Aleaciones moleculares. Sincristalizacion en la serie de paradihalosubstituidos del benceno

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Calvet Pallàs, Maria Teresa

1990-01-01

La sincristalización orgánica constituye un campo de investigación relativamente nuevo, en el que entran en juego interacciones muy diversas, y variaciones en las propiedades de los materiales a menudo muy sensibles a las condiciones de temperatura, presión y sobre todo a la composición. Por lo tanto, cualquier estudio sobre el tema debe comprender muchas líneas de enfoque: control de pureza de los materiales de partida, síntesis de las aleaciones, estudio de los equilibrios de las fases que ...

Relación entre factores micro- estructurales e impacto repetido en aleaciones de alto cromo para bolas de molino.

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E. Albertin

2008-01-01

Full Text Available Las aleaciones de alto cromo son empleadas para la fabricación de bolas de molino en industrias de procesamiento de minerales. Los usuarios y fabricantes requieren lograr mejores resultados técnicos-económicos en sus aplicaciones, por lo que necesitan aumentar los conocimientos relacionados con los aspectos estructurales de estos materiales. En este trabajo se realiza una investigación con vistas a establecer relaciones entre la estructura de las aleaciones y su comportamiento ante el impacto repetido que es un fenómeno característico en estos procesos. Se funden bolas con varias aleaciones hipo eutécticas, eutécticas, e hipereutécticas; se prueban en un equipo que simula el impacto repetido. Los resultados permiten comprobar los buenos resultados de aleaciones hipo eutécticas con relaciones de Cr/C altas y a su vez altos contenidos de Cr y de aleaciones eutécticas para menores relaciones de Cr/C y menores contenidos de Cr, en ambos casos los carburos eutécticos son de forma simétrica, regulares y no forman redes continuas de carburos asimétricos bordeando los granos, que presentan peores comportamiento en el impacto repetido y que son el caso de las hipoeutécticas con bajas relaciones Cr/C y las hipereutécticas donde aparecen también grandes carburos primarios.High Chromium alloys are used to manufacture grinding balls for the Industry of Construction Materials. Customers and users need to improve their knowledge about the relationships between microstructure and the parts damage in these alloys to obtain better technical-economics results. In this paper the results of a research to obtain different microstructures of eutectics, hipoeutectics and hipereutectics alloys are presented, searching for the lesser damage in these alloys. These alloys are tested in a repeated impact testing machine that simulate its mechanical behaviour .The results show a good behaviour for hipoeutectic alloys with high relations of Cr/C and high

Fabricación de la aleación Au-Si para utilización como soldadura blanda de aleaciones de oro

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Julián Tobón

2013-09-01

Full Text Available La Aleación Au-Si en su composición eutéctica presenta un punto de fusión cercano a los 369ºC y color similar al oro de alta ley. En este estudio se presentan resultados de fabricación de las aleaciones de oro con 2,5; 2,8 y 3,0 % de silicio, por medio de la fusión en un horno de plasma con atmósfera inerte de argón. Se realizó caracterización de composición química por espectroscopía de dispersión de energía (EDS y espectrometría de dispersión de longitud de onda (WDS, análisis metalográfico y microestructural por microscopía óptica, SEM y DRX, dureza y microdureza Vickers, evaluación del punto de fusión por DSC y determinación de las coordenadas colorimétricas SCIELab. A nivel microestructural las aleaciones muestran pequeñas formaciones dendríticas ricas en oro y el constituyente eutéctico formado por precipitados de silicio aciculares en una matriz de oro. Los resultados de dureza y microdureza dieron valores alrededor de los 110HV, presentándose un importante aumento en las propiedades mecánicas con respecto a las aleaciones tradicionales de oro de alta pureza. La temperatura de fusión para las aleaciones se ubicó en los 374°C, además de presentar un color muy cercano a los valores del oro puro.

Influencia de la composición y el tratamiento térmico en las propiedades mecánicas de aleaciones de bronce al aluminio

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Cenoz-Echeverría, I.

2007-08-01

Full Text Available Aluminium bronzes are copper-base alloys containing aluminium within the limits between 5-12 %. Additions of Fe, Ni and Mn are used as alloying elements forming a family of complex alloys noted for their exceptional strength and corrosion resistance. In present paper the Ni:Fe ratio and heat treatments have been analyzed by determining the mechanical properties for three different aluminium bronze alloys containing Cu-Al10-Fe3, Cu-Al10-Fe5-Ni5 and Cu-Al10-Fe4-Ni8. The effect of as cast, quenched and quenched and tempered structures has been investigated regarding hardness, proof and ultimate tensile strength, elongation, modulus of elasticity, Poisson ratio, fracture toughness, fatigue strength, crack propagation and Charpy impact properties. The influence of temperature has been studied by testing the elastic modulus, Poisson ratio, the proof stress, tensile strength and the Charpy impact properties at –20 °C, 24 °C and 100 °C.

Los cuproaluminios son aleaciones de cobre con contenidos de aluminio del 5-12 % que pueden incorporar hierro, níquel, y manganeso para formar una familia de aleaciones con unas excelentes propiedades de resistencia mecánica y a la corrosión. En el presente artículo se estudia el efecto que la relación Ni:Fe y que los tratamientos térmicos ocasionan en las propiedades mecánicas como dureza, límite elástico, tensión de rotura, alargamiento, módulo de elasticidad, coeficiente de Poisson, tenacidad a la fractura estática, resiliencia, fatiga y propagación de grieta. Para ello, se analizan tres aleaciones en tres estados. Las composiciones nominales son Cu-Al10-Fe3, Cu-Al10-Fe5-Ni5 y Cu- Al10-Fe4-Ni8. Las estructuras de las aleaciones son las correspondientes a: bruto de colada, temple y temple seguido de revenido. La caracterización del módulo de elasticidad y coeficiente de Poisson, así como los ensayos de tracción y resiliencia, se realizan a –20 °C, 24 °C y 100 °C.

Propiedades mecánicas y mecanismos de deformación en aleaciones del sistemas Fe-xMn-3,2Al-0,2C (12 ≤ x ≤ 43

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Rodríguez, V. F.

1998-05-01

Full Text Available Microstructure and mechanical properties of Fe-xMn-3,2Al-0,23C alloys with 12 ≤ x ≤ 43 (mass % at 77 and 290 K have been studied to determine the mechanisms controlling plastic deformation. Austenitic alloys (Mn ≥ 22 show an increase of elongation to failure with decreasing temperature of testing (inverse ductility. This behavior has been related to formation of deformation twins, which is favored at 77 K. Alloys with manganese content lower than 17 % present a two-phase microstructure (α' + γ. The martensite volume fraction increases as the manganese content decreases. These alloys show a loss of ductility, especially at 77 K. In contrast to asutenitic alloys, this different mechanical behavior has been associated with a TRIP mechanism (transformationinduced plasticity.

Se han estudiado la microestructura y las propiedades mecánicas a 77 y 290 K de una serie de aleaciones Fe-xMn-3,2Al-0,23C con 12 ≤ x ≤ 43 (% en masa con objeto de determinar los mecanismos que controlan la deformación plástica. Se ha comprobado que, en las aleaciones con estructura austenítica (Mn ≥ 22, el alargamiento a rotura aumenta al disminuir la temperatura de ensayo (ductilidad inversa. Este comportamiento se ha relacionado con un proceso de deformación por maclaje favorecido a 77 K. Las aleaciones con contenidos de manganeso < 17 % presentan una estructura bifásica (α' + γ, siendo mayor la fracción de volumen de martensita a medida que disminuye la concentración de manganeso. Estas aleaciones presentan una disminución del alargamiento a rotura especialmente a 77 K. El diferente comportamiento mecánico con respecto al de las aleaciones austeníticas se asocia a un proceso de transformación a martensita inducida por deformación (TRIP.

Análisis multielemental secuencial de aleaciones mediante plasma de argón generado por acoplamiento inductivo de radiofrecuencia

OpenAIRE

Farías de Funes, Silvia

1996-01-01

En el presente trabajo se describe la caracterización espectroscópica y analítica de un espectrómetro óptico constituido por el acoplamiento de una fuente de plasma inductivo de argón (IPC) y un monocromador programable de alta resolución, aplicable a la determinación secuencial de Mg, Mn, Cr, Mo en aleaciones de aluminio y de base Cu-Ni. Después de una discusión general sobre las características fundamentales del dispositivo instrumental empleado, se consideran aspectos básicos relacionados ...

Aluminio pulvimetalúrgico: desarrollo y mejora de sus aleaciones y materiales compuestos

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Ruiz-Navas, E. M.

2008-06-01

Full Text Available Powder metallurgy components demand is increasing in the last few years mainly due to the necessity of products assigned to automotive and aerospace industries, which has allow an important development of aluminium alloys and composites (AMCs. Consolidation of aluminium alloys by sintering present a main problem: the oxide layer that cover aluminium particles. Several alternatives are studied in this work as solution to the oxide layer problem during the sintering of series 2xxx aluminium alloys. One of these solutions is related to the addition of tin traces, and the other is the addition of a second alloy. Moreover, aluminium metal matrix composites are characterized by excellent properties as combination of properties which comes from the matrix and from the reinforcement. The last part of this study is focused to the analysis of one aluminium matrix composite as the influence of several quantities of reinforcement.

El auge en la demanda de componentes pulvimetalúrgicos destinados principalmente al sector automovilístico y aeroespacial ha permitido un fuerte desarrollo tanto de aleaciones como de MMCs base aluminio (AMCs. El principal problema a la hora de consolidar estos materiales vía pulvimetalúrgica es la capa de óxido que recubre a las partículas de aluminio. En este trabajo se presentan varias alternativas como solución a este problema, aplicadas a la consolidación de aleaciones de aluminio pertenecientes a la serie 2xxx, entre ellas, la adición de trazas de estaño y la adición de una aleación Al-Si. En cuanto a los materiales compuestos de matriz de aluminio, se caracterizan por presentar propiedades únicas como combinación de las propiedades individuales que caracterizan tanto a la matriz como al refuerzo. En la última parte de este trabajo se estudia la consolidación de un material compuesto así como la influencia de las distintas cantidades de refuerzo.

Influencia del rayado sobre la resistencia electroquímica de les aleaciones de NiTi tratadas por un nuevo tratamiento térmico para aplicaciones biomédicas

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Soualah, Lakhdar

2005-01-01

Las aleaciones de níquel-titanio son aleaciones que se utilizan cada vez más en aplicaciones biomédicas, por sus propiedades interesantes de superelasticidad, de memoria de forma, de resistencia a la corrosión y de biocompatibilidad. Sin embargo, los resultados obtenidos de su resistencia a la corrosión son muy variables, dependiendo del estado de superficie. Así, para mejorar, la resistencia a la corrosión de este material, se diseñó en un trabajo anterior un nuevo tratamie...

Metalografía a color en aleaciones Al-Si comerciales. Optimización de las técnicas de caracterización microestructural mediante microscopía óptica de reflexión

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Vander-Voort, G. F.

2010-10-01

Full Text Available The present demand on alloy production with improved quality requires the optimization of the metallographic procedures used on its characterization. Traditional etching techniques commonly employed for phase identification by optical metallography in aluminium alloys are not always suitable for a detailed analysis of existing phases, nor to accurately predict the mechanisms that govern the solidification process in certain detail. This work explores the potential of colour metallography to reveal at its best as-cast microstructures in Al-Si 12 alloys. For this purpose a colour etching technique, specifically developed for aluminium alloys and based on the Weck reagent. The application of such etchant has allowed the qualitative characterization of the microstructure. And it has also shown the advantages of colour metallography over black and white (B&W etching techniques.La demanda de aleaciones con calidades optimizadas conlleva la mejora continua de estas calidades, lo que viene suscitando la necesidad de mejora y optimización permanentes de las técnicas de caracterización metalográfica. Las técnicas de ataque tradicionales, utilizadas en la observación microscópica de las aleaciones de aluminio, no permiten un análisis detallado de la evolución microestructural de las fases presentes ni de parte de los mecanismos que rigen la solidificación. En el presente trabajo, se explora el potencial de la metalografía en color aplicada a las estructuras de solidificación de aleaciones Al-Si 12. Se ha utilizado un procedimiento de ataque en color, basado en un reactivo desarrollado porWeck para aleaciones de aluminio. El empleo de esta técnica ha permitido la evaluación cualitativa de la microestructura. La técnica ha permitido revelar características microestructurales que los métodos de ataque en blanco-negro no revelan.

Desarrollo de materiales de base Fe a partir de la síntesis de precursores por aleado mecánico

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González, A.

2005-12-01

Full Text Available Fe rich alloys with ZrNi or Nb and with non metallic B were developed by means of mechanical alloying. The material is nanocrystalline with a minoritary amorphous phase (about 12%. The reduction of the crystallite size is favoured by the addition of Zr, Nb or B. The mechanical alloying parameters were optimised to obtain a nanocrystalline state at low milling time. Furthermore, the apparent activation energy of the crystallisation processes was obtained by thermal treatment, controlled by differential scanning calorimetry. Typical values between 280 and 410 kJ mol-1 are associated to crystalline growth. The control of the crystal size is related to the kinetic study of the non-equilibrium transformations where the incipient phase as different composition that the initial phase.

Se han producido mediante síntesis mecánica aleaciones ricas en Fe, con Zr o Nb y con un no metal, B obteniéndose materiales nanoestructurados con una incipiente fase amorfa (entorno 12%. Tanto el Zr y el Nb como el B facilitan la reducción del tamaño de los nanocristales. Se han optimizado las condiciones de proceso, minimizando el tiempo de molturación. Además, el posterior tratamiento térmico, controlado mediante calorimetría diferencial, de las diferentes aleaciones permite obtener la energía de activación de los procesos de cristalización, con valores entre 280 y 410 kJ mol-1 asociados al crecimiento cristalino. El control del tamaño de los nanocristales se enmarca en el estudio de la cinética de las transformaciones fuera del equilibrio en las que la fase incipiente tiene composición diferente a la de la fase inicial.

Surpresa refrativa pós-facoemulsificação em distrofia corneana posterior amorfa Post-phacoemulsification refractive surprise in a posterior amorphous corneal dystrophy patient

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Giuliano de Oliveira Freitas

2010-02-01

Full Text Available Relato de um caso de surpresa refracional pós-operatória não pretendida em paciente portador de distrofia corneana posterior amorfa submetida à facoemulsificação. A provável causa do erro, bem como a conduta tomada a partir do reconhecimento da mesma, são discutidas neste relato.One case of post-phacoemulsification refractive surprise in a posterior amorphous corneal dystrophy patient is reported herein. Its likely causative factor, as well as our approach once it was recognized are discussed in this report.

Super plastic forming of the Cd-17.4 Zn alloy; Conformado superplastico de la aleacion Cd-17.4 Zn

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Llanes Briceno, J. A.; Torres Villasenor, G. [Instituto de Investigaciones en Materiales, UNAM, Mexico, D.F. (Mexico)

2000-06-01

In the present work the necessary steps to carry on the superplastic forming of the Cd-17.4 Zn alloy are defined. The use of either atmospheric pressure or gas pressure as forming tools is analyzed. The optimum values of the variables involved (temperature, maximum strain and sensitivity index) are determined while a method for the characterization of future superplastic alloys is set forth. The experimental characterization of the superplastic forming is achieved with free bulging of circular membranes of 12, 16, 24, 32 and 40 mm in diameter and with three different membrane thicknesses (0.4, 0.6 and 0.8 mm). [Spanish] Se definen los pasos necesarios para el conformado superplastico de la aleacion Cd-17.4Zn. Se comparan la presion atmosferica y el gas a presion como herramientas de conformado. Se determinan los valores optimos de las variables involucradas (temperatura, deformacion maxima e indice de sensibilidad) y se plantea una metodologia para la caracterizacion de futuras aleaciones superplasticas. El conformado superplastico se caracteriza experimentalmente mediante el inflado libre de membranas circulares de 12, 16, 24, 32 y 40 mm de diametro y tres diferentes espesores (0.4, 0.6 y 0.8 mm).

Desarrollo calorimétrico del proceso de precipitación en aleaciones Cu-Co-Si

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Donoso, E.

2005-12-01

Full Text Available Using differential scanning calorimetry (DSC the precipitation processes of supersaturated solid solutions of three Cu-Co-Si alloys, with a constant cobalt composition, were studied. Thermograms, and previous studies, reveal that the decomposition begins with cobalt precipitation. Clustering of cobalt initiates the silicon precipitation, finally Co₂Si stoichiometric particles are formed. Volume fractions are determined by the amount of cobalt present in these alloys. It is inferred that surplus silicon atoms retained in the solution increase the reaction rate. Kinetic parameters were calculated by a method based in the Mehl-Johnson-Avrami (MJA formalism. The lower activation energy obtained, associated with cobalt clustering is attributed to the contribution of quenched-in vacancies.

Mediante calorimetría diferencial de barrido (DSC se estudió el proceso de precipitación de soluciones sólidas supersaturadas de tres aleaciones de Cu-Co-Si, con composición de cobalto constante. Evaluaciones entalpimétricas y estudios previos, revelaron que la descomposición comienza con la precipitación de cobalto. El agrupamiento de átomos de cobalto inicia la precipitación del silicio, formándose finalmente partículas de composición estequiométricas de Co₂Si. Las fracciones volumétricas fueron determinadas en función de la cantidad de cobalto presente en estas aleaciones. Se infiere que el superávit de átomos de silicio retenidos en la solución aumenta la velocidad de reacción. Los parámetros cinéticos fueron calculados a partir de un método basado en el formalismo de Mehl- Johnson-Avrami (MJA. La energía de activación más baja obtenida, asociada con el apilamiento de cobalto, se atribuyó a la contribución de las vacantes retenidas por temple.

Relación estructura-propiedades en aleaciones inteligentes con memoria de forma Cu-Al-Ag de alta temperatura de transformación martensítica termoelástica

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Guilemany, J. M.

1998-05-01

Full Text Available New shape memory alloys have been developed in the last few years with high martensitic transformation temperatures. However, the highest martensitic transformation temperatures are lower than 200°C and they are achieved with very complex alloys. New Cu-Al-Ag shape memory alloys have been developed with martensitic transformation temperatures ranging from 250 to 400°C. It is really interesting to increase the knowledge of the phase stability behaviour when cycling the alloy above or below the martensitic transformation temperature because of the high temperatures involved. Two Cu-Al-Ag shape memory alloys with very different composition have been thermal cycled in a DSC following the amount of energy release during the forward and reverse transformation and the changes of the martensitic transformation temperatures in order to follow the phase changes that takes place during cycling.

En los últimos años, se han desarrollado nuevas aleaciones con memoria de forma, de altas temperaturas de transformación martensítica. Sin embargo, las temperaturas de transformación martensítica más elevadas son inferiores a 200°C e implican aleaciones de gran complejidad. Nuevas aleaciones con memoria de forma Cu-Al-Ag han sido desarrolladas con temperaturas de transformación entre 250 y 400°C. Es de gran importancia incrementar el conocimiento de la estabilidad de las fases durante el ciclado por encima o por debajo de la temperatura de transformación martensítica a causa de las altas temperaturas involucradas. Dos aleaciones con memoria de forma Cu-Al-Ag con muy diferente composición química han sido cicladas en el DSC midiendo la cantidad de energía liberada durante las transformaciones directa e inversa, así como los cambios en las temperaturas de transformación, con objeto de caracterizar las transformaciones de fase que tienen lugar durante el ciclado.

Elaboración de aleaciones de Cu-Al-Ni con efecto memoria de forma mediante pulvimetalurgia

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Pérez-Sáez, R. B.

1998-05-01

Full Text Available During the production of shape memory alloys, a very fine grain size should be obtained in order to obtain better mechanical properties and a good thermomechanical behaviour during cycling. The classically used grain refiners show some secondary effects on the martensitic transformations that could be at the origin of some technological problems. For this reason, a new processing method by powder metallurgy has been developed for this kind of alloys. The three proceeding stages are described: Atomization, hot isostatic pressing and hot rolling. The microstructure of the materials is characterized. The martensitic transformation and the thermomechanical properties are also studied.

En la elaboración de aleaciones Cu-Al-Ni con efecto memoria de forma es importante conseguir un tamaño de grano fino, para mejorar las propiedades mecánicas y el comportamiento durante el ciclado termomecánico. Clásicamente, esto se ha conseguido mediante la adición de refinadores de grano; sin embargo, los efectos secundarios que éstos producen pueden ser problemáticos. Por esta razón, se ha desarrollado un nuevo método de procesado de este tipo de aleaciones mediante pulvimetalurgia. En este trabajo se presenta el proceso de elaboración consistente en tres etapas: atomización, compactación isostática en caliente y laminación en caliente. Se estudia la microestructura del material, se caracteriza la transformación martensítica y se determinan las propiedades termomecánicas.

Medidas de efecto hall y resistividad en aleaciones magnéticas amorfas basadas en cofe

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Melo-Quintero, Jhon; Rosales-Rivera, Andrés; Giraldo-Daza, Helver

2012-01-01

En este trabajo, presentamos el diseño y la automatización de un sistema de medición de efecto Hall de corriente directa (DC) y corriente alterna (AC) usando un método de cuatro puntas. Este sistema consiste en una fuente de corriente directa y alterna (Modelo 6221 CD-CA, Keithley Instruments Inc.) acoplada a un nano-voltímetro (Modelo 2182 A, Keithley Instruments Inc.), y un electroimán (Phylatex) que proporciona campos magnéticos de hasta 0,8 T. Este sistema tiene varias capacidades de medi...

Superplastic forming of the Cd-17.4Zn alloy; Conformado superplastico de la aleacion Cd-17.4Zn

Energy Technology Data Exchange (ETDEWEB)

Llanes-Briceno, J. A.; Torres-Villasenor, G. [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)

2000-06-01

In the present work the necessary steps to carry on the superplastic forming of the Cd-17.4Zn alloy are defined. The use of either atmospheric pressure or gas pressure as forming tools is analyzed. The optimum values of the variable involved (temperature, maximum strain and sensitivity index) are determined while a method for the characterization of futures superplastic alloys is set forth. The experimental characterization of the superplastic forming is achieved with free bulging of circular membranes of 12, 16, 24, 32 and 40 mm in diameter and with three different membrane thicknesses (0.4, 0.6, 0.8 mm). [Spanish] Se definen los pasos necesarios para el conformado superplastico de la aleacion Cd-17.4 Zn. Se comparan la presion atmosferica y el gas a presion como herramientas de conformado. Se determinan los valores optimos de la variables involucradas (temperatura, deformacion maxima e indice de sensibilidad) y se plantea una metodologia para la caracterizacion de futuras aleaciones superplasticas. El conformado superplastico se caracteriza experimentalmente mediante el inflado libre de membranas circulares de 12, 16, 24, 32 y 40 mm de diametro y tres diferentes espesores (0.4, 0.6 y 0.8 mm). Se muestra la estructura perlitica (enfuiada al aive Cd-17.4Zn) y la estructura grano fino. Se muestra la profundidad de deformacion en tres espesores (0.4, 0.6, 0.8 mm) a P=200 Kpa y T = 200 y a T = 230.

Solución numérica de procesos de transferencia de calor en aleaciones con condiciones de contorno no lineales

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Alhama, F.

2005-12-01

Full Text Available Thermal properties of a great number of alloys, especially specific heat, show a sharply temperature dependence both during the phase change and the allotropic transformations. This fact, in conjunction with the existence of convection or radiation boundary conditions, or both simultaneously, increase the complexity of the transient heat transfer problem because of the inherent no linearity. The numerical model proposed for the solution of this problem is able to assume the above hypothesis as well as the temperature dependencies of the thermal conductivity. Applications to alloys are presented.

Las propiedades térmicas de numerosas aleaciones, especialmente la capacidad calorífica, acusan una marcada dependencia con la temperatura tanto en los cambios de fase como en las transformaciones alotrópicas. Este hecho, junto con la aplicación de condiciones de contorno de convección, radiación o ambas, simultáneamente, aumentan la complejidad del problema de transferencia de calor en los procesos transitorios debido a la no linealidad inherente. El modelo numérico propuesto para la solución de este problema es capaz de asumir las hipótesis anteriores así como las posibles dependencias de la conductividad térmica con la temperatura. Se presentan aplicaciones a procesos térmicos en aleaciones.

Modificación superficial de aleaciones de base aluminio (anodizadas y no anodizadas mediante recubrimientos de sílice

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García-Heras, M.

2004-04-01

Full Text Available Transparent and colourless silica coatings were deposited on anodising and non-anodising substrates of aluminium-base alloys (series 6063. Coatings were prepared by soLgel (dipping method from a silica alkoxide and a mixture of both silica alkoxide and silica alkylalkoxide. Preparations were optimised from viscosity, density, surface tension, and contact angle measurements. Densification was carried out at 60 and 120 °C. Reflectance attenuation of coated samples was analysed by UV-VIS-NIR spectroscopy. The results indicated that -10 % of attenuation is reached. Durability and resistance against degradation tests of the metal/coating system were undertaken by immersion into aqueous solutions. Electrochemical impedance measurements and potential corrosion of the metallic substrate for variable times were performed.

Se han depositado recubrimientos transparentes e incoloros de sílice sobre sustratos anodizados y no anodizados de aleaciones de base aluminio (serie 6063. Los recubrimientos se prepararon por sol-gel (inmersión-extracción a partir de un alcóxido de silicio y de una mezcla de alcóxido y alquilalcóxido de silicio. La optimización de las fonnulaciones se basó en medidas de viscosidad, densidad, tensión superficial y ángulo de contacto. La densificación se llevó a cabo a 60 y 120 °C. La atenuación de la reflectancia luminosa de las muestras recubiertas se analizó por espectroscopia UV-VIS-IRP. Los resultados indicaron que se alcanza casi un 10 % de atenuación. Los ensayos de durabilidad y resistencia a la degradación del sistema metal/recubrimiento se realizaron por inmersión en disoluciones acuosas, aplicando medidas de impedancia electroquímica y del potencial de corrosión del sustrato metálico, para tiempos variables.

Transformaciones de fase en aleaciones Zn-22%Al-2%Cu y Zn-22%Al-2%Cu-X (X = 1, 2 y 3%Ag envejecidas isotérmicamente

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Flores-Ramos, Alfredo

2014-12-01

Full Text Available The study of phase transformations that take place in Zn-22%Al-2%Cu and Zn-22%Al-2%Cu-X (X = 1, 2 and 3%Ag alloys was carried out using X-Ray Diffraction (XRD and Scanning Electron Microscopy (SEM. Alloys were homogenized at 350 °C during 10 days and quenched at ~2 °C. Subsequently, samples were aged at 200 °C for different times. The initial microstructure consists in a matrix of fine equiaxial grains of α and η phases for all the alloys. Besides isolated particles of ε and Φ were observed without and with Ag addition, respectively. During the aging, the four phase reaction, α + ε→η + τ’, takes place to obtain the equilibrium η, α and τ’ phases. However, the Ag addition promotes the formation of the Φ phase, which retards or inhibits the four phase reaction. The stability of the Φ phase is obtained with 3%Ag, which could improve the dimensional stability of the alloy for future industrial applications.En el presente estudio sobre las transformaciones de fase en las aleaciones Zn-22%Al-2%Cu y Zn-22%Al-2%Cu-X (X = 1, 2 y 3%Ag se utilizó Difracción de Rayos X (DRX y Microscopía Electrónica de Barrido (MEB. Las aleaciones fueron homogeneizadas a 350 °C durante 10 días, templadas a ~2 °C y posteriormente envejecidas a 200 °C durante diferentes tiempos. Todas las aleaciones ensayadas presentaron una microestructura inicial formada por una matriz de granos finos y equiaxiales de las fases α y η. Además, para las aleaciones sin Ag se observa la presencia de partículas de la fase ε (CuZn4 y de Φ ((Ag, Cu Zn4 en las que se adicionó Ag. Durante el envejecido, ocurre la reacción de cuatro fases, α + ε→η + τ’, para obtener las fases de equilibrio η, α y τ’. Sin embargo, la adición de Ag promueve la formación de la fase Φ, la cual retarda e incluso inhibe la reacción de cuatro fases. La estabilidad de la fase Φ se obtiene con 3%Ag, lo que podría mejorar la estabilidad dimensional de la aleación para

Desempeño ante la corrosión y tribocorrosión de aleaciones comerciales de aluminio anodizadas

OpenAIRE

Rodríguez, Samantha; Carrasquero, Edwuin J.; López, Luis M.; Fajardo, Jorge I.

2016-01-01

El presente trabajo muestra la evaluación del desempeño de dos aleaciones comerciales de aluminio anodizadas ante la corrosión y tribocorrosión. Para el anodizado se emplearon dos tipos de electrolitos distintos (H2SO4 y H2C2O4), un valor constante de densidad de corriente y dos tiempos de anodizado (30 y 45 minutos). Usando una de las técnicas de microscopía electrónica de barrido (MEB) y espectroscopía por dispersión de la energía de rayos X (EDX) se caracterizaro...

Comparison of brazed joints made with BNi-1 and BNi-7 nickel-base brazing alloys

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Zorc, Borut

2000-04-01

Full Text Available Kinetics of the processes are different with different types of brazing alloys. Precipitation processes in the parent metal close to the brazing gap are of great importance. They control the mechanical properties of the joint area when the brittle eutectic has disappeared from the gap. A comparative study of brazed joints on austenitic stainless alloys made with BNi-7 (Ni-P type and BNi-1 (Ni-Si-B type brazing alloys was made. Brazing alloys containing phosphorus behave in a different manner to those containing boron.

Las aleaciones de níquel se producen mediante tres sistemas de aleación: Ni-P, Ni-Si y Ni-B. Durante las reacciones metalúrgicas con el metal de base, la eutéctica frágil en la separación soldada puede transformarse en la solución dúctil-sólida con todas aleaciones. La cinética del proceso varía según el tipo de aleación. Los procesos de precipitación en el metal de base cerca de la separación soldada son de mucha importancia, ya que controlan las propiedades mecánicas de la área de unión después de desaparecer la eutéctica frágil de la separación. Se ha hecho un análisis comparativo de uniones soldadas en aleaciones austeníticas inoxidables realizadas con aleaciones BNi-7 (tipo Ni-P y BNi-1 (tipo Ni-Si-B. Las aleaciones que contienen fósforo se comportan de una manera diferente, tanto con el cambio de la eutéctica a la solución sólida, como con los procesos de precipitación en el metal de base cerca de la unión soldada.

Comportamiento térmico de aleaciones de aluminio de la serie 2XXX sinterizadas : estudio de la influencia de la aleación mecánica y adiciones de SN y TICN

OpenAIRE

Santos Sánchez, Enrique

2011-01-01

Las principales propiedades que hacen del aluminio un material atractivo son su baja densidad, su buena resistencia mecánica específica, su ductilidad y su elevada resistencia a la corrosión. Debido a la combinación única de estas propiedades, los materiales base aluminio están cada vez más integrados y demandados en la sociedad actual. Las propiedades termomecánicas de los metales y sus aleaciones se pueden mejorar mediante la utilización de diversos tipos de refuerzos; pueden ser fibras de ...

Estudio comparativo de los métodos de fabricación aditiva para el titanio y sus aleaciones

OpenAIRE

Romero Fuentes, Sergio

2017-01-01

El tema del proyecto que se plantea es el proceso de producción industrial de objetos conocido como fabricación aditiva o “Additive manufacturing”. Concretamente, se estudiará su aplicación a la fabricación de piezas de aleaciones de titanio. El proyecto recogerá los orígenes y evolución de la fabricación aditiva, dando una visión global de las distintas tecnologías y métodos aplicados a los distintos materiales. También revelará de forma general el estado del arte actual de la fabricación ad...

Soldadura TIG y MIG de las aleaciones de aluminio 6061 y 7020. Estudios microestructurales y de propiedades mecánicas

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Gómez de Salazar, J. M.

1998-05-01

Full Text Available The aluminium alloys of the 6XXX and 7XXX series, are actually considered of medium and high strength, and are been profusely used in different industries such as aeronautical, automotive, etc. However, its wide application as structural material needs of the proper development of their joining process. The present work describes the results obtained from the microstructural evaluation, both with optical and scanning electronic microscopies (OM and SEM, and of the mechanical one (hardness changes of the weld produced in the alloys using two different are welding techniques: GTAW (TIG and GMAW (MIG. For the last one, a filler metal with a composition of Al-5Mg, AWS denomination A5.10-92 (AA5356, has been used.

Las aleaciones de las series AA6XXX y AA7XXX están consideradas como de media y alta resistencia, y se utilizan con gran profusión en tecnologías como: aeronáutica, automoción, etc. Pero su aplicación como materiales estructurales pasa, sin duda, por el adecuado desarrollo de sus procesos de unión. En este trabajo, se realiza una evaluación microestructural, tanto mediante técnicas de microscopía óptica (MO como electrónica (MEB-EDS y de las propiedades mecánicas (evolución de la dureza de estas aleaciones, una vez que han sido sometidas a procesos de soldadura con arco, como son GTAW (TIG y GMAW (MIG, empleando un aporte de aleación de aluminio de composición Al-5Mg, cuya denominación es AWS A5.10-92 (AA5356.

Estudio de la corrosión de diferentes aleaciones en sales de carbonatos fundidos con la técnica de espectroscopía de impedancia electroquímica

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Pérez, F. J.

2000-06-01

Full Text Available In the present work the corrosion behavior of different alloys (AISI 304, AISI 430 and TiAl6V in molten carbonates at 650EC are compared. By using the Electrochemical Impedance Technique different corrosion parameters such as the corrosion rate and the oxyde concentration and others features of the different layers of corrosion products are "in situ" determined. Take into account, the corrosion product characterization by X-ray Diffraction (XRD, Scanning Electron Microscopy (SEM and Electrochemical impedance Spectroscopy (EIS a corrosion mechanism for every tested alloy is proposed. In all cases, the corrosion mechanisms during the first hours are similar to a high temperature oxidation mechanism. When the equilibrium is established, the lithiation began by the formation of different double-layers on the surface of Li-metal oxydes. At the end of the corrosion process, one or two inner layers of metallic oxydes and one or two outer layers of Li-metal oxydes were formed. The corrosion mechanisms of the stainless steels (AISI 304 ans AISI 310S are a function of their chromium contents. TiAl6V alloy showed the best behavior against the corrosion of molten carbonates by the formation of a protective layer of mixed Li-Ti oxydes.

En el presente trabajo se compara el comportamiento frente a la corrosión de diferentes aleaciones (aceros inoxidables AISI 304 y AISI 310S y aleación TiAl6V en un electrolito de carbonatos fundidos a 650°C. Con la técnica de impedancia se determina “in situ” la velocidad de corrosión de las aleaciones, la resistencia del electrolito, es decir, la concentración del óxido disuelto y otras características de las capas de productos de corrosión. Teniendo en cuenta la caracterización de los productos de corrosión mediante difracción de rayos X (XRD y microscopía electrónica de barrido (SEM y los resultados de espectroscopía de impedancia (EIS, se propone un mecanismo para cada una de las aleaciones. En

Comportamiento a la corrosión electroquímica de aleaciones MgAl con recubrimientos de materiales compuestos Al/SiCp mediante proyección térmica

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Pardo, A.

2010-04-01

Full Text Available The corrosion protection of Mg-Al alloys by flame thermal spraying of Al/SiCp composite coatings was evaluated by electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The volume fraction of SiC particles (SiCp varied between 5 and 30%. The as-sprayed Al/SiCp composite coatings revealed a high number of micro-channels, largely in the vicinity of the SiC particles, that facilitated the penetration of the electrolyte and the subsequent galvanic corrosion of the magnesium substrates. The application of a cold-pressing post-treatment reduced the degree of porosity of the coatings and improved the bonding at the coating/substrate and Al/SiC interfaces. This resulted in improved corrosion resistance of the coated specimens. The effectiveness of the coatings slightly decreased with the addition of 5-30 vol.% SiCp compared with the unreinforced thermal spray aluminium coatings.

Se estudia, mediante espectroscopía de impedancia electroquímica en solución 3,5 % NaCl, la protección frente a la corrosión de aleaciones Mg-Al recubiertas por proyección térmica con materiales compuestos Al/SiCp. Se varió la fracción de volumen de las partículas de SiC (SiCp entre 5 y 30 %. Los recubrimientos efectuados por proyección térmica revelan un elevado número de microcanales, en la vecindad de las partículas de SiC, que facilitan la penetración del electrolito originando procesos de corrosión galvánica en los substratos de las aleaciones de magnesio. Un tratamiento posterior mediante la aplicación de una presión en frío reduce el grado de porosidad de los recubrimientos y mejora la unión, tanto entre el substrato y el recubrimiento como entre las partículas de aluminio y SiC, mejorando la resistencia a la corrosión de las aleaciones recubiertas. La efectividad de los recubrimientos disminuye ligeramente con la adición de SiCp cuando se comparan con los mismos recubrimientos de aluminio sin refuerzo.

Predicción de la dureza de aleaciones Al-Cu-Zn en estado de colada y templado

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Villegas-Cárdenas, José D.

2014-06-01

Full Text Available This work presents a new experimental and numerical methodology in order to predict the hardness in the as-cast, and solution treated and quenched Al-Cu-Zn alloys. Chemical composition of alloys is located inside two straight lines represented by two equations. Eight different compositions were selected from each line. All the alloys were characterized for light microscope, scanning electron microscope, X-ray diffraction and Rockwell B hardness test. The equilibrium phases were obtained at different temperatures by Thermo-Calc. The microstructure characterization and regression analysis enabled to determine the phase transformations and two equations of hardness assessment. The combination of hardness equations and composition line equations permitted to estimate the hardness of any alloy composition inside this zone. This was verified by calculating hardness with the information reported in other works, with an error lower than 7% in the estimated hardness.Este trabajo presenta una nueva metodología experimental y numérica para pronosticar la dureza de las aleaciones Al-Cu-Zn, tanto en estado de colada como solubilizadas y templadas, cuyas composiciones químicas se encuentren dentro de dos líneas limítrofes, representadas por dos ecuaciones. De cada una de las líneas limítrofes se seleccionaron ocho composiciones diferentes que se caracterizaron por metalografía óptica, microscopía electrónica de barrido, difracción de rayos X y dureza. Las fases en equilibrio a diferentes temperaturas se obtuvieron por medio del programa Thermo-Calc. De la caracterización microestructural y análisis de regresión se obtuvieron los diferentes cambios de fase y dos ecuaciones de dureza. Al combinar las ecuaciones de dureza con las ecuaciones limítrofes se puede deducir la dureza de cualquier aleación con composición química dentro de esta zona. Para comprobar la exactitud de este método, se pronosticó la dureza de aleaciones a partir de los

Formación de porosidad durante la soldadura láser de Nd: YAG de onda continua en aleaciones de aluminio para aplicaciones automotrices

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Pastor, Mario

2000-04-01

Full Text Available Pore formation is an important concern in laser welding of automotive aluminum alloys. This paper investigates the influence of the laser beam defocusing on pore formation during continuous wave Nd: YAG laser welding of aluminum automotive alloys 5182 and 5754. It was found that the instability of the keyhole during welding was a dominant cause of pore formation while hydrogen rejection played an insignificant role. The defocusing of the laser beam greatly affected the stability of the keyhole. Finally, the mechanism of the collapse of the keyhole and pore formation is proposed.

La formación de poros es un aspecto de gran preocupación durante la soldadura láser de aleaciones de aluminio. En este trabajo se ha investigado la influencia del desenfoque del haz del láser sobre la formación de poros durante la soldadura láser (Nd: YAG de onda continua de las aleaciones de aluminio 5182 y 5754, las mismas que se usan en aplicaciones automotrices. Los resultados obtenidos indicaron que la causa dominante de formación de poros fue la inestabilidad de la cavidad de vapor o keyhole mientras que la influencia del hidrógeno fue prácticamente insignificante. El grado de desenfoque del láser tuvo gran influencia sobre la inestabilidad de la cavidad de vapor. Finalmente, en este artículo se propone el mecanismo de formación de poros a causa del colapso de la cavidad de vapor (keyhole.

Soldadura por fricción lineal de las aleaciones de titanio: caracterización de una soldadura longitudinal mediante ensayos a tracción

OpenAIRE

Grand, Arnaud

2006-01-01

Doble titulació La unión entre los álabes y el disco de una turbina de avión está en plena evolución por la aplicación del proceso de soldadura por fricción lineal (LFW) a las aleaciones de titanio. Ello permite conseguir una pieza única llamada blisk (blade + disk). Hasta ahora, la unión álabe / disco se hacía por un ensamblaje mecánico, pero estos sufren un fenómeno de fatiga por fretting en el punto de anclaje. A parte de evitar ese fenómeno, la soldadura por fricción lin...

Uso de sistemas bioactivos en la formación de apatita en la superficie de aleaciones base cobalto

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Cortés, D. A.

2004-10-01

Full Text Available To promote a bioactive surface on cobalt base alloys a biomimetic method was used. The metallic substrates were alkali- and heat-treated. The treated substrates were immersed in simulated body fluid for 21 days in presence of wollastonite ceramics or bioactive glass. Two different simulated body fluids were used, one with an ion concentration close to human blood plasma (SBF and other with a concentration of 1.5 times of that of the SBF (1.5SBF. Some tests were performed by soaking the samples for 7 days in SBF with bioactive material, followed by an immersion in 1.5SBF (re-immersion method. Tests with no bioactive material were also performed in all the cases. A bonelike apatite layer was formed on the substrates treated with wollastonite and bioactive glass. The morphology more similar to that of the existing bioactive systems was obtained by using the re-immersion method with wollastonite. No apatite layer was formed on the substrates treated with no bioactive material, apart from the cases when the re-immersion method was used.

Se utilizó un método biomimético con el fin de bioactivar la superficie de dos aleaciones base cobalto. Después de tratarse química y térmicamente, los sustratos se colocaron sobre wollastonita o biovidrio dentro de una solución fisiológica por 21 días. Se utilizaron dos soluciones, una con una concentración cercana a la del plasma sanguíneo humano (SBF y otra con una concentración 1.5 veces la de la anterior (1.5SBF. Además de sumergir los sustratos por 21 días en SBF o 1.5SBF, se trataron algunas muestras por 7 días en SBF con material bioactivo + 14 días en 1.5SBF (método de re-inmersión. Se realizaron también pruebas sin la presencia de material bioactivo. Se formó una capa de apatita de características similares a las de la fase mineral del hueso en la superficie de las muestras tratadas con wollastonita y biovidrio en todos los casos. Las capas cerámicas de morfología más similar a

Recubrimientos micro/nanoestructurados de aleaciones ligeras mediante proyección fría para la protección y reparación de componentes de elevado valor añadido: Estado del arte

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Bedoya, J.

2013-06-01

Full Text Available The Cold Gas Spray - CGS technique has greatly attracted the attention of the researchers in the last decade due to advantages compared to other conventional thermal spray processes. It presents outstanding characteristics such as high density coatings and absence of thermal degradation (oxidation or phase transformation. In addition, CGS is an efficient and green technology. This paper presents a bibliographic review related to micro/nanostructured aluminium-based coatings of by CGS on light alloy substrates. It provides an overview of the feasibility of using the Cold Gas Spray as a technique for the protection, recovery and repair of high value-added components, especially those made of light alloys (aluminium and magnesium base which, by their low density and mechanical properties, are widely used in several industrial sectors such as transport, aerospace and power generation.La técnica de Proyección Fría (Cold Gas Spray - CGS ha atraído considerablemente la atención de los investigadores en la última década dadas sus ventajas respecto a otras técnicas convencionales de proyección térmica, como la obtención de recubrimientos de altísima densidad y sin degradación (ya sea oxidación o cambios de fase, además de su gran potencial a nivel económico y ambiental por ser un proceso más eficiente y respetuoso con el medio ambiente. Este estudio presenta una revisión bibliográfica respecto a la obtención de recubrimientos micro/nanoestructurados base aluminio mediante proyección fría sobre sustratos de aleaciones ligeras, el cual permitirá tener una visión global sobre la viabilidad de utilizar la proyección fría como técnica para la protección, recuperación y restauración de componentes de elevado valor añadido, especialmente aquéllos fabricados con aleaciones ligeras (base aluminio y magnesio los cuales, por su baja densidad y propiedades mecánicas, son ampliamente utilizados en diferentes sectores de la industria

Factores termodinámicos y microestructurales para el diseño de aleaciones tixotrópicas

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Azpilgain, Z.

2005-12-01

Full Text Available Semisolid forming is an hybrid process between forging and casting, that is based on the thixotropic properties of some alloys that have been shake during their solidification process. This new process presents some advantages compared with traditional processes, like less quantity of defects than in die casting parts, or the chance to obtain more complicated parts than in forging processes, to mention some. In this article is presented the work that is being carried out at MGEP in the field of semisolid forming of aluminium alloys. Microstructural and thermodynamic quality factors which allow to characterize the material thixotropic behaviour are described.

El proceso de conformado en estado semisólido es un proceso híbrido entre la fundición y la conformación por deformación, que se basa en las propiedades tixotrópicas que presentan algunos materiales que han sido agitados durante su proceso de solidificación. Este nuevo proceso presenta una serie de ventajas respecto a los procesos tradicionales, como son un menor número de defectos que las piezas inyectadas o la posibilidad de conformar formas más complejas que por deformación en estado sólido, por citar algunos. En este artículo se presenta el trabajo que se está realizando en MGEP en el campo del conformado en estado semisólido de aleaciones de aluminio. Se describen los indicadores de calidad, tanto microestructurales como termodinámicos, que permiten caracterizar la adecuada tixotropía del material.

Thermal treatment of the amorphous base alloy Fe 2605SA1, analysis of its defects and microhardness; Tratamiento termico de la aleacion amorfa base Fe 2605SA1, analisis de sus defectos y microdureza

Energy Technology Data Exchange (ETDEWEB)

Contreras V, J.A.; Cabral P, A.; Garcia Santibanez S, F.; Ramirez, J.; Lopez M, J.; Villaverde L, A.; Montoya E, A.; Merino, F.J. [Facultad de Ciencias, Universidad Autonoma del Estado de Mexico. El Cerillo Piedras Blancas, 50000 Toluca, Estado de Mexico (Mexico)

2007-07-01

By means of the use of the positron lifetime technique those characteristics of the present crystalline defects in an amorphous base alloy Fe (SA1) are determined, when this is subjected to thermal treatments from 293 K until 808 K. Also, some results about the microhardness and electric resistivity are presented. (Author)

Proposición de dos aleaciones fundidas para su estudio en la construcción de martillos de molinos desmeduladores de bagazo. // Proposition of two casted alloys for their study in the construction of bagasse crush mills hammers.

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F. Diez Torres

2005-05-01

Full Text Available El presente trabajo constituye un análisis teórico que tiene como objetivo la determinación de cuáles serían las aleaciones autilizar y la tecnología de colada adecuada para la fabricación de los martillos de los desmeduladores de bagazo a partir dealeaciones fundidas resistentes al desgaste.Se analizan los resultados de las experiencias realizadas con recubrimientos por soldadura de recargue duro, con los cualesse corroboraron las hipótesis sobre los mecanismos de desgaste ocurrentes y las estructuras metalográficas adecuadas paracada perfil del martillo.Se propone la realización de ensayos de campo con martillos construidos con hierros al cromo debido a que se caracterizanpor poseer carburos de cromo con la posibilidad de obtener diferentes contenidos y distribución de los mismos en matricesque van desde la austenítica a martensítica. Se propone realizar los ensayos con las aleaciones 15-3 y 20-3 con y sintratamiento térmico y con colada en coquilla, con diferentes velocidades de enfriamiento en cada perfil de trabajo con el finde obtener la estructura metalográfica adecuada.Palabras claves: Aleaciones, martillos desmenuzadores de bagazo, recubrimiento por soldadura.____________________________________________________________________________Abstract.The present paper constitutes a theoretical analysis for the determination of an appropriate cast technology determinationfor the production of bagasse crush hammers with wear cast iron alloys.The results of welding hard facing coatings with the wear mechanisms hypothesis and appropriate metallographic structureswere corroborated.Field tests with chromium cast iron hammers are proposed due that this alloys is characterized to posses chromiumcarbides, with the possibility to obtain different contents and distribution in austenitic, martensitic or intermediate metalmatrices. Tests with 15-3 and 20-3 alloys with or without thermal treatment and metal mold casting with different

Magnesium Cermets and Magnesium-Beryllium Alloys; Cermets au magnesium et au magnesium-beryllium; Metallokeramicheskie magnievye i magnievo-berillievye splavy; Cermets de magnesio y aleaciones de magnesio y berillio

Energy Technology Data Exchange (ETDEWEB)

Ivanov, V. E.; Zelenskij, V. F.; Fajfer, S. I.; Zhdanov, S. M.; Maksimenko, V. I.; Savchenko, V. I. [Fiziko-Tekhnicheskij Institut an USSR, Khar' kov, SSSR (Russian Federation)

1963-11-15

{sup o}C une forte resistance a l'oxydation pendant plus de 12 000 a 14000 heures. La duree de leur resistance a la chaleur est determinee avant tout par leur teneur en beryllium et augmente avec celle-ci. Les alliages PMB se distinguent egalement par leur forte resistance a une surchauffe de courte duree. Les cermets au magnesium et au magnesium-beryllium, dont une des particularites caracteristiques est la resistance accrue a la chaleur, peuvent trouver une large application dans differents domaines de la technique. (author) [Spanish] Los autores exponen algunos resultados de sus estudios sobre cermets de magnesio-oxido de magnesio y sobre aleaciones superrefractarias de magnesio y berilio, preparadas mediante procedimientos pulvimetalurgicos. La incorporacion de proporciones insignificantes de oxido de magnesio finamente disperso al magnesio basta para provocar un aumento de resistencia cuya magnitud crece con la concentracion del primero, aunque las variaciones de concentracion del oxido entre el 0,3 y el 5% en peso solo influyen ligeramente en las correspondientes variaciones de la tension de rotura (ensayo rapido) en todo el intervalo de temperaturas estudiado. Para los cermets se observan los valores siguientes a 20{sup o}C: {sigma}{sub {beta}} = 28 a 31 kg/mm{sup 2} y {delta} = 3,5 a 4,5%, mientras que a 500{sup o}C resulta {sigma}{sub {beta}} = 2,6 a 3,2 kg/mm{sup 2} y {delta} = 30 a 40%. El efecto positivo de la fase oxido finamente dispersa se manifiesta sobre todo en los ensayos prolongados. Para los cermets de magnesio, {sigma}(300)/100 adopta el valor 2,2 kg/mm{sup 2}. Caracteriza particularmente a estas mezclas la constancia de las propiedades de resistencia al variar la temperatura, que se debe ante todo a la estabilidad termodinamica, dentro de la matriz metalica, de la fase oxido que acrecienta la resistencia. El empleo de los metodos pulvimetalurgicos ha permitido obtener aleaciones d e magnesio y berilio superrefractarias con elevada concentracion

Efecto de las variables de proceso sobre el comportamiento a flexión de aleaciones Ti - 3% at. X (X = Nb, Ta obtenidas por pulvimetalurgia

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Franconetti, P.

2013-12-01

Full Text Available Niobium and tantalum are added to titanium alloys to form new beta alloys with higher biocompatibility for biomedical applications. Both elements have a high melting point, that is the reason for their limited solid state diffusion. In this work samples of titanium with 3% at. niobium and tantalum have been manufactured by powder metallurgy. The effect of the compacting pressure, temperature and the sintering time on the strength, elasticity and ductility in bending has been studied. The results show that both elements behave similarly: flexural strength increases between 20-25%, elasticity between 0-10% and ductility over 150%. Therefore, the addition of these elements is beneficial to mechanical properties. Statistical analysis shows that the effect of temperature and pressure are important, while the effect of time is insignificant and even harmful in these alloys.El niobio y el tantalio se añaden al titanio para formar nuevas aleaciones beta con mayor biocompatibilidad para aplicaciones biomédicas. Ambos elementos tienen un elevado punto de fusión, por lo que su difusión en estado sólido es limitada. En este trabajo se han fabricado por pulvimetalurgia muestras de titanio con 3% atómico de niobio o tantalio. Se estudia el efecto de la presión de compactación, la temperatura y el tiempo de sinterizado sobre la resistencia, la elasticidad y la ductilidad a flexión. Los resultados muestran que ambos elementos se comportan de manera semejante: aumenta la resistencia entre 20-25%, la elasticidad entre 0-10% y la ductilidad en más de un 150%. Por tanto, la adición de estos elementos es beneficiosa para las propiedades mecánicas. El análisis estadístico muestra que el efecto de la temperatura y presión son importantes mientras que el efecto del tiempo es poco significativo e incluso perjudicial en estas aleaciones.

Hydrogen absorption in Mg1.95Ti0.05Ni0.95Cu0.05 alloy prepared with mechanical alloying and thermal treatment; Absorcion de hidrogeno en la aleacion Mg1.95Ti0.05Ni0.95Cu0.05 preparada por aleado mecanico y tratamiento termico

Energy Technology Data Exchange (ETDEWEB)

Martinez, Juan Bonifacio; Urena Nunez, Fernando [Instituto Nacional de Investigaciones Nucleares, Ocoyoacac, Estado de Mexico (Mexico)]. E-mail: juan.bonifacio@inin.gob.mx

2009-09-15

This work presents hydrogen absorption in quaternary alloy Mg1.95Ti0.05Ni0.95Cu0.05 obtained by the mechanical alloying method, followed by thermal treatment in ultra-high pure argon atmosphere. The composition of the phases, microstructure and morphology of ground powders and with thermal treatment were characterized by DRX, SEM/EDS and TEM. After 20 hours of mechanical grinding and recooked at 300 degrees Celsius/1h in argon atmosphere, the quaternary alloy has a Mg{sub 2}Ni crystalline hexagonal structure with a crystallite size under 10 nm. The absorption measurements were performed under a pressure of 0.2 to 1.2 MPa at a temperature of 200 degrees Celsius in a micro-reactor. The quantification of absorption-desorption of hydrogen in the intermetallic was conducted in a TGA-DSC simultaneous calorimeter. Metallic hydride-dehydride powder was characterized with SEM and XRD. [Spanish] En este trabajo se presenta la absorcion de hidrogeno en la aleacion cuaternaria Mg1.95Ti0.05Ni0.95Cu0.05 obtenida por el metodo de aleado mecanico, seguida de tratamiento termico en atmosfera de argon de ultra alta pureza. La composicion de las fases, microestructura y morfologia de los polvos molidos y con tratamiento termico fue caracterizada por DRX, SEM/EDS y TEM. Despues de 20 h de molienda mecanica con recocido a 300 grados Celsios/1h en atmosfera de argon, la aleacion cuaternaria tiene una estructura cristalina hexagonal Mg{sub 2}Ni con tamano de cristalito menor a 10 nm. Las mediciones de absorcion fueron realizadas bajo una presion de 0.2 a 1.2 MPa a una temperatura de 200 grados Celsios en un micro-reactor. La cuantificacion de absorcion-desorcion de hidrogeno en el intermetalico se realizo en un calorimetro simultaneo TGA-DSC. Se determino que la cantidad maxima absorbida de hidrogeno en la aleacion cuaternaria fue de 3.24% en peso cuando la presion fue de 0.8 MPa a dicha temperatura. Polvos metalicos hidrurados-deshidrurados se caracterizaron por SEM y XRD.

Influencia del contenido metálico sobre las constantes ópticas de laminas delgadas amorfas de composición As33S67 fotodopadas con Ag

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Márquez, E.

2000-08-01

Full Text Available Agx(As0.33S0.67100-x amorphous chalcogenide thin films have been prepared by the process of photodissolution or photodoping, reaching silver concentrations of up to 16.5 at. %. The optical constants of the photodoped thin-film samples have been calculated from the envelopes of the transmission spectra, taken at normal incidence. The dispersion of the refractive index was analysed on the basis of the single-oscillator model proposed by Wemple and DiDomenico. This model allows obtaining structural information of the silver-photodoped layers from optical data. The optical absorption edge is described using the non-direct transition model suggested by Tauc, and a clear decrease of the optical gap of the photodoped product, with the silver content, has been found.Se han preparado láminas delgadas amorfas calcogenuras de composición Agx(As0.33S0.67100-x, mediante el fenómeno fotoinducido conocido como fotodisolución o fotodopaje, alcanzándose concentraciones de Ag en las muestras de hasta un 16.5 % at. Las constantes ópticas de las láminas fotodopadas, se han determinado haciendo uso de un método de caracterización basado en las envolventes de los espectros de transmisión óptica obtenidos en incidencia normal. El análisis de la dispersión del índice de refracción se ha realizado siguiendo el modelo propuesto por Wemple-DiDomenico, basado en la aproximación del oscilador armónico simple. Este modelo ha permitido obtener información estructural de las láminas fotodopadas, a partir de los resultados ópticos. El borde de absorción óptica de las láminas fotodopadas se ha analizado sobre la base del modelo de transición no directa propuesto por Tauc, encontrando una disminución del gap óptico del producto fotodopado, con el contenido de plata.

Stainless-Steel-Gadolinium Alloys; Alliages Acier Inoxydable-Gadolinium; Splavy iz nerzhaveyushchej stali i gadoliniya; Aleaciones de Acero Inoxidable-Gadolinio

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Copeland, M.; Kato, H. [Albany Metallurgy Research Center, Bureau Of Mines, United States Department of the Interior, Albany, OR (United States)

1964-06-15

mineures ont une grande influence sur les structures resultant de traitements equilibrants et sur les possibilites de transformation des aciers. Lorsque le gadolinium est melange a de l 'acier au chrome et au nickel, deux phases mineures, Fe{sub 9}Gd et Ni{sub 7}Gd, fondent a 1080 Degree-Sign C, ce qui impose une limite superieure aux temperatures de traitement a chaud et de transformation. Les auteurs ont pu facilement transformer des alliages comprenant jusqu'a 5 Degree-Sign Io en poids de gadolinium et determiner leurs caracteristiques mecaniques et leur resistance a la corrosion. Ils n'ont observe aucun changement dans les caracteristiques mecaniques de l'acier ou sa resistance a la corrosion par l'eau chaude, lorsqu'ils lui ont ajoute'jusqu'a 3% en poids de gadolinium. En raison des limites imposees aux temperatures de transformation des aciers au chrome et au nickel par le point de fusion des phases mineures, les auteurs ont etudie les effets du gadolinium sur des aciers au chrome. Ils ont releve une seule phase mineure qui fond a 1320 Degree-Sign C en etudiant l 'isoplethe du gadolinium a 10% en poids dans l 'alliage chrome-fer-gadolinium. Cette propriete permettrait d'equilibrer et de transformer ces aciers au gadolinium aux temperatures auxquelles on opere normalement. (author) [Spanish] En vista de la excelente resistencia a la corrosion de los aceros inoxidables y del interes que presenta el gadolinio como veneno nuclear, se han estudiado aleaciones de esos dos metales. El gadolinio fue aleado con aceros inoxidables de tipo AISI-304 y al cromo, y se estudiaron las relaciones de fase, la facilidad de trabajo y las propiedades de estas aleaciones. Se observo que en las aleaciones que contienen bajos porcentajes de gadolinio, los puntos de fusion de las fases menores ejercen un efecto muy marcado sobre las estructuras resultantes de los tratamientos de equilibracion y sobre la facilidad de trabajo de los afceros. Cuando se alea el gadolinio con acerce al cromo

Estudio de la oxidación a elevada temperatura de ocho aleaciones en atmósferas de combustión de biomasa

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Berlanga-Labari, C.

2008-08-01

Full Text Available The combustion of biomass, especially wheat straw, generates very corrosive media particularly near the superheater tubes. Chlorine is known to be the main corrosive agent in biomass-fired plants. This paper focuses on the study of the corrosivity of such environments composed of gases and ashes, at high temperature, on eight commercial alloys with different chromium and nickel contents. These have been: AISI 347 CG (1.4550, AISI 347 FG(1.4550, AISI 316LN (1.4910, ESSHETE 1250 (1.4982, AC 66 (1.4877, X20CrMoV12:1 (1.4922 and AISI 347 coated with Inconel 625 and Inconel 686. Corrosion tests in the boiler have been performed during 8.000 h and 15.000 h at temperatures between 500 °C y 550 °C in the biomass plant of Sangüesa (Navarra, Spain. Experimental results showed an unacceptable behaviour far the martensitic steel, acceptable far the austenitics and good far the inconels. The appearance of the corrosion attack was also investigated to obtain understanding of the corrosion mechanism. The corrosion mechanism by molten salts has been rejected. The active oxidation corrosion mechanism has been proposed as the most probable in order to interpretate the corrosion behaviour of these materials in these environments.

La combustión de biomasa, especialmente de paja de cereal, genera un ambiente muy corrosivo, particularmente, cerca de los tubos sobrecalentadores. El cloro es el principal agente corrosivo en las plantas de biomasa. Este trabajo se centra en comprobar el comportamiento de ocho aleaciones comerciales en una ambiente de combustión de biomasa. Los materiales estudiados han sido las siguientes: AISI 347 CG (1.4550, AISI 347 FG (1.4550, AISI 316LN (1.4910, ESSHETE 1250 (1.4982, AC 66 (1.4877, X20CrMoV12:1 (1.4922 y AISI 347 recubiertos con Inconel 625 e Inconel 686. Los ensayos se han realizado en la caldera de la planta de biomasa de Sangüesa (Navarra, España durante 8.000 y 15.000 h a una temperatura de 500-550 °C. Los

Corrosión e inhibición en aleaciones de aluminio de media resistencia

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Davó, B.

2004-12-01

Full Text Available The use of chromâtes in aluminum alloys with aeronautical applications has been limited because of the high toxicity of these compounds. This has spurred intensive efforts to develop alternative effective and innocuous inhibitors. In this work, corrosion inhibition of a light and high strength Al-Li-Cu alloy (8090 is studied in NaCl solutions with CeCl₃ and LaCl₃ lanthanide salts added. The corrosion rate is reduced at least one order of magnitude with concentrations between 100-10,000 ppm. SEM, EDS and XPS techniques are used to characterize the rare earth cations incorporated into the surface as oxides and hydroxides.

La elevada toxicidad de los cromatos limita cada vez más su uso en los tratamientos superficiales que se aplican a las aleaciones de aluminio en la industria aeronáutica. Por ello, es urgente encontrar inhibidores, no sólo tan eficaces como los cromatos sino, también, inocuos. En este sentido, se ha estudiado la inhibición de la corrosión de una aleación ligera de alta resistencia Al-Li-Cu (8090 en soluciones de NaCl con sales lantánidas de CeCl₃ y LaCl₃. Se ha comprobado que concentraciones comprendidas entre 100 y 10.000 ppm disminuyen la cinética de corrosión, al menos, un orden de magnitud. La superficie se modifica por la formación de una capa de óxidos e hidróxidos del catión lantánido que se ha caracterizado mediante SEM, EDS y XPS.

Influencia del cobre en la transformación de fase de la aleación Zn - 22 % p Al, durante la homogenización

OpenAIRE

Rangel Lara, S.; Bernal, J. L.; Ita de la Torre, A. de

2011-01-01

Las aleaciones fueron producidas por fundición y enfriadas en aire quieto a temperatura ambiente, la microestructura dendrítica fue analizada en un trabajo anterior [1]. Muestras de las aleaciones obtenidas fueron sometidas a un tratamiento de homogenización a 375 °C por 120 horas, se observó la modificación de la microestructura a 60, 100 y 120 horas en las aleaciones Zn - 22 % p Al y Zn - 22 % p Al - 2 % p Cu. Las fases presentes en las aleaciones se identificaron por microscopia óptica. Se...

Efecto de la adición de un 10 % en volumen de cromo en el comportamiento a tracción de aleaciones pulvimetalúrgicas NiAlCr

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García-Barriocanal, J.

2005-08-01

Full Text Available The mechanical properties of Ni₃Al-Cr reinforced with 10% in volume fraction of chromium particles produced by powder metallurgy have been studied. For this purpose, milled powders with composition of Ni-20.9Al-8Cr-0.49B (% at. with and without the addition of 10% in volume fraction of chromium particles have been produced. Both alloys were consolidated by hot isostatic pressing (HIP. After HIP, heat treatment was applied to homogenize the microstructure. The chromium reinforcement has an important effect in the yield strength and ultimate strength increase. The reinforced alloy presents a yield strength of 1300 MPa at room temperature with respect to 800 MPa for the un-reinforced material. After heat treatment, the yield strength of both alloys does not change significantly. However, a decrease in ductility and ultimate tensile strength have been observed

En este trabajo se estudia la influencia de la adición de un 10 % en volumen, de cromo en las propiedades mecánicas de aleaciones Ni₃Al-Cr procesadas por vía pulvimetalúrgica. Para ello se prepararon dos aleaciones: la primera, se obtuvo por molienda de polvo de composición Ni-20,9Al-8Cr-0,49B (% at. y, a la segunda, se le añadió un 10 % en volumen de partículas de cromo, mediante un proceso de mezcla, previo al de molienda. Ambas, fueron consolidadas mediante compactación isostática en caliente (HIP y, por último, se les aplicaron tratamientos térmicos para homogeneizar la microestructura. Los resultados experimentales han mostrado que el refuerzo de cromo tiene como efecto un importante aumento del límite elástico y de la resistencia. Así, el material reforzado presenta un límite elástico cercano a 1.300 MPa, a temperatura ambiente, frente a los 800 MPa que presenta el material sin reforzar, a la misma temperatura. En relación con las propiedades mecánicas de los materiales tratados térmicamente, se observa que ambos experimentan un acusado

Uranium-Based Cermet Alloys; Cermets a base d'uranium; Metallokeramicheskie splavy na osnove urana; Cermets a base de uranio

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Ivanov, V. E.; Zelenskij, V. F.; Voloshchuk, A. I.; Grishok, V. N. [Fiziko-Tekhnicheskij Institut an USSR, Khar' kov, SSSR (Russian Federation)

1963-11-15

The paper describes certain features of dispersion-hardened uranium-based cermets. As possible hardening materials, consideration was given to UO{sub 2}, UC, Al{sub 2}O{sub 3}, MgO and UBe{sub 13}. Data were obtained on the behaviour of uranium alloys containing the above-mentioned admixtures during creep tests, short-term strength tests and cyclic thermal treatment. The corrosion resistance o f UBe{sub 13}-based uranium alloys was also studied. )author) [French] Les auteurs decrivent certaines proprietes de cermets a base d'uranium, dont la resistance a ete accrue a l'aide de particules dispersees. Les materiaux utilises a cette fin sont notamment: UO{sub 2}, UC, Al{sub 2}O{sub 3}, MgO et UBe{sub 13}. Les auteurs indiquent les donnees obtenues sur le comportement des cermets a l'uranium; durant les essais de fluage, les essais de resistance a court terme et le traitement thermique cyclique, en mentionnant les substances ajoutees. Ils etudient enfin la resistance a la corrosion des cermets d'uranium et UBe{sub 13}. (author) [Spanish] Los autores describen algunas propiedades de los cermets a base de uranio, reforzados por particulas de diversos compuestos en dispersion. En calidad de posibles materiales de refuerzo, ensayaron el UO{sub 2}, el UC, el Al{sub 2}O{sub 3}, el MgO y el UBe{sub 13}. Obtuvieron datos sobre el comportamiento de esas aleaciones en ensayos de fluencia, ensayoe rapidos de resistencia y tratamiento termico ciclico. Por ultimo, estudiaron la resistencia a la corrosion de las aleaciones de uranio a base de UBe{sub 13}. (author) [Russian] Daetsya opisanie nekotorykh svojstv metallokeramicheskikh splavov urana, uprochnennykh dispersionnymi chastitsami. V kachestve vozmozhnykh uprochnyayushchikh materialov izuchalis' UO{sub 2}, UC, Al{sub 2}O{sub 3} , MgO i UBe{sub 13}. Polucheny dannye o povedenii splavov urana s ukazannymi primesyami pri kripovykh ispytaniyakh, pri kratkovremennykh prochnostnykh ispytaniyakh i pri tsiklicheskoj termoobrabotke

Efectos de la adición del tantalio sobre la biocompatibilidad de los implantes de titanio

OpenAIRE

Bolaños Rodríguez, Víctor

2016-01-01

Programa de doctorado: Tecnología Industrial (Bienio 2006-2008). La fecha de publicación es la fecha de lectura [ES]El desarrollo de esta Tesis trata de comprobar el comportamiento a nivel de biocompatibilidad y osteointegración de la adición de Tantalio en diversas aleaciones de Titanio como elemento base. Nos preguntamos ¿ porqué utilizar Tantalio en estas aleaciones ?. Todo surge por unas intervenciones quirúrgicas realizadas en el Hospital Universita...

Estudio del comportamiento en caliente del Inconel 718

OpenAIRE

Thomas, Amandine

2005-01-01

Las aleaciones Inconel son superaleaciones base níquel-cromo, que cubren un amplio espectro de composiciones y de propiedades. Son superaleaciones que tienen buenas propiedades de resistencia mecánica y a la corrosión que se mantienen a temperaturas altas. Las aplicaciones de estas aleaciones son muy amplias: recipientes para tratamiento térmico, turbinas, aviación, plantas nucleares generadoras de energía, etc... El Inconel 718 en particular es una aleación endurecible por precipitación, ...

