• International Journal of Aeronautical and Space Sciences
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• v.16 no.3
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• pp.339-346
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• 2015

Aerodynamic flow control phenomena were investigated with a low-current DC surface discharge plasma actuator. The plasma actuator was found to operate in three different discharge modes with similar discharge currents of about 1 mA or less. Stable continuous DC discharge without audible noise was obtained at higher ballast resistances and lower discharge currents. However, even with continuous DC power input, a low-frequency self-pulsed discharge was obtained at lower ballast resistances, and a high-frequency self-pulsed discharge was obtained at higher set-point currents and higher ballast resistances, both with audible noise. The Schlieren image reveals that the low-frequency self-pulsed mode produces a synthetic jet-like flow implying that a gas heating effect plays a role, even though the discharge current is small. The high-frequency self-pulsed mode produces pulsed jets in a tangent direction, and the continuous DC mode produces a steady straight pressure wave. Particle image velocimetry (PIV) images reveal that the induced flow field by the low-frequency self-pulsed mode has flow propagating in the radial direction and centered between the electrodes. The high-frequency self-pulsed mode and continuous DC mode produce flow from the anode to the cathode. The perturbed region downstream of the cathode is larger in the high-frequency self-pulsed mode with similar maximum speeds.

• Journal of the Korean Society of Physical Medicine
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• v.7 no.3
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• pp.349-356
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• 2012

Purpose : This study was designed to investigate the effects of pulsed electromagnetic field on functional recovery and expression of GAP-43 after incomplete spinal cord injury (SCI) in rats. Methods : To confirm the damage of SCI and effects of pulsed electromagnetic field, 20 Sprague-Dawley male rats were used and divided randomly 2groups (SCI, PEMF). Incomplete SCI was induced by using modified NYU drop model. After operation, functional recovery test, immunohistochemistry and western blot analysis were measured at 1, 2, 3 weeks. Pulsed electromagnetic field were apply three weeks (one times a day, five days a week and twenty minutes a session). Results : In the this study, applications of pulsed electromagnetic field after incomplete SCI induced the significant improvement in functional recovery and expression of neurotrophic factor. The results were as follows; Foot print test, PEMF were significantly decreased than the SCI (p<.05). Expression of GAP-43, PEMF were significantly increased than the SCI at 2 and 3 weeks (p<.05). Conclusion : In conclusion, pulsed electromagnetic field were positive effect in functional recovery and expression of GAP-43 after incomplete SCI in rats.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.156-160
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• 1994

Use of engineering ceramics has been increasing due to the outstanding physical and chemical properties. Conventional machining processes, however, are not applicable due to their hardness and brittleness. Laser cutting is a promising alternative for these ceramics. In this study, experimental data of CO $_{2}$ laser cutting of $Al_{2}$ $O_{3}$ and Si $_{3}$ N $_{4}$ are obtained to give a guide in the industry. Results of $Al_{2}$ $O_{3}$ cutting showed extreme weakness to thermal crack and it was found that pulsed beam has to be used for thick $Al_{2}$ $O_{3}$ specimen. Si $_{3}$ N $_{4}$ showed good results for both CW and pulsed beams. Using pulsed beam resulted narrower kerf width with increased surface roughness a nd reduced cutting speed. It was also found that a parameter call path energy is useful for representing minimum threshold value for possible cutting range with pulsed beam.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.3
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• pp.380-388
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• 2011

In this paper, we developed the X-band 63 watt pulsed SSPA(Solid State Power Amplifier) by using HMIC(Hybrid Microwave Integrated Circuits). The pulsed SSPA consists of power supply and 3-stage amplifier modules : pre-amplifier stage, driver-amplifier stage, final-amplifier stage. The developed pulsed SSPA provides more than 63 watts of output power with a short pulse width and the duty cycle of up to 1.2 % at $70^{\circ}C$. The fabricated module offers great than 37 dB of saturated gain across the operating band. Input and output VSWR is <1.5:1. This module has an average current of 400 mA typical and operates at a +28 $V_{dc}$ supply. The developed SSPA in this paper can apply to pulsed Doppler radar with high speed operation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.236-236
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• 2011

