Un acercamiento al estudio del impacto de una secuencia de enseñanza-aprendizaje para mejorar la definición de tecnología

La ponencia se enmarca en el Proyecto Iberoamericano sobre la Naturaleza de la Ciencia y la Tecnología que busca mejorar en estudiantes la comprensión sobre la Naturaleza de la Ciencia y Tecnología (NdCyT), a partir del desarrollo de secuencias de enseñanza-aprendizaje (SEA) como lo es, en este caso, Tecnología: mucho más que aparatos. Ésta pretende hacer evolucionar creencias reduccionistas de estudiantes de nivel medio de Neuquén-Argentina respecto a la definición de Tecnología, involucrándolos en la resolución de una situación problemática como lo es el diseño de un baño en un campamento. Esperando culmine el procesamiento de resultados del pre y post test estandarizado aplicado para valorar el impacto pormenorizado sobre las mismas, adelantamos un somero análisis orientativo de sus respuestas a la actividad de reflexión metacognitiva

Los minerales gema: una propuesta práctica.

The main objective of this practical session is to introduce the student in the study of physical properties of minerals and specifically optical and mechanical properties. This is one of the most interesting fields in Mineralogy and we can use these properties to obtain the mineral identification. Activities that we propose have the study of gem-minerals as a basic objective that is the minerals that according to special characteristics and after cutting by man we use as a precious stones or gems. All techniques that we use are not destructives that is without any modification in the specimen, a very important question when we use minerals as gemstones. The practical session are distributed in six working groups with a reduced number of students (2-3), using this system we can combine the necessary equipment in the best possible way. Main objectives of the practical session are: showing one of the practical uses of minerals and the use of special techniques for to obtain the identification of gem-minerals. Also is very important to compare the theoretical concepts with the practical applications

Wet and dry African dust episodes over eastern Spain

The impact of the African dust on levels of atmospheric suspended particulate matter (SPM) and on wet deposition was evaluated in eastern Iberia for the period 1996-2002. An effort was made to compile both the SPM and wet episodes. To this end, the time series of levels of TSP and PM10 in Levantine air quality monitoring stations were evaluated and complemented with the computation of back trajectories, satellite images, and meteorological analysis. Wet deposition frequency was obtained from weekly collected precipitation data at a rural background station in which the African chemical signature was identified (mainly pH and Ca2+ concentrations). A number of African dust episodes (112) were identified (16 episodes per year). In 93 out of the 112 (13 episodes per year) the African dust influence caused high SPM levels. In 49 out of 112 (7 episodes per year), wet deposition was detected, and the chemistry was influenced by dust. There is a clear seasonal trend with higher frequency of dust outbreaks in May-August, with second modes in March and October. Wet events followed a different pattern, with a marked maximum in May. Except for one event, December was devoid of African air mass intrusions. On the basis of seasonal meteorological patterns affecting the Iberian Peninsula, an interpretation of the meteorological scenarios causing African dust transport over Iberia was carried out. Four scenarios were identified with a clear seasonal trend. The impact of the different dust outbreak scenarios on the levels of PM10 recorded at a rural site (Monagrega, Teruel, Spain) in the period 1996-2002 was also evaluated

Role of soil properties in sewage sludge toxicity to soil collembolans

Soil properties are one of the most important factors explaining the different toxicity results found in different soils. Although there is knowledge about the role of soil properties on the toxicity of individual chemicals, not much is known about its relevance for sewage sludge amendments. In particular little is known about the effect of soil properties on the toxicity modulation of these complex wastes. In addition, in most studies on sewage sludges the identity of the main substances linked to the toxicity and the influence of soil properties on their bioavailability remains unknown. In this study, the toxicity of a sewage sludge to the soil collembolan Folsomia candida was assessed in nine natural soils from agricultural, grassland and woodland sites, together with the OECD soil. Correlations between the relative toxicity of sludge for collembolans in the different soils and their physical and chemical soil properties were assessed in order to identify the main compounds responsible for the effects observed. Furthermore, the relationships between the toxic effects to collembolans and water-soluble ions released by sludge, pH and electric conductivity were also assessed, together with the modulating effects of soil properties. Sludge toxicity was directly linked to the water extractable ammonium, which explained most of the mortality of the collembolans, and part of the inhibition of reproduction. For the last endpoint, nitrite also contributed significantly to the inhibition observed. The varied levels in water extractable ammonium in the different soils at equal dosages seem to be, in turn, modulated by some soil properties. Higher organic carbon contents were associated with lower toxicity of sludge, both for survival and reproduction, probably related to its higher ammonium sorption capacity. In addition, for reproduction, increasing the C/N ratio and pH appeared to increase the toxicity, probably due to both the greater difficultly in nitrification and the known unsuitability of alkaline soils for this species

