Effect of thermal treatment on various characteristics of undoped and V2O5-doped Co3O4/TiO2 catalysts

The thermal treatment of undoped and V₂O₅-doped Co₃O₄/TiO₂ catalysts was studied in the temperature range, 330–600° C both in vacuum and in air. The wide difference in the catalytic behaviour of the two catalysts could be attributed to surface as well as bulk diffusion of the active cobalt oxide particles. Although in both cases the total Co³⁺ ions of various energy states were considered to be the active species for the given reaction, the distribution of various cobalt species, namely Co-t and Co-o, occupying tetrahedral and octahedral sites in the support-defective structure, seemed to be seriously affected by doping with V₂O₅. This dopant was supposed to have two-fold effect: part is incorporated into the surface Co₃O₄ crystallites leading to smaller more mobile particles, easily reducible and more dispersed, and another part diffuses a few atomic layers deeper in the support causing the redistribution of cobalt species. Upon heating, the increased mobility and the increased availability of the support tetrahedral sites may be responsible for the deactivation behaviour. The bulk diffusion enhanced by doping might cause some modification in the porosity characteristics of the titania support.     

Effect of rare earth metal oxide additions to tungsten electrodes

A comparative study has been made on the operating characteristics of gas-tungsten arc (GTA) welding for several types of electrodes. The work was carried out with a pure tungsten electrode and tungsten electrodes activated with a small quantity of the rare earth metal oxides, La₂O₃, Y₂O₃, CeO₂, and with ZrO₂, ThO₂, and MgO. Their behaviors during arcing were analyzed and compared from the points of view of arc starting characteristics, electrode consumption, change in shape due to long-term operation, and incompleteness of insert gas shielding and electrode temperature. The results indicated that W-La₂O₃ electrodes have superior characteristics among those tested. Metallographic studies of the electrodes indicate that the superiority of operating characteristics strongly depends on the behavior of the rare earth metal oxides during arc burning. It is observed that the rare earth metal oxides form tungstate or oxytungstate during arc burning. These newly formed compounds have low melting points and migrate from the low temperature zones to the high temperature zones throughout the electrode tip, while ThO₂ reacts with tungsten, forming pure Th. Also, the investigation demonstrates good stability of La₂O₃ during arc burning compared with the other oxides. Particular attention was also paid to the electrode temperature measurement and the important phenomena concerning the emissivity of a particular surface as one of the thermal properties. The investigation reveals the effects of temperature and oxide distribution on the spectral emissivity of the electrode in addition to the main different effect of oxides added to tungsten. Observations of the cathode tip microstructure during and after arc burning were made, and important phenomena concerning the formation of a tungsten “rim” at the periphery of the cathode area, which governs the durability of the electrode and the stability of the arc, are discussed theoretically and experimentally based on the temperature measurement of the tip and the oxidation of tungsten. ALBER A. SADEK, formerly with the Welding Research Institute, Osaka University     

Application of methods of feasible directions to structural optimization problems

A general approach to structural optimization which has received much attention in recent years is that of using mathematical programming (numerical search) techniques. These techniques may be separated into direct and indirect methods. Of the direct methods of attack on general nonlinear inequality constrained problems, the largest class is called methods of feasible directions. This paper presents the application fo Zoutendijk's method of feasible directions [5] to structural optimization problems. The algorithm requires the analytic gradient of the objective function and the constraint functions which are active at a given stage in the design process. A considerable improvement in convergence has been achieved by considering each pushoff factor as a linear function of the corresponding active constraint. A comparison of the half-step versus full-step search procedure is presented. An initial step length based on a present decrement of objective function is used. A discussion of the linear versus quadratic interpolations of a constraint function in search for a bound point is presented. The algorithm is demonstrated with elastic design of a 25-bar space tower, a 3-bay single storey and a double bay double storey rigid jointed plane frames. Data on the differences in the optimum designs obtained from different starting points is reported.     

Dynamic optimization of a sandwich beam

Analytical procedure for the determination of the least weight design sandwich beam which satisfies a specific frequency requirement is presented. The approach is to modify an initial design by varying the thickness of each of its different layers. This is accomplished using gradient equations to first obtain the correct beam fundamental frequency and then, while this frequency is held constant, to minimize the weight. The gradient equations are derived in matrix notation suitable for the use of digital computers. For practical as well as other considerations, imposing lower bounds on layers' thicknesses have been found necessary. The equations of motion used include all the higher order effects like inertia, extension and shear of all the layers. Hence the procedure is applicable for short as well as long, soft or stiff cored beams. The design procedure has been completely automated in a computer program. Results of numerical examples show that the method is convergent and that optimized configurations can be determined in a few redesign cycles.     

Effect of alkali roasting and sulfatization on the extraction of different metal oxides from waste alum sludge

Water treatment plants (WTP) generate a significant amount of sludge as byproducts with environmentally harmful elements. Thus, this work focused on the recycling of alum sludge through the extraction of different metal oxides, i.e., Al₂O₃, Fe₂O₃ and SiO₂, for use in different applications, such as ceramics, cement, and agriculture. The extraction of Al₂O₃, Fe₂O₃, and SiO₂ from alum sludge was performed using sulfatization and roasting to compare which of the two processes could produce the metal oxides of the highest purity. Precipitated powders were calcined at 700°, 900° and 1100 °C. Moreover, the obtained prepared and calcined powders were characterized by studying their phase compositions, microstructure, particle size, and surface area. Results indicated that roasting achieved the highest yield of alumina. Iron oxide was extracted mostly in maghemite form through roasting after calcination at 1100 °C. Further, silica was obtained in cristobalite and quartz phases after calcination at 1100 °C for the samples prepared through sulfatization. However, these phases of silica were combined with albite and obtained after calcination at 1100 °C for the samples prepared through roasting method.     

