Characterization of the TiSiO4 structure and its pressure-induced phase transformations: density functional theory study

Theoretical investigations concerning the possible titanium silicate polymorphs have been performed using density functional theory at B3LYP level. Total-energy calculations and geometry optimizations have been carried out for all phases involved. The following sequence of pressure-driven structural transitions has been found: CrVO4 -type, Cmcm in parenthesis the transition pressure , → zircon-type, I41 / amd 0.8 GPa , → scheelite-type, I41 / a 3.8 GPa . At higher pressure the last phase is found to be stable at least up to 25 GPa. The equation of state of the different polymorphs is also reported. We found that the highest bulk modulus corresponds to the zircon and scheelite phases with values of 248 and 238 GPa, respectively. The orthorhombic Cmcm phase is the most compressible of all the studied structures with a bulk modulus of 124 GPa, being also the most stable phase at ambient pressure. Finally, calculations of the electronic structure, vibrational and dielectric properties of TiSiO4 are also reporte

Polymorphs of ZnV2O6 Under Pressure: a First Principle Investigation

This work presents first-principle calculations on the pressure-dependence of the stabilities, structures, and electronic properties of several polymorphs of ZnV2O6 under the pressure range 0-30 GPa. These properties are analyzed and discussed in detail using the different parameterizations of the exchange-correlation functional (B3LYP, HSE06, and PBE), and the results are compared with available experimental data. An extensive search process was carried out on the potential energy surface for a set of twelve possible polymorphs. Ten of them are stationary points, but only five have positive frequency values in the range of 0-30 GPa, i.e., monoclinic brannerite (C2/m and C2), orthorhombic columbite (Pbcn), trigonal CaAs2O6-type (P321), and triclinic NiV2O6-type (P1̅). The monoclinic ThTi2O6-type (C2/c) phase presents a very low imaginary frequency around 50 cm-1 . Orthorhombic SrV2O6-type and BaV2O6-type, tetragonal trirutile and trigonal PbSb2O6 -type structures show several imaginary negative frequencies between -400 and -100 cm-1 . These imaginary frequencies are indicative of structural instabilities. All attempts to try to converge the calculations to obtain the MoLa2O6-type and HgV2O6-type polymorphs, by using the three functionals, have been unsuccessful. For both brannerite,ThTi2O6-type, columbite, CaAs2O6-type, NiV2O6-type structures numerical and analytical fittings were performed to obtain the lattice parameters, the bulk modulus, B, and their pressure derivative, B′, and the energy-volume relationship of phases are analyzed. Vibrational calculations were performed at each pressure for each polymorph and compared with available experimental data

Análisis del impacto en la implementación del trabajo remoto, respecto del aumento de ataques de ingeniería social en las Empresas del Sector Retail

El presente proyecto de monografía busca abordar el aumento de los ataques de ingeniería social como práctica para obtener información privada, con el impacto que ha tenido la implementación del trabajo remoto en las empresas del sector retail a partir el factor humano y los errores atribuibles al desconocimiento y falta de formación en materia de seguridad informática. Este enfoque es de vital importancia para la ingeniería, ya que la ciberseguridad ha evolucionado con el tiempo y requiere una comprensión más completa de los riesgos asociados; además de una orientación al análisis de los programas de información por parte de la empresa, se busca abordar de manera integral el tema de la ingeniería social. Además, se definen las técnicas más utilizadas por los ciberdelincuentes para acceder a la seguridad informática en las empresas del sector retail, poniendo énfasis en las vulnerabilidades que surgen de la implementación del trabajo remoto. Se examinarán detalladamente técnicas como Phishing, Smishing, Pharming y Vishing, y se analizará su impacto en el sector. Se expone una evaluación de las medidas preventivas que deben implementarse en las empresas del sector retail para contrarrestar los ataques de ingeniería social más comunes, de tal manera que sea posible establecer pautas claras y efectivas para proteger los sistemas informáticos y la información confidencial, teniendo en cuenta las normas establecidas por la NTC. Finalmente, con este proyecto, se espera contribuir al conocimiento en el campo de la seguridad informática y proporcionar recomendaciones prácticas para mejorar la protección contra los ataques de ingeniería social en el sector retail.This monograph project seeks to address the increase in social engineering attacks as a practice to obtain private information, with the impact that the implementation of remote work has had on companies in the retail sector based on the human factor and errors attributable to ignorance. and lack of training in computer security. This approach is of vital importance for engineering, as cybersecurity has evolved over time and requires a more complete understanding of the associated risks; In addition to an orientation to the analysis of information programs by the company, it seeks to comprehensively address the issue of social engineering. In addition, the techniques most used by cybercriminals to access computer security in companies in the retail sector are defined, placing emphasis on the vulnerabilities that arise from the implementation of remote work. Techniques such as Phishing, Smishing, Pharming and Vishing will be examined in detail and their impact on the industry will be analyzed. An evaluation of the preventive measures that must be implemented in companies in the retail sector to counteract the most common social engineering attacks is presented, in such a way that it is possible to establish clear and effective guidelines to protect computer systems and confidential information, taking into account takes into account the standards established by the NTC. Finally, with this project, we hope to contribute to knowledge in the field of computer security and provide practical recommendations to improve protection against social engineering attacks in the retail sector

