• Tribology and Lubricants
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• v.35 no.1
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• pp.77-86
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• 2019

The present study focuses on the effect of staggered integration factor (SIF) on Morton effect simulation results. The Morton effect is a synchronous rotordynamic instability problem caused by the temperature differential across the journal in fluid film bearings. Convection and conduction of heat in the thin film displaces the hot spot, which is the hottest circumferential position in the thin film, from -20 to 40 degrees ahead of the high spot, where the minimum film clearance is experienced. The temperature differential across the journal causes a bending moment and the corresponding thermal bow in the rotating frame acts like a distributed synchronous excitation in the fixed frame. This thermal bow may cause increased vibrations and continued growth of the synchronous orbit into a limit cycle. The SIF is developed assuming that the response of the rotor-lubricant-bearing dynamic system is much quicker than that of the bearing-journal thermal system, and it is defined as the ratio between the simulation time of the thermal system and the rotor-spinning period. The use of the SIF is unavoidable for efficient computing. The value of the SIF is chosen empirically by the software users as a value between 100 and 400. However, the effect of the SIF on Morton effect simulation results has not been investigated. This research produces simulation results with different values of SIF.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.48-54
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• 2022

This research describes a quantitative procedure used to estimate the effect of concrete cracking on stiffness degradation of concrete shear walls and provides analytical references for the seismic design of concrete shear walls. As preliminary research on the seismic response of concrete shear walls, nonlinear transient analysis was performed with commercial FE software. The study presents the nonlinear time history analysis results in terms of concrete damage and cracking behavior induced by seismic input motions. By varying the input motions, concrete strength and shear wall thickness, the seismic responses of a shear wall were examined with nonlinear time history analysis, and the progressive cracking behavior and corresponding hysteresis loop were described. Based on the analysis results, frequency and stiffness degradation of the shear wall from progressive concrete damage and cracking were captured with respect to the seismic levels. The results of this study suggest that stiffness degradation from concrete cracking should be appropriately considered when determining the seismic capacity of RC shear wall structures.

• Radiation Oncology Journal
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• v.25 no.3
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• pp.170-176
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• 2007

Purpose: To determine the role of radiotherapy for the treatment of portal vein thrombosis (PVT) from hepatocellular carcinoma (HCC). Material and Methods: A retrospective analysis was performed on 70 patients that had been diagnosed with HCC and were treated with three-dimensional conformal radiotherapy (3D-CRT) for the PVT. The radiation dose ranged from 40 Gy to 60 Gy (median dose: 48 Gy) and the biological effective dose (BED) ranged from 31.3 Gy to 78.0 $Gy_{10}$ (median dose: 61.6 $Gy_{10}$). Response was determined by measuring the extent of the PVT on a CT image at 0, 1 and 3 months after completion of the radiotherapy. The median follow-up period was 9 months. Results: The response rate was 47.1% (33 patients), with two patients (2.9%) showing a complete response, 31 patients (44.3%) showing a partial response, and 35 patients (50%) showing stable disease or no response. The 1-year progression-free survival rate was 60%, and the median progression-free survival time was 17 months. The median overall survival time was 11 months, the median survival time in the responders was 15 months and in the nonresponders was 8 months (p=0.032). Four patients (5.7%) had transient liver function impairment during treatment. Radiation induced liver disease (RILD) was observed in only one patient (1.4%). Conclusion: Three-dimensional conformal radiotherapy for the treatment of PVT from advanced HCC was a relatively effective and safe method.

• Polymer(Korea)
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• v.33 no.5
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• pp.496-500
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• 2009

Optically compensated bend liquid crystal display (OCB-LCD) has many application fields owing to its fast response time and wide viewing angle. However, in order to operate the OCB-LCD in bend state, this device needs quick transitions from the initial splay state to bend state. Unlike conventional approach using transient high voltage for the transition, the OCB-LCD with high surface tilt angle, which was achieved by polymerization of UV curable reactive mesogen monomer under certain voltage, was manufactured and the cell showed bend state initially. Electro-optic and electrical characteristics of the cell were analyzed. The cell shows a fast response time owing to high surface pretilt angle and very low residual DC less than 0.1 V although another polymer layer is formed above polymer alignment layers.

• Journal of Advanced Navigation Technology
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• v.14 no.3
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• pp.439-445
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• 2010

The signal transmission of human body is processed by the action potential from each cell unit. This kind of action potential is taken place and transmitted by the ions through cell membrane, and ultimately explained as an electrical signal concept. The fact that the information is established as an electrical status as well as various senses from the bio-organozm has been addressed through several studies. By the way, this nervous transmission relation has been described and analyzed qualitatively in the mean time. I established new algorithm to analyze these relations quantitatively and implemented them using existing bio-data in this paper. The study, however, was limited to underthreshold potential to excite the nervous system against the outer stimulation. This is very much analog to electrical transient of the switching circuit, and therefore, I analyzed it based on this analog. I made it clear that the results derived here is the basis further study topic.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.6
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• pp.59-66
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• 2005

