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1.
Holistic tin-plating on the outer conductor is one of the key processes in the manufacture of semi-flexible coaxial cable, which is widely applied to the third generation (3G) mobile communication system. However, in the traditional horizontal tin-plating process, disadvantages such as the pinhole defects and low productivity effect cannot be avoided. In this paper, a vertical tin-plating process was proposed to reduce the pinhole defects and improve the tincoating quality. Compared with the traditional horizontal tin-plating process, the immersion length was reduced from 300-400 mm to 10-100 mm and the tin-plating time was reduced from 7 s to 3 s in the proposed method. The experimental results indicate that immersion length and time are key parameters for the tin-plating quality. With this new tin-plating process, the experimental results show that the pinhole defects can be eliminated effectively by controlling the immersion depth below 100 mm and tin-plating time at 3 s. The thickness of tin-coating increased from not more than 5 μm to 12.3 μm with the proposed vertical tin-plating process. Meanwhile, the thickness of the intermetallic compounds (IMCs) layer between the tin-coating and copper wires was reduced from 3.26 μm to 0.62 μm if the immersion time decreased from 30 s to 1 s. Besides, a self-developed flux, which possesses a boiling point or decomposed temperature of active components over 300℃, exhibits a better efficiency in reducing the pinhole formation.  相似文献   

2.
This paper reports on a statistical study of English and Hungarian teachers' conceptions of mathematics and its teaching. A questionnaire was developed and distributed to teachers of mathematics in 200 English and40 Hungarian schools teaching children in the 11–14 age range. Factor analyses identified four conceptions of mathematics and five of mathematics teaching. These were compared with those yielded by an earlier study involving the same English teachers and found to be consistent indicating the existence of similar conceptions in different educational systems. Differences and similarities in the strengths with which those conceptions are held were suggestive of both global and national conceptual traditions. The significant similarity to emerge concerned teachers from both countries sharing, with similar strengths, a general conception of mathematics teaching incorporating the teaching of mathematical skills, a variety of classroom approaches including investigations and problem-solving, and a recognition that mathematics provides an essential lifetool. Multi-dimensional scaling indicated that English teachers have their perspectives informed by two underlying, and possibly conflicting, traditions– pedagogic relevance and mathematical utility. The Hungarians appeared concerned only with notions of pedagogic relevance – those practices perceived to facilitate effective learning of a subject which is untainted by utilitarian perspectives. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
Studies from different theoretical traditions investigating children’s inheritance and genetics concepts have adopted a cross-sectional method. This paper is the first to examine both cross-sectional and longitudinal changes in children’s basic genetic concepts. It forms part of a larger investigation into the development of intuitive inheritance and genetics concepts in childhood. Four age cohorts (4–5 years, 7–8 years, 10–11 years, 14–15 years) were interviewed individually at two measurement occasions (T1, N = 182; T2, N = 164) separated by a 1-year interval. Cross-sectional analyses revealed an increase in children’s knowledge of genetics by 10 years. Between 10 and 14 years, there were fewer changes in the content of children’s knowledge, especially at the level of scientific genetic understanding. There was little evidence of longitudinal changes over the 1-year period. Overall, children may hold an understanding of genetics that is tied to knowledge of inheritance within families. This may pose challenges for acquiring more abstract and formal concepts of genes.  相似文献   

4.
Nanocrystalline Fe25Ni75 powders were prepared by the mechanical alloying process. They were investigated by X-ray diffraction and magnetic measurements. The ball milling time dependence of grain size, internal strain and magnetic properties has been discussed. The results show that the formation of Fe25Ni75 alloy phase is almost completed after milling for 30 hours. The reduction of grain size accompanied by the growth of internal strain was observed after extended milling. An average grain size about 10–20 nm of alloyed powders has been determined by Sherrer formula estimation. The saturation magnetisation Ms has a slight increase when the average grain size continues to decrease by intensive milling. This fine size of mechanically alloyed powders (10–20 nm) results in a single domain magnetic structure and the formation of superparamagnetic phase.  相似文献   

5.
The Technology Enhanced Elementary and Middle School Science II project (TEEMSS), funded by the National Science Foundation, produced 15 inquiry-based instructional science units for teaching in grades 3–8. Each unit uses computers and probeware to support students’ investigations of real-world phenomena using probes (e.g., for temperature or pressure) or, in one case, virtual environments based on mathematical models. TEEMSS units were used in more than 100 classrooms by over 60 teachers and thousands of students. This paper reports on cases in which groups of teachers taught science topics without TEEMSS materials in school year 2004–2005 and then the same teachers taught those topics using TEEMSS materials in 2005–2006. There are eight TEEMSS units for which such comparison data are available. Students showed significant learning gains for all eight. In four cases (sound and electricity, both for grades 3–4; temperature, grades 5–6; and motion, grades 7–8) there were significant differences in science learning favoring the students who used the TEEMSS materials. The effect sizes are 0.58, 0.94, 1.54, and 0.49, respectively. For the other four units there were no significant differences in science learning between TEEMSS and non-TEEMSS students. We discuss the implications of these results for science education.  相似文献   

