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Tillandsia recurvata como parásita estructural de Prosopis laevigata: evidencia experimental en el sur del Desierto Chihuahuense
Get PDF"La interacción entre epífitas y sus plantas hospederas comúnmente implica el desarrollo de las epífitas sin que éstas dañen a las hospederas. Sin embargo, recientemente se ha encontrado que algunas epífitas tienen efectos perjudiciales directos sobre sus anfitriones (forofitos), provocando mortalidad de brotes y ramas. Tillandsia recurvata es una epífita con elevado éxito reproductivo en zonas áridas y semiáridas de México, presentándose principalmente en árboles de Prosopis laevigata, especie de importancia ecológica y económica que ha mostrado alta mortalidad de brotes, ramas y hasta de individuos completos en el centro-norte del país. El objetivo de esta investigación fue evaluar el efecto de T. recurvata en individuos chicos y grandes de P. laevigata. La zona de estudio se localizó en el municipio de Mexquitic, SLP, donde se ubicaron ramas con y sin presencia de T. recurvata. Se evaluaron variables de respuesta a nivel ecofisiológico (eficiencia fotoquímica efectiva del fotosistema II (?PSII) y patrón de flujo de agua). También se evaluaron variables de respuesta anatómicas como el número de vasos y el área efectiva de conducción, así como cambios estructurales en floema, xilema y peridermis. Para el experimento del patrón de flujo de agua se seleccionaron ramas de diámetro chico (4.5 cm) y grande (8 cm). Por otra parte, para el experimento de anatomía se escogieron individuos de T. recurvata juveniles y reproductivos y se evaluó el daño causado por sus raíces en las ramas hospederas. Tillandsia recurvata modifica la anatomía (xilema, floema y peridermis) del hospedero P. laevigata; a su vez, estas modificaciones estructurales afectan el flujo de agua (xilema) y disminuyen la eficiencia cuántica efectiva del fotosistema II (?PSII). El efecto negativo de T. recurvata en la ?PSII es más fuerte en la época de sequía y precisamente en esta época se encontró la modificación en el flujo del agua. Además, a mayor desarrollo de T. recurvata mayor es el daño anatómico ocasionado a P. laevigata. Todas estas modificaciones en las ramas de P. laevigata son las causantes de la alta mortalidad de las mismas. La bromelia T. recurvata no absorbe agua ni nutrientes de su hospedero, pero si modifica el flujo de agua que es de suma importancia en los procesos fotosintéticos por lo que se considera como “parásita estructural” de P. laevigata en el sur del Desierto Chihuahuense.""The interaction between epiphytes and their host plants implies that the development of the former does not damage the host. However, it has been recently found that some epiphytes have negative effects on their hosts (forophytes), provoking death of branches. Tillandsia recurvata is an epiphyte having elevated reproductive success in arid and zemiarid zones of México, growing mainly on Prosopis laevigata trees, a species of ecological and economical importance, having high mortality of branches and even of complete trees in Central-Northern México. The aim of this research was to evaluate the effect of T. recurvata in small and large P. laevigata individuals. The study zone is located in the Municipality of Mexquitic, SLP, where P. laevigata branches with and without T. recurvata were marked. The response variables evaluated were: (i) ecophysiological: the effective quantum yield of photosystem II (?PSII) and the water flux pattern, and (ii) anatomical: the number of vessels and the effective area of conduction, as well as structural changes in phloem, xilem, and peridermis. In a water flux pattern experiment, branches of small diameter (4.5 cm) and large diameter (8 cm) were chosen. For the anatomical experiment, juvenile and reproductive T. recurvata individuals lwere chosen and the damage caused by the roots in the hosts was evaluated. Tillandsia recurvata modifies the anatomy (xilem, phloem y periderm) of the host P. laevigata; and these structural modifications affect the the water flux (xilema) and diminish the effective quantum yield of photosystem II (?PSII). The negative effect of T. recurvata in the ?PSII is higher in the drought period, and in this period water flux modifications were found. In addition, at higher development of T. recurvata higher is the anatomical damage caused to P. laevigata. All these modifications in the P. laevigata branches are the cause of their high mortality. The bromeliad T. recurvata do not absorb water nor nutrients from it host, but modifies the water flux that is very important for the photosynthetic proceses. Thus, it is considered as “structural parasite” of P. laevigata in the Southern Chihuahuan Desert.
