Estimation of Molten Content of the Spray Stream from Analysis of Experimental Particle Diagnostics

Particle melting is one of the key issues in air plasma spray processing of high temperature ceramics such as Yttria Stabilized Zirconia (YSZ). The significance of assessing, monitoring, and controlling the molten content in spray stream on achieving an efficient process and reproducible coating characteristics and properties is known. This study aims to estimate the molten content of the spray stream (as an ensemble) from experimental measurement of in-flight (individual) particle characteristics. In a previous study by Streibl et al. the presence of melting signature in the particle temperature distribution was observed, which has been confirmed by simulation and through independent experimental observation by Mauer et al. Based on this observation, the particle temperature distribution could be delineated into the different achievable particle states in-flight (unmolten, partially molten, and completely molten) to a first approximation. This in-turn would enable estimation of the molten content in the spray stream. Thus obtained percentage molten content (referred in this study as Spray Stream Melting Index—SSMI) has been observed to correlate well with the experimentally measured deposition efficiency for a wide range of process conditions and feedstock characteristics. The implications of estimating SSMI for other materials and processes are also discussed.     

Performance,emission and combustion characteristics of a variable compression ratio engine using methyl esters of waste cooking oil and diesel blends

The performance, emission and combustion characteristics of a single cylinder four stroke variable compression ratio multi fuel engine when fueled with waste cooking oil methyl ester and its 20%, 40%, 60% and 80% blends with diesel (on a volume basis) are investigated and compared with standard diesel. The suitability of waste cooking oil methyl ester as a biofuel has been established in this study. Bio diesel produced from waste sun flower oil by transesterification process has been used in this study. Experiment has been conducted at a fixed engine speed of 1500 rpm, 50% load and at compression ratios of 18:1, 19:1, 20:1, 21:1 and 22:1. The impact of compression ratio on fuel consumption, combustion pressures and exhaust gas emissions has been investigated and presented. Optimum compression ratio which gives best performance has been identified. The results indicate longer ignition delay, maximum rate of pressure rise, lower heat release rate and higher mass fraction burnt at higher compression ratio for waste cooking oil methyl ester when compared to that of diesel. The brake thermal efficiency at 50% load for waste cooking oil methyl ester blends and diesel has been calculated and the blend B40 is found to give maximum thermal efficiency. The blends when used as fuel results in reduction of carbon monoxide, hydrocarbon and increase in nitrogen oxides emissions.     

Effect of Activated Flux on the Microstructure, Mechanical Properties, and Residual Stresses of Modified 9Cr-1Mo Steel Weld Joints

A novel variant of tungsten inert gas (TIG) welding called activated-TIG (A-TIG) welding, which uses a thin layer of activated flux coating applied on the joint area prior to welding, is known to enhance the depth of penetration during autogenous TIG welding and overcomes the limitation associated with TIG welding of modified 9Cr-1Mo steels. Therefore, it is necessary to develop a specific activated flux for enhancing the depth of penetration during autogeneous TIG welding of modified 9Cr-1Mo steel. In the current work, activated flux composition is optimized to achieve 6 mm depth of penetration in single-pass TIG welding at minimum heat input possible. Then square butt weld joints are made for 6-mm-thick and 10-mm-thick plates using the optimized flux. The effect of flux on the microstructure, mechanical properties, and residual stresses of the A-TIG weld joint is studied by comparing it with that of the weld joints made by conventional multipass TIG welding process using matching filler wire. Welded microstructure in the A-TIG weld joint is coarser because of the higher peak temperature in A-TIG welding process compared with that of multipass TIG weld joint made by a conventional TIG welding process. Transverse strength properties of the modified 9Cr-1Mo steel weld produced by A-TIG welding exceeded the minimum specified strength values of the base materials. The average toughness values of A-TIG weld joints are lower compared with that of the base metal and multipass weld joints due to the presence of δ-ferrite and inclusions in the weld metal caused by the flux. Compressive residual stresses are observed in the fusion zone of A-TIG weld joint, whereas tensile residual stresses are observed in the multipass TIG weld joint.     

Optical techniques in optogenetics

Optogenetics is an innovative technique for optical control of cells. This field has exploded over the past decade or so and has given rise to great advances in neuroscience. A variety of applications both from the basic and applied research have emerged, turning the early ideas into a powerful paradigm for cell biology, neuroscience, and medical research. This review aims at highlighting the basic concepts that are essential for a comprehensive understanding of optogenetics and some important biological/biomedical applications. Further, emphasis is placed on advancement in optogenetics-associated light-based methods for controlling gene expression, spatially controlled optogenetic stimulation and detection of cellular activities.     

Intelligent Modeling Using Adaptive Neuro Fuzzy Inference System (ANFIS) for Predicting Weld Bead Shape Parameters During A-TIG Welding of Reduced Activation Ferritic-Martensitic (RAFM) Steel

Reduced-activated ferritic-martensitic steels are considered to be the prime candidate for structural material of the fusion power plant reactor design. Tungsten inert gas (TIG) welding is preferred for welding of those structural materials. However, the depth of penetration achievable during autogenous TIG welding is very limited and hence productivity is poor. Therefore, activated-flux tungsten inert gas (A-TIG) welding, a new variant of TIG welding process has been developed in-house to increase the depth of penetration in single pass welding. In structural materials produced by A-TIG welding process, weld bead width, depth of penetration and HAZ width decide the mechanical properties and in turn the performance of the weld joints during service. To obtain the desired weld bead geometry, HAZ width and make a reliable quality weld, it becomes important to develop predictive tools using soft computing techniques. In this work, adaptive neuro fuzzy inference system is used to develop independent models correlating the welding parameters like current, voltage and torch speed with bead shape parameters like weld bead width, depth of penetration, and HAZ width. During ANFIS modeling, various membership functions were used. Triangular membership function provided the minimum RMS error for prediction and hence, ANFIS model with triangular membership functions were chosen for predicting for weld bead shape parameters as a function of welding process parameters.     

