Dissipative control for a class of uncertain nonlinear control systems

A general dissipative controller is proposed to achieve robust tracking control performance for a class of uncertain single‐input single‐output (SISO) nonlinear systems. The feedback linearization technique is employed to transform the nonlinear system into an assignable inner linear system with a differential control input so that the relationship of the external (input) power and the stored energy of system can be shown clearly. Then, a dissipative controller with an assignable attenuation level is proposed to make the system energy dynamics fit a required dissipative inequality. The unstable factors of the system can then be attenuated accordingly. The system stability is guaranteed even if the system has permanent unavoidable uncertainties. The proposed design can be achieved without the use of traditional means, i.e. optimal control, which requires solution of a Hamilton inequality (or Riccati equation). The Lyapunov stable condition is assured in our approach when the system uncertainties belong to L _∞. Moreover, due to the compatibility of the proposed controller, the controller can be embedded into the designs of other controllers. In those designs, knowledge of the system functions is not required. Basically, the proposed dissipative controller is independent of the system functions. The use of the bounds of the system function is considered to prove the system stability only. Two simulations are given to illustrate the effectiveness of the proposed controller. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Particle focusing in a contactless dielectrophoretic microfluidic chip with insulating structures

The focusing of biological and synthetic particles in microfluidic devices is a crucial step for the construction of many microstructured materials as well as for medical applications. The present study examines the feasibility of using contactless dielectrophoresis (cDEP) in an insulator-based dielectrophoretic (iDEP) microdevice to effectively focus particles. Particles 10?μm in diameter were introduced into the microchannel and pre-confined hydrodynamically by funnel-shaped insulating structures near the inlet. The particles were repelled toward the center of the microchannel by the negative DEP forces generated by the insulating structures. The microchip was fabricated based on the concept of cDEP. The electric field in the main microchannel was generated using electrodes inserted into two conductive micro-reservoirs, which were separated from the main microchannel by 20-μm-thick insulating barriers made of polydimethylsiloxane (PDMS). The impedance spectrum of the thin insulating PDMS barrier was measured to investigate its capacitive behavior. Experiments employing polystyrene particles were conducted to demonstrate the feasibility of the proposed microdevice. Results show that the particle focusing performance increased with increasing frequency of the applied AC voltage due to the reduced impedance of PDMS barriers at high frequencies. When the frequency was above 800?kHz, most particles were focused into a single file. The smallest width of focused particles distributed at the outlet was about 13.1?μm at a frequency of 1?MHz. Experimental results also show that the particle focusing performance improved with increasing applied electric field strength and decreasing inlet flow rate. The usage of the cDEP technique makes the proposed microchip mechanically robust and chemically inert.     

A Sensor Network Web Platform Based on WoT Technology

This study proposes a Web platform, the Web of Things (WoT), whose Internet of Things (IoT) architecture is used to develop the technology behind a new standard Web platform. When a remote sensor passes data to a microcontroller for processing, the protocol is often not known. This study proposes a WoT platform that enables the use of a browser in a mobile device to control a remote hardware device. An optimized code is written using an artificial intelligence-based algorithm in a microcontroller. Digital data convergence technology is adopted to process the packets of different protocols and place them on the Web platform for access by other mobile devices. The platform has high efficiency and cross-platform advantages, with no limitation on the operating system. Message queueing telemetry transport (MQTT) technology is used to simplify the original HTTP protocol. Assume that the mobile device is a subscriber, i.e., the controller, and a microcontroller that connects the sensing device is the publisher. The publishers and subscribers of MQTT need not know each other if they share a message broker. The intermediate agent role is much like a router. Publishers and subscribers do not need to interact, and publishers do not have to wait for subscriber confirmation to cause interactive permission be locked. Nor must publishers and subscribers be online at the same time, and they are free to choose when to get messages. The proposed WoT method is compared with the traditional IoT method regarding data transfer. The results show that the proposed method can save time in processing large amounts of data, as the traditional IoT method wastes time, especially in data format transfer.     

Effects of screen size and visual presentation on visual fatigue based on regional brain wave activity

Advances in information technologies have resulted in people spending increasing amounts of time staring at electronic screens. Long-term use of computers, mobile phones, and tablets can cause eye soreness and fatigue, but can also cause more serious conditions including myopia, cataracts, and glaucoma. This study assesses changes in brain wave activity detected by eight electrodes targeting different brain regions to identify and assess the brain wave patterns in the regions associated with visual fatigue under various visual presentation methods. Furthermore, linear discriminant analysis and Min–Max scaling techniques are applied to develop a visual fatigue assessment model to quantify visual fatigue. Finally, experiments are run to assess the impact of screen size (smartphone, tablet, computer) and visual presentation mode (2D, 3D, AR, VR) on visual fatigue. This study finds that (1) the brain wave features which influence the reaction to 2D and 3D imaging are the delta and theta waves at the prefrontal Fp1 and Fp2 poles. When viewing AR images, the alpha bands at the O1 and O2 poles of the occipital lobe show a relatively clear impact, while the delta and theta waves at the C3 pole in the left center area are associated with VR images; (2) larger screens cause greater visual fatigue, indicating that excessive visual stimulation will increase visual loading and thus produce greater visual fatigue; (3) the results show that VR can cause quite severe visual fatigue, along with motion sickness passed on sensory mismatch. Therefore, it is recommended to avoid viewing experiences that are inconsistent with the brain’s physiological experience, such as walking while viewing a mobile phone, or reading in a moving car. The proposed visual fatigue assessment model provides easy and objective quantification of visual fatigue indicators, contributing to the reduction of risk for eye injury and disease.