Effect of NaCl upon an Al-Si casting alloy hipoeutec; Efecto del NaCl sobre una aleacion de Al-Si hipoeutectica vaciada

Energy Technology Data Exchange (ETDEWEB)

Martinez Delgado, E.J.; Ortega de la Rosa, R. [Istituto Tecnologico de Zacatecas, Zacatecas (Mexico)]. E-mail: enriquemartinez_1999@yahoo.com; rubin_ortega_2002@yahoo.com.mx; Cisneros Guerrero, M.A. [Instituto Tecnologico de Saltillo, Saltillo, Coahuila (Mexico)]. E-mail: cisneros@its.mx; Haro Rodriguez, S. [Universidad Autonoma de Zacatecas, Zacatecas, Zacatecas (Mexico)]. E-mail: haros907@hotmail.com

2009-10-15

This work, comprehends the study about the effect of NaCl kind Halite upon the morphology of eutectic Silicon and porosity in a cast hipoeutectic Al-Si alloy. The melting was carried out in two furnaces, the first to combustion of LP gas in graphite crucible to increase the content of Si in the alloy from 0.13 to 5% wt using metallic silicon with a purity of 99.35% wt, and the second of electric resistances in the same kind of crucible to control the temperature at 750 degrees Celsius. The melting material was casting into molds of sand shell. To add the salt into the metallic bath, two techniques were used; one with injection by means of Argon gas and the other on by gravity, both cases three quantities of salt were used, 0.5, 1.5 and 2.5% wt respectively, powdered and preheated at 150 degrees Celsius during 60 min. The obtained samples were analyzed metallographily evidencing the modification of the eutectic Si, presenting the best results the samples with 1.5 and 2.5% wt of salt added by gravity. Too was obtained effect of Salt upon the degassing of bath metallic, where the simples with 1.5% wt presented the best results. Finally, by means of Scanning Electron Microscopy, the precipitates present were characterized in the samples. [Spanish] Este trabajo comprende el estudio del efecto del NaCl tipo Halita sobre la morfologia del Si eutectico y la porosidad en una aleacion fundida Al-Si hipoeutectica. La fusion se llevo a cabo en dos hornos, el primero a combustion con gas LP en crisol de grafito con la finalidad de incrementar el contenido de Si en la aleacion de 0.13 a 5% en peso, utilizando silicio metalico con una pureza de 99.35%, y el segundo de resistencias electricas en el mismo tipo de crisol para controlar la temperatura a 750 grados Celsios. El material fundido fue vaciado en modelos de arena. La sal se anadio al bano metalico a 0.5, 1.5 y 2.5% en peso, respectivamente, pulverizada y precalentada a 150 grados Celsios durante 60 min, mediante dos

Determination of the Uranium Content of Aluminium Alloys; Determination de la Teneur en Uranium dans les Alliages a Base d'Aluminium; Opredelenie soderzhaniya urana v splavakh na osnove alyuminiya; Determinacion del Contenido de Uranio en las Aleaciones a Base de Aluminio

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Gerard, J.; Van Hove, L. [S.A. Metallurgie et Mecanique Nucleaires Dessel (Belgium)

1965-09-15

exact de la teneur en {sup 235}U. En conclusion, on montre que la mesure de la teneur en uranium doit se faire en plusieurs etapes faisant intervenir toutes les ressources de methodes relativement simples. On indique la valeur et les limites de chaque etape. Le choix des etalons est base sur l'examen de cliches radiographiques. La mesure de leur teneur exacte en {sup 235}U est effectuee grace a des analyses chimiques et isotopiques. Le controle en cadence industrielle est realise par mesure de densite de l'alliage ou par comptage de l'emission gamma de {sup 235}U. La precision des deux methodes est comparable ({+-} 0,5% relatif). Au point de vue economique, on en arrive a recommander la determination de la teneur par comptage gamma chaque fois qu'une grande serie d'examens est necessaire sur des pieces de forme determinee. Ce sujet a deja ete traite. Le memoire relate et discute les resultats d'une experience industrielle. (author) [Spanish] Muchos reactores para ensayo de materiales utilizan como combustible una aleacion de aluminio y de uranio enriquecido. Es necesario conocer con precision la cantidad de uranio-235 contenida en cada elemento combustible. Los procedimientos utilizados para esa determinacion son en principio sencillos y ademas variados; pueden citarse los siguientes: la medicion de la densidad de la aleacion, el recuento de la emision gamma del uranio- 234, el analisis quimico, la determinacion del contenido isotopico y la evaluacion del ennegrecimiento de una placa radiografica. Por desgracia cada uno de esos metodos ofrece inconvenientes mas o menos graves cuando se los utiliza para controlar una produccion importante. La medicion de la densidad de la aleacion por el metodo de Arquimedes da resultados bastante precisos cuando se procede con cautela y cuando se conoce con exactitud la densidad de los metales que constituyen la aleacion. Ahora bien, las condiciones en que se realiza la operacion hacen que el metodo sea algo lento. Ademas, es necesario

Evaluación mecánica mediante técnicas de indentación de soldaduras por fricción lineal en aleaciones de titanio

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Corzo, M.

2005-12-01

Full Text Available This article shows the results of a project that focuses on the characterization of the weld interface region of dissimilar joints between titanium alloys for aeronautical applications, specifically Ti-6Al-2Sn-4Zr-Mo with Ti-6Al4V, and Ti-6Al-2Sn4Zr-6Mo with Ti-6Al- 2Sn-4Zr-2Mo. The uniaxial flow stress and hardening response of the material containing the weld were analyzed following the finite elements simulations and mathematical formulations to correlate hardness and the amount of pile-up and sinking-in phenomena around sharp indenters with uniaxial mechanical properties. This allows to accurately stablishing the influence that welding process has on the mechanical response of the parts. Tests performed on these friction-welded specimens showed that the fine grained microstructures in the welds exhibited better properties than the base materials.

Este artículo presenta los resultados de un proyecto cuyo objetivo es evaluar la integridad estructural de soldaduras por fricción lineal entre diferentes aleaciones de titanio de aplicación aeronáutica. Concretamente se han estudiado dos uniones: Ti-6Al-2Sn-4Zr- 6Mo con Ti-6Al-W, y Ti-6Al-2Sn-4Zr-6Mo con Ti-6Al-2Sn4Zr-2Mo. El límite elástico y el coeficiente de endurecimiento por deformación de las uniones soldadas y del metal base son inferidos mediante una novedosa metodología de indentación. En los metales base, los resultados experimentales de indentación son confrontados con los obtenidos mediante ensayos convencionales de tracción. Las variaciones en propiedades mecánicas sugieren que la fina microestructura en la zona afectada térmicamente mejora las propiedades con respecto al metal base

Influencia de la distribución de las fibras en la conductividad térnnica de materiales compuestos con matrices de aleaciones de titanio y de magnesio

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Alcaraz, D.

2005-12-01

Full Text Available Metal matrix composites are materials with an increasing use in industrial applications. Generally, the estimation of their thermal conductivity does not take into account the type of reinforcements distribution within the matrix. By applying the Network Simulation Method, a 2-D network model is designed and simulated to determinate precise numerical values of thermal conductivity of composites with random distributions. The proposed model is applied to titanium and magnesium matrix composites reinforced with different types of continuous fibers.

Los "composites" de matriz metálica son materiales de uso creciente en distintas aplicaciones industriales. En general, la determinación de su conductividad térmica no considera el tipo de distribución de los refuerzos en el seno de las matrices. Aplicando el Método de Redes, se diseña un modelo (2D cuya simulación numérica permite obtener valores precisos de conductividad en "composites" con distribuciones aleatorias. El modelo se aplica a "composites" con matrices de aleaciones de titanio y magnesio reforzados con diferentes tipos de fibras continuas.

El método de Newton para la optimización de una nueva ecuación constitutiva para la fluencia plástica dependiente de la deformación. Aplicación a las aleaciones de magnesio AZ80 y AZ61

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Gutiérrez, V.

2013-10-01

Full Text Available A new numerical algorithm has been developed, based on Newton's method, for optimizing the parameters of a new strain dependent constitutive equation, based on the Garofalo equation. The adjustment is direct, with second order algorithms, for an equation derived from that of Garofalo with a nonlinear objective function. This new optimization algorithm has been applied to creep data of two magnesium alloys AZ80 and AZ61, having an unusual plastic behavior. A certain pseudo-stationary exists in the curves studied, in the sense that the usual deformation states are not manifested in an obvious way. The parameters of the new constitutive equation, dependent on strain, have been determined for these alloys. For analyzing the precision of the parameters and the accuracy of modeling of the stress-strain curves, a statistical treatment has been applied which allows assessing the quality of the constitutive equation proposed and the consistency of these parameters. Stress-strain curves have been compared with the modeling results, reaching a good agreement between the experimental data and the resulting modeling.Se ha desarrollado un nuevo algoritmo numérico, basado en el método de Newton, para la optimización de los parámetros de una nueva ecuación constitutiva, dependiente de la deformación, derivada de la ecuación de Garofalo. El ajuste es directo, con algoritmos de segundo orden, de una ecuación derivada de la de Garofalo con una función objetivo no lineal. Este nuevo algoritmo de optimización ha sido aplicado a los datos de fluencia de dos aleaciones de magnesio, AZ80 y AZ61, con un comportamiento plástico inusual, existiendo una pseudo-estacionariedad en algunas de las curvas estudiadas, en el sentido de que no se manifiestan de forma evidente los estados usuales de deformación. Se han obtenido los parámetros de la nueva ecuación constitutiva, dependiente de la deformación, para estas aleaciones. Para el análisis de la precisión de

Análisis de las dependencias composicionales de las propiedades opticas de láminas semiconductoras amorfas del sistema As-S-Se

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González-Leal, J. M.

2004-04-01

Full Text Available Amorphous As40S60-xSex (x = 0, 20, 30, 40 and 60 at. % films have been prepared by vacuum thermal evaporation. Values for the refractive index and the absorption coefficient of these films have been determined from their transmission spectra, measured at normal incidence, in the spectral range from 400 to 2200 nm. It has been found that the refractive index of the samples increases with increasing Se content, over the entire spectral range. This behaviour can be explained, according to the Lorentz-Lorenz relationship, by the increased polarizability of the larger Se atoms, in comparison with S atoms. The values of the As effective coordination number, Nc, have been estimated from the analysis of the dispersion of the refractive index, in terms of a model based on the single-oscillator formula. The increase in Nc with increasing Se content, from around 3.0 to 3.4, which has been inferred from this analysis, suggests an increase in the structural compactness of the films when substituting S by Se. This conclusion is supported by the decrease observed in the intensity of the first sharp diffraction peak, in the X-ray patterns. Finally, it has been found a decrease in the optical bandgap with increasing Se content, from 2.38 to 1.79 eV, which can be plausibly explained considering the lower bonding energy of As-Se bonds compared with that of As-S bonds.

Se han preparado láminas semiconductoras amorfas de composiciones químicas As40S60-xSex (con x = 0, 20, 30, 40 y 60 % at., mediante la técnica de evaporación térmica en vacío. Los valores del índice de refracción y del coeficiente de absorción de estas láminas, se determinaron a partir de los espectros de transmisión óptica, obtenidos en incidencia normal, en el intervalo espectral comprendido entre 400 y 2200 nm. Se ha encontrado un aumento en los valores del índice de refracción con el contenido de Se, dentro del intervalo espectral en estudio. El análisis de la dependencia

Synthesis and structural characterization of amorphous alloys of the Fe-Ni-B type; Sintesis y caracterizacion estructural de aleaciones amorfas del tipo Fe-Ni-B

Energy Technology Data Exchange (ETDEWEB)

Cabral P, A.; Jimenez B, J.; Garcia S, I. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

2004-07-01

It was prepared the alloy FeNiB for chemical reduction, using four p H values (5, 6, 7 and 7.5). To p H=6 partially oxidized particles were obtained, between 16 and 20%. In the synthesis to other p H values, the obtained particles were highly oxidized (65-90%) according to the X-ray diffraction results, in all the preparations the particles were partially crystallized, with crystal size that varied between 4 and 10 nm. The structure of these particles can be consider that they are formed by a nucleus due to the alloy and an oxide armor recovering it. (Author)

Recubrimientos de TiN depositados mediante ACPVD sobre aleaciones de magnesio AM60

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Pichel, M.

2013-06-01

Full Text Available Magnesium alloys are reaching special interest due to their good specific properties, low cost and good manufacturing properties. However, their low hardness, wear and corrosion resistance limit their applications in certain sectors of industry. These drawbacks can be solved by applying hard ceramic coatings, such as nitrides or metal carbides. TiN is one of the most used coatings due to its high adhesion, hardness, low coefficient of friction and chemical stability. Physical vapor deposition by cathodic arc CAPVD, is a versatile technique, which uses low temperatures and high ionization energies, generating homogeneous coatings. To achieve coatings with high quality, a careful control of the manufacturing parameters is required, such as bias voltage, gas flow or intensity. This paper focuses on magnesium alloys, AM60, coated with TiN using physical vapor deposition cathodic arc technique (CAPVD at different intensity values (40A and 100A and surface preparation (grinding up to 4000 grit and polished to 3μm. It was included a final condition with an intermediate Al film. The samples were characterized by X-ray diffraction, roughness, optical microscopy and scanning electron.Las aleaciones de magnesio están alcanzando especial interés gracias a sus buenas propiedades específicas, bajo coste y buenas propiedades de moldeabilidad. No obstante su baja dureza, resistencia a desgaste y corrosión, limita sus aplicaciones en ciertos campos de la industria. Estos inconvenientes se pueden solucionar aplicando recubrimientos duros cerámicos, como nitruros o carburos metálicos. El TiN es uno de los más utilizados debido a su alta adherencia, dureza, bajo coeficiente de fricción y estabilidad química. La deposición física en fase vapor mediante arco catódico, ACPVD, es una técnica muy versátil, que emplea bajas temperaturas y altas energías de ionización, generando recubrimientos de bajo espesor, homogéneos y de calidad. Para alcanzar

Rare-Earth-Rich Alloys; Alliages a Teneur Elevee en Terres Rares; Splavy, obogashchennye redkozemel'nymi ehlementami; Aleaciones Ricas en Tierras Raras

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Copeland, M.; Kato, H. [Albany Metallurgy Research Center, Bureau of Mines, United States Department of the Interior, Albany, OR (United States)

1964-06-15

ainsi que leurs effets sur les points de fusion, les transformations de l'etat solide et la resistance a la corrosion. Ils ont etabli des diagrammes de phases jusqu'au premier compose ou entectique a teneur elevee en terres rares, selon que l'un ou l'autre apparaissait le premier. Une fois cette partie des travaux termines, ils ont fabrique des alliages qu'ils ont traites a chaud pour obtenir le maximum de solubilite a l'etat solide du metal d'alliage qui n'est pas une terre rare,, et ils ont fait des essais d'oxydation et de corrosion. Ils n'ont observe aucune amelioration de la resistance des terres rares a l 'oxydation dans l 'atmosphere a la suite de l 'operation; en fait, la plupart des metaux d'addition se sont reveles nuisibles. L'aluminium augmentait fortement la resistance a la corrosion par l'eau chaude des terres rares ayant fait l'objet des essais; d'autres metaux n'augmentaient cette resistance des terres rares qu'a un moindre degre. (author) [Spanish] Los metales de las tierras raras presentan interes en el control de reactores de potencia debido a su elevada seccion eficaz de captura de neutrones termicos, pero por desgracia se corroen con facilidad. Partiendo del supuesto de que ciertos metales no pertenecientes al grupo de las tierras raras pueden alearse con disprosio, erbio, gadolinio y samario mejorando sus propiedades, los autores estudiaron los efectos que esta aleacion ejerce sobre las tierras raras. Estudiaron la solubilidad de metales como el circonio, vanadio, cromo, hierro, niquel, cobre, aluminio y silicio en disprosio, erbio, gadolinio y samario, y determinaron sus efectos sobre los respectivos puntos de fusion, las transformaciones de estado solido y la resistencia a la corrosion. Prepararon diagramas de fase hasta el primer compuesto rico en tierra rara o hasta el eutectico, segun cual apareciera primero. A l terminar esta parte del trabajo, prepararon aleaciones, que sometieron a un tratamiento termico para obtener un maximo de

Evaluation of nickel-rich alloys for the electrolytic generation of hydrogen in an alkaline medium; Evaluacion de aleaciones ricas en niquel para la generacion electrolitica de hidrogeno en medio alcalino

Energy Technology Data Exchange (ETDEWEB)

Ortiz Verdin, A.A.; Ortega Borges, R.; Trejo Cordova, G.; Meas Vong, Y. [Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, S.C., Pedro Escobedo, Queretaro (Mexico)]. E-mail: aortiz@cideteq.mx

2009-09-15

The simultaneous electrodeposition of Ni with metals such as Zn to form alloys enables obtaining surfaces with high electrocatalytic activity or particular characteristics that resist wear and abrasion. This work presents the results of the study of the electrochemical characterization of different types of nickel electrodeposition and compositions, used as cathodes, and measurements of the electrocatalytic activity in the release of hydrogen in an alkaline medium. Curves I through IV were generated, which were potentiostatically obtained in a nitrogen atmosphere in a NaOH alkaline solution. The morphology of the deposits was evaluated with sweep electron micrscopy(SEM). The results enabled evaluating its potential application as electrode materials for the generation of electrolytic hydrogen in alkaline medium, given the good electrocatalytic activity of nickel-rich materials. [Spanish] El electrodeposito simultaneo del Ni, con metales como el Zn para formar aleaciones, permite obtener superficies con elevada actividad electrocatalitica o con caracteristicas particulares de resistencia al desgaste y abrasion. En este trabajo se presentan los resultados del estudio de la caracterizacion electroquimica de los electrodepositos a base de niquel de diferente naturaleza y composicion utilizandolos como catodos midiendo la actividad electrocatalitica con respecto a la reaccion de desprendimiento de hidrogeno (RDH) en medio alcalino. Se realizaron curvas I vs V obtenidas potenciostaticamente bajo atmosfera de nitrogeno en una solucion alcalina de NaOH. La morfologia de los depositos se evaluo mediante SEM (microscopio electronico de barrido). Los resultados permiten evaluar su potencial aplicacion como materiales de electrodo para la generacion electrolitica de hidrogeno en medio alcalino, dada la buena actividad electrocatalitica de los materiales ricos en niquel.

Catalizadores anodicos basados en platino para celdas de combustible de etanol

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BIBIAN HOYOS

2007-01-01

Full Text Available Se estudió el comportamiento electro catalítico de platino puro y aleaciones basadas en él con Ru, Sn, Ir y Os soportados en carbón para la electro oxidación de etanol con el propósito de desarrollar catalizadores anódicos para celdas de combustible directas de etanol. Adicionalmente, se construyeron electrodos porosos y ensambles electrodo-membrana para celdas de combustible poliméricas, en las cuales se probaron los ánodos. La caracterización de los catalizadores se realizó mediante voltametría cíclica, mientras que las pruebas del desempeño de las celdas se realizaron mediante pruebas de polarización corriente-potencial. En general, todas las aleaciones mostraron un menor potencial de inicio de la reacción y mayor actividad catalítica que el platino puro. Sin embargo en la zona de altos sobre potenciales, el platino puro tiene mayor actividad catalítica que las aleaciones. De acuerdo con estos resultados, las aleaciones estudiadas podrían ser útiles en celdas de combustible operando a corrientes moderadas y bajas

Estudo do comportamento óptico-estrutural do LiNbO3

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Pinheiro C. D.

2003-01-01

Full Text Available Realizou-se um estudo teórico-experimental sobre as estruturas cristalina e amorfa de niobato de lítio, para verificar a influência dos defeitos sobre as propriedades ópticas desse semicondutor. Filmes finos cristalinos de LiNbO3 (c-LN e amorfo (a-LN foram preparados pelo método dos precursores poliméricos, sendo caracterizados por difração de raios X e microscopia de força atômica. As propriedades ópticas foram estudadas por UV-Visível e espectroscopia Raman. Em particular, o filme amorfo apresentou luminescência, cuja posição do pico varia de acordo com o comprimento de onda de excitação. A diferença de energia entre os níveis HOMO (Highest Occupied Molecular Orbital e LUMO (Lowest Unoccupied Molecular Orbital revela que o gap de banda da fase cristalina é maior que aquele exibido pela fase amorfa, em acordo com os dados experimentais de UV-visível. Observou-se o surgimento de novos níveis eletrônicos na região do gap de banda na estrutura amorfa, este fato pode explicar as propriedades ópticas particulares observadas sobre o filme amorfo.

Protección contra la corrosión de aleaciones de aluminio mediante recubrimientos sol-gel

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Conde, A.

2002-06-01

Full Text Available Present paper studies the corrosion protection of three new nanomeric coatings obtained from modified silanes and cured at low temperatures. The synthesis of these coatings is carried out starting from a mixture of two sols separately prepared: a prehydrolized GPTS (glicidoxipropiltrimetoxisilano and a second sol TEOS/MTES. Adding to this initial sol a colloidal solution of 25% in weight of commercial particles of SiO2, Aerosil 300 and Aerosil R972 respectively can be obtained thicker nanomeric coatings. Once synthesized, they were deposited by means of the spin coating method onto two aluminum alloys, 5555 and 3005 used as substrates. The final thickness of the coatings is about 10 μm, for the coating without particles and slightly higher, 12-14 μm approximately, for the coatings with particles. The electrochemical results indicated that, in all cases, the coated samples presented an improvement in the corrosion behavior in comparison with bare alloys in aggressive media of NaCl. The corrosion rate decreased three orders of magnitude for the coatings with particles and lower for those that do not contain particles.

En el presente trabajo se estudia la protección frente a la corrosión que proporcionan tres nuevos recubrimientos nanoméricos de baja temperatura de curado obtenidos a partir de silanos modificados. La síntesis de estos recubrimientos se realiza a partir de una mezcla de dos soles, GPTS (glicidoxipropiltrimetoxisilano prehidrolizado y un segundo sol TEOS/MTES. Añadiendo a este sol inicial una disolución coloidal de partículas se obtienen recubrimientos nanoméricos de mayor espesor. En el presente trabajo los recubrimientos particulados se obtuvieron incorporando un 25% en peso de partículas comerciales de SiO2, Aerosil 300 y Aerosil R972 respectivamente. Una vez sintetizados, se depositaron mediante el método de centrifugado, sobre dos aleaciones de aluminio, 5555 y 3005 empleadas como substratos. El espesor final

Avaliação das propriedades mecânicas de juntas cerâmicas usando fitas amorfas como metal de adição Evaluation of the mechanical properties of ceramic joint using amorphous ribbons as filler metals

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Danielton Gomes dos Santos

2009-09-01

Full Text Available Este trabalho teve como objetivo determinar os melhores parâmetros para brasagem de juntas cerâmicas de Al2O3 pré-metalizadas com Ti por processo a plasma utilizando fitas amorfas de ligas Cu49Ag45Cx e como metal de adição. As ligas foram preparadas em forno a arco, e, posteriormente processadas por melt-spinning, variando conteúdo Ce de 4-6. %. A brasagem foi realizada em forno à vácuo e as seguintes variáveis analisadas: tempo de deposição do filme de Ti e temperatura e tempo de brasagem , que foram relacionados com a resistência à flexão em 3 pontos da junta brazada. A equação de regressão linear foi obtida, e verificou-se a interação entre estes fatores. As superfícies cerâmicas metalizadas apresentaram excelente uniformidade e as juntas brasadas muito boa adesão atingindo valores de resistência à flexão de até 176,8 MPa.This work had as objective to establish de best brazing parameter to joint Al2O3 pre-metalized with Ti by plasma process using amorphous ribbons of Cu49g45Ce x alloys as filler metals. The alloys were prepared in arc furnace and processed by melt-spinning process varying the Ce percentiles from 4 to 6. % . The brazing was accomplished in vacuum furnace and the following variables analyzed: deposition time of Ti film, brazing temperature and brazing times which were related to the brazed joint 3-point bending resistance. The interaction between those factors was obtained by linear regression equation. The metalized ceramic surfaces presented an good uniformity and the joint a very good adhesion reaching bending resistance up to 176,8 MPa.

Óxidos de estaño: nuevos anodos para baterías de Ion-Litio

OpenAIRE

Morales Palomino, Julián; Sánchez, L.

1999-01-01

La reacci n entre el litio y xidos aleaciones de esta o es reversible cuando se realiza por m todos electroqu micos y a bajos potenciales con respecto al electrodo de litio. Esta propiedad permite el uso de estos materiales como electrodos negativos en el dise o y construcci n de bater as tipo ion-litio. En el caso de xidos de esta o la reacci n de inserci n de litio en la matriz conduce a la formaci n de aleaciones Li-Sn. La presencia de agregados grandes de tomos de esta o, fo...

Influencia del grado de molienda en la actividad puzolánica de arcillas que contienen caolinita y halloysita

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Leonardo Cabrera

2016-01-01

Full Text Available El objetivo de este trabajo es analizar la influencia del grado de molienda en la actividad puzolánica de diferentes arcillas que contienen los minerales Caolinita y/o Halloysita. Se utilizaron 4 arcillas, cuantificando la fase amorfa formada durante la calcinación a 700 ºC y realizando distintos procesos de molienda. Se determinó que la actividad puzolánica de las arcillas calcinadas depende de la composición mineralógica y defectos superficiales, cantidad de fase amorfa y finura. La mayor actividad puzolánica fue obtenida para la arcilla con un elevado contenido de Halloysita finamente molida. La utilización de un 25% de reemplazo de cemento Portland (CP por esta muestra permite superar la resistencia a la compresión respecto al mortero-CP a partir de los 7 días.

Estudio numerico y experimental del proceso de soldeo MIG sobre la aleacion 6063--T5 utilizando el metodo de Taguchi

Science.gov (United States)

Meseguer Valdenebro, Jose Luis

improvement on mechanical properties in aluminum metal joint. Los procesos de soldadura por arco electrico representan unas de las tecnicas mas utilizadas en los procesos de fabricacion de componentes mecanicos en la industria moderna. Los procesos de soldeo por arco se han adaptado a las necesidades actuales, haciendose un modo de fabricacion flexible y versatil. Los resultados obtenidos numericamente en el proceso de soldadura son validados experimentalmente. Los principales metodos numericos mas empleados en la actualidad son tres, metodo por diferencias finitas, metodos por elementos finitos y metodo por volumenes finitos. El metodo numerico mas empleado para el modelado de uniones soldadas, es el metodo por elementos finitos, debido a que presenta una buena adaptacion a las condiciones geometricas y de contorno ademas de que existe una diversidad de programas comerciales que utilizan el metodo por elementos finitos como base de calculo. Este trabajo de investigacion presenta un estudio experimental de una union soldada mediante el proceso MIG de la aleacion de aluminio 6063-T5. El metodo numerico se valida experimentalmente aplicando el metodo de los elementos finitos con el programa de calculo ANSYS. Los resultados experimentales obtenidos son: las curvas de enfriamiento, el tiempo critico de enfriamiento t4/3, geometria del cordon, microdurezas obtenidas en la union soldada, zona afectada termicamente y metal base, dilucion del proceso, areas criticas intersecadas entre las curvas de enfriamiento y la curva TTP. Los resultados numericos son: las curvas del ciclo termico, que representan tanto el calentamiento hasta alcanzar la temperatura maxima y un posterior enfriamiento. Se calculan el tiempo critico de enfriamiento t4/3, el rendimiento termico y se representa la geometria del cordon obtenida experimentalmente. La zona afectada termicamente se obtiene diferenciando las zonas que se encuentran a diferentes temperaturas, las areas criticas intersecadas entre las

Propiedades mecánicas de la aleación AZ31 procesada por una ruta eco-sostenible

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D’Errico, F.

2013-12-01

Full Text Available Recently it has been proved that molding of defect-free components of various commercial alloys of magnesium can be carried out succesfully when small amounts of CaO are added to the melt, making unnecessary the use of SF6 coverage. In the case of AZ alloys, this process also remarkably improves their mechanical properties not only by the greater cleaning of alloys but also by the formation of CaAl2 phase. This work, part of the Green project Metallurgy (http://www.green-metallurgy.eu funded by the European Union (LIFE+2009, studies the influence of different CaO additions on the microstructure and mechanical properties of AZ31 Eco-Mg alloy. The alloy was processed by a conventional route involving extrusion of as-cast rods as well as by a powder metallurgy route (PM using chips as starting material. The objective was to analyze the viability of recycling machining chips to manufacture components for the automobile industry and transportation in general, because of its low cost and environmental impact. It has been demostrated that alloys processed from chips exhibit the highest tensile stress values, close to 320 MPa.Recientemente se ha demostrado la posibilidad de fabricar por moldeo, componentes libres de defectos de diferentes aleaciones comerciales de magnesio, añadiendo CaO al caldo, sin emplear SF6. En el caso de las aleaciones AZ este proceso, además, mejora notablemente las propiedades mecánicas, no sólo por la mayor limpieza de las aleaciones sino también por la presencia de la fase CaAl2 que se forma por la incorporación de calcio al caldo. Este trabajo, enmarcado dentro del proyecto Green Metallurgy (http://www.green-metallurgy.eu financiado por la Unión Europea (Programa LIFE+2009, estudia la influencia de diferentes adiciones de CaO en la microestructura y propiedades mecánicas de la aleación Eco-Mg AZ31. El estudio se lleva a cabo en aleaciones AZ31 con 0,5, 1 y 1,5% CaO procesadas por dos rutas diferentes, aleaciones

Intermetallics: past, present and future

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Morris, D. G.

2005-12-01

Full Text Available Intermetallics have seen extensive world-wide attention over the past decades. For the most part these studies have examined multi-phase aluminide based alloys, because of their high stiffness, combined with reasonable strength and ductility, good structural stability and oxidation resistance, and attempted to improve current Ni-base superalloys, Ti-base alloys, or Fe-base stainless steels for structural aerospace applications. The current status of development and application of such materials is briefly reviewed. Future developments are taking intermetallics from the realm of "improved high-temperature but low-ductility metallic alloys" into the realm of "improved aggressive-environment, high-toughness ceramic-like alloys". Such evolution will be outlined.

Durante los últimos décadas ha habido un desarrollo de los intermetálicos, sobre todo por aplicaciones estructurales a alta temperatura en aplicaciones aeroespaciales, donde, por su rigidez alta, en combinación con una resistencia mecánica y ductilidad razonable, su buena estabilidad estructural y resistencia a la oxidación, han sido vistos como versiones avanzadas y mejoradas de las aleaciones metálicas como, por ejemplo, las superaleaciones a base de nitrógeno y las aleaciones de titanio. Se discute el desarrollo importante durante las últimas décadas, y también los nuevos desarrollos probables durante los próximos años. Se podrían ver los intermetálicos como versiones mejoradas de los cerámicos.

Influencia de los parámetros de la soldadura metálica fría en las aleaciones AA5083 y AA6061//Influence of the colt metal welding parameters on the AA5083 and AA6061 aluminum

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René Eduardo de‐Luna‐Alanís

2015-01-01

Full Text Available El trabajo tuvo como objetivo evaluar la influencia de la velocidad de la soldadura y de las correcciones del arco y pulso en el proceso de Transferencia Metálica Fría sobre las propiedades mecánicas de las aleaciones AA5083 y AA6061. Se desarrolló un diseño experimental de tipo factorial multinivel, con 4 factores independientes (Corrección de Arco, Pulso, Velocidad de Soldadura y Aleación. Los parámetros fundamentales fueron: Corriente de base 250 A; Voltaje de arco 21 V y Polaridad (Direct current electrode positive, DCEP. La evaluación se realizó a través de un ensayo de tracción transversal sobre probetas planas obtenidas de los cupones soldados. Se demuestra que el modelo aplicado es adecuado, revelándose en los experimentos diferencias sustanciales en las propiedades Tensión de fluencia 29,56 %, Módulo de elasticidad 51,16 % y Trabajo específico de deformación elástica 42,30 %, el cual no posee una dependencia lineal con elresto de las propiedades anteriores.Palabras claves: transferencia metálica fría, aleación AA5083, aleación AA6061, propiedades mecánicas._______________________________________________________________________________AbstractThe work objective was to evaluatethe influence of Cold Metal Transfer process arc and pulse corrections and welding speed on the mechanical properties of AA5083 and AA6061 aluminum alloys. For it, a Factorial Multilevel experimental design whit 4 independent factor (arc correction, pulse correction, welding speed and alloy was developed. The essential welding parameters employed were: base current 250 A; arc voltage 21 V and polarity (DCEP. The evaluation was made whit a transverse traction test of plate welded coupons. The experimental model applied wasadequate and substantial differences was showed between yield tensile strength 29,56 %, elasticity module (51,16 % and specific work of elastic deformation 42,30 %, which it does not possess a lineal dependence whit the rest

Electron microscopy characterization of mechanically alloyed and hot consolidates Cu-Cr₃C₂ particles

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López, M.

2005-08-01

Full Text Available Mechanically alloyed copper-ceramic composites have been obtained with the purpose of studying their use as copper-based material for electrical equipment. For high-temperature applications, dispersion-strengthened copper alloys are attractive due to their excellent combination of thermal and electrical conductivity, mechanical strength retention and microstructural stability. In this work, powder mixtures of pure copper with 2 vol % Cr₃C₂, milled during 4, 6, 10, 12 and 15 h in a high-energy planetary balls mill under argon atmosphere, were consolidated by hot isostatic pressing, applying a pressure of 100 MPa at 1073 K for two hours, to obtain materials with a fine microstructure. The Cu-Cr₃C₂ alloys were studied by scanning electron microscopy (SEM, electron microprobe (EPMA and transmission electron microscopy (TEM. Mechanical properties and electrical conductivity were also studied. The average tensile strength and electrical conductivity were found to be 500 MPa and 50 % IACS, respectively. The Cr₃C₂ ceramics show good stability during hot consolidation. Contributing to a further strengthening of the alloy during the hot consolidation, uniformly-distributed Fe-carbide particles of nanometric size precipitated in the copper matrix. Fe-Cr oxycarbides formed in the interphase between Cr₃C₂ particles and the copper matrix cause the low ductility of Cu-Cr₃C₂ alloys. Said particles are attributed to impurities/contamination generated from the milling process.

Se obtuvieron aleaciones compuestas de Cu-Cr₃C₂, aleadas mecánicamente, para estudiar futuras aplicaciones en componentes eléctricos. A altas temperaturas, las aleaciones de base cobre reforzadas por dispersión, son atractivas por su excelente conductividad térmica y eléctrica, propiedades mecánicas y estabilidad microstructural. En este estudio

Thermodynamic Properties of Alloys of Iron and Silicon; Proprietes Thermodynamiques des Alliages Fer-Silicium; Termodinamicheskie svojstva splavov zheleza s kremniem; Propiedades Termodinamicas de las Aleaciones de Hierro y Silicio

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Vecher, R. A.; Gejderih, V. A.; Gerasimov, Ja. I. [Moskovskij Gosudarstvennyj Universitet Im.M.V. Lomonosova, Moskva, SSSR (Russian Federation)

1966-01-15

-Harpoon-Over-Leftwards-Harpoon {alpha}' est une veritable transformation de phase. La region a deux phases est plus large que ne semble l'indiquer le diagramme d'equilibre (etabli d'apres les valeurs publiees). L'activite du fer en solution liquide calculee a partir de celle du fer en solution solide est en bon accord avec les valeurs trouvees par Chipman. (author) [Spanish] El diagrama de equilibrio Fe-Si es muy complejo. A 1000 Degree-Sign K se observa la presencia de las fases siguientes: FeSi{sub 2}({beta}), FeSi y soluciones solidas de silicio en hierro {alpha} and {alpha}'. Los autores midieron las fuerzas electromotrices de las celdas electroquimicas: Fe|Fe{sup 2+} , KI + Nal|Fe-Si at 600-800 Degree-Sign C fundidos Las aleaciones se prepararon a partir de componentes puros por pulvimetalurgia y se sometieron a un recocido prolongado. Los autores estudiaron diez aleaciones con un contenido de silicio comprendido entre 85% y 4%, situadas en todas las fases del diagrama de equilibrio a 1000 Degree-Sign K. Calcularon los valores integrales de {Delta}G, {Delta}H y {Delta}S correspondientes a la formacion de los siliciuros FeSi{sub 2}({beta}), FeSi y Fe{sub 3}Si a la temperatura media del intervalo experimental (1000 Degree-Sign K), asi como (utilizando el calor especifico de los siliciuros de hierro y del silicio) a 298, 1188 y 1798 Degree-Sign K. Los calores de formacion de los mencionados siliciuros a 298 Degree-Sign K ascienden a -19,4, -17,6 y -22,4 kcal/mol, respectivamente. Los datos publicados permiten calcular el calor de formacion del FeSi{sub 2,33} - ({alpha}-leboita) a 298 Degree-Sign K, que es igual a -14,4 kcal/mol. Los calores calculados por los autores son superiores a los datos experimentales de Corber y de Olsen en 1,5 - 3 kcal. Por otra parte, los calores de mezcla, calculados para las aleaciones liquidas, concuerdan satisfactoriamente con los datos publicados. Los datos obtenidos pueden explicarse como un resultado de la modificacion que sufre el caracter del enlace en los

Fabricación y caracterización de materiales Ag-Cd/CdO producidos mediante incorporación de partículas de CdO en aleaciones Ag-Cd líquidas

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Equihua-Guillén, Fabián

2014-03-01

Full Text Available In the present work it has been investigated the kinetic behavior of internal oxidation processes of strips of Ag-Cd/CdO materials fabricated by adding CdO particles (size of 5 and 20 μm in liquid Ag-Cd alloys. It has been established the metallurgical mechanism that controls the formation of the thickness covered with CdO particles produced by internal oxidation of the Ag-Cd/CdO material. It has been developed, successfully, a metallographic preparation technique for characterizing the morphology, size and distribution of CdO particles produced by heat treatment of internal oxidation on the surface of each sample based on the distance from the original surface to the boundary of dispersed CdO particles. The material strips were sequentially roughed on its surface and the roughing thickness was measured in the cross section of each new surface to determine the number of particles per area and average particle size.En el presente trabajo se investigó el comportamiento cinético del proceso de oxidación interna de láminas del material Ag-Cd/CdO fabricado mediante adición de partículas de CdO con tamaño de 5 y 20 μm en aleaciones Ag-Cd en estado líquido. Se ha establecido el mecanismo metalúrgico que controla la formación del espesor cubierto con partículas de CdO producido por oxidación interna del material Ag-Cd/CdO. Se desarrolló con éxito una técnica de preparación metalográfica para caracterizar el tamaño y distribución de partículas de CdO producidas por oxidación interna sobre la superficie de cada lámina en función de la distancia a partir de la superficie original hasta el límite de partículas de CdO dispersas. Las placas del material fueron desbastadas secuencialmente sobre su superficie y se midió el espesor desbastado en la sección transversal de cada nueva superficie para determinar el número de partículas por unidad de área y el tamaño promedio de partícula.

Procedimiento para la obtención de micro- o nanopartículas sólidas

OpenAIRE

Ventosa Rull, Nora; Veciana Miró, Jaume; Cano-Sarabia, Mary; Sala Vergés, Santiago

2008-01-01

Procedimiento para la obtencion de micro- o nanoparticulas solidas. La invencion proporciona un nuevo procedimiento para la obtencion de micro- o nanoparticulas solidas con estructura homogenea. Se proporciona un procedimiento que permite obtener micro- o nanoparticulas solidas de estructura homogenea, con un tamano de particula inferior a 10 ƒÊm donde el compuesto solido procesado revela la naturaleza, cristalina, amorfa, polimorfica, etc..., propia del compuesto d...

Carburization of austenitic and ferritic alloys in hydrocarbon environments at high temperature

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Serna, A.

2003-12-01

Full Text Available The technical and industrial aspects of high temperature corrosion of materials exposed to a variety of aggressive environments have significant importance. These environments include combustion product gases and hydrocarbon gases with low oxygen potentials and high carbon potentials. In the refinery and petrochemical industries, austenitic and ferritic alloys are usually used for tubes in fired furnaces. The temperature range for exposure of austenitic alloys is 800-1100 °C, and for ferritic alloys 500-700 °C, with carbon activities a_c > 1 in many cases. In both applications, the carburization process involves carbon (coke deposition on the inner diameter, carbon absorption at the metal surface, diffusion of carbon inside the alloy, and precipitation and transformation of carbides to a depth increasing with service. The overall kinetics of the internal carburization are approximately parabolic, controlled by carbon diffusion and carbide precipitation. Ferritic alloys exhibit gross but uniform carburization while non-uniform intragranular and grain-boundary carburization is observed in austenitic alloys.

La corrosión a alta temperatura, tal como la carburación de materiales expuestos a una amplia variedad de ambientes agresivos, tiene especial importancia desde el punto de vista técnico e industrial. Estos ambientes incluyen productos de combustión, gases e hidrocarburos con bajo potencial de oxígeno y alto potencial de carbono. En las industrias de refinación y petroquímica, las aleaciones austeníticas y ferríticas se utilizan en tuberías de hornos. El rango de temperatura de exposición para aleaciones austeníticas está entre 800-1.100°C y para aleaciones ferríticas está entre 500-700°C, con actividades de carbono a_c>1 en algunos casos. En tuberías con ambas aleaciones, el proceso de carburación incluye deposición de carbón (coque en el diámetro interno, absorción de carbono en la superficie

Posibles efectos en la salud asociados con la metalurgia precolombina.

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Alvaro Javier Idrovo

2005-09-01

Full Text Available En el Viejo Mundo algunos investigadores piensan que los efectos adversos en la salud relacionados con la exposición a arsénico influyeron para que se cambiara de usar aleaciones de cobre con arsénico a otras menos tóxicas. En este artículo se evalúa esta hipótesis para las tres grandes tradiciones metalúrgicas precolombinas: Andes centrales, área intermedia y occidente mexicano. Los artefactos metálicos revelan que las concentraciones de arsénico en los Andes centrales fueron similares a las del Viejo Mundo (0,5% a 1%, en el área intermedia los valores eran muy inferiores, mientras en el occidente mexicano fueron muy superiores (7% a 25%. En los Andes centrales se observó inicialmente el uso de bronce arsenical, pero rápidamente se conocieron las aleaciones de cobre-estaño; estas últimas fueron cada vez más preferidas y difundidas por todo el imperio inca. Las evidencias, osteológicas y en objetos artísticos, de amputaciones de los pies entre individuos moches de los Andes centrales apoyan la idea de la presencia de la ?enfermedad del pie negro? entre las poblaciones precolombinas. En conclusión, es posible que los efectos nocivos del arsénico se hayan observado en el Nuevo Mundo, y favorecido el cambio hacia aleaciones menos tóxicas. Se requieren nuevos estudios específicos para verificar esta hipótesis.

Evolución Microestructural en Uniones de la Aleación Ti-6Al-4V Mediante el Proceso de Soldadura de Punto por Fricción-agitación

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Flor Araceli Garcia-Castillo

Full Text Available Resumen La soldadura de punto por fricción-agitación (Friction Stir Spot Welding, FSSW es un tema de reciente desarrollo e interés, principalmente en aleaciones de Titanio, ya que existen estudios previos realizados en aleaciones de aluminio, magnesio, aceros y polímeros. Las aleaciones de Titanio tienen una amplia aplicación en la industria aeronáutica, principalmente como componentes en el tren de aterrizaje en aviones comerciales, por lo cual este trabajo se centra en la aleación Ti-6Al-4V, este tipo de aleación presenta fases alfa (α y beta (β, brindado mejor balance en propiedades mecánicas de dureza y esfuerzo a la tensión. El proceso FSSW se realizó mediante un centro de maquinado de alta velocidad, utilizando una velocidad de rotación de 500 RPM, una velocidad de penetración de la herramienta de 2 mm/s y 3 s en tiempo de sostenimiento, en láminas con un espesor de 1,5 mm y una longitud de traslape de 20 mm. Los resultados mostraron el efecto de las variables del proceso de soldadura FSSW sobre la microestructura de la aleación Ti-6Al-4V ocasionada por el efecto térmico y la deformación plástica del proceso de la soldadura, concluyendo que una adecuada combinación de parámetros permite realizar una unión sin defectos.

Aleación superficial de superaleaciones base níquel mediante láser

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Rodríguez, G. P.

1998-04-01

Full Text Available Ni based superalloys present a high oxidation resistance at high temperature as well as good mechanical properties. But new tecnhology developments forcé to research in this materials to improve their properties at high temperature. In this work, two Ni based superalloys (Nimonic 80A and Inconel 600 were surface alloyed with aluminium using a high power laser. SEM and EDX were used to study the microstructure of the obtained coatings. Alloyed specimens were tested at 1.273 K between 24 and 250 h. Results showed the generation of a protective and continuous coating of alumina on the laser treated specimens surface that can improve oxidation resistance.

Las superaleaciones base níquel presentan una elevada resistencia a la oxidación a alta temperatura, así como excelentes propiedades mecánicas. Los nuevos desarrollos tecnológicos (condiciones cada vez más agresivas obligan a una casi continua modificación de dichas aleaciones. En el presente trabajo, dos superaleaciones base níquel (Nimonic 80A e Inconel 600 se alean superficialmente con aluminio utilizando un láser de alta potencia. Se estudia la microestructura de la capas obtenidas mediante SEM y EDX. Se realizan ensayos de oxidación a 1.273 K sobre las probetas aleadas y sobre el material base durante tiempos variables entre 24 y 250 h. Los resultados indican la formación de una capa protectora de alúmina sobre las probetas aleadas que puede incrementar la resistencia a la oxidación.

Alloy 690 in PWR type reactors; Aleaciones base niquel en condiciones de primario de los reactores tipo PWR

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Gomez Briceno, D.; Serrano, M.

2005-07-01

Alloy 690, used as replacement of Alloy 600 for vessel head penetration (VHP) nozzles in PWR, coexists in the primary loop with other components of Alloy 600. Alloy 690 shows an excellent resistance to primary water stress corrosion cracking, while Alloy 600 is very susceptible to this degradation mechanisms. This article analyse comparatively the PWSCC behaviour of both Ni-based alloys and associated weld metals 52/152 and 82/182. (Author)

Description of hypoeutectic Al-Si-Cu alloys based on their known chemical compositions

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Djurdjevic, M. B.

2013-10-01

caso de los sistemas base hierro y de la equivalencia con el aluminio para las aleaciones multi-componentes base magnesio.

Metallurgical and mechanical properties of Inconel 600 and stellite; Estudio del comportamiento mecanico-metalurgico de alceacion inconel 600 y estelita

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Cstillo, Martin; Villa, Gabriel; Vite, Manuel [Instituto Politecnico Nacional, Mexico D.F. (Mexico); Palacios, Francisco [Instituto Nacional de Investigacion Nuclear (ININ), Estado de Mexico (Mexico); Hernandez, Luis H; Urriolagoita, Guillermo [Instituto Politecnico Nacional, Mexico D.F. (Mexico)

2005-01-15

The present work studies the metallurgical and mechanical properties of two alloys, Inconel 600 and stellite, which are within the group of high hardness alloys or superalloys, which are deposited through the electrical weld process to the metallic arc with coated electrode (SMAW) and thereinafter analyzed through electron microscopy, diffractometry and abrasion, Impact and hardness test. The relationship between the microstructure and the final properties of the coating (hardness and abrasion wear resistance) was observed. [Spanish] Este trabajo presenta el estudio sobre las propiedades metalurgicas y mecanicas de dos aleaciones, inconel 600 y estelita, clasificadas dentro del grupo de aleaciones de alta dureza o superaleaciones; las cuales fueron depositadas mediante el proceso de soldadura electrica al arco metalico con electrodo revestido (SMAW) y fueron analizadas mediante microscopia electronica (SEM), difractometria pruebas de abrasion, impacto y dureza. Se observo la relacion entre la microstructura y las propiedades del recubrimiento, como son: dureza, resistencia a la abrasion, resistencia al impacto, ente otras.

Mg amorphous alloys for biodegradable implants; Ligas amorfas de magnesio utilizadas em implantes consumiveis

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Danez, G.P., E-mail: gabidanez@hotmail.co [Universidade Federal de Sao Carlos (PPG-CEMUFSCar), SP (Brazil). Programa de Pos-Graduacao em Ciencia e Engenharia de Materiais; Koga, G.Y.; Tonucci, S.; Bolfarini, C.; Kiminami, C.S.; Botta Filho, W.J. [Universidade Federal de Sao Carlos (DEMa/UFSCar), SP (Brazil). Dept. de Engenharia de Materiais

2010-07-01

The use of implants made from amorphous alloys magnesium-based with additions of zinc and calcium are promising. Properties such as biocompatibility, low density, high mechanical strength, low modulus (as compared to alloys such as stainless steel and titanium), corrosion resistance and wear resistance make it attractive for use in implants. Moreover, the by-products of corrosion and wear are not toxic and may contribute to fixation. Aiming to understand the tendency of this amorphous ternary (Mg-Zn-Ca) and expand the information about this system, this work involved the use of the topological criterion of instability ({lambda}) and the criterion of electronegativity ({Delta}e) to the choice of compositions. The alloys were processed into wedge-shaped and analyzed structurally and in X-ray diffraction and scanning electron microscopy. (author)

Posterior amorphous corneal dystrophy: case report

OpenAIRE

Oliveira, Lauro Augusto de [UNIFESP; Vieira, Luiz Antônio [UNIFESP; Freitas, Denise de [UNIFESP; Sousa, Luciene Barbosa de [UNIFESP

2006-01-01

O objetivo deste trabalho é alertar o oftalmologista da possibilidade de se deparar com casos raros de distrofias corneanas. Neste caso correlacionamos os achados clínicos da distrofia amorfa posterior com refração, topografia e biomicroscopia ultra-sônica.The purpose of this paper is to warn the ophthalmologist about the possibility of facing rare cases of corneal dystrophies. Clinical findings of a case of posterior amorphous dystrophy were correlated with refraction, topography, and ultras...

Evaluación de la corrosión por picadura en aluminio AA1050

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Luis Garita-Arce

2014-09-01

Los ensayos realizados según la norma ASTM G100- 89 para las aleaciones consideradas no indicaron diferencias significativas, aunque sí se observó que la aleación AA1050 presenta mayor susceptibilidad a la picadura en ámbitos de un pH= 7 y con deformaciones elevadas.

Riesgo de exposición al sílice y prevención de la silicosis en la industria

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Camasi Pariona, Oswaldo

2015-01-01

La Sílice es un material que se encuentra en los minerales. Es el componente principal de la arena y se presenta principalmente en las formas: cristalina (cuarzo, cristobalita, tridimita), amorfa (tierra de diatomea, ópalo). Esta sustancia se utiliza en las actividades de minería, tratamiento de minerales, limpieza por arenado, industria del cemento, fabricación de asfalto, cerámica, limpieza abrasiva, demolición, industria del vidrio, molienda de cuarzo, moldes de fundición, pulido de superf...

Análisis de la absorción de hidrógeno y de su influencia en el comportamiento mecánico de cinco aleaciones férreas

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Albístur-Goñi, A.

2008-04-01

Full Text Available A study of the influence of hydrogen on the mechanical behaviour of five iron alloys with different carbon state, morphology and content (as spheroidal or lamellar graphite or combined as CFe³ is described here. Experimental observations from tensile (carried out at different crosshead speeds, Charpy impact resistance, hardness, fracture toughness tests and fractographic analysis show that internal or dissolved hydrogen, apart from producing a significant loss of ductility, hardens steels and softens cast irons. The results also provide convincing evidence of the important role that the strain rate plays in the mechanism of hydrogen induced cracking. Additionally, glow discharge optical emission spectroscopy (GDOES technique is used to evaluate the concentration of hydrogen that has been absorbed by the samples as a function of depth and time. It can be deduced from the innovative use of this technique not only that diffusivity of hydrogen in ductile cast irons is greater than in steels or grey cast irons, but also that hydrogen interacts with different trapping sites.

El objetivo de este trabajo es el estudio de la influencia del hidrógeno en el comportamiento mecánico de cinco aleaciones férreas con distinto contenido, estado y morfología de carbono (grafito libre; esferoidal y laminar y combinado como CFe₃. Los resultados experimentales extraídos de los ensayos de tracción llevados a cabo a diferentes velocidades de desplazamiento entre mordazas, flexión por choque sobre probeta Charpy, tenacidad de fractura y del análisis fractográfico indican que el hidrógeno interno o disuelto, además de producir una importante pérdida de ductilidad, provoca un endurecimiento en los aceros y un ablandamiento en las fundiciones. Estos resultados también proporcionan una evidencia del importante papel que juega la velocidad de deformación en el mecanismo de daño inducido por hidrógeno. Asimismo, se ha utilizado

Laser surface alloying of aluminium-transition metal alloys

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Almeida, A.

1998-04-01

Full Text Available Laser surface alloying has been used as a tool to produce hard and corrosion resistant Al-transition metal (TM alloys. Cr and Mo are particularly interesting alloying elements to produce stable highstrength alloys because they present low diffusion coefficients and solid solubility in Al. To produce Al-TM surface alloys a two-step laser process was developed: firstly, the material is alloyed using low scanning speed and secondly, the microstructure is modified by a refinement step. This process was used in the production of Al-Cr, Al-Mo and Al-Nb surface alloys by alloying Cr, Mo or Nb powder into an Al and 7175 Al alloy substrate using a CO₂ laser. This paper presents a review of the work that has been developed at Instituto Superior Tecnico on laser alloying of Al-TM alloys, over the last years.

En el presente trabajo se estudia la aleación superficial mediante láser de aluminio con metales de transición. El cromo y el molibdeno son particularmente interesantes porque producen aleaciones de alta resistencia y por el bajo coeficiente de difusión y solución sólida en aluminio. Para producir estas aleaciones se ha seguido un procedimiento desarrollado en dos partes. En primer lugar, el material se alea usando una baja velocidad de procesado y en segundo lugar la estructura se modifica mediante un refinamiento posterior. Este procedimiento se ha empleado en la producción de aleaciones Al-Cr, Al-Mo y Al-Nb mediante aleación con láser de CO₂ de polvos de Cr, Mo o Nb en aluminio y la aleación 7175. Este trabajo es una revisión del desarrollado en el Instituto Superior Técnico de Lisboa en los últimos años.

Innovaciones en el diseño del instrumental manual en endodoncia

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Roig Cayón, Miguel; Brau Aguadé, Esteban; Canalda Sahli, Carlos

1994-01-01

En este artículo de divulgación los autores hacen una serie de consideraciones sobre los nuevos instrumentos endodóncicos que están apareciendo en el mercado, con nuevos diseños y diferentes aleaciones, y tratando de enjuiciar su efecto en la preparación biomecánica de los conductos radiculares.

Sensibilidad del análisis termomecánico a las variables de termofijado del poliéster.

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Gacén Guillén, Joaquín; Bernal Sánchez, Fernando; Juárez Quero, Dionisio

1989-01-01

El estudio por Análisis Termomecánico de las fibras de poliester termofijadas detecta una extensión a temperaturas próximas de transiaón vítrea, cuyo origen puede atribuirse a la movilización de las zonas amorfas. A mayores temperaturas se inicia un encogimiento cuya temperatura caracteristica está muy relacionada con la temperatura efectiva del termofijado. Esta temperatura (TIE) constituye una buena medida de la estabilidad dimensional al calor seco, aumentando tras el descrudado, tras el t...

Application of the N-Alkane molecular alloys to thermally protected containers for catering

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Arjona, F.

2000-08-01

Full Text Available A thermally controlled transport device was designed and tested. As hot food needs to be transported at temperatures between 60 and 70ºC in order to avoid contamination by microorganisms, the use of Molecular Alloy Phase Change Materials (MAPCM can lead to improvements in this field of application. A heat transfer numerical simulation of the box used for transporting the food was conducted. Despite obvious simplifications, a good agreement between numerical simulation and experimental results was obtained. Furthermore, we compared our experimental results with those from other experiments related to the transport of hot food. Here, pizza is taken as the example, and it is shown that delivering time can be increased three-fold.

Para evitar la proliferación de microorganismos, los alimentos cocinados deben ser transportados a temperaturas entre 60 y 70ºC. Los Materiales con Cambio de Fase a base de Aleaciones Moleculares (MAPCM representan una solución en este tipo de aplicaciones. Para ello hemos diseñado y probado un contenedor que permite el transporte a temperatura controlada. Se ha realizado la experimentación y simulación numérica de la transferencia de calor en el dispositivo con el objetivo de determinar su rendimiento. A pesar de las necesarias simplificaciones, hemos obtenido un buen acuerdo entre resultados experimentales y de simulación. En este trabajo hemos tomado el transporte de pizzas como ejemplo, mostrando que el tiempo de protección térmica puede ser incrementado utilizando aleaciones moleculares.

Optimización del proceso de soldadura GTAW en placas de Ti6Al4V

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Celso Cruz

2014-03-01

Full Text Available La soldadura de aleaciones ferrosas ha sido ampliamente utilizada durante muchos años en México. Con la llegada de la industria Aeroespacial, nuevas aleaciones, procesos y retos también. Un ejemplo de esto es la soldadura GTAW en materiales como el Titanio 6Al4V utilizada en partes de los aviones. En este trabajo se realizaron pruebas mecánicas y no destructivas con la finalidad de probar parámetros fijos y móviles para la obtención de los criterios de calidad adecuadas al proceso y aportar a la industria datos que le permitan mejorar dichos procesos y ser competitiva. Para esto se seleccionaron tres niveles de parámetros y calores de aporte pues esta variable está relacionada con las características metalúrgicas y en cierto grado con la sanidad. Se probaron niveles altos, medios y bajos variando el voltaje, amperaje y la velocidad encontrando que los valores supuestos no cumplían la tenacidad a la entalla Charpy. Para optimizarlo y alcanzar el valor objetivo se realizó un diseño central compuesto utilizando los tratamientos medio y alto que arrojaron mejores propiedades encontrando el cumplimiento con las criterios de calidad y los parámetros, y el calor de aporte adecuados para tener una respuesta óptima. El experimento logró mejorar la tenacidad de la soldadura hasta 12 Joules cumpliendo con la resistencia a la tensión, esfuerzo de cedencia y elongación mínimo especificado para el material base.

Una perspectiva de los biomateriales vista desde un diseño específico: la prótesis total de cadera

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Alejandro Echavarría

2003-01-01

Full Text Available La prótesis total de cadera, diseño característico de un reemplazo de una articulación funcional, ha sufrido una serie de modificaciones desde el primer implante, hecho por John Charnley, a mediados del siglo pasado, utilizando cemento de polimetilmetacrilato (PMMA. El estado del arte actual de dicho diseño incluye una serie de biomateriales en diversas presentaciones, que utilizan aleaciones metálicas como el TiAlV, el acero inoxidable ASTM F138 o las aleaciones de cobalto-cromo forjadas (en las áreas donde se requiera la máxima resistencia mecánica a flexión, materiales cerámicos en el punto donde se requiera la máxima resistencia a la abrasión e inercia química (en el caso de la cabeza esférica se utiliza zirconia estabilizada con itrio, en conjunto con materiales de alta capacidad de carga pero muy bajo coeficiente de fricción (como el UHMWPE. Para asegurar la adherencia del implante al hueso cortical se utilizan agregados de hidroxiapatita (HA o cemento acrílico de PMMA.

Alternativas al cromo en la industria del acabado superficial del aluminio. Tratamientos superficiales de bajo impacto ambiental

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Aballe Villero, Álvaro

2001-02-01

Full Text Available Chromates are one of the most commonly used compounds in anticorrosive protection systems because of its excellent rate efficiency/cost. In the case of aluminium alloys, these compounds are employed as inhibitors as well as in the anticorrosive pretreatments to develop protective films. However, chromates are highly toxic and its use involves a high risk for health and environment. Consequently, in the last years intensive efforts have been achieved in the surface treatment industry to find ecological alternatives to this kind of compounds. In this work, the main alternatives proposed in literature to substitute chromates in the surface treatments of aluminium alloys are reviewed. To begin with, the role of chromates in these systems and their environmental consequences has been briefly reviewed.

Los cromatos son unas de las sustancias más comúnmente empleadas en los sistemas de protección frente a la corrosión de aleaciones metálicas, debido a su excelente relación eficacia/coste. En el caso de las aleaciones de aluminio, estos compuestos se aplican tanto como inhibidores, incorporados al medio agresivo, como en pretratamientos anticorrosivos para la formación de películas protectoras. Sin embargo, los cromatos son altamente tóxicos y su uso conlleva un elevado riesgo para la salud laboral y el medio ambiente. Por esta razón, dentro de la industria del acabado superficial, en los últimos tiempos, se ha venido realizando un intenso esfuerzo para buscar alternativas ecológicamente aceptables a este tipo de compuestos. En este trabajo se revisan las principales alternativas planteadas en la bibliografía para sustituir a los cromatos en los tratamientos superficiales de las aleaciones de aluminio. Como punto de partida, se ha llevado a cabo un breve repaso al papel que juegan los cromatos en los sistemas de protección frente a la corrosión y las implicaciones medioambientales que conlleva su uso.

Sueños dentro-fuera: algunos usos del sueño en la teoría social y la investigación etnográfica

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Marko Zivkovic

2006-01-01

En la última década, los ciudadanos de Serbia han venido describiendo su desconcertante mundo social a través del lenguaje del realismo mágico, las teorías de la conspiración, sustancias amorfas, parábolas kakfianas sobre la burocracia, crepúsculos, estados de conciencia alterados. El mundo social se ha asociado también a un sueño o a una pesadilla. Retomando el hilo de los informantes, en este ensayo cuestiono si el “imaginario” serbio no podría representarse de una forma más fructífera como...

Efeito da modificação de superfície de fibras nas propriedades mecânicas de compósitos a base de poli (tereftalato de butileno reforçado por fibras naturais inorgânicas

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Felipe Darabas Rzatki

2014-06-01

Full Text Available O presente trabalho visa investigar a viabilidade de utilização de fibras naturais de sílica amorfa (FNSA como agente de reforço em polímeros de engenharia, assim como avaliar o seu potencial como alternativa às fibras de vidro curtas em aplicações industriais. Diferentes modificações na química de superfície dessas fibras foram avaliadas buscando melhorar a adesão na interface entre fibras e matriz, e consequentemente, melhorar as propriedades mecânicas do compósito. As modificações superficiais das FNSA foram realizadas através de agentes de acoplamento do tipo silano, providos com funções orgânicas distintas. O PBT foi selecionado como matriz devido a sua conhecida facilidade de processamento, mesmo após a incorporação de grandes quantidades de aditivos. A modificação das FNSA foi avaliada a partir da análise termogravimétrica acoplada à espectroscopia no infravermelho com transformada de Fourier. A resistência mecânica e fratura dos compósitos foi investigada por ensaios de tração e microscopia eletrônica de varredura. Finalmente, obtiveram-se compósitos com fibras modificadas com resistência à tração 40% superior ao material base puro.

Synthesis and electrochemical characterization of palladium-based cathode catalysts, resistant to the presence of methanol; Sintesis y caracterizacion electroquimica de catalizadores catodicos base paladio, resistentes a la presencia de metanol

Energy Technology Data Exchange (ETDEWEB)

Salvador, Jose J. [Centro de Investigacion y de Estudios Avanzados del IPN, Mexico D.F. (Mexico)] e-mail: jsalvador@cinvestav.mx; Collins, Virginia H. [Centro de Investigacion en Materiales Avanzados, Chihuahua, Chihuahua (Mexico); Solorza Feria, Omar [Centro de Investigacion y de Estudios Avanzados del IPN, Mexico D.F. (Mexico)

2009-09-15

This work presents the synthesis and characterization of palladium-based electrocatalysts (PdSn and PdPtSn) prepared with the salt-reduction method for oxygen reduction reaction (ORR). The compounds obtained are characterized by sweep electron microscopy, electron transmission microscopy and x-ray diffraction of powder. The electrocatalysts obtained had particle sizes less than 10 nm. The evaluation of the catalytic activity of the catalysts was performed using cyclic voltametry and rotating disc electrode. These experiments were conducted in an H{sub 2}SO{sub 4} 0.5 M solution with different methanol concentrations. The presence of methanol improved the catalytic activity of PdSn, but did not show any effect on the PdPtSn alloy. The performance of the DMFC mono cell using PdPtSn as a cathode showed a potential of 10 mW cm{sup -2} at 50 degrees Celsius. [Spanish] En este trabajo se presenta la sintesis y caracterizacion de electrocatalizadores de base Paladio (PdSn y PdPtSn) preparados mediante el metodo de reduccion de sales, para la reaccion de reduccion de oxigeno (RRO). Los compuestos obtenidos se caracterizaron por microscopia electronica de barrido, microscopia electronica de transmision y difraccion de rayos X de polvos. Los electrocatalizadores obtenidos presentaron un tamano de particula menores a 10 nm. La evaluacion de la actividad catalitica de los catalizadores se llevo a cabo mediante voltametria Ciclica y electrodo de disco rotatorio, estos experimentos fueron realizados en una solucion de H{sub 2}SO{sub 4} 0.5 M con diferentes concentraciones de metanol. La presencia de metanol mejoro la actividad catalitica de PdSn, pero no mostro ningun efecto sobre la aleacion PdPtSn. El desempeno de la monocelda de DMFC usando como catodo PdPtSn, mostro una potencia de 10 mW cm{sup -2} a 50 grados centigrados.

Modelización termodinámica de las aleaciones Ag-Zn

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Gómez-Acebo, T.

1998-05-01

Full Text Available A thermodynamic assessment of the Ag-Zn system has been done using a computerized CALPHAD (calculation ofphase diagrams technique. The liquid, α, β, ε and η phases are described by a regular solution model, the ζ phase by a two-sublattices model, and the γ phase by a four-sublattices model, both based on considerations of their crystal structure and compatibility with the same phase in other systems. Some calculated phase and property diagrams are presented.

Se ha realizado una modelización termodinámica del sistema Ag-Zn mediante la técnica computarizada CALPHAD (calculation of phase diagrams. Las fases líquida, α, β, ε y η se describen mediante el modelo de disolución regular, la fase ζ mediante un modelo de dos subredes, y la fase γ mediante un modelo de cuatro subredes, ambos basados en consideraciones de su estructura cristalina y la compatibilidad del mismo modelo en otros sistemas. Se presentan algunos diagramas de fases y de propiedades calculados.

Estudio de la combinación de los procesos de afinamiento de grano de colada y filtrado en latones

Directory of Open Access Journals (Sweden)

Bustos, O.

1999-08-01

Full Text Available This work considered the evaluation of different parameters and properties of binary brasses 70/30 and 63/37. These materials were previously characterized and then submitted to grain refinement (by mean of chemical additions and/or filtered. Additionally, SEM observations were carried out to identify the grain refinement mechanisms involved in this process. The results obtained from the grain refinement and especially from the combination of both processes show an important grain size decrease and better mechanical properties. Due to the complexity of the Cu-based alloys, it can be concluded that it is necessary to take into account many factors to understand the mechanisms of the grain refinement-filtered process. The present work shows that probably zirconium (in presence of phosphorus, magnesium, iron, sulphur, nitrogen and oxygen could be an effective grain refiner to produce grain refínenme in brasses.

Se consideró la evaluación de diferentes parámetros y propiedades en latones binarios 70/30 y 63/37 previamente caracterizados y sometidos posteriormente a un afinamiento de grano (por medio de adiciones químicas y/o filtrado. Adicionalmente, se realizaron estudios de microscopía electrónica de barrido (MEB tendentes a esclarecer el mecanismo de afinamiento de grano, presente en este proceso. Los resultados obtenidos a partir del afinamiento de grano, y especialmente del acoplamiento de los procesos en cuestión, muestran una disminución importante del tamaño de grano y una mejora en las propiedades mecánicas de ambas aleaciones. Debido a la complejidad de las aleaciones base cobre es necesario considerar una serie de factores para esclarecer el mecanismo de afinamiento de grano y filtrado conjunto. El presente trabajo muestra que existe una alta probabilidad de que el zirconio, en presencia de fósforo, magnesio, hierro, azufre, nitrógeno y oxígeno, sea efectivo para producir afinamiento de grano en latones.

Óxidos de estaño: nuevos ánodos para baterías de Ion-Litio

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Morales, J.

1999-12-01

Full Text Available The electrochemical reaction between Li and tin-based compounds, is reversible and takes place at low potentials measured against the Li electrode. This feature allows the use of these materials as negative electrodes in the manufacturing of Li-ion batteries. The lithium insertion in the tin oxides leads to the formation of Li-Sn alloys. The presence of large tin clusters, formed during the reaction, causes the cracking and crumblimg of the anodic material and the electronic contact between the particles is lost. The electrochemical performance of these materials can be optimized by controlling the growing and size of tin aggregates.

La reacción entre el litio y óxidos o aleaciones de estaño es reversible cuando se realiza por métodos electroquímicos y a bajos potenciales con respecto al electrodo de litio. Esta propiedad permite el uso de estos materiales como electrodos negativos en el diseño y construcción de baterías tipo ion-litio. En el caso de óxidos de estaño la reacción de inserción de litio en la matriz conduce a la formación de aleaciones Li-Sn. La presencia de agregados grandes de átomos de estaño, formados durante la inserción de litio, origina la fragmentación y el desmoronamiento del material anódico. Este efecto provoca la pérdida del contacto eléctrico entre partículas, con el consiguiente deterioro de la batería. La optimización del rendimiento electroquímico de estos materiales se puede lograr mediante el control del crecimiento y tamaño de los agregados de estaño.

Lo sagrado en las sociedades secularizadas

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González Noriega, Santiago

1993-10-01

Full Text Available Not available.

La potencia tutelar burocrática asume la custodia de una masa amorfa. Frente a ella ha de afirmarse una sociedad civil a partir de núcleos de ciudadanos activos. El motor de esta ciudadanía es la formación de un núcleo básico de creencias -«lo sagrados-e- que desempeña un papel comparable, en cuanto a capacidad de movilización, al de las viejas religiones. Lo sagrado «laico» o «filosófico» apunta a aquello que el hombre puede considerar perdurable y conferir sentido a su existencia.

Efecto magnetocalórico en materiales con transiciones de fase de segundo orden: Optimización de la capacidad de refrigeración

OpenAIRE

Caballero Flores, Rafael

2011-01-01

La tesis presenta un estudio del efecto magnetocalórico en materiales con transiciones de fase de segundo orden. Se centra esencialmente en la dependencia con el campo magnético aplicado de la variables termodinámicas relevantes del proceso, estudio de aleaciones basadas en hierro para minimizar los costos de los materiales refrigerantes, y fabricación de composites para minimizar los valores de las intensidades del campo requeridas en el proceso de refrigeración.

Aplicación de técnicas de electrodeposición mediante pulsos de corriente para la obtención de recubrimientos metálicos

OpenAIRE

Imaz Molina, Naroa

2013-01-01

En la presente tesis doctoral se han aplicado herramientas quimiométricas en el estudio y optimización de los parámetros implicados en la electrodeposición de metales y aleaciones mediante pulsos de corriente, centrando el trabajo en dos procesos determinados: • Cromo duro: con objeto de mejorar la funcionalidad y durabilidad de estos recubrimientos tan extendidos industrialmente, se ha investigado el efecto de la electrodeposición mediante pulsos de corriente...

L10 ordered structures in Al-Cu-(Mg alloys at the early stages of elevated temperature aging

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Fuzhong, Xia

2016-09-01

bibliografía, se concluye que la estructura ordenada L10 en Al-3Cu envejecido consiste de átomos de Al y Cu, y en la aleación Al-3Cu-1.78Mg envejecida consisten de átomos de Al, Cu y Mg. Sobre la base de la termodinámica del crecimiento de los precipitados, se propone que la estructura ordenada L10 actúa como de nucleación de las zonas GP en las aleaciones Al-Cu-(Mg durante el envejecimiento.

Preparação e caracterização de membranas assimétricas de poli (fluoreto de vinilideno suportadas em poliéster - I: efeito do tratamento térmico nas propriedades das membranas Preparation and characterization of asymmetric membranes of poly (vinylidene fluoride supported in polyester - I: effect of heat treatment in the properties of membranes

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Mônica B. Thürmer

2010-09-01

Full Text Available O poli(fluoreto de vinilideno (PVDF é um polímero semicristalino contendo uma fase amorfa e uma cristalina. Essa característica é importante para o preparo de membranas assimétricas, pois a fase cristalina tem grande influência na formação da estrutura da membrana e a fase amorfa na porosidade. Membranas de PVDF foram preparadas pelo processo de inversão de fases e avaliadas quanto à permeabilidade e morfologia, bem como o efeito do tratamento térmico. Foram comparadas as seguintes membranas: membrana sem tratamento térmico, membrana com tratamento térmico e membrana comercial. Ensaios de resistência química, fluxo permeado de água a várias pressões, difusão de íons, Microscopia Eletrônica de Varredura (MEV, Calorimetria Exploratória Diferencial (DSC e Análise Termogravimétrica (TGA foram realizados para verificar o comportamento das membranas.Poly(Vinylidene Fluoride (PVDF is a semicrystalline polymer containing an amorphous and a crystalline phase. This characteristic is important for the preparation of asymmetric membranes, because the crystalline phase has great influence on the membranes structure, while the amorphous phase affects the porosity. PVDF membranes were prepared by the phase inversion process, which were then evaluated with regard to permeability and morphology, as well as the thermal treatment effect. The following membranes were compared: without thermal treatment, with thermal treatment and commercially-available membrane. The analysis of chemical resistance, water permeability flux to different pressures and diffusion of ions, in addition to studies with Scanning Electron Microscopy (SEM, Differential Scanning Calorimetry (DSC and Thermogravimetric Analysis (TGA, were performed to investigate the membranes properties.

