Repositorio IPICYT
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Energetics and the magnetic state of Mn2 adsorbed on Au(111): Dimer bond distance dependence
Get PDF"In this work we present a theoretical study of the adsorption Mn2 dimer on the Au(111) surface. Here we use the density functional theory to construct a map of adsorption energies, EA, of Mn2 on a Au(111) surface as a function of interatomic bond distance, , among Mn atoms. We employed a 4×4 supercell of Au(111) surface which lead us to reach values in the range from 2.6 to 6.8 Å. To make a full study of the adsorption energies we considered the antiferromagnetic (AFM) and ferromagnetic (FM) states of the Mn2 on the surface. The energy landscape contains local minima when the Mn atoms are adsorbed above triangular sites and barriers that the Mn adatoms have to overcome when they move across the Au(111) surface along various paths. Our results show that the lowest energy state corresponds to the state in which the Mn atoms are next-nearest neighbors and are antiferromagnetically coupled. Furthermore, all the local minima with higher bonding energy are also those in the antiferromagnetic state. Nevertheless we find a short interval in which the FM state has lower energy than the AFM one. Finally, scanning tunneling microscope simulations for various dimer configurations on surface are reported.
Rheological behavior from light to heavy oils: construction of master curves
Get PDF"In this work, the rheological behavior of heavy and light stabilized (dead) oils is presented. The viscosity measurements were carried out in two different apparatuses to ensure the repetitiveness and accuracy: a Stabinger viscometer and an Ares G2 strain-controlled rheometer. The samples were previously conditioned with an established methodology. For heavy oils, shear thinning was observed. The zero shear viscosity appears to correlate with the American Petroleum Institute (API) gravity for the case of light oils. However, for heavy oils, the viscosity definitively does not correlate with the API gravity. For example, the viscosity of fluids with an API gravity of around 12° may differ up to a full order of magnitude because of differences in the molecular structure. Saturate, aromatic, resin, and asphaltene analysis is also reported. Viscosity master curves were used to characterize oils. They were produced by applying the time–temperature superposition principle to the isothermal shear rate sweeps. The Williams, Landel, and Ferry equation was used to correlate the shift factor with the temperature. Rheological curves for all of the oils were quite reproduced with this method in all of the operational range.
Carbón activado de carácter básico para recuperar oro de lixiviados cianurados
Get PDF"Una de las actividades que ha sido etiquetada como altamente riesgosa,
perjudicial y causante de diversos impactos al medio ambiente es la minería,
usualmente conocida como la actividad enfocada en la extracción selectiva de
minerales así como de otros materiales de los cuales se obtiene un beneficio
económico. Hoy en día, una problemática que afronta la industria minera es la
recuperación de oro de soluciones con concentraciones diluidas (?g/L) del mismo.
Esto derivado del lavado de las PAD (Pila de Lixiviación), en lo que se conoce
como actividades de cierre de mina. El estudio de la recuperación de oro mediante
el proceso de adsorción, en específico con carbón activado (CA) ha sido
ampliamente estudiado, sin embargo, hasta la fecha son escasos los estudios de
adsorción de oro en soluciones diluidas que contienen menos de 20 ?g/L. En el
presente estudio se evaluó el uso de CA de carácter básico para recuperar oro de
soluciones con concentraciones diluidas (?g/L) del metal. Los resultados de
caracterización física demostraron la heterogeneidad de cuatro CA: Se obtuvieron
dos materiales altamente microporosos, y el CA F400 reportó la mayor área
específica (> 900 m2/g). Se determinó la presencia de grupos funcionales del tipo
carboxilo, lactona, y fenol para los cuatro adsorbentes. De los cuatro CA el que
mayor capacidad de adsorción mostró fue el F400, donde en estudios posteriores
se compara con CA modificados térmica y químicamente. Además, las cinéticas
de adsorción del F400 mostraron que se alcanza el equilibrio de adsorción en 24 h
para un tamaño de partícula de 1.68 x 0.5 mm y en 4 h para un tamaño fino (0.25
x 0.09 mm). El efecto de pH inicial en solución no mostró tendencia clara en
cuanto a la capacidad de adsorción, sin embargo las mayores capacidades se
lograron en un medio ajustado con cal (CaO) grado comercial. La modificación
química realizada al material F400 (CMQ) exhibió un aumento en su punto de
carga cero (PCC), al pasar de 9.44 a 10.84, sin embargo la capacidad de
adsorción fue muy similar con respecto del material pristino. Por otro lado la
modificación térmica realizada al F400 (CMT) aumentó ligeramente su PCC al
registrar un valor de 9.75. Al comparar el F400 con los CA modificados, las
mayores capacidades de adsorción de oro fueron para el CMT en un medio
ajustado con NaOH. Finalmente las cinéticas de adsorción de oro de los
materiales modificados mostraron que el tiempo para alcanzar el equilibrio de
adsorción es de 24 h.""One of the activities that has been labeled as highly risky, harmful and responsible
for several environmental impacts is mining, which is usually known as the activity
focused on the selective extraction of minerals and other materials from which an
economic benefit is obtained. Nowadays, a problem facing the mining industry lies
in the recovery of gold from dilute solutions of the same concentrations. This is
derived from the washing of the PAD, in what is known as mine closure activities.
