Stresses in radiative annular fin under thermal loading and its inverse modeling using sine cosine algorithm (SCA)

This work presents a novel mathematical model for the analysis of thermal stresses in a radiative annular fin with temperature-dependent thermal conductivity and radiative parameter. An approximate analytical solution for thermal stresses is derived using a homotopy perturbation method (HPM)-based closed-form solution of steady-state nonlinear heat transfer equation, coupled with classical elasticity theory. The effect of thermal parameters on the temperature field and the thermal stress fields are discussed. The various thermal parameters, such as a parameter describing the temperature-dependent thermal conductivity, coefficient of thermal expansion, coefficient of radiative parameter, and the variable radiative parameter, are inversely estimated for a given stress field. For inverse modeling, a population-based sine cosine algorithm (SCA) was employed to estimate the thermal parameters. The inverse modeling is verified by using the estimated thermal parameters in the closed-form solution of stress field. The reconstructed stress fields obtained from the inversely estimated parameters are then compared with the reference stress field. Results show a very good agreement between the reference stress field and the inversely estimated stress fields.     

Frequency and temperature dependence dielectric behavior of barium zirconate titanate nanocrystalline powder obtained by mechanochemical synthesis

Nanocrystalline barium zirconium titanate ceramic has been synthesized by high-energy ball milling. This nano-ceramic is characterized by X-ray diffraction, scanning electron microscopy, dielectric study and impedance spectroscopy. The X-ray diffraction pattern shows single phase ceramic of tertragonal symmetry with space group P4 mm. Temperature and frequency dependent dielectric study of the sample shows a normal ferroelectric phase transition behavior. Impedance spectroscopy analyses reveal a non-Debye type relaxation phenomenon. A significant shift in impedance loss peaks toward higher frequency side indicates conduction in material and favoring the long range motion of mobile charge carriers. Grain and grain boundary conduction is observed from complex impedance spectrum by the appearance of two semicircular arcs in the Nyquist plot. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The variation of dc conductivity exhibited a negative temperature coefficient of resistance behavior.     

Effect of the aspect ratio of the pre-existing rectangular adhesion failure on the structural integrity of the adhesively bonded single lap joint

Non-linear three dimensional (3-D) finite element analyses (FEA) of the single lap joints (SLJs) having pre-existing rectangular adhesion failure in the interface of the strap adherend and the adhesive have been carried out. The effect of the size, the shape and the aspect ratio of the pre-existing rectangular adhesion failure on (i) the strength, (ii) the interfacial stresses and (iii) the strain energy release rates (SERRs) in the vicinity of the adhesion failure front have been presented in this research work. The SLJ is subjected to uniformly applied tensile load. The adherends are made with very high strength steels and the adhesive is a commercially available AV119. The analyses of the adhesion failure propagation have been carried out by sequentially releasing the constraints of the nodes ahead of the pre-existing adhesion failure front in finite element model. The SERR values in the vicinity of the adhesion failure fronts are computed using the virtual crack closure technique (VCCT) for assessment of the structural integrity of the SLJ. The strength of the SLJ, the interfacial stresses, and the three modes of strain energy release rates (SERRs) have been found to be significantly affected by the shape and size of adhesion failures. The SERRs and interfacial stresses along the rectangular adhesion failure front are compared with the corresponding values around the circular adhesion failure front of same area, pre-existing in the SLJ. It is observed that the circular and rectangular adhesion failures of the same area will have dissimilar growth rate and the mode II is the dominant failure mode. The total strain energy release rate and the failure strength, computed from the 3-D FEA of the SLJ is in good agreement with the experimental fracture toughness of the AV119 adhesive and the experimentally obtained failure loads, respectively.     

BisGMA/TiO2 Organic-Inorganic Hybrid Nanocomposite

BisGMA (Bisphenol-A-glycidyldimethacrylate) resin had been modified by incorporating TiO₂ nanoparticles (0.5–2% by weight). An ultrasonic mixing process was used to disperse the particles into the resin system prior to casting and curing test specimens. TEM investigation showed that the particles were nano size (5–60 nm) and dispersed throughout the entire volume of the resin. In dynamic mechanical analysis, nanophase resin showed increase in storage modulus and glass transition temperature from neat resin system. Thermogravimetric analysis revealed better thermal stability. Flexural loading, T _g and flexural modulus of the nanocomposites were enhanced as the particle volume fraction was enhanced and than decreased.     

BIODEGRADATION OF NEYVELI LIGNITE AND ASSAM COAL

Neyveli lignite and Assam coal were subjected to biodegradation using bacteria and microfungi in the solid state fermentation technique. Neyveli lignite was found to show more biosolubilization than Assam coal. Neyveli lignite was also subjected to biodegradation using liquid state fermentation technique employing corynebacterium renale, Pseudomonas striata, Escherichia coli, spherotilus natans, streptococci microfungi. Solid state fermentation technique yielded better biosolubilization results than liquid state fermentation technique. Extractability of biodegraded coal in chloroform was enhanced. The IR spectral studies indicated oxidation and demineralization of microbially treated coals.     

