• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.775-786
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• 1992

Studies are made of the turbulent separation bubble in a two-dimensional semi-infinite blunt plate aligned to a uniform free stream when the oncoming free stream contains a pulsating component. The discrete-vortex method is applied to simulate this flow situations because this approach is effective to represent the unsteady motions of turbulent shear layer and the effect of viscosity near the solid surface. The two key external paramenters in the free stream, i.e., the amplitude of pulsation, A, and the frequency parameter St[=fH/ $U_{1}$], are dealt with in the present numerical computations, A particular frequency gives a minimum reattachment which is related to the drag reduction and the most effective frequency is dependent on the most amplified shedding frequency. The turbulent flow structure is scrutinized. A comparison between the unperturbed flow and the perturbed at the particular frequency of the minimum reattachment length of the separation bubble suggests that the large-scale structure is associated with the shedding frequency and the flow instabilities.

• Journal of the Korea Furniture Society
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• v.10 no.2
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• pp.73-78
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• 1999

This paper describes the relationship between the bending strength properties of sloped finger-jointed woods and the acoustic emissions(AEs) generated during the test. Rhus verniciflua pieces were cut in sloped-finger types and glued with three kinds of adhesives(polyvinyl acetate, polyvinyl-acryl acetate and oilic urethane resin). The slope ratios of finger joints were 0, 1.0, 1.5, and 2.0. The AE cumulative event count and cumulative count were measured during the bending test. The results were as follows: The lower the bending strength(load) was, the generation time of AE event count got and the higher the increasing rate of AE event count became in the sloped finger-jointed specimens bonded with polyvinyl acetate, polyvinyl-acryl acetate oilic urethane resin adhesives. Therefore, the slope from load-AE cumulative event count was very steep. The patterns of AE event count and count were very similar. The relationship between the MOR and the AE parameter from load and AE cumulatve event count in the early stage of the sloped finger-jointed specimens bonded with polyvinyl acetate, polyvinyl-acryl and oilic urethane resin adhesives was much greater than that between the MOE and the MOR. Therefore, the AE signals obtained during bending test are useful for estimating the strength of sloped finger-jointed Rhus verniciflua specimens.

• Phonetics and Speech Sciences
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• v.4 no.4
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• pp.155-162
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• 2012

The population of Korea is ageing as the number of elderly people increases due to improvements in health care and diet. Accordingly, it is expected that interest in how to live actively during the years after retirement and how to communicate effectively will increase the demand for voice improvement methods and technology. However, the criteria to evaluate the voice strength and characteristics of the elderly are lacking. In this study, we analyzed the acoustic characteristics of elderly women living in the community according to residential status and mental health status (e.g. depressive mood). Accordingly, we selected women (n=63) above the age of 65 age who were living in the Seoul metropolitan area and Daegu Gyeongbuk. The selected subjects were divided into two groups: a normal speaker group (n=40) and a speaker group comprised of those suffering from depressive mood (n=23). This study analyzed the voice characteristics of subjects based on collected data through the sustained phonation of the vowel /a/. It was shown that there were differences among MPT, F0, Jitter, Shimmer and NHR depending on location of residence but no difference with regard to depressive mood. Therefore, we must consider location of residence in elderly as the key factor in demonstrating the voice norms of seniors.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.9
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• pp.791-796
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• 2010

Installing noise barriers is the most common method for reducing the highway traffic noise to the road side residential area. After the report about edge potential concept of a noise barrier, various types of noise reducing devices(NRDs) called "noise reducers" have been suggested for getting more shielding effect on the top of highway noise barriers. But, it has been doubtful about effect of the NRDs in field because there was no appropriate and unified method to estimate the acoustic performance by using field measurement of the NRDs in Korea. In this study, the authors have considered to setup a practical method to test and estimate the acoustic performance of NRDs. For eliminating the noise reduction effect of the NRDs height itself, the source and measuring points are adjusted as highly as the NRDs height. For the frequency weighting in the estimation of the NRDs effect, the highway noise spectra were measured at asphalt and concrete road side and then averaged for a unit spectral parameter.

• Phonetics and Speech Sciences
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• v.7 no.2
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• pp.47-54
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• 2015

The objectives of this study are to research the frequency of depression symptom in patients with voice disorders and to investigate parameters associated with depression from voice evaluation. A hundred ninety six patients(106 males and 90 females) who had been diagnosed with voice disorders first in their lifetime were selected. All the patients were examined by laryngeal stroboscopy. For depression and voice study, personal interview, acoustic and aerodynamic analysis, voice handicap index(VHI), reflux symptom index(RSI), and beck depression index(BDI) were done respectively. Mild to severe BDI were seen in 26.2%(52 patients) of the whole patients. A BDI mean score of female patients was $8.8{\pm}7.5$ which was higher than that of male patients($5.6{\pm}6.6$), the difference observed being statistically significant(p<0.001). In the acoustic analysis, the score of sent_duration parameter was increasing in the patients with depression, which was significantly higher than the score of the patients without depression(p<0.05). In the addition, the scores of VHI and RSI were higher in the patients with depression(p<0.001). Our findings suggest that the prevalence of depression in patients with voice disorders is related to female, speaking velocity, and self-questionnaire. This result can be used for psychologically based approach to therapy.

