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Highly Efficient Dual-Switch Hybrid Switching Supply Modulator for Envelope Tracking Power Amplifier
Dongsu Kim,Daehyun Kang,Jooseung Kim,Yunsung Cho,Bumman Kim IEEE 2012 IEEE microwave and wireless components letters Vol.22 No.6
<P>This letter describes a highly efficient dual-switch hybrid switching supply modulator for an envelope tracking power amplifier (PA). The supply modulator has a combined structure of a linear amplifier and a switching amplifier. For an improved efficiency, the switching amplifier employs two buck converters and realizes an adaptive slew rate control of the switching amplifier's current. An implemented envelope tracking PA delivers an efficiency of 39.1% at an output power of 27 dBm for long term evolution signal with 10 MHz channel bandwidth.</P>
A Highly Integrated Triple-Band RF Front-End Module for WiMAX Applications
KIM, Dongsu,KIM, Dong Ho,RYU, Jong In,PARK, Chong-Dae,KIM, Jun Chul,PARK, Jong Chul The Institute of Electronics, Information and Comm 2010 IEICE transactions on electronics Vol.93 No.8
<P>This paper presents a compact and highly integrated triple-band RF front-end module (FEM) for worldwide interoperability for microwave access (WiMAX) applications using multilayer low temperature co-fired ceramic (LTCC) technology. The proposed RF FEM is composed of a TX triplexer, an RX triplexer, and a TX/RX switch. Both TX and RX triplexers are fully embedded in an LTCC substrate and the TX/RX switch is placed on the substrate. The TX triplexer consists of 2- and 5-GHz lowpass filters, a 3-GHz highpass filter, and a matching circuit. On the other hand, the RX triplexer consists of miniaturized 2-, 3-, 5-GHz coupled-resonator bandpass filters and a matching circuit, which are stacked up for space saving. In TX path, the RF FEM provides an insertion loss of 1.8dB, 2.1dB and 2.5dB at 2-, 3-, and 5-GHz band, respectively, with a high second-harmonic suppression characteristic. In RX path, the RF FEM also provides a low insertion loss at three passbands with high attenuation at other passbands. The size of the proposed RF FEM is only 4.0mm × 5.0mm with a substrate thickness of 0.73mm. The measured results are in good agreement with the simulated results.</P>
Dongsu Kim,Gu Seomun,Jongho Yoon,Heejin Cho 대한설비공학회 2022 대한설비공학회 학술발표대회논문집 Vol.2022 No.11
This study develops an optimized HVAC control framework using the whole building energy simulation program (i.e., EnerguPlus) and functional mock-up unit (FMU) in the Python environment. To develop and implement this framwork, a building energy model using EnergyPlus was developed based on the existing test facility. The model was initially validated using measured data (e.g., indoor air temperature comparison) before implementing the co-simulation framework. For the co-simulation framework using EnergyPlus and FMU, there are four (4) steps: 1) a real-time weather file modification by FMU, 2) an optimization process (i.e., GenOpt application) based on one hour ahead prediction weather data, 3) an optimized signal point application to EnergyPlus IDF file, and 4) output extraction from the completed simulation within the functional mock-up interface (FMI) with Python. The weather file modification was performed based on onsite measured and obtained weather data values. This study adopted some weather data from the public weather station API. The GenOpt application was also implemented within the Python environment under a developed GUI automated workflow by modifying the GenOpt source code. The PMV-based control scheme is considered in this study to determine the optimized signal point. Based on such framework development. This study identifies that the co-simulation environment can predict hour-ahead loads by considering optimized thermal comfort and real-time weather data. Such predicted outputs (e.g., thermal loads and setpoints) can be expected to use for further building energy management, such as BEMS, by applying an HVAC control scheme. Additionally, the developed framework techniques will help to be a key solution to implement the digital twins of smart homes and buildings.
STRONG INFLUENCE OF THE GALACTIC MAGNETIC FIELD ON THE PROPAGATION OF ULTRA-HIGH ENERGY COSMIC RAYS
KIM, JIHYUN,KIM, HANG BAE,RYU, DONGSU The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
The galactic magnetic field (GMF) and the intergalactic magnetic field (IGMF) affect the propagation of ultra-high energy cosmic rays (UHECRs) from the source to us. Here we examine the influences of the GMF/IGFM and the dependence of their sky distribution on galactic latitude, b. We analyze the correlation between the arrival direction (AD) of UHECRs observed by the Pierre Auger Observatory and the large-scale structure of the universe in regions of sky divided by b. Specifically, we compare the AD distribution of observed UHECRs to that of mock UHECRs generated from a source model constructed with active galactic nuclei. Our source model has the smearing angle as a free parameter that reflects the deflection angle of UHECRs from the source. The results show that larger smearing angles are required for the observed distribution of UHECRs in lower galactic latitude regions. We obtain, for instance, a $1{\sigma}$ credible interval for smearing angle of $0^{\circ}{\leq}{\theta}_s{\leq}72^{\circ}$ at high galactic latitudes, $60^{\circ}$ < $\left|{b}\right|{\leq}90^{\circ}$, and of $75^{\circ}{\leq}{\theta}_s{\leq}180^{\circ}$, $-30^{\circ}{\leq}b{\leq}30^{\circ}$, at low galactic latitudes, respectively. The results show that the influence of the GMF is stronger than that of the IGMF. In addition, we can estimate the strength of GMFs by these values; if we assume that UHECRs would have heavier nuclei, the estimated strengths of GMF are consistent with the observational value of a few ${\mu}G$. More data from the future experiments may make UHECR astronomy possible.