Microstructural characterization of copper based alloys produced by reactive milling; caracterizacion microestructural de aleaciones base cobre obtenidas mediante molienda reactiva

Energy Technology Data Exchange (ETDEWEB)

Palma, R.; Sepulveda, A.; Zuniga, A.; Donoso, E.; Dianez, M. J.; Criado, J. M.

2010-07-01

The micro and nano structure of Cu-Al, Cu-V and Cu-Ti alloys produced by reactive milling were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Samples with different milling times (t= 0, 10, 20 and 30 h) were considered. The grain size, dislocation density and residual micro strain were evaluated form the XRD data using the Williamson-Hall and Klug-Alexander methods. The evolution of texture as a function of milling time was also studied using XRD. It was found, using TEM, that the grain size and dispersoid size were nano metric in all three alloys considered. (Author) 12 refs.

Ar cinku aizvietotu hidroksilapatītu pētījumi

OpenAIRE

Komarovska, Laura

2013-01-01

Darbā apkopota informācija par hidroksilapatītu īpašībām, to sintēzes iespējām un izmantošanu. Apkopota informācija arī par izmantotajām darba un analīzes metodēm. Eksperimentālajā daļā veikta ar cinku, cēriju un cinku - cēriju aizvietotu hidroksilapatītu sintēze, izmantojot hidrotermisko metodi, kā sākotnējo izejvielu izmantojot amorfas vai kristāliskas fāzes hidroksilapatītu. Iegūtie pulveri raksturoti izmantojot pulvera rentgendifraktometriju un Furjē transformācijas infrasarkano spektrosk...

Preparação e caracterização de catalisadores baseados em pentóxido de nióbio e óxido de cobre(II) aplicados em reações de esterificação e transesterificação

OpenAIRE

Braga, Valdeilson Souza

2007-01-01

Os catalisadores contendo Nb O /SiO -Al O , CuO/Nb O /SiO -Al O , 2 5 2 2 3 2 5 2 2 3 Nb O /CCA (CCA=cinza de casca de arroz) cristalina ou amorfa e CuO/CCA 2 5 investigados neste estudo, foram preparados via diferentes rotas (impregnação em meio aquoso (incipiente ou evaporação) ou grafitização em meio orgânico, em variadas proporções (2, 5, 10, 15, 20 e 25 % em massa). Estes materiais foram aplicados em reações de esterificação de ácido acético com álcoois (etanol, n-butanol e iso-pentanol)...

A modification of the method for determining current efficiency of aluminium electrolytic cells; Modification de la methode permettant de determiner le rendement des cuves dans la production d'aluminium par electrolyse; Izmenenie metoda opredeleniya ehffektivnosti toka v alyuminievykh ehlektroliticheskikh bakakh; Modificacion del metodo para determinar el rendimiento de las celdas utilizadas en la produccion de aluminio por electrolisis

Energy Technology Data Exchange (ETDEWEB)

Pradzynski, A [Institute of Basic Technical Problems, Polish Academy of Sciences. Warsaw (Poland); Orman, Z [Institute of Nonferrous Metals, Gliwice (Poland)

1962-01-15

de faciliter l'application de cette methode dans les usines d'aluminium et d'eviter toutes les restrictions et tous les dangers qu'entraine la manipulation, en dehors des laboratoires speciaux pour l'etude des radioisotopes, de sources radioactives non scellees. De l'or inactif a ete introduit dans' l'alliage type et dans le bain de la cuve electrolytique. La concentration d'or dans les echantillons d'alliage type et dans les echantillons preleves dans la cuve a ete mesuree apres irradiation de ces echantillons dans un reacteur nucleaire. (author) [Spanish] El procedimiento para determinar el rendimiento de las celdas para la produccion de aluminio por electrolisis fue descrito inicialmente por Rempel y col. y fue perfeccionado por Bozoky y col. que emplearon el radioisotopo {sup 198}Au. Este procedimiento consiste en preparar aleaciones tipo de aluminio con {sup 198}Au y medir la elevada actividad especifica de muestras de la aleacion con un tubo Geiger-Mueller, introduciendo plomo como absorbente entre el tubo y la muestra. Los autores midieron la actividad especifica de la aleacion tipo despues de diluirla con una cantidad conocida de aluminio puro. De esta manera, las muestras de aleacion tipo diluida y las muestras tomadas en la celda electrolitica tienen una actividad especifica del mismo orden de magnitud, que puede ser medida sin necesidad de absorbente. Los autores han recurrido al analisis por radiactivacion con objeto de facilitar la aplicacion de este procedimiento en las fabricas de aluminio y evitar las restricciones y los peligros que supone la utilizacion de fuentes de radiacion no encerradas fuera .de los laboratorios de radioisotopos. El procedimiento consiste en introducir oro inactivo en la aleacion tipo y en la masa fundida de la celda electrolitica. Se extraen muestras de la aleacion y del electrolito y, despues de irradiarlas en un reactor nuclear, se determina la concentracion de oro. (author) [Russian] Metod opredeleniya ehffektivnosti toka v

Músculos Inteligentes en Robots Biológicamente Inspirados: Modelado, Control y Actuación

OpenAIRE

Colorado Montaño, Julián; Barrientos Cruz, Antonio; Rossi, Claudio

2011-01-01

Resumen: Las aleaciones metálicas que exhiben una propiedad conocida como efecto de memoria de forma, pertenecen a la clase de materiales inteligentes cuya aplicación más notable en el campo de la robótica se refleja en el uso de actuadores musculares artificiales, ó músculos inteligentes. Estos materiales tienen una estructura cristalina uniforme que cambia radicalmente en función de su temperatura de transición, causando su deformación. Se les denomina materiales inteligentes por la capacid...

Estudio de la conductividad de un material compuesto por cobre y óxido de grafeno reducido

OpenAIRE

Rodríguez Escudero, Miguel Ángel

2016-01-01

Desde el descubrimiento de la corriente eléctrica, la principal aplicación del cobre es como conductor en todas aquellas aplicaciones relacionadas con ella, principalmente como componente eléctrico. En la actualidad, con el desarrollo de materiales metálicos, numerosos estudios científicos e industriales han llevado a crear diferentes tipos de aleaciones de cobre, con aplicaciones cada vez más amplias o altamente especializadas. En este desarrollo de materiales y tecnologías que mejoren la co...

Estudio del comportamiento tribologico y de las interacciones de superficie de nuevos nanofluidos ionicos

Science.gov (United States)

Espinosa Rodriguez, Tulia

tribocorrosion processes. The formation of a coating layer on magnesium alloys from phosphonate imidazolium ionic liquids by immersion and by chronoamperometry has been described. The new coatings reduce the abrasive wear in the magnesium-aluminium alloy but they are not effective in the magnesium-zinc alloy, which prevent the formation of continuous coatings. Los liquidos ionicos son sales liquidas a temperatura ambiente o bajas temperaturas que presentan excelentes propiedades fisico-quimicas. En el presente trabajo se estudian como lubricantes en problemas tribologicos complejos como la lubricacion de metales contra si mismos, el desarrollo de lubricantes base agua y de nuevas superficies autolubricadas. Cuando no es posible reducir la friccion y desgaste mediante lubricacion, como en las aleaciones de magnesio, los liquidos ionicos se han estudiado como precursores de recubrimientos protectores. Se han determinado las interacciones superficiales y los procesos de corrosion sobre cobre y sobre acero con diferentes liquidos ionicos proticos y aproticos para desarrollar nuevos lubricantes y aditivos. En el contacto cobre/cobre, excepto el liquido ionico protico derivado del oleato, todos los liquidos ionicos estudiados presentan mejor comportamiento tribologico que el lubricante comercial Polialfaolefina 6. En el contacto acero/zafiro, los nuevos liquidos ionicos proticos son buenos lubricantes cuando se utilizan en estado puro, y, como aditivos en agua, generan peliculas adsorbidas sobre la superficie del metal reduciendo la friccion y el desgaste tras la evaporacion del agua. Para evitar el periodo de alta friccion inicial en presencia de agua, se han generado peliculas superficiales de liquido ionico sobre el acero en condiciones estaticas. El mejor comportamiento lubricante tanto en el contacto cobre/cobre como en el contacto acero/zafiro se obtiene para el liquido ionico protico derivado del anion adipato, con dos grupos carboxilicos. Las interacciones de los grupos

An electrochemical investigation of the corrosion behavior of Al-Si-Cu hypereutectic alloys in alcoholic environments

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Traldi, S. M.

2003-12-01

Full Text Available Al-Si-Cu hypereutetic alloys produced by spray forming are mostly used in the automotive industry, especially for cylinder liners. They have the advantage of low weight associated with low coefficient of thermal expansion and excellent mechanical properties - mainly wear resistance at high temperatures. The corrosion resistance of these alloys in fuels, particularly alcoholic media, however is not yet known. In this investigation, electrochemical impedance spectroscopy (EIS and potentiodynamic polarisation have been used to evaluate the corrosion resistance of a hypereutectic Al-Si-Cu alloy in alcoholic environments. The EIS tests were carried out in pure ethanol, and ethanol with small additions (1 mM of acid and chloride, to investigate the effect of these contaminants on corrosion resistance. The corrosion resistance of a grey cast iron has also been evaluated in pure ethanol for comparison. The Al-Si-Cu alloy showed high corrosion resistance in pure ethanol, far superior to that of grey cast iron in the same medium.

Aleaciones hipereutécticas producidas por conformación por spray son muy empleadas en la industria automovilística, especialmente en los revestimientos de los cilindros. Tienen la ventaja de añadir menos peso con bajo coeficiente de expansión térmica y excelentes propiedades mecánicas, sobre todo resistencia al desgaste en altas temperaturas. Todavía, la resistencia a la corrosión de estas aleaciones en combustibles no es conocida. En este estudio fueron utilizadas las técnicas de espectroscopia de impedancia electroquímica y polarización potenciodinámica, para evaluar la resistencia a la corrosión de una aleación hipereutéctica Al-Si-Cu en medio alcohólico. Las pruebas fueron conducidas en etanol puro y etanol con pequeñas adiciones (1 mM de ácido y cloruro, con la finalidad de investigar el efecto de estos contaminantes en la resistencia a la corrosión. Hierro fundido gris, también fue

Biochemical analysis of the Hormoconis resinae fungal mycelium in the corrosion of aeronautical aluminium alloys

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Araya, R.

2007-06-01

Full Text Available Biochemical analyses of the Hormoconis resinae fungal mycelium would explain behaviour differences of corrosive and non-corrosive strains on Al and its aeronautical alloys. In previous works its aggressiveness had been studied through SEM-EDX surface analysis, electrochemical techniques and immersion testing. In this paper separation of the proteins of the mycelium produced by a non-corrosive strain and its culture along three generations was performed. Cultures were prepared in batch in the presence and absence of pure Al and AA 2024, AA 7005 and AA 7075 alloys. The mycelia grown throughout the three generations increasingly
recovered usual characteristics at the third replication, included their corrosiveness on Al and its alloys previously shown by all our strains. Amongst the bio-molecule fractions isolated and analysed during this preliminary study only the proteins revealed changes with the generation grown. When this fungal strain was cultured in the presence of alloy metal sheets electrophoresis of the protean fraction was correlative with the distinct mycelia behaviour observed, including corrosiveness on Al and its alloys.

Las diferencias entre el comportamiento corrosivo y no corrosivo de una cepa del hongo Hormoconis resinae sobre aluminio y sus aleaciones aeronáuticas se explicarían a través de análisis bioquímicos del micelio. En trabajos previos, el comportamiento corrosivo se estudió mediante análisis de superficie SEM-EDX, técnicas electroquímicas y ensayos de inmersión. En este trabajo, se llevó a cabo la separación de proteínas del micelio producido por una cepa que perdió su corrosividad y su cultivo a través de tres generaciones. Cultivos en batch, en presencia y ausencia de aluminio y sus aleaciones AA 2024, AA 7005 y AA 7075, a través de tres generaciones del micelio crecido, fueron recuperando sus características, incluida su habitual corrosividad, en la tercera replicaci

Estudio de corrosión galvánica en pares latón/acero inoxidable y latón/fundición de hierro

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Ohanian, M.

2011-08-01

Full Text Available Corrosion attack in heat exchanger systems is a topic of main interest for the maintenance in each industrial plant. These are multigalvanic systems with particular geometric and fluidodynamic complexity. Corrosive damages include zinc selective dealeation in copper alloys. In order to explain zinc dealeation attack, this paper deals with laboratory scale testing, characterization and interactions between two copper and zinc alloys (Yellow brass –UNS C268– and Admiralty brass –UNS C443– compared to AISI 316 stainless steel and cast iron. The tests were performed at 20 °C in 1.5 % NaCl and 1.5 % Na₂SO₄ solutions, pH 8 and each material was characterized by potentiodynamic sweeps. The couples are analyzed by studying transient galvanic currents. We conclude about the cause of the analyzed pathology, brass protection potential ranges and its coupling compatibility with other metals.

El ataque por corrosión en los sistemas intercambiadores de calor constituye un problema para el mantenimiento de cualquier planta industrial. Se trata de sistemas multigalvánicos con particular complejidad geométrica y fluidodinámica. Las patologías corrosivas incluyen el fenómeno de dealeación selectiva de cinc en las aleaciones de cobre. A fin de explicar un caso particular de ataque por decinficación (deterioro en placa de intercambiador de calor de tubos de inoxidable, el presente trabajo aborda en ensayos a escala de laboratorio, la caracterización e interacciones entre dos aleaciones de cobre y cinc, (Yellow brass –UNS C268– y Admiralty brass –UNS C443–, respecto a acero inoxidable AISI 316 y fundición gris de hierro. Los ensayos se realizan a 20 °C en disoluciones de NaCl 1,5 % y Na₂SO₄ 1,5 % y pH 8. Se caracterizan electroquímicamente las aleaciones y materiales involucrados mediante barridos potenciodinámicos. Los pares galvánicos formados se analizan mediante el

Análisis numérico y experimental del desgaste de herramienta e integridad superficial en los procesos de torneado de Inconel 718

OpenAIRE

Díaz Álvarez, José

2013-01-01

En el sector de fabricación mecánica, un elevado volumen de trabajo está asociado a los procesos de arranque de viruta. El mecanizado es un proceso termomecánico complejo en el que influyen muchos factores, principalmente el material de la pieza, el material y geometría de la herramienta, los parámetros de mecanizado y el uso o no de fluido de corte. Esta tesis se enmarca en los procesos de mecanizado de aleaciones termorresistentes. La tesis está centrada en un solo material, en este caso la...

Caracterización de un robot para aplicaciones de mecanizado con requerimientos de tolerancias

OpenAIRE

Ferreras Higuero, Eugenio

2014-01-01

El presente Trabajo fin Fin de Máster, versa sobre una caracterización preliminar del comportamiento de un robot de tipo industrial, configurado por 4 eslabones y 4 grados de libertad, y sometido a fuerzas de mecanizado en su extremo. El entorno de trabajo planteado es el de plantas de fabricación de piezas de aleaciones de aluminio para automoción. Este tipo de componentes parte de un primer proceso de fundición que saca la pieza en bruto. Para series medias y altas, en función de las pr...

Simulación numérica de la descomposición espinodal en sistemas de aleación hipotéticos A-B y A-B-C

Directory of Open Access Journals (Sweden)

Avila-Dávila, E. O.

2012-06-01

Full Text Available The phase field method is based on the thermodynamics, mechanism and kinetic of the precipitation reactions in alloys. This method can be used to simulate numerically the microstructural evolution in an alloy system, and constitutes a powerful tool to predict the phase transformations. The phase field method solves the nonlinear Cahn- Hilliard partial differential equation and offers computational advantages. The effect of the parameters into this equation on the morphology and kinetics of the phase separation in binary A-B and ternary A-B-C hypothetical alloy systems with a miscibility gap was analyzed. The results showed that the atomic mobility modifies the phase separation kinetics. In contrast, elastic-strain energy is an important parameter that affects the morphology of phases causing changes from spheres to cuboids or plates with preferential crystallographic alignment.

El Método de Campo de Fases, basado en fundamentos de termodinámica, mecanismos y cinética de reacciones de precipitación en aleaciones, es útil para simular numéricamente la solidificación de aleaciones de interés industrial, su microestructura y su evolución durante ciclos térmicos. Este método resuelve la ecuación diferencial parcial de Cahn y Hilliard y ofrece como ventajas su sencillez y rapidez computacional. En este trabajo se analizó el efecto de los parámetros que intervienen en tal ecuación sobre la morfología y cinética de la separación de fases de sistemas de aleación hipotéticos A-B y A-B-C con laguna de inmiscibilidad. Los resultados obtenidos mostraron que los cambios en la movilidad atómica modifican la cinética de la separación. En contraste, la energía de deformación elástica afecta directamente la morfología de las fases, causando que la morfología pase de esferas a cubos con bordes redondeados o placas con alineación cristalográfica preferencial.

Alternative methods to attach components in printed circuit boards to improve their recyclability

Directory of Open Access Journals (Sweden)

André Canal-Marques

2014-01-01

Full Text Available Las Placas de Circuitos Impresos constituyen la base de la industria electrónica. Sin embargo, generan residuos de difícil eliminación y reciclaje, debido a la diversidad de materiales y componentes presentes y su difícil separación. La sustitución de soldaduras de Pb-Sn por aleaciones libres de plomo intenta minimizar la toxicidad que implica la presencia de Pb, pero no aborda la separación de los componentes para su posterior reutilización y/o reciclaje. Este artículo presenta una revisión bibliográfica sobre el problema ambiental que constituyen las placas de circuitos impresos, el estudio de alternativas de fijación, pruebas de fiabilidad para comparar con las placas convencionales y sistemas comerciales para validar o servir de base para futuras investigaciones, enfocadas hacia el desmontaje de PCI. Además, se muestran algunos estudios incipientes mediante prototipos para la realización de pruebas visuales y funcionales.

Ultrasonic Inspection following Heat Treatment of Uranium Alloys; Controle des Traitements Thermiques d'Alliage d'Uranium par Ultrasons; Kontrol' termicheskoj obrabotki uranovykh splavov s pomoshch'yu ul'trazvuka; Control Ultrasonico de los Tratamientos Termicos de Aleaciones de Uranio

Energy Technology Data Exchange (ETDEWEB)

Destribats, Marie-Therese; Cherpentier, C.; Papezik, F.; Pigeon, M. [Centre d' Etudes Nucleaires Desaclay (France)

1965-10-15

necessaire. Il s'est avere indispensable de pouvoir effectuer un controle sur l'ensemble de l'element et la totalite d'une production afin de connaitre exactement la qualite du combustible utilise. Ce controle ne pouvait etre envisage par micrographie en raison de la duree trop longue des operations et de leurs resultats partiels. Le controle auquel les auteurs ont procede est base sur le principe de l'absorption des ultrasons par les materiaux. L'absorption est fonction de la structure du milieu. Si {lambda} est petit par rapport a la taille du grain G, elle est faible; si G est de l'ordre de {lambda}/2, elle est tres grande. Les tout premiers essais ont ete faits dans l'air, par echos multiples, puis en mesurant la hauteur du premier echo, ensuite par transmission dans l'eau, en comparant la hauteur de l'echo transmis a celle de l'echo initial. Dans le controle industriel, on compare l'amplitude de l'echo transmis par le materiau a l'echo obtenu avec un etalon bien traite de meme nuance et de meme forme geometrique. L'examen se fait dans une machine speciale; les materiaux sont entraines en rotation par des galets et les traducteurs orientables se deplacent le long de l'element. L'exploration helicoiedale s'effectue avec un pas inferieur a 5 mm. Le generateur d'ultrasons comporte un systeme de regulation qui maintient l'echo de reference constant. On montrera, une serie d'enregistrements obtenus sur divers alliages, en particulier des defauts observes sur les elements traites par induction au defile. Des zones mal traitees inferieures a 1 cm{sup 2} sont detectees. Actuellement, on controle ainsi tous les combustibles en uranium faiblement allies des divers reacteurs G2, EL3, EDF1, EDF2 et INCA, c'est-a-dire des barres et tubes de diametre compris entre 20 et 95 mm. (author) [Spanish] Con el fin de aumentar en los reactores la estabilidad de las aleaciones con bajo contenido de uranio resulta a menudo necessario afinar el grano mediente tratamientos termicos. Para conocer

Application of oxide coatings to metals in electrolyte solutions by microplasma methods

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Vladimirovich Timoshenko, Aleksander

2000-10-01

Full Text Available Microplasma oxidation of aluminium alloys in alkaline colloidal and finely dispersed solutions is analysed. Oxidation causes both electrolyte and alloy components to be incorporated into resultant coatings, which affect the deposition parameters and coating properties. Oxidation process has been studied at spark, micro-are, and are stages under an alternating current polarisation and under purely anodic polarisation. It is shown that the cathodic component of the alternating current not only facilitates subsequent anodic process, but also contributes to the formation of an oxide layer.

Se ha examinado la aplicación de procesos de oxidación por microplasma de las aleaciones de aluminio en electrólitos alcalinos, tanto en estado coloidal como microdisperso. Se descubrió que durante el proceso de la oxidación, en la estructura del recubrimiento óxido, van incluyéndose tanto los componentes del electrólito como los de la aleación, lo que modifica las propiedades y parámetros de deposición de las aleaciones obtenidas. El proceso de la oxidación se examinó a lo largo de las siguientes etapas: chispas, micro-arco y arco, tanto bajo la polarización de la corriente alterna como en condiciones de polarización anódica. Se ha demostrado que la componente catódica de la corriente alterna polarizante no sólo facilita los siguientes procesos anódicos, sino que además contribuye a los procesos de formación de la capa óxida.

Synthesis and evaluation of Pt-alloys supported on MWCNTS as ethylene glycol-tolerant ORR cathodes

Energy Technology Data Exchange (ETDEWEB)

Morales-Acosta, D.; Arriaga, L.G. [Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, Pedro Escobedo, Queretaro (Mexico); Alvarez-Contreras, L. [Centro de Investigacion en Materiales Avanzados S. C., Chihuahua, Chihuahua (Mexico); Fraire Luna, S.; Rodriguez Varela, F.J. [Cinvestav, Unidad Saltillo, Ramos Arizpe, Coahuila (Mexico)]. E-mail: javier.varela@cinvestav.edu.mx

2009-09-15

In this work, a Pt-Co/MWCNT alloy (atomic ratio 70:30) was synthesized and evaluated as oxygen reduction reaction (ORR) cathode for Direct Ethylene Glycol Fuel Cells (DEGFC) applications. The alloy showed good performance for the ORR in acid medium, while in the presence of 0.125M EG (C{sub 2}H{sub 6}O{sub 2}) the MWCNTs-supported electrocatalyst showed a very high selectivity for the cathodic reaction and a high degree of tolerance to the organic fuel, i.e., a very small shift in the onset potential for the ORR, Eonset, and no peak current densities associated to the oxidation of EG, a detrimental effect of organic fuels normally observed in the case of Pt-alone electrocatalysts. [Spanish] En este trabajo, se sintetizo y evaluo una aleacion Pt-Co/NTCMP (razon atomica 70/30) como catodo de reaccion de reduccion de oxigeno (RRO) para aplicaciones de celdas de combustible de glicol de etileno directo (CCGED). La aleacion mostro buen desempeno para la RRO en medio acido, en tanto que la presencia de 0.125M de GE (C{sub 2}H{sub 6}O{sub 2}) del electrocatalizador soportado por NTCMP mostro una muy alta selectividad para la reaccion catodica y un alto grado de tolerancia al combustible organico, es decir, un corrimiento muy pequeno del potencial de inicio para la RRO, Einicio, y no densidades de corriente asociadas a la oxidacion del GE, efecto perjudicial de los combustibles organicos que se observa en el caso del electrocatalizadores solo de Pt.

Ab-initio electronic and magnetic properties of Fe-Al alloys

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Apiñaniz, E.

2000-06-01

Full Text Available This work presents ab-initio self-consistent calculations performed with the TB-LMTO code to study the different phases of the Fe-Al phase diagram, corresponding to the ordered structures B2, DO3 and B32 and for Fe50Al50 and Fe3Al compositions. Both, unpolarized and spin-polarized calculations have been performed to deduce the energetic difference between the paramagnetic and ferromagnetic state of the corresponding structure. Calculations for the disordered structures have also been performed for the previously mentioned compositions. These results show that by disordering the alloy magnetism is enhanced and that the equilibrium lattice parameter increases.

En este trabajo se presentan cálculos autoconsistentes ab-initio realizados con el método TB-LMTO (Tight Binding Linear Muffin Tin Orbital con el fin de estudiar las diferentes estructuras que se presentan en el diagrama de fases de las aleaciones Fe-Al. Se han estudiado las estructuras ordenadas B2, DO3 y B32 para las siguientes concentraciones: Fe50Al50 y Fe3Al. Asimismo, se han realizado cálculos teniendo y sin tener en cuenta la polarización de spin con el fin de poder deducir la diferencia energética entre los estados ferromágneticos y paramágneticos de la misma estructura. Por otra parte se han realizado estos mismos cálculos para estructuras desordenadas y las mismas concentraciones. Los resultados muestran que mediante el desorden aumenta el magnetismo de estas aleaciones y crece el parámetro de red.

Estudio microestructural y de resistencia de uniones soldadas de la aleación AW7020 por procedimiento MIG en función de la preparación de bordes

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Bloem, Carlos Alberto

2000-02-01

Full Text Available Medium strength AW7XXX aluminium alloys are widely used as welded structures and in transportation. The applications of these alloys are limited by the behavior of the welded joints. There is not an agreement on the joint geometry that must be used on the 5 mm aluminium welds. The microhardness evolution is one of the most important strength indicator, For this reason, the aim of this work is to study the welded joint geometry influence on microhardness profile and on microstructure of a welded aluminium alloy AW7020 MIG, filled with AW5356.

Las aleaciones de aluminio de la serie AW7XXX de medias prestaciones se están empleando ampliamente en el sector del transporte, así como en la construcción de estructuras soldadas. La posibilidad de que estas aleaciones se empleen con mayor profusión está condicionada a un mayor conocimiento del comportamiento de la unión soldada. La evolución de la microdureza como un indicador de resistencia es ampliamente utilizado, pero no hay acuerdo sobre el efecto de la preparación de bordes previo a la soldadura y es por ello que el objetivo de este trabajo sea estudiar la influencia de la preparación de bordes sobre el perfil de microdureza y microestructura de la unión soldada de una aleación de aluminio AW7020, soldada mediante el proceso MIG, empleando como metal de aporte AW5356.

Catalizadores Fe/SiO2 para la oxidación selectiva de metano hasta formaldehido

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Carlos Alberto Guerrero Fajardo

2006-05-01

Full Text Available La oxidación selectiva de metano a formaldehido fue analizada con catalizadores de hierro soportados sobre sílice preparados por el método sol-gel, el cual permite obtener gran área superficial del soporte facilitando una alta dispersión del hierro sobre la matriz amorfa de la sílice. Se prepararon siete (7 catalizadores, uno de ellos correspondiente al soporte de sIlice, otros cinco (5 con cargas de hierro entre 0,1-0,5 % en peso. El catalizador No. 7 (0,5% Fe en peso se prepara con control de pH neutro y resultó de características más homogéneas ya que no se presentaron especies aisladas de hierro, corroborado por análisis SEM y TEM. Las áreas BET mayores son del orden de 1 757 y 993 m2.g-1 para los catalizadores de 0,5% Fe, con porcentajes promedio del 36% de microporosidad y 43% de mesoporosidad. La difracción de rayos X confirma la estructura amorfa del catalizador. La actividad catalítica es realizada con el catalizador No. 7 a presión atmosférica en reactor de cuarzo, mezcla de reacción CH / 0 /N =7.5/1/4, intervalo de temperatura 400-750°C. Los productos de reacción son analizados por cromatografía 2 2 de gases con TCD. Los catalizadores heterogéneos presentan mayor conversión de metano pero con selectividad al metanol, mientras que el catalizador homogéneo No. 7 da mejores resultados en formaldehido. Para el catalizador 7, el porcentaje más alto de conversión (8,60 mol% se presenta a 650°C. La selectividad al formaldehido está en 50 mol% entre 600-650°C y en este intervalo se encuentra el máximo rendimiento (0,31 g HCH0/kg catalizador,considerando así que la temperatura de operación es de 650°C.

“MEDICION DE PARAMETROS GENERADORES DE ESFUERZOS RESIDUALES DURANTE EL PROCESO DE SOLDADURA DE ACERO INOXIDABLE AUSTENITICO AISI 304L”.

OpenAIRE

García López, Christian Jesus

2012-01-01

En la actualidad los procesos de soldadura por arco eléctrico se han convertido en la técnica por excelencia para la unión del acero y sus aleaciones. Se puede mencionar que la importancia de la soldadura, es tal, que sin ella no serían posibles muchos de los productos y servicios que cotidianamente son consumidos o requeridos por las sociedades contemporáneas actuales. Cada vez con mayor longitud y diámetro se instalan líneas de tubería para la distribución y conducción de tod...

Fenómenos de corrosión galvánica en las uniones aluminio y acero

OpenAIRE

Domínguez Parra, Alberto

2009-01-01

La corrosión es un proceso de degradación de un material al interactuar con el ambiente que le rodea. El presente proyecto trata de la corrosión galvánica de aceros y fundiciones, en contacto con aleaciones de aluminio. Su experimentación se ha realizado con acero AE 275 B, y fundición EN-GS 400 12. Se utilizó lingote de aluminio A356 obtenido por colada por gravedad, y dos tipos de muestras, con y sin tratamiento térmico T6, de A 356 producidas por el procedimiento de sub-liquidus casting...

Estudio del proceso de solidificación en fundición de aluminio para brazos del sistema de freno de un ascensor, mediante elementos finitos

OpenAIRE

Cangás Herrera, Juan Gabriel; Valverde Paredes, Edgar Alexander

2014-01-01

163 hojas : ilustraciones, 29 x 21 cm + CD-ROM 5695 El presente trabajo contiene el estudio del proceso de fundición de aluminio para brazos del sistema de freno de un ascensor eléctrico mediante elementos finitos, con la utilización del software Click2Cast. Se realiza un marco teórico sobre temas inherentes al objeto de este trabajo, como son los procesos de fundición, aleaciones de aluminio, defectología en los procesos de fundición y solidificación de metales, así como una introducció...

Adaptación de una corona metal cerámica como pilar de una prótesis parcial removible preexistente

OpenAIRE

Torres Herbozo, Melissa; Quintana del Solar, Martin; Castillo Andamayo, Diana

2016-01-01

El presente artículo muestra el reporte de un caso clínico donde se confeccionó una corona metal cerámica que fue adaptada a una prótesis parcial removible pre existente. Por lo general el tratamiento para estos casos es la confección de una nueva prótesis parcial removible adaptada a la nueva corona, lo cual implica mayor tiempo de trabajo y costo para el paciente. Diversos materiales y técnicas pueden ser utilizados para la realización de la corona como por ejemplo coronas de aleaciones met...

Chemical and microstructural diversity of steel grades

Directory of Open Access Journals (Sweden)

Zorc, B.

2002-12-01

Full Text Available The aim of the paper is to show, using theoretical and practical analyses, chemical and microstructural differences among individual types of steel grades 355 found in the market. The mechanical properties required for these steels are achieved by alloying or thermomechanical treatment. It was found that the individual types of this steel are poorly weldable, particularly those of large thickness.

El objetivo del artículo es presentar, en base a un análisis teórico y práctico, las diferencias químicas y microestructurales entre los diferentes tipos de aceros calidad 355 que pueden encontrarse en el mercado. Las características mecánicas requeridas en estos aceros se consiguen con aleaciones, o bien a través de tratamientos termo-mecánicos.Se ha llegado a la conclusión de que determinados tipos de acero son más difíciles de soldar, en especial cuando se trata de espesores grandes.

Estudo da Faciologia Orgânica em Rochas Geradoras Marinhas Cretáceas do Grupo Villeta, Bacia do Valle Superior del Magdalena,Colômbia: Implicações Paleoambientais.

Directory of Open Access Journals (Sweden)

Juliana Andrade Iemini

2007-07-01

Full Text Available As rochas pelíticas do Cretáceo superior são asgeradoras da maior parte das reservas de petróleo naColômbia. A Bacia do Valle Superior Del Magdalena(VSM, possui afloramentos de boa qualidade e comníveis de evolução térmica, que variam desde oimaturo até o fim da “janela” de geração de óleo,tornando esta região como uma das mais propíciaspara o estudo dos processos de geração e migraçãoprimária do petróleo no Cretáceo superior. O objetivoprincipal consistiu no estudo de fácies orgânicaatravés da caracterização geoquímica e análisepalinofaciológica das rochas geradoras de petróleocretáceas do VSM numa seção aflorante (QuebradaBambuca, objetivando o entendimento do controleexercido pela evolução paleoambiental sobre opotencial gerador e as variações composicionaisda matéria orgânica a partir da integração dosdados geoquímicos e palinofaciológicos. Paratanto, foram utilizadas análises organogeoquímicas(Carbono Orgânico Total - COT e Pirólise Rock-Eval, cedidas pelo Instituto Colombiano doPetróleo ICP - ECOPETROL e palinofaciológicasem amostras das Formações Tetuan Bambuca e LaLuna, Grupo Villeta, Bacia do Valle Superior delMagdalena. As rochas dessa formação apresentamum elevado conteúdo orgânico, com valores deCOT de até 23%. As lâminas organopalinológicasforam analisadas através de técnicas de palinofácies(microscopia em luz branca transmitida e luz azul/ultravioleta incidente-fluorescência realizando acontagem dos componentes orgânicos particuladosdos grupos do querogênio (fitoclasto, palinomorfoe matéria orgânica amorfa e da determinação doÍndice de Coloração de Esporos (ICE. A analisemicroscópica revelou um predomínio de matériaorgânica amorfa. Os palinomorfos são representadospor dinoflagelados e esporomorfos, sendo osdinoflagelados os mais representativos. A matériaorgânica amorfa apresenta fluorescência amarelaa laranja. O material lenhoso representa a

Overview on the permanent magnets technology of rare earth based on Nd-Fe-B; Panorama general sobre tecnologia de imanes permanentes de tierras raras a base de Nd-Fe-B

Energy Technology Data Exchange (ETDEWEB)

Rosales Vazquez, Maria Ines [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

1991-12-31

In this paper the technological development in the area of permanent magnetic materials, is shown, from the 1930`s when the first aluminum-nickel-cobalt (Al-Ni-Co) magnets appeared. As a result of the continuous worldwide research in this field, it was made known, during the 1980`s decade of a new type of magnets based on Neodymium (Nd). In accordance with the outstanding magnetic properties of these magnets, at the Instituto de Investigaciones Electricas (IIE), their development was initiated, focussed on the stages and parameters definition of their manufacturing process. Up to now, the research has been oriented to the preparation of magnets of the isotropic agglutinated type and the manufacturing process encompasses the following stages: a) Alloy preparation; b) Microcrystals obtainment; c) Magnet preparation. The preliminary results that have been obtained in the magnetic characterization show that the quality of the prepared magnets is comparable to the quality of the imported magnets and/or to the ones other research groups report. [Espanol] En este trabajo se muestra el desarrollo tecnologico del area de materiales magneticos permanentes a partir de los anos treinta en que surgieron los primeros imanes de aluminio-niquel-cobalto (Al-Ni-Co). Como resultado de la constante investigacion a nivel mundial en ese campo, durante el decenio de los ochenta se informo en torno a un nuevo tipo de imanes a base de neodimio (Nd). Atendiendo a las propiedades magneticas sobresalientes de estos imanes, en el Instituto de Investigaciones Electricas (IIE), se inicio el desarrollo de los mismos, enfocandolo a la definicion de las etapas y parametros del proceso de fabricacion. Hasta ahora, la investigacion se ha orientado a la preparacion de imanes de tipo isotropico aglutinado y el proceso de fabricacion comprende las etapas: a) preparacion de la aleacion; b) obtencion de microcristales, y c) preparacion de los imanes. Los resultados preliminares que se han obtenido en la

Overview on the permanent magnets technology of rare earth based on Nd-Fe-B; Panorama general sobre tecnologia de imanes permanentes de tierras raras a base de Nd-Fe-B

Energy Technology Data Exchange (ETDEWEB)

Rosales Vazquez, Maria Ines [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

1990-12-31

In this paper the technological development in the area of permanent magnetic materials, is shown, from the 1930`s when the first aluminum-nickel-cobalt (Al-Ni-Co) magnets appeared. As a result of the continuous worldwide research in this field, it was made known, during the 1980`s decade of a new type of magnets based on Neodymium (Nd). In accordance with the outstanding magnetic properties of these magnets, at the Instituto de Investigaciones Electricas (IIE), their development was initiated, focussed on the stages and parameters definition of their manufacturing process. Up to now, the research has been oriented to the preparation of magnets of the isotropic agglutinated type and the manufacturing process encompasses the following stages: a) Alloy preparation; b) Microcrystals obtainment; c) Magnet preparation. The preliminary results that have been obtained in the magnetic characterization show that the quality of the prepared magnets is comparable to the quality of the imported magnets and/or to the ones other research groups report. [Espanol] En este trabajo se muestra el desarrollo tecnologico del area de materiales magneticos permanentes a partir de los anos treinta en que surgieron los primeros imanes de aluminio-niquel-cobalto (Al-Ni-Co). Como resultado de la constante investigacion a nivel mundial en ese campo, durante el decenio de los ochenta se informo en torno a un nuevo tipo de imanes a base de neodimio (Nd). Atendiendo a las propiedades magneticas sobresalientes de estos imanes, en el Instituto de Investigaciones Electricas (IIE), se inicio el desarrollo de los mismos, enfocandolo a la definicion de las etapas y parametros del proceso de fabricacion. Hasta ahora, la investigacion se ha orientado a la preparacion de imanes de tipo isotropico aglutinado y el proceso de fabricacion comprende las etapas: a) preparacion de la aleacion; b) obtencion de microcristales, y c) preparacion de los imanes. Los resultados preliminares que se han obtenido en la

Dispersion-Type Absorbing Materials for the Control Organs of Thermal Reactors; Absorbants du Type a Dispersion pour les Organes de Commande des Reacteurs a Neutrons Thermiques; Pogloshchayushchie materialy dispersionnogo tipa dlya organov regulirovaniya teplovykh reaktorov; Absorbentes de Tipo Dispersion para los Organos de Mando de los Reactores Termicos

Energy Technology Data Exchange (ETDEWEB)

Nosov, V. I.; Ponomarjov-Stepnoj, H. H.; Portnoj, K. I.; Savel' ev, E. G.

1964-06-15

type nimonik auxquels on a ajoute des. oxydes de terres rares ont des caracteristiques d'endurance et des.caracteristiques thermo-physiques d'une valeur relativement elevee (o{sub B}, E, {lambda}) a des temperatures elevees pour les valeurs de la concentration de l 'absorbant voisines de 10%. Les materiaux du type a dispersion de ce genre ont une radioresistance satisfaisante dans un champ de rayonnement ( Tilde-Operator 3 * 10{sup 20}n/cm{sup 2}) aux hautes temperatures. (author) [Spanish] Los autores exponen los resultados de su estudio de las caracteristicas fisicas de las aleaciones absorbentes del tipo 'nimonic' con oxidos de las tierras raras (gadolinio, samario, europio, etc.) dispersos en ellas. Examinan las variaciones de la capacidad de absorcion segun la composicion del material, indican las propiedades mecanicas y termofisicas de los materiales absorbentes en funcion de la concentracion del absorbente incorporado a la aleacion y, por ultimo, presentan los resultados de un estudio acerca de los efectos de la irradiacion sobre esas propiedades. . Demuestran que las aleaciones absorbentes que contienen oxidos de las tierras raras dispeisos en la matriz metalica poseen una elevada capacidad de absorcion para una proporcion relativamente baja de absorbente en la aleacion ( Tilde-Operator 5 a 10%). Las caracteristicas de resistencia y las propiedades termofisicas (o{sub B}, E, {lambda}) de las aleaciones del tipo 'nimonic' con adicion de oxidos de las tierras raras asumen valores comparativamente elevados al ascender la temperatura, cuando la concentracion del absorbente es del orden del 10%. A temperaturas elevadas los materiales de tipo dispersion de esa indole ofrecen una radiorresistencia satisfactoria dentro del campo de irradiacion estudiado ( Tilde-Operator 3 x 10{sup 20} n/cm{sup 2}). (author) [Russian] Privodjatsja rezul'taty issledovanija fizicheskih harakteristik pogloshhajushhih splavov tipa nimonik s dispergirovannymi v nih okislami redkozemel

Influencia del tratamiento HIP en la distribución de los carburos en prótesis Co-Cr-Mo

Directory of Open Access Journals (Sweden)

Amigó, V.

2004-04-01

Full Text Available The development of porous coatings by microspheres sintering is made on cobalt alloys at high temperatures. These temperatures modify the base alloy microstructure, and some partial fusions can appear if temperatures are about eutectic temperature. High temperature is conditioned by diffusion in these alloy, needed to form adequate bonds between beads and substrate Solution annealing and hot isostatic pressing process (HIP modify the casting microstructure and reduce the porosity. These treatments involve high temperatures like 1200°C, dissolving carbides and modifying its morphology and distribution. The influence of HIP treatment in the evolution of distribution and morphology of carbides is studied.

El desarrollo de recubrimientos porosos por sinterizado de microesferas en prótesis de cobalto precisa de una sinterización a temperaturas elevadas, a las que se producen cambios microestructurales notables e incluso fusiones parciales al superar la temperatura de transformación eutéctica de estas aleaciones Co-Cr-Mo. Las temperaturas tan elevadas de tratamiento de sinterización vienen condicionadas por la difusividad en estas aleaciones y la necesidad de crear los cuellos necesarios entre las bolas y éstas con el material base, de manera que permitan unas características mecánicas adecuadas a la aplicación de las prótesis. Estos cambios microestructurales, desde la microestructura de colada de la aleación, pueden ser controlados mediante los tratamientos complementarios de solubilización. Además, es frecuente someter al material de colada, para reducir la porosidad residual y modificar la distribución de los poros, a prensado isostático en caliente, HIP, a temperaturas alrededor de los 1200°C. Este nuevo tratamiento permite una redisolución de parte de los carburos con una modificación importante del lugar de precipitación de los mismos durante el enfriamiento lento que los lleva hacia borde de grano, con un notable

Pt, PtCo and PtNi electrocatalysts prepared with mechanical alloying for oxygen reduction reaction in alkaline medium; Electrocatalizadores de Pt, PtCo y PtNi preparados por aleado mecanico para la reaccion de reduccion de oxigeno en medio alcalino

Energy Technology Data Exchange (ETDEWEB)

Garcia-Contreras, M.A.; Fernandez-Valverde, S.M. [Instituto Nacional de Investigaciones Nucleares, Ocoyoacac, Estado de Mexico (Mexico)]. E-mail: miguel.garcia@inin.gob.mx; Vargas-Garcia, J.R. [ESIQIE-IPN, Mexico D.F. (Mexico

2009-09-15

Pt, PtCo and PtNi electrocatalysts were prepared using mechanical alloying and their electrocatalytic activity was investigated for oxygen reduction reaction (ORR) in KOH 0.5 M using cyclic voltametry and rotary disc electrode (RDE) techniques. The electrocatalysts were characterized using x-ray diffraction, sweep electron microscopy, dispersive x-ray transmission and chemical analysis. The physical characterization indicated that all the electrocatalysts are alloys formed by agglomerated particles composed of nanocrystals. The chemical analysis showed the presence of iron in the alloys. For the electrocatalytic evaluation, polarization curves and Koutecky-Levich and Tafel graphs were obtained to determine the kinetic parameters of the electrocatalysts in the study. With the same experimental conditions, the PtCo presented better electrocatalytic performance with a higher exchange current density. [Spanish] Se prepararon electrocatalizadores de Pt, PtCo y PtNi por aleado mecanico y se investigo su actividad electrocatalitica para la reaccion de reduccion de oxigeno (RRO) en KOH 0.5 M utilizando las tecnicas de Voltametria ciclica y Electrodo de Disco Rotatorio. Los electrocatalizadores se caracterizaron por difraccion de rayos X, Microscopia electronica de Barrido, de Transmision y analisis quimico por dispersion de rayos X. La caracterizacion fisica indico que todos los electrocatalizadores son aleaciones formadas de particulas aglomeradas, compuestas de nanocristales. El analisis quimico mostro la presencia de hierro en las aleaciones. Para la evaluacion electrocatalitica se obtuvieron curvas de polarizacion, graficas de Koutecky-Levich y de Tafel para determinar los parametros cineticos de los electrocatalizadores en estudio. En las mismas condiciones experimentales, el PtCo presento el mejor desempeno electrocatalitico con la densidad de corriente de intercambio mas alta.

Review about laser nitriding of titanium alloys; Revision sobre nitruraciones laser de aleaciones de titanio

Energy Technology Data Exchange (ETDEWEB)

Perez-Artieda, M.G.; Fernandez-Carrasquilla, J.

2010-07-01

A common technique used to improve the wear response of titanium alloys is to nitride the surface, using chemical or physical vapour deposition, ion implantation or surface remelting in a nitrogen atmosphere. In this revision nitriding systems with laser technology are studied, used in titanium alloys surface treatments.For high temperature, high strength applications, titanium based alloys are an attractive light-weight alternative to steel, due to their high strength to weight ratio and corrosion resistance. In applications that require good wear resistance, titanium alloys pose a problem due to their poor tribological characteristics.Titanium alloys used with a suitable nitriding treatment could allow the replacement of steel in different applications, obtaining weight savings in fabricated components. (Author). 68 refs.

Resistencia a la corrosión localizada de juntas soldadas en un acero inoxidable duplex saf 2205

OpenAIRE

LEÓN, JOSÉ B; ARIAS, RAFAEL; SÁNCHEZ, ABBY; SUÁREZ, MARIBEL; QUINTERO, AMADO

2008-01-01

La corrosión por picadura es uno de los mecanismos de falla más frecuentes que se presentan en la industria química, petrolera y petroquímica. El hecho de que metales o aleaciones metálicas estén expuestos a ambientes agresivos inducen a fenómenos de corrosión como la «corrosión por picadura». El conocimiento de cómo se originan y la detección temprana de este mecanismo se traducen en ahorros económicos considerables debido a que se evitaría la interrupción momentánea de operaciones de una ac...

Sílica gel obtida de escória de alto forno: Marabá, Pará

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M. M. Rebelo

2015-09-01

Full Text Available ResumoSílica gel com propriedades similares à sílica comercial foi obtida a partir de escória de alto forno (EAF, utilizando digestão com ácido clorídrico. A EAF-sílica obtida foi caracterizada por diferentes técnicas, mostrando-se amorfa, com pureza 99,7% e área específica 282 m2/g. Apresentou caráter hidrofílico alto (12,27%, com água de constituição de ~ 6,18%, o que foi confirmado pela perda de massa durante a análise termogravimétrica. As partículas de EAF-sílica apresentaram tamanhos micrométricos (< 1 µm em forma de agregados, distribuição granulométrica unimodal e D50 7,0 µm.

Desarrollo y caracterización de un material compuesto de matriz de aluminio 6061 y partículas de TiB2

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Plaza, L. M.

2010-12-01

Full Text Available The incorporation of ceramic particles has been one of the ways developed to improve the mechanical properties of aluminium alloys during the last years. The main objective of this work has been to develop the manufacturing process of the reinforced aluminium alloy and analyse its mechanical properties and microstructure. Details about an innovative MMC manufacturing process and the results obtained in the development of a new family of TiB2- reinforced aluminium alloys for forging and extrusion applications are presented. It has been observed that the considered manufacturing process, consisting in the fabrication of particles by SHS and their incorporation into the selected alloy, is a feasible process to manufacture reinforced alloys that can be subsequently extruded or forged. The final result is the development of a material suitable for extrusion and forging applications and that presents an improvement of fatigue and tensile properties of the matrix alloy.Una de las vías desarrolladas, en los últimos años, para la mejora de las propiedades mecánicas de las aleaciones de aluminio es la de la incorporación de refuerzos cerámicos en forma de partículas cerámicas. El objetivo principal del trabajo ha sido desarrollar el proceso de fabricación de una aleación de aluminio 6061 reforzada con partículas de diboruro de titanio, TiB2, y analizar las propiedades del material obtenido. Se ha observado que el proceso de fabricación planteado, consistente en la fabricación de las partículas por medio del proceso de síntesis autopropagada a alta temperatura SHS (Self propagating high temperature synthesis y su posterior incorporación a la aleación 6061, es un proceso viable para la fabricación de aleaciones reforzadas adecuadas para la realización de procesos subsiguientes de extrusión o forja. El resultado final es la obtención de un material adecuado para la fabricación de componentes extruidos y que presenta una mejora de sus

Recubrimientos superficiales con láseres de diodos de alta potencia

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Molpeceres, J. L.

1998-04-01

Full Text Available Nowadays, high power diode laser systems are available in the market. These systems, based on arrays of small diode lasers, can achieve more than 1 kW of output power and are currently offering new possibilities in the field of laser material processing where CO₂ and Nd:YAG lasers were used up to the present. The results obtained in some materials cladding based on cobalt and nickel alloys as additional materials is presented. The instrumental set-up used in these experiments are described.

La posibilidad de disponer actualmente de láseres de diodos con una potencia de emisión óptica superior a 1 kW permite abordar un gran número de aplicaciones en el ámbito del procesado de materiales con láser, dominado tradicionalmente por los láseres de CO₂ y Nd:YAG. En el presente trabajo, se muestra la aplicación de los láseres de diodos de alta potencia al recubrimiento de materiales metálicos con aleaciones de base cobalto y níquel. Se describen las características del sistema empleado y se muestran los resultados obtenidos.

Effect of replacement of vanadium by iron on the electrochemical behaviour of titanium alloys in simulated physiological media

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Mareci, D.

2009-02-01

Full Text Available The electrochemical behaviour of Ti6Al4V, Ti6Al3.5Fe and Ti5Al2.5Fe alloys has been evaluated in Ringer’s solution at 25 °C. The effect of the substitution of vanadium in Ti6Al4V alloy has been specifically addressed. The evaluation of the corrosion resistance was carried out through the analysis of the open circuit potential variation with time, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS tests. Very low current densities were obtained (order of nA/cm² from the polarization curves and EIS, indicating a typical passive behaviour for all investigated alloys. The EIS results exhibited relative capacitive behaviour (large corrosion resistance with phase angle close to –80° and relative high impedance values (order of 105 Ω•cm² at low and medium frequencies, which are indicative of the formation of a highly stable film on these alloys in Ringer’s solution. In conclusion, the electrochemical behaviour of Ti6Al4V is not affected by the substitution of vanadium with iron.

El comportamiento electroquímico de las aleaciones Ti6Al4V, Ti6Al3.5Fe y Ti5Al2.5Fe fue evaluado en una disolución Ringer a 25 °C. Se ha estudiado especialmente el efecto de la sustitución del vanadio en la aleación Ti6Al4V. La evaluación de la resistencia a la corrosión se ha llevado a cabo a través del análisis de la variación del potencial de un circuito abierto con el tiempo, las curvas de polarización potenciodinámicas y los ensayos de espectroscopía de impedancia electroquímica (EIS. Se han obtenido densidades de corriente muy bajas (del orden de nA/cm² en las curvas de polarización y EIS, indicando un comportamiento pasivo típico para todas las aleaciones investigadas. Los resultados de la EIS mostraron un comportamiento capacitivo relativo (gran resistencia a la corrosión con ángulos de fase próximos a –80° y valores de impedancia relativamente altos (del orden de

Aleaciones cuasicristalinas Al93Fe3Cr2Ti2

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García-Escorial, Asunción

2015-12-01

Full Text Available Aluminium alloy powder having a nominal composition of Al93Fe3Cr2Ti2 (at% has been prepared using gas atomisation. The atomised powder present a microstructure of an aluminium matrix reinforced with a spherical quasicrystalline icosahedral phase, in the range of nanometre in size. The powder was consolidated into bars using warm extrusion. The microstructure of the extruded bars retains the quasicrystalline microstructure and the bars present outstanding mechanical properties, i.e. proof stress of 280 MPa at 300 °C. Upon heating the microstructure evolves towards the equilibrium. The thermal evolution was investigated by means of x-ray diffraction, differential scanning calorimeter, scanning electron microscopy and transmission electron microscopy. According to these observations a transformation in two steps is proposed. A first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases.Se ha obtenido por atomización por gas polvo de la aleación Al93Fe3Cr2Ti2 (at%. Este polvo presenta una microestructura de una matriz de aluminio reforzada por precipitados icosaédricos de tamaño nanométrico. El polvo fue consolidado por extrusión en forma de barras cilíndricas. La microestructura de las barras retiene la microestructura cuasicristalina de las partículas de polvo. El material consolidado presenta propiedades mecánicas prometedoras, como un límite elástico de 280 MPA a 300 °C. Con los tratamientos térmicos, la microestructura evoluciona hacia el equilibrio. Esta evolución se estudia por difracción de rayos x, calorimetría diferencial de barrido, microscopías electrónicas de barrido y de transmisión. A la luz de los resultados obtenidos se propone que la transformación de las fases con el tiempo de tratamiento térmico ocurre en dos pasos. Primeramente, tiene lugar la descomposición de la solución solida sobresaturada, tanto en la matriz como en los cuasicristales, y posteriormente los cuasicristales se transforman en las fases de equilibrio del sistema: α-Al, Al13Fe4, Al13Cr2 y Al3Ti.

Deterioro de aleaciones de cobre por acción humana

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Duran, A.

2008-02-01

Full Text Available Results are presented from several samples taken from leaves of the Pardon Portico of Mosque-Cathedral of Cordoba, where an alteration on their surface was detected. Metal samples analyzed using X-ray microanalysis and powder xray diffraction were predominantly constituted by copper with some amounts of zinc attributed to brass, whereas other samples were also constituted by copper, tin and lead attributed to bronze. Surface samples were analyzed using the same techniques. In addition Fourier transform infrared spectroscopy was also used.The main compound identified in all the surface of the leaves is copper chloride hydroxide (atacamite. Lead chlorides have also been found. These data show that the sudden alteration that appears may be attributed to the use of some cleaning product containing chloride. Other compounds detected in the surface were gypsum, quartz and oxalates coming from environmental contamination.

Se exponen los resultados de algunas muestras alteradas procedentes de la Puerta del Perdón, pertenecientes a la Mezquita de Córdoba. Algunas de las muestras de metal analizadas mediante difracción de rayos X y microanálisis por energía dispersiva de rayos X estaban constituidas por latón (cobre con pequeñas cantidades de zinc, mientras que otras estaban constituidas por bronce (cobre, estaño y plomo. La superficie de las muestras se analizó empleando las mismas técnicas. Asimismo, se usó espectroscopia de infrarrojos. El componente principal identificado en la superficie de la puerta es cloruro básico de cobre (atacamita. Además se han encontrado cloruros de plomo. Estos datos demuestran que la repentina alteración de la superficie se puede atribuir al uso de productos de limpieza con alto contenido en cloro. Otros compuestos procedentes de la contaminación externa, como yeso, cuarzo y oxalatos también se detectaron en la superficie.

Efecto del amperaje en las propiedades de recubrimientos duros resistentes a la abrasión aplicados por soldadura

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Héctor Iván Monsalve Gil

2004-01-01

Full Text Available Se estudió el efecto del amperaje en la microestructura, la dureza y la resistencia al desgaste abrasivo de dos aleaciones para recubrimientos duros con base hierro, alto Cr y C. Se aplicaron dos y tres capas de cada electrodo mediante el proceso SMAW sobre platinas de acero ASTM A36. La resistencia al desgaste abrasivo se calculó midiendo la masa perdida después de un ensayo de acuerdo al estándar internacional ASTM G65. La microestructura fue analizada usando microscopio óptico y microscopio electrónico de barrido (SEM y el porcentaje de dilución fue calculado en forma gráfica para un cordón de soldadura. Los resultados muestran que al disminuir la entrada de calor se reduce el porcentaje de dilución y se promueve la formación de carburos primarios. La más alta resistencia al desgaste abrasivo se obtiene cuando la microestructura estuvo compuesta de carburos primarios y una matriz eutéctica.

Producción y tratamiento de películas de Si_1-xGe_x mediante técnicas asistidas por láser de excímero

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Castro, J.

1998-04-01

Full Text Available Heterostructures of Si_1-xGe_x alloys on Si (100 have been achieved using two different excimer laser techniques. The first one, the Laser Induced Chemical Vapour Deposition (LCVD, was used in order to deposit germanium on Si (100 substrates via photolysis of GeH₄ as precursor gas. The resulting films show a very homogeneous and amorphous structure as determined by HREM, XRD and Raman analysis. These deposited amorphous germanium films and a part of their underlaying Si (100 substrate were melted using the second technique, the Pulsed Laser Induced Epitaxy (PLIE, inducing an epitactic recrystallization of a Si-Ge alloy. The analysis of the obtained alloys by HREM, XRD, and XPS, reveals a strong dependence of the crystal quality and of the germanium concentration profile from the number of pulses.

El creciente interés que suscita la búsqueda de nuevas técnicas para la obtención de materiales semiconductores, compatibles con la tecnología del silicio, ha llevado a desarrollar un sistema de depósito y postprocesado en alto vacío (HV de Si-Ge mediante técnicas asistidas por láser excímero. Se han obtenido películas amorfas de germanio mediante el depósito químico en fase vapor inducido por láser (LCVD, que posteriormente han sido recristalizadas con uso de la inducción de epitaxia por medio de láser pulsado (PLIE. Las películas depositadas sobre substratos de silicio fueron caracterizadas mediante XRD, HREM y Raman, revelándose que son amorfas con un alto grado de homogeneidad. Se ha estudiado la morfología y la estequiometría de las muestras por medio de XRD, HREM y XPS tras el tratamiento para inducir la cristalinidad de la aleación sobre el substrato de silicio, observándose la dependencia del grado de heteroepitaxia y variación de la composición en la aleación, con el número y la energía de los pulsos del láser.

The corrosion behaviour of nanograined metals and alloys

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Herrasti, P.

2012-10-01

Full Text Available There has been considerable interest in the properties of nanocrystalline materials over the last decade. Such materials include metals and alloys with a crystal size within the order of 1 to 100 nm. The interest arises due to the substantial differences in electrical, optical and magnetic properties and also due to their high adsorption capability and chemical reactivity compared to their larger grained counterparts. In this paper, the corrosion of nanocrystalline metals and alloys is investigated and compared to the corrosion of microcrystalline materials having a similar composition. The focus is on the corrosion of nickel, copper, cobalt and iron alloys. Key aspects of different corrosion behaviour such grain boundaries and size are identified.

En la última década ha habido un gran interes en las propiedades de materiales nanocristalinos. Estos materiales incluyen metales y aleaciones con un tamaño de cristal del orden de 1 a 100 nm. El interes por estos materiales es debido a las grandes diferencias en cuanto a sus propiedades electricas, opticas y magneticas, asi como a su alta capacidad de adsorción y reactividad química en relación a los mismos materiales con tamaños de grano mayores. En este trabajo se ha investigado y comparado la corrosión de materiales nano y microcristalinos de similar composición química. Principalmente se ha centrado en la corrosión de metales tales como niquel, cobre, cobalto y aleaciones de hierro. Se ha comprobado que los diferentes comportamientos frente al proceso de corrosión están intimamente ligados con los bordes de grano y el tamaño de dichos granos.

Determinación de los mecanismos de fractura de un material multicapa de aluminio de alta resistencia y excelente tenacidad a impacto basado en la aleación aeroespacial Al 7075

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Cepeda-Jiménez, C. M.

2012-08-01

Full Text Available An aluminium multilayer laminate has been processed by hot rolling. It is constituted by 19 alternated layers of high-strength aluminium alloy (Al 7075-T6, 82 % vol and thinner pure aluminium layers (Al 1050-H24, 18 % vol. The microstructure of the constituent alloys and the composition gradient across the interfaces has been characterized. The multilayer laminate and the as-received aluminium alloys have been tested at room temperature by Vickers microhardness, three-point bend test and impact Charpy test. The outstanding improvement in damage tolerance, which is 18 times higher than that for the as-received Al 7075 alloy, is due to both intrinsic and extrinsic fracture mechanisms operating in the multilayer laminate during mechanical testing.

En este trabajo se ha procesado mediante laminación en caliente un material multicapa constituido por 19 capas alternadas de aluminio de alta resistencia (Al 7075-T6, 82 %vol y capas de aluminio puro (Al 1050-H24, 18 %vol de menor espesor. Se ha caracterizado la microestructura de las aleaciones constituyentes después del procesado, así como el gradiente de composición generado alrededor de las intercaras. Las propiedades mecánicas a temperatura ambiente, tanto del material multicapa como de las aleaciones de partida, se han estudiado mediante microdureza Vickers, flexión en tres puntos y ensayos de impacto Charpy. El material multicapa procesado presenta una tenacidad a impacto Charpy 18 veces superior a la de la aleación de partida Al 7075. Este espectacular aumento de tolerancia al daño es debido a los mecanismos de fractura, tanto extrínsecos como intrínsecos, que operan en el material multicapa durante las diferentes solicitaciones mecánicas a las que ha sido sometido.

Radio-tracer techniques in the study of corrosion by molten fluorides; Etude, a l'aide d'indicateurs radioactifs, de la corrosion provoquee par les fluorures fondus; Primenenie metodov radioaktivnykh indikatorov nrn izuchenii korrozii, prichinyaemoj rasplavlennymi ftoristymi soedineniyami; Estudio con indicadores radiactivos de la corrosion ocasionada por fluoruros fundidos

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Grimes, W R; Watson, G M; DeVan, J H; Evans, R B [Oak Ridge National Laboratory, Oak Ridge, TN (United States)

1962-03-15

coefficients de diffusion mesures experimentalement; il est permis d'en conclure que le coefficient d'autodiffusion du chrome est insensible aux modifications de la teneur en chrome de l'alliage Inor-8. (author) [Spanish] Si se someten el Inconel o el Inor-8 a la accion de una mezcla de fluoruros fundidos, que contenga sustancias reducibles, el cromo sufre una oxidacion selectiva y es extraido de la aleacion. Con ayuda del indicador radiactivo {sup 51}Cr, los autores han evaluado los coeficientes de autodifusion del cromo en el Inconel y en el lnor-8, y han comprobado que los datos obtenidos son validos para las aleaciones expuestas a la corrosion. Han calculado los coeficientes globales 1) midiendo el paso del {sup 51}Cr de las capsulas de aleacion (empleado en forma do CrF{sub 2}) a los fluoruros no corrosivos fundidos, y 2) comparando la radiactividad total medida en las muestras de aleacion expuestas con la radiactividad de la sal a cuya accion fueron sometidas. Ademas, calcularon los coeficientes midiendo los perfiles do concentracion del indicador por pulidos electroliticos sucesivos de las muestras. Los coeficientes globales y los obtenidos por pulido electrolitico concuerdan satisfactoriamente para el Inconel a temperaturas elevadas, y para el lnor-8 a todas las temperaturas. Los valores obtenidos por pulido electrolitico del Inconel tratado a temperaturas inferiores a 760{sup o} C superan a los valores globales; en este caso, el proceso de difusion masica no es uniforme. Los coeficientes medios de difusion encontrados concuerdan siempre con los que se calculan por extrapolacion de los valores publicados, que fueron obtenidos con aleaciones de Cr-Ni similares, a temperaturas mas elevadas. Los autores se sirvieron de un par de buees politermicos de Inor-8 para hacer circular una masa de fluoruros no corrosivos fundidos que contenian {sup 51}Cr (en forma de CrF{sub 2}). Sacrificaron uno de estos bucles para evaluar la cantidad de {sup 51}Cr absorbida por la aleacion; el

Determinación de la acidez de sólidos por la prueba catalítica de la deshidratación del 1-butanol

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Jaime Olmedo Pérez Oliveros

2005-01-01

Full Text Available En este trabajo se examina la deshidratación catalítica de 1-butanol para determinar la naturaleza de los centros ácidos de muestras de circonia sulfatada con o sin el dopaje de Ce, Sb o W así como, muestras de ZSM-5, Al-MCM-41 y permutita (aluminosilicato de naturaleza amorfa. La acidez de los diferentes catalizadores se ordenó dependiendo de la medida de la actividad catalítica y de la magnitud de las relaciones de abundancia relativa de los isómeros cis-buteno/trans-buteno (CB/TB, 1-buteno/trans-buteno (1B/TB e isobuteno/trans-buteno (IB/TB. Se encontró que la actividad aumenta a mayor contenido de sulfato en la circonia. Además, el catalizador Al-MCM-41 muestra un comportamiento similar a la mejor muestra de circonia sulfatada.

Thermal treatment of the Fe{sub 78}Si{sub 9}B{sub 13} alloy in it amorphous phase studied by means of Moessbauer spectroscopy; Tratamiento termico de la aleacion Fe{sub 78}Si{sub 9}B{sub 13} en su fase amorfa estudiado por medio de la espectroscopia Moessbauer

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Cabral P, A. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico); Lopez, A.; Garcia S, F. [Facultad de Ciencias, UAEM, 50000 Toluca, Estado de Mexico (Mexico)

2003-07-01

The magnetic and microhardness changes, dependents of the temperature that occur in the Fe{sub 78}Si{sub 9}B{sub 13} alloy in it amorphous state were studied by means of the Moessbauer spectroscopy and Vickers microhardness. According to the Moessbauer parameters and in particular that of the hyperfine magnetic field, this it changes according to the changes of the microhardness; i.e. if the microhardness increases, the hyperfine magnetic field increases. The registered increment of hardness in the amorphous state of this alloy should be considered as anomalous, according to the prediction of the Hall-Petch equation, the one that relates negative slopes with grain sizes every time but small. (Author)

Condrossarcoma mesenquimal extraesquelético em um gato: relato de caso

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T.N. Guim

2014-04-01

Full Text Available Condrossarcoma mesenquimal extraesquelético (CME é um neoplasma maligno e raro em animais domésticos. Descreve-se um caso de CME em uma gata que apresentava uma massa firme, branco-amarelada, medindo 18cm de diâmetro, aderida à musculatura do membro pélvico esquerdo. O exame citológico revelou presença de células fusiformes individualizadas pleomórficas e agregados de pequenas células ovais, sem bordas definidas em meio à matriz intercelular amorfa. Devido à impossibilidade de tratamento e ao prognóstico desfavorável, foi realizada eutanásia. Microscopicamente foram observadas células fusiformes indiferenciadas e agregados de células condroides pleomórficas. O diagnóstico de CME foi confirmado pelas técnicas de azul alciano, tricrômico de Masson e pela prova imunoistoquímica, utilizando-se anticorpos antivimentina.

Análisis y ajuste de las variables de proceso para la fabricación de polvos de aleaciones base estaño mediante un atomizador centrífugo

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Ayllón Muro, Àxel

2017-01-01

En el presente proyecto se ha realizado la puesta a punto de un prototipo para la atomización de polvo metálico mediante la técnica de atomización centrífuga, incluyendo los diferentes componentes que intervienen en el proceso para su correcto funcionamiento. En particular, el metal que se atomizará será una aleación base estaño (SnPb). En él, se pretenden llevar a cabo las atomizaciones oportunas con el estudio de unas variables de operación concretas y éstas variables de proceso son el e...

Estimation of consumption of the useful life in the nozzles of a gas turbine by the phenomenon of thermal fatigue; Estimacion de consumo de vida util en las toberas de una turbina de gas por el fenomeno de fatiga termica

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Perez Hernandez, Efrain [Centro Nacional de Investigacion y Desarrollo Tecnologico (Cenidet), Cuernavaca, Morelos (Mexico); Mazur C, Zdzislaw; Garcia Illescas, R. [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)

2007-11-15

damage. [Spanish] La estimacion de vida util en los componentes calientes de las turbinas de gas como toberas y alabes es importante ya que sufren de cambios criticos de temperatura los cuales producen fatiga termomecanica durante los arranques, paros y cambios de fatiga para estimacion de vida util en las toberas de turbina de gas fabricados de aleacion base cobalto FSX-414 en las cuales se han desarrollado grietas durante la operacion. La inspeccion visual y metalografia de la tobera revelo muchas grietas por fatiga termomecanica en la superficie del alabe ademas de deterioracion de la aleacion. En los limites de grano se encontro una pelicula continua de carburos y tambien aumento de fraccion de carburos dentro de los granos. Esta densa y continua red de carburos reduce la ductilidad y aumenta la fragilidad, junto con la reduccion de energia de impacto (Charpy), facilita la iniciacion y propagacion de grietas. La iniciacion y propagacion de grieta en la aleacion fue debido a un mecanismo de fatiga termica y termofluencia que fue facilitado por fragilidad del material debido al deterioro previamente mencionado y a significativos niveles de esfuerzos termomecanicos. En el presente articulo se presentan los resultados de analisis de esfuerzos termicos a partir de los resultados de temperatura obtenidas de estudios previos de un analisis de transferencia de calor y flujo de fluidos mediante el programa Star-CD basado en volumen finito. Se muestra la metodologia empleada y las distribuciones de esfuerzos, los cuales se emplearon para el analisis de fatiga para la estimacion de vida util. Para eso se utilizo un modelo de elementos finitos en el programa NISA, asi como el programa de analisis de fatiga nCode. Para el conteo de ciclo de utilizo el metodo de Rainflow y se compararon los modelos de vida por fatiga de Manson-Coffin, Basquin, Morrow y Smih-Watson-Topper. La variacion de las propiedades mecanicas con la temperatura de la superaleacion empleada en esos componentes

Experiencias en Cuba de la producción de piezas fundidas de fundición gris esferoidal (FGE, un material de elevadas cualidades y propiedades.

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Francisco Mondelo García

2005-09-01

Full Text Available El trabajo expone alternativas posibles de acceder a fabricar fundiciones grises esferoidales(FGE, así como conocimientos, experiencias y métodos empleados en su producción en Cuba,contando por lo tanto con un material de elevadas cualidades y propiedades tecnológicas enexplotación. Se dan materiales básicos utilizados en los procesos de obtención de la FGE, locual incluye el proceso de recarburación de estas aleaciones ferrosas, más las operaciones denodulización e inoculación, junto a los controles bases en sus operaciones fundamentales, parafabricar piezas con la calidad y certificación requeridas. Se tienen resultados experimentalesproductivos de estas fundiciones nodulares, con marcas de diversas estructuras, propiedadesmecánicas y composiciones. Se valora además resultados de la sustitución de piezas deaceros por FGE con posibilidades de obtener, por tratamiento térmico los hierrosaustemperados (ADI y elementos económicos comparativos de la factibilidad de fabricación dela fundición sintética en piezas FGE con chatarras de aceros básicamente y recarburantesnacionales de carbón vegetal, como variante alternativa.

PRODUCCIÓN Y CARACTERIZACIÓN DE PARTÍCULAS Y FIBRAS CORTAS DE β-SiC OBTENIDAS A PARTIR DE CÁSCARA DE ARROZ

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Marco Valencia

Full Text Available El aprovechamiento de la cáscara de arroz (CA es mínimo en la mayoría de los países latinoamericanos y solo una pequeña porción se utiliza eficientemente como abono o combustible. Los productos obtenidos por pirólisis de CA son, sin embargo, útiles para la fabricación de productos abrasivos y refractarios a base de carburo de silicio (SiC. Hay aplicaciones de reciente desarrollo y de mayor exigencia que consisten en usar el SiC como refuerzo de aleaciones metálicas para la fabricación de composites metálicos. En esta investigación se han obtenido fibrillas cortas y partículas finas de SiC por pirólisis controlada de CA. La síntesis del SiC se llevó a cabo en un horno de gas diseñado y puesto a punto durante el desarrollo del proyecto. El proceso fue optimizado mediante un diseño experimental que incluyó como variables la temperatura, el tiempo de pirólisis, el tipo de catalizador y la atmósfera de proceso.

