Microstructures and mechanical properties of welded Fe-12Cr-20Mn austenitic stainless steel

The effects of welding on the tensile and fatigue properties of fully annealed and cold-worked Fe-12Cr-20Mn austenitic stainless steel were evaluated. Room temperature and 500 °C tensile tests and room temperature cantilever beam fatigue tests were accomplished on specimens that contained autogenous bead-on-plate welds. The tensile and fatigue properties of the fully annealed material were not significantly influenced by welding. The tensile properties of the welded cold-worked material were also not significantly affected by the presence of a weldment. However, welding caused a large reduction of the fatigue life of the cold-worked material. Fatigue cracks preferentially initiated at large Mn-Si inclusions that formed in the fusion zones of the weldments.     

Room temperature oxidation of lead-indium alloy films

The kinetics of growth of thin (14 to 40Å) oxide layers on lead-indium alloys was investigated ellipsometrically, using: 3000Å thick films at 23°C; and oxygen exposures at 760 torr for times ranging from five minutes to five days. Assuming that the oxide layer is comprised of a two-phase mixture of PbO and In₂O₃ having a negligible extinction coefficient made it possible to estimate the oxide composition from the ellipsometrically-obtained oxide refractive index. Under these oxidizing conditions, the volume fraction of PbO in the oxide mixture decreases from a value of unity for pure lead to zero for alloys containing more than 30 at. percent In, in agreement with the Auger Electron Spectroscopy results of Chou and coworkers. The oxidation rate equals a exp (X₁/X), where α and X₁ will be seen to vary complexly with alloy composition. A theoretical explanation of these results is also presented.     

Tailored microstructure of zirconia and hafnia-based thermal barrier coatings with low thermal conductivity and high hemispherical reflectance by EB-PVD

Zirconia and hafnia based thermal barrier coating materials were produced by industrial prototype electron beam-physical vapor deposition (EB-PVD). Columnar microstructure of the thermal barrier coatings were modified with controlled microporosity and diffuse sub-interfaces resulting in lower thermal conductivity (20–30% depending up on microporosity volume fraction), higher thermal reflectance (15–20%) and more strain tolerance as compared with standard thermal barrier coatings (TBC). The novel processed coating systems were examined by various techniques including scanning electron microscopy (SEM), X-ray diffraction, thermal conductivity by laser technique, and hemispherical reflectance.     

A High-Frequency Variable-Voltage-Fed Inverter

A half-bridge inverter circuit capable of providing a wide range of ac output voltages and frequencies is presented. The inverter uses asymmetrical thyristors (ASCR's), which have the advantages of high-power handling capability, small turn-on and turn-off times, and exhibit the same ruggedness associated with conventional thyristors in regards to surge current and gating requirements. By using ASCR's for the main and auxiliary devices, the inverter offers other advantages such as low snubber-power loss, low commutation loss, simple protection circuits, and the ability to operate at high frequencies with different types of loads. Output voltage control is obtained by feeding the inverter from a variable dc source. Two fixed-value auxiliary dc sources are used to obtain a constant-current interruption capability. The performance of the inverter is evaluated both analytically and experimentally.     

High-throughput method for the production and analysis of large natural product libraries for drug discovery

High-throughput methods were applied to the production, analysis, and characterization of libraries of natural products in order to accelerate the drug discovery process for high-throughput screening in the pharmaceutical and biotechnology industries. Library production integrates automated flash chromatography, solid-phase extraction, filtration, and high-throughput parallel four-channel preparative high-performance liquid chromatography to obtain the libraries in 96- or 384-well plates. Libraries consist of purified fractions with approximately one to five compounds per well. Libraries are analyzed prior to biological screening by a high-throughput parallel eight-channel liquid chromatography-evaporative light scattering detection-mass spectrometry system to determine the molecular weight, number, and quantity of compounds in a fraction. After biological screening, active fractions are rapidly purified at the microgram level and individual compounds are rescreened for confirmation of activity. Structures of active compounds are elucidated by NMR spectroscopy and mass spectrometry. Utilization of a novel microcoil probe allows NMR data to be gathered on 50 microg. As a demonstration, a library was made from the stem bark of Taxus brevifolia. Biological screening in the National Cancer Institute's in vitro panel of three cancer cell lines demonstrates that the process enables the discovery of active anticancer compounds not detected in the flash fractions from which the library originates.     

