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91.
M.L. Martin B.P. Somerday R.O. Ritchie P. Sofronis I.M. Robertson 《Acta Materialia》2012,60(6-7):2739-2745
Using a combination of high-resolution scanning and transmission electron microscopy, the basic mechanisms of hydrogen-induced intergranular fracture in nickel have been revisited. Focused-ion beam machining was employed to extract samples from the fracture surface to enable the examination of the microstructure immediately beneath it. Evidence for slip on multiple slip systems was evident on the fracture surface; immediately beneath it, an extensive dislocation substructure exists. These observations raise interesting questions about the role of plasticity in establishing the conditions for hydrogen-induced crack initiation and propagation along a grain boundary. The mechanisms of hydrogen embrittlement are re-examined in light of these new results. 相似文献
92.
Scott J. Robertson Marina B. Ruggles-Wrenn Randall S. Hay Theodore Shillig Ronald Mitchell Brian Kroeger Logan Gumucio 《Journal of the American Ceramic Society》2020,103(2):1358-1371
A facility for testing SiC fiber tows in static fatigue and creep at elevated temperatures in air and steam was developed. Static fatigue of Hi-Nicalon™-S fibers was investigated at 800°C-1100°C at applied stresses between 115 and 1250 MPa in air, in Si(OH)4(g)-saturated steam, and in unsaturated steam. Fibers tested in Si(OH)4(g)-saturated steam and in air had silica scales throughout the test sections, but those tested in unsaturated steam did not develop scales near the steam injection point. Fiber lifetimes in static fatigue were shortest in unsaturated steam, intermediate in Si(OH)4(g)-saturated steam, and longest in air. Failure strains did not exceed 0.3%. Steady-state strain rates and static fatigue lifetimes are modelled empirically by the Monkman-Grant relationship. Failure mechanisms are discussed. 相似文献
93.
Effects of air temperature and discharge on Upper Mississippi River summer water temperatures 下载免费PDF全文
Recent interest in the potential effects of climate change has prompted studies of air temperature and precipitation associations with water temperatures in rivers and streams. We examined associations between summer surface water temperatures and both air temperature and discharge for 5 reaches of the Upper Mississippi River during 1994–2011. Water–air temperature associations at a given reach approximated 1:1 when estimated under an assumption of reach independence but declined to approximately 1:2 when water temperatures were permitted to covary among reaches and were also adjusted for upstream air temperatures. Estimated water temperature–discharge associations were weak. An apparently novel feature of this study is that of addressing changes in associations between water and air temperatures when both are correlated among reaches. 相似文献
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A Web-based remote interactive laboratory (RIL) developed to deliver Internetworking laboratory experience to geographically remote graduate students is presented in this paper. The onsite Internetworking program employs hands-on laboratories in a group setting that correlates with the constructivist and collaborative pedagogical approach. This paper discusses the pedagogical and technical considerations that influence the design and implementation of the remote laboratory environment given the constraints of the special hardware and learning outcomes of the program. For wide-ranging usability, the remote Internetworking (INWK) laboratory uses de facto networking standards and commercial and broad-band Internet connectivity to ensure real-time secure interaction with equipment. A four-tier role architecture consisting of faculty, local facilitators, remote facilitators, and students has been determined appropriate to maintain academic integrity and ensure good quality of interaction with the remote laboratory. A survey employing a five-point scale has been devised to measure the usability of the remote access INWK laboratory. 相似文献
98.
Hiskett PA Buller GS Loudon AY Smith JM Gontijo I Walker AC Townsend PD Robertson MJ 《Applied optics》2000,39(36):6818-6829
The performance of selected, commercially available InGaAs/InP avalanche photodiodes operating in a photon-counting mode at an incident wavelength of 1.55 mum is described. A discussion on the optimum operating conditions and their relationship to the electric field distribution within the device is presented. 相似文献
99.
1. A major issue facing nursing, and society as a whole, is the longstanding and continuing nursing shortage in long-term care. 2. The demand for RNs in nursing homes will continue to intensify into the next century as the population of older adults with complex care needs continues to grow. 3. The findings of this study suggest that RN recruitment needs in long-term care include having enough qualified and dedicated staff, supportive and competent administration; competitive salaries and benefits; functional, attractive facilities; improved professional and public image; a caring, supportive environment; realistic regulations; decreased paperwork; progressive nurse practice models; and opportunities for educational advancement and career growth. 相似文献
100.
FI Meredith RT Riley CW Bacon DE Williams DB Carlson 《Canadian Metallurgical Quarterly》1998,61(8):1034-1038
The purpose of this study was (i) to determine whether pure fumonisin B1 could be incorporated into, recovered, and detected by high-pressure liquid chromatographic analysis from the semipurified Oregon test diet (OTD) used in rainbow trout feeding studies, and (ii) to determine if the incorporated fumonisin B1 was biologically available using the change in free sphingoid bases in liver, kidney, and serum as a mechanism-based biomarker. The results indicate that fumonisin is not easily quantified in the OTD. Recoveries ranged from 12 to 81% of the calculated concentrations based on the fumonisin B1 added to the OTD. However, the fumonisin B1 in the OTD was readily absorbed and biologically active as evidenced by marked increases in free sphinganine in liver, kidney, and serum. The magnitude of the increase in free sphinganine at 100 ppm in the OTD was comparable to that known to be associated with liver toxicity in rats, pigs, and ponies. 相似文献