Bismuth Modified Porous Silica Preparation,Characterization and Photocatalytic Activity Evaluation for Degradation of Isoproturon

Porous silica prepared by using an acrylic emulsion has been impregnated with bismuth ion resulting in Bi₂SiO₅ species containing surface.The as-prepared materials have been characterized by X-ray diffraction spectroscopy （XRD）,X-ray photoelectron spectroscopy（XPS）,UV-Vis diffuse reflectance spectroscopy（UV-Vis DRS）, scanning electron microscopy（SEM）,energy dispersive analysis of X-ray（EDAX）,transmission electron microscopy（TEM）,Fourier transform infrared spectroscopy（FTIR） and N₂ adsorption/desorption techniques. EDAX analysis confirms the penetration of bismuth ions into the framework of silica to form Bi₂SiO₅,which is substantiated by XRD.The UV—Vis DRS shows that the catalysts are optically active and XPS confirms the inclusion of bismuth into the framework of silica.FTIR spectra illustrate the formation of Bi—O—Si linkages in the porous silica framework.SEM and TEM show the spherical morphology,whereas N₂ adsorption/desorption study confirms the porosity of the prepared materials.The photocatalytic activity of the material is evaluated for the degradation of isoproturon herbicide and it is found that the material is active as compared to the commercial P-25 Degussa TiO₂.     

Heat and mass transfer analysis in air-cooling of spherical food productsTransfert de chaleur et de masse dans le refroidissement par air des aliments sphériques

The one dimensional transient heat conduction equation, in spherical co-ordinates, is solved with convective surface boundary condition, during air-cooling. The enthalpy potential concept is used to include the cooling effect of desiccation. A calculation scheme is proposed in which, up to half the cooling time, the calculation is made with both heat and mass transfer from the product surface, thereafter it is continued with heat transfer only. The calculated temperatures for apples and potatoes are compared with the measured values available in the literature, and good agreement is observed.     

Dielectric relaxator behaviour of the system Sr1−xLaxTi1−xCoxO3 (x ⩽ 0.40)

The dielectric behaviour of the valence-compensated solid solution Sr_1–x La _x Ti_1–x Co_xO₃ (x=0.05, 0.10, 0.20, 0.30 and 0.40) has been studied as a function of temperature and frequency. Compositions withx=0.20, 0.30 and 0.40 exhibit high values of dielectric constant. This high dielectric constant is due partly to the presence of interfacial polarization, and partly to the formation of grain-boundary barrier layers in these materials. The presence of barrier layers is shown by complex plane impedance analysis.     

Cool-down of foam insulated cryogenic transfer lines

An experimental programme is presented for estimating cool-down time for foam insulated cryogenic transfer lines. The results show that there is good agreement between theoretical and experimental cool-down curves. The integral method is shown to be an accurate way to determine the position of cooling front as the cool-down proceeds. It was also found that the mass flow rate does not significantly affect the cool-down of short transfer lines.     

Dielectric dispersion in ZnF2-Bi2O3-TeO2 glass system

Dielectric constant , loss tan and ac conductivity of ZnF₂-Bi₂O₃-TeO₂ glasses with varying concentrations of Bi₂O₃ (from 5 to 20%) are studied as a function of frequency and temperature over moderately wide ranges. The dielectric breakdown strength for these glasses is also determined in air medium. From the analysis of these studies along with the IR spectra & DTA recordings of these glasses, the structural changes in ZnF₂-Bi₂O₃-TeO₂ glass system with change in the concentration of Bi₂O₃, are discussed.     

Study of flow instabilities in double-channel natural circulation boiling systems

Natural circulation boiling systems consisting of parallel channels can undergo different types of oscillations (in-phase or out-of-phase) depending on the geometric parameters and operating conditions. Disturbances in one channel affect the flow in other channels, which triggers thermal–hydraulic oscillations. In the present work, the modes of oscillation under different operating conditions and channel-to-channel interaction during power fluctuations and on-power refueling in a double-channel natural circulation boiling system are investigated. The system is modeled using a lumped parameter mathematical model and RELAP5/MOD3.4. Parametric studies are carried out for an equal-power double-channel system, at different operating conditions, with both the models, and the results are compared. Instabilities, non-linear oscillations, and effects of recirculation loop dynamics and geometric parameters on the mode of oscillations, are studied using the lumped model. The two channels oscillate out-of-phase in Type-I region, but in Type-II region, both the modes of oscillation are observed under different conditions. Channel-to-channel interaction and on-power refueling studies are carried out using the RELAP model. At high powers, disturbances in one channel significantly affect the stability of the other channel. During on-power refueling, a near-stagnation condition or low-velocity reverse flow can occur, the possibility of reverse flow being higher at lower pressures.     

Measurement of thermophysical properties and analysis of heat transfer during freezing of slab-shaped food commoditiesMesure des propriétés thermophysiques et analyse du transfert de chaleur au cours de la congélation d'aliments en forme de plaques

Experiments have been designed to measure water content, packing density and transient temperatures during cooling and freezing of fresh green peas packed in rectangular containers. Specific heat capacity in unfrozen and frozen states and latent heats of fusion are calculated from the measured water content. Experimental temperature records are used to calculate bulk thermal diffusivity, both in the frozen and unfrozen states, on the basis of transient heat transfer analysis. In the frozen state, the measured thermal diffusivity was found to vary almost linearly with temperature. A calculation scheme has been presented and applied to compute temperature variations during immersion and air-freezing of peas, using the measured thermal properties. The proposed scheme yielded the calculated freezing time lying within ±8% of its measured values. The calculated temperatures, with both first and second (Von Neumann) type of boundary conditions, were in good agreement with the measurements of present and earlier investigations.     

Intelligent selection of threshold in covariance-based spectrum sensing for cognitive radio networks

Wireless Networks - The radio spectrum sensing has been an important issue of research in cognitive radio networks over the last decade and the appropriate selection of threshold plays a crucial...     

Speed enhancement of a class of digital phase locked loops (DPLLs) by dynamic gain control technique

A dynamic gain modification algorithm of a class of digital phase locked loops (DPLLs) has been proposed. It has been shown analytically that the modified DPLL based on the proposed algorithm can be designed to have a faster transient response besides having steady-state response and frequency acquisition range same as that of a conventional DPLL. Numerical simulation results have been given to support the analytical predictions.