Thermal characteristics of packed bed storage system

The thermal behaviour of a packed bed storage system charged with hot air is modelled using two partial differential equations representing the energy conservation in the air and solid phases constituting the bed. These two equations are coupled through the heat exchange process between the two phases. A fully implicit numerical scheme based on forward, upwind and central differencing for the time, first and second space derivatives, respectively, is used to solve the modelling equations. Marching technique is used for the air equation and a tri-diagonal matrix solver is employed to solve the solid equation. The solution yields the thermal structure of the bed, namely the air and solid temperature distribution inside the bed at any particular time, and the variation of total energy stored in the bed with time. The effect of bed length, solid diameter and void fraction on the thermal characteristics of the packed bed is studied. Further, the performance of the bed under variable inlet air temperature and mass flow rate is investigated.     

Study of thermal properties of glass system 77% B2O3-23% PbO doped with ZnO in the temperature range 300 to 700 K

The thermal properties: specific heat capacity (C _p), thermal conductivity (), and thermal diffusivity (a) of the glass system 77% B₂O₃-23% PbO doped with ZnO, were measured in the temperature range 300 to 700 K. It was found that electronic conduction has no significant contribution to the thermal conductivity. The main mechanism of heat transfer is therefore due to both phonons and photons. A discussion of the results is made in view of various theoretical aspects.     

On a Population of Labile Synthesized Relaxation Oscillators

A labile synthesized relaxation oscillator (SRO), exhibiting rhythmic activity when excited by an appropriate stimulus, is proposed. Such an oscillator can be used to represent a stimulus-dependent (or labile) biological rhythm. A population of coupled labile SRO's is investigated and its generic equation is presented. The relationship between an input stimulus and an output rhythmic activity of an SRO is described in a computer-simulated example. Also, a tubular structure of nine coupled labile SRO's exhibiting apparently propagating bursts of rhythmic activity is simulated.     

Measurement of thermal properties of liquids with an AC heated-wire technique

An apparatus for the simultaneous absolute measurement of the thermal activity, thermal diffusivity, thermal conductivity, and heat capacity of nonconducting liquids with the AC heated-wire (strip) technique is described. The main advantage of this technique is that the temperature oscillations field can be confined around the sensor in a liquid layer thin enough to suppress the hydrodynamic currents. This leads to the elimination of the convective heat transport. Carrying measurements at different frequencies, the inertia of the sensor can be considered, and the radiative heat transport can be estimated for liquids with known optical properties. The apparatus was constructed and tested using six different liquids in a limited temperature range. The thermal properties of these liquids at 20°C are reported. The thermal conductivity data of toluene and n-heptane (recommended as proposed thermal conductivity standards) are given in the temperature range 10–40°C. Good agreement was found with data reported by other investigators at 20°C, but there is still a considerable discrepancy in the temperature coefficient of thermal conductivity.     

Navigator echo motion artifact suppression in synthetic aperture ultrasound imaging

We develop a simple yet effective technique for motion artifact suppression in ultrasound images reconstructed from multiple acquisitions. Assuming a rigid-body motion model, a navigator echo is computed for each acquisition and then registered to estimate the motion in between acquisitions. By detecting this motion, it is possible to compensate for it in the reconstruction step to obtain images that are free of lateral motion artifacts. The theory and practical implementation details are described and the performance is analyzed using computer simulations as well as real data. The results indicate the potential of the new method for real-time implementation in lower cost ultrasound imaging systems.     

Infrared spectra,X-ray investigations and electrical conductivity of lithium borosilicate glasses containing transition metal oxides

The conductivities of lithium borosilicate glasses containing 2.5 mol % V₂O₅, MnO, Cr₂O₃, Fe₂O₃ and CoO were measured for untreated and heat-treated glasses (for 5 h at 480, 580 and 680°C). Both IR and X-ray diffraction techniques were used to investigate the microstructure of these glasses before and after heat-treatment. Lithium metasilicate and lithium metaborate were the main separated phases in addition to lithium disilicate in samples containing Fe₂O₃. The silicon ions are coordinated to four oxygens in tetrahedral coordination and some borons changed from triangular to tetrahedral.     

Compression of stereoscopic images using pyramid and prune DCT encoding

This paper details a compression system for stereoscopic (3-D) images that takes advantage of the disparity compensation effect by heavily compressing one image and a lightly compressing the other. Two methods were tried for the creation of the heavily compressed image: Lossy Pyramid coding and Pruned Discrete Cosine Transform (PDCT) with Variable Length Coding VLC. Both versions of the program used a lightly quantized PDCT image for the clear image.A detailed explanation of the algorithms, the effect of compression level, and the effect of compression method on stereoscopic perception is presented. A method of creating a pseudo 3-D image from a single image is also discussed.     

Monitoring and correcting spatio-temporal variations of the MR scanner’s static magnetic field

The homogeneity and stability of the static magnetic field are of paramount importance to the accuracy of MR procedures that are sensitive to phase errors and magnetic field inhomogeneity. It is shown that intense gradient utilization in clinical horizontal-bore superconducting MR scanners of three different vendors results in main magnetic fields that vary on a long time scale both spatially and temporally by amounts of order 0.8–2.5 ppm. The observed spatial changes have linear and quadratic variations that are strongest along the z direction. It is shown that the effect of such variations is of sufficient magnitude to completely obfuscate thermal phase shifts measured by proton-resonance frequency-shift MR thermometry and certainly affect accuracy. In addition, field variations cause signal loss and line-broadening in MR spectroscopy, as exemplified by a fourfold line-broadening of metabolites over the course of a 45 min human brain study. The field variations are consistent with resistive heating of the magnet structures. It is concluded that correction strategies are required to compensate for these spatial and temporal field drifts for phase-sensitive MR protocols. It is demonstrated that serial field mapping and phased difference imaging correction protocols can substantially compensate for the drift effects observed in the MR thermometry and spectroscopy experiments.