Las imágenes sobre enlace químico usadas en los libros de texto de educación secundaria : análisis desde los resultados de la investigación educativa

En este artículo se analizan las imágenes o ilustraciones contenidas en libros de texto en relación con el enlace químico. El objetivo ha sido desvelar si estas imágenes se adecuan a los fundamentos teóricos hallados en la bibliografía sobre el tema. Se han analizado 12 libros de texto pertenecientes a los niveles argentinos de EGB 3 (12-14 años) y Polimodal (15-17 años). Esto ha supuesto un total de 16 imágenes de EGB 3 y de 62 imágenes de Polimodal. Los resultados, a pesar de ser muy heterogéneos, muestran una relación escasa texto-imagen, y un predominio del tipo de texto expositivo. Además, en EGB 3, el 70%[ de las imágenes son modelos de bajo nivel (sin configuración electrónica), frente al 30% que son de alto nivel, mientras que en Polimodal ocurre prácticamente lo contrario.In this article, the images or illustrations contained in textbooks related to chemical bonds are analyzed. The objective was to reveal whether or not these images are adapted to the previous theoretic outcomes. 12 Argentina junior high school (12-14 years old) and senior high school (15-17 years old) textbooks were analyzed. A total of 16 junior high school images and 62 senior high school images were studied. Despite the fact that they are very heterogeneous, the results show a very scarce text-image relationship, and a prevalence for expositive types of text. In addition, in junior high school, 70% of the images are low level models (without electronical configuration), as opposed to the 30% that are high level whereas in senior high school, practically the opposite occurs

Quantum Lattice Fluctuations and Luminescence in C_60

We consider luminescence in photo-excited neutral C_60 using the Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the luminescence we use a collective coordinate method where our collective coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon mode and extrapolates between the ground state "dimerisation" and the exciton polaron. There is good agreement for the existing luminescence peak spacing and fair agreement for the relative intensity. We predict the existence of further peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn, 36.90+

Modelling the Canes Venatici I dwarf spheroidal galaxy

The aim of this work is to find a progenitor for Canes Venatici I (CVn I), under the assumption that it is a dark matter free object that is undergoing tidal disruption. With a simple point mass integrator, we searched for an orbit for this galaxy using its current position, position angle, and radial velocity in the sky as constraints. The orbit that gives the best results has the pair of proper motions $\mu_\alpha$ = -0.099 mas yr$^{-1}$ and $\mu_\delta$ = -0.147 mas yr$^{-1}$, that is an apogalactic distance of 242.79 kpc and a perigalactic distance of 20.01 kpc. Using a dark matter free progenitor that undergoes tidal disruption, the best-fitting model matches the final mass, surface brightness, effective radius, and velocity dispersion of CVn I simultaneously. This model has an initial Plummer mass of 2.47 x $10^7$ M$_\odot$ and a Plummer radius of 653 pc, producing a remnant after 10 Gyr with a final mass of 2.45 x 10$^5$ M$_\odot$, a central surface brightness of 26.9 mag arcsec$^{-2}$, an effective radius of 545.7 pc, and a velocity dispersion with the value 7.58 km s$^{-1}$. Furthermore, it is matching the position angle and ellipticity of the projected object in the sky.Comment: 11 pages, 14 figures, accepted by A&

Polaron Excitations in Doped C60: Effects of Disorders

Effects on C$_{60}$ by thermal fluctuations of phonons, misalignment of C$_{60}$ molecules in a crystal, and other intercalated impurities (remaining C$_{70}$, oxygens, and so on) are simulated by disorder potentials. The Su-Schrieffer-Heeger--type electron-phonon model for doped C$_{60}$ is solved with gaussian bond disorders and also with site disorders. Sample average is performed over sufficient number of disorder configurations. The distributions of bond lengths and electron densities are shown as functions of the disorder strength and the additional electron number. Stability of polaron excitations as well as dimerization patterns is studied. Polarons and dimerizations in lightly doped cases (C$_{60}^{-1,-2}$) are relatively stable against disorders, indicated by peak structures in distribution functions. In more heavily doped cases, the several peaks merge into a single peak, showing the breakdown of polaron structures as well as the decrease of the dimerization strength. Possibility of the observation of polaronic lattice distortions and electron structures in doped C$_{60}$ is discussed.Comment: Note: This manusript was accepted for publication in Physical Review B. Figures will be sent to you via snail (conventional) mai

The search for gametic maturity markers in the gametogenic cycle of Crassostrea gigas (Thunberg, 1873)

One of the aims of bivalve culture is obtaining high quality broodstocks in hatcheries. Spawning feasibility depends on a suitable breeder's feeding, and can be artificially induced. Some external factors (environmental) and internal (neuroendocrinal) seem to contribute to gamete maturation. Crassostrea gigas (Thunberg, 1873) gametogenic cycle is characterised by long resting periods during which a high rate of degradation and cellular atresia has been observed. There are also remarkable differences between male and female protein profiles during gametogenic development. Our group has been searching for molecular indicators of the state of maturation, and the most suitable moment for spawning induction. One of our most promising results was the appearance of a membrane protein in females thought to be a signal receptor in oocyte maturation and spawning.El cultivo de bivalvos se ve limitado por la obtención de semilla de calidad en los criaderos. El éxito de las puestas depende de la alimentación adecuada de los reproductores, y pueden ser inducidas artificialmente mediante choque osmótico, térmico u otras técnicas. Algunos factores externos, como los ambientales, e internos, de carácter neuroendocrino, parecen contribuir a la maduración de los gametos. El ciclo gametogénico de Crassostrea gigas (Thunberg, 1873) se caracteriza por largos periodos de reposo gonadal, en los que se ha encontrado una tasa elevada de degradación y atresia celular. También se aprecian diferencias considerables entre hembras y machos en los perfiles proteínicos durante el desarrollo gametogénico. El presente trabajo está orientado a la búsqueda de marcadores del estado de madurez de los gametos como indicadores del momento más adecuado para inducir la puesta. Uno de los resultados obtenidos ha sido la visualización de una proteína de membrana en hembras, que se muestra en la fase de madurez de los ovocitos y en las puestas, que podría constituir uno de los macadores buscados.Instituto Español de Oceanografí