Hunt Model Research Articles

The Model of Public Relations Practices in Indonesia

Objective - This research aims to compare the government public relations with business public relations in Indonesia. The research proves the hypothesis that either government or business public relations in Indonesia have already applied symmetric model on their communication activities. Methodology/Technique - A national survey involves 160 practitioners of government and business public relations. The research reinforces Grunig and Hunt's model of public relations that business public relations tends practice two-way symmetrical communication. On the other hands, the research also differs with Grunig and Hunt's model that government public relations tend to apply public information model. Findings - It is concluded that both government and business public relations in Indonesia have implemented two-way communication models. The findings have confirmed that public relations practices have grown along with the development of democracy in Indonesia. Novelty - The research contributes to develop scientific knowledge in public relations study and practices. Type of Paper: Empirical Keywords: Business Public Relations; Democracy; Government Public Relations; Indonesia; Public Relations Model; Symmetric Model; Transparency of Public Information. JEL Classification: H11, H83.

Effects of Strontium, Magnesium Addition, Temperature Gradient, and Growth Velocity on Al–Si Eutectic Growth in a Unidirectionally-solidified Al–13 wt% Si Alloy

Al–Si eutectic growth mechanism was investigated in a directionally-solidified Al–13 wt% Si alloy with different strontium (Sr) and magnesium (Mg) additions, growth velocities and temperature gradients. Macro- and micro-scale metallographic analyses revealed that addition level of Sr and Mg, temperature gradient and growth velocity are important factors affecting stability of solidifying Al–Si eutectic front and the final morphology of eutectic grains in the solidified Al–13 wt% Si alloys. By varying (tailoring) these factors, a variety of eutectic grain structures and morphologies such as planar front, cellular structure, a mix of cellular and columnar, or equiaxed dendrites, can be obtained. Increasing temperature gradient, reducing growth velocity, or decreasing Sr and Mg contents is beneficial to stabilizing planar growth front of eutectic grains, which is qualitatively in accordance with constitutional supercooling criterion for binary eutectic growth. In contrast, adding more Sr and Mg, increasing growth velocity, or decreasing temperature gradient produces large constitutional supercooling, leading to columnar-equiaxed transition (CET) of eutectic structure, which can be interpreted on the basis of Hunt's Model. It is also found that both solute concentration and solidification variables have significant impact not only on eutectic growth, but also on gas porosity formation.

The influence of vanadium pentoxide on the structure and dielectric properties of poly(vinyl alcohol)

AbstractPolymers containing metal oxides of nanoscale dimensions have attracted attention because of their unique properties and new findings concerning technological applications. Polymers containing vanadium pentoxide (V2O5) have attracted our interest in respect of their potential applications in memory and switching devices. Poly(vinyl alcohol) (PVA) containing different concentrations of V2O5 ranging from 0 to 0.5 wt% were prepared. The synthesized PVA/V2O5 composites were cast as self‐standing flexible films. The composites were characterized using X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. An attempt was made to study the relaxation characteristics of PVA/V2O5 samples. The permittivity and dielectric loss were determined as a function of V2O5 concentration. The results show that the optimum concentration is 0.3 wt%. The electrical conductivity and dielectric modulus in the temperature range 303–433 K at various frequencies (10–100 kHz) for the optimum concentration were investigated. XRD and FTIR results show that the addition of V2O5 reduces the crystallinity of PVA due to the interaction of vanadium ions with the OH groups of PVA. The application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The frequency dependence of the electrical conductivity follows the Jonscher universal dynamic law. The conductivity in the direct regime is described by the small polaron model. The electrical conductivity and dielectric properties show that Hunt's model is well adapted to PVA/V2O5 films. Copyright © 2010 Society of Chemical Industry

Prediction of Solidification Microstructure and Columnar-to-equiaxed Transition of Al–Si Alloy by Two-dimensional Cellular Automaton with “Decentred Square” Growth Algorithm

A Cellular Automaton (CA) -Finite Difference (FD) coupling model was developed to analyze the evolution of solidification microstructure and the columnar-to-equiaxed transition (CET) in Al–Si alloy. Kobayashi's microsegregation equation was adopted to describe the solute diffusion in solid phase, and a “decentred square” growth algorithm with coordinate transformation was performed to describe the grain growth and the entrapment of neighbor cells. Through the examination on the effects of operation parameters and nucleation parameters on solidification morphologies, it was found that the length of columnar grains is controlled by the dendrite tip growth kinetics, and that the width of columnar grains is controlled by the implicit relationship between nucleation density and cooling rate at ingot surface. It was also found that the size of equiaxed grains is controlled by the competition of the nucleation and the grain growth. With the controllability of nucleation density in the bulk of liquid for equiaxed grain size, the nucleant and the nucleation density in actual Al–Si alloy were estimated. Both of the CET criteria based on the solidification path by CA-FD coupling model and the one based on the curves of critical temperature gradient conditions by Hunt's model were strongly dependent on nucleation undercooling and Si concentration. A good agreement was obtained between these two.

