Influence of melt pouring temperature and plate inclination on solidification and microstructure of A356 aluminum alloy produced using oblique plate

The preparation of semisolid slurry of A356 aluminum alloy using an oblique plate was investigated. A356 alloy melt undergoes partial solidification when it flows down on an oblique plate cooled from underneath by counter flowing water. It results in continuous formation of columnar dendrites on plate wall. Due to forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously to produce semisolid slurry at plate exit. Melt pouring temperature provides required condition of solidification whereas plate inclination enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained was solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets were heat treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets were analyzed. Effects of melt pouring temperature and plate inclination on solidification and microstructure of billets produced using oblique plate were described. The investigations involved four different melt pouring temperatures (620, 625, 630 and 635 degrees C) associated with four different plate inclinations (30 degrees, 45 degrees, 60 degrees and 75 degrees). Melt pouring temperature of 625 degrees C with plate inclination of 60 degrees shows fine and globular microstructures and it is the optimum.

Influence of plate length and plate cooling rate on solidification and microstructure of A356 alloy produced by oblique plate

A356 alloy melt solidifies partially when it flows down on an oblique plate cooled from bottom by counter flowing water. Columnar dendrites are continuously formed on the plate wall. Because of the forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously by producing semisolid slurry at plate exit. Plate cooling rate provides required extent/amount of solidification whereas plate length enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained is solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets are also heat-treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets are compared. The effects of plate length and plate cooling rate on solidification and microstructure of billets produced by using oblique plate are illustrated. Three different plate lengths (200 mm, 250 mm, 300 mm) associated with three different heat transfer coefficients (1000, 2000 and 2500 W/(m(2).K)) are involved. Plate length of 250 mm with heat transfer coefficient of 2000 W/(m(2).K) gives fine and globular microstructures and is the optimum as there is absolutely no possibility of sticking of slurry to plate wall.

Photo-induced optical bleaching in Ge12Sb25S63 amorphous chalcogenide thin films: effect of 532 nm laser illumination

The photo-induced effects of Ge12Sb25S63 films illuminated with 532 nm laser light are investigated from transmission spectra measured by FTIR spectroscopy. The material exhibits photo-bleaching (PB) when exposed to band gap light for a prolonged time in a vacuum. The PB is ascribed to structural changes inside the film as well as surface photooxidation. The amorphous nature of thin films was detected by x-ray diffraction. The chemical composition of the deposited thin films was examined by energy dispersive x-ray analysis (EDAX). The refractive indices of the films were obtained from the transmission spectra based on an inverse synthesis method and the optical band gaps were derived from optical absorption spectra using the Tauc plot. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. It was found that the mechanism of the optical absorption follows the rule of the allowed non-direct transition. Raman and x-ray photoelectron spectra (XPS) were measured and decomposed into several peaks that correspond to the different structural units which support the optical changes.

Numerical study of solidification of A356 aluminum alloy flowing on an oblique plate with experimental validation

Molten A356 aluminum alloy flowing on an oblique plate is water cooled from underneath. The melt partially solidifies on plate wall with continuous formation of columnar dendrites. These dendrites are continuously sheared off into equiaxed/fragmented grains and carried away with the melt by producing semisolid slurry collected at plate exit. Melt pouring temperature provides required solidification whereas plate inclination enables necessary shear for producing slurry of desired solid fraction. A numerical model concerning transport equations of mass, momentum, energy and species is developed for predicting velocity, temperature, macrosegregation and solid fraction. The model uses FVM with phase change algorithm, VOF and variable viscosity. The model introduces solid phase movement with gravity effect as well. Effects of melt pouring temperature and plate inclination on hydrodynamic and thermo-solutal behaviors are studied subsequently. Slurry solid fractions at plate exit are 27%, 22%, 16%, and 10% for pouring temperatures of 620 degrees C, 625 degrees C, 630 degrees C, and 635 degrees C, respectively. And, are 27%, 25%, 22%, and 18% for plate inclinations of 30, 45, 60, and 75, respectively. Melt pouring temperature of 625 degrees C with plate inclination of 60 generates appropriate quality of slurry and is the optimum. Both numerical and experimental results are in good agreement with each other. (C) 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

RF plasma enhanced MOCVD of yttria stabilized zirconia thin films using octanedionate precursors and their characterization

