Properties of mechanically milled and spark plasma sintered Al–15 at.% MgB2 composite materials

Air-atomized pure aluminium powder with 15 at.% MgB₂ was mechanically milled (MMed) by using a vibrational ball mill, and MMed powders were consolidated by spark plasma sintering (SPS) to produce composite materials with high specific strength. Solid-state reactions of MMed powders have been examined by X-ray diffraction (XRD), and mechanical properties of the SPSed materials have been evaluated by hardness measurements and compression tests. Orientation images of microstructures were obtained via the electron backscatter diffraction (EBSD) technique.

The solid-state reactions in the Al–15 at.% MgB₂ composite materials occurred between the MMed powders and process control agent (PCA) after heating at 773–873 K for 24 h. The products of the solid-state reaction were a combination of AlB₂, Al₃BC and spinel MgAl₂O₄. Mechanical milling (MM) processing time and heating temperatures affect the characteristics of those intermetallic compounds. As the result of the solid-state reactions in MMed powders, a hardness increase was observed in MMed powders after heating at 573–873 K for 24 h. The full density was attained for the SPSed materials from 4 h or 8 h MMed powders in the Al–15 at.% MgB₂ composite materials under an applied pressure of 49 MPa at 873 K for 1 h. The microstructure of the SPSed materials fabricated from the MMed powders presented the bimodal aluminium matrix grain structure with the randomly distributions. The Al–15 at.% MgB₂SPSed material from powder MMed for 8 h exhibited the highest compressive 0.2% proof strength of 846 MPa at room temperature.

Synthesis of Al3BC from mechanically milled and spark plasma sintered Al-MgB2 composite materials

The aluminium-rich ternary aluminium borocarbide, Al₃BC was synthesised for the first time by solid-state reactions occurring during heat treatments after mechanical milling (MM) of pure aluminium with 15 or 50 at% MgB₂ powder mixtures in the presence of the process control agent (PCA).

The solid-state reactions in the Al–15 and 50 at% MgB₂ composite materials occurred between the MMed powders and process control agent (PCA) after heating at 773–873 K for 24 h. The products of the solid-state reaction induced Al₃BC, AlB₂, γ-Al₂O₃ and spinel MgAl₂O₄. MM processing time and heating temperatures in the Al–15 and 50 at% MgB₂ composite materials affected the selection of those intermetallic compounds. When MM processing time was increased for a given composition, the formation of the Al₃BC compound started at lower heat treatment temperatures. However, when the amount of MgB₂ was increased in the 4 h MM processing regime, the formation of the Al₃BC compound during heating was suppressed. As a result of the solid-state reactions in MMed powders the hardness was observed to increase after heating at 573–873 K for 24 h.

The fully dense bulk nano-composite materials have been successfully obtained through the combination of the MM and spark plasma sintering (SPS) processes for the 4 h or 8 h MMed powders of the Al–15 at% MgB₂ composite materials sintered under an applied pressure of 49 MPa at 873 K for 1 h.

Processing of fine-grained aluminum foam by spark plasma sintering

Porous materials are now becoming attractive to researchers interested in both scientific and industrial applications due to their unique combinations of physical, mechanical, thermal, electrical and acoustic properties in conjunction with excellent energy absorption characteristics. Metallic foams allow efficient conversion of impact energy into deformation work, which has led to increasing applications in energy absorption devices. In particular, foams made of aluminum and its alloys are of special interest because they can be used as lightweight panels, for energy absorption in crash situations and sound or heat absorbing functions in the automotive industry with the aim to reduce weight to improve crashworthiness, safety and comfort.

Mechanically alloyed and spark plasma sintered aluminium/precious metal oxide composite materials

Air-atomised pure aluminium powder with additions of 10 at.% of AgO, PtO₂ or PdO was mechanically alloyed (MAed) by using a vibrational ball mill, and MAed powders were consolidated into bulk materials by a spark plasma sintering (SPS) process. Mechano-chemical reactions among pure Al, precious metal oxide and stearic acid, added as a process control agent, during the mechanical alloying (MA) process and subsequent heat treatments were investigated by X-ray diffraction. The mechanical properties of MAed powders obtained under various heat treatment conditions and those of the SPS materials were evaluated by hardness tests. Mechano-chemical reactions occurred in Al/precious metal oxide composite powders during 36 ks of the MA process to form AlAg₂, Pt and Al₃Pd₂ for the Al-AgO, Al-PtO₂ and Al-PdO systems, respectively. Further solid-state reactions in MAed powders have been observed after heating at 373 K to 873 K for 7.2 ks. The hardness of MAed powders initially increased significantly after heating at 373 K and then generally decreased with increasing heating temperatures. The full density was obtained for the SPS materials under the conditions of an applied pressure of 49 MPa at 873 K for 3.6 ks. All the SPS materials exhibited hardness values of over 200 HV in the as-fabricated state.

