On connections between 3-d microstructures and their 2-d images

The problem of recovery of three-dimensional microstructural parameters from two-dimensional images is addressed in its inverse form. Three-dimensional inhomogeneous solids with known microstructures are generated virtually and images of their cross-sections are analyzed. Three different types of randomly oriented microcracks and microcracks having preferential orientation with some scatter. Somewhat unexpected result is that, in all the cases considered, three-dimensional defect densities are very close to average values of corresponding two-dimensional parameters.     

Consolidation and properties of binderless sub-micron tungsten carbide by field-activated sintering

The rapid sintering of nano-structured WC hard materials in a short time is introduced with a focus on the manufacturing potential of this spark plasma sintering process. The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. A dense pure WC hard material with a relative density of up to 97.6% was produced with simultaneous application of 60 MPa pressure and electric current of 2800 A within 2 min. A larger current caused a higher rate of temperature increase and therefore a higher densification rate of the WC powder. The finer the initial WC powder size the higher is the density and the better are the mechanical properties. The fracture toughness and hardness values obtained were 6.6 MPa m^1/2 and 2480 kg/mm², respectively under 60 MPa pressure and 2800 A using 0.4 μm WC powder.     

Modeling expert problem solving in a game of chance: a Yahtzee© case study

Although developments on software agents have led to useful applications in automation of routine tasks such as electronic mail filtering, there is a scarcity of research that empirically evaluates the performance of a software agent versus that of a human reasoner, whose problem-solving capabilities the agent embodies. In the context of a game of a chance, namely Yahtzee©, we identified strategies deployed by expert human reasoners and developed a decision tree for agent development. This paper describes the computer implementation of the Yahtzee game as well as the software agent. It also presents a comparison of the performance of humans versus an automated agent. Results indicate that, in this context, the software agent embodies human expertise at a high level of fidelity.     

Characterization of nickel-bearing ferrites obtained as by-products of hydrochemical wastewater purification processes

The efficiency of the ‘ferrite process’ for the purification of wastewater heavily contaminated with nickel is evaluated, and the solid residues formed are characterised. The efficiency of the purification process is always above 99.9% for Fe²⁺/Ni²⁺ ratios greater than 3. The tested Fe²⁺/Ni²⁺ molar ratios (15/1, 7/1 and 3/1) yielded three different nickel ferrites. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES), potentiometric titration, X-ray fluorescence (XRF), X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) yielded Ni_xFe_1−x^IIFe₂^IIIO₄ (x=0.18, 0.40 and 0.65, respectively) as the most probable stoichiometry, and inverse spinel as the most probable structure. Heating at 600 °C causes the transformation of the solids into a mixture of NiFe₂O₄, α-Fe₂O₃ and NiO. Electrochemical analysis of the solid nickel ferrites was performed using carbon paste electrodes (CPEs) in HClO₄ and HCl media. In each case, the first cyclic voltammogram showed the participation of solid species in the electrochemical transformation process, since the shape of the redox peaks could be related to the structure and stoichiometry of the ferrites. In second and successive scans, the voltammograms indicated the redox couples Fe_ads³⁺+1e⁻⇔Fe_ads²⁺ (0.525 V vs. Ag/AgCl) and Ni_ads²⁺+2e⁻⇔Ni(s) (−0.470 V) in HClO₄, and FeCl_2,ads⁺+1e⁻⇔FeCl_ads⁺+Cl⁻ (0.475 V) and NiCl_x,ads^(x−2)−+2e⁻⇔Ni(s)+xCl⁻ (−0.550 V) in HCl.     

Simultaneous synthesis and densification of transparent,photoluminescent polycrystalline YAG by current activated pressure assisted densification (CAPAD)

We report a method for the synthesis and processing of transparent bulk polycrystalline yttrium aluminum garnet (YAG) and photoluminescent Ce-doped YAG ceramics via solid-state reactive-current activated pressure assisted densification (CAPAD). The process uses commercially available γ-Al₂O₃, Y₂O₃, and CeO₂ nanopowders. The nanopowders were reacted and densified simultaneously at temperatures between 850 °C and 1550 °C and at a maximum pressure of 105 MPa. The solid-state reaction to phase pure YAG occurs in under 4 min at processing temperatures 1100 °C which is significantly faster (on the order of tens of hours) and occurs at much lower temperatures (∼600 °C) compared to conventional reaction sintering. We found that the reaction significantly improves densification – the shrinkage rate of reaction-produced YAG was three times higher than that of YAG using pre-reacted powder. The Ce additions were found to retard the reaction driven shrinkage kinetics by a factor ∼3, but are still faster (by a factor ∼1.6) than those associated with direct densification (no synthesis). Densities >99% were achieved in both pure YAG and Ce doped YAG (Ce:YAG). Results of optical measurements show good transparency in the visible and photoluminescence (PL) in the Ce:YAG. The PL peak is broad and appears white when excited using blue light confirming that the ceramics can be used in solid state lighting to produce white light.     

