The Quantum-Mechanical Position Operator in Extended Systems

The position operator (defined within the Schroedinger representation in the standard way) becomes meaningless when periodic boundary conditions are adopted for the wavefunction, as usual in condensed matter physics. We show how to define the position expectation value by means of a simple many-body operator acting on the wavefunction of the extended system. The relationships of the present findings to the Berry-phase theory of polarization are discussed.Comment: Four pages in RevTe

Electron Localization in the Insulating State

The insulating state of matter is characterized by the excitation spectrum, but also by qualitative features of the electronic ground state. The insulating ground wavefunction in fact: (i) sustains macroscopic polarization, and (ii) is localized. We give a sharp definition of the latter concept, and we show how the two basic features stem from essentially the same formalism. Our approach to localization is exemplified by means of a two--band Hubbard model in one dimension. In the noninteracting limit the wavefunction localization is measured by the spread of the Wannier orbitals.Comment: 5 pages including 3 figures, submitted to PR

Relación del conocimiento del etiquetado “Semáforo Nutricional” en el estado nutricional de adolescentes ecuatorianos/List of labeling knowledge: "Nutritional traffic light" in the nutritional status of Ecuadorian adolescents

El semáforo nutricional (SN) es un tipo de etiquetado de alimentos creado para mejorar la comprensión del contenido de nutrientes (sodio, azúcar y grasa) en los alimentos procesados. En Ecuador, el SN es de uso obligatorio desde el año 2012. Objetivo: Evaluar la relación del conocimiento del etiquetado SN en el estado nutricional de adolescentes ecuatorianos. Métodos: Estudio transversal. Con 599 adolescentes (14- 18 años). Se recopilaron datos antropométricos, actividad física (IPAQ-A) e ingesta alimentaria utilizando 3 encuestas de recordatorio de 24 horas, el conocimiento del SN se evaluó con un cuestionario preparado para este fin: puntuaciones >5 significaron adecuado conocimiento (AC). Las relaciones entre las variables se determinaron mediante prueba t de student, utilizando el software STATA-14. Resultados: 55% de los adolescentes presentaron diagnóstico de sobrepeso, el 28% obesidad, según los indicadores IMC//Edad, el 48% un AC. Los adolescentes que mostraron inadecuado conocimiento evidenciaron medias más altas de IMC//edad, circunferencia de la cintura, circunferencia de la cadera y porcentaje de masa grasa (p<0.001), no se encontró diferencias en la ingesta alimentaria y conocimiento del SN. Conclusiones: El conocimiento del SN puede estar relacionado con el sobrepeso-obesidad en adolescentes, se necesita realizar más estudios para conocer cuál es el impacto de SN sobre el estado nutricional de la población en general. Nutritional traffic light (NT) is a type of food labeling created to improve the understanding of nutrient content (sodium, sugar and fat) in industrialized foods. In Ecuador, the TN is mandatory since 2012. Objective: To evaluate the relationship of NT labeling knowledge in the nutritional status of Ecuadorian adolescents. Methods: cross-sectional study. With 600 teenagers (14-18 years old). Anthropometric data, physical activity (IPAQ-A), and food intake were collected using 3 reminder surveys of 24 hours. Knowledge of NT was assessed with a questionnaire prepared for this purpose: scores> 5 meant adequate knowledge (AK). The relationships between the variables were determined by student’s T-test, using the STATA-14 software. Results: 55% of the adolescents presented a diagnosis of overweight and 28% of the adolescents presented a diagnosis of obesity according to the BMI indicators // age 48% presented a AK. Adolescents who presented inadequate knowledge presented higher means of BMI // age, waist circumference, hip circumference and percentage of fat mass (p <0.001), no differences were found in food intake and NT knowledge. Conclusions: Knowledge of NT may be related to overweight-obesity in adolescents, more studies are needed to establish these associations. Palabras clave: Semáforo nutricional, estado nutricional, adolescentes, Ecuador. Keywords: Nutritional traffic light, nutritional status, adolescents, Ecuador

Background studies and shielding effects for the TPC detector of the CAST experiment