This paper presents some features and statistics of electromagnetic pulses radiated from intracloud lightning discharges. The LabVIEW based-measurement system of time-dependent electromagnetic fields was constructed. The frequency bandwidth of the measuring system ranged from 300[Hz] to 1[MHz], and the response sensitivity was 2.78(mV/nT). The resolution and the maximum recording length of the data acquisition system were 12(bits) and 100[ms], respectively. In the electromagnetic pulses radiated from intracloud discharges, a pronounced bipolar pulse appeared with one or more fast pulses superimposed on the initial front part of the bipolar pulse. The mean duration of intracloud discharges was $1.05{\pm}0.32[ms]$, and an average of about 8 outburst pulses appeared for a period.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.5
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• pp.378-383
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• 2009

Hydrogen is the primary fuel in fuel cell systems. Because of high inflammation and explosion possibility of hydrogen, fuel cell systems require safety measures to prevent hydrogen hazard upon leakage. In this study, a model enclosure was made by referring to a commercial residential fuel cell system and hydrogen leakage experiments and computational simulations were conducted therein. Hydrogen was injected into the cavity through leakage holes located at the bottom while its flow rate was precisely controlled using MFC. The transient sensor signals from hydrogen sensors installed inside the enclosure were recorded and analyzed. The hydrogen sensor signals showed different delay times depending on their position relative to a leakage point, which indicated that hydrogen generally moves upward and accumulates at the upper region of a closed cavity. The inflammable regions with hydrogen concentration over 4% LEL were observed to locate near the leakage hole initially, and broaden towards the upper cavity region afterward. The simulation result showed that detection time at the hydrogen sensor was similar to the pattern of experimental results. However, the maximum concentration of hydrogen had a gap between experiment and simulation at detect point due to measurement errors and reaction rate.

• Journal of Communications and Networks
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• v.11 no.6
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• pp.544-555
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• 2009

This work continues a trend of developments aimed at exploiting the physical layer of the open systems interconnection (OSI) model to enhance wireless network security. The goal is to augment activity occurring across other OSI layers and provide improved safeguards against unauthorized access. Relative to intrusion detection and anti-spoofing, this paper provides details for a proof-of-concept investigation involving "air monitor" applications where physical equipment constraints are not overly restrictive. In this case, RF fingerprinting is emerging as a viable security measure for providing device-specific identification (manufacturer, model, and/or serial number). RF fingerprint features can be extracted from various regions of collected bursts, the detection of which has been extensively researched. Given reliable burst detection, the near-term challenge is to find robust fingerprint features to improve device distinguishability. This is addressed here using wavelet domain (WD) RF fingerprinting based on dual-tree complex wavelet transform (DT-$\mathbb{C}WT$) features extracted from the non-transient preamble response of OFDM-based 802.11a signals. Intra-manufacturer classification performance is evaluated using four like-model Cisco devices with dissimilar serial numbers. WD fingerprinting effectiveness is demonstrated using Fisher-based multiple discriminant analysis (MDA) with maximum likelihood (ML) classification. The effects of varying channel SNR, burst detection error and dissimilar SNRs for MDA/ML training and classification are considered. Relative to time domain (TD) RF fingerprinting, WD fingerprinting with DT-$\mathbb{C}WT$ features emerged as the superior alternative for all scenarios at SNRs below 20 dB while achieving performance gains of up to 8 dB at 80% classification accuracy.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.77-86
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• 1997

The advanced development in many fields of engineering and science has caused much interests and demands for crashworthiness and non-linear dynamic transient analysis of structure response. Crash and impact problems have a dominant characteristic of large deformation with material plasticity for short time scales. The structural material shows strain rate-dependent behaviors in those cases. Conventional rate-independent constitutive equations used in the general purposed finite analysis programs are inadequate for dynamic finite strain problems. In this paper, a rate-dependent constitutive equation for elastic-plastic material is developed. The plastic stretch rate is modeled based on slip model with dislocation velocity and its density so that there is neither yielding condition, nor loading conditions. Non-linear hardening rule is also introduced for finite strain. Material constants of present constitutive equation are determined by experimental data of mild steel, and the constitutive equation is applied to uniaxile tension loading.

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.1
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• pp.27-32
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• 2001

We have characterized the aftereffects of impulse activities on the transmission of afferent sensory to the primary somatosensory (SI) cortex of the anesthetized rats (n=22). Following conditioning stimulation (CS, 10 sec, either 5 Hz or 200 Hz) to the receptive field (RF), quantitative determination of the changes of afferent sensory transmission was done by generating post-stimulus time histogram of unit response to the testing stimulation (TS, at 0.5 Hz) to the RF center (RFC) for 60 min. In one group of experiments, CS was delivered to the RF center (RFC). In another group of experiments, CSs were simultaneously given to both RFC and RF outside (RFO, either forepaw or hindpaw). CS of 5 Hz to RFC exerted irreversible facilitation of sensory transmissions evoked by TS. Simultaneous CSs of 5 Hz to RFC and hindpaw RFO exerted reversible suppression of afferent transmission. However, CSs of 5 Hz to RFC and forepaw RFO did not significantly altered afferent sensory transmission to SI cortex neurons. CS of 200 Hz to RFC exerted irreversible suppression of sensory transmissions up to 60 min of experimental period. Simultaneous CSs of 200 Hz to RFC and RFO did not significantly altered afferent sensory transmission to SI cortex neurons. The profiles of CS-induced modulation of afferent sensory transmission were significantly different between two CS conditions. Thus, this study suggests that activity-dependent modulation of afferent transmission from a RF center to the SI cortex may be significantly altered when remote body part was simultaneously activated.