Effect of microwave sintering on the microstructure and electrical properties of low-voltage ZnO varistors

Coarse-grained ZnO varistors for low-voltage applications were prepared by microwave sintering technique under different soaking times of 5–150?min. For comparison, a low-voltage ZnO varistor was also prepared through a conventional sintering process. Microwave sintering remarkably enhanced the grain growth rate of ZnO varistors. Average grain size of the sample prepared by microwave sintering in 15?min was about 20?µm, which is similar to the grain size of sample prepared conventionally in 150?min time. In addition to grain growth, an increase in microwave sintering time led to precipitation of zinc titanate (Zn₂TiO₄) on the top surface of samples which sintered for long dwell times. X-ray diffraction and scanning electron microscopy results from different points of the samples declared that precipitation of Zn₂TiO₄ phase is due to the high rate of bismuth evaporation of Bi-rich liquid from top surface and the reaction between remaining titanium ions on the surface with ZnO. The results showed that increasing sintering time from 5 to 150?min increased the grain size from 14 to 33?µm, consequently, the breakdown field decreased from 90 to 27?V/mm, respectively. These changes led to a switch in the varistor application, from low to very low voltage.     

Nanosilicon carbide/hydroxyapatite nanocomposites: structural,mechanical and in vitro cellular properties

In this study, bioceramic nanocomposites were synthesized by sintering compacted bodies of hydroxyapatite (HA) mixed with 5 or 15 wt% nanosilicon carbide at 1100 or 1200°C in a reducing atmosphere. Pure hydroxyapatite was also prepared for comparison. Phase compositions, structural and physical properties of the composites were studied using appropriate techniques. Some in vitro biological properties of the composites were also investigated by using newrat calvaria osteoblastic cells. X-ray diffraction analysis indicated that tricalcium phosphate (TCP) comprising negligible α-TCP and considerable β-TCP were formed in composites during sintering meanwhile hydroxyapatite and silicon carbide (SiC) were also existed in the composition. Based on the results, that composite made of 5 wt% nanosilicon carbide exhibited higher bending strength, fracture toughness and bulk density than pure HA and composite with 15 wt% silicon carbide. The scanning electron microscopy coupled with energy dispersive X-ray analysis revealed that the addition of nanosilicon carbide suppressed the grain growth and yielded a feature of island-type clusters consisting of blistered calcium phosphate (HA and TCP) and SiC grains. Also, in this study, better proliferation rate and alkaline phosphatase activity were observed for the osteoblastic cells seeded on top of the composites compared to pure HA. Overall, the results indicated that the composite of 95 wt% hydroxyapatite and 5 wt% SiC exhibited better mechanical and biological properties than pure HA and further addition of SiC failed strength and toughness.     

Synthesis and Analysis of Triphenylamine: A Review

In this paper, synthesis and characteristic of arylamine‐type molecules, particularly triphenylamine are discussed. An overview of the physical properties and chemical characteristics of these types of molecules is provided. Different synthesis methods and mechanisms involved for the production of these molecules and their analysis by HPLC are presented. Finally, a brief note about their purification is presented.     

Characterization and solubility measurement and prediction of selected arylamines in hexane, methanol and benzene

The solubility of nine arylamine molecules in benzene, methanol and hexane was measured. These molecules were: triphenylamine, N-(4-methyl phenyl) N,N bis phenyl amine, N-(3-methyl phenyl) N,N bis phenyl amine, N,N-bis(4-methyl phenyl) N-phenyl amine, N,N-bis(3-methyl phenyl) N-phenyl amine, tritolylamine (N,N,N-tris-(4-methylphenyl)amine), N,N-bis-(4-methylphenyl)-N-(3-methylphenyl)amine, N,N-bis-(3-methylphenyl)-N-(4-methylphenyl)amine, and N,N,N-tris-(3-methylphenyl)amine. The solubility of these molecules was estimated using ideal solution theory, the Hildebrand equation, and UNIQUAC method. The ideal solution theory and the Hildebrand equation were not able to estimate solubility with high precision. However, UNIQUAC method was able to estimate the solubility with good accuracy. It was found that substitution of methyl group regardless of its number in aryl ring increases the solubility. In addition, meta-substitution always results in higher solubility regardless of the nature of the solvent. Physical properties, as well as electrochemical properties of these materials were also provided. Based on these data, the most promising candidates for device preparation should be: mTTA, TTA, mmmTTA, and mono-TPA. However, the only way to prove the above ranking would be to test the candidates in actual devices, which is outside the scope of this paper.     

