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Eigenvalue problems, spectral parameter power series, and modern applications
Get PDF"Our review is dedicated to a wide class of spectral and transmission problems arising in di?erent branches of applied physics. One of the main di?culties in studying and solving eigenvalue problems for operators with variable coe?cients consists in obtaining a corresponding dispersion relation or characteristic equa-tion of the problem in a su?ciently explicit form. Solutions of the dispersion relation are the eigenvalues of the problem. When the dispersion relation is known the eigenvalues are found numerically even for relatively simple problems with constant coe?cients because even in those cases as a rule the dispersion relation represents a transcendental equation the exact solutions of which are unknown.
Optimization of bioethanol production from coffee mucilage
Get PDF"A response surface methodology with 2(k) full factorial design was applied to obtain optimum conditions for bioethanol production using coffee mucilage (CM) as the substrate and Saccharomyces cerevisiae NRRL Y-2034 as the inoculum. CM is an agro-industrial residue mainly composed of simple sugars; the product yield and productivity process were analyzed with respect to the fermentation, pH, temperature, and the initial sugar concentration. Employing the following predicted optimum operational conditions attained the highest bioethanol production: pH 5.1, temperature 32 degrees C, and initial sugar concentration 61.8 g/L. The estimated bioethanol production was 15.02 g/L, and the experimental production was 16.29 g/L +/- 0.39 g/L, with a bioethanol yield of 0.27 g/L and a productivity process of 0.34 g/Lh. Glycerol was the predominant byproduct of the fermentative metabolism of S. cerevisiae. The response surface methodology was successfully employed to optimize CM fermentation. In the fermentative processes with yeast, optimizing the conditions of the culture medium is needed to fully exploit the potential of the strains and maximize the production of bioethanol.
Estudio de la microestructura y el efecto elastocalórico en aleaciones Cu-Al-Be
Get PDFTesis (Maestría en Nanociencias y Nanotecnología)"Algunos materiales experimentan un cambio de temperatura cuando son sujetos a un cambio repentino de un campo externo aplicado (eléctrico, mecánico, magnético…). A esta propiedad se le conoce como efecto calórico y puede ser medido por un cambio de entropía isotérmico (ΔSisotérmico) o un cambio de temperatura adiabático (ΔTadiabático); dicho efecto puede emplearse en refrigeración de estado sólido. En el caso específico de la aplicación de un esfuerzo, conocido como efecto elastocalórico, las aleaciones con memoria de forma han presentado buenos resultados. En el presente trabajo se llevó a cabo la medición del efecto elastocalórico en aleaciones con memoria de forma de Cu-Al-Be para su posible aplicación en refrigeración de estado sólido. Fueron tres las aleaciones estudiadas, de las cuales una se presentó en forma de lámina y las otras dos en forma de cinta (elaboradas por solidificación rápida). Se realizaron mediciones del cambio de longitud en función de la temperatura alrededor de la transición de fase martensítica (de primer orden) a esfuerzo aplicado constante en tensión. El ΔSisotérmico inducido por tensión fue calculado a partir de las mediciones de ε (T,σ), en base a las relaciones de Maxwell. En las tres aleaciones se observó una dependencia en el cambio de entropía máximo alcanzado y la capacidad refrigerativa en función del esfuerzo aplicado. Los resultados obtenidos muestran que todas las aleaciones presentan este efecto; los mayores valores se obtuvieron en una de las cintas con composición Cu- 12.1wt.% Al- 0.5wt.% Be, la cual presentó un ΔSisotérmico de -2.7 J/kg-K y una capacidad refrigerativa (RCP) de 55.1 J/kg para un esfuerzo aplicado de 29.2MPa.""Some materials undergo a temperature change when are subjected to a sudden change of an external field (which can be electric, mechanical, magnetic…). This property is known as caloric effects and can be measure by a change in the entropy at isothermic condition (ΔSisothermic) or the change of temperature at adiabatic condition (ΔTadiabatic); those effects could be useful for solid-state refrigeration. In the specific case of the use of mechanical field, known as elastocaloric effect, shape memory alloys have been referred as good candidates. In this work, the measurement of the elastocaloric effect was carried out in shape memory alloys of Cu-Al-Be for its possible application in solid state refrigeration. Three alloys was analyzed, one like thin layer and the others two like ribbons (made by melt spinning technique). We report the measurements of deformation as a function of temperature across the martensitic transformation (first order transition) at constant applied stress. From the data obtained of the ε (T,σ) measurements, the ΔSisothermic was calculated by the Maxwell relation. In the three alloys were observed a dependence behavior in the maximum value of ΔSisothermic and the refrigerant capacity (RCP) as function of applied stress. The results shown that the alloys present this effect; the maximum values obtained was from a ribbon with composition of Cu- 12.1wt.% Al- 0.5wt.% Be, which present an ΔSisothermic of -2.7 J/kg-K and a RCP of 55.1 J/kg for an applied stress of 29.2 MPa.
