Theory of double-resonant Raman spectra in graphene: intensity and line shape of defect-induced and two-phonon bands

We calculate the double resonant (DR) Raman spectrum of graphene, and determine the lines associated to both phonon-defect processes, and two-phonons ones. Phonon and electronic dispersions reproduce calculations based on density functional theory corrected with GW. Electron-light, -phonon, and -defect scattering matrix elements and the electronic linewidth are explicitly calculated. Defect-induced processes are simulated by considering different kind of idealized defects. For an excitation energy of $\epsilon_L=2.4$ eV, the agreement with measurements is very good and calculations reproduce: the relative intensities among phonon-defect or among two-phonon lines; the measured small widths of the D, $D'$, 2D and $2D'$ lines; the line shapes; the presence of small intensity lines in the 1800, 2000 cm$^{-1}$ range. We determine how the spectra depend on the excitation energy, on the light polarization, on the electronic linewidth, on the kind of defects and on their concentration. According to the present findings, the intensity ratio between the $2D'$ and 2D lines can be used to determine experimentally the electronic linewidth. The intensity ratio between the $D$ and $D'$ lines depends on the kind of model defect, suggesting that this ratio could possibly be used to identify the kind of defects present in actual samples. Charged impurities outside the graphene plane provide an almost undetectable contribution to the Raman signal

MODIFIED SERIES RESISTANCE MODEL - DETERMINATION OF MEAN CONCENTRATION BY INTEGRAL TRANSFORMATION

There are several mathematical models that describe permeate flow in membrane separation processes. Among these, the series resistance model plays a prominent role. It takes into account membrane strength, concentration polarization, polarized layer and fouling to describe the permeate flow over time. In this work, an analysis of the modified series resistance model was performed, in which the resistance by polarization of the concentration is defined as being directly proportional to the transmembrane pressure. The proportionality constant is given by the product of a specific coefficient of resistance – which is determined by means of experimental data – the thickness of the boundary layer of concentration and the mean concentration. Due to the inability to obtain experimentally the value of the average concentration within the boundary layer of concentration, its simulation is carried out from the conservation equation of the chemical species. Thus, the objective of the present work was to solve the equation of the conservation of chemical species using GITT (Generalized Integral Transform Technique) and apply the modified series resistance model to describe the permeate flow of a solution of dextran through a permeable tube under laminar flow. GITT provided satisfactory results for the mean concentration, verified by comparison with the permeate flow obtained by the series resistance model with experimental results reported in the literature

HACIA UN NUEVO PARADIGMA EN ORIENTACIÓN VOCACIONAL

El objetivo del presente trabajo investigativo es formular algunas sugerencias dirigidas a la elaboración de una nueva propuesta paradigmática en el área de la Orientación Vocacional, actualizada y más relacionada con el ámbito latinoamericano. En el mismo se hace una breve revisión de la Orientación Vocacional en el Mundo, en América Latina y en Venezuela. También se presentan algunas definiciones y opiniones de autores relevantes que sugieren un cambio en la forma como ha sido concebida la Orientación Vocacional, y además se comentan las necesidades actuales que presenta el campo ante el surgimiento de nuevas problemáticas sociales. La principal sugerencia que puede hacerse al final de este trabajo es que se necesita una nueva forma de actuar y de concebir la Orientación Vocacional, con un tipo de Orientación, que pudiera denominarse Confluente, ya que la propuesta es que todas las dimensiones humanas deberían ser consideradas al mismo tiempo y sin fragmentaciones que sean irreales y fantasiosas. Este modelo de Orientación Confluente será presentado posteriormente.Palabras Clave: Orientación Vocacional, Propuesta Paradigmática, Problemáticas Sociales y Orientación. TOWARD A NEW PARADIGM IN VOCATIONAL GUIDANCEABSTRACTThe objective of this paper is to make some suggestions to the development of a proposed new paradigm in the area of Vocational Guidance, updated and more related to the Latin American.This research paper presents a brief review of career guidance n the World, Latin America and Venezuela. It also presents some definitions and opinions of relevant authors that suggest a change in the way Vocational Guidance has been conceived, and also discusses the current needs of the field before the emergence of new social problems. The main suggestion to do at the end of this paper is that it requires a new way of thinking and acting Vocational Guidance, Guidance, that it could call Confluent, since the proposal is that all human dimensions should be considered at the same time and without fragmentations that are unrealistic and fanciful. This model of Confluent Guidance will be presented later.Key Words: Vocational Guidance, Paradigmatic Proposal, Guidance and Social Problems