Perspectives on the Market Globalization of Korean Herbal Manufacturers: A Company-Based Survey
Kim, Dongsu,Ahn, Miyoung,Jung, Jeeyoun,Kwon, Soohyun,Park, Eun-Ji,Koo, Ki Hoon,Woo, Jong-Min Hindawi Publishing Corporation 2015 Evidence-based Complementary and Alternative Medic Vol.2015 No.-
<P>The growth of herbal markets has increased substantially in South Korea, but the worldwide market share remains small despite significant governmental efforts. This study aimed to characterize manufacturing employment and identify employees' general perceptions of market expansion. A survey study covering 567 companies was conducted using face-to-face interviews in 2012. Data were analyzed using comparisons among three manufacturing groups (i.e., the herbal dietary supplement manufacturing group, the herbal medicine manufacturing group, and the personal care product manufacturing group) or among the manufacturers themselves. We found that the majority of the manufacturing employee respondents were regular permanent and production workers. The domestic distributors were primarily chain stores/direct outlets or retailers/wholesalers, and the dominant product was red ginseng (<I>hongsam</I>). Although the responding companies exhibited a variety of perspectives, “advertisement/public relations” was cited as the most important factor in the development of the herbal industry. In contrast, “low manpower/seeking business partners” were the most crucial limiting and challenging factors for market globalization. Our results can be used to design a proper national plan by reducing the gaps in perspective between herbal product producers and policy makers.</P>
SGX-Tor: A Secure and Practical Tor Anonymity Network With SGX Enclaves
Kim, Seongmin,Han, Juhyeng,Ha, Jaehyeong,Kim, Taesoo,Han, Dongsu Institute of Electrical and Electronics Engineers, 2018 IEEE/ACM transactions on networking Vol.26 No.5
<P>With Tor being a popular anonymity network, many attacks have been proposed to break its anonymity or leak information of a private communication on Tor. However, guaranteeing complete privacy in the face of an adversary on Tor is especially difficult, because Tor relays are under complete control of world-wide volunteers. Currently, one can gain private information, such as circuit identifiers and hidden service identifiers, by running Tor relays and can even modify their behaviors with malicious intent. This paper presents a practical approach to effectively enhancing the security and privacy of Tor by utilizing Intel SGX, a commodity trusted execution environment. We present a design and implementation of Tor, called SGX-Tor, that prevents code modification and limits the information exposed to untrusted parties. We demonstrate that our approach is practical and effectively reduces the power of an adversary to a traditional network-level adversary. Finally, SGX-Tor incurs moderate performance overhead; the end-to-end latency and throughput overheads for HTTP connections are 3.9% and 11.9%, respectively.</P>
Kim, Dongsu,Lee, Jaeseon ELSEVIER 2019 INTERNATIONAL JOURNAL OF THERMAL SCIENCES Vol.141 No.-
<P><B>Abstract</B></P> <P>In this study, the relationship between the shock structure of impinging jet flow and target wall heat transfer characteristics was investigated. In the case of a high Reynolds number impinging jet that can enter the supersonic flow regime, the stagnation temperature of the impinged surface is affected by the jet structure as well as other factors, such as the nozzle to plate distance and radial distance. When the jet flow velocity becomes supersonic, shock structures form at the downstream of the nozzle exit. Complicated shock structures, such as the Mach shock disk and plate shock, are expected to affect the heat transfer characteristics of the impingement surface. In this study, the cooling performance of a supersonic nitrogen (N<SUB>2</SUB>) jet is investigated by measuring the impinged surface temperature, and the flow of the jet is visualized by schlieren imaging. The visualized image and surface temperature are compared to clarify the shock structure-related heat transfer characteristics. Under experimental conditions where the nozzle pressure ratio changes to a moderate and highly under-expanded regime, the surface temperature fluctuates according to the changes of jet structures in each condition. According to a position of Mach crossing point, which is an intersection of oblique shock structures, a behavior of jet fluid is decided to be trapped inside the recirculation zone or to be spread to wall jet region. In case that the jet fluid is trapped, the cooling performance of the supersonic jet is significantly reduced and vice versa. Therefore, the heat transfer characteristics can be explained by roles of the jet flow field structures including the recirculation flows and shock locations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Jet target wall stagnation temperature fluctuations are strongly related with supersonic impinging jet shock. </LI> <LI> Under-expanded shock structures of imping jet were visualized by Schlieren imaging. </LI> <LI> Change in the recirculation flow direction near the jet stagnation zone affects wall cooling performance. </LI> </UL> </P>