Propiedades morfológicas y estructurales de recubrimientos nitruro de titanio aluminio producidos por magnetron sputtering tríodo

TixAl1-xN coatings were grown using the triode magnetron sputtering technique varying the bias voltage between -40 V and -150V. The influence of bias voltage on structural and morphological properties was analyzed by means of energy dispersive spectroscopLos recubrimientos TixAl1-xN se cultivaron usando la técnica de pulverización catódica con magnetrón triodo, variando el voltaje de polarización entre -40 V y -150V. La influencia del voltaje de polarización en las propiedades estructurales y morfológica

Methods employed in optical emission spectroscopy analysis: a review

In this work, different methods employed for the analysis of emission spectra are presented -- The proposal is to calculate the excitation temperature (Texc), electronic temperature (Te) and electron density (ne) for several plasma techniques used in the growth of thin films -- Some of these techniques include magnetron sputtering and arc discharges -- Initially, some fundamental physical principles that support the Optical Emission Spectroscopy (OES) technique are described; then, some rules to consider during the spectral analysis to avoid ambiguities are listed -- Finally, some of the more frequently used spectroscopic methods for determining the physical properties of plasma are describe

Valoración de la garantía de pensión en las cuentas de ahorro individual en Colombia

El comportamiento del individuo como persona que aporta, y futuro beneficiario de una pensión, es determinante para cuantificar los efectos que su densidad de aportes tiene sobre el sistema de ahorro individual y la exigibilidad de las diferentes garantías. Por esta razón, en el presente trabajo se intenta buscar desde las finanzas personales una visión alterna a lo expuesto en diferentes estudios que sobre la materia se han realizado, no solo en Colombia sino a nivel internacional, y brindar una aproximación a la solución del problema de sostenibilidad en el retiro. Para calcular la magnitud de las garantías, se desarrolló un procedimiento que combina metodologías de modelos estocásticos con modelos de lógica difusa y con el cálculo actuarial. De esta forma, y soportado en resultados de otros estudios, se logró determinar el ahorro individual potencial alcanzable por cada individuo en función de su género y su cohorte salarial, y el posible déficit existente para conseguir una pensión mínima de retiro. Los resultados encontrados indican que en las condiciones de baja densidad de aportes es muy difícil para las cohortes de bajo y medio ingreso asegurar una pensión mínima sin el agotamiento de las garantías existentes y la participación del gobierno

Decaying neutralino dark matter in anomalous U(1)HU(1)_H models

In supersymmetric models extended with an anomalous $U(1)_H$ different R-parity violating couplings can yield an unstable neutralino. We show that in this context astrophysical and cosmological constraints on neutralino decaying dark matter forbid bilinear R-parity breaking neutralino decays and lead to a class of purely trilinear R-parity violating scenarios in which the neutralino is stable on cosmological scales. We have found that among the resulting models some of them become suitable to explain the observed anomalies in cosmic-ray electron/positron fluxes.Comment: 19 pages, 3 figures. References added, typos corrected, accepted version in Phys Rev

Context-Based Defading of Archive Photographs

We present an algorithm for the enhancement of contrast in digitized archive photographic prints. It aims at producing an adaptive enhancement based on the local context of each pixel and is able to operate without direct user's intervention. A relation between the variation of contrast at different resolutions and the local Lipschitz regularity of the image is exploited. In this way, each pixel is defaded according to its nature: noise, edge, or smooth region. This strategy provides for an algorithm that drastically reduces typical, annoying artifacts like halo effects and noise amplification

Decoherence induced by an ordered environment

This Letter deals with the time evolution of a qubit weakly coupled to a reservoir which has a symmetry broken state with long range order at finite temperatures. In particular, we model the ordered reservoir by a standard BCS superconductor with s-wave pairing. We study the reduced density matrix of a qubit using both the time-convolutionless and Nakajima-Zwanzig approximations. We study different kinds of couplings between the qubit and the superconducting bath. We find that ordering in the superconducting bath generically leads to an unfavorable non- Markovian faster-than-exponential decay of the qubit coherence. On the other hand, a coupling of the qubit to the non-ordered sector of the bath can result in a Markovian decoherence of the qubit with a drastic reduction of the decoherence rate. Since these behaviors are endemic to the ordered phase, qubits can serve as useful probes of continuous phase transitions in their environment. We also briefly discuss the validity of our main result, faster than exponential decay of the qubit coherences, for a qubit coupled to a generic ordered bath with a spontaneously broken continuous symmetry at finite temperatures.Comment: 6 pages, 3 figure

