Accurate stresses in laminated piezoelectric finite length cylinders subjected to electro-thermo-mechanical loadings

A mixed semi-analytical computational model is presented which accounts for the coupled electrical, mechanical and thermal response of layered piezoelectric finitely long hollow circular cylinders. Boundary value problem (BVP) of an axisymmetric cylinder is considered here as a two-dimensional plane strain problem in the (r, z) plane, which is based on the exact theory of elasticity. After assuming diaphragmsupported end conditions in the longitudinal (z) direction, the resulting mathematical model is cast in the form of first-order simultaneous ordinary differential equations which are integrated through an effective numerical integration technique by first transforming the BVP into a set of initial value problems. New results of finite length cylinders are generated and presented for future reference

Broadband dielectric response of CaCu3Ti4O12: From dc to the electronic transition regime

We report on phonon properties and electronic transitions in CaCu3Ti4O12, a material which reveals a colossal dielectric constant at room temperature without any ferroelectric transition. The results of far- and mid-infrared measurements are compared to those obtained by broadband dielectric and millimeter-wave spectroscopy on the same single crystal. The unusual temperature dependence of phonon eigenfrequencies, dampings and ionic plasma frequencies of low lying phonon modes are analyzed and discussed in detail. Electronic excitations below 4 eV are identified as transitions between full and empty hybridized oxygen-copper bands and between oxygen-copper and unoccupied Ti 3d bands. The unusually small band gap determined from the dc-conductivity (~200 meV) compares well with the optical results.Comment: 7 pages, 8 figure

Calibration and validation of parking search time function

Large off-street car parks are traditionally modelled as self-standing traffic zones representing origins/destinations in standard network assignment models. However, such a treatment precludes the drivers from choosing alternative car parks as it assumes the car parks are their final destinations. This paper discusses the feasibility of bringing car park choice and the effects of capacity within a traditional network assignment model. The search time within car parks depends on the car park occupancy and can be represented by a flow-delay type function on the car park occupancy/capacity. This research calibrates the search-time function based on practically observed occupancy and search time at two city-centre car parks in Leeds, England. The analysis follows a simple fixed search-time method as well as a sophisticated variable search-time method. The results are validated against the observed occupancies at the car parks. A car park specific constant was introduced to account for the unobserved preference for a given type of parking facility. In a multiperiod assignment, when car park occupancies are passed on dynamically, both fixed and variable search-time approaches are seen as an improvement over the standard approach, with the variable search time outperforming the fixed time approach