• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.68.2-68.2
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• 2016

We present the variability and time lag measurements of PG 0934+013 based on the photometric and spectroscopic monitoring campaign over two years. We obtained 46 epochs of data from the spectroscopic campaign, which was carried out using the South African Large Telescope with 1 week cadence over two sets of 4 month-long observing period, while we obtained 80 epochs of B band data from the campaign. Due to the six month gap between two campaigns, we separately measured the time lag of the $H{\beta}$ emission line by comparing the emission line light curve with the B band continuum light curve using the cross-correlation function techniques. We determined the time lags and black hole mass.

• The Journal of the Acoustical Society of Korea
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• v.29 no.7
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• pp.411-421
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• 2010

A time-reversal mirror (TRM) is useful in diverse areas, such as reverberation ing, target echo enhancement and underwater communication. In underwater communication, the bit error rate has been improved significantly due to the increased signal-to-noise ratio by spatio-temporal focusing. This paper deals with two issues. First, the optimal number of array elements for a given environment was investigated based on the exploitation of spatial diversity. Second, an algorithm was developed to determine the optimal location of the given number of array elements. The formulation is based on a genetic algorithm maximizing the contrast between the foci and area of interest as an objective function. In addition, the developed algorithm was applied to the matched field processing with ocean experimental data for verification. The sea-going data and simulation showed almost 3 dB improvement in the output power at the foci when the array elements were optimally distributed.

• The Journal of the Acoustical Society of Korea
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• v.9 no.2
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• pp.42-52
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• 1990

A method of measuring impulse response of acoustic system, two kinds of cross-correlation methods (the direct correlation method and the M-sequence modulation correlation method) were applied. According to the direct correlation method, by using stationary random noise source and by calculating the cross-correlation function between the sourece and the output signal, equivalent impulse response can be obtained not being influenced by the back ground noises. By applying this method, the measurement of echo-time patterns in rooms and oblique incident sound absorption characteristics of sound absorbing materials was carried out. In the case of the M-sequence modulation correlation method which was contrived by Aoshima, an intermittent random nosie modulated by M-sequence signal is used as the source signal, and the cross-correlation function between the M-sequence signal and the squared output signal is calculated. According to this method, equivalent energy impulse response (squared impulse response) of te propagation system can be obtained without being influenced by the back ground noises and the air fluctuation caused by wind. As the applcaition of this measuring method to the architectural acoustics, the meaurements of echo-time patterns, reverberation decays and sound pressure lev디 distributions in rooms and sound insulation efficiencies in buildings were carried out. From these experimental studies, it has been found that this M-sequence modulation correlation method is markedly useful especially for the field masurement of sound insulation under high back ground noise condition.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.76.4-77
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• 2017

We have been performing a long term AGN Monitoring project, to measure the time lag of H beta line with respect to AGN optical continuum based on the reverberation mapping method. From October 2015, 69 AGNs have been monitored with BVR band photometry, using the MDM 1.3m & 2.4m and LOAO 1m telescopes, and long-slit spectroscopy, using the Lick 3m and MDM 2.4m telescopes. In this poster, we report the preliminary results of the variability study of a subsample of 9 AGNs, particularly with a few of tentative time rag measurements between B band magnitude and H beta luminosity based on the 1st year data set from February 2016 - January 2017.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.50.2-50.2
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• 2017

We have been carrying out the long-term (3-5 years) AGN monitoring project since October 2015 to investigate the variability and measure the H beta line time lag of 69 nearby (0.06 < z < 0.47) AGNs based on the reverberation mapping method. Our targets have B band magnitudes of 14.4-18.6, luminosities of log L5100 = 45.6-48.1 erg/s, and the expected time lags of 28-597 light days. BVR band images are being taken with ~20-day cadence using MDM 1.3m, LOAO 1m and MDM 2.4m telescopes. Recently, Nickel 1m at Lick and DOAO 1m at Deokheung observatory are joined with photometric observations. Follow-up spectroscopic observations are on-going using the Lick 3m and MDM 2.4m telescopes. In this poster, we will describe our project including sample selection and the observational strategy, and present the preliminary results based on the 1st year photometry.

