• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.55.2-55.2
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• 2020

Radio relics in the outskirts of galaxy clusters are interpreted as synchrotron radiation due to the relativistic electrons produced via diffusive shock acceleration (DSA) in shocks with low sonic Mach numbers, Ms ≤ 3 in high beta ICM plasma. Electron injection into the DSA process at such weak shocks is one of the key elements, which has yet to be fully understood. In this study, we explore the nature of kinetic microinstabilities excited in weak quasi-perpendicular shocks through 2D particle-in-cell simulations. We find Alfven-ion cyclotron (AIC), whistler, and mirror instabilities can be triggered by ion and electron temperature anisotropy in the immediate downstream of supercritical shocks with Ms > Mcrit ~ 2.3. In particular, AIC instability causes rippling of the shock surface, which in turn generates plasma waves on multi-scales and faciliates the electron preacceleration. Our results may contribute to understanding the origins of radio relics.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.5
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• pp.365-372
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• 1998

The method of measuring the nonlinear effect of ultrasonic waves is suggested as a new approach for the effective evaluation of material degradation. In sonic wave propagation, the existence of nonlinear effect can be demonstrated by the generation of higher order harmonic waves. So, at first, the mechanism of generating higher order harmonic components due to nonlinear effect was explained by using nonlinear elasticity. Next, we attempted to measure how much of the higher order harmonic component was generated in the degraded material. For this purpose, a measurement system mainly based on a high-powered nonlinear ultrasonic signal analysis system was constructed, and SS41 and SS45 specimen intentionally degraded by tensile load and fatigue load were tested. From the results, we confirmed that the measurement of nonlinear acoustic effect may be useful for the evaluation of material degradation.

• Journal of Physiology & Pathology in Korean Medicine
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• v.22 no.3
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• pp.672-677
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• 2008

In order to explore the anti-oxidization effect of oriental medicine and cereal medium(OCM) where Tricholoma matsutake mycelia were cultured, measurement of hot water extract and UMPM(extraction method using ultra sonic waves, micro waves, micro bubble) extract, the total polyphenol content of crude polysaccharide from each extract, SOD-like activity, electron donating ability(EDA), xanthine oxidase inhibitory activity, and tyrosinase inhibitory activity was conducted. The total polyphenol content of each extract was found to be 16.36% for hot water extract(HE) group and 15.73% for UMPM extract(UE) group and the amount of crude polysaccharide precipitated into ethanol of extracts was found to be 8.79% for UMPM ethanol extract(UEE) group and 6.48% for hot water ethanol extract(HEE) group. As a result of measurement of SOD-like activity by concentration of each extract, it was found to be 96.17% for UE group, 91.23% for HE group, 91.33% for UEE group, and 87.11% for HEE group at 20 mg/mL. In the case of EDA, it was found to be 47.55% for UE group, 44.93% for HE group, 25.38% for UEE group, and 18.36% for HEE group. And in the cases of the rates of xanthine oxidase inhibitory activity and tyrosinase inhibitory activity, as the concentration of each extract increased, the inhibition rate increased accordingly. As a result of comparison between hot water extract method and UMPM extract method using extracts obtained from oriental medicine compound medium where Tricholoma matsutake mycelia were cultured, all of the extracts were judged to have a high anti-oxidization effect. In particular, UMPM extracts were found to have higher polyphenol content, SOD-like activity, EDA, xanthine oxidase inhibitory activity and tyrosinase inhibitory activity compared to hot water extract method. In this regard, extracts obtained from OCM where Tricholoma matsutake mycelia were cultured are considered to have high availability as functional material when and if they are prepared using UMPM extract method.

• Journal of Society of Preventive Korean Medicine
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• v.12 no.2
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• pp.1-12
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• 2008

The purpose of this study was to investigate extract from mixed culture with Trichloloma matsutake mycelium in oriental medicine and cereal medium(OCM) to develop new material for pharmaceutical products and medicinal food. To evaluate of physiological activity of OCM extracts, we examined ${\beta}$-glucan contents, SOD-like activity, nitric oxide production and cytotoxicity by MTT assay. ${\beta}$-glucan contents was found to be 52.85% for crude polysaccharide of hot water extracts of OCM(HEE) and 49.74% for crude polysaccharide of ultra sonic waves, micro waves, and micro bubble extracts of OCM (UEE). SOD like activity was showed UE 74.66%, HE 67.16%, UEE 31.34%, HEE 26.10%, respectively. NO production of UEE and HEE, at LPS 1 ug/mL, 1 mg/mL UEE showed 66.62 uM and HEE 45.68 uM. at LPS 10 ug/mL, 1 mg/mL UEE showed 63.91 uM and HEE 51.74 uM. The inhibitory effect against HT1080 was increased dose-dependently in UEE.

• Current Research on Agriculture and Life Sciences
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• v.15
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• pp.47-52
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• 1997

The experiment was carried out to find the optimal condition for seed germination in vitro of Calanthe species. Seeds of Calanthe spp. after 90 days self pollination were well germinated in the MS medium. Germination condition of cross seeds between C. discolor and C. striata was much improved by pretreatment of micro sonic waves for 10 min. The days of germination was more shortened. and protocorm growth was more promoted in microsonic wave treatment than in non-treatment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1403-1412
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• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates through the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study calculated the effect of porous walls on the compression wave propagating into a model tunnel. Two-dimensional unsteady compressible equations were differenced by using a Piecewise Linear Method. Calculation results show that the cavity/porous wall system is very effective for a compression wