Reseñas

Stephan SUHNER, Resistiendo al olvido. Tendencias recientes del movimiento social y de las organizaciones campesinas en Colombi

CO2 Electroreduction on Silver Catalysts Under Controlled Mass Transport Conditions

The electrochemical reduction of carbon dioxide (CO2RR) to value-added chemicals using excess intermittent electric power from renewable energy sources is considered a promising approach to mitigate global warming caused by anthropogenic CO2 emissions. The product selectivity of the CO2RR can be controlled by the chemical nature and the morphology of the catalyst material. Among the various products of the CO2RR, the production of carbon monoxide (CO) is highly desirable because it can be used as feedstock in the Fischer–Tropsch synthesis to produce higher long-chain hydrocarbons and alcohols. Silver is well known as a promising catalyst material for CO production. Most of the screening experiments to test the activity, selectivity, and stability of an electrocatalyst have been carried out in H-type cell configurations using aqueous electrolytes. However, the low solubility of CO2 in aqueous electrolytes under ambient conditions imposes severe mass transport limitations. This PhD thesis has addressed this challenge, by carrying out classical half-cell measurements in aqueous environments extended to a zero-gap gas-fed electrolyzer. The catalytic properties of two colloidal silver nanomaterials with different morphologies were studied (nanocubes and nanowires). The electrocatalysts studied herein present high selectivity and activity towards CO formation, e.g., in the case of silver nanocubes, a partial current density of ~625 mA cm−2 and a faradaic efficiency of ~85% for CO were attained. Besides, it is particularly pointed out that the reaction environment plays an essential role in the product distribution of the reaction; formate is generated with higher selectivities and activities in a highly alkaline environment than in a weak one. Furthermore, identical location scanning electron microscopy (IL-SEM) is herein demonstrated as a powerful technique to study the structural degradation of the electrocatalysts. By imaging the same spot on the catalyst before and after the CO2RR, it is possible to directly visualize changes of the catalyst morphology on a nm-length scale attributed to the electrolysis reaction. Limitations of this analysis technique are discussed based on surfactant-protected nanocatalysts. Additionally, a new electrochemical surfactant removal method based on potentiostatic CO2RR electrolysis was developed to remove polyvinylpyrrolidone or PVP (the capping agent) from Ag nanowire and nanocube surfaces, resulting in a substantially improved selectivity towards CO formation. Overall, the studies presented herein clearly demonstrate the importance of performing CO2RR under more realistic conditions to bring this process closer to what is needed for the scale-up of this reaction, which means that high faradaic efficiencies, partial current densities, and long stability are pursued

Análisis sobre la influencia de la densidad en la termografía de infrarrojos y el alcance de esta técnica en la detección de defectos internos en la madera

This paper shows the results of a laboratory phase for the determination of the 1limits of infrared thermography in detecting internal defects in wood and, furthermore, it analyses how the density of this material can influence the surface temperature displayed in a thermogram. To this end, experimental work is carried out whereby a series of work and environmental parameters are monitored (such as environmental temperature, relative humidity, distance to target), and the process is systematized by using pieces of different wood species (different densities) and by devising a set of samples for which various possible cases are analysed in terms of size and internal position of the damage. Similarly, using these samples, a study has been conducted on the effect on the thermal image produced by an increase of humidity inside the defect phenomena normally associated with wood decay.En el presente artículo se muestran los resultados obtenidos en una fase de laboratorio al tratar de determinar el alcance de la termografía de infrarrojos en la detección de defectos internos en la madera y, por otro lado, cómo interviene la densidad de este material sobre la temperatura superficial mostrada en un termograma. Para ello se ha desarrollado un trabajo experimental donde se han controlado una serie de parámetros ambientales y de trabajo (temperatura ambiente, humedad relativa, distancia al objetivo…), y se ha sistematizado el proceso utilizando piezas de distintas especies de madera (distintas densidades) y diseñando una serie de probetas donde se han analizado varias casuísticas posibles en cuanto a tamaño y posición interna de los daños. Análogamente, sobre estas probetas se ha estudiado el efecto que produce sobre la imagen termográfica un incremento de humedad interna en el defecto asociada normalmente a los fenómenos de pudrición de la madera