Hyperchaotic encryption based on multi-scroll piecewise linear systems
Get PDF"A hyperchaotic multi-scroll piecewise linear system in R4 is binarized to generate a pseudo-random sequence which encrypt a grayscale image via symmetric-key algorithm. The sequence is analyzed throughout statistical tests according to the National Institute of Standards and Technology (NIST) specifications. The scrolls of the system are the result of a switching law that changes between the saddle hyperbolic equilibria of piecewise linear systems with eigenvalues as follows: two negative real and one pair of complex conjugate eigenvalues with positive real part. Thus, the encryption quality is evaluated depending on the variation of the number of scrolls.
Oxidación anaerobia de metano acoplada a la reducción de sustancias húmicas y sus análogos estructurales
Get PDF"Las sustancias húmicas (SH), provenientes de la descomposición de materia vegetal, juegan importantes roles en el medio ambiente. Un ejemplo, es la capacidad de las SH para ser aceptores finales de electrones (AFE) en la respiración microbiana. El humus, puede además fungir como transportador de electrones, entre microorganismos anaerobios, y aceptores de electrones sólidos como los óxidos metálicos. Esta reactividad de las SH, y su ubicuidad en ecosistemas terrestres y acuáticos, las colocan como piezas clave en el metabolismo microbiano en suelos y sedimentos carentes de O2. La oxidación anaerobia de metano (OAM), contribuye como sumidero de este gas de efecto invernadero en el océano, ríos, lagos y humedales. La OAM convierte biológicamente el CH4 en CO2, en total ausencia de oxígeno, es decir, la OAM convierte una molécula que tiene un potencial de calentamiento global de 25 en una que tiene 1. La OAM, a la fecha, ha sido documentada bajo el acoplamiento a la reducción de AFEs alternativos de relevancia ambiental, sin embargo, aunque teórica y termodinámicamente es posible, la ocurrencia de la OAM acoplada a la reducción de SH no ha sido documentada. En este trabajo se buscó microbiota con la capacidad de acoplar la OAM a la reducción de SH y sus análogos estructurales en sedimentos de cinco cuerpos de agua mexicanos. Sólo un sedimento proveniente de una Ciénega Yucateca (Ciénega Sisal), mostró la capacidad de acoplar la OAM a la reducción de un análogo de las SH (antraquinona,2-6,disulfonato), y a una forma de ácidos húmicos (leonardita) a través de varios ciclos. Este estudio muestra evidencia de que las SH y los microorganismos que las reducen, tienen el potencial de actuar como sumidero de CH4 en cuerpos de agua. Adicionalmente, se documenta el efecto de los óxidos de Fe y Mn (goethita y vernadita, respectivamente) sobre el proceso al aumentar el consumo de CH4 re-oxidando los ácidos húmicos.""Humic substances (HS) is the name given to the recalcitrant molecules formed through the chemical and biochemical decomposition of organic matter. HS constitute a highly relevant terminal electron acceptor (TEA) due to its widespread presence in terrestrial and aquatic environments. Humus reducing microorganisms have shown biotechnological potential by oxidizing priority pollutants using both, HS and their structural analogues (model quinones i.e.: anthraquinone,2- 6,disulfonate; AQDS) to accomplish its respiratory pathway. One important biological process regulating the emission of CH4 to the atmosphere is anaerobic methane oxidation (AMO). In the AMO process, anaerobic microorganisms uptake methane as carbon and energy source at the time they reduce an alternative TEA. Sulfate, nitrate, nitrite and metallic ions, such as iron and manganese, have been reported to serve as TEA in AMO taking place at the ocean and fresh water bodies, like lakes and wetlands. Although energetically favorable and theoretically feasible, the AMO process coupled to HS reduction has not been reported to date, underestimating what could be an important sink of CH4 in soils and anoxic sediments of a variety of water bodies. The aim of this work was to evaluate the capacity of five Mexican anoxic sediments to accomplish the oxidation of CH4 coupled to the reduction of HS and the humic model compound, AQDS. A sediment from the Sisal marsh (Yucatán, Mexico) was capable of performing the AMO process coupled to AQDS and Leonardite (a form of humic acids) reduction through several cycles. Also, the re-oxidizing effect of Fe & Mn oxides (goethite and vernadite, respectively) was evaluated. To our knowledge, this is the first evidence of the existence of a CH4 sink in which HS and the microorganisms capable of reducing them play a major role on AMO.
