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Design concept development of a variable magnetization motorwith improved efficiency and controllable stiffness for roboticapplications

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Science China(Technological Sciences) 2019年第1期62卷 39-46页

作者： BAI Kun ZHU Lang YUAN Mi lee kok-meng State Key Lab of Digital Manufacturing Equipment and Technology Huazhong University of Science and Technology Woodruff School of Mechanical Engineering Georgia Institute of Technology

A variable magnetization(VM) motor by incorporating magnets that can be flexibly configured with variable magnetization process is proposed to meet the emerging requirements on motor efficiency and actuator compliance in robotic applications. A generalized spin torque model is established which provides a relationship between the motor torque and two different types of motor inputs, the current inputs and the magnet magnetizations. Avariable magnetization process is proposed based on the study of the hysteresis properties of the magnetic materials and the design criteria for implementing the variable magnetization process with current pulses are established. The feasibility of the variable magnetization is validated with experimental data and the motor functions and performances are numerically demonstrated and evaluated. The results show that the VM motor can maintain high efficiency by switching between two actuation modes. Controllable stiffness at different equilibria can be also achieved with the VM motor with instantaneous magnetizing current pulses.

关键词： compliant actuators direct-drive motors variable stiffness motors variable magnetization motors

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基于电涡流阻尼的薄壁盘加工振动抑制

机械工程学报 2018年第17期54卷 76-84页

作者：程明迪郭家杰李卓李国民华中科技大学数字制造装备与技术国家重点实验室武汉430074 佐治亚理工学院乔治伍德拉夫机械工程学院美国亚特兰大30332-0405

薄壁零件具有重量轻、相对强度高等优良特性,在航空航天等领域有着广泛应用;然而由于刚度小,薄壁工件在加工过程中容易发生变形和振动,导致产品难以满足尺寸精度和表面质量要求。为此,提出一种非接触式的电涡流阻尼器设计方法,旨在用于... 详细信息

薄壁零件具有重量轻、相对强度高等优良特性,在航空航天等领域有着广泛应用;然而由于刚度小,薄壁工件在加工过程中容易发生变形和振动,导致产品难以满足尺寸精度和表面质量要求。为此,提出一种非接触式的电涡流阻尼器设计方法,旨在用于抑制加工过程中薄壁盘类工件的多模态振动。通过建立薄壁盘-电涡流阻尼器的耦合动力学模型,描述时空分布的系统惯量、刚度和阻尼;通过物理模型的模态降维和局部线性化,获得电涡流阻尼和薄壁盘振动位移的线性关系式。利用数值计算,分析电涡流在盘面分布的有效范围,揭示永磁铁的尺寸和位置对电涡流阻尼的影响规律,并提出永磁铁的优化布置方案,仿真分析薄壁盘-阻尼器的耦合动力学行为,为电涡流阻尼器的设计提供依据。最后,理论模型和仿真分析结果通过薄壁盘-阻尼器耦合的阶跃振动和车削加工试验验证;试验结果表明,电涡流阻尼器对薄壁盘振动有较好的抑制作用,在薄壁件加工减振应用中提供一种简单可行的有效方案。

关键词：薄壁盘振动抑制电涡流阻尼永磁铁动力学

Multiple hashes of single key with passcode for multiple accounts

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第8期8卷 1183-1190页

作者： lee kok-wah EWE Hong-tat Faculty of Engineering & Technology Multimedia UniversityJalan Ayer Keroh Lama75450 Bukit BeruangMelakaMalaysia Faculty of Information Technology Multimedia UniversityJalan Multimedia63100 CyberjayaSelangorMalaysia

A human's e-life needs multiple offline and online accounts. It is a balance between usability and security to set keys or passwords for these multiple accounts. Password reuse has to be avoided due to the domino effect of malicious administrators and crackers. However,human memorability constrains the number of keys. Single sign-on server,key hashing,key strengthening and petname system are used in the prior arts to use only one key for multiple online accounts. The unique site keys are derived from the common master secret and specific domain name. These methods cannot be applied to offline accounts such as file encryption. We invent a new method and system applicable to offline and online accounts. It does not depend on HTTP server and domain name,but numeric 4-digit passcode,key hashing,key strengthening and hash truncation. Domain name is only needed to resist spoofing and phishing attacks of online accounts.

