Curva de calentamiento del etanol. Un caso para el manejo de datos experimentales

Se presenta una actividad experimental sencilla, de bajos riesgo y costo, para estudiantes de los primeros cursos experimentales del área química enfocada a la obtención y manejo de datos; en particular, para aplicar el método gráfico y, a partir de cambios de variable, obtener una relación funcional empírica entre las variables relevantes del experimento. El experimento consiste en calentar etanol, desde una temperatura menor a O ºC, hasta la temperatura ambiente. Se presentan resultados de un grupo de estudiantes junto con su propuesta de cambio de variables y la relación funcional que encuentran a partir de ella. Se mencionan algunas sugerencias que se les hicieron para mejorar, tanto la obtención de datos, como su tratamiento y, a partir de ellas, reflexionar acerca de qué y cuáles son las variables relevantes del experimento. Con las nuevas variables obtienen una representación gráfica que mostró una tendencia cercana a la lineal.A simple experimental activity, which is low in risk and cost, is presented. lt is intended for the first-year college students to develop abilities to obtain and manage data from the experiments, to use them in graphical method and, by proposing an adequate variable change, to get an empirical relationship between the experiment relevant variables. The experiment consists in heating ethanol from temperatures lower than O ºC to room temperature. Results from the analysis performed by a group of students, together with his proposal about variable change and the relationship they found from it are mentioned. Sorne ideas which were suggested to them to improve the way they collect data as well as its analytical treatment are also mentioned, in such a way, that students think about what and which ones the relevant variables are. With their proposal they got a graphical representation which resembles a linear tendency

Simultaneous adsorption of quinoline and dibenzothiophene over Ni-based mesoporous materials at different Si/Al ratio

In this study, two mesoporous materials such as MCM-41 and Ni/MCM-41 were modified with Al at different Si/Al ratios. The mesoporous materials were proved as sorbents of heterocyclic nitrogen and sulfur compounds employing quinoline (Q) and dibenzothiophene (DBT), respectively, as model molecules of that precursor pollutants at the same concentrations of ppmw of nitrogen and sulfur (N:S = 1 ratio). The sample with the highest Si/Al ratio showed the highest specific surface, and at low Si/Al decreased the specific surface. With X-ray diffraction (XRD) the Ni containing in MCM-41, there is a clear trend and the highly hexagonal ordered sample is the one without Al and once the Al is added, the hexagonal ordering is highly modified. Employing NH3-TPD and NMR revealed that the samples with Si/Al = 5 and 16 have higher Lewis acid sites than another ratio of Si/Al. The modification successfully added small amounts of Ni that did not collapse the pore structure but increased the density of surface (acidic) groups that in turn favored the uptake of the sulfur compound through π-complexation adsorption mechanism. It is also possible to recognize that the samples with a Si/Al ratio of 5 and 16 revealed the presence of the highest surface density of weak acid sites for both sorbents. Adsorption experiments were carried out in a batch adsorption system at 313 K and atmospheric pressure using a model mixture from diesel containing: DBT, Q, and 40 ml of dodecane. The sulfur adsorption was substantially improved when Ni was incorporated to MCM-41; for example, at 250 ppmw of N uptake of DBT was almost twice than MCM-41 alone. This result would indicate that Ni/MCM-41 could remove both molecules but mainly the nitrogen molecule at high concentrations. The Langmuir and Freundlich adsorption isotherms were used for all materials considering Q in the presence of DBT depending on the Si/Al ratio. This behavior did not happen for the DBT whose behavior was modelled by an isotherm of the Freundlich type for Ni/MCM-41 and adsorbed in acid sites and multilayer. Lastly, experimental results indicated that MCM-41 with Si/Al = ∞ has the highest (Q/DBT) selectivity of 13,390 at 50 ppmw N compared to another Si/Al ratio, for example, at 250 ppmw N

High-Temperature Oxidation of Superalloy C-263 of Rings for Aircraft Engines

The present investigation was conducted to study the oxidation kinetics of nickel-based superalloy 263, used in the manufacture of rings for aircraft engines. For carrying out this study, we first conducted microstructural characterization of the pieces using the techniques of optical microscopy, scanning electronic microscopy, and X-ray diffraction. Subsequently, using the thermogravimetric analysis, the kinetic oxidation of the metal was performed in a temperature range between 700 and 1000°C, using atmospheres of O2. The results of the micrographs show the formation of a protective oxide film on the surface of the material in different oxidizing agents. Finally, it was found that the kinetics of high-temperature oxidation of the superalloy C-263 obeys the parabolic rate law

Selective adsorption of nitrogen compounds using silica-based mesoporous materials as a pretreatment for deep hydrodesulfurization

