An improved damage diagnostic technique based on Singular Spectrum Analysis and time series models

An approach to enhance the sensitivity of the damage index using the prediction errors of autoregressive – autoregressive exogenous models by augmenting Singular Spectrum Analysis (SSA) to detect and locate minor damage is presented. Numerical simulation studies are carried out by considering a simply supported beam with single and multiple cracks. An experimental study on a reinforced cement concrete beam has been carried out to validate the technique using different levels of damage. The studies emphasise that the SSA improves the sensitivity of the damage index for detection and also localisation, handling environmental/operational variability and measurement noise.     

Effect of prior treatment on the low cycle fatigue behaviour of aluminium alloy RR58 at 423K

The effect of the quenching medium and of varying the microstructure on low cycle fatigue behaviour of aluminium alloy RR58 has been investigated at 423K. It is observed that fatigue resistance is significantly impaired if, following solutionizing, the alloy is quenched in water instead of in oil. Thermal as well as thermomechanical treatments were employed to produce different microstructures. The overaged microstructure displayed the highest fatigue life. It is shown with the help of fractographic observations that differences in fatigue resistance due to differences in severity in quenching or in microstructure arise mainly due to the influence of these variables on crack initiation and early crack propagation. It has also been demonstrated that as the rate of hardening or softening is increased, cyclic strength coefficient K′ and fatigue hardening exponent n′ increase; the fatigue ductility coefficient ?′_f decreases as a result of varying microstructures, and the fatigue resistance at 423K of the alloy is lowered. When compared with the behaviour at ambient temperature, the test temperature of 423K has been found to have no significant effect on the fatigue life/strain plot.     

Mass transfer and biochemical reaction in enzyme membrane reactor systems—I. Single enzyme reactions

The effective use of an enzyme as a biological catalyst for process scale conversion is greatly enhanced by immobilizing the enzyme within the matrix of a membrane whose walls are permeable to the substrate and product. The enzyme is thus stabilized for reuse, but the apparent activity is reduced compared to that obtained with the free enzyme because of transport resistances in the bulk fluid near the membrane and within the membrane itself. To account for this reduction, solutions to the differential equations describing the mass transport-kinetic models can be obtained for certain important cases. The reaction is considered to be first-order and isothermal, and to occur in one of two modes of operation: fixed-bed or batch (limited volume). Irreversible and reversible reactions and plane sheet and spherical geometries of the membrane are considered. An example of the application of these solutions to actual data obtained with a laboratory scale immobilized enzyme reactor is presented.     

Directory-based composite routing and scheduling policies for dynamic multimedia environments

In this paper we present and evaluate algorithms to address combined path and server selection (CPSS) problems in highly dynamic multimedia environments. Our goal is to ensure effective utilization of network and server resources while tolerating imprecision in system state information. Components within the framework implement the optimized scheduling policies as well as collect/update the network and server parameters using a directory service. We present and analyze multiple policies to solve the CPSS problem. In addition, we study multiple techniques for updating the directory service with system state information. We further evaluate the performance of the CPSS policies under different update mechanisms and study the implications of the CPSS policies on directory service management.     

Thermal instability in a micropolar fluid layer subject to a magnetic field

In the present paper we have considered thermal instability in a heat conducting micropolar fluid layer under the influence of a transverse magnetic field. Assuming the bounding surfaces to be rigid the eigenvalue problem is solved using finite-difference and Wilkinson's iteration techniques. Here it is seen that the instability sets in not only for adverse temperature gradient but also for positive temperature gradient. Both the microtation and the magnetic field are seen to stabilize the fluid layer. However, the stabilizing effect of microrotation becomes less significant when the strength of the magnetic field is large. In the case of heating from below, the critical wave number is seen to be insensitive to increase in the strength of the magnetic field, while it increases significantly when the fluid is heated from above.     

Kinetics of pyrolysis of pure and doped cobalt oxalate

The object of the present work was to illustrate the effect of impurities on the kinetics and energetics of the thermal decomposition of pure cobalt oxalate. Cationic impurities like Mg²⁺, Mn²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Zr⁴⁺ have been introduced into pure cobalt oxalate dihydrate and differential thermal analysis has been used to determine the enthalpy and energy of activation for the decomposition reaction of pure and doped samples.     

Microstructural and magnetic studies on P/M processed (Nd14.9Dy1.9)(Fe65.0Co8.0Cu1.0Ga1.0Nb0.7) B7.5 alloy

Sintered samples of (Nd_14.9 Dy_1.9) (Fe₆₅ Co₈ Cu_1.0 Ga_1.0 Nb_0.7)B_7.5 were prepared and subjected to stepwise annealing in the temperature range 875 K–675 K. The XRD and metallographic (optical and electron microscopy) studies reveal a multi-phase microstructure with each phase showing different solubility of the alloying additions. This alloy has T _C of 705 K with an intrinsic coercivity of 1000 kA/m and energy product of 250 kJ/m³ at RT. Solubility of Co into the matrix phase and that of Ga and Cu into the Nd-rich grain boundary phase are considered to be the main contributing factors for the significant enhancement in T _C and H _ci respectively of the multi-component alloy when compared to those of ternary NdFeB, wherein H _ci = 720 kA/m and T _C = 585 K.