The study of gold recovery by the adsorption process, specifically with activated
carbon (AC) has been extensively studied, however only a few studies have deal
with gold adsorption on diluted solutions containing less than 20 ?g/L. In the
present study the application of a basic AC to recover gold from diluted solutions
(?g/L) was investigated. The results of physical characterization showed four
heterogenous AC: obtaining two highly micropourous materials and the AC F400
reporting the highest surface area (> 900 m2/g). The presence of functional groups
such as carboxyl, lactone, phenol was determined for the four adsorbents. Out of
the four AC the F400 showed the higher adsorption capacity, which in further
studies is compared with activated carbon chemically and termical modified.
Furthermore adsorption kinetics of the F400 showed that the equilibrium was
reached within 24 h for a particle size of 1.68 x 0.5 mm and 4 h for a fine size (0.25
x 0.09 mm). The effect of initial pH in solution showed no clear trend in the
adsorption capacity, yet the largest capacities were achieved in a medium adjusted
with commercial grade lime (CaO). Chemical modification made to the material
F400 (CMQ) exhibited an increase in its point of zero charge (pHPZC), from 9.44 to
10.84, however the adsorption capacity was similar respect to the pristine material.
On the other hand the thermal modification to the F400 (CMT) slightly increased its
pHPZC to a register value of 9.75. Comparing the F400 with the modified AC, the
largest gold adsorption capacities were recorded for the CMT in a medium
adjusted with NaOH. Finally the gold adsorption kinetics of the modified materials
showed that the time to reach the equilibrium is of 24 h.
Tuning emission in violet, blue, green and red in cubic GaN/InGaN/GaN quantum wells
Get PDF"Light emission in the three primary colors was achieved in cubic GaN/InGaN/GaN heterostructures grown by molecular beam epitaxy on MgO substrates in a single growth process. A heterostructure with four quantum wells with a width of 10 nm was grown; this quantum wells width decrease the segregation effect of In. Photoluminescence emission produced four different emission signals: violet, blue, green-yellow and red. Thus, we were able to tune energy transitions in the visible spectrum modifying the In concentration in cubic InxGa1?xN ternary alloy.
A note on stability of functional difference equations
Get PDF"In this note, we consider perturbed linear functional difference equations with discrete and distributed delays which play a fundamental role in several stability and stabilizability problems of time-delay systems. Linear and nonlinear perturbations are considered. Sufficient conditions for exponential stability of the perturbed solutions are given.
Matas de microalgas termófilas que crecen sobre la estructura de madera de una torre de enfriamiento de una central termoeléctrica en el centro de México
Get PDF"The aims of this research are to identify and describe a periphyton community of thermophilic microalgae in order to expand our knowledge on biodiversity of a particular environment. Conspicuous biomass of thermophilic microalgae (48 °C) inhabits the cooling towers of the thermoelectric power plant of Villa de Reyes (Central Mexico). Aggregate samples or microalgal mats were taken in three different areas of the top of a cooling tower, for identification. According to the sequencing analysis of 16S and 18S rDNA genes, the community is dominated by 3 species of Cyanoprokaryota: Chlorogloeopsis fritschii, Arthronema africanum and Chroococcidiopsis sp., previously reported as thermophiles. Also, 2 species of the Chlorophyte or green algae Scenedesmus. Finally, 12 species of diatoms comprise the microalgal community; diatoms were only microscopically identified within the mats, suggesting that the mats constitute a suitable microenvironment in thermal ambiences. The identified species are of particular interest because their habitat represents an extreme and an artificial biotope. To the best of our knowledge, this is the first report of thermophilic communities of microalgae in Mexico from a power plant; also, this is the first report of A. africanum for the country.""Esta investigación tiene por objetivo identificar y describir la comunidad perifítica de microalgas termófilas, para expandir nuestro conocimiento de la biodiversidad en ambientes particulares, como las microalgas termófilas (48 °C) que crecen de manera conspicua en la zona superior de la torre de enfriamiento de la central termoeléctrica de Villa de Reyes (centro de México). Se tomaron muestras de agregados o tapetes microalgales en 3 zonas distintas de la parte superior de una torre de enfriamiento, para su identificación. Una vez realizada la amplificación, la clonación y el análisis de los genes que codifican para las subunidades 16S y 18S del rDNA, se observó el predominio de 3 especies de Cyanoprokaryota: Chlorogloeopsis fritschii, Arthronema africanum y Chroococcidiopsis sp., especies descritas como termófilas en trabajos previos. Además, se identificaron 2 especies de Chlorophyta (algas verdes) del género Scenedesmus y 12 especies de diatomeas; la identificación de diatomeas se realizó a partir de observaciones por microscopia electrónica de barrido. Característicamente, las diatomeas solo se observaron dentro los densos tapetes algales que se conforman, sugiriendo que estos tapetes constituyen un microambiente conveniente en ambientes térmicos. Las especies identificadas son de particular interés, ya que su hábitat representa un biotopo extremo y artificial. Por lo que sabemos, este trabajo constituye el primer registro de microalgas termófilas que habitan en torres de enfriamiento y Arthronema africanum se documenta por primera vez para México.
