• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.6
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• pp.35-42
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• 2010

This paper describes a 10 bit 80MHz CMOS D/A converter for wireless communication system. The proposed circuit in the paper is implemented with a $0.18{\mu}m$ CMOS n-well 1-poly 6-metal process. The architecture of the circuit consists of the 4bit LSB with binary decoder, and both the 3bit ULSB and the 3bit MSB with the thermometer decoder. The measurement results demonstrates SFDR of 60.42dBc at sampling frequency 80MHz, input frequency 1MHz and ENOB of 8.75bit. INL and DNL have been measured to be ${\pm}$0.38LSB and ${\pm}$0.32LSB and glitch energy is measured to be 4.6$pV{\cdot}s$. Total power dissipation is 48mW at 80MHz(maximum sampling frequency) with a single power supply of 1.8V.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.194.1-194.1
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• 2015

Transition metal dichalcogenide (TMD) with layered structure, has recently been considered as promising candidate for next-generation flexible electronic and optoelectronic devices because of its superior electrical, optical, and mechanical properties.[1] Scalability of thickness down to a monolayer and van der Waals expitaxial structure without surface dangling bonds (consequently, native oxides) make TMD-based thin film transistors (TFTs) that are immune to the short channel effect (SCE) and provide very high field effect mobility (${\sim}200cm^2/V-sec$ that is comparable to the universal mobility of Si), respectively.[2] In addition, an excellent photo-detector with a wide spectral range from ultraviolet (UV) to close infrared (IR) is achievable with using $WSe_2$, since its energy bandgap varies between 1.2 eV (bulk) and 1.8 eV (monolayer), depending on layer thickness.[3] However, one of the critical issues that hinders the successful integration of $WSe_2$ electronic and optoelectronic devices is the lack of a reliable and controllable doping method. Such a component is essential for inducing a shift in the Fermi level, which subsequently enables wide modulations of its electrical and optical properties. In this work, we demonstrate n-doping method for $WSe_2$ on poly-4-vinylphenol and poly (melamine-co-formaldehyde) (PVP/PMF) insulating layer and adjust the doping level of $WSe_2$ by controlling concentration of PMF in the PVP/PMF layer. We investigated the doping of $WSe_2$ by PVP/PMF layer in terms of electronic and optoelectronic devices using Raman spectroscopy, electrical measurements, and optical measurements.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.4 no.3
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• pp.174-181
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• 2011

A new registration method for IR image and EO image is proposed in this paper. IR sensor is applicable to many area because it absorbs thermal radiation energy unlike EO sensor does. However, IR sensor has difficulty to extract and match features due to low contrast compared to EO image. In order to register both images, we used modified SIFT(Scale Invariant Feature Transform) and block processing to increase feature distinctiveness. To remove outlier, we applied RANSAC(RANdom SAample Concensus) for each block. Finally, we unified matching features into single coordinate system and remove outlier again. We used 3~5um range IR image, and our experiment result showed good robustness in registration with IR image.

• Tribology and Lubricants
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• v.33 no.4
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• pp.134-140
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• 2017

With the increase in adoption of tilting pad journal bearings (TPJBs), various failure mechanisms related to TPJBs have been reported, of which pad wear is a frequently reported one. Pad wear causes change in geometry of the bearing, which can sometimes result in the failure of the entire system. The objective of this research is to investigate the influence of pad wear on the pad temperature, which is one of the widely used condition monitoring methods for TPJBs. For the theoretical investigation, thermohydrodynamic (THD) analysis was conducted by solving the generalized Reynolds equation and the 3D energy equation. The results of the analysis show that the temperature of the loaded pad increases while that of the unloaded pad decreases, when there is wear on the loaded pads. In addition, the minimum film thickness decreases with an increase in the wear depth. A validation test was conducted with a test rig, which mimics the axial turbine when a test rotor is supported by two TPJBs. The test bearing consists of five pads with a diameter of 60 mm, and a resistance temperature detector (RTD) is installed in the pad for temperature monitoring. The test was performed by replacing the two loaded pads with the worn pad. The test result for the TPJB with wear depth of $30{\mu}m$ show that the temperatures of the loaded pads are $8^{\circ}C$ higher and that of the unloaded pad is $2.5^{\circ}C$ lower than that of the normal TPJB. In addition, the predicted pad temperature shows good agreement with the measured pad temperatures.

• Journal of Internet Computing and Services
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• v.12 no.3
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• pp.77-88
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• 2011

In distributed cognitive radio networks, cognitive radio devices which perform the channel sensing individually, are seriously affected by radio channel environments such as noise, shadowing and fading such that they can not property satisfy the maximum allowable interference level to the primary user. In the paper, we propose a Q-learning based channel access scheme for cognitive radios so as to satisfy the maximum allowable interference level to the primary user as well as to improve the throughput of cognitive radio by opportunistically accessing on the idle channels. In the proposed scheme, the pattern of channel usage of the primary user will be learned through Q-learning during the pre-play learning step, and then the learned channel usage pattern will be utilized for improving the sensing performance during the Q-learning normal operation step. Through the simulation, it is shown that the proposed scheme can provide bettor performance than the conventional energy detector in terms of the interference level to primary user and the throughput of cognitive radio under both AWGN and Rayleigh fading channels.

