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Now showing items 1 - 16 of 338

  • EFFECT OF INITIAL MICROSTRUCTURE ON HOT FORGING OF MG ALLOYS

    KWON, Y.   LEE, Y.   KIM, S.   LEE, J.  

    Magnesium alloys still have a lot of technical challenges to be solved for more applications. There have been many research activities to enhance formability of magnesium alloys. One is to design new alloy composition having better formability. Also, low formability of wrought alloys can be improved by optimizing the processing variables. In the present study, effect of process variables such as forging temperature and forging speed were investigated to forgeability of three different magnesium alloys such as AZ31, AZ61 and ZK60. To understand the effect of process variables more specifically, both numerical and experimental works have been carried out on the model which contains both upsetting and extrusion geometries. Forgeability of magnesium alloys was found to depend more on the forging speed rather than temperature. Forged sample showed a significant activity of twinning, which was found to be closely related with flow uniformity.
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  • The topology and morphology of bicontinuous interfaces during coarsening

    Kwon, Y.   Thornton, K.   Voorhees, P. W.  

    We investigate the late-stage coarsening of three-dimensional two-phase mixtures via conserved dynamics over a range of volume fractions. We find that the phases remain bicontinuous at volume fractions as low as 36%. The morphologies of these bicontinuous structures depend on the volume fraction, and they differ from the corresponding structure of a symmetric mixture coarsening via nonconserved dynamics. However, these structures have nearly the same scaled genus of approximately 0.13, possibly indicating a universality in the topology of bicontinous structures undergoing self-similar coarsening. Copyright (C) EPLA, 2009
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  • Sensor-based Remote Quality Control Application in Automotive Components Assembly

    Kwon, Y.   Park, Y.   Hong, J.   Park, S. C.  

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  • Double sided arc welding of AA5182 aluminium alloy sheet

    Kwon, Y.   Weckman, D. C.  

    The feasibility and merits of using the double sided arc welding (DSAW) process for making square welds in 1.2 mm thick AA5182-O aluminium sheets in the butt-joint configuration for applications such as tailor welded blanks (TWB) has been studied. Full penetration, conduction mode DSAW welds were made using a balanced square wave AC, constant current power supply at welding speeds of 30 to 40 mm s(-1) when using 2.1 kW welding power and between 40 and 60 mm s(-1) when using 3.4 kW welding power. There was good cathodic cleaning of the oxide on both sides of the sheet and the weld bead quality and properties were excellent. All welds exhibited a columnar to equiaxed grain transition with up to 40% equiaxed grain area. The DSAW process was found to be capable of producing welds of equal or better quality and at comparable welding speeds to those produced using more traditional welding processes for TWB applications.
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  • Interference-Aware Transmission Power Control for Wireless Sensor Networks

    KIM, J.   KWON, Y.  

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  • Self-oscillating current-fed inverter with low switching loss for wireless power transfer

    Kwon, Y.   Ahn, D.  

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  • A Study on the Changes of China\"s FDI Policies after WTO: Implications for Korean Firms

    Kwon, Y.   Zhou, W.  

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  • High-efficiency CMOS stacked-FET power amplifier for W-CDMA applications using SOI technology

    Kwon, Y.   Woo, J.   Jeon, M.-S.   Kim, U.  

    A linear CMOS power amplifier (PA) is developed for wideband code-division multiple-access (W-CDMA) application using 0.18 mum silicon-on-insulator (SOI) technology. By adopting a quadruple-stacked FET structure, 1W of output power is achieved at 4V supply voltage. A negative capacitance circuit is employed to maximise the efficiency of the PA by cancelling out the excessive capacitance at the source terminal of the common-gate stage. Besides, a lineariser based on the variable capacitor circuit is added to reduce the inherent AM-PM distortion of the CMOS FET. Using W-CDMA modulation at 837MHz, the fabricated PA module delivers a PAE of 47.5% and an adjacent channel leakage ratio of - 36dBc at the output power of 27.1dBm.
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  • Safety of transorally-inserted anvil for esophagojejunostomy in laparoscopic total gastrectomy

    Kwon, Y.   Cho, S.-I.   Kwon, Y.-J.   Yang, K.-S.   Jang, Y.-J.   Kim, J.-H.   Park, S.-H.   Mok, Y.-J.   Park, S.  

