• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.639-645
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• 1992

Effects of additives on electromagnetic properties of a Ni-Cu-Zn ferrite for a noise filter in high frequency regions were studied. Both resistivity and permeability were increased with the amount of Mn2O3 up to 1wt%, then decreased with further addition. Addition of Co2O3 decreased the permeability of the ferrite and shifted the resonance frequency to a higher frequency region, which was thought due to the stabilization of domain walls. Therefore it was possible to improve both the permeability and the loss and to control the cut-off frequency by the concurrent addition of Mn2O3 and Co2O3.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.58-63
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• 2005

The estimation of springing responses for recent ships is carried out, and application to a ship design is described. To this aim, springing effects on hull girder were re-evaluated, including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder, using the superposition method. The quadratic strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level, and addedasymptotic interpolation along the high frequency range. Several applications were carried out on the following existing ships: The Bishop and Price's container ship, S-175 container ship, large container, VLCC, and ore carrier. One of them is compared with the ship measurement result, while another with that of the model test. The comparison between the analytical solution and the numerical solution for a homogeneous beam-type artificial ship shows good agreement. It is found that Most springing energy comesfrom high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega$$\^{-3}$ instead of $\omega$$\^{-4}$ or $\omega$$\^{-5}$ for the springing calculation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.173-178
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• 2004

The estimation of springing responses for recent ships are carried out and application to a ship design are described. To this aim, springing effects on hull girder were re-evaluated including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder by the superposition method. The strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level and added asymptotic interpolation along the high frequency range. Several applications to the existing ships were carried out. They are Bishop and Price's container ship, S-175 container ship, large container, VLCC and ore carrier. One of them is compared with ship measurement result while another with that of model test. Comparison between analytical solution and numerical one for homogeneous beam type artificial ship shows good agreement. It is found that most springing energy came from high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega^{-3}\;instead\;of\;\omega^{-4}\;or\;\omega^{-5}$ for springing calculation.

• Biomedical Science Letters
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• v.19 no.1
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• pp.55-60
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• 2013

This study was to know the effects of massage on the back region in order to reduce stress in middle age women. To investigate the effects of massage to the stress levels of middle aged women, we evaluated blood pressure (BP), heart rate variability (HRV), and ultrasonography before and after back massage. The blood pressure after massage was reduced when compared to that of pre-massage. The HRV spectrum analysis was used Frequency domain analysis such as Mean HRV, normalized low frequency (norm LF), norm high frequency (norm HF), and LF/HF ratio. Post-massage BP tended to be low, but not statistical significant. After Massage, the Mean HRV, norm LF, and LF/HF ratio were significantly reduced, while norm HF was significantly increased as compared with pre-massage. The muscle layer and fat layer were significantly diminished by massage. The study was suggested that massage may be an effective treatment for relief of stress.

• The Journal of Korean Medicine
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• v.29 no.2
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• pp.107-115
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• 2008

Objectives: The objective of this study was to assess the effects of acupuncture applied at PC6 and SP4 points on heart rate variability (HRV) in normal subjects under mental stress Methods: 24 healthy male subjects were recruited and randomized to a treatment group (12 subjects) or a control group (12 subjects). Both groups performed a mental arithmetic stress test and then acupuncture needles were inserted on PC6 and SP4 for the study group. In the control group, they took sham acupuncture as a control. Heart rate variability (HRV) was measured during the whole study period by FM-150 (digital Holter ECG recorder). Results: In the both groups, low frequency (LF) power and ratio of low frequency to high frequency (LF/HF) was significantly increased after mental stress. Acupuncture induced significant decrease in low frequency (LF) power and ratio of low frequency to high frequency (LF/HF) which were increased after mental stress test. But sham acupuncture induced no changes. Results: In both groups, low frequency (LF) power and ratio of low frequency to high frequency (LF/HF) significantly increased after mental stress. Acupuncture induced significant decrease in low frequency (LF) power and ratio of low frequency to high frequency (LF/HF) which increased after mental stress test. In contrast, sham acupuncture induced no changes. Conclusions: Acupuncture on PC6 and SP4 could be useful to decrease sympathetic activity and balance autonomic nervous system for those who are under stress.