A Realistic Timing Test Model and Its Applications in High-Speed Interconnect Devices

This paper extends the timing test model in [5] to be more realistic by including the effects of the test fixtures between a device under test and a tester. The paper enables analyzing the trade-offs that arise between the predicted yield and the required overall test environment timing accuracy (OTETA) which involves the tester overall timing accuracy (OTA) and the test fixtures' impacts. We specifically focus on the application of the extended model to predict the test yield of standard high-speed interconnects, such as PCI Express, Parallel/Serial RapidIO, and HyperTransport. The extended model reveals that achieving an actual yield of 80% with a test escape of 300 DPM (Defects Per Million) requires an equivalent OTETA that is about half the acceptable absolute limit of the tested parameter. Baosheng Wang received his B.S. degree from Beijing University of Aeronautics and Astronautics (BUAA), Beijing, P.R. China, in 1997 and M.S. degree from Precision Instrument & Mechanical Engineering from the Tsinghua University, Beijing, P. R. China in 2000. In 2005, he received his Ph.D. degree in Electrical Engineering from the University of British Columbia (UBC), Vancouver, BC, Canada. During his Master study, he was doing MEMS, Micro Sensors and Digital Signal processing. From 2000 to 2001, he worked in Beijing Gaohong Telecommunications Company as a hardware engineer in ATM technology. Currently, he is a Design-for-Test (DFT) engineer at ATI Technologies Inc., Markham, Ontario, Canada. He publishes widely at international conferences and journals. His primary research interests are time-driven or timing-oriented testing methodologies for System on-a-Chip (SoC). These fields include test time reduction for SRAMs, accelerated reliability test for non-volatile memories, yield analysis for SoC timing tests, SoC path delay timing characterization and embedded timing measurements. Andy Kuo is currently a Ph.D student of System on a Chip (SoC) Research Lab at the Department of Electrical and Computer Engineering, University of British Columbia. He received his M.A.Sc. and B.A.Sc in electrical and computer engineering from University of British Columbia and University of Toronto in 2004 and 2002 respectively. His research interests include high-speed signal integrity issues, jitter measurement, serial communications. Touraj Farahmand received the B.Sc. degree in Electrical Engineering from Esfahan University of Technology, Esfahan, Iran in 1989 and the M.Sc. in Control Engineering from Sharif university of Technology, Tehran, Iran in 1992. After graduation, he joined the Electrical and Computer Research center of Esfahan University of Technology where he was involved in the DSP algorithm development and design and implementation of the control and automation systems. Since October 2001, he has been working in the area of high-speed signal timing measurement at SoC (System-on-a-Chip) lab of UBC (University of British Columbia) as a research engineer. His research interests are signal processing, jitter measurement, serial communication and control. André Ivanov is Professor in the Department of Electrical and Computer Engineering, at the University of British Columbia. Prior to joining UBC in 1989, he received his B.Eng. (Hon.), M. Eng., and Ph.D. degrees in Electrical Engineering from McGill University. In 1995–96, he spent a sabbatical leave at PMC-Sierra, Vancouver, BC. He has held invited Professor positions at the University of Montpellier II, the University of Bordeaux I, and Edith Cowan University, in Perth, Australia. His primary research interests lie in the area of integrated circuit testing, design for testability and built-in self-test, for digital, analog and mixed-signal circuits, and systems on a chip (SoCs). He has published widely in these areas and holds several patents in IC design and test. Besides testing, Ivanov has interests in the design and design methodologies of large and complex integrated circuits and SoCs. Dr. Ivanov has served and continues to serve on numerous national and international steering, program, and/or organization committees in various capacities. Recently, he was the Program Chair of the 2002 VLSI Test Symposium (VTS'02) and the General Chair for VTS'03 and VTS'04. In 2001, Ivanov co-founded Vector 12, a semiconductor IP company. He has published over 100 papers in conference and journals and holds 4 US patents. Ivanov serves on the Editorial Board of the IEEE Design and Test Magazine, and Kluwer's Journal of Electronic Testing: Theory and Applications. Ivanov is currently the Chair of the IEEE Computer Society's Test Technology Technical Council (TTTC). He is a Golden Core Member of the IEEE Computer Society, a Senior Member of the IEEE, a Fellow of the British Columbia Advanced Systems Institute and a Professional Engineer of British Columbia. Yong Cho received the B.S. degree from Kyung Pook National Unviersity, Korea, in 1981 and the M.S. degree from in electrical and computer engineering from the University of South Carolina, Columbia, S.C., in 1988 and the Ph.D. degree in electrical engineering and applied physics from Case Western Reserve University, Cleveland, OH, in 1992. He is currently a Professor with the Department of Electronics Engineering, Konkuk University, Seoul, Korea. His recent research interests include SoC Design and Verification, H/W and S/W co-design, and embedded programming on SoC. Sassan Tabatabaei received his PHD in Electrical Engineering from the University of British Columbia, Vancouver, Canada in 2000. Since then, he has held several senior technical positions at Vector12 Corp, Guide Technology, and Virage Logic. His professional and research interests include mixed-signal design and test, and signal integrity and jitter test methodologies for high-speed circuits and multi-Gbps serial interfaces. He has published several papers and holds a US patent in the area of timing and jitter measurement. Currently, he holds the position of the director for embedded test at Virage Logic Corporation.     