关键词： management Memorability Key hashing Key strengthening Multiple accounts Information security

Compensation of hysteresis in piezoelectric actuator with iterative learning control

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控制理论与应用（英文版） 2010年第2期8卷 176-180页

作者： kok Kiong TAN Andi Sudjana PUTRA Tong Heng lee Department of Electrical and Computer Engineering National University of Singapore Singapore 117576 Graduate School for Integrative Sciences and Engineering National University of Singapore Singapore 117576

This paper presents the application of iterative learning control (ILC) to compensate hysteresis in a piezoelectric actuator. The proposed controller is a hybrid of proportional-integral-differential (PID) control, whose main function is for trajectory tracking, and a chatter-based ILC, whose main function is for hysteresis compensation. Stability analysis of the proposed ILC is presented, with the PID included in the dynamic of the piezoelectric actuator. The performance of the proposed controller is analysed through simulation and verified with experiment with a piezoelectric actuator.

关键词： Iterative learning control Hysteresis Piezoelectric actuator Stability analysis

Influence of Internal Stresses in Few-Mode Fiber on the Thermal Characteristics of Regenerated Gratings

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Photonic Sensors 2019年第2期9卷 162-169页

作者： Nurul Asha MOHD NAZAL kok Sing LIM Yen Sian lee Muhammad Aizi MAT SALIM Harith AHMAD Photonics Research Centre University of Malaya Kuala Lumpur 50603 Malaysia Laser Center Ibnu Sina Institute for Scientific and Industrial Research Universiti Teknologi MalaysiaJohor Bahru 81310Malaysia

The pre-treatment of few-mode fibers (FMFs) has been successfully done with CO2 laser The wavelength difference, AA between the two resonant wavelengths in the few-mode fiber Bragg grating (FMFBG) varies with temperature increment during the annealing process. The results show that the treated fibers with lower stresses have lower thermal sensitivity in △λ than that of non-treated fiber. However, the treated fibers produce FMFBGs with better thermal durability and regeneration ratio. It is conceived that the presence of those stresses in the pristine fiber is responsible for the high thermal sensitivity in △λ. The thennal relaxation of stresses and structural rearrangement during the thennal annealing process are responsible for the degradation of the strength and resilience of the regenerated grating.

关键词： Regenerated fiber Bragg grating few-mode fiber thermal stress relaxation CO2 laser annealing thennal resilience

Advances in surgical management for locally recurrent rectal cancer: How far have we come?

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World Journal of Gastroenterology 2017年第23期23卷 4170-4180页

作者： Daniel Jin-Keat lee Peter M Sagar Gaitri Sadadcharam kok-Yang Tan Department of Surgery Khoo Teck Puat Hospital John Goligher Colorectal Surgery Unit St James’s University Hospital

Locally recurrent rectal cancer(LRRC) is a complex disease with far-reaching implications for the patient. Until recently, research was limited regarding surgical techniques that can increase the ability to perform an en bloc resection with negative margins. This has changed in recent years and therefore outcomes for these patients have improved. Novel radical techniques and adjuncts allow for more radical resections thereby improving the chance of negative resection margins and outcomes. In the past contraindications to surgery included anterior involvement of the pubic bone, sacral invasions above the level of S2/S3 and lateral pelvic wall involvement. However, current data suggests that previously unresectable cases may now be feasible with novel techniques, surgical approaches and reconstructive surgery. The publications to date have only reported small patient pools with the research conducted by highly specialised units. Moreover, the short and long-term oncological outcomes are currently under review. Therefore although surgical options for LRRC have expanded significantly, one should balance the treatment choices available against the morbidity associated with the procedure and select the right patient for it.

