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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The benefits of adhesively bonded structures are well known. However, the most significant factor limiting the extensive application of metal bonding in primary aerospace structures is the prevailing lack of confidence in its long term durability under hostile environmental conditions.1,2 相似文献
992.
The graft copolymerization of methyl methacrylate onto natural rubber (NR) was carried out varying the concentration of monomer, initiator, thiourea, and silver nitrate over a wide range. The grafting reaction was temperature-dependent. From the Arrhenius plot, the overall energy of activation was computed. A suitable reaction scheme and rate expression for the rate of polymerization was suggested. 相似文献
993.
Instructional texts rewritten by five expert teams: Revisions and retention improvements. 总被引:1,自引:0,他引:1
Britton Bruce K.; Van Dusen Lani; Gulg?z Sami; Glynn Shawn M. 《Canadian Metallurgical Quarterly》1989,81(2):226
700 undergraduates were tested in 3 experiments on original or rewritten versions of 52 instructional texts about Army job tasks, general science, philosophy, and history. Five experts had rewritten various sets of the texts and stated hypotheses about the efficacious features of their revisions. We tested their hypotheses and several others. Recall and recognition tests were given immediately and after a 24-hr delay. Results showed that revisions made by 3 of the 5 experts improved retention of text information. The kind and number of revisions and improvements varied across the text sets. Most expert hypotheses were not supported, and they made many revisions they were declaratively unaware of. Some of our hypotheses about the revision features were supported, but different features were effective for different sets of texts. It was concluded that some experts have effective knowledge about improving instructional text, but it exists primarily in procedural form. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
994.
In an experiment on the effects of different feedback conditions on motivationally relevant variables, R. Butler (see record 1988-21628-001) tested the hypothesis that the effects of feedback on intrinsic motivation would depend on whether that feedback promotes a task-involving or ego-involving orientation. She interpreted the findings as they relate to J. G. Nicholls's (see record 1984-28719-001) theory of task/ego involvement and our cognitive evaluation theory (E. L. Deci and R. M. Ryan, 1985). Although the data were very interesting, Butler failed to review a series of highly relevant studies, she misportrayed cognitive evaluation theory, and she drew conclusions that were not necessarily warranted given her experimental manipulations and data. This article provides a commentary on that research and presents a discussion of the relation between the two theories that Butler claimed to have tested. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
L. J. SCHREINER J. C. MACTAVISH L. MILJKOVI M.M. PINTAR R. BLINC G. LAHAJNAR D. LASIC L. W. REEVES 《Journal of the American Ceramic Society》1985,68(1):10-16
The proton free induction decay of a portland cement paste in an advanced stage of hydration can be roughly divided into three main components: (1) a component with a very short spin-spin relaxation time, T2 , representing the protons of the solid OH groups and the water of crystallization, (2) a component with an intermediate T, representing the bonded water in the gel phase, and (3) a third component with a relatively long T2 representing the water in the micropores and layers. The dependences of the intensities, T2 's, and spin-lattice relaxation times (T1 's) of these three components on the cement hardening time have been determined. The proton spin-lattice relaxation time of the "solid" component increases with hardening time whereas T1 decreases for the other two components. The observed time dependence of the diffusion coefficient, D, of water in a tricalcium silicate paste supports the findings of the above correlation study. 相似文献
996.
A model is presented for the thermal shock damage in plates subjected to a sudden rise in temperature. Spalling is assumed to follow localized buckling caused by the thermally induced compressive stresses above subsurface flaws. The minimum size o flaw required to cause spalling is determined as a function of the material properties of the plate, the temperature rise, the position of the paw, and the time after the thermal shock. 相似文献
997.
J. T. DICKINSON L. C. JENSEN W. DAVID WILLIAMS 《Journal of the American Ceramic Society》1985,68(5):235-240
We present measurements of the electron, positive ion, and photon emission accompanying the fracture in vacuum of poly-crystalline 95/5 lead zirconate-titanate. The intensities of the charged-particle components of this fractoemission are shown to depend strongly on the direction (relative to the direction of fracture) and magnitude of polarization. The most intense emission is observed when the fracture surfaces are perpendicular to the polarization direction. The emission intensity increases monotonically with polarization. These results are interpreted in terms of a model involving charge separation on the fracture surfaces leading to a microdischarge during fracture. Implications to the interpretation of triboluminesence effects are discussed. 相似文献
998.
Previous solid state analyses of sintering in Ti4+ -doped-commercial alumina are shown to be in error because a liquid phase exists in the appropriate region of the Al2 O3 −TiO3 −Na2 Ophase diagram at least by 1350° C, a temperature lower than that at which "solid state" studies were conducted. It is suggested that liquid-phase sintering is a much more common occurrence than was realized formerly. 相似文献
999.
M. A. Amer D. B. Kupranycz B. E. Baker 《Journal of the American Oil Chemists' Society》1985,62(11):1551-1557
Both summer and winter butterfats were fractionated using a laboratory procedure which was designed to simulate a commercial
fractionation process. The process is based on a slow, controlled cooling of the melted fat, a short stabilization time at
the fractionation temperature, and separation of the crystals from the liquid oil by vacuum filtration using a stainless steel
perforated disc. Fractionation temperatures of 29, 26, 23 and 19 C for winter butterfat and 29 and 19 C for summer butterfat
were used to obtain solid and liquid fractions at each temperature. Three replications at each temperature showed good reproducibility
of results. The fractions were characterized by their fatty acid and triglyceride compositions, melting and crystallization
behavior, iodine value, peroxide value and melting point.
Presented at the AOCS meeting in Philadelphia in May 1985. 相似文献
1000.
D. A. Morgan D. B. Shaw M. J. Sidebottom T. C. Soon R. S. Taylor 《Journal of the American Oil Chemists' Society》1985,62(2):292-299
The results presented in the literature, which attempt to elucidate the mechanisms by which triglyceride oils are bleached
by earths, are reviewed. The impact of this work and how the mechanistic proposals affect changes in oil properties are considered,
with particular emphasis on the needs of the palm oil processor. Important properties include color, metals and phosphorus
content and oxidative stability of the oil.
Investigations made in our own laboratories have been aimed at elucidating the effect of varying physical and chemical properties
of the bleaching earth on the quality of bleached and deodorized oils. Techniques used in this work are pore-size distribution,
surface area, scanning and transmission electron microscopy and a variety of chemical and X-ray analysis methods.
The ability to vary such parameters in montmorillonite clays by alteration of process conditions to give materials with specific
performance characteristics is demonstrated.
Comparisons are made between acid-activated montmorillonites and other clay types. 相似文献