Fast Spin Echo Imaging-Based Electric Property Tomography With K-Space Weighting via <tex> ${T}_{2}$</tex> Relaxation (rEPT)

Jaewook Shin,Min-Oh Kim,Sungmin Cho,Dong-Hyun Kim IEEE 2017 IEEE transactions on medical imaging Vol.36 No.8

<P>Magnetic resonance electrical property tomography (MREPT) is a technique used to extract the electrical properties of tissues (conductivity in particular) using a magnetic resonance imaging system. In this paper, we propose an improved data acquisition scheme for the electrical property tomography technique by utilizing T-2 modulation in fast spin echo (FSE) imaging. This technique was motivated by a numerical analysis of conductivity reconstruction in the frequency domain; results reveal the spatial frequency-dependent noise texture of conventional methods. A data-acquisition scheme using the FSE sequence was formulated to concentrate the signal within a specific frequency range where notable noise amplification is observed in the conventional method. Through numerical studies, the performance of the proposed acquisition was investigated. Furthermore, a compensation scheme was applied to reduce quantification errors due to tissuespecific T-2 modulation, which is inherent in FSE imaging. The technique was applied to phantom and in vivo experiments. Results showed improved conductivity contrasts in both experiments, as compared with conventional MREPT methods.</P>

Thermal Characteristics of Various Substrates at Different Moisture Contents under the Pipe Coolin

Jaewook Shin,Byungkwan Lee,Minh Duy Pham,Hyunseung Hwang,Meiyan Cui,Hyein Lee,Jeesang Myung,Changhoo Chun 한국원예학회 2021 한국원예학회 학술발표요지 Vol.2021 No.10

Root-zone pipe cooling is a method to overcome the high air temperature in the summer season without high cooling load and cost in the greenhouse by using cooling pipes in close contact with the substrate. Few studies have been conducted on the substrate’s thermal characteristics and suitability for pipe cooling. We investigated the thermal characteristics of four substrates; coir, commercial growing media (Plant World; Nong Woo Bio, Suwon, Korea), perlite, and rockwool at two moisture contents; 40 and 80% (w/w). A silicone tube (8 mm in diameter) was coiled six times inside a container (170 mm in diameter), and chilled water of 15°C was circulated with a rate of 2.7 L min<SUP>-1</SUP>. Smaller pots (150 mm in diameter, 1.4 L) were filled with each type of substrates and adjusted to the moisture content of 40 or 80%. The smaller pot was then inserted into the container with the cooling pipe and cooled for 80 min. During the study, the average air temperature and relative humidity was set as 25°C and 63%, respectively. The temperature was measured with thermocouples at four positions (upper, middle, lower, and side points). The pipe cooling method reduced the temperature of substrate by 7.9–16.4°C depending on the type and moisture content showing that this is an effective method for controlling root-zone temperature. The average cooling rate (°C min<SUP>-1</SUP>) of perlite was the fastest at both moisture contents. At the moisture content of 40%, rockwool showed the second fastest cooling rate after perlite, followed by commercial growing media and coir. At the moisture content of 80%, commercial growing media showed the second fastest cooling rate, followed by coir and rockwool. In all substrates, the cooling rate was faster in the moisture content of 40% treatment than in 80% treatment. The temperature difference between the center (the mean value of upper, middle, and lower positions) and the side position of the substrate was the largest in coir in both moisture content treatments, followed by commercial growing media. The temperature difference between the center and the side positions at the moisture content of 40% was greater than that at 80% for all substrates. The substrate with a faster cooling rate showed a tendency to have a smaller temperature difference between the center and the side positions indicating a more uniform internal heat distribution. We expect that the thermal characteristics of substrates obtained from the study could help to select optimal substrates for energy-efficient and effective root-zone cooling methods to produce horticultural plants in the greenhouse.

