Topological defects in 1D elastic waves

It has been recently shown theoretically that a topological defect in a 1D periodic potential may give rise to two localized states within the energy gaps. In this work we present an experimental realization of this effect for the case of torsional waves in elastic rods. We also show numerically that three, or even more, localized states can be present if the parameters characterizing the topological defect are suitably varied.Comment: 3 pages, 4 figures, accepted in Physica

Anderson Localization in Disordered Vibrating Rods

We study, both experimentally and numerically, the Anderson localization phenomenon in torsional waves of a disordered elastic rod, which consists of a cylinder with randomly spaced notches. We find that the normal-mode wave amplitudes are exponentially localized as occurs in disordered solids. The localization length is measured using these wave amplitudes and it is shown to decrease as a function of frequency. The normal-mode spectrum is also measured as well as computed, so its level statistics can be analyzed. Fitting the nearest-neighbor spacing distribution a level repulsion parameter is defined that also varies with frequency. The localization length can then be expressed as a function of the repulsion parameter. There exists a range in which the localization length is a linear function of the repulsion parameter, which is consistent with Random Matrix Theory. However, at low values of the repulsion parameter the linear dependence does not hold.Comment: 10 pages, 6 figure

Doorway States and Billiards

Whenever a distinct state is immersed in a sea of complicated and dense states, the strength of the distinct state, which we refer to as a doorway, is distributed in their neighboring states. We analyze this mechanism for 2-D billiards with different geometries. One of them is symmetric and integrable, another is symmetric but chaotic, and the third has a capricious form. The fact that the doorway-state mechanism is valid for such highly diverse cases, proves that it is robust.Comment: 7 pages, 6 figures, Accepted in Proceedings of "Symmetries in Nature", Symposium in Memoriam Marcos Moshinsk

InContext: A mobile application for the improvement of learning strategies at University // InContext: Una aplicación móvil para mejorar las estrategias de aprendizaje en la Universidad

InContext is a custom-designed mobile application for writing assignments intended for university students in journalism and research methodology courses. In these disciplines, it has been observed that there is a need for an educational and technological tool to guide the writing of text using preloaded templates in which students can input text and multimedia material to create articles or write research reports. Besides its ease of use, the app was intended to improve metacognitive thinking. This led to the establishment of six working hypotheses in an exploratory study. For the study, a random sample of students enrolled in the aforementioned courses was selected during the August-December 2019 semester at a private university in Mexico. They took a pre-test using the “Motivated Strategies for Learning Questionnaire” (MSLQ) that had been translated into Spanish and already validated in Mexico. Subsequently, the students used the application and then answered the same questionnaire as a post-test. The study aimed to compare the results of the tests to see whether there was an improvement in cognitive skills. The results showed an increase in four skills: critical thinking, data search, cognitive self-regulation, and regulation of effort. The research results did indicate metacognitive development that would benefit the academic and professional work of future graduates

InContext: A mobile application for the improvement of learning strategies at University // InContext: Una aplicación móvil para mejorar las estrategias de aprendizaje en la Universidad

InContext is a custom-designed mobile application for writing assignments intended for university students in journalism and research methodology courses. In these disciplines, it has been observed that there is a need for an educational and technological tool to guide the writing of text using preloaded templates in which students can input text and multimedia material to create articles or write research reports. Besides its ease of use, the app was intended to improve metacognitive thinking. This led to the establishment of six working hypotheses in an exploratory study. For the study, a random sample of students enrolled in the aforementioned courses was selected during the August-December 2019 semester at a private university in Mexico. They took a pre-test using the “Motivated Strategies for Learning Questionnaire” (MSLQ) that had been translated into Spanish and already validated in Mexico. Subsequently, the students used the application and then answered the same questionnaire as a post-test. The study aimed to compare the results of the tests to see whether there was an improvement in cognitive skills. The results showed an increase in four skills: critical thinking, data search, cognitive self-regulation, and regulation of effort. The research results did indicate metacognitive development that would benefit the academic and professional work of future graduates

InContext: A mobile application for the improvement of learning strategies at University

