• Korean Journal of Materials Research
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• v.21 no.7
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• pp.403-409
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• 2011

Micro speakers are used to reproduce sound in small electric and information and communications devices, such as cellular phones, PMPs, and MP3 players. The acoustical properties and sound quality, which are changed due to the decreased size of the speaker, are often adjusted varying the type and thickness of the diaphragm. The most widely used diaphragm material is thin polymer. It was previously reported by the author of this paper that the resonance frequency of a micro speaker is changed by the type and thickness of a polymer diaphragm. In this paper, the frequency response near the resonance frequency of a micro speaker was studied as functions of the type and thickness of the polymer diaphragm. While $R_{max}$ and $R_{DC}$ were affected by the type and thickness, an analysis of the electrical impedance curve revealed that $R_o(= R_{max}/R_{DC})$ and ${\Delta}f$ were not changed. Thus, $Q_{TS}$ which was function of $R_o$, ${\Delta}f$, and the resonance frequency, is only related to the resonance frequency. The increase of the resonance frequency led to a proportional rise of $Q_{TS}$. The change of the frequency response near the resonance frequency was not dependent on the type or thickness of the polymer diaphragm, but was affected by the resonance frequency.

• Journal of dental hygiene science
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• v.13 no.4
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• pp.461-470
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• 2013

In order to examine the anticariogenic effect after fluoride varnish was applied to sound enamel and artificial caries enamel, anterior teeth of healthy cattle were used and divided into four groups such as group 1 (sound enamel), group 2 (application of fluoride varnish to sound enamel), group 3 (artificial caries enamel) and group 4 (application of fluoride varnish to artificial caries enamel). Remineralization on the surface of enamel and changes of crystalline structure after demineralization were observed by using a field emission scanning electron microscope (FE-SEM). Quantitative analysis of Ca and P was measured by using the energy dispersive X-ray spectrophotometer (EDS). The following conclusions were obtained: 1)Surface pattern of enamel was the roughest in group 3 due to the defects caused by porosity and microcracks. Group 4, group 1 and group 2 were followed in order; 2) It was found that pattern of crystalline structures in a group of application of fluoride varnish and a group of no application showed bigger change in artificial caries enamel than that in sound enamel. In other words, groups 4 and 1 showed a similar pattern; 3) The contents of Ca and P were higher in groups of application of fluoride varnish (group 2 and group 4) than in groups of no application of fluoride varnish (group 1 and group 3). Taken results of this study together, in the case of application of fluoride varnish, crystalline structure was changed by remineralization even in the sound enamel. In particular, porous structures showed a smooth and uniform pattern due to the recalcification in the artificial caries enamel. In addition, according to results of EDS analysis, the contents of Ca and P were increased and it had great anticariogenic effects which inhibit decalcification of sound enamel and artificial caries enamel.

• Korean Journal of Microbiology
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• v.3 no.1
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• pp.1-6
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• 1965

Over a period of 1962-64, a transmission-experiment of witchess' broom of jujube tree by stem-grafting was conducted. When stem-grafting of sound scions upon diseased roots or diseased scions upon sound roots were carried out, disease transmission of high rate was witnessed; 99% in the former and, in the latter, 62% of the stocks which saw union by callussing and had new shoots. Even when the diseased scions by stem-grafting or the diseased buds by budding upon sound stock died away, the transmission rate was 21% in stem-grafting and 14% in budding which seems to show that, when tissues of diseased plants and stocks are kept contacted over a certain period, the disease transmission occurs. And when the recovered scions taken from once diseased tree were grafted upon diseased roots, the transmission rate was 100 % and therefore it is presumed that the immunity could not be acquired even under the assumption of complete recovery from the disease. In stem-grafting of the diseased scions upon sound roots, 98% of the scions which were stored in the cellar, overwintered and grafted in spring was diseased, whereas the disease rate of the scions which were cut and grafted in spring was only 33%. It was particularly noteworthy that 90% of the scions in the former case and only 3% in the latter case were diseased as of June 18th approximately 2 months after the actual grafting and then the latter advanced to 33% with the passage of time. It appears that the pathogen in branches and shoots of the diseased trees standing outdoors become inactivated or diminished during winter. Through its symptom, pathological change in tissue, and easy transmission of the disease via stem-grafting, it seems certain that the pathogen of the witches broom disease in jujube tree is a virus.

