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The high surface energy makes metal nano-particles reactive and easy to get oxidized or burned in the open air, which results in decreasing or entirely losing their functions and properties. In this paper, the magnetic property behavior of iron nano-particle, which is one kind of the typical magnetic nano-materials, has been investigated. The iron nano-particles were heated to different temperatures in an open-air stove. After that, they were firstly examined by TEM to observe the changes of their outline of shapes and then measured by VSM to trace the changes of their magnetic properties. The test results show that iron nano-particles can keep their magnetic property with saturation magnetic induction intensity B. around 136--161 emu/g,remanent magnetic induction intensity Br around 14.8--17.4 emu/g and coercive force He around 290--302 Oe when the temperature goes up to 523 K. The explanation to such outstanding oxidization-proof ability has been given that there exists a single crystal and lattice-shared Gamma-Fe2O3 shell covering the pure iron core, which prevents the spherical iron nano-particles from further oxidization. 相似文献
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A new style of hydraulic steel gate based on the principle of bionics is proposed in this paper. It has a fish-like shape and consists of right arches, invert arches, connection components and a face plate. It would be first applied in the project of Caoe River Sluice, used as both tidal barrage and flood gate. Compared with conventional hydraulic steel gate of beam grids, this new style of hydraulic steel gate can save up to 30%-50% of steel consumption. The dynamic behavior of the new gate under the impact load of tidal bore is investigated. The impact load of tidal bore is considered by a load spectrum obtained by field observation over a long period of time. Then a numerical analysis of the gate under the load spectrum is carried out by finite element method. The fluid-structure interaction is considered in the analysis. And a comparison between the response of the gate under the impact load and the response of the gate under the corresponding static load is conducted and indicates that the gate has a dynamic magnification factor of 1.2. 相似文献
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王均安 《上海大学学报(英文版)》2001,5(3):241-246
A review was made on the research progress of wear behavior of sintered steels in recent years.Wear is not an intrinsic property of sintered steels,which is strongly influenced by the wear test conditions.Howerver,many other factors that determine the mechanical properties of sintered steels also affect the wear behavior.Porosity has different effects on the wear of sintered steels depending on the application conditions.Under dry sliding condition ,higher porosity results in lower wear resistance.The influence of microstructures on wear resistance is in the order;Carbide,martensite,bainite and lamellar pearlite,The wear resistance increases with hardness,but this relationship changes with the porosity and microstructures of sintered steels. 相似文献
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Timothy M. Flynn 《Journal of Experimental Education》2013,81(2):46-51
A multiple-choice behavioral observation scale designed to be used by preschool teachers (N = 424) was factor analyzed to obtain factor coefficients. The four factors obtained were cognitive skills, self-control, relationship with achievement model, and dependency. The factor coefficients were then applied to the ratings of 153 preschool disadvantaged children by 33 teachers and 64 teacher aides. Three multi-trait, multi-rater matrices were analyzed using Campbell and Fiske’s convergent discriminant validation procedures. The analyses supported convergent and discriminant validity of three of the four traits. 相似文献
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The deformation behavior of hot isostatic pressing (HIP) FGH96 superalloy was characterized in the temperature range of 1 000-1 100℃and strain rate range of 0.001-0.1s-1 using hot compression testing. The flow curves of HIP FGH96 superalloy during hot deformation was analyzed systematically. The results show that deformation temperature, strain rate and strain are the main influence factors on flow stress of HIP FGH96 superalloy during hot deformation. The flow stress displays a peak at a critical strain and then decreases with further increase in strain. For a given strain, the flow stress decreases with the increase of deformation temperature, and increases with the increase of strain rate. A mathematical model of these flow curves was established through regression analysis and taking the strain as a modification factor. The calculated stress values agree well with the experimental values. 相似文献
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INTRODUCTION Externally bonded fiber reinforced polymer (FRP) composites can be used to improve the flexural strength of structural members. To evaluate the flex-ural performance of the strengthened members, it is necessary to study the flexural stiffness of FRP- strengthened RC members at different stages, such as pre-cracking, post-cracking and post-yielding. Up to now, only very few studies were focused on the structural members strengthened under pre-loading or pre-cracking (Arduin… 相似文献