6.
分析了采用煤矸石制备烧结普通砖时粉料颗粒级配对样品性能的影响。测试结果表明:细颗粒比例的增大有助于提高制品的抗折和抗压强度,而吸水率则随细颗粒比例的增大呈降低趋势。样品的最佳颗粒级配为0.45～0.80mm占30%,0.30～0.45mm占14%,0.20～0.30mm占32%,0.20mm以下占24%。  相似文献   

7.
1Introduction Generally,ultrafiltration(UF)asaseparationtech nologyofhighefficiencyandlowenergyconsumption haswidelybeenappliedinvariousindustries.Inin dustrialapplications,therearesixbasicUF modules[1]:(1)tubular,withinnerchannel diameters>4mm;(2)hollowfibers,withinnerdia metersof0.2-3mm;(3)plateunits;(4)spiral woundmodules;(5)pleated sheetcartridges;and(6)rotarymodules.However,hollowfiberUFmoduleis oneofmostimportantmodulesbecauseofitshigh areapackingdensity.Besides,UFtechnologyalsois us…  相似文献   

8.
To improve the processing efficiency and the quality of orbital milling hole of aerospace Al-alloy, the big-pitch influence on cutting force and hole quality was studied experimentally. First, a program based on horizontal lathe was proposed based on kinematics analysis of orbital milling. Then, the cutting force at different stages and the hole quality with different pitches were measured. Results show that the axial force and radial force increase with the pitch amplification during orbital milling. However, the axial force in the orbital milling hole is about 8—10 times smaller than that in the conventional drilling. The diameter error of milling hole is 48—93 μm, and the surface roughness of milling hole is 1.2—1.7 μm. Finally, an orbital milling device with big pitch was designed.  相似文献   

9.
Performance of cross-shaped concrete columns confined by stirrups   总被引：1，自引：0，他引：1  
The stress-strain curves of confined concrete were obtained based on tests of seven cross-shaped columns confined by stirrups under axial load. The experiment results showed that the strength and deformation of confined concrete can be enhanced effectively by stirrups for cross-shaped columns. Compared with the non-confined concrete, when the stirrup characteristic value is in the range of 0.046--0.230, the confined concrete compressive strengths has an increase of 8%--43%, and the strain corresponding to the peak stress of confined concrete has an increase of 25%-- 195%. According to the test results, the effects of stirrup characteristic and stirrup spacing on the compressive strength and strain of confined concrete were analysed. It is shown that the compressive strength of confined concrete has a linear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient, and the strain corresponding to the peak stress of confined concrete has a nonlinear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient. The stress-strain curve equation of confined concrete was proposed for cross-shaped columns, and the calculated curves are in good agreement with the experimental curves.  相似文献   

10.
The purpose of this study was to investigate the predictive value of optimism, perceived support from family and perceived support from faculty in determining life satisfaction of college students in Turkey. One hundred and thirty three students completed the Satisfaction with Life Scale (Diener et al., Journal of Personality Assessment 49(1):71–75, 1985), Perceived Social Support Scale-Revised (Yıldırım, Eğitim Araştırmaları–Eurasian, Journal of Educational Research 17:221–236, 2004), and Life Orientation Test (Scheier and Carver, Health Psychology 4(3):219–247, 1985) and provided demographic information about themselves. Independent samples t-test, correlation, and multiple regression analyses were performed for data analysis. Significant relationships were found among the variables, with regression analysis indicating that perceived support from family, perceived faculty support, and optimism were statistically significant predictors of life satisfaction. The implications of these results are discussed and suggestions made for counseling practice and future research.  相似文献   

11.
对新奥法在大型地下洞室施工中的二次支护时间的现有判据进行分析,发现其考虑因素欠全面,主要以变形量或变形速率为主,洞室位移相对值不适应大型洞室.以围岩变形为研究对象,提出大型洞室围岩变形达到总变形的80%、洞室周边水平收敛速度小于0．2 mm/d、顶拱或者底板垂直位移速率小于0．1 mm/d、隧洞周边水平收敛速度以及拱顶或底板垂直位移速度明显下降、位移加速度应基本接近于0作为大型地下洞室最佳支护时间的判据.为了验证该判据的合理性,选择了向家坝大型地下洞室一个断面,按照实际开挖顺序,计算了不同开挖层的最佳支护时间.向家坝地下洞室该断面处围岩拱顶、不同开挖层上下游侧边墙最佳支护时间在8~18 d之间,较好地符合了向家坝实际支护时间.  相似文献   