Morphology of Spiny Sow Thistle (Sonchus asper (L.) Hill) Leaves as Affected by Different Light Intensities during the Early Growth Stage in a Plant Factory with Artificial Lighting

Jaewook Shin,Meiyan Cui,Hyein Lee,Byungkwan Lee,Jeesang Myung,Seohyun Choi,Nakhyun Lee,Sehee Kang,Changhoo Chun 한국원예학회 2023 한국원예학회 학술발표요지 Vol.2023 No.10

A Fast and High-Precision VCO Frequency Calibration Technique for Wideband <tex> $\Delta \Sigma $</tex> Fractional-N Frequency Synthesizers

Jaewook Shin,Hyunchol Shin IEEE 2010 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS PART 1 R Vol.57 No.7

<P>A VCO frequency calibration technique suitable for a wideband fractional-N PLL is presented. It provides a fast and high-precision search for an optimal discrete tuning curve of an LC VCO during the coarse tuning process in a fractional-N PLL. A high-speed frequency error detector (FED) converts the VCO frequency to a digital value and computes the exact frequency difference from a target frequency. A minimum error code finder finds an optimal code that is closest to the target frequency. Due to the pure digital domain operation, a ΔΣ modulator in PLL can be deactivated during the calibration process, which makes this technique fast and accurate especially for a ΔΣ fractional-N PLL. We achieve a single-bit calibration time of only kT<SUB>REF</SUB> for obtaining a frequency resolution of f<SUB>REF</SUB>/k, and compared to the conventional techniques, which is the best performance in terms of the calibration time versus resolution. Such fast VCO frequency calibration can greatly reduce the total lock time in a PLL. A 2.3-3.9 GHz fractional-N PLL employing the proposed calibration technique is implemented in 0.13 μm CMOS. Successful operation is verified through experimental results. The measured calibration time for a 6-bit capbank is 1.09 and 2.03 μs for a frequency resolution of 19.2 and 4.8 MHz, respectively.</P>

A Sequential Selection Normalized Subband Adaptive Filter with Variable Step-Size Algorithms

Shin, JaeWook,Baek, Hyun Jae,Park, Bum Yong,Cho, Jaegeol Hindawi Limited 2018 Mathematical problems in engineering Vol.2018 No.-

<P>This letter proposes a sequential selection normalized subband adaptive filter (SS-NSAF) in order to reduce the computational complexity. In addition, a variable step-size algorithm is also proposed using the mean-square deviation analysis of the SS-NSAF. To enhance the performance in terms of the convergence speed, we propose an improved variable step-size SS-NSAF using a two-stage concept. The simulation results show the low computational complexity and low misalignment errors using the proposed algorithm.</P>

Multiple linear regression and GRU model for the online prediction of catalyst activity and lifetime in counter-current continuous catalytic reforming

Shin Yongbeom,박명남,Lee Jaewook,Kang Kibyung,Wang Sungki,Lee Eunsung,Song Seongkeun,Shin Dongil 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.6

In the catalytic reforming process, aromatic yield is a standard for evaluating the production quality of the process, and studies are underway to improve productivity by optimizing the cost and energy. In particular, the activity and lifetime prediction of reforming catalysts can contribute to overall process efficiency improvement, such as product quality, productivity, and predictive maintenance. However, it is difficult to predict real-time catalyst activity and lifetime according to changes in process operation with the existing method that requires experimental data. In this study, a multiple linear regression (MLR) model and GRU model with the real process operating data are proposed for long-term plant operation and optimization in the counter-current continuous catalytic reforming. The MLR-GRU model predicts catalyst performance degradation and lifetime according to operating conditions by defining a new variable, reforming catalyst activity. The proposed model can predict the future reformate yield with an error of less than 1%. As a result of predicting the catalyst lifetime according to various operating temperatures, feed flow patterns, and feed quality, the feed flow rate had the greatest influence on the catalyst lifetime profile. In terms of the amount of produced reformate oil, the case with maximum feed rate is the worst (−25.6%); on the other hand, the case with minimum feed rate is the best (+11.4%). Thus, it is important to establish an appropriate production plan of the produced reformate oil. The model proposed in this study can predict the reformate yield and lifetime, reflecting the degradation of catalyst performance according to the operating profile in real-time, which is expected to improve productivity by production scheduling, optimization, and predictive maintenance.