Dielectric relaxation studies in transition metal ions doped tellurite glasses

Vanadotellurite and vanado-cobalt tellurite glasses were investigated for dielectric properties in the frequency range 50 Hz to 5 MHz and temperature range 300–500 K. Hunt's model has been invoked to analyze the data and the results indicated that the relaxation process has a local character and can be described by hops between each pair of sites. Activation energies for dielectric loss process were determined and they were in close agreement with dc activation energies. Barton, Nakijama and Namikawa's (BNN) linear relation between ac and dc conductivities has been verified in both the glass systems.

Effect of a yellow filter on brightness evaluated by asymmetric matching: measurements and predictions

We found that yellow filters reduce the mean brightness of a set of coloured samples significantly less with blue surrounds than with black, achromatic or yellow ones, in comparison with the naked eye and less than a yellow surround in comparison with a luminance-matched grey filter. The predictions of Hunt's model and Guth's ATD95 agree with these results. The yellow filter is actually capable of significantly increasing the brightness with the blue surround both in comparison with the naked eye (although only for our younger observer) and with the neutral filter. We show that in some samples the yellow filter causes global response increments in the chromatic mechanisms that compensate the response reduction in the achromatic mechanism, resulting in increased brightness. Although global chromatic response increments may arise from any chromatic mechanism, the blue–yellow mechanism determines in most cases the final result, even when the response of the red–green mechanism decreases.

Directional solidification of Al–1.5 wt% Ni alloys under diffusion transport in space and fluid-flow localisation on earth

We present results of a comparative experimental study in Space (diffusion transport) and on Earth (convection and diffusion transport) of solute macrosegregation and directional solidification microstructure in bulk Al–1.5 wt% Ni alloys, which possess a stabilising solutal effect in directional upward solidification on ground. The growth parameters are in the cell–dendrite transition so that cells (no sidebranches) and dendrites (sidebranches) are simultaneously observed, the later having larger spacing. In the benchmark microstructures solidified in microgravity, it is found for the first time that the conditions for the analogy with viscous fingering are satisfied (spacing Peclet number ≪1 and tip constitutional supercooling of order one). The experimental primary spacing is about half the numerical prediction by Lu and Hunt's model. It is suggested that the full panorama of the symmetric and non-symmetric cellular and dendritic branches may explain the misfit. Also, the longitudinal solute macrosegregation across the mushy zone is discussed and modelled, which imposes to depart from the classical Flemings profile. Due to fluid flow driven by the radial temperature gradient, the ground samples show a large macroscopic deformation of the growth front concomitant with microstructure localisation. Cells then appear in the core and dendrites at the periphery. In addition, the measured primary spacing in the centre is smaller than in the corresponding microgravity experiments, which enables to estimate the downward component of the flow velocity in this region.

Application of cellular automaton–finite element model to the grain refinement of directionally solidified Al–4.15 wt% Mg alloys

Cellular automaton–finite element simulations and Bridgman experiments are used to study the grain refinement of directionally solidified Al–4.15 wt% Mg. The simulations can successfully map the conditions (velocity and temperature gradient) for columnar or equiaxed growth and account for variations in grain size in equiaxed structures. The simulations show that the latent heat released by dendritic solidification gives a quasi-isothermal zone interrupting the temperature gradient. This zone is important in limiting the degree of grain refinement which can be achieved, but also facilitates growth of equiaxed rather than elongated grains. The columnar-to-equiaxed transition is gradual, and its dependence on the addition level of refiner has been characterized. Hunt's model of the transition is supported by microstructural studies of quenched Bridgman samples.

Dc and ac Conductivities of (V 2O 5) x(B 2O 3) 1− x oxide glasses

Glasses of composition (V 2O 5) x (B 2O 3) 1− x with x=0.1, 0.3, 0.5, 0.7 and 0.9 were obtained by a quenching technique. Conductivity measurements using σ ac were performed on compact pellets of these materials. The conductivity behavior in direct regime, σ dc, is described by the “small polaron” model. The room temperature variation of log σ dc with the activation energy of each composition, suggests an adiabatic hopping character to the conduction. Application of Hunt's model to describe the ac conductivity behavior shows that the relaxation process has a local character and can be described by hops between each pair of sites.

