Adsorption of arsenate on Fe-(hydr)oxide

Adsorption using metal oxide materials has been demonstrated to be an effective technique to remove hazardous materials from water, due to its easy operation, low cost, and high efficiency. The high number of oxyanions in aquatic ecosystems causes serious pollution problems. Removal of arsenate (H2AsO4 -), is one of the major concerns, since it is a highly toxic anion for life. Within the metal oxides, the iron oxide is considered as a suitable material for the elimination of oxyanions. The adsorption of H2AsO4 - on Fe-(hydr)oxide is through the formation of inner or outer sphere complexes. In this work, through computational methods, a complete characterization of the adsorbed surface complexes was performed. Three different pH conditions were simulated (acidic, intermediate and basic), and it was found that, the thermodynamic favourability of the different adsorbed complexes was directly related to the pH. Monodentate complex (MM1) was the most thermodynamically favourable complex with an adsorption energy of -96.0kJ/mol under intermediate pH conditions. © Published under licence by IOP Publishing Ltd

SANS study of hybrid silica aerogels under "in situ" uniaxial compression

We have modified the inorganic silica network of aerogels with polydimethylsiloxane (PDMS), a hydroxyl-terminated polymer, to obtain an organic modified silicate (ORMOSIL). Reactions were assisted by high-power ultrasounds. The resulting gels were dried under supercritical conditions of the solvent to obtain a monolithic sono-aerogel. The mechanical behaviour of these aerogels can be tuned from brittle to rubbery as a function of the organic polymer content. In order to determine the links between the mechanical behaviour and modifications made to the microstructure, SANS (small-angle neutron scattering) experiments were carried out. To measure the intensities under "in situ" uniaxial compression of the aerogel, a specific sample-holder was built. Under uniaxial compression the 2D-diagrams were significantly anisotropic (butterfly pattern), indicating the rearrangement of the polymer. The form factor of these aerogels is described well by two correlation lengths, small microporous silica clusters surrounded by entangled polymer chains of 6 nm average size (blobs), which form a larger secondary level of agglomerates governed by the "frozen-in" elastic constraints.Comisión Interministerial de Ciencia y Tecnología MAT2005-1583European Commission CT-2003-50592

Resección de la primera fila del carpo: indicaciones y resultados

La resección de la primera fila del carpo (RPC) es un conocido procedimiento para conservar la función en muñecas afectadas por procesos degenerativos de la articulación radiocarpiana. En el presente trabajo nuestra experiencia con este tipo de intervención. Material y Métodos: Análisis retrospectivo de pacientes intervenidos en nuestro centro mediante RPC. Se valoraron: datos demográficos, dolor, movilidad y fuerza, y evolución radiológica tras la cirugía. Resultados: 1 pacientes de edad media 58 años, con seguimiento medio de 16 meses. Tras la RPC se observó mejoría del arco de movilidad de la muñeca y de la fuerza de prensión. Cuatro pacientes no tenían dolor. Seis pacientes pudieron reincorporarse a su trabajo. Un paciente evolucionó con rigidez y artrosis radio-hueso grande, que precisó artrodesis al año y medio de la cirugía. Conclusiones: La PRC es una buena intervención para el tratamiento de la artrosis evolucionada de la muñeca.Proximal Row Carpectomy (PRC) is a recognised procedure to preserve motion for wrists which are affected by degenerative diseases at the radiocarpal joint. Material and Methods: Retrospective review of patients subjected to a PRC in our Institution. Demographic data, pain, mobility and grip force, and radiologic evolution before and after surgery were determined. Results: Seven patients, with an average age of 58 years-old. Average follow-up of 16 months. After PRC there was an improvement of mobility and grip force. Four of the seven patients were pain-free. Six patients were able to return to work. One patient developed arthritis of the wrist, being subjected to a wrist arthrodesis one year after surgery. Results: PRC is a good intervention for advanced arthritis of the radiocarpal joint

1-methylcyclopropeneand storage temperature effect in postharvest of mandarin (Citrus reticulata L.) var. Arrayana