Yttria stabilized zirconia thin films have been deposited by RF plasma enhanced MOCVD technique on silicon substrates at substrate temperature of 400 degrees C. Plasma of precursor vapors of (2,7,7-trimethyl-3,5-octanedionate) yttrium (known as Y(tod)(3)), (2,7,7-trimethyl-3,5-octanedionate) zirconium (known as Zr(tod)(4)), oxygen and argon gases is used for deposition. To the best of our knowledge, plasma assisted MOCVD of YSZ films using octanediaonate precursors have not been reported in the literature so far. The deposited films have been characterized by GIXRD, FTIR, XPS, FESEM, AFM, XANES, EXAFS, EDAX and spectroscopic ellipsometry. Thickness of the films has been measured by stylus profilometer while tribological property measurement has been done to study mechanical behavior of the coatings. Characterization by different techniques indicates that properties of the films are dependent on the yttria content as well as on the structure of the films. (C) 2015 Elsevier B.V. All rights reserved.

Effect of laser irradiation on optical properties of Ge12Sb25Se63 amorphous chalcogenide thin films

The change in photo-induced optical properties in thermally evaporated Ge12Sb25Se63 chalcogenide thin film under 532-nm laser illumination has been reported in this paper. The structure and composition of the film have been examined by X-ray diffraction and energy dispersive X-ray analysis, respectively. The optical properties such as refractive index, extinction coefficient and thickness of the films have been determined from the transmission spectra based on inverse synthesis method and the optical band gap has been derived from optical absorption spectra using the Tauc plot. It has been found that the mechanism of the optical absorption is due to allowed indirect transition. The optical band gap increases by 0.05 eV causing photo-bleaching mechanism, while refractive index decreases because of reduction in structural disordering. Deconvolution of Raman and X-ray photoelectron spectra into several peaks provides different structural units, which supports the optical photo-bleaching.

Enhanced Metastatic Potential in a 3D Tissue Scaffold toward a Comprehensive in Vitro Model for Breast Cancer Metastasis

Metastasis is clinically the most challenging and lethal aspect of breast cancer. While animal-based xenograft models are expensive and time-consuming, conventional two-dimensional (2D) cell culture systems fail to mimic in vivo signaling. In this study we have developed a three-dimensional (3D) scaffold system that better mimics the topography and mechanical properties of the breast tumor, thus recreating the tumor microenvironment in vitro to study breast cancer metastasis. Porous poly(e-caprolactone) (PCL) scaffolds of modulus 7.0 +/- 0.5 kPa, comparable to that of breast tumor tissue were fabricated, on which MDA-MB-231 cells proliferated forming tumoroids. A comparative gene expression analysis revealed that cells growing in the scaffolds expressed increased levels of genes implicated in the three major events of metastasis, viz., initiation, progression, and the site-specific colonization compared to cells grown in conventional 2D tissue culture polystyrene (TCPS) dishes. The cells cultured in scaffolds showed increased invasiveness and sphere efficiency in vitro and increased lung metastasis in vivo. A global gene expression analysis revealed a significant increase in the expression of genes involved in cell cell and cell matrix interactions and tissue remodeling, cancer inflammation, and the PI3K/Akt, Wnt, NF-kappaB, and HIFI signaling pathways all of which are implicated in metastasis. Thus, culturing breast cancer cells in 3D scaffolds that mimic the in vivo tumor-like microenvironment enhances their metastatic potential. This system could serve as a comprehensive in vitro model to investigate the manifold mechanisms of breast cancer metastasis.

A Salmonella Typhimurium-Typhi genomic chimera: a model to study Vi polysaccharide capsule function in vivo.

The Vi capsular polysaccharide is a virulence-associated factor expressed by Salmonella enterica serotype Typhi but absent from virtually all other Salmonella serotypes. In order to study this determinant in vivo, we characterised a Vi-positive S. Typhimurium (C5.507 Vi(+)), harbouring the Salmonella pathogenicity island (SPI)-7, which encodes the Vi locus. S. Typhimurium C5.507 Vi(+) colonised and persisted in mice at similar levels compared to the parent strain, S. Typhimurium C5. However, the innate immune response to infection with C5.507 Vi(+) and SGB1, an isogenic derivative not expressing Vi, differed markedly. Infection with C5.507 Vi(+) resulted in a significant reduction in cellular trafficking of innate immune cells, including PMN and NK cells, compared to SGB1 Vi(-) infected animals. C5.507 Vi(+) infection stimulated reduced numbers of TNF-α, MIP-2 and perforin producing cells compared to SGB1 Vi(-). The modulating effect associated with Vi was not observed in MyD88(-/-) and was reduced in TLR4(-/-) mice. The presence of the Vi capsule also correlated with induction of the anti-inflammatory cytokine IL-10 in vivo, a factor that impacted on chemotaxis and the activation of immune cells in vitro.