The band gap of II-Vi ternary alloys in a tight-binding description

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Olguin, Daniel; Blanquero, Rafael [Instituto Politecnico Nacional, Mexico, D.F (Mexico); De Coss, Romeo [Instituto Politecnico Nacional, Yucatan (Mexico)

2001-02-01

We present tight-binding calculations for the band gap of II-Vi pseudobinary ternary alloys. We use an sp{sup 3} s* tight-binding Hamiltonian which include spin-orbit coupling. The band gap composition dependence is calculated using a extended version of the virtual crystal approximation, which introduce an empirical correction factor that takes into account the non-linear dependence of the band gap with the composition. The results compare quite well with the experimental data, both for the ternary alloys with wide band gap and for the narrow band gap ones. [Spanish] Presentamos el calculo de la banda de energia prohibida de aleaciones ternarias de compuestos II-VI. El calculo, que incluye interaccion espin-orbita, se hace con el metodo de enlace fuerte, utilizando una base ortogonal de cinco orbitales atomicos por atomo (sp{sup 3} s*), en conjunto con la aproximacion del cristal virtual. En la aproximacion del cristal virtual, incluimos un factor de correccion que toma en cuenta la no linealidad de la banda de energia prohibida como funcion de la concentracion. Con esta correccion nuestros resultados reproducen aceptablemente los datos experimentales hallados en la literatura.

Combined effect of nano-SiO2 and nano-Fe2O3 on compressive strength, flexural strength, porosity and electrical resistivity in cement mortars; Influencia de la combinación de nano-SiO2 y nano-Fe2O3 en la resistencia a compresión, resistencia a tracción, porosidad y resistividad eléctrica de morteros de cemento.

Energy Technology Data Exchange (ETDEWEB)

Sanjuán, M.A.; Argiz, C.; Gálvez, J.C.; Reyes, E.

2018-04-01

The compressive strength, flexural strength, porosity and electrical resistivity properties of cement mortars with nano-Fe2O3 and nano-SiO2 are studied. Amorphous silica is the main component of pozzolanic materials due to its reaction with calcium hydroxide formed from calcium silicate (C3S and C2S) hydration. The pozzolanic reaction rate is not only proportional to the amount of amorphous silica but also to the surface area available for reaction. Subsequently, fine nano-Fe2O3 and nano-SiO2 particles in mortars are expected to improve mortar performance. The experimental results showed that the compressive strength of mortars with nano-Fe2O3 and nano-SiO2 particles were lower than those obtained with the reference mortar at seven and 28 days. It was shown that the nano-particles were not able to enhance mechanical strength on every occasion. The continuous microstructural progress monitored by mercury intrusion porosimetry (MIP) measurements, pore-size distribution (PSD), total porosity and critical pore diameter also confirmed such results. [Spanish] Se estudia la resistencia a compresión y flexión, porosidad y resistividad eléctrica de morteros de cemento con nano-Fe2O3 y nano-SiO2. La sílice amorfa reacciona con el hidróxido de calcio formado en la hidratación del C3S y C2S. La tasa de reacción puzolánica es proporcional a la cantidad de sílice amorfa y la superficie disponible para la reacción, esperando que las partículas finas de nano-Fe2O3 y nano-SiO2 mejoren las propiedades de los morteros. Los resultados experimentales han mostrado que la resistencia a compresión a siete y 28 días de morteros con partículas de nano-Fe2O3 y nano-SiO2 era, en ocasiones, inferior a la obtenida con el mortero de referencia. Se muestra que las nano-partículas no siempre son capaces de mejorar la resistencia de los morteros. Las medidas mediante porosimetría de intrusión de mercurio (PIM) de la distribución de tamaño de poro (DTP), porosidad total y di

Microestructura y comportamiento plástico de perovsquitas conductoras protónicas de alta temperatura

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López-Robledo, M. J.

2005-10-01

Full Text Available The creep behaviour of high temperature proton conducting perovskites SrCe0.9Y0.1O3-δ and Sr3Ca1.18Nb1.82O9-δ fabricated by laser fusion has been studied. Their microstructure has been studied both in the as-received and crept samples by means of Scanning Electron Microscopy (SEM and Electron BackScattering Diffraction (EBSD, to correlate plastic behaviour with the evolution of the microstructure. The materials show a cellular structure consisting of elongated grains embedded in an amorphous phase and a strong bi-axial crystallographic texture. Deformation tests at constant stress (creep tests have been performed both in Ar atmosphere and in air. Rigid grain rotation has been observed in the crept samples by EBSD. The amorphous phase flows outside the sample during creep. Plastic behaviour of these materials is independent of the environmental atmosphere and is consistent with a mechanism of viscous flow of the amorphous phase controlled by diffusion.

Se ha estudiado el comportamiento en fluencia de perovsquitas conductoras protónicas de alta temperatura fabricadas por fusión láser, en particular los sistemas SrCe0.9Y0.1O3-δ y Sr3Ca1.18Nb1.82O9-δ. Se ha estudiado la microestructura antes y después de los ensayos mecánicos mediante Microscopía Electrónica de Barrido (MEB y Difracción de Electrones Retrodispersados (Electron BackScattering Diffraction, EBSD, con el objetivo de correlacionar el comportamiento plástico de estos materiales con su evolución microestructural. Los materiales analizados tienen una estructura celular de granos alargados, separados por una fase amorfa, y presentan una fuerte textura cristalográfica bi-axial. Se han realizado ensayos de deformación a carga constante (fluencia a diversas tensiones y temperaturas, en atmósfera inerte de Ar y en aire. Tras los ensayos, la fase intercelular fluye hacia el exterior de la muestra y se ha comprobado mediante EBSD que los granos rotan de forma rígida. El

Cinética de segregación de soluto a las dislocaciones parciales en Cu-5 % at. Mn

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Donoso, E.

1999-02-01

Full Text Available A model is proposed to describe, the kinetics of solute segregation to partial dislocations in solid solutions of cold-rolled alloys. The case for half-edge and half-screw dislocations is considered. The model gives account of the kinetic behaviour observed in a deformed Cu-5 at. % Mn alloy where two unknown processes were assessed during calorimetric isothermal experiments. The faster process corresponds to segregation to screw dissociated dislocations while the slower one corresponds to segregation to edge dissociated dislocations. Effective activation energies, larger for edge dislocations, are close to that for pipe diffusion along the partials corrected by pinner binding energy terms. It is also predicted that segregation occurs faster as the dislocation density is increased.

Se propone un modelo para describir la cinética de segregación de soluto a las dislocaciones parciales en soluciones sólidas de aleaciones deformadas en frío. Se considera el caso en que la mitad de las dislocaciones son en arista y la otra mitad helicoidales. El modelo da cuenta del comportamiento cinético observado en aleaciones de Cu-5% at. Mn, durante las experiencias calorimétricas isotérmicas donde fueron estimados dos procesos. El proceso más rápido corresponde a segregación a las dislocaciones disociadas helicoidales, mientras que el más lento corresponde a la segregación a las dislocaciones disociadas en arista. Las energías efectivas de activación, las cuales son mayores para dislocaciones en arista, resultan ser cercanas a aquellas para la difusión tubular a lo largo de las componentes parciales, corregidas por términos de energía de interacción de anclaje. Se predice también que la segregación es más rápida cuando la densidad de dislocaciones aumenta.

Fluorimetric determination of uranium in zirconium and zircaloy alloys; Determinacion fluorimetrica de uranio en aleaciones de zirconio y zircaloy

Energy Technology Data Exchange (ETDEWEB)

Acosta L, E [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

1991-05-15

The objective of this procedure is to determine microquantities of uranium in zirconium and zircaloy alloys. The report also covers the determination of uranium in zirconium alloys and zircaloy in the range from 0.25 to 20 ppm on 1 g of base sample of radioactive material. These limit its can be variable if the size of the used aliquot one is changed for the final determination of uranium. (Author)

Spectrographic analysis of uranium-molybdenum alloys; Analisis espectrografico de aleaciones uranio-molibdeno

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Roca, M

1967-07-01

A spectrographic method of analysis has been developed for uranium-molybdenum alloys containing up to 10 % Mo. The carrier distillation technique, with gallium oxide and graphite as carriers, is used for the semiquantitative determination of Al, Cr, Fe, Ni and Si, involving the conversion of the samples into oxides. As a consequence of the study of the influence of the molybdenum on the line intensities, it is useful to prepare only one set of standards with 0,6 % MoO{sub 3}. Total burning excitation is used for calcium, employing two sets of standards with 0,6 and 7.5 MoO{sub 3}. (Author) 5 refs.

Puesta a punto de un equipo de anodizado para aleaciones de aluminio

OpenAIRE

Vélez Leache, Javier

2014-01-01

En este proyecto se realiza la anodización, en planta piloto de laboratorio, de muestras de aluminio de pequeñas dimensiones, sometiendo posteriormente estas muestras anodizadas a los ensayos exigidos por las normas ISO para este tratamiento de superficie Máster Universitario en Ingeniería de Materiales y Fabricación Unibertsitate Masterra Materialen eta Fabrikazioaren Ingeniaritzan

Non-Destructive Examination of the Heat-Affected Zone of Welded Zr-Nb Alloy; Controle Non Destructif de la Zone d'Un Alliage Zr-Nb Affectee par la Chaleur Lors du Soudage; Nedestruktivnoe ispytanie zony svarnogo shva iz tsirkonij-niobij splava, kotoryj podverzhen teplovomu vliyaniyu; Examen No Destructivo de la Zona de Soldadura Afectada por el Calor en las Aleaciones de Circonio y Niobio

Energy Technology Data Exchange (ETDEWEB)

Hanstock, R. F.; Walker, D. C.B. [U.K.A.E.A. Reactor Materials Laboratory, Culcheth (United Kingdom)

1965-10-15

chaleur qui sont susceptibles de corrosion pouvaient etre decelees par controle non destructif, en mesurant le potentiel thermoelectrique aux bornes d'une sonde metallique chauffee, en contact avec des parties determinees de la soudure et le metal adjacent. La sonde thermoelectrique est similaire a celle mise au point par l'Association britannique de recherches sur les metaux non ferreux en vue de mesurer l'epaisseur des revetements de plaques de metal; un instrument en vente sur le marche et muni de ce type de sonde peut etre utilise, apres une legere modification, pour le controle des soudures dans les alliages Zr-Nb. Le memoire donne un exemple de la variation de la reponse de la sonde dans des zones affectees par la chaleur lors du sondage; les resultats sont compares a ceux d'un examen en autoclave. (author) [Spanish] Las aleaciones de circonio con 2 Vulgar-Fraction-One-Half % de niobio ofrecen, gracias al tratamiento termico, la ventaja de resistir la presion en los reactores moderados por agua. Por otra parte, ese tratamiento afecta considerablemente a la resistencia a la corrosion en las condiciones de funcionamiento del reactor, siendo de seuealar que pueden surgir puntos especialmente vulnerables en las zonas de las soldaduras sometidas al calor. Las zonas susceptibles de corrosion pueden localizarse mediante tratamiento en autoclase, pero no es conveniente aplicarlo cuando extensos circuitos de presion se arman mediante soldadura. Se ha comprobado que las zonas afectadas por el calor que son vulnerables a la corrosion pueden localizarse por metodos no destructivos consistentes en medir el potencial termoelectrico entre la punta de una sonda metalica caliente en contacto con determinadas partes de la soldadura y el del metal adyacente. La sonda es analoga a la que ha diseueado la British-ferrous Metals Research Association para medir el espesor del chapado de sustratos metalicos. Los instrumentos comerciales equipados con ese tipo de sonda sirven con una

Caracterización de un cemento puzolánico

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Hugo Rincón

2010-03-01

Full Text Available Se caracterizáron las materias primas (caliza, yeso, y material pulozánico para la producción de cemento portland y el clinker obtenido en este proceso, por medio del análisis químico elemental y espectroscopia infrarroja. Se estudio el comportamiento al IR y a la comprensión de morteros elaborados a partir de cemento testigo y variaciones de material pulozánico (15, 35, 50 y 60 %. El cálculo de la composición potencial de las fases presentes en el clinker, al igual que el análisis por IR muestran un predominio de la fase C3S (56.09%, característica que concuerda con la naturaleza de las materias primas. El estudio por IR de los diferentes morteros de ensayo mostró el predominio de la forma amorfa en relación directa con el contenido de puzolana en estos. La resistencia a la compresión presenta finalmente un descenso en relación con el aumento de material puzolánico.

Caracterização físico-química da superfície de filmes de poli(tereftalato de etileno

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Pinto Georgia V. V. V.

1999-01-01

Full Text Available Dentre as diversas técnicas de caracterização superficial de filmes poliméricos, foram utilizadas nos filmes de PET do presente estudo a refratometria, rugosidade, análises de coeficiente de atrito e ângulo de contato. As amostras de filmes de PET analisadas têm 12mim de espessura e compreendem três tipos de estuturas superficiais: filme de homopolímero PET, filme PET com tratamento corona e filme de poli(tereftalato de etileno-co-ciclohexanodimetanol. O filme com tratamento corona apresentou o maior valor de tensão superficial em função da maior parcela dos grupos polares. Resultados de índice de refração indicam que a superfície do filme com copoliéster é menos cristalina que as superfícies dos demais filmes avaliados. A estruturas amorfa e elevado nível de tensão superficial de filmes tratados deverão favorecer a um aumento dos níveis de adesão a tintas e revestimentos.

DEL EDITOR. LA IMPORTANCIA DE LLAMARSE AFINIDAD QUÍMICA. PARTE II: LA SEMILLA GERMINA

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GUILLERMO SALAS-BANUET

2013-01-01

Full Text Available El concepto de afinidad química abre su desarrollo desde la protohistoria. Se alimenta del pensamiento creativo, liberándose de las creencias de la época y de posiciones de poder, nutriéndose del intercambio de ideas, absorbiendo conocimientos de Egipto y Babilonia. El pensamiento griego -representado por un grupo de jonios y atenienses- centrado en Aristóteles, lleva al inicio de la germinación del concepto de la afinidad química, con los conceptos de átomo, elemento y materia y con la noción de atracción y repulsión entre elementos, que es la precursora de la “afinidad”. Esta época, centrada en el conocimiento, pensamiento y sentido común de Aristóteles, fue la base del pensamiento occidental. La experimentación, la práctica, para responder a situaciones y necesidades que se presentaban, corrió a su ritmo desde la edad de bronce, pero independiente del desarrollo del pensamiento griego. Mediante ésta, se conocen y dominan aleaciones, procedimientos y sustancias, y se reconocen otros que intervienen o son subproductos de procesos y reacciones debidas a la afinidad química.

Empleo de cromitas refractarias para la obtención de fundentes aglomerados utilizados en la soldadura automática por arco sumergido (SAW

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Perdomo-González, L.

2003-08-01

Full Text Available In the present work high carbon ferrochrome (load ferrochrome and slags are obtained, starting frora the métallurgie reductive processing of refractory chromites. The obtaining of alloys and slags is studied using an experiment design based in the relationships among components. The chemical compositions of alloys and slags guarantee their application for the conformation of alloys loads and matrix fluxes amassed for the superficial filling by means of submerged arc welding (SAW. The melting-reduction process is carried out in an electric arc furnace.

En el presente trabajo se obtienen ferrocromo de alto carbono (ferrocromo de carga y escorias a partir del proceso de reducción de cromitas refractarias. Mediante la utilización de un diseño de experimento de relaciones entre componentes, se estudia la obtención de aleaciones y escorias. La composición química de ambas garantiza su aplicación para la conformación de cargas aleantes y matrices de fundentes aglomerados, para el relleno superficial mediante soldadura automática por arco sumergido (SAW. El proceso de fusión-reducción se realiza en un horno eléctrico de arco.

Uniones de nitruro de silicio. Superaleaciones

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Barea, R.

2000-10-01

Full Text Available Industrial applications of silicon nitride materials are limited by the difficulty and cost of making complex shapes. In the present work, the use of some superalloys as bonding interlayer between two silicon nitride pieces has been investigated. Three types of Ni based superalloys have been chosen because their technological interest. Joining experiments have been performed by thermocompression at different temperatures and pressures, in a medium vacuum atmosphere. Reactions taking place at the superalloy / Si3N4 interface have been studied using energy dispersive X-ray spectroscopy and scanning electron microscopy. A comparative study among the three superalloys /Si3N4 interfaces has been done.

El posible uso del nitruro de silicio en el ámbito industrial se ve limitado por la dificultad y el coste que supone mecanizar geometrías complicadas. En el presente trabajo se estudia la posibilidad del uso de superaleaciones como interlámina de unión entre piezas de este material. Se han seleccionado tres superaleaciones con base niquel-cromo debido a su interés tecnológico. Las uniones se han llevado a cabo por termocompresión en vacío, utilizando varias presiones y temperaturas. Se ha realizado un estudio comparativo de las intercaras de unión en las tres aleaciones, analizando mediante microanálisis por energías dispersadas de Rayos X y microscopía electrónica de barrido las reacciones que tienen lugar.

Caracterización mecánica y microestructural de aceros de baja activación candidatos como primera pared en los reactores de fusión por confinamiento magnético

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Hernández, M. T.

1996-04-01

Full Text Available Currently, the design development of fusion reactors and the possible materials to use in them are being studied in parallel. One of the most critical problems in this research is the structural material selection for the first wall and blanket. The aim of the present work is to study three low activation alloys designed in Germany in which niobium has been substituted by tantalum or cerium. The mechanical results show that the alloys containing cerium are in the same order of the low activation materials known to date, but the tantalum doped alloy produces TaC₃ precipitation that destabilizes the matrix and provokes large microstructural changes. This causes a decrease of the mechanical properties at about 600 °C. This fact makes this alloy unsuitable for the first wall on fusion reactors, because the working temperature is near 550 °C.

Actualmente, se está estudiando de forma paralela al desarrollo del diseño de los reactores de fusión los posibles materiales a emplear en estos. Una de las cuestiones más críticas en esta investigación es la selección del material estructural a emplear como primera pared y envoltura. En el presente trabajo se estudian tres aleaciones de diseño alemán de baja activación, en las que se ha sustituido el niobio por tantalio o por cerio. Los resultados mecánicos muestran que las aleaciones, en las que se ha añadido cerio de forma controlada, están en la línea de las de baja activación existentes hasta ahora, pero la adición de tantalio presenta problemas al provocar una precipitación primaria y masiva de carburos TaC₃ que desestabiliza la matriz y origina cambios microestructurales muy acusados. Así, ocurre un descenso en las propiedades mecánicas en torno a los 600 °C, que la incapacita para la aplicación como primera pared, ya que la temperatura de trabajo de ésta se halla en torno a los 550 °C.

Preparation and characterization of clay bonded high strength silica refractory by utilizing agriculture waste

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Aman Bhardwaj

2017-11-01

Full Text Available Clay bonded silica refractory was prepared by utilizing agriculture waste called rice husk ash (RHA and refractory grog. Various samples were prepared with different compositions based upon partial replacement of quartz by RHA. Rectangular samples were prepared by following semi dry process prior to pressing in a uniaxial hydraulic press and sintering at a temperature of 1200 °C in air atmosphere. Various physical, mechanical and thermal characterizations were done like X-ray diffraction (XRD, scanning electron microscope (SEM, apparent porosity (AP, bulk density (BD, cold crushing strength (CCS, refractoriness and thermal conductivity measurement. The sample utilizing 30% of RHA was considered most optimum composition which produced cold crushing strength of 38 MPa and thermal conductivity of 2.08 W/m K at 800 °C with a considerable good refractoriness. Enhancement in the mechanical as well as thermal properties may be considered as attributed to the amorphous silica which has reacted more easily and efficiently with other material surrounding giving rise to the densification and produced stable crystalline phase to the refractory material. These promising characteristics suggests that the RHA may lead to be used as a potential material for the preparation of clay bonded high strength silica refractories. Resumen: Se preparó sílice refractaria unida a arcilla con residuos agrícolas conocidos como ceniza de cascarilla de arroz (rice husk ash [RHA] y grog refractario. Se prepararon varias muestras con diferentes composiciones basadas en la sustitución parcial de cuarzo por RHA. Las muestras rectangulares se prepararon siguiendo un proceso semiseco antes de prensarlas en una prensa hidráulica uniaxial y sinterizarlas a una temperatura de 1.200 °C en atmósfera de aire. Se realizaron diversas caracterizaciones físicas, mecánicas y térmicas, como la difracción de rayos X, el microscopio electrónico de barrido, la porosidad

Aplicação da dermatoscopia no auxílio diagnóstico da ocronose exógena Use of dermoscopy for diagnosis of exogenous ochronosis

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Sandra Adolfina Reyes Romero

2011-08-01

Full Text Available A ocronose exógena consiste em hiperpigmentação crônica de áreas previamente tratadas com agentes tópicos como: a hidroquinona, a resorcina, os antimaláricos e o fenol. O diagnóstico precoce permite suspender prontamente o agente causador, uma vez que as opções terapêuticas disponíveis são escassas e com resultados insatisfatórios. Reportam-se três casos de ocronose exógena na face, diagnosticados pela dermatoscopia. O estudo dermatoscópico evidenciou estruturas amorfas de coloração cinza-enegrecido, algumas obliterando as aberturas foliculares. O exame histopatológico corroborou o diagnósticoExogenous ochronosis consists of chronic hyperpigmentation of areas previously treated with topical agents such as hydroquinone, resorcinol, antimalarials and phenol. Early diagnosis allows to promptly suspend the causative agent and it is imperative since the available therapeutic options are scarce and have presented so far unsatisfactory results. Three cases of exogenous ochronosis on the face which were diagnosed with the use of dermoscopy are presented. Dermatoscopy showed blackish-gray amorphous structures, some obliterating the follicular openings. Histopathological examination confirmed the diagnosis

Caracterización estructural de vidrios con altos contenidos de óxidos de hierro obtenidos a partir de un residuo de la hidrometalurgia del zinc

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Romero, M.

1997-10-01

Full Text Available It has been carried out the structural characterization of high oxide content glasses obtained by melting of a goethite industrial waste from the zinc hydrometallurgy with other raw materials as dolomite and glass cullet. The structural characterization has been carried out by X-Ray Diffraction (XRD, X-Ray Diffraction by Amorphous Dispersion (RDF and Mossbauer spectroscopy. It has been determined the interatomic distance, the oxidation state and the coordination of iron atoms in these glasses.

En este trabajo se ha llevado a cabo la caracterización estructural de vidrios con altos contenidos de óxidos de hierro obtenidos por fusión de un residuo industrial de goethita procedente de la hidrometalurgia del zinc con otras materias primas (dolomita y casco de vidrio. El estudio estructural se ha realizado por difracción de rayos-X (DRX, difracción de rayos-X por dispersión amorfa (RDF y espectroscopia Mössbauer, determinándose las distancias interatómicas, el estado de oxidación y la coordinación de los átomos de hierro en este nuevo tipo de vidrios.

Regularities in the Changes of Absorber Material Properties as a Function of Absorber Concentration; Regularite des Variations des Proprietes des Substances Absorbantes en Fonction de la Concentration de l'Absorbant; Zakonomernosti izmeneniya svojstv poglashchayushchikh materialov v zavisimosti ot kontsentratsii poglotitelya; Leyes de Variacion de las Propiedades de los Materiales Absorbentes en Funcion de la Concentracion del Absorbente

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Portnoj, K. I.

1964-06-15

pouvoir absorbant, en tant que fonction de la concentration de l'absorbant, varie d'apres une courbe caracteristique d'un phenomene de saturation et depend du spectre de neutrons. L'auteur formule une hypothese sur l'obtention du pouvoir absorbant maximum grace a la combinaison de plusieurs absorbants. Cette hypothese a ete largement confirmee par des experiences effectuees, dans des reacteurs a neutrons thermiques et intermediaires, sur de nombreuses combinaisons d'absorbants metalliques ou non. (author) [Spanish] En esta memoria se exponen las leyes que rigen las variaciones de las propiedades mecanicas y termofisicas y del poder de absorcion, en funcion de la concentracion del absorbente, en aleaciones destinadas a los reactores de neutrones termicos e intermedios. La conductividad y el coeficiente de dilatacion termica de las aleaciones absorbentes a base de boro y oxidos de las tierras raras se reducen al aumentar dicha concentracion. En el caso de las aleaciones con oxidos de las tierras raras, la variacion del coeficiente de dilatacion es lineal, mientras que para las alea,- ciones de boro esa caracteristica aditiva se altera. Ello se debe a que a temperaturas elevadas se forman fases de boruro con distintas redes cristalinas. En cuanto al poder absorbente, varia segun una curva de saturacion y depende tambien del espectro neutronico. El autor propone una hipotesis para explicar la aparicion de un maximo en la curva del poder absorbente, que atribuye a un fenomeno de interaleacion de los absorbentes. Esta hipotesis ha sido confirmada ampliamente por los resultados de experimentos efectuados con muchos sistemas absorbentes metalicos y no metalicos, de variada composicion, en reactores de neutrones termicos e intermedios. (author) [Russian] Doklad stavit cel'ju izlozhit' poluchennye zakonomernosti izmenenija mehanicheskih i teplofizicheskih svojstv, a takzhe pogloshhajushhej sposobnosti v zavisimosti ot koncentracii poglotitelej v sp lav a h , prednaznachennyh dlja

Caracterización de la superaleación ODS MA 956 para aplicaciones biomédicas

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Escudero, M. I.

1998-05-01

Full Text Available Since the MA 956 was proposed as a possible new biomaterial due to its good corrosion resistance values in physiological fluids a long way, still not finished, has been done. An exhaustive characterization of this alloy at room temperature has been developed. The technological objectives are well established: the possible use of this material for biomedical applications as hip or knee prostheses and as dental implants. The study was performed comparing the results of this alloy with the materials used nowadays as surgical implants, i.e., titanium alloys and polyethylene.

Desde que la MA 956 fue propuesta como posible nuevo biomaterial en base a su buena resistencia a la corrosión frente a sueros fisiológicos, un largo camino, aún sin finalizar, se ha recorrido, en el que se ha llevado a cabo una caracterización exhaustiva de esta aleación a temperatura ambiente con fines tecnológicos bien definidos: su posible uso en aplicaciones biomédicas, bien sea como prótesis de cadera o de rodilla y para implantes dentales. Los estudios se han llevado a cabo comparando esta aleación con los materiales más comúnmente utilizados en implantes ortopédicos como aleaciones de titanio y polietileno.

Microstructural effects of phosphorus on pressure die cast Al-12Si components

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Suárez-Peña, B.

2007-10-01

Full Text Available The refinement of cuboidal silicon in eutectic Al-Si alloys by phosphorus additions used to manufacture pressure die cast components was studied. The results show that the addition of phosphorus in the form of AlFeP mother alloy before process degassing, leads to the best refinement of the size of the Si-cuboids phase, among several phosphorus additions analysed in the present research.

Se ha estudiado el afino del silicio cuboidal en aleaciones eutécticas Al-Si por acción del fósforo, en piezas obtenidas mediante la técnica de fundición a presión. Tras la adición de fósforo en pruebas industriales, en las que dicho elemento se incorpora al baño con diversas composiciones, los mejores resultados se obtienen con la adición de la aleación madre AlFeP, previa al desgasificado industrial.

Obtención de ferromanganeso alto carbono y escoria para el desarrollo de materiales para soldar

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Lorenzo Perdomo-González

2000-03-01

Full Text Available En el presente trabajo se realiza un análisis de la posibilidad de empleo de pirolusita en el desarrollo de aleaciones al manganeso y escorias con un sistema de óxidos MnO-SiO2-CaO con características propias para el desarrollo de fundentes para la soldadura automática para arco sumergido (SAAS. A partir de la composición química del mineral de manganeso se realizan los cálculos del proceso de reducción con el empleo de la tecnología sin fundente en presencia de coque como reductor, obteniéndose las adecuadas composiciones y las propiedades de los productos del proceso. Se realiza una corrida experimental de obtención de ferromanganeso con adiciones de dolomita, caolín y fluorita como correctores de la escoria. Se conforma una matriz de fundente para arco sumergido con la escoria y se le evalúan las propiedades tecnológicas de soldadura.

Repair by weld of steam and gas turbine rotors made of Cr-Mo-V steel; Reparacion por soldadura de rotores de turbinas de vapor y de gas fabricados con aceros al Cr-Mo-V

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Mazur C, Zdzislaw; Hernandez R, Alejando [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico); Orozco S, Julian; Banuelos P, Jose E. [Comision Federal de Electricidad (Mexico)

2003-07-01

In this article an analysis is presented of the typical damages in steam and gas turbine rotors made of Cr-Mo-V low alloy steels. An analysis of the weldability of the Cr-Mo-V steel is carried out and a classification of the possible types of repairs of the turbine rotors is presented, starting off from the causes and ways of presentation of the faults/deterioration of the rotor materials during the operation of the turbine. With base on the damages detected in the rotor of a gas turbine of 20.65 MW, the development of the repairing technology carried out by weld in site is presented. After the repair process, the rotor was put again in operation. [Spanish] En este articulo se presenta un analisis de los danos tipicos en rotores de turbinas de vapor y de gas fabricados con aceros de baja aleacion al Cr-Mo-V. Se lleva a cabo un analisis de la soldabilidad de los aceros al Cr-Mo-V y se presenta una clasificacion de los posibles tipos de reparaciones de los rotores de turbinas, partiendo de las causas y modos de presentacion de las fallas/deterioro del material de los rotores durante la operacion de la turbina. Con base en los danos detectados en el rotor de una turbina de gas de 20.65 MW, se presenta el desarrollo de la tecnologia de reparacion por soldadura llevada a cabo en sitio. Despues del proceso de reparacion, el rotor fue puesto nuevamente en servicio.

Terra-cotta figurines from the Roman theatre of Malaga (Spain: An archaeometric study

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Compaña, J. M.

2014-06-01

amorfas. Los resultados analíticos permiten proponer una procedencia local/regional para la mayor parte de las muestras, siendo esta información de gran interés para algunas piezas descontextualizadas debido a alteraciones estratigráficas en el yacimiento. Adicionalmente, algunas piezas relevantes, como un fragmento de máscara teatral (TRC005 son posiblemente piezas de importación. La cuantificación de la fracción amorfa indica que la magnitud de ésta no puede ser despreciada en las cuantificaciones, llegando a ser cercana al 50 wt %. Tecnológicamente, todas las terracotas son muy similares, fabricándose en arcillas calcáreas cocidas entre unos 700 y 950 ºC.

Fabricación de soportes anódicos metálicos para SOFC por vía pulvimetalúrgica

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Arahuetes, E.

2008-10-01

Full Text Available The commercialization of environmentally-friendly power production technologies as solid oxide fuel cells (SOFC implies the cost reduction of the materials initially used in their design. The employment of a porous metallic support that significantly reduces the amount of active ceramic material is an interesting option. In this work, the processing of four different alloys (two Fe-based and two Ni-based is evaluated for their possible use as porous metallic supports in SOFC. A binder system is proposed that, mixed with big-sized metallic powders, allows to obtain materials with the required porosity level (≥ 30%. Moreover, a stage of grinding prior to compaction of mixes binder-metallic powder allows the manufacturing of dimensionally stable components during binder removal, even although their high porosity.

La comercialización de tecnologías de producción de energía medioambientalmente respetuosas, como las pilas de óxido sólido (SOFC, implica el abaratamiento de los materiales con que han sido, inicialmente, diseñadas. El empleo de un soporte metálico poroso que reduzca significativamente la cantidad de material cerámico activo es una opción muy interesante. En este trabajo se estudia el procesado de 4 aleaciones diferentes (dos base Fe y dos base Ni para su posible utilización como soportes metálicos porosos en SOFC. Se propone un sistema ligante que, mezclado con polvos metálicos de gran tamaño, permita obtener materiales con el nivel de porosidad requerida (≥ 30 %. Además, la realización de una etapa de granulado previa a la compactación de las mezclas de polvo metálico permite fabricar piezas que mantienen, pese a su elevada porosidad, la estabilidad dimensional durante el proceso de eliminación del ligante.

Recubrimientos bioactivos sobre aleaciones de titanio depositados por la técnica sol-gel

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Claudia García

2006-01-01

Full Text Available Entre los materiales de uso ortopédico, los metales son de amplio uso, principalmente por las exigencias mecánicas que cumplen durante el uso. A pesar de ello, los metales presentan limitaciones importantes como la degradación in situ y la necesidad de cementación o fijación externa. Estas restricciones afectan la integridad estructural de la prótesis y producen elementos resultantes de la corrosión ante los cuales el organismo produce respuestas adversas. Una opción para minimizar la liberación de productos de corrosión por parte de los implantes metálicos al organismo, es el desarrollo de recubrimientos cerámicos o vítreos. Si además, los recubrimientos poseen material bioactivo, no se hace necesario utilizar fijación externa o cemento para generar la unión con el hueso. En el presente trabajo se describe la metodología para depositar recubrimientos doble capa con partículas bioativas producidos por la técnica sol-gel sobre la aleación Ti6Al4V y se caracteriza el material recubierto en cuanto a su resistencia a la corrosión mediante ensayos electroquímicos en fluido fisiológico simulado (SBF y en cuanto a su bioactividad mediante ensayos in vitro.

Crystallization characteristics and physico-chemical properties of glass–ceramics based on Li2O–ZnO–SiO2 system; Características de cristalización y propiedades físico-químicas de los materiales vitrocerámicos compuestos a base del sistema Li2O-ZnO-SiO2

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Salman, Saad M.; Salama, Samia N.; Abo-Mosallam, Hany A.

2017-11-01

ámicas. El coeficiente de expansión térmica de las muestras cristalinas varió de 72×10−7 a 149×10−7°K−1 (25-600) y los valores de densidad en el intervalo 2,67-3,29g/cm3. La adición de reemplazos de Al2O3 y MO/ZnO en el vidrio base produjo una mejora de la durabilidad química de las muestras vitrocerámicas. Como resultado de las propiedades térmicas y físico-químicas de la vitrocerámica estudiada, los materiales adquieren excelentes propiedades y pueden utilizarse para sellar una variedad de diferentes metales y aleaciones.

Estructura y propiedades del material compuesto de base cobre reforzado con partículas intermetálicas de TiB2. // Structure and properties of copper base reinforced with intermetallic particles of TiB2 material.

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M. López J.

2002-09-01

Full Text Available Se estudió las propiedades mecánicas y eléctricas de la aleación compuesta de base cobre reforzada mediante la dispersiónde cerámicas intermetálicas TiB2. La mezcla mecánica cobre-cerámica, se obtuvo aleando cobre en polvo de tamaño 140mm con 1% y 2% de TiB2 en volumen, además de dispersante en un molino planetario de inoxidable martensítico de altaenergía, con moliendas de 12 y 36 horas en atmósfera de argón y razón de carga bolas/masa en polvo de 10:1. Laconsolidación del aleado en polvo se realizó en dos etapas. Primeramente, se compactó uniaxialmente a 650ºC y 90MPa depresión en atmósfera de argón durante 2 horas. Finalmente el compacto se laminó en caliente a 800ºC con un 20% dereducción de área.El objetivo del estudio, es investigar la evolución de las propiedades mecánicas y eléctricas asociadas a los cambiosmicroestructurales producidos por el proceso de compactación y laminación en caliente.Se constató que el proceso de laminación en caliente actúa como un tratamiento de precipitación de fases frágiles, quedisminuyen la dureza y la resistencia a la tracción sin aumentar la ductilidad de los compactos. Cuando la compactaciónuniaxial es uniforme, el laminado en caliente posterior puede obviarse, obteniendo aleaciones con mejores propiedadesmecánicas en desmedro de las eléctricas. La caracterización microestructural realizada con TEM y Microsonda electrónicaWDX, confirma que las cerámicas de TiB2 dispersadas son estables y no se descomponen en otros compuestosintermetálicos con el cobre en el rango de los 800ºC. Microanálisis con TEM muestran la precipitación de fases frágiles deltipo Sigma (s provenientes de la contaminación de los medios de molienda.Palabras claves: Aleación de cobre, propiedades mecánicas, microestructura, laminado en caliente.____________________________________________________________________AbstractIn this paper an analisys of mechanical and electric properties of

RESISTENCIA AL DESGASTE EROSIVO-CORROSIVO DE ACEROS AUSTENÍTICOS FERMANAL RESISTÊNCIA AO DESGASTE EROSIVO-CORROSIVO DE AÇOS AUSTENÍTICOS FERMANAL EROSIVE-CORROSIVE WEAR RESISTANCE OF FERMANAL AUSTENITIC STEELS

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Willian Aperador

2012-12-01

Full Text Available Se obtuvieron aleaciones austeníticas del sistema Fe-Mn-Al, en el intervalo Fe-(4,9~11,0 wt% de Al-(17,49~34,3 wt% de Mn-(0,43~1,25 wt% de C, las cuales fueron fundidas en un horno de inducción a partir de materiales de alta pureza. Las aleaciones se evaluaron con respecto a fenómenos de corrosión, erosión en medio húmedo y corrosión-erosión, a un ángulo de impacto de 90º. Para la evaluación de la corrosión se empleó una solución compuesta por 0,5 M de NaCl y partículas de sílice con tamaño entre 210 y 300 µm, con el fin de analizar el efecto del contenido de manganeso y aluminio en la resistencia a la erosión y a la corrosión-erosión de estas aleaciones. Para la caracterización de la respuesta corrosiva se usó la técnica con curvas de polarización potenciodin ámicas y la extrapolación de Tafel, la caracterización microestructural mediante microscopia electrónica de barrido (MEB y los productos de corrosión a través de difracción de rayos X (DRX.Obtiveram-se ligas austeníticas do sistema Fe-Mn-Al, no intervalo Fe-(4,9~11.0 wt% de Al-(17,49~34.3 wt% de Mn-(0, 43~1.25 wt% de C, as quais foram fundidas em um forno de indução a partir de materiais de alta pureza. As ligas avaliaram-se com respeito a fenômenos de corrosão, erosão em médio úmido e corrosão-erosão, a um ângulo de impacto de 90º. Para a avaliação da corrosão empregou-se uma solução composta por 0,5 M de NaCl e partículas de sílice com tamanho entre 210 e 300 µm, com o fim de analisar o efeito do conteúdo de manganês e alumínio na resistência à erosão e à corrosão-erosão destas ligas. Para a caracterização da resposta corrosiva usou-se a técnica com curvas de polarização potenciodinâmicas, a extrapolação de Tafel, a caracteriza ção microestructural mediante microscopia eletrônica de varredura (MEV e os produtos de corrosão através de difração de raios X (DRX.We obtained austenitic alloys of the Fe-Mn-Al, Fe in

Electrochemical performance in the hydrogen evolution reaction of Ni-TR (TR= La, Ce) materials synthesized using the solid state reaction method; Desempeno electroquimico en la reaccion de evolucion de hidrogeno de materiales de electrodo Ni-TR (TR = La, Ce) sintetizados por el metodo de reaccion de estado solido

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Torres-Huerta, A. M.; Dominguez-Crespo, M. A.; Ramirez-Meneses, E.; Yanez-Zamora, C. [CICATA, IPN, Altamira, Tamaulipas (Mexico); Avila-Garcia, I. [IPN, ESIQIE, UPALM, Mexico, D.F. (Mexico)]. E-mail: mdominguezc@ipn.mx; adcrespo2000@yahoo.com.mx

2009-09-15

relacionados con su operacion. El material de electrodo con mayor electroactividad es el Pt, pero debido a su costo elevado se han tenido que buscar electrocatalizadores alternativos con un balance entre costo y actividad. Uno de los materiales que mas se ha utilizado es el Niquel en conjunto con algunas de sus aleaciones. Este material ha demostrado un buen desempeno utilizando bajos sobrepotenciales en reacciones tradicionales como las reacciones de evolucion de hidrogeno (REH) y oxigeno (REO), asi como una alta resistencia a la corrosion y bajo costo. Particularmente, aleaciones binarias y ternarias han demostrado un incremento importante en la actividad de la REH al compararla con los materiales en su estado puro o masivo. Por esta razon, en la busqueda de nuevas alternativas con una aceptable eficiencia al compararla con los materiales a bajo costo, en este trabajo se obtuvieron materiales Ni-TR (TR = La, Ce) por el metodo de reaccion de estado solido, a partir de: a) acetilacetonatos metalicos y b) polvos metalicos. Estos materiales se sinterizaron durante 3 h a diferentes temperaturas (795 o 920 , 1000 y 1200 grados centigrados) a fin de evaluar su efecto en el desempeno electroquimico de los electrocatalizadores. La caracterizacion estructural y morfologica de materiales se realizo por las tecnicas de DRX y MEB, respectivamente. Asimismo, el desempeno electroquimico de los materiales de electrodo se evaluo en la REH utilizando voltametria ciclica (VC) y curvas potenciodinamicas. Los resultados obtenidos muestran que a bajas temperaturas se obtiene una mezcla de oxidos (NiO, CeO{sub 2} y LaNiO{sub 3}); sin embargo a medida que la temperatura de sinterizado se incrementa, se alcanza la formacion de las aleaciones NiO-CeO{sub 2} y NiO-LaNiO{sub 3}, respectivamente. Al mismo tiempo se observo una clara dependencia de la actividad electrocatalitica con la fuente obtencion de estos materiales (Ni-TR).

PHYSICOCHEMICAL CHARACTERIZATION OF NATURAL AND ACETYLATED THERMOPLASTIC CASSAVA STARCH

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JOSE MINA

2011-01-01

Full Text Available Almidón de Yuca natural y acetilado fueron plastifi cados empleando un extrusor de doble husillo y almacenados a 25 °C y 54 % de humedad relativa. El índice de cristalinidad, estimado como el cociente de las bandas de FTIR a 1047 (fase cristalina y a 1022 cm-1 (fase amorfa disminuyó en ambos almidones debido al proceso de plastifi cación. Mediante las micrografías de SEM se pudo observar que el proceso de plastifi cación destruyó casi por completo la estructura granular de los almidones. Los resultados de TGA mostraron que la energía de activación, Ea, disminuyó con el proceso de plastifi cación. Por otra parte se encontró que el almidón termoplástico acetilado presentó una Tg, absorción de agua y resistencia a tensión menores en comparación con el almidón termoplástico natural, mientras que su elongación a la ruptura fue mayor. Este comportamiento sugirió que la esterifi cación de los grupos hidroxilos del almidón natural redujeron las interacciones entre las cadenas del almidón plastifi cado.

Immobilization of Jacobsen type catalysts on modified silica

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Jairo Cubillos

2011-01-01

Full Text Available Varios catalizadores tipo Jacobsen fueron inmovilizados por enlace covalente en sílica amorfa previamente funcionalizada con 3-aminopropiltrietoxisilano (3-APTES. La caracterización de estos catalizadores y sus precursores por FTIR, DR UV-VIS, TGA y AAS permitió confirmar la inmovilización de los complejos de salen de Mn(III. Los catalizadores heterogéneos se evaluaron en la epoxidación diastereoselectiva de R-(+-limoneno utilizando dimetildioxirano (DMD generado in situ como agente oxidante, obteniéndose 1,2-epóxido como producto mayoritario. Bajo las mismas condiciones de reacción, los catalizadores heterogéneos mostraron una leve reducción en la selectividad en comparación con el catalizador homogéneo. La selectividad inicial se mantuvo en tres ensayos consecutivos de los catalizadores. Sin embargo, después de tres reusos, se observó pérdida de selectividad del catalizador inmovilizado. Los resultados FTIR sugieren la degradación parcial del catalizador heterogenizado. A pesar de que el método de inmovilización se seleccionó de tal manera que se minimizaran los cambios en la estructura del catalizador homogéneo, el exceso diastereomérico (d.e. se redujo considerablemente con los catalizadores inmovilizados.

Resistencia a la corrosión y desgaste de recubrinnientos deTiN obtenidos por PVD

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Conde, A.

2005-12-01

Full Text Available Surface hardening techniques for metallic alloys are widely used to achieve layers of very high hardness and corrosion and wear resistance. In the present paper TiN coatings are obtained by PVD on a tool steel. The films are characterized by SEM, X-ray diffraction and XPS. Corrosion behaviour in NaCl solution showed the importance of the presence of defects on the PVD coating due to the different electrochemical behaviour of the steel base. Pin-on-disk measurements at approximately 40% RH against a corundum (Al₂O₃ ball showed a significant decrease in the wear rate compared with the results for the standard tool steel.

Los tratamientos de endurecimiento superficial de aleaciones metálicas se utilizan para lograr capas de muy elevada dureza, resistencia a la corrosión y desgaste. En este trabajo, se estudia el comportamiento de recubrimientos de TiN obtenidos mediante PVD sobre aceros de herramientas. Las capas obtenidas se caracterizan mediante microscopía electrónica de barrido, difracción de rayos X y XPS. Se analiza el comportamiento frente a la corrosión de las capas protectoras, así como la influencia del substrato en su comportamiento en soluciones de NaCl. Finalmente, se realizan ensayos de desgaste por deslizamiento en seco mediante la técnica de pin-on-disk, comprobándose la mayor resistencia de estas capas.

EVALUACIÓN DE LA CAPACIDAD PROTECTORA DE RECUBRIMIENTOS Ni-SiC y Ni-Co-W DEPOSITADOS POR PROYECCIÓN TÉRMICA

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JUAN E. MONTOYA

2009-01-01

Full Text Available Recubrimientos de aleaciones de alto contenido de níquel, níquel-cobalto-tungsteno y carburo de silicio-níquel fueron depositados mediante rociado térmico y se estudió la capacidad de dichos recubrimientos para proteger un sustrato de acero de la corrosión en un medio agresivo. Los resultados obtenidos muestran que los recubrimientos realizados, a pesar de su porosidad, tienen la capacidad de aislar y proteger al sustrato de sustancias liquidas corrosivas, debido a que la porosidad de los depósitos es aislada y por lo tanto dificulta la difusión de dichas sustancias a través del recubrimiento. Los resultados permiten establecer que el recubrimiento monocapa de níqueltiene buena capacidad de proteger al sustrato y que los sistemas bicapa (níquel / níquel cobalto-tungsteno y tricapa (níquel, / níquel-cobalto-tungsteno / carburo de silicio-níquel, mejoran aún más la capacidad protectora del recubrimiento.

Influence of the brazing parameters on microstructure and mechanical properties of brazed joints of Hastelloy B2 nickel base alloy; Influencia de los parametros de soldeo fuerte en la microestructura y propiedades mecanicas de la union de la aleacion base niquel Hastelloy B2

Energy Technology Data Exchange (ETDEWEB)

Sotelo, J. C.; Gonzalez, M.; Porto, E.

2014-07-01

A study of the high vacuum brazing process of solid solution strengthened Hastelloy B2 nickel alloy has been done. A first stage of research has focused on the selection of the most appropriate brazing filler metal to the base material and vacuum furnace brazing process. The influence of welding parameters on joint microstructure constituents, relating the microstructure of the joint to its mechanical properties, has been evaluated. Two gaps of 50 and 200 micrometers, and two dwell times at brazing temperature of 10 and 90 minutes were studied. The braze joint mainly consists of the nickel rich matrix, nickel silicide and ternary compounds. Finally, the results of this study have shown the high bond strength for small gaps and increased dwell times of 90 minutes. (Author)

Comportamiento Tribológico y Microestructural en Recubrimientos Aplicados por GTAW y HVOF (Proceso Térmico de Espreado y Usado en Recuperación de Aceros Grado Herramienta AISI/SAE D2

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Carlos Alberto Guevara Chávez

Full Text Available Resumen Las aleaciones de Fe-Cr-Mo se utilizan en recubrimientos para proteger componentes que están sometidos a condiciones de desgaste y corrosión. La alta velocidad de deposición del metalizado térmico (HVOF (High Velocity Oxi-Fuel aplicado en aleaciones de acero grado herramienta para trabajo en frío con la aplicación de sustratos Fe-Cr-Mo ha mostrado buenos resultados en los campos de proyección. El HOVF es un método atractivo para aplicar revestimientos y recuperar diámetros que fueron desgastados durante el proceso de operación. Nuevas superficies y materiales pueden ser provistos sin la distorsión causada por los procesos convencionales de soldadura. Para aquellos materiales que son susceptibles a agrietarse gracias a la formación de fases fuera de equilibrio duras con composiciones con altos contenidos de carbono y de cromo, debido a las condiciones del proceso que combinan una temperatura de la flama relativamente baja y con un tiempo de baja exposición. La microestructura las características del recubrimiento son determinadas por las propiedades físicas y químicas de las partículas impregnadas en el sustrato que a su vez dependen de una gran cantidad de parámetros como el diseño de pistola, la relación de oxígeno / combustible, método de inyección, tamaño de partícula y forma, entre otros La presente investigación estudia la influencia de los parámetros de procesamiento sobre las propiedades mecánicas y microestructurales del recubrimiento Diamalloy 1008 (aleación en mezcla de Fe-Cr-Mo revestimiento aplicado con Oxí-combustible de alta velocidad (HVOF y cinco diferentes tipos de electrodos aplicados por soldadura, TIG (GTAW en un acero grado herramienta para trabajo en frio. El objetivo de estos recubrimientos se utiliza habitualmente como una protección contra la corrosión y el desgaste, pero también tienen la capacidad de recuperar las zonas dañadas como es el caso de los dados de estampado de la

LA PAROLA E IL SILENZIO IN VIRGINIA WOOLF E NATHALIE SARRAUTE

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Annalisa Federici

2014-12-01

Full Text Available L’idea della creazione letteraria come equivalente verbale di una realtà altra, come trasposizione dall’ordine della sensazione o del pensiero all’ordine della parola, accomuna la concezione estetica di Virginia Woolf a quella di Nathalie Sarraute. Ambedue le scrittrici manifestano una smisurata fascinazione nei confronti del linguaggio pur non perdendone di vista i limiti e le manchevolezze, che rendono necessario lo sforzo di  ricondurlo alle sue origini preverbali, emotive, pulsionali. L’enfasi, infatti, è posta sull’incommensurabilità tra una realtà fluttuante e amorfa quale è l’universo psichico, o la labilità delle impressioni, e la fissità, la rigidezza, la linearità del medium linguistico, che rischia in ogni momento di immobilizzare e devitalizzare la sensazione o il pensiero di cui è espressione. Entrambe le autrici esplorano dunque le potenzialità della sfera del nondetto, di quel silenzio che talvolta possiede un valore comunicativo superiore a quello della parola e ne evidenzia/compensa i limiti, manifestando una assenza e al contempo un surplus di significato. Lo stile di Virginia Woolf e di Nathalie Sarraute si farà quindi vago e allusivo, secondo un’estetica dell’indeterminatezza e dell’incompiuto (data, tra l’altro, dall’uso pervasivo dell’ellissi e dei puntini di sospensione finalizzata a congiungere la sfera psichica e la realtà del linguaggio, anche tramite la sua assenza.

Celulas solares e sensores de filme fino de silicio depositados sobre substratos flexiveis =

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Pinto, Emilio Sergio Marins Vieira

Celulas solares flexiveis de filmes finos de silicio sao geralmente fabricadas a baixa temperatura sobre substratos de plastico ou a mais elevadas temperaturas sobre folhas de aco. Esta tese reporta o estudo da deposicao de filmes finos sobre diferentes substratos de plastico, transparentes e coloridos, para celulas solares do tipo sobrestrato e substrato, respectivamente. Como objetivo co-lateral, os filmes dopados depositados sobre plastico foram usados como sensores de deformacao, utilizando as suas propriedades piezo-resistivas. Elevadas taxas de deposicao dos filmes de silicio depositados sobre plastico foram obtidas a baixa temperatura do substrato (150ºC) por rf-PECVD. A influencia de diferentes parametros de deposicao sobre as propriedades e taxa de deposicao dos filmes resultantes foram estudados e correlacionados. Celulas solares de filmes finos de silicio amorfo e microcristalino foram desenvolvidas a baixas temperaturas sobre plasticos. Eficiencias de 5 - 6.5% foram alcancadas para as celulas amorfas e 7.5% para as celulas microcristalinas. Efeitos de aprisionamento da luz foram estudados atraves da texturizacao por ablacao laser de substratos de plastico e corrosao umida de TCO sobre plastico. Filmes finos de silicio microcristalino, depositados por HW-CVD, com fator piezoresistivo de -32.2, foram usados para fabricar sensores de deformacao em uma membrana plastica muito fina (15 μm). Estruturas de teste em textil e a miniaturizacao dos sensores piezoresistivos depositados sobre substratos flexiveis de poliimida foram abordados.

Obtention of Al-Mg alloys of porous morphology; Obtencion de aleaciones Al-Mg de morfologia porosa

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Barragan V, J.; Zamora R, L.; Sandoval J, A.R.; Iturbe G, J.L. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

2006-07-01

With the objective of using it as fuel cell, a Mg{sub 25}AI alloy of porous morphology was obtained. The material it was hydrogenates at 200 C by different time. It was analyzed by Scanning Electron Microscopy SEM and X-ray diffion, XRD. Those XRD diffractographs present peaks run toward the origin, that which indicates a volume increase of the unitary cell by effect of the hydrogen absorption. (Author)

Direct-reading spectrochemical analysis of magnesium alloys; Analisis espectroquimico de lectura directa de aleaciones de magnesio

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Roca Adell, M

1964-07-01

A Quantometer has been applied to the determination of aluminum, berylium, calcium, iron, silicon and zinc in magnesium alloys Magnox, after the conversion of the samples to the oxide. For the aluminum, whose concentration is relatively high, the conducting briquets technique with an interrupted discharge is employed, using the magnesium as the internal standard. For the other elements a total burning method with direct current arc is employed, using also the magnesium as the internal standard. (Author) 7 refs.

Estudio DRX en Materiales Catalizadores Cu-Ni-SiO2 para Hidrogenación de aceite de soya. Desarrollo de estructura cristalina y actividad catalítica

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Gloria I. Cubillos

2009-01-01

Full Text Available Para buscar elementos experimentales que soporten la hipótesis según la cual se forman estructuras cristalinas Cu-Ni o eventualmente Cu-Ni-SiO2 en la síntesis de catalizadores para la hidrogenación de aceite de soya, se prepararon mezclas de estos tres materiales a partir de sales de los metales con sílice (aerosil. Se calcinaron a 270oC y se redujeron a 330oC en atmósfera de hidrógeno. En  los materiales reducidos se  estudió el difractógrama de RX en el rango 37 a 53 grados, y se comparó con el difractógrama de aleaciones Cu-Ni, en las cuales se conoce la formación  de cristales mixtos, y  con los difractógramas de los elementos puros Cu y Ni.  Los resultados muestran que se presentan señales de difracción diferentes a las señales de los componentes puros. La actividad catalítica se muestra diferente en los materiales que presentan distorsión en su estructura cristalina.  

Influence of silicon on wear behaviour of “Silal” cast irons

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Ana I. García-Diez

2014-01-01

Full Text Available En este trabajo se ha evaluado la influencia del contenido de s ilicio en la resistencia frente al desgaste y en las propiedade s mecánicas de diferentes fundiciones con alto c ontenido en silicio del tipo S ilal. Para ello se ha variado el contenido en carbono y en sili cio de las muestras, evaluando posteriormen te la modificación en la dureza , determinada mediante la escala Brinell, y en el comportamient o tribológico, estudiado mediante e nsayos de desgaste normalizado s Pin-on-Disk. Todo ello se ha complementado con un estudio metalográfico para determinar la influencia de la microestructu ra en las propiedades analizadas. Se ha determinado que el mejo r comportamiento al desgaste lo pre sentan aquellas aleaciones cuy a composición y proceso de colada garantizan el grafito esferoi dal frente a las que lo presentan con estruc tura laminar. A dicionalmente, se ha experimentado con diferentes procesos de colada para la fabricación de las fundiciones para determinar su influe ncia en la aparició n del grafito esferoidal.

Characterization of internal surface finishing of tubes for CAREM 25 fuel rods

International Nuclear Information System (INIS)

Loureiro, N.V; Juarez, G; Bianchi, D; Flores, A; Vizcaino, P

2012-01-01

One of the factors that ensure the good behavior of the fuel claddings of the nuclear power reactors is the internal surface quality. In the present work has been carried out a study of the internal surface of the tube after a cold rolling process developed in the Departamento de Tecnologia de Aleaciones de Circonio and applied by FAE-SA and PPFAE-CNEA in each rolling stage to obtain the fuel claddings for the reactor CAREM 25. The inner surface has been observed by scanning electron microscopy, SEM, being the objective of this study to verify not only the good internal surface but also infer about how starting from tubes of different initial diameter reduction the quality of the final product will be affected. The manufacturing process of the tubes for this new fuel went through modifications during the development, adding intermediate chemical pickling stages in order to improve the internal surface quality of the final product. From determinations made with ultrasound, the defects charts obtained made it possible to compare the observed signals more relevant and the micrographs in these areas in order to characterize possible defects (author)

Deformación incremental de lámina sin matriz (DIELESS como alternativa viable a procesos de conformación de lámina convencionales

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Gabriel Páramo Bermúdez

2013-01-01

Full Text Available El proceso de deformación incremental sin matriz (Dieless es un proceso reciente (año 1994 con respecto a otras técnicas de procesos convencionales de deformación de lámina metálica tales como el repujado, estampado, embutido, entre otros, los cuales son costosos y suponen altos volúmenes y lotes de producción para su construcción y funcionamiento. El objetivo del presente trabajo es demostrar a través de pruebas experimentales la viabilidad de este proceso tecnológico y analizar los resultados obtenidos, con fines de aplicabilidad industrial. Se presenta a dieless como un proceso de manufactura alternativo, su principio de funcionamiento, parámetros del mismo, ventajas y desventajas, así como el estado del arte respecto a resultados de proyectos e investigaciones que se han hecho a la luz del mismo en láminas de aleaciones de aluminio, acero y aplicaciones industriales en específico, que se han desarrollado en el último par de años en la Universidad EAFIT, de Medellín.

Spectrophotometric determination of titanium with ascorbic acid in aluminium alloys and other materials. Determinacion espectrofotometrica de titanio con acido ascorbico en aleaciones de base aluminio y otros materiales

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Bosch Serrat, F. (Departamento de Quimica Analitica. Facultad de Qauimica. Valencia (Spain))

1994-01-01

A spectrophotometric determination of titanium with ascorbic acid in aluminium alloys and bauxite is described. The proposed procedures permit to determine levels of titanium down to 5.10 ''3% with a good accuracy and precision. (Author) 13 refs.

Evaluaciones calorimétricas de la precipitación en aleaciones Cu-Co-Si, ricas en Cu

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Donoso, Eduardo

2001-08-01

Full Text Available The precipitation process of cobalt and silicon atoms from supersaturated solid solutions of Cu-Co-Si for two compositions was studied by differential scanning calorimetry (DSC. Calorimetric traces analysis showed the presence of two overlapping exothermic reactions (stages 1 and 2, which can are attributed to two precipitation processes. First stage correspond to the preceding formation of a cobalt precipitate, while the second stage correspond to the formation of stoichiometric CO₂Si composition which takes place by silicon diffusion to the first precipitate. Heat contents during the stages 1 and 2 are proportional to precipitates volume fractions. Activation energies of both precipitates, calculated from the Kissinger method, are consistent with those corresponding to diffussion of Co in Cu and Si in Cu. Both processes can be decribed by the Johnson-Mehl Avrami (JMA equation. Values of n are compatible with precipitate nucleation from the solid solution (stage 1 and with growth of paticles from preexisting Co precipitates. Furthermore,, the kinetic of the concentration decay of Co and Si in the matrix was estimated as function of the transformated fraction for each thermal event and from their respective volume fractions.

Mediante calorimetría diferencial de barrido (DSC se estudió el proceso de precipitación de átomos de cobalto y silicio a partir de dos soluciones sólidas supersaturadas de Cu-Co- Si. El análisis de las trazas calorimétricas muestra la presencia de dos reacciones exotérmicas traslapadas (etapas 1 y 2, que se interpretan como la formación de dos tipos de precipitados. La primera etapa corresponde a la formación precursora de un precipitado de cobalto, en tanto que la etapa 2 corresponde a la formación de un precipitado de composición estequiométrica CO₂Si producido por difusión de silicio hacia la primera partícula. Los calores liberados durante las etapas 1 y 2 son proporcionales a las fracciones volumétricas de los precipitados. Las energías de activación de ambas reacciones, calculadas por el método de Kissinger, son consistentes con aquellas correspondientes a la difusión de Co en Cu y Si en Cu, respectivamente. Ambos procesos pueden ser descritos mediante la ecuación de Johnson-Mehl-Avrami (JMA, cuyos valores de n son cornpatibles con la nucleación de precipitados a partir de la solución sólida (etapa 1 y con crecimiento de partículas a partir de precipitados pre

Thermal characterization of partially hydrolyzed cassava (Manihot esculenta starch granules

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Luiz Gustavo Lacerda

2008-12-01

Full Text Available Cassava starch, partially hydrolyzed by fungal á-amylase, was characterized using thermal analysis, light microscopy and X-ray diffraction. Thermal degradation was initiated at lower degradation temperatures after enzymatic treatment and the DSC (Differential scanning calorimetry analysis showed almost similar range of gelatinization temperature, but the enthalpies of gelatinization were quite increased for the partially hydrolyzed starch granules. The results suggested that the partial degradation of the starch granules was concentrated in the amorphous regions.Amilases fúngicas são comumente empregadas a amidos com o intuito de otimizar o rendimento de leveduras, modificar a textura de produtos panificados e prolongar a vida de prateleira do produto final. A hidrólise parcial enzimática pode auxiliar no entendimento da estrutura do amido ganular. Amido de mandioca parcialmente hidrolisado por á-amilase fúngica foi investigado utilizando-se técnicas termoanalíticas, microscopia ótica e difratometria por raios X. A degradação térmica iniciou-se a temperaturas menores após o tratamento enzimático e a análise por DSC mostrou uma próxima faixa de temperatura de gelatinização, porém, a entalpia necessária para o evento foi maior para os grânulos parcialmente hidrolisados. Os resultados sugerem que a degradação parcial do amido granular foi concentrada em regiões amorfas.

Variación de la energía libre de Gibbs de la caolinita en función de la cristalinidad y tamaño de partícula

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La Iglesia, A.

1989-12-01

Full Text Available The effect of grinding on crystallinity, particle size and solubility of two samples of kaolinite was studied. The standard Gibbs free energies of formation of different ground samples were calculated from solubility measurements, and show a direct relationship between Gibbs free energy and particle size-crystallinity variation. Values of -3752.2 and -3776.4 KJ/mol. were determinated for ΔGºl (am and ΔGºl (crys of kaolinite, respectively. A new thermodinamic equation that relates ΔGºl to particle size is proposed. This equation can probably be extended to clay mineals.Se estudia el efecto de la molienda prolongada sobre la cristalinidad, tamaño de partícula y solubilidad de dos muestras de caolinita. Se ha calculado la energía libre estandar de formación del mineral a partir de medidas de solubilidad, encontrando una relación directa entre ΔGºl, y las variaciones de tamaño de partícula y cristalinidad de las muestras. Por extrapolación, se han obtenido los valores de -3752,0 y -3776,4 KJ/mol. para ΔGºl caolinita amorfa y cristalina. Se propone una ecuación termodinámica que relaciona ΔGºl y el tamaño de partícula de la caolinita; esta ecuación puede aplicarse también a otros minerales de la arcilla.

Goma de cajueiro (Anacardium occidentale: Avaliação das modificações químicas e físicas por extrusão termoplástica

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Kelita C. S. Andrade

2013-01-01

Full Text Available Países tropicais, como o Brasil, são depositários de uma grande variedade de fontes de polissacarídeos vegetais conhecidos e outros ainda não explorados que possuem grande potencial em aplicações industriais. Alguns estudos reportam a possibilidade de aplicação industrial da goma exsudada do cajueiro em substituição à goma arábica devido à semelhança estrutural e química. Neste estudo propôs-se caracterizar comparativamente algumas propriedades destas duas gomas, antes e após dois tratamentos de extrusão termoplástica. Nos resultados de composição centesimal as amostras de goma de cajueiro in natura e processadas destacaram-se pelo alto teor de fibra solúvel. Por outro lado, apresentaram menor teor de minerais que a goma arábica. Por meio da análise de viscosidade rápida, foi observado que este parâmetro aumentou nas amostras de goma arábica processadas, enquanto nas amostras processadas de goma de cajueiro houve redução. Nos resultados da análise de difração de raios X predominou-se a conformação amorfa das cadeias poliméricas de ambas as amostras. A partir dos parâmetros avaliados, a goma de cajueiro poderia ser indicada como substituta da goma arábica.

Material for the storage of Mg-Ni-Based hydrogen produced by mechanical alloying; Materiales para almacenamiento de hidrogeno base Mg-Ni producidas por aleado mecanico

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Zaldivar-Cadena, A. A. [Universidad Autonoma de Nuevo Leon, San Nicolas de los Garza, Nuevo Leon (Mexico); Leon Santiago, M.; Suarez Alcantara, K.; Morales-Hernandez, J.; Cabanas Moreno, J. G. [Instituto Politecnico Nacional, UPALM, Mexico, D.F. (Mexico)]. E-mail: gcabanas@esfm.ipn.mx

2009-09-15

caracterizacion de la microestructura y composicion de los polvos. Las caracteristicas de absorcion-desorcion de hidrogeno de las aleaciones fueron evaluadas por tecnicas de analisis termico como DTA-TGA. Experimentos preliminares del tipo Batch dieron como resultado una variacion de las cantidades de MgH{sub 2} en los polvos hidrurados dependiendo de la composicion y condiciones de hidruracion. Experimentos de gravimetria en mezclas de polvos de Mg-5%Ni indicaron contenidos de hidrogeno de aproximadamente 5.59% - 6.12% en peso mostrando una rapida cinetica de hidruracion a temperaturas menores de 250 grados centogrados. Aunque el proceso de deshidruracion ocurrio razonablemente rapido solamente a temperaturas de 250 y 300 grados centogrados. El comportamiento de hidruracion/deshidruracion es influenciado por la tendencia a formar Mg{sub 2}Ni en los polvos aleados mecanicamente. Esta tendencia es promovida con altos contenidos de Ni, tiempos largos de molienda y temperaturas de hidruracion altas. Los mejores resultados son aparentemente obtenidos con un balance optimo de la dispersion del Ni el cual depende del con tenido de Ni y tiempo de molienda.

Metallurgical production from North-east of the Iberian Peninsula during III millennium cal. BC: the Bauma del Serrat del Pont (Tortellá, Girona workshop

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Alcalde, Gabriel

1998-06-01

Full Text Available We examine the third millennium cal. BC levels from the small rockshelter of Bauma del Serrat del Pont. The site was settled by a small group, building a perishable structure except in the II. 5 level. Some evidence suggests a seasonal occupation of the site. Multidisciplinary research shows a broad spectrum of local resources involved in the dairy life of this people, including those related to metallurgical activity. We find very old tin alloys, plain or bell beaker decorated pot-furnaces (used to smelt copper ores and clay tuyeres.

Se presentan los resultados de la excavación en los niveles del III milenio cal. AC del pequeño abrigo rocoso de la Bauma del Serrat del Pont. El yacimiento fue ocupado por un grupo pequeño que organizó el espacio interno con una estructura de material perecedero, excepto en el nivel II.5. Algunos datos indican que las ocupaciones pudieron tener un carácter estacional. Los estudios multidisciplinares reconstruyen un aprovechamiento diversificado de recursos locales, entre los que se integran los dedicados a las tareas metalúrgicas. Se documentan aleaciones intencionadas de bronce de gran antigüedad, el empleo de vasijas horno con o sin decoración campaniforme, y toberas de arcilla.

ESTUDIO DE MEZCLA DE NANOPARTÍCULAS SULFURADAS Y OXIDADAS DE Mo Y DE Ni SOPORTADAS EN ALÚMINA, OBTENIDAS POR EL MÉTODO DE DESCOMPOSICIÓN TÉRMICA

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Susana Martínez

2011-01-01

Full Text Available Se sintetizó una mezcla de nanopartículas sulfuradas y oxidadas de Mo y de Ni por el método de descomposición térmica, empleando un sistema de reflujo, dimetil disulfuro como agente sulfidizante, nonano como disolvente y una alúmina comercial que fungía como soporte. El sólido gris resultante se eliminó primero por decantación y luego por evaporación del líquido remanente bajo condiciones de vacío con el fin de evitar cambios, específicamente en las nanopartículas obtenidas. Una vez obtenidas las nanopartículas soportadas en alúmina se determinaron sus propiedades fisicoquímicas (morfología, estructura cristalina, estado de oxidación y composición elemental empleando las técnicas de HR-TEM, XPS e ICP. Los resultados de XPS y MET-HR muestran que el sólido esta conformado por nanopartículas de los metales seleccionados en sus formas oxidadas y sulfuradas tales como MoO3, MoS2, Ni2O3 y NiS, siendo la fase mayoritaria el MoO3. En los resultados no se evidenciaron fases mixtas o aleaciones de Mo y Ni.

Estudio cinético de la eliminación de magnesio en las aleaciones de aluminio mediante la inyección de polvos de sílice

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Escobedo, J. C.

2003-06-01

Full Text Available A kinetic study on the magnesium removal from molten aluminium alloys using submerged SiO₂ powders injection is presented. The variables analysed were the chemical content and the particle size of the solid agents, the melt temperature and the injection rate. It was possible to decrease the magnesium content from 1.2 to 0.02wt %, with a low inclusions content. As the main mechanism of the magnesium removal process is of diffusive type, the global process rate increases as the temperature and the injection rate are increased, while decreasing particle size. In all the cases studied, a first order global process was determined and the global rate constants were also evaluated.

Se presenta un estudio cinético de la eliminación de magnesio de una aleación base aluminio líquida, utilizando la técnica de inyección de agentes sólidos base SiO₂ transportados por un gas inerte. Las variables estudiadas son: la composición de los agentes sólidos, la temperatura del baño metálico, la velocidad de inyección y el tamaño de partícula de los agentes sólidos. Se logró disminuir el contenido de magnesio en la aleación, desde 1,2 hasta 0,02 % en peso, encontrándose que, debido a que el mecanismo que gobierna la cinética de eliminación de magnesio es de carácter difusivo, la velocidad de reacción aumenta al incrementarse la temperatura y la velocidad de inyección y al disminuirse el tamaño de partícula. También, se determinó que el proceso de eliminación de magnesio es de primer orden, evaluándose, además, las constantes de velocidad del proceso global a las diferentes condiciones experimentales empleadas.

Corrosión en soldaduras de aparatos de ortodoncia

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Vázquez, S. M.

