排序方式： 共有28条查询结果，搜索用时 15 毫秒
1.
Ali Karami-Mollaee Hamed Tirandaz Oscar Barambones 《Journal of The Franklin Institute》2019,356(8):4577-4600
Mismatched uncertainty and chattering appear as two challenges in sliding mode control. To overcome the problem of mismatched uncertainty, multiple sliding surfaces with virtual inputs are proposed. Accordingly, we have proposed two new methods based on designed neural observer: sliding mode control (SMC) and dynamic sliding mode control (DSMC) methods. Although, the proposed SMC can significantly cope with the mismatched uncertainties, but it suffers from chattering phenomenon. The chattering problem can be removed in DSMC, because an integrator is placed before the system. This results in increased number of the system states. This new state can be identified with the proposed neural observer. Note that in both proposed approaches, the robust performance (invariance property) of system is reserved, even in the presence of mismatch uncertainties. Then, to have a valid comparison the proposed DSMC is also designed using loop transfer recovery observer (LTRO). This comparison shows the good performance of the DSMC based neural networks. Moreover, the upper bound of uncertainties is not used in SMC and DSMC controllers and also in the neural observer and LTRO, which is important in practical implementation. Finally, comparing the equations, one can see the simplicity of DSMC in concept and also in realization. 相似文献
2.
Hamed Jabbari Asl Tatsuo Narikiyo Michihiro Kawanishi 《Journal of The Franklin Institute》2019,356(13):7144-7163
In this study, we addressed the problem of design of high-performance tracking controller for uncertain systems described by the Euler–Lagrange formulation. The main objective was to combine the advantages of the robust integral of the sign of the error (RISE) controller with those of the prescribed performance (PP) controller. In particular, we aimed to obtain asymptotic tracking for the uncertain systems through a continuous control command while ensuring the transient performance. Two controllers were developed. First, the PP property was injected into the RISE controller assuming no constraint on the actuation amplitude existed, and then this property was incorporated into the saturated RISE controller. The performance of the proposed controllers was validated through experimental and simulation tests. 相似文献
3.
This paper proposes a pursuit formation control scheme for a network of double-integrator mobile agents based on a vector field approach. In a leaderless architecture, each agent pursues another one via a cyclic topology to achieve a regular polygon formation. On the other hand, the agents are exposed to a rotational vector field such that they rotate around the vector field centroid, while they keep the regular polygon formation. The main problem of existing approaches in the literature for cyclic pursuit of double-integrator multiagent systems is that under those approaches, the swarm angular velocity and centroid are not controllable based on missions and agents capabilities. However, by employing the proposed vector field approach in this paper, while keeping a regular polygon formation, the swarm angular velocity and centroid can be determined arbitrary. The obtained results can be extended to achieve elliptical formations with cyclic pursuit as well. Simulation results for a team of eight mobile agents verify the accuracy of the proposed control scheme. 相似文献
4.
Shaymaa M. M. Yahya Shadia A. Fathy Zakaria A. El-Khayat Safinaz E. El-Toukhy Ahmed R. Hamed Marwa G. A. Hegazy Heba K. Nabih 《Indian journal of clinical biochemistry : IJCB》2018,33(1):21-30
Hepatocellular carcinoma (HCC) is a hypervascular primary liver cancer characterized by rapid progression, besides, resistance to traditional chemotherapeutic agents. It has been shown that microRNAs play critical roles in regulation of tumor cell sensitivity to drugs through modulating the expression of genes involved in drug transport. The present study investigated whether restoration of miR-122 in HCC cells could alter the cell cycle distribution and the expression of multidrug resistance (MDR)-related genes (ABCB1, ABCC1, ABCG2 and ABCF2). After overexpression of miR-122 in HepG2 cells treated or untreated with doxorubicin doses, total RNAs and protein extracts were isolated for application of QRT-PCR and western blotting techniques. Moreover, cell cycle distribution was monitored by flow cytometry. Our results revealed that, the over expression of miR-122 in HepG2 cells treated or untreated with doxorubicin could modulate the sensitivity of cells to chemotherapeutic drug through downregulation of MDR-related genes, ABCB1 and ABCF2. Interpretation of cell cycle distribution revealed that, the anti-proliferative effect of miR-122 is associated with the accumulation of cells in G0/G1 phase. Moreover, treatment with miR-122 and doxorubicin resulted in high percentage of HCC cells in G0/G1 phase. Taken together, our findings revealed that, overexpression of miR-122 inhibited HCC cell growth by inducing cell cycle arrest and this arrest is associated with down-regulation of MDR-related genes. 相似文献
5.
