LONGITUDINAL DISPERSION IN RECTILINEAR FLOW OF DILUTE POLYMERIC LIQUIDS: LIKELY ROLE OF STRESS-INDUCED MIGRATION†

The likely role of stress-induced macromolecular migration in interpreting certain anomalous observations in longitudinal dispersion is discussed. In majority of the cases considered, the migration phenomenon affords an explanation for such behaviour, although in some instances, the operational regime for the dispersion process can itself explain the anomalies.

In those cases, where stress-induced migration could be a contributory factor, a semi-quantitative discussion based on our current understanding of the phenomenon is presented. Such a development, though rather simplistic in nature, enables (at least) a semi-quantitative elucidation of the pertinent variables which may affect the longitudinal dispersion processes involving polymeric media     

OPTIMAL STATE FEEDBACK CONTROL OF A CURRENT SOURCE INVERTER-FED INDUCTION MOTOR DRIVE USING A NEW ROTOR CURRENT OBSERVER

ABSTRACT

ABSTRACT The design, implementation and performance of a multivariable optimal state feedback controller for a Current Source Inverter-fed Induction Motor (CSI-IM) drive using a new reduced order observer to estimate rotor currents have been reported in this paper. A quadratic performance index together with a set of prescribed closed loop eigenvalues for placement are considered for application to a d-q axes state space linearized model of the drive to derive the control law - for achieving prescribed degree of stability in contrast to an earlier design with only pole-placement. The optimal control law derived is a function of all the states, the inaccessible states like d-q axes rotor currents being estimated by a new observer whose structure is simpler than that of one used in an earlier case. The controller-observer is implemented using an inexpensive microprocessor kit and the experimental results are presented along with the digital simulation results for the controlled drive to show its performance under step changes of load torque and references.     

Nanoscale characterization of gold nanoparticles created by in situ reduction at a polymeric surface

Transmission Electron Microscopy is used as a quantitative method to measure the shapes, sizes and volumes of gold nanoparticles created at a polymeric surface by three different in situ synthesis methods. The atomic number contrast (Z‐contrast) imaging technique reveals nanoparticles which are formed on the surface of the polymer. However, with certain reducing agents, the gold nanoparticles are additionally found up to 20 nm below the polymer surface. In addition, plan‐view high‐angle annular dark‐field scanning transmission electron microscopy images were statistically analyzed on one sample to measure the volume, height and effective diameter of the gold nanoparticles and their size distributions. Depth analysis from high‐angle annular dark‐field scanning transmission electron microscopy micrographs also gives information on the dominant shape of the nanoparticles.     

Effect of individual opinions on group interactions

We have evaluated the effectiveness of a probabilistic reciprocity scheme for promoting co-operation among self-interested agents. The probabilistic reciprocity mechanism is used to determine whether an agent should co-operate when approached for help by another agent. The situation becomes more complex when a group of agents seeks help from another group. The opinions of the members of the helping group about each of the asking group members can be combined to evaluate such a request for help. Exploitative agents would want to be part of groups that receive help from other groups, but will try to prevent its group from helping other groups. Such agents, revealing false opinion about the reputation of others, can cause unwarranted rejection of help requests from other groups. This leads to global performance degradation in terms of reduced inter-group co-operation and increased cost for the individual agents. We study the viability of reciprocative agents in randomly formed groups and when groups are formed by agents contracting other helpful agents. Group helping decisions are based on both average and worst combined ratings of group members. A key result from our study is that lying exploitative agents, who provide false opinions about other agents, become ineffective when focused group selection is enabled.     

Economics of sugar production: a case study

The manufacture of sugar from crushed sugar-cane involves processing through a number of stages. The yield of crystalline sugar per unit of processed juice depends on a variety of process parameters. Increased yield is also related to the determination of a suitable mix of in-process ingredients. In this paper a case study is presented where the use of product mix has been made. The product mix in this case is arrived at by considering the profit motive of the entrepreneur and keeping in view the constraints imposed by the processing times at various stages and the capacities of the equipment at each stage. The problems of implementation of the proposed product mix were then explored and a suitable production schedule has been suggested taking into consideration certain important constraints imposed by the Indian environment.     

Velocity Distributions of Food Particle Suspensions In Holding Tube Flow: Distribution Characteristics and Fastest-Particle Velocities

Velocity distributions of model food particles were investigated by videotaping particles suspended in sodium carboxymethylcellulose (CMC) solutions during passage through a transparent holding tube similar in dimension to that of commercial aseptic processing systems. The distributions could be well described by log-normal models. Fastest particle velocities were below theoretical centerline velocities for Newtonian fluids but were above theoretical values for the fluids used. Results indicated that for particle concentration levels used in these studies, channeling and particle-fluid interaction effects may be significant.     

OPTIMIZATION OF COMPOSITE LAMINATES WITH CUTOUTS USING GENETIC ALGORITHM,VARIABLE METRIC AND COMPLEX SEARCH METHODS

Optimization of composite laminates with cutouts is a complex problem, involving non-differentiable objective function and constraints. Choice of the optimization method is generally based on the nature and complexity of the objective function, constraints and how easily and/or accurately the first derivatives can be found. Many researchers have attempted and applied different classical optimization techniques for non-convex optimization problems. This paper clearly brings out the advantages of a non-traditional optimization method-Genetic algorithm (GA) over conventional techniques, the limitations of conventional techniques and GA's ability to approach the global optimum in an n-dimensional search space, for composite laminates.     

Transferability of specimen J–R curve to straight pipe with circumferential surface flaw

Specimen J–R curve is extensively used for structural integrity of large components. It is well known that J–R curve heavily depends on constraint level ahead of crack tip in remaining ligament. In earlier work, it was demonstrated that J–R curve from Three Point Bending (TPB) specimen is transferable to straight pipe with circumferential through wall crack. In this paper, the transferability of J–R curve is investigated from TPB specimen to pipe with circumferential surface crack. A 16 in. diameter pipe with circumferential surface crack and TPB specimen machined from same piping material (SA333Gr6 Steel) are tested. Consequently, 3D finite element analysis (FEA) has been performed on surface cracked pipe and TPB specimen. Crack‐initiation load is also predicted for surface cracked pipe by FEA and compared with experimental result. J–R curve is calculated for the pipe using experimental data, that is, load, load line displacement and crack growth. J–R curve of pipe is compared with TPB specimen and it is found that the pipe is predicting much higher J–R curve than TPB. This difference of J–R curve is investigated by evaluating stress triaxiality in remaining ligament for both cases. Stress triaxiality is quantified using triaxiality factor (h) ahead of crack tip for pipe and TPB specimen. It is found that the TPB specimen has considerably higher constraint level than pipe with surface crack, which is well supported by trend of J–R curves for specimen and pipe. A study has also been carried out to investigate the effect of internal pressure on the stress triaxiality. It is found that there is negligible difference in stress triaxiality because of internal pressure. The stress triaxiality is re‐established as a qualitative parameter to assess the transferability of J–R curve from specimen to component.