InContext es una aplicación móvil, diseñada a medida, para elaborar trabajos de redacción para estudiantes universitarios de los cursos de periodismo y de metodología de la investigación. En estas disciplinas se observó que había una necesidad de contar con una herramienta educativa y tecnológica que guiara la redacción utilizando plantillas precargadas en las cuales los estudiantes pudieran agregar texto y material multimedia para con ello construir artículos periodísticos o reportes de investigación. Además de la facilidad de uso, se esperaba que la app mejorara el pensamiento metacognitivo, por lo cual se establecieron seis hipótesis de trabajo en un estudio exploratorio. Para la investigación se seleccionó una muestra aleatoria de estudiantes inscritos en los cursos durante el semestre agosto-diciembre 2019 en una universidad privada de México. Los alumnos realizaron un pretest utilizando el cuestionario Motivated Strategies for Learning Questionnaire (MSLQ) traducido al español y ya validado en México; posteriormente utilizaron la aplicación y contestaron el mismo cuestionario a manera de postest, con el objetivo de comparar si había una mejora en las habilidades cognitivas. Los resultados indican que existe un aumento en cuatro habilidades: pensamiento crítico, búsqueda de datos, autorregulación cognitiva y regulación del esfuerzo, pero no lo hubo en organización ni en búsqueda de ayuda. Estos resultados indican un desarrollo metacognitivo que beneficia el trabajo académico y profesional de los futuros egresadosInContext is a custom-designed mobile application for writing assignments intended for university students in journalism and research methodology courses. In these disciplines, it has been observed that there is a need for an educational and technological tool to guide the writing of text using preloaded templates in which students can input text and multimedia material to create articles or write research reports. Besides its ease of use, the app was intended to improve metacognitive thinking. This led to the establishment of six working hypotheses in an exploratory study. For the study, a random sample of students enrolled in the aforementioned courses was selected during the August-December 2019 semester at a private university in Mexico. They took a pre-test using the “Motivated Strategies for Learning Questionnaire” (MSLQ) that had been translated into Spanish and already validated in Mexico. Subsequently, the students used the application and then answered the same questionnaire as a post-test. The study aimed to compare the results of the tests to see whether there was an improvement in cognitive skills. The results showed an increase in four skills: critical thinking, data search, cognitive self-regulation, and regulation of effort. The research results did indicate metacognitive development that would benefit the academic and professional work of future graduate

Wannier-Stark ladders in one-dimensional elastic systems

The optical analogues of Bloch oscillations and their associated Wannier-Stark ladders have been recently analyzed. In this paper we propose an elastic realization of these ladders, employing for this purpose the torsional vibrations of specially designed one-dimensional elastic systems. We have measured, for the first time, the ladder wave amplitudes, which are not directly accessible either in the quantum mechanical or optical cases. The wave amplitudes are spatially localized and coincide rather well with theoretically predicted amplitudes. The rods we analyze can be used to localize different frequencies in different parts of the elastic systems and viceversa.Comment: 10 pages, 6 figures, accepted in Phys. Rev. Let

Photosynthetic production in the central Arctic Ocean during the record sea-ice minimum in 2012

The ice-covered central Arctic Ocean is characterized by low primary productivity due to light and nutrient limitations. The recent reduction in ice cover has the potential to substantially increase phytoplankton primary production, but little is yet known about the fate of the ice-associated primary production and of the nutrient supply with increasing warming. This study presents results from the central Arctic Ocean collected during summer 2012, when sea-ice extent reached its lowest ever recorded since the onset of satellite observations. Net primary productivity (NPP) was measured in the water column, sea ice and melt ponds by 14CO2 uptake at different irradiances. Photosynthesis vs. irradiance (PI) curves were established in laboratory experiments and used to upscale measured NPP to the deep Eurasian Basin (north of 78° N) using the irradiance-based Central Arctic Ocean Primary Productivity (CAOPP) model. In addition, new annual production has been calculated from the seasonal nutrient drawdown in the mixed layer since last winter. Results show that ice algae can contribute up to 60% to primary production in the central Arctic Ocean at the end of the productive season (August–September). The ice-covered water column has lower NPP rates than open water due to light limitation in late summer. As indicated by the nutrient ratios in the euphotic zone, nitrate was limiting primary production in the deep Eurasian Basin close to the Laptev Sea area, while silicate was the main limiting nutrient at the ice margin near the Atlantic inflow. Although sea-ice cover was substantially reduced in 2012, total annual new production in the Eurasian Basin was 17 ± 7 Tg C yr-1, which is within the range of estimates of previous years. However, when adding the contribution by sub-ice algae, the annual production for the deep Eurasian Basin (north of 78° N) could double previous estimates for that area with a surplus of 16 Tg C yr-1. Our data suggest that sub-ice algae are an important component of the productivity in the ice-covered Eurasian Basin of the central Arctic Ocean. It remains an important question whether their contribution t