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By employing quantitative research methods, the paper investigates college students' preferences to English classroom behaviors and the relations between behaviors and achievements. The results indicate that there are significant differences among the subjects' behavior, cognitive and emotional elements, and their classroom behaviors are mainly visual, individual, imitative and exterior-motivated; there are significant differences in behavior element and emotional element between high-result group and low-result group; confident and oral classroom behaviors have prominent relations with CET-4 achievements, and different teaching methods may make learning behaviors produce good or bad effects to achievements. 相似文献
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《语数外学习(初中版)》2007,(5)
Where did you go yesterday?Did you hear1at any of thoseplaces?Today in most stores and restaurants you can hear music.Youmight2hear music in an office or on a farm.Scientists believe thatmusicchanges the3of people’s(举止).According to some scientists,the… 相似文献
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郭克晴 《语数外学习(初中版)》2007,(5Z):60-62
Where did you go yesterday?Did you hear1at any of thoseplaces?Today in most stores and restaurants you can hear music.Youmight2hear music in an office or on a farm.Scientists believe thatmusicchanges the3of people’s(举止).According to some scientists,the sound of western(古典的)music makes people4richer.When classical music isplayed in a restaurant,people spend5money on food and drinks.When there is6music,people spend less money.With7music,people spend even less.Scientists also8that loud,fa… 相似文献
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Asweknow ,thenormalplainconcreteisakindofbrittlematerialanditsfailureisabruptunderincreasingload.Thecontrolofcrackinginconcretestructureshasbeenaprobleminthedesignandconstructionofbuild ings .Atpresent ,theuseofdifferentkindsoffiberstoimprovethedeformationperformanceandthemechanicalbehaviorofconcretehasattractedmanyengineersandre searchersintheworld .Ingeneral,compositefiberscanpreventtheoccurrenceofcracksandrestrictthedevelop mentofcracksinconcreteduetoshrinkage ,andstrengthencrack resistinga… 相似文献
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Mehmet Erdogan Ahmet Ok Thomas Joseph Marcinkowski 《Environmental Education Research》2012,18(4):507-540
Though environmentally responsible behavior (ERB) has been a focus of many studies in the field of environmental education, very few scales have been developed to assess children’s ERB. In this regard, this article focuses on the development and validation of Children’s Responsible Environmental Behavior Scale (CREBS) and also reports the psychometric properties of this scale. The items in the CREBS were developed initially from the responses to four open-ended items by 229 fourth and fifth grade students. This initial form was pilot tested with 673 fourth and fifth graders and then subjected to exploratory factor analysis. Later, the revised version of the scale was administrated to 2412 fifth graders, and those results were subjected to confirmatory factor analysis and reliability analysis. CREBS consists of 23 items measured using a seven-point Likert-type scale, which have been organized into four sub-scales: political action (six items, α?=?.92); eco-management (six items, α?=?.70); consumer and economic action (five items, α?=?.70); and Individual and Public Persuasion (six items, α?=?.80). Study results indicate that CREBS can be used for exploring the extent to which elementary school students in Turkey demonstrate four types of behavior to help prevent and resolve environmental problems and issues. 相似文献
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This study investigated the relationship between children’s ability to regulate emotions and display of appropriate behavior
in social settings. A sample of 33 children representing a wide range of social economic status was randomly selected from
a Head Start Program and an Early Childhood Development Center in the Midwest. Data were collected using the Emotion Regulation
Checklist (ERC) developed by Shields and Cicchetti (Dev Psychol 33:906–916, 1997, J Clin child Psychol, 27:231–395, 1998). A “Behavior Recording” checklist was developed and used to record appropriate and inappropriate behavior observed during
children social interactions. Teacher ratings identified children as generally high emotion regulators. Girls had generally
higher scores than boys in emotion regulation ability. A high relationship (r = .76) was also found between emotion regulation and display of appropriate behavior. Results indicate the importance of
emotions in relation to a child’s well being and academic achievement. Additionally, these findings suggest a need for parents
and early childhood educators to teach children appropriate emotional behavior when confronted with situations that are in
conflict with societal norms. 相似文献
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In order to study the seismic behavior of frame with specially shaped columns,the hysteretic curve was analyzed based on a quasi-static test of a two-span,three-story frame with specially shaped columns.The top layer framework curve and the corresponding resilience model were obtained from the hysteretic curve.And the stiffness and strength degeneration were also investigated.The results indicated that the stiffness degeneration is not obvious,thus the frame with specially shaped columns has high earthquake-resistant behavior.The resilience model calculated from the test can provide reference for design and nonlinear finite element analysis. 相似文献
