Time response characteristics of microcapsulated liquid-crystal particles

Microcapsulated liquid-crystal particles are widely used as temperature sensors in the field of heat transfer engineering. Conventionally, these particles are painted on a surface of a heated plate for temperature measurements. The temperature is measured by tracing the color changes of the microcapsulated liquid-crystal particle through the color digital image processing technique. Recently, these particles are often suspended in thermal fluid flows as temperature tracers of the flows. For the use of a microcapsulated liquid-crystal particle itself as a temperature sensor in the suspending method, the heat capacity of the capsule covering the liquid crystal should be regarded as an important factor in predicting the time response of the microcapsulated liquid-crystal particle which is directly injected into a thermal fluid flow. The heat capacity of the liquid crystal and the capsule can produce a delayed time response for the temperature change of the outside fluids and eventually produce erroneous measurement data. Without a new temperature sensor smaller than the particle, it is very difficult to measure the time response of the microcapsulated liquid-crystal particle since the particles move with the working thermal fluid in different flow conditions. Therefore, a numerical simulation for the time response of the particle is made and its usable limit is discussed in detail for the measurement of turbulent thermal flows. Responses for a temperature step change, fluctuating temperature changes, and the thermal inertia of the working fluid temperature are considered. The response time of the microcapsulated liquid-crystal particle has been evaluated to be as much as 150 ms time delay for a step change of the working fluid temperature, which means the physical properties of the particle itself must be considered for outside temperature changes. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(5): 390–398, 1998     

Characterizations and electrochemical performance of pure and metal-doped Li4Ti5O12 for anode materials of lithium-ion batteries

Pure and metal (Cu, Al, Sn, and V)-doped Li₄Ti₅O₁₂ powders are prepared with solid-state reaction method. The effects of dopants on the physical and electrochemical properties are characterized by using TGA, XRD, and SEM. Compared with pure Li₄Ti₅O₁₂, metal-doped Li₄Ti₅O₁₂ powders show structural stability and enhanced lithium ion diffusivity brought by doped metal ions. Voltage characteristics and initial charge–discharge characteristics according to the C rates in pure and metal-doped Li₄Ti₅O₁₂ electrode materials are studied. Pure Li₄Ti₅O₁₂ powder shows a relatively good discharge capacity of 164 mAh/g at a rate 0.2C, and some of metal-doped Li₄Ti₅O₁₂ powders show higher discharge capacities. Metal-doped Li₄Ti₅O₁₂ powders are promising candidates as anode materials for lithium-ion batteries.     

Effective strain of RC beams strengthened in shear with FRP

The failure modes of Reinforced Concrete (RC) beams strengthened in shear with Fiber Reinforced Polymer (FRP) sheets or strips are not well understood as much as those of RC beams reinforced with steel stirrups. When the beams are strengthened in shear with FRP composites, beams may fail due to crushing of the concrete before the FRP reaches its rupture strain. Therefore, the effective strain of the FRP plays an important role in predicting the shear strength of such beams. This paper presents the results of an analytical and experimental study on the performance of reinforced concrete beams strengthened in shear with FRP composites and internally reinforced with conventional steel stirrups. Ten RC beams strengthened with varying FRP reinforcement ratio, the type of fiber material (carbon or glass) and configuration (continuous sheets or strips) were tested. Comparisons between the observed and calculated effective strains of the FRP in the tested beams failing in shear showed reasonable agreement.     

