Effect of tungsten carbide,silicon carbide and graphite particulates on the mechanical and microstructural characteristics of AA 5052 hybrid composites

Reinforced aluminium metal matrix composite materials are being used extensively in diverse fields that include aerospace and automobile. In this investigation, we introduce two distinct and novel types of aluminium hybrid composites and characterize their mechanical properties and microstructure. The first type was fabricated by reinforcing aluminium alloy (AA 5052) with tungsten carbide (WC) and graphite particulates and the second type was fabricated by reinforcing AA 5052 with silicon carbide (SiC) and graphite particulates. The composite material was processed through the melt-stir casting method and characterized by analyzing their densities, micro hardness, Charpy impact strength, tensile strength and peak elongation. Melt-stir casting method was chosen due to its cost effectiveness and productivity. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) studies were conducted to analyze thorough mixing of the reinforcements in the aluminium matrix metal. It was found that addition of tungsten carbide and graphite particulates with AA 5052 resulted in an increase in micro hardness and Charpy impact strength by 10.3% and 34.2% respectively, which are found to be better when compared to that of adding SiC and graphite particulates with AA 5052. Moreover, tensile tests revealed that there was a drop in tensile strength for the Al/SiC/graphite composites, while the peak elongation increases for both composites. On the other hand, while adding WC and graphite particulates the tensile strength of the composite improved by 15.12%. Also, the SEM fractographs taken for Al/SiC/graphite composite samples, subjected to Charpy impact and tensile tests revealed the presence of particle fractures and cracks and confirmed the possibility of plastic deformation. The results showed the Al/WC/graphite composites to be the superior among the two fabricated composites in terms of mechanical properties and therefore have good potential for structural applications.     

The Role of Systemic Filtrating Organs in Aging and Their Potential in Rejuvenation Strategies

Advances in aging studies brought about by heterochronic parabiosis suggest that aging might be a reversable process that is affected by changes in the systemic milieu of organs and cells. Given the broadness of such a systemic approach, research to date has mainly questioned the involvement of “shared organs” versus “circulating factors”. However, in the absence of a clear understanding of the chronological development of aging and a unified platform to evaluate the successes claimed by specific rejuvenation methods, current literature on this topic remains scattered. Herein, aging is assessed from an engineering standpoint to isolate possible aging potentiators via a juxtaposition between biological and mechanical systems. Such a simplification provides a general framework for future research in the field and examines the involvement of various factors in aging. Based on this simplified overview, the kidney as a filtration organ is clearly implicated, for the first time, with the aging phenomenon, necessitating a re-evaluation of current rejuvenation studies to untangle the extent of its involvement and its possible role as a potentiator in aging. Based on these findings, the review concludes with potential translatable and long-term therapeutics for aging while offering a critical view of rejuvenation methods proposed to date.     

Origin of problems encountered in rice bran oil processing

Rice bran oil, not being a seed‐derived oil, has a composition qualitatively different from common vegetable oils and the conventional vegetable oil processing technologies are not adaptable without incurring huge losses. The oil's unusual high content of waxes, free fatty acids, unsaponifiable constituents, phospholipids, glycolipids and its dark color, all cause difficulties in the refining process. An attempt was made in this investigation to look into factors that are responsible for such difficulties and to develop suitable methodologies for physical refining of rice bran oil. Special attention was given to dewaxing, degumming and deacidification steps. The high content of glycolipids (∼6%) present in the oil was found to be a central problem and their removal appeared crucial for successful processing of the oil. We have also isolated and identified, for the first time, phosphorus‐containing glycolipids that are unique to this oil. These compounds prevent a successful degumming of the oil and their high surface activity leads to unusually high refining losses during alkali refining. A number of simple processes has been evolved, including 1) a simultaneous dewaxing and degumming process, 2) an unusual enzymatic process to degum the oil, 3) processes for the removal of the glycolipids including the phosphoglycolipids and 4) a process for the isolation of the glycolipids which may have potential applications in the food, cosmetic and pharmaceutical industries. The processing protocol suggested here becomes the first and only one to produce an oil with less than 5 ppm of phosphorus from crude rice bran oil, rendering it thus suitable for physical refining. We believe that the present results are very significant and should contribute to a better utilization of this valuable oil.     