Creating scientific dialogue through social media: exploration of Saudi pre-service science teachers
Amani K. H. Alghamdi Fayadh Hamed Alanazi 《Research in Science & Technological Education》2013,31(4):471-491
Background: This study explored how Saudi Arabian pre-service science teachers’ (PST) use of social media (SM) creates scientific dialogue.Design and method: Data were collected via (a) in-depth interviews with eight science PSTs completing their practice teaching during a field experience course (2017 academic year at a Saudi Arabia Eastern province university), (b) focus groups with 21 female science students being taught by the PSTs, and (c) an analysis of SM artifacts (i.e. PST’s students’ Tweets and Snapchat comments about their SM-based science homework).Results: Findings from content analyses indicate that the PSTs overwhelmingly perceived SM-based science teaching as providing their students with opportunities to pose critical questions, improve science learning, and engage in scientific dialogue and argumentation. Students welcomed the SM-based science learning, saying it excited them, made them want to learn science and helped with collaborative science learning. The majority (87%) of PST’s students expressed an interest in using SM to engage with science concepts. Also, findings affirmed that social media serve as mediating agents for reaching students in their learning Zone of Proximal Development; that is, SM-scaffolded science learning. The findings are considered in terms of further pre-service science teacher education and Saudi-based educational research. 相似文献
6.
Internet evolution has affected all industrial, commercial, and especially learning activities in the new context of e-learning. Due to cost, time, or flexibility e-learning has been adopted by participators as an alternative training method. By development of computer-based devices and new methods of teaching, e-learning has emerged. The effectiveness of such programs is dependent on powerful learning management systems. In this paper, a neuro-fuzzy approach is proposed based on an evolutionary technique to obtain an optimal learning path for both instructor and learner. The neuro-fuzzy synergy allows the diagnostic model to imitate instructor in diagnosing learners’ characteristics, and equips the intelligent learning environment with reasoning capabilities. These reasoning capabilities can be used to drive pedagogical decisions based on the learning style of the learner. The neuro-fuzzy implementation helps to encode both structured and non-structured knowledge for the instructor. On the other hand, for learners, the neural network approach has been applied to make personalized curriculum profile based on individual learner requirements in a fuzzy environment. 相似文献
7.
Ivan K. Farrell Kastro M. Hamed 《Journal of Research on Technology in Education》2017,49(3-4):161-181
Utilizing a correlational research design, we sought to examine the relationship between the technological pedagogical content knowledge (TPACK) of in-service teachers and student achievement measured with each individual teacher's Value-Added Model (VAM) score. The TPACK survey results and a teacher's VAM score were also examined, separately, with respect to teacher attributes. Upon examination of VAM scores and teacher attributes, the subject area, the percentage of economically disadvantaged students at the teacher's school, and the grade level of the teacher were all significantly related to VAM scores. In addition, the TPACK survey results overall and its constructs were examined with teacher attributes. The significant relationships were gender, subject area, the number of certifications, highest degree held by the teacher, years teaching, and teaching in/out of area. The analysis showed no significant relationship between a teacher's VAM score and the TPACK survey overall or its individual constructs. 相似文献
8.