• Phonetics and Speech Sciences
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• v.10 no.2
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• pp.15-24
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• 2018

Earlier studies reported that the /o/ and /u/ phonemes of Seoul Korean were currently merging in the F1/F2 space. However, studies on perception tests have shown that rates of correctness were high, even in cases where the two vowels overlapped. This study explores whether there is another acoustic parameter that differentiates /o/ from /u/, besides the F1/F2 contrast. Seventy-five native speakers of Seoul Korean, born between 1953 and 1999, participated in a production test. The data collected were analyzed in terms of F1 and F2, H1-H2, and F0. The result shows that the /o/ and /u/ of female speakers almost overlap in the F1/F2 space for all ages, while H1-H2 values are significantly different between the two vowels regardless of age. On the other hand, the /o/ and /u/ of male speakers are largely well separated in the F1/F2 space, while the H1-H2 values between the two vowels are very close at all ages. F0 effect is relatively small for both male and female speakers, even though there is a statistically significant difference. The result of this study provides evidence that female speakers use phonation differences to distinguish /o/ from /u/, and that the F1/F2 contrast has been replaced by H1-H2 values.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.6
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• pp.997-1002
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• 2017

Underwater communication, which is used acoustic channel of 1500[m/s] speed being different of wireless electric wave in terrestrial communication, is sensitive on water temperature and salinity and also affected from 3D underwater space. 3D underwater communication is sensitive on propagation loss of acoustic wave and underwater noise with complexity of communication space. In this paper, transmission performance with consideration of these characteristics of 3D underwater communication environments is measured and analyzed on MANET operated on 3D underwater communication environments. Some underwater MANET operation conditions will be suggested. Computer simulation with underwater simulator based on NS-2 will be used for performance measure, performance parameter like as throughput, transmission delay, packet loss rate and consumed energy will be used in simulation for performance measure.

• Journal of information and communication convergence engineering
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• v.11 no.4
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• pp.229-234
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• 2013

Diversity-multiplexing tradeoff (DMT) characterizes the fundamental relationship between the diversity gain in terms of outage probability and the multiplexing gain as the normalized rate parameter r, where the limiting transmission rate is give by rlog SNR (here, SNR denote the received signal-to-noise ratio). In this paper, we analyze the DMT and performance of an underwater network with a cooperative relay. Since over an acoustic channel, the propagation delay is commonly considerably higher than the processing delay, the existing transmission protocols need to be explained accordingly. For this underwater network, we briefly describe two well-known relay transmissions: decode-and-forward (DF) and amplify-and-forward (AF). As our main result, we then show that an instantaneous DF relay scheme achieves the same DMT curve as that of multiple-input single-output channels and thus guarantees the DMT optimality, while using an instantaneous AF relay leads at most only to the DMT for the direct transmission with no cooperation. To validate our analysis, computer simulations are performed in terms of outage probability.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1341-1346
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• 2001

In this study, the acoustic properties of steel-wire sound absorbing materials with different thickness and bulk density were investigated in terms of characteristic impedance, propagation constant, and absorption coefficient. The well-known two-cavity method was used for evaluating those acoustic parameter values in experiments. Also, in order to validate the experimentally measured values, the results were compared with the results obtained from Chung and Blaser's transfer function method and SWR method. The experimentally measured values of normal absorption coefficients were generally agreed well with the corresponding values from the transfer function method and the SWR method. Based on the experimental results, the following conclusions could be made. The magnitude of the absorption coefficient and the frequency range of the maximum absorption coefficient were controllable by changing the thickness and bulk density of the sound absorbing materials. Also, the magnitude of the absorption coefficient depended on the characteristic impedance and the propagation constant. As large as the air cavity depth at the rear side of the steel-wire sound absorbing materials, the maximum magnitude of the absorption coefficient occurred at the lower frequency ranges.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1589-1595
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• 2007

Recently many communication systems ate adapting the OFDM(Orthogonal Frequency Division Multiplexing) for multimedia data services. However, OFDM has some problems that PAPR is increased when sub-carries are summed up with same phases. This problem causes severe signal distortions while the signal is passing through non-linear system such as power amplifier resulting in performance degradation of transmission system. In this paper, we use IF-Clipping method to solve PAPR problem and the signal distortion caused by clipping is limited by use of SAW (Surface Acoustic Wave) filter and power amplifier(TWTA). And we derive the optimal parameter(PAPR, Backoff) values to meet the spectrum mask of WiBro system.