La producción de mandarina dentro del grupo de los cítricos tiene un aporte significativo en Colombia. El uso del 1-metilciclopropeno (1-MCP) inhibe la acción del etileno y es una práctica común para prolongar la vida poscosecha de productos perecederos. En frutos cítricos, especialmente en mandarina var. Arrayana, no se tiene caracterizado el efecto del 1-MCP en combinación con temperatura de almacenamiento. Por tanto, es importante establecer el efecto del 1-MCP y de la temperatura de almacenamiento sobre el comportamiento poscosecha del fruto de mandarina (Citrus reticulata L.) var. Arrayana cosechados en madurez comercial. Para este estudio se utilizó un diseño completamente al azar (DCA) con arreglo factorial 3 x 2: con temperaturas de almacenamiento de 6, 12 y 18°C (ambiente) como primer factor y la presencia o ausencia de 1-MCP (0,5 μL L-1 con 2 h de tratamiento) como segundo factor. Se midieron las variables sólidos solubles totales, tasa respiratoria, acidez total titulable, firmeza, clorofila total e índice de color cada 7 días durante 34 días de almacenamiento. A los 22 días de almacenamiento, independientemente de la aplicación de 1-MCP, el tratamiento a 12°C estimula cambios en la coloración de la epidermis, mayor degradación de clorofilas y mayor índice de color. A esta temperatura no se presenta daño por frío y no es importante la aplicación de 1-MCP. No obstante, a temperaturas menores (6°C) la conservación es mayor, el desverdizado es lento y se presenta menor índice de color, lo que conlleva a mayor tiempo de conservación. De acuerdo con los resultados, la temperatura de 12°C es adecuada para el desverdizado de mandarina var. Arrayana hasta los 22 días de almacenamiento, y 6°C es una temperatura alternativa para almacenamientos más prolongados, hasta de 34 días; manejos poscosecha no reportados anteriormente para esta variedad.Mandarin accounts for a significant part of citrus production in Colombia. The use of 1-methylcyclopropene (1-MCP) inhibits the action of ethylene and constitutes a common practice for extending the postharvest life of perishable products. In citrus fruits, especially tangerine var. Arrayana, the effect of 1-MCP in combination with storage temperature has not been characterized. It is therefore important to establish the effect of these two combined factors on the postharvest behavior of mandarin fruits (Citrus reticulata L.) var. Arrayana harvested at commercial maturity. A completely randomized design with a 3 x 2 factorial arrangement was employed for the study: the first factor corresponded to storage temperatures of 6, 12 and 18°C (room temperature), while the second factor was the presence or absence of 1-MCP (0,5 μL L-1 for two hours). The fruits were kept in storage room for a period of 34 days, during which total soluble solids, respiratory rate, total titratable acidity, firmness, total chlorophyll and color index were assessed every 7 days. After 22 days of storage, and regardless of the application of 1-MCP, 12°C treatment stimulate fruit skin discoloration and increased chlorophyll degradation and color index. At this temperature, no frost damage occurred and the application of 1-MCP was not important. However, at temperatures below 6°C, lower degreening and color index values were observed, thus leading to longer shelf life times. According to the results, 12°C is a suitable temperatur for the degreening of tangerine var. Arrayana until 22 days of storage; and 6°C is an alternative temperature for longer storage times, up to 34 days. No postharvest management had been previously reported for this variety.Fil: Gómez, Carlos A.. Universidad Nacional de ColombiaFil: Herrera, Aníbal O.. Universidad Nacional de ColombiaFil: Flórez, Víctor J.. Universidad Nacional de Colombi

Aprender a enseñar ciencias vinculando el museo como recurso didáctico para la enseñanza del sistema circulatorio humano

Esta investigación se centró en describir cómo aprende a enseñar ciencias una profesora de secundaria en formación continua, incorporando el Museo de Ciencias en la enseñanza del sistema circulatorio. A través de la clínica didáctica, se buscaron evidencias sobre las modificaciones en el estatus de sus ideas respecto a este recurso en el marco de su PCK, las cuales se interpretaron desde el cambio conceptual en relación con el papel regulador de la metacognición. Los resultados indican que la idea es inteligible y plausible en su discurso, destacando el potencial del museo para la enseñanza y el aprendizaje, pero la fructibilidad se alcanza cuando la profesora reflexiona sobre sus acciones, luego de ejecutar la unidad didáctica

Bioactivity of wollastonite/aerogels composites obtained from a TEOS-MTES matrix

Organic-inorganic hybrid materials were synthesized by controlled hydrolysis of tetraethoxysilane (TEOS), methyltrimethoxysilane (MTES), synthetic wollastonite powders and polydimethylsiloxane (PDMS) in an ethanol solution. Aerogels were prepared from acid hydrolysis of TEOS and MTES with different volume ratio in ethanol, followed by addition of wollastonite powder and PDMS in order to obtain aerogels with 20 wt% of PDMS and 5 wt% of CaO of the total silica. Finally, when the wet gels were obtained, they were supercritically dried at 260°C and 90 bar, in ethanol. In order to obtain its bioactivity, one method for surface activation is based on a wet chemical alkaline treatment. The particular interest of this study is that we introduce hybrid aerogels, in a 1 M solution of NaOH, for 30 s at room temperature. We evaluate the bioactivity of TEOS-MTES aerogel when immersed in a static volume of simulated body fluid (SBF). An apatite layer of spherical-shaped particles of uniform size smaller than 5 microns is observed to form on the surface of the aerogels after 25 days soaking in SBF.Ministerio de Ciencia e Innovación MAT2005-01583Junta de Andalucía TEP 79