Amorphous Cobalt-Boron Alloy Electrodeposition and Dissolution

Co-B alloy has been deposited on steel from an alkaline citrate bath. Uniform deposits have been obtained in the current density range of 8–15 Adm ^?2.Cvclic voltammetric studies on platinum from this bath reveal that the cobalt citrate complexes undergo stepwise electronation with the participation of hydroxyl ions. The borates undergo reduction to boron in the alloy deposition. The hydrogen evolution reaction has been found to be hindered by cobalt and borate ions. Stripping voltammetric curves on the alloy film suggest the dissolution of cobalt from a cobalt rich phase.     

Corrosion behaviour of 304LN activated tungsten inert gas and flux-cored arc weld metals

Activated tungsten inert gas (A-TIG) and flux-cored arc (FCA) weld metals were prepared using 304LN stainless steel plate. The weld metals were thermally aged at 923, 973 and 1023?K for 100?h to study the decomposition of initial δ-ferrite in A-TIG (～10 ferrite number (FN)) and FCA (～5 FN) weld metals into secondary phases like M₂₃C₆ carbides, χ and σ. Ferrite number is the measurement of δ-ferrite based on the principle of magnetic property using ferritescope. Preliminary microstructural studies revealed the formation of carbides in FCA weld metals aged at 923?K for 100?h, which was correlated with higher carbon content (0.04?wt-%), and also ageing at higher temperature transformed δ-ferrite into χ/σ phases. However, A-TIG weld metals showed the transformation of δ-ferrite mainly into χ/σ phases. The δ-ferrite transformation kinetics was found to be sluggish in A-TIG weld metals compared to FCA weld metals. This difference was attributed to the difference in the carbon contents of A-TIG and FCA welds. Activated tungsten inert gas weld metals showed better uniform and pitting corrosion resistance compared to FCA weld metals in as-deposited and thermally aged conditions. Presence of higher amount of initial δ-ferrite content in A-TIG weld metal helped diffusion of minor alloying elements like sulphur and phosphorous into it, thereby reducing their microsegregation at the δ/γ interface boundaries and subsequent pitting corrosion attack. Thus, A-TIG welding process was found to be superior compared to FCA welding process.     

An experimental investigation on fatigue crack growth of AL6XN stainless steel

The crack growth behavior of AL6XN stainless steel was experimentally investigated using round compact tension (CT) specimens. The influences of the R-ratio (the ratio of the minimum load over the maximum applied load in a cycle), the tensile and compressive overloads, and the loading sequence on crack growth were studied in detail. The results from the constant-amplitude experiments show a sensitivity of the crack growth rate to the R-ratio. The application of a tensile overload has a profound effect on crack growth, resulting in a significant retardation in the crack propagation rate. A compressive overload (underload) leads to a short-lived acceleration in crack growth. Results from the two-step high-low loading reveal a period of crack growth retardation at the beginning of the lower amplitude step, an effect similar to that of a single overload. A crack driving force parameter together with a modified Wheeler model is found to correlate the crack growth experiments well.     

Effect of interface, height and density of long vertically aligned carbon nanotube arrays on their thermal conductivity: an experimental study

The ever-growing need to dissipate larger amounts of heat from components and structures requires the development of novel materials with superior thermal conductivity. Aligned carbon nanotube arrays that are integrated in composite materials and structures may prove useful in increasing heat transfer through their thickness. Theoretical studies have shown the potential of carbon nanotubes to reach a thermal conductivity of 6600 Wm(-1)K(-1). Experimental results on the arrays however have shown much lower thermal conductivity values. A study was conducted to better understand heat conduction in mm-long carbon nanotube arrays and to experimentally determine their thermal conductivity. Emphasis was placed on the effect of various parameters including the height and density of the array and the thermal resistance at the array interface. A method was devised to measure the thermal conductivity of the array relying on Fourier's law while maintaining a steady state one-dimensional heat flow. The study reveals that the taller the array and the higher its density, the larger the thermal conductivity of the array. Quantitative data is also provided on the effect of various interface materials and their deposition technique on the thermal conductivity of the arrays.     

Failure Diagram for Chemically Assisted Crack Growth

A failure diagram that combines the thresholds for failure of a smooth specimen to that of a fracture mechanics specimen, similar to the modified Kitagawa diagram in fatigue, is presented. For a given material/environment system, the diagram defines conditions under which a crack initiated at the threshold stress in a smooth specimen becomes a propagating crack, by satisfying the threshold stress intensity of a long crack. In analogy with fatigue, it is shown that internal stresses or local stress concentrations are required to provide the necessary mechanical crack tip driving forces, on one hand, and reaction/transportation kinetics to provide the chemical potential gradients, on the other. Together, they help in the initiation and propagation of the cracks. The chemical driving forces can be expressed as equivalent mechanical stresses using the failure diagram. Both internal stresses and their gradients, in conjunction with the chemical driving forces, have to meet the minimum magnitude and the minimum gradients to sustain the growth of a microcrack formed. Otherwise, nonpropagating conditions will prevail or a crack formed will remain dormant. It is shown that the processes underlying the crack nucleation in a smooth specimen and the crack growth of a fracture mechanics specimen are essentially the same. Both require building up of internal stresses by local plasticity. The process involves intermittent crack tip blunting and microcrack nucleation until the crack becomes unstable under the applied stress.