Conductivity, dielectric behaviour and magnetoelectric effect in copper ferrite-barium titanate composites

Composites of CuFe₂O₄ and BaTiO₃ were prepared using a conventional ceramic double sintering process. The presence of both phases was confirmed by X-ray diffraction. The variations of resistivity and thermo emf with temperature in these samples were studied. All the composites showed n-type behaviour. The variation of dielectric constant (έ′) in the frequency range 100 Hz to 1 MHz and with temperature at constant frequency were studied. The conduction phenomenon was explained on the basis of a small polaron-hopping model. Also confirmation of this phenomenon was made with the help of a.c. conductivity measurements. The static value of the magnetoelectric conversion factor, i.e. d.c. (ME)_H was studied as a function of intensity of the magnetic field. The maximum value of ME coefficient was observed for 75% ferroelectric phase composite.     

Sensitivity of river sediment transport and bridge scour to effects of flow,temperature, and sea level

Sediment transport has implications for activities such as fishing, flood control, scour countermeasures, and dredging through altered flow depths and sediment transport, bank erosion, and bridge scour. To estimate the changes in sediment transport and bridge scour, river discharge, water surface slope, water temperature, and tailwater depth (to simulate sea‐level rise) were altered in existing sediment transport and scour models. It was found that (a) in uniform flow upstream of sea‐level rise effects, sediment transport is sensitive to discharge but not to temperature; (b) in non‐uniform flow affected by sea‐level rise, sediment transport is sensitive to water surface slope and discharge but not to temperature; (3) the discharge value to restore the sediment transport rate existing before sea‐level rise is proportional to the water surface slope ratio to the fourth power; (4) the discharge value to restore the bed sediment size existing before sea‐level rise is proportional to the water surface slope ratio to the three‐fourth power; (5) abutment scour is weakly inversely proportional to the water surface slope but more strongly proportional to the discharge in a logarithmic relation; (6) pier scour is weakly proportional to the water surface slope but more strongly proportional to the discharge in a logarithmic relation; and (7) the discharge to restore both abutment and pier scour depths to their original values prior to sea‐level rise is proportional to the water surface slope ratio to the 9/25^th power. Full equations for each of these relationships are given in the article. These relationships can be used for future application and planning purposes.     

Hygrothermal characterization of the viscoelastic properties of Gore-Select® 57 proton exchange membrane

When a proton exchange membrane (PEM) based fuel cell is placed in service, hygrothermal stresses develop within the membrane and vary widely with internal operating environment. These hygrothermal stresses associated with hygral contraction and expansion at the operating conditions are believed to be critical in membrane mechanical integrity and durability. Understanding and accurately modeling the viscoelastic constitutive properties of a PEM is important for making hygrothermal stress predictions in the cyclic temperature and humidity environment of operating fuel cells. The tensile stress relaxation moduli of a commercially available PEM, Gore-Select^® 57, were obtained over a range of humidities and temperatures. These tests were performed using TA Instruments 2980 and Q800 dynamic mechanical analyzers (DMA), which are capable of applying specified tensile loading conditions on small membrane samples at a given temperature. A special humidity chamber was built in the form of a cup that encloses tension clamps of the DMA. The chamber was inserted in the heating furnace of the DMA and connected to a gas humidification unit by means of plastic tubing through a slot in the chamber. Stress relaxation data over a temperature range of 40–90°C and relative humidity range of 30–90% were obtained. Thermal and hygral master curves were constructed using thermal and hygral shift factors and were used to form a hygrothermal master curve using the time temperature moisture superposition principle. The master curve was also constructed independently using just one shift factor. The hygrothermal master curve was fitted with a 10-term Prony series for use in finite element software. The hygrothermal master curve was then validated using longer term tests. The relaxation modulus from longer term data matches well with the hygrothermal master curve. The long term test showed a plateau at longer times, suggesting an equilibrium modulus.     

Propylene polymerization using supported Ziegler–Natta catalyst systems with mixed donors

Magnesium dichloride supported titanium catalyst incorporated with varying concentration of ethylbenzoate and diisobutyl phthalate together as internal donor are synthesized. The synthesized catalysts are characterized and compared with respect to composition, phase characteristics, crystallite size, and particle morphology. Performance of catalysts containing mixed donors is compared with the conventional single donor-based catalysts. The polymerization studies of the catalysts for propylene polymerization show dependence of polymerization kinetics on relative concentration of diisobutyl phthalate and ethylbenzoate. Molecular weight characteristics of polypropylene obtained from these catalysts are studied and correlated with the nature and concentration of donors present in the catalyst. Morphology replication from catalyst precursor to polymer is observed irrespective of the nature of donor being incorporated in the synthesized catalyst. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Solution of the poisson equation: Comparison of the Galerkin and control-volume methods

The two-dimensional Poisson equation is solved by the finite element method which uses rectangular elements and the bilinear shape function. Two kinds of weighting functions are employed, which correspond to the Galerkin method and the control-volume method. The results for three test problems, for which exact analytical solutions are available, show that the control-volume method leads to errors that are about one-half of the errors given by the Galerkin method. Incidentally, the five-point finite difference method is found to give errors which are nearly equal to those for the Galerkin method.     

Global search algorithm for automated maintenance planning and scheduling of parts requests

The work content variability in a shop or field maintenance system is significant. The key to efficient maintenance operation is an effective diagnostic system that narrows the problem to a small ambiguity group, explicit mechanisms to leverage the knowledge of repairs and isolation tests that would be useful to fix the ambiguous fault condition and immediate communication with the parts store regarding availability of parts. Such scenario calls for the concept of dynamic optimization, which seeks optimal solutions to maintenance planning and scheduling problems subject to the dynamics such as outcomes of isolation tests or repair actions already execute to fix the ambiguous fault condition. This paper presents a global search algorithm to solve this dynamic optimization problem. An objective function is derived that takes into account the cost of parts that might be used for maintenance, the restocking fee for the parts that might be ordered and returned because they are not used, the labor cost of maintenance and the cost of waiting for ordered parts to be delivered. The global search algorithm was found to perform at satisfactory speeds for ambiguity groups containing up to five repairs. This covers majority of the cases in the field.