Dwell-Fatigue of Ni-Based Superalloys with Serrated and Planar Grain Boundary Morphologies: The Role of the γ′ Phase on Strain Accumulation and Cavitation

The effect of grain boundary (GB) morphology on the cavitation behavior in a Ni-based superalloy, RR1000, was studied during elevated temperature dwell-fatigue at 700 °C. Following a solution heat treatment, the material was control cooled at two different rates, resulting in high angle GB morphologies that were tailored as either serrated or planar. The resulting γ′ precipitate structures were characterized near GBs and within grains. Along serrated GBs coarsened and elongated γ′ precipitates formed and consequently created adjacent regions that were denuded of γ′ precipitates. Cyclic dwell-fatigue experiments were performed at low and high stress amplitudes to vary the amount of imparted strain on the specimens. A combination of electron backscatter diffraction and digital image correlation were used to resolve strain localization relative to the GBs, in which strain accumulation was found to precede cavity formation. Additionally, the regions denuded of the γ′ precipitates were observed to localize strain and to be initial sites of cavitation. These results present a quantitative strain analysis between two variants of an RR1000 alloy, which provides the micromechanical rationale to assess the increased proclivity for serrated GBs to form cavities.

     

ScholOnto: an ontology-based digital library server for research documents and discourse

The internet is rapidly becoming the first place for researchers to publish documents, but at present they receive little support in searching, tracking, analysing or debating concepts in a literature from scholarly perspectives. This paper describes the design rationale and implementation of ScholOnto, an ontology-based digital library server to support scholarly interpretation and discourse. It enables researchers to describe and debate via a semantic network the contributions a document makes, and its relationship to the literature. The paper discusses the computational services that an ontology-based server supports, alternative user interfaces to support interaction with a large semantic network, usability issues associated with knowledge formalisation, new work practices that could emerge, and related work. Published online: 22 September 2000     

平板投影光楔的图象质量

我们报道了一种厚度为20mm的14英寸平板投影显示屏,其亮度可达5000尼特、分辨率为600×800。这种显示器由现成的有机玻璃制成,使用只带梯形预畸变的无需调节的视频投影仪。在厚度为20mm对角线为50英寸屏幕上光学模拟预示XGA分辨率,亮度为500尼特、对比度与传统投影仪相当。     

Solving Recent Challenges for Wrought Ni-Base Superalloys

Metallurgical and Materials Transactions A - This paper reviews the status of technology in design and manufacture of new wrought polycrystalline Ni-base superalloys for critical engineering...     

Reversal of multidrug resistance phenotype by surfactants: relationship to membrane lipid fluidity

Previous studies have suggested that multidrug resistance (MDR) reversal by polyoxyethylene surfactants involves alterations in plasma membrane lipid physical state of resistant cells as one of the possible mechanism(s). To date, however, a detailed and critical examination of the relationship between membrane lipid fluidity and MDR reversal by these surfactants has not been performed. In the present studies, therefore, a series of experiments were conducted to critically examine the role of membrane lipid physical state in MDR reversal by employing a unique class of clinically important nontoxic lipophilic surfactants and the KB-8-5-11 drug-resistant cell line. MDR reversal was assessed by rhodamine-123 uptake. The effect of surfactants on plasma membrane lipid fluidity of these cells was assessed utilizing a fluorescence polarization technique with fluorophores DPH, TMA. DPH, 2-AS, and 12-AS. Our studies demonstrated that: (i) in vitro addition of active MDR-reversing surfactants (Solutol HS-15, Tween 40, and Cremophor EL, 10 micrograms/ml each) decreased lipid fluidity of isolated crude plasma membranes of resistant cells; (ii) the inactive surfactants (octylglucoside, hecameg) failed to influence membrane lipid fluidity; (iii) cells grown in the presence of active surfactants also exhibited a decreased plasma membrane lipid fluidity as measured with intact cells utilizing the probe TMA.DPH; and (iv) active surfactants did not influence lifetimes of the excited state of the fluorophores. These findings demonstrate that decrease of the plasma membrane lipid fluidity of KB 8-5-11 resistant cells may be one of the important mechanism(s) of MDR reversal by polyoxyethylene surfactants.     

Measurement of the absorption spectrum of polytetrafluoroethylene in the near millimetre region by an untuned cavity

The absorption spectrum of polytetrafluoroethylene has been measured between 3 and 15 cm^?1, a region which until now has been virtually unexplored. Absorption was found to arise almost entirely from amorphous regions of the sample and absorption in crystalline regions is small. A novel feature of the investigation is that measurements are made in an untuned cavity which has the advantage for low loss materials, that losses from reflection, scatter, and diffraction become unimportant. Loss measurements can be made on samples even when they are in the form of fine powder.