Determination of local hydrodynamic parameters in bubble columns by the electrodiffusion method with oxygen as depolarizer

An electrodiffusional three-segment probe was developed with which local axial and radial liquid velocities can be determined. Application of this probe in gas-liquid flow yields information on local gas hold-up. In coalescing media the commonly used redox-system Fe(CN) ₆ ³⁻ /Fe(CN) ₆ ⁴ should be replaced by dissolved oxygen as depolarizer. Measurements of local axial and radial liquid velocity and turbulence intensity in different bubble columns (D = 150 and 600 mm) showed good agreement with data obtained by hotfilm anemometry. This paper was presented at the International Workshop on Electrodiffusion Diagnostics of Flows held in Dourdan, France, May 1993.     

The correlation between electrical properties and structure of substituted polyacetylenes

Summary The electrical conductivity of polyphenylacetylenes and polyhalophenylacetylenes was measured in dependence on the temperature and on the type of catalyst used for polymerization. The electrical conductivity increased with increasing temperature. The energy gap was calculated from the temperature dependence on the electrical conductivity; it decreased with increasing number of conjugated double bonds in the polymer chain and with the regularity of structure of the polymer. The number of double bonds, cyclization and configurations were determined by ¹H and ¹³C-NMR. In polyphenylacetylenes only aliphatic carbons deriving from cyclohexadiene units were found but no such units were found in polyhalophenylacetylenes. By UV-vis measurement the number of conjugated double bonds in segments was estimated. The synthesized polymers were amorphous. Their molecular weight was between 2000 and 74.000.     

Seeding effects on crystallization temperatures of cordierite glass powder

The role of solid state epitaxy in the crystallization of nanocomposite cordierite glass to glass ceramic was investigated. The use of isostructural (-cordierite) seeds in cordierite glass led to a lowering in the crystallization temperature to form glass ceramic by about 50 °C compared to the unseeded glass. The use of non-isostructural seeds such as ZrO₂ and TiO₂ did not lower the crystallization temperature of cordierite glass to glass ceramic, and in the case of the TiO₂-seeded glass the crystallization temperature increased by about 50 °C compared to the unseeded-cordierite glass. The lowering in crystallization temperature by-cordierite seeding can be attributed to the nucleation and epitaxial growth mechanism.     

IMPROVEMENT ON FATIGUE LIFE OF ALLOY LY12CZ AFTER LASER RADIATION AND ITS DAMAGE EVOLUTION

The change of microstructure of fatigue specimens before and after laser radiation was studiedby transmission electron microscopy.The results show that the diameter of dislocation cell λtends to a constant at fatigue failure.Based on the principles of continuous damagemechanics,expressions of the fatigue damage criterion and processes of fatigue damage evolu-tion for L Y12CZ have been derived.     

An interactive lung field segmentation scheme with automated capability

Feasible clinical application of any automated segmenting methodology demands more than just accuracy. Amendment to the automated delineation is necessary when the algorithm fails, however, integrated solution to such a scenario is largely absent in literature. Hence in this survey we devised an architecture that does both the automated and interactive lung field localizations using a single segmenting engine—random walker algorithm—so that intuitive amendment is only necessary when the automated generated delineation is unsatisfactory. The algorithm proceeds by first extracting 18 intensity profiles running horizontally, each of them equally spacing apart, and in each intensity profile three extreme points denoting the two lungs and the esophagus are determined through profile matching. This done, the algorithm removes profiles that do not intersect with the lung, and the rest of the extreme points are plugged into random walker algorithm to perform segmentation. The achieved accuracy in localization by the above was 0.8875 in terms of overlap measure (the maximum value for this parameter is 1) over 341 images. In the case where unsatisfactory delineation prompts amendment necessary, the user can interactively segment the lung by just a shift on some of the previous-determined points to the desired locations, and random walker algorithm is run again with the amended input. By such a fusion, the benefits of both the automated and interactive segmentation are shared in a single architecture.     

Kelvin Probe measurements of polymer coated gold substrates: Mechanism studies

The origin of work-function changes induced in polymer/metal structures (polyacrylic acid (PAA), ammonium and sodium polyacrylate) upon ammonia exposure is studied. To understand and explain the mechanism systematic measurements of uncoated and polymer coated metals are performed in Kelvin Probe (KP) setups. Additional data have been acquired through gravimetric and electrochemical experiments (cyclic voltammetry (CV)). The results obtained confirm that the field effect sensitive processes are taking place at the metal/polymer interface and allow their modelling. The intrinsic sensitivity of metallic samples upon ammonia exposure is influenced by the presence of coating polymers, by their ability to sorb water and to keep the metal surface wet or dry.     

Developments in micro-electron beam welding

At the ISF (Joining and Welding Institute, RWTH Aachen University) the long-established electron beam (EB) welding process is investigated to meet the requirements of the field of micro-applications. A modified LEO ZEISS DSM 962 scanning electron microscope (SEM) is being used as a Micro-EB welding machine. The diameter of the beam in welding mode is about 20 μm, with a maximum beam power of 6 Watt at 30 kV acceleration voltage. The process-specific advantages, such as the inertia-free movement of the tool electron beam, the very small beam diameter, the clean room environment which is due to processing in a vacuum (no shielding gas needed) and the excellent applicability for visual quality control offer the best preconditions for hybrid micro-assembly purposes. If the technology is down-scaled to a micro-level, physical effects occur whose consequences must be met with new approaches of solution. Joining of micro-components presupposes optimal contact conditions. If the micro-components are of a flexible type, those optimal conditions are difficult to implement. The ratio of forces during the joining process and also the low stiffness of the components which is due to the small dimensions require, on the one hand, the application of a suitable handling technique or, on the other hand, a specific beam manipulation strategy. Especially in the field of micro-applications, the possibility to exert influence on the thermal distortion by symmetrical heating and solidification processes is of particular importance. Therefore, the reproducibility of the welded joints is one of the great challenges in the field of microwelding. The investigations and developments done at the ISF show successful results in joining stainless steel sheet materials down to 30 μm thickness and steel wire down to 50 μm in diameter, whereas other materials (Tungsten, Aluminum, Titanium, Nickel) are under investigation.     

Ring resonator for lasers with annular gain media

A ring resonator for lasers with annular gain media is presented. The resonator consists of two annular mirrors. While the radiation is reflected back and forth between the two annular mirrors, diffraction effects induce an additional azimuthal radiation flux. Output coupling is obtained through a decentered coupling aperture on the circumference of one of the two mirrors. The azimuthal radiation flux permits the extraction of optical power from the whole gain volume through the coupling aperture. The azimuthal radiation flux can revolve in two directions. The associated modes are degenerate, and random jumping between unidirectional and bidirectional operation is observed. Unidirectional operation has been stabilized but remains very sensitive to mirror alignment. High extraction efficiencies have been demonstrated experimentally with this resonator with a diffusion-cooled CO(2) laser and 2 times diffraction-limited beams have been obtained. An empty resonator model that shows the effect of edge diffraction at the coupling aperture on the resonator modes is also given.