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51.
52.
"A reevaluation of cross-sectional versus longitudinal models of residential mobility...casts doubt on the study by Davies and Pickles in 1985 in which it was argued that cross-sectional analysis is inadequate.... With the use of data from the [U.S.] Panel Study of Income Dynamics (PSID), the conclusion of this reevaluation is that longitudinal analysis increases our understanding of the processes and provides a richer understanding of migration and mobility but does not undermine the work that has been produced from cross-sectional analysis." 相似文献
53.
A. V. Clark C. M. Fortunko M. G. Lozev S. R. Schaps M. C. Renken 《Research in Nondestructive Evaluation》1992,4(3):165-182
An electromagnetic-acoustic transducer (EMAT) system was used in conjunction with a sampled CW signal-processing method to generate, receive, and process longitudinal and shear waves in thin steel sheets. Using the system, swept-frequency measurements were made up to 7.5 MHz. To relate the measurements to sheet steel formability, a dimensionless frequency ratio,K, was computed from the resonant frequencies. From theoretical considerations,K should be related to a measure of steel sheet formability,
. This parameter is traditionally measured by plastically deforming uniaxial tension specimens. Good correlation was found betweenK and
for a set of steel sheet representative of those typically used to produce automobile body parts.Contribution of NIST; not subject to copyright.NIST Guest Researcher; on leave from Technical University of Plovdiv, Bulgaria. 相似文献
54.
55.
As part of a study of the chemistry of the steam-stimulated recovery of heavy oils, the hydrolysis and subsequent desulphurization of tetrahydrothiophene and thiophene by aqueous solutions of vanadyl and nickel salts was investigated. Vanadyl sulphate and vanadyl chloride were shown to behave very differently, emphasizing that these salts have different molecular species in aqueous solutions. 相似文献
56.
Career visual searchers such as radiologists and airport security screeners strive to conduct accurate visual searches, but despite extensive training, errors still occur. A key difference between searches in radiology and airport security is the structure of the search task: Radiologists typically scan a certain number of medical images (fixed objective), and airport security screeners typically search X-rays for a specified time period (fixed duration). Might these structural differences affect accuracy? We compared performance on a search task administered either under constraints that approximated radiology or airport security. Some displays contained more than one target because the presence of multiple targets is an established source of errors for career searchers, and accuracy for additional targets tends to be especially sensitive to contextual conditions. Results indicate that participants searching within the fixed objective framework produced more multiple-target search errors; thus, adopting a fixed duration framework could improve accuracy for career searchers. 相似文献
57.
Ultrafiltration of lake water for potable water production 总被引:1,自引:0,他引:1
Ultrafiltration with coagulation or powdered activated carbon pretreatment is used to treat water from a public water supply. While UF without pretreatment is effective in removing turbidity, pretreatment prior to UF greatly enhances the removal of natural organic matter and trihalomethane precursors. Short-term flux loss can be minimized with backflushing, while long-term irreversible fouling seems to be affected most by the type of membrane polymer. 相似文献
58.
A prototype wind-powered reverse osmosis desalination system was constructed and tested on Coconut Island off the northern coast of Oahu, Hawaii, for brackish water desalination. The system has four major subsystems: a multi-vaned windmill/pump, a flow/pressure stabilizer, a reverse osmosis module, and a control mechanism. The feedback control mechanism, developed by this study, allowed this prototype system to be operated satisfactorily under mild ambient wind of 5 m/s or less. No auxiliary power source was needed. The system operational data showed that at an average wind speed of 5 m/s, brackish feedwater at a total dissolved solids concentration of 3000 mg/1 and at a flow rate of 13 1/min could be processed by this system. The average rejection rate of this prototype system was 97% and the average recovery ratio was 20%. The energy efficiency of the system was measured at 3 5%, which is comparable to the typical energy efficiency of well-operated multi-vaned windmills. Generally, the system's energy efficiency decreases as wind speed increases. 相似文献
59.
Norbert Koppenhagen Benjamin Mueller Alexander Maedche Ye Li Stephanie Hiller 《Information Systems and E-Business Management》2016,14(3):613-636
E-procurement and supplier-relationship management systems have helped to substantially advance process execution in supply management. However, current supply network systems still face challenges of high data integration efforts, as well as the decoupling of structured data and processes from the growing amount of digitalized unstructured interactions of supply management professionals. Inspired by the room for improvement posed by this challenges, our research proposes a design for a supply network artifact in supplier qualification that addresses these problems by enabling holistic integration of data, processes, and people. The artifact is developed following an action design research approach. Building on a set of meta-requirements derived from literature and practice explorations, we conceptualize two design principles and derive corresponding design decisions that have been implemented in an software artifact. Finally, we formulate testable hypotheses and evaluate the artifact and its design in the context of supplier qualification. Our results show that the proposed design reduces mental effort of supply management professionals and significantly increases efficiency when performing typical supply network tasks such as supplier qualification. 相似文献
60.
Photosynthesis and nutrient status measurements were compared in size fractioned water samples collected in southern Lake Malawi in three different seasons. The size fractions analyzed were 0–2.0 μm, 0–20 μm, and 0–200 μm. Total chlorophyll concentrations were relatively invariant at about 1 μg L?1 in all seasons (wet stratified, deep mixing, dry stratified). Over 90% of total chlorophyll was < 20 μm and 40–50% < 2 μm. Stoichiometric ratios of carbon (C):nitrogen (N) and C:phosphorus (P) for the < 2-μm seston were similar to < 20-μm and < 200-μm seston samples and indicated that all size fractions were moderately N and P deficient in all seasons. N and P uptake experiments demonstrated that when the < 2-μm picoplankton were isolated from the larger sizes, they showed high N and P nutrient debts, apparently in response to the removal of nano- and micrograzers. This effect was strongest for N debt in the dry stratified season, but was apparent for P debt in all seasons. The chlorophyll-normalized light saturated rate of photosynthesis, Pbm, was always higher in whole water samples compared to the rates of the isolated picophytoplankton which were lowest in the dry season. We infer that nano- and micrograzers were an especially important source of regenerated nutrients when the lake was stratified although their removal as a source of nutrient to the picophytoplankton may affect Pbm in all seasons. Nitrogen regeneration was especially critical to the picophytoplankton in the dry stratified season but less important in the windy deep mixing season. 相似文献