Riesgo por emisiones de radón en el área metropolitana de San Luis Potosí
Get PDF"El radón (222Rn), es un gas radiactivo de origen natural, el cual aporta la mayor parte de la radiación que recibe el ser humano a lo largo de su vida; el radón no tiene olor, color ni sabor, por lo que la forma de detectarlo a través de la radiación que emite en forma de partículas alfa. El radón se emite constantemente del suelo y de algunos materiales de construcción. El contacto con este gas en concentraciones elevadas es nocivo para la salud, pues su inhalación puede producir cáncer de pulmón. Por esta razón se midieron las concentraciones de 222Rn en el suelo del Área Metropolitana de San Luis Potosí con la finalidad de conocer los niveles que existen y generar un mapa de riesgo por emisiones de este gas. Los niveles de radón se obtuvieron por dos métodos, uno pasivo, en el cual se emplearon detectores solidos de trazas nucleares, usando CR-39 como material detector, y otro activo con el que se tomaron muestras por medio del dispositivo RAD7. La zona de estudio presentó un promedio de 5,723 Bq/m3 con un máximo de 47,100 Bq/m y un mínimo de 400.5 Bq/m3; con los resultados de ambas técnicas se realizaron mapas de concentración de 222Rn para el área de estudio. Las condiciones geológicas, el relieve de la zona de estudio y la influencia antropogénica son los principales factores que influyen en la distribución y niveles de radón encontrados en la ciudad de San Luis Potosí. La zona del valle donde se tiene una capa sedimentaria más gruesa y donde se encuentra la mayor parte de la ciudad cuenta con los niveles más altos de radón a diferencia de las zonas montañosas o de loma que tienen concentraciones mucho menores. La combinación de las capas de concentración de radón, las densidades de población de la zona metropolitana, la capa de asfalto y el tipo de material geológico que compone el valle da como resultado el mapa de riesgo por emisiones de radón. La zona con mayor riesgo se localizó al sureste de la ciudad en los alrededores del Boulevard Río Españita, es un área de valle con altas densidades de población y concentraciones de radón bastante elevadas que llegan a rebasar los 40,000 Bq/m3 y donde habitan alrededor de 250,000 personas.""Radon (222Rn) is a natural occurring radioactive gas, it provides most of the radiation received by man throughout his life; radon is odorless, colorless and tasteless, so the way to detect it is through the radiation emitted in the form of alpha particles. Radon is constantly emitted from soil and some construction materials; contact with this gas is a health hazard, because its inhalation may cause lung cancer. For this reason, radon concentrations were measured in soil of San Luis Potosí metropolitan area, in order to know the levels that exist in the city and generate a risk map for radon emissions. Radon levels were obtained using 2 methods, a passive one, in which solid nuclear track detectors were employed, using CR-39 as track detector; and an active one, which samples were taken by the RAD7 device; the study area had an average of 5,723 Bq/m3, with a maximum of 47,100 Bq/m3 and a minimum of 400.5 Bq/m3; the results of both techniques were used in the mapping of radon concentration in the study area. Geological conditions, the relief of the study area and anthropogenic influence are so important in the radon levels in the city of San Luis Potosi. The highest levels are found in the valley zone, which has a thicker layer of sediments and where most of the city is established. The mountain or hill areas had much lower radon concentrations. The combination of layers of radon concentration, population density, and type of geological material making up the valley has resulted in the risk map for radon emissions. The most risk area is located in the southeast of the city near of Río Españita Boulevard; it is a valley area with high population densities and fairly high concentrations of radon that exceed 40,000 Bq/m3 and where around 250,000 people live.
Enlarged sheet of ZnS(en)0.5 hybrid semiconductors with photocatalytic activity
Get PDF"Sheets of ZnS(en)0.5 hybrid semiconductors were prepared by the precipitation method in an ethylenediamine–water solution and it was enlarged by varying the aging at a long period time. The characterization of the hybrid material was carried out by different techniques such as FTIR, DRS-UV–vis spectroscopies and scanning electron microscopy (SEM). The number of intercalated ZnS layers in a ZnS(en)0.5 hybrid semiconductor was proposed to be determined by XRD. The photocatalytic activity of the enlarged sheet of ZnS(en)0.5 hybrid was investigated in the photoreduction of 4-nitrophenol to 4-aminophenol in the presence of hydrazine under UV light irradiation. The intrinsic photocatalytic activity of the ZnS(en)0.5 semiconductor sheets was associated with the number of intercalated ZnS layers, and possible mechanism of the electron transfer process was discussed.