A cidade: espaço de construção do sujeito

In the development of the western culture the city has been considered as a space through which a formation ideal is manifested. The origin of the city goes back to the Greek polis with its democratic practices, it goes modifying with the pass of the time until to the contemporary city that presents characteristic different to the other times, it develops a new formation ideal that guides the inhabitants of the city to create identification spaces and ownership through socialization processes and pedagogic that they facilitate the fellow's recognition and the city in historical-social construction, so that the ordinary inhabitant can decide autonomously to participate in and the civic culture is developed where it is recognized to the other one significant, to the common space to share and take place relationships of respect and solidarity among the habitants of the city in a such way it becomes optimal environment of construction of the fellow that inhabits it in the same one.En el desarrollo de la cultura occidental la ciudad se ha considerado como un espacio a través del cual se manifiesta un ideal de formación. El origen de la ciudad se remonta a la polis griega con sus prácticas democráticas, se va modificando con el paso del tiempo hasta llegar a la ciudad contemporánea que presenta características diferentes a las otras épocas, pero que desarrolla un nuevo ideal de formación que orienta a los habitantes de la ciudad para crear espacios de identificación y pertenencia a través de procesos de socialización y pedagógicos que facilitan el reconocimiento del sujeto y la ciudad en construcción histórico-social, a fin de que el habitante común y corriente pueda decidir autónomamente participar en ésta y se desarrolle la cultura ciudadana donde se reconozca al otro significativo, al espacio común para compartir y se produzcan relaciones de respeto y solidaridad entre los habitantes de la ciudad de forma tal que la misma se convierta en ámbito de construcción del sujeto que la habita.No desenvolvimento da cultura ocidental a cidade considerou-se como um espaço através do qual se manifesta um ideal de formação. A origem da cidade remonta-se à polis grega com suas práticas democráticas, vai-se modificando com o passo do tempo até chegar à cidade contemporânea que apresenta características diferentes às outras épocas, mas que desenvolve um novo ideal de formação que orienta aos habitantes da cidade para criar espaços de identificação e pertença através de processos de socialização e pedagógicos que facilitam o reconhecimento do sujeito e a cidade em construção histórico-social, a fim de que o habitante comum e corrente possa decidir autonomamente participar nesta e se desenvolva a cultura cidadã onde se reconheça ao outro significativo, ao espaço comum para compartilhar e se produzam relações de respeito e solidariedade entre os habitantes da cidade de forma tal que a mesma se converta em âmbito de construção do sujeito que a habita

Iridoids as DNA topoisomerase I poisons

The discovery of new topoisomerase I inhibitors is necessary since most of the antitumor drugs are targeted against type II and only a very few can specifically affect type I. Topoisomerase poisons generate toxic DNA damage by stabilization of the covalent DNA-topoisomerase cleavage complex and some have therapeutic efficacy in human cancer. Two iridoids, aucubin and geniposide, have shown antitumoral activities, but their activity against topoisomerase enzymes has not been tested. Here it was found that both compounds are able to stabilize covalent attachments of the topoisomerase I subunits to DNA at sites of DNA strand breaks, generating cleavage complexes intermediates so being active as poisons of topoisomerase I, but not topoisomerase II. This result points to DNA damage induced by topoisomerase I poisoning as one of the possible mechanisms by which these two iridoids have shown antitumoral activity, increasing interest in their possible use in cancer chemoprevention and therapy.Ministerio de Ciencia y Tecnología de España. SAF 2000-016

Characterisation of recycled ceramic mortars for use in prefabricated beam-filling pieces in structural floors

This study analyses a procedure to manufacture mortars with different percentages of ceramic waste as partial replacement for aggregates. The study also examines the physical, chemical and mechanical properties of the new mortars, analysing substitution ratios that range from 10% to 50%. Prior to this, all the materials used in the production of the mortar were characterised using X-ray diffraction (XRD) and fluorescence (XRF). The objective was to determine the similarity between different types of ceramic waste, as well as the differences in the minerology and chemical composition with the aggregate. The results of the study show that it is possible to obtain mortars with lower densities compared to the same product with no recycled content. The product’s characteristics make it ideal for the manufacture of prefabricated components for structural floors for rehabilitation works. Finally, the pieces are used in a real rehabilitation case study, highlightining the structural advantages.Caracterización de morteros con cerámica reciclada y su uso en piezas prefabicadas para entrevigado de forjados. Este trabajo analiza morteros con diferentes porcentajes de cerámica reciclada como sustituto parcial de la arena. Además el estudio examina las propiedades físicas, químicas y mecánicas de los nuevos morteros, empleando diferentes porcentajes de sustitución (10% - 50%). Con anterioridad, se caracterizaron todos los materiales empleados en este trabajo mediante difracción y fluorescencia de rayos-X. El objetivo fue determinar las diferencias y similitudes en la composición química y mineralógica de los distintos tipos de residuos cerámicos y del resto de áridos utilizados. Los resultados muestran que es posible obtener morteros con menor densidad frente a las muestras sin contenido reciclado. Sus características los hacen idóneos para la creación de piezas prefabricadas de entrevigado para rehabilitación de forjados. Finalmente. Las piezas se usaron en un caso de estudio real, destacando las ventajas estructurales que conlleva su uso