Escherichia coli and its application to biohydrogen production
Get PDF"Hydrogen is an attractive energy carrier because of its high energy density, and used as a raw material in various chemical processes. Nowadays, hydrogen demand is supplied from non-renewable sources, and alternative sources are becoming mandatory. Hydrogen production by biological methods uses renewable resources as substrate and its production occurs at ambient temperature and atmospheric pressure. Thus, it is less energy intensive than the chemical and thermochemical methods used to produce hydrogen. This review is focused on fermentative hydrogen production by Escherichia coli. The hydrogen production pathway, the genetic manipulations, and expression of non-native pathways into this microorganism are reviewed. The hydrogen production using alternative substrates is a critical point to develop sustainable process by this reason the principal substrates for hydrogen production using E. coli are revised. Other strategies like two stages processes and immobilized cells are also discussed.
Imposex en Plicopurpura pansa (Neogastropoda: Thaididae) en Nayarit y Sinaloa, México
No full text"Imposex is the development of male features in female prosobranch gastropods, caused by organotin compounds. In the Mexican Pacific coast, imposex was observed in Plicopurpura pansa . This snail has been used by indigenous people to dye cotton and traditional fabric clothing. During 2010 and 2011, 5 habitats were visited along the coastline of Nayarit and Sinaloa, Mexico. At low tide, 675 snails were collected. Shell length, sex ratio and imposex incidence were measured. Imposex incidences were higher in the samples collected near harbor areas.""El imposex es el desarrollo de características masculinas en hembras de gasterópodos prosobranquios, causado por compuestos organoestañosos. En la costa del Pacífico mexicano se observó el imposex en el caracol Plicopurpura pansa . Este caracol ha sido utilizado por grupos indígenas para teñir algodón y fabricar su ropa tradicional. Durante 2010 y 2011, se visitaron 5 hábitats en la costa de Nayarit y Sinaloa, México. Se recolectaron 675 caracoles durante la marea baja; se midió la longitud de la concha, proporción de sexos y la incidencia de imposex. De acuerdo con los resultados, la incidencia de imposex fue más alta en las muestras recolectadas en las áreas cercanas a los muelles.
Genomic organization of purinergic P2X receptors
Get PDF"Purinergic P2X receptors are a family of ligand-gated cationic channels activated by extracellular ATP. P2X subunit protein sequences are highly conserved between vertebrate species. However, they can generate a great diversity of coding splicing variants to fulfill several roles in mammalian physiology. Despite intensive research in P2X expression in both central and peripheral nervous system, there is little information about their homology, genomic structure and other key features that can help to develop selective drugs or regulatory strategies of pharmacological value which are lacking today. In order to obtain clues on mammalian P2X diversity, we have performed a bioinformatics analysis of the coding regions and introns of the seven P2X subunits present in human, simian, dog, mouse, rat and zebrafish. Here we report the arrangements of exon and intron sequences, considering its number, size, phase and placement; proposing some ideas about the gain and loss of exons and retention of introns. Taken together, these evidences show traits that can be used to gain insight into the evolutionary history of vertebrate P2X receptors and better understand the diversity of subunits coding the purinergic signaling in mammals.
GaN haeckelite single-layered nanostructures: monolayer and nanotubes
Get PDF"Nowadays, III-V semiconductors are interesting candidate materials for the tailoring of two dimensional (2D) graphene-like structures. These new 2D materials have attracted profound interest opening the possibility to find semiconductor materials with unexplored properties. First-principles density functional theory calculations are performed in order to investigate the electronic properties of GaN planar and nanotube morphologies based on Haeckelite structures (containing octagonal and square membered rings). Optimized geometries, band-structures, phonon dispersion, binding energies, transmission electron microscopy images simulations, x-ray diffraction patterns, charge densities, and electronic band gaps are calculated. We demonstrated that GaN Haeckelite structures are stable exhibiting a semiconducting behavior with an indirect band gap. Furthermore, it was found that GaN Haeckelite nanotubes are semiconductor with a band gap nature (direct or indirect) that depends of the nanotube´s chirality and diameter. In addition, it was demonstrated that surface passivation and the interaction with hydrazine, water, ammonia, and carbon monoxide molecules can change the band-gap nature. Our results are compared with the corresponding GaN hexagonal honeycomb structures.