Evaluación de la calidad de la información geográfica voluntaria mediante un enfoque de análisis multivariado - caso de estudio malla vial Bogotá-Colombia

El aumento en la producción de información geográfica voluntaria (VGI) ha venido creciendo considerablemente y se han realizado diversos estudios al respecto. Sin embargo, el desconocimiento de la calidad de la información generada en forma voluntaria y participativa, plantea retos y cuestionamientos sobre el uso de este tipo de información. Este trabajo tiene como objetivo realizar un análisis de la calidad de la información geográfica voluntaria (VGI) desde una perspectiva multivariada. Para ello se compararán los datos colectados a través de la plataforma Open Street Map (OSM) para el año 2017, respecto a la malla vial de Bogotá-Colombia, proveniente esta de una fuente oficial (Infraestructura de datos Espaciales de Bogotá catastro Distrital IDECA). En la revisión efectuada para el caso colombiano no se identificaron estudios relacionados con el tema; en consecuencia, se evaluó la calidad VGI de la malla vial de Bogotá bajo un enfoque multivariado, usando las medidas de completitud, exactitud posicional y exactitud temática. Esta evaluación se realizó por medio de un proceso semiautomático que usa un buffer móvil y el centroide de las vías para realizar las comparaciones correspondientes entre dos fuentes de datos. Los resultados encontrados revelan que el método empleado permitió comparar hasta el 85% de los datos, además se calculó que la malla OSM (Open Street Maps) tiene una completitud del 85.42%, sobre toda el área de Bogotá. Una exactitud posicional de 3.98 m y en general una calidad VGI deficiente, pues el porcentaje de error encontrado fue de aproximadamente 60.3%. Se concluyó que los datos VGI gozan de una completitud aceptable, una exactitud posicional óptima y una exactitud temática deficiente.Abstract: The increase in the production of voluntary geographic information (VGI) has been growing considerably and many studies have focused on studying this phenomenon. The problem to use this type of information it's related specifically in the ignorance of its quality and as in Colombia there are still no studies related to the subject. In this paper, the VGI quality of the Bogotá road network was evaluated using completeness, positional accuracy and thematic accuracy. This evaluation was made through a semi-automatic process that uses a mobile buffer and the centroid of the lines to perform the corresponding comparisons between two data sources. The results revealed that the method used could match 85% of the data, and it was calculated that OSM has a completeness of 85.42%, over the entire area of Bogotá. A positional accuracy of 3.97 m and generally, a poor VGI quality : Because the percentage of mistake found was over 60.3%, It was concluded that VGI data enjoy acceptable completeness, optimal positional accuracy and poor thematic accuracy.Maestrí

Habilidades sociales en los adolescentes estudiantes de segundo año de Bachillerato General y opción Administrativo Contable sección “A” y “B” del turno matutino del Instituto Nacional de Usulután, durante el año 2016

La investigación tuvo como objetivo principal conocer las habilidades sociales de los adolescentes estudiantes de Segundo año de Bachillerato General y Administrativo Contable A y B del Instituto Nacional de Usulután y establecer la frecuencia de dichas habilidades así como también identificar si existen diferencias en las habilidades sociales según el tipo de familia y los factores que se dan en el desarrollo de las habilidades sociales. El diseño fue descriptivo, en esta investigación se aplico una ficha de evaluación para seleccionar a la población que sería encuestada, esto permitió conocer el tipo de familia de la cual provenía el adolescente para conformar la población por estratos de familias integradas y desintegras con ello se seleccionaron los participantes de manera intencionada y es a esta población a la cual se le aplico el inventario de Habilidades Sociales que permite conocer los niveles en cuatro áreas asertividad, autoestima, comunicación y toma de decisiones. Se utilizo el método cuantitativo que consistió en utilizar la recolección de datos y posteriormente aplicar la prueba Z, aceptando la hipótesis de investigación y rechazando la nula. El tipo de investigación es cuantitativo descriptivo porque se tiene una variable en estudio habilidades sociales la cual fue medida con una prueba y esta dio datos que se analizaron, dando resultados favorables ya que se poseen conductas socialmente hábiles. La población es de 232 adolescentes del sexo masculino y femenino, la muestra se obtuvo a través del programa de decisión de análisis STATS T M y se selecciono a 140 estudiantes 73 son de familias integradas y 67 de familias desintegras estos grupos fueron la población en la cual se investigo las habilidades sociales

Intercalation processes and diffusion paths of lithium ions in spinel-type structured Li1+xTi2O4: density functional theory study

