• MALSORI
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• no.67
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• pp.121-133
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• 2008

To estimate directions of multi-sound sources, we consider an approach based on zero crossings which provided more robust results to diffuse noise than the conventional cross-correlation-based method [6][7]. In reverberant environments, the performance of source direction estimation can be improved by using signal components through direct paths from sources to microphones. Since a cepstral prefiltering technique [8] removes the effect of reverberation, we propose a source direction estimation method which can find out intervals of the direct-path components by comparing original and cepstral-prefiltered envelopes. Simulations demonstrate that the proposed method can improve the performance of source direction estimation in reverberant environments.

• Journal of KSNVE
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• v.10 no.5
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• pp.880-885
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• 2000

In a verical type, vibratory gyroscope, the coupled motion between the reference and sensing vibrations causes the zero-point output which means non-zero sensing vibration without angular velocity. This structural coupling leaks to an inherent discrepancy between the natural frequencies of the reference and sensing oscillations, causing the degradation of the sensing performance and dynamic stability. In this paper, the dynamic characteristics associated the coupling phenomenon are theoretically analyzed. Effects of reference frequency and coupling factor on the rotational direction and amplitude of elliptic oscillation are studied. A technique to predict the existence of curve veering of crossing in frequency trajectories is introduced to apply the design of micro gyroscopes with decoupled structures.

• Journal of Power Electronics
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• v.16 no.3
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• pp.915-924
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• 2016

A digital self-sustained phase shift modulation (DSSPSM) strategy that allows for good soft switching and dynamic response performance in the presence of step variations is presented in this paper. The working principle, soft switching characteristics, and voltage gain formulae of a LLC converter with DSSPSM have been provided separately. Furthermore, the method for realizing DSSPSM is proposed. Specifically, some key components of the proposed DSSPSM are carefully investigated, including a parameter variation analysis, the start-up process, and the zero-crossing capture of the resonant current. The simulation and experiment results verify the feasibility of the proposed control method. It is observed that the zero voltage switching of the switches and the zero current switching of the rectifier diodes can be easily realized in presence of step load variations.

• Journal of Power Electronics
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• v.15 no.4
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• pp.1131-1138
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• 2015

This study presents an input-powered high-efficiency interface circuit for energy harvesting systems, and introduces a zero standby power design to reduce power consumption significantly while removing the external power supply. This interface circuit is composed of two stages. The first stage voltage doubler uses a positive feedback control loop to improve considerably the conversion speed and efficiency, and boost the output voltage. The second stage active diode adopts a common-grid operational amplifier (op-amp) to remove the influence of offset voltage in the traditional comparator, which eliminates leakage current and broadens bandwidth with low power consumption. The system supplies itself with the harvested energy, which enables it to enter the zero standby mode near the zero crossing points of the input current. Thereafter, high system efficiency and stability are achieved, which saves power consumption. The validity and feasibility of this design is verified by the simulation results based on the 65 nm CMOS process. The minimum input voltage is down to 0.3 V, the maximum voltage efficiency is 99.6% with a DC output current of 75.6 μA, the maximum power efficiency is 98.2% with a DC output current of 40.4 μA, and the maximum output power is 60.48 μW. The power loss of the entire interface circuit is only 18.65 μW, among which, the op-amp consumes only 2.65 μW.

• Journal of Korea Water Resources Association
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• v.30 no.3
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• pp.225-233
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• 1997

The nonlinear effects on the statistical properties of wave groups in terms of the average nomber of waves in a group and the mean number of waves in a high run is studied in this paper utilizing the complex envelope and total phase function, random variable transformation technique and perturbation method. It tures out that the phase distribution is modified significantly by nonlinearities and it show systematic excess of values near the mean phase and the corresponding symmetrical deficiency on both sides away from the mean. for the case of threshold crossing rate, it turns out that threshold crossing rate reaches its maxima just below the mean water level rather than zero and considerable amount of probability mass is shifted toward the larger values of water surface elevation as nonlinearity is getting profound. Furthermore, the mean waves in a high run associated with nonlinear wave are shown to have larger values than the linear counterpart. Similar trend can also be found in the average number of waves in a group.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.5
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• pp.239-246
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• 2017

In case of observing only wave height and period in the field, various wave characteristics are mainly calculated by wave by wave analysis method. In this paper, an wave by wave analysis program using MATLAB language is developed. It is possible to perform a function such as 1) correction for mean water level, 2) calculation for zero crossing time, 3) calculation for individual wave height, 4) time interval by using zero upcrossing and downcrossing method. The applicability of the developed program to the data of 0.2 second interval observed by using the WaveGuide Radar installed on HeMOSU-1 was examined. Tidal level variation removal and zero crossing time estimation were determined by linear or quadratic interpolation. It was judged that the Goda method was appropriate for calculating individual wave height, and the method proposed in this study seems to be improved through subsequent research. Due to the fineness of the sample, it can be seen that characteristics of representative waves are different from the results calculated by zero upcrossing and downcrossing method.

• Journal of the Korean Society of Visualization
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• v.2 no.1
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• pp.32-38
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• 2004

A new PIV technique was developed for decreasing optical error which was created during simultaneous measurements of velocity fields at a wall-normal plane and wall-parallel plane by a plane PIV and a Stereo-PIV systems. For experimental study, two different Reynolds number based on momentum thickness, Re$_{ =514 and 934 were generated in a blowing type wind tunnel under the condition of zero pressure gradient. The two Nd:Yag laser systems and three CCD cameras were synchronized. to obtain instantaneous velocity fields at the same time. To avoid optical noise at the crossing line by the two laser light sheets, a new optical arrangement using polarization was applied. The obtained velocity fields show the existence of hairpin packet structure vividly and the idealized hairpin vortex signature is confirmed by experiment.

• Journal of Korean Society of Forest Science
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• v.88 no.4
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• pp.485-489
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• 1999

The germination percentages of Quercus hybrid seeds produced in 1994 using stored pollens were low. The survival rate and height growth within 2 years differed according to crossing combinations. The survival rate and growth of seedlings from hybrid seeds produced in 1991 and 1993 were investigated. The survival rates of five-year-old and three-year-old seedlings were from 71 to 100% and from 33 to 100%, respectively. The survival rates differed according to cross combinations. The mortality of seedlings increased in proportion to the increase of percentages of dwarf seedlings. The growth of five-year-old seedlings, of which mother tree was Q. aliena, was the best. The growth of seedlings produced by artificial crossing tended to be worse than that of natural crossing.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.29B no.8
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• pp.44-53
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• 1992

In this paper, a matching method is proposed to improve the correct matching rate in stereo correspondence matching in which the fingerprint of zero-crossing points on the scale-space is used as the robust matching feature. The dynamic programming, which is appropriate for the fingerprint feature, is introduced for correspondence matching. We also improve the matching rate by using the post-processing for correcting mismatched points. In simulation, we apply the proposed algorithm to the synthetic and real images and obtain good matching results.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.88-92
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• 1993

In speech signal processing, it is necessary to detect exactly the pitch. The algorithms of pitch extraction which have been proposed until now are difficult to detect pitches over wide range speech signals. Thus we propose a new algorithm which uses the G-peak extraction to do it. It is the method that finds the most MZI(maximum zero-crossing interval) at each frame and convolve it with speech signal ; this is the same with passing speech signals to variable LPF. Finally we obtained the pitch, improve the accuracy of pitch detection and extract it with the high speed.