1997-10-01

Full Text Available The study of corrosion-related problems of dental materials has undergone a considerable development in recent years in order to avoid the use of materials with insufficient corrosion resistance in patients' mouth. The subject of the present work was to study a particular type of corrosion: galvanic corrosion. One of the most common case of galvanic couples in patients' mouth are the orthodontic appliances. The materials studied in the present work were stainless steel strips and silver-copper wires, isolated and welded between them. The electrochemical tests were performed in a NaCl 0.1M and Lactic Acid 0.1M solution (pH 2.3, and after test, the specimens were observed using the optical and scanning electron microscope. The results show that when stainless steel is coupled with a silver solder, the last is the anode of the galvanic couple. As a consequence of this, the silver solder undergone a severe attack. Stainless steel orthodontic appliances with silver solder are feasibly destroyed due to a severe attack on the filler metal disjoining the welded parts.

En los últimos años se ha desarrollado considerablemente el estudio de los problemas relacionados con la corrosión de aleaciones dentales a efectos de evitar la utilización de materiales con una deficiente resistencia a la corrosión en la boca de los pacientes. El objetivo del presente trabajo fue estudiar la corrosión de aparatos de ortodoncia fabricados con acero inoxidable con soldadura por punto o por aporte de aleación de plata. Los resultados obtenidos mostraron que cuando el acero inoxidable contiene aportes de soldadura de material de base plata, ésta actúa como ánodo disolviéndose preferencialmente a una velocidad considerable. Los aparatos de ortodoncia construidos con acero inoxidable soldado con aporte de material de base plata, corren el riesgo de destrucción debido a un ataque intenso en el cordón de soldadura con el consiguiente despegue de las piezas

Magnetic shape memory alloys: Basic properties and applications; Aleaciones magneticas con memoria de forma: propiedades basicas y aplicaciones

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Barandiaran, J. M.; Lazpita, P.; Guiterrez, J.; Garcia Arribas, A.; Feuchtwanger, J.; Asua, E.; Etxebarria, V.; Chernenko, V. A.

2010-07-01

These materials can undergo large deformations when subjected to external stresses when they are in the phase low temperature due to the super elasticity property. Super elasticity properties and memory effect form derived from the martensitic transformation, which thermoelastic transformation is involved in effort as well as temperature. The transformation autoacomodante called for a single crystal phase austenite gives rise to several crystals spontaneously martensite with their axes oriented in different directions to accommodate the deformation of the network. These crystals called variant or twins and their movement and change orientation gives rise to the super elasticity. (Author) 3 refs.

TEORIA DE BILL MUNDY Y EL ANGULO EFECTIVO DE ATAQUE DE HERRAMIENTAS DE CORTE EN ALEACIONES DE COBRE

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Godoy R, Juan Miguel; Vergara D, Jorge; Oviedo O, Percy; Quispe Y, Martín; Gallardo M, Edward; Ramírez H, Leandro

2007-01-01

Magazines like American Machinist and Manufacturing Engineering, have explained the Bill Mundy theory about the effective rake angle of cutting tools. These articles show the effective rake angle of cutting tools for carbon steel, steel , alloys, cast iron, aluminium and stainless steel. In the present work the theory is applied to cutting tools used in brass and bronze. The effective rake angle for these materials was obtained with the tensile stress test. The rake angles in the cutting tool...

Calcificações malignas da mama: correlação mamografia-anatomia patológica

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Vianna Alberto Domingues

2002-01-01

Full Text Available Neste trabalho foram realizados 30 estudos de correlação entre os achados da mamografia e da anatomia patológica em 29 pacientes com tumores malignos na mama, cujas mamografias apresentaram calcificações relacionadas com as lesões. Os objetivos principais foram: verificar se as formas das calcificações corresponderam a tipos específicos de tumores e se as formas das calcificações estavam relacionadas aos locais onde eram formadas. Foram estudados dois aspectos objetivos das calcificações identificados nas mamografias: forma e distribuição. Este estudo concluiu que os carcinomas tipo comedo tiveram elevada freqüência de calcificações pleomorfas (95,5% e padrão de distribuição ductal em 66,5% dos casos. Os carcinomas tipo cribriforme, quando não associados ao tipo comedo, evidenciaram somente calcificações arredondadas em 66,5% dos casos e predominância de distribuição indefinida (78,5%. Os tumores micropapilares, quando não associados ao tipo comedo, mostraram somente calcificações arredondadas em 66,5% dos casos e predominância do padrão de distribuição indefinido (66,5%. Nenhum tumor mostrou padrão de distribuição lobular. Calcificações amorfas na ausência de nódulo tumoral são suspeitas de carcinoma ductal infiltrante. De acordo com o padrão histológico arquitetural dos 30 tumores, 24 (80% tiveram calcificações com as formas esperadas.

ESTUDIO FISICOQUÍMICO DE MEZCLAS DE ALMIDÓN TERMOPLÁSTICO (TPS Y POLICAPROLACTONA (PCL

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JOSE MINA H.

Full Text Available Se estudiaron las propiedades físico-químicas de un almidón termoplástico (TPS de yuca, plastificado con glicerol, y el efecto de la incorporación de policaprolactona (PCL en el desarrollo de tres mezclas binarias TPS-PCL a proporciones 60-40, 50-50 y 40-60. El estudio inició con la preparación por extrusión del TPS y su posterior mezcla en caliente con la policaprolactona. El análisis de los resultados se enfocó principalmente a la identificación y seguimiento de la retrogradación, que se dio en el almidón termoplástico para diferentes tiempos de acondicionamiento (a 54% H.R. y 25ºC. Con el proceso de plastificación del almidón se generó una masa predominantemente amorfa, evidenciada por los resultados obtenidos con SEM, DRX y FTIR. Con la incorporación de la PCL se obtuvieron mezclas inmiscibles, en las cuales el TPS se constituyó en la fase dispersa y que conservaron una tendencia en la variación de las propiedades con el tiempo de acondicionamiento, similar a la observada en el TPS solo; indicando este hecho que las interacciones físico-químicas generadas entre el TPS y la policaprolactona no fueron lo suficientemente fuertes, como para incidir en la variación estructural del TPS, la cual se dio independiente del contenido de PCL.

Polímeros com condutividade iônica: desafios fundamentais e potencial tecnológico Polymers with ionic conductivity: fundamental challenges and technological potential

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Virgínia P. R. Silva

2005-11-01

Full Text Available Polímeros condutores iônicos ou eletrólitos poliméricos constituídos por um sistema de sal dissolvido em uma matriz polimérica sólida são materiais que apresentam interesse científico e potencial tecnológico. A dissolução de sais em uma matriz polimérica amorfa ou semicristalina sólida leva a estudos sobre intrigantes aspectos estruturais, que podem ser abordados por técnicas físico-químicas diversas tais como RMN, Raman e Espectroscopia de Vida Média de Pósitrons. Os estudos estruturais são correlacionados com propriedades eletroquímicas visando à utilização desses materiais em dispositivos tais como baterias, supercapacitores e células solares. Grupos brasileiros têm gradativamente ampliado os estudos e aplicações de eletrólitos poliméricos sólidos.Ionic conducting polymers or polymer electrolytes prepared with the addition of a soluble salt in a solid polymeric matrix are very important materials, associated with an intense research activity and technological efforts. Structural studies in a system of salt dissolved in an amorphous or semicrystalline solid polymeric matrix can be done with various techniques, such as NMR, Raman and Positron Annihilation Spectroscopy. The structural studies are correlated with electrochemical properties in order to evaluate these materials for applications in batteries, supercapacitors and solar cells. Brazilian researchers are contributing to the fundamental research and development of new applications of polymeric electrolytes.

Regional models of metal production in Western Asia in the Chalcolithic, Early and Middle Bronze Ages

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Avilova, Liudmila

2008-06-01

Full Text Available The objective of this work is the reconstruction and comparative analysis of regional models of metal production in the Chalcolithic, Early and Middle Bronze Ages. The work is based on the statistical analysis of unique computer database on archaeological metal finds from four regions of the Near East: Anatolia, Mesopotamia, the Levant, and Iran. The materials are analysed by four indicators: distribution by the chronological periods, artefacts’ function, proportion of used metals and copper- based alloys. The author presents a series of conclusions concerning the preconditions for the beginnings of metal production in Western Asia and the pioneering role of Iran in its emergence, the important role the piedmont territories played in the development of metal production, the leap-like pattern of production dynamics shown by the periods, and its relation to the spread of a producing economy, long-distance exchange, and the emergence of the early civilizations.

El objetivo de este trabajo es la reconstrucción y análisis comparativo de modelos regionales de producción metalúrgica del Calcolítico y la Edad del Bronce Inicial y Media. Se basa en el análisis estadístico de una base de datos única sobre hallazgos metálicos de cuatro regiones del Próximo Oriente: Anatolia, Mesopotamia, el Levante e Irán. Los materiales se analizan atendiendo a cuatro variables: períodos cronológicos, función de los artefactos, proporción de los metales usados y las distintas aleaciones del cobre. La autora aporta una serie de conclusiones respecto a las precondiciones para los inicios de la producción metalúrgica en el Oeste Asiático; sobre el papel pionero de Irán en su aparición; la importancia de los piedemontes en su desarrollo; el patrón no continuo que se observa en las dinámicas de producción por periodos; y su relación con la expansión de la economía de producción, el intercambio a larga distancia y la aparición de las

Resistencia a la oxidación de aleaciones Ni-Cr-Al plaqueadas por láser sobre aceros al carbono e inoxidables austeníticos

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de Damborenea, J.

1995-04-01

Full Text Available Laser surface cladding has been carried out by means of a 5 kW CO₂ continuous wave laser on both a mild and a stainless steel. A powder injection technique has been used to deliver a Ni-Cr-Al alloy onto the steel molten pool. After processing, samples were analyzed by optical and scanning electron microscopy in order to know the microstructure and composition of present phases. High temperature corrosion resistance tests were done in an oxidant environment at temperatures of 950 °C. Phase transformations and corrosion behaviour are discussed. A general conclusion is the suitability of these alloys to bear oxidation due to the formation of protective oxide layers on their surface.

Se realiza un estudio sobre la obtención de recubrimientos de superficie mediante un láser continuo de CO₂ de 5 kW de potencia de salida. Mediante la técnica de inyección de partículas, se realizaron plaqueados en superficie de Ni-Cr-Al sobre un acero suave y otro inoxidable de tipo 316. Tras el procesado, se estudió la microestructura de las probetas obtenidas. Posteriormente, se procedió a su ensayo en atmósfera oxidante a 950 °C, observándose la evolución de la microestructura, la formación de las capas de óxido y la cinética del proceso. Como conclusión general, destaca, independientemente de la base sobre la que se obtienen los recubrimientos, la gran resistencia del material a la oxidación, seguramente debida a la formación de capas de alúmina que actúan como barreras frente al ataque del oxidante.

Estudio mediante EIS de capas lantánidas de conversión desarrolladas mediante activación térmica sobre aleaciones de Al-Mg

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Bethencourt, M.

2005-12-01

Full Text Available Nowadays, a lot of anticorrosive treatments that can be used as alternative processes to Cr(IV-based treatments are developing. Some of them involve the use of lanthanide compounds. The present work show a morphologic and anticorrosive study of conversion coatings developed on samples of AA5083 alloy from Ce (III solutions, by treatments of immersion to 323K in baths of cerium salts. SEM/EDS analysis of treated sampled shows the existence of an heterogeneous coating composed of an aluminium hydroxide/oxide on the metallic matrix and Ce island over cathodic intermetallic. Protected with conversion coatings, AA5083 samples were immersed in NaCl and EIS tests were registered both to evaluate the protection degree of the developed coatings and to characterize the individual contribution of the electrochemical response of the system.

En la actualidad, se encuentran en desarrollo una gran variedad de tratamientos anticorrosivos que pueden emplearse como alternativas a los basados en Cr(VI. Algunos conllevan el empleo de lantánidos. En este trabajo, se lleva a cabo un estudio de las características morfológicas y anticorrosivas de capas desarrolladas sobre la aleación AA5083 a partir de disoluciones de Ce(III, mediante tratamientos de inmersión a 323K en baños de sal de cerio. Estudios SEM/EDS sobre la muestras tratadas han puesto de manifiesto la existencia de una capa heterogénea formada por una película de óxido/hidróxido de aluminio sobre la matriz y una serie de islas dispersas de cerio, sobre los intermetálicos catódicos. Para evaluar el grado de protección de las capas de conversión desarrolladas, así como para caracterizar la contribución individual de la respuesta electroquímica del sistema en NaCl, se han llevado a cabo ensayos de EIS.

Análisis del comportamiento mecánico de una aleación Ni-Cr-Mo para pilares dentales/Analysis of Mechanical Behavior of Ni-Cr-Mo alloy for Dental Abutments

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Luis Alberto Laguado Villamizar

2012-12-01

Full Text Available El presente estudio caracteriza una aleación aplicable al diseño de pilares para implantes dentales. Se propone un material biocompatible y de alta resistencia mecánica como alternativa a las aleaciones de Titanio, disminuyendo los costos de materia prima y procesamiento. Se realizan pruebas mecánicas de tracción y de compresión a la aleación de Ni-Cr-Mo, posteriormente se realiza modelado 3D y simulación de sus propiedades mecánicas por medio de análisis de elementos finitos. Como resultado se obtiene que el material disminuye su resistencia mecánica después del proceso de fundición empleado. El modelo de simulación es válido para análisis de resistencia en pilares dentales.This study presents the characterization of a dental implant alloy for abutments. It proposes a biocompatible material and high mechanical resistance as an alternative to Titanium alloys, lowering costs of raw materials and processing. Mechanical testing of the Ni-Cr-Mo alloy and subsequently perform simulations of its mechanical properties by means of finite element analysis. As a result is obtained that the material reduces its mechanical strength after the casting for electric induction molding process. The simulation model is valid to make analysis of resistance to this type of dental devices.

Síntesis y almacenamiento de carga de la nueva aleación polipirrol/poli(ácido maleico-olefina

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D´eramo, F.

2000-06-01

Full Text Available The influence that the electrosynthesis conditions of the polypyrrole/poly(maleic acid-co-olefin blend have on the charge storage ability (amount of electrical charge stored (mC per unit mass (mg of electrogenerated polymer has been analysed. This is the initial step for the optimisation, pyrrole and poly (maleic acid-co-olefin concentrations and the polymerisation temperature have been the studied parameters. Optimising these ones, we could obtain materials with average storage charge of 120mc.mg-1.

Se ha analizado la influencia de diversas variables de síntesis sobre la capacidad de almacenamiento de carga (mC de carga almacenada / mg de polímero electrogenerado de aleaciones poliméricas de polipirrol/poli(ácido maléico-co-olefina, como paso inicial para la optimación de este material para su aplicación en baterías todo orgánicas. Las variables de estudio han sido: el potencial y el tiempo de polimerización, las concentraciones de pirrol y poli(ácido maléico-co-olefina y la temperatura de la solución de polimerización. Optimando estos parámetros se ha logrado sintetizar materiales con una capacidad promedio de almacenamiento de carga de 120 mC. mg-1.

Mineral trioxide aggregate as root canal filing material: comparative study of physical properties = MTA como cimento endodôntico: estudo comparativo de propriedades físicas

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Silva, Wander José da

2010-01-01

Full Text Available Objetivo: Este estudo avaliou as propriedades físicas de dois cimentos MTA disponíveis comercialmente. Metodologia: A resistência a compressão (CS dos materiais avaliados foi realizada após 21 horas e 14 dias de imersão em água. A avaliação da radiopacidade (RD dos materiais foi mensurada em função de espessura de alumínio. Com relação à propriedade de tempo de presa (ST, tanto os tempos de presa inicial e final foram mensurados. A solubilidade foi calculada em função da percentagem de massa perdida após armazenamento em água. Os valores de pH foram mensurados em três diferentes tempos (inicial, 1 e 24 horas de armazenamento em água. Todos os testes foram realizados de acordo com a norma ISO 6876-2: 2001. Resultados: Ambos os materiais apresentaram valores de CS e pH em acordo com os valores da norma ISO. Os dois cimentos apresentaram RD superiores ao limite de 3 mm de alumínio. Ambos os materiais mostraram resultados de SB inferiores ao limite de 3%. ST e pH também estão de acordo com a norma ISO 6876-2: 2001. Adicionalmente foram avaliadas as superfícies dos materiais por MEV, e ambos apresentaram fases estruturais amorfas e cristalinas. Conclusão: Concluiu-se que ambos os materiais avaliados estão de acordo com as normas ISO, permitindo o seu uso como material de preenchimento de canais radiculares

The corrosion resistance of materials used for the manufacture of ear piercing studs

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Correa, O. V.

2003-12-01

Full Text Available Nickel containing alloys have been widely used as substrates for the manufacture of studs used for ear piercing. Unfortunately, nickel has also been related to the development of allergic contact dermatitis caused by skin sensitization due to Ni²⁺ ions. Nickel ions can be leached out into the body fluids due to corrosion reactions. Defect free coatings are very difficult to produce, and therefore nickel free materials should be used as substrates of ear piercing studs, although the commercial alloys used usually contain this element. In this study, the corrosion resistance of two kinds of commercial studs prepared with nickel containing substrates and a titanium laboratory made stud was determined in a culture medium. The corrosion resistance of the studs was investigated by means of potentiodynamic polarization tests and electrochemical impedance spectroscopy as a function of immersion time in the culture medium. The elements that leached out into the medium due to corrosion reactions were analyzed by instrumental neutron activation analysis. The surfaces of the commercial gold-coated studs were examined by scanning electron microscopy and analyzed by energy dispersive spectroscopy, both before and after exposure to the culture medium. The cytotoxicity of the tested studs was also determined in the culture medium.

Aleaciones conteniendo níquel se han utilizado como substratos para la fabricación de aretes perforantes para orejas. Desafortunadamente, el níquel ha sido relacionado con el desarrollo de una reacción alérgica conocida como dermatitis de contacto, causada por la sensibilización debido a los iones de Ni²⁺. Estos iones pueden ser liberados hacia los fluidos corporales debido a las reacciones de corrosión. Los aretes, habitualmente, se revisten con películas de oro. Sin embargo, es muy difícil hacer los revestimientos libres de defectos superficiales. Por lo tanto, materiales sin níquel deber

Biocorrosion and biofouling of metals and alloys of industrial usage. Present state of the art at the beginning of the new millennium

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Videla, H. A.

2003-12-01

Full Text Available An overview on the present state of the art on Biocorrosion and Biofouling of metals and alloys of industrial usage is offered on the basis of the experience gathered in our laboratory over 25 years of research. The key concepts to understand the main effects of microorganisms on metal decay are briefly discussed. New trends in monitoring and control strategies to mitigate biocorrosion and biofouling deleterious effects are also described. Several relevant cases of biocorrosion studied by our research group are successively described: i biocorrosion of aluminum and its alloys by fungal contaminants of jet fuels; ii Sulfate-reducing bacteria SRB induced corrosion of steel; iii biocorrosion and biofouling interactions in the marine environment; iv monitoring strategies for assessing biocorrosion in industrial water systems; v microbial inhibition of corrosion; vi use and limitations of electrochemical techniques for evaluating biocorrosion effects. The future perspective of the field is made considering the potential of innovative techniques in microscopy (environmental scanning electron microscopy, confocal scanning laser microscopy, atomic force microscopy, new spectroscopical techniques used for the study of corrosion products and biofilms (energy dispersion X-ray analysis, X-ray photoelectron spectroscopy, electron microprobe analysis and electrochemistry (electrochemical impedance spectroscopy, electrochemical noise analysis.

Se ofrece una revisión del estado actual del conocimiento sobre Biocorrosión y Biofouling de metales y aleaciones de uso industrial basada en la experiencia desarrollada en nuestro laboratorio durante 25 años de investigación en el área. Se discuten brevemente los conceptos clave necesarios para entender los principales efectos de los microorganismos en el deterioro de los metales. También se presentan las nuevas tendencias seguidas para el monitoreo y las nuevas estrategias de control para mitigar

Preparação da Liga Amorfa Co72Nb24B4 como Catalisador na Reação de Oxidação do Metanol

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Luciano Nascimento

2015-12-01

Full Text Available This study aims to investigate and characterize the amorphous alloy Co72Nb24B4 the catalytic oxidation of methanol in products that serve as primary reagents for organic synthesis, such as formaldehyde and other intermediate products. The technique for obtaining the amorphous alloy was electric arc smelting furnace. The amorphous alloy catalyst Co72Nb24B4 was characterized by XRD, SEM / EDS, BET and thermal analysis TGA and DTA. The objective of this work is to develop and study the application of amorphous alloy as catalysts and catalyst supports, due to its thick this oxide layer on its surface capable of oxidizing methanol and intermediates of methanol oxidation reaction. The amorphous alloy structure Co72Nb24B4 is still stable after the catalytic test, since the formation of intermetallic and amorphous phases are rich in active sites that are important for the catalytic processes at the surface of these amorphous materials. DOI: http://dx.doi.org/10.17807/orbital.v7i4.768

Fabricación y caracterización de aleaciones porosas de Ti y Ti6Al4V producidas mediante sinterización con espaciador

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Tojal, C.

2013-02-01

Full Text Available Titanium is well-known to be a biocompatible material with good corrosion properties and good strength, taking into account their low specific weight. In powder metallurgy field, titanium has been used in order to obtain porosity materials for biomedical applications. Recently, porous materials have been investigated for their use like hips implants. The principal reason is based on a reduction of stiffness implants, minimizing effects of stress shielding. The purpose of the present work is produced porous materials by space holder technique using ammonium bicarbonate like spacer. Scaffolds of titanium have been fabricated by powders of titanium with different grades of particle size and compacting pressure. Before sintering, stability of green parts has been studied by mechanical test. After sintering, porosity has been evaluated besides mechanical properties and elastic modulus by three points bending test. The microstructural characterisation is performed by optical and electron microscopy.

El titanio es un material biocompatible que, además de presentar buenas propiedades a la corrosión, posee una elevada resistencia mecánica teniendo en cuenta su baja densidad. En el campo de la pulvimetalurgia, entre otras aplicaciones, este material se usa con objeto de obtener materiales porosos para aplicaciones biomédicas. Recientemente se ha investigado la aplicación de los materiales porosos en la fabricación de implantes de cadera. La razón principal está basada en la reducción de la rigidez de los implantes, lo cual minimiza los efectos del “apantallamiento de tensiones”, al aproximarse su módulo elástico al del hueso. El propósito del presente trabajo, es producir materiales porosos mediante la técnica de sinterización con espaciador, usando el bicarbonato de amonio como propulsor de la formación de poros. Para la obtención de los mismos, se ha utilizado polvo de titanio de diferentes tamaños de partícula, usando

Electrodeposición de nanohilos magnéticos: aleaciones de FeNi y óxidos de hierro y de cobalto

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Llavona Serrano, Ángel

2013-01-01

El principal objetivo del trabajo de esta tesis doctoral ha sido la fabricación de nanohilos con diferentes aplicaciones tecnológicas mediante electrodeposición dentro de los poros de membranas de policarbonato, el estudio de los procesos de crecimiento y el estudio de sus propiedades estructurales, magnéticas y luminiscentes.

Obtención de microestructuras de grano ultrafino en aleaciones de aluminio mediante extrusión en canal angular (ECAE

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Alkorta, J.

2004-04-01

Full Text Available Al 5083 samples have been subjected to 90º equal-channel angular extrusion (ECAE at 270ºC. After ECAE, the microhardness was measured and the texture for the plane perpendicular to the extrusion direction was analysed by X-Rays and EBSD. The microstructure was characterized by optical microscopy and EBSD. As deformation accumulates the hardness increases until it reaches saturation at an effective strain of about ε∼4. With regard to the texture, it has been shown that a high density of {111} planes are oriented parallel to the shear plane of the last pass.

Varias muestras de aluminio 5083 se han sometido a extrusiones en canal angular de 90º a 270ºC. A continuación se midieron las durezas de las muestras obtenidas y se caracterizó la textura en el plano perpendicular a la dirección de extrusión mediante Rayos-X y difracción de electrones retrodispersados (EBSD. La caracterización microestructural se hizo mediante microscopio óptico y EBSD. Se ha observado que la dureza aumenta sensiblemente con el grado de deformación y que alcanza un nivel máximo de saturación a partir de ε∼4. En cuanto a la textura, se observa que los planos {111} tienden a orientarse paralelos al plano de la última cortadura.

Fusion technology for the production of PbLi eutectic alloys; Obtencion de aleaciones eutecticas PbLi mediante procesos de fusion

Energy Technology Data Exchange (ETDEWEB)

Barrena, M. J.; Gomez de Salazar, J. M.; Quinones, J.; Pascual, L.; Soria, A.

2012-07-01

The development of thermonuclear experimental reactor (ITER), whose objective is to produce energy from nuclear fusion, has raised the study of Pb-Li eutectic alloys, as they have been selected for the manufacture of test blanket modules (TBM). However, during the manufacturing process of the Pb-Li alloys, thermal conditions used result in a loss of litium element, which inhibits the formation of eutectic structures. In this work we have done fusion of pure lead and lithium, evaluating different process parameters to obtain Pb-Li (17 at. %) eutectic alloys. The alloys manufactured were characterized by DSC, SEM-EDX and microhardness tests. From these studies we noted that the used of an induction reactor and the process parameters optimized to obtain Pb-Li alloy allow for completely eutectic ingots and high chemical homogeneity and microstructural. (Author) 26 refs.

Efecto de la biopelícula en la corrosión de aceros inoxidables

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Bethencourt, M.

2010-02-01

Full Text Available In this work, the influence of the biofilms in the corrosion process of different alloys of stainless steel was studied in two sampling points in a wastewater treatment plant during 4 years. The physicochemical microenvironment within the biofilms was characterized through O₂, H₂S and pH microelectrodes. Corrosion rates were quantified from the number, diameter and depth of pits. The results show a remarkable development of the biofilm and a significantly greater number of pits in the grit removal channel than in the sludge recirculation channel. Based on the characteristics of the water phase and microelectrode measurements, our results suggest that biofilms induced corrosion throughout 3 mechanisms: creation of differential aeration cells, areas with different pH and areas having high sulphide production which may react with metal ions.

En este trabajo se ha estudiado la influencia de las biopelículas en los procesos de corrosión de diferentes aleaciones de acero inoxidable, situadas durante 4 años en dos puntos de una estación depuradora de aguas residuales. Se caracterizó el microambiente físico-químico en el interior de las biopelículas mediante microelectrodos de O₂, H_2S y pH, y se cuantificaron las tasas de corrosión a partir del número, diámetro y profundidad de picadura. Los resultados obtenidos muestran un desarrollo más notable de las biopelículas y un número de picaduras significativamente mayor en el canal de salida de desbastes que en el canal de recirculación de fangos. Con base en las características del agua sobrenadante y en las medidas realizadas con microelectrodos, se sugiere que la biopelícula induce la corrosión a través de tres posibles mecanismos: creación de celdas de aireación diferencial, zonas con diferente pH y zonas con elevada producción de sulfuro capaz de reaccionar con iones metálicos.

Músculos Inteligentes en Robots Biológicamente Inspirados: Modelado, Control y Actuación

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J. Colorado

2011-10-01

Full Text Available Resumen: Las aleaciones metálicas que exhiben una propiedad conocida como efecto de memoria de forma, pertenecen a la clase de materiales inteligentes cuya aplicación más notable en el campo de la robótica se refleja en el uso de actuadores musculares artificiales, ó músculos inteligentes. Estos materiales tienen una estructura cristalina uniforme que cambia radicalmente en función de su temperatura de transición, causando su deformación. Se les denomina materiales inteligentes por la capacidad de recordar su configuración inicial después de recibir dicho estímulo térmico. Este artículo presenta la implementación de un actuador muscular inteligente aplicado en un micro-robot aéreo bio-inspirado tipo murciélago. Esto mamíferos voladores desarrollaron poderosos músculos que se extienden a lo largo de la estructura ósea de las alas, adquiriendo una asombrosa capacidad de maniobra gracias a la capacidad de cambiar la forma del ala durante el vuelo. Replicar este tipo de alas mórficas en un prototipo robótico requiere el análisis de nuevas tecnologías de actuación, abordando los problemas de modelado y control que garanticen la aplicabilidad de este actuador compuesto por fibras musculares de SMAs. Palabras clave: Aleación con Memoria de Forma (SMA, Robots bio-inspirados, Alas mórficas

Modelación del perfil de soldadura y de la cavidad de vapor en la aleación de aluminio 5182 soldada con láser. // Welding profile and steam cavity modelation in aluminum 5182 alloy welded with laser.

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M. Pastor

2002-09-01

Full Text Available El presente trabajo incursiona en el desarrollo de modelos para predecir la forma de la cavidad de vapor y el perfil de laaleación de aluminio 5182 con soldadura láser, para lo cual ha sido empleado el paquete profesional de elementos finitosCOSMOS/M. La modelación de la soldadura ha sido realizada considerando como variable el grado de desenfoque del hazde láser, considerando el flujo de calor según un modelo Gaussiano, con un coeficiente de absorción de 0.24 para lacondición de haz enfocado y 0.16 para las condiciones de desenfoque negativo y positivo. La validez de los resultadosobtenidos se comprobó mediante los resultados obtenidos en pruebas experimentales.Palabras claves: Aleaciones de aluminio, láser de Nd:YAG._______________________________________________________________________AbstractThe purpose of this research is the study of laser welding process for the 5182 aluminum alloys and the development ofmodels by means of the COSMOS/M package, in order to predict the shape of the steam cavity and the weldingtemperatures profile. Modeling has been done considering the degree of defocusing. The heat flow applied on the modelswas a Gauss flow, with a coefficient of absorption of 0.24 for the condition of the focused face and 0.16 for the conditionsof negative and positive defocusing. The validity of the models has been demonstrated comparing their results with thoseobtained by experimental tests.Key words: Aluminum alloys, Nd: YAG laser.

Reciclaje de aluminio: oportunidades de desarrollo en Bogotá (Colombia

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Federico Millan Delgado

2015-07-01

Full Text Available La resistencia a la corrosión y ligereza que caracterizan al aluminio permiten que este metal y sus aleaciones sean sustitutos de materiales como el acero en diversas aplicaciones industriales como: construcción, autopartes, empaques, maquinaría y aeronáutica. En consecuencia, la demanda de aluminio se ha incrementado, así como la búsqueda de minas de bauxita, mineral a partir del cual se obtiene este metal. La transformación de la bauxita en aluminio se realiza mediante la explotación y extracción del mineral que posteriormente es sometido a procesos químicos de Bayer y de electrólisis, los cuales generan emisiones nocivas para el medio ambiente y demandan un alto consumo de energía. Ante la necesidad de reducir los costos de producción del proceso y su impacto ambiental, una alternativa como fuente de materia prima es el reciclaje de aluminio, como lo indican investigaciones sobre el aprovechamiento de materiales en países como Brasil y Estados Unidos que han demostrado la viabilidad de obtener aluminio a partir de residuos metálicos. Lo anterior plantea un interrogante sobre los avances en esta materia en Bogotá, una ciudad con una cadena de reciclaje informal de numerosos eslabones y con escasa regulación que ha generado pocos logros en comparación con otras capitales del mundo.

Síntesis de nitruro de titanio mediante láser y energía solar concentrada

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García, I.

1998-04-01

Full Text Available The possibility of the employment of solar energy concentrated by Fresnel lens is investigated in order to synthesize materials by gas-solid reaction. These first results are compared by two similar techniques as high power laser and xenon are lamp. The TiN coatings obtained with xenon are lamp and Fresnel lens are homogenous, without pores or defects, with a uniform thickness of about 6 μm for treatments of 2 min. The good quality of the TiN coating for all the testing conditions was confirmed by the x-ray diffraction measurements.

Se presenta la utilización de la energía solar concentrada mediante lentes de Fresnel para la síntesis de materiales por reacción gas-sólido. Estos primeros resultados sobre nitruración superficial de titanio y aleaciones de titanio se comparan con los obtenidos con técnicas similares como el láser de alta potencia y la lámpara de descarga de xenón. Las capas de nitruro de titanio obtenidas mediante energía solar concentrada por lentes de Fresnel y lámpara de xenón son homogéneas, sin grietas ni defectos, y con un espesor uniforme de 6 μm en tiempos de sólo 2 min. La buena calidad de estas capas se confirma mediante difracción de rayos X.

Desarrollo de intermetálicos TiAl mediante técnicas pulvimetalúrgicas convencionales y de alta densificación

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Vicente Amigó-Borrás

2014-01-01

Full Text Available Cada día hay más demanda de materiales que ofrezcan altas temperaturas de servicio y bajo peso; pero su fabricación es compleja y costosa, particularmente la de las superaleaciones de base cobalto y la de las aleaciones de titanio; dentro de estas últimas, los intermetálicos TiAl y Ti3Al son ampliamente reconocidos para satisfacer las necesidades actuales; sin embargo, la colada y forja de estos intermetálicos, que tienen una mejor resistencia frente a la oxidación a elevadas temperaturas, resulta muy compleja, y es por lo que, partiendo de polvo prealeado, se busca obtener productos prácticamente acabados con un coste razonable. El presente trabajo analiza la influencia de las variables de procesado de polvos intermetálicos Ti48Al2Cr2Nb, mediante técnicas pulvimetalúrgicas convencionales y Spark Plasma Sintering (SPS, en su microestructura y en sus propiedades mecánicas. Se obtienen muestras a diferentes temperaturas de sinterización a partir de polvos obtenidos por atomización. La influencia en las propiedades mecánicas se observa mediante su microdureza y resistencia a la compresión, realizándose un seguimiento de la microestructura mediante microscopía óptica y electrónica de barrido.Las condiciones de procesado muestran un gran efecto en la microestructura obtenida, fundamentalmente en la formación de la fase α2, que acompaña las propiedades mecánicas finales. Sin embargo, es con el proceso de máxima densificación donde se obtienen las propiedadesadecuadas, lo cual hace pensar que es una alternativa clara a los procesos actuales de colada y deformación plástica.

Processamento e caracterização de espumas cerâmicas de microfibras naturais de sílica amorfa obtidas pelo método de réplica

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Karina Donadel

2008-01-01

Full Text Available Cellular ceramics are brittle materials containing high porosity and constituted by a regular and tridimensional arrangement of hollow cells. The great interest on this group of materials is related to their specific properties such as low density, low thermal conductivity and high permeability. In this work, ceramic foams were processed by the replication method. Commercial polyurethane foams with different cell sizes were used to produce foams constituted by microfibers of natural amorphous silica. The polymeric foams were immersed in the ceramic suspension (natural amorphous silica fibers- NASF, bentonite, sodium silicate and water and then dried and heat-treated for consolidation. The polymeric foam was burned out at 400°C and sintering was carried out at 1150° C for 15-120 min. The obtained sintered samples were subjected to mechanical strength tests, so that compression strength values between 6 and 260 kPa were obtained.

Liberação de nutrientes durante a decomposição de palha de aveia preta (Avena strigosa com diferentes teores de silício

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L. S. Silva

2001-06-01

Full Text Available O Si absorvido pelas plantas é, em sua maior parte, depositado na parte externa da parede celular de folhas como uma camada de sílica amorfa (SiO2.nH2O e poderia afetar a decomposição da palha no solo. Com o objetivo de avaliar o efeito da presença deste elemento no tecido vegetal sobre a decomposição da palha, foi desenvolvido um experimento. Nesse experimento, a parte aérea de plantas de aveia preta, cultivadas em solução nutritiva com e sem adição de Si, foi incubada em tubos de PVC com areia e solo. Aos 6, 14, 30, 66, 100 e 182 dias, foram realizadas percolações com água destilada e determinados os teores de Si, carbono orgânico solúvel, N mineral, Ca, Mg, Na e K. Os resultados dos teores dos elementos na água percolada em cada período foram convertidos em quantidade liberada por kg de substrato (solo ou areia e acumulados no tempo para serem utilizados como índices da decomposição da palha. Em todos os parâmetros avaliados, não houve diferença significativa entre a palha c/Si e s/Si, exceto para o teor de Si e este somente quando a palha foi decomposta na areia. O silício absorvido pelas plantas de aveia preta, quando comparado com plantas cultivadas sem adição deste elemento, não alterou a liberação de carbono e nutrientes presentes na água de percolação durante o período de 182 dias da decomposição da palha.

Production and characterization of LaMnO3 thin films prepared by Sol–Gel technique; Producción y caracterización de láminas delgadas de LaMnO3 preparadas por la técnica de Sol-Gel

Energy Technology Data Exchange (ETDEWEB)

Ebeoğlugil, M.F.

2017-09-01

In this study, lanthanum manganite (LaMnO3) thin films were prepared by sol-gel method for magnet technology. With this context, precursor solutions with low contact angles were synthesized from all nitrate salts of the respective cations (La, Mn), using ethanol as solvent and acetyl acetone as chelating agents. A dense amorphous film was deposited on silicon (Si) substrate. crystallization of the films was carried out at temperatures between 850 and 1000 °C. The thermal, phase, elemental, microstructural and magnetic properties of the obtained samples were determined by TG/DTA, FTIR, XRD, XPS, SEM and VSM. The results show that sustained perovskite polycrystalline films were grown on the [100]-oriented Si substrates. In addition, the films show ferromagnetic behavior. [Spanish] Se prepararon películas delgadas de manganita de lantano (LaMnO3) mediante el método Sol-gel para la tecnología del imán. Se sintetizaron soluciones precursoras con bajos ángulos de contacto a partir de sales de nitrato de los respectivos cationes (La, Mn), utilizando etanol como disolvente y acetil acetona como agente quelante. Se depositó una película amorfa y densa sobre sustrato de silicio (Si). La cristalización de las láminas se llevó a cabo a temperaturas entre 850 y 1000 ºC. El comportamiento térmico, especies químicas, microestructura y propiedades magnéticas se determinaron mediante TG / DTA, FTIR, XRD, XPS, SEM y VSM respectivamente. Los resultados muestran que láminas policristalinas de perovskita crecieron sobre los sustratos de Si orientados en el plano [100]. Finalmente, las láminas muestran un comportamiento ferromagnético.

Riqueza de galhas entomógenas em áreas antropizadas e preservadas de caatinga

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Sheila Patricia Carvalho-Fernandes

2012-04-01

Full Text Available Insetos indutores de galhas, também denominados cecidógenos, são considerados mais especializados por possuírem interação direta com tecidos internos da planta, modificando-os em seu benefício e tornando-se mais dependentes da espécie hospedeira. Este estudo investigou a fauna de insetos galhadores em espécies hospedeiras da Caatinga, em ambientes com diferentes intensidades de ação antrópica. As áreas foram selecionadas de acordo com uma escala de sucessão ecológica (preservadas, intermediárias e antropizadas, sendo três réplicas de cada, totalizando nove áreas. Em cada área foram amostradas oito parcelas de 10 m² cada, distanciadas 10 m entre si. Foram encontrados 25 morfotipos de galhas distribuídos em 18 espécies hospedeiras pertencentes a oito famílias vegetais. Fabaceae foi a família com maior riqueza de galhas, com seis morfotipos, sendo Caesalpinia pyramidalis Tul. a espécie com maior número de galhas, com quatro morfotipos. Em relação aos órgãos atacados, 68% das galhas ocorreram em folhas, 28% em ramos e 4% em botões florais. A maioria das galhas encontradas ocorreu isoladamente (84%, glabra (56% e de formas esféricas (32%, amorfas (28%, discoides (12% e globoides (12%. No estrato arbóreo foi encontrada a maior riqueza de galhas, com 16 morfotipos, seguido do estrato arbustivo e herbáceo, respectivamente com sete e dois morfotipos. A riqueza de galhas sofreu influência do grau de conservação das áreas, e houve diferenças entre os ambientes preservados e antropizados.

Comportamiento de las aleaciones termorresistentes AISI HH y HK-40 ante los procesos de carburización y nitruración

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Eleno Alfonso-Brindis

2001-03-01

Full Text Available Se evalúa el comportamiento de los aceros austeníticos fundidos AISI HH y HK- 40 (de producción nacional ante los procesos de carburización y nitruración en los rangos de temperaturas desde 750 hasta 1 000 °C. Se estudia la cinética y la termodinámica de las posibles reacciones y los productos de las mismas se caracterizan mediante técnicas de Microscopía Óptica, Microscopía Electrónica de Barrido y Microanálisis (MEB-EDAX. En el análisis microscópico se observó la formación de carburos de cromo después de la carburización, mientras que la nitruración dio lugar a la formación de nitruros de cromo. Se concluye que la aleación AISI HK-40 posee una elevada resistencia intrínseca a la carburización y a la nitruración, que hace factible su empleo en componentes de hornos de soleras múltiples para la reducción de minerales lateríticos

Electrooxidación del etanol y bioetanol sobre catalizadores de naturaleza amorfa de composición Ni59Nb40Pt1 y Ni59Nb39Pt2

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Artutxa, E.; Pierna, A.; Lorenzo, A.; del Val, J.

2014-01-01

La ecotoxicidad de las disoluciones provenientes de las pilas de combustible de etanol directo (DEFC) disminuyetras el proceso de electrooxidación con electrodos de naturalezaamorfa. Esta disminución es función del potencialaplicado y de la composición del electrodo utilizado.El proceso de electrooxidación del etanol y bioetanol, sucedetras una secuencia de reacciones, donde se formanvarios productos intermedios que pueden afectar al procesogeneral de electrooxidación de los alcoholes.El bioe...

Long-term performance of different aluminum alloy designs as sacrificial anodes for rebars

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de Rincón, O.

2003-12-01

Full Text Available This paper presents the performance of various cathodic-protection designs using Aluminum alloys to protect prestressed piles. The results obtained with different system designs (bracelete type-Al/Zn/In alloy, thermosprayed aluminum (3-year evaluation and conventional Al/Zn/In anocies in an epoxy-painted steel bracelet (12-year evaluation, indicated that all of these systems may be used as sacrificial anodes for pile protection. However, the thermosprayed aluminum type can not be used in prestressed concrete piles because the very negative potentials ( < -1100 mV vs. Cu/CuSO₄ they supply to the reinforcement could lead to hydrogen embrittlement.

Este trabajo presenta la realización de varios diseños de protección catódica utilizando aleaciones de aluminio para la protección de pilotes pretensados. Los resultados obtenidos con diferentes diseños (aleación de Al/Zn/In, tipo brazalete y aluminio termorociado (3 años de evaluación y ánodos convencionales de Al/Zn/In colocados en un brazalete de acero pintado con epoxy (12 años de evaluación, indicaron que todos estos sistemas pueden ser utilizados como ánodos de sacrificio para la protección de los pilotes. Sin embargo, el sistema con aluminio termorociado no puede ser utilizado en pilotes de acero pretensado debido al potencial muy negativo alcanzado por la armadura (<-1100 mV vs Cu/CuSO₄, lo cual podría inducir a daños por hidrógeno.

Efecto de los componentes del agua de mar durante el fenómeno de corrosión por picaduras del cobre

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García, E.

1995-10-01

Full Text Available Copper is the main component in Cu-Ni alloys recommended for sea water applications. This work presents the electrochemical behaviour of copper in presence of different sea water components and its influence on the corrosion attack. The combined action of chloride and sulphate ions are the main responsible factor for the localized corrosion attack in the form of pitting. A significant parabolic relation exists between the critical pitting potential (E_p and the weight ratio of chloride to sulphate (Cl^-/SO₄^2- ions. Therefore sulphate ions are an important component for pitting corrosion of copper.

El cobre es el elemento principal de las aleaciones Cu-Ni recomendadas para aplicaciones marinas. En este trabajo se presenta el comportamiento electroquímico del cobre con los diferentes componentes del agua de mar y el efecto de estos sobre la forma de ataque del cobre. Se observó que los iones cloruro, en unión con los iones sulfato, son los principales causantes del fenómeno de corrosión por picaduras, existiendo, además, una relación significativa entre el potencial crítico de picado (E_p y la relación (Cl^-/SO₄^2- de tipo parabólico, lo cual pone de manifiesto la importancia del ion sulfato en el fenómeno de corrosión por picaduras como promotor de este tipo de mecanismo.

Postes prefabricados de fibra: Consideraciones para su uso clínico

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Hugo Calabria Díaz

Full Text Available En la década de los 90 los Postes Prefabricados de Fibra (PPF se introdujeron al mercado como alternativa a los sistemas metálicos o cerámicos. Hasta la fecha se mantienen en uso, modificando de manera constante sus presentaciones comerciales y estrategias de fijación. Sus cualidades mecánicas como su bajo Módulo Elástico (ME similar al dentinario, introducen un nuevo paradigma en la rehabilitación del Diente Endodonticamente Tratado (DET: .ldquo;el poste debe acompañar en forma solidaria la flexión de los tejidos dentarios frente a las cargas.rdquo;. Sus actuales cualidades estéticas, la fácil remoción y la posibilidad de su cementado adhesivo, los han convertido en una alternativa válida a las soluciones convencionales. Sin embargo, algunos resultados contradictorios junto con la importante dificultad de lograr hibridación en la dentina radicular, mantienen interrogantes a resolver en el futuro. Se indican en casos en donde se prevea retratamiento, en pacientes jóvenes, de alta exigencia estética y toda vez que se quiera y pueda eludir los costos de aleaciones nobles. En el presente artículo se analizan los fundamentos clínicos y experimentales de distintos autores, extrapolándose consideraciones prácticas para su uso. Los mismos se ilustran en un caso clínico para un paciente joven, con antecedente de traumatismo y con altas expectativas estéticas

Efecto del V y el Si Sobre la Microestructura de Depósitos Realizados con Electrodos Tubulares Revestidos de Alto Contenido de Mn (Hadfield

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Manuel Rodríguez

2017-10-01

Full Text Available Resumen: Las aleaciones para el relleno superficial Fe-Mn-C (Hadfield han demostrado una excelente resistencia al desgaste bajo altas cargas dinámicas. En los últimos años se han realizado numerosos estudios para aumentar la resistencia al desgaste y mejorar su desempeño, a través de la introducción de otros elementos de aleación. En el presente trabajo se investiga la microestructura y dureza de los depósitos de relleno con alto contenido de Mn y adiciones de 1.2% de V y 2.4% de Si. Los depósitos estudiados se realizaron utilizando electrodos tubulares revestidos fabricados a escala de laboratorio. Las fases y microconstituyentes en el metal depositado se identificaron mediante microscopía óptica (MO, electrónica de barrido (MEB, difracción de rayos X (DRX, dureza y microdureza. De acuerdo a los resultados obtenidos, la adición de V al sistema aleante originó que la fase predominante fuera la austenita. Además, contribuyó a la formación de carburos de vanadio (VC en la microestructura de la capa de relleno, sin observarse la presencia de carburos complejos. Por otra parte, la presencia de Si favoreció la formación de una red de ferrita interdendrítica. La adición de estos elementos de aleación mejoró las propiedades de estos depósitos, potencializando su uso en aplicaciones que requieren alta resistencia al desgaste bajo altas cargas.

Influencia del medio de ensayo y dirección de aplicación de la carga en el comportamiento a corrosión bajo tensiones de la aleación de aluminio 7075

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Badía, J. M.

2004-12-01

Full Text Available The goal of this work is to prove the validity of using synthetic sea water as an alternative method instead of the NaCl solution used in stress corrosion crack growth tests in aluminium alloys, according to ASTM G 44. Several samples of 7075 alloy have been tested in different conditions and directions in both environments, which can be considered as equivalent. Only the samples tested in thickness direction have shown crack growth during the test. The use of sea water entails a great advantage in practice, by less superficial alteration, and lets therefore a much more reliable measure of the crack.

El objetivo de este trabajo es comprobar la validez del empleo de agua de mar sintética como método alternativo a la solución de NaCl utilizada en los ensayos de crecimiento de grieta por corrosión bajo tensiones en aleaciones de aluminio, según la norma ASTM G- 44. Para ello, se ha procedido al ensayo de muestras de aleación 7075 en diferentes estados de tratamiento y con distintas orientaciones en ambos medios, comprobándose que pueden considerarse equivalentes. Sólo las probetas ensayadas en la dirección del espesor mostraron crecimiento de grieta durante los ensayos. La utilización del agua de mar representa una gran ventaja práctica ya que altera mucho menos la superficie de las muestras y permite, por tanto, una medida mucho más fiable de la grieta durante el ensayo.

Determinación experimental de los factores que controlan el desprendimiento de polvos en el conformado de chapas de acero recubiertas con Zn-Ni

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Cárcel, A. C.

1995-04-01

Full Text Available Powder detachment from coatings during press forming of Zn-Ni precoated steel sheets increases die wear and maintenance costs. Experimental design helped to establish that powder detachment rises by increasing coating thickness or bath temperature. Otherwise, the use of high flow rates and the presence of an intermediate layer of nickel help to reduce powdering. Temperature and flow rate affect the alloy composition. In the range 10 to 15 % Ni, powdering increases as the alloy becomes richer in nickel. This behaviour is attributed to changes in structure and ductility of the alloy.

El desprendimiento de polvos del recubrimiento durante la embutición constituye uno de los principales problemas en las líneas de prensas que emplean chapas de acero recubiertas con aleaciones Zn-Ni. El uso de técnicas de diseño de experiencias permitió determinar que la cantidad de polvos aumenta al incrementarse el espesor del depósito y la temperatura del baño, y disminuye al aplicar un flash intermedio de níquel o al aumentar la velocidad relativa cátodo-electrólito. Los efectos de la velocidad y de la temperatura afectan a la composición de la aleación. En el rango comprendido entre el 10-15 % Ni, el desprendimiento aumenta con el contenido en níquel, lo que se atribuye a los cambios de estructura y de ductilidad de la aleación.

Procesamiento, caracterización y ensayos biológicos de titanio modificado electroquímicamente para implantes dentales

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Sandra Liliana Arias Suarez

2013-01-01

Full Text Available Las aplicaciones biomédicas del titanio y sus aleaciones son posibles debido a que éste material posee características deseables para el reemplazo de huesos, incluyendo buenas propiedades mecánicas, excelente resistencia a la corrosión y alta biocompatibilidad. Sin embargo, una de sus principales limitaciones radica en el encapsulamiento del material por un delgado tejido fibroso, el cual puede estar relacionado con el aflojamiento del implante. Como una alternativa para dar solución a esta limitación, en el presente trabajo se realizaron modificaciones químicas y electroquímicas a la superficie del titanio para evaluar su influencia en la oseointegración de los implantes, para lo cual se realizaron ensayos in vitro del material en contacto con osteoblastos. Los resultados de caracterización por microscopía electrónica de barrido (SEM, de medición de parámetros de rugosidad y de morfología de los osteoblastos, indicaron que existe una relación entre la rugosidad superficial y la adhesión de las células óseas. Las superficies con los mayores parámetros verticales de rugosidad, para las condiciones evaluadas, permitieron una mejor adhesión celular. Estos resultados sugieren que la combinación de técnicas químicas y electroquímicas puede permitir el control de la rugosidad de los implantes dentales de titanio y, por tanto, la optimización de su oseointegración.

Estudio de la influencia de la morfología y de la distribución de tamaños de partícula del polvo en la obtención de aleaciones base Cu y base Ni mediante la tecnología MIM

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Contreras Andújar, José Manuel

2008-01-01

En las últimas dos décadas, el procesado mediante moldeo por inyección de polvos metálicos (MIM) ha sido una tecnología que ha experimentado un notable crecimiento año tras año debido a que constituye una alternativa rentable para la fabricación de piezas de pequeño tamaño y difícil geometría. Sin embargo, una de sus mayores limitaciones como tecnología es el alto coste que presentan los polvos metálicos con morfología esférica y pequeño tamaño de partícula que se utilizan normalmente en esta...

Desarrollo y caracterización de nuevos materiales de cátodo basados en aleaciones de níquel para la reacción de evolución de hidrógeno en medio alcalino

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González Buch, Cristina

2016-01-01

[EN] The current energy system, based basically on the use of fossil fuels is a non-sustainable system and the research for new energy alternatives is necessary. Hydrogen is an ideal energy carrier to become the future fuel, creating a new energy system called "Hydrogen Economy". To achieve this aim a method for producing hydrogen in a clean and renewable way is necessary. Alkaline water electrolysis is a simple and proven technology for hydrogen production in a clean and renewable way. Ho...

Improved Oxidation Resistance of Zirconium Resulting from Addition of Small Amounts of Copper; Amelioration de la Resistance a l'Oxydation du Zirconium par de Faibles Additions de Cuivre; Povyshenie soprotivlyaemosti k okisleniyu tsirkoniya posle dobavlenij nebol'shikh kolichestv medi; Aumento de la Resistencia del Circonio a la Oxidacion por Agregado de Pequenas Cantidades de Cobre

Energy Technology Data Exchange (ETDEWEB)

Loriers, H.; Darras, R.; Baque, P. [Centre d' Etudes Nucleaires de Saclay (France)

1966-02-15

600 et 700 Degree-Sign C. En effet, les alliages correspondants, notamment celui a 2,5% de cuivre, semblent offrir des possibilites interessantes comme materiaux de gainage ou de structure pour les elements combustibles des reacteurs de la filiere eau lourde-gaz carbonique. La corrosion du zirconium par le gaz carbonique se ramene essentiellement a une oxydation, au cours de laquelle deux processus interferent: 1. l'edification d'une couche de zircone monoclinique, a travers laquelle l'oxygene diffuse par migration des lacunes anioniques, 2. la dissolution et la diffusion de l'oxygene, qui passe en insertion dans le metal. La combinaison des donnees gravimetriques et des mesures d'epaisseur des couches d'oxyde permet d'evaluer les deux coefficients de diffusiqn correspondants. Ce calcul a ete etendu par analogie au cas des alliages binaires zirconium-cuivre, de concentration en cuivre inferieure ou egale a 4% en poids. La comparaison des resultats obtenus montre que le coefficient de diffusion apparent de l'oxygene dans la couche d'oxyde formee decroit lorsque la teneur en cuivre de l'alliage envisage augmente; d'autre part, le coefficient de diffusion apparent de l'oxygene dans l'alliage, s'il est peu modifie a 600 Degree-Sign C, decroit a 700 Degree-Sign C lorsque la teneur en cuivre augmente jusqu'a 2,5%. L'amelioration de la resistance a l'oxydation, liee au ralentissement des processus de diffusion, se traduit en particulier par le maintien prolonge d'une cinetique du type parabolique, alors que, dans le cas du zirconium non allie ou d'autres alliages, la fissuration de la couche d'oxyde conduit rapidement a une cinetique d'oxydation lineaire, a la suite du phenomene de desquamation. (author) [Spanish] Los autores procuraron interpretar el efecto favorable que pequenas cantidades de cobre ejercen sobre la resistencia del circonio a la oxidacion por accion del anhidrido carbonico a presion, entre 600 y 700 Degree-Sign C. Las aleaciones correspondientes y, en

Aleaciones con memoria de forma, una filosofía diferente en la ingeniería y el diseño con materias

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Peña Andrés, Fco. Javier

2002-01-01

Los materiales con memoria de forma también llamados materiales inteligentes poseen propiedades que los diferencian del resto de materiales. Estas propiedades no son propiedades mejoradas respecto a los materiales convencionales, sino que son nuevas propiedades que hacen que el proceso de diseño con materiales haya de ser modificado. La comprensión de estas nuevas propiedades y la estandarización de todos los parámetros que las caracterizan por parte de todas aquellas personas involucradas en...

Propiedades estructurales y magnéticas de aleaciones Gd0.257 -xTbxFe0.743 obtenidas por aleamiento mecánico

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Mauricio Galvis-Patiño

2017-01-01

Full Text Available En el presente trabajo se reporta el estudio de las propiedades estructurales y magnéticas de la composición en forma de polvo de Gd0.257-xTbxFe0.743 con x=0,  0.1285,  0.257,preparados por Aleamiento Mecánico (AM en atmosfera de argón durante 72 horas mediante un molino planetario de alta energía ;la caracterización estructural se realizó por medio de Difractometría de rayos X(DRX, para la caracterización magnética se utilizó la espectroscopía Mössbauer, los ciclos de histéresis se llevaron a cabo a través de  PPMS (Physical Property Measurement System, Sistema de Medidas de Propiedades Físicas. La fase de α-Fe se presenta en los tres difractogramas mediante un pico característico cuya  intensidad disminuye al reemplazar el Tb por el Gd, presentándose la menor en x= 0 así mismo se observa un aumento de su ancho atribuible a la presencia de átomos de Gd en lugares propios del Fe. Los espectros Mössbauer (EM fueron ajustados con sextetos, dobletes, singletes y distribuciones de campo hiperfino lo que señala que el orden magnético se ve alterado al sustituir el Tb por el Gd en la composición. Las propiedades magnéticas extrínsecas de la composición en estudio, la caracterizan como materiales magnéticamente semiduros.

Fabricación de micro-componentes mediante arranque de viruta. análisis del acabado superficial en aleaciones de aluminio y titanio

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Francisco Mata Cabrera

2011-07-01

Se proponen modelos de predicción de la rugosidad, con buen grado de aproximación, para ayudar a la caracterización de los procesos de micro-mecanizado. Micro-machining is the most adequate technology for manufacturing of micro-components in the industry. This is a manufacturing precision process with applications in certain industrial field, for example the machining construction. The objective of this research is to analyze the surface quality in micro-machining processes and to evaluate her possible application in mechanical industry (surface roughness, geometry, aspect, etc. This work presents the experimental study of surface roughness (Ra and Rt using a specific micro-turning process. The measures of surface roughness reveal how it is possible to obtain superficial very good qualities up to diameters of 0.05 mm. For low diameters, it worsens the superficial quality and the faults of form increase, due to the low inflexibility of the piece. Prediction models of surface roughness are proposed to the characterization of micro-machining processes.  

Corrosión en medio ácido cítrico de una aleacion metálica de cobre aplicada en la odontologia

OpenAIRE

Vaz, Luís Geraldo; Guastaldi, Antônio Carlos; Marques de Brito, Adriano

2007-01-01

RESUMEN El objetivo de este trabajo fue caracterizar y estudiar el efecto del tratamiento térmico hecho en una aleación metálica de cobre para el uso odontológico, con relación a su comportamiento frente a la corrosión, en un medio que simula la agresividad del ambiente bucal. La caracterización de la aleación fue hecha por medio de análisis de la composición química y microscopia óptica y los ensayos de corrosión comprendieran en la obtención de las curvas de polarización potenciostáticas en...

Evaluaciones microcalorimétricas no-isotermas en aleaciones de Cu-9Ni-5,5Sn templadas y deformadas en frío

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Donoso, E.

2012-02-01

Full Text Available The thermal aging of both a quenched and a cold rolled homogeneous supersaturated Cu-9 % wt Ni-5.5 wt % Sn alloy has been studied from differential scanning calorimetry (DSC and microhardness measurements. An increase of the hardness during the aging of the quenched sample, because of the precipitation of a Υ´ phase, takes place. On the contrary, no hardness increase was observed during the aging of the cold rolled sample. A theoretical analysis of the enthalpy determined from the first DSC exothermic peak suggests that a segregation of the solute towards the dislocations occurs during the aging of the cold rolled alloy. The values of the n Avrami-Erofeev coefficients estimated from the kinetic analysis supports the above interpretations.

Se ha estudiado por calorimetría diferencial de barrido (DSC y medidas de microdureza, el comportamiento durante el recocido de una aleación Cu-9 % Ni-5,5 % Sn templada y deformada por laminación en frio al 50 %, respectivamente. Se ha concluido que durante el tratamiento térmico de la muestra templada tiene lugar un aumento de la microdureza atribuido a la precipitación de una fase Υ´ de composición (Cu_xNi_1x3Sn. Sin embargo, no se ha observado un aumento de dureza durante el recocido de la muestra deformada en frío. Este comportamiento se ha interpretado considerando que las dislocaciones generadas por la laminación en frío, favorecen la segregación de soluto (níquel y estaño hacia las dislocaciones en lugar de la formación de la fase (Cu_xNi1-x₃Sn. Tanto el análisis teórico de la entalpía determinada para esta etapa como los valores de los coeficientes n de Avrami-Erofeev determinados a partir de un análisis cinético apoyan esta interpretación.

Rapid solidification of Ni{sub 50}Nb{sub 28}Zr{sub 22} glass former alloy through suction-casting; Solidificacao rapida da liga formadora de fase amorfa Ni{sub 50}Nb{sub 28}Zr{sub 22} atraves de fundicao em coquilha por succao

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Miyamoto, M.I.; Santos, F.S.; Bolfarini, C.; Botta Filho, W.J.; Kiminami, C.S., E-mail: issao16@gmail.co [Universidade Federal de Sao Carlos (DEMa/UFSCar), SP (Brazil). Dept. de Engenharia de Materiais

2010-07-01

To select new alloys with high glass forming ability (GFA) to present amorphous structure in millimeter scale, several semi-empirical models have been developed. In the present work, a new alloy, Ni{sub 50}Nb{sub 28}Zr{sub 22}d, was designed based on the combination of topological instability lambda (A) criterion and electronegativity difference ({Delta}e). The alloy was rapidly solidified in a bulk wedge sample by cooper mold suction casting in order to investigate its amorphization. The sample was characterized by the combination of scanning electron microscopy (MEV), X-ray diffraction (XRD) and differential scanning calorimeter (DSC). For the minimum thickness of 200 {mu}m analyzed, it was found that the alloy did not show a totally amorphous structure. Factor such as low cooling rate, existence of oxides on the surface of the elements and presence of oxygen in the atmosphere of equipment did not allowed the achievement of higher amorphous thickness. (author)

Genotoxic valuation of Zinalco, a zinc base alloy, by the mutation and somatic recombination test in Drosophila Melanogaster.; Valoracion genotoxica de la aleacion Zinalco mediante la prueba de mutacion y recombinacion somatica en Drosophila Melanogaster.

Energy Technology Data Exchange (ETDEWEB)

Ramirez V, P

1995-10-01

Zinalco is an eutectoid alloy made of zinc, aluminium and copper (78% , 20% and 2%), because of its physical, chemical and mechanical characteristics, it has been established as a structural material and valued as a feasible bio material. Previous authors have studies on the cytotoxic effect of Zinalco, so for concluded that it is harmless to the organism. However, was considered necessary to evaluate its potential genotoxicity. The present work was done with the fruit fly Drosophila Melanogaster. The objectives were: to determine the administered particle size, to evaluate its ingestion zinalco and to score the genotoxic effect by means of the SMART test in wing cells of D. Melanogaster. The protocol consisted of an oral chronic treatment, to groups of 72th age larvae, with concentrations of 0,1,2,4,8 and 16 mg of zinalco in ml of water on 1.5 g of synthetic medium. Statistical analysis was done through the SMART program. The results obtained showed an average particle size of 16 m long x 5.9 m wide. The normal amount of the alloy elements in the larvae was increased and finally, no genotoxicity at any of the administered doses could be detected. (Author).

Study of amorphous films of TiAlN prepared by reactive cathodic erosion by radiofrequencies; Estudio de peliculas amorfas de TiAlN preparadas por erosion catodica reactiva por radiofrecuencias

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Garcia G, L. [Programa de Posgrado en Materiales del Centro de Investigacion y de Estudios Avanzados del IPN, Unidad Queretaro, Libramiento Norponiente No. 2000, Fracc. Real de Juriquilla, 76230 Queretaro (Mexico); Morales H, J. [Programa de Posgrado en Ingenieria de la Facultad de Ingenieria de la Universidad Autonoma de Queretaro, (Mexico); Bartolo P, J.P.; Ceh S, O. [Centro de Investigacion y de Estudios Avanzados del IPN, Unidad Merida, Km. 6 Antigua Carretera a Progreso, A.P. 73 Cordemex 97310 Merida, Yucatan (Mexico); Munoz S, J.; Espinoza B, F.J. [Centro de Investigacion y de Estudios Avanzados del IPN, Unidad Queretaro, Libramiento Norponiente No. 2000, Fracc. Real de Juriquilla, 76230 Queretaro, (Mexico)

2004-07-01

Using the reactive magnetron r f sputtering technique, we prepared TiAlN films with amorphous structure on Corning glass and steel substrates in a reactive atmosphere of nitrogen and argon using a target of Ti-AI (40/60 wt. %). The average temperature of the substrates was about 25 C, with the purpose of obtaining amorphous films. The ratio of partial pressure of nitrogen to argon, PN/PAr was varied according to these values: 0.14, 0.28, and 0.43; fixing these values during whole the evaporation. Further on, films were prepared introducing nitrogen in periodic pulses with maximum values of PN/PAr 4.7 during 45 seconds, with fixed periods of 10, 15 and 20 minutes. In all cases amorphous films were obtained, according to X-ray Diffraction. The chemical composition of the samples was measured by electron dispersive spectroscopy, showing a clear dependence with the evaporation conditions. In spite of the amorphous structure of the material, atomic force microscopy measurements showed a surface morphology dependent on the nitrogen content. Additionally, measurements of electronic spectroscopy for chemical analysis and Raman scattering spectroscopy for identification of chemical bonds were carried out. Measurements of mechanical properties of the samples were carried out using nano indentation and micro-hardness Vickers's tests. (Author)

Effect of milling conditions on the properties of Cu-NbC alloys obtained by powder metallurgy; Efecto de las variables de molienda en las propiedades de aleaciones Cu-NbC obtenidas por pulvimetalurgia

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Lopez, M.; Jimenez, J. A.; Ruano, O.; Benavente, R.

2006-07-01

Copper-base composite materials were obtained by reinforcing with homogeneous dispersions of 0.5 and 1% vol. of very fine NbC particles, through mechanical milling process in a planetary mill during 8 and 24 h at two different rotational speeds. The consolidation of the alloyed reinforced particles was achieved through a hot uniaxial pressing at 923K under 90 MPa during 2 h under a protective argon atmosphere. Factors to the suitable combination of electrical conductivity and mechanical properties attained are the hardness and good thermal stability of the niobium carbide which affords furthers refinement in the size of copper particles and the reinforcement of the alloy. A lower embrittlement and higher electrical conductivity of this alloys was observed, as a consequence of the smaller amount of impurities (Fe, Cr, C and O) incorporated during the lower-energy milling. Scanning and transmission electron microscopy and X-ray diffraction show and additional strengthening of the grain substructure by precipitation of nanometer-size impurities. (Author) 18 refs.

Spectrochemical analysis of aluminum and its alloys, and S. A. P.; Analisis espectroquimico de aluminio y sus aleaciones y de S.A.P.

Energy Technology Data Exchange (ETDEWEB)

Roca, M

1966-07-01

Three different techniques have been employed for the spectrochemical analysis of aluminum, aluminum alloys, and S.A.P. :1) Point to plane with condensed spark and direct reading spectrometry; from the study on the instantaneous spectral-line intensities a long pre integration time has been established. 1) Powdered samples technique with direct current arc and also direct reading spectrometry; samples are transformed into Al{sub 2}O{sub 3} and mixed with graphite powder (1:1). A complete study on the different elements in aluminium oxide, aluminium sulfate and their mixtures with graphite, has been carried out. 3) Carrier distillation method with photographic recording for very low concentrations of boron and cadmium in S. A.P. (Author) 10 refs.

Dermatitis de contacto por prótesis ortopédicas Contact dermatitis for orthopaedic prostheses

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C.A. Danielo

2007-09-01

Full Text Available Diversas aleaciones son utilizadas en la fabricación de prótesis ortopédicas (ej: titanio, vitalio, etc, dentro de las cuales la más utilizada es la de acero inoxidable. El níquel, parte importante de esta aleación, es capaz de liberarse y provocar sensibilización, desencadenando reacciones cutáneas locales y sistémicas. De los materiales que componen la aleación para formar acero inoxidable, el níquel es el que más frecuentemente se ve implicado en reacciones cutáneas por sensibilidad, en tanto que otros como el cromo y cobalto, la posibilidad de pérdida de material a partir de la prótesis es discutida. Presentamos el caso de una paciente con dermatitis alérgica al níquel con lesiones generalizadas, que aparecieron luego del implante de prótesis ortopédicas de acero inoxidable, dando positivo para níquel sulfato en las pruebas epicutáneas.Several alloys are used in the manufacture of orthopaedics prostheses (ie: titanium, vitalium. Stainless steel is the most frequently used among them. Nickel is an important component of this alloy and may release and provoke sensitivity. Arising local and systemic cutaneous reactions. Nickel is the material composing stainless steel that ordinary is implicated in cutaneous reactions of sensitivity; the role of chrome or cobalt is still uncertain. Our patient is a woman affected of nickel contact dermatitis, with generalized reactions that appear after an implant of a stainless steel orthopaedic prosthesis. Epicutaneous tests were performed, confirming a strong sensitivity to nickel sulphate.

Fatiga oligocíclica de la aleación Ti₆Al₄V nitrurada termoquímicamente

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Rodríguez, D.

2001-04-01

Full Text Available The use of titanium and its alloys in applications with the presence of friction is limited, due to low hardness and reduced tribological properties. Some surface treatments are available in order to correct these problems, like the thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Oligocyclic fatigue behaviour in air of Ti₆Al₄V alloy has been studied. Results show a reduction of oligocyclic fatigue loads up to 10 % compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.

El uso del titanio y sus aleaciones en aplicaciones con existencia de fricción es limitado, debido a su baja dureza y malas propiedades tribológicas. Existen diversos tratamientos superficiales capaces de corregir dichos problemas, como el tratamiento térmico superficial mediante difusión gaseosa del nitrógeno a alta temperatura. El nitrógeno penetra en el material a tratar por difusión, formando una capa superficial de elevada dureza. Se ha estudiado el comportamiento a fatiga oligocíclica en aire del Ti₆Al₄V nitrurado. Los resultados muestran una disminución de la resistencia a fatiga oligocíclica de hasta un 10 % respecto al material sin nitrurar. Los estudios sugieren que se debe a cambios en la microestructura causados por el tratamiento a altas temperaturas, y no por la capa superficial de nitruros de titanio.

El eurocódigo 9 "Proyecto de estructuras de aluminio"

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Ramírez, J. L.

1999-06-01

Full Text Available Aluminium is an interesting structural material because its lightness and minimum maintenance needs, together with and important strength. The lack of knowledge of design rules with this material owing to the shortage of design guides, together with its higher cost, are factors that leed to the very scarce use of aluminium in the construction of structures. In present article it is dealt with a brief look to the tipology and properties of the structural aluminium alloys, and it is described the content of Eurocode 9 "Design of aluminium structures", approved by CEN (European Committee for Standardization in may 1998 that it is foreseen to be published in Spanish by AENOR in short time.

El aluminio es un material estructural de interés, por unir ligereza y mínimas necesidades de protección, junto con una resistencia importante. La falta de conocimiento de las reglas de proyecto con el material, debido a la escasa disponibilidad de guías o recomendaciones de diseño, junto con un precio elevado, son factores que condicionan la muy escasa presencia del aluminio en la construcción de estructuras. En el presente artículo se expone una visión sucinta de la tipología y propiedades de las aleaciones de aluminio y se describe el contenido del Eurocódigo 9 "Proyecto de estructuras de aluminio" aprobado por el CEN (Comité Europeo de Normalización en mayo de 1998 y que aparecerá en castellano en breve publicada por AENOR, como Norma Europea Experimental.

