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Above-gap Conductance Anomaly Studied in Superconductor-Graphene-Superconductor Josephson Junctions
Jae-Hyun Choi,이후종,도용주 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.1
We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. At low voltage bias, we observed the conventional proximity-coupled Josephson effect, such as supercurrent flow through graphene, a sub-gap structure of differential conductance due to Andreev reflection, and a periodic modulation of the critical current Ic when a perpendicular magnetic field H is applied to the graphene. For high bias above the superconducting gap voltage, however, we observed an anomalous jump of the differential conductance, the voltage position of which is sensitive to the backgate voltage Vg. Our extensive study with varying Vg, temperature, and H reveals that the above-gap structure takes place at a characteristic power P*, irrespective of Vg, for a given junction. The temperature and the H dependences of P are well explained by an increase in the electron temperature in graphene.
Design of an FMCW Radar Altimeter for Wide-Range and Low Measurement Error
Jae-Hyun Choi,Jong-Hun Jang,Jin-Eep Roh Institute of Electrical and Electronics Engineers 2015 IEEE Transactions on Instrumentation and Measureme Vol. No.
<P>This paper presents the design of a frequency-modulated continuous-wave radar altimeter with wide altitude range and low measurement error. A wide altitude range is attained by employing an optical delay in the path of transmission to reduce the dynamic range of the altitude being measured. The transmitter power and receiver gain are also controlled to facilitate a reduction in the dynamic range of the received power. In addition, low measurement error was obtained by improving the sweep linearity using a direct digital synthesizer and minimizing phase noise by employing a phase-locked loop with the offset frequency driven by a reference clock (Ref_CLK). The performance of the radar altimeter was experimentally verified using an optical-delay simulator, which provided a delay time corresponding to a 200-m radar distance. To assess the performance of the system in a realistic setting, the radar altimeter was tested using a crane setup. The crane test demonstrated that the design described in this paper resulted in a reduced measurement-error rate.</P>
Efficient Analysis of IT Facility Security Vulnerability Topics by Utilizing R Programming
Jaehyun Choi,Hoojin Lee 대한전자공학회 2019 IEIE Transactions on Smart Processing & Computing Vol.8 No.3
The recent development of domestic information and communications technologies (ICT) has made it possible to use the Internet anywhere in society, consequently exposing various security threats. Specifically, there is frequent leakage of personal information as well as system infringements, which are mainly caused by either internal or external security weaknesses. Besides, there is no exception for private companies or public corporations that have well-equipped security systems. In order to adequately prepare countermeasures against infringement incidents, security officers have been concerned every year. Hence, the government has designated information and communications infrastructures for major national facilities as a measure against the security threats and, since 2001, has enacted and promulgated the Information and Communication Infrastructure Protection Act. In this paper, we attempt to analyze the trends associated with the vulnerability status of information technology (IT) facilities, and to evaluate the weak points in IT facilities. And finally, we derive the most-mentioned vulnerabilities by effectively utilizing the R program to obtain statistical calculation and visualization, and thus, a common denominator for IT environments.
Case Report : Paranoid Adipsia-induced Severe Hypernatremia and Uremia treated with Hemodialysis
( Jae Hyun Choi ),( Hee Seung Lee ),( Sun Moon Kim ),( Hye Young Kim ),( Soon Kil Kwon ) 대한전해질학회 2013 Electrolytes & Blood Pressure Vol.11 No.1
We describe a patient with severe hypernatremia and uremia caused by paranoid adipsia who was treated successfully with hydration and hemodialysis. A previously healthy 40-year-old woman developed the paranoid idea that her water was poisoned, so she refused to drink any water. On admission, her blood urea nitrogen was 208mg/dL, creatinine 4.90mg/dL, serum osmolality 452mOsm/L, serum sodium 172mEq/L, urine specific gravity ≥1.030, urine osmolality 698mOsm/L, and urine sodium/potassium/chloride 34/85.6/8mEq/L. We diagnosed her with uremic encephalopathy and started intravenous dextrose, but the sodium correction was incomplete. She underwent two sessions of hemodialysis to treat the uremic encephalopathy and hypernatremia, and recovered fully without neurological sequelae. Although the standard treatment for severe hypernatremia is hydration, hemodialysis can be an additional treatment in cases of combined uremic encephalopathy.
Jae Hyun Choi,Jung Yoon,Sungkun Chung,Namhyeong Kim,HangJin Jo Korean Nuclear Society 2023 Nuclear Engineering and Technology Vol.55 No.7
In this study, the validity of reducing the number of gas turbine stages designed for a nitrogen Brayton cycle coupled to a sodium-cooled fast reactor was assessed. The turbine performance was evaluated through computational fluid dynamics (CFD) simulations under different off-design conditions controlled by a reduced flow rate and reduced rotational speed. Two different multistage gas turbines designed to extract almost the same specific work were selected: two- and three-stage turbines (mid-span stage loading coefficient: 1.23 and 1.0, respectively). Real gas properties were considered in the CFD simulation in accordance with the Peng-Robinson's equation of state. According to the CFD results, the off-design performance of the two-stage turbine is comparable to that of the three-stage turbine. Moreover, compared to the three-stage turbine, the two-stage turbine generates less entropy across the shock wave. The results indicate that under both design and off-design conditions, increasing the stage loading coefficient for a fewer number of turbine stages is effective in terms of performance and size. Furthermore, the Ellipse law can be used to assess off-design performance and increasing exponent of the expansion ratio term better predicts the off-design performance with a few stages (two or three).
Service Discovery and Backup Technique for Distributed Systems based on OSGi
Jae-Hyun Choi,Jea-Won Park,Jong-Bae Kim 한국정보통신학회 2014 2016 INTERNATIONAL CONFERENCE Vol.6 No.1
A Java-based service platform OSGi (Open Service Gateway Initiative) has been used in many areas including mobile phones, embedded applications, and home area networks. Although, it is not suitable for enterprise areas because it does not support for auto-managing distributed systems and does not provide a backup strategy. A service location protocol as a dynamic configurations protocol can be used to auto-manage the distributed systems, but the protocol cannot ensure the stability of distributed systems. In this paper, we present a technique of automated service discovery in distributed systems based on OSGi. The proposed technique defines four components and four type profiles to achieve automated service discovery and backup functions. By using the technique, OSGi could be widely used for developing distributed systems.