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61.
P. K. Khare J. M. Keller M. S. Gaur Ranjeet Singh S. C. Datt 《Polymer International》1994,35(4):337-343
The electrical conductivity of solution-grown ethyl cellulose (EC) films, 5–30 μm thick, has been studied in the sandwich configuration (metal–EC–metal) as a function of iodine concentration from 0.5 to 5.0 wt% ratio. The studies were conducted in the temperature range 333–383 K, while the field was varied over the range (3.0–5.5) × 104V/cm. Aluminium was used as the lower electrode, while the upper electrode was of Al, Ag, Cu, Au or Sn. Certain transient effects such as a large burst of current immediately after the application of field were observed. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories of electrical conduction. The results show that the electrical conduction follows Ohm's law at lower fields, while at higher fields, space-charge limited current (SCLC) was observed. It was also found that Richardson–Schottky emission was responsible, to some extent, for the transport of charge carriers in the polymer. The conductivity of the films increased on doping with iodine. The dopant molecules are considered to act as additional trapping centes and provide links between the polymer molecules in the amorphous region, thus resulting in the formation of charge transfer complexes. 相似文献
62.
M. Peacock 《Journal of Computer Assisted Learning》1988,4(3):162-172
Abstract Selections of English Language and Literature CSE (now GCSE) course work essays are graded by a total of 411 teachers in two forms: handwritten and wordprocessed. Mistakes in the original handwritten versions are not edited out. It is found that the wordprocessed English Language essays are, on average, marked up a grade. However, it is found that relatively high quality English Literature work is not affected. Results suggest:
— that the less directly pupil work is specifically related to an external referent (such as a work of literature), the more likely it is that computer-assisted methods of presentation will significantly enhance its apparent quality relative to handwritten work.
— that relatively lower quality work will tend to be enhanced more than relatively higher quality work.
The implications of the results for examination boards are also considered. 相似文献
— that the less directly pupil work is specifically related to an external referent (such as a work of literature), the more likely it is that computer-assisted methods of presentation will significantly enhance its apparent quality relative to handwritten work.
— that relatively lower quality work will tend to be enhanced more than relatively higher quality work.
The implications of the results for examination boards are also considered. 相似文献
63.
利用循环伏安法、交流阻抗法和充放电曲线等方法测定了Ni_(2.5)Mo_6S_(6.7)电极在1M LiClO_4,PC DME(1:1)有机电解质溶液中的可充电性。结果表明,该材料具有高的可充电性,有可能用作二次锂电池的正极材料。 相似文献
64.
The ALCHEMI method for locating the sites of foreign atoms within crystals is known to be sensitive to the delocalized emission of X-rays. This can result in large errors in some cases through differences in delocalization for different excitations or by error amplification in the ratio method of analysis. An alternative approach to the analysis of ALCHEMI data, using multivariate statistical analysis, is extended to the case of multiple impurities. Initial results from zone-axis channelling experiments for a Yb-doped zirconolite (CaZrTi2O7) are shown to confirm the improved accuracy of this method, especially for axial orientations. Data were collected using a 400-keV analytical electron microscope fitted with an intrinsic Ge X-ray detector. The potential advantages for ALCHEMI analysis of Ge detectors are considered. 相似文献
65.
Determination of Boundary Shear Stress and Reynolds Shear Stress in Smooth Rectangular Channel Flows 总被引:1,自引:0,他引:1
A method for computing three-dimensional Reynolds shear stresses and boundary shear stress distribution in smooth rectangular channels is developed by applying an order of magnitude analysis to integrate the Reynolds equations. A simplified relationship between the lateral and vertical terms is hypothesized for which the Reynolds equations become solvable. This relationship has the form of a power law with an exponent of n = 1, 2, or infinity. The semiempirical equations for the boundary shear distribution and the distribution of Reynolds shear stresses are compared with measured data in open channels. The power-law exponent of 2 gave the best overall results while n=infinity gave good results near the boundary. 相似文献
66.
铁电材料用于阴极发射的研究 总被引:1,自引:0,他引:1
铁电材料作为一种新型的阴极材料,具有真空要求低、制作简单、功函数低、响应速度快等特点。本文讨论了铁电阴极发射的机理,回顾了主要铁电阴极材料的发射实验,包括低电压铁电发射实验,最后对铁电阴极材料的应用做了讨论和展望。 相似文献
67.
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69.
Woo Yong Sung Seung Min Lee Wal Jun Kim Jong Girl Ok Ho Young Lee Yong Hyup Kim 《Diamond and Related Materials》2008,17(6):1003-1007
Complementary electroplating combined with electrophoresis enhanced the field emission characteristics of emitters by improving the adhesions between CNT emitters and substrate. The emitting current of the CNT emitters prepared by our combined method increased nine times higher than that of CNT emitters prepared by electrophoresis only, since electroplating improved the adhesion of CNT emitters. During the life-time measurement for 10 h, the emitting current of CNT emitters fabricated by electrophoresis only was drastically decreased to 13% of the initial current, while that prepared by the combination of electrophoresis and successive electroplating decreased to 64% of the initial current. We suggest that our method is a promising approach for the efficient fabrication of reliable CNT emitters. 相似文献
70.
Many research projects require accurate delineation of different secondary succession (SS) stages over large regions/subregions of the Amazon basin. However, the complexity of vegetation stand structure, abundant vegetation species, and the smooth transition between different SS stages make vegetation classification difficult when using traditional approaches such as the maximum likelihood classifier (MLC). Most of the time, classification distinguishes only between forest/non-forest. It has been difficult to accurately distinguish stages of SS. In this paper, a linear mixture model (LMM) approach is applied to classify successional and mature forests using Thematic Mapper (TM) imagery in the Rondônia region of the Brazilian Amazon. Three endmembers (i.e., shade, soil, and green vegetation or GV) were identified based on the image itself and a constrained least-squares solution was used to unmix the image. This study indicates that the LMM approach is a promising method for distinguishing successional and mature forests in the Amazon basin using TM data. It improved vegetation classification accuracy over that of the MLC. Initial, intermediate, and advanced successional and mature forests were classified with overall accuracy of 78.2% using a threshold method on the ratio of shade to GV fractions, a 7.4% increase over the MLC. The GV and shade fractions are sensitive to the change of vegetation stand structures and better capture biophysical structure information. 相似文献