• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.688-698
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• 2018

Quasi Z-Source Multilevel Inverter (QZMLI) topology has attracted grid connected Photovoltaic (PV) systems in recent days. So there is a remarkable research thrust in switching techniques and control strategies of QZMLI. This paper presents the mathematical analysis of Phase shift- Pulse Width Amplitude Modulation (PS-PWAM) for QZMLI and emphasizes on the advantages of the technique. The proposed technique uses the maximum and minimum envelopes of the reference waves for generation of pulses and proportion of it to generate shoot-through pulses. Hence, it results in maximum utilization of input voltage, lesser switching loss, reduced Total Harmonic Distortion (THD) of the output voltage, reduced inductor current ripple and capacitor voltage ripple. Due to these qualities, the QZMLI with PS-PWAM emerges to be the best suitable for PV based grid connected applications compared to Phase shift-Pulse Width Modulation (PS-PWM). The detailed math analysis of the proposed technique has been disclosed. Simulation has been performed for the proposed technique using MATLAB/Simulink. A prototype has been built to validate the results for which the pulses were generated using FPGA /SPARTAN 3E.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.80-85
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• 2009

An experimental study of energy absorption and x-ray emission from ultrashort laser pulse irradiation of in-situ produced solid clusters has been performed. Silver clusters produced by a 30 mJ, 300 ps laser pulse were irradiated up to an intensity of $3{\times}10^{17}\;W/cm^2$ by a 70 mJ, 45 fs compressed laser pulse from the same Ti:sapphire laser. Absorption of the laser light exceeding 70% was observed, resulting in an x-ray yield (>1 keV) of ${\sim}60{\mu}J$ pulse. This may constitute a much simpler means of intense x-ray generation using ultrashort laser pulses as compared to the irradiation of structured / pre-deposited cluster targets, and it offers higher x-ray conversion efficiency than that from gas clusters and planar solid targets.

• Korean Journal of Optics and Photonics
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• v.12 no.6
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• pp.503-506
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• 2001

When DC voltages from 5 V up to 90 V are applied to a transmitter chip excited by an ultrafast lacer beam, the terahertz electromagnetic pulses and their spectra are changed. The spectrum shifts to the high frequency range when the high DC voltage is applied to the chip. At that time, the signal-to-noise ratio is increased from 250: 1 to 10,000: 1. The spectrum can expand up to 4 THz by optimal realignment of the THz system. Also, two terahertz electromagnetic pulses are generated from a receiver chip when the laser detection beam is reflected to the back side of the chip.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.59-62
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• 1999

Inception and propagation of electrical tree and properties of Partial discharge(PD) pulses accompanying with tree as a function of needle tip radius in low density polyethylene were discussed. To study on these characteristics in different tip radius, we used specimens with needle-plane electrode system made of LDPE, observed inception and propagation of electrical tree by optical microscope with computer and investigated the characteristics of the phase resolved PD pulses accompanying with propagation of electrical tree. The PD quantities detected and analysed were PD magnitude, mean phase angle, average discharge, and the statistical characteristics of the PD pulses. As the tip radius ${\gamma}$ increases, tree inception stress E$\sub$i/ converges to constance value. This result suggests that tree inception stress E$\sub$i/ increases due to stress relaxation when the tip radius is small. Branch-type electrical tree was formed When E$\sub$i/ is 640-750[kV/mm]. bush-type electrical tree when E$\sub$i/ is 370∼400[kV/mm], branch-like electrical tree when E$\sub$i/ is 370-400[kV/mm].

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.11
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• pp.59-65
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• 2015

By harnessing the thermal hysteresis behavior of vanadium dioxide($VO_2$), we demonstrated multi-resistance states in a two-terminal electronic device based on a $VO_2$ thin film by using a 966nm infrared laser diode as an excitation light source for resistance modulation. Before stimulating the device using 966nm laser pulses, the thermal hysteresis behavior of the device resistance was measured by using a temperature chamber. After that, the $VO_2$ device was thermally biased at ${\sim}71.6^{\circ}C$ so that its temperature fell into the thermal hysteresis region of the device resistance. Six multi-states of the device resistance could be obtained in the fabricated $VO_2$ device by five successive laser pulses with equal 10ms duration and increasing power. Each resistance states were maintained while the temperature bias was applied. And, the resistance fluctuation level was within 2.2% of the stabilized resistance and decreased down to less than 0.9% of the stabilized resistance 5s after the illumination.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.8
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• pp.157-164
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• 2000

This paper presents a method to detect a rotor position and to drive a BLDC motor from standstill to medium speed without any position sensor comparing the current responses due to the inductance variation in the rotor position. A rotor position at a standstill is identified by the current responses of six pulses injected to each phase of a motor. Once the motor stars up pulse train that is composed of long and short pulses is injected to the phase corresponding to produce the maximum torque and the next phase continuously. it provides not only the torque but also the information of the next commutation time effectively when the response of long and short pulses crosses each other after the same time delay. This method which is verified experimentally using a DSP can drive a BLDC motor to the medium speed smoothly without any rattling and time delay compared with the conventional sensorless algorithm.

