Effect of particle size on the dielectric behaviour of double propionates

Introduction Dicalcium strontium propionate (DCSP) undergoes a ferroelectric phase transition at about 28 1.5 K, with the spontaneous polarization occurring along the tetragonal C-axis.1 Takashige et al.2,3 have recently reported ferroelectricity in annealed samples of dicalcium lead propionate (DCLP) in the range 191 K to 331 K. The removal of the inner biasing field by annealing has been known in the case of DCLP3 and DCSP.4 Because of the possible dependence of the inner biasing field on the particle size, a study of the temperature dependence of the dielectric behaviour of the powdered samples of these compounds was undertaken.

Experimental studies and phase field modeling of microstructure evolution during solidification with electromagnetic stirring

Thixocasting requires manufacturing of billets with non-dendritic microstructure. Aluminum alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic stirrer. Subsequent heat treatment was used to produce a transition from rosette to globular microstructure. The current and the duration of stirring were explored as control parameters. Simultaneous induction heating of the billet during stirring was quantified using experimentally determined thermal profiles. The effect of processing parameters on the dendrite fragmentation was discussed. Corresponding computational modeling of the process was performed using phase-field modeling of alloy solidification in order to gain insight into the process of morphological changes of a solid during this process. A non-isothermal alloy solidification model was used for simulations. The morphological evolution under such imposed thermal cycles was simulated and compared with experimentally determined one. Suitable scaling using the thermosolutal diffusion distances was used to overcome computational difficulties in quantitative comparison at system scale. The results were interpreted in the light of existing theories of microstructure refinement and globularisation.

Dielectric properties of electron irradiated PbZrO3 thin films

The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric properties of PbZrO3 thin films grown by sol-gel technique. The films were (0.62 mu m thick) subjected to electron irradiation using Microtron accelerator (delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron irradiated films. T (c) was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of E >'(T) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies do not change the general shape of the AFE hysteresis loop but they increase P (s) of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties to the structural defects such as oxygen vacancies and radiation induced charges. The shift in T (C), increase in dielectric constant, broader hysteresis loop, and increase in P (r) can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were retained indicative of AFE nature of the films.

Electron field emission from sp (2)-induced insulating to metallic behaviour of amorphous carbon (a-C) films

The influence of concentration and size of sp (2) cluster on the transport properties and electron field emissions of amorphous carbon films have been investigated. The observed insulating to metallic behaviour from reduced activation energy derived from transport measurement and threshold field for electron emission of a-C films can be explained in terms of improvements in the connectivity between sp (2) clusters. The connectivity is resulted by the cluster concentration and size. The concentration and size of sp (2) content cluster is regulated by the coalescence of carbon globules into clusters, which evolves with deposition conditions.

A bibliographical review of the high pressure studies of ferroelectric phase transitions

A brief review of the various high pressure studies on the phase transitions in ferroelectric crystals carried out over the past two decades is presented. The theoretical framework in which high pressure studies have to be viewed is given. The pressure data of ferroelectric crystals are organized in the form of tables. High pressure spectroscopic and structural studies are included. The review contains a bibliography of over two hundred references.

An experimental study of suddenly expanded rectangular jet flow field

Flow through a rectangular Passage which is expanded suddenly into another rectangular duct of larger Cross-sectional area has been studied experimentally with stagnation Pressures from 3.5 atmospheres to 1.25 atmospheres. The length to height ratio of the enlarged duct varied from 5.769 to 1.923 and three models with length to height ratios 5.769, 3.846, and 1.923 were studied. The influence of stagnation Pressures and length to height ratio of the enlarged duct on base pressure and flow field mean pressures in the enlarged duct is discussed. The results of the present investigation indicate that the oscillatory nature of the mean pressure flow field in the enlarged portion with rectangular cross-section is appreciably different from that for circular cross-section at similar flow conditions.

Flow And Heat-Transfer Over An Upstream Moving Wall With A Magnetic-Field And A Parallel Free Stream

The flow and heat transfer over an upstream moving non-isothermal wall with a parallel free stream have been considered. The magnetic field has been applied in the free stream parallel to the wall and the effect of induced magnetic field has been included in the analysis. The boundary layer equations governing the steady incompressible electrically conducting fluid flow have been solved numerically using a shooting method. This problem is interesting because a solution exists only when the ratio of the wall velocity does not exceed a certain critical value and this critical value depends on the magnetic field and magnetic Prandtl number. Also dual solutions exist for a certain range of wall velocity.

Electric Field Modelling of Composite High Voltage Insulators

This paper deals with the two-dimensional electric field modelling and electric field stress calculations of different types of composite insulators used in high voltage distribution and transmission systems. The computer simulations are carried out by using a commercially available software package. The potential and electric filed results obtained for the actual insulator profiles for three types of composite/polymeric insulators are discussed and presented.

