Microwave study of chemically synthesized conducting polyaniline on alumina

Polyaniline (PANI) thin film on alumina was prepared by the chemical oxidation of aniline with ammonium peroxydisulphate in acidic aqueous medium. DC conductivity, microwave transmission and reflection, microwave conductivity, shielding effectiveness and microwave dielectric constant of the conducting PANI films are reported. DC conductivity was between 0.15 × 10^?3 and 3.13 × 10^?3 S/cm. Microwave conductivity was between 0.2 and 10 S/cm. The PANI films coated on alumina gave shielding effectiveness value of ?1 to ?4 db. The ?′ was between 2 and 350 whereas ?″ was between 437 and 60. Measurements have been carried over the frequency range of 8.2–18 GHz.     

Structural and Dielectric Properties of Ca Doped Barium Iron Niobate

Ceramic materials with high dielectric constant are being used in many electric and electro-optics applications. Ca substituted barium iron niobate with general formula (Ba_1-xCa_x) (Fe_0.5Nb_0.5)O₃ with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by conventional solid state reaction method. Structural properties were investigated using X-ray diffraction and scanning electron microscope. Two types of phases were observed for 0.4 ≤ x ≤ 08. Dielectric constant and loss tangent were measured using impedance analyzer in the frequency range of 20 Hz–1 MHz at room temperature. Dielectric constant and loss tangent were found to decrease with increasing the frequency. A relatively good combination of dielectric constant and loss tangent was obtained for x = 0.2 (?_r = 1441 and tan δ = 0.19) at 10 KHz.     

Wave structure in Stokes' second problem for a dipolar fluid with nonclassical heat conduction

Summary The classical heat conduction law of Fourier associates an infinite speed of propagation to a thermal disturbance in a material body. Such behavior is a violation of the causality principle. In recent years, several modifications of Fourier's heat law have been proposed. In this work, a modified form of Fourier's heat law, based on the Maxwell-Cattaneo-Fox (MCF) model, is used to analyze the heat conduction effects in Stokes' second problem for a dipolar fluid. The structure of the waves and the influence of the dipolar constants on the velocity field is investigated. These results are then compared to the viscous fluid case. In addition, the displacement thickness and skin friction at the plate are determined.     

Modelling non-Newtonian two-phase flow in conventional and helical-holding tubes

Summary The research described in this communication was undertaken to test the hypothesis that the fluid mechanics and heat-transfer aspects involved in aseptic processing could be modelled. In order to do this, a finite difference FORTRAN program (using the fourth-order, four-stage explicit Runge–Kutta method) was written by the authors to compute the velocity of fluid elements and particles during fully 3-dimensional flow in conventional and helical-holding tubes. The effect of particles on the fluid-flow field and the interaction between particles was taken into account during the modelling. Simulation results showed that an increase in specific gravity, tube diameter or coil diameter resulted in an increase in the residence time of the particles, while an increase in the flow rate decreased the residence time of the particles. An increase in the particle diameter or the flow rate narrowed the Residence Time Distribution (RTD) of the particles, while an increase in specific gravity or the tube diameter increased the RTD of the particles.     

Numerical modeling—A new tool for understanding shotcrete

The analytical flow simulation of fresh concrete is a recent challenge to researchers. Due to its heterogeneity, the concrete mix shows neither a perfectly viscous nor perfectly particulate behavior. However, the particulate behavior of fresh concrete flow like arching and blocking in pipes and in complex boundary conditions, is very common. This is further magnified due to high pressure in the case of shotcreting. For the first time in shotcrete research, authors propose the application of the Distinct Element Method [1] (DEM) to predict particle behavior and amount of rebound loss, and to assess the quality of the shotcrete analytically. Also, the effect of an accelerating agent, the way its effect is modeled, effects of gradual change in shooting pressure, the resulting rebound is shown. The void of the attached concrete is also compared with that of normal cast concrete in an analytical way.     

ADSORPTION EQUILIBRIUM OF CARBON TETRACHLORIDE ON DRY SOILS

Vapor phase adsorption equilibrium of carbon tetrachloride, a priority pollutant, on dry soils was studied at 288, 293, and 298 K. Using a gravimetric adsorption apparatus, adsorption /desorption isotherms of carbon tetrachloride were generated on two different soil samples. The effects of temperature and soil characteristics were examined. Isosteric heals of adsorption were calculated and heat curves were constructed.

Adsorption isotherms of carbon tetrachloride on dry soil samples were Type II, indicating formation of multilayers of adsorbate on the soil particle surface. Considerable hysteresis effects, associated with capillary condensation, were observed upon desorption. Thermal data confirmed that the adsorption of carbon tetrachloride vapor on soil was primarily physical adsorption. Heat curves showed that the soil samples had energetically heterogeneous surfaces. A positive correlation between The soil's specific surface area and its sorption capacity was observed. Clay content and pore size were also dominating factors.

The experimental data were correlated by the Polanyi Potential, the BET, and the GAB models in order to provide input lo fate and transport models predicting the degradation or movement of volatile organic pollutants in soil. The BET equation gave accurate data fit, within a deviation range of 2·63-5·40%, for up to 40% of the saturation pressure. The GAB equation provided superior fit of the data for the entire relative pressure range. Absolute error percentages from the GAB model ranged from 1·77 to 5·38%. Results followed the Potential Theory satisfactorily and led to a single temperature-independent characteristic curve.     

Design and development of multicolor MWIR/LWIR and LWIR/VLWIR detector arrays

Multicolor infrared (IR) focal planes are required for high-performance sensor applications. These sensors will require multicolor focal plane arrays (FPAs) that will cover various wavelengths of interest in mid wavelength infrared/long wavelength infrared (MWIR/LWIR) and long wavelength infrared/very long wavelength infrared (LWIR/VLWIR) bands. There has been significant progress in HgCdTe detector technology for multicolor MWIR/LWIR and LWIR/VLWIR FPAs.^1–3 Two-color IR FPAs eliminate the complexity of multiple single-color IR FPAs and provide a significant reduction of weight and power in simpler, reliable, and affordable systems. The complexity of a multicolor IR detector MWIR/LWIR makes the device optimization by trial and error not only impractical but also merely impossible. Too many different geometrical and physical variables need to be considered at the same time. Additionally, material characteristics are only relatively controllable and depend on the process repeatability. In this context, the ability of performing “simulation experiments” where only one or a few parameters are carefully controlled is paramount for a quantum improvement of a new generation of multicolor detectors for various applications.