Mechanosynthesis of nanocomposites in TiO2–B2O3–Mg–Al quaternary system

The mechanochemical behavior of TiO₂–B₂O₃–Mg–Al quaternary system to synthesize various composite nanopowders was studied. A mixture of boron oxide and titanium dioxide powders along with different amounts of magnesium and aluminum was milled using a high-energy planetary ball mill to persuade necessary conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR). Results showed that the formation of composite nanopowders was influenced strongly by the reducing agents content. In the absence of Al (100 wt% Mg), TiB₂ nanopowder was formed after 34 min of milling. In the presence of x wt% Mg–y wt% Al (x=40 and 70; y=100−x), mechanical activation was completed after 37–40 min which caused the formation of TiB₂–MgFe_0.6Al_1.4O₄ composite nanopowders. In the case of 10 wt% Mg–90 wt% Al, a ternary nanocomposite (TiB₂–MgAl₂O₄–Al₂O₃) was produced after 43 min of milling. Besides, Al₂O₃–TiB₂ nanocomposite was formed after 90 min of milling in the absence of Mg (100 wt% Al). From the SEM images, mechanochemical process reached a steady state after short milling times where the particles have become homogenized in size and shape. The reaction mechanism steps were proposed to clarify the reactions occurring during mechanochemical process.     

Correction to: Employing singular value decomposition and similarity criteria for alleviating cold start and sparse data in context-aware recommender systems

Electronic Commerce Research -     

New Insights of the Glycine-Nitrate Process For the Synthesis of Nano-Crystalline 8YSZ

Nano-crystalline 8YSZ was synthesized by the glycine-nitrate process in a muffle furnace using zirconyl nitrate and yttrium nitrate as sources of oxidants. The effect of changing the elemental stoichiometric coefficient over a wide range (0.756–1.605) on the product characteristics (crystallite size, percent unreacted, surface area) has been investigated. It is demonstrated that the combustion reaction proceeds most efficiently in the fuel-lean region. A novel and simple mathematical model is presented that allows to evaluate the thickness of the sheet-like particles of the foamy final product based on BET data. The calculated thickness values are in good agreement with the experimental data. For the first time, the effect of using ammonium nitrate as a combustion aid for the stoichiometric precursor composition has been studied. The optimum amount of combustion aid addition has been determined.     

Seismic design and assessment of structures with viscous dampers at limit state levels: Focus on probability of damage in devices

During large earthquakes, the seismic demand of viscous dampers may exceed their capacity. In this regard, current design codes must consider extreme conditions and preserve the damper at limit state levels. Here, by adjusting the damping coefficient, a procedure is introduced to mitigate device damages during severe earthquakes. To assess the procedure, 15 special moment resisting frames with a different number of stories (two, four, and eight) were designed by three methods: The recommended novel procedure, the seismic provisions of ASCE7, and the procedure proposed by Miyamoto et al. 1 for structures, installed with supplemental damping devices. A series of incremental dynamic analyses were then performed by modeling the limit state behavior of viscous dampers. Results indicated that the novel method reduces the damage probability of dampers as well as the maximum demands on the structure at different seismic hazard levels.