Monitoring lipase/esterase activity by stopped flow in a sequential injection analysis system using p-nitrophenyl butyrate
Get PDF"Lipases and esterases are biocatalysts used at the laboratory and industrial level. To obtain the maximum yield in a bioprocess, it is important to measure key variables, such as enzymatic activity. The conventional method for monitoring hydrolytic activity is to take out a sample from the bioreactor to be analyzed off-line at the laboratory. The disadvantage of this approach is the long time required to recover the information from the process, hindering the possibility to develop control systems. New strategies to monitor lipase/esterase activity are necessary. In this context and in the first approach, we proposed a lab-made sequential injection analysis system to analyze off-line samples from shake flasks. Lipase/esterase activity was determined using p-nitrophenyl butyrate as the substrate. The sequential injection analysis allowed us to measure the hydrolytic activity from a sample without dilution in a linear range from 0.05-1.60 U/mL, with the capability to reach sample dilutions up to 1000 times, a sampling frequency of five samples/h, with a kinetic reaction of 5 min and a relative standard deviation of 8.75%. The results are promising to monitor lipase/esterase activity in real time, in which optimization and control strategies can be designed.
Conectividad entre las poblaciones de jaguar en la Sierra Madre Oriental, México
Get PDF"Introduction: The jaguar (Panthera onca) is an apex carnivore that is vulnerable to habitat fragmentation, and some of its populations are believed to be isolated in México where it is classed as endangered. The main the objective of our study was to evaluate connectivity of available jaguar habitat from the Sierra Madre Oriental of México (SMO) towards southern México.
Methods: We determined least-cost pathways for jaguar movements among habitat patches in the SMO and identified potential corridors from the SMO. We used recent jaguar presence data and maximum entropy modeling to identify habitat patches in the SMO. We then used the Analytical Hierarchy Process to generate input values for a resistance (landscape permeability) matrix for jaguar movements that we generated using Multi-Criteria-Evaluation with a weighted linear combination. We then modeled least-cost pathways for both dispersal and local movements of jaguars.
Results: We identified 581 potential highly suitable habitat patches for the jaguar. Of these, three were > 100 km2 and thus met the criteria for fundamental (i. e. capable of supporting a viable jaguar population) patches. The resistance matrix contained 3 % of low cost and 49 % intermediate cost areas for jaguar movements. Least-cost pathways analysis showed 61 dispersal routes totaling > 2,000 km and > 200 travel routes, with the largest number of both route types in Hidalgo. We also identified potentially five significant corridors for jaguar movement within the SMO and south towards southern México populations.
Discussion and implications: We determined that the SMO contains significant jaguar habitat with multiple biological corridors for connectivity with more southern populations of jaguar in México. Based on this, we recommend development of management strategies to facilitate exchange of individuals from the SMO with other known jaguar populations in southern states (i. e. Oaxaca, Tabasco, Guerrero). Principal strategies may focus on habitat management of fundamental patches and habitat restoration between or around stepping-stones. Promoting connectivity among patches and populations which inhabit the SMO will increase its potential as a biodiversity conservation area.
Effects of nitrogen-doped multiwall carbon nanotubes on murine fibroblasts
Get PDF"The effect of nitrogen-doped multiwall carbon nanotubes (CNx) on the proliferation of NIH-3T3murine fibroblasts is presented. CNTs were dispersed in distillated water and incubated with mammalian cells in order to evaluate their toxicity. Also, the influence of factors such as dosage (7 and 70 mu g/mL), exposure time (24 to 96 h), and the exposure route (before and after cell liftoff) on the cell proliferation was evaluated. When the CNx were simultaneously incubated with the cells, the control culture reached a maximum cell concentration of 1.3 x 10(5) +/- 3.4 x 10(4) cells per well at 96 h, whereas cultures with 7 mu g/mL reached a concentration of 2.6 x 10(4) +/- 5.3 x 10(3) cells. In the case of 70 mu g/mL of CNx most of the cells were dead. The CNx that were added 24 h after cell dissociation showed that live cells decreased, with a cell concentration of 9.6 x 10(4) +/- 9 x 10(3) for 7 mu g/mL and 5.5 x 10(4) +/- 9.5 x 10(3) for 70 mu g/mL, in contrast to control cultures with 1.1 x 10(6) +/- 1.5 x 10(4). The results showed that the CNx had cytotoxic effects depending on the concentration and exposure route.