¿Cómo flotan los cuerpos que flotan? Concepciones de los estudiantes

A research was canied on pupil's ideas, from Primary School to University, on the flotation of cork, wood and ice on water. Different alternative ideas were found, being the commonest the belief in some bodies floating over the water surface, without any submerged volume. Causes of these altemative conceptions are discussed, and some implications for Science teaching-learning suggested

Project Vitamin Sea

As climate change takes effect across the world, temperatures rise to new highs and so does sea level. Major cities around the world now face the challenge of accepting and combating climate change quicker than the rest of the world, due to their geographic location and surrounding environment. In Miami, sea level is predicted to rise by 1 foot by 2060; however, more than 2,500 houses in Miami Dade county are less than 1 foot above sea level1. Project Vitamin Sea is a small-scale trial run reverse osmosis desalination plant that is going to be installed 75 kilometers off the coast of South Florida to alleviate climate change from two perspectives: sea level rise and drought. The plant is considered innovative in comparison to past desalination attempts because it will be powered by reverse osmosis through a renewable energy source: the ocean’s static pressure above the plant, or the weight of 615 meters of ocean above the plant5. In other words, the plant will not require vast amounts of energy making it inexpensive and practical for real time use. As per the Red Queen Hypothesis, countering climate change, or in Miami’s case specifically, sea level rise, is going to take more than one renewable energy sourced desalination plant to even come close to the possibility of stopping sea level rise, let alone reversing its effects. So, the purpose of this project is to allow for this trial with the smaller plant to take its course to see if this type of desalination plant is a plausible solution for future endeavors in alleviating climate change and its effects, like drought, ocean acidification, and sea level rise, worldwide. This project will also be environmentally conscious by performing a deep ocean clean up prior to construction throughout the whole area of where the plant will be located. Afterwards, small coral species, ideally, can be added to the installed plant in efforts to increase biodiversity in the surrounding environment, thus promoting health and the success of the plant in its environment. This overall proposal promotes a one health concept of attempting to relieve the increasingly significant effects of climate change through an environmentally friendly and conscious effort for the safety of humans, animals, and, very importantly, their precious shared environment

Unusual Kondo physics in a Co impurity atom embedded in noble-metal chains

We analyze the conduction bands of the one dimensional noble-metal chains that contain a Co magnetic impurity by means of ab initio calculations. We compare the results obtained for Cu and Ag pure chains, as well as O doped Cu, Ag and Au chains with those previously found for Au pure chains. We find similar results in the case of Cu and Au hosts, whereas for Ag chains a different behavior is obtained. Differences and similarities among the different systems are analyzed by comparing the electronic structure of the three noble-metal hosts. The d-orbitals of Cu chains at the Fermi level have the same symmetry as in the case of Au chains. These orbitals hybridize with the corresponding ones of the Co impurity, giving rise to the possibility of exhibiting a two-channel Kondo physics.Comment: Accepted in IEEE Trans. Magn. - April 201

Continuous-variable entanglement of two bright coherent states that never interacted

We study continuous-variable entanglement of bright quantum states in a pair of evanescently coupled nonlinear $\chi^{(2)}$ waveguides operating in the regime of degenerate down-conversion. We consider the case where only the energy of the nonlinearly generated fields is exchanged between the waveguides while the pump fields stay independently guided in each original waveguide. We show that this device, when operated in the depletion regime, entangles the two non-interacting bright pump modes due to a nonlinear cascade effect. It is also shown that two-colour quadripartite entanglement can be produced when certain system parameters are appropriately set. This device works in the traveling-wave configuration, such that the generated quantum light shows a broad spectrum. The proposed device can be easily realized with current technology and therefore stands as a good candidate for a source of bipartite or multipartite entangled states for the emerging field of optical continuous-variable quantum information processing.Comment: 10 pages, 12 figure

Characterization of goethites from surficial environments of Galicia and estimates of the substitution of Fe by Al

[Resumen] Se examinan cincuenta muestras ricas en goetita y de morfología y génesis variada (placas en sedimentos, suelos ricos en sesquióxidos, costras y menas de Fe), caracterizando su mineralogía y composición química por medio de diversas técnicas instrumentales y extractantes selectivas. Se estima el grado de sustitución isomorfa de Fe por Al mediante análisis químico y por el desplazamiento de las líneas de difracción de RX de la goetita. Por ambos métodos se obtienen resultados similares, dando porcentajes de sustitución que no sobrepasan en general el 15 O/o molar, lo que se considera un bajo grado de reemplazamiento y se explica en función de las condiciones de formación de estas concentraciones de hierro.[Abstract] Fifty samples with high goethite contents, differing in their morphology and formed in diverse environments are examined. They include ironpans, crusts, soils high in sesquioxides and iron ores. Several instrumental techniques are used for their mineralogical characterization, together with selective extractants of cristaBine and amorphous iron. The extent of the isomorphus replacement ofFe by Al in goethite is estimated by chemical analyses and by the shift ofXRD diffraction línes. Both methods give similar results, showing porcentages of substitution that not exceed in general 15 mole O/o. This can be considered a low degree of replacement and is discussed in sight of the formatíon conditions of these iron accumulations

Structure and energetics of ammonia clusters (NH3)n (n=3-20) investigated using a rigid-polarizable model derived from ab initio calculations

An analytical model has been developed to describe the interaction between rigid ammonia molecules including the explicit description of induction. The parameters of the model potential were chosen by fitting high quality ab initio data obtained using second-order Moller-Plesset (MP2) perturbation theory and extended basis sets. The description of polarization effects is introduced by using a noniterative form of the "charge on spring model", the latter accounting for more than 95% of the dipole induction energy and of the increased molecular dipole. Putative global minima for (NH3)(n) (n = 3-20) have been optimized using this new model, the structure and energetics of the clusters with n = 3-5 being found in good agreement with previous ab initio results including electronic correlation. Results for larger species have been compared with previous structural studies where only nonpolarizable models were employed. Our model predicts larger binding energies for any cluster size than previous analytical surfaces, the results often suggesting a reorganization of the relative energy ranking and a different structure for the global minimum

Artificial Rheotaxis

Motility is a basic feature of living microorganisms, and how it works is often determined by environmental cues. Recent efforts have focused on develop- ing artificial systems that can mimic microorganisms, and in particular their self-propulsion. Here, we report on the design and characterization of syn- thetic self-propelled particles that migrate upstream, known as positive rheo- taxis. This phenomenon results from a purely physical mechanism involving the interplay between the polarity of the particles and their alignment by a viscous torque. We show quantitative agreement between experimental data and a simple model of an overdamped Brownian pendulum. The model no- tably predicts the existence of a stagnation point in a diverging flow. We take advantage of this property to demonstrate that our active particles can sense and predictably organize in an imposed flow. Our colloidal system represents an important step towards the realization of biomimetic micro-systems withthe ability to sense and respond to environmental changesComment: Published in Science Advances [Open access journal of Science Magazine