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* Due to snow accumulation and ice formation onhighways, traffic accidents happen frequently in win-ter, causing great losses of economy and lives. Soroad snowremoval has been given great concern[1]. Geothermal road snow-melting system (GRSS)with solar energy storage is an effective, non-pollutionapplied sustainable energy technology developed in re-cent years. Its prominent advantage is to realize sea-sonal thermal storage and improve energy efficien-cy[2]. In Sapporo of Japan, a GRSS sys… 相似文献
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A new type of green reactive powder concrete (GRPC) with compressive strength of 200 MPa is prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, toughness, fracture energy and interfacial bonding strength) of GRPC specimens, cured in three different types of regimes, are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the powder binders that is composed of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume are better than the others'. The corresponding compressive strength, flexural strength and fracture energy are more than 200 MPa, and 30 000 J/ m2 respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the split Hopkinson pressure bar (SHPB) according to the spalling phenomenon. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of GRPC. With the increase of strain rate, its peak stress and relevant strain increase. The GRPC exhibits an excellent strain ratio stiffening effect under the dynamic tensile load with high strain ratio, resulting in a significant change of the fracture pattern. 相似文献
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Ali Kamali 《美中教育评论》2014,(10):705-715
Many studies have focused on factors affecting e-learning and its effectiveness by comparing e-learning with face-to-face traditional classes. This study, however, aspires to contribute to the literature by exploring factors that contribute to student success in the e-learning environment. This study tested the assumption that a student＇s success in e-learning is a function of the specificities that are linked to this pedagogical model. It further postulated that these attributes are outcomes of an affective learning behavior. Data for this study were collected from a random sample of 486 respondents （close to 10% of the total student population） in a small university. The empirical data helped map out the hierarchy of the attributes that contribute to the development and experiences with e-learning. This study further provided suggestions to improve the areas that seem essential for a successful e-learning environment. 相似文献
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ZHANG Yunsheng SUN Wei LIU Sifeng JIAO Chujie LAI Jianzhong 《天津大学学报(英文版)》2006,12(B09):258-263
A new type of green reactive powder concrete （GRPC） with compressive strength of 200 MPa is prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The quasi-static mechanical properties （mechanical strength, toughness, fracture energy and interfacial bonding strength） of GRPC specimens, cured in three different types of regimes, are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the powder binders that is composed of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume are better than the others＇. The corresponding compressive strength, flexural strength and fracture energy are more than 200 MPa, and 30 000 J/ m^2 respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the split Hopkinson pressure bar （SHPB） according to the spalling phenomenon. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of GRPC. With the increase of strain rate, its peak stress and relevant strain increase. The GRPC exhibits an excellent strain ratio stiffening effect under the dynamic tensile load with high strain ratio, resulting in a significant change of the fracture pattern. 相似文献
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Researchershavebecomeincreasinglyinterestedinironaluminideintermetallics (includingFe3AlandFeAl)since 1970sinviewofthecombinationoflowcost,lowerdensity ,remarkableresistancetoerosion ,sulfidizingandoxidizingathightemperature .However ,industrialap plicationofthesealloyshasbeenverylimitedduetotheirpoorductilityandfracturetoughnessatroomtemperatureaswellastheirdifficultyinshaping[1] .Somestudieshaveindicatedthatcoatingstructuralmaterialswithironaluminidesbyusingthermalsprayingwillnotonlysolveth… 相似文献
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Dynamical Behavior of Nonlinear Viscoelastic Timoshenko Beams with Damage on a Viscoelastic Foundation 总被引：2，自引：0，他引：2
Based on convolution-type constitutive equations for linear viscoelastic materials with damage and the hypotheses of Timoshenko beams with large deflections, the nonlinear equations governing dynamical behavior of Timoshenko beams with damage on viscoelastic foundation were firstly derived. By using the Galerkin method in spatial domain, the nonlinear integro-partial differential equations were transformed into a set of integro-ordinary differential equations. The numerical methods in nonlinear dynamical systems, such as the phase-trajectory diagram, Poincare section and bifurcation figure, were used to solve the simplified systems of equations. It could be seen that simplified dynamical systems possess the plenty of nonlinear dynamical properties. The influence of load and material parameters on the dynamic behavior of nonlinear system were investigated in detail. 相似文献