Combined Effects of the Nutrient Solution Heating and Organ-based Heating on the Growth, Flowering, and Yield of Strawberries Cultivated in a Greenhouse during the Winter Season

Jaewook Shin,Byungkwan Lee,Meiyan Cui,Hyein Lee,Jeesang Myung,Changhoo Chun 한국원예학회 2022 한국원예학회 학술발표요지 Vol.2022 No.5

Robust Common Rail Pressure Control for Diesel Engines using a Quantitative Feedback Theory

Jaewook Shin,Seungwoo Hong,Inseok Park,Minkwang Lee,Myoungho Sunwoo 한국자동차공학회 2012 한국자동차공학회 학술대회 및 전시회 Vol.2012 No.11

This paper proposes a common rail pressure controller for passenger car diesel engines. The common rail system of diesel engine has some difficulties to control rail pressure. The rail pressure is influenced by interaction between a metering unit (MeUn) and a pressure control valve (PCV). The interaction increases complexity of control algorithm. In order to solve this problem, we present a common rail pressure controller based on the quantitative feedback theory (QFT). For the controller design, a plant model of the common rail system is approximated by a first order transfer function, and the PCV driving current and the rail pressure are used as input/output variables of this model. The rail pressure variation by MeUn is represented as parametric uncertainty. Then, requirement specifications for stability and reference tracking are defined, and the control algorithm is designed to satisfy these requirements using the QFT method. In order to validate the proposed controller, engine experiments are performed. The QFT based rail pressure controller successfully satisfies the tracking performance. Furthermore, the control robustness is evaluated when the MeUn driving current is abruptly changed.

Variable Step-Size Sign Subband Adaptive Filter

JaeWook Shin,JinWoo Yoo,PooGyeon Park IEEE 2013 IEEE signal processing letters Vol.20 No.2

<P>This letter proposes a variable step-size sign subband adaptive filter (SSAF) based on the minimization of mean-square deviation (MSD). In the process of minimizing the MSD, because it is not feasible to know the exact value of the MSD, the step size is derived by minimizing the upper bound of the MSD in each iteration. The proposed algorithm uses this step size in the SSAF update equation so as to improve the filter performance in terms of the convergence rate and the steady-state estimation error. The proposed algorithm is tested in a system-identification scenario that includes impulsive noise. Simulation results show that the proposed algorithm performs better than the previous algorithms.</P>

A Delta-Sigma Fractional-N Frequency Synthesizer for Quad-Band Multi-Standard Mobile Broadcasting Tuners in 0.18-µm CMOS

Jaewook Shin,Jongsik Kim,Seungsoo Kim,Hyunchol Shin 대한전자공학회 2007 Journal of semiconductor technology and science Vol.7 No.4

A fractional-N frequency synthesizer supports quadruple bands and multiple standards for mobile broadcasting systems. A novel linearized coarse tuned VCO adopting a pseudo-exponential capacitor bank structure is proposed to cover the wide bandwidth of 65 %. The proposed technique successfully reduces the variations of KVCO and per-code frequency step by 3.2 and 2.7 times, respectively. For the divider and prescaler circuits, TSPC (true single-phase clock) logic is extensively utilized for high speed operation, low power consumption, and small silicon area. Implemented in 0.18-μm CMOS, the PLL covers 154 ~ 303 MHz (VHF-III), 462 ~ 911 MHz (UHF), and 1441 ~ 1887 MHz (L1, L2) with two VCO’s while dissipating 23 mA from 1.8 V supply. The integrated phase noise is 0.598 and 0.812 degree for the integer-N and fractional-N modes, respectively, at 750 MHz output frequency. The in-band noise at 10 kHz offset is -96 dBc/Hz for the integer-N mode and degraded only by 3 dB for the fractional-N mode.