• Sleep Medicine and Psychophysiology
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• v.28 no.2
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• pp.53-69
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• 2021

Sleep disorders, increasingly prevalent in the general population, induce impairment in daytime functioning and other clinical problems. As changes in cortical excitability have been reported as potential pathophysiological mechanisms underlying sleep disorders, multiple studies have explored clinical effects of modulating cortical excitability through non-invasive brain stimulation in treating sleep disorders. In this study, we critically reviewed clinical studies using non-invasive brain stimulation, particularly transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), for treatment of sleep disorders. Previous studies have reported inconsistent therapeutic effects of TMS and tDCS for various kinds of sleep disorders. Specifically, low-frequency repetitive TMS (rTMS) and cathodal tDCS, both of which exert an inhibitory effect on cortical excitability, have shown inconsistent therapeutic effects for insomnia. On the other hand, high-frequency rTMS and anodal tDCS, both of which facilitate cortical excitability, have improved the symptoms of hypersomnia. In studies of restless legs syndrome, high-frequency rTMS and anodal tDCS induced inconsistent therapeutic effects. Single TMS and rTMS have shown differential therapeutic effects for obstructive sleep apnea. These inconsistent findings indicate that the distinctive characteristics of each non-invasive brain stimulation method and specific pathophysiological mechanisms underlying particular sleep disorders should be considered in an integrated manner for treatment of various sleep disorders. Future studies are needed to provide optimized TMS and tDCS protocols for each sleep disorder, considering distinctive effects of non-invasive brain stimulation and pathophysiology of each sleep disorder.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.18-23
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• 2022

This paper examines the electromagnetic shielding structure of ultra-high frequency (UHF) RF modules used in aircraft. Advances in electrical and electronic technologies have increased the need for electronic equipment in aircraft. High-frequency wireless devices have become integrated circuits in the form of UHF integrated circuits to support a wide range of frequencies and miniaturisation. To ensure the functionality and performance of these integrated devices in aviation, shielding is necessary to prevent unexpected electromagnetic interference, which could be detrimental to aircraft safety. A shield structure was designed to protect the RF chipset from malfunctioning, and the shielding effectiveness was improved through the application of various geometric shapes.

• Journal of electromagnetic engineering and science
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• v.3 no.1
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• pp.57-61
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• 2003

The effects of high frequency noises on a perturbational inversion technique for a stratified dispersive medium are investigated in this paper. It is shown that the perturbational solution becomes unstable under high frequency noises. The physical origin of this instability is described. In order to enhance the robustness of the perturbational inverse scattering solution, a parametric inversion technique is introduced. The examples for the 2-pole and the 3-pole reflection coefficients are compared and contrasted, and improvement of the robustness of the solutions is shown.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.975-978
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• 1999

The transmission line effects of IC interconnects have a substantial effect on a hish-speed VLSI circuit performance. The effective transmission lime parameters are changed with the increase of the operation frequency because of the skin of the skin effect, proximity effect, and silicon substrate. A new signal delay estimation methodology based on the RLC-distributed circuit model is presented ［2］. The methodology is demonstrated by using SPICE simulation and a high-frequency experiment technique.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.17 no.4
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• pp.531-538
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• 2010

Purpose: This study was done to identify the effects of Qi hand reflexology on autonomic nerve activity in patients admitted to hospital. Method: A non-equivalent control group and quasi-experimental research with pre/post test design were used and 59 patients on a medical ward were assigned to either the experimental group (32) or the control group (27). The study variables included vital signs, autonomic nerve activities (ALF (absolute low frequency), AHF (absolute high frequency), nLF (normalized low frequency), nHF (normalized high frequency), SDNN (standard deviation of all normal-normal intervals)) and were evaluated using the QECG-3 system. The experimental group was treated with Qi hand reflexology for 10 minutes per day, for 3days. Results: Skin temperature and systolic blood pressure in the experimental decreased with treatment. ALF, AHF and SDNN for the experimental group increased with regulating proportion (nLF: nHF=6:4) and a significant difference between the groups was observed. Conclusion: The results indicated that application of Qi hand reflexology for patients in the hospital is effective in regulating the autonomic nervous system activation. Implication of finding should be useful for future research.