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1.
Hagbi N Bergig O El-Sana J Billinghurst M 《IEEE transactions on visualization and computer graphics》2011,17(10):1369-1379
Nestor is a real-time recognition and camera pose estimation system for planar shapes. The system allows shapes that carry contextual meanings for humans to be used as Augmented Reality (AR) tracking targets. The user can teach the system new shapes in real time. New shapes can be shown to the system frontally, or they can be automatically rectified according to previously learned shapes. Shapes can be automatically assigned virtual content by classification according to a shape class library. Nestor performs shape recognition by analyzing contour structures and generating projective-invariant signatures from their concavities. The concavities are further used to extract features for pose estimation and tracking. Pose refinement is carried out by minimizing the reprojection error between sample points on each image contour and its library counterpart. Sample points are matched by evolving an active contour in real time. Our experiments show that the system provides stable and accurate registration, and runs at interactive frame rates on a Nokia N95 mobile phone. 相似文献
2.
Stephen M. Walls John V. Kucsera Joshua D. Walker Taylor W. Acee Nate K. McVaugh Daniel H. Robinson 《Computers & Education》2010
Instructors in higher education are disseminating instructional content via podcasting, as many rally behind the technology’s potential benefits. Others have expressed concern about the risks of deleterious effects that might accompany the adoption of podcasting, such as lower class attendance. Yet, relatively few studies have investigated students’ perceptions of podcasting for educational purposes, especially in relation to different podcasting forms: repetitive and supplemental. The present study explored students’ readiness and attitudes towards these two forms of podcasting to provide fundamental information for future researchers and educators. The results indicated that students may not be as ready or eager to use podcasting for repetitive or supplemental educational purposes as much as we think they are, but they could be persuaded. 相似文献
3.
Taking tests enhances learning. But what happens when one cannot answer a test question—does an unsuccessful retrieval attempt impede future learning or enhance it? The authors examined this question using materials that ensured that retrieval attempts would be unsuccessful. In Experiments 1 and 2, participants were asked fictional general-knowledge questions (e.g., “What peace treaty ended the Calumet War?”). In Experiments 3–6, participants were shown a cue word (e.g., whale) and were asked to guess a weak associate (e.g., mammal); the rare trials on which participants guessed the correct response were excluded from the analyses. In the test condition, participants attempted to answer the question before being shown the answer; in the read-only condition, the question and answer were presented together. Unsuccessful retrieval attempts enhanced learning with both types of materials. These results demonstrate that retrieval attempts enhance future learning; they also suggest that taking challenging tests—instead of avoiding errors—may be one key to effective learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
Experimental observations are presented that demonstrate that diffusion induced grain boundary migration in copper foils exposed
to zinc vapor, from a Cu-15 pct Zn alloy, can be studied directly after treatment without etching. The general characteristics
of migration are in accord with previous investigations, but novel changes in the surface topography are described. Pits were
formed on the surface of areas swept by boundary migration; also, the surface was often converted into a series of corrugations.
The formation of pits suggests that the grain boundary diffusivity of zinc exceeds that of copper. The corrugations are believed
to indicate that boundaries sometimes move in an intermittent manner. 相似文献
5.
S. F. Clugston J. R. Weertman P. G. Shewmon 《Metallurgical and Materials Transactions A》1983,14(3):695-699
An investigation has been made of the cause of enhancement of hydrogen attack (HA) by prior cold working. Bars of 1020 Si-killed steel deformed in three point bending were found to contain microcracks at ferrite/ferrite grain boundaries containing cementite inclusions and at ferrite/pearlite boundaries. Very long cementite plates crack, but shorter cementite inclusions (? ?2 μm) suffer decohesion from the matrix at or near the inclusion ends. The observed anisotropy of microcracking with respect to grain boundary orientation and sign of the deformation stress can be understood in terms of the stress state at the inclusion/matrix interface during deformation. The microcracks are not eliminated by an annealing treatment which is known to cancel the effect of deformation on HA. It is concluded that residual stresses arising from the difference in deformability between cementite particles and matrix are responsible for the influence of deformation on HA. Formerly with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60201 相似文献
6.
7.