• Journal of The Korean Astronomical Society
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• v.52 no.4
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• pp.109-119
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• 2019

While the reverberation mapping technique is the best available method for measuring black hole mass in active galactic nuclei (AGNs) beyond the local volume, this method has been mainly applied to relatively low-to-moderate luminosity AGNs at low redshift. We present the strategy of the Seoul National University AGN Monitoring Project, which aims at measuring the time delay of the $H{\beta}$ line emission with respect to AGN continuum, using a sample of relatively high luminosity AGNs out to redshift z ~ 0.5. We present simulated cross correlation results based on a number of mock light curves, in order to optimally determine monitoring duration and cadence. We describe our campaign strategy based on the simulation results and the availability of observing facilities. We present the sample selection, and the properties of the selected 100 AGNs, including the optical luminosity, expected time lag, black hole mass, and Eddington ratio.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.461-470
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• 2009

We investigate and analyze the problems encountered in frame-based estimation of TDOA (Time Difference of Arrival) using CPSP function. Spectral leakage occurring in framing of a speech signal by a rectangular window could make estimation of CPSP spectrum inaccurate. Framing with other windows to reduce the spectral leakage distorts the signal due to the asynchronous weighting around the frame specifically both ends of the frame. These problems degrade the performance of the CPSP-based TDOA estimation. In this paper, we propose a method to alleviate those problems by pre-emphasis of the speech signal. It reduces the influence of the spectral leakage by reducing dynamic range of the spectrum of a speech signal with pre-emphasis. To validate the proposed method of pre-emphasis, we carry out TDOA estimation experiments in various noise and reverberation conditions, Experimental results have shown that the framing of pre-emphasized microphone output by a rectangular window achieves higher success rate of TDOA estimation than any other framing methods.

• The Journal of the Acoustical Society of Korea
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• v.29 no.7
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• pp.458-467
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• 2010

In this paper, a new audio reproduction system was developed in which the cross-talk signals would be reasonably cancelled at an arbitrary listener position. To adaptively remove the cross-talk signals according to the listener's position, a method of tracking the listener position was employed. This was achieved using the two microphones, where the listener direction was estimated using the time-delay between the two signals from the two microphones, respectively. Moreover, room reverberation effects were taken into consideration where linear prediction analysis was involved. To remove the cross-talk signals at the left-and right-ears, the paths between the sources and the ears were represented using the KEMAR head-related transfer functions (HRTFs) which were measured from the artificial dummy head. To evaluate the usefulness of the proposed listener tracking system, the performance of cross-talk cancellation was evaluated at the estimated listener positions. The performance was evaluated in terms of the channel separation ration (CSR), a -10 dB of CSR was experimentally achieved although the listener positions were more or less deviated. A real-time system was implemented using a floating-point digital signal processor (DSP). It was confirmed that the average errors of the listener direction was 5 degree and the subjects indicated that 80 % of the stimuli was perceived as the correct directions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.236-241
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• 2007

Recently, in accordance with the cultural progress and the improvement of citizen's consciousness level, it is the real situation that the construction of small-scaled Multi-Purpose Hall where various cultural events could be performed, is on increasing. However, because the most of Multi-Purpose Hall had been designed and built up without any consideration on Acoustic Factor, many problems are on occurring thereat. Because those small-scaled Multi-Purpose Hall have been mostly used with the finishing material which contains a high degree of Acoustic Absorption indiscreetly, both diffusion and reflection of sound are not establishing properly, and since the reverberation of sound is very low, in case of musical performance by musical instrument, its sound hears too arid and stiff, there occurs some acoustic defect such as it becomes difficult for music appreciation with sufficient timbre, so that the capability improvement on the matter is urgently requiring situation. On this viewpoint, this Research has caught the Authenticity of the forecasted value and actually measured value using Acoustic Simulation on the subject of the small-scaled Multi-Purpose Hall, and then intended to propose the optimum acoustic condition on the basis of the Authenticity. As the result, it could be designed a Multi-Purpose Hall equipped with the satisfactory acoustic performance compare with the time before improvement, so that it is considered that such research result could be practically used as the fundamental material when design for other similar small-scaled Multi-Purpose Hall in the future.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.715-719
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• 2007

Recently, since there appear the quality improvement in both educational and cultural level at the college campus also, thus the lecture room is requiring by the students where the intimacy degree among the students can be raised, also a smoother interaction between the professor and the student is able to be generated. Particularly in case of College of Music, the Practical Technique Training Rooms such as Orchestral Music Room, Pipe Music Concert Room, Music-Part Practice Room are more important for the interaction between Professor and Student or Student attends at the lesson, than the lecture rooms of any other colleges. Likewise, while such music practice room should be designed with consideration of the acoustic characteristics, so as to obtain the feel as if hear it performs at a music hall, but since the most of music practice room was designed with consideration of the convenience of construction work and its economical efficiency only, it has been exposed with many acoustic defects after the completion of construction. Therefore in this thesis, it has grasped the physical acoustic characteristics on the object of the two orchestral music rooms, pipe music concert room and ensemble practice room, among the newly constructed practice rooms of the Music College, W University, and it is considered that it could be utilized as the fundamental data on the base of this material when designing of the college music practice room, for the future.