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排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
In this study, the effect of animation enhanced conceptual change texts (CCT–CA) on grade 6 students’ understanding of the particulate nature of matter (PNM) and transformation during the phase changes was investigated. A quasi-experimental design and one control group (CG, N = 25) and one experimental group (EG, N = 26) were used. While the control group taught traditional instruction, the experimental group received CCT–CA instruction. Two different tests, The Particulate Nature of Matter Concept Test (ParNoMaC) and The Transformation of Matter Statement Test (ToMaSaT), were administered as pretest, posttest and delayed test to collect data. Results indicate that while there is no statistically significant difference between groups in pretest, performance of EG students is greater than the CG ones in posttest and delayed test. And also, the EG students are better in remediating their alternative conceptions related to the PNM and transformations during the phase changes. Based on the study, it is concluded that CCT–CA combination may be effective way to improve students’ understanding of basic science and chemical concepts. 相似文献
982.
In this paper, a new algorithm for solving constrained nonlinear programming problems is presented. The basis of our proposed algorithm is none other than the necessary and sufficient conditions that one deals within a discrete constrained local optimum in the context of the discrete Lagrange multipliers theory. We adopt a revised particle swarm optimization algorithm and extend it toward solving nonlinear programming problems with continuous decision variables. To measure the merits of our algorithm, we provide numerical experiments for several renowned benchmark problems and compare the outcome against the best results reported in the literature. The empirical assessments demonstrate that our algorithm is efficient and robust. 相似文献
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986.
Fazhan Geng 《Computers & Mathematics with Applications》2011,62(4):1641-1644
In this paper, we introduce a piecewise variational iteration method for treating a nonlinear oscillator of a mass attached to a stretched elastic wire. For the nonlinear oscillator, the present method can produce a good approximation to the exact solution in a very large region, while the standard variational iteration method (VIM) gives a good approximation only in a small region. The numerical results obtained show that the present method does not share the drawback of the standard VIM and can provide very accurate analytical approximate solutions for both small and large values of the oscillation amplitude and parameter. 相似文献
987.
This paper investigates the problem of lag synchronization for a kind of chaotic neural networks with discrete and distributed delays (mixed delays). The driver system has uncertain parameters and uncertain nonlinear external perturbations, while the response system has channel noises. A simple but all-powerful robust adaptive controller is designed to circumvent the effects of uncertain external perturbations such that the response system synchronize with the driver system. Based on the invariance principle of stochastic differential equations and some suitable Lyapunov functions, several sufficient conditions are developed to solve this problem. Moreover, under certain conditions, parameters of the uncertain master system can be estimated. Numerical simulations are exploited to show the effectiveness of the theoretical results. 相似文献
988.
Fevzi C. KivancAuthor VitaeShawn LitsterAuthor Vitae 《Sensors and actuators. B, Chemical》2011,151(2):394-401
This paper presents the use of mesoporous silica skeletons as substrates for electroosmotic (EO) micropumps. Mesoporous silica skeletons have bimodal pore size distributions consisting of macropores and cation-permselective mesopores. These materials have the potential for high flow rate per power because the cation-permselective mesopores can generate an induced charge layer (ICL) and electroosmosis of the second kind (EO-2) under high applied electric fields. The diffuse charge layers induced by the electric field result in an EO-2 flow rate that increases quadratically with increasing electric field. In contrast, the flow rate of the more common electroosmosis of the first kind (EO-1) is linearly proportional to electric field. Here, we investigate the impact of finite pressure loads on the EO-2 flow rate with experiments and an engineering model to evaluate the potential of mesoporous skeletons for micropumping applications. Our results include analyses of maximum flow rate, maximum pressure, and flow rate with intermediate pressure loads. The results indicate the existence of a critical pressure load at which reverse pressure-driven flow significantly diminishes the EO-2 flow. We also investigate the scaling of flow rate per power with respect to substrate thickness and area, demonstrating significant increases in flow rate per power with thinner substrates and favorable scaling for miniaturization of EO-2 pumps. 相似文献
989.
Yu-Jin ChenAuthor Vitae Gang XiaoAuthor VitaeTie-Shi WangAuthor Vitae Fan ZhangAuthor VitaeYang MaAuthor Vitae Peng GaoAuthor Vitae Chun-Ling ZhuAuthor VitaeEndi ZhangAuthor Vitae Zhi XuAuthor VitaeQiu-hong LiAuthor Vitae 《Sensors and actuators. B, Chemical》2011,155(1):270-277
Crystalline α-MoO3/TiO2 core/shell nanorods are fabricated by a hydrothermal method and subsequent annealing processes under H2/Ar flow and in the ambient atmosphere. The shell layer is composed of crystalline TiO2 particles with a diameter of 2-6 nm, and its thickness can be easily controlled in the range of 15-45 nm. The core/shell nanorods show enhanced sensing properties to ethanol vapor compared to bare α-MoO3 nanorods. The sensing mechanism is different from that of other one-dimensional metal oxide core/shell nanostructures due to very weak response of TiO2 nanoparticles to ethanol. The enhanced sensing properties can be explained by the change of type II heterojunction barrier formed at the interface between α-MoO3 and TiO2 in the different gas atmosphere. The present results demonstrate a novel sensing mechanism available for gas sensors with high performance. 相似文献
990.
N.M. ShaalanAuthor Vitae T. YamazakiAuthor Vitae T. KikutaAuthor Vitae 《Sensors and actuators. B, Chemical》2011,156(2):784-790
Electrodes with micro-gaps are fabricated by using dc-sputtering and FIB techniques. SnO2 nanowires are deposited on the micro-gap (1-30 μm) by suspension dropping method to fabricate a micro-gas sensor. The sensing ability of various SnO2 micro-gap sensors is measured. A comparison between sensors reveals that the short-gap electrode has numerous advantages in terms of reliability, high sensitivity and detection of low concentrations of NO2, while the large-gap electrode is relatively sensitive for high concentrations. Conductance measurements are carried out at different surface temperatures and NO2 concentrations in order to investigate the effects that the gap size has on the overall sensor conductance. The results suggest that the interface between the electrode and sensitive layer has a very important role for the sensing mechanism of tin dioxide gas sensors. 相似文献