Hot-tearing in Aluminium Copper Alloys

An experimental technique has been developed to investigate hot tearing. In this technique either the load or strain built up during casting could be measured as a function of the mould wall temperature. Experiments were carried out in Al—Cu alloys. Although there was considerable scatter in the results, it was concluded that strength began to build up in the casting when either the liquid volume fraction reached about 4% or when the eutectic temperature was reached. It was also concluded that the initial crack or hot tear occurred in a thin film of liquid or in the solid just below the eutectic temperature. It is suggested that the crack occurs in the liquid when the alloy composition is less than the most susceptible hot tearing composition and in the solid for higher compositions. The crack occurs in the liquid when the liquid volume fraction reaches about 2%. A numerical analysis was made of the heat flow in the casting so that corrections could be made to the thermocouple readings and a technique was developed to calculate the heat transfer coefficient from temperatures measured near the mould wall.     

Coupled BEM and FEM Analysis of Functionally Graded Material Layers

ABSTRACT

This study presents the development of a boundary element method (BEM) capable of including functionally graded materials in order to capture the correct behavior of the underfill material in electronic packages. In order to take advantage of the salient features of both FEM and BEM, this study also couples the BEM solution with the conventional FEM solution while satisfying the continuity of displacements and equilibrium of tractions along the interfaces.     

Effect of Purity Levels on the High-Temperature Deformation Characteristics of Severely Deformed Titanium

In the present investigation, high-temperature compression tests were conducted at strain rates of 0.001 to 0.1 s^?1 and at temperatures of 873 K to 1173 K (600 °C to 900 °C) in order to study the hot deformation characteristics and dynamic softening mechanisms of two different grades of commercial purity titanium after severe plastic deformation. It was observed that the effects of deformation rate and temperature are significant on obtained flow stress curves of both grades. Higher compressive strength exhibited by grade 2 titanium at relatively lower deformation temperatures was attributed to the grain boundary characteristics in relation with its lower processing temperature. However, severely deformed grade 4 titanium demonstrated higher compressive strength at relatively higher deformation temperatures (above 800 °C) due to suppressed grain growth via oxygen segregation limiting grain boundary motion. Constitutive equations were established to model the flow behavior, and the validity of the predictions was demonstrated with decent agreement accompanied by average error levels less than 5 pct for all the deformation conditions.     

Application of magnetic immuno-polymerase chain reaction assay for detection of <Emphasis Type="Italic">Salmonella</Emphasis> spp. in chicken meats

Since contaminated chicken meats have been the principal foodborne source of the contamination of Salmonella to human beings and cultural detection methods are labor-intensive and time-consuming, a study evaluating the performance of the combination of two techniques that are immunomagnetic separation (IMS) and polymerase chain reaction (PCR) for the detection of Salmonella in chicken meats was conducted. The IMS and PCR assay combines selective extraction of Salmonella by specific antibodies with primer-specific (primer pair based on the sequence of invA gene) PCR amplification. Initially chicken meat samples, in which no Salmonella contamination had been determined by using ISO 6579 reference method, were inoculated with Salmonella Enteritidis culture and subsequently the shortest non-selective pre-enrichment time, that had been needed for the detection of approximately 1 or 10 CFU/mL chicken meat levels of target bacteria by magnetic immuno-PCR assay, was found by using 14, 12, 10 and 8-h periods. In conclusion, it was found that magnetic immuno-PCR assay was able to detect 1–10 CFU Salmonella/25 g chicken meat, after only incorporating a non-selective pre-enrichment period of 12 h. Therefore, an overall 16-h (magnetic immuno-PCR assay in conjunction with 12-h non-selective pre-enrichment) magnetic immuno-PCR assay statistically evaluated as sufficient (p = 0.182 > 0.05) for rapid and sensitive detection of approximately 1–10 CFU Salmonella from 25 g chicken meat samples. Accordingly, 16-h magnetic immuno-PCR assay can be promising for routine use in the detection of Salmonella in chicken meat samples, and it consequently may prevent the risk of Salmonella infections in regard to chicken meats.     