Novel scan path generation method based on area division for SFFS

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process of fabrication using variable materials, and SLS extends the application to machinery and automobiles. Due to the time delay in the sintering process, shrinkage and warping often occur. Curling also occurs due to laser and scan delays. These problems affect not only the accuracy of the fabricated product but also the total system efficiency. These deficiencies can be overcome by reducing the total processing time of the SFF system. To accomplish this, the laser scanning time, from mark (laser on) to jump (laser off), must be reduced as it contributes the major part of the total processing time. This can be done by employing area division scan path generation, which promotes digital efficiency. A simulation and an experiment was carried out in this study to evaluate the developed scan path method. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Kyung-Hyun Choi received his B.S. and M.S. degrees in Mechanical Engineering from Pusan National University, Korea, in 1983 and 1990,. He then received his M.S. and Ph.D. degrees from University of Ottawa in 1995. Dr. Choi is currently a professor at the School of Mechanical Engineering at Cheju National University, Korea. His research interests include micro-machining, printed Electronics. Hyung-Chan Kim received his B. S. and M. S. degrees in Electronics Engineering from Cheju National University, Korea, in 2006 and 2008, respectively. Mr. Kim is currently a Ph.D. candidate at the School of Electronics Engineering at Cheju National University, Korea. His research interests include RP System, micro-machining, printed Electronics. Yang-Hoi Doh received his B.S. and M.S. degrees in Electronics Engineering from KyungBuk National University, Korea, in 1982 and 1984, respectively. He then received his Ph.D. degree from University of Kyung Buk National University, Korea, in 1988. Dr. Doh is currently a Professor at the School of Electronics Engineering at Cheju National University, Korea. His research interests include micro-machining, Digital signal processing. Dong-Soo Kim received his M.S. and Ph.D. degrees in Mechanical Engineering from Yung Nam University, Korea, in 1991 and 2001, respectively. Dr. Kim is currently the general manager at Nano Mechanical System Research Division at Korea Institute of Machinery & Materials. His research interests include printed Electronics, R2R printing, RP system.     

Simultaneous synthesis and consolidation of nanocrystalline Fe2Al5 and Fe2Al5-Al2O3 by pulsed current activated sintering and their mechanical properties

Nanopowders of Fe, Al and Fe₂O₃ are fabricated by high energy ball milling. Using the pulsed current activated sintering method, the densification of nanocrystalline Fe₂Al₅ and Al₂O₃ reinforced Fe₂Al₅ composites were simultaneously synthesized and consolidated within two minutes from mechanically activated powders. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanostuctured materials. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid to the application of nanomaterials. Not only the hardness but also the fracture toughness of the Fe₂Al₅-Al₂O₃ composite was higher than that of monolithic Fe₂Al₅ due to the addition of the hard phase of Al₂O₃ and the crack deflection by Al₂O₃.     

Properties and pulsed current activated consolidation of nanostuctured MgSiO3-MgAl2O4 composites

Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. Nanopowders of MgO, Al₂O₃ and SiO₂ were made by high energy ball milling. The simultaneous synthesis and consolidation of nanostuctured MgAl₂O₄-MgSiO₃ composites from milled 2MgO, Al₂O₃ and SiO₂ powders was investigated by the pulsed current activated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured MgAl₂O₄-MgSiO₃ composites were produced with a simultaneous application of 80 MPa pressure and a pulsed current of 2000A within 1min. The fracture toughness of MgAl₂O₄-Mg₂SiO₄ composites sintered from 60 mol%MgO-20 mol%Al₂O₃-20mol%SiO₂ powders milled for 4 h was 3.2MPa·m^1/2. The fracture toughness of MgAl₂O₄-MgSiO₃ composite is higher than that of monolithic MgAl₂O₄.     

Loading algorithms for flexible manufacturing systems with partially grouped unrelated machines and additional tooling constraints

This paper considers the loading problem for flexible manufacturing systems with highly flexible partial machine grouping, i.e., machines are tooled differently, but each operation can be assigned to multiple machines. Loading is the problem of allocating operations and their associated cutting tools to machines for a given set of parts. As an extension of the existing studies, we consider unrelated machines, i.e., processing time of an operation depends on the speed of the machine to which it is allocated, and dedicated machines, i.e., certain part types must be processed on a specific machine. Also, we consider the constraints associated with cutting tools: (a) tool life restrictions and (b) number of available tool copies. An integer linear programming model is suggested for the objective of balancing the workloads assigned to machines and then due to the complexity of the problem, we suggest two-stage heuristics in which an initial solution is obtained using modified bin-packing algorithms and then it is improved by a simple search technique. The two-stage heuristics suggested in this study were tested on various test instances, and the results show that they can give reasonable quality solutions within a very short amount of computation time. Also, a sensitivity analysis was done on the tightness of the tooling constraints, and the results are reported.     