12.
Many studies of changes in learning approaches have used data from different age groups at one point in time only (Gow and Kember, High Educ 19:307–322, 1990; Watkins and Hattie, Br J Educ Psychol 51:384–393, 1981) or have analyzed the effects of just two or three factors using single level analytical techniques (Cano, Br J Educ Psychol 75:203–221, 2005; Duckwall et al., Res High Educ 32(1):1–13, 1991; Jay and Love, NCSSSMST J 7(2):4–8, 2002; Loo, Educ Psychol, 17(1/2), 1997; Watkins and Hattie, Hum Learn 4:127–141, 1985; Zeegers, Br J Educ Psychol 71:115–132, 2001). This study employs multilevel modeling as a more appropriate technique for the analysis of longitudinal data to examine factors influencing changes in the learning approaches of 153 international undergraduate students over a 3-year period. Specifically, using hierarchical linear modeling (HLM), the effects of personal values (level-2) on learning approaches and changes in them over time (level-1) are examined. Results show no changes within students in the deep and surface approaches to learning but a significant decline for the achieving approach, particularly for students who previously experienced a more formal teaching authority. Furthermore, students’ personal values in terms of security, achievement and hedonism affect the achieving approach while no effects emerge for the personal values of tradition, conformity, universalism, self-direction and stimulation. Finally, these effects can be observed while no significant effects emerge for gender, discipline and ability.  相似文献   

13.
１　Ｉｎｔｒｏｄｕｃｔｉｏｎ　Ｍｉｌｌｉｍｅｔｅｒｓｉｚｅｍｉｃｒｏｍａｃｈｉｎｅｓｂａｓｅｄｏｎｍｏｄｅｒｎｐｒｅｃｉｓｉｏｎｍａｃｈｉｎｉｎｇｈａｖｅｐｏｔｅｎｔｉａｌａｐｐｌｉｃａｔｉｏｎｉｎｉｎｄｕｓｔｒｙ．Ｓｏｍｅｎａｒｒｏｗｓｐａｃｅｓｏｒｓｍａｌｌａｒｅａｓｎｅｅｄｔｈｅｓｅｍｉｃｒｏｍａｃｈｉｎｅｓｔｏｉｎｓｐｅｃｔａｎｄｒｅｐａｉｒｄｅｆｅｃｔｓ．Ｒｅｓｅａｒｃｈｅｒｓｈａｖｅｗｏｒｋｅｄｏｎｆａｂｒｉｃａｔｉｏｎｏｆｖａｒｉｅｄｖｅｈｉｃｌｅｓｗｉｔｈｗｈｅｅｌｓ,ｍｏｂ…  相似文献   

14.
In China’s current educational fiscal decision making, problems are as follows: no law to trust or not abiding by available laws, absence of equity and efficiency, as well as the standardization of decision-making procedures. It is necessary to set up effective fiscal decision-making mechanism in education and rationally devise reliable paths. Translated from Jiaoyu Lilun Yu Shijian 教育理论与实践 (Theory and Practice of Education), 2006, (4): 14–17  相似文献   

15.
The rice water weevil, Lissorhoptrus oryzophilus Kuschel, has two generations in southern Zhejiang, China. To determine oogenesis in first-generation females （summer females） and its relations to temperature, females were collected from a rice field in early and mid-July and reared on young rice plants at 28, 31 and 34 ℃ in the laboratory. Percentage of females having oocytes, number of oocytes of different stages （stage-Ⅰ, from early previtellogenesis to middle vitellogenesis; stage-Ⅱ, late vitellogenesis; and matute-oocyte stage）, and length of ovarioles were determined every 10 d of feeding. At each temperature, oogenesis took place in over 40% of females after 20-40 d of feeding, but only 0.0-3.3 stage-Ⅰ, 0.0-0.8 stage-Ⅱ and 0.0-1.1 mature oocytes were observed at each observation date. Temperature had significant effect on number of stage-Ⅰ oocytes but not on number of stage-Ⅱ and mature oocytes in early July females; temperature had no significant effect on number of oocytes of either stage in mid-July females. Conclusively, in southern Zhejiang, summer L. oryzophilus females have great potential to become reproductive on rice, but their oogenesis activity is very low, with the overall procedures little affected by temperature.  相似文献   

16.
INTRODUCTION With the development of modern electronics,there is a growing trend of designing a low-voltagehigh precision current reference in many mixed-signaland analog circuits such as data converters (Mehr andSinger, 2000; Oh et al., 2004), oscillators and PLLs(Razavi, 2001; Banba and Shiga, 1999). Low-costreasons need the reference to be realized in simplestandard CMOS logic process technology, withoutresorting to the use of BiCMOS process and specialdevices such as floating-g…  相似文献   