Condiciones de estabilidad de controladores PD para modelos con retardo de redes TCP/AQM
Get PDF"Esta tesis aborda el problema de estabilización de los modelos con retardo de redes TCP / AQM(Transmission Control Protocol / Active QueueManagement) mediante el uso de un controlador Proporcional-Derivativo (PD) como estrategia AQM. Se obtienen condiciones necesarias y su cientes para la estabilidad exponencial de los modelos linealizados en lazo cerrado. Como consecuencia, se determina el conjunto completo de controladores PD AQM que estabilizan exponencialmente los sistemas lineales con retardo correspondientes, en contraparte con los trabajos existentes en la literatura que sólo proporcionan una estimación del mismo. Adicionalmente, se proporciona un procedimiento simple para la determinación de las ganancias del controlador que proporcionan un controlador PD no frágil que admite perturbaciones en los coeficientes de controlador.""This thesis addresses the stabilization problem of delay models of Transmission Control Protocol/Active Queue Management (TCP/AQM) by using a Proportional-Derivative (PD) controller as AQM strategy. Necessary and su¢ cient conditions for the exponential stability of the closed-loop linearized models are derived. As a consequence, the complete set of PD AQM controllers that exponentially stabilize the corresponding linear time-delay systems is determined in counterpart with the existing works in the literature which only provide an estimate of it. Additionally, a simple procedure for determining the controller gains providing a non-fragile PD controller that admits controller coefficient perturbations is provided.
Integrable equations with Ermakov-Pinney nonlinearities and Chiellini damping
Get PDF"We introduce a special type of dissipative Ermakov-Pinney equations of the form v?? + g(v)v? + h(v) = 0, where h(v) = h0(v) + cv?3 and the nonlinear dissipation g(v) is based on the corresponding Chiellini integrable Abel equation. When h0(v) is a linear function, h0(v) = ?2v, general solutions are obtained following the Abel equation route. Based on particular solutions, we also provide general solutions containing a factor with the phase of the Milne type. In addition, the same kinds of general solutions are constructed for the cases of higher-order Reid nonlinearities. The Chiellini dissipative function is actually a dissipation-gain function because it can be negative on some intervals. We also examine the nonlinear case h0(v) = ?20(v ? v2) and show that it leads to an integrable hyperelliptic case.
Formation and atomic structure of hierarchical boron nitride nanostructures
Get PDF"We report a combined experimental and theoretical study of boron nitride (BN) nanostructures synthesized by ball milling methodology. The BN nanostructures were obtained using h-BN powder under low-vacuum conditions and steel balls of different sizes. The HRTEM images of our samples show the formation of spheroidal BN nanoparticles with diameters as small as 7 nm which self-assemble into different hierarchical nanostructures such as two-dimensional layered materials, spheroidal configurations, and one-dimensional solid BN chains. The Raman spectra reveal an intense absorption band in the 300-600 cm1 region, which is absent in the spectra of BN nanotubes, previously synthesized BN nanoparticles, and in all bulk boron nitride polymorphs. Density functional theory calculations show that the Raman spectra are consistent with the formation of fullerene-like BN particles which also exhibit an intense absorption band in the 200-800 cm1 range dominated by a complex mixture of tangential, stretching, and radial breathing modes. Finally, by means of electron-beam irradiation experiments additional structural transformations can be induce on our hierarchical BN particles consisting in the formation of nanoholes of the order of 5 nm. Our here-reported BN nanostructures might lead to a wide range of potential applications.
Vesicle motion during sustained exocytosis in chromaffin cells: numerical model based on amperometric measurements
Get PDF"Chromaffin cells release catecholamines by exocytosis, a process that includes vesicle docking, priming and fusion. Although all these steps have been intensively studied, some aspects of their mechanisms, particularly those regarding vesicle transport to the active sites situated at the membrane, are still unclear. In this work, we show that it is possible to extract information on vesicle motion in Chromaffin cells from the combination of Langevin simulations and amperometric measurements. We developed a numerical model based on Langevin simulations of vesicle motion towards the cell membrane and on the statistical analysis of vesicle arrival times. We also performed amperometric experiments in bovine-adrenal Chromaffin cells under Ba2+ stimulation to capture neurotransmitter releases during sustained exocytosis. In the sustained phase, each amperometric peak can be related to a single release from a new vesicle arriving at the active site. The amperometric signal can then be mapped into a spike-series of release events. We normalized the spike-series resulting from the current peaks using a time-rescaling transformation, thus making signals coming from different cells comparable. We discuss why the obtained spike-series may contain information about the motion of all vesicles leading to release of catecholamines. We show that the release statistics in our experiments considerably deviate from Poisson processes. Moreover, the interspike-time probability is reasonably well described by two-parameter gamma distributions. In order to interpret this result we computed the vesicles' arrival statistics from our Langevin simulations. As expected, assuming purely diffusive vesicle motion we obtain Poisson statistics. However, if we assume that all vesicles are guided toward the membrane by an attractive harmonic potential, simulations also lead to gamma distributions of the interspike-time probability, in remarkably good agreement with experiment. We also show that including the fusion-time statistics in our model does not produce any significant changes on the results. These findings indicate that the motion of the whole ensemble of vesicles towards the membrane is directed and reflected in the amperometric signals. Our results confirm the conclusions of previous imaging studies performed on single vesicles that vesicles' motion underneath plasma membranes is not purely random, but biased towards the membrane.
