Phase Field Simulation of Equiaxed Microstructure Formation during Semi-solid Processing of A380 Al Alloy

A phase field modelling approach is implemented in the present study towards simulation of microstructure evolution during cooling slope semi solid slurry generation process of A380 Aluminium alloy. First, experiments are performed to evaluate the number of seeds required within the simulation domain to simulate near spherical microstructure formation, occurs during cooling slope processing of the melt. Subsequently, microstructure evolution is studied employing a phase field method. Simulations are performed to understand the effect of cooling rate on the slurry microstructure. Encouraging results are obtained from the simulation studies which are validated by experimental observations. The results obtained from mesoscopic phase field simulations are grain size, grain density, degree of sphericity of the evolving primary Al phase and the amount of solid fraction present within the slurry at different time frames. Effect of grain refinement also has been studied with an aim of improving the slurry microstructure further. Insight into the process has been obtained from the numerical findings, which are found to be useful for process control.

Formation of annular austenitic ring between outer ferrite layer and solid globule in a semi-solid processed SS 304L

The microstructure of an austenitic SS 304L rapidly quenched from its semi-solid state shows a unique annular austenitic ring in between the core of each globule and its ferritic outer layer. On the basis of experimental results and microstructural analysis, it is proposed that the ring is formed as a result of preferential austenitic phase nucleation in a small quantity of liquid entrapped between adjacent solid globules during rapid quenching, in spite of the fact that ferrite is the thermodynamically stable phase for the alloy. (C) 2014 Elsevier B.V. All rights reserved.

Study of Microstructure Evolution during Semi-Solid Processing of an In-Situ Al Alloy Composite

In the present work, effect of pouring temperature (650 degrees C, 655 degrees C, and 660 degrees C) on semi-solid microstructure evolution of in-situ magnesium silicide (Mg2Si) reinforced aluminum (Al) alloy composite has been studied. The shear force exerted by the cooling slope during gravity driven flow of the melt facilitates the formation of near spherical primary Mg2Si and primary Al grains. Shear driven melt flow along the cooling slope and grain fragmentation have been identified as the responsible mechanisms for refinement of primary Mg2Si and Al grains with improved sphericity. Results show that, while flowing down the cooling slope, morphology of primary Mg2Si and primary Al transformed gradually from coarse dendritic to mixture of near spherical particles, rosettes, and degenerated dendrites. In terms of minimum grain size and maximum sphericity, 650 degrees C has been identified as the ideal pouring temperature for the cooling slope semi-solid processing of present Al alloy composite. Formation of spheroidal grains with homogeneous distribution of reinforcing phase (Mg2Si) improves the isotropic property of the said composite, which is desirable in most of the engineering applications.

Optimality Conditions and Duality for Semi-Infinite Mathematical Programming Problem with Equilibrium Constraints

This article considers a semi-infinite mathematical programming problem with equilibrium constraints (SIMPEC) defined as a semi-infinite mathematical programming problem with complementarity constraints. We establish necessary and sufficient optimality conditions for the (SIMPEC). We also formulate Wolfe- and Mond-Weir-type dual models for (SIMPEC) and establish weak, strong and strict converse duality theorems for (SIMPEC) and the corresponding dual problems under invexity assumptions.

Retrieval and Multi-scale Validation of Soil Moisture from Multi-temporal SAR Data in a Semi-Arid Tropical Region

The current study presents an algorithm to retrieve surface Soil Moisture (SM) from multi-temporal Synthetic Aperture Radar (SAR) data. The developed algorithm is based on the Cumulative Density Function (CDF) transformation of multi-temporal RADARSAT-2 backscatter coefficient (BC) to obtain relative SM values, and then converts relative SM values into absolute SM values using soil information. The algorithm is tested in a semi-arid tropical region in South India using 30 satellite images of RADARSAT-2, SMOS L2 SM products, and 1262 SM field measurements in 50 plots spanning over 4 years. The validation with the field data showed the ability of the developed algorithm to retrieve SM with RMSE ranging from 0.02 to 0.06 m(3)/m(3) for the majority of plots. Comparison with the SMOS SM showed a good temporal behaviour with RMSE of approximately 0.05 m(3)/m(3) and a correlation coefficient of approximately 0.9. The developed model is compared and found to be better than the change detection and delta index model. The approach does not require calibration of any parameter to obtain relative SM and hence can easily be extended to any region having time series of SAR data available.