Indentation of sintered alumina clay composite - an experimental discussion of a combined Boussinesq and blister stress field approach

Surface elastic strain field generated in conical indentation of sintered alumina clay composite was measured to verify the suitability of a superposed combination of Boussinesq and blister stress fields, used previously for analysing the indentation problem. The residual strain measured in the elastic hinterland is used to estimate the blister field strength without any reference to stress relation within that field. The approach may be useful in fracture studies of brittle materials.

Structure and representation of correlation functions and the density matrix for a statistical wave field in optics

A systematic structure analysis of the correlation functions of statistical quantum optics is carried out. From a suitably defined auxiliary two‐point function we are able to identify the excited modes in the wave field. The relative simplicity of the higher order correlation functions emerge as a byproduct and the conditions under which these are made pure are derived. These results depend in a crucial manner on the notion of coherence indices and of unimodular coherence indices. A new class of approximate expressions for the density operator of a statistical wave field is worked out based on discrete characteristic sets. These are even more economical than the diagonal coherent state representations. An appreciation of the subtleties of quantum theory obtains. Certain implications for the physics of light beams are cited.

Radio interference measurements on a ceramic disc insulator string with field reduction electrode

This paper presents a laboratory study of the discharge radio noise generated by ceramic insulator strings under normal conditions. In the course of study, a comparison on the performance of two types of insulator strings under two different conditions was studied namely (a) normal disc insulators in a string and (b) disc insulators integrated with a newly developed field reduction electrode fixed to the disc insulator at the pin junction. The results obtained during the study are discussed and presented.

Comment on “Southward magnetic field in the neutral sheet produced by wavy motions Propagating in the dawn‐dusk direction”

In a recent paper Nakagawa and Nishida [1989] have suggested that wavy motions of the neutral sheet can be generated by the Kelvin‐Helmholtz instability if the dawn‐dusk flow of only several tens of km/s is present. However, their mathematical analysis is based on the choice of particular magnetic field directions in the three regions consisting of north, south lobes and the neutral sheet. In an earlier paper Uberoi [1986] discussed the Kelvin‐Helmholtz instability of a similar structured plasma layer without any assumptions either on velocity field directions or on the magnetic field directions, thus pointing out the angle effect due to variation in magnetic field directions on the instability criterion. The relevance of these results to the problem of wavy motions of the neutral sheet are pointed out. In particular it is found that when the y‐component of the magnetic field in each lobe is taken into consideration the Kelvin‐Helmholtz instability can be exicted only when the dawn‐dusk flow is of several hundreds of km/s a order of ten higher than that arrived in the analysis by Nakagawa and Nishida [1989].

Estimation of soil hydraulic properties and their uncertainty: comparison between laboratory and field experiment

Often the soil hydraulic parameters are obtained by the inversion of measured data (e.g. soil moisture, pressure head, and cumulative infiltration, etc.). However, the inverse problem in unsaturated zone is ill-posed due to various reasons, and hence the parameters become non-unique. The presence of multiple soil layers brings the additional complexities in the inverse modelling. The generalized likelihood uncertainty estimate (GLUE) is a useful approach to estimate the parameters and their uncertainty when dealing with soil moisture dynamics which is a highly non-linear problem. Because the estimated parameters depend on the modelling scale, inverse modelling carried out on laboratory data and field data may provide independent estimates. The objective of this paper is to compare the parameters and their uncertainty estimated through experiments in the laboratory and in the field and to assess which of the soil hydraulic parameters are independent of the experiment. The first two layers in the field site are characterized by Loamy sand and Loamy. The mean soil moisture and pressure head at three depths are measured with an interval of half hour for a period of 1 week using the evaporation method for the laboratory experiment, whereas soil moisture at three different depths (60, 110, and 200 cm) is measured with an interval of 1 h for 2 years for the field experiment. A one-dimensional soil moisture model on the basis of the finite difference method was used. The calibration and validation are approximately for 1 year each. The model performance was found to be good with root mean square error (RMSE) varying from 2 to 4 cm(3) cm(-3). It is found from the two experiments that mean and uncertainty in the saturated soil moisture (theta(s)) and shape parameter (n) of van Genuchten equations are similar for both the soil types. Copyright (C) 2010 John Wiley & Sons, Ltd.

Hypersonic stagnation‐point boundary layers with massive blowing in the presence of a magnetic field

The effect of massive blowing rates on the steady laminar hypersonic boundary‐layer flow of an electrically conducting fluid in the stagnation region of an axisymmetric body with an applied magnetic field has been studied. The governing equations have been solved numerically by combining the implicit finite‐difference scheme with the quasi‐linearization technique. It is observed that the effect of massive blowing rates is to remove the viscous layer away from the boundary, whereas the effect of the magnetic field is just the opposite. It is also found that the velocity overshoot increases with blowing rates and also with magnetic field. The effect of the variation of the density‐viscosity product across the boundary layer is strong only when the blowing rate is small, but for the massive blowing rate the effect is negligible.