Comparison of deformation induced precipitation behaviour in Alloy 718 under two microstructural conditions

Alloy 718 samples under two initial microstructural conditions, viz., solution annealed to form only γ phase (ST) and aged to precipitate only δ particles (DELTA), were deformed in tension till fracture in the temperatures range from 200°C–700°C. From the comparison of the evolved microstructure of deformed and undeformed specimens that have been subjected to similar thermal history, deformation induced precipitation could be identified. Deformation in the range of 550°C to 650°C promoted the precipitation of γ′ and γ″ phases in both structures. In case of DELTA alloy, the γ′ precipitation was found to precede the γ′ phase precipitation while no such preference for precipitation could be identified in ST specimens. This difference in the precipitation behaviour and the sequence of precipitation has been explained on the basis of the relative concentration of solutes in the matrix of the starting microstructures of ST and DELTA specimens.     

Biodiesel production through hydrodynamic cavitation and performance testing

This paper presents the details of development of a biodiesel production test rig based on hydrodynamic cavitation followed by results of experimental investigation carried out on a four cylinder, direct injection water cooled diesel engine operating on diesel and biodiesel blend of Citrullus colocyntis (Thumba) oil. The experiment covers a wide range of engine rpm. Results show that biodiesel of Thumba oil produced through hydrodynamic cavitation technique can be used as an alternative fuel with better performance and lower emissions compared to diesel. The most significant conclusions are that (i) Biodiesel production through hydrodynamic cavitation technique seems to be a simple, efficient, time saving, eco-friendly and industrially viable process. (ii) 30% biodiesel blend of Thumba oil shows relatively higher brake power, brake thermal efficiency, reduced bsfc and smoke opacity with favourable p–θ diagram as compared to diesel.     

Frequency dependent electrical transport properties of 4,4′,4″-tris(N-3-methylphenyl-N-phenylamine)triphenylamine by impedance spectroscopy

The frequency dependent ac conduction mechanism in 4,4′,4″-tris(N-3-methylphenyl-N-phenylamine)triphenylamine (m-MTDATA) has been studied as a function of applied bias and temperature. The Cole–Cole plot shows a slightly depressed semicircle indicating Debye type relaxation. This result has been explained by an equivalent circuit of the device designed as a two parallel resistor and capacitance network in series with contact resistance. The ac conduction studies under dc bias for hole only devices shows an increase in device conductivity with the increase in bias. The variation of bulk resistance with applied bias indicates Space Charge Limited Conduction (SCLC) mechanism for hole conduction. The hole mobility of the material has also been evaluated from SCLC as 8.859 × 10^?6 cm²/V s. The temperature dependent impedance studies show two activation energies indicating two different phase of the material with a phase transition at 235 K.     

Biaxial tensile behavior of spunbonded nonwoven geotextiles

Geotextiles can be successfully employed for any geotechnical application when they are able to sustain pre-defined levels of tensile stresses. The biaxial tensile test has an advantage over other tensile test methods in that it does not allow “necking” during deformation which simulates the operational conditions of geotextiles under confined stresses. In this study, the model for uniaxial tensile behavior of nonwovens has been modified to investigate the biaxial tensile behavior of spunbonded geotextiles. The model has included the effect of fiber re-orientation, stress-strain behavior of constituent fibers, and physical characteristics of nonwovens when the geotextile specimen is laterally constrained. A comparison is made between predicted and experimental stress-strain curves obtained from previous work (Bais-Singh and Goswami, 1998). Theoretical findings of biaxial tensile behavior obtained using the layer theory are also critically discussed. In addition, it has been revealed that fiber re-orientation is a key factor in translating the random spunbonded nonwoven geotextiles to anisotropic structures under defined biaxial tensile stresses.     

Use of chalcopyrite semiconductors CuXSe2 (X=Al,Ga and In) in solar cells: a theoretical study

The energy of sunlight falling on surface of the earth can be directly converted into electricity by means of the solar cells. Among the various materials used for photovoltaics, the chalcopyrite compounds CuXSe₂ (X=Al, Ga, In) are very promising as semiconductors and have received much attention in the recent years. To check the applicability of these materials in solar cells, we have computed the energy bands, density of states, optical dielectric tensors, reflectivity, refraction and absorption coefficients using the full potential linearized augmented plane wave method. It is seen that the energy bandgap reduces from X=Al→In. The dielectric property of these materials is discussed in terms of interband transitions. The absorption coefficients of these materials in the region of solar radiation (0–5 eV energy) are discussed to explore their use in the fabrication of solar cells.     

Synthesis and characterization of zirconia-based catalyst for the isomerization of n-hexane

Sulfated zirconia is a very strong solid acid catalyst which can be utilized for various reactions. The present study focuses on synthesis of zirconia-based catalyst with high acidity and high surface area, particularly for isomerization reaction. Sulfated zirconia has been obtained by sulfation of zirconia prepared by hydrothermal route. The catalyst was developed by impregnating tungstophosphoric acid on sulfated zirconia by wet incipient method. The catalyst was characterized through Brunauer–Emmett–Teller (BET) surface area, temperature-programmed desorption of ammonia, temperature program reduction of hydrogen, Fourier transmission infrared spectroscopy, and thermogravimetric analysis. The results revealed that the catalyst is crystalline in nature with surface area 190–225?m² g^?1 and acidity 0.135–0.558?mmol?g^?1. Twenty-five percent conversion was obtained (as confirmed by gas chromatography) at 225°C using n-hexane as model hydrocarbon in fixed-bed microreactor.     

Densification of nanocrystalline Y2O3 ceramic powder by spark plasma sintering

Nanocrystalline Y₂O₃ powders with 18 nm crystallite size were sintered using spark plasma sintering (SPS) at different conditions between 1100 and 1600 °C. Dense specimens were fabricated at 100 MPa and 1400 °C for 5 min duration. A maximum in density was observed at 1400 °C. The grain size continuously increased with the SPS temperature into the micrometer size range. The maximum in density arises from competition between densification and grain growth. Retarded densification above 1400 °C is associated with enhanced grain growth that resulted in residual pores within the grains. Analysis of the grain growth kinetics resulted in activation energy of 150 kJ mol^?1 and associated diffusion coefficients higher by 10³ than expected for Y³⁺ grain boundary diffusion. The enhanced diffusion may be explained by combined surface diffusion and particle coarsening during the heating up with grain boundary diffusion at the SPS temperature.     

On controllability and trajectory tracking of a kinematic vehicle model

This paper presents some further results concerning the issues of controllability and trajectory tracking regarding a front-wheel drive vehicle kinematic model. A simple procedure for computing an open-loop control strategy that transfers the system between given initial and final states, is presented. In particular, the input function is computed by means of a set of linear algebraic equations. The resulting motion planning procedure allows us to present a control scheme for solving the trajectory (a time-parameterized reference signal) tracking problem. Various applications of the approach in forward and backward motions are considered, and simulation results are presented.     

Swing-up and stabilization of a cart–pendulum system under restricted cart track length

This paper describes the swing-up and stabilization of a cart–pendulum system with a restricted cart track length and restricted control force using generalized energy control methods. Starting from a pendant position, the pendulum is swung up to the upright unstable equilibrium configuration using energy control principles. An “energy well” is built within the cart track to prevent the cart from going outside the limited length. When sufficient energy is acquired by the pendulum, it goes into a “cruise” mode when the acquired energy is maintained. Finally, when the pendulum is close to the upright configuration, a stabilizing controller is activated around a linear zone about the upright configuration. The proposed scheme has worked well both in simulation and a practical setup and the conditions for stability have been derived using the multiple Lyapunov functions approach.