Nanoskin: uso para reposição de volume na cavidade anoftálmica

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Natalia Mussi

2016-06-01

Full Text Available RESUMO Objetivo: Avaliar a biocompatibilidade da Nanoskin para reposição de volume em cavidades enucleadas ou evisceradas de coelhos. Métodos: Estudo experimental, utilizando implantes de Nanoskin (Innovatecs®, São Carlos, Brasil, celulose bacteriana produzida pela bactéria Acetobacter xylinum tendo como substrato o chá-verde. Implantes de 10mm de diâmetro/5mm de espessura foram colocados em cavidades enucleadas (G1 ou evisceradas (G2 de 21 coelhos, avaliados clinicamente todos os dias, sacrificados aos 7, 30 e 90 dias após a cirurgia. O material foi removido e preparado para exame de microscopia óptica. Resultados: Sinais flogísticos discretos no pósoperatório imediato, não tendo sido evidenciados sinais infecciosos ou extrusão de nenhum implante. Houve aparente redução do volume ao longo do período experimental. Histologicamente ambos os grupos foram muito semelhantes, apresentando aos 7 dias células inflamatórias (predominantemente monócitos e neutrófilos, rede de fibrina e hemácias. A Nanoskin apresentava-se como pequenas esferas, de cor rósea, com pequenos espaços entre elas, permeados por escassas células inflamatórias. As células inflamatórias se modificaram ao longo de período experimental, sendo possível observar aos 30 dias células gigantes multinucleadas e fibroblastos maduros permeando o implante. Aos 90 dias, a estrutura do implante apresentava-se desorganizada, amorfa, com restos necróticos e com áreas ovoides, revestidas por fina membrana rósea, que pareciam se agrupar, vazias ou preenchidas por material acelular, róseo ou acinzentado. Conclusão: A Nanoskin provocou reação inflamatória que levou à reabsorção e redução do volume do implante. Novas formulações devem ser estudadas a fim de ter um produto que seja permanente para reparo da cavidade anoftálmica.

Las alteraciones silíceas de las lavas de Montaña Señalo, erupción de Timanfaya (1730-1736 (Lanzarote, Islas Canarias

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García, A.

2009-06-01

Full Text Available The presence of hydrothermal alterations within the lavas of Timanfaya eruption (1730-1736, with high proportions of quartz and opal, suggests the effective circulation of hot fluids. The source of these fluids would be located under the island, where silica would be dissolved from sandstones and radiolarites, moving this way towards the surface as Si(OH4 colloids. Study of opal indicates the presence of A-initial CT and C phases in the collected samples, which, considering the time needed for producing this phase transformations in the diagenetic evolution of opal (10,000-50,000 years, suggests an accelerating process, probably related with either the presence of fluid circulation or weathering processes. Such circumstances are necessary for explaining the presence of such components affecting 300 years old lavas.La presencia de alteraciones de origen hidrotermal entre las lavas de la erupción de Timanfaya (1730-36, con altas proporciones del cuarzo y ópalo, indica la circulación efectiva de fluidos calientes. El origen de estos fluidos estaría en zonas profundas por debajo de la isla, donde se produciría la disolución de la sílice a partir de areniscas y radiolaritas, movilizándose de esta manera este componente hacia la superficie en forma de coloides de Si(OH4. El estudio en profundidad del ópalo indica la presencia de fases tipo A-inicio de CT y C. Si se tiene en cuenta el tiempo en el que se producen estas transformaciones en la evolución diagenética de esta fase amorfa (10.000-50.000 años, indicaría la presencia de un proceso acelerador que podría estar relacionado con una importante circulación de fluidos o con procesos de alteración meteórica, capaces de producir estas transformaciones en unas lavas de menos de 300 años.

Naturaleza del cemento en las areniscas del Flysch numidiense (sur de España

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Ruiz Cruz, M. D.

1990-04-01

Full Text Available Several size-fractions were centrifuged from the Aljibe sandstones to determinate both, nature and genesis of the cement. These samples are been analized by X-ray power diffraction, infrared spectroscopy, differential thermal analysis, termogravimetry and scanning electron microscopy. Two types of kaolinite were distinguished: Detrital kaolinite with low values of crystalIinity and b-parameter and authigenic kaolinite with higher values of crystallinity and b-parameter. Dickite is also presente in less extent. In the fractions analized, the detrital matrix is formed by disordered kaolinite, illite and mixed-layers illite/smectite. The cement is formed by ordered kaolinite, dickite and amorphous material. The controlling factors in the development of these materials are: primary porosity of sandstones, pore-fluid composition and burial.Se ha realizado el análisis de diferentes fracciones granulométricas en niveles deareniscas de la unidad del Aljibe con objeto de determinar la naturaleza y génesis del material cementante de las mismas. Las técnicas utilizadas han sido: Difracción de rayos X, espectroscopía de infrarrojos, análisis térmico diferencial, termogravimetría y microscopía electrónica de barrido. En función de los parámetros cristaloquímicos determinados han podido diferenciarse dos tipos de caolinita: Caolinita heredada, con valores bajos de la cristalinidad y del parámetro b0 y caolinita autigénica con valores elevados de la cristalinidad y de b0-. La dickita aparece bien desarrollada en ciertas secuencias. En las fracciones analizadas la matriz detrítica está constituida por caolinita desordenada, ilita e interestratificados ilita-esmectita. El cemento está constituido fundamentalmente por caolinita ordenada, dickita y materia amorfa. Los factores que han controlado el desarrollo de estos materiales han sido: porosidad primaria de las areniscas, composición de los fluidos intersticiales y grado de enterramiento.

Rice husk ash as a source of silica in alkali-activated fly ash and granulated blast furnace slag systems

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Mejía, J. M.

2013-09-01

Full Text Available This study assesses the viability of using an agro-industrial by-product, rice husk ash (RHA from a Colombian rice company’s combustion facility, as a total replacement for the commercial sodium silicate ordinarily used in alkaliactivated binders. Fly ash (FA, granulated blast furnace slag (GBFS and binary 50FA:50GBFS blended pastes were activated with a mix of sodium hydroxide and either sodium silicate or one of two types of RHA. The pastes were characterised for strength, mineralogy and microstructure. The findings showed that the agro-industrial by-product can be used to yield alkali-activated materials with 7-day mechanical strengths on the order of 42 MPa. The study confirmed that both amorphous silica and part of the crystalline silica present in RHA participate in the alkaline activation process, providing the alkalinity is suitably adjusted.Este estudio evalúa la viabilidad de utilizar un subproducto agroindustrial, la ceniza de cascarilla de arroz (RHA proveniente de un equipo combustor de una empresa Arrocera en Colombia, como reemplazo total de la sílice aportada por el silicato de sodio comercial en sistemas cementicios activados alcalinamente. Se prepararon pastas de ceniza volante (FA, de escoria de alto horno (GBFS y un sistema binario 50FA:50GBFS, que fueron activadas por una mezcla de silicato de sodio e hidróxido de sodio, y por dos tipos de RHA. Las mezclas se caracterizaron mecánica, mineralógica y microestructuralmente. Los resultados demuestran que es posible obtener materiales activados alcalinamente con resistencias mecánicas del orden de 42 MPa, a 7 días de curado, utilizando el subproducto agroindustrial. Este estudio corrobora que tanto la sílice amorfa como parte de la sílice cristalina presente en RHA tienen la posibilidad de participar en el proceso de activación alcalina, siempre y cuando las condiciones de alcalinidad estén adecuadamente ajustadas.

Fuzzy knowledge bases integration based on ontology

OpenAIRE

Ternovoy, Maksym; Shtogrina, Olena

2012-01-01

the paper describes the approach for fuzzy knowledge bases integration with the usage of ontology. This approach is based on metadata-base usage for integration of different knowledge bases with common ontology. The design process of metadata-base is described.

Foundation: Transforming data bases into knowledge bases

Science.gov (United States)

Purves, R. B.; Carnes, James R.; Cutts, Dannie E.

1987-01-01

One approach to transforming information stored in relational data bases into knowledge based representations and back again is described. This system, called Foundation, allows knowledge bases to take advantage of vast amounts of pre-existing data. A benefit of this approach is inspection, and even population, of data bases through an intelligent knowledge-based front-end.

Kinetic study of the annealing reactions in Cu-Ni-Fe alloys; Estudio cinetico de las reacciones de recocido en aleaciones de Cu-Ni-Fe

Energy Technology Data Exchange (ETDEWEB)

Donoso, E.

2014-07-01

The thermal aging of a Cu-45Ni-4Fe, Cu-34Ni-11Fe and Cu-33Ni-22Fe alloys tempered from 1173 K have been studied from Differential Scanning Calorimetry (DSC) and microhardness measurements. The analysis of DSC curves, from room temperature to 950 K, shows the presence of one exothermic reaction associated to the formation of FeNi{sub 3} phase nucleating from a modulate structure, and one endothermic peak attributed to dissolution of this phase. Kinetic parameters were obtained using the usual Avrami-Erofeev equation, modified Kissinger method and integrated kinetic functions. Microhardness measurements confirmed the formation and dissolution of the FeNi{sub 3} phase. (Author)

Diffuse Scattering from Alloys and Disordered Systems: Experimental Techniques and Potentialities; Diffusion dans les Alliages et les Systemes Desordonnes; Methodes Experimentales et Possibilites d'Application; Diffuznoe rasseyanie na splavakh i razuporyadochennykh sistemakh. ehksperimental'nye metody i potentsial'nye vozmozhnosti; Dispersion Difusa en Aleaciones y Sistemas Desordenados; Tecnicas Experimentales y Posibilidades

Energy Technology Data Exchange (ETDEWEB)

Low, G. G. [Atomic Energy Research Establishment, Harwell, Berks (United Kingdom)

1965-04-15

The purpose of this paper is to review, both with regard to principles and practice, the types of information that may be obtained by studying the elastic diffuse scattering of neutrons. Attention will be concentrated on systems where there is a random arrangement of defects each of which may be assumed to be unaffected by the presence of its fellows, either because of dilution or because of an intrinsic lack of dependence on environment. In these circumstances the pattern of scattered intensity is proportional to the square of the modulus of a Fourier transform over the disturbance in scattering amplitude associated with a defect. Thus, information on the spatial distribution of defect scattering amplitude can be obtained by carrying out the relevant neutron scattering measurements and performing a Fourier inversion. In practice, because of the large number of processes contributing to the diffuse scattering background, measurements have so far been possible only in a limited number of fields. In particular considerable progress has been made in connection with magnetic defects in ferromagnets where the magnetic cross-section may be controlled by changing the direction of magnetization relative to the neutron scattering vector. In this way the scattering of interest can be isolated from the non-magnetic effects as a difference between two intensity measurements. A process contributing to the diffuse scattering background which is partly magnetic in character and therefore not eliminated by the above technique is multiple Bragg scattering in a magnetic polycrystal. This may be avoided by the use of a single -crystal specimen or by employing long wavelength neutrons such that no Bragg processes are possible. An instrument based on the latter principle has been developed at Harwell and used in connection with a wide range of measurements on dilute ferromagnetic alloys. These observations are discussed along with a number of other likely future developments in the

On the feasibility of BLISK produced by linear friction welding

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Mateo, Antonio

2014-09-01

muestra resultados relativos a la caracterización, tanto microestructural como mecánica, de un prototipo de BLISK diseñado para el compresor de presión intermedia de un motor aeronáutico. Además, considerando que las requerimientos de diseño de discos y álabes son diferentes, se seleccionaron aleaciones de titanio disimilares para cada parte, para así mejorar el rendimiento del BLISK. Los resultados obtenidos demuestran que la soldadura por fricción lineal es un proceso fiable, que puede producir uniones libres de defectos y con propiedades mecánicas comparables a las de los correspondientes materiales base.

Case-based reasoning: The marriage of knowledge base and data base

Science.gov (United States)

Pulaski, Kirt; Casadaban, Cyprian

1988-01-01

The coupling of data and knowledge has a synergistic effect when building an intelligent data base. The goal is to integrate the data and knowledge almost to the point of indistinguishability, permitting them to be used interchangeably. Examples given in this paper suggest that Case-Based Reasoning is a more integrated way to link data and knowledge than pure rule-based reasoning.

Electrochemical behavior of synthesized Al{sub x}Sn{sub y} with mechanical grinding in hydrogen evolution reaction (HER); Comportamiento electroquimico del Al{sub x}Sn{sub y} sintetizado por molienda mecanica en la REH (Reaccion de Evolucion de Hidrogeno)

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Olvera Vazquez, S. L.; Arce Estrada, E. M. [Instituto Politecnico Nacional, Mexico, D.F. (Mexico )]. E-mail: seydyliz@hotmail.com

2009-09-15

Currently, the best catalyst for HER is Pt, nevertheless because of its high costs, many studies have been performed with a variety of materials, including AI, which is a promising source of hydrogen. Therefore, this work studied the effect of tin on Al{sub x}Sn{sub y} alloys obtained by mechanical grinding. The materials obtained were characterized with electron sweep microscopy, x-ray diffraction and electrochemical techniques. It was determined that the synthesized materials have a micrometer size and present at least two phases. The electrochemical characterization for use as electrocatalysts for the hydrogen evolution reaction (HER) was performed in an NaCl 2 M solution using potentiodynamic polarization and chronoamperometry techniques, showing that the materials with low tin contents have better electrocatalytic activity for HER. [Spanish] Actualmente el mejor catalizador para la REH es el Pt, sin embargo debido a sus altos costos se han realizado numerosos estudios con diversos materiales entre los cuales se encuentra el Al, que es una promisoria fuente de hidrogeno. Por tal motivo en este trabajo se realizaron estudios del efecto que presenta el contenido de estano en aleaciones Al{sub x}Sn{sub y} obtenidas por molienda mecanica. Los materiales obtenidos se caracterizaron por microscopia electronica de barrido, difraccion de rayos X y tecnicas electroquimicas. Se determino que los materiales sintetizados son de tamano micrometrico y que al menos presentan dos fases. La caracterizacion electroquimica para su uso como electrocatalizadores para la reaccion de evolucion de hidrogeno, REH, se llevo a cabo en una solucion de NaCl 2 M, empleando las tecnicas de polarizacion potenciodinamica y cronoamperometria, observandose que los materiales con contenidos bajos de estano presentan una mejor actividad electrocatalitica para la REH.

Evaluation of the behavior of PtPd/MWCNT electrocatalysts as ethylene glycol-tolerant electrodes for oxygen oxidation reaction (ORR); Evaluacion del comportamiento de electrocatalizadores tipo PtPd/MWCNT como electrodos para la reaccion de oxidacion del oxigeno (ORR) tolerantes al etilenglicol

Energy Technology Data Exchange (ETDEWEB)

Morales-Acosta, D.; Arriaga, L.G. [Centro de Investigacion y Desarrollo Tecnologico en Electroquimica, Pedro Escobedo, Queretaro (Mexico)]. E-mail: dmorales@cideteq.mx; Alvarez-Contreras, L. [Centro de Investigacion en Materiales Avanzados S. C., Chihuahua, Chihuahua (Mexico); Fraire Luna, S.; Rodriguez Varela, F.J. [Cinvestav, Unidad Saltillo, Ramos Arizpe, Coahuila, (Mexico)

2009-09-15

Pt-Pd/MWCNTs (atomic ratio Pt:Pd 43:57) and Pt/MWCNTs electrocatalysts were synthesized and evaluated as cathodes for oxygen reduction reaction (ORR) with the application of direct ethylene glycol fuel cells (DEGFC). A commercial PtC material was also evaluated as a reference. It was found that Pt-Pd/MWCNT has a capability for high tolerance to ethylene glycol (EG) and higher selectivity for ORR compared to a single Pt- cathode. As a result, the change in onset potential of the ORR, Eonset, in Pt-Pd/MWCNTs was considerably less than the change in Pt/MWCNTs or Pt/C. The average particle size (XRD) was 3.5nm and 4nm for Pt/MWCNTs and Pt-Pd/MWCNTs, respectively. A moderate degree of alloying was determined for the material. The application of Pt-Pd electrocatalysts in DEGFCs should be advantageous. [Spanish] Electrocatalizadores Pt-Pd/MWCNTs (relacion atomic Pt:Pd 43:57) y Pt/MWCNTs fueron sintetizados y evaluados como catodos para la reaccion de reduccion del oxigeno (ORR) con aplicacion del celdas de consumo directo de etilenglicol (Direct Ethylene Glycol Fuel Cells, o DEGFC). Como referencia, un material comercial tipo Pt/C fue tambien evaluado. Se encontro que Pt-Pd/MWCNTs tiene una alta capacidad de tolerancia al etilenglicol (EG) y una selectividad mayor hacia la ORR comparado con el catodo basado en Pt-solo. Como resultado, el cambio en potencial de inicio de la ORR, Eonset, en Pt-Pd/MWCNTs fue considerablemente menor que el cambio en Pt/MWCNTs o Pt/C. La talla de particula promedio (de XRD) fue 3.5 nm y 4 nm para Pt/MWCNTs y Pt-Pd/MWCNTs, respectivamente. Un moderado grado de aleacion fue determinado para el material. Una aplicacion ventajosa para electrocatalizadores tipo Pt-Pd debe ser en DEGFCs.

Efectos del tratamiento térmico en la fractura de aceros

Directory of Open Access Journals (Sweden)

Héctor Hernández A.

1992-05-01

Full Text Available No obstante de los avances logrados en otros tipos de aleaciones, los aceros se siguen utilizando en forma extensiva en la construcción de elementos estructurales, porque con una adecuada selección y tratamiento técnico, los aceros permiten obtener una conveniente combinación de propiedades mecánicas ante unas exigencias específicas de servicio. La fractura en elementos de máquinas frecuentemente se encuentra asociada a una discontinuidad, la cual provoca una concentración de esfuerzo, lo que puede originar sitios de iniciación de una falla por fractura. La carga límite de fractura es afectada por parámetros geométricos, naturaleza y tipo de carga y propiedades mecánicas del material. La mayoría de fallas por fractura de elementos de máquinas son fallas por fatiga; por lo general una fractura por fatiga tiene lugar por una progresiva generación y crecimiento de grietas hasta obtenerse una condición crítica de fractura súbita de la sección residual resistente. Frecuentemente en una fractura por fatiga se observan marcas de playa, las cuales son evidencias de la posición del frente de grietas antes que se alcance la condición de fractura súbita final. En este trabajo se muestra como el tratamiento térmico de temple y revenido de los aceros afecta el esfuerzo límite de falla por fractura para carga de tracción estática y carga de fatiga uniaxial con la presencia de una entalla severa. También se estudia el efecto del tratamiento térmico en la tenacidad de fractura, propiedad que cuantifica la resistencia al crecimiento súbito de una grieta bajo carga estática.

Efecto de los ciclos térmicos sobre la ZAT de una soldadura multipasos de un acero inoxidable superdúplex SAF 2507 Effect of thermal cycles on the HAZ of a stainless steel multipass weld of superduplex SAF 2507

Directory of Open Access Journals (Sweden)

D. Villalobos

2010-09-01

Full Text Available Los ciclos térmicos de una soldadura multipasos que experimenta un acero inoxidable superdúplex SAF 2507, pueden promover la precipitación de fases secundarias reduciendo significativamente las propiedades mecánicas y la resistencia a la corrosión. Debido a su aplicación en la industria petroquímica, el estudio de las aleaciones superdúplex es de suma importancia para predecir su comportamiento en servicio cuando están involucrados procesos de soldadura por arco eléctrico. En este trabajo, se estudia el cambio microestructural de la zona afectada térmicamente correspondiente al primer cordón depositado de una unión multipasos de acero inoxidable superdúplex SAF 2507 mediante el proceso GTAW y bajo tres temperaturas de interpasos. Los resultados muestran que la temperatura de interpasos tiene una influencia sobre la precipitación de fase sigma en la zona afectada térmicamente del primer cordón depositado.Thermal cycles experienced by a superduplex stainless steel SAF 2507 when is welded, can promote the precipitation of secondary phases which decrease the mechanical properties as well as the corrosion resistance. Due to the application of the duplex alloys in the petrochemical industry, the study of these alloys has become very important in order to predict its service behavior. The aim of this work is to study the microstructural changes in the superduplex stainless steel weld joint after applying the GTAW process under three interpass temperatures after the deposition of every single pass. The results showed that slow cooling rates promoted by the deposition of the subsecuent passes and the higher interpass temperature, promote the precipitation of sigma phase in the HAZ while rapid cooling rates promoted by the lower interpass temperature do not promote the sigma phase precipitation.

Aportaciones de estaño-plata y estaño-cobre en la soldadura blanda por capilaridad de canalizaciones de cobre

Directory of Open Access Journals (Sweden)

Durán, J.

2001-04-01

Full Text Available It is studied the influence of the type of alloy used as filling material on the defects of the soldering joints in copper piping installations, which induce the fluid leak of the systems. The different eutectic temperatures and solidus-liquidus ranges of these alloys, require the setting of the soldering heat input in each case to obtain the suitable capillarity features and alloying temperatures to achieve for the correct formation of the bondings. Most defects in the joints are demonstrated to be generated by bad dossification of thermal inputs, which led depending on the filler alloy used to variations in its fluidity that may produce penetration failures in the bonds or insufficient consistency for the filling of the joints.

Se estudia la influencia del tipo de aleación utilizada como material de aporte, en los defectos resultantes en las uniones de soldadura blanda por capilaridad en instalaciones de tubería de cobre, que provocan la fuga del fluido de las canalizaciones. Las diferentes temperaturas eutécticas y de los rangos solidus-líquidus de estos tipos de aleaciones, obligan a ajustar los aportes del calor de soldeo en cada caso para conseguir las propiedades de capilaridad y temperaturas de aleación adecuadas para la correcta formación de las soldaduras. Se demuestra que, la mayoría de los defectos en las uniones se produce por mala dosificación de los aportes térmicos, lo que conduce, dependiendo de la aleación utilizada, a variaciones en la fluidez de la aportación que pueden dar lugar a fallos en la penetración de las juntas o a insuficiente consistencia para el relleno de las uniones.

Characterization of dissimilar welding: carbon steel E309L-E308L-ERNiCr3-ENiCrFe3 alloy 600; Caracterizacion de la soldadura disimilar: acero al carbono E309L-E308L-ERNiCr3-ENiCrFe3 aleacion 600

Energy Technology Data Exchange (ETDEWEB)

Mucino G, O.

2015-07-01

Most BWR type reactors have internal support components, which need to be attached to the inner surface by welding. Specifically, in these joints two materials interact, such as stainless steel and nickel base alloys. Nickel base alloys such as alloy 82 (ERNiCr3) and alloy 182 (ENiCrFe-3) are used for the joining of both dissimilar materials. For joints made with both nickel base alloys, the alloy 182 is prone to stress corrosion cracking (SCC); so it is essential to carry out studies related to this contribution material. In the nuclear industry any study related to this alloy is of importance because experience is gained in its behavior when is part of a system of an operation reactor. This work presents the characterization of the weld deposit of a stainless steel coating (with electrodes E309L and E308L) on a carbon steel plate type A36 and the joining with an Inconel 600 plate, simulating the joining of the internal coating of vessel and the heel of the support leg of the envelope of a BWR reactor. In this work, the mechanical and micro-structural characterization of the alloy deposit 182 was performed. (Author)

Mechanical properties of AZ31 alloy processed by a green metallurgy route; Propiedades mecanicas de la aleacion AZ31 procesada por una ruta eco-sostenible

Energy Technology Data Exchange (ETDEWEB)

D' Enrico, F.; Garces, G.; Hofer, M.; Kim, S. K.; Perez, P.; Cabeza, S.; Adeva, P.

2013-07-01

Recently it has been proved that molding of defect-free components of various commercial alloys of magnesium can be carried out successfully when small amounts of CaO are added to the melt, making unnecessary the use of SF{sub 6} coverage. In the case of AZ alloys, this process also remarkably improves their mechanical properties not only by the greater cleaning of alloys but also by the formation of CaAl{sub 2} phase. This work, part of the Green project Metallurgy (http://www.green-metallurgy.eu) funded by the European Union (LIFE+2009), studies the influence of different CaO additions on the microstructure and mechanical properties of AZ31 Eco-Mg alloy. The alloy was processed by a conventional route involving extrusion of as-cast rods as well as by a powder metallurgy route (PM) using chips as starting material. The objective was to analyze the viability of recycling machining chips to manufacture components for the automobile industry and transportation in general, because of its low cost and environmental impact. It has been demonstrated that alloys processed from chips exhibit the highest tensile stress values, close to 320 MPa. (Author)

From oil-based mud to water-based mud

International Nuclear Information System (INIS)

Christiansen, C.

1991-01-01

Maersk Olie og Gas AS has used low toxic oil-based muds extensively since 1982 for drilling development wells and later in the development of horizontal well drilling techniques. However, in view of the strong drive towards a reduction in the amount of oil discharged to the North Sea from the oil industry, Maersk Olie og Gas AS initiated trials with new or improved types of water-based mud, first in deviated wells (1989) and then in horizontal wells (1990). The paper reviews Maersk Olie og Gas As experience with oil-based mud since the drilling of the first horizontal well in 1987, specifically with respect to cuttings washing equipment, oil retention on cuttings, and the procedure for monitoring of this parameter. It describes the circumstances leading to the decision to revert to water-based mud systems. Finally, it reviews the experience gained so far with the new improved types of water-based mud systems, mainly glycol and KCl/polymer mud systems. Comparison of operational data, such as rate of penetration, torque and drag, etc., is made between wells drilled with oil-based mud and water-based mud. The trials with the new improved types of water-based mud systems have been positive, i.e. horizontal wells can be drilled successfully with water-based mud. As a result, Maersk Olie og and Gas AS has decided to discontinue the use of low toxic oil-based muds in the Danish sector of the North Sea

Microestructura y propiedades mecánicas de materiales compuestos de matriz Al-Mg-Si-Cu reforzada con AlNp, procesados por extrusión de polvos

Directory of Open Access Journals (Sweden)

Ortiz, José Luis

2000-10-01

Full Text Available This article presents an experimental investigation on the structure and mechanical properties of an Al-Mg-Si-Cu P/M alloy reinforced with 5 %, 10 % and 15 % aluminum nitride, produced by extrusión of cold compacted powders mixtures. Mechanical properties in "as extruded" and T6 conditions are compared. Differential Scanning Calorimetry and Dilatometric analysis were conducted to gain further insight into the precipitation process of these materials. Low cost 6061Al/AlNp composites can be produced with rare and small porosity by extrusión of cold compacted shapes without canning. The mechanical properties of the MMCs obtained by this process have limitations for high particles fractions because of clustering effects. All materials are always harder than the matrix and shows a similar behavior during aging processes but kinetics is changed. Potential applications of dilatometric techniques in the aging investigations of aluminum alloys and aluminum matrix composites have been established.

Se presenta una investigación experimental sobre la relación entre la estructura y las propiedades mecánicas de materiales obtenidos mediante la extrusión en caliente de preformas de polvos compactados en frío y cuya matriz es una aleación Al-Mg-Si-Cu con composición cercana a la AA6061, reforzada con tres proporciones diferentes (5, 10 y 15 % en volumen de partículas de AlN. Se utilizó Calorimetría Diferencial de Barrido y Dilatometría sobre las muestras solubilizadas y templadas para complementar el estudio del efecto de las partículas sobre el envejecimiento de la aleación base. Se establece que es posible producir, a bajo costo, materiales compuestos de matriz metálica, MMCs, de matriz de aleación AA6061 reforzada con partículas de AlN con baja porosidad y buenas propiedades mecánicas, mediante la extrusión de mezclas de polvos compactados en frío, sin necesidad de enlatado. Sin embargo, las aglomeraciones de partículas, para

Computer-based multi-channel analyzer based on internet

International Nuclear Information System (INIS)

Zhou Xinzhi; Ning Jiaoxian

2001-01-01

Combined the technology of Internet with computer-based multi-channel analyzer, a new kind of computer-based multi-channel analyzer system which is based on browser is presented. Its framework and principle as well as its implementation are discussed

Combining Host-based and network-based intrusion detection system

African Journals Online (AJOL)

These attacks were simulated using hping. The proposed system is implemented in Java. The results show that the proposed system is able to detect attacks both from within (host-based) and outside sources (network-based). Key Words: Intrusion Detection System (IDS), Host-based, Network-based, Signature, Security log.

NMR studies concerning base-base interactions in oligonucleotides

International Nuclear Information System (INIS)

Hoogen, Y.T. van den.

1988-01-01

Two main subjects are treated in the present thesis. The firsst part principally deals with the base-base interactions in single-stranded oligoribonucleotides. The second part presents NMR and model-building studies of DNA and RNA duplexes containing an unpaired base. (author). 242 refs.; 26 figs.; 24 tabs

XML-Based SHINE Knowledge Base Interchange Language

Science.gov (United States)

James, Mark; Mackey, Ryan; Tikidjian, Raffi

2008-01-01

The SHINE Knowledge Base Interchange Language software has been designed to more efficiently send new knowledge bases to spacecraft that have been embedded with the Spacecraft Health Inference Engine (SHINE) tool. The intention of the behavioral model is to capture most of the information generally associated with a spacecraft functional model, while specifically addressing the needs of execution within SHINE and Livingstone. As such, it has some constructs that are based on one or the other.

Relation between the microstructure and technological properties of porcelain stoneware. A review

Directory of Open Access Journals (Sweden)

Romero, M.

2015-12-01

Full Text Available Porcelain stoneware is a strongly sintered ceramic material fabricated from ball clays-quartz-feldspar mixtures. Porcelain stoneware is characterized by its excellent technical and functional properties (low water absorption, high mechanical properties, resistant to chemical substances and cleaning agents, aesthetic possibilities …. These characteristic and technical features make that among the different types of ceramic tile, porcelain stoneware is the ceramic product that in the last years has best withstood the economic crisis in the construction sector. These properties are related to the microstructure of porcelain stoneware, which is a grain and bond type with large particles of filler (quartz, mullite crystals, a silica-rich amorphous phase and porosity. The understanding of the relationship between the microstructure and the properties of porcelain stoneware is hardly important for the development and design of these materials whose tendency is the manufacture of thinner tiles with higher dimensions but must continue to comply the specific technical requirements.El gres porcelánico es un material sinterizado fabricado a partir de una mezcla de arcillas, cuarzo y feldespato. Tecnológicamente, el gres porcelánico se caracteriza por sus excelentes características técnicas y funcionales (baja absorción de agua, buenas propiedades mecánicas, resistente a substancias químicas, posibilidades estéticas…. Estas cualidades han propiciado que, entre los diferentes tipos de baldosa cerámica, es el gres porcelánico el producto que mejor ha resistido la crisis económica sufrida por el Sector de la Construcción. Las propiedades tecnológicas están relacionadas con su microestructura, compuesta de partículas de cuarzo, cristales de mullita, fase amorfa y porosidad. El conocimiento de la relación entre la microestructura y las propiedades tecnológicas del gres porcelánico es de gran importancia para avanzar en el diseño y

Communication Base Station Log Analysis Based on Hierarchical Clustering

Directory of Open Access Journals (Sweden)

Zhang Shao-Hua

2017-01-01

Full Text Available Communication base stations generate massive data every day, these base station logs play an important value in mining of the business circles. This paper use data mining technology and hierarchical clustering algorithm to group the scope of business circle for the base station by recording the data of these base stations.Through analyzing the data of different business circle based on feature extraction and comparing different business circle category characteristics, which can choose a suitable area for operators of commercial marketing.

Value-based metrics and Internet-based enterprises

Science.gov (United States)

Gupta, Krishan M.

2001-10-01

Within the last few years, a host of value-based metrics like EVA, MVA, TBR, CFORI, and TSR have evolved. This paper attempts to analyze the validity and applicability of EVA and Balanced Scorecard for Internet based organizations. Despite the collapse of the dot-com model, the firms engaged in e- commerce continue to struggle to find new ways to account for customer-base, technology, employees, knowledge, etc, as part of the value of the firm. While some metrics, like the Balance Scorecard are geared towards internal use, others like EVA are for external use. Value-based metrics are used for performing internal audits as well as comparing firms against one another; and can also be effectively utilized by individuals outside the firm looking to determine if the firm is creating value for its stakeholders.

Integrated Case Based and Rule Based Reasoning for Decision Support

OpenAIRE

Eshete, Azeb Bekele

2009-01-01

This project is a continuation of my specialization project which was focused on studying theoretical concepts related to case based reasoning method, rule based reasoning method and integration of them. The integration of rule-based and case-based reasoning methods has shown a substantial improvement with regards to performance over the individual methods. Verdande Technology As wants to try integrating the rule based reasoning method with an existing case based system. This project focu...

Knowledge base verification based on enhanced colored petri net

Energy Technology Data Exchange (ETDEWEB)

Kim, Jong Hyun; Seong, Poong Hyun [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

1998-12-31

Verification is a process aimed at demonstrating whether a system meets it`s specified requirements. As expert systems are used in various applications, the knowledge base verification of systems takes an important position. The conventional Petri net approach that has been studied recently in order to verify the knowledge base is found that it is inadequate to verify the knowledge base of large and complex system, such as alarm processing system of nuclear power plant. Thus, we propose an improved method that models the knowledge base as enhanced colored Petri net. In this study, we analyze the reachability and the error characteristics of the knowledge base and apply the method to verification of simple knowledge base. 8 refs., 4 figs. (Author)

Knowledge base verification based on enhanced colored petri net

Energy Technology Data Exchange (ETDEWEB)

Kim, Jong Hyun; Seong, Poong Hyun [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

1997-12-31

Verification is a process aimed at demonstrating whether a system meets it`s specified requirements. As expert systems are used in various applications, the knowledge base verification of systems takes an important position. The conventional Petri net approach that has been studied recently in order to verify the knowledge base is found that it is inadequate to verify the knowledge base of large and complex system, such as alarm processing system of nuclear power plant. Thus, we propose an improved method that models the knowledge base as enhanced colored Petri net. In this study, we analyze the reachability and the error characteristics of the knowledge base and apply the method to verification of simple knowledge base. 8 refs., 4 figs. (Author)

Influence of cobalt and chromium additions on the precipitation processes in a Cu-4Ti alloys; Influencia de la adicion de cobalto y cromo en el proceso de precipitacion en una aleacion de Cu-4Ti

Energy Technology Data Exchange (ETDEWEB)

Donoso, E.

2010-07-01

The influence of 0.5% atomic cobalt and 1% atomic chromium additions on the precipitation hardening of Cu-4Ti alloy was studied by differential scanning calorimetry (DSC) and microhardness measurements. The analysis of the calorimetric curves, for binary alloy, shows the presence of two overlapping exothermic reactions (stages 1 and 2) attributed to the formation of Cu{sub 4}Ti and Cu{sub 3}Ti particles in the copper matrix, respectively. DSC curves for Cu-4Ti-0.5Co alloy shows three exothermic effects (overlapping stages 3 and 4 and stage 5) associated to the formation of phases Ti{sub 2}Co, TiCo and Cu{sub 4}Ti, respectively. DSC curves for Cu-4Ti1Cr alloy shows three exothermic reactions (stages 6, 7 and 9) and one endothermic peak (stage 8). The exothermic reactions correspond to the formation of phases Cr{sub 2}Ti, Cu{sub 4}Ti and Cu{sub 3}Ti, respectively, and the endothermic reactions are attributed to the Cr{sub 2}Ti dissolution. The activation energies calculated using the modified Kissinger method were lower than the ones corresponding to diffusion of cobalt, chromium, and titanium in copper. Kinetic parameters were obtained by a convolution method based on the Johnson-Mehl-Avrami (JMA) formalism. Microhardness measurements confirmed the formation of the mentioned phases. Also, these measurements confirmed the effect of cobalt and chromium addition on the binary alloy hardness. (Author). 31 refs.

Computer-based and web-based radiation safety training

Energy Technology Data Exchange (ETDEWEB)

Owen, C., LLNL

1998-03-01

The traditional approach to delivering radiation safety training has been to provide a stand-up lecture of the topic, with the possible aid of video, and to repeat the same material periodically. New approaches to meeting training requirements are needed to address the advent of flexible work hours and telecommuting, and to better accommodate individuals learning at their own pace. Computer- based and web-based radiation safety training can provide this alternative. Computer-based and web- based training is an interactive form of learning that the student controls, resulting in enhanced and focused learning at a time most often chosen by the student.

Content-Based Image Retrial Based on Hadoop

Directory of Open Access Journals (Sweden)

DongSheng Yin

2013-01-01

Full Text Available Generally, time complexity of algorithms for content-based image retrial is extremely high. In order to retrieve images on large-scale databases efficiently, a new way for retrieving based on Hadoop distributed framework is proposed. Firstly, a database of images features is built by using Speeded Up Robust Features algorithm and Locality-Sensitive Hashing and then perform the search on Hadoop platform in a parallel way specially designed. Considerable experimental results show that it is able to retrieve images based on content on large-scale cluster and image sets effectively.

Fusion and characterization of an alloy Cu-Zn-Al-Ni of nuclear interest; Fusion y caracterizacion de una aleacion Cu-Zn-Al-Ni de interes nuclear

Energy Technology Data Exchange (ETDEWEB)

Santana M, J.S

2003-07-01

The present work is the result of the study of a non ferrous quatenary alloy of Cu-Zn-Al-Ni (Foundry 3), it was chosen of a series of alloys to obtain so much information of its microstructural properties like mechanical, evaluating them and comparing them with the previously obtained ternary alloys of Cu-AI-Ni (Foundry 1) and Cu-Zn-AI (Foundry 2) identified as alloys of memory effect and superalloys. These were carried out starting from the foundry of their pure elements of Cu, Zn, Al, Ni. When physically having the ingot of each alloy, different techniques were used for their characterization. The used techniques were through the metallographic analysis, by scanning electron microscopy (SEM), X-ray dispersive energy spectroscopy (EDS), X-ray diffraction (XRD), mechanical essays and Rockwell hardness. The non ferrous quaternary alloy Cu-Zn-AI-Ni by means of the metallographic analysis didn't show significant differences in their three sections (superficial, longitudinal and transverse) since result an homogeneous alloy at the same that the both ternaries. The grain size of the quaternary alloy is the finest while the ternary alloy of Cu-AI-Ni is the one that obtained the biggest grain size. Through MEB together with the analysis by EDS and the mapping of the elements that constitute each alloy, show that the three foundries were alloyed, moreover the presence of aggregates was also observed in the Foundries 2 and 3. These results by means of the analysis of XRD corroborate that these alloys have more of two elements. Relating the microstructural properties with those mechanical show us that as minor was the grain size, better they were his mechanical properties, in this case that of the quaternary alloy. With regard to the test of Rockwell hardness the Foundry 1 were the softest with the temper treatment, while that the Foundries 2 and 3 were the hardest with this same treatment, being still harder the Foundry 2 but with very little difference, for what great variety of properties can be obtained in the copper alloys modifying their composition and the thermal treatments and mechanics to those that are subjected. (Author)

Fusion and characterization of a Cu-Zn-Al-Ni alloy of nuclear interest; Fusion y caracterizacion de una aleacion Cu-Zn-Al-Ni de interes nuclear

Energy Technology Data Exchange (ETDEWEB)

Zamora R, L.; Arenas A, J.A.; Santana M, J.S. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

2003-07-01

The first part of the work was made in the Melting Laboratory where an ingot of each alloy was obtained under the same conditions. When having the ingots physically, the following thing consisted, in using different techniques for their characterization in the laboratories of Metallography, Scanning Electron Microscopy, (Sem), X-ray diffraction (XRD) and that of mechanical assays. (Author)

Micro/nano structured coatings of light alloys by cold spray for surface protection and repair of high value-added components: State of the art; Recubrimientos micro/nanoestructurados de aleaciones ligeras mediante proyeccion fria para la proteccion y reparacion de componentes de elevado valor anadido: Estado del arte

Energy Technology Data Exchange (ETDEWEB)

Bedoya, J.; Cinca, N.; Guilemany, J. M.

2013-09-01

The Cold Gas Spray - CGS technique has greatly attracted the attention of the researchers in the last decade due to advantages compared to other conventional thermal spray processes. It presents outstanding characteristics such as high density coatings and absence of thermal degradation (oxidation or phase transformation). In addition, CGS is an efficient and green technology. This paper presents a bibliographic review related to micro/nano structured aluminium-based coatings of by CGS on light alloy substrates. It provides an overview of the feasibility of using the Cold Gas Spray as a technique for the protection, recovery and repair of high value-added components, especially those made of light alloys (aluminium and magnesium base) which, by their low density and mechanical properties, are widely used in several industrial sectors such as transport, aerospace and power generation. (Author)

Home-based versus centre-based cardiac rehabilitation.

Science.gov (United States)

Taylor, Rod S; Dalal, Hayes; Jolly, Kate; Moxham, Tiffany; Zawada, Anna

2010-01-20

The burden of cardiovascular disease world-wide is one of great concern to patients and health care agencies alike. Traditionally centre-based cardiac rehabilitation (CR) programmes are offered to individuals after cardiac events to aid recovery and prevent further cardiac illness. Home-based cardiac rehabilitation programmes have been introduced in an attempt to widen access and participation. To determine the effectiveness of home-based cardiac rehabilitation programmes compared with supervised centre-based cardiac rehabilitation on mortality and morbidity, health-related quality of life and modifiable cardiac risk factors in patients with coronary heart disease. We updated the search of a previous review by searching the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2007, Issue 4), MEDLINE, EMBASE and CINAHL from 2001 to January 2008. We checked reference lists and sought advice from experts. No language restrictions were applied. Randomised controlled trials (RCTs) that compared centre-based cardiac rehabilitation (e.g. hospital, gymnasium, sports centre) with home-based programmes, in adults with myocardial infarction, angina, heart failure or who had undergone revascularisation. Studies were selected independently by two reviewers, and data extracted by a single reviewer and checked by a second one. Authors were contacted where possible to obtain missing information. Twelve studies (1,938 participants) met the inclusion criteria. The majority of studies recruited a lower risk patient following an acute myocardial infarction (MI) and revascularisation. There was no difference in outcomes of home- versus centre-based cardiac rehabilitation in mortality risk ratio (RR) was1.31 (95% confidence interval (C) 0.65 to 2.66), cardiac events, exercise capacity standardised mean difference (SMD) -0.11 (95% CI -0.35 to 0.13), as well as in modifiable risk factors (systolic blood pressure; diastolic blood pressure; total cholesterol

14 CFR 119.47 - Maintaining a principal base of operations, main operations base, and main maintenance base...

Science.gov (United States)

2010-01-01

... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Maintaining a principal base of operations, main operations base, and main maintenance base; change of address. 119.47 Section 119.47 Aeronautics... Under Part 121 or Part 135 of This Chapter § 119.47 Maintaining a principal base of operations, main...

Model-Based Requirements Management in Gear Systems Design Based On Graph-Based Design Languages

Directory of Open Access Journals (Sweden)

Kevin Holder

2017-10-01

Full Text Available For several decades, a wide-spread consensus concerning the enormous importance of an in-depth clarification of the specifications of a product has been observed. A weak clarification of specifications is repeatedly listed as a main cause for the failure of product development projects. Requirements, which can be defined as the purpose, goals, constraints, and criteria associated with a product development project, play a central role in the clarification of specifications. The collection of activities which ensure that requirements are identified, documented, maintained, communicated, and traced throughout the life cycle of a system, product, or service can be referred to as “requirements engineering”. These activities can be supported by a collection and combination of strategies, methods, and tools which are appropriate for the clarification of specifications. Numerous publications describe the strategy and the components of requirements management. Furthermore, recent research investigates its industrial application. Simultaneously, promising developments of graph-based design languages for a holistic digital representation of the product life cycle are presented. Current developments realize graph-based languages by the diagrams of the Unified Modelling Language (UML, and allow the automatic generation and evaluation of multiple product variants. The research presented in this paper seeks to present a method in order to combine the advantages of a conscious requirements management process and graph-based design languages. Consequently, the main objective of this paper is the investigation of a model-based integration of requirements in a product development process by means of graph-based design languages. The research method is based on an in-depth analysis of an exemplary industrial product development, a gear system for so-called “Electrical Multiple Units” (EMU. Important requirements were abstracted from a gear system

Solid Base Catalysis

CERN Document Server

Ono, Yoshio

2011-01-01

The importance of solid base catalysts has come to be recognized for their environmentally benign qualities, and much significant progress has been made over the past two decades in catalytic materials and solid base-catalyzed reactions. The book is focused on the solid base. Because of the advantages over liquid bases, the use of solid base catalysts in organic synthesis is expanding. Solid bases are easier to dispose than liquid bases, separation and recovery of products, catalysts and solvents are less difficult, and they are non-corrosive. Furthermore, base-catalyzed reactions can be performed without using solvents and even in the gas phase, opening up more possibilities for discovering novel reaction systems. Using numerous examples, the present volume describes the remarkable role solid base catalysis can play, given the ever increasing worldwide importance of "green" chemistry. The reader will obtain an overall view of solid base catalysis and gain insight into the versatility of the reactions to whic...

Evidence-based monitoring and evaluation of the faith-based ...

African Journals Online (AJOL)

Background: The Islamic Medical Association of Uganda, has been implementing the faith-based approach to HIV prevention without baseline data on expected positive outcomes. Objectives: To establish evidence-based baseline data on expected positive outcomes of the faith-based approach to HIV prevention. Methods: ...

Covariance-Based Measurement Selection Criterion for Gaussian-Based Algorithms

Directory of Open Access Journals (Sweden)

Fernando A. Auat Cheein

2013-01-01

Full Text Available Process modeling by means of Gaussian-based algorithms often suffers from redundant information which usually increases the estimation computational complexity without significantly improving the estimation performance. In this article, a non-arbitrary measurement selection criterion for Gaussian-based algorithms is proposed. The measurement selection criterion is based on the determination of the most significant measurement from both an estimation convergence perspective and the covariance matrix associated with the measurement. The selection criterion is independent from the nature of the measured variable. This criterion is used in conjunction with three Gaussian-based algorithms: the EIF (Extended Information Filter, the EKF (Extended Kalman Filter and the UKF (Unscented Kalman Filter. Nevertheless, the measurement selection criterion shown herein can also be applied to other Gaussian-based algorithms. Although this work is focused on environment modeling, the results shown herein can be applied to other Gaussian-based algorithm implementations. Mathematical descriptions and implementation results that validate the proposal are also included in this work.

Model-Based Learning Environment Based on The Concept IPS School-Based Management

Directory of Open Access Journals (Sweden)

Hamid Darmadi

2017-03-01

Full Text Available The results showed: (1 learning model IPS-oriented environment can grow and not you love the cultural values of the area as a basis for the development of national culture, (2 community participation, and the role of government in implementing learning model of IPS-based environment provides a positive impact for the improvement of management school resources, (3 learning model IPS-based environment effectively creating a way of life together peacefully, increase the intensity of togetherness and mutual respect (4 learning model IPS-based environment can improve student learning outcomes, (5 there are differences in the expression of attitudes and results learning among students who are located in the area of conflict with students who are outside the area of conflict (6 analysis of the scale of attitudes among school students da SMA result rewards high school students to the values of unity and nation, respect for diversity and peaceful coexistence, It is recommended that the Department of Education authority as an institution of Trustees and the development of social and cultural values in the province can apply IPS learning model based environments.

Potencial da cinza do bagaço da cana-de-açúcar como material de substituição parcial de cimento Portland Potential of sugarcane bagasse ash as a partial replacement material for Portland cement

Directory of Open Access Journals (Sweden)

Marcos O. de Paula

2009-06-01

Full Text Available Este trabalho, voltado para a avaliação do potencial da cinza do bagaço da cana-de-açúcar (CBC como material de substituição parcial do cimento Portland em argamassa, objetivou apresentar opção viável para a destinação deste resíduo, cuja quantidade gerada aumentará significativamente nos próximos anos, em decorrência da ampliação do setor de produção de álcool combustível; além disso, o emprego da CBC como adição mineral, substituindo parte do cimento em argamassas e concretos, contribui para a redução do impacto ambiental desses materiais, em boa parte decorrente da produção do cimento. O procedimento experimental abordou não só caracterização da CBC mas também a avaliação, através de ensaios físicos e mecânicos, em que os resultados mostraram que o bagaço apresenta rendimento de CBC de 10%, com a cinza sendo composta de 84% de SiO2 e 5% de Carbono. A sílica na CBC apresenta-se na fase amorfa e nas fases cristalinas de cristobalita e quartzo. Os índices de atividade pozolânica comprovam a reatividade da CBC. Do ponto de vista da resistência à compressão, argamassas com teores de CBC entre 0 e 30% indicaram a possibilidade de substituição de até 20% do cimento pela CBC.This study is focused on the evaluation of the effects of the partial replacement of Portland cement by sugarcane bagasse ash (CBC in mortars. The main objective was to find a suitable destination for an agricultural residue generated in an increasing amount in Brazil, as a result of the boom of the use of ethanol as an alternative fuel to gasoline. Also, the use of CBC as a mineral admixture in mortars and concretes contributes to a decrease in the environmental impact of these materials related to cement production. Experimental techniques were applied both for the CBC characterization and for the evaluation of its use as a mineral admixture in mortars, based on mechanical and physical tests. The yield of CBC from sugarcane

A Web-Based Learning Support System for Inquiry-Based Learning

Science.gov (United States)

Kim, Dong Won; Yao, Jingtao

The emergence of the Internet and Web technology makes it possible to implement the ideals of inquiry-based learning, in which students seek truth, information, or knowledge by questioning. Web-based learning support systems can provide a good framework for inquiry-based learning. This article presents a study on a Web-based learning support system called Online Treasure Hunt. The Web-based learning support system mainly consists of a teaching support subsystem, a learning support subsystem, and a treasure hunt game. The teaching support subsystem allows instructors to design their own inquiry-based learning environments. The learning support subsystem supports students' inquiry activities. The treasure hunt game enables students to investigate new knowledge, develop ideas, and review their findings. Online Treasure Hunt complies with a treasure hunt model. The treasure hunt model formalizes a general treasure hunt game to contain the learning strategies of inquiry-based learning. This Web-based learning support system empowered with the online-learning game and founded on the sound learning strategies furnishes students with the interactive and collaborative student-centered learning environment.

Design of Composite Structures Using Knowledge-Based and Case Based Reasoning

Science.gov (United States)

Lambright, Jonathan Paul

1996-01-01

A method of using knowledge based and case based reasoning to assist designers during conceptual design tasks of composite structures was proposed. The cooperative use of heuristics, procedural knowledge, and previous similar design cases suggests a potential reduction in design cycle time and ultimately product lead time. The hypothesis of this work is that the design process of composite structures can be improved by using Case-Based Reasoning (CBR) and Knowledge-Based (KB) reasoning in the early design stages. The technique of using knowledge-based and case-based reasoning facilitates the gathering of disparate information into one location that is easily and readily available. The method suggests that the inclusion of downstream life-cycle issues into the conceptual design phase reduces potential of defective, and sub-optimal composite structures. Three industry experts were interviewed extensively. The experts provided design rules, previous design cases, and test problems. A Knowledge Based Reasoning system was developed using the CLIPS (C Language Interpretive Procedural System) environment and a Case Based Reasoning System was developed using the Design Memory Utility For Sharing Experiences (MUSE) xviii environment. A Design Characteristic State (DCS) was used to document the design specifications, constraints, and problem areas using attribute-value pair relationships. The DCS provided consistent design information between the knowledge base and case base. Results indicated that the use of knowledge based and case based reasoning provided a robust design environment for composite structures. The knowledge base provided design guidance from well defined rules and procedural knowledge. The case base provided suggestions on design and manufacturing techniques based on previous similar designs and warnings of potential problems and pitfalls. The case base complemented the knowledge base and extended the problem solving capability beyond the existence of

Feature-Based versus Category-Based Induction with Uncertain Categories

Science.gov (United States)

Griffiths, Oren; Hayes, Brett K.; Newell, Ben R.

2012-01-01

Previous research has suggested that when feature inferences have to be made about an instance whose category membership is uncertain, feature-based inductive reasoning is used to the exclusion of category-based induction. These results contrast with the observation that people can and do use category-based induction when category membership is…

WPS criterion proposition based on experimental data base interpretation

International Nuclear Information System (INIS)

Chapuliot, S.; Izard, J.P.; Moinereau, D.; Marie, S.

2011-01-01

This article gives the background and the methodology developed to define a K J based criterion for brittle fracture of Reactor Pressure Vessel (RPV) submitted to Pressurized Thermal Shock (PTS), and taking into account Warm Pre Stressing effect (WPS). The first step of this methodology is the constitution of an experimental data base. This work was performed through bibliography and partnerships, and allows merging experimental results dealing with: -) Various ferritic steels; -) Various material states (as received, thermally aged, irradiated...); -) Various mode of fracture (cleavage, inter-granular, mixed mode); -) Various specimen geometry and size (CT, SENB, mock-ups); -) Various thermo-mechanical transients. Based on this experimental data base, a simple K J based limit is proposed and compared to experimental results. Parametric studies are performed in order to define the main parameters of the problem. Finally, a simple proposition based on a detailed analysis of tests results is performed. This proposition giving satisfactory results in every cases, it constitutes a good candidate for integration in French RSE-M code for in service assessment. (authors)

Set-Based Discrete Particle Swarm Optimization Based on Decomposition for Permutation-Based Multiobjective Combinatorial Optimization Problems.

Science.gov (United States)

Yu, Xue; Chen, Wei-Neng; Gu, Tianlong; Zhang, Huaxiang; Yuan, Huaqiang; Kwong, Sam; Zhang, Jun

2017-08-07

This paper studies a specific class of multiobjective combinatorial optimization problems (MOCOPs), namely the permutation-based MOCOPs. Many commonly seen MOCOPs, e.g., multiobjective traveling salesman problem (MOTSP), multiobjective project scheduling problem (MOPSP), belong to this problem class and they can be very different. However, as the permutation-based MOCOPs share the inherent similarity that the structure of their search space is usually in the shape of a permutation tree, this paper proposes a generic multiobjective set-based particle swarm optimization methodology based on decomposition, termed MS-PSO/D. In order to coordinate with the property of permutation-based MOCOPs, MS-PSO/D utilizes an element-based representation and a constructive approach. Through this, feasible solutions under constraints can be generated step by step following the permutation-tree-shaped structure. And problem-related heuristic information is introduced in the constructive approach for efficiency. In order to address the multiobjective optimization issues, the decomposition strategy is employed, in which the problem is converted into multiple single-objective subproblems according to a set of weight vectors. Besides, a flexible mechanism for diversity control is provided in MS-PSO/D. Extensive experiments have been conducted to study MS-PSO/D on two permutation-based MOCOPs, namely the MOTSP and the MOPSP. Experimental results validate that the proposed methodology is promising.

Evidence-based guidelines, time-based health outcomes, and the Matthew effect

NARCIS (Netherlands)

M.L.E. Essink-Bot (Marie-Louise); M.E. Kruijshaar (Michelle); J.J.M. Barendregt (Jan); L.G.A. Bonneux (Luc)

2007-01-01

textabstractBackground: Cardiovascular risk management guidelines are 'risk based'; health economists' practice is 'time based'. The 'medical' risk-based allocation model maximises numbers of deaths prevented by targeting subjects at high risk, for example, elderly and smokers. The time-based model

Evidence-based guidelines, time-based health outcomes, and the Matthew effect

NARCIS (Netherlands)

Essink-Bot, Marie-Louise; Kruijshaar, Michelle E.; Barendregt, Jan J.; Bonneux, Luc G. A.

2007-01-01

BACKGROUND: Cardiovascular risk management guidelines are 'risk based'; health economists' practice is 'time based'. The 'medical' risk-based allocation model maximises numbers of deaths prevented by targeting subjects at high risk, for example, elderly and smokers. The time-based model maximises

0-6621 : developing a mixture-based specification for flexible base.

Science.gov (United States)

2012-08-01

The Texas Department of Transportation : (TxDOT) currently utilizes Item 247, Flexible : Base, to specify a foundation course of flexible : base utilized in a pavement. Base materials are : not allowed to be used by the contractors until : the ...

Acids and bases solvent effects on acid-base strenght

CERN Document Server

Cox, Brian G

2013-01-01

Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base strengths and to the rates and equilibria of many processes: for example, synthetic reactions involving acids, bases and nucleophiles; isolation of pharmaceutical actives through salt formation; formation of zwitter- ions in amino acids; and chromatographic separation of substrates. This book seeks to enhance our understanding of acids and bases by reviewing and analysing their behaviour in non-aqueous solvents. The behaviour is related where possible to that in water, but correlations and contrasts between solvents are also presented.

Characteristic-Based, Task-Based, and Results-Based: Three Value Systems for Assessing Professionally Produced Technical Communication Products.

Science.gov (United States)

Carliner, Saul

2003-01-01

Notes that technical communicators have developed different methodologies for evaluating the effectiveness of their work, such as editing, usability testing, and determining the value added. Explains that at least three broad value systems underlie the assessment practices: characteristic-based, task-based, and results-based. Concludes that the…

Designing Android Based Augmented Reality Location-Based Service Application

Directory of Open Access Journals (Sweden)

Alim Hardiansyah

2018-01-01

Full Text Available Android is an operating system for Linux based smartphone. Android provides an open platform for the developers to create their own application. The most developed and used application now is location based application. This application gives personalization service for mobile device user and is customized to their location. Location based service also gives an opportunity for the developers to develop and increase the value of service. One of the technologies that could be combined with location based application is augmented reality. Augmented reality combines the virtual world with the real one. By the assistance of augmented reality, our surrounding environment could interact in digital form. Information of objects and environment surround us could be added to the augmented reality system and presented. Based on the background, the writers tried to implement those technologies on now rapidly developing android application as a final project to achieve bachelor degree in Department of Informatics Engineering, Faculty of Information Technology and Visual Communication, Al Kamal Science and Technology Institute. This application could be functioned to locate school by using location based service technology with the assistance of navigational applications such as waze and google maps, in form of live direction process through the smartphone

Selective Distance-Based K+ Quantification on Paper-Based Microfluidics.

Science.gov (United States)

Gerold, Chase T; Bakker, Eric; Henry, Charles S

2018-04-03

In this study, paper-based microfluidic devices (μPADs) capable of K + quantification in aqueous samples, as well as in human serum, using both colorimetric and distance-based methods are described. A lipophilic phase containing potassium ionophore I (valinomycin) was utilized to achieve highly selective quantification of K + in the presence of Na + , Li + , and Mg 2+ ions. Successful addition of a suspended lipophilic phase to a wax printed paper-based device is described and offers a solution to current approaches that rely on organic solvents, which damage wax barriers. The approach provides an avenue for future alkali/alkaline quantification utilizing μPADs. Colorimetric spot tests allowed for K + quantification from 0.1-5.0 mM using only 3.00 μL of sample solution. Selective distance-based quantification required small sample volumes (6.00 μL) and gave responses sensitive enough to distinguish between 1.0 and 2.5 mM of sample K + . μPADs using distance-based methods were also capable of differentiating between 4.3 and 6.9 mM K + in human serum samples. Distance-based methods required no digital analysis, electronic hardware, or pumps; any steps required for quantification could be carried out using the naked eye.

VectorBase

Data.gov (United States)

U.S. Department of Health & Human Services — VectorBase is a Bioinformatics Resource Center for invertebrate vectors. It is one of four Bioinformatics Resource Centers funded by NIAID to provide web-based...

Owner-Based Role-Based Access Control OB-RBAC

NARCIS (Netherlands)

Saffarian, M.; Sadighi, Babak

Administration of an access control model deals with the question of who is authorized to update policies defined on the basis of that model. One of the models whose administration has absorbed relatively large research is the Role-Based Access Control (RBAC) model. All the existing role-based

Characteristics Data Base: Programmer's guide to the LWR Quantities Data Base

International Nuclear Information System (INIS)

Jones, K.E.; Moore, R.S.

1990-08-01

The LWR Quantities Data Base is a menu-driven PC data base developed as part of OCRWM's waste, technical data base on the characteristics of potential repository wastes, which also includes non-LWR spent fuel, high-level and other materials. This programmer's guide completes the documentation for the LWR Quantities Data Base, the user's guide having been published previously. The PC data base itself may be requested from the Oak Ridge National Laboratory, using the order form provided in Volume 1 of publication DOE/RW-0184

Interaction between scene-based and array-based contextual cueing.

Science.gov (United States)

Rosenbaum, Gail M; Jiang, Yuhong V

2013-07-01

Contextual cueing refers to the cueing of spatial attention by repeated spatial context. Previous studies have demonstrated distinctive properties of contextual cueing by background scenes and by an array of search items. Whereas scene-based contextual cueing reflects explicit learning of the scene-target association, array-based contextual cueing is supported primarily by implicit learning. In this study, we investigated the interaction between scene-based and array-based contextual cueing. Participants searched for a target that was predicted by both the background scene and the locations of distractor items. We tested three possible patterns of interaction: (1) The scene and the array could be learned independently, in which case cueing should be expressed even when only one cue was preserved; (2) the scene and array could be learned jointly, in which case cueing should occur only when both cues were preserved; (3) overshadowing might occur, in which case learning of the stronger cue should preclude learning of the weaker cue. In several experiments, we manipulated the nature of the contextual cues present during training and testing. We also tested explicit awareness of scenes, scene-target associations, and arrays. The results supported the overshadowing account: Specifically, scene-based contextual cueing precluded array-based contextual cueing when both were predictive of the location of a search target. We suggest that explicit, endogenous cues dominate over implicit cues in guiding spatial attention.

Measurement of electrochemical noise for the study of corrosion processes of metallic alloys; Medida de ruido electroquimico para el estudio de rocesoso de corrosion de aleaciones metalicas

Energy Technology Data Exchange (ETDEWEB)

Sanchez-Amaya, J. M.; Bethencourt, M.; Gonzalez-Rovira, L.; Botana, F. J.

2009-07-01

Electrochemical noise (EN) is a technique that allows the estimation of both the rate and the corrosion mechanism of different metallic alloys by means of the measurement and the analysis of the fluctuations of current and voltage. Its main advantage against other electrochemical techniques is that during the measurement process, the corrosive systems under study are not instrumentally disturbed, and therefore, the systems are kept at their natural corrosion potential. Two steps are necessary to use this technique: measurement and analysis of the EN signals. In this paper, the most important concepts related only to the measurement of EN are revised. The parameters most employed in the literature to analyse the EN signals will be described in another paper. In the present article, the experimental devices normally used to measure EN signals are firstly analysed. Subsequently, the most important properties of the EN signals are studied. Finally, the external sources of instrumental noise that can affect to the EN signals are described. (Author) 65 refs.

Stress corrosion crack growth rate in dissimilar metal welds; Evolucion microestructural de la ZAC en la union soldada con MIG sobre una aleacion del aluminio AA7020

Energy Technology Data Exchange (ETDEWEB)

Bloem, C. A.; Salvador, M. D.; Amigo, V.; Busquets, D.

2003-07-01

The aim of the present study is to evaluate the changes through the HAZ, analyzed under two different but complementary techniques. These are Transmission Electronic Microscopy (TEM) and Differential Scanning Calorimetry (DSC). The results shown that there are remarkable changes in size and morphology of the precipitates, being in accordance with the results obtained by DSC. (Author) 10 refs.

Brain-Based Learning and Standards-Based Elementary Science.

Science.gov (United States)

Konecki, Loretta R.; Schiller, Ellen

This paper explains how brain-based learning has become an area of interest to elementary school science teachers, focusing on the possible relationships between, and implications of, research on brain-based learning to the teaching of science education standards. After describing research on the brain, the paper looks at three implications from…

BEAT: A Web-Based Boolean Expression Fault-Based Test Case Generation Tool

Science.gov (United States)

Chen, T. Y.; Grant, D. D.; Lau, M. F.; Ng, S. P.; Vasa, V. R.

2006-01-01

BEAT is a Web-based system that generates fault-based test cases from Boolean expressions. It is based on the integration of our several fault-based test case selection strategies. The generated test cases are considered to be fault-based, because they are aiming at the detection of particular faults. For example, when the Boolean expression is in…

Rule-Based and Case-Based Reasoning in Housing Prices

OpenAIRE

Gabrielle Gayer; Itzhak Gilboa; Offer Lieberman

2004-01-01

People reason about real-estate prices both in terms of general rules and in terms of analogies to similar cases. We propose to empirically test which mode of reasoning fits the data better. To this end, we develop the statistical techniques required for the estimation of the case-based model. It is hypothesized that case-based reasoning will have relatively more explanatory power in databases of rental apartments, whereas rule-based reasoning will have a relative advantage in sales data. We ...

Object-Based Benefits without Object-Based Representations

OpenAIRE

Alvarez, George Angelo; Fougnie, Daryl; Cormiea, Sarah M

2012-01-01

The organization of visual information into objects strongly influences visual memory: Displays with objects defined by two features (e.g. color, orientation) are easier to remember than displays with twice as many objects defined by one feature (Olson & Jiang, 2002). Existing theories suggest that this ‘object-benefit’ is based on object-based limitations in working memory: because a limited number of objects can be stored, packaging features together so that fewer objects have to be remembe...

An Ontology-Based Tourism Recommender System Based on Spreading Activation Model

Science.gov (United States)

Bahramian, Z.; Abbaspour, R. Ali

2015-12-01

A tourist has time and budget limitations; hence, he needs to select points of interest (POIs) optimally. Since the available information about POIs is overloading, it is difficult for a tourist to select the most appreciate ones considering preferences. In this paper, a new travel recommender system is proposed to overcome information overload problem. A recommender system (RS) evaluates the overwhelming number of POIs and provides personalized recommendations to users based on their preferences. A content-based recommendation system is proposed, which uses the information about the user's preferences and POIs and calculates a degree of similarity between them. It selects POIs, which have highest similarity with the user's preferences. The proposed content-based recommender system is enhanced using the ontological information about tourism domain to represent both the user profile and the recommendable POIs. The proposed ontology-based recommendation process is performed in three steps including: ontology-based content analyzer, ontology-based profile learner, and ontology-based filtering component. User's feedback adapts the user's preferences using Spreading Activation (SA) strategy. It shows the proposed recommender system is effective and improves the overall performance of the traditional content-based recommender systems.

AN ONTOLOGY-BASED TOURISM RECOMMENDER SYSTEM BASED ON SPREADING ACTIVATION MODEL

Directory of Open Access Journals (Sweden)

Z. Bahramian

2015-12-01

Full Text Available A tourist has time and budget limitations; hence, he needs to select points of interest (POIs optimally. Since the available information about POIs is overloading, it is difficult for a tourist to select the most appreciate ones considering preferences. In this paper, a new travel recommender system is proposed to overcome information overload problem. A recommender system (RS evaluates the overwhelming number of POIs and provides personalized recommendations to users based on their preferences. A content-based recommendation system is proposed, which uses the information about the user’s preferences and POIs and calculates a degree of similarity between them. It selects POIs, which have highest similarity with the user’s preferences. The proposed content-based recommender system is enhanced using the ontological information about tourism domain to represent both the user profile and the recommendable POIs. The proposed ontology-based recommendation process is performed in three steps including: ontology-based content analyzer, ontology-based profile learner, and ontology-based filtering component. User’s feedback adapts the user’s preferences using Spreading Activation (SA strategy. It shows the proposed recommender system is effective and improves the overall performance of the traditional content-based recommender systems.

Contests versus Norms: Implications of Contest-Based and Norm-Based Intervention Techniques.

Science.gov (United States)

Bergquist, Magnus; Nilsson, Andreas; Hansla, André

2017-01-01

Interventions using either contests or norms can promote environmental behavioral change. Yet research on the implications of contest-based and norm-based interventions is lacking. Based on Goal-framing theory, we suggest that a contest-based intervention frames a gain goal promoting intensive but instrumental behavioral engagement. In contrast, the norm-based intervention was expected to frame a normative goal activating normative obligations for targeted and non-targeted behavior and motivation to engage in pro-environmental behaviors in the future. In two studies participants ( n = 347) were randomly assigned to either a contest- or a norm-based intervention technique. Participants in the contest showed more intensive engagement in both studies. Participants in the norm-based intervention tended to report higher intentions for future energy conservation (Study 1) and higher personal norms for non-targeted pro-environmental behaviors (Study 2). These findings suggest that contest-based intervention technique frames a gain goal, while norm-based intervention frames a normative goal.

Contests versus Norms: Implications of Contest-Based and Norm-Based Intervention Techniques

Directory of Open Access Journals (Sweden)

Magnus Bergquist

2017-11-01

Full Text Available Interventions using either contests or norms can promote environmental behavioral change. Yet research on the implications of contest-based and norm-based interventions is lacking. Based on Goal-framing theory, we suggest that a contest-based intervention frames a gain goal promoting intensive but instrumental behavioral engagement. In contrast, the norm-based intervention was expected to frame a normative goal activating normative obligations for targeted and non-targeted behavior and motivation to engage in pro-environmental behaviors in the future. In two studies participants (n = 347 were randomly assigned to either a contest- or a norm-based intervention technique. Participants in the contest showed more intensive engagement in both studies. Participants in the norm-based intervention tended to report higher intentions for future energy conservation (Study 1 and higher personal norms for non-targeted pro-environmental behaviors (Study 2. These findings suggest that contest-based intervention technique frames a gain goal, while norm-based intervention frames a normative goal.

EIS, Mott Schottky and EFM analysis of the electrochemical stability and dielectric properties of Ca-P-Ag and Ca-P-Si-Ag coatings obtained by plasma electrolytic oxidation in Ti6Al4V

Directory of Open Access Journals (Sweden)

Sara María Leal-Marin

2017-01-01

Full Text Available El Ti6Al4V ELI (ASTM F136 es una de las aleaciones más empleadas en dispositivos de osteosíntesis y reemplazo articular. Sin embargo, las propiedades de esta aleación pueden ser mejoradas respecto a su biocompatibilidad y osteointegración con el tejido óseo a través de recubrimientos. El objetivo de este trabajo fue evaluar el comportamiento electroquímico de un recubrimiento obtenido por oxidación por plasma electrolítico sobre Ti6Al4V ELI empleando soluciones electrolíticas enriquecidas con iones de PO4 2-, Ca+2, Si+4 y varias concentraciones de Ag+1. Los recubrimientos se caracterizaron mediante espectroscopia de impedancia electroquímica (EIS y Mott-Schottky (M-S en una celda de tres electrodos con una solución fisiológica simulada. El comportamiento electroquímico se contrastó con microscopía de fuerza electrostática (EFM, donde se analizó el potencial eléctrico del recubrimiento. Los resultados de EIS mostraron mejores propiedades de estabilidad frente a la corrosión en los sustratos recubiertos con Ca- P-Ag, comparados con los recubiertos con Ca-P-Si-Ag. Los espectros de Nyquist y Bode mostraron relajaciones relacionadas con la transferencia de carga hacia la doble capa electroquímica como reflejo de los cambios microestructurales y de conductividad de los recubrimientos, dada por la presencia particular en cada caso, de los elementos contenidos en estos. De acuerdo con los resultados de M-S, todas las muestras ensayadas presentaron un comportamiento con dopado tipo n, cuya conductividad incrementó con la inclusión de plata. Mediante EFM se observaron mayores contrastes en el potencial, fase y la amplitud de los recubrimientos con mayor cantidad de plata respecto al Ti6Al4V sin recubrir.

New strategy for the optimal design and manufacture of high performance milling heads

Directory of Open Access Journals (Sweden)

Bustillo, A.

2011-12-01

Full Text Available High-performance mechanical-transmission heads are one of the most complex, costly and problematic parts of a milling machine, owing to the large amount of piping required for transporting fluids and to the high level of mechanical performance that is required from them. This study proposes a strategy for optimising the design and manufacture of head bodies by using aluminium alloys and by integrating tubular stainless steel inserts in the casting of the head. These tubular inserts that are integrated into the aluminium mass are an alternative to cooling conduits currently made by machine drilling. As demonstrated in the experimental validation of the first prototype, the new method has created a design that retains the same mechanical performance, increases its reliability and reduces the weight of the milling machine’s moving parts.

