• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.4
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• pp.406-412
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• 2017

Vocalizations of the common dolphin Delphinus Delphis, were recorded from a single hydrophone while coastal visual survey was performed in the East Sea in March 2017. Like most Delphinidae, common dolphins produce whistles, echolocation clicks, and burst-pulsed calls, with repertoires that differ between species and geographically separated populations. This study focuses on using frequency analysis to classify sounds into three categories and to compare them with those of other common dolphin populations. The fundamental frequencies of the whistles were high in the 6 to 14 kHz range, while echolocation clicks were in the 40 to 90 kHz frequency band. These results are similar to high-energy distributions in the same frequency band in other regions. Based on this study of the acoustic characteristics of dolphins off the east coast of Korea, cetacean vocalizations can be classified using a database of cetacean sounds in Korea. In addition, this technique could improve data quality for visual whale surveys and could be applied to various other research subjects.

• Journal of the Korean Society of Physical Medicine
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• v.15 no.4
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• pp.111-119
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• 2020

PURPOSE: In adults with hamstring tightness, stretching is considered a therapeutic exercise that improves flexibility. However, previous studies have reported efficacy of numerous methods, and are inconclusive in determining the most effective stretching techniques. This study aims to compare the outcomes of Evjenth-Hamberg stretching (E-HS), proprioceptive neuromuscular facilitation stretching (PNFS), and static stretching (SS), on muscle tone and flexibility. METHODS: A total of 30 subjects were assigned to each of the three stretching groups:; E-HS (n₁ = 10), PNFS (n₂ = 10), and SS (n₃ = 10). Muscle tone of the hamstring muscle, active knee extension (AKE), and passive knee extension (PKE) were assessed by range of motion. RESULTS: After the intervention, statistically significant differences were obtained between groups for muscle tone (p < .05). The post hoc test, showed statistically significant differences in muscle tone between the E-HS and PNFS groups (p < .05), and PNFS and SS groups (p < .05). Post hoc test after intervention, also revealed statistically significant differences in flexibility (p < .05) between the E-HS and PNFS groups (p < .05), E-HS and SS groups (p < .05), and PNFS and SS groups (p < .05). Moreover, a statistically significant difference was observed in PKE scores between the E-HS and SS groups (p < .05), and PNFS and SS groups (p < .05). CONCLUSION: This study indicates that E-HS may be the most effective stretching technique for muscle tone and flexibility, in adults with hamstring tightness.

• Nuclear Engineering and Technology
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• v.34 no.6
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• pp.545-552
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• 2002

We developed an ultra low background gamma ray spectrometer particularly suitable for experiment which require lower detection limit. The background of a germanium spectrometer is suppressed by applying active and passive shielding technique at the same time. The active shielding devices consist of plastic scintillating plates of 50 mm thick and anti-coincidence electronic system. The shielding is made of 150 mm thick walls of very low activity lead,20 mm with activity of <10 Bq/kg and 130 mm with activity of <50 Bq/kg. The observed background count rates are 1.2 $s^{-1}$ and 0.36 $s^{-1}$ without and with the active shielding, respectively, overall the energy regions from 30 keV to 3 MeV The cosmic ray induced background is suppressed by a rate of 0.8 $s^{-1}$ at the present work. The detection efficiency curve necessary to obtain the radioactivity of environmental samples has been precisely determined on the energy regions from 80 to 2000 keV with a 10$^3$ ml marinelli beaker sample, consisting of the calibrated radionuclides $^{109}$ Cd, $^{57}$ CO, $^{139}$ Ce, $^{203}$ Hg, $^{113}$ Sn, $^{85}$Sr, $^{137}$ Cs, $^{60}$ Co and $^{88}$ Y. Virtues Of the method are demonstrated by measuring the activity of $^{137}$ Cs contained in the powdered milk.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.12
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• pp.1069-1074
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• 2016

This paper presents a V-band two-stage power amplifier integrated circuit using TSMC 65 nm CMOS process. The simple input, output, and inter-stage matching networks based on passive components are integrated. By compensating for power gain characteristics using a pre-distortion technique, the linearity of the power amplifier was improved. The implemented two-stage power amplifier showed a power gain of 10.4 dB, a saturated output power of 9.7 dBm, and an efficiency of 20.8 % with a supply voltage of 1 V at the frequency band of 58.8 GHz.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.125-133
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• 2016

In order to obtain high-resolution seafloor images, research on SA (Synthetic Aperture) processing and the development of related underwater systems have been performed in many countries. Recently the SA processing is also recognized as an important technique in Korea and researchers started related basic study. However, most previous studies ignored the Doppler effect by a moving receiver array. In this paper reconstructed SAS (Synthetic Aperture Sonar) images and position errors are analyzed according to the speed of a moving array for understanding its moving effect on the SAS images. In the analysis the spatial frequency domain interpolation algorithm is used. The results show that as the moving speed of the array increases the estimated position error also increases and image distortion gets worse when we do not consider the array motion. However, if the compensated receiver signals considering the array motion are used the position error and image distortion can be eliminated. In conclusion a signal processing scheme which compensates the Doppler effect is necessary especially in the condition where the array speed is over 1 m/s.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.255-262
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• 2020

In modern passive sonar systems, a towed array sensor is used to minimize the effects of own ship noise and to get a higher SNR. The thin and long towed array sensor can be guided in a non-linear form according to the maneuvering of tow-ship. If this change of the array shape is not considered, the performance of beamformer may deteriorate. In order to properly beamform the elements in the array, an accurate estimate of the array shape is required. Various techniques exist for estimating the shape of the linear array. In the case of a method using a heading sensor, the estimation performance may be degraded due to the effect of heading sensor noise. As means of removing this potential error, weighted polynomial fitting technique for estimating array shape is developed here. In order to evaluate the performance of proposed method, we conducted computer simulation. From the experiments, it was confirmed that the proposed method is more robust to noise than the conventional method.

