• Journal of Mechanical Science and Technology
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• v.19 no.9
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• pp.1790-1800
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• 2005

The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper, a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency of oscillation. Also the average temperature of vapor plugs decreased.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.174-174
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• 2001

Purpose： Dimensions of body RF coil composed of 4 rectangular loops for low field open MRI hav been optimized. The design result shows the field inhomogeneity of B1 field below 1.5 dB in the 25 cm DSV can be achieved. Method： Our low field RF coil is composed of 4 rectangular strip loops that assumed to b located at both the bottom and top sides of permanent magnet. All the loops have identica dimensions and current amplitude. First, the inductance of a loop is calculated. Second, the current distribution on the coil strip is calculated by using finite difference time doma method (FDTD). It takes as much as 4 days in FDTD simulation for low frequency RF field That's why the electrical dipole radiation method is used for simulation. With the curren distribution obtained using the FDTD simulation, for various dimensional parameters th magnetic field has been calculated by electric dipole radiation method, where the curren elements are regarded as electric dipole radiation sources. The field pattern from electri dipole radiation is almost same as that from FDTD simulation. Also, it is same as that fro the result using the Viot-Savart equation, for far tone radiation term becomes zero and th Bl field amplitude of near one radiation is the same as the B field due to static current The field homogeneity is calculated in the 25 cm BSV.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.53-61
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• 2011

Edge notched A16061-T6 aluminum was repaired with a GFRP composite patch as a function of the number of stacking, Damage progress of specimen for tension load has been monitored by acoustic emission(AE), AE energy rate, hit rate, amplitude, waveform and 1st peak frequency distribution were analyzed. Fracture processes were classified into Al cracking, Fiber breakage, Resin cracking and Delamination. Displacement of a specimen can be divided into Region I, II and ill according to acoustic emission characteristics. Region II where the patch itself was actually fractured was focused on to clarify the AE characteristics difference for the number of stacking.

• Solar Energy
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• v.17 no.1
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• pp.103-111
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• 1997

The purpose of this research is the study of characteristics of heat transfer in a heat pipe controlled by solenoid valve. A solenoid valve located to the adiabatic section between evaporator and condenser of heat pipe was used to control the valve action for effective energy transfer of the industrial exchanger machine. By the results presented in this study temperature difference between evaporator and condenser increases with increasing the temperature frequency and with decreasing the temperature amplitude. When inclination angle and flow rate of cooling water increases, the temperature amplitude is reached to the steady state rapidly with increasing the temperature frequncy.

• Journal of Magnetics
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• v.20 no.4
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• pp.427-431
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• 2015

The aim of this study was to investigate whether repetitive transcranial magnetic stimulation (rTMS) can improve motor recovery in the lower extremities of the patients with subacute stage spinal cord injury (SCI). This study was conducted with 19 subjects diagnosed with paraplegia because of SCI. The experimental group included 10 subjects who underwent active rTMS, and the control group included 9 subjects who underwent sham rTMS. The SCI patients in the experimental group underwent conventional rehabilitation therapy, and active rTMS was applied daily to the hotspot of the lesional hemisphere. The SCI patients in the control group underwent sham rTMS and conventional rehabilitation therapy. The participants in both the groups received therapy five days per week for six weeks. Latency, amplitude, and velocity were assessed before and after the six-week therapy period. A significant difference in post-treatment gains for the latency and velocity was observed between the experimental and control groups (p < 0.05). However, no significant differences in the amplitude were observed between the two groups (p > 0.05). The results of this study indicate that rTMS may be beneficial in improving motor recovery in the lower extremities of subacute stage SCI patients.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.3
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• pp.188-198
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• 1990

Turbulent characteristics of turbulent pulsating flows were studied experimentally in a square duct. Velocity waveforms, velocity profiles, and turbulent intensity of turbulent pulsating flow were investigated by using a hot-wire anemometer with data acquisition and a processing system in a square duct with a ratio of 1 ($40mm{\times}40mm$) to 4,000mm long. Turbulent components were shown to be larger in decelerating than in accelerating regions and also larger for a large phase of velocity and U'rms distribution of turbulent flow. The effect of velocity amplitude ratio does not exist for specified time [${\theta}(z^{\prime})$], amplitude ratio (${\mid}U^{\prime}_{rms.os.1}{\mid}/{\mid}U_{m.os.1}{\mid}$), and phase difference (${\Delta}U^{\prime}_{rms.os.1}-{\Delta}U_{m.os.1}$) in either turbulent oscillating or cross-sectional mean velocity components. The effect of dimensionless angular frequency for specified time [${\theta}(z^{\prime})$] can be disregarded because the dimensionless angular frequency does not affect the specified time. The velocity distributions of turbulent pulsating flows for various time-averaged Reynolds numbers are in approximate agreement with the velocity distributions for equivalent Reynolds numbers and 1/7th power law of steady flow.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.285-288
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• 2008