Properties of flavonoids isolated from the bark of eysenhardtia polystachya and their effect on oxidative stress in streptozotocin-induced diabetes mellitus in mice
Get PDF"Six new flavonoids 2′,4′-dihydroxychalcone-6′-O-β-D-glucopyranoside (1), α,3,2′,4′-tetrahydroxy-4-methoxy-dihydrochalcone-3′-C-β-glucopyranosy-6′-O-β-D-glucopyranoside (2), 7-hydroxy-5,8′-dimethoxy-6′α-L-rhamnopyranosyl-8-(3-phenyl-trans-acryloyl)-1-benzopyran-2-one (3), 6′7-dihydroxy-5,8-dimethoxy-8(3-phenyl-trans-acryloyl)-1-benzopyran-2-one (4), 9-hydroxy-3,8-dimethoxy-4-prenylpterocarpan (5), and α,4,4′-trihydroxydihydrochalcone-2′-O-β-D-glucopyranoside (6) were isolated from bark of Eysenhardtia polystachya.Antidiabetic activity of compounds 1–5 in terms of their cellular antioxidant and free radical scavenging and also in streptozotocin- (STZ-) induced diabetic mice was evaluated on liver transaminases, lipid peroxidation, total bilirubin, total protein, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (CSH-Px), and glutathione reductase (GSH). Results indicated that 1–5 scavenged 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl (), nitric oxide radicals (), superoxide anion radical (), radical cation (), and hydrogen peroxide (H2O2) radical, and protection against H2O2 induced BSA damage was also observed. Furthermore, 1–5 showed ability to decrease the oxidative stress in H9c2 cell. Diabetic mice present high levels of lipid peroxide, total protein, SGPT, SGOT, ALP, and TB. However, treatment of STZ-induced diabetes in mice with 1–5 reduced levels of these enzymes leading to protector effect of liver. In addition, with treatment with 1–5, increases in radical scavenging enzymes of CSH-Px, SOD, GSH, and CAT have also been observed in diabetic mice. The antioxidant properties of compounds 1–5 are a promising strategy for ameliorating therapeutic effects by avoiding disorders in the normal redox reactions in healthy cells which consequently could alleviate complications of diabetes.
Integrable Abel equations and Vein's Abel equation
Get PDF"We first reformulate and expand with several novel findings some of the basic results in the integrability of Abel equations. Next, these results are applied to Vein's Abel equation whose solutions are expressed in terms of the third-order hyperbolic functions, and a phase space analysis of the corresponding nonlinear oscillator is also provided.