• Asian Journal of Atmospheric Environment
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• v.2 no.2
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• pp.81-89
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• 2008

The numerical simulation of wind and ozone ($O_3$) transport in mountainous regions was performed with a computational fluid dynamics technique. A dry deposition model for $O_3$ was designed to estimate $O_3$ deposition in complex terrain, and the qualitative validity of the predicted $O_3$ concentration field was confirmed by comparison with observed data collected with passive samplers. The simulation revealed that wind velocity increases around ridge lines and peaks of mountains. The areas with strong wind corresponded well with the sites of tree decline at high altitudes, suggesting that it is an important factor in the localization of tree/forest decline. On the other hand, there is no direct relationship between forest decline and $O_3$ concentration. The $O_3$ concentration, however, tends to increase as wind velocity becomes higher, thus the $O_3$ concentration itself may be a potential secondary factor in the localized decline phenomena. While the diffusion flux of $O_3$ is not related to localized tree decline, the pattern of advection flux is related to those of high wind velocity and localized tree decline. These results suggest that strong wind with large advection flux of $O_3$ may play a key role in the promotion of tree/forest decline at high mountain ridges and peaks.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.64.1-64.1
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• 2011

MIRIS (Multipurpose Infra-Red Imaging System), is a small infrared space telescope which is being developed by KASI, as the main payload of Science and Technology Satellite 3 (STSAT-3). Two wideband filters (I and H) of the MIRIS enables us to study the cosmic infrared background by detecting the absolute background brightness. The narrow band filter for Paschen ${\alpha}$ emission line observation will be employed to survey the Galactic plane for the study of warm ionized medium and interstellar turbulence. The opto-mechanical design of the MIRIS is optimized to operate around 200K for the telescope, and the cryogenic temperature around 90K for the sensor in the orbit, by using passive and active cooling technique, respectively. The engineering and qualification model of the MIRIS has been fabricated and successfully passed various environmental tests, including thermal, vacuum, vibration and shock tests. The flight model was also assembled and is in the process of system optimization to be launched in 2012 by a Russian rocket. The mission operation scenario and the data reduction software is now being developed. After the successful mission of FIMS (the main payload of STSAT-1), MIRIS is the second Korean space telescope, and will be an important step towards the future of Korean space astronomy.

• Nuclear Engineering and Technology
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• v.43 no.6
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• pp.557-566
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• 2011

A cold spray coating (CSC) of copper was studied for its application to a high-level radioactive waste (HLW) disposal canister. Several copper coatings of 10 mm thick were fabricated using two kinds of copper powders with different oxygen contents, and SS 304 and nodular cast iron were used as their base metal substrates. The fabricated CSC coppers showed a high tensile strength but were brittle in comparison with conventional non-coating copper, hereinafter defined to as "commercial copper". The corrosion behavior of CSC coppers was evaluated by comparison with commercial coppers, such as extruded and forged coppers. The polarization test results showed that the corrosion potential of the CSC coppers was closely related to its purity; low-purity (i.e., high oxygen content) copper exhibited a lower corrosion potential, and high-purity copper exhibited a relatively high corrosion potential. The corrosion rate converted from the measured corrosion current was not, however, dependent on its purity: CSC copper showed a little higher rate than that of commercial copper. Immersion tests in aqueous HCl solution showed that CSC coppers were more susceptible to corrosion, i.e., they had a higher corrosion rate. However, the difference was not significant between commercial copper and high-purity CSC copper. The decrease of corrosion was observed in a humid air test presumably due to the formation of a protective passive film. In conclusion, the results of this study indicate that CSC application of copper could be a useful option for fabricating a copper HLW disposal canister.

• PNF and Movement
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• v.13 no.3
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• pp.135-143
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• 2015

Purpose: The purpose of this study was to assess the effect of the proprioceptive neuromuscular facilitation (PNF) relaxation technique (hold relax; HR, contract relax; CR) and static stretch (SS) on hamstring flexibility and vertical jump performance in healthy adults over a four-week period. Methods: Twenty-four healthy adults volunteered to participate in PNF and static stretch sessions. The subjects were divided into three groups as follows: 8 subjects in the SS group, 8 subjects in the HR group, and 8 subjects in the CR group. In the HR and CR groups, contractions lasted 15 seconds per trial and consisted of 5 sets of 15 seconds of hamstring contraction immediately followed by 15 seconds of passive static hamstring stretching. For the static group, the participants were asked to stretch by hanging a leg over a table for 30 seconds. Subjects in all groups performed the exercises three days per week for 4 weeks. The active straight leg raising (ASLR) test, active knee extension (AKE) test, and vertical jump test were performed before the intervention and after 1, 2, and 4 weeks. Results: The SS, HR, and CR techniques effected positive improvement in hamstring flexibility and vertical jump performances but neither of the stretching methods had any statistically significant different effects according to group, although there were interactions (between group and time) in the ALSR group from 1 week to 2 week and in the AKE test from pretest to 1 week. Conclusion: Based on the results of the current study, SS, HR, and CR were shown to affect hamstring flexibility and vertical jump performance in healthy adults. In particular, it was determined that within a short period, hamstring flexibility could be attributed more to CR than to SS.