• Current Optics and Photonics
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• v.1 no.5
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• pp.525-528
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• 2017

High-energy, high-power, quasi-continuous wave (QCW) operation of double-clad Yb fiber lasers incorporating an incoherent signal combiner is reported. We constructed four efficient, high-power Yb fiber lasers, each of which produced rectangular pulses at 1080 nm with a pulse energy greater than 15 J, and a pulse duration of 10 ms at a repetition rate of 10 Hz, corresponding to an average power of over 150 W and a peak power of over 1.5 kW for ~200 W of incident pump power at 915 nm. These laser outputs were combined by a homemade incoherent fiber signal combiner with low loss, yielding a maximum peak power of ~6.0 kW in a beam with $M^2{\approx}12.5$. The detailed laser characteristics and prospects for further power scaling in QCW operation are discussed.

• Phonetics and Speech Sciences
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• v.2 no.4
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• pp.19-28
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• 2010

The purpose of this study was to increase the current understanding of the acoustic characteristics of voices with advancing age. The relationship between age-related changes in body physiology and certain acoustic characteristics of voice was studied in a sample of 80 men representing four chronological age groupings (20-29, 50-59, 60-69, 70-79) who were all of good physical condition. Each subject was asked to phonate the vowel /a/, /i/, and /u/ for as long as possible at comfortable frequency and intensity level and read the sentence. A promising voice analysis program (Multi-Dimensional Voice $Program^{TM}$) was used to measure the fundamental frequency ($f_0$), jitter, shimmer, $f_0$ variation, peak-amplitude variation, smoothed pitch perturbation quotient, smoothed amplitude perturbation quotient, soft phonation index, $f_0$-tremor intensity index, amplitude tremor intensity index, and noise-to-harmonics ratio from the samples.

• KIEE International Transactions on Electrophysics and Applications
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• v.3C no.3
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• pp.77-80
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• 2003

An innovative ozonizer has been developed using a high frequency, surface discharge and a high purity Ti-Si-AI ceramic catalyst as a dielectric component. Using a type of thin film, a thin cylindrical compound ceramic catalyst layer was adhered to the outside surface of its inner electrode. An alternating current (AC) exciting voltage with frequencies from 0.6 KHz to 1.0 KHz and peak-to-peak voltages of 4-6 ㎸ was applied between the electrodes to produce a stable high-frequency silent discharge. A substantial reduction of the exciting voltage was also enabled by means of a thin Ti-Si-Al ceramic catalyst tube. As a result, the ozonizer can effortlessly obtain the required ozone concentration (50-60 g/$m^2$ for oxygen) and high ozone efficiency consumption power (180 g/kWh for oxygen) with-out the assistance of any particular methods. For purposes of this experiment, oxygen gas temperature was set at 2$0^{\circ}C$, with an inner reactor pressure of 1.6 atm at 600 Hz and a flow rate of 2 l/min.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.200-202
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• 1996

MgO film was deposited on the glass substrate by the hollow cathode discharge ion plating method and the characteristics of the MgO thin film such as deposition rate, crystalline orientation, surface morphology and secondary electron coefficient were investigated. The deposition rate of MgO thin films were $430^{\sim}1270{\AA}$/min at various temperatures and biases. The crystalline orientation of the MgO thin film changed from (200) to (220) upon increasing the HCD current from 100A to 200A. These results indicated that the crystallin orientation of the MgO thin film was determined by the super-saturation ratio. The (200) peak decreased and the (220) peak increased as the substrate bias increased, while both peaks increased as the substrate temperature increased. The grain size increased as the substrate bias increased and the secondary electron emission coefficient increased as the substrate bias increased.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1568-1569
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• 2006

An electric probe is a conductor inserted into the plasma, by which plasma density and electron temperature can be deduced from the collected current (I) versus applied voltage (V) to the probe. In RF plasma the I-V characteristics of electric probe is distorted due to the RF fluctuation of plasma potential, so that it is hard to measure the real plasma parameters, especially the electron temperature. To eliminate the RF fluctuation, several compensation methods are developed such as RF compensation probe, peak-to-peak method, asymmetric double probe. By comparing proposed methods, a suitable method is to be introduced in determining electron temperatures in RF plasma.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.29-34
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• 1993

a-Si : H photodiodes for image sensor have been fabricated and characterized. Photosensitivity of a ITO/a-Si : H/Al photodiode without blocking layer was 0.7 under the applied voltage of 5 V and peak spectral sensitivity in visible region was found at 620 nm. Dark current of ITO/a-SiN : H/a-Si : H/p-a-Si : H/Al photodiode was suppressed by hole blocking layer and electron blocking layer at the value of lower than 1.5 pA to the applied voltage of 10 V. Also maximum photosensitivity was about 1 under the applied voltage of 3 V and peak spectral sensitivity was found at 540 nm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.71-74
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• 2005

This experimental study describes the propagation characteristics and reduction of impulse noises emitted from a high voltage COS(Cut Out Switch) fuse of a transformer. When a high voltage COS fuse becomes a short circuit by the over current. The peak sound Pressure above 150dB(A) is generated. In this study, an impulse noise generator is designed for generating the impulse noises similar to the noise level of COS fuse, which is utilized to test the noise reduction of a reactive silencer. The reactive silencers have been tested for 10 different types with each different porosity, hole diameter and length. From the experimental results, it is found that the reactive silencer has an excellent performance to greatly suppress the impulse noise and that its performance is closely connected with the porosity and hole diameter.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.6 s.111
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• pp.658-664
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• 2006

Shock vibrations are usually experienced in vehicles excited by impulsive input, such as bumps. The frequency weighting functions of the current standards in ISO 2631 and BS 6841 are to help objectively predict the amount of discomfort of stationary vibration. This experimental study was designed to develop frequency weighting shape for shock vibration having various fundamental frequencies from 0.5 to 16Hz. The specks were produced from the response of single. degree-of-freedom model to a half-sine force input. Fifteen subjects used the magnitude estimation method to judge the discomfort of vertical shock vibration generated on the rigid seat mounted on the simulator. The magnitudes of the shocks, expressed in terms of both peak-to-peak value and un-weighted vibration dose values (VDVs) , were correlated with magnitude estimates of the discomfort. The frequency weighting shapes from the correlation were developed and investigated having nonlinearity due to the magnitude of the shock.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.6
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• pp.419-427
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• 2014

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

• Journal of the Korean Applied Science and Technology
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• v.8 no.2
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• pp.153-159
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• 1991

The electrochemical oxidation of p-methoxyphenol and hydroquinone for wastewater treatment application was investigated on platinum anode. At the cyclic voltammetry, it was observed that nagative shift of peak potential of p-methoxyphenol and hydroqinone as the pH of electrolytes increases and the peak current showed higher at strong electrolytes than weak electrolytes. In the case of p-methoxyphenol, the optimum electrode potential of controlled potential electrolysis was observed at the potential region of 0.8-1.0 (V vs. SCE) and hydroquinone was showed at the potential of l.0(V vs. SCE). Specially the oxidation rate of p-methoxyphenol and hydroquinone was showed high value in the acid electrolytes.