본 연구 축전 결합형 고주파 플라즈마(CCP) 식각장비에 펄스 직류(Pulse DC) 전원을 인가하여 오실로스코프(oscilloscope)를 분석하여 전기적 특성을 평가하는 것이다. 펄스 직류전원 플라즈마 시스템에서는 다양한 변수를 이해하여야 한다. 본 실험에서 사용한 공정 변수는 Pulsed DC Voltage 300~500 V, Pulsed DC reverse time $0.5{\sim}2.0{\mu}s$, Pulsed DC Frequency 100~250 kHz 이었다. 실험 결과를 정리하면 1) Pulsed DC Voltage 가 증가할수록 Input voltage의 최대값은 336~520 V, 최소값은 -544~-920 V로 변하여 피크 투 피크 (peak to peak)값은 880~1460 V로 증가였다. Input current 또한 최대값은 1.88~2.88 A, 최소값은 -0.84~-1.28 A로 변하여 피크 투피크 값은 2.88~4.24 A로 증가하였다. 이는 척에 인가되는 전류와 파워의 증가를 의미한다. 2) Pulsed DC reverse time이 증가하면 Input voltage와 Input current값이 증가했다 (Input voltage의 피크 투 피크 값은 1200~1440 V, Input current의 피크 투 피크 값은 3.56~4.56 A). 3) Pulsed DC frequency가 증가하면 주기가 짧아져 Input voltage와 Input current값이 증가 한다 (Input voltage의 피크 투 피크 값은 900~1320 V, Input current의 피크 투 피크 값은 2.36~3.64 A). 결론적으로 펄스 직류 플라즈마의 다양한 전기적 변수들은 반응기 내부에 인가되는 Input voltage와 Input current의 값에 큰 영향을 준다는 것을 알 수 있었다.

• Journal of the Korean Vacuum Society
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• v.5 no.3
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• pp.229-238
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• 1996

The electromigration phenomena and the characterizations of the conductor lifetime (Time-To-Failure, TTF) in Al-1%Si thin film interconnections under D.C. and Pulsed D.C. conditions were investigated . Meander type test patterns were fabricated with the dimensions of 21080$mu \textrm{m}$ length, 3$\mu\textrm{m}$ width, 0.7$\mu\textrm{m}$ thickness and the 0.1$\mu\textrm{m}$/0.8$\mu\textrm{m}$($SiO_2$/PSG)dielectric overlayer. The current densities of $2 \times10^6 A/\textrm{cm}^2$ and $1 \times10^7 A/\textrm{cm}^2$ were stressed in Al-1%Si thin film interconnection s under a D.C. condition. The peak current densities of $2 \times10^6 A/\textrm{cm}^2$ and $1 \times10^7 A/\textrm{cm}^2$ were also applied under a Pulsed D.C. condition at frequencies of 200KHz, 800KHz, 1MHz, and 4MHz with the duty factor of 0.5. THe time-to-failure under a Pulsed D.C.($TTF_{pulsed D.C}$) was appeared to be larger than that under a D.C. condition. It was found that the TTF under both a D.C. and a Pulsed D.C. condition. It was found that the TTF under both a D.C. and a Pulsed D.C. condition largely depends upon the appiled current densities respectively . This can be explained by a relaxation mechanism view due to a duty cycle under a Pulsed D.C. related to the wave on off. The relaxation phenomena during the pulsed off period result in the decayof excess vacancies generated in the Al-1%Si thin film interconnections because of the electrical and mechanical stress gradient . Hillocks and voids formed by an electromigration were observed by using a SEM (Scanning Electron Microscopy).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.18-21
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• 2014

Because the Pb-based piezoelectric materials showed problems such as an environmental pollution. lead-free $O_3$ materials were studied in the present study. The $O_3$ thin films were deposited at $640^{\circ}C$ on $Pt/Ti/SiO_2$ substrate by pulsed laser deposition (PLD) and were annealed for 5 min at $750^{\circ}C$ using rapid thermal annealing (RTA) in nitrogen atmosphere. Samples annealed at $750^{\circ}C$ showed a smooth morphology and an improvement of the dielectric and leakage properties, as compared with as-grown samples. However, electrical properties of the $O_3$ thin films obtained in the present study should be improved for piezoelectric applications.