• Asian Journal of Atmospheric Environment
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• v.6 no.1
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• pp.14-22
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• 2012

This paper is focused on the comprehensive and detailed interpretation for the chemical transformation of individual Asian dust (hereafter called "AD") particles during long-range transport from source regions to receptor area. A multi-stage particle sampler was operated at a ground-based site in Taean, Korea directly exposed to the outflow of air masses from China during AD period in April 2003. Both quantitative and qualitative analyses for size-classified individual particles were carried out by a microbeam X-ray fluorescence (XRF) method and a microbeam Particle Induced X-ray Emission (micro-PIXE), respectively. Among major characteristic elements, the elemental masses of soil derived components, sulfur, and chloride varied as a function of particle size showing the monomodal maximum with a steeply increasing at 3.3-4.7 ${\mu}m$ particle size. Although the details on chemical composition of AD particle collected on a straight line from source area to our ground-based site are needed, a large amount of Cl coexisted in and/or on AD particles suggests that AD particles collected in the present study might be actively engaged in chemical transformation by sea-salt and other Cl containing pollutants emitted from the China's domestic sources. Through the statistical analyses it was possible to classify individual AD particles into six distinct groups. The internally mixed AD particles with Cl, which has various sources (e.g., sea-salt, coal combustion origin HCl, gaseous HCl derived from the adsorption of acids to sea-salt, and Cl containing man-made particles) were thoroughly fractionated by the elemental spectra drivened by the double detector system of micro-PIXE.

• Journal of the Korean Society of Systems Engineering
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• v.9 no.1
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• pp.33-45
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• 2013

Systems Engineering Approach was applied to the development of operator-support core management system based on the on-site operation experience and document of core management procedures, which is for enhancing operability and safety in PHWR (Pressurized Heavy Water Reactor) operation. The dissertation and definition of the system were given on th basis of investigating and analyzing the core management procedures. Fuel management, detector calibration, safety management, core power distribution monitoring, and integrated data management were defined as main user's requirements. From the requirements, 11 upper functional requirements were extracted by considering the on-site operation experience and investigating documents of core management procedures. Detailed requirements of the system which were produced by analyzing the upper functional requirements were identified by interviewing members who have responsibility of the core management procedures, which were written in SRS (Software Requirement Specification) document by using IEEE 830 template. The system was designed on the basis of the SRS and analysis in terms of nuclear engineering, and then tested by simulation using on-site data as a example. A model of core power monitoring related to the core management was suggested and a standard process for the core management was also suggested. And extraction, analysis, and documentation of the requirements were suggested as a case in terms of systems engineering.

• Journal of the Korean Society for Railway
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• v.13 no.1
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• pp.37-43
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• 2010

Catenary (Overhead Contact Lines) and Pantograph are used to transmit electrical energy to electric railways. An Arc occurs by unstable contact between catenary and pantograph during electric railways operation, which causes malfunctioning or even an accident. Therefore, to prevent a arc or electric contact loss are required arc detection systems with catenary maintenance capability. This paper describes developing of catenary arc detection system using photo detector in order to detect arc incidence in a indirect way. This developed system can also achieve Video-recordings and environmental conditions such as wire voltage/current, pantograph height, speed, position of electric railways, and temperature/humidity. This system have been evaluated at the section that bounds for dongdaegu from seoul. From the experimental results, the occurrence of arc and intensity of arc are mainly effected by wire voltage/current, pantograph height and speed of electric railways.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.9-16
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• 2007

Currently, the measurement of RF parameters for a base station in operation is typically limited to easily measured forward path items. In this paper, the forward monitoring ports of base stations are used to measure the reverse RF performance. The system has been implemented and effectiveness has been proven on an operating base station. The receiver sensitivity is measured using an internal CDMA modem which is used to monitor the output power based on closed loop power control when the modem is connected to the base station via a voice call. In order to improve accuracy, in addition to the modem Tx adjust(TxAdj) parameter, the detector's actual measurement is used. For accurate receiver sensitivity, the measurement should be made when there is no traffic which is not possible on an operating base station. Therefore, pilot channel chip energy to received signal power spectral density ratio$(E_c/I_o)$ compensation method is used to offset the receiver sensitivity degradation with voice traffic increase.

• IEIE Transactions on Smart Processing and Computing
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• v.6 no.1
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• pp.66-70
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• 2017

Radioactive materials are used in medicine, non-destructive testing, and nuclear plants. Source localization is especially important during nuclear decommissioning and decontamination because the actual location of the radioactive source within nuclear waste is often unknown. The coded-aperture imaging technique started with space exploration and moved into X-ray and gamma ray imaging, which have imaging process characteristics similar to each other. In this study, we simulated $21{\times}21$ and $37{\times}37$ coded aperture collimators based on a modified uniformly redundant array (MURA) pattern to make a gamma imaging system that can localize a gamma-ray source. We designed a $21{\times}21$ coded aperture collimator that matches our gamma imaging detector and did feasibility experiments with the coded aperture imaging system. We evaluated the performance of each collimator, from 2 mm to 10 mm thicknesses (at 2 mm intervals) using root mean square error (RMSE) and sensitivity in a simulation. In experimental results, the full width half maximum (FWHM) of the point source was $5.09^{\circ}$ at the center and $4.82^{\circ}$ at the location of the source was $9^{\circ}$. We will continue to improve the decoding algorithm and optimize the collimator for high-energy gamma rays emitted from a nuclear power plant.