Impact of Wetting–Drying Cycles on the Mechanical Properties and Microstructure of Wood Waste–Gypsum Composites

Large amounts of wood waste are generated each year in the world. In an attempt to identify a good recovery option for those residues, wood waste from construction and demolition works were used as raw materials in gypsum plasters. However, wood is a biodegradable material which implies that the products or materials that contain it are susceptible to su ering an important deterioration, due to exposure in certain environments. For that reason, the aim of this work was to simulate the e ects that, in the long term, the atmospheric exposure of wood waste–gypsum composites would have. To do that, the plasters were subjected to 5, 10, and 15 wetting–drying cycles in a climatic chamber. In this study, the density, flexural and compressive strength, and ultrasonic velocity of these composites were determined by the influence of the aging process on their mechanical properties. Furthermore, in order to detect changes on their internal structure, scanning electron microscopy tests (SEM) were used. The results showed that they were suitable to be used as indoor coverings of buildings. However, a treatment to reduce the moisture absorption of the wood waste must be studied if mixtures with high percentages of wood shavings (WS20) are used in wet rooms

Modelado de la dispersión de luz por bacterias en contacto con nanopartículas de plata

"En este trabajo abordamos como tema principal de estudio la respuesta óptica de una bacteria con nanopartículas de plata (NPs Ag) sobre su superficie. Para realizar un estudio sistemático primero estudiamos las eficiencias de una bacteria sola, después la respuesta óptica de un arreglo de NPs Ag en diferentes posiciones y finalmente sistemas de bacteria-nanopartículas. Modelamos las eficiencias ópticas de absorción, dispersión y extinción de los sistemas de interés empleando la aproximación de dipolo discreto. Calculamos el patrón de dispersión de luz por una bacteria Staphylococcus aureus (S. aureus, gram-positiva), cuya principal característica es su morfología esférica, consideramos bacterias de diferente diámetro y composición, esto último a través de un modelo sencillo para estimar un índice de refracción efectivo asociado a la compleja composición de la bacteria. Estudios similares se realizaron para una bacteria Escherichia coli (E. coli, gram-negativa) con morfología esferocilíndrica. Del análisis de nuestros resultados concluimos que a mayor tamaño, los patrones de dispersión presentan un mayor número de mínimos. Además, bacterias con diferente composición presentan patrones de dispersión con el mismo número de mínimos y solo varían ligeramente sus intensidades. Se estudiaron arreglos de NPs Ag con 4, 5, 10, 15 y 30 partículas en diferentes distribuciones espaciales. Del análisis de los cálculos de las eficiencias ópticas se logró identificar que la línea espectral de la eficiencia de absorción tiene un máximo entre 400 y 410 nm. La intensidad de los espectros aumenta a medida que aumenta el número de NPs Ag. El sistema bacteria-NPs se estudio considerando una bacteria S. aureus con NPs de Ag sobre su superficie, considerando los arreglos mencionados anteriormente. La interacción bacteria-nanopartículas tiene como principal característica líneas espectrales similares a las de los arreglos de NPs solas, pero con intensidades 100 veces menores.

Cohesive crack model for mixed mode fracture of brick

This paper presents a numerical procedure for mixed mode fracture of brickworkmasonry. Themodel is an extension of the cohesive model prepared by the authors for concrete, and takes into account the anisotropy of the material. After the crack path is obtained, an interface finite element (using the cohesive fracture model) is incorporated into the trajectory. Such a model is then implemented into a commercial code by means of a user subroutine, consequently being contrasted with experimental results. Fracture properties of masonry are independently measured for two directions on the composed masonry, and then input in the numerical model. This numerical procedure accurately predicts the experimental mixedmode fracture records for different orientations of the brick layers and two homothetic sizes on masonry panels