• The Korean Journal of Pain
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• v.21 no.3
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• pp.202-205
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• 2008

Background: Lumbar radicular pain is a frequent and often debilitating event. Although many treatment methods have been described in several studies, the available evidences regarding efficacy is not sufficient enough to draw definitive conclusions on an optimal therapy regime. Pulsed radiofrequency (RF) treatment was found to exert a beneficial effect on intractable radicular pain in individuals. The purpose of this study was to assess the efficacy of pulsed RF of the dorsal root ganglion for chronic lumbar radicular pain. Methods: Twenty five patients with chronic lumbar radicular pain that was refractory to selective nerve root blockage met the inclusion criteria of our study and received pulsed RF treatment. The average numeric rating scale (NRS) for leg pain during usual activities and the Oswestry disability index (ODI) were measured at 1 and 3 months after the procedure. Results: Of the 25 patients accepted for pulsed RF treatment, one dropped out due to a vertebral compression fracture during this study. ODI and NRS showed a positive trend in favor of the pulsed RF treatment. No significant complications were observed during the study period. Conclusions: It appears that pulsed RF treatment of the lumbar spinal dorsal root ganglion may be an effective treatment method for patients suffering from lumbar radicular pain, and who were not responsive to selective nerve root blockage.

• Journal of the Korean Magnetics Society
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• v.15 no.4
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• pp.250-255
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• 2005

A 8 MA/m-class pulsed field magnetometer has been constructed by composing a pulsed field magnet, a pickup coil, analog integrators, a digital storage oscilloscope and a personal computer. For precision measurements, a 3-axis compensation principle has been applied for the fabrication of pickup coil, and the compensation level of the order of $10^{-6}$ and the sensitivity of $5{\cdot}10^{-7}\;Am^2$ for magnetic moment have been obtained. The high sensitivity of the magnetometer is good enough for measurements of magnetic properties of rare earth magnets in small size or thin films shorter than $3\;mm{\phi}$ in diameter.

• Journal of International Academy of Physical Therapy Research
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• v.5 no.2
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• pp.752-756
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• 2014

This study investigated the effects of changes to the pulsation factor of pulsed direct currents on wound healing. Patients with a pressure ulcer at a care hospital for the elderly were randomly divided into three groups: Group 1 involved the application of $100{\mu}s$ in pulse duration, 10 ms in pulse period, 100 pps in a pulsation factor, 15 mA in pulse amplitude, and polarity red+ by using pulsed direct currents; Group 2 involved a change of pulse period to 8 ms; and Group 3 received general wound management. Although there were no statistically significant differences in the changing stages of pressure ulcers among the groups, all the groups dropped in numerical stages. In the two groups to which pulsed direct currents were applied, there was a statistically significant reduction in the stages of pressure ulcers from the initial assessment to the 12-week assessment (p<.05). Even though there were no statistically significant differences in changes to the area of pressure ulcers among the groups, a statistically significant decrease was found in pulsed direct current group 2 whose pulse period was shortened (p<.05). There was no difference in the healing rate of pressure ulcers among the groups, but it made a numerical increase in pulsed direct current group 1 and group 2 and a numerical decrease in group 3. There were no significant differences in the characteristics of those who had a full recovery among the groups. Those findings indicate that pulsed direct currents have positive effects on the wound healing of patients with a pressure ulcer and that a treatment with pulsed direct currents whose pulsation factor is raised by reducing the pulse duration is especially effective.