Adhesión de partículas coloidales sobre superficies sólidas de interés tecnológico : aspectos cinéticos y predicciones termodinámicas

En esta tesis doctoral se ha estudiado la adhesión de partículas coloidales (adherente) sobre distintas superficies sólidas (sustrato). los materiales utilizados han sido (adherente/substrato): carbonato calcico/vidrio, sulfuro de zinc/vidrio y sulfuro de zinc/silicio. Las técnicas experimentales utilizadas para la determinación de la adhesión han sido la de placa rotatoria y la de lecho poroso. en el caso de la primera técnica mencionada, se ha estudiado el efecto que producen sobre la adhesión las siguientes variables: velocidad de rotación de la placa, temperatura, y concentración ionica del medio acuoso. Se ha encontrado que la cantidad adherida aumenta con la velocidad angular y la temperatura, hasta que se produce la transición de flujo laminar a turbulento. El aumento de la concentración de iones-calcio aumenta igualmente la cantidad adherida, mientras que los iones magnesio tienen un efecto contrario. con la técnica de lecho poroso ha sido posible analizar la cinética de adhesión, variando en este caso el tipo y concentración de iones en el medio y el ph del mismo. se ha considerado también el efecto de la aplicación de un campo eléctrico de radiofrecuencia durante el proceso de deposición. en general, se ha encontrado que las variaciones de la cantidad adherida son consecuencia de modificaciones en las fuerzas de interaccion interfacial partícula-partícula y partícula-sustrato. Se ha contemplado un modelo de fuerzas interfaciales que incluyen las electrostáticas, Van der Waals y polares o acido-base de Lewis icaTesis Universidad de Granada. Departamento de Física Aplicad

Effect of interfacial properties on mechanical stability of ash deposit

The paper presents a study on the cohesion of volcanic ash particles using surface free energy determination and zeta potential analyses. This is a subject of great interest in physical volcanology, as many researches on volcanic particle aggregation are frequently reported. In this case, special attention is paid to the role of structural or hydration forces between hydrophilic surfaces, which are a consequence of the electron-donor/electron-acceptor character of the interface. From this point of view, the results are potentially interesting as they could give valuable insights into this process. The results are presented in terms of the total energy of interaction between dispersed particles, computed from the extended DLVO theory. Contributions to the total free energy of interaction were determined from the zeta potential and surface free energy of ash, measured under different experimental conditions. Two samples of basaltic volcanic ash (black and white) with silica contents of 44% and 63% respectively are studied. The surface free energy and zeta potential were analysed for ashes immersed in different electrolytes (NaCl, CaCl2, FeCl3). The presence of electrolytes changes the surface properties of the solid materials. The analysis of total interaction energy between the ash particles in aqueous medium shows that soil cohesion strongly depends on ash surface properties, chemical nature, the adsorbed cation on the surface, and pH value

Cells electric charge analyses define specific properties for cancer cells activity.

The surface electrical charge of cells is conditioned by the ionic medium in which they are immersed. This charge is specific for each cell type and is especially important in tumour cells because it determines their state of aggregation and their adhesion in the different organs. This study analyses the variations in surface charge of cells when pH, electrolytes, and their concentration are modified. The modification of these factors leads to changes in the surface charge of tumour cells; therefore, their states of aggregation and behaviour can be modified. This may even have a use in the prognosis and treatment of various tumours. Some studies conclude that the activity associated with the glycolysis process is accompanied by a change in the surface charge of cells. Notably, there is a high rate of glycolysis in tumours. Our results show that surface charge of cells strongly depends on nature of ionic medium in which they are found, with the valence of the majority ion being the most important factor. When ionic strength was high, the charge decreased dramatically. On the other hand, charge becomes zero or positive in an acidic pH, while in a basic pH, the negative charge increases

EFECTO DE LA MATERIA ORGÁNICA SOBRE LAS PROPIEDADES FÍSICAS DEL SUELO EN UN SISTEMA AGROFORESTAL DE LA LLANURA COSTERA NORTE DE NAYARIT, MÉXICO

Se planteo analizar el comportamiento del contenido de materia orgánica de un suelo bajo un sistema agroforestal y los cambios ocurridos en algunas propiedades físicas. Este trabajo se llevó a cabo en un sistema agroforestal en la Llanura Costera Norte del estado de Nayarit, en el cual se valuaron propiedades del suelo, como son: materia orgánica (MO) y propiedades físicas, como humedad (W), densidad aparente (Da), porosidad total (Pt) y la capacidad de campo (CC). En el 2005, se realizó el perfil y se describió en cam- po y laboratorio, presentando una textura arcillosa (arena 29.1 %, limo 18.0 % y arcilla 52.8 %), pH medio (7.0), MO 0.51 %, capacidad de intercambio catiónico (CIC) 24.0 cmol.kg-1, Da 1.4 kg dm-3 CC y 24.3 %. El suelo se clasificó como Fluvisol haplico. Se caracterizó el suelo a una profundidad de 0-20 cm por coincidir con el espesor del horizonte A del suelo, considerando que es el horizonte más influenciado a corto plazo por la hojarasca. Se dió un seguimiento de dos muestreos por año hasta 2010, los resultados más sobresalientes a 6 años de implantado el sistema indican una disminución enlaDade1.09kgdm-3,unaumentoenlaMOde 3.85 %, Pt de 58 %, porosidad de aireación (Pa) 22.1%yenlaCC35.9%

383 A/C tumor necrosis factor receptor 1 polymorphism and ankylosing spondylitis in Mexicans: A preliminary study

The objective of this study was to evaluate the differences in allele and genotype frequencies of -383 tumor necrosis factor receptor 1 (TNFR1) polymorphism between ankylosing spondylitis (AS) and controls. Mexican Mestizos with AS were matched by gender, age, and ethnicity with healthy controls and compared in allele and genotype frequencies of the -383 TNFR1 polymorphism. Polymorphisms were genotyped using PCR-RFLP. The AA genotype occurred at a higher frequency in the AS group (92%) compared with controls (79%, P = 0.03). A allele was increased in AS (96% vs. 88%, P = 0.015) and was associated with genetic susceptibility for AS (odds ratio = 3.48, 95% CI = 1.23-10.61). This preliminary study is the first assessing the association of the -383 A/C TNFR1 polymorphism with AS, although it has the limitation of a small sample size. These data are of interest for the genetic epidemiology of AS in the Mexican population, requiring further investigation in other countries. © Springer-Verlag 2011