Room-Temperature Synthesis of 2D Janus Crystals and their Heterostructures

Janus crystals represent an exciting class of 2D materials with different atomic species on their upper and lower facets. Theories have predicted that this symmetry breaking induces an electric field and leads to a wealth of novel properties, such as large Rashba spin–orbit coupling and formation of strongly correlated electronic states. Monolayer MoSSe Janus crystals have been synthesized by two methods, via controlled sulfurization of monolayer MoSe₂ and via plasma stripping followed thermal annealing of MoS₂. However, the high processing temperatures prevent growth of other Janus materials and their heterostructures. Here, a room-temperature technique for the synthesis of a variety of Janus monolayers with high structural and optical quality is reported. This process involves low-energy reactive radical precursors, which enables selective removal and replacement of the uppermost chalcogen layer, thus transforming classical transition metal dichalcogenides into a Janus structure. The resulting materials show clear mixed character for their excitonic transitions, and more importantly, the presented room-temperature method enables the demonstration of first vertical and lateral heterojunctions of 2D Janus TMDs. The results present significant and pioneering advances in the synthesis of new classes of 2D materials, and pave the way for the creation of heterostructures from 2D Janus layers.     

Prediction of Scour Downstream of Grade-Control Structures Using Neural Networks

A new approach for predicting local scour downstream of grade-control structures based on neural networks is presented. An explicit neural networks formulation (ENNF) is developed using a transfer function (sigmoid) and optimal weights obtained from a training process. A genetic algorithm was used to optimize the neural network architecture and the optimal weights for input and output parameters were obtained using the Levenberg–Marquardt back-propagation algorithm. Experimental data available in the literature, including large-scale results were used for training and validation of the proposed model. The predictive performance of the ENNF was found superior to other regression-based equations and the robustness of ENNF was evaluated using field data.     

A hypermedia authoring tool for augmented and virtual reality

Most existing hypermedia authoring systems are intended for use on desktop computers. These systems are typically designed for the creation of 2D documents and therefore employ 2D authoring mechanisms. In contrast, authoring systems for nontraditional multimedia/hypermedia experiences for 3D virtual or augmented worlds focus mainly on creating separate media objects and embedding them within the user's surroundings. As a result, linking these media objects to create 3D hypermedia is a tedious manual task. To address this issue, we present an authoring tool for creating and editing linked 3D hypermedia narratives that are interwoven with a wearable computer user's surrounding environment. Our system is designed for use by authors who are not programmers, and allows them to preview their results on a desktop workstation, as well as with an augmented or virtual reality system.     

Ferrocene clicked polypyrrole derivatives: effect of spacer group on electrochemical properties and post-polymerization functionalization

In this study, novel ferrocene-functionalized N-alkyl substituted pyrrole derivatives, namely 4-ferrocenyl-1-[3-(pyrrol-1-yl)propyl]-1H-1,2,3-triazole (Py3Fc), 4-ferrocenyl-1-[4-(pyrrol-1-yl)butyl]-1H-1,2,3-triazole (Py4Fc), and 4-ferrocenyl-1-[6-(pyrrol-1-yl)hexyl]-1H-1,2,3-triazole (Py6Fc), were synthesized via click reaction and the monomers were characterized by ¹H NMR, ¹³C NMR, FTIR, and HRMS techniques. Redox properties of the monomers were investigated by cyclic voltammetry (CV) studies. Contrary to general literature, both Py4Fc and Py6Fc were electrochemically polymerized without loss in redox activity of ferrocene group. Moreover, click chemistry was utilized in post-polymerization functionalization. For this purpose, three azide-containing polypyrroles, P(Py3N₃), P(Py4N₃), and P(Py6N₃) were electrochemically synthesized and subjected to click reaction in the presence of ethynylferrocene. CV studies of the post-polymerization functionalized polymers revealed quasi-reversible waves, while only P(Py6-post-Fc) showed the characteristic redox behavior of both polypyrrole and ferrocene. Thus, in this study preparation of a conducting homopolymers of pyrrole having covalently bonded ferrocene units was demonstrated and effect of spacer group is investigated.     

Determination of process parameters through a mechanistic force model of milling operations

Mechanistic process parameters for the end milling operation are determined for 11L17 free machining steel, 2024 aluminum and 62-35-3 free machining brass by analyzing the measured cutting force data and using a mechanistic force model. It has been found that pressure and friction acting on the cutter-chip interface decrease with the increase of feed rate, while the cutting speed has a negligible effect on some of the material-dependent parameters. Process parameters are summarized into empirical equations as functions of feed rate and tool rotation angle for each workpiece material. The use of sampled force data in the computation of the process parameters reduces the amount of testing greatly compared to those methods that utilize only average force data.