A new theoretical model is proposed for the erosion of metals by particles at normal incidence. The model employs a criterion of critical plastic strain to determine when the material will be removed. This critical plastic strain is defined as the strain at which the deformation in the target localizes and hence results in the lip formation. It is shown that, under typical erosion conditions, the “localization” model is more appropriate than the “fatigue” models. Finally, it is demonstrated that the new model predicts quite well all the essential features of the normal impact erosion process. 相似文献
8.
Intergranular stress corrosion cracking (IGSCC) of Alloy 600 in high-temperature, deaerated water or steam has been termed
“hydrogen-induced IGSCC.” We believe these cracks are initiated by the nucleation of a high density of bubbles on the grain
boundary under the combined action of the applied stress and high pressure methane formed from carbon in solution reacting
with hydrogen injected by corrosion. The bubbles then grow together by grain boundary diffusion to give local failure. This
is supported by transmission electron microscope (TEM) observations of two-stage replicas, which show the subsurface formation
of closely spaced (0.2μm) bubbles along boundaries, and their growth into fine cracks before they open to communicate with the corroding atmosphere.
The kinetics are examined and shown to be in quantitative agreement with several experimental observations. This mechanism
involves no grain boundary dissolution of the metal, the only role of corrosion being the injection of hydrogen at a high
fugacity. It predicts an activation energy roughly equal to that for grain boundary dψusion of nickel in Alloy 600. 相似文献
9.
Nate Topham Mark Kalivoda Yu-Mei Hsu Chang-Yu Wu Sewon Oh Kuk Cho 《Journal of aerosol science》2010,41(3):326-330
Hexavalent chromium (Cr6+) emission from stainless steel welding operations poses a serious threat to worker safety and ambient air quality. In this study, tetraethyloxysilane (TEOS) was used as a silica precursor additive to welding shield gas during gas tungsten arc welding (GTAW) operations to determine the feasibility of using these chemicals for Cr6+ exposure reduction. Fume aerosol samples were analyzed for Cr6+ concentration using ion chromatography (IC) and for total Cr by inductively coupled plasma with atomic emission spectroscopy (ICP-AES).At high temperature, silica precursors are pyrolyzed to form amorphous silica (SiO2) which can condense on the existing metal aerosols. The inert silica layer surrounding the aerosols can prevent further chromium oxidation by insulating chromium aerosols. Experimental results showed approximately 45% Cr6+ reductions when 3.0% TEOS was added to the shield gas. Nitrate concentration also decreased by 53%, indicating that reactive oxygen species were also reduced. Transmission electron microscopy (TEM) images of collected fume aerosols showed SiO2 coating on metal particles, verifying the proposed mechanism. 相似文献
10.
Crack growth in 2.25Cr-lMo steels exposed to 3000 psi hydrogen has been investigated in the temperature range 440 °C to 500
°C, using modified wedge-opening loaded specimens to vary stress intensity. Under conditions of temperature and hydrogen pressure,
where general hydrogen attack does not occur, the crack propagated by the growth and coalescence of a high density of methane
bubbles on grain boundaries, driven by the synergistic influence of internal methane pressure and applied stress. Crack growth
rates were measured in base metal, and the heat-affected zones (HAZs) of welds were tempered to different strength levels.
The crack growth rate increased with material strength. Above a threshold of about Kl = 20 MPa√m (at 480 °C), the crack growth rate increased rapidly with stress intensity, increasing as roughly Kl
6.5. Because of better creep resistance, stronger materials can sustain higher levels of stress intensity to drive crack growth
and nucleate the high density of voids necessary for crack growth. Stress relaxation by creep reduces the stress intensity,
and thus the growth rate, especially in weaker materials. The crack growth rate in the heat-affected zone was found to be
substantially faster than in the base metal of the welds. Analysis indicates that Kl rather than C* is the appropriate crack-tip loading parameter in the specimen used here and in a thick-walled pressure vessel.
The DC potential drop technique met with limited success in this application due to the spatially discontinuous manner of
crack growth and limited crack-tip opening displacement.
Formerly Graduate Student, Materials Science and Engineering Department, The Ohio State University 相似文献