     

Synthesis and characterization of polyimide/modified mCOC composites

Two types of monomers, 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride and 4,4′‐oxydianiline, were employed to synthesize poly(amic acid) (PAA) as a precursor of polyimide (PI). Through the addition of modified metallocene cyclic olefin copolymer (mCOC), PAA/mCOC composites were formed. PI/mCOC composites were obtained through a blade coating and multistep thermal curing process. The structure of the prepared PI/mCOC composites was characterized through Fourier transform infrared spectrometry. The results showed that the copolymerization of PAA and modified mCOC improved thethermal stability and hydrophobic and electrical properties of the PI/mCOC composites. The formation of a network structure between PI and modified mCOC considerably reduced the mobility of PI molecules, thereby improving the glass transition temperature and thermal properties of the composite. The thermal and hydrophobic properties were improved by increasing the mCOC grafting ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44144.     

Functional levels of floor surface roughness for the prevention of slips and falls: Clean-and-dry and soapsuds-covered wet surfaces

Literature has shown a general trend that slip resistance performance improves with floor surface roughness. However, whether slip resistance properties are linearly correlated with surface topographies of the floors or what roughness levels are required for effective slip resistance performance still remain to be answered. This pilot study aimed to investigate slip resistance properties and identify functional levels of floor surface roughness for practical design applications in reducing the risk of slip and fall incidents. A theory model was proposed to characterize functional levels of surface roughness of floor surfaces by introducing a new concept of three distinctive zones. A series of dynamic friction tests were conducted using 3 shoes and 9 floor specimens under clean-and-dry as well as soapsuds-covered slippery wet environments. The results showed that all the tested floor-shoe combinations provided sufficient slip resistances performance under the clean-and-dry condition. A significant effect of floor type (surface roughness) on dynamic friction coefficient (DFC) was found in the soapsuds-covered wet condition. As compared to the surface roughness effects, the shoe-type effects were relatively small. Under the soapsuds-covered wet condition, floors with 50?μm in Ra roughness scale seemed to represent an upper bound in the functional range of floor surface roughness for slip resistance because further increase of surface roughness provided no additional benefit. A lower bound of the functional range for slip resistance under the soapsuds-covered wet condition was estimated from the requirement of DFC?>?0.4 at Ra???17?μm. Findings from this study may have potential safety implications in the floor surface design for reducing slip and fall hazards.     

Efficient algorithms for discovering high utility user behavior patterns in mobile commerce environments

Mining user behavior patterns in mobile environments is an emerging topic in data mining fields with wide applications. By integrating moving paths with purchasing transactions, one can find the sequential purchasing patterns with the moving paths, which are called mobile sequential patterns of the mobile users. Mobile sequential patterns can be applied not only for planning mobile commerce environments but also for analyzing and managing online shopping websites. However, unit profits and purchased numbers of the items are not considered in traditional framework of mobile sequential pattern mining. Thus, the patterns with high utility (i.e., profit here) cannot be found. In view of this, we aim at integrating mobile data mining with utility mining for finding high-utility mobile sequential patterns in this study. Two types of algorithms, namely level-wise and tree-based methods, are proposed for mining high-utility mobile sequential patterns. A series of analyses and comparisons on the performance of the two different types of algorithms are conducted through experimental evaluations. The results show that the proposed algorithms outperform the state-of-the-art mobile sequential pattern algorithms and that the tree-based algorithms deliver better performance than the level-wise ones under various conditions.     

Optimization and comparison of photonic crystal resonators for silicon microcantilever sensors

Microcantilever sensors have been known as a fundamental design used in force sensors, strain sensors and biochemical sensors. The fast-growing applications in nanoelectromechanical systems (NEMS) lead to strong demands in new sensing mechanism in order to downsize the sensing elements to nanometer scale. Photonic crystal (PC) based resonators have been investigated as promising solutions because the bandgap structure and resonator characteristics are extremely sensitive to the deformation and position shift of holes in PC resonators. In addition to the well-known nano-cavity resonator (NCR), we proposed hexagonal nano-ring resonators (NRR) of two different layout configurations. When a microcantilever under different force loads, both of the resonant wavelength and the resonant wavelength shift can be measured as a linear function of force load. The linear relationship between wavelength shifts and strain is observed as well. The minimum detectable force and detectable strain for NRR configuration 1 is derived as small as 0.0757 μN and 0.0023%. The outstanding sensing capability renders PC resonators as a promising nanomechanical sensing element to be integrated in various transducers for NEMS applications.     

Group differences in computer supported collaborative learning: Evidence from patterns of Taiwanese students’ online communication

This study explored the differences among online elementary school student groups based on their communication features. Two hundred and ninety-one Taiwanese students, ranging in age from 11 to 12 years old, participated in this study. The students were randomly arranged within-class into three-member groups. Each group was asked to use a collaborative learning system to accomplish a group task generating a shared concept map. The textual discussions in each group during collaboration were collected, coded, categorized, and quantified to profile their communication characteristics. Cluster analysis on the resulting communication characteristics resulted in four types of small student groups, including passive or reticent, frequently off-task, actively participating, and knowledge emphasizing. Most student groups (56%) were found to be relatively passive or reticent. Frequently off-task student groups made a protrusive amount of messages for off-task social purposes. The actively participating student groups were characterized by abundant discussion, particularly for continuing task, managing procedure and coordinating efforts. The distinctive feature of knowledge emphasizing student groups was that they devoted particular attention to task related knowledge. In addition, they performed better in task accomplishment.