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Yoo, Byung-Han,Min, Byung-Kwon,Lee, Sang-Jo 한국정밀공학회 2010 International Journal of Precision Engineering and Vol.11 No.4
Electrical discharge machining (EDM) is a process that can be used effectively to machine conductive metals regardless of their hardness. In the EDM process, material removal occurs because of the thermal energy of the plasma channel between the electrode and the workpiece. During EDM, the electrode as well as the workpiece is abraded by the thermal energy. Tool wear adversely affects the machining accuracy and increases tooling costs. Many previous studies have focused on mitigating the problems of tool wear by investigating various EDM parameters. In this study, the tool wear problem was investigated on the basis of the mobilities of electrons and ions in the plasma channel. The material removal volumes of both the electrode and the workpiece were compared as functions of the gap voltage. The material removal difference according to the capacitance was also investigated. The tool wear ratio was calculated under different EDM condition and an EDM conditions for reducing the tool wear ratio was suggested.
Predictive link trigger mechanism for seamless handovers in heterogeneous wireless networks
Yoo, Sang-Jo,Cypher, David,Golmie, Nada John Wiley Sons, Ltd. 2009 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.9 No.5
<P>Effective and timely link-layer trigger mechanisms can significantly influence the handover performance. The handover process will not perform the correct decision and execution unless adequate and timely link-layer trigger information is delivered. In this paper, a predictive link trigger mechanism for seamless horizontal and vertical handovers in heterogeneous wireless networks is proposed. Unlike previous link trigger algorithms based on pre-defined signal level thresholds, the link layer triggers in this study are adaptively and timely fired in accordance with the network conditions. Firstly, the time required to perform a handover is estimated based on the neighboring network conditions. Secondly, the time to trigger a Link_Going_Down to initiate a handover is determined using a least mean square linear prediction in which the prediction interval (k<SUB>h</SUB>) is dynamically determined based on the estimated handover time. An upper bound for the packet loss rate during a handover is derived for a Gaussian shadowing channel. A manner in which this approach can be applied to IEEE 802.21 is shown in media independent handover scenarios. Simulation results of the proposed predictive link triggering mechanism show that it provides a timely proactive handover. The packet loss rate observed in a Gaussian shadowing channel remains low during a handover. Copyright © 2008 John Wiley & Sons, Ltd.</P>
Blind nasal intubation as an alternative to difficult intubation approaches
Yoo, Hwanhee,Choi, Jae Moon,Jo, Jun-young,Lee, Sukyung,Jeong, Sung-Moon The Korean Dental Society of Anesthsiology 2015 Journal of Dental Anesthesia and Pain Medicine Vol.15 No.3
Airway difficulties are a major concern for anesthesiologists. Even though fiberoptic intubation is the generally accepted method for management of difficult airways, it is not without disadvantages-requires patient cooperation, and cannot be performed on soiled airway or upper airways with pre-existing narrowing pathology. Additionally, fiberoptic bronchoscopy is not available at every medical institution. In this case, we encountered difficult airway management in a 71-year-old man with a high Mallampati grade and a thick neck who had undergone urologic surgery. Several attempts, including a bronchoscope-guided intubation, were unsuccessful. Finally, blind nasal intubation was successful while the patient's neck was flexed and the tracheal cartilage was gently pressed down. We suggest that blind nasal intubation is a helpful alternative in difficult airway management and it can be a lifesaving technique in emergencies. Additionally, its simplicity makes it a less expensive option when advanced airway technology (fiberoptic bronchoscopy) is unavailable.
DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks
Yoo, Sang-Jo,Nan, Hao,Hyon, Tae-In John Wiley Sons, Ltd. 2009 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.9 No.5
<P>The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.</P>
QoS Supported Dynamic Channel Scanning for Seamless Handovers in Wireless Networks
YOO, Sang-Jo,GOLMIE, Nada The Institute of Electronics, Information and Comm 2009 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.92 No.6
<P>Channel scanning is an important aspect of seamless handovers since it is required in order to find a target point of attachment (PoA). However, channel scanning in single radio devices may cause severe service disruptions with the current PoA so that the provided QoS will be further degraded during a handover. In this letter, we propose a dynamic channel scanning algorithm that supports QoS. Simulation results show that the proposed mechanism reduces the service disruptions and provides the desired QoS to users during the scanning period.</P>
Sang Jo Han,장성일,Sung Hwan Yoo,이동기 소화기인터벤션의학회 2020 Gastrointestinal Intervention Vol.9 No.1
Liver transplantation (LT) is a viable treatment for fatal end-stage liver disease. Anastomotic bile leakage and anastomotic stricture are considered as major post-LT complications. Stent insertion by endoscopic retrograde cholangiopancreatography and percutaneous transhepatic biliary drainage is the conventional treatment for post-LT anastomotic biliary stricture. In cases in which these conventional modalities fail, magnet compression anastomosis (MCA) can be applied. We reported a case in which post-LT bile leakage and anastomotic stricture were treated by MCA and using a fully covered self-expandable metal stent (FCSEMS). The FCSEMS was removed 3 months later, at which time the stricture and the leakage had resolved.
Policy-based scanning with QoS support for seamless handovers in wireless networks
Yoo, Sang-Jo,Golmie, Nada John Wiley Sons, Ltd. 2010 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.10 No.3
<P>Supporting seamless handovers between different wireless networks is a challenging issue. One of the most important aspects of a seamless handover is finding a target network and point of attachment (PoA). This is achieved by performing a so-called channel scanning. In most handovers, such as between universal mobile telecommunications system (UMTS), wireless local area network (WLAN), and worldwide interoperability for microwave access (WiMAX), channel scanning causes severe service disruptions with the current PoA and degrades the quality of service (QoS) during the handover. In this paper, a new architecture for QoS supported scanning that can be generalized to different wireless networks is proposed. It employs two techniques. The first is for determining a policy-based order for the channel scanning sequence. With this technique, depending on the network costs and user requirements, the policy engine determines the channel scanning order for different network types and sets up a scanning sequence of PoAs for a given network type. This policy-based scanning order provides a faster discovery of the target PoA that meets the QoS demands of the user. The second technique consists of a QoS supported dynamic scanning algorithm where the scanning frequency and duration are determined based on the user QOS requirements. Most importantly, the scanning duration is scheduled to guarantee the user QoS requirements while the scan progresses. Simulation results show that the proposed mechanism achieves relatively short service disruptions and provides the desired quality to users during the scanning period. Copyright © 2009 John Wiley & Sons, Ltd.</P> <B>Graphic Abstract</B> <P>In this paper, a new architecture for QoS supported scanning that can be generalized to different wireless networks is proposed. It employs two techniques. The first is for determining a policy-based order for the channel scanning sequence depending on the network costs and user requirements. The second technique consists of a QoS supported dynamic scanning algorithm where the scanning frequency and duration are determined based on the user QoS requirements. <img src='wiley_img/15308669-2010-10-3-WCM774-gra001.gif' alt='wiley_img/15308669-2010-10-3-WCM774-gra001'> </P>