A semi-automated, field-portable microscopy platform for clinical diagnostic applications

Clinical microscopy is a versatile diagnostic platform used for diagnosis of a multitude of diseases. In the recent past, many microfluidics based point-of-care diagnostic devices have been developed, which serve as alternatives to microscopy. However, these point-of-care devices are not as multi-functional and versatile as clinical microscopy. With the use of custom designed optics and microfluidics, we have developed a versatile microscopy-based cellular diagnostic platform, which can be used at the point of care. The microscopy platform presented here is capable of detecting infections of very low parasitemia level (in a very small quantity of sample), without the use of any additional computational hardware. Such a cost-effective and portable diagnostic device, would greatly impact the quality of health care available to people living in rural locations of the world. Apart from clinical diagnostics, it's applicability to field research in environmental microbiology has also been outlined. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Coupling geomorphology parameters with lithology for micro-level groundwater resource assessment: a case study from semi-arid hard rock terrain in Tamil Nadu, India

The standard procedure of groundwater resource estimation in India till date is based on the specific yield parameters of each rock type (lithology) derived through pumping test analysis. Using the change in groundwater level, specific yield, and area of influence, groundwater storage change could be estimated. However, terrain conditions in the form of geomorphological variations have an important bearing on the net groundwater recharge. In this study, an attempt was made to use both lithology and geomorphology as input variables to estimate the recharge from different sources in each lithology unit influenced by the geomorphic conditions (lith-geom), season wise separately. The study provided a methodological approach for an evaluation of groundwater in a semi-arid hard rock terrain in Tirunelveli, Tamil Nadu, India. While characterizing the gneissic rock, it was found that the geomorphologic variations in the gneissic rock due to weathering and deposition behaved differently with respect to aquifer recharge. The three different geomorphic units identified in gneissic rock (pediplain shallow weathered (PPS), pediplain moderate weathered (PPM), and buried pediplain moderate (BPM)) showed a significant variation in recharge conditions among themselves. It was found from the study that Peninsular gneiss gives a net recharge value of 0.13 m/year/unit area when considered as a single unit w.r.t. lithology, whereas the same area considered with lith-geom classes gives recharge values between 0.1 and 0.41 m/year presenting a different assessment. It is also found from this study that the stage of development (SOD) for each lith-geom unit in Peninsular gneiss varies from 168 to 230 %, whereas the SOD is 223 % for the lithology as a single unit.

Die Filling Behaviour of Semi Solid A356 Al Alloy Slurry During Rheo Pressure Die Casting

The present work discusses the findings obtained from simulations of semi solid die filling of a steering knuckle, prior to actual component development using in-house developed rheo pressure die casting system. Die filling capability of A356 Al alloy at semi-solid state has been investigated using commercial software Flow-3Dcast to optimise the pouring temperature of semi-solid slurry into the die cavity, while all other variables such as gating design, die preheat temperature and injection velocity are kept constant based on the prior knowledge obtained from trial numerical simulations and experimentation. Efforts have been made to nullify the essence of costly, time consuming experiments towards obtaining high-quality castings out of the findings obtained from numerical simulations. The optimum pouring temperature identified in the present study is 610 A degrees C, which facilitates smoother slurry flow, minimum surface defect concentration, uniform temperature field and solid fraction distribution within the component cavity.

Investigations of aerosol black carbon from a semi-urban site in the Indo-Gangetic Plain region