Variation of soluble and insoluble calcium in red rains related to dust sources and transport patterns from North Africa to northeastern Spain

We use the chemical composition of African dust delivered by red rains at a rural site in northeastern Spain (Montseny, 41460 N, 2210 E) to describe its relationship with the possible provenance areas and the processes occurring during transport. To this end, we obtained the red rain insoluble composition for the major elements (Al, Fe, Ca, Mg, K, P, Ti, and Na) in 30 filters, the 210Pb concentration in 23 filters, and the soluble cation concentrations (Na, K, Ca, and Mg) in 28 coincident red rain samples. These samples comprised most major events occurring at the site from 1983 to 2002. On the basis of back trajectories and satellite images, a distinction has been made between an eastern and western air mass flux with respect to 0 Greenwich for the analyzed samples. Principal component and ANOVA analyses between the two provenance groups have shown striking differences in the insoluble phase, with eastern samples being significantly richer in insoluble Ca, Mg, and Sr compared to western samples. Conversely, western samples had significantly higher concentrations of insoluble Al, Fe, K, V, and 210Pb than eastern samples. Therefore, in the insoluble phase, the ratios of various elements to Ca were significantly higher in western provenances. However, these differences disappeared when considering bulk Ca ratios (bulk Ca = insoluble + soluble Ca). Neither of the ratios Fe/Al and Ti/Fe showed significant differences. This lack of differences is interpreted in view of a similar carbonated lithology broadly underlying both areas. The difference in insoluble Ca with respect to total Ca between provenances (Cainsoluble/Catotal = 0.10 and 0.70 for western and eastern trajectories, respectively) is interpreted as a difference in calcite dissolution during transport. Evidence from 210Pb data and from the length of the back trajectories indicates that western trajectories covered a longer distance than the eastern ones; their higher soluble Ca could be due to (1) higher calcite dissolution due to longer contact with wet fronts from the Atlantic and (2) particle segregation during transport, with finer (carbonate) particles more prone to dissolution due to a higher surface to volume ratio

Atmospheric fluxes of ²¹⁰Pb to the western Mediterranean Sea and the Saharan dust influence

Pb 210 is a well known tracer of particle dynamics in the marine environment. Geochemical models partially rely on the knowledge of its atmospheric input. Unfortunately, this is poorly known in the western Mediterranean Sea, especially regarding long-term records. In this work we have evaluated the ²¹⁰Pb annual atmospheric flux to this region from the analysis of 12 soil cores collected from coastal and island sites and total atmospheric deposition collected in Corsica during 1 year. The ²¹⁰Pb fluxes ranged from 34 ± 3 to 121 ± 12 Bq m¯² yr¯¹ , with an average of 75 Bq m¯² yr¯¹, and were strongly correlated (R²= 0.95) with mean annual rainfall. This provides the possibility to determine ²¹⁰Pb fluxes in a given location if the mean annual rainfall is well known, a useful outcome for both marine biogeochemical and soil erosion studies in this region. We have also estimated the mean annual atmospheric flux of ²¹⁰Pb due to Saharan dust events registered in total deposition north of Barcelona during the last 17 years, yielding a value of 20 Bq m¯² yr¯¹ . This flux represents a fraction of about 16% of the total atmospheric deposition of ²¹⁰Pb in this area, but it could be up to 50% in sites with lower rainfall