• Hwankyungkyoyuk
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• v.8 no.1
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• pp.98-106
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• 1995

A current environmental issue, 'Enviromentally Sound and Sustainable Development(ESSD)' is very important in that it is for our common future. Environmental education is essential as a long-term strategy to realize sustainable environments and society. So we developed a new program about ESSD. The purposes of development were as follows. First, introduce ESSD to students, second, make them know ESSD appropriate to our nation, third, make change from economy-centered thoughts to environmental economy-centered thoughts, ultimately make form behaviors related to ESSD. To verify the effects of new developed program, the direct learning was carried out by 212 students in total. Post test scores of experimental groups were significantly higher than those of control groups about four goals, respectively. Therefore this program is effective to achieve four goals of environmental education for ESSD.

• KCID journal
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• v.17 no.2
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• pp.49-56
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• 2010

This study was carried out to survey for morphological change of lower tidal flat near Byunsan-Gosapo beach using single-beam echosounder and sound velocity profiler. Since October 2009 in the center of the region, the erosion occurred about 10~50cm, while either side of the study area is little change. Erosion occurred at the beach, each beach area in the southwest area rather than further accumulation occurred sandbank formed. Observed in the study area near the center of the erosion is the result of ongoing changes that were temporarily due to seasonal changes is not clear. However, the northwestward waves were expected to be a major source of erosion. Because of this, continue to observe the terrain and the local ocean circulation studies will be required.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.3
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• pp.295-301
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• 2008

Bathymetric data collected using a multi-beam echo sounder during marine scientific survey is essential for geologic and oceanographic research works. Accurate measurment of sound velocity profile(SVP) in water-column is important for bathymetric data processing. SVP can vary at different locations during the survey undertaken for wide areas. In addition, an observational error can occur when different equipments(Sound Velocity Profiler, Conductivity Temperature Depth, eXpendable BathyThermograph) are used for measuring SVP at the same water column. In this study, we used an MB-system software to show changes in bathymetry caused by variation of SVP. The analyses showed that the sound velocity(SV) changes due to the depth and thickness of thermocline had more significant effects on the resulting bathymetric data than those of surface mixed layer. The observational errors between SVP measuring instruments did not cause much differneces in the processed bathymetric data. Bathymetric survey line is better to be established to the direction that the change of temperature can be minimize to reduce the variation of SVP during the data acquisition along the survey line.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1425-1429
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• 2007

Consumer's product selection measures are being shifted from the units' operational performance to overall performance. Low noise, low vibration, and low power consumption rate, etc. which used to be additional quality indices, now become vital performance factors. Especially, noise and vibration characteristics are being considered as equivalent to/or even more critical than operational performance in certain products such as office machines and home entertainment systems, which share the same space with human being's daily life. Therefore, noise reduction and sound quality improvement technology becomes an inevitable design issue for those applications. Qualitative noise characteristics of rotating polygonal disk applied to digital printer systems are presented. Overall sound pressure level change and tonal noise variation with respect to the geometrical properties of polygonal disk, operational speed, and others are briefly discussed based on experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.1168-1173
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• 2001

Compressors are the main source of noise of refrigerators and air-conditioning unit. Recent studies on the sound propagation of rotary compressors showed that the accumulator is a significant source of noise generation. This paper describes a design change of a rotary compressor for noise reduction using topology optimization. Topology optimization has been developed and used to find the most effective structural configuration in the early stage of design procedures. FE model of the rotary compressor composed of all the components is built for the topology optimization. Topology optimization results show that the empirical design for the present structure fail to constrain some resonance modes and a new component is required.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.333.1-333
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• 2002

This paper suggests the noise reduction method of the engine cooling fan. It was estimated the fannoise contribution at the engine room and identified the noise source at the rotating fan by sound intensity method, first. And it has been developed the program for predicting the noise spectrum of axial flow fan. The radiated acoustic pressure is expressed the discrete frequency noise peaks at BPF and its harmonics and the line spectrum at the broad band by the noise generation mechanisms. In this paper it is shown that the comparison of the measuted and calculaed noise spectra of fn for the validation of the noise predictiong program. And this paper presents the characteristics of a fan noise due to modify the design parameters. Accordingly, it was obtained the design parameter values for noise reduction of fan.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.6
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• pp.606-611
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• 2008

Consumer's product selection measures are being shifted from the units' operational performance to overall performance. Low noise, low vibration, and low power consumption rate, etc. which used to be additional quality indices, now become vital performance factors. Especially, noise and vibration characteristics are being considered as equivalent to/or even more critical than operational performance in certain products such as office machines and home entertainment systems, which share the same space with human being's daily life. Therefore, noise reduction and sound quality improvement technology becomes an inevitable design issue for those applications. Qualitative noise characteristics of rotating polygonal disk applied to digital printer systems are presented. Overall sound pressure level change and tonal noise variation with respect to the geometrical properties of polygonal disk, operational speed, and others are briefly discussed based on experimental results.