Visualización y talento matemático: una experiencia docente

Un debate abierto en educación matemática estudia qué relación existe entre visualización y talento matemático. En este artículo describimos una experiencia con alumnos con talento matemático, encaminada a observar la visualización durante la realización de actividades geométricas y a analizar algunas de las dimensiones de la visualización que ponen en juego este tipo de alumnos

Collective action for the conservation of on-farm genetic diversity in a center of crop diversity: an assessment of the role of traditional farmers' networks

"This project explored the possible role of collective action among small-scale farmers in managing and maintaining genetic resources in a center of crop diversity. It focused on the local institutions that ensure the supply of seed of diverse maize landraces to small-scale farmers in the Central Valleys of Oaxaca, Mexico. The key hypothesis was that the medium-to-long-term supply of a diverse set of varieties to any individual small-scale maize farmer depends on an agreement among a group of farmers to manage and supply the seed of these landraces to each other, if the need arises, and that this constitutes a form of collective action. Six communities were studied, three of them in-depth. Methodologies used included in-depth semi-structured interviews with key informants, focus group discussions, and a tracer study—following the flows of seed among different farmers. The results show that, while there is a well-developed local seed supply system based on sets of social relationships and involving multiple types of transactions, there is no evidence of collective action. Most farmers rely on and prefer to select and save seed from their own harvests. There are seed flows, however, and most seed transactions take place among people with social links, but not within a well-defined group. There are no specialized suppliers of seed, either individuals or groups. Most transactions are bilateral and while the most common transaction is the sale and purchase of seed, this is not done for profit but out of a sense of moral obligation. The system is based on the creation of trust, which is needed because seed is not transparent—that is, it is not possible to fully predict the plant phenotype that may result from a given seed simply by looking at the seed. Farmers demand different types of maize and they believe that there is a strong genotype-by-environment interaction, hence “foreign” maize types may not be appropriate for them. At the same time, farmers also find occasional experimentation beneficial and believe that they can slowly modify the characteristics of “foreign” landraces. In this system, there are strong incentives to be conservative, but also to try new landraces and experiment. The local seed system of these farmers is resilient but able to innovate as well. Interventions to support the conservation of landraces on farm, based on specialized networks for seed that rely on collective action, may not work.." Author's AbstractCentral America, Europe and North America, Small farmers, Collective action, Informal seed systems, Crop diversification, Seed supply, Trust,

Green Synthesis of Metallic and Carbon Nanostructures

The technological and biomedical applications of low toxicity and eco-friendly organic compounds are nowadays increasingly attracting the attention of researchers in nanoscience, who are aiming for more biocompatible and nanostructured systems for their application in antineoplastic therapies. This study presents the significance of “green components” in the production of graphene, metallic, and semiconductor nanoparticles, due to their antioxidant and antitumor properties. The formation of nanostructures is caused during green synthesis methods by organic molecules or carboxylic acid groups present in some plant extracts; for this reason, we include here a recapitulation and analysis of the role of carboxylic acids in those systems (organic). Furthermore, we propose the use of the extract from Opuntia ficus-indica cladodes to obtain metallic and carbon nanostructures, as an alternative biosynthesis method for the development of future nanobiotechnological applications

Vegetative growth response of beets and lettuce to stored human urine

ArticleIn this work, we present the experimental results of the effect of stored human urine (SHU) on the growth of beets (Beta vulgaris L) and lettuce (Lactuca sativaL). We apply different amounts of SHU according to the recommended dose of nitrogen, considering soil from farmland and vermiculite as substrates. The last allows us to determine with high precision the isolated effect of SHU over the vegetative development of beet plants, without considering other nutrients present in common soils. Experimental results demonstrate that the application of SHU has no significant effects on lettuce vegetative growth under our soil conditions. In contrast, SHU can be used successfully as a fertilizer of beets. The optimum dose was found at 120kgN ha-1and resulted in average dry weight of 125g. However, if the dose exceeds the optimum levels, the growth of the plant is inhibited. Beets fertilized with SHU does not pose any hygienic risk for human consumption. Our findings represent a promising alternative to propose expanding the use of SHU as fertilizer in medium-sized greenhouses and to provide benefits to families in rural areas, with little or no available water supplies

Identification of two fnr genes and characterisation of their role in the anaerobic switch in Sphingopyxis granuli strain TFA