Long-term (2009-2012) data from ground-based measurements of aerosol black carbon (BC) from a semi-urban site, Pantnagar (29.0 degrees N, 79.5 degrees E, 231 m amsl), in the Indo-Gangetic Plain (IGP) near the Himalayan foothills are analyzed to study the regional characterization. Large variations are seen in BC at both diurnal and seasonal scales, associated with the mesoscale and synoptic meteorological processes, and local/regional anthropogenic activities. BC diurnal variations show two peaks (morning and evening) arising from the combined effects of the atmospheric boundary layer (ABL) dynamics and local emissions. The diurnal amplitudes as well as the rates of diurnal evolution are the highest in winter season, followed by autumn, and the lowest in summer-monsoon. BC exhibits nearly an inverse relation with mixing layer depth in all seasons; being strongest in winter (R-2 = 0.89) and weakest (R-2 = 0.33) in monsoon (July-August). Unlike BC, co-located aerosol optical depths (AOD) and aerosol absorption are highest in spring over IGP, probably due to the presence of higher abundances of aerosols (including dust) above the ABL (in the free troposphere). AOD (500 nm) showed annual peak (>0.6) in May-June, dominated by coarse mode, while fine mode aerosols dominated in late autumn and early winter. Aerosols profiles from CALIPSO show highest values close to the surface in winter/autumn, similar to the feature seen in surface BC, whereas at altitudes > 2 km, the extinction is maximum in spring/summer. WRF-Chem model is used to simulate BC temporal variations and then compared with observed BC. The model captures most of the important features of the diurnal and seasonal variations but significantly underestimated the observed BC levels, suggesting improvements in diurnal and seasonal varying BC emissions apart from the boundary layer processes. (C) 2015 Elsevier Ltd. All rights reserved.

Effect of semi-solid heat treatment on elevated temperature plasticity of 304L stainless steel

The present work explores the potential of semi-solid heat treatment technique by elucidating its effect on the plastic behavior of 304L SS in hot working domain. To accomplish this objective, hot isothermal compression tests on 304L SS specimens with semi-solid heat treatment and conventional annealing heat treatment have been carried out within a temperature range of 1273-1473 K and strain rates ranging from 0.01 to 1 s(-1). The dynamic flow behavior of this steel in its conventional heat-treated condition and semi-solid heat-treated condition has been characterized in terms of strain hardening, temperature softening, strain rate hardening, and dynamic flow softening. Extensive microstructural investigation has been carried out to corroborate the results obtained from the analysis of flow behavior. Detailed analysis of the results demonstrates that semi-solid heat treatment moderates work hardening, strain rate hardening, and temperature sensitivity of 304L SS, which is favorable for hot deformation. The post-deformation hardness values of semi-solid heat-treated steel and conventionally heat-treated steel were found to remain similar despite the pre-deformation heat treatment conditions. The results obtained demonstrate the potential of semi-solid heat treatment as a pre-deformation heat treatment step to effectively reduce the strength of the material to facilitate easier deformation without affecting the post-deformation properties of the steel.

Flame Propagation of H_2-Air in a Semi-Open Obstructed Tube

针对氢／空气混合物,通过实验研究了其预混火焰在半开口管道中的火焰传播加速现象,结果表明,火焰传播状态随着氢气当量比的变化而发生改变。当氢／空气混合物被点燃后,由于障碍物的扰动,火焰在管道中不断加速传播,并最终到达一准稳态传播。在氢气当量比0.31附近时,火焰速度发生跃变。当氢气当量比足够大时,火焰传播由爆燃态转变为爆轰态。在本实验条件下,爆燃转准爆轰的临界条件是d/Lambda>=2.6（d是圆环形障碍物内径,人是爆轰格胞尺度）。障碍物阻塞比的变化对最大火焰速度和压力提升的影响不明显。

Implementación de tres métodos de cosecha para la evaluación de producción y calidad en semilla de pasto Brachiaria brizantha. CIAT-6780 c.v Marandu