EL CULTIVO HIDROPÓNICO DE LECHUGA: Una experiencia pedagógica creativa

La presente investigación tuvo como objetivo evaluar la aplicación de un modelo pedagógico para la enseñanza y el aprendizaje del cultivo hidropónico de lechuga (Lactuca sativa L.). Se realizó bajo un enfoque cualitativo de tipo descriptivo y el análisis basado en el método hermenéutico. Estuvo desarrollado en 04 fases: (a) período de preparación, (b) determinación del escenario, (c) trabajo de campo, (d) análisis e interpretación de la información. El escenario fue una Escuela Técnica Agropecuaria del Estado Yaracuy, Venezuela, se trabajó con 02 secciones de 30 alumnos cursantes del 1º año de Educación Media Diversificada y Profesional (EMDP) durante el II lapso del año escolar 2006 - 2007. Los informantes claves fueron: 02 docentes y 20 estudiantes seleccionados al azar. Las técnicas para la recolección de la información: (a) observación, (b) entrevista y (c) análisis de contenido. Los instrumentos utilizados: el diario de campo, el cuestionario, las grabaciones y fotografías. Para el análisis e interpretación de la información recaudad, se aplicaron la codificación y la categorización. Como resultado, de los docentes surgieron 05 categorías para valorar la utilidad del modelo hacia el enfoque en la enseñanza de las ciencias agrícolas, mientras que de los alumnos emergieron 03 categorías para reconocer en el modelo sus alcances en el aprendizaje.Palabras clave: Cultivo hidropónico, lechuga, modelo pedagógico.THE HYDROPONIC CULTURE OF LETTUCE (Lactuca sativa L.).A creative pedagogical experienceABSTRACTThe objective of this study was to evaluate the application of a model for teaching and learning hydroponics culture of lettuce (Lactuca sativa L.). It was a qualitative, descriptive, hermeneutic study, developed in four phases: (a) preparation, (b) determination of location, (c) field work and (d) analysis and interpretation of data. The location was an agriculture school in Yaracuy, Venezuela. Two 30 pupils, first year senior secondary students were selected during the second half of 2006-2007 term. Key informants were two teachers and 20 randomly selected students. Data was collected through participant observation, interviews and content analysis. Instruments were field notes, questionnaires, recordings and pictures. Data was interpreted through codes and categories. As a result, five categories emerged from teachers and two from students to value this model as a valid alternative in agricultural education.Key words: Hydroponic culture, Lettuce, Educational models.

Emergence of local magnetic moments in doped graphene-related materials

Motivated by recent studies reporting the formation of localized magnetic moments in doped graphene, we investigate the energetic cost for spin polarizing isolated impurities embedded in this material. When a well-known criterion for the formation of local magnetic moments in metals is applied to graphene we are able to predict the existence of magnetic moments in cases that are in clear contrast to previously reported Density Functional Theory (DFT) results. When generalized to periodically repeated impurities, a geometry so commonly used in most DFT-calculations, this criterion shows that the energy balance involved in such calculations contains unavoidable contributions from the long-ranged pairwise magnetic interactions between all impurities. This proves the fundamental inadequacy of the DFT-assumption of independent unit cells in the case of magnetically doped low-dimensional graphene-based materials. We show that this can be circumvented if more than one impurity per unit cell is considered, in which case the DFT results agree perfectly well with the criterion-based predictions for the onset of localized magnetic moments in graphene. Furthermore, the existence of such a criterion determining whether or not a magnetic moment is likely to arise within graphene will be instrumental for predicting the ideal materials for future carbon-based spintronic applications.Comment: Submitted to PR

Imprisonment and internment: Comparing penal facilities North and South

Recent references to the ‘warehouse prison’ in the United States and the prisión-depósito in Latin America seem to indicate that penal confinement in the western hemisphere has converged on a similar model. However, this article suggests otherwise. It contrasts penal facilities in North America and Latin America in terms of six interrelated aspects: regimentation; surveillance; isolation; supervision; accountability; and formalization. Quantitatively, control in North American penal facilities is assiduous (unceasing, persistent and intrusive), while in Latin America it is perfunctory (sporadic, indifferent and cursory). Qualitatively, North American penal facilities produce imprisonment (which enacts penal intervention through confinement), while in Latin America they produce internment (which enacts penal intervention through release). Closely entwined with this qualitative difference are distinct practices of judicial involvement in sentencing and penal supervision. Those practices, and the cultural and political factors that underpin them, represent an interesting starting point for the explanation of the contrasting nature of imprisonment and internment

BASES TEÓRICAS DEL MODELO DE PRINCIPIOS CIENTÍFICO-DIDÁCTICOS PARA LA ENSEÑANZA DE LA GEOGRAFÍA Y DE LA HISTORIA

El modelo metodológico basado en la implementación de Principios Científico-Didácticos en la enseñanza de la Geografía y de la Historia, conforma una opción epistemológicamente fundada y de gran utilidad en el aprendizaje de estas dos disciplinas, ya que es consustancial con el carácter científico de ellas y con la construcción y especificidad de su conocimiento; el mismo ayuda a entender el conjunto de relaciones humanas en su universalidad; es meta explicativa y otorga significado a la complejidad de hechos e informaciones subsistentes; se adapta a la individualidad de los alumnos; desarrolla habilidades y destrezas, y educa en valores, actitudes y normas. Con la aplicación de esta metodología se fomenta una construcción científica del conocimiento, que otorga un nuevo sentido a estas disciplinas, a fin de que retomen el gran valor formativo que poseen, tanto para el desarrollo humanizado de la sociedad en general, como para la propia personalidad del alumno que le constituye en un ciudadano responsable, crítico, comprometido y transformador de su entorno habitacional.Palabras Clave: Principios Científicos – Didácticos, Enseñanza, Geografía e Historia.THEORETICAL BASES OF THE MODEL OF SCIENTIFIC-DIDACTIC PRINCIPLES FORTHE TEACHING OF GEOGRAPHY AND HISTORYAbstractThe methodological model based on the implementation of Scientific-Didactic Principles in the teaching of geography and history shapes an epistemologically founded and useful option in learning these two disciplines, because it is consubstantial with their scientific nature and the construction and specificity of their knowledge. The model helps to  understand the whole of human relations in their universality, it is meta-explanatory and it grants meaning to the complex facts and lasting information; it adapts to the individuality of students, develops skills and abilities, and educates in values, attitudesand norms. The application of this methodology fosters the scientific construction of knowledge, which assigns new meaning to these disciplines in order to regain their great educational value for both the humanistic development of society in general and for the very personality of the students as critical and responsible citizens, engaged in transforming their living environment.Key words: Scientific-Didactic Principles, Education, Geography and History