Media targets: When a spark in social media develops into a mainstream media storm

This chapter investigates how public relations professionals can best manage social media crises of high interest to mainstream news media. It explores this question through a a case study of mass market retailer Target's 2012 media crisis over its fashions for girls aged 7-14. The case offers insights on the importance of monitoring social media and being prepared to step in and speak up in order to steer the public conversation that now takes place across multiple platforms

Structural evolution of spark plasma sintered AlFeCuCrMgx (x = 0, 0.5, 1, 1.7) high entropy alloys

The present paper reports synthesis of novel AlFeCuCrMgx (x = 0, 0.5, 1, 1.7 mol) high entropy alloys (HEAs) by mechanical alloying (MA) followed by spark plasma sintering (SPS). Phase evolution, microstructure and phase transformation study of the sintered alloy were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). XRD of the sintered alloys revealed the formation of two BCC phases in the AlFeCuCr alloy and more complex structures in AlFeCuCrMgx (x = 0.5, 1, 1.7) alloys containing AlFe type, BCC, and Cu2Mg type phases. TEM bright field image and selected area diffraction pattern (SAED) revealed the formation of tetragonal closed packed Cr precipitates within the Cu2Mg phase of AlFeCuCrMgx alloys (x = 0.5, 1, 1.7). DSC study of the alloys revealed no substantial phase change up to 1000 °C for AlFeCuCr alloy. Although, for x = 0.5, 1 & 1.7 phase transformation occurs at 818 °C, 885 °C & 483 °C respectively. Mg content had a significant effect on hardness, increasing to a peak hardness of 853 HVN for AlFeCuCrMg0.5 alloy before decreasing to 533 HVN for the AlFeCuCrMg1.7 alloy. The phase evolution in these alloys has been considered using thermodynamic parameters, and the structure-property relationship has also been proposed by conventional strengthening mechanisms.

A parallel random forest algorithm for big data in a spark cloud computing environment

With the emergence of the big data age, the issue of how to obtain valuable knowledge from a dataset efficiently and accurately has attracted increasingly attention from both academia and industry. This paper presents a Parallel Random Forest (PRF) algorithm for big data on the Apache Spark platform. The PRF algorithm is optimized based on a hybrid approach combining data-parallel and task-parallel optimization. From the perspective of data-parallel optimization, a vertical data-partitioning method is performed to reduce the data communication cost effectively, and a data-multiplexing method is performed is performed to allow the training dataset to be reused and diminish the volume of data. From the perspective of task-parallel optimization, a dual parallel approach is carried out in the training process of RF, and a task Directed Acyclic Graph (DAG) is created according to the parallel training process of PRF and the dependence of the Resilient Distributed Datasets (RDD) objects. Then, different task schedulers are invoked for the tasks in the DAG. Moreover, to improve the algorithm's accuracy for large, high-dimensional, and noisy data, we perform a dimension-reduction approach in the training process and a weighted voting approach in the prediction process prior to parallelization. Extensive experimental results indicate the superiority and notable advantages of the PRF algorithm over the relevant algorithms implemented by Spark MLlib and other studies in terms of the classification accuracy, performance, and scalability.

Electromagnetic receiving properties of overhead power line

This paper examines the use of overhead power transmission lines as electromagnetic sensors for detecting electric discharges caused by defective power transmission equipment. The experimental study involved the use of a spark gap (point-point configuration) and two HV conductors of different lengths to simulate electric discharge that takes place on transmission line. The experimental results show that large amount of energy are coupled onto the conductors and the amount of electromagnetic energy is dependent on the length of the conductor and the distance between the source and the conductor.

Auditor independence and the nexus with corporate governance-quo vadis?

"Where were the auditors?" Yet again, the independence of the auditor has come under close, critical scrutiny with ongoing collapses of large listed companies, which have global implications for the proper functioning of investment markets. The most recent collapse being that of ENRON in the United States of America, (USA).

"Who are the auditors?" The nexus of auditor independence with corporate governance is examined drawing on Foucault's notion of the relationships between power I knowledge and ethics in the construction of ethical identity. In the face of declining public confidence and demands for more stringent regulation, the tensions between greater self-regulation of auditors by the accounting profession and moves by governments to impose more stringent legislation I regulation, including the creation of public oversight bodies is apparent. This paper presents a comparative analysis of recent developments internationally, with particular reference to South Africa and Australia, intended to more rigorously enforce auditor independence and improve corporate governance. Five key areas identified by various Commissions and regulatory bodies that are regarded as posing significant threats to auditor independence are highlighted. Recommendations for changes to independence requirements in professional codes of ethics and corporate legislation, intended to safeguard auditor independence and to enhance investor protection, are critically examined. It is argued that the "new" independence recommendations while providing more detailed guidance for dealing with the independence threats fail to introduce any new concepts and may be found as ineffective as the plethora of earlier regulations. (This paper represents work in progress, which is intended to spark debate, and accordingly, the authors invite comment from readers to develop further aspects of research into this critical area).