El presente trabajo tuvo, como objetivo evaluar en términos biológicos y económicos, el efecto de la implementación de 3 métodos de cosecha, (Cosecha normal, cosecha escalonada y recolección del suelo), para la evaluación de producción y calidad en semilla de Brachiaria brizantha CIAT 6780 cv Marandú. Este se llevó acabo en el km.14 ½ de la carretera norte, 2 km. al sur, en el Instituto Nacional de Investigación Agropecuaria (INTA)-(CNIA). El análisis de calidad de la semilla se realizó, empleando la metodología utilizada por el CIAT, para el análisis de calidad de semillas brozosas (con gran cantidad de residuos de inflorescencias). Se utilizó un diseño de bloque completo al azar con tres métodos de cosecha como tratamiento y tres repeticiones por tratamiento. Los resultados demuestran que los métodos de cosecha tuvieron efectos estadísticamente significativos (P<0.01) sobre el rendimiento de semilla cruda y semilla pura por hectárea. El incremento en el rendimiento de semilla cruda estuvo influenciado por la mayor cantidad de material inerte contenido en la muestra del tratamiento tres (Recolección del suelo) similar comportamiento presentaron los componentes estructurales longitud del raquiz, longitud del raquisillo, número de raquisillo y espiguillas por raquisillo (promedio). En el caso de los componentes estructurales número de plantas y número de espiguillas por raquisillo no hubo diferencias de efectos sobre el rendimiento. Para el análisis estadístico de las variables de calidad en la semilla, se realizó la prueba de Duncan para las diferencias de proporciones. El porcentaje de semilla pura presentó su máximo de valor con el método de cosecha normal aplicado como tratamiento uno. Para el porcentaje de viabilidad el valor más alto resultó con el método de barrido o recolección del suelo aplicado como tratamiento tres, estos resultados coinciden con lo reportado por el CIAT 1980; García y Ferguson, 1984 comparan la eficiencia relativa de los diferentes métodos de cosecha, en la cual la recolección de semilla caída ofrece el mayor porcentaje de germinación. De todos los tratamientos evaluados, el máximo beneficio monetario se obtuvo con la implementación del método de cosecha escalonado (US$565/ha). Sin embargo la cosecha normal fue el tratamiento con el que se obtuvo el mayor margen de ingreso bruto (83% del ingreso total), en comparación a los otros dos métodos de cosecha aplicados como tratamiento.

Estudio del crecimiento del camarón de agua dulce (M rosenbergu), en condiciones semi-intensivas en la comunidad de Alos Encuentros, Municipio de Limay, Esteli

Con el propósito de determinar el comportamiento de rasgos de crecimiento del camarón de agua dulce M. rosenbergii. Se montó un ensayo en la comunidad de los Encuentros, municipio de Limay, Estelí. Para tal efecto se utilizaron tres estanques de tierra de 200m 3 c/u en los que se sembraron 5 post larvas/m2. La alimentación fue a base de concentrado con 35%, 25%, 20% de proteína respectivamente de manera igual para los tres estanques. Se efectuaron muestreos, de talla, peso con respecto a la edad siendo estos el primer muestreo al momento de la siembra el segundo a los 30 días y los restantes cada 20 días, hasta los 190 días que culminó el ensayo, para determinar el crecimiento de los camarones de agua dulce M. rosenhergií mediante análisis estadísticos se empleó el modelo no lineal sugerido por Pearl-read (1923) y = k/1+bea:. Para realizar un menor ajuste de los datos se procedió a linealizarlos por medio de una regresión con la ecuación: Ln (k/y)-1 = Lnb±ax. Para el primer estanque se construyó el modelo Ln(k/y)-1 = 6.69459 = 0.97948 (cm), el error estándar para Lnb y a son de 0.338010.57300 respectivamente, laPr> ltl iguala 1.0001con r2 = 0.976605 y C.V= 29.66412. En el segundo estanque se obtuvo Ln(kly)-1 = 6.53469- 0.89897 (cm) el error standard para Lnb y a son de 0.4235;0.6858. La Pr > ltl para ambos son de 0.0001 con r1 = 0.96084 y C.V= 36.20477, para el tercer estanque se tiene valores de Ln (k/y)-1 = 6.93459- 1.116595 (cm) con error standard de Lnb y a = 1.04923; 0.180752 y para Pr > ltl fue de 0.0003;0.0005 con un r2= 0.8450 y C.V = 126.7102, al hacer un análisis de regresión combinando los tres estanques se obtuvo valores deLn(k/y)-1 = 5.5224-0.8068 (cm) con errores standard de Lnb y a= O.2878; 0.480 y para Pr > ltl fue de 0.0001 con un r2=; 0.9700 y C.V = 31.489, el comportamiento de crecimiento de los camarones de agua dulce M. rosenbergii sometidos a estudio bajo las mismas condiciones de cultivo tuvieron diferencias de talla y peso siendo éstas de 0.331 cm; 2.S02 g. del estanque 2 vs estanque 1; 1.093 cm, 4.3500 g del estanque 2 vs estanque 3 y 0.762 cm; 1.848 g para el estanque 1 vs estanque 3, sin embargo para los estanques en estudio se observó un aumento de talla y peso entre los 110-130 días de edad.