Understanding the effects of changes on the cost‐effectiveness of regression testing techniques

Regression testing is an expensive testing process used to validate modified software. Regression test selection and test‐case prioritization can reduce the costs of regression testing by selecting a subset of test cases for execution, or scheduling test cases to meet testing objectives better. The cost‐effectiveness of these techniques can vary widely, however, and one cause of this variance is the type and magnitude of changes made in producing a new software version. Engineers unaware of the causes and effects of this variance can make poor choices in designing change integration processes, selecting inappropriate regression testing techniques, designing excessively expensive regression test suites and making unnecessarily costly changes. Engineers aware of causal factors can perform regression testing more cost‐effectively. This article reports the results of an embedded multiple case study investigating the modifications made in the evolution of four software systems and their impact on regression testing techniques. The results of this study expose tradeoffs and constraints that affect the success of techniques and provide guidelines for designing and managing regression testing processes. Copyright © 2003 John Wiley & Sons, Ltd.     

A novel method for etching trenches in silicon carbide

In this paper, a novel trench etching technique for silicon carbide is described. In this technique, ion implantation is used to first create an amorphous silicon carbide region. The amorphous layer is then etched away by wet chemical etching. Trenches of 0.3 to 0.8 μ have been obtained using a single implantaion/etching step. It has been demonstrated that deeper trenches can be obtained by repeating the implantation/etching step with platinum as a masking material. The etched surface was found to be smooth when compared with reactive ion etched surfaces reported for silicon carbide.     

Microstructural Characterisation of Ti Containing Fe-7Al-0.35C Based Low-Density Steel

In this paper, the role of Ti on the in-situ formation of carbides and its effect on the microstructure of Fe-7Al-0.35C alloy have been investigated. Initially, Thermo-Calc software was used to predict the phases present in the alloys which were validated by experimental work. Vacuum arc remelting process was used to make an alloy pancake of 10-mm thickness, which was hot-rolled to 2-mm thickness. The alloys were characterised by X-ray diffraction, optical, scanning electron microscope and electron probe micro-analysis. The results show that all the alloys exhibit two types of TiC precipitates, which are dark cuboidal as primary and dark acicular type as secondary precipitates along with grey-coloured needle-shaped κ-carbide precipitate in α(Fe–Al) matrix. The carbon present in the alloy is partitioned between TiC and κ-carbide precipitates. Addition of Ti has also resulted in grain refinement of all the alloys.     

Dynamic Modeling and Metabolic Flux Analysis for Optimized Production of Rhamnolipids

A comprehensive metabolic network based on the fundamental pathways representing the central metabolism of rhamnolipid by Pseudomonas aeruginosa is proposed and a dynamic model compatible with the underlying metabolic network is developed involving the macro-reactions derived from the elementary flux modes of the reaction network. The experimentally validated mathematical model is then coupled with a global optimization technique called differential evolution (DE) to optimize the medium composition as well as the extracellular and intracellular fluxes of the metabolic network. The analysis of the results shows the usefulness of the integrated approach involving the development of a dynamic model based on the metabolic network structure and model-based optimization of the medium composition and metabolic fluxes by an efficient evolutionary optimization technique to enhance the productivity of rhamnolipid.     

Passive mechanical properties of ovine rumen tissue

Mechanical and structural properties of ovine rumen tissue have been determined using uniaxial tensile testing of tissue from four animals at five rumen locations and two orientations. Animal and orientation did not have a significant effect on the stress-strain response, but there was a significant difference between rumen locations. Histological studies showed two orthogonal muscle layers in all regions except the reticulum, which has a more isotropic structure. A quasi-linear viscoelastic model was fitted to the relaxation stage for each region. Model predictions of the ramp stage had RMS errors of 13–24% and were within the range of the experimental data.