Comparison of static and dynamic engine models on the transient performance of a passenger vehicle powertrain

This paper presents experimental and computational results obtained on the Ford Barra 190 4.0 litres I6 gasoline engine and on the Ford Falcon car equipped with this engine. Measurements of steady engine performance, fuel consumption and exhaust emissions were first collected using an automated test facility for a wide range of cam and spark timings vs. throttle position and engine speed. Simulations were performed for a significant number of measured operating points at full and part load by using a coupled Gamma Technologies GT-POWER/GT-COOL engine model for gas exchange, combustion and heat transfer. The fluid model was made up of intake and exhaust systems, oil circuit, coolant circuit and radiator cooling air circuit. The thermal model was made up of finite element components for cylinder head, cylinder, piston, valves and ports and wall thermal masses for pipes. The model was validated versus measured steady state air and fuel flow rates, cylinder pressure parameters, indicated and brake mean effective pressures, and temperature of metal, oil and coolant in selected locations. Computational results agree well with experiments, demonstrating the ability of the approach to produce fairly accurate steady state maps of BMEP and BSFC, as well as to optimize engine operation changing geometry, throttle position, cam and spark timing. Measurements of the transient performance and fuel consumption of the full vehicle were then collected over the NEDC cycle. Simulations were performed by using a coupled Gamma Technologies GT-POWER/GT-COOL/GT-DRIVE model for instantaneous engine gas exchange, combustion and heat transfer and vehicle motion. The full vehicle model is made up of transmission, driveshaft, axles, and car components and the previous engine model. The model was validated with measured fuel flow rates through the engine, engine throttle position, and engine speed and oil and coolant temperatures in selected locations. Instantaneous engine states following a time dependent demand for torque and speed differ from those obtained by interpolating steady state maps of BSFC vs. BMEP and speed. Computational results agree well with experiments, demonstrating the utility of the approach in providing a more accurate prediction of the fuel consumption over test cycles.

Processing and characterization of porous aluminum

Aluminum foams are now being introduced into automotive industry to reduce weight, to absorb energy in crash situations and to carry sound or heat absorbing functions. In the present study, a novel Spark Plasma Sintering (SPS) process for producing porous aluminums with controlled pore size and porosity and superior energy absorption has been developed. Experimental procedures included the mixing of starting powders, compacting, SPS sintering and leaching out of the space-holding particles. Porous aluminums with various porosities and a wide range of pore size distributions can be produced by the SPS process. Optical microscopy, scanning electron microscopy (SEM) and quantitative image analyses were used to characterize the porous aluminums. Compressive tests were carried out on the aluminum foams to evaluate the mechanical properties.

Angiotensin converting enzyme inhibition lowers body weight and improves glucose tolerance in C57BL/6J mice maintained on a high fat diet

The renin–angiotensin system (RAS) is functional within adipose tissue and angiotensin II, the active component of RAS, has been implicated in adipose tissue hypertrophy and insulin resistance. In this study, captopril, an angiotensin converting enzyme (ACE) inhibitor that prevents angiotensin II formation, was used to study the development of diet-induced obesity and insulin resistance in obesity prone C57BL/6J mice. The mice were fed a high fat diet (w/w 21% fat) and allowed access to either water or water with captopril added (0.2 mg/ml). Body weight was recorded weekly and water and food intake daily. Glucose tolerance was determined after 11–12 weeks. On completion of the study (after 16 weeks of treatment), the mice were killed and kidney, liver, epididymal fat and extensor digitorum longus muscle (EDL) were weighed. Blood samples were collected and plasma analysed for metabolites and hormones. Captopril treatment decreased body weight in the first 2 weeks of treatment. Food intake of captopril-treated mice was similar to control mice prior to weight loss and was decreased after weight loss. Glucose tolerance was improved in captopril-treated mice. Captopril-treated mice had less epididymal fat than control mice. Relative to body weight, captopril-treated mice had increased EDL weight. Relative to control mice, mice administered captopril had a higher plasma concentration of adiponectin and lower concentrations of leptin and non-esterified fatty acids (NEFA). The results indicate that captopril both induced weight loss and improved insulin sensitivity. Thus, captopril may eventually be used for the treatment of obesity and Type 2 diabetes.