关键词： Recurrent rectal cancer Sacrectomy Pelvic exenteration Pelvic sidewall Radical resection

Traumatic optic neuropathy:a review of 24 patients

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International Journal of Ophthalmology(English edition) 2010年第2期3卷 175-178页

作者： kok Foo lee Nor Idahriani Muhd Nor Azhany Yaakub Wan Hazabbah Wan Hitam Department of Ophthalmology School of Medical SciencesUniversiti Sains MalaysiaHealth Campus16150 Kubang KerianKelantanMalaysia

AIMTo evaluate the clinical presentations of traumatic optic neuropathy and to assess the visual outcome of three groups of patients managed differently (conservative, intravenous corticosteroids only and combination ... 详细信息

关键词： traumatic optic neuropathy orbital fractures corticosteroids

Free-matrix-based time-dependent discontinuous Lyapunov functional for synchronization of delayed neural networks with sampled-data control

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Chinese Physics B 2017年第11期26卷 127-134页

作者：王炜曾红兵 kok-Lay Teo School of Electrical and Information Engineering Hunan University of Technology Key Laboratory for Electric Drive Control and Intelligent Equipment of Hunan Province Department of Mathematics and Statistics Curtin University

This paper is concerned with the synchronization of delayed neural networks via sampled-data control. A new technique, namely, the free-matrix-based time-dependent discontinuous Lyapunov functional approach, is adopted in constructing the Lyapunov functional, which takes advantage of the sampling characteristic of sawtooth input delay. Based on this discontinuous Lyapunov functional, some less conservative synchronization criteria are established to ensure that the slave system is synchronous with the master system. The desired sampled-data controller can be obtained through the use of the linear matrix inequality（LMI） technique. Finally, two numerical examples are provided to demonstrate the effectiveness and the improvements of the proposed methods.

关键词： neural networks synchronization sampled-data control free-matrix-based inequality

Growth and photosynthesis of Chlorella strains from polar,temperate and tropical freshwater environments under temperature stress

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Journal of Oceanology and Limnology 2018年第4期36卷 1266-1279页

作者： kok-Keong lee Phaik-Eem LIM Sze-Wan POONG Chiew-Yen WONG Siew-Moi PHANG John BEARDALL Institute of Ocean and Earth Sciences University of Malaya Institute of Graduate Studies University of Malaya School of Health Sciences International Medical University National Antarctic Research Centre University of Malaya Institute of Biological Sciences University of Malaya School of Biological Sciences Monash University

Elevated temperatures as a consequence of global warming have significant impacts on the adaptation and survival of microalgae which are important primary producers in many ecosystems. The impact of temperature on the photosynthesis of microalgae is of great interest as the primary production of algal biomass is strongly dependent on the photosynthetic rates in a dynamic environment. Here, we examine the effects of elevated temperature on Chlorella strains originating from different latitudes, namely Antarctic, Arctic, temperate and tropical regions. Chlorophyll fluorescence was used to assess the photosynthetic responses of the microalgae. Rapid light curves(RLCs) and maximum quantum yield( F_v/F_m) were recorded. The results showed that Chlorella originating from different latitudes portrayed different growth trends and photosynthetic performance. The Chlorella genus is eurythermal, with a broad temperature tolerance range, but with strain-specific characteristics. However, there was a large overlap between the tolerance range of the four strains due to their "eurythermal adaptivity". Changes in the photosynthetic parameters indicated temperature stress. The ability of the four strains to reactivate photosynthesis after inhibition of photosynthesis under high temperatures was also studied. The Chlorella strains were shown to recover in terms of photosynthesis and growth(measured as Chl a) when they were returned to their ambient temperatures. Polar strains showed faster recovery in their optimal temperature compared to that under the ambient temperature from which they were isolated.

关键词： Antarctic Arctic Fv/Fm microalgae pigments recovery