Prediction of simultaneous contrast between map colors with Hunt's model of color appearance

Prediction of simultaneous contrast between map colors with Hunt's model of color appearance

Multi-level leadership: Grounded theory and mainstream theory applied to the case of general motors

Selected aspects of Hunt's (1991) extended multiple-organizational-level leadership model are used in an illustrative analysis of a case narrative emphasizing Roger Smith's almost decade-long tenure as chair and CEO at General Motors. The illustrative analysis compares and contrasts ways in which grounded theory and mainstream perspectives can be applied to help explain what occurred at various hierarchical-organizational levels during Smith's tenure. Propositions based on the case narrative and selected aspects of Hunt's model are developed and discussed in terms of grounded theory and mainstream perspectives. Two illustrative propositions are analyzed using levels-of-analysis theory in combination with the hierarchical organizational levels emphasized in Hunt's framework.

Solidification of binary and Sr-modified AlSi eutectic alloys: Theoretical analysis of solute fields

This paper analyses experimental data in available literature concerning the eutectic spacing λ and growth undercooling ΔT in the AlSi binary eutectic and in the strontium-modified eutectic. The expression for ΔT obtained in Jackson and Hunt's model is used, before application of the minimum undercooling growth criterion. It is shown that, for the binary eutectic, the results can be interpreted quantitatively by means of this equation. On the other hand, it is shown that the results for the modified ally cannot be interpreted on this basis and that a contribution of the kinetic undercooling for growth of Si has to be taken into account. A high level of kinetic undercooling is found (ranging from 5 to 15 K depending on the solidification rate). This analysis also predicts a significant silicon-enrichment of the interfacial liquid, especially in the modified eutectic (up to 2 wt %).

Minimum undercooling condition as a particular case of the criterion of minimum entropy production

The attempt to compare the diffusional-thermal model based on the criterion of minimum entropy production to diffusional one based on the condition of minimum undercooling has been presented for regular eutectic growth. Finally, the general relationship describing lamellar structure formation is to be reduced to another one proposed by Jackson and Hunt's theory. This reduction has been in great part obtained. However, it remain some equivalent terms, which are not identical. It is probably produced by some imperfections of Jackson and Hunt's model, as well as any other adversities, e.g., some different assumptions in both compared models. The reduction of the criterion of minimum entropy production to the condition of minimum undercooling has also been suggested.

Dendrite characteristics in directionally solidified Pb-8 Pct Au and Pb-3 Pct Pd alloys

Pb-8 pct Au and Pb-3 pct Pd alloy specimens partially directionally solidified and then quenched have been examined in order to characterize their dendritic microstructural details and solute composition profiles. Dendrite tip radii have been measured by a controlled sectioning technique. Dendrite tip radius, solute content of quenched liquid at the dendrite tip, solute profile within the interdendritic region and ahead of the dendrite tip, cell length, and the primary arm spacing values obtained experimentally have been compared with the theoretical predictions. Two groups of models, one based on the minimum undercooled dendrite tip criterion and the other based on the marginal stability at the dendrite tip, have been examined. The Burden and Hunt model, based on the “minimum undercooling” approach, does not predict the observed behavior. However, a modification of the Burden and Hunt's model recently proposed by Laxmanan shows a good fit to the experimentally observed parameters. The models based on the marginal stability approach also predict most of the observed behavior well. It is concluded that quantitative comparison of the primary arm spacing measurements can not form the basis of distinguishing among the various dendrite growth models in a positive temperature gradient. There is a critical need to carry out carefully controlled directional solidification experiments in a well characterized metallic alloy system to help distinguish between the minium dendrite tip undercooling and the marginal stability approaches. New experiments based on simultaneous measurements of (a) dendrite tip radius, (b) dendrite tip temperature, and (c) the solute profile ahead of the dendrite tip—all in a convection free atmosphere—are required.

The Effects of Tailing Dam Profiles on Relative Wind Erosion Rates

AbstractErosion from mine treatment and associated residue areas can pose a significant environmental problem for surrounding locations from dust and other transported materials. The shape of such residue areas can influence windfield behaviour by causing significant wind speed increases. Residue areas are often unprotected so that increasing the speed of wind passing over these areas will cause extra erosion. Values of wind speed‐up predicted by an empirical model for wind flow over hills of low slope were compared with measured values over approach slopes to tailings dam. Hunt's model used in this study relates wind speed from a point on the hill to that observed if there was no hill. Measured values are in agreement with those predicted by the model. Shear stress values calculated from the wind flow model are then used to determine the friction velocity which, in turn, predict the relative rates of erosion. This prediction is based on the cubic relation between the friction velocity and erosion rate observed by Bagnold. These calculations are repeated for the various possible hill shapes allowed by the plant layout and the need to integrate long term spoil heaps with existing topography. A strategy for minimizing erosion of mine tailings through shape selection can then form part of the environmental considerations associated with tailings dams.