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Shim, Jae-Hyeok,Hwang, Byoungchul,Lee, Myoung-Gyu,Lee, Joonho Elsevier 2018 CALPHAD, computer coupling of phase diagrams and t Vol.62 No.-
<P><B>Abstract</B></P> <P>In order to satisfy the demands for both safety and global warming reduction, a high-strength seismic reinforced steel bar is required in the structural steel market. Recent developments in computational thermodynamics and related application software have made it possible to design a suitable material as well as support engineers of steel manufacturing companies in the production of the designed material with minimum benchmarks in practical operations. This paper reports our recent success in developing grade 600 MPa reinforced steel bars for seismic safety in South Korea. First, conventional alloy design based on CALPHAD-type computational thermodynamics was carried out. For this purpose, a typical alloy system of Fe-0.30C-0.23Si-1.37Mn-0.14V-0.22Cu (in wt%) was selected, and thermodynamic and kinetic calculations were carried out using MatCalc and JMatPro software. Second, in order to reduce V content in the steel for economic reasons, a cooling process designed using finite element (FE) simulation based on the thermodynamic database was performed. For this application, Fe-0.34C-0.22Si-1.34Mn-0.04 V (in wt%) alloy was chosen, and the FE software ABAQUS was applied for modeling the TempCore process. The mechanical properties of the steel products with a diameter of 32 mm produced based on the simulated results satisfy the required properties for grade 600 MPa seismic reinforced steel bars.</P>
Lead Screw Driven Revolute Joint for Remote Center of Motion Mechanism
Seongbo Shim,Hyojeong Cha,Joonho Seo 제어로봇시스템학회 2020 제어로봇시스템학회 국제학술대회 논문집 Vol.2020 No.10
The purpose of the Remote Center of Motion (RCM) mechanism is to mechanically guide the orientation of the medical instrument inserted into the skin. In order to avoid a collision between the inserted instrument and a patient, each rotation range, pitch and roll, should not exceed 180°. In the tilting mechanism for the pitch rotation, not only RCM but also the limitation of the rotation range is generally achieved by the mechanical structure. However, since the roll rotation is generally implemented by a typical revolute joint using rotary motor, the rotation range must be confined by a software based method. To avoid the risk of electrical malfunctions and ensure the surgical safety, both rotation ranges should be confined by the mechanism itself. In this paper, we proposed a new type of revolute joint using a lead screw driven actuator. The proposed mechanism mechanically confined the range of 140°. In addition, the proposed revolute joint can improve the angular resolution and reduce the applied load torque compared to the conventional joint. Through a series of static analyses, it was confirmed that the resolution is improved by approximately 75 times and the load torque is reduced by approximately 42 times.
Formation of ZnO nanocones using wet chemical etching of ZnO nanorods in an aqueous solution of HCl.
Bae, Joonho,Shim, Ee-Le,Park, T Y,Kang, C J,Choi, Young Jin American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.12
<P>In this report, a simple wet chemical etching of ZnO nanorods to fabricate large area ZnO nanocones is demonstrated. The cone-like morphology formation utilizes anisotropic etching rate on the different crystal planes of ZnO nanorods in an aqueous solution of HCl (HCl [aq]). To form ZnO nanocones, single crystalline ZnO nanorods with a flat hexagonal shape are synthesized on p-Si(100) using hydrothermal method at 90 degrees C and then, are immersed in HCl [aq]. Electron microscopy reveals that the HCl [aq] treatment of ZnO nanorods significantly etched sidewalls of nanorods, resulting in the cone-like morphology formation. The nanocone formation is the most noticeable when the etching occurred in HCl [aq] with a pH of 2.5-3.0 for 5 min etching time. Geometrical analysis using the electron microscopy reveals that the sidewall of a ZnO nanocone have formed a plane indexed as (0-111) after the etching process.</P>
Bae, Joonho,Shim, Ee Le,Park, Yeonsang,Kim, Hyunjin,Kim, Jong Min,Kang, C J,Choi, Y J IOP Pub 2011 Nanotechnology Vol.22 No.28
<P>We report, for the first time, direct observation of enhanced cathodoluminescence (CL) emissions from ZnO nanocones (NCs) compared with ZnO nanowires (NWs). For direct and unambiguous comparison of CL emissions from NWs and nanocones, periodic arrays of ZnO NW were converted to nanocone arrays by our unique HCl [aq] etching technique, enabling us to compare the CL emissions from original NWs and final nanocones at the same location. CL measurements on NW and nanocone arrays reveal that emission intensity of the nanocone at ∼ 387 nm is over two times larger than that of NW arrays. The enhancement of CL emission from nanocones has been confirmed by finite-difference time-domain simulation of enhanced light extraction from ZnO nanocones compared to ZnO NWs. The enhanced CL from nanocones is attributed to its sharp morphology, resulting in more chances of photons to be extracted at the interface between ZnO and air. </P>