Surface segregation in MCrAlY alloys

This paper presents a study of surface segregation in NiCrAlY and FeCrAlY type alloys. The segre-gation was measured using Auger electron spectroscopy. Samples were heated in the spectrometer to temperatures between 800 and 1100 °C, and segregation was measured at temperature as a function of time. The results show that when yttrium and sulfur were present in the alloy, they segregated to the surface where their concentrations were greatly enriched over their bulk concentrations. The presence of yttrium in the alloy did not eliminate sulfur segregation. The surface concentration of aluminum appeared, in most cases, to be greater than its bulk concentration. However, because of uncertainty in sensitivity factors for Auger emission, this point could not be conclusively proven. Cobalt and chromium, in contrast, were depleted from the surface. Sulfur segregation was also ex-amined in Ni-S, Cr-S, Al-S, and Y-S binary alloys. Sulfur was found to segregate extensively in the nickel and chromium alloys, but to a much less extent in aluminum. No sulfur segregation was ob-served in the yttrium alloy.     

Oxidative damage to the eye lens caused by cigarette smoke and fuel smoke condensates

The degree to which a reformed U.S. health care system relies on an adequate supply of primary care physicians will determine the urgency of change in the composition of the medical workforce. In many areas of the United States, the demand for primary care physicians, particularly in managed care settings, far exceeds the supply. In contrast, reports of reduced practice opportunities for medical and surgical subspecialists in the same settings are increasing. As opportunities for and incomes of primary care physicians are enhanced, some medical subspecialists may seek retraining in primary care. This article provides a context for understanding the development of physician retraining programs, examines precedents for retraining physicians, describes four possible pathways through which medical subspecialists might acquire primary care training, and emphasizes the importance of defining the scope of practice and necessary skills for providing primary care. Obstacles to retraining appear to be economic (Who will pay? Is the cost worth the benefit?) and jurisdictional (Who will define core competencies? Who will credential programs and trainees?). The current absence of demand for such retraining programs suggests either that marketplace-induced changes will not take place or that the notion of a primary care provider shortage and an oversupply of medical subspecialists is overstated. The inclusion of physician retraining programs in proposed health reform legislation suggests that policymakers are convinced that such programs offer one viable solution to the nation's medical workforce needs.     

Analysis of Forces Transmitted by Upper Complete Dentures to the Supporting Tissue to Contribute to Better Denture Design

In this communication, a denture cross-sectional rib through the molars is analyzed for the applied masticatory force transmission to the supporting tissue. The denture arch is analyzed in order to determine how the arch geometry and dimensions influence the manner in which the arch transfers the support forces and moments (which represent the masticatory loads) to the supporting tissue. The analysis is carried out for a circular denture arch conforming to a circular palatal section. Factors representing ratios of masticatory loads (in terms of forces acting at the arch supports) to the tissue-bearing pressure are presented as nomograms, for various denture arch dimensions.     

Simultaneous sulfidation-oxidation of nickel at 603°c in argon-so2 atmospheres

The simultaneous oxidation-sulfidation rate of nickel has been measured as a function of SO₂ pressure (0.04 to 1 atm) in Ar-SO₂ gas mixtures at 603°C. The observed corrosion rates are about 10⁷ times faster than the oxidation rate of nickel in oxygen at 1 atm. The product scale consists of an inner Ni₃S₂ layer and an outer two-phase layer of NiO and Ni₃S₂. A linear rate law is observed during an initial time period, and the most probable rate-controlling step is dissociation of SO₂. An increase in the scale-gas interfacial area increases the corrosion rate during intermediate time periods. With increasing time, parabolic corrosion rates are measured for SO₂ pressures of 0.25 and 1 atm. Values of the nickel diffusivity in Ni₃S₂ calculated from our measured parabolic-rate constants are in good agreement with recently reported values. This agreement indicates that an interconnected Ni₃S₂ phase in the outer two-phase layer provides rapid transport paths for nickel diffusion through the scale. Formerly a Graduate Student in the Department of Metallurgy and Materials Science at the University of Pennsylvania, Philadelphia, PA     

Low Temperature Hot Corrosion of Cobalt-Base Alloys: PartI. Morphology of the Reaction Product

Accelerated oxidation tests have been conducted on a number of Co-Cr, Co-Al, and Co-Cr-Al alloys coated with a thin film of Na₂SO₄ and exposed at 600 to 750 °C in O₂-SO₂-SO₃ environments containing 0.0095-5 pct (SO₂ + SO₃). Generally, Co-Cr and Co-Cr-Al alloys reacted nonuniformly, usually in the form of pits, and Co-Al alloys suffered broad frontal attack. The morphology of the reaction product was observed to be dependent on temperature andP _SO3 Under all conditions, a thin sulfur-rich band containing sulfides was observed at the alloy/scale interface, and cobalt dissolved near this interface and formed Co₃O₄ and/or CoSO₄(s) in different regions of the reaction product.     