Los cabezales de transmisión mecánica de altas prestaciones son una de las partes más complejas, costosas y problemáticas de una maquina fresadora. Esto es debido a la gran cantidad de canalizaciones para la transmisión de fluidos que deben de contener y a las altas prestaciones mecánicas que se les exigen. En este trabajo se presenta una estrategia para optimizar el diseño y la fabricación de los cuerpos de estos cabezales basada en la incorporación de aleaciones de aluminio y la inclusión de insertos tubulares de acero en la propia fundición que conforma el cabezal. Los insertos tubulares sustituyen a los canales de refrigeración realizados actualmente por taladros de mecanizado y quedan integrados en la masa de aluminio. La nueva metodología ha permitido realizar un diseño que mantiene las prestaciones mecánicas, aumenta la fiabilidad y reduce la masa de estos elementos móviles de fresadoras como ha demostrado la validación experimental de un primer prototipo.

Corrosión por picaduras del aluminio y de la aleación Al-6201 en soluciones de NaCl

Directory of Open Access Journals (Sweden)

Vera, R.

1998-06-01

Full Text Available The susceptibility of pure aluminum and aluminum 6201 alloy to pitting was investigated in sodium chloride solutions through determination of the corrosion, repassivation and pitting potentials. Potentiodynamic polarization including scratching techniques were employed being also determined the type and relative amount of corrosion damage to the metals. The morphology of the attack was determined using scanning electron microscopy (SEM. The results showed a similar performance for aluminum 6201 alloy and aluminum. It was also observed that an increase in chloride concentration resulted in a decrease in the corrosion, pitting and repassivation potentials of both materials.

Gran cantidad de estudios realizados sobre el comportamiento del aluminio y sus aleaciones han demostrado su excelente resistencia a diversos medios corrosivos. Sin embargo, en las líneas de transmisión de energía eléctrica de aluminio o de la aleación comercial Al-6201, instaladas en las costas de Valparaíso, Chile, se detectaron fallos del material, consistentes en picaduras profundas y roturas. En este estudio se evalúa la corrosión por picaduras sufrida por el aluminio y la aleación Al-6201, utilizando soluciones de diferentes concentraciones de NaCl que es el principal agente agresivo en ambientes marinos. Se determinaron los potenciales de corrosión (E_c, de repasivación (E_r y de picado (E_p, mediante el empleo de curvas de polarización potenciodinámicas y técnica de raspado. La morfología del ataque se determinó mediante microscopía electrónica de barrido. Los resultados mostraron un comportamiento similar entre el aluminio y la aleación 6201. También se observó que el aumento en la concentración de cloruro conlleva una disminución en los potenciales de corrosión, de picaduras y de repasivación en ambos materiales.

Estabilidad de la aleación Cu - 2,5 % Li en el rango 298 a 673 K

Directory of Open Access Journals (Sweden)

Ortiz, M.

2005-10-01

Full Text Available Contributing to the slight information about the Cu-Li alloys that is nowadays in scientific literature, this work reports the evolution with the temperature of the Cu - 2,5 wt % Li alloy. This alloy is obtained as powder by an electrodeposition process from salts. Powder samples, room temperature compacted tablets and the copper cathodes used in the process are analyzed. The samples were annealed in the rank from 293 to 673 K by different times and then characterized by means of x-rays diffraction. The lithium content was determined by atomic absorption. The analysis of the results shows a decomposition of the alloy as the temperature increases, with a loss of lithium towards the surface of the samples, where this element easily reacts with the atmosphere forming soluble water compounds.

Contribuyendo a la escasa información que se encuentra actualmente en la literatura científica acerca de las aleaciones Cu-Li, este trabajo informa la evolución de la aleaciónCu-2,5 % Li en peso, en función de la temperatura. La aleación se obtiene en forma de polvo, en un proceso de electrodepósito desde sales fundidas. Se analizan muestras en polvo, pastillas compactadas a temperatura ambiente y los cátodos de cobre utilizados en el proceso. Las muestras son sometidas a tratamientos térmicos en el rango de 293 a 673 K, por diferentes periodos de tiempo y caracterizadas mediante difracción de rayos X y determinación del contenido de litio por absorción atómica. El análisis de los resultados muestra una descomposición de la aleación conforme aumenta la temperatura, con una pérdida de litio hacia la superficie de las muestras, donde este elemento reacciona fácilmente con el ambiente, formando compuestos solubles en agua

Embracing a competency-based specialty curriculum for community-based nursing roles.

Science.gov (United States)

Levin, Pamela F; Swider, Susan M; Breakwell, Susan; Cowell, Julia M; Reising, Virginia

2013-01-01

The Quad Council competencies for public health nursing (PHN) provide guidance in developing curricula at both the generalist and specialist level. However, these competencies are based on nursing roles in traditional public health agencies and community/public health is defined more broadly than official agency practice. The question arises as to whether community-based specialties require largely the same knowledge and skill set as PHN. The purpose of the competency cross-mapping project reported here was to (a) assess the intersection of the Quad Council competencies with four community-based specialties and (b) ensure the appropriateness of a Quad Council-based curriculum to prepare graduates across these four specialties (home health, occupational health, environmental health, and school nursing). This article details the multistep cross-mapping process, including validation with practice leaders. Results indicate strong alignment of community-based specialty competencies with Quad Council competencies. Community-based specialty-specific content that did not align well is identified, along with examples of didactic and clinical strategies to address gaps. This work indicates that a Quad Council-based curriculum is appropriate to prepare graduates in community-based specialties when attention to the specialty-specific competencies in the clinical setting is included. This work guides the development of a doctorate of nursing practice curriculum in PHN, encompassing the four additional community-based specialties. © 2013 Wiley Periodicals, Inc.

Foundry based approach for InP based PIC development

NARCIS (Netherlands)

Smit, M.K.

2014-01-01

Europe is making significant investments in development of generic photonic foundry platform infrastructures for InP-based and Silicon Photonic ICs. Here we present the present status for the InP-based JePPIX platform.

Managing the Gap between Curriculum Based and Problem Based Learning

DEFF Research Database (Denmark)

Bygholm, Ann; Buus, Lillian

2009-01-01

/or but rather both/and. In this paper we describe an approach to design and delivery of online courses in computer science which on the one hand is based on a specified curriculum and on the other hand gives room for different learning strategies, problem based learning being one of them. We discuss......Traditionally there has been a clear distinction between curriculum based and problem based approaches to accomplish learning. Preferred approaches depend of course on conviction, culture, traditions and also on the specific learning situation. We will argue that it is not a question of either...

Groebner Bases Based Verification Solution for SystemVerilog Concurrent Assertions

Directory of Open Access Journals (Sweden)

Ning Zhou

2014-01-01

of polynomial ring algebra to perform SystemVerilog assertion verification over digital circuit systems. This method is based on Groebner bases theory and sequential properties checking. We define a constrained subset of SVAs so that an efficient polynomial modeling mechanism for both circuit descriptions and assertions can be applied. We present an algorithm framework based on the algebraic representations using Groebner bases for concurrent SVAs checking. Case studies show that computer algebra can provide canonical symbolic representations for both assertions and circuit designs and can act as a novel solver engine from the viewpoint of symbolic computation.

A Computer-Based Simulation of an Acid-Base Titration

Science.gov (United States)

Boblick, John M.

1971-01-01

Reviews the advantages of computer simulated environments for experiments, referring in particular to acid-base titrations. Includes pre-lab instructions and a sample computer printout of a student's use of an acid-base simulation. Ten references. (PR)

Research on the comparison of performance-based concept and force-based concept

Science.gov (United States)

Wu, Zeyu; Wang, Dongwei

2011-03-01

There are two ideologies about structure design: force-based concept and performance-based concept. Generally, if the structure operates during elastic stage, the two philosophies usually attain the same results. But beyond that stage, the shortage of force-based method is exposed, and the merit of performance-based is displayed. Pros and cons of each strategy are listed herein, and then which structure is best suitable to each method analyzed. At last, a real structure is evaluated by adaptive pushover method to verify that performance-based method is better than force-based method.

Priority-Based Hierarchical Operational Management for Multiagent-Based Microgrids

Directory of Open Access Journals (Sweden)

Takumi Kato

2014-03-01

Full Text Available Electricity consumption in the world is constantly increasing, making our lives become more and more dependent on electricity. There are several new paradigms proposed in the field of power grids. In Japan, especially after the Great East Japan Earthquake in March 2011, the new power grid paradigms are expected to be more resilient to survive several difficulties during disasters. In this paper, we focus on microgrids and propose priority-based hierarchical operational management for multiagent-based microgrids. The proposed management is a new multiagent-based load shedding scheme and multiagent-based hierarchical architecture to realize such resilient microgrids. We developed a prototype system and performed an evaluation of the proposed management using the developed system. The result of the evaluation shows the effectiveness of our proposal in power shortage situations, such as disasters.

Feature-based attention is functionally distinct from relation-based attention: The double dissociation between color-based capture and color-relation-based capture of attention.

Science.gov (United States)

Du, Feng; Jiao, Jun

2016-04-01

The present study used a spatial blink task and a cuing task to examine the boundary between feature-based capture and relation-based capture. Feature-based capture occurs when distractors match the target feature such as target color. The occurrence of relation-based capture is contingent upon the feature relation between target and distractor (e.g., color relation). The results show that color distractors that match the target-nontarget color relation do not consistently capture attention when they appear outside of the attentional window, but distractors appearing outside the attentional window that match the target color consistently capture attention. In contrast, color distractors that best match the target-nontarget color relation but not the target color, are more likely to capture attention when they appear within the attentional window. Consistently, color cues that match the target-nontarget color relation produce a cuing effect when they appear within the attentional window, while target-color matched cues do not. Such a double dissociation between color-based capture and color-relation-based capture indicates functionally distinct mechanisms for these 2 types of attentional selection. This also indicates that the spatial blink task and the uninformative cuing task are measuring distinctive aspects of involuntary attention. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

Skull base tumours

Energy Technology Data Exchange (ETDEWEB)

Borges, Alexandra [Instituto Portugues de Oncologia Francisco Gentil, Servico de Radiologia, Rua Professor Lima Basto, 1093 Lisboa Codex (Portugal)], E-mail: borgesalexandra@clix.pt

2008-06-15

With the advances of cross-sectional imaging radiologists gained an increasing responsibility in the management of patients with skull base pathology. As this anatomic area is hidden to clinical exam, surgeons and radiation oncologists have to rely on imaging studies to plan the most adequate treatment. To fulfil these endeavour radiologists need to be knowledgeable about skull base anatomy, about the main treatment options available, their indications and contra-indications and needs to be aware of the wide gamut of pathologies seen in this anatomic region. This article will provide a radiologists' friendly approach to the central skull base and will review the most common central skull base tumours and tumours intrinsic to the bony skull base.

Skull base tumours

International Nuclear Information System (INIS)

Borges, Alexandra

2008-01-01

With the advances of cross-sectional imaging radiologists gained an increasing responsibility in the management of patients with skull base pathology. As this anatomic area is hidden to clinical exam, surgeons and radiation oncologists have to rely on imaging studies to plan the most adequate treatment. To fulfil these endeavour radiologists need to be knowledgeable about skull base anatomy, about the main treatment options available, their indications and contra-indications and needs to be aware of the wide gamut of pathologies seen in this anatomic region. This article will provide a radiologists' friendly approach to the central skull base and will review the most common central skull base tumours and tumours intrinsic to the bony skull base

State-based versus reward-based motivation in younger and older adults.

Science.gov (United States)

Worthy, Darrell A; Cooper, Jessica A; Byrne, Kaileigh A; Gorlick, Marissa A; Maddox, W Todd

2014-12-01

Recent decision-making work has focused on a distinction between a habitual, model-free neural system that is motivated toward actions that lead directly to reward and a more computationally demanding goal-directed, model-based system that is motivated toward actions that improve one's future state. In this article, we examine how aging affects motivation toward reward-based versus state-based decision making. Participants performed tasks in which one type of option provided larger immediate rewards but the alternative type of option led to larger rewards on future trials, or improvements in state. We predicted that older adults would show a reduced preference for choices that led to improvements in state and a greater preference for choices that maximized immediate reward. We also predicted that fits from a hybrid reinforcement-learning model would indicate greater model-based strategy use in younger than in older adults. In line with these predictions, older adults selected the options that maximized reward more often than did younger adults in three of the four tasks, and modeling results suggested reduced model-based strategy use. In the task where older adults showed similar behavior to younger adults, our model-fitting results suggested that this was due to the utilization of a win-stay-lose-shift heuristic rather than a more complex model-based strategy. Additionally, within older adults, we found that model-based strategy use was positively correlated with memory measures from our neuropsychological test battery. We suggest that this shift from state-based to reward-based motivation may be due to age related declines in the neural structures needed for more computationally demanding model-based decision making.

Image based Monument Recognition using Graph based Visual Saliency

DEFF Research Database (Denmark)

Kalliatakis, Grigorios; Triantafyllidis, Georgios

2013-01-01

This article presents an image-based application aiming at simple image classification of well-known monuments in the area of Heraklion, Crete, Greece. This classification takes place by utilizing Graph Based Visual Saliency (GBVS) and employing Scale Invariant Feature Transform (SIFT) or Speeded......, the images have been previously processed according to the Graph Based Visual Saliency model in order to keep either SIFT or SURF features corresponding to the actual monuments while the background “noise” is minimized. The application is then able to classify these images, helping the user to better...

Convergent Filter Bases

Directory of Open Access Journals (Sweden)

Coghetto Roland

2015-09-01

Full Text Available We are inspired by the work of Henri Cartan [16], Bourbaki [10] (TG. I Filtres and Claude Wagschal [34]. We define the base of filter, image filter, convergent filter bases, limit filter and the filter base of tails (fr: filtre des sections.

QuickBase

CERN Document Server

Conner, Nancy

2007-01-01

Ready to put Intuit's QuickBase to work? Our new Missing Manual shows you how to capture, modify, share, and manage data and documents with this web-based data-sharing program quickly and easily. No longer do you have to coordinate your team through a blizzard of emails or play frustrating games of "guess which document is the right one."QuickBase saves your organization time and money, letting you manage and share the information that makes your business tick: sales figures, project timelines, drafts of documents, purchase or work requests--whatever information you need to keep business flowi

Merits of using andalusite-based refractories compared to bauxite-based refractories

OpenAIRE

Nyoka, M.; Brazier, D.; Courtney, T.; Parry, R.A.

2013-01-01

Historically bauxite-based refractories have been used in applications where andalusite-based refractories could work. Bauxite-based refractories were chosen over andalusite-based refractories mainly because of the availability of low-cost Chinese bauxite and also because many furnaces were designed by international companies that cannot easily access high-quality products. Currently, the availability of low-cost bauxite is under threat as a result of high export duties and tariffs as well as...

Swarm-based medicine.

Science.gov (United States)

Putora, Paul Martin; Oldenburg, Jan

2013-09-19

Occasionally, medical decisions have to be taken in the absence of evidence-based guidelines. Other sources can be drawn upon to fill in the gaps, including experience and intuition. Authorities or experts, with their knowledge and experience, may provide further input--known as "eminence-based medicine". Due to the Internet and digital media, interactions among physicians now take place at a higher rate than ever before. With the rising number of interconnected individuals and their communication capabilities, the medical community is obtaining the properties of a swarm. The way individual physicians act depends on other physicians; medical societies act based on their members. Swarm behavior might facilitate the generation and distribution of knowledge as an unconscious process. As such, "swarm-based medicine" may add a further source of information to the classical approaches of evidence- and eminence-based medicine. How to integrate swarm-based medicine into practice is left to the individual physician, but even this decision will be influenced by the swarm.

Touch BASE

CERN Multimedia

Antonella Del Rosso

2015-01-01

In a recent Nature article (see here), the BASE collaboration reported the most precise comparison of the charge-to-mass ratio of the proton to its antimatter equivalent, the antiproton. This result is just the beginning and many more challenges lie ahead.   CERN's AD Hall, where the BASE experiment is set-up. The Baryon Antibaryon Symmetry Experiment (BASE) was approved in June 2013 and was ready to take data in August 2014. During these 14 months, the BASE collaboration worked hard to set up its four cryogenic Penning traps, which are the heart of the whole experiment. As their name indicates, these magnetic devices are used to trap antiparticles – antiprotons coming from the Antiproton Decelerator – and particles of matter – negative hydrogen ions produced in the system by interaction with a degrader that slows the antiprotons down, allowing scientists to perform their measurements. “We had very little time to set up the wh...

Evaluation of radiosurgery techniques–Cone-based linac radiosurgery vs tomotherapy-based radiosurgery

International Nuclear Information System (INIS)

Yip, Ho Yin; Mui, Wing Lun A.; Lee, Joseph W.Y.; Fung, Winky Wing Ki; Chan, Jocelyn M.T.; Chiu, G.; Law, Maria Y.Y.

2013-01-01

Performances of radiosurgery of intracranial lesions between cone-based Linac system and Tomotherapy-based system were compared in terms of dosimetry and time. Twelve patients with single intracranial lesion treated with cone-based Linac radiosurgery system from 2005 to 2009 were replanned for Tomotherapy-based radiosurgery treatment. The conformity index, homogeneity index (HI), and gradient score index (GSI) of each case was calculated. The Wilcoxon matched-pair test was used to compare the 3 indices between both systems. The cases with regular target (n = 6) and those with irregular target (n = 6) were further analyzed separately. The estimated treatment time between both systems was also compared. Significant differences were found in HI (p = 0.05) and in GSI (p = 0.03) for the whole group. Cone-based radiosurgery was better in GSI whereas Tomotherapy-based radiosurgery was better in HI. Cone-based radiosurgery was better in conformity index (p = 0.03) and GSI (p = 0.03) for regular targets, whereas Tomotherapy-based radiosurgery system performed significantly better in HI (p = 0.03) for irregular targets. The estimated total treatment time for Tomotherapy-based radiosurgery ranged from 24 minutes to 35 minutes, including 15 minutes of pretreatment megavoltage computed tomography (MVCT) and image registration, whereas that for cone-based radiosurgery ranged from 15 minutes for 1 isocenter to 75 minutes for 5 isocenters. As a rule of thumb, Tomotherapy-based radiosurgery system should be the first-line treatment for irregular lesions because of better dose homogeneity and shorter treatment time. Cone-based Linac radiosurgery system should be the treatment of choice for regular targets because of the better dose conformity, rapid dose fall-off, and reasonable treatment time

Evaluation of radiosurgery techniques–Cone-based linac radiosurgery vs tomotherapy-based radiosurgery

Energy Technology Data Exchange (ETDEWEB)

Yip, Ho Yin, E-mail: hoyinyip@yahoo.com.hk [Department of Radiotherapy, Hong Kong Sanatorium and Hospital, Happy Valley, Hong Kong (China); Mui, Wing Lun A.; Lee, Joseph W.Y.; Fung, Winky Wing Ki; Chan, Jocelyn M.T.; Chiu, G. [Department of Radiotherapy, Hong Kong Sanatorium and Hospital, Happy Valley, Hong Kong (China); Law, Maria Y.Y. [Medical Physics and Research Department, Hong Kong Sanatorium and Hospital, Happy Valley, Hong Kong (China)

2013-07-01

Performances of radiosurgery of intracranial lesions between cone-based Linac system and Tomotherapy-based system were compared in terms of dosimetry and time. Twelve patients with single intracranial lesion treated with cone-based Linac radiosurgery system from 2005 to 2009 were replanned for Tomotherapy-based radiosurgery treatment. The conformity index, homogeneity index (HI), and gradient score index (GSI) of each case was calculated. The Wilcoxon matched-pair test was used to compare the 3 indices between both systems. The cases with regular target (n = 6) and those with irregular target (n = 6) were further analyzed separately. The estimated treatment time between both systems was also compared. Significant differences were found in HI (p = 0.05) and in GSI (p = 0.03) for the whole group. Cone-based radiosurgery was better in GSI whereas Tomotherapy-based radiosurgery was better in HI. Cone-based radiosurgery was better in conformity index (p = 0.03) and GSI (p = 0.03) for regular targets, whereas Tomotherapy-based radiosurgery system performed significantly better in HI (p = 0.03) for irregular targets. The estimated total treatment time for Tomotherapy-based radiosurgery ranged from 24 minutes to 35 minutes, including 15 minutes of pretreatment megavoltage computed tomography (MVCT) and image registration, whereas that for cone-based radiosurgery ranged from 15 minutes for 1 isocenter to 75 minutes for 5 isocenters. As a rule of thumb, Tomotherapy-based radiosurgery system should be the first-line treatment for irregular lesions because of better dose homogeneity and shorter treatment time. Cone-based Linac radiosurgery system should be the treatment of choice for regular targets because of the better dose conformity, rapid dose fall-off, and reasonable treatment time.

Nasal base narrowing: the combined alar base excision technique.

Science.gov (United States)

Foda, Hossam M T

2007-01-01

To evaluate the role of the combined alar base excision technique in narrowing the nasal base and correcting excessive alar flare. The study included 60 cases presenting with a wide nasal base and excessive alar flaring. The surgical procedure combined an external alar wedge resection with an internal vestibular floor excision. All cases were followed up for a mean of 32 (range, 12-144) months. Nasal tip modification and correction of any preexisting caudal septal deformities were always completed before the nasal base narrowing. The mean width of the external alar wedge excised was 7.2 (range, 4-11) mm, whereas the mean width of the sill excision was 3.1 (range, 2-7) mm. Completing the internal excision first resulted in a more conservative external resection, thus avoiding any blunting of the alar-facial crease. No cases of postoperative bleeding, infection, or keloid formation were encountered, and the external alar wedge excision healed with an inconspicuous scar that was well hidden in the depth of the alar-facial crease. Finally, the risk of notching of the alar rim, which can occur at the junction of the external and internal excisions, was significantly reduced by adopting a 2-layered closure of the vestibular floor (P = .01). The combined alar base excision resulted in effective narrowing of the nasal base with elimination of excessive alar flare. Commonly feared complications, such as blunting of the alar-facial crease or notching of the alar rim, were avoided by using simple modifications in the technique of excision and closure.

Developing effective web-based regional anesthesia education: a randomized study evaluating case-based versus non-case-based module design.

Science.gov (United States)

Kopp, Sandra L; Smith, Hugh M

2011-01-01

Little is known about the use of Web-based education in regional anesthesia training. Benefits of Web-based education include the ability to standardize learning material quality and content, build appropriate learning progressions, use interactive multimedia technologies, and individualize delivery of course materials. The goals of this investigation were (1) to determine whether module design influences regional anesthesia knowledge acquisition, (2) to characterize learner preference patterns among anesthesia residents, and (3) to determine whether learner preferences play a role in knowledge acquisition. Direct comparison of knowledge assessments, learning styles, and learner preferences will be made between an interactive case-based and a traditional textbook-style module design. Forty-three Mayo Clinic anesthesiology residents completed 2 online modules, a knowledge pretest, posttest, an Index of Learning Styles assessment, and a participant satisfaction survey. Interscalene and lumbar plexus regional techniques were selected as the learning content for 4 Web modules constructed using the Blackboard Vista coursework application. One traditional textbook-style module and 1 interactive case-based module were designed for each of the interscalene and lumbar plexus techniques. Participants scored higher on the postmodule knowledge assessment for both of the interscalene and lumbar plexus modules. Postmodule knowledge performance scores were independent of both module design (interactive case-based versus traditional textbook style) and learning style preferences. However, nearly all participants reported a preference for Web-based learning and believe that it should be used in anesthesia resident education. Participants did not feel that Web-base learning should replace the current lecture-based curriculum. All residents scored higher on the postmodule knowledge assessment, but this improvement was independent of the module design and individual learning styles

Mindfulness-based and acceptance-based interventions in sport and performance contexts.

Science.gov (United States)

Gardner, Frank L; Moore, Zella E

2017-08-01

Since mindfulness-based and acceptance-based practice models were first conceptualized and applied in sport in an attempt to enhance performance and overall well-being of athletes and performers, these state-of-the-art theoretical and practice models have substantially broadened our knowledge base and have been successfully incorporated into sport and performance practice domains worldwide. Evolving from a sound empirical foundation, mindfulness-based and acceptance-based models in sport psychology have accumulated a strong basic and applied empirical foundation. In the nearly 20 years since their incorporation in the context of sport, empirical findings have demonstrated efficacious outcomes associated with performance and personal well-being, as well as supported their theorized mechanisms of change. Particularly as sport and performance environments increasingly call upon practitioners to provide more comprehensive care to clientele, including a range of care from performance enhancement and maintenance, to general personal well-being, to subclinical and clinical issues, mindfulness-based and acceptance-based practitioners have the tools to offer robust, empirically informed interventions that can enhance skills and quality of life, and/or ameliorate personal struggles. Copyright © 2017 Elsevier Ltd. All rights reserved.

VO2-based radiative thermal transistor with a semi-transparent base

Science.gov (United States)

Prod'homme, Hugo; Ordonez-Miranda, Jose; Ezzahri, Younès; Drévillon, Jérémie; Joulain, Karl

2018-05-01

We study a radiative thermal transistor analogous to an electronic one made of a VO2 base placed between two silica semi-infinite plates playing the roles of the transistor collector and emitter. The fact that VO2 exhibits an insulator to metal transition is exploited to modulate and/or amplify heat fluxes between the emitter and the collector, by applying a thermal current on the VO2 base. We extend the work of precedent studies considering the case where the base can be semi-transparent so that heat can be exchanged directly between the collector and the emitter. Both near and far field cases are considered leading to 4 typical regimes resulting from the fact that the emitter-base and base-collector separation distances can be larger or smaller than the thermal wavelength for a VO2 layer opaque or semi-transparent. Thermal currents variations with the base temperatures are calculated and analyzed. It is found that the transistor can operate in an amplification mode as already stated in [1] or in a switching mode as seen in [2]. An optimum configuration for the base thickness and separation distance maximizing the thermal transistor modulation factor is found.

Facilitators' perceptions of problem-based learning and community-based education

Directory of Open Access Journals (Sweden)

Annali E Fichardt

2000-10-01

Full Text Available In 1997 the School for Nursing, University of the Orange Free State, changed from the traditional lecture method of teaching to problem-based learning and from a curative to a community-based approach. Lecturers from a traditional environment became facilitators and new skills such as listening, dialogue, negotiation, counselling and problemsolving were expected from them. Besides the role change, the environment changed from a structural classroom to an unstructured community. The aim of this research was to determine the perceptions and experiences of facilitators in problem-based learning and community-base education. *Please note: This is a reduced version of the abstract. Please refer to PDF for full text.

Frame-based safety analysis approach for decision-based errors

International Nuclear Information System (INIS)

Fan, Chin-Feng; Yihb, Swu

1997-01-01

A frame-based approach is proposed to analyze decision-based errors made by automatic controllers or human operators due to erroneous reference frames. An integrated framework, Two Frame Model (TFM), is first proposed to model the dynamic interaction between the physical process and the decision-making process. Two important issues, consistency and competing processes, are raised. Consistency between the physical and logic frames makes a TFM-based system work properly. Loss of consistency refers to the failure mode that the logic frame does not accurately reflect the state of the controlled processes. Once such failure occurs, hazards may arise. Among potential hazards, the competing effect between the controller and the controlled process is the most severe one, which may jeopardize a defense-in-depth design. When the logic and physical frames are inconsistent, conventional safety analysis techniques are inadequate. We propose Frame-based Fault Tree; Analysis (FFTA) and Frame-based Event Tree Analysis (FETA) under TFM to deduce the context for decision errors and to separately generate the evolution of the logical frame as opposed to that of the physical frame. This multi-dimensional analysis approach, different from the conventional correctness-centred approach, provides a panoramic view in scenario generation. Case studies using the proposed techniques are also given to demonstrate their usage and feasibility

From conventional software based systems to knowledge based systems

International Nuclear Information System (INIS)

Bologna, S.

1995-01-01

Even if todays nuclear power plants have a very good safety record, there is a continuous search for still improving safety. One direction of this effort address operational safety, trying to improve the handling of disturbances and accidents partly by further automation, partly by creating a better control room environment, providing the operator with intelligent support systems to help in the decision making process. Introduction of intelligent computerised operator support systems has proved to be an efficient way of improving the operators performance. A number of systems have been developed worldwide, assisting in tasks like process fault detection and diagnosis, selection and implementation of proper remedial actions. Unfortunately, the use of Knowledge Based Systems (KBSs), introduces a new dimension to the problem of the licensing process. KBSs, despite the different technology employed, are still nothing more than a computer program. Unfortunately, quite a few people building knowledge based systems seem to ignore the many good programming practices that have evolved over the years for producing traditional computer programs. In this paper the author will try to point out similarities and differences between conventional software based systems, and knowledge based systems, introducing also the concept of model based reasoning. (orig.) (25 refs., 2 figs.)

Case-based reasoning

CERN Document Server

Kolodner, Janet

1993-01-01

Case-based reasoning is one of the fastest growing areas in the field of knowledge-based systems and this book, authored by a leader in the field, is the first comprehensive text on the subject. Case-based reasoning systems are systems that store information about situations in their memory. As new problems arise, similar situations are searched out to help solve these problems. Problems are understood and inferences are made by finding the closest cases in memory, comparing and contrasting the problem with those cases, making inferences based on those comparisons, and asking questions whe

Lotus Base

DEFF Research Database (Denmark)

Mun, Terry; Bachmann, Asger; Gupta, Vikas

2016-01-01

exploration of Lotus genomic and transcriptomic data. Equally important are user-friendly in-browser tools designed for data visualization and interpretation. Here, we present Lotus Base, which opens to the research community a large, established LORE1 insertion mutant population containing an excess of 120...... such data, allowing users to construct, visualize, and annotate co-expression gene networks. Lotus Base takes advantage of modern advances in browser technology to deliver powerful data interpretation for biologists. Its modular construction and publicly available application programming interface enable...... developers to tap into the wealth of integrated Lotus data. Lotus Base is freely accessible at: https://lotus.au.dk....

Three dimensional pattern recognition using feature-based indexing and rule-based search

Science.gov (United States)

Lee, Jae-Kyu

In flexible automated manufacturing, robots can perform routine operations as well as recover from atypical events, provided that process-relevant information is available to the robot controller. Real time vision is among the most versatile sensing tools, yet the reliability of machine-based scene interpretation can be questionable. The effort described here is focused on the development of machine-based vision methods to support autonomous nuclear fuel manufacturing operations in hot cells. This thesis presents a method to efficiently recognize 3D objects from 2D images based on feature-based indexing. Object recognition is the identification of correspondences between parts of a current scene and stored views of known objects, using chains of segments or indexing vectors. To create indexed object models, characteristic model image features are extracted during preprocessing. Feature vectors representing model object contours are acquired from several points of view around each object and stored. Recognition is the process of matching stored views with features or patterns detected in a test scene. Two sets of algorithms were developed, one for preprocessing and indexed database creation, and one for pattern searching and matching during recognition. At recognition time, those indexing vectors with the highest match probability are retrieved from the model image database, using a nearest neighbor search algorithm. The nearest neighbor search predicts the best possible match candidates. Extended searches are guided by a search strategy that employs knowledge-base (KB) selection criteria. The knowledge-based system simplifies the recognition process and minimizes the number of iterations and memory usage. Novel contributions include the use of a feature-based indexing data structure together with a knowledge base. Both components improve the efficiency of the recognition process by improved structuring of the database of object features and reducing data base size

NSCT BASED LOCAL ENHANCEMENT FOR ACTIVE CONTOUR BASED IMAGE SEGMENTATION APPLICATION

Directory of Open Access Journals (Sweden)

Hiren Mewada

2010-08-01

Full Text Available Because of cross-disciplinary nature, Active Contour modeling techniques have been utilized extensively for the image segmentation. In traditional active contour based segmentation techniques based on level set methods, the energy functions are defined based on the intensity gradient. This makes them highly sensitive to the situation where the underlying image content is characterized by image nonhomogeneities due to illumination and contrast condition. This is the most difficult problem to make them as fully automatic image segmentation techniques. This paper introduces one of the approaches based on image enhancement to this problem. The enhanced image is obtained using NonSubsampled Contourlet Transform, which improves the edges strengths in the direction where the illumination is not proper and then active contour model based on level set technique is utilized to segment the object. Experiment results demonstrate that proposed method can be utilized along with existing active contour model based segmentation method under situation characterized by intensity non-homogeneity to make them fully automatic.

Data base EQDB - data base of the qualified equipment's for NPP

International Nuclear Information System (INIS)

Rovny, K.

2009-01-01

In the contribution, there is presented the project of the data base for qualified equipment's for nuclear power plants. The data base is operated by the 'Certification body which certified the products - the chosen equipment's for nuclear power plants', reg. No. P-028, at VUJE, Inc. Trnava. Data base will serve to the designers, the operators of the nuclear power plants and the workers from Nuclear regulatory authority of the Slovak Republic as a source of information about the state of concrete type equipment's qualification. In the first part of the contribution, there is information about the legislation and technical requirements for equipment's qualification, the way of demonstration and importance of the qualification for the operator. In the next part, there is presented the own structure of data base and the works with own data base regarding the examples of concrete equipment's. The data base will be accessible after the free registration on address WWW.EQDB.sk from 1.5.2009

Evidence-based radiography

International Nuclear Information System (INIS)

Hafslund, Bjorg; Clare, Judith; Graverholt, Birgitte; Wammen Nortvedt, Monica

2008-01-01

Evidence-based practice (EBP) offers the integration of the best research evidence with clinical knowledge and expertise and patient values. EBP is a well known term in health care. This paper discusses the implementation of EBP into radiography and introduces the term evidence-based radiography. Evidence-based radiography is radiography informed and based on the combination of clinical expertise and the best available research-based evidence, patient preferences and resources available. In Norway, EBP in radiography is being debated and radiographers are discussing the challenges of implementing EBP in both academic and clinical practice. This discussion paper explains why EBP needs to be a basis for a radiography curriculum and a part of radiographers' practice. We argue that Norwegian radiographers must increase participation in research and developing practice within their specific radiographic domain

Competency-Based Teaching in Radiology - Implementation and Evaluation of Interactive Workstation-Based Learning to Apply NKLM-Based Content.

Science.gov (United States)

Koestner, Wolfgang; Otten, Wiebke; Kaireit, Till; Wacker, Frank K; Dettmer, Sabine

2017-11-01

Purpose  New teaching formats are required to implement competency-based teaching in radiology teaching. Therefore, we have established and evaluated two practical competency-based radiological courses. Materials and Methods  The courses were held in a multimedia room with 25 computers and a professional DICOM viewer. Students were taught basic image analysis and presented clinical cases with a DICOM viewer under supervision of an instructor using desktop monitoring software. Two courses (elective course and obligatory course) were evaluated by the students (n = 160 and n = 100) and instructors (n = 9) using an anonymized online survey. Results  Courses were evaluated positively by the students and instructors. From the perspective of the students, the courses increased understanding of cross-sectional anatomy (elective/obligatory course: 97 %/95 %) and radiologic findings (97 %/99 %). Furthermore, the course increased the students' interest in radiology (61 %/65 %). The students considered this way of teaching to be relevant to their future occupation (92 % of students in the obligatory course). The higher incidence of teacher-student interaction and the possibility of independent image analysis were rated positively. The majority of instructors did not observe increased distractibility due to the computers (67 %) or notice worse preparation for MC tests (56 %). However, 56 % of instructors reported greater preparation effort. Conclusion  Practical competency-based radiological teaching using a DICOM viewer is a feasible innovative approach with high acceptance among students and instructors. It fosters competency-based learning as proposed by the model curriculum of the German Radiological Society (DRG) and the National Competency-based Catalogue of Learning Objectives for Undergraduate Medical Education (NKLM). Key Points   · Practical competency-based radiological teaching is highly accepted by students and instructors

Cultural and Rhetorical Bases for communicating knowledge in web based communities

DEFF Research Database (Denmark)

Kampf, Constance; Kommers, Piet

2008-01-01

Cultural and Rhetorical Bases for communicating knowledge in web based communities How can we extend learner-centred theories for educational technology to include, for instance, the cultural and rhetorical backgrounds which influence participants in online communities as they engage in knowledge...... via web-based communities the intersection of culture and rhetoric in web-based communication rhetoric and discourse in the process of communicating knowledge via technology heuristics for knowledge communication from teaching in online forums connections between identity and knowledge communication...... This call for papers invites papers focused on theoretical frameworks or empirical research which highlights the cultural and/or rhetorical aspects of communicating knowledge in web based communities. We are looking for work that brings together methods and perspectives across disciplines...

Characteristics Data Base: Programmer's guide to the High-Level Waste Data Base

International Nuclear Information System (INIS)

Jones, K.E.; Salmon, R.

1990-08-01

The High-Level Waste Data Base is a menu-driven PC data base developed as part of OCRWM's technical data base on the characteristics of potential repository wastes, which also includes spent fuel and other materials. This programmer's guide completes the documentation for the High-Level Waste Data Base, the user's guide having been published previously. 3 figs

An Alternative Collaborative Supervision Practice between University-Based Teachers and School-Based Teachers

Science.gov (United States)

Steele, Annfrid R.

2017-01-01

There is an increased focus in teacher education on research-based teaching as a means to develop a more research-based professional knowledge. However, research from several Western countries shows that neither school-based nor university-based teachers are familiar with how to integrate research-based knowledge in professional teacher practice.…

Paper based electronics platform

KAUST Repository

Nassar, Joanna Mohammad; Sevilla, Galo Andres Torres; Hussain, Muhammad Mustafa

2017-01-01

A flexible and non-functionalized low cost paper-based electronic system platform fabricated from common paper, such as paper based sensors, and methods of producing paper based sensors, and methods of sensing using the paper based sensors

Cholinesterase-based biosensors.

Science.gov (United States)

Štěpánková, Šárka; Vorčáková, Katarína

2016-01-01

Recently, cholinesterase-based biosensors are widely used for assaying anticholinergic compounds. Primarily biosensors based on enzyme inhibition are useful analytical tools for fast screening of inhibitors, such as organophosphates and carbamates. The present review is aimed at compilation of the most important facts about cholinesterase based biosensors, types of physico-chemical transduction, immobilization strategies and practical applications.

Strengths-based Learning

DEFF Research Database (Denmark)

Ledertoug, Mette Marie

-being. The Ph.D.-project in Strength-based learning took place in a Danish school with 750 pupils age 6-16 and a similar school was functioning as a control group. The presentation will focus on both the aware-explore-apply processes and the practical implications for the schools involved, and on measurable......Strength-based learning - Children͛s Character Strengths as Means to their Learning Potential͛ is a Ph.D.-project aiming to create a strength-based mindset in school settings and at the same time introducing strength-based interventions as specific tools to improve both learning and well...

Using Web-Based Peer Benchmarking to Manage the Client-Based Project

Science.gov (United States)

Raska, David; Keller, Eileen Weisenbach; Shaw, Doris

2013-01-01

The complexities of integrating client-based projects into marketing courses provide challenges for the instructor but produce richness of context and active learning for the student. This paper explains the integration of Web-based peer benchmarking as a means of improving student performance on client-based projects within a single semester in…

Novel nonlinear knowledge-based mean force potentials based on machine learning.

Science.gov (United States)

Dong, Qiwen; Zhou, Shuigeng

2011-01-01

The prediction of 3D structures of proteins from amino acid sequences is one of the most challenging problems in molecular biology. An essential task for solving this problem with coarse-grained models is to deduce effective interaction potentials. The development and evaluation of new energy functions is critical to accurately modeling the properties of biological macromolecules. Knowledge-based mean force potentials are derived from statistical analysis of proteins of known structures. Current knowledge-based potentials are almost in the form of weighted linear sum of interaction pairs. In this study, a class of novel nonlinear knowledge-based mean force potentials is presented. The potential parameters are obtained by nonlinear classifiers, instead of relative frequencies of interaction pairs against a reference state or linear classifiers. The support vector machine is used to derive the potential parameters on data sets that contain both native structures and decoy structures. Five knowledge-based mean force Boltzmann-based or linear potentials are introduced and their corresponding nonlinear potentials are implemented. They are the DIH potential (single-body residue-level Boltzmann-based potential), the DFIRE-SCM potential (two-body residue-level Boltzmann-based potential), the FS potential (two-body atom-level Boltzmann-based potential), the HR potential (two-body residue-level linear potential), and the T32S3 potential (two-body atom-level linear potential). Experiments are performed on well-established decoy sets, including the LKF data set, the CASP7 data set, and the Decoys “R”Us data set. The evaluation metrics include the energy Z score and the ability of each potential to discriminate native structures from a set of decoy structures. Experimental results show that all nonlinear potentials significantly outperform the corresponding Boltzmann-based or linear potentials, and the proposed discriminative framework is effective in developing knowledge-based

Using bio-based polymers for curing cement-based materials

NARCIS (Netherlands)

Zlopasa, J.; Koenders, E.A.B.; Picken, S.J.

2014-01-01

Curing is the process of controlling the rate and extent of moisture loss from the surface of cement based materials. It is the final stage in the production of cement-based materials and it is the essential part for achieving continuous hydration of cement, while avoiding cracking due to drying

Carbon-based sputtered coatings for enhanced chitosan-based films properties

Science.gov (United States)

Fernandes, C.; Calderon V., S.; Ballesteros, Lina F.; Cerqueira, Miguel A.; Pastrana, L. M.; Teixeira, José A.; Ferreira, P. J.; Carvalho, S.

2018-03-01

In order to make bio-based packaging materials competitive in comparison to petroleum-based one, some of their properties need to be improved, among which gas permeability is of crucial importance. Thus, in this work, carbon-based coatings were applied on chitosan-based films by radiofrequency reactive magnetron sputtering aiming to improve their barrier properties. Chemical and morphological properties were evaluated in order to determine the effect of the coatings on the chemical structure, surface hydrophobicity and barrier properties of the system. Chemical analysis, performed by electron energy loss spectroscopy and Fourier transform infrared spectroscopy, suggests similar chemical characteristics among all coatings although higher incorporation of hydrogen as the acetylene flux increases was observed. On the other hand, scanning transmission electron microscopy revealed that the porosity of the carbon layer can be tailored by the acetylene flux. More importantly, the chitosan oxygen permeability showed a monotonic reduction as a function of the acetylene flux. This study opens up new opportunities to apply nanostructured coatings on bio-based polymer for enhanced oxygen barrier properties.

Computer-based teaching is as good as face to face lecture-based teaching of evidence based medicine: a randomised controlled trial

Science.gov (United States)

2007-01-01

Background At postgraduate level evidence based medicine (EBM) is currently taught through tutor based lectures. Computer based sessions fit around doctors' workloads, and standardise the quality of educational provision. There have been no randomized controlled trials comparing computer based sessions with traditional lectures at postgraduate level within medicine. Methods This was a randomised controlled trial involving six postgraduate education centres in the West Midlands, U.K. Fifty five newly qualified foundation year one doctors (U.S internship equivalent) were randomised to either computer based sessions or an equivalent lecture in EBM and systematic reviews. The change from pre to post-intervention score was measured using a validated questionnaire assessing knowledge (primary outcome) and attitudes (secondary outcome). Results Both groups were similar at baseline. Participants' improvement in knowledge in the computer based group was equivalent to the lecture based group (gain in score: 2.1 [S.D = 2.0] versus 1.9 [S.D = 2.4]; ANCOVA p = 0.078). Attitudinal gains were similar in both groups. Conclusion On the basis of our findings we feel computer based teaching and learning is as effective as typical lecture based teaching sessions for educating postgraduates in EBM and systematic reviews. PMID:17659076

A model-based framework for design of intensified enzyme-based processes

DEFF Research Database (Denmark)

Román-Martinez, Alicia

This thesis presents a generic and systematic model-based framework to design intensified enzyme-based processes. The development of the presented methodology was motivated by the needs of the bio-based industry for a more systematic approach to achieve intensification in its production plants...... in enzyme-based processes which have found significant application in the pharmaceutical, food, and renewable fuels sector. The framework uses model-based strategies for (bio)-chemical process design and optimization, including the use of a superstructure to generate all potential reaction......(s)-separation(s) options according to a desired performance criteria and a generic mathematical model represented by the superstructure to derive the specific models corresponding to a specific process option. In principle, three methods of intensification of bioprocess are considered in this thesis: 1. enzymatic one...

Stolen Base Physics

Science.gov (United States)

Kagan, David

2013-01-01

Few plays in baseball are as consistently close and exciting as the stolen base. While there are several studies of sprinting, the art of base stealing is much more nuanced. This article describes the motion of the base-stealing runner using a very basic kinematic model. The model will be compared to some data from a Major League game. The…

An Evidence-Based Assessment of Faith-Based Programs: Do Faith-Based Programs "Work" to Reduce Recidivism?

Science.gov (United States)

Dodson, Kimberly D.; Cabage, Leann N.; Klenowski, Paul M.

2011-01-01

Faith-based organizations administer many of the prison-based programs aimed at reducing recidivism. Many of these organizations also manage treatment programs for substance abusers, at-risk juveniles, and ex-offenders. Much of the research on religiosity and delinquency indicates that the two are inversely related. Therefore, it seems plausible…

Case-based reasoning diagnostic technique based on multi-attribute similarity

Energy Technology Data Exchange (ETDEWEB)

Makoto, Takahashi [Tohoku University, Miyagi (Japan); Akio, Gofuku [Okayama University, Okayamaa (Japan)

2014-08-15

Case-based diagnostic technique has been developed based on the multi-attribute similarity. Specific feature of the developed system is to use multiple attributes of process signals for similarity evaluation to retrieve a similar case stored in a case base. The present technique has been applied to the measurement data from Monju with some simulated anomalies. The results of numerical experiments showed that the present technique can be utilizes as one of the methods for a hybrid-type diagnosis system.

Risk-based safety indicators

International Nuclear Information System (INIS)

Szikszai, T.

1997-01-01

The presentation discusses the following issues: The objectives of the risk-based indicator programme. The characteristics of the risk-based indicators. The objectives of risk-based safety indicators - in monitoring safety; in PSA applications. What indicators? How to produce the risk based indicators? PSA requirements

Supporting Case-Based Learning in Information Security with Web-Based Technology

Science.gov (United States)

He, Wu; Yuan, Xiaohong; Yang, Li

2013-01-01

Case-based learning has been widely used in many disciplines. As an effective pedagogical method, case-based learning is also being used to support teaching and learning in the domain of information security. In this paper, we demonstrate case-based learning in information security by sharing our experiences in using a case study to teach security…

A web-based data-querying tool based on ontology-driven methodology and flowchart-based model.

Science.gov (United States)

Ping, Xiao-Ou; Chung, Yufang; Tseng, Yi-Ju; Liang, Ja-Der; Yang, Pei-Ming; Huang, Guan-Tarn; Lai, Feipei

2013-10-08

Because of the increased adoption rate of electronic medical record (EMR) systems, more health care records have been increasingly accumulating in clinical data repositories. Therefore, querying the data stored in these repositories is crucial for retrieving the knowledge from such large volumes of clinical data. The aim of this study is to develop a Web-based approach for enriching the capabilities of the data-querying system along the three following considerations: (1) the interface design used for query formulation, (2) the representation of query results, and (3) the models used for formulating query criteria. The Guideline Interchange Format version 3.5 (GLIF3.5), an ontology-driven clinical guideline representation language, was used for formulating the query tasks based on the GLIF3.5 flowchart in the Protégé environment. The flowchart-based data-querying model (FBDQM) query execution engine was developed and implemented for executing queries and presenting the results through a visual and graphical interface. To examine a broad variety of patient data, the clinical data generator was implemented to automatically generate the clinical data in the repository, and the generated data, thereby, were employed to evaluate the system. The accuracy and time performance of the system for three medical query tasks relevant to liver cancer were evaluated based on the clinical data generator in the experiments with varying numbers of patients. In this study, a prototype system was developed to test the feasibility of applying a methodology for building a query execution engine using FBDQMs by formulating query tasks using the existing GLIF. The FBDQM-based query execution engine was used to successfully retrieve the clinical data based on the query tasks formatted using the GLIF3.5 in the experiments with varying numbers of patients. The accuracy of the three queries (ie, "degree of liver damage," "degree of liver damage when applying a mutually exclusive setting

Feature-Based Analysis of Plasma-Based Particle Acceleration Data

Energy Technology Data Exchange (ETDEWEB)

Rubel, Oliver [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Geddes, Cameron G. R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Chen, Min [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Cormier-Michel, Estelle [Tech-X Corp., Boulder, CO (United States); Bethel, E. Wes [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2014-02-01

Plasma-based particle accelerators can produce and sustain thousands of times stronger acceleration fields than conventional particle accelerators, providing a potential solution to the problem of the growing size and cost of conventional particle accelerators. To facilitate scientific knowledge discovery from the ever growing collections of accelerator simulation data generated by accelerator physicists to investigate next-generation plasma-based particle accelerator designs, we describe a novel approach for automatic detection and classification of particle beams and beam substructures due to temporal differences in the acceleration process, here called acceleration features. The automatic feature detection in combination with a novel visualization tool for fast, intuitive, query-based exploration of acceleration features enables an effective top-down data exploration process, starting from a high-level, feature-based view down to the level of individual particles. We describe the application of our analysis in practice to analyze simulations of single pulse and dual and triple colliding pulse accelerator designs, and to study the formation and evolution of particle beams, to compare substructures of a beam and to investigate transverse particle loss.

Composition and Vacancy Flux Effects in Tracer Diffusion in Silver-Gold Alloys; Effets de la Composition et du Flux de Lacunes sur la Diffusion des Indicateurs dans les Alliages d'Or et d'Argent; Vliyanie sostava i potoka vakansij pri diffuzii indikatorov v splavakh serebra i zolota; Efectos de la Composicion y del Flujo de Huecos Sobre la Difusion de Indicadores en Aleaciones Plata-Oro

Energy Technology Data Exchange (ETDEWEB)

Meyer, R. O.; Slifkin, L. [University of North Carolina, Chapel Hill, NC (United States)

1966-02-15

Self-diffusion studies in silver-gold alloys show that the activation energies decrease monotonically with increasing gold concentration. These results are not explained by theories based on corresponding states, size effects, or heats of solution; however, LeClaire's extension of Lazarus' electrostatic theory gives semiquantitative agreement. The decrease of the pre-exponential factors with increasing gold concentration indicates that the vacancy entropy of migration decreases linearly with composition by 1.5 R from pure silver to pure gold. For either tracer at a fixed temperature, the diffusion coefficient D versus composition exhibits a broad minimum. Using these data as a test of theories of vacancy-impurity interaction, only those of Manning and Lidiard give satisfactory and consistent results. Addition of the more mobile silver to the less mobile gold actually decreases D for both tracers; analysis indicates that the presence of a silver atom adjacent to a vacancy and a gold atom reduces the gold atom jump frequency by a factor of approximately 0.4. The existence of the broad minimum in the plot of D versus composition allows an investigation of the effect of a vacancy flux on tracer diffusion. A Kirkendall couple is prepared from compositions symmetrically displaced about the minimum. The interface contains a thin layer of gold tracer and is marked with fine particles of radioactive hafnium oxide. During the diffusion anneal the vacancy flux produces a drift of the centre of mass of the gold tracer distribution, which remains undistorted since D is almost independent of position. The fine, inert marker locates the original interface to within several microns. Results as of February, 1965 indicate drifts of the centre of the gold tracer distribution of approximately 20 microns toward the silver-rich end. (author) [French] Les etudes sur l'autodiffusion dans les alliages d'or et d'argent montrent que les energies d'activation decroissent de faqon monotone

Convex-based void filling method for CAD-based Monte Carlo geometry modeling

International Nuclear Information System (INIS)

Yu, Shengpeng; Cheng, Mengyun; Song, Jing; Long, Pengcheng; Hu, Liqin

2015-01-01

Highlights: • We present a new void filling method named CVF for CAD based MC geometry modeling. • We describe convex based void description based and quality-based space subdivision. • The results showed improvements provided by CVF for both modeling and MC calculation efficiency. - Abstract: CAD based automatic geometry modeling tools have been widely applied to generate Monte Carlo (MC) calculation geometry for complex systems according to CAD models. Automatic void filling is one of the main functions in the CAD based MC geometry modeling tools, because the void space between parts in CAD models is traditionally not modeled while MC codes such as MCNP need all the problem space to be described. A dedicated void filling method, named Convex-based Void Filling (CVF), is proposed in this study for efficient void filling and concise void descriptions. The method subdivides all the problem space into disjointed regions using Quality based Subdivision (QS) and describes the void space in each region with complementary descriptions of the convex volumes intersecting with that region. It has been implemented in SuperMC/MCAM, the Multiple-Physics Coupling Analysis Modeling Program, and tested on International Thermonuclear Experimental Reactor (ITER) Alite model. The results showed that the new method reduced both automatic modeling time and MC calculation time

Knowledge base mechanisms

Energy Technology Data Exchange (ETDEWEB)

Suwa, M; Furukawa, K; Makinouchi, A; Mizoguchi, T; Mizoguchi, F; Yamasaki, H

1982-01-01

One of the principal goals of the Fifth Generation Computer System Project for the coming decade is to develop a methodology for building knowledge information processing systems which will provide people with intelligent agents. The key notion of the fifth generation computer system is knowledge used for problem solving. In this paper the authors describe the plan of Randd on knowledge base mechanisms. A knowledge representation system is to be designed to support knowledge acquisition for the knowledge information processing systems. The system will include a knowledge representation language, a knowledge base editor and a debugger. It is also expected to perform as a kind of meta-inference system. In order to develop the large scale knowledge base systems, a knowledge base mechanism based on the relational model is to be studied in the earlier stage of the project. Distributed problem solving is also one of the main issues of the project. 19 references.

Iron-based amorphous alloys and methods of synthesizing iron-based amorphous alloys

Science.gov (United States)

Saw, Cheng Kiong; Bauer, William A.; Choi, Jor-Shan; Day, Dan; Farmer, Joseph C.

2016-05-03

A method according to one embodiment includes combining an amorphous iron-based alloy and at least one metal selected from a group consisting of molybdenum, chromium, tungsten, boron, gadolinium, nickel phosphorous, yttrium, and alloys thereof to form a mixture, wherein the at least one metal is present in the mixture from about 5 atomic percent (at %) to about 55 at %; and ball milling the mixture at least until an amorphous alloy of the iron-based alloy and the at least one metal is formed. Several amorphous iron-based metal alloys are also presented, including corrosion-resistant amorphous iron-based metal alloys and radiation-shielding amorphous iron-based metal alloys.

Comparing grapheme-based and phoneme-based speech recognition for Afrikaans

CSIR Research Space (South Africa)

Basson, WD

2012-11-01

Full Text Available This paper compares the recognition accuracy of a phoneme-based automatic speech recognition system with that of a grapheme-based system, using Afrikaans as case study. The first system is developed using a conventional pronunciation dictionary...

Culture and group-based emotions: could group-based emotions be dialectical?

Science.gov (United States)

Lu, Minjie; Hamamura, Takeshi; Doosje, Bertjan; Suzuki, Satoko; Takemura, Kosuke

2017-08-01

Group-based emotions are experienced when individuals are engaged in emotion-provoking events that implicate the in-group. This research examines the complexity of group-based emotions, specifically a concurrence of positive and negative emotions, focusing on the role of dialecticism, or a set of folk beliefs prevalent in Asian cultures that views nature and objects as constantly changing, inherently contradictory, and fundamentally interconnected. Study 1 found that dialecticism is positively associated with the complexity of Chinese participants' group-based emotions after reading a scenario depicting a positive intergroup experience. Study 2 found that Chinese participants experienced more complex group-based emotions compared with Dutch participants in an intergroup situation and that this cultural difference was mediated by dialecticism. Study 3 manipulated dialecticism and confirmed its causal effect on complex group-based emotions. These studies also suggested the role of a balanced appraisal of an intergroup situation as a mediating factor.

Interdisciplinarity in translation teaching: competence-based education, translation task-based approach, context-based text typology

Directory of Open Access Journals (Sweden)

Edelweiss Vitol Gysel

2017-05-01

Full Text Available In the context of competence-based teaching, this paper draws upon the model of Translation Competence (TC put forward by the PACTE group (2003 to establish a dialogue between cognitive-constructivist paradigms for translation teaching and the model of the Context-based Text Typology (MATTHIESSEN et al., 2007. In this theoretical environment, it proposes a model for the design of a Teaching Unit (TU for the development of the bilingual competence in would-be-translators.To this end, it explores translation as a cognitive, communicative and textual activity (HURTADO ALBIR, 2011 and considers its teaching from the translation task-based approach (HURTADO ALBIR, 1999. This approach is illustrated through the practical example of the design of a TU elaborated for the subject ‘Introduction to Specialized Translation’,part of the curricular grid of the program ‘Secretariado Executivo’ at Universidade Federal de Santa Catarina. Aspects such as the establishment of learning objectives and their alignment with the translation tasks composing the TU are addressed for this specific pedagogical situation. We argue for the development of textual competences by means of the acquisition of strategies derived from the Context-based Text Typology to solve problems arising from the translation of different text types and contextual configurations.

Evidence-Based Toxicology.

Science.gov (United States)

Hoffmann, Sebastian; Hartung, Thomas; Stephens, Martin

Evidence-based toxicology (EBT) was introduced independently by two groups in 2005, in the context of toxicological risk assessment and causation as well as based on parallels between the evaluation of test methods in toxicology and evidence-based assessment of diagnostics tests in medicine. The role model of evidence-based medicine (EBM) motivated both proposals and guided the evolution of EBT, whereas especially systematic reviews and evidence quality assessment attract considerable attention in toxicology.Regarding test assessment, in the search of solutions for various problems related to validation, such as the imperfectness of the reference standard or the challenge to comprehensively evaluate tests, the field of Diagnostic Test Assessment (DTA) was identified as a potential resource. DTA being an EBM discipline, test method assessment/validation therefore became one of the main drivers spurring the development of EBT.In the context of pathway-based toxicology, EBT approaches, given their objectivity, transparency and consistency, have been proposed to be used for carrying out a (retrospective) mechanistic validation.In summary, implementation of more evidence-based approaches may provide the tools necessary to adapt the assessment/validation of toxicological test methods and testing strategies to face the challenges of toxicology in the twenty first century.

Fabrication and characterization of Ag-Cd/CdO materials produced by incorporation of CdO particles to liquid Ag-Cd alloys; Fabricacion y caracterizacion de materiales Ag-Cd/CdO producidos mediante incorporacion de particulas de CdO en aleaciones Ag-Cd liquidas

Energy Technology Data Exchange (ETDEWEB)

Equihua-Guillen, F.; Ruiz-Mondragon, J.; Servin-Castaneda, R.; Orozco-Gonzalez, P.; Zaldivar-Cadena, A.; Martinez-Villafane, F.; Villarreal-Garza, E. J.

2014-04-01

In the present work it has been investigated the kinetic behavior of internal oxidation processes of strips of Ag-Cd/CdO materials fabricated by adding CdO particles (size of 5 and 20 {mu}m) in liquid Ag-Cd alloys. It has been established the metallurgical mechanism that controls the formation of the thickness covered with CdO particles produced by internal oxidation of the Ag-Cd/CdO material. It has been developed, successfully, a metallographic preparation technique for characterizing the morphology, size and distribution of CdO particles produced by heat treatment of internal oxidation on the surface of each sample based on the distance from the original surface to the boundary of dispersed CdO particles. The material strips were sequentially roughed on its surface and the roughing thickness was measured in the cross section of each new surface to determine the number of particles per area and average particle size. (Author)

Aperiodic-metamaterial-based absorber

Directory of Open Access Journals (Sweden)

Quanlong Yang

2017-09-01

Full Text Available The periodic-metamaterial-based perfect absorber has been studied broadly. Conversely, if the unit cell in the metamaterial-based absorber is arranged aperiodically (aperiodic-metamaterial-based absorber, how does it perform? Inspired by this, here we present a systematic study of the aperiodic-metamaterial-based absorber. By investigating the response of metamaterial absorbers based on periodic, Fibonacci, Thue-Morse, and quasicrystal lattices, we found that aperiodic-metamaterial-based absorbers could display similar absorption behaviors as the periodic one in one hand. However, their absorption behaviors show different tendency depending on the thicknesses of the spacer. Further studies on the angle and polarization dependence of the absorption behavior are also presented.

Concurrent array-based queue

Science.gov (United States)

Heidelberger, Philip; Steinmacher-Burow, Burkhard

2015-01-06

According to one embodiment, a method for implementing an array-based queue in memory of a memory system that includes a controller includes configuring, in the memory, metadata of the array-based queue. The configuring comprises defining, in metadata, an array start location in the memory for the array-based queue, defining, in the metadata, an array size for the array-based queue, defining, in the metadata, a queue top for the array-based queue and defining, in the metadata, a queue bottom for the array-based queue. The method also includes the controller serving a request for an operation on the queue, the request providing the location in the memory of the metadata of the queue.

Metal-mediated DNA base pairing: alternatives to hydrogen-bonded Watson-Crick base pairs.

Science.gov (United States)

Takezawa, Yusuke; Shionoya, Mitsuhiko

2012-12-18

With its capacity to store and transfer the genetic information within a sequence of monomers, DNA forms its central role in chemical evolution through replication and amplification. This elegant behavior is largely based on highly specific molecular recognition between nucleobases through the specific hydrogen bonds in the Watson-Crick base pairing system. While the native base pairs have been amazingly sophisticated through the long history of evolution, synthetic chemists have devoted considerable efforts to create alternative base pairing systems in recent decades. Most of these new systems were designed based on the shape complementarity of the pairs or the rearrangement of hydrogen-bonding patterns. We wondered whether metal coordination could serve as an alternative driving force for DNA base pairing and why hydrogen bonding was selected on Earth in the course of molecular evolution. Therefore, we envisioned an alternative design strategy: we replaced hydrogen bonding with another important scheme in biological systems, metal-coordination bonding. In this Account, we provide an overview of the chemistry of metal-mediated base pairing including basic concepts, molecular design, characteristic structures and properties, and possible applications of DNA-based molecular systems. We describe several examples of artificial metal-mediated base pairs, such as Cu(2+)-mediated hydroxypyridone base pair, H-Cu(2+)-H (where H denotes a hydroxypyridone-bearing nucleoside), developed by us and other researchers. To design the metallo-base pairs we carefully chose appropriate combinations of ligand-bearing nucleosides and metal ions. As expected from their stronger bonding through metal coordination, DNA duplexes possessing metallo-base pairs exhibited higher thermal stability than natural hydrogen-bonded DNAs. Furthermore, we could also use metal-mediated base pairs to construct or induce other high-order structures. These features could lead to metal-responsive functional

Selective Sequential Zero-Base Budgeting Procedures Based on Total Factor Productivity Indicators

OpenAIRE

A. Ishikawa; E. F. Sudit

1981-01-01

The authors' purpose in this paper is to develop productivity-based sequential budgeting procedures designed to expedite identification of major problem areas in bugetary performance, as well as to reduce the costs associated with comprehensive zero-base analyses. The concept of total factor productivity is reviewed and its relations to ordinary and zero-based budgeting are discussed in detail. An outline for a selective sequential analysis based on monitoring of three key indicators of (a) i...

Replacing fossil based plastic performance products by bio-based plastic products-Technical feasibility.

Science.gov (United States)

van den Oever, Martien; Molenveld, Karin

2017-07-25

Larger scale market introduction of new bio-based products requires a clear advantage regarding sustainability, as well as an adequate techno-economic positioning relative to fossil based products. In a previous paper [Broeren et al., 2016], LCA results per kg and per functionality equivalent of bio-based plastics were presented, together with economic considerations. The present paper discusses the mechanical and thermal properties of a range of commercially available bio-based plastics based on polylactic acid (PLA), cellulose esters, starch and polyamides, and the feasibility of replacing fossil-based counterparts based on performance. The evaluation is approached from an end user perspective. First, potentially suitable bio-based plastics are selected based on manufacturers' specifications in technical data sheets, then a first experimental evaluation is performed on injection moulded ISO specimens, and finally a further selection of plastics is tested on large 50×70cm panels. This technical feasibility study indicates that so far bio-based plastics do not completely match the properties of high performance materials like flame retardant V-0 PC/ABS blends used in electronic devices. The performance gap is being decreased by the development of stereocomplex PLA and hybrid PLA blends with polycarbonate, which offer clearly improved properties with respect to maximum usage temperature and toughness. In addition, several materials meet the V-0 flammability requirements needed in specific durable applications. On the other hand, improving these properties so far has negative consequences for the bio-based content. This study also shows that replacement of bulk polymers like PS is feasible using PLA compounds with a bio-based content as high as 85%. Copyright © 2016 Elsevier B.V. All rights reserved.

From scientifically based research to evidence based learning

Directory of Open Access Journals (Sweden)

Rosa Cera

2016-02-01

Full Text Available This essay is a reflection on the peculiarities of the scientifically based research and on the distinctive elements of the EBL (evidence based learning, methodology used in the study on the “Relationship between Metacognition, Self-efficacy and Self-regulation in Learning”. The EBL method, based on the standardization of data, explains how the students’ learning experience can be considered as a set of “data” and can be used to explain how and when the research results can be considered generalizable and transferable to other learning situations. The reflections present in this study have also allowed us to illustrate the impact that its results have had on the micro and macro level of reality. They helped to fill in the gaps concerning the learning/teaching processes, contributed to the enrichment of the scientific literature on this subject and allowed to establish standards through rigorous techniques such as systematic reviews and meta-analysis.

Space Launch System Base Heating Test: Environments and Base Flow Physics

Science.gov (United States)

Mehta, Manish; Knox, Kyle S.; Seaford, C. Mark; Dufrene, Aaron T.

2016-01-01

The NASA Space Launch System (SLS) vehicle is composed of four RS-25 liquid oxygen- hydrogen rocket engines in the core-stage and two 5-segment solid rocket boosters and as a result six hot supersonic plumes interact within the aft section of the vehicle during ight. Due to the complex nature of rocket plume-induced ows within the launch vehicle base during ascent and a new vehicle con guration, sub-scale wind tunnel testing is required to reduce SLS base convective environment uncertainty and design risk levels. This hot- re test program was conducted at the CUBRC Large Energy National Shock (LENS) II short-duration test facility to simulate ight from altitudes of 50 kft to 210 kft. The test program is a challenging and innovative e ort that has not been attempted in 40+ years for a NASA vehicle. This presentation discusses the various trends of base convective heat ux and pressure as a function of altitude at various locations within the core-stage and booster base regions of the two-percent SLS wind tunnel model. In-depth understanding of the base ow physics is presented using the test data, infrared high-speed imaging and theory. The normalized test design environments are compared to various NASA semi- empirical numerical models to determine exceedance and conservatism of the ight scaled test-derived base design environments. Brief discussion of thermal impact to the launch vehicle base components is also presented.

The physics data base

International Nuclear Information System (INIS)

Gault, F.D.

1984-01-01

The physics data base is introduced along with its associated data base management system. The emphasis is on data and their use and a classification of data and of data bases is developed to distinguish compilation organizations. The characteristics of these organizations are examined briefly and the long term consequences of the physics data base discussed. (orig.)

Glow discharge preparation and electrooptical characterisation of amorphous silicon alloys for solar cells. Preparacion por descarga luminiscente y caracterizacion electrooptica de aleaciones de silicio amorfo para celulas solares

Energy Technology Data Exchange (ETDEWEB)

Carabe, J

1990-11-01

A study is presented, focused on the preparation and characterisation of hydrogenated amorphous silicon alloy thin films for their application as p type window layers in pin silicon solar cells. The preparation technique used was radio frequency glow discharge. The samples were characterised optically (visible, near infrared and infrared absorption spectrophotometry) and electrically (dark and photoconductivities at ambient temperature and as functions of temperature). The influence of each of the preparation parameters on film properties has been systematically studied. The results have been analysed according to the existing models. Chapter 1 is an introduction to the material in question and its photovoltaic applications. Chapter 2 describes the experimental procedure used. Capter 3 shows and discusses the most relevant results obtained in the study of intrinsic amorphous silicon, p type amorphous silicon and p type amorphous silicon carbide window layers, with special emphasis on the influence of the use of an alternative dopant gas: boron trifluoride. Finally, chapter 4 summarises the most relevant conclusions drawn from this research work. (Author)

Characteristic properties of Fibonacci-based mutually unbiased bases

Energy Technology Data Exchange (ETDEWEB)

Seyfarth, Ulrich; Alber, Gernot [Institut fuer Angewandte Physik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Ranade, Kedar [Institut fuer Quantenphysik, Universitaet Ulm, Albert-Einstein-Allee 11, 89069 Ulm (Germany)

2012-07-01

Complete sets of mutually unbiased bases (MUBs) offer interesting applications in quantum information processing ranging from quantum cryptography to quantum state tomography. Different construction schemes provide different perspectives on these bases which are typically also deeply connected to various mathematical research areas. In this talk we discuss characteristic properties resulting from a recently established connection between construction methods for cyclic MUBs and Fibonacci polynomials. As a remarkable fact this connection leads to construction methods which do not involve any relations to mathematical properties of finite fields.

Querying archetype-based EHRs by search ontology-based XPath engineering.

Science.gov (United States)

Kropf, Stefan; Uciteli, Alexandr; Schierle, Katrin; Krücken, Peter; Denecke, Kerstin; Herre, Heinrich

2018-05-11

Legacy data and new structured data can be stored in a standardized format as XML-based EHRs on XML databases. Querying documents on these databases is crucial for answering research questions. Instead of using free text searches, that lead to false positive results, the precision can be increased by constraining the search to certain parts of documents. A search ontology-based specification of queries on XML documents defines search concepts and relates them to parts in the XML document structure. Such query specification method is practically introduced and evaluated by applying concrete research questions formulated in natural language on a data collection for information retrieval purposes. The search is performed by search ontology-based XPath engineering that reuses ontologies and XML-related W3C standards. The key result is that the specification of research questions can be supported by the usage of search ontology-based XPath engineering. A deeper recognition of entities and a semantic understanding of the content is necessary for a further improvement of precision and recall. Key limitation is that the application of the introduced process requires skills in ontology and software development. In future, the time consuming ontology development could be overcome by implementing a new clinical role: the clinical ontologist. The introduced Search Ontology XML extension connects Search Terms to certain parts in XML documents and enables an ontology-based definition of queries. Search ontology-based XPath engineering can support research question answering by the specification of complex XPath expressions without deep syntax knowledge about XPaths.

Problem Based Learning

DEFF Research Database (Denmark)

de Graaff, Erik; Guerra, Aida

, the key principles remain the same everywhere. Graaff & Kolmos (2003) identify the main PBL principles as follows: 1. Problem orientation 2. Project organization through teams or group work 3. Participant-directed 4. Experiental learning 5. Activity-based learning 6. Interdisciplinary learning and 7...... model and in general problem based and project based learning. We apply the principle of teach as you preach. The poster aims to outline the visitors’ workshop programme showing the results of some recent evaluations.......Problem-Based Learning (PBL) is an innovative method to organize the learning process in such a way that the students actively engage in finding answers by themselves. During the past 40 years PBL has evolved and diversified resulting in a multitude in variations in models and practices. However...

High stability vector-based direct power control for DFIG-based wind turbine

DEFF Research Database (Denmark)

Zhu, Rongwu; Chen, Zhe; Wu, Xiaojie

2015-01-01

This paper proposes an improved vector-based direct power control (DPC) strategy for the doubly-fed induction generator (DFIG)-based wind energy conversion system. Based on the small signal model, the proposed DPC improves the stability of the DFIG, and avoids the DFIG operating in the marginal...