Germ-line mutations in the neurofibromatosis 2 gene: correlations with disease severity and retinal abnormalities

Neurofibromatosis 2 (NF2) features bilateral vestibular schwannomas, other benign neural tumors, and cataracts. Patients in some families develop many tumors at an early age and have rapid clinical progression, whereas in other families, patients may not have symptoms until much later and vestibular schwannomas may be the only tumors. The NF2 gene has been cloned from chromosome 22q; most identified germ-line mutations result in a truncated protein and severe NF2. To look for additional mutations and clinical correlations, we used SSCP analysis to screen DNA from 32 unrelated patients. We identified 20 different mutations in 21 patients (66%): 10 nonsense mutations, 2 frameshifts, 7 splice-site mutations, and 1 large in-frame deletion. Clinical information on 47 patients from the 21 families included ages at onset and at diagnosis, numbers of meningiomas, spinal and skin tumors, and presence of cataracts and retinal abnormalities. We compared clinical findings in patients with nonsense or frameshift mutations to those with splice-site mutations. When each patient was considered as an independent random event, the two groups differed (P < or = .05) for nearly every variable. Patients with nonsense or frameshift mutations were younger at onset and at diagnosis and had a higher frequency and mean number of tumors, supporting the correlation between nonsense and frameshift mutations and severe NF2. When each family was considered as an independent random event, statistically significant differences between the two groups were observed only for mean ages at onset and at diagnosis. A larger data set is needed to resolve these discrepancies. We observed retinal hamartomas and/or epiretinal membranes in nine patients from five families with four different nonsense mutations. This finding, which may represent a new genotype-phenotype correlation, merits further study.     

Melting behavior of solid polymers on a metal surface at processing conditions

The melting or plasticating behavior of seven commercial polymers (high density polyethylene, low density polyethylene, polypropylene, polyoxymethylene copolymer, polystyrene, poly(methyl methacrylate), and polycarbonate (PC) was investigated using an experimental apparatus specifically designed to measure the melting rate and the viscous shear stress of a solid polymer on a steel surface under precisely controlled conditions of temperature, velocity, pressure and sample width comparable to actual processing. The melting rate (per unit polymer solid/metal contact area) was found to increase with increasing temperature for all polymers except PC, to decrease with increasing sample width and to increase less than proportionally to velocity. Pressure increased the melting rate somewhat for most of the polymers. The viscous shear stress decreased with increasing temperature for all polymers except PC, decreased with increasing sample width and increased with increasing velocity. Pressure generally increased the viscous shear stress. PC showed an unusual behavior with a maximum in the melting rate near 4200°F(215.5°C) and also a maximum in the viscous shear stress near 445°F (229.4°C). The present melting model could be examined unequivocally for the first time using our experimental results. Comparison of our experimental results with the predictions of the present melting model clearly indicates the inadequacy of the present melting model, Our experimental results will provide a basis for rational development of a reliable melting model.     

Rashba Conduction Band Spin-Splitting for Asymmetric Quantum Well Potentials

Asymmetric quantum well potentials are expected to produce a conduction band spin-splitting which contributes to Dyakonov–Perel (Sov. Phys. Solid State 13:3023, 1971) spin relaxation. Much experimental work has focused on the effect of an electric field on spin dynamics (Karimov et al., in Phys. Rev. Lett. 91:246601, 2003) and little on asymmetry from alloy engineering. By combining time-resolved Kerr rotation measurements with transient spin grating measurements in GaAs/AlGaAs quantum wells we have compared the conduction band spin-splitting resulting from asymmetric alloy engineering with that from applied electric field. The latter is easily measurable, whilst the former is no greater than that in symmetric wells. These results are consistent with an envelope function approximation model that considers the potential profile in both the conduction and the valence bands (Winkler, in Springer Tracts in Modern Physics, vol. 191, 2003).