The adsorption of quinoline (Q) and dibenzothiophene (DBT)—model compounds for nitrogen and sulfur in diesel fuels—over mesoporous SBA-15, SBA-16, and MCM-41 was studied. The Langmuir model was suitable for describing the adsorption of nitrogen-containing compounds from a simulated diesel fuel. A pseudo-second order kinetic model better fitted the Q adsorption data than a first-order rate model when describing the adsorption rates on all materials. Comparison of the adsorption of Q and DBT confirmed that the nitrogen compound was selectively removed, and MCM-41 was found to have better adsorption characteristics than SBA-15 and SBA-16. DBT was not adsorbed in any experiment. The adsorbents were characterized using N2-physisorption, powder X-ray diffraction, and high-resolution transmission electron microscopy to describe the morphologies of the adsorbents. The characterization results revealed that the specific area and the structure of the adsorbent are key parameters required to explain the adsorption process

Effect of Ni on MCM-41 in the Adsorption of Nitrogen and Sulfur Compounds to Obtain Ultra-Low-Sulfur Diesel

Adsorption of heterocyclic sulfur and nitrogen compounds like dibenzothiophene (DBT) and quinoline (Q), respectively, was carried out using mesostructured adsorbent MCM-41 and Ni/MCM-41 in calcined (C) and reduced (R) form. These materials were proved in a batch adsorption system using a model fuel diesel: a mixture of dodecane, DBT and Q with the same concentrations of ppmw of sulfur and nitrogen at 313 K and atmospheric pressure. When MCM-41 was impregnated with Ni, an important modification of the adsorption properties was observed, for example, the uptake of DBT was increased and this adsorption was twice in Ni/MCM-41 in reduce form than in the calcined form. On the other hand, for the nitrogen adsorption of Q diminished by 62 and 58%, considering Ni/MCM-41 in reduce form and in calcined form as adsorbent, respectively. This is a significant achievement regarding the desulfurization and denitrogenation, especially for commercial diesel without pretreatment. Moreover, the kinetic results were adjusted with second order considering Q as nitrogen and DBT as sulfur molecule. Data fitting for Q was achieved better by the Langmuir model for all materials than the Freundlich model, meanwhile the experimental adsorption data of DBT was fitted to the Freundlich model for Ni/MCM-41 calcinated and reduced form

Tránsito en cuerda fija: su utilización en ámbitos educativos

El grupo de Investigación en Educación Física y Andinismo ha sido constituido en el Centro Regional Universitario Bariloche de la Universidad Nacional del Comahue como consecuencia de los estudios que en el marco de la carrera Profesorado en Educación Física (PEF) y de su orientación en actividades regionales de montaña, están siendo realizados. El objeto de esta comunicación se inscribe en la línea de trabajo que se comenzó a desarrollar en el año 2010 y a la que hemos denominado: Análisis de las prácticas de andinismo en ámbitos educativos. (Goicoechea Gaona, Palacio, 2014) En esta ocasión se trata de conceptualizar la práctica de tránsito por cuerda fija propia de la escalada. La misma forma parte de los contenidos de las asignaturas de formación docente del PEF Deportes Regionales Estivales I y II (DREI y II). Siguiendo la metodología de trabajo del grupo, se determinarán los aspectos específicos que hacen de dicha práctica un contenido de la Educación Física, es decir, resulta apropiada para ser enseñada y realizada en el ámbito educativo. De este modo damos continuidad a la tarea de sistematización de nuevas prácticas que por estar apareciendo en el contexto escolar requiere del estudio y tratamiento de especialistas en andinismo y educación.Mesa de trabajo 3: Educación física e investigaciónFacultad de Humanidades y Ciencias de la Educació

Perfil microbiológico y sensibilidad a antibióticos de microorganismos aislados de infecciones conjuntivales en el Instituto de Oftalmología Fundación Conde de Valenciana. Reporte del año 2012