Research on Fault Diagnosis Method Based on Rule Base Neural Network

Directory of Open Access Journals (Sweden)

Zheng Ni

2017-01-01

Full Text Available The relationship between fault phenomenon and fault cause is always nonlinear, which influences the accuracy of fault location. And neural network is effective in dealing with nonlinear problem. In order to improve the efficiency of uncertain fault diagnosis based on neural network, a neural network fault diagnosis method based on rule base is put forward. At first, the structure of BP neural network is built and the learning rule is given. Then, the rule base is built by fuzzy theory. An improved fuzzy neural construction model is designed, in which the calculated methods of node function and membership function are also given. Simulation results confirm the effectiveness of this method.

A comparative review of petroleum-based and bio-based acrolein production.

Science.gov (United States)

Liu, Lu; Ye, X Philip; Bozell, Joseph J

2012-07-01

Acrolein is an important chemical intermediate for many common industrial chemicals, leading to an array of useful end products. This paper reviews all the synthetic methods, including the former (aldol condensation) and contemporary (partial oxidation of propylene) manufacturing methods, the partial oxidation of propane, and most importantly, the bio-based glycerol-dehydration route. Emphasis is placed on the petroleum-based route from propylene and the bio-based route from glycerol, an abundantly available and relatively inexpensive raw material available from biodiesel production. This review provides technical details and incentives for industrial proyduction that justify a transition toward bio-based acrolein production. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Value-based pricing

OpenAIRE

Netseva-Porcheva Tatyana

2010-01-01

The main aim of the paper is to present the value-based pricing. Therefore, the comparison between two approaches of pricing is made - cost-based pricing and value-based pricing. The 'Price sensitively meter' is presented. The other topic of the paper is the perceived value - meaning of the perceived value, the components of perceived value, the determination of perceived value and the increasing of perceived value. In addition, the best company strategies in matrix 'value-cost' are outlined. .

Research-based design & design-based research: Affordances, limitations and synergies

NARCIS (Netherlands)

McKenney, Susan

2015-01-01

Research-based design is an orientation to educational development that is explicitly informed by existing research as well as formative evaluation. Design-based research is a genre of inquiry in which the design of innovative solutions to problems in educational practice provides the context for

Autopsy practice in forensic pathology - Evidence-based or experience-based?

DEFF Research Database (Denmark)

Colville-Ebeling, Bonnie; Freeman, Michael; Banner, Jytte

2014-01-01

Current autopsy practice in forensic pathology is to a large extent based on experience and individual customary practices as opposed to evidence and consensus based practices. As a result there is the potential for substantial variation in how knowledge is applied in each case. In the present case......-gathering and the use of check lists specific to certain injury causes are likely to result in less deviation from evidence-based practices in forensic pathology. Pre-autopsy data-gathering and check lists will help ensure a higher degree of standardization in autopsy reports thus enhancing the quality and accuracy...

Value-based management: Theoretical base, shareholders' request and the concept

Directory of Open Access Journals (Sweden)

Kaličanin Đorđe M.

2005-01-01

Full Text Available The pressure of financial markets, which is a consequence of shareholder revolution, directly affects the solution to the following dilemma: is the mission of corporations to maximize shareholders' wealth or to satisfy interests of other stakeholders? The domination of shareholder theory has caused the appearance of the valuebased management concept. Value-based management is a relevant concept and a process of management in modern environment. The importance of shareholder value requires transformation of traditional enterprise into value driven enterprise. This paper addresses theoretical base, shareholder revolution and the main characteristics of value-based management.

Elucidating the hard/soft acid/base principle: A perspective based on half-reactions

International Nuclear Information System (INIS)

Ayers, Paul W.; Parr, Robert G.; Pearson, Ralph G.

2006-01-01

A comprehensive analysis is presented for the acid-base double-exchange reaction as well as the associated acid-displacement and base-displacement 'half-reactions' with the goal of elucidating the meaning of the hard/soft acid/base (HSAB) principle and the conditions for its validity. When electron-transfer effects are important and other effects are negligible, the HSAB principle is driven by the surpassing stability of the soft acid/soft base product. When electrostatic effects dominate the reactivity, the HSAB principle is driven by the surpassing stability of the hard acid/hard base product. Because electron-transfer effects favor soft/soft interactions, while electrostatic effects favor hard/hard interactions, acid-base exchange reactions may be used to determine whether a reagent's reactivity is dominated by electron-transfer or by electrostatic effects. Because electron-transfer and electrostatic considerations separately favor the HSAB principle whenever the electronic chemical potentials of the acids and bases involved in the reaction are similar, our analysis provides strong support for the HSAB principle. The electronic chemical potential measures the intrinsic strength of acids and bases

Disolución de sílice biogénica en sedimentos de lagos utilizados como bioindicadores de calidad del agua

Directory of Open Access Journals (Sweden)

Hermes U. Ramírez S.

2007-01-01

Full Text Available El objetivo de este trabajo es mostrar que la disoluci n de s lice amorfa de origen biog nico (diatomeas y fitolitos es un bioindicador de calidad del agua de lagos, valid ndose con la determinaci n de par metros f sico-qu micos. La determinaci n de diatomeas y fitolitos se realiz sobre n cleos de sedimentos del Lago Chapala, M xico. Las diatomeas y fitolitos fueron separados, depositados en laminillas y observados con microscop a de luz polarizada y electr nica de barrido. En forma paralela se analiz la calidad del agua del lago durante la d cada de 1990-2000 monitoreando 38 par metros f sicoqu micos en 25 estaciones. El estudio de diatomeas evidenci que la mayor a de ellos presentan fr stulas no preservadas, alto grado de disoluci n, fitolitos fragmentados y/o disueltos y una importante cantidad de debris de s lice. La determinaci n de fitolitos fue deficiente, con m s diatomeas en estado de disoluci n y debris de s lice opalino que fitolitos. Los resultados del an lisis f sico-qu mico del agua muestran valores de pH de 7,20-9,45, altas concentraciones de: nitr geno org nico (1,57 mg/l, nitr geno amoniacal (0,48 mg/l, nitratos (0,18 mg/l, f sforo org nico (0,16 mg/l, ortofosfatos (0,40 mg/l, f sforo total (0,57 mg/l y conductividad (867,53 S/cm lo que refleja altas concentraciones de sales, sobresaturaci n de CaCO3 con dureza total y c lcica de 221,35 y 142,67 mg/l respectivamente; alcalinidad total y c lcica de 307,29 y 29,90 mg/l respectivamente; todos factores que influyen en la disoluci n de diatomeas y fitolitos en los lechos del lago. Los resultados del estudio micropaleontol gico del Lago de Chapala han evidenciado disoluci n de diatomeas, fitolitos y la presencia de gran cantidad de debris de s lice amorfo y baja calidad de sus aguas, lo cual ha sido verificado con los par metros fisicoqu micos de la ultima d cada. Los fen menos de disoluci n de diatomeas y fitolitos por el momento son asociados a valores de pH>9, a condiciones eutr

Cristalización de vidrios ricos en sílice preparados mediante sol-gel en el sistema alúmina-circona-sílice

Directory of Open Access Journals (Sweden)

Popa, M.

2004-02-01

Full Text Available The crystallization of ZrSiO4 and its evolution with temperature from chemically homogeneous alumina-silica-zirconia powders prepared by sol-gel method from alcoxide mixtures was studied in the silica-rich region. A glass with the same composition was obtained by quenching in water from the melt. The gel-glasses evolution and microstructure were studied by means of XRD, IR and SEM/EDX, in the range of temperatures up to 1650oC. The materials consisted mainly of amorphous phase up to 1200oC, at which partial crystallization of cristobalite was observed. IR spectroscopy analysis showed zircon bands after thermal treatment at 1200oC. The crystallization of zircon and zirconia particles at 1550oC was confirmed by SEM/EDX analysis. At 1650oC the only stable crystalline phase observed after 40 h of thermal treatment was zircon.

La cristalización de ZrSiO4 y su evolución con la temperatura se ha estudiado en la región rica en sílice, a partir de polvos amorfos y químicamente homogéneos de alumina-sílice-circona, preparados mediante método sol-gel usando mezclas de alcóxidos. Se obtuvo un vidrio con idéntica composición mediante enfriamiento rápido por inmersión en agua del material fundido. La evolución y la microestructura de los vidrios obtenidos se estudió mediante difracción de rayos X, infrarrojos, microscopía electrónica de barrido y análisis químico, en el rango de temperaturas hasta 1650oC. Los materiales están formados principalmente por fase amorfa hasta 1200oC, temperatura a la cual se observa la cristalización parcial de cristobalita. El análisis por espectroscopía de infrarrojos muestra bandas de circón en muestras tratadas térmicamente por encima de 1200oC. Las observaciones mediante microscopía electrónica confirman la cristalización de partículas de circón y circona a 1550oC. A 1650oC la cristobalita ha fundido y la única fase cristalina estable detectada mediante XRD tras 40 h a esta temperatura

Anatomía de la dispersión urbana en Barcelona

Directory of Open Access Journals (Sweden)

Iván Muñiz

2013-01-01

Full Text Available No existe una definición comúnmente aceptada de dispersión urbana (urban sprawl, de modo que la investigación aplicada ha trabajado con diferentes indicadores que pretenden a su vez capturar los distintos significados con que se ha dotado al término. En este trabajo se mide cómo ha evolucionado la dispersión de la población y del empleo de la Región Metropolitana de Barcelona (RMB entre 1986 y 2001. Las dimensiones exploradas se dividen en dos grupos: i forma urbana (desconcentración, baja densidad y discontinuidad y ii estructura urbana. A diferencia de algunos trabajos donde el policentrismo y el crecimiento lineal se presentan como dos formas de dispersión, en nuestro caso contraponemos la idea de expansión urbana estructurada (lineal o policéntrica con la de expansión urbana desestructurada (amorfa, caótica o aleatoria, equiparando esta última con la cuarta dimensión de la dispersión. Los resultados obtenidos indican que la población y el empleo de la RMB se han descentralizado de forma desconcentrada y la densidad residencial se ha reducido. Sin embargo, la RMB no ha crecido de forma discontinua ni desestructurada, sino todo lo contrario.There is no commonly accepted definition of urban sprawl, and therefore applied research has worked with different indicators aiming to grasp the diverse meanings assigned to the term. This study measures how the dispersion of population and employment in the Barcelona Metropolitan Region (BMR developed between 1986 and 2001. The dimensions that were investigated are divided into two groups. The first one involves dimensions of urban form (decentralization, low density and discontinuity, and the second, of urban structure. As opposed to some studies, where polycentrism and linear growth are presented as two forms of sprawl, in our case we contrast the idea of structured urban expansion (linear or poly-centric with de structured urban expansion (amorphous, chaotic or random, identifying

Odontoma compuesto. Una patología oral a considerar

Directory of Open Access Journals (Sweden)

Jonathan Harris Ricardo

2013-10-01

Full Text Available Resumen El odontoma es el tumor odontogénico mixto con mayor frecuencia de aparición, las células y los tejidos son normales pero de estructura defectuosa, la etiología se le relaciona con restos paradentales de malassez y traumatismos, son de crecimiento limitado, asintomáticos, producen retención dentaria; se clasifica en compuesto y complejo, radiográficamente se presenta halo radiolúcido con múltiples imágenes radiopacas en su interior, con un patrón ordenado para el odontoma compuesto y en el odontoma complejo se presenta imagen radiopaca como conglomeraciones amorfas, con un patrón desordenado. El tratamiento es quirúrgico y su recurrencia es baja. Se reporta caso de paciente femenina de 30 años de edad, que acudió a la consulta del servicio de estomatología y cirugía oral de la Universidad de Cartagena Colombia, porque presentó, lesión tumoral que comprometía la zona de órganos dentarios 33 y 34, se realizó examen radiográfico, con diagnóstico presuntivo de odontoma compuesto, se programó la cirugía y se realizó enucleación de la lesión tumoral la cual se envió a patología; en el reporte histopatológico se diagnosticó odontoma compuesto. (DUAZARY 2010, 91 - 94Abstract The odontoma is the mixed odontogenic tumor observed with greater frequency. Cells and tissues are normal in structure but is defective in pattern. Etiology is associated with remainders of malassez paradentales tissues and trauma and injuries. They are growing limited, asymptomatic, produce tooth retention. They were classified as compound and complex radiographic radiolucent halo is presented with multiple radiopaque images inside it, with a pattern for the ordered compound odontoma and complex odontoma presents the image as radiopaque amorphous clusters with a disordered pattern. The treatment is surgical and recurrence is low. We report the case of female patient aged 30, who attended the service of dentistry and oral surgery at the

La Problemática de los fenómenos naturales: potenciales efectos de la erupción del Complejo Volcánico Puyehue-Cordón Caulle (CVPCC sobre la salud humana y el medio ambiente en distintos sectores de la localidad de Villa la Angostura, Neuquén

Directory of Open Access Journals (Sweden)

Maria Elena Canafoglia

2012-12-01

Full Text Available El trabajo aborda la problemática ambiental de una zona de riesgo volcánico localizada al sur del paralelo 33°, focalizando la atención en el estudio de cenizas de caída reciente o removilizadas por el viento, cinco meses después del inicio de la erupción del Complejo Volcánico Puyehue-Cordón Caulle (CVPCC en junio de 2011. El muestreo se realizó en tres zonas de Villa La Angostura situada a 40 Km al E del foco emisor: (Laguna Piré, Tres Cerros y Escuela CPEM N°17. Considerando los efectos socio-económico-sanitarios de la caída de cenizas en dicha comunidad se ha encarado el estudio de la caracterización físico química de la fracción mas fina del material volcánico (100-5?m. El trabajo, realizado conjuntamente con docentes de la CPEM N°17, se ha efectuado mediante la aplicación de diversas técnicas como difracción por rayos X (DRX, microscopia electrónica (SEM y análisis químico por microsonda (EDS-EDAX. Los resultados de DRX indican que en general la fracción fina es prácticamente amorfa y procede de un proceso de fragmentación de material pumíceo. Sin embargo, eventualmente se observan  algunas líneas de difracción de fases silíceas, particularmente plagioclasa. La morfología del material fino, de composición riolítica (relación SiO2/Al2O3 del orden de 5, se caracteriza por la presencia de bordes agudos y fractura concoide. Presenta contenidos menores en hierro, alcalinos y alcalino-térreos. Se han realizado ensayos químicos adicionales a fin de analizar la alteración del material y su relación con los efectos de corrosión observados en la zona. El conocimiento del material en contacto con la población así como la continuidad en la emisión de particulado fino y la re-movilización del mismo por los vientos, es de vital importancia en lo que se refiere a las acciones de prevención y mitigación de problemas vinculados a la salud y al cuidado del medio ambiente.

Scaling control in superficial installations at the Las Tres Virgenes, geothermal field, BCS; Control de incrustacion en instalaciones superficiales del campo geotermico de Las Tres Virgenes, BCS

Energy Technology Data Exchange (ETDEWEB)

Tapia Salazar, Ruth [Comision Federal de Electricidad (Mexico)]. E-mail: ruth.tapia@cfe.gob.mx

2007-01-15

Silica scaling is one of the most important problems in the Las Tres Virgenes geothermal field. It affects not only the superficial installations, like brine injection pipelines, but also the injection wells where it reduces injection capacity. Separated brine passes from production wells to injection wells by means of steel pipelines 10 and 14 inches in diameter. The pipelines are affected by silica scaling that occurs when the two-phase fluid is discharged at atmospheric pressure and the separated brine is cooled and concentrated and then over saturated with amorphous silica. Even when the pipelines were cleaned periodically, it was necessary to implement a technique for prevent scaling. Two methods considered appropriate to the specific field conditions were studied, and finally the technique of modifying the brine pH was adopted. After over a year of using this technique in the general injection system, no mechanical cleaning of the pipelines has been necessary-and once cleaning was needed at least every third day. This represents an important improvement in the steam supply system. [Spanish] Uno de los problemas mas importantes en el campo geotermico de Las Tres Virgenes es la incrustacion por silice, la cual afecta no solo a instalaciones superficiales como lineas de inyeccion de salmuera, sino tambien a los pozos inyectores al reducir su capacidad de aceptacion. El agua producida por los pozos productores se conduce hasta los pozos inyectores por medio de tuberias de acero al carbon de 10 y 14 pulgadas de diametro, que se ven afectadas por la incrustacion de silice. La incrustacion ocurre debido a que cuando el fluido en dos fases es descargado a presion atmosferica, la salmuera separada, enfriada y concentrada, esta usualmente sobresaturada con respecto a la solubilidad de la silice amorfa. Aunque las tuberias se limpiaban mecanicamente, fue necesario seleccionar una tecnica para prevenir la incrustacion, para lo cual se estudiaron dos de los metodos que

Estudo comparativo de amidos termoplásticos derivados do milho com diferentes teores de amilose Comparative studies of corn thermoplastic starches with different amylose content

Directory of Open Access Journals (Sweden)

Elisângela Corradini

2005-11-01

Full Text Available Amidos de milho contendo aproximadamente 72 e 100 % de amilopectina foram convertidos em amidos termoplásticos por processamento em um misturador intensivo a 160 ºC, usando glicerol como plastificante. Os amidos termoplásticos foram condicionados em ambiente de 53 ± 2% u.r. e caracterizados por medidas de absorção de água, difração de raios X, ensaios mecânicos de tração e por análises dinâmico mecânicas (DMA. O amido com menor teor de amilopectina apresentou maior viscosidade durante o processamento, que foi atribuída à estrutura da amilose. Os amidos termoplásticos TPS1 (72% de amilopectina e TPS2 (100% de amilopectina não mostraram diferenças apreciáveis nas propriedades de absorção de água. Após duas semanas de armazenamento, o TPS1 apresentou estrutura semicristalina, enquanto o TPS2 apresentou estrutura totalmente amorfa. Após seis semanas ocorreu um aumento da cristalinidade do TPS1 e ocorreu a formação de estruturas cristalinas no TPS2. As propriedades mecânicas e dinâmico-mecânicas foram afetadas pela cristalinidade do amido que é função da razão amilose/amilopectina.Corn starches with approximately 72% and 100 % of amylopectin were processed in an intensive mixer connected to a torque rheometer in the presence of glycerol (plasticizer at 160ºC. The thermoplastic starches were conditioned at 53 ± 2% of relative humidity for two weeks and characterized by X-ray diffraction, tensile test and dynamical mechanical analysis (DMA. The starch with lower amylopectin content presented higher viscosity during the processing which was attributed to linear amylose chains. The thermoplastic starches TPS1 (72% of amylopectin and TPS2 (100% of amylopectin did not display significant differences in water absorption. After two weeks of aging, TPS1 exhibited semicrystalline structure, whereas TPS2 presented a amorphous structure. After six weeks, the crystallinity of TPS1 increased and some crystalline behavior could

Síntesis por implantación iónica de nanocristales semiconductores para dispositivos en tecnología de Si

Directory of Open Access Journals (Sweden)

Pérez-Rodríguez, A.

2000-08-01

Full Text Available In this paper, we present the synthesis and the detailed characterisation of elemental and compound semiconducting nanoparticles ion beam synthesised in SiO2. In the case of Si nanoparticles, a systematic study has been developed in order to make the link between the characteristics of the precipitates and the optical properties. Ge nanoparticles, which emission is weak but having a strong contrast in Transmission Electron Microscopy, have been fabricated in order to develop a new method of precipitate density measurement. On the other hand, ZnS nanocrystals doped with Mn have been synthesised for the first time with this technique and show a PL emission centred at 2.12 eV, characteristics of an intra-Mn transition. Moreover, the first optical results of Si+ and C+ co-implanted layers are presented here and show three PL emissions, linked to the presence of three different types of nanoparticles. The simultaneous emission of these three peaks has allowed the observation of an intense white light.

En este artículo se estudia la síntesis de nanocristales semiconductores elementales y compuestos elaborados por implantación iónica en SiO2. En el caso de los nanocristales de Si, se ha desarrollado un estudio sistemático que correlaciona las características de los precipitados y sus propiedades de luminiscencia. Nanopartículas de Ge, que presentan menor emisión pero mayor contraste en Microscopía Electrónica de Transmisión, han sido fabricadas para desarrollar un nuevo método de medida de la densidad de nanocristales en matrices amorfas. Por otro lado, nanopartículas de ZnS dopadas con Mn han sido elaboradas por primera vez con esta técnica, observando la emisión de un pico de luminescencia característico de una transición intra-Mn. Finalmente, se presentan los primeros resultados ópticos de capas coimplantadas con Si+ y C+, que muestran la presencia de tres picos intensos de luminescencia en las regiones roja, verde y azul

Substâncias ergásticas foliares de espécies amazônicas de Oenocarpus Mart. (Arecaceae: caracterização histoquímica e ultra-estrutural Leaf ergastic substances of Amazonian species of Oenocarpus Mart. (Arecaceae: histochemical and ultrastructural characterization

Directory of Open Access Journals (Sweden)

Rolf Junior Ferreira Silva

2009-01-01

Full Text Available O presente estudo teve por objetivo diagnosticar e caracterizar as substâncias ergásticas foliares de Oenocarpus bacaba Mart., O. distichus Mart., O. mapora H. Karst. e O. minor Mart. através de microscopias óptica e eletrônica de varredura, análises histoquímicas e microanálises físicas. Secções transversais e longitudinais, assim como maceração foram realizadas em material botânico fixado. As análises histoquímicas foram empregadas em material botânico in natura, seguindo-se protocolos específicos para mucilagem, amido e sílica. Microanálises físicas foram feitas com Energy Dispersive Spectroscopy (EDS detector. Nas espécies estudadas de Oenocarpus Mart., as substâncias ergásticas foliares correspondem a mucilagem amorfa; grãos de amido poliédricos do tipo simples e sílica opalina sob a forma de corpos elípticos e esféricos-globosos de superfície espiculada, ambos com elevado teor de dióxido de silício. As observações microscópicas, os testes histoquímicos e as microanálises físicas permitiram diagnosticar, caracterizar e elucidar a estrutura e ultra-estrutura das substâncias ergásticas ocorrentes nas folhas dos táxons analisados de Oenocarpus Mart.The purpose of this study was to diagnose and characterize the leaf ergastic substance of Oenocarpus bacaba Mart., O. distichus Mart., O. mapora H. Karst. and O. minor Mart. by light and scanning electron microscopy, histochemical analyses and physical microanalyses. Transverse and longitudinal sections as well as maceration were made in fixed botanical material. The histochemical analyses were made in non-fixed botanical material, using specific tests for mucilage, starch and silica. An Energy Dispersive Spectroscopy (EDS detector was used for the physical microanalyses. In the Oenocarpus Mart. species studied, the leaf ergastic substances corresponded to amorphous mucilage, simple-type polyhedrical starch grain and opaline silica in the shape of elliptical

Base-By-Base: single nucleotide-level analysis of whole viral genome alignments.

Science.gov (United States)

Brodie, Ryan; Smith, Alex J; Roper, Rachel L; Tcherepanov, Vasily; Upton, Chris

2004-07-14

With ever increasing numbers of closely related virus genomes being sequenced, it has become desirable to be able to compare two genomes at a level more detailed than gene content because two strains of an organism may share the same set of predicted genes but still differ in their pathogenicity profiles. For example, detailed comparison of multiple isolates of the smallpox virus genome (each approximately 200 kb, with 200 genes) is not feasible without new bioinformatics tools. A software package, Base-By-Base, has been developed that provides visualization tools to enable researchers to 1) rapidly identify and correct alignment errors in large, multiple genome alignments; and 2) generate tabular and graphical output of differences between the genomes at the nucleotide level. Base-By-Base uses detailed annotation information about the aligned genomes and can list each predicted gene with nucleotide differences, display whether variations occur within promoter regions or coding regions and whether these changes result in amino acid substitutions. Base-By-Base can connect to our mySQL database (Virus Orthologous Clusters; VOCs) to retrieve detailed annotation information about the aligned genomes or use information from text files. Base-By-Base enables users to quickly and easily compare large viral genomes; it highlights small differences that may be responsible for important phenotypic differences such as virulence. It is available via the Internet using Java Web Start and runs on Macintosh, PC and Linux operating systems with the Java 1.4 virtual machine.

Value-based pricing

Directory of Open Access Journals (Sweden)

Netseva-Porcheva Tatyana

2010-01-01

Full Text Available The main aim of the paper is to present the value-based pricing. Therefore, the comparison between two approaches of pricing is made - cost-based pricing and value-based pricing. The 'Price sensitively meter' is presented. The other topic of the paper is the perceived value - meaning of the perceived value, the components of perceived value, the determination of perceived value and the increasing of perceived value. In addition, the best company strategies in matrix 'value-cost' are outlined. .

An Analysis of Delay-based and Integrator-based Sequence Detectors for Grid-Connected Converters

DEFF Research Database (Denmark)

Khazraj, Hesam; Silva, Filipe Miguel Faria da; Bak, Claus Leth

2017-01-01

-signal cancellation operators are the main members of the delay-based sequence detectors. The aim of this paper is to provide a theoretical and experimental comparative study between integrator and delay based sequence detectors. The theoretical analysis is conducted based on the small-signal modelling......Detecting and separating positive and negative sequence components of the grid voltage or current is of vital importance in the control of grid-connected power converters, HVDC systems, etc. To this end, several techniques have been proposed in recent years. These techniques can be broadly...... classified into two main classes: The integrator-based techniques and Delay-based techniques. The complex-coefficient filter-based technique, dual second-order generalized integrator-based method, multiple reference frame approach are the main members of the integrator-based sequence detector and the delay...

Gender-based violence and the need for evidence-based primary ...

African Journals Online (AJOL)

Gender-based violence is a significant problem globally and in South Africa. The public and political discourse has been dominated by calls for increased penalties and convictions for perpetrators of various types of gender-based violence. However, these responses are unlikely to prevent such violence from occurring in ...

Skull base tumours part I: Imaging technique, anatomy and anterior skull base tumours

Energy Technology Data Exchange (ETDEWEB)

Borges, Alexandra [Instituto Portugues de Oncologia Francisco Gentil, Centro de Lisboa, Servico de Radiologia, Rua Professor Lima Basto, 1093 Lisboa Codex (Portugal)], E-mail: borgesalexandra@clix.pt

2008-06-15

Advances in cross-sectional imaging, surgical technique and adjuvant treatment have largely contributed to ameliorate the prognosis, lessen the morbidity and mortality of patients with skull base tumours and to the growing medical investment in the management of these patients. Because clinical assessment of the skull base is limited, cross-sectional imaging became indispensable in the diagnosis, treatment planning and follow-up of patients with suspected skull base pathology and the radiologist is increasingly responsible for the fate of these patients. This review will focus on the advances in imaging technique; contribution to patient's management and on the imaging features of the most common tumours affecting the anterior skull base. Emphasis is given to a systematic approach to skull base pathology based upon an anatomic division taking into account the major tissue constituents in each skull base compartment. The most relevant information that should be conveyed to surgeons and radiation oncologists involved in patient's management will be discussed.

Applications of lipid based formulation technologies in the delivery of biotechnology-based therapeutics.

Science.gov (United States)

du Plessis, Lissinda H; Marais, Etienne B; Mohammed, Faruq; Kotzé, Awie F

2014-01-01

In the last decades several new biotechnologically-based therapeutics have been developed due to progress in genetic engineering. A growing challenge facing pharmaceutical scientists is formulating these compounds into oral dosage forms with adequate bioavailability. An increasingly popular approach to formulate biotechnology-based therapeutics is the use of lipid based formulation technologies. This review highlights the importance of lipid based drug delivery systems in the formulation of oral biotechnology based therapeutics including peptides, proteins, DNA, siRNA and vaccines. The different production procedures used to achieve high encapsulation efficiencies of the bioactives are discussed, as well as the factors influencing the choice of excipient. Lipid based colloidal drug delivery systems including liposomes and solid lipid nanoparticles are reviewed with a focus on recent advances and updates. We further describe microemulsions and self-emulsifying drug delivery systems and recent findings on bioactive delivery. We conclude the review with a few examples on novel lipid based formulation technologies.

Skull base tumours part I: Imaging technique, anatomy and anterior skull base tumours

International Nuclear Information System (INIS)

Borges, Alexandra

2008-01-01

Advances in cross-sectional imaging, surgical technique and adjuvant treatment have largely contributed to ameliorate the prognosis, lessen the morbidity and mortality of patients with skull base tumours and to the growing medical investment in the management of these patients. Because clinical assessment of the skull base is limited, cross-sectional imaging became indispensable in the diagnosis, treatment planning and follow-up of patients with suspected skull base pathology and the radiologist is increasingly responsible for the fate of these patients. This review will focus on the advances in imaging technique; contribution to patient's management and on the imaging features of the most common tumours affecting the anterior skull base. Emphasis is given to a systematic approach to skull base pathology based upon an anatomic division taking into account the major tissue constituents in each skull base compartment. The most relevant information that should be conveyed to surgeons and radiation oncologists involved in patient's management will be discussed

Comparison of MRI-based and CT/MRI fusion-based postimplant dosimetric analysis of prostate brachytherapy

International Nuclear Information System (INIS)

Tanaka, Osamu; Hayashi, Shinya; Matsuo, Masayuki; Sakurai, Kota; Nakano, Masahiro; Maeda, Sunaho; Kajita, Kimihiro R.T.; Deguchi, Takashi; Hoshi, Hiroaki

2006-01-01

Purpose: The aim of this study was to compare the outcomes between magnetic resonance imaging (MRI)-based and computed tomography (CT)/MRI fusion-based postimplant dosimetry methods in permanent prostate brachytherapy. Methods and Materials: Between October 2004 and March 2006, a total of 52 consecutive patients with prostate cancer were treated by brachytherapy, and postimplant dosimetry was performed using CT/MRI fusion. The accuracy and reproducibility were prospectively compared between MRI-based dosimetry and CT/MRI fusion-based dosimetry based on the dose-volume histogram (DVH) related parameters as recommended by the American Brachytherapy Society. Results: The prostate volume was 15.97 ± 6.17 cc (mean ± SD) in MRI-based dosimetry, and 15.97 ± 6.02 cc in CT/MRI fusion-based dosimetry without statistical difference. The prostate V100 was 94.5% and 93.0% in MRI-based and CT/MRI fusion-based dosimetry, respectively, and the difference was statistically significant (p = 0.002). The prostate D90 was 119.4% and 114.4% in MRI-based and CT/MRI fusion-based dosimetry, respectively, and the difference was statistically significant (p = 0.004). Conclusion: Our current results suggested that, as with fusion images, MR images allowed accurate contouring of the organs, but they tended to overestimate the analysis of postimplant dosimetry in comparison to CT/MRI fusion images. Although this MRI-based dosimetric discrepancy was negligible, MRI-based dosimetry was acceptable and reproducible in comparison to CT-based dosimetry, because the difference between MRI-based and CT/MRI fusion-based results was smaller than that between CT-based and CT/MRI fusion-based results as previously reported

Problem-Oriented Corporate Knowledge Base Models on the Case-Based Reasoning Approach Basis

Science.gov (United States)

Gluhih, I. N.; Akhmadulin, R. K.

2017-07-01

One of the urgent directions of efficiency enhancement of production processes and enterprises activities management is creation and use of corporate knowledge bases. The article suggests a concept of problem-oriented corporate knowledge bases (PO CKB), in which knowledge is arranged around possible problem situations and represents a tool for making and implementing decisions in such situations. For knowledge representation in PO CKB a case-based reasoning approach is encouraged to use. Under this approach, the content of a case as a knowledge base component has been defined; based on the situation tree a PO CKB knowledge model has been developed, in which the knowledge about typical situations as well as specific examples of situations and solutions have been represented. A generalized problem-oriented corporate knowledge base structural chart and possible modes of its operation have been suggested. The obtained models allow creating and using corporate knowledge bases for support of decision making and implementing, training, staff skill upgrading and analysis of the decisions taken. The universal interpretation of terms “situation” and “solution” adopted in the work allows using the suggested models to develop problem-oriented corporate knowledge bases in different subject domains. It has been suggested to use the developed models for making corporate knowledge bases of the enterprises that operate engineer systems and networks at large production facilities.

Web-Based Learning Environment Based on Students’ Needs

Science.gov (United States)

Hamzah, N.; Ariffin, A.; Hamid, H.

2017-08-01

Traditional learning needs to be improved since it does not involve active learning among students. Therefore, in the twenty-first century, the development of internet technology in the learning environment has become the main needs of each student. One of the learning environments to meet the needs of the teaching and learning process is a web-based learning environment. This study aims to identify the characteristics of a web-based learning environment that supports students’ learning needs. The study involved 542 students from fifteen faculties in a public higher education institution in Malaysia. A quantitative method was used to collect the data via a questionnaire survey by randomly. The findings indicate that the characteristics of a web-based learning environment that support students’ needs in the process of learning are online discussion forum, lecture notes, assignments, portfolio, and chat. In conclusion, the students overwhelmingly agreed that online discussion forum is the highest requirement because the tool can provide a space for students and teachers to share knowledge and experiences related to teaching and learning.

Home Based Training: Main Strategy in Community Based Rehabilitation in Iran

Directory of Open Access Journals (Sweden)

Peiman Salamati

2006-10-01

Full Text Available Objective: Study of effectiveness of “home based training” in community based rehabilitation program on disabled people, under supervised of 21 pilot cities health and medical networks, who were trained and evaluated at the end of the course. Materials & Methods: In a cross-sectional study, 614 disabled people who had participated in “home based training” were selected with stratified random sampling method. They were evaluated according to function progress level variables by community based rehabilitation programme experts. Age, sex, disability groups, employment state and teacher’s relation variables were studied from their files and recording datas. Statistical analysis was performed with Chi-square test. Results: There was a relationship between age group and disability group with functional progress level (P = 0.014 & P <0.001. Low age groups, visional disabled group, epileptic patients and individuals with learning problems had the best results. High age groups, mixed disability group and individuals with verbal and hearing problems had the least results. There was a relationship between teacher’s relation with progress or nonprogress state (P = 0.038. Individuals that they were own teachers had the best results and individuals with teachers other than first or second relation or health worker had the least results. Conclusion: Home based training in community based rehabilitation programme is an effective method for improving disabled people in some selected groups.

How evidence-based are the recommendations in evidence-based guidelines?

Directory of Open Access Journals (Sweden)

Finlay A McAlister

2007-08-01

Full Text Available BACKGROUND: Treatment recommendations for the same condition from different guideline bodies often disagree, even when the same randomized controlled trial (RCT evidence is cited. Guideline appraisal tools focus on methodology and quality of reporting, but not on the nature of the supporting evidence. This study was done to evaluate the quality of the evidence (based on consideration of its internal validity, clinical relevance, and applicability underlying therapy recommendations in evidence-based clinical practice guidelines. METHODS AND FINDINGS: A cross-sectional analysis of cardiovascular risk management recommendations was performed for three different conditions (diabetes mellitus, dyslipidemia, and hypertension from three pan-national guideline panels (from the United States, Canada, and Europe. Of the 338 treatment recommendations in these nine guidelines, 231 (68% cited RCT evidence but only 105 (45% of these RCT-based recommendations were based on high-quality evidence. RCT-based evidence was downgraded most often because of reservations about the applicability of the RCT to the populations specified in the guideline recommendation (64/126 cases, 51% or because the RCT reported surrogate outcomes (59/126 cases, 47%. CONCLUSIONS: The results of internally valid RCTs may not be applicable to the populations, interventions, or outcomes specified in a guideline recommendation and therefore should not always be assumed to provide high-quality evidence for therapy recommendations.

Microfluidic paper-based biomolecule preconcentrator based on ion concentration polarization.

Science.gov (United States)

Han, Sung Il; Hwang, Kyo Seon; Kwak, Rhokyun; Lee, Jeong Hoon

2016-06-21

Microfluidic paper-based analytical devices (μPADs) for molecular detection have great potential in the field of point-of-care diagnostics. Currently, a critical problem being faced by μPADs is improving their detection sensitivity. Various preconcentration processes have been developed, but they still have complicated structures and fabrication processes to integrate into μPADs. To address this issue, we have developed a novel paper-based preconcentrator utilizing ion concentration polarization (ICP) with minimal addition on lateral-flow paper. The cation selective membrane (i.e., Nafion) is patterned on adhesive tape, and this tape is then attached to paper-based channels. When an electric field is applied across the Nafion, ICP is initiated to preconcentrate the biomolecules in the paper channel. Departing from previous paper-based preconcentrators, we maintain steady lateral fluid flow with the separated Nafion layer; as a result, fluorescent dyes and proteins (FITC-albumin and bovine serum albumin) are continuously delivered to the preconcentration zone, achieving high preconcentration performance up to 1000-fold. In addition, we demonstrate that the Nafion-patterned tape can be integrated with various geometries (multiplexed preconcentrator) and platforms (string and polymer microfluidic channel). This work would facilitate integration of various ICP devices, including preconcentrators, pH/concentration modulators, and micro mixers, with steady lateral flows in paper-based platforms.

Jobs to Manufacturing Careers: Work-Based Courses. Work-Based Learning in Action

Science.gov (United States)

Kobes, Deborah

2016-01-01

This case study, one of a series of publications exploring effective and inclusive models of work-based learning, finds that work-based courses bring college to the production line by using the job as a learning lab. Work-based courses are an innovative way to give incumbent workers access to community college credits and degrees. They are…

Base-By-Base: Single nucleotide-level analysis of whole viral genome alignments

Directory of Open Access Journals (Sweden)

Tcherepanov Vasily

2004-07-01

Full Text Available Abstract Background With ever increasing numbers of closely related virus genomes being sequenced, it has become desirable to be able to compare two genomes at a level more detailed than gene content because two strains of an organism may share the same set of predicted genes but still differ in their pathogenicity profiles. For example, detailed comparison of multiple isolates of the smallpox virus genome (each approximately 200 kb, with 200 genes is not feasible without new bioinformatics tools. Results A software package, Base-By-Base, has been developed that provides visualization tools to enable researchers to 1 rapidly identify and correct alignment errors in large, multiple genome alignments; and 2 generate tabular and graphical output of differences between the genomes at the nucleotide level. Base-By-Base uses detailed annotation information about the aligned genomes and can list each predicted gene with nucleotide differences, display whether variations occur within promoter regions or coding regions and whether these changes result in amino acid substitutions. Base-By-Base can connect to our mySQL database (Virus Orthologous Clusters; VOCs to retrieve detailed annotation information about the aligned genomes or use information from text files. Conclusion Base-By-Base enables users to quickly and easily compare large viral genomes; it highlights small differences that may be responsible for important phenotypic differences such as virulence. It is available via the Internet using Java Web Start and runs on Macintosh, PC and Linux operating systems with the Java 1.4 virtual machine.

Demographic-Based Content Analysis of Web-Based Health-Related Social Media.

Science.gov (United States)

Sadah, Shouq A; Shahbazi, Moloud; Wiley, Matthew T; Hristidis, Vagelis

2016-06-13

An increasing number of patients from diverse demographic groups share and search for health-related information on Web-based social media. However, little is known about the content of the posted information with respect to the users' demographics. The aims of this study were to analyze the content of Web-based health-related social media based on users' demographics to identify which health topics are discussed in which social media by which demographic groups and to help guide educational and research activities. We analyze 3 different types of health-related social media: (1) general Web-based social networks Twitter and Google+; (2) drug review websites; and (3) health Web forums, with a total of about 6 million users and 20 million posts. We analyzed the content of these posts based on the demographic group of their authors, in terms of sentiment and emotion, top distinctive terms, and top medical concepts. The results of this study are: (1) Pregnancy is the dominant topic for female users in drug review websites and health Web forums, whereas for male users, it is cardiac problems, HIV, and back pain, but this is not the case for Twitter; (2) younger users (0-17 years) mainly talk about attention-deficit hyperactivity disorder (ADHD) and depression-related drugs, users aged 35-44 years discuss about multiple sclerosis (MS) drugs, and middle-aged users (45-64 years) talk about alcohol and smoking; (3) users from the Northeast United States talk about physical disorders, whereas users from the West United States talk about mental disorders and addictive behaviors; (4) Users with higher writing level express less anger in their posts. We studied the popular topics and the sentiment based on users' demographics in Web-based health-related social media. Our results provide valuable information, which can help create targeted and effective educational campaigns and guide experts to reach the right users on Web-based social chatter.

Enriched Title-Based Keyword Index Generation Using dBase II.

Science.gov (United States)

Rajendran, P. P.

1986-01-01

Describes the use of a database management system (DBMS)--dBaseII--to create an enriched title-based keyword index for a collection of news items at the Renewable Energy Resources Information Center of the Asian Institute of Technology. The use of DBMSs in libraries in developing countries is emphasized. (Author/LRW)

Workplace Based Assessment in Psychiatry

Directory of Open Access Journals (Sweden)

Ayse Devrim Basterzi

2009-11-01

Full Text Available Workplace based assessment refers to the assessment of working practices based on what doctors actually do in the workplace, and is predominantly carried out in the workplace itself. Assessment drives learning and it is therefore essential that workplace-based assessment focuses on important attributes rather than what is easiest to assess. Workplacebased assessment is usually competency based. Workplace based assesments may well facilitate and enhance various aspects of educational supervisions, including its structure, frequency and duration etc. The structure and content of workplace based assesments should be monitored to ensure that its benefits are maximised by remaining tailored to individual trainees' needs. Workplace based assesment should be used for formative and summative assessments. Several formative assessment methods have been developed for use in the workplace such as mini clinical evaluation exercise (mini-cex, evidence based journal club assesment and case based discussion, multi source feedback etc. This review discusses the need of workplace based assesments in psychiatry graduate education and introduces some of the work place based assesment methods.

Proximity-Based Asynchronous Messaging Platform for Location-Based Internet of Things Service

Directory of Open Access Journals (Sweden)

Hyeong gon Jo

2016-07-01

Full Text Available The Internet of Things (IoT opens up tremendous opportunities to provide location-based applications. However, despite the services around a user being physically adjacent, common IoT platforms use a centralized structure, like a cloud-computing architecture, which transfers large amounts of data to a central server. This raises problems, such as traffic concentration, long service latency, and high communication cost. In this paper, we propose a physical distance-based asynchronous messaging platform that specializes in processing personalized data and location-based messages. The proposed system disperses traffic using a location-based message-delivery protocol, and has high stability.

Design-Based Research

DEFF Research Database (Denmark)

Gynther, Karsten; Christensen, Ove; Petersen, Trine Brun

2012-01-01

I denne artikel introduceres Design Based Research for første gang på dansk i et videnskabeligt tidsskrift. Artiklen præsenterer de grundlæggende antagelser, som ligger til grund for Design Based Research-traditionen, og artiklen diskuterer de principper, som ligger til grund for gennemførelse af...... et DBR-forskningsprojekt. Med udgangspunkt i forsknings- og udviklingsprojektet ELYK: E-læring, Yderområder og Klyngedannelse, præsenteres den innovationsmodel, som projektet har udviklet med udgangspunkt i Design Based Research traditionen. ELYKs DBR innovationsmodel har vist sig effektiv i forhold...

Memory-Based Shallow Parsing

NARCIS (Netherlands)

Tjong Kim Sang, E.F.

2002-01-01

We present memory-based learning approaches to shallow parsing and apply these to five tasks: base noun phrase identification, arbitrary base phrase recognition, clause detection, noun phrase parsing and full parsing. We use feature selection techniques and system combination methods for improving

‘"Education-based Research"

DEFF Research Database (Denmark)

Degn Johansson, Troels

This paper lays out a concept of education-based research-the production of research knowledge within the framework of tertiary design education-as an integration of problem-based learning and research-based education. This leads to a critique of reflective practice as the primary way to facilitate...... learning at this level, a discussion of the nature of design problems in the instrumentalist tradition, and some suggestions as to how design studies curricula may facilitate education-based research....

Memory-Based Shallow Parsing

OpenAIRE

Sang, Erik F. Tjong Kim

2002-01-01

We present memory-based learning approaches to shallow parsing and apply these to five tasks: base noun phrase identification, arbitrary base phrase recognition, clause detection, noun phrase parsing and full parsing. We use feature selection techniques and system combination methods for improving the performance of the memory-based learner. Our approach is evaluated on standard data sets and the results are compared with that of other systems. This reveals that our approach works well for ba...

Changing from a Rules-based to a Principles-based Accounting Logic: A Review

Directory of Open Access Journals (Sweden)

Marta Silva Guerreiro

2014-06-01

Full Text Available We explore influences on unlisted companies when Portugal moved from a code law, rules-based accounting system, to a principles-based accounting system of adapted International Financial Reporting Standards (IFRS. Institutionalisation of the new principles-based system was generally facilitated by a socio-economic and political context that increasingly supported IFRS logic. This helped central actors gain political opportunity, mobilise important allies, and accommodate major protagonists. The preparedness of unlisted companies to adopt the new IFRS-based accounting system voluntarily was explained by their desire to maintain social legitimacy. However, it was affected negatively by the embeddedness of rule-based practices in the ‘old’ prevailing institutional logic.

Constructing regional advantage: platform policies based on related variety and differentiated knowledge bases.

NARCIS (Netherlands)

Asheim, B.T.; Boschma, R.A.; Cooke, P.

2011-01-01

Constructing regional advantage: platform policies based on related variety and differentiated knowledge bases, Regional Studies. This paper presents a regional innovation policy model based on the idea of constructing regional advantage. This policy model brings together concepts like related

An Intelligent Fleet Condition-Based Maintenance Decision Making Method Based on Multi-Agent

OpenAIRE

Bo Sun; Qiang Feng; Songjie Li

2012-01-01

According to the demand for condition-based maintenance online decision making among a mission oriented fleet, an intelligent maintenance decision making method based on Multi-agent and heuristic rules is proposed. The process of condition-based maintenance within an aircraft fleet (each containing one or more Line Replaceable Modules) based on multiple maintenance thresholds is analyzed. Then the process is abstracted into a Multi-Agent Model, a 2-layer model structure containing host negoti...

The ground based plan

International Nuclear Information System (INIS)

1989-01-01

The paper presents a report of ''The Ground Based Plan'' of the United Kingdom Science and Engineering Research Council. The ground based plan is a plan for research in astronomy and planetary science by ground based techniques. The contents of the report contains a description of:- the scientific objectives and technical requirements (the basis for the Plan), the present organisation and funding for the ground based programme, the Plan, the main scientific features and the further objectives of the Plan. (U.K.)

Content-Based Image Retrieval Based on Electromagnetism-Like Mechanism

Directory of Open Access Journals (Sweden)

Hamid A. Jalab

2013-01-01

Full Text Available Recently, many researchers in the field of automatic content-based image retrieval have devoted a remarkable amount of research looking for methods to retrieve the best relevant images to the query image. This paper presents a novel algorithm for increasing the precision in content-based image retrieval based on electromagnetism optimization technique. The electromagnetism optimization is a nature-inspired technique that follows the collective attraction-repulsion mechanism by considering each image as an electrical charge. The algorithm is composed of two phases: fitness function measurement and electromagnetism optimization technique. It is implemented on a database with 8,000 images spread across 80 classes with 100 images in each class. Eight thousand queries are fired on the database, and the overall average precision is computed. Experimental results of the proposed approach have shown significant improvement in the retrieval performance in regard to precision.

Risk based modelling

International Nuclear Information System (INIS)

Chapman, O.J.V.; Baker, A.E.

1993-01-01

Risk based analysis is a tool becoming available to both engineers and managers to aid decision making concerning plant matters such as In-Service Inspection (ISI). In order to develop a risk based method, some form of Structural Reliability Risk Assessment (SRRA) needs to be performed to provide a probability of failure ranking for all sites around the plant. A Probabilistic Risk Assessment (PRA) can then be carried out to combine these possible events with the capability of plant safety systems and procedures, to establish the consequences of failure for the sites. In this way the probability of failures are converted into a risk based ranking which can be used to assist the process of deciding which sites should be included in an ISI programme. This paper reviews the technique and typical results of a risk based ranking assessment carried out for nuclear power plant pipework. (author)

Synthesis and photoluminescence properties of novel Schiff base type polymer-rare earth complexes containing furfural-based bidentate Schiff base ligands

Science.gov (United States)

Gao, Baojiao; Zhang, Dandan; Li, Yanbin

2018-03-01

Luminescent polymer-rare earth complexes are an important class of photoluminescence and electroluminescence materials. Via molecular design, two furfural-based bidentate Schiff base ligands, furfural-aniline (FA) type ligand and furfural-cyclohexylamine (FC) type ligand, were bonded on the side chains of polysulfone (PSF), respectively, forming two functionalized macromolecules, PSF-FA and PSF-FC. And then through respective coordination reactions of the two functionalized macromolecules with Eu(Ⅲ) ion and Tb(Ⅲ) ion, novel luminescent binary and ternary (with 1,10-phenanthroline as the second ligand) polymer-rare earth complexes were synthesized. For these complexes, on basis of the characterization of their chemical structures, they photoluminescence properties were main researched, and the relationship between their luminescent properties and structures was explored. The experimental results show that the complexes coming from PSF-FA and Eu(Ⅲ) ion including binary and ternary complexes emit strong red luminescence, indicating that the bonded bidentate Schiff base ligand FA can sensitize the fluorescence emission of Eu(III) ion. While the complexes coming from PSF-FC and Tb(Ⅲ) ion produce green luminescence, displaying that the bonded bidentate Schiff base ligand FC can sensitize the fluorescence emission of Tb(Ⅲ) ion. The fluorescence emission intensities of the ternary complexes were stronger than that of binary complexes, reflecting the important effect of the second ligand. The fluorescence emission of the solid film of complexes is much stronger than that of the solutions of complexes. Besides, by comparison, it is found that the furfural (as a heteroaromatic compound)-based Schiff base type polymer-rare earth complexes have stronger fluorescence emission and higher energy transfer efficiency than salicylaldehyde (as a common aromatic compound)-based Schiff base type polymer-rare earth complexes.

Review of performance-based incentives in community-based family planning programmes

Science.gov (United States)

Bellows, Nicole M; Askew, Ian; Bellows, Benjamin

2015-01-01

Background One strategy for improving family planning (FP) uptake at the community level is the use of performance-based incentives (PBIs), which offer community distributors financial incentives to recruit more users of FP. This article examines the use of PBIs in community-based FP programmes via a literature search of the peer-reviewed and grey literature conducted in April 2013. Results A total of 28 community-based FP programmes in 21 countries were identified as having used PBIs. The most common approach was a sales commission model where distributors received commission for FP products sold, while a referral payment model for long-term methods was also used extensively. Six evaluations were identified that specifically examined the impact of the PBI in community-based FP programmes. Overall, the results of the evaluations are mixed and more research is needed; however, the findings suggest that easy-to-understand PBIs can be successful in increasing the use of FP at the community level. Conclusion For future use of PBIs in community-based FP programmes it is important to consider the ethics of incentivising FP and ensuring that PBIs are non-coercive and choice-enhancing. PMID:25037703

Unifying Model-Based and Reactive Programming within a Model-Based Executive

Science.gov (United States)

Williams, Brian C.; Gupta, Vineet; Norvig, Peter (Technical Monitor)

1999-01-01

Real-time, model-based, deduction has recently emerged as a vital component in AI's tool box for developing highly autonomous reactive systems. Yet one of the current hurdles towards developing model-based reactive systems is the number of methods simultaneously employed, and their corresponding melange of programming and modeling languages. This paper offers an important step towards unification. We introduce RMPL, a rich modeling language that combines probabilistic, constraint-based modeling with reactive programming constructs, while offering a simple semantics in terms of hidden state Markov processes. We introduce probabilistic, hierarchical constraint automata (PHCA), which allow Markov processes to be expressed in a compact representation that preserves the modularity of RMPL programs. Finally, a model-based executive, called Reactive Burton is described that exploits this compact encoding to perform efficIent simulation, belief state update and control sequence generation.

Problem based Learning versus Design Thinking in Team based Project work

DEFF Research Database (Denmark)

Denise J. Stokholm, Marianne

2014-01-01

project based learning issues, which has caused a need to describe and compare the two models; in specific the understandings, approaches and organization of learning in project work. The PBL model viewing the process as 3 separate project stages including; problem analysis, problem solving and project......All educations at Aalborg University has since 1974 been rooted in Problem Based Learning (PBL). In 1999 a new education in Industrial design was set up, introducing Design Based Learning (DBL). Even though the two approaches have a lot in common they also hold different understandings of core...... report, with focus on problem solving through analysis. Design Based Learning viewing the process as series of integrated design spaces including; alignment, research, mission, vision, concept, product and process report, with focus on innovative ideation though integration. There is a need of renewing...

Measuring Costs to Community-Based Agencies for Implementation of an Evidence-Based Practice.

Science.gov (United States)

Lang, Jason M; Connell, Christian M

2017-01-01

Healthcare reform has led to an increase in dissemination of evidence-based practices. Cost is frequently cited as a significant yet rarely studied barrier to dissemination of evidence-based practices and the associated improvements in quality of care. This study describes an approach to measuring the incremental, unreimbursed costs in staff time and direct costs to community-based clinics implementing an evidence-based practice through participating in a learning collaborative. Initial implementation costs exceeding those for providing "treatment as usual" were collected for ten clinics implementing trauma-focused cognitive behavioral therapy through participation in 10-month learning collaboratives. Incremental implementation costs of these ten community-based clinic teams averaged the equivalent of US$89,575 (US$ 2012). The most costly activities were training, supervision, preparation time, and implementation team meetings. Recommendations are made for further research on implementation costs, dissemination of evidence-based practices, and implications for researchers and policy makers.

Ratio-based vs. model-based methods to correct for urinary creatinine concentrations.

Science.gov (United States)

Jain, Ram B

2016-08-01

Creatinine-corrected urinary analyte concentration is usually computed as the ratio of the observed level of analyte concentration divided by the observed level of the urinary creatinine concentration (UCR). This ratio-based method is flawed since it implicitly assumes that hydration is the only factor that affects urinary creatinine concentrations. On the contrary, it has been shown in the literature, that age, gender, race/ethnicity, and other factors also affect UCR. Consequently, an optimal method to correct for UCR should correct for hydration as well as other factors like age, gender, and race/ethnicity that affect UCR. Model-based creatinine correction in which observed UCRs are used as an independent variable in regression models has been proposed. This study was conducted to evaluate the performance of ratio-based and model-based creatinine correction methods when the effects of gender, age, and race/ethnicity are evaluated one factor at a time for selected urinary analytes and metabolites. It was observed that ratio-based method leads to statistically significant pairwise differences, for example, between males and females or between non-Hispanic whites (NHW) and non-Hispanic blacks (NHB), more often than the model-based method. However, depending upon the analyte of interest, the reverse is also possible. The estimated ratios of geometric means (GM), for example, male to female or NHW to NHB, were also compared for the two methods. When estimated UCRs were higher for the group (for example, males) in the numerator of this ratio, these ratios were higher for the model-based method, for example, male to female ratio of GMs. When estimated UCR were lower for the group (for example, NHW) in the numerator of this ratio, these ratios were higher for the ratio-based method, for example, NHW to NHB ratio of GMs. Model-based method is the method of choice if all factors that affect UCR are to be accounted for.

Capability-based computer systems

CERN Document Server

Levy, Henry M

2014-01-01

Capability-Based Computer Systems focuses on computer programs and their capabilities. The text first elaborates capability- and object-based system concepts, including capability-based systems, object-based approach, and summary. The book then describes early descriptor architectures and explains the Burroughs B5000, Rice University Computer, and Basic Language Machine. The text also focuses on early capability architectures. Dennis and Van Horn's Supervisor; CAL-TSS System; MIT PDP-1 Timesharing System; and Chicago Magic Number Machine are discussed. The book then describes Plessey System 25

Comparison of Subset-Based Local and Finite Element-Based Global Digital Image Correlation

KAUST Repository

Pan, Bing; Wang, B.; Lubineau, Gilles; Moussawi, Ali

2015-01-01

Digital image correlation (DIC) techniques require an image matching algorithm to register the same physical points represented in different images. Subset-based local DIC and finite element-based (FE-based) global DIC are the two primary image matching methods that have been extensively investigated and regularly used in the field of experimental mechanics. Due to its straightforward implementation and high efficiency, subset-based local DIC has been used in almost all commercial DIC packages. However, it is argued by some researchers that FE-based global DIC offers better accuracy because of the enforced continuity between element nodes. We propose a detailed performance comparison between these different DIC algorithms both in terms of measurement accuracy and computational efficiency. Then, by measuring displacements of the same calculation points using the same calculation algorithms (e.g., correlation criterion, initial guess estimation, subpixel interpolation, optimization algorithm and convergence conditions) and identical calculation parameters (e.g., subset or element size), the performances of subset-based local DIC and two FE-based global DIC approaches are carefully compared in terms of measurement error and computational efficiency using both numerical tests and real experiments. A detailed examination of the experimental results reveals that, when subset (element) size is not very small and the local deformation within a subset (element) can be well approximated by the shape function used, standard subset-based local DIC approach not only provides better results in measured displacements, but also demonstrates much higher computation efficiency. However, several special merits of FE-based global DIC approaches are indicated.

Comparison of Subset-Based Local and Finite Element-Based Global Digital Image Correlation

KAUST Repository

Pan, Bing

2015-02-12

Digital image correlation (DIC) techniques require an image matching algorithm to register the same physical points represented in different images. Subset-based local DIC and finite element-based (FE-based) global DIC are the two primary image matching methods that have been extensively investigated and regularly used in the field of experimental mechanics. Due to its straightforward implementation and high efficiency, subset-based local DIC has been used in almost all commercial DIC packages. However, it is argued by some researchers that FE-based global DIC offers better accuracy because of the enforced continuity between element nodes. We propose a detailed performance comparison between these different DIC algorithms both in terms of measurement accuracy and computational efficiency. Then, by measuring displacements of the same calculation points using the same calculation algorithms (e.g., correlation criterion, initial guess estimation, subpixel interpolation, optimization algorithm and convergence conditions) and identical calculation parameters (e.g., subset or element size), the performances of subset-based local DIC and two FE-based global DIC approaches are carefully compared in terms of measurement error and computational efficiency using both numerical tests and real experiments. A detailed examination of the experimental results reveals that, when subset (element) size is not very small and the local deformation within a subset (element) can be well approximated by the shape function used, standard subset-based local DIC approach not only provides better results in measured displacements, but also demonstrates much higher computation efficiency. However, several special merits of FE-based global DIC approaches are indicated.

Influencing factors for condition-based maintenance in railway tracks using knowledge-based approach

NARCIS (Netherlands)

Jamshidi, A.; Hajizadeh, S.; Naeimi, M.; Nunez Vicencio, Alfredo; Li, Z.

2017-01-01

In this paper, we present a condition-based maintenance decision method using
knowledge-based approach for rail surface defects. A railway track may contain a considerable number of surface defects which influence track maintenance decisions. The proposed method is based on two sets of

A comparison of arc-based and static mini-multileaf collimator-based radiosurgery treatment plans

International Nuclear Information System (INIS)

Kubo, Hideo Dale; Pappas, Conrad T.E.; Wilder, Richard B.

1997-01-01

Background: The purpose of this study is to compare arc-based and mini-multileaf collimator (mMLC)-based radiosurgery treatment plans using isodose distributions and dose-volume histograms. Methods: Of 11 patients who underwent conventional arc-based radiosurgery for intracranial malignancies, four were treated with one isocenter, four were treated with two isocenters and three were treated with three isocenters. The same cases were re-planned using a test version of mMLC-based radiosurgery software for multiple static non-coplanar fields. Results and conclusion: For non-spherical targets, treatment planning is relatively intuitive with mMLC-based radiosurgery, reducing the amount of time required for planning. Moreover, a lower dose of radiation is delivered to normal tissue with mMLC-based radiosurgery than with arc-based radiosurgery, which theoretically should lead to a reduced risk of complications

Performance-Based Funding Brief

Science.gov (United States)

Washington Higher Education Coordinating Board, 2011

2011-01-01

A number of states have made progress in implementing performance-based funding (PFB) and accountability. This policy brief summarizes main features of performance-based funding systems in three states: Tennessee, Ohio, and Indiana. The brief also identifies key issues that states considering performance-based funding must address, as well as…

Office-based anaesthesia

African Journals Online (AJOL)

infection, and consistency in nursing personnel. In the USA 17 -. 24% of all elective ambulatory surgery is ... knowledge base or personality to deal with the OBA environment. Compared with hospitals, office-based facilities currently ... disease or major cardiovascular risk factors). Intravenous access via a flexible cannula is.

Conceptual Pathway Querying of Natural Logic Knowledge Bases from Text Bases

DEFF Research Database (Denmark)

Andreasen, Troels; Bulskov, Henrik; Nilsson, Jørgen Fischer

2013-01-01

language than predicate logic. Natural logic accommodates a variety of scientific parlance, ontologies and domain models. It also supports a semantic net or graph view of the knowledge base. This admits computation of relationships between concepts simultaneously through pathfinding in the knowledge base...

Tracing the Base: A Topographic Test for Collusive Basing-Point Pricing

NARCIS (Netherlands)

Bos, Iwan; Schinkel, Maarten Pieter

2009-01-01

Basing-point pricing is known to have been abused by geographically dispersed firms in order to eliminate competition on transportation costs. This paper develops a topographic test for collusive basing-point pricing. The method uses transaction data (prices, quantities) and customer project site

Tracing the base: A topographic test for collusive basing-point pricing

NARCIS (Netherlands)

Bos, I.; Schinkel, M.P.

2008-01-01

Basing-point pricing is known to have been abused by geographically dispersed firms in order to eliminate competition on transportation costs. This paper develops a topographic test for collusive basing-point pricing. The method uses transaction data (prices, quantities) and customer project site

Moving from Rule-based to Principle-based in Public Sector: Preparers' Perspective

OpenAIRE

Roshayani Arshad; Normah Omar; Siti Fatimah Awang

2013-01-01

The move from cash accounting to accrual accounting, or rule-based to principle-based accounting, by many governments is part of an ongoing efforts in promoting a more business-like and performance-focused public sector. Using questionnaire responses from preparers of financial statements of public universities in Malaysia, this study examines the implementation challenges and benefits of principle-based accounting. Results from these responses suggest that most respondents perceived signific...

Thulium-based bulk metallic glass

International Nuclear Information System (INIS)

Yu, H. B.; Yu, P.; Wang, W. H.; Bai, H. Y.

2008-01-01

We report the formation and properties of a thulium-based bulk metallic glass (BMG). Compared with other known rare-earth (RE) based BMGs, Tm-based BMGs show features of excellent glass formation ability, considerable higher elastic modulus, smaller Poisson's ratio, high mechanical strength, and intrinsic brittleness. The reasons for the different properties between the Tm-based and other RE-based BMGs are discussed. It is expected that the Tm-based glasses with the unique properties are appropriate candidates for studying some important issues in BMGs

Feature-based and object-based attention orientation during short-term memory maintenance.

Science.gov (United States)

Ku, Yixuan

2015-12-01

Top-down attention biases the short-term memory (STM) processing at multiple stages. Orienting attention during the maintenance period of STM by a retrospective cue (retro-cue) strengthens the representation of the cued item and improves the subsequent STM performance. In a recent article, Backer et al. (Backer KC, Binns MA, Alain C. J Neurosci 35: 1307-1318, 2015) extended these findings from the visual to the auditory domain and combined electroencephalography to dissociate neural mechanisms underlying feature-based and object-based attention orientation. Both event-related potentials and neural oscillations explained the behavioral benefits of retro-cues and favored the theory that feature-based and object-based attention orientation were independent. Copyright © 2015 the American Physiological Society.

THE DESIGN OF KNOWLEDGE BASE FOR SURFACE RELATIONS BASED PART RECOGNITION APPROACH

Directory of Open Access Journals (Sweden)

Adem ÇİÇEK

2007-01-01

Full Text Available In this study, a new knowledge base for an expert system used in part recognition algorithm has been designed. Parts are recognized by the computer program by comparing face adjacency relations and attributes belonging to each part represented in the rules in the knowledge base developed with face adjacency relations and attributes generated from STEP file of the part. Besides, rule writing process has been quite simplified by generating the rules represented in the knowledge base with an automatic rule writing module developed within the system. With the knowledge base and automatic rule writing module used in the part recognition system, simple, intermediate and complex parts can be recognized by a part recognition program.

Game-based versus traditional case-based learning: comparing effectiveness in stroke continuing medical education.

Science.gov (United States)

Telner, Deanna; Bujas-Bobanovic, Maja; Chan, David; Chester, Bob; Marlow, Bernard; Meuser, James; Rothman, Arthur; Harvey, Bart

2010-09-01

To evaluate family physicians' enjoyment of and knowledge gained from game-based learning, compared with traditional case-based learning, in a continuing medical education (CME) event on stroke prevention and management. An equivalence trial to determine if game-based learning was as effective as case-based learning in terms of attained knowledge levels. Game questions and small group cases were developed. Participants were randomized to either a game-based or a case-based group and took part in the event. Ontario provincial family medicine conference. Thirty-two family physicians and 3 senior family medicine residents attending the conference. Participation in either a game-based or a case-based CME learning group. Scores on 40-item immediate and 3-month posttests of knowledge and a satisfaction survey. Results from knowledge testing immediately after the event and 3 months later showed no significant difference in scoring between groups. Participants in the game-based group reported higher levels of satisfaction with the learning experience. Games provide a novel way of organizing CME events. They might provide more group interaction and discussion, as well as improve recruitment to CME events. They might also provide a forum for interdisciplinary CME. Using games in future CME events appears to be a promising approach to facilitate participant learning.

The roles of constraint-based and dedication-based influences on user's continued online shopping behavior.

Science.gov (United States)

Chang, Su-Chao; Chou, Chi-Min

2012-11-01

The objective of this study was to determine empirically the role of constraint-based and dedication-based influences as drivers of the intention to continue using online shopping websites. Constraint-based influences consist of two variables: trust and perceived switching costs. Dedication-based influences consist of three variables: satisfaction, perceived usefulness, and trust. The current results indicate that both constraint-based and dedication-based influences are important drivers of the intention to continue using online shopping websites. The data also shows that trust has the strongest total effect on online shoppers' intention to continue using online shopping websites. In addition, the results indicate that the antecedents of constraint-based influences, technical bonds (e.g., perceived operational competence and perceived website interactivity) and social bonds (e.g., perceived relationship investment, community building, and intimacy) have indirect positive effects on the intention to continue using online shopping websites. Based on these findings, this research suggests that online shopping websites should build constraint-based and dedication-based influences to enhance user's continued online shopping behaviors simultaneously.

Content-based intermedia synchronization

Science.gov (United States)

Oh, Dong-Young; Sampath-Kumar, Srihari; Rangan, P. Venkat

1995-03-01

Inter-media synchronization methods developed until now have been based on syntactic timestamping of video frames and audio samples. These methods are not fully appropriate for the synchronization of multimedia objects which may have to be accessed individually by their contents, e.g. content-base data retrieval. We propose a content-based multimedia synchronization scheme in which a media stream is viewed as hierarchial composition of smaller objects which are logically structured based on the contents, and the synchronization is achieved by deriving temporal relations among logical units of media object. content-based synchronization offers several advantages such as, elimination of the need for time stamping, freedom from limitations of jitter, synchronization of independently captured media objects in video editing, and compensation for inherent asynchronies in capture times of video and audio.

Secure base stations

NARCIS (Netherlands)

Bosch, Peter; Brusilovsky, Alec; McLellan, Rae; Mullender, Sape J.; Polakos, Paul

2009-01-01

With the introduction of the third generation (3G) Universal Mobile Telecommunications System (UMTS) base station router (BSR) and fourth generation (4G) base stations, such as the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) Evolved Node B (eNB), it has become important to

Zero-Based Budgeting.

Science.gov (United States)

Wichowski, Chester

1979-01-01

The zero-based budgeting approach is designed to achieve the greatest benefit with the fewest undesirable consequences. Seven basic steps make up the zero-based decision-making process: (1) identifying program goals, (2) classifying goals, (3) identifying resources, (4) reviewing consequences, (5) developing decision packages, (6) implementing a…

Combining Correlation-Based and Reward-Based Learning in Neural Control for Policy Improvement

DEFF Research Database (Denmark)

Manoonpong, Poramate; Kolodziejski, Christoph; Wörgötter, Florentin

2013-01-01

Classical conditioning (conventionally modeled as correlation-based learning) and operant conditioning (conventionally modeled as reinforcement learning or reward-based learning) have been found in biological systems. Evidence shows that these two mechanisms strongly involve learning about...... associations. Based on these biological findings, we propose a new learning model to achieve successful control policies for artificial systems. This model combines correlation-based learning using input correlation learning (ICO learning) and reward-based learning using continuous actor–critic reinforcement...... learning (RL), thereby working as a dual learner system. The model performance is evaluated by simulations of a cart-pole system as a dynamic motion control problem and a mobile robot system as a goal-directed behavior control problem. Results show that the model can strongly improve pole balancing control...

Culture and group-based emotions? : Could group-based emotions be dialectical

NARCIS (Netherlands)

Lu, M.; Hamamura, T.; Doosje, B.; Suzuki, S.; Takemura, K.

2016-01-01

Group-based emotions are experienced when individuals are engaged in emotion-provoking events that implicate the in-group. This research examines the complexity of group-based emotions, specifically a concurrence of positive and negative emotions, focusing on the role of dialecticism, or a set of

Methods for Model-Based Reasoning within Agent-Based Ambient Intelligence Applications

NARCIS (Netherlands)

Bosse, T.; Both, F.; Gerritsen, C.; Hoogendoorn, M.; Treur, J.

2012-01-01

Within agent-based Ambient Intelligence applications agents react to humans based on information obtained by sensoring and their knowledge about human functioning. Appropriate types of reactions depend on the extent to which an agent understands the human and is able to interpret the available

Benefit-based tree valuation

Science.gov (United States)

E.G. McPherson

2007-01-01

Benefit-based tree valuation provides alternative estimates of the fair and reasonable value of trees while illustrating the relative contribution of different benefit types. This study compared estimates of tree value obtained using cost- and benefit-based approaches. The cost-based approach used the Council of Landscape and Tree Appraisers trunk formula method, and...

Electrophysiological correlates of strategic monitoring in event-based and time-based prospective memory.

Directory of Open Access Journals (Sweden)

Giorgia Cona

Full Text Available Prospective memory (PM is the ability to remember to accomplish an action when a particular event occurs (i.e., event-based PM, or at a specific time (i.e., time-based PM while performing an ongoing activity. Strategic Monitoring is one of the basic cognitive functions supporting PM tasks, and involves two mechanisms: a retrieval mode, which consists of maintaining active the intention in memory; and target checking, engaged for verifying the presence of the PM cue in the environment. The present study is aimed at providing the first evidence of event-related potentials (ERPs associated with time-based PM, and at examining differences and commonalities in the ERPs related to Strategic Monitoring mechanisms between event- and time-based PM tasks.The addition of an event-based or a time-based PM task to an ongoing activity led to a similar sustained positive modulation of the ERPs in the ongoing trials, mainly expressed over prefrontal and frontal regions. This modulation might index the retrieval mode mechanism, similarly engaged in the two PM tasks. On the other hand, two further ERP modulations were shown specifically in an event-based PM task. An increased positivity was shown at 400-600 ms post-stimulus over occipital and parietal regions, and might be related to target checking. Moreover, an early modulation at 130-180 ms post-stimulus seems to reflect the recruitment of attentional resources for being ready to respond to the event-based PM cue. This latter modulation suggests the existence of a third mechanism specific for the event-based PM; that is, the "readiness mode".