Sunset solar axions traversing the intense magnetic field of the CERN Axion Solar Telescope (CAST) experiment may be detected in a Time Projection Chamber (TPC) detector, as X-rays signals. These signals could be masked, however, by the inhomogeneous background of materials in the experimental site. A detailed analysis, based on the detector characteristics, the background radiation at the CAST site, simulations and experimental results, has allowed us to design a shielding which reduces the background level by a factor of ~4 compared to the detector without shielding, depending on its position, in the energy range between 1 and 10 keV. Moreover, this shielding has improved the homogeneity of background measured by the TPC.Comment: 14 pages, 5 figures, accepted in New Journal of Physic

Humanly space objects — Perception and connection with the observer

Expanding humanity into space is an inevitable step in our quest to explore our world. Yet space exploration is costly, and the awaiting environment challenges us with extreme cold, heat, vacuum and radiation, unlike anything encountered on Earth. Thus, the few pioneers who experience it needed to be well protected throughout their spaceflight. The resulting isolation heightens the senses and increases the desire to make humanly connections with any other perceived manifestation of life. Such connections may occur via sensory inputs, namely vision, touch, sound, smell, and taste. This then follows the process of sensing, interpreting, and recognizing familiar patterns, or learning from new experiences. The desire to connect could even transfer to observed objects, if their movements and characteristics trigger the appropriate desires from the observer. When ordered in a familiar way, for example visual stimuli from lights and movements of an object, it may create a perceived real bond with an observer, and evoke the feeling of surprise when the expected behavior changes to something no longer predictable or recognizable. These behavior patterns can be designed into an object and performed autonomously in front of an observer, in our case an astronaut. The experience may introduce multiple responses, including communication, connection, empathy, order, and disorder. While emotions are clearly evoked in the observer and may seem one sided, in effect the object itself provides a decoupled bond, connectivity and communication between the observer and the artist-designer of the object. In this paper we will discuss examples from the field of arts and other domains, including robotics, where human perception through object interaction was explored, and investigate the starting point for new innovative design concepts and future prototype designs, that extend these experiences beyond the boundaries of Earth, while taking advantage of remoteness and the zero gravity environment. Through a form of emotional connection and design, these concepts will focus on the connection and brief emotional bond between a humanly animate object in space and a co-located observer in spaceflight. We conclude that beyond providing creative expressions for humanly contacts, these experiences may also provide further insights into human perception in spaceflight, and could be tested on the International Space Station, and serve as a stepping-stone towards use on long-duration spaceflight to Mars

Grapevine leaf uptake of mineral elements influenced by sugar foam amendment of an acidic soil

The use of sugar foam (industrial waste from sugar beet extraction) as an acidic soil (raña) liming agent has been studied in a singular winegrowing region. The contents of the major elements (Al, Ca, Fe, K, Na, Mg, S, Si) and trace elements (As, Ba, Ce, Co, Cr, Cs, Cu, Ga, Hf, La, Mo, Nb, Nd, Ni, Pb, Rb, Sc, Sn, Sr, Ta, Th, U, V, W, Y, Zn, Zr) in the original soil, the amended soil and in grapevine leaves has been measured by X-ray fluorescence. The addition of sugar foam modified the agronomic properties of the original soil. The amendment caused a slight increase in major elements (Ca, 10.4 g·kg-1; Mg, 1.9 g·kg-1 and K, 12.9 g·kg-1) and decreased Al (from 62 to 57.8 g·kg-1) and Fe (from 41.2 to 26.5 g·kg-1) content. Regarding trace elements, there was an increase in levels of Ba, Rb and Sr in the amended soil in comparison to the original soil. The major elements that accumulated in the vine leaf were Ca, Mg and S (Biological Absorption Coefficient, BAC, greater than 1). As for trace elements in leaf, Ba and Sr had a "medium" BAC (0.27 and 0.8, respectively) whereas Rb had a "slight"value (0.08). It is worth noting that the bioaccumulation rate of Zn was greater than 1. The use of sugar foam as a liming agent did not have a negative effect on the absorption of major and trace elements in vine leaves and led to improved BAC values for essential elements in the grapevine. The treatment did not increase the amount of trace elements in the soil above the reference levels for the region.