Comprehensive studies on polyethylenimine filled polypropylene and its potential application in carbon dioxide sequestration

Polypropylene (PP) was blended with branched polyethylenimine (PEI) with the aim to prepare blends having CO₂ adsorption property. The CO₂ adsorption properties will be conferred due to the presence of variety of amine functionality in PEI. PEI contains primary, secondary as well as tertiary amine groups. Before testing CO₂ adsorption, PP–PEI blends were characterized using variety of techniques, for example, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, scanning electron microscopy, and polarized light optical microscopy. In this work, we have studied in detail both compatibilized as well as noncompatibilized blends of PP and PEI. The compatibilization was achieved via addition of maleic anhydride grafted PP. Finally, all the compatibilized as well as noncompatibilized blends were studied for CO₂ adsorption. The compatibilized blends showed better thermal, mechanical as well as CO₂ adsorption properties as compared to the noncompatibilized blends. POLYM. ENG. SCI., 59:2092–2102, 2019. © 2019 Society of Plastics Engineers     

Radiosynthesis of (R,S)-[18F]GE387: A Potential PET Radiotracer for Imaging Translocator Protein 18 kDa (TSPO) with Low Binding Sensitivity to the Human Gene Polymorphism rs6971

Translocator protein (TSPO) is a biomarker of neuroinflammation, which is a hallmark of many neurodegenerative diseases and has been exploited as a positron emission tomography (PET) target. Carbon-11-labelled PK11195 remains the most applied agent for imaging TSPO, despite its short-lived isotope and low brain permeability. Second-generation radiotracers show variance in affinity amongst subjects (low-, mixed-, and high-affinity binders) caused by the genetic polymorphism (rs6971) of the TSPO gene. To overcome these limitations, a new structural scaffold was explored based on the TSPO pharmacophore, and the analogue with a low-affinity binder/high-affinity binder (LAB/HAB) ratio similar (1.2 vs. 1.3) to that of (R)-[¹¹C]PK11195 was investigated. The synthesis of the reference compound was accomplished in six steps and 9 % overall yield, and the precursor was prepared in eight steps and 8 % overall yield. The chiral separation of the reference and precursor compounds was performed using supercritical fluid chromatography with >95 % ee. The absolute configuration was determined by circular dichroism. Optimisation of reaction conditions for manual radiolabelling revealed acetonitrile as a preferred solvent at 100 °C. Automation of this radiolabelling method provided R and S enantiomers in respective 21.3±16.7 and 25.6±7.1 % decay-corrected yields and molar activities of 55.8±35.6 and 63.5±39.5 GBq μmol⁻¹ (n=3). Injection of the racemic analogue into a healthy rat confirmed passage through the blood–brain barrier.     

Modulation of HLA-DQ-restricted collagen-induced arthritis by HLA-DRB1 polymorphism

Mouse class II-deficient HLA-DQB1*0302, DQA1*0301 (DQ8) transgenic mice are susceptible to severe collagen-induced arthritis (CIA), an animal model for rheumatoid arthritis. To examine whether polymorphism at the DRB1 locus can modulate DQ-restricted arthritis, we generated double-transgenic (DR/DQ) mice. HLA-DRB1*1502 (DR2) and DRB1*0301 (DR3) were introduced separately into CIA susceptible DQ8.Abeta transgenic mice to generate DQ8/DR2.Abeta and DQ8/ DR3.AbetaO mice. The HLA-DR molecules in these mice were found to be functional on the basis of their positive/negative selection of the Vbeta T cell repertoire. Introduction of the DR2 gene led to a significant decrease in disease incidence in DQ8.Abeta mice, while the DR3 transgene had no effect. In vitro T cell proliferative responses against bovine Cll collagen in primed mice were higher in DQ8/DR3 mice compared with DQ8/DR2 mice. Cytokine analysis showed a Th2 profile in DQ8/DR2 mice, while DQ8/DR3 mice showed a Th1 profile. These results suggest that DRB1 polymorphism can modulate the disease.     

Analysis of maximum entropy processing in the space-angle domain: Two target case

Performance of maximum entropy (ME) processing in the space-angle domain is analyzed. The effects on the ME images of phase differences between coherent sources, observed in simulation results, are explained. The effect of noise on the resolution of incoherent sources is analyzed. It is shown theoretically that the minimum required signal-to-noise power ratio at the output of the array is proportional to the inverse cube of the desired resolution.