DC Electrical Resistivity Study of Granularity in YBa2CU3O7/Ag Composites

Temperature-dependent electrical resistivity in a set of YBa₂Cu₃O_7–x /Ag composites, all prepared under an identical sintering schedule, is analyzed to extract granularity information. The weak-link resistivity _wl across the grain boundaries and the percolation factor arising due to current frustration caused by misalignment of anisotropic grains and sample defects such as voids and cracks are estimated from the residual resistivity ₀ and the temperature coefficient of resistivity d/dT. Variation of these parameters with Ag vol.% quantifying the extent of granularity indicates that granularity in the composites decreases and their electrical characteristics tend to be identical to that of Ag-free YBa₂Cu₃O_7–x single crystals and epitaxial thin films as Ag vol.% approaches a value where onset of current percolation occurs through Ag channels. The increased and decreased _wl observed at higher Ag vol.% explains the larger grains in the composites with narrow size distribution.     

Reduced‐order sliding function design for a class of nonlinear systems

In this paper, the design of first order sliding mode control (SMC) and twisting control based on the reduced order sliding function is proposed for the robust stabilization of an class of uncertain nonlinear single‐input system. This method greatly simplifies the control design as the sliding function is linear, which is based on reduced order state vector. The nonlinear system is represented as a cascade interconnection of two subsystems driving and driven subsystems. Sliding surface and SMC are designed for only the driving subsystem that guarantees the asymptotic stability of the entire system. To show the effectiveness of the proposed control schemes, the simulation results of translational oscillator with rotational actuator are illustrated.     

Effect of operating temperature on performance of microbial fuel cell

The performance of dual chambered mediator-less microbial fuel cell (MFC) operated under batch mode was evaluated under different operating temperatures, ranging between 20 and 55 degrees C, with step increase in temperature of 5 degrees C. Synthetic wastewater with sucrose as carbon source having chemical oxygen demand (COD) of 519-555 mg/L was used in the study. Temperature was a crucial factor in the performance of MFCs for both COD removal and electricity production. The MFC demonstrated highest COD removal efficiency of 84% and power density normalized to the anode surface area of 34.38 mW/m2 at operating temperature of 40 degrees C. Higher VSS to SS ratio was observed at the operating temperature between 35 and 45 degrees C. Under different operating temperatures the observed sludge yield was in the range of 0.05 to 0.14 g VSS/g COD removed. The maximum Coulombic and energy efficiencies were obtained at 40 degrees C, with values of 7.39 and 13.14%, respectively. Internal resistance of the MFC decreased with increase in operating temperature. Maximum internal resistance of 1,150 omega was observed when the MFC was operated at 20 degrees C; whereas the minimum internal resistance (552 omega) was observed at 55 degrees C.     

Fluctuating flow of a viscoelastic liquid between two parallel plates with time-varying suction

The non-steady flow of a viscoelastic liquid between two parallel porous plates was studied when the suction velocity normal to the plate oscillates in magnitude but not in direction about a non-zero constant mean and one plate is at rest and the other oscillates harmonically about a non-zero constant mean. The response of skin friction to fluctuating flow and suction velocity was studied for variations in the suction parameter A, the elastic parameter Λ and the frequency parameter Ω. The effect of the elastic parameter is to decrease the amplitude of skin friction at the upper plate as the suction parameter increases and to decrease the amplitude of the skin friction at the lower plate as the suction parameter decreases.     

Dielectric,impedance and modulus spectroscopy of BaBi2Nb2O9

Barium Bismuth Niobate (BaBi₂Nb₂O₉) has been synthesized by solid state reaction method. The X-ray diffraction study confirms the formation of compound. Morphological analysis has been carried out from the scanning electron microscopy images and the elemental analysis from the energy dispersive spectroscopy profiles. Investigation of dielectric and ferroelectric properties of the sample was done by varying the temperature from 25 °C - 500 °C in a frequency range of 1 kHz- 1 MHz. At 100 kHz, the phase transition was observed at 214.02°C. Further, this ferroelectric bi-layered perovskite exhibits an interesting relaxor behavior with a strong dispersion of the dielectric permittivity. A detailed study on the impedance spectroscopy over a wide range of temperature and frequency exhibits the contribution of grain ad grain boundary on different electrical parameters. From modulus spectroscopy, the presence of non-Debye type of relaxation in the material has been manifested. The complex modulus plots support the negative temperature coefficient of resistance (NTCR) type behavior of the material.