Surface modified semiconductors with metal nanoparticles: photocatalysts with high activity under solar light
Get PDF"La modificación del TiO2-P25, con uno o dos-metales, han atraído una considerable atención en los últimos años, como una clase de catalizadores y photocatalizadores altamente activos bajo la radiación UV y la luz visible. Estructuras de uno o dos metales, tales como Au, Ag, Ag@CuO y CuO depositados sobre TiO2-P25, tienen la capacidad de absorber la luz visible en una amplia gama de longitudes de onda. La modificación superficial del TiO2 con nanopartículas metálicas (como, Cu Au, Ag) absorben la luz visible debido a su propiedad de la resonancia localizada del plasmón de superficie (RLPS). En el caso de la unión de dos semiconductores, el sistema es foto-activo bajo la luz visible debido al valor de la banda de energía prohibida del segundo semiconductor, (procurando que esta sea menor que la del TiO2-P25), por lo tanto, la modificación con uno o dos metales, induce una mayor actividad bajo la región del visible comparado con el TiO2 puro. Por otro lado, bajo la radiación UV, pueden mejorar la velocidad de captura de electrones foto-excitados e inhibir el proceso de recombinación debido a su capacidad de almacenamiento de electrones foto-excitados. En esta tesis presentamos la preparación y aplicación ambiental de la modificación del TiO2-P25 con uno o dos metales, las nanopartículas de Au, fueron sintetizadas por método químico usando tetrakis(hydroxymethyl) phosphonium chloride (THPC), y las nanopartículas de Ag, Ag@CuO y CuO-NPs fueron sintetizadas por irradiación gamma. Además, estudiamos y discutimos los efectos de diversos parámetros (tales como el tamaño y forma de las partículas, y la cantidad de metales) en la actividad fotocatalítica (oxidación de fenol, 2-propanol y ácido acético y generación de hidrogeno) fue también estudiado. La dinámica de portadores de carga fue estudiada mediante la conductividad de microondas resuelta en el tiempo (TRMC).""The modification of TiO2-P25 with one or two metal-based nanoparticles have attracted considerable attention in recent years as a new class of highly active catalysts and photocatalysts under both UV and visible light irradiation. One or two-metal-based structures, such as Au, Ag, Ag@CuO and CuO deposited on TiO2-P25 have the ability to absorb visible light in a wide spectral range. Surface modified TiO2 with metal nanoparticles (such as Cu, Au, Ag) absorb visible light due to the localized surface plasmon resonance (LSPR). In the case of semiconductor heterojunctions, they absorb visible light due to the narrow band gap of the second semiconductor, lower than TiO2-P25. The modification with one or two metal-based nanoparticles induces a higher activity under visible light compared to pure TiO2-P25, due to the transfer of electrons to the conduction band of TiO2-P25. On the other hand, under UV irradiation, the speed of trapping photoexcited electrons can be improved, to inhibit the recombination process and have the capability to store photoexcited electrons. This thesis presents recent advances in the preparation and environmental application of the surface modification of TiO2-P25 with one or two-metal-based nanoparticles: The Au-NPs were synthesized by chemical method using tetrakis(hydroxymethyl) phosphonium chloride (THPC), and the nanoparticles of Ag, Ag@CuO and CuO-NPs were synthesized by gamma irradiation. Moreover, the effects of various parameters (such as particle size, shape of the nanoparticles and amount of metals) on the photocatalytic activity (phenol, 2-propanol and acetic acid oxidation, as well as hydrogen generation) were also studied. The charge carrier dynamics was studied by time resolve microwave conductivity (TRMC).
Comparative shotgun proteomic analysis of wild and domesticated Opuntia spp. species shows a metabolic adaptation through domestication
Get PDF"The Opuntia genus is widely distributed in America, but the highest richness of wild species are found in Mexico, as well as the most domesticated Opuntia ficus-indica, which is the most domesticated species and an important crop in agricultural economies of arid and semiarid areas worldwide. During domestication process, the Opuntia morphological characteristics were favored, such as less and smaller spines in cladodes and less seeds in fruits, but changes at molecular level are almost unknown. To obtain more insights about the Opuntia molecular changes through domestication, a shotgun proteomic analysis and database-dependent searches by homology was carried out. > 1000 protein species were identified and by using a label-free quantitation method, the Opuntia proteomes were compared in order to identify differentially accumulated proteins among wild and domesticated species. Most of the changes were observed in glucose, secondary, and 1C metabolism, which correlate with the observed protein, fiber and phenolic compounds accumulation in Opuntia cladodes. Regulatory proteins, ribosomal proteins, and proteins related with response to stress were also observed in differential accumulation. These results provide new valuable data that will help to the understanding of the molecular changes of Opuntia species through domestication.
Biological significance
Opuntia species are well adapted to dry and warm conditions in arid and semiarid regions worldwide, and they are highly productive plants showing considerable promises as an alternative food source. However, there is a gap regarding Opuntia molecular mechanisms that enable them to grow in extreme environmental conditions and how the domestication processes has changed them. In the present study, a shotgun analysis was carried out to characterize the proteomes of five Opuntia species selected by its domestication degree. Our results will help to a better understanding of proteomic features underlying the selection and specialization under evolution and domestication of Opuntia and will provide a platform for basic biology research and gene discovery.