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Magnetotactic bacteria (MTB) are ubiquitous aquatic microorganisms that form intracellular nanoparticles of magnetite (Fe3O4) or greigite (Fe3S4) in a genetically controlled manner. Magnetite and greigite synthesis requires MTB to transport a large amount of iron from the environment. Most intracellular iron was proposed to be contained within the crystals. However, recent mass spectrometry studies suggest that MTB may contain a large amount of iron that is not precipitated in crystals. Here, we attempted to resolve these discrepancies by performing chemical and magnetic assays to quantify the different iron pools in the magnetite-forming strain Magnetospirillum magneticum AMB-1, as well as in mutant strains showing defects in crystal precipitation, cultivated at various iron concentrations. All results show that magnetite represents at most 30% of the total intracellular iron under our experimental conditions and even less in the mutant strains. We further examined the iron speciation and subcellular localization in AMB-1 using the fluorescent indicator FIP-1, which was designed for the detection of labile Fe(II). Staining with this probe suggests that unmineralized reduced iron is found in the cytoplasm and associated with magnetosomes. Our results demonstrate that, under our experimental conditions, AMB-1 is able to accumulate a large pool of iron distinct from magnetite. Finally, we discuss the biochemical and geochemical implications of these results.IMPORTANCE Magnetotactic bacteria (MTB) produce iron-based intracellular magnetic crystals. They represent a model system for studying iron homeostasis and biomineralization in microorganisms. MTB sequester a large amount of iron in their crystals and have thus been proposed to significantly impact the iron biogeochemical cycle. Several studies proposed that MTB could also accumulate iron in a reservoir distinct from their crystals. Here, we present a chemical and magnetic methodology for quantifying the iron pools

Magnetotactic bacteria (MTB) are ubiquitous aquatic microorganisms that form intracellular nanoparticles of magnetite (Fe3O4) or greigite (Fe3S4) in a genetically controlled manner. Magnetite and greigite synthesis requires MTB to transport a large amount of iron from the environment. Most intracellular iron was proposed to be contained within the crystals. However, recent mass spectrometry studies suggest that MTB may contain a large amount of iron that is not precipitated in crystals. Here, we attempted to resolve these discrepancies by performing chemical and magnetic assays to quantify the different iron pools in the magnetite-forming strain Magnetospirillum magneticum AMB-1, as well as in mutant strains showing defects in crystal precipitation, cultivated at various iron concentrations. All results show that magnetite represents at most 30% of the total intracellular iron under our experimental conditions and even less in the mutant strains. We further examined the iron speciation and subcellular localization in AMB-1 using the fluorescent indicator FIP-1, which was designed for the detection of labile Fe(II). Staining with this probe suggests that unmineralized reduced iron is found in the cytoplasm and associated with magnetosomes. Our results demonstrate that, under our experimental conditions, AMB-1 is able to accumulate a large pool of iron distinct from magnetite. Finally, we discuss the biochemical and geochemical implications of these results.IMPORTANCE Magnetotactic bacteria (MTB) produce iron-based intracellular magnetic crystals. They represent a model system for studying iron homeostasis and biomineralization in microorganisms. MTB sequester a large amount of iron in their crystals and have thus been proposed to significantly impact the iron biogeochemical cycle. Several studies proposed that MTB could also accumulate iron in a reservoir distinct from their crystals. Here, we present a chemical and magnetic methodology for quantifying the iron pools

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.

Perform probabilistic assessment of seismic hazard (PSHA) is a fundamental activity that offer valuable information to the seismic risk management of cities. In the present work some relevant aspects about a recent analysis about the seismic hazard of Colima, Mexico are mentioned.

This paper explores the application of learning designs featuring formalised and structured technology enhanced peer learning. These include student produced learning elements, peer review discussions and peer assessment in the BSc/MSc level summer course Restoration of European Ecosystems and Freshwaters (REEF), the Master thesis preparation seminars for the Master of Public Health (MPH) and the MOOC course Global Environmental Management (GEM). The application of student produced learning elements and peer review discussions is investigated by analyzing quotes from course evaluations and performing focus group interviews. The application of peer assessment is investigated by analyzing the agreement of peer assessment between students assessing the same assignment. Our analyses confirm previous research on the value of peer learning and peer assessment and we argue that there could also be a huge benefit from developing learning design patterns that facilitate informal peer learning and reinforce knowledge sharing practices.

Online learning communities are a foundational element of online and blended learning. Many learning activities in online and blended learning courses require students to collaborate and work together with their peers. In order for these learning activities to be successful it is important that participants are engaged socially and emotionally in their online interaction to create a sense of community and cohesion, corresponding to what constitutes Social Presence in the Community of Inquiry Framework model. As teachers, we therefore focus on creating learning designs that facilitate the development of online learning communities. In this article, we examine the development of online learning communities in online discussion forums. We map a selection of discussion threads from three university-level courses using the NodeXL software, and discuss the implications of e.g. structure, facilitation and group size on the online learning community that emerges. We find that the framework for participation in discussions (e.g. level of guidance and role of facilitators) affects the degree of connectivity within the online learning community and the prevalence of “social” posting, which has implications for strengthening the community and student-to-student support throughout the course.

En este trabajo se presenta la visión de Amiano Marcelino, historiador romano del siglo IV, el cual es considerado como el último expositor de la historiografía clásica. Específicamente acerca de la visión que el autor presenta de la sociedad romana en sus digresiones, las cuales son paralelas al relato propiamente tal. Junto con los problemas en las fronteras occidentales y orientales, la situación interna de la sociedad romana, la polarización social, la concentración de las tierras por parte de los patricios y la pobreza e indigencia de las clases más pobres, generaron un alejamiento de las obligaciones militares y una mayor presión fiscal. Amiano usando el método histórico clásico refleja el estado de la sociedad en los últimos siglos del Imperio

En este trabajo se presenta la visión de Amiano Marcelino, historiador romano del siglo IV, el cual es considerado como el último expositor de la historiografía clásica. Específicamente acerca de la visión que el autor presenta de la sociedad romana en sus digresiones, las cuales son paralelas al relato propiamente tal. Junto con los problemas en las fronteras occidentales y orientales, la situación interna de la sociedad romana, la polarización social, la concentración de las tierras por parte de los patricios y la pobreza e indigencia de las clases más pobres, generaron un alejamiento de las obligaciones militares y una mayor presión fiscal. Amiano usando el método histórico clásico refleja el estado de la sociedad en los últimos siglos del Imperio