Copyright © The Author(s) 2020. Sphingopyxis granuli strain TFA is able to grow on the organic solvent tetralin as the only carbon and energy source. The aerobic catabolic pathway for tetralin, the genes involved and their regulation have been fully characterised. Unlike most of the bacteria belonging to the sphingomonads group, this strain is able to grow in anoxic conditions by respiring nitrate, though not nitrite, as the alternative electron acceptor. In this work, two fnr-like genes, fnrN and fixK, have been identified in strain TFA. Both genes are functional in E. coli and Sphingopyxis granuli although fixK, whose expression is apparently activated by FnrN, seems to be much less effective than fnrN in supporting anaerobic growth. Global transcriptomic analysis of a ΔfnrN ΔfixK double mutant and identification of Fnr boxes have defined a minimal Fnr regulon in this bacterium. However, expression of a substantial number of anaerobically regulated genes was not affected in the double mutant. Additional regulators such regBA, whose expression is also activated by Fnr, might also be involved in the anaerobic response. Anaerobically induced stress response genes were not regulated by Fnr but apparently induced by stress conditions inherent to anaerobic growth, probably due to accumulation of nitrite and nitric oxide.Grants BIO2014-57545-R and PGC2018-097151-B-I00, co-funded by the Spanish Ministerio de Ciencia e Innovación and the European Regional Development Fund; fellowships from the FPU program (Ministerio de Universidades, Spain)

The response of Sphingopyxis granuli strain TFA to the hostile anoxic condition

© The Author(s) 2019. Sphingomonads comprises a group of interesting aerobic bacteria because of their ubiquity and metabolic capability of degrading many recalcitrant contaminants. The tetralin-degrader Sphingopyxis granuli strain TFA has been recently reported as able to anaerobically grow using nitrate as the alternative electron acceptor and so far is the only bacterium with this ability within the sphingomonads group. To understand how strain TFA thrives under anoxic conditions, a differential transcriptomic analysis while growing under aerobic or anoxic conditions was performed. This analysis has been validated and complemented with transcription kinetics of representative genes of different functional categories. Results show an extensive change of the expression pattern of this strain in the different conditions. Consistently, the most induced operon in anoxia codes for proteases, presumably required for extensive changes in the protein profile. Besides genes that respond to lack of oxygen in other bacteria, there are a number of genes that respond to stress or to damage of macromolecules, including genes of the SOS DNA-damage response, which suggest that anoxic conditions represent a hostile environment for this bacterium. Interestingly, growth under anoxic conditions also resulted in repression of all flagellar and type IV pilin genes, which suggested that this strain shaves its appendages off while growing in anaerobiosis.Grant BIO2014-57545-R, co-funded by the Spanish Ministerio de Educación y Ciencia and the European Regional Development Fund; fellowships from the FPU program (Ministerio de Educación y Ciencia, Spain)

Spectrophotometric analysis of GRB afterglow extinction curves with X-shooter

In this work we use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modeling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, eight of them belonging to the long-duration and one to the short-duration class. Dust is modeled using the average extinction curves of the Milky Way and the two Magellanic Clouds. We derive the rest-frame extinction of the entire sample, which fall in the range $0 \lesssim {\it A}_{\rm V} \lesssim 1.2$. Moreover, the SMC extinction curve is the preferred extinction curve template for the majority of our sample, a result which is in agreement with those commonly observed in GRB lines-of-sights. In one analysed case (GRB 120119A), the common extinction curve templates fail to reproduce the observed extinction. To illustrate the advantage of using the high-quality X-shooter afterglow SEDs over the photometric SEDs, we repeat the modeling using the broadband SEDs with the NIR-to-UV photometric measurements instead of the spectra. The main result is that the spectroscopic data, thanks to a combination of excellent resolution and coverage of the blue part of the SED, are more successful in constraining the extinction curves and therefore the dust properties in GRB hosts with respect to photometric measurements. In all cases but one the extinction curve of one template is preferred over the others. We show that the modeled values of the extinction and the spectral slope, obtained through spectroscopic and photometric SED analysis, can differ significantly for individual events. Finally we stress that, regardless of the resolution of the optical-to-NIR data, the SED modeling gives reliable results only when the fit is performed on a SED covering a broader spectral region.Comment: 17 pages, 7 figures, 4 tables, accepted for publication in Astronomy & Astrophysic

Electro-remediation in the presence of ferrous sulfate as an ex-situ alternative treatment for hydrocarbon polluted soil

Hydrocarbons in soil have become a growing concern due to their chronic toxicity and their impact on human health and the environment. Various conventional physical, chemical and biological technologies are available for the treatment of contaminated sites; however, they are unsuccessful in the remediation of soils that contain compounds with low solubility, such as hydrocarbons. Electrokinetic remediation is one of the most promising technologies for the remediation of soils. In this process, application of an electric field between two electrodes inserted in the contaminated mass allows the separation of contaminants, with or without the addition of chemical reagents. This study investigates the feasibility of using an enhanced electrokinetic process in the presence of FeSO4 under acidic conditions for the remediation of hydrocarbons contained in Vertisol pelic and Gleysol soil. Hydrocarbon removal was more efficient in Vertisol than in Gleysol soil when this electrochemical treatment was applied