Problemática, metodología y teoría: el recorrido de un grupo de investigación en enseñanza de las ciencias

This paper discusses some results obtained from research on the teaching of mechanics to initial university courses in Brazil, together with the epistemological problems arising

Los significados de entropía : mecanismos para su adquisición

Dotar de significado a expresiones abstractas se logra asignando cualidades; creando diferencias; elaborando entidades; transformando el conocimiento y dando sentido al tema. En este trabajo presentamos los mecanismos de adquisición de significado del concepto “entropía”. Los registros empleados fueron ensayos escritos por estudiantes de ingeniería, sobre el concepto de entropía. Se identificaron diferentes modalidades de adquirir significado: por aplicación del concepto a una entidad conocida; a través de la asignación de atributos; mediante ejemplos; por hiponimia y con explicaciones. El estudio permite identificar el empleo de recursos explicativos heterogéneos, con relación semántica de pertenencia o bien localización de la entropía en el universo; el atributo predominante es la función creciente y la hiponimia preferida desorden o irreversibilidad

Production of high purity silica by microfluidic-inclusion fracture using microwave pre-treatment

© 2018 Demand for high purity silica used in component manufacture is set to outstrip current supply in the near future. As such, alternative processing routes to feed-stock materials suitable for use in lighting and solar cell fabrication are required, without having to rely on reject material from semi-conductor manufacture. In this work, we report a facile, environmentally friendly method of producing quartz powder with a total residual impurity level of 30 ± 3 ppm from whole pebbles having an initial impurity level of 158 ± 22 ppm. This has been achieved using a metallurgical upgrading process incorporating microwave pre-treatment, crushing and milling, High Intensity Wet Magnetic Separation (HIWMS) and acid leaching. This process yielded a quartz powder having an 80% reduction in residual impurities compared to the untreated quartz pebbles. Pre-treatment of whole quartz pebbles in a multimode microwave cavity for 10 min yielded a reduction of the residual elemental impurity content associated with micro-fluidic inclusion sites containing calcium, potassium and sodium of 84, 78, and 50% respectively. Statistically significant reduction in residual aluminium phases was also observed (83%) compared to the as received material to below the IOTA® specification for Ultra High Pure Quartz produced by Sibleco. Mechanistically, this has been achieved by selectively heating impurity containing micro-fluidic inclusion sites. Resulting in their explosive decrepitation and enabling removal of the impurities in subsequent processing steps. It has been concluded that natural quartz pebbles can be upgraded through a combination of microwave treatment, magnetic and chemical refinement to produce a viable feedstock for the subsequent production of solar grade silicon

Loss of hippocampal serine protease BSP1/neuropsin predisposes to global seizure activity

Serine proteases in the adult CNS contribute both to activity-dependent structural changes accompanying learning and to the regulation of excitotoxic cell death. Brain serine protease 1 (BSP1)/neuropsin is a trypsin-like serine protease exclusively expressed, within the CNS, in the hippocampus and associated limbic structures. To explore the role of this enzyme, we have used gene targeting to disrupt this gene in mice. Mutant mice were viable and overtly normal; they displayed normal hippocampal long-term synaptic potentiation (LTP) and exhibited no deficits in spatial navigation (water maze). Nevertheless, electrophysiological studies revealed that the hippocampus of mice lacking this specifically expressed protease possessed an increased susceptibility for hyperexcitability (polyspiking) in response to repetitive afferent stimulation. Furthermore, seizure activity on kainic acid administration was markedly increased in mutant mice and was accompanied by heightened immediate early gene (c-fos) expression throughout the brain. In view of the regional selectivity of BSP1/neuropsin brain expression, the observed phenotype may selectively reflect limbic function, further implicating the hippocampus and amygdala in controlling cortical activation. Within the hippocampus, our data suggest that BSP1/neuropsin, unlike other serine proteases, has little effect on physiological synaptic remodeling and instead plays a role in limiting neuronal hyperexcitability induced by epileptogenic insult

Twisting of graded quantum groups and solutions to the quantum Yang-Baxter equation

Let $H$ be a Hopf algebra that is $\mathbb Z$-graded as an algebra. We provide sufficient conditions for a 2-cocycle twist of $H$ to be a Zhang twist of $H$. In particular, we introduce the notion of a twisting pair for $H$ such that the Zhang twist of $H$ by such a pair is a 2-cocycle twist. We use twisting pairs to describe twists of Manin's universal quantum groups associated to quadratic algebras and provide twisting of solutions to the quantum Yang-Baxter equation via the Faddeev-Reshetikhin-Takhtajan construction.Comment: In this version, our title is new and Section 3 is updated with applications of twisting pairs to obtain new solutions to the quantum Yang-Baxter equatio

One at a time, live tracking of NGF axonal transport using quantum dots

Retrograde axonal transport of nerve growth factor (NGF) signals is critical for the survival, differentiation, and maintenance of peripheral sympathetic and sensory neurons and basal forebrain cholinergic neurons. However, the mechanisms by which the NGF signal is propagated from the axon terminal to the cell body are yet to be fully elucidated. To gain insight into the mechanisms, we used quantum dot-labeled NGF (QD-NGF) to track the movement of NGF in real time in compartmentalized culture of rat dorsal root ganglion (DRG) neurons. Our studies showed that active transport of NGF within the axons was characterized by rapid, unidirectional movements interrupted by frequent pauses. Almost all movements were retrograde, but short-distance anterograde movements were occasionally observed. Surprisingly, quantitative analysis at the single molecule level demonstrated that the majority of NGF-containing endosomes contained only a single NGF dimer. Electron microscopic analysis of axonal vesicles carrying QD-NGF confirmed this finding. The majority of QD-NGF was found to localize in vesicles 50–150 nm in diameter with a single lumen and no visible intralumenal membranous components. Our findings point to the possibility that a single NGF dimer is sufficient to sustain signaling during retrograde axonal transport to the cell body

Unguided low intensity cognitive behaviour therapy for anxiety and depression during the COVID-19 pandemic: A randomised trial.

The COVID-19 pandemic has had a severe impact on mental health worldwide, with increased rates of anxiety and depression widely documented. The aim of this study was to examine unguided low intensity cognitive behaviour therapy for anxiety and depression during the pandemic. A sample of 225 individuals in Australia and the United Kingdom (M age 37.79, SD = 14.02, range 18-80 years; 85% female) were randomised into intervention or waitlist control. The intervention group demonstrated significant decreases in anxiety (d = 0.36 [0.18, 0.54]) and depression (d = 0.28 [0.11, 0.45]) compared to controls. The majority of participants (96%) rated the intervention as useful, and most (83%) reported they spent 30 min or less reading the guide, with 83% agreeing the intervention was easy to read. The results indicate that low intensity cognitive behaviour therapy has efficacy in reducing anxiety and depression during the COVID-19 pandemic. There is an urgent need to disseminate low intensity psychological therapies to improve mental health in this challenging time