ResumenIntroducciónLa conjuntiva es el tejido ocular que se infecta con mayor frecuencia. Los agentes patógenos más frecuentes de la conjuntivitis suelen ser los virus y las bacterias. El uso indiscriminado de antibióticos de amplio espectro para tratar la conjuntivitis ha generado microorganismos resistentes.ObjetivoIdentificar los microorganismos más frecuentes aislados de muestras de origen conjuntival y conocer su susceptibilidad antibiótica.Material y métodosRevisión retrospectiva de cultivos provenientes de raspados conjuntivales obtenidos durante el 2012.ResultadosSe obtuvieron 44 muestras de origen conjuntival. Estas provinieron de 21 varones y 23 mujeres. La mediana (25%, 75%) de la edad fue 62 años (39-68). El cultivo fue positivo en 13 de las muestras obtenidas, identificándose 5 microorganismos diferentes. Staphylococcus epidermidis fue el microorganismo aislado con mayor frecuencia (9 cepas). Todas las cepas de S. epidermidis fueron sensibles a vancomicina, gentamicina, cefotaxima, moxifloxacino y ofloxacino. La mayoría de las cepas de S. epidermidis (6/9) mostraron resistencia a múltiples antibióticos.ConclusionesStaphylococcus epidermidis fue el microorganismo aislado con mayor frecuencia en muestras provenientes de infecciones conjuntivales. Todas las cepas de S. epidermidis fueron sensibles a vancomicina, gentamicina y moxifloxacino y la mayoría de ellas fueron multirresistentes a los antibióticos en evaluación.AbstractIntroductionThe conjunctiva is the tissue of the eye that gets infected with more frequency. The most common pathogens of conjunctivitis are viruses and bacteria. The indiscriminate use of broad-spectrum antibiotics to treat conjunctivitis generated resistant microorganisms.ObjectiveIdentify the most common microorganisms isolated from samples of conjunctival origin and know their antibiotic susceptibility.Material and methodsRetrospective review of culture from conjunctival swabs obtained during 2012.ResultsWe collected 44 samples of conjunctival origin. They came from 21 males and 23 women. The median (25%, 75%) of age was 62 years (39-68). The culture was positive in 13 samples, identifying five different microorganisms. Staphylococcus epidermidis was the most common isolated microorganism (9 strains). All strains of S. epidermidis were sensitive to vancomycin, gentamicin, cefotaxime, ofloxacin and moxifloxacin. The multiple antibiotic resistance was identified in the majority of strains of S. epidermidis (6/9).ConclusionsStaphylococcus epidermidis was the most common isolated microorganism from samples of conjuntival infections. All strains of S. epidermidis were sensitive to vancomycin and moxifloxacin and most of them showed multidrug resistance to antibiotics

Delamination and Tensile Effect of Fine z-Binder Reinforced on Fiberglass/Polyester Composite for Aerospace Applications

Delamination propagation in laminated composite materials is a common issue that always concerns us when we consider composites for structural purpose. Many possible solutions have been studied; the most famous is the three-dimensional (3D) woven composites materials, which have promising interlaminar fracture resistance but at the cost of increasing density, which for aerospace industry is very important. In this chapter, mode 1 double cantilever beam (DCB) interlaminar fracture toughness tests according to the American Society for Testing and Materials (ASTM) D5528 standard were performed on composite specimens made of E-Glass Saertex 830 g/m2 Biaxial (+/−45°) with Sypol 8086 CCP polyester resin with orthogonal z-axis oriented yarn woven of 0.22 mm diameter nylon monofilament. Four specimens were made with a longitudinal distance between the warp binders of 0.5, 1, 1.5, and 2 cm, respectively. A tensile test according to the ASTM D3039 standard was performed to study how z-binder may affect tensile resistance. The results show a considerable increase in interlaminar fracture toughness, several stress concentrators have been created because of the new yarn and premature failure in the matrix

Delamination and tensile effect of fine z-binder reinforced on fiberglass/polyester composite for aerospace applications

Delamination propagation in laminated composite materials is a common issue that always concerns us when we consider composites for structural purpose. Many possible solutions have been studied; the most famous is the three-dimensional (3D) woven composites materials, which have promising interlaminar fracture resistance but at the cost of increasing density, which for aerospace industry is very important. In this chapter, mode 1 double cantilever beam (DCB) interlaminar fracture toughness tests according to the American Society for Testing and Materials (ASTM) D5528 standard were performed on composite specimens made of E-Glass Saertex 830 g/m2 Biaxial (+/−45°) with Sypol 8086 CCP polyester resin with orthogonal z-axis oriented yarn woven of 0.22 mm diameter nylon monofilament. Four specimens were made with a longitudinal distance between the warp binders of 0.5, 1, 1.5, and 2 cm, respectively. A tensile test according to the ASTM D3039 standard was performed to study how z-binder may affect tensile resistance. The results show a considerable increase in interlaminar fracture toughness, several stress concentrators have been created because of the new yarn and premature failure in the matrix

Corrosion behavior of aluminum-carbon fiber/epoxy sandwich composite exposed on NaCl solution

For years, the aeronautical industry has employed different types of materials to satisfy its high-performance requirements. Fiber-metal laminates are used due to their combination of lighter weight and the high mechanical properties of reinforced metal and carbon. We therefore made two different composites of laminate-metal and laminate-metal-laminate of carbon fiber-reinforced polymer and aluminum with an ALCLAD layer. The samples were characterized by salt fog (0, 48, and 96 h) at 5 wt% NaCl and electrochemical impedance spectroscopy (EIS) with an electrolyte of 3.5 wt% NaCl. All samples were studied by electron scanning microscopy (SEM). The results demonstrated that the samples of laminate-metal-laminate presented an adsorption process after 0 and 48 h of salt fog exposition; meanwhile, the samples of laminate-metal showed a capacitive behavior for all the samples; however, corrosion resistance decreased when the salt fog exposition time increased