Judith Lederman Norman Lederman Selina Bartels Juan Jimenez Mark Akubo Shereen Aly Chengcheng Bao Estelle Blanquet Ron Blonder Mariana Bologna Soares de Andrade Catherine Buntting Mustafa Cakir Heba EL-Deghaidy Ahmed ElZorkani Estelle Gaigher Shuchen Guo Arvi Hakanen Soraya Hamed Al-Lal Cigdem Han-Tosunoglu Annemarie Hattingh Anne Hume Serhat Irez Gillian Kay Ozgur Kivilcan Dogan Kerstin Kremer Pi-Chu Kuo Jari Lavonen Shu-Fen Lin Cheng Liu Enshan Liu Shiang-Yao Liu Bin Lv Rachel Mamlok-Naaman Christine McDonald Irene Neumann Yaozhen Pan Eric Picholle Ana Rivero García Carl-Johan Rundgren David Santibáñez-Gómez Kathy Saunders Renee Schwartz Frauke Voitle Jakob von Gyllenpalm Fangbing Wei Jocelyn Wishart Zhifeng Wu Huang Xiao Yalcin Yalaki Qiaoxue Zhou 《科学教学研究杂志》2019,56(4):486-515
Although understandings of scientific inquiry (as opposed to conducting inquiry) are included in science education reform documents around the world, little is known about what students have learned about inquiry during their elementary school years. This is partially due to the lack of any assessment instrument to measure understandings about scientific inquiry. However, a valid and reliable assessment has recently been developed and published, Views About Scientific Inquiry (VASI; Lederman et al. [2014], Journal of Research in Science Teaching, 51, 65–83). The purpose of this large-scale international project was to collect the first baseline data on what beginning middle school students have learned about scientific inquiry during their elementary school years. Eighteen countries/regions spanning six continents including 2,634 students participated in the study. The participating countries/regions were: Australia, Brazil, Chile, Egypt, England, Finland, France, Germany, Israel, Mainland China, New Zealand, Nigeria, South Africa, Spain, Sweden, Taiwan, Turkey, and the United States. In many countries, science is not formally taught until middle school, which is the rationale for choosing seventh grade students for this investigation. This baseline data will simultaneously provide information on what, if anything, students learn about inquiry in elementary school, as well as their beginning knowledge as they enter secondary school. It is important to note that collecting data from all of the approximately 200 countries globally was not humanly possible, and it was also not possible to collect data from every region of each country. The results overwhelmingly show that students around the world at the beginning of grade seven have very little understandings about scientific inquiry. Some countries do show reasonable understandings in certain aspects but the overall picture of understandings of scientific inquiry is not what is hoped for after completing 6 years of elementary education in any country. 相似文献
9.
Advanced fault detection and accommodation schemes are required for ensuring efficient and reliable operation of modern wind turbines. This paper presents a novel approach in designing a fault detection and diagnosis (FDD) and fault-tolerant control (FTC) scheme for a wind turbine using fuzzy modeling, identification and control techniques. First, an improved gain-scheduled proportional-integral (PI) control system based on fuzzy gain scheduling (FGS) technique for multi-input and multi-output wind turbine system is designed. Then, to accommodate sensor faults and based on a signal correction algorithm, an active fault-tolerant control system (AFTCS) is developed as an extension of the gain-scheduled PI control system. The AFTCS exploits the fault information from a model-based FDD scheme developed using fuzzy modeling and identification method. The proposed schemes are evaluated by a series of simulations on a well-known large off-shore wind turbine benchmark in the presence of wind turbulences, measurement noises, and different realistic fault scenarios. All results indicate high effectiveness and robustness of the designed control systems in both fault-free and faulty operations of the wind turbine. 相似文献
10.
Gregory J. Tierney Hamed Joodaki Tron Krosshaug Jason L. Forman Jeff R. Crandall Ciaran K. Simms 《Sports biomechanics / International Society of Biomechanics in Sports》2018,17(1):33-47
Player-to-player contact inherent in many unhelmeted sports means that head impacts are a frequent occurrence. Model-Based Image-Matching (MBIM) provides a technique for the assessment of three-dimensional linear and rotational motion patterns from multiple camera views of a head impact event, but the accuracy is unknown for this application. The goal of this study is to assess the accuracy of the MBIM method relative to reflective marker-based motion analysis data for estimating six degree of freedom head displacements and velocities in a staged pedestrian impact scenario at 40 km/h. Results showed RMS error was under 20 mm for all linear head displacements and 0.01–0.04 rad for head rotations. For velocities, the MBIM method yielded RMS errors between 0.42 and 1.29 m/s for head linear velocities and 3.53–5.38 rad/s for angular velocities. This method is thus beneficial as a tool to directly measure six degree of freedom head positional data from video of sporting head impacts, but velocity data is less reliable. MBIM data, combined in future with velocity/acceleration data from wearable sensors could be used to provide input conditions and evaluate the outputs of multibody and finite element head models for brain injury assessment of sporting head impacts. 相似文献