Estudio de la adaptación y estabilidad fenotípica de veintitrés variedades de sorgo granífero evaluadas en Nicaragua

Se analizo la adaptación y estabilidad fenotipica de 23 variedades de sorgo granifero usando los rendimientos en grano obtenidos al evaluarlas en un periodo de diez años (1964-1973), en once localidades de Nicaragua. Para el análisis se usaron las variedades muestreadas que presentaron resultados de cinco años, por lo menos, y sembradas de primera postrera y algunas de riego. El estudio de adaptación de la población total de variedades se facilito por la transformación de los rendimientos a escala logarítmica, ya que por este medio se induce linealidad y homogeneidad del error experimental. Para cada variedad se calculo el coeficiente de regresión lineal de rendimiento individual, utilizando como variable dependiente el rendimiento de la variedad en cada localidad y año con su respectiva época de siembra y como variable independiente, el promedio del rendimiento de todas las variedades por localidad y año con su respectiva época de siembra, como medida del ambiente. Los dos indices importantes en este tipo de análisis fueron el coeficiente de regresión y el rendimiento de la variedad en todos los ambientes, que graficados como coordenadas en un plano de dos dimensiones "Diagrama de dispersión" facilito la identificación de la adaptación de cada variedad y su grado de estabilidad fenotipica, lo mismo que las lineas de regresión. El rendimiento de todas las variedades por cada sitio y época proporcionaron una clasificación cuantitativa de los medios ambientes y debido al análisis descrito, pueden ser identificables las variedades específicamente adaptadas a buenas o malas estaciones, y las que muestran una estabilidad general. Fue estudiada la adaptación de variedades de sorgo granifero provenientes de los centros de distribución comercial: DEKALB, PIONEER, NORTHRUP KING, ASGROW SEED CO en su mayoría. Fue evidente tanto en el rendimiento como en la sensibilidad al medio ambiente (al representarse por el coeficiente de regresión) la variación de respuestas de las variedades. Como puede apreciarse en las respuestas extraordinarias del genotipo en distintos ambientes. Las variedades analizadas presentaron variación específicamente definidas; muchas de las cuales se adaptaron bien a los ambientes en donde se evaluaron (con coeficiente de regresión próximos a b=1.0) otro grupo como el caso de NK-280, Flare con estabilidad notablemente superior al grupo estudiado, se adaptan bien a ambientes desfavorables. Por otro lado Hegary, E-57 tienden a adaptarse a ambientes favorables.

Evaluación del rendimiento de sorgos híbridos comerciales para grano

La importancia que posee el presente trabajo, estriba en que suministra un valioso aporte al agriculturado nacional, como fuente de información acerca de los híbridos que más rinden y se adaptan mejor a nuestro clima. Las variedades comerciales objeto del estudio fueron 30, de las cuales 28 son híbridos, una es un sorgo mejorado y otra un sorgo criollo o testigo local. Estas variedades se sembraron de acuerdo al diseño experimental "Bloques al azar con cuatro repeticiones", parcelas con tres surcos cada una, de cinco metros de largo por un metro de separación entre surco. La siembra se efectuó a chorrillo seguido. Los resultados de este ensayo se concretan a lo siguiente: Los rendimientos de las variedades mostraron diferencias altamente significativas comparadas a nivel de 5 por ciento. El mayor rendimiento de grano se obtuvo con el híbrido Dekald D-50-A con 5.075 kilogramos de grano por hectárea, en la prueba de Duncan resulta significativamente diferente a las demás. El siguiente rendimiento corresponde desde el híbrido Dekald D-D-50 con 4.521 kilogramos por hectárea, que no resulta significativo con los subsiguientes 13 híbridos hasta el Dekalb F-63 con 2.982 kilogramos por hectárea. Luego el Dekalb B-R-60 con 3.967 kilogramos por hectárea rendimiento que no resulta significativo con los 20 híbridos que le siguen hasta el Payneo que rindió 2.588 kilogramos por hectárea. El cuarto y último rendimiento es a partir del NK-300 cuyo rendimiento de 3.319 kilogramos de grano por hectárea no manifiesta diferencia significativa con ninguno de los siguientes rendimientos. (ver cuadro N° 3). En base a la prueba de rango múltiple de Duncan, resultan los cuatro rendimientos citados, de los cuales los tres primeros grupos abarcan un total de 22 variedades cuyos rendimientos se consideran buenos. Es importante hacer notar que los rendimientos descritos corresponden a una sola cosecha, no se verificó la segunda porque se manifestó una irregularidad en la cosecha ocasionada por la inundación y plaga de pájaros.