Intercalation processes and corresponding diffusion paths of Li ions into spinel-type structured Li1+xTi2O4 0 x 0.375 are systematically studied by means of periodic density functional theory calculations for different compositions and arrangements. An analysis of the site preference for intercalation processes is carried out, while energy barriers for the diffusion paths have been computed in detail. Our results indicate that the Li insertion is thermodynamically favorable at octahedral sites 16c in the studied composition range, and Li migration from tetrahedral sites 8a to octahedral sites 16c stabilizes the structure and becomes favorable for compositions x 0.25. Diffusion paths from less stable arrangements involving Li migrations between tetrahedral and octahedral sites exhibit the lowest energy barrier since the corresponding trajectories and energy profiles take place across a triangle made by three neighboring oxygen anions without structural modification. Theoretical and experimental diffusion coefficients are in reasonable agreemen

Experimental and theoretical investigation of ThGeO4 at high pressure

We report here the combined results of angle-dispersive x-ray diffraction experiments performed on ThGeO4 up to 40 GPa and total-energy density-functional theory calculations. Zircon-type ThGeO4 is found to undergo a pressure-driven phase transition at 11 GPa to the tetragonal scheelite structure. A second phase transition to a monoclinic M-fergusonite type is found beyond 26 GPa. The same transition has been observed in samples that crystallize in the scheelite phase at ambient pressure. No additional phase transition or evidence of decomposition of ThGeO4 has been detected up to 40 GPa. The unit-cell parameters of the monoclinic high-pressure phase are a=4.98(2) Å, b=11.08(4) Å, c=4.87(2) Å, and β=90.1(1), Z=4 at 28.8 GPa. The scheelite-fergusonite transition is reversible and the zircon-scheelite transition nonreversible. From the experiments and the calculations, the room-temperature equation of state for the different phases is also obtained. The anisotropic compressibility of the studied crystal is discussed in terms of the differential compressibility of the Th-O and Ge-O bond

Enhancement of optical absorption by modulation of the oxygen flow of TiO2 films deposited by reactive sputtering

Oxygen-deficient TiO2 films with enhanced visible and near-infrared optical absorption have been deposited by reactive sputtering using a planar diode radio frequency magnetron configuration. It is observed that the increase in the absorption coefficient is more effective when the O2 gas supply is periodically interrupted rather than by a decrease of the partial O2 gas pressure in the deposition plasma. The optical absorption coefficient at 1.5 eV increases from about 1 102 cm 1 to more than 4 103 cm 1 as a result of the gas flow discontinuity. A red-shift of 0.24 eV in the optical absorption edge is also observed. High resolution transmission electron microscopy with composition analysis shows that the films present a dense columnar morphology, with estimated mean column width of 40 nm. Moreover, the interruptions of the O2 gas flow do not produce detectable variations in the film composition along its growing direction. X-ray diffraction and micro-Raman experiments indicate the presence of the TiO2 anatase, rutile, and brookite phases. The anatase phase is dominant, with a slight increment of the rutile and brookite phases in films deposited under discontinued O2 gas flow. The increase of optical absorption in the visible and near-infrared regions has been attributed to a high density of defects in the TiO2 films, which is consistent with density functional theory calculations that place oxygen-related vacancy states in the upper third of the optical bandgap. The electronic structure calculation results, along with the adopted deposition method and experimental data, have been used to propose a mechanism to explain the formation of the observed oxygen-related defects in TiO2 thin films. The observed increase in sub-bandgap absorption and the modeling of the corresponding changes in the electronic structure are potentially useful concerning the optimization of efficiency of the photocatalytic activity and the magnetic doping of TiO2 films

Simulation of a solar-assisted air-conditioning system applied to a remote school

Producción CientíficaIn this work, we present an absorption cooling system with 35 kW capacity driven by solar thermal energy, installed in the school of Puertecitos, Mexico, an off-grid community with a high level of social marginalization. The cooling system provides thermal comfort to the school’s classrooms through four 8.75-kW cooling coils, while a 110-m2 field of evacuated tube solar collectors delivers the thermal energy needed to activate the cooling machine. The characteristics of the equipment installed in the school were used for simulation and operative analysis of the system under the influence of typical factors of an isolated coastal community, such as the influence of climate, thermal load, and water consumption in the cooling tower, among others. The aim of this simulation study was to determine the best operating conditions prior to system start-up, to establish the requirements for external heating and cooling services, and to quantify the freshwater requirements for the proper functioning of the system. The results show that, with the simulated strategies implemented, with a maximum load operation, the system can maintain thermal comfort in the classrooms for five days of classes. This is feasible as long as weekends are dedicated to raising the water temperature in the thermal storage tank. As the total capacity of the system is distributed in the four cooling coils, it is possible to control the cooling demand in order to extend the operation periods. Utilizing 75% or less of the cooling capacity, the system can operate continuously, taking advantage of stored energy. The cooling tower requires about 750 kg of water per day, which becomes critical given the scarcity of this resource in the community.CONACYT-SENER-SUSTENTABILIDAD ENERGÉTICA (project P09)Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo (project 518RT0558