Estudio de propiedades térmicas y magnéticas en aleaciones Ni-Fe-Ga-X (X= Al, Sn)
Get PDFTesis (Maestría en Nanociencias y Nanotecnología)"Algunas aleaciones ferromagnéticas del sistema Ni-Fe-Ga tienen temperatura de Curie por encima de la ambiente y además presentan transformación martensítica a temperaturas por debajo de la temperatura ambiente. Se ha reportado que el aumento en el contenido de Fe en estas aleaciones aumenta la temperatura de Curie y por otro lado, las temperaturas de transformación martensítica bajan. Con el objeto de obtener aleaciones con transición de fase martensítica en estado ferromagnético se realizó el presente estudio en las aleaciones ferromagnéticas con memoria de forma del Sistema Ni-Fe-Ga dopado con Sn y con Al sustituyendo Ga. Se sintetizaron aleaciones con diferentes contenidos de Sn a partir de la aleación ternaria Ni55Fe18Ga27: Ni55Fe18Ga27-XSnX (X= 1, 1.5, 3). Asimismo se prepararon aleaciones variando contenido de Al a partir de la ternaria Ni54Fe19Ga27: Ni54Fe19Ga27-YAly (Y= 1, 1.5, 3). Se encontró que el contenido de estaño a la aleación ternaria hace que las temperaturas de transformación martensítica bajen considerablemente (> 100K), con un descenso menos rápido en la temperatura de Curie. Lo cual permitió obtener aleaciones con la transformación de primer orden en el estado ferromagnético. Sin embargo se presentan decrementos tanto de la magnetización de saturación como de la entalpía y entropía de transformación. Se encontró que el contenido de aluminio a la aleación ternaria hace que la temperatura de transformación martensítica y la temperatura de Curie disminuyan ( 30 K), acompañadas de un aumento de la magnetización remanente. Además la magnetización de saturación aumentó ligeramente y la entalpía y la entropía de transformación se mantienen con poca variación. La microestructura presenta pequeños precipitados de fase gamma la cual varió ligeramente entre las aleaciones ternarias y las cuaternarias, principalmente localizada en la frontera de grano. Los resultados de Difracción de Rayos X mostraron que el tratamiento térmico permite obtener una estructura cristalina ordenada (Heusler) tipo L21.""Some ferromagnetic alloys of the Ni-Fe-Ga system has a Curie temperature above the room temperature and also present a martensitic transformation below room temperature. It has been reported that an increase of Fe content in those alloys produces a Curie temperature growth, while martensitic transition temperatures decrease. In order to obtain alloys with a martensitic transformation in the ferromagnetic state the present study was carried out in the ferromagnetic shape memory alloys of Ni-Fe-Ga doped with Sn and/or Al replacing Ga. Alloys with different Sn contents were synthetized from Ni55Fe18Ga27 ternary alloy: Ni55Fe18Ga27-XSnX (X= 1, 1.5, 3). Also alloys with different Al contents from the ternary alloy Ni54Fe19Ga27 were elaborated: Ni54Fe19Ga27-YAly (Y= 1, 1.5, 3). It has been found that Sn addition produces a rapid decrease of martensitic transformation temperatures besides a lower decrease of Curie temperature is shown. It allows obtain alloys with the first order transition in the ferromagnetic state. Nevertheless, important decreases are shown in saturation magnetization and in transformation enthalpy and entropy. Besides the Al content produces a slight decrease of both martensitic transition and Curie temperatures with an increase of remnant magnetization. Moreover, saturation magnetization shows a light increase, and no important variation are shown in the transformation enthalpy and entropy. Gamma phase precipitates are shown in most of alloys, and mainly located at the grain borders. X ray diffraction shows that performed thermal treatments produces a Heusler ordered crystalline structure L21 type.