Development of a tomographic PTV

A new tomographic PTV (Tomo-PTV) was proposed, and then its performance was compared with that of tomographic PIV (Tomo-PIV). To construct the new tomographic PTV for calculation of vector fields, an affine transformation was introduced. The vectors obtained by match probability method were used as the initial data for the final vectors. Four camera-based tomographic PTV and PIV systems were constructed. By introducing a new factor called degree of reality, the real particles were easily separated from the ghost particle groups. Two flow fields, a ring vortex and an impinging jet, were measured by the constructed tomographic PTV and the conventional tomographic PIV. Eight image frames (two consecutive image frames for each camera) were used for the construction of threedimensional voxel images. The construction method used for the voxel images was MLOS-MART.     

Carbon contamination analysis and its effect on extreme ultra violet mask imaging performance using coherent scattering microscopy/in-situ accelerated contamination system

The coherent scattering microscopy/in-situ accelerated contamination system (CSM/ICS) is a developmental metrology tool designed to analyze the impact of carbon contamination on the imaging performance. It was installed at 11B EUVL beam-line of the Pohang Accelerator Laboratory (PAL). Monochromatized 13.5 nm wavelength beam with Mo/Si multilayer mirrors and zirconium filters was used. The CSM/ICS is composed of the CSM for measuring imaging properties and the ICS for implementing acceleration of carbon contamination. The CSM has been proposed as an actinic inspection technique that records the coherent diffraction pattern from the EUV mask and reconstructs its aerial image using a phase retrieval algorithm. To improve the CSM measurement accuracy, optical and electrical noises of main chamber were minimized. The background noise level measured by CCD camera was approximately 8.5 counts (3 sigma) when the EUV beam was off. Actinic CD measurement repeatability was <1 A (3 sigma) at 17.5 nm line and space pattern. The influence of carbon contamination on the imaging properties can be analyzed by transferring EUV mask to CSM imaging center position after executing carbon contamination without a fine alignment system. We also installed photodiode and ellipsometry for in-situ reflectivity and thickness measurement. This paper describes optical design and system performance observed during the first phase of integration, including CSM imaging performance and carbon contamination analysis results.     

Synthesis,calcination and characterization of Nanosized ceria powders by self-propagating room temperature method

Nanometric ceria powders with fluorite-type structure were obtained by applying self-propagating room temperature method. The obtained powders were subsequently thermally treated (calcined) at different temperatures for different times. Powder properties such as specific surface area, crystallite size, particle size and lattice parameter have been studied. Roentgen diffraction analysis (XRD), BET and Raman scattering measurements were used to characterize the as-obtained (uncalcined) powder as well as powders calcined at different temperatures.It was found that the average diameter of the as-obtained crystallites is in the range of 3–5 nm whereas the specific surface area is about 70 m²/g. The subsequent, 15 min long, calcination of as-obtained powder at different temperatures gradually increased crystallite size up to ～60 nm and reduced specific surface down to 6 m²/g. Raman spectra of synthesized CeO_2?y depicts a strong red shift of active triply degenerate F_2 g mode as well as additional peak at 600 cm^?1. The frequency of F_2 g mode increased while its line width decreased with an increase in calcination temperature. Such a behavior is considered to be the result of particle size increase and agglomeration during the calcination. After the heat treatment at 800 °C crystallite size reached value larger than 50 nm. Second order Raman mode, which originates from intrinsic oxygen vacancies, disappeared after calcination.