The electrical properties of magnetite-loaded polyethylene composites

Magnetite–polyethylene composites containing various concentrations of magnetite have been prepared and their electrical properties have been investigated. The electrical resistivities of the specimens were studied as function of filler concentration and temperature. The current density-electric field characteristic and the current variation with time were measured. The thermionic and field emission models provide good explanations for the electrical conduction in the specimens, and space-charge-limited conduction is discussed based on the results.     

SATS: Structure‐Aware Touch‐Based Scrolling

Non‐linear document navigation refers to the process of repeatedly reading a document at different levels to provide an overview, including selective reading to search for useful information within a document under time constraints. Currently, this function is not supported well by small‐screen tablets. In this study, we propose the concept of structure‐aware touch‐based scrolling (SATS), which allows structural document navigation using region‐dependent touch gestures for non‐sequential navigation within tablets or tablet‐sized e‐book readers. In SATS, the screen is divided into four vertical sections representing the different structural levels of a document, where dragging into the different sections allows navigating from the macro to micro levels. The implementation of a prototype is presented, as well as details of a comparative evaluation using typical non‐sequential navigation tasks performed under time constraints. The results showed that SATS obtained better performance, higher user satisfaction, and a lower usability workload compared with a conventional structural overview interface.     

Development of a novel 3-degrees of freedom flexure based positioning system

Flexure mechanisms have been widely used for nanometer positioning systems. This article presents a novel conceptual design of an ultra-precision 3-degrees of freedom (XYθ(Z)) positioning system with nanometer precision. The main purpose of this novel stage design is for the application of measurement equipment, in particular biological specimens. The stage was designed as a hollow type and with a compact size for the inverted microscope. This stage includes piezoelectric transducer actuators, double compound amplification mechanisms, moving plate, and capacitor sensors. The double compound amplification mechanism was designed using a mathematical model and analyzed by the finite element method. Since the relationship between the variables of the hinge parameters and system performances are complicated, an optimization procedure was used to obtain the optimal design parameters, which maximized the system bandwidth. Based on the solution of the optimization problem, the design of the stage and FEM simulation results are presented. Finally, the stage was manufactured and tested.     

Investigation of the plasma uniformity in an internal linear antenna-type inductively coupled plasma source by applying dual frequency

A large area inductively coupled plasma source with an internal linear-type antenna was operated in dual frequency mode (2 MHz/13.56 MHz), and the electrical/plasma characteristics of the ICP source were examined as a function of the relative rf power ratio. When the source was operated in single frequency mode (13.56 MHz only), approximately 8.5% plasma uniformity was observed at 5 kW of 13.56 MHz rf power for the substrate size of 880 mm × 660 mm. The plasma uniformity improved with increasing rf power. However, a further improvement in plasma uniformity to approximately 6.3% could be obtained using the dual frequency mode by applying 0.9 kW of 2 MHz rf power in addition to 5 kW of 13.56 MHz. For 15 mTorr Ar, the plasma density at a dual frequency rf power of 0.9 kW 2 MHz/5 kW 13.56 MHz was 1.6 × 10¹¹/cm³ and the electron temperature was approximately 3 eV. The addition and increase in 2 MHz rf power to the 13.56 MHz power increased the plasma density without increasing the electron temperature.     

Preliminary design of the ITER AC/DC converters supplied by the Korean Domestic Agency

The preliminary design for ITER AC/DC converters under the responsibility of the Korean Domestic Agency is performed on the basis of the engineering experience of previous R&D for a full-scale 6-pulse CS (Central Solenoid) converter unit. This paper describes key features of the preliminary design for the respective sub-systems; integrated self-supporting aluminium structure and symmetrical thyristor assembly for strong and reliable converters, optimised impedance of the converter transformer to limit short circuit current, coaxial-type AC bus bars to shield high magnetic field around wall penetrations, compact components to fit into given building space. The insulation and the minimisation of electrical loops of concrete rebar below the converter installations are essential to prevent floor heating. Required output voltage or current of converters is provided by a conventional controller. A master controller is designed to collect predicted reactive powers from each converter and deliver processed data to the reactive power compensation (RPC) system to improve the regulation speed of the RPC controller with fast feed-forward compensation under fast reactive power transients.     

An education model of a nano-positioning system for mechanical engineers

The increasing use of nano-positioners in a wide variety of laboratory and industrial applications has created a need for nano-mechatronics education in all engineering disciplines. The subject of nano-mechatronics is broad and interdisciplinary. This article focuses on the way nano-mechatronics is taught in department of mechanical engineering at Korea Advanced Institute of Science and Technology (KAIST). As one model of nano-positioning systems, design and experimental methodology is presented in this article. For design phase, the stiffness and resonant frequencies are found analytically and verified by using a commercial finite element analysis program. Next, for experimental phase, various tests are performed to access the performances of the designed nano-positioner, for example, sine-tracking, multi-step response and travel-range check etc. Finally, the definition of “separation frequency” is described and some comments are discussed.     