Optical properties of transparent nanocrystalline yttria stabilized zirconia

The optical properties of transparent nanocrystalline zirconia produced using a current activated method were characterized over the entire visible spectrum. The resolutions of the samples were characterized using standard resolution targets. All of the samples produced were found to have as high a resolution as detectable from the test, i.e., they are transparent not translucent. Transmission, reflectance, and absorption coefficients are reported for various wavelengths. The absorption coefficients were found to be highly dependent on processing time. Annealing experiments helped determine that oxygen vacancies (with free electrons) are the primary absorption centers in the visible wavelengths. In addition it was found that grain boundary cores or their associated defects do not contribute significantly to light absorption in the visible range. The lack of an influence of the grain boundary regions is discussed in terms of low oxygen vacancy concentration in the grain boundary space charge layer.     

Carbon source utilization‐based metabolic activity of Salmonella Oranienburg and Salmonella Saintpaul in river water

The presence of introduced or non‐native bacteria in river water can create a selective pressure due to their ability to overcome fluctuations in physicochemical conditions and carbon source availability. The carbon source concentrations (monosaccharides and polysaccharides), physicochemical parameters (turbidity, total dissolved solids, biochemical oxygen demand, temperature and pH) and metabolic activity of Salmonella Oranienburg and Saintpaul were determined in water from the central Sinaloa state rivers. This study's results revealed that the carbohydrate availability and physicochemical conditions of river water make it a suitable niche for the establishment of Salmonella serotypes. Metabolic profiles showed that Salmonella Typhimurium could consume a wide variety of carbon sources but only at moderate levels; in contrast, Salmonella Oranienburg and Salmonella Saintpaul demonstrated intense carbon source utilization of a limited diversity of carbon sources. Carbohydrates, amino acids and carboxylic acids were the metabolites most utilized by the environmental Salmonella strains, demonstrating their superior ability to adapt to and survive in river water.     

Analysis of residual stress and work-hardened profiles on Inconel 718 when face turning with large-nose radius tools

Surface integrity (SI) and, particularly, the residual stress profile, has a great influence on the fatigue life of machined aeronautical critical parts. Among the different cutting parameters that affect the final SI, tool geometry is one of the most important factors. In particular, tool nose radius determines the surface roughness, as well as the thermoplastic deformation of the workpiece. Indeed, the use of large tool nose radius in the industry enables (1) increasing the feed rate while keeping the roughness values below specifications and (2) reducing the influence of the tool wear in the surface roughness. Therefore, in this study, the influence of tool nose radius in the induced residual stress profile and work-hardened layer when face turning Inconel 718 is analysed for a cutting speed range between (30–70 m/min) and a feed rate range of (0.15–0.25 mm/rev). For this purpose, residual stress profiles and work-hardened layer were measured by x-ray diffraction method after machining with a 4 mm nose radius. Then, results have been compared against different tool nose radius studies carried out by other authors for the specified working conditions. Results revealed that residual stress profiles varied when machining with different nose radius for the studied range. In particular, the increase of the nose radius brought to a higher difference between surface tensile stress and subsurface compressive peak stress, which is attributed to an increase of the thermal effect. Moreover, thicker work-hardened layer (around 100 μm) was observed when machining with large-nose radius for the studied working conditions.     

Steric and electronic effects on mesophase stability of segmented liquid crystalline polymers with arylazomethine pendant groups

Summary The kinetics of DL-lactide polymerization was studied in CH₂Cl₂ at 25°C and in toluene at 70°C with HAPENAlOMe, a new Schiff's base complex derived from 2-hydroxyacetophenone and ethylenediamine. A higher polymerization rate is observed with this initiator as compared to other previously reported Al-alkoxides complexes. The polymerization with HAPENAlOMe is also shown to be a living process in both solvents. Moreover, the polymerization proceeds to quite high conversion without significant occurrence of transesterification reactions as confirmed from ¹³C NMR and SEC analysis. Received: 4 October 1999/Accepted: 6 December 1999