We analyzed evaporation data in the Japanese Ocean Flux Data Sets with Use of Remote Sensing Observations (J-OFURO) Ver.2. There exists huge evaporation in Gulf Stream, Kuroshio Extension, the ocean dessert and the southern part of the Indian Ocean. The temporal variation of evaporation is overwhelmingly large, of which the standard deviation is more than 120(mm), in the Kuroshio Extension region. Also, the result of harmonic analysis gives that this large variation is closely related to annual variation. In addition, the first EOF mode shows long-term variation showing the maximum amplitude between 1992 and 1994 and remarkable decrease after 1994, and large amplitude in the equatorial region and northeast of Australia. The second and third modes were strongly influenced by El Nino. Moreover, we compared J-OFURO2 evaporation product with other products. We used six kinds of data sets (HOAPS3 and GSSTF2 of satellite data, NRA1, NRA2, ERA40 and JRA25 of reanalysis data) for comparison. Most products show underestimation in the most regions, in particular, in the northern North Pacific, mid-latitudes of the eastern South Pacific, and high-latitudes of the South Pacific compared with J-OFUR02. On the other hand, JRA25 and NRA2 show large overestimation in the equatorial regions. RMS difference between NRA2 and J-OFURO2 in the Kuroshio Extension was significantly large, more than 120(mm).

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.2 no.3
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• pp.37-49
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• 2004

The purpose of this study was to determine the effect of spinal motor neuron excitability by cranial electrostimulation(CES). The fifteen Sparague-Dawley adult male rats were assigned to the three groups; GroupI(control), GroupII(low rate CES), GroupIII(high rate CES). Spinal motor neuron excitability was measured to use a computerized H reflex. The results of this study was as follows; M latency, M amplitude and H latency were no significant difference in all groups on repeated measured ANOVA(p>.05) but low rate CES and high rate CES groups were lower than ether group in comparative measurement of H amplitude and Hmax/Mmax ratio(p<.05). These results lead to the conclusion that spinal neuron excitability was influenced by CES. These results suggest that CES had the capability to lower spinal motor neuron excitability used synaptic blockade in spinal segment.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.113-118
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• 2009

Grounding systems set the reference voltage level of electric circuits and suppress the Ground Potential Rise (GPR) by flowing fault currents to the ground safely. There are several parameters which evaluate the performance of grounding systems as ground resistance, touch voltage and step voltage. The touch and step voltages, which is called "risk voltage", are especially important to ensure the safety of human body. This paper dealt with the influence of current sources with the different frequency components on the touch and the step voltages. Three types of current sources as commercial frequency, square wave, and surge with the fast risetime of $50\;ns{\sim}500\;ns$ were used to analyze the risk voltages in a grounding system. The risk voltages showed remarkable difference in the same current amplitude depending on the current sources, and increased linearly with the current amplitude in the same current source. From the experimental results, it was confirmed that the risk voltages can be evaluated by a small current application in large-scale grounding systems and the possible largest risk voltage can be calculated by a surge current with the risetime of 200 ns or a current source with the same frequency component as the surge current.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.5
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• pp.858-865
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• 2008

In this paper, Capacitive Telemetry RF Sensor System using Recursive Least Square (RLS) algorithm was proposed. General Telemetry RF Sensor System means that it should be "wireless", "implantable" and "batterless". Conventional Telemetry RF Sensor System adopts Integrated Circuit type, but there are many defects like complexity of structure and the limitation of large power consumption in some cases. In order to overcome these disadvantages, Telemetry RF Sensor System based on inductive coupling principle was proposed in this paper. Proposed Telemetry RF Sensor System is very simple because it consists of R, L and C and measures the changes of environment like pressure and humidity in the type of capacitive value. This system adopted RLS algorithm for estimation of this capacitive parameter. For the purpose of applying RLS algorithm, proposed system was mathematically modelled with phasor method and was quasi-linearized. As two parameters such as phase and amplitude of output voltage for estimation were needed, Phase Difference Detector and Amplitude Detector were proposed respectively which were implemented using TMS320C2812 made by Texas Instrument. Finally, It is verified that the capacitance of proposed telemetry RF Sensor System using RLS algorithm can be estimated efficiently under noisy environment.