17.
Sustainable management of marine resources raises great challenges. Working with this socio-scientific issue in the classroom requires students to apply complex models about energy flow and trophic pyramids in order to understand that food chains represent transfer of energy, to construct meanings for sustainable resources management through discourse, and to connect them to actions and decisions in a real-life context. In this paper we examine the process of elaboration of plans for resources management in a marine ecosystem by 10th grade students (15–16 year) in the context of solving an authentic task. A complete class (N = 14) worked in a sequence about ecosystems. Working in small groups, the students made models of energy flow and trophic pyramids, and used them to solve the problem of feeding a small community for a long time. Data collection included videotaping and audiotaping of all of the sessions, and collecting the students’ written productions. The research objective is to examine the process of designing a plan for sustainable resources management in terms of the discursive moves of the students across stages in contextualizing practices, or different degrees of complexity (Jiménez-Aleixandre & Reigosa International Journal of Science Education, 14(1): 51–61 2006), understood as transformations from theoretical statements to decisions about the plan. The analysis of students’ discursive moves shows how the groups progressed through stages of connecting different models, between them and with the context, in order to solve the task. The challenges related to taking this sustainability issue to the classroom are discussed.  相似文献   

18.
MBE growth of ZnSxSe1−x thin films on ITO coated glass substrates were carried out using ZnS and Se sources with the substrate temperature ranging from 270°C to 330°C. The XRD σ/2σ spectra resulted from these films indicated that the as-grown polycrystalline ZnSxSe1−x thin films had a preferred orientation along the (111) planes. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks showed strong growth temperature dependence, with the optimized temperature being about 290 °C. Both AFM and TEM measurements of these thin films also indicated a similar growth temperature dependence. High quality ZnSxSe1−x thin film grown at the optimized temperature had the smoothest surface with lowest RMS value of 1.2 nm and TEM cross-sectional micrograph showing a well defined columnar structure. Project supported by the National Science Council of PRC (No. 59910161981) and RGC grant from the Hong Kong Government under Grant (No. NS-FC/HKUST 35)  相似文献   

19.
Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite. The fractured rock model (height 1502.5 mm, width 904 mm, and thickness 300 mm), embedded with two vertical and two horizontal fractures of pre-set apertures, was constructed using 18 pieces of intact granite. The granite was taken from a site currently being investigated for a high-level nuclear waste repository in China. The experiments involved different heat source temperatures and vertical water fluxes in the embedded fractures either open or filled with sand. A finite difference scheme and computer code for calculation of water flow and heat transfer in regularly fractured rocks was developed, verified against both the experimental data and calculations from the TOUGH2 code, and employed for parametric sensitivity analyses. The experiments revealed that, among other things, the temperature distribution was influenced by water flow in the fractures, especially the water flow in the vertical fracture adjacent to the heat source, and that the heat conduction between the neighboring rock blocks in the model with sand-filled fractures was enhanced by the sand, with larger range of influence of the heat source and longer time for approaching asymptotic steady-state than those of the model with open fractures. The temperatures from the experiments were in general slightly smaller than those from the numerical calculations, probably due to the fact that a certain amount of outward heat transfer at the model perimeter was unavoidable in the experiments. The parametric sensitivity analyses indicated that the temperature distribution was highly sensitive to water flow in the fractures, and the water temperature in the vertical fracture adjacent to the heat source was rather insensitive to water flow in other fractures.  相似文献   

20.
Isolation of new bacterial strains and recognition of their metabolic activities are highly desirable for sustainability of natural ecosystems. Biodegradation of dimethyl phthalate (DMP) under anoxic conditions has been shown to occur as a series of sequential steps using strain CW-1 isolated from digested sludge of Sibao Wastewater Treatment Plant in Hangzhou,China. The microbial colony on LB medium was yellowish,3～5 mm in diameter,convex in the center,and embedded in mucous externally. The individual cells of strain CW-1 are irregular rods,measuring (0.6～0.7)×(0.9～1.0) μm,V-shaped,with clubbed ends,Gram positive and without any filaments. 16S rDNA (1438 bp) sequence analysis showed that the strain was related to Arthrobacter sp. CW-1 and can degrade PAEs utilizing nitrate as electron acceptor,but cannot mineralize DMP completely. The degradation pathway was recommended as: dimethyl phthalate (DMP)→monomethyl phthalate (MMP)→phthalic acid (PA). DMP biodeg-radation was a first order reaction with degradation rate constant of 0.3033 d-1 and half-life 2.25 d. The DMP conversion to PA by CW-1 could be described by using sequential kinetic model.  相似文献   

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