Effect of compaction method on the undrained strength of fiber-reinforced clay

The use of discrete fibers in reinforcing soils is of interest to the geotechnical engineering community. Two limitations exist in experimental studies involving fiber-reinforced clays. First, fiber-reinforced clay specimens are generally prepared in the lab using conventional “impact” compaction, whereas the compaction of clay systems in the field typically involves “kneading” action. Second, the majority of tests reported in the literature use synthetic fibers to the exclusion of other types. This paper addresses these limitations through an experimental triaxial testing program that: (1) supplements the scarce data available in the literature on the undrained load response of clays reinforced with “natural” fibers and that are compacted by “kneading”, and (2) assesses the capacity of the experimental procedures that involve “impact” compaction to produce responses that are relevant to actual field conditions. Results from 73 unconsolidated undrained triaxial tests indicate that the percent improvement in the undrained strength of the fiber-reinforced clay is highly dependent on the compaction method, with specimens that are prepared using impact compaction yielding improvements up to three times larger than identical specimens prepared by kneading. This discrepancy in the behavior can be traced back to differences in the fiber orientation distributions between specimens that were compacted by impact and kneading.     

From narrow-band to ultra-wide-band microwave sensors in direct skin contact for breast cancer detection

In this paper, the design and test of different microwave antennas and sensors for breast cancer detection are presented. The sensors are designed and optimized to be used in direct skin contact, and for this purpose a specific breast phantom model is proposed. First, a miniaturized microstrip back-cavity Hilbert fractal antenna, operating in the ISM band (2.4–2.5 GHz), was designed. Then, this antenna was used to investigate the possibility of detecting the presence of breast tumors based on a narrowband frequency method that monitors the shift of the antenna frequency response. The antenna prototype was fabricated and tested in real in vivo measurement conditions on two different patients diagnosed with breast cancer. Measurement results have led after a comparison with the retro-simulation results of the structure to a more realistic breast model and to draw the limitations of this narrowband frequency method. As a time domain study seems to be more relevant, an UWB monopole antenna of dimensions 3 cm × 3 cm, to be used in direct contact with the breast model was designed. This antenna was optimized to both enhance the antenna/human body matching and to maximize the transfer of energy into the breast phantom by using a cavity, increasing by this way the detection potential. In order to improve the sensor’s directivity and enhance the electromagnetic field level inside the breast, a balanced antipodal Vivaldi antenna was also designed and optimized for a direct breast contact to operate in the 3.1–10.6 GHz band. A mono static and a bi static study in the time domain are finally proposed to investigate the presence of the tumor.     

Overview of the Structural Design of World Trade Center 1, 2, and 7 Buildings

This paper summarizes the primary structural systems that comprised World Trade Center (WTC) 1, 2, and 7, which were destroyed in the terrorist attacks of September 11, 2001. There were four major structural subsystems in the towers: the exterior walls, the core, the floor system, and the hat truss. The major structural systems within WTC 7 were the foundation, exterior moment frames, floor system, interior columns, and column transfer trusses and girders. At the time of design and construction, the WTC towers were innovative in many ways, and resulted in a tremendous increase of open-plan commercial office space in downtown Manhattan. As the first of four papers, this paper summarizes the structural and passive fire protection features of each building, and focuses on the structural systems which played a critical role in the outcome of the attacks of September 11, 2001. Three companion papers address the effects of aircraft impact damage on the WTC towers and debris damage on WTC 7, the effects of fire on the three buildings, and how these events contributed to building collapse by describing the contribution of key structural systems to the overall building behavior and collapse, such as the floor systems and hat trusses in WTC 1 and WTC 2 and the floor connections around Column 79 in WTC 7.     

Weld interference detection based on airborne acoustical monitoring of the MIG/MAG process

The sound of the welding process is a consequence of the modulation in amplitude of the current for the voltage of the electric arc. Previous experiments demonstrated that an experienced welder has an absolute dependence on the acoustics in the control of the welding process. In this work, a new technique for the detection of welding defects is presented, based on the stability of the airborne acoustics of the MIG/MAG process for the short-circuit transfer mode. Statistical parameters of the sound pressure and of the sound pressure level were determined for welding without defects from multiple tests; an algorithm was developed from these results for detecting defects based on a moving window that moves through the statistical signals calculated from the acoustical process. Finally, a group of test plates with and without defects was tested; the algorithm based on the airborne acoustics of the developed process showed satisfactory results for the detection of defects.     

Thermal-hydraulic analysis of UO2 and MOX fuel considering different cladding materials at various burnup levels in pressurized water reactor

Thermal analysis of fuel elements with UO₂ and mixed-oxide (MOX) fuels at different fuel burnup levels has been performed analytically and by simulation using ANSYS. Results showed that UO₂ incurred a lower fuel temperature than MOX under all conditions. Higher fuel element temperatures were obtained for higher levels of burnup for UO₂ fuel. For MOX fuel, higher temperatures were obtained for low and high burnup fuel. Radial temperature, thermal gradient, and thermal heat flux were determined across reactor pressure vessel (RPV), demonstrating the highest value at the center of the RPV. The maximum linear power density was determined for UO₂ and MOX, showing that using UO₂ fuel at 2 at% burnup rendered the highest allowable linear power density. Furthermore, the transient analysis showed that there was a small rise in fuel temperature for a decrease in mass flow rate from 100% to 60% followed by a rapid increase in temperature for further reduction in flow rate.