• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.142-152
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• 2019

This study aimed to explore the association between obesity index and heart rate variability (HRV) in college-aged male smokers. A total of 85 male college students (> 10 cigarettes per day for at least 3 years) were participated in this study. According to a standardized protocol, body mass index (BMI), percent body fat (%BF), waist circumference (WC), and waist-to-hip ratio (WHR) were taken as obesity indices. Resting r-r interval was monitored for HRV analysis as an indicator of cardiac autonomic regulation. Compared with low WHR subjects, high WHR subjects had significantly lower values of rMSSD, pNN50, HF, and SD1, suggesting decreased parasympathetic activity. No such differences in LF/HF ratio were found between the WHR-based subgroups. Bivariate correlation analysis showed that obesity indices of WC, WHR, and %BF were significantly associated with rMSSD, pNN50, HF, and SD1, with a tendency for correlation coefficient to be higher with WHR than with WC or %BF. No significant association was found between BMI and HRV parameters indicative of parasympathetic activity. This study suggest that central obesity is significantly associated with decrease in parasympathetic activation, independent of BMI as an indicator of obesity, in male college smokers.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.1
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• pp.1-11
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• 2021

POGO is a dynamic axial instability phenomenon that occurs in liquid-propelled rockets. As the natural frequencies of the fuselage and those of the propellant supply system become closer, the entire system will become unstable. To predict POGO, the propellant (oxidant and fuel) tank in the first stage is modeled as a shell element, and the remaining components, the engine and the upper part, are modeled as mass-spring, and structural analysis is performed. The transmission line model is used to predict the pressure and flow perturbation of the propellant supply system. In this paper, the closed-loop transfer function is constructed by integrating the fuselage structure and fluid modeling as described above. The pogo suppressor consists of a branch pipe and an accumulator that absorbs pressure fluctuations in a passive manner and is located in the middle of the propellant supply system. The design parameters for its design optimization to suppress the decay phenomenon are set as the diameter, length of the branch pipe, and accumulator. Multiple-objective function optimization is performed by setting the energy minimization of the closed loop transfer function in terms of to the mass of the pogo suppressor and that of the propellant as the objective function.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.10
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• pp.1409-1415
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• 2021

The Gysel divider has the advantage of easily setting the resistor in the circuit. If the line impedance in the Gysel divider is set differently, the input signal can be distributed to the two output ports at various distribution ratios. This paper proposes the Gysel divider that can change the power distribution to 1:3 or 3:1 by changing the line impedance. The impedance change of the line can be implemented by placing a floating copper plate on the bottom of the microstrip-line. When the floating copper plate and the ground plane are connected, the line operates as the microstrip-line, and when the floating copper plate and the ground plane are disconnected, the line operates as the coplanar-line. The proposed Gysel divider was fabricated at the center frequency of 1.5GHz. The fabricated 3:1 Gysel divider has a stable value S₁₁ of below -17dB, S₂₁/S₃₁ of 4.8±0.2dB, S₂₁(to high output port) of -1.39±0.12dB and S₃₁(to low output port) of -6.15±0.08dB over 1.3~1.7GHz.

• Journal of Navigation and Port Research
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• v.45 no.1
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• pp.26-32
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• 2021

In ocean field, the spread of the Fourth Industrial Revolution based on information and communication technology requires high precision and stable PNT&D (Position, Navigation, Timing and Data). As the IMO (International Maritime Organization) and IALA (The International Association of Marine Aids to Navigation and Lighthouse Authorities) are requiring backup systems due to mitigate vulnerabilities and the increase of dependency on GNSS (Global Navigation Satellite System), Korea is conducting a research & development of R-Mode. An DGPS (Differentiate Global Positioning System) reference station that uses MF, an existing maritime infrastructure, and AIS (Automatic Identification System) base stations that use 34 integrity station and VHF will be utilized in this study to avoid redundant investment. Because there are radio shadow areas that display low signal levels in the west sea, the establishment of new R-Mode reference and integrity station will be intended to resolve problems regrading the radio shadow area. Because the frequency has a characteristic in that radio wave transmits well along the ground (water surface) in low frequency band, simulation and measurement were conducted therefore this paper to propose candidate sites for R-Mode reference and integrity station resulted through p wave's propagation characteristics analysis. Using this paper, R-Mode reference and integrity station can be established at appropriate locations to resolve radio shadow areas in other regions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.6
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• pp.383-390
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• 2021

The experiments in coastal engineering are very complex and a lot of components should be concerned. The experience has an important role in the successful execution. Hydraulic model experiments have been improved with the development of the wave generator and the advanced measuring apparatus. The hydraulic experiments have the advantage, that is, the stability of coastal structures and the hydraulic characteristics could be observed more intuitively rather than the numerical modelings. However, different experimental results can be drawn depending on the model scale, facilities, apparatus, and experimenters. In this study, two-dimensional hydraulic experiments were performed to suggest the guide of the test wave(random wave) generation, which is the most basic and important factor for the model test. The techniques for generating the random waves with frequency energy spectrum and the range for the incident wave height [(H_S)_M/(H_S)_T = 1~1.05] were suggested. The proposed guide for the test wave generation will contribute to enhancing the reliability of the experimental results in coastal engineering.

• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.326-334
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• 2022

In this paper, we propose speech enhancement algorithm as a pre-processing for robust speech recognition in noisy environments. Auxiliary-function-based Independent Vector Analysis (AuxIVA) is performed with weighted covariance matrix using time-varying variances with scaling factor from target masks representing time-frequency contributions of target speech. The mask estimates can be obtained using Neural Network (NN) pre-trained for speech extraction or diffuseness using Coherence-to-Diffuse power Ratio (CDR) to find the direct sounds component of a target speech. In addition, outputs for omni-directional noise are closely chained by sharing the time-varying variances similarly to independent subspace analysis or IVA. The speech extraction method based on AuxIVA is also performed in Independent Low-Rank Matrix Analysis (ILRMA) framework by extending the Non-negative Matrix Factorization (NMF) for noise outputs to Non-negative Tensor Factorization (NTF) to maintain the inter-channel dependency in noise output channels. Experimental results on the CHiME-4 datasets demonstrate the effectiveness of the presented algorithms.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.11
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• pp.801-807
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• 2022

In this paper, we propose an ultra compact S-Band PCM/FM telemetry transmitter. The equipment is compact, so it can be applied to a limited space and capable of stable data transmission was designed and manufactured even with specifications set differently for each operating environment and system. RF direct conversion structure is used for the miniaturization of equipment, an RF transmission board, Power distribution board, and a signal processing board were implemented on a single PCB, so that the function of the transmitter could be performed with a minimum device. According to the target specification, variable output of 1~10W and variable data rate of 390kbps~12.5Mbps is possible in S-Band(2,200~2,400MHz) without degradation of performance. To verify the performance of the equipment, the RF performance test and BER measurement test were performed after the equipment was manufactured. It was confirmed that the OBW, null-to-null bandwidth, 1st IMD, Spurious emission, Phase noise specification of the PCM/FM modulated signal which is presented by the IRIG standard were satisfied, and we can confirm the data received using the transmitter inspection equipment were transmitted normally without distortion.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.287-301
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• 2009

The novel cut-and-cover tunnel construction method using rib-reinforced pre-cast arch segments has been recently developed and applied for practice to secure a structural stability of high covering and wide width section tunnels. Cut-and-cover tunnels are usually damaged by the seismic behavior of backfill grounds in case of a low covering condition. Seismic analyses are performed in this study to characterize the dynamic behavior of rib-reinforced pre-cast arch cut-and-cover tunnels. Seismic analyzes for 2 lane cast-in-place and rib-reinforced pre-cast arch cut-and-cover tunnels are carried out by using the commercial FDM program (FLAC2D) considering various field conditions such as the covering height embankment slope and excavation slope. It can be concluded that the amplification of seismic wave is reduced due to an increase in the structural stiffness induced by rib-reinforcement. The results show that the rib-reinforced pre-cast arch cut-and-cover tunnels are more effective against the seismic loading, compared to the cast-in-place cut-and-cover tunnels.

• Journal of Advanced Navigation Technology
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• v.28 no.3
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• pp.254-261
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• 2024

Accurate guidance during landing and take-off is important, and instrument landing system (ILS) has been used for stability and verification. Regular inspections are conducted for stable operation, and there is research to perform inspection using drones in addition to ground vehicles and measurement aircraft. Using SDR and single board computer, which can receive wide frequency range, we designed a small system that receives and processes localizer signals through GNU Radio. To check signal processing characteristics through GNU Radio, we simulated with MATLAB Simulink and confirmed the theoretical values. Difference in depth of modulation (DDM) and approach angle can be calculated when the aircraft enters the runway. And GNU Radio implemented real-time signal processing wirelessly using transmission control protocol (TCP). This gives the results within the error of 0.5% when the aircraft entered the runway center line and 0.27% for the angle of 1° degree. Compared to the inspecting and maintaining ILS signals using aircraft or ground vehicles, it is possible to implement a receiving system using small SDR that can be mounted for drone.

• The Journal of the Acoustical Society of Korea
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• v.13 no.6
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• pp.75-82
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• 1994

The ray paths and travel times of sound wave in the ocean depend on the physical properties of the propagating media. Ocean Acoustic Tomography(OAT), which is inversely estimate the travel time variations between fixed sources and receivers the physical properties of the corresponding media can he understood. To apply ocean survey technology by using the OAT, the tomographic procedure requires forward problem that variation of the travel times be identified with the variability of the medium. Also, received signals must be satisfied the necessary conditions of ray path stability, identification and resolution in order for OAT to work. The canonical ocean has been determined based on the historical data and its travel time and ray path are used as reference values. The sound speed of canonical ocean in the East Sea is about 1523 m/s at the surface and 1458 m/s at the sound channel axis(400m). Sound speeds in the East Sea are perturbed by warm eddy whose horizontal extension is more than 100 km with deeper than 200 m in depth scale. In this study, an acoustic source and receiver are placed at the depth above the sound channel axis, 350 m, and are separated by 200 km range. Ray paths are identified by the ray theory methed in a range dependent medium whose sound speeds are functions of a range and depth. The eigenray information obtained from interpolation between the rays bracketing the receiver are used to simulate the received signal by convolution of source signal with the eigenray informations. The source signal is taken as a 400 Hz rectangular pulse signal, bandwidth is 16 Hz and pulse length is 64 ms. According to the analysis of the received signal and identified ray path by using numerical model of underwater sound propagation, simulated signals satisfy the necessary conditions of OAT, applied in the East Sea.