    Background: To assess the safety of transorally-inserted anvil (TOA) for use during esophagojejunostomy (EJ) reconstruction during laparoscopic total gastrectomy (LTG). Methods: Between March 2009 and December 2011, 39 consecutive open total gastrectomies (OTGs) and 36 LTGs using TOA for gastric cancer were comparatively evaluated. We investigated postoperative complications, using the Clavien-Dindo classification. To evaluate the effect of a learning period in using TOA for LTG, we also investigated shifts in the patterns of complications and changes in total operation time over the course of the study. Results: The patient characteristics at baseline were not different between both groups, except for the extent of lymphadenectomy (P < 0.001) and depth of tumor invasion (P = 0.003). Multivariate analysis revealed that TOA usage elevated the occurrence of infectious complications significantly (OR = 3.32, P = 0.042), but was not associated with El-related complications. TOA usage did not need a learning period for the length of time required to complete the operation, or the likelihood of developing an El-related or infectious complication. Conclusions: TOA use for El during LTG is relatively simple and easy enough not to require a learning period for surgeons. This procedure did not elevated the occurrence of El-related complications compared to circular stapling in open surgery, but it does require special prevention efforts to avoid infectious complications. (C) 2013 Elsevier Ltd. All rights reserved.
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  • Wafer Bonding Using Dielectric Polymer Thin Films in 3D Integration

    Kwon, Y.   Lu, J.-Q.   Kraft, R. P.   McDonald, J. F.   Gutmann, R.J.   Cale, T. S.  

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  • A case of cerebral venous sinus thrombosis associated with Crohn\"s disease: dilemma in management

    Kwon, Y.   Koene, R. J.   Cho, Y.  

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  • High-performance X-band MMIC LNAs using dry recessed PHEMTs

    Kwon, Y.   Sovero, E.A.   Deakin, D.S.   Higgins, J.A.  

    The authors report compact and low-DC-power LNAs using dry recessed PHEMTs. Dry recess and optimum circuit design were used to reduce the chip size and DC power consumption while improving uniformity and yield. Two-stage PHEMT LNAs showed a noise figure of 1.45dB at 10GHz with a 22dB gain. The active chip size was 0.9mm(2) and DC power consumption was 75mW.
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  • What Are the Differences in Sleep Skills Between Insomnia Patients with and Without Need of Hypnotics?

    Kwon, Y.   Jon, D.   Lee, K.   Kim, M.   Lee, S.   Yoon, B.   Kim, W.   Seo, J.   Bahk, W.  

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  • Association of sleep characteristics with atrial fibrillation: the Multi-Ethnic Study of Atherosclerosis

    Kwon, Y.   Gharib, S. A.   Biggs, M. L.   Jacobs, D. R.   Alonso, A.   Duprez, D.   Lima, J.   Lin, G.-M.   Soliman, E. Z.   Mehra, R.   Redline, S.   Heckbert, S. R.  

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  • Identification of rice variety using near infrared spectroscopy

    Kwon, Y.   Cho, R.  

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  • Stability constraints in the formulation of viscoelastic constitutive equations

    Kwon, Y.   Leonov, A.I.  

    This paper discusses the criteria for both global Hadamard and dissipative stabilities of viscoelastic constitutive equations (CEs) with instantaneous elasticity. In order to formulate as generally as possible the conditions of stability analyses, we used some unified forms for CEs of differential Maxwell-like and factorable single integral types. The obtained criteria formulate the constraints which have to be imposed on parameters or functions in CEs to avoid the unphysical instabilities in the whole range of Deborah numbers, independent of the flow situation. The problem of Hadamard stability for the viscoelastic CEs is reduced to that well known in the theory of nonlinear elasticity where the complete solution of the problem was found recently in an algebraic form. The criteria of dissipative stability, which have been established previously, are also discussed. When applied to many popular viscoelastic models, the combined stability criteria impose a set of such severe constraints that no single integral CE with time-strain separability proposed in the literature, could satisfy them, and only few differential models have proved to be stable.
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