecipitation process on lechuguilla was evinced.
Hydrochory in seeds of Agave victoriae-reginae T. Moore endangered species: Morphology and anatomy as facilitators of hydro-dispersion and germination
Get PDF"Agave victoriae-reginae es una especie endémica del Desierto Chihuahuense y crece sobre paredes en cañones. Posee semillas aplanadas que pueden ser dispersadas durante eventos episódicos de inundación. La presente investigación se basó en determinar posibles adaptaciones morfológicas y anatómicas en las semillas que favorecen la hidro-dispersión. Se realizó un análisis morfológico y anatómico de las semillas mediante microscopía electrónica de barrido (MEB). Se evaluaron aspectos de permeabilidad, flotabilidad, germinación y velocidad de germinación (T50) por tratamientos y tamaños de semilla. Las semillas son diferentes en longitud, diámetro, espesor y no en peso; con forma lacriforme semi- planas y cubierta porosa con cámaras de aire en la hipodermis y son consideradas fotoblásticas neutras. Se concluye que las semillas de la especie poseen características propias para la hidro-dispersión.""Agave victoriae-reginae is an endemic species from Chihuahuan Desert which grows on canyon walls. It has flattened seeds that can be dispersed during episodic flood events. This study was focused on examining possible morphological and anatomical adaptations which promote seed hydro-dispersion. A morphological and anatomical seed analysis by scanning electron microscopy (SEM) was performed. Aspects of permeability, flotation, germination and germination rate (T50) for treatment and seed sizes were evaluated. The seeds are different in length, diameter, thickness, but not in weight; lacryform semi-flat shape and covered with porous air chambers in the hypodermis and were considered neutral photoblastic. We conclude that seeds of A. victoriae-reginae have hydro-dispersion characteristics.
Ag-coated heterostructures of ZnO-TiO2/delaminated montmorillonite as solar photocatalysts
Get PDF"Heterostructures based on ZnO-TiO2/delaminated montmorillonite coated with Ag have been prepared by sol–gel and photoreduction procedures, varying the Ag and ZnO contents. They have been thoroughly characterized by XRD, WDXRF, UV–Vis, and XPS spectroscopies, and N2 adsorption, SEM, and TEM. In all cases, the montmorillonite was effectively delaminated with the formation of TiO2 anatase particles anchored on the clay layer’s surface, yielding porous materials with high surface areas. The structural and textural properties of the heterostructures synthesized were unaffected by the ZnO incorporated. The photoreduction led to solids with Ag nanoparticles decorating the surface. These materials were tested as photocatalysts for the degradation of several emerging contaminants with different nitrogen-bearing chemical structures under solar light. The catalysts yielded high rates of disappearance of the starting pollutants and showed quite stable performance upon successive applications.
Enzymatic degradation of nitrogen-doped multiwall carbon nanotubes
Get PDF"Es bien conocido que a la fecha la toxicidad de los nanotubos de carbono aún no está bien estudiada. Muy recientemente se estableció que los nanotubos de carbono llamados MWCNT-7 sean clasificados como posiblemente carcinogénicos para los humanos [1]. Este resultado es muy importante ya que promueve una evaluación muy cuidadosa de las nanoestructuras de carbono cada vez que se pretenda comercializarlos mediante una aplicación. Por tanto, el estudio de la interacción de estos materiales de carbono con sistemas biológicos es de fundamental importancia para el desarrollo seguro de nanomateriales, en particular de nanomateriales de carbono. En este trabajo presentamos resultados referentes a la respuesta de nanotubos de carbono multicapas dopados con nitrógeno (N-MWCNTs) al estar expuestos a la enzima peroxidasa de rábano picante (horseradishperoxidase, HRP, por sus siglas en inglés).De acuerdo a los resultados de la caracterización de microscopia electrónica de barrido y de transmisión, encontramos que la degradación de los N-MWCNTs aumenta a medida que el tiempo de exposición aumenta. Los mecanismos de degradación se discuten de acuerdo a estos resultados.""It is well known that to date the toxicity of carbon nanotubes is not well studied. Most recently it was established that carbon nanotubes called MWCNT-7 are classified as possibly carcinogenic to humans [1]. This result is very important because it promotes a very careful assessment of the carbon nanostructures whenever intended to market by a specific application. Therefore, the study of the interaction of these carbon materials with biological systems is critical to the safe development of nanomaterials, particularly carbon nanomaterials. We present results concerning the response of nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) when exposed to the enzyme horseradish peroxidase (HRP). According to the results of the characterization of scanning electron microscopy and transmission, we found that the degradation of N-MWCNTs increases as the exposure time increases. The mechanism of degradation is discussed according to these results.