Damage in carbon fibre composites due to repetitive low-velocity impact loads

The effect of repetitive impacting with increasing impact energy on unsupported thermoset matrix and thermoplastic matrix carbon fibre laminates was studied. In the case of the thermoset laminates, there were two abrupt losses in stiffness, the first corresponding to through-the-thickness damage and the second to the damage extending to the specimen edges. The thermoplastic matrix laminates exhibited a continuous decline in stiffness but again the damage sequence was through-the-thickness followed by extension to the specimen edges. Static bend testing of these composites resulted in the same type and extent of damage as was observed for impact loading. The effect of increasing the unsupported area and laminate thickness were investigated. Impacting with increasing impact energy was compared to repetitive impacting at a constant impact energy.     

A novel multiplex PCR assay for rapid and simultaneous detection of five pathogenic bacteria: Escherichia coli O157:H7, Salmonella, Staphylococcus aureus, Listeria monocytogenes, and Vibrio parahaemolyticus

Rapid and sensitive detection techniques for foodborne pathogens are important to the food industry. However, traditional detection methods rely on bacterial culture in combination with biochemical tests, a process that typically takes 4 to 7 days to complete. Thus, this study was conducted to address the issue of time lag inherent in traditional methods by developing a novel PCR assay for each of five foodborne pathogenic bacteria. This new system consists of a simultaneous screening method using multiplex PCR in a single reaction tube for the rapid and sensitive detection of each of the five bacteria. Specific primers for multiplex PCR amplification of the Shiga-like toxin (verotoxin type II), femA (cytoplasmic protein), toxR (transmembrane DNA binding protein), iap (invasive associative protein), and invA (invasion protein A) genes were designed to allow simultaneous detection of Escherichia coli O157:H7, Staphylococcus aureus, Vibrio parahaemolyticus, Listeria monocytogenes, and Salmonella, respectively. To confirm the specificity of each primer pair for the respective target gene, three types of experiments were carried out using boiled cell lysates and their DNAs. In the multiplex PCR with mixed DNA samples, specific bands for corresponding genes were simultaneously detected from a single reaction. The detection of all five foodborne pathogenic bacteria could be completed in less than 24 h with this novel PCR method.     

Synthesis and characterization of cholic acid‐containing biodegradable hydrogels by photoinduced copolymerization

A cholic acid (CA)‐containing biodegradable hydrogel (PLA‐PEG‐PLA‐co‐MACAH) was synthesized from the photoinduced copolymerization of a CA‐modified methacrylate monomer (MACAH), bearing a spacer of hexane‐1,6‐diol spacer between the methacryloyl and the cholanoate moieties, and a macromonomer (PLA‐PEG‐PLA‐DA), bearing two acryloyl end groups derived from a poly(lactic acid)‐b‐poly(ethylene glycol)‐b‐poly(lactic acid) triblock copolymer. The structure of MACAH was confirmed by FTIR, ¹H‐NMR, and MS. The hydrogel PLA‐PEG‐PLA‐co‐MACAH was characterized by scanning electron microscopy and X‐ray diffraction. The experiment results showed that the swelling ratios of the hydrogels decreased with the increase of the CA fraction. The investigation on the in vitro degradation of the hydrogel showed that the CA‐containing hydrogels degraded much slower than the hydrogels without CA component. The bioactivity of the synthesized hydrogels was assessed by the simulated body fluid method. The observed formation of hydroxyapatite on the scaffold of the hydrogels indicated that the hydrogels possess good bioactivity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Optimal design of high precision XY-scanner with nanometer-level resolution and millimeter-level working range

This article presents the design and performance evaluation of a compact high precision XY-scanner providing nanometer-level resolution and a millimeter-level travel range. The proposed XY-scanner is composed of a voice coil motor (VCM) and double compound linear spring flexure guide mechanism. The challenge was to determine design variables properly while simultaneously satisfying the requirements of high resolution, long working range, high response speed, and compact size, because the relationships between the design variables and the system parameters are complex. Therefore, we developed a design that would provide the optimal tradeoff in terms of design variables. The objective was to maximize the first resonant frequencies of the XY-scanner to increase response speed while limiting the size of the scanner to 100 mm × 100 mm × 50 mm. The XY-scanner was fabricated with optimally-designed values, and its performance was evaluated. From the experimental results, the first resonant frequencies of XY-scanner were 26.68 Hz for the X-axis and 22.79 Hz for the Y-axis. The measured results of the 10 nm resolution and 2 mm working range confirmed that the designed scanner could be successfully used in precision fields requiring nanometer-level resolution and millimeter-level travel range.