• Korean Journal of Optics and Photonics
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• v.13 no.5
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• pp.430-434
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• 2002

We present the magnitude of terahertz electromagnetic pulses when femtosecond laser pulses are moving along to a dipole antenna. The dipole antenna chip has maximum 4.7 nA THz current, generated at 11 DC volt. This current is 3.4 times bigger than the current of a $300{\mu}{\textrm}{m}$ separated transmission line structure chip that has 70 DC volt. We also apply an AC square wave voltage to the dipole antenna from 0.1 volt to 10 volt for binary signals using the terahertz electromagnetic pulses.

• The Korean Journal of Physiology and Pharmacology
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• v.19 no.2
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• pp.167-175
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• 2015

A retinal prosthesis is being developed for the restoration of vision in patients with retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Determining optimal electrical stimulation parameters for the prosthesis is one of the most important elements for the development of a viable retinal prosthesis. Here, we investigated the effects of different charge-balanced biphasic pulses with regard to their effectiveness in evoking retinal ganglion cell (RGC) responses. Retinal degeneration (rd1) mice were used (n=17). From the ex-vivo retinal preparation, retinal patches were placed ganglion cell layer down onto an $8{\times}8$ multielectrode array (MEA) and RGC responses were recorded while applying electrical stimuli. For asymmetric pulses, 1st phase of the pulse is the same with symmetric pulse but the amplitude of 2nd phase of the pulse is less than $10{\mu}A$ and charge balanced condition is satisfied by lengthening the duration of the pulse. For intensities (or duration) modulation, duration (or amplitude) of the pulse was fixed to $500{\mu}s$($30{\mu}A$), changing the intensities (or duration) from 2 to $60{\mu}A$(60 to $1000{\mu}s$). RGCs were classified as response-positive when PSTH showed multiple (3~4) peaks within 400 ms post stimulus and the number of spikes was at least 30% more than that for the immediate pre-stimulus 400 ms period. RGC responses were well modulated both with anodic and cathodic phase-1st biphasic pulses. Cathodic phase-1st pulses produced significantly better modulation of RGC activity than anodic phase-1st pulses regardless of symmetry of the pulse.

• Journal of Korean Medical classics
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• v.13 no.1
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• pp.44-73
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• 2000

I examined throughout where Sa Gi Gang Boo Byung Hyung(邪氣藏府病形) was shown. It is shown in many books, such as Young Chu(靈樞), Kab Eul Kyung(甲乙經), Nan Kyung(難經), Yu Kyung(類經), etc. Sa Gi Gang Boo Byung Hyung got its name by how its contents pointed to the mechanism of getting harmed by Sa Gi(邪氣), and the forms of diseases which were led from five organs and six hollow viscera getting harmed by Sa Gi(邪氣). Sa Gi Gang Boo Byung Hyung is divided into three chapters which are divided altogether into nine sections. The first chapter is on the mechanism of Sa Gi(邪氣)' s harming the five organs and the six hollow viscera. Going into details, it discusses that Sa Gi has got two different ways which are divided into Yum Yang(陰陽) to harm the organs and the hollow viscera. Next, it discusses how faces can endure the cold that well. The second chapter is on the essences such as symptoms, face colors, shapes of pulse, and conditions on the interior part of the elbow. In the first section, it discusses how figures, colors and pulses relate together. In the second section, it discusses different diseases have different pulses and conditions on the interior part of the elbow. The third section is on forms of diseases in five organs and six hollow viscera. The third chapter is on acupuncture. The first section is about acupuncturing six channels. The second is about acupuncture points which is compared to the sea by its function. The third is about the forms of diseases with discussing symptoms and acupuncture points. The forth is about the essence of acupuncture. The ten different pulses of each five organs, and the masses of five organs in Nan Kyung(難經), and Jang Bu Mak Jin Beob(臟腑脈診法) in Eu Hak Yib Moon(醫學入門) are based on 'The six different pulses of each five organs' which is shown in the third section, second chapter. Besides, it plays an important role in study and it can play an important role as well in doctoring such as inspecting, taking pulses and so on. Thus, I found Sa Gi Gang Boo Byung Hyung worth while to study. But, Sa Gi Gang Boo Gyung Hyung was written in ancient letters and was omitted in many parts, which led successive doctors to write different explanatory notes. Thus, I researched the exact meaning through successive explanatory notes.

• Korean Journal of Optics and Photonics
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• v.17 no.6
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• pp.556-563
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• 2006

We present a comprehensive study of a chirped pulse Ti:sapphire regenerative amplifier system operating at 1 kHz. Main constituents of the system are described in detail. The amplifier stage was first converted to a repetition rate-tunable kHz gain-switched nanosecond Ti:sapphire laser. Operation characteristics at different repetition rates such as build-up times of laser pulses, pump power-dependent output powers and pulse durations, damage thresholds, and tunability ranges were studied. Based on the results achieved, the switching time of the Pocket's cell used and the round trip numbers in the regenerative amplifier were optimized at 1 kHz. The output pulses with a pulse width of 50fs from a home-made Ken lens mode-locked Ti:sapphire oscillator were used as seed pulses. The pulses were expanded to 120ps in a grating stretcher prior to coupling into the 3-mirror amplifier cavity. After amplification and recompression, a stable 1kHz Ti:sapphire regenerative amplifier system, which delivers 85-fs, $320-{\mu}J$ pulses, was fully constructed.