Forced and self-excited oscillations of an optomechanical cavity

We experimentally study forced and self oscillations of an optomechanical cavity which is formed between a fiber Bragg grating that serves as a static mirror and between a freely suspended metallic mechanical resonator that serves as a moving mirror. In the domain of small amplitude mechanical oscillations, we find that the optomechanical coupling is manifested as changes in the effective resonance frequency, damping rate and cubic nonlinearity of the mechanical resonator. Moreover, self oscillations of the micromechanical mirror are observed above a certain optical power threshold. A comparison between the experimental results and a theoretical model that we have recently presented yields a good agreement. The comparison also indicates that the dominant optomechanical coupling mechanism is the heating of the metallic mirror due to optical absorption.Comment: 11 pages, 6 figure

Factores relacionados con la deserción estudiantil en el programa de enfermería de la universidad libre de pereira

Introduction: The college dropout rate has become a problem which requires evaluation to ensure quality retention mechanisms, which the accreditation of academic programs process demands. Methodology: We made a descriptive study of 36 nursing program drop outs at the Libre University of Pereira and it was characterized by socio-demographic variables. The ratios calculated were compared with those in a previous study of the general nursing student population and established the differences between proportions. Inquiries were made about the drop out student’s assessment on the reasons for entering the program and the factors that led to the desertion using Likert scales. Results: 27.8% and 16.7% of drop outs occurred in the first and second semesters. There were no significant differences in the variables of sex, age, marital status, and social strata with those in the general population of nursing students. The factor associated with dropouts that obtained a higher rating by students was financial, followed by low motivation and enthusiasm for the career. 33.3% of drop out students received academic support, 3.8% psychological and financial support of 2.8%. Recommendations: the selection process and the psychological, economic, and academic achievement support must be improved, particularly in the first semester when the bulk of desertion occurs.Introducción. La deserción estudiantil universitaria se constituye en un problema que es necesario evaluar para garantizar los mecanismos de retención con calidad, que exigen los procesos de acreditación de los programas académicos. Metodología: Se realizó un estudio descriptivo en 36 estudiantes desertores del programa de enfermería de la Universidad Libre de Pereira y se caracterizaron por variables sociodemográficas. Las proporciones calculadas se compararon con las observadas en un estudio anterior en la población general de estudiantes de enfermería y se establecieron las diferencias de proporciones. Se indagó sobre las apreciaciones de los estudiantes desertores acerca de los motivos para ingresar al programa y los factores que los indujeron a la deserción mediante escalas tipo Likert. Resultados: El 27.8% y 16,7% de la deserción ocurrió en primero y segundo semestre, respectivamente. No se observaron diferencias significativas en las variables de sexo, edad, estado civil y estrato con las observadas en la población general de estudiantes de enfermería. El factor asociado a la deserción que obtuvo una mayor calificación por parte de los estudiantes fue el económico, seguido de la baja motivación y el gusto por la carrera. El 33,3% de los estudiantes desertores recibió apoyo académico, 3,8% apoyo psicológico y económico el 2,8%. Recomendaciones: Se deben mejorar los procesos de selección y los apoyos psicológico, económico, y académico, particularmente en los primeros semestres cuando ocurre el grueso de la deserció

Hunter-gatherer foraging networks promote information transmission

Central-place foraging (CPF), where foragers return to a central location (or home), is a key feature of hunter–gatherer social organization. CPF could have significantly changed hunter–gatherers’ spatial use and mobility, altered social networks and increased opportunities for information-exchange. We evaluated whether CPF patterns facilitate information-transmission and considered the potential roles of environmental conditions, mobility strategies and population sizes. We built an agent-based model of CPF where agents moved according to a simple optimal foraging rule, and could encounter other agents as they moved across the environment. They either foraged close to their home within a given radius or moved the location of their home to new areas. We analysed the interaction networks arising under different conditions and found that, at intermediate levels of environmental heterogeneity and mobility, CPF increased global and local network efficiencies as well as the rate of contagion-based information-transmission. We also found that central-place mobility strategies can further improve information transmission in larger populations. Our findings suggest that the combination of foraging and movement strategies, as well as the environmental conditions that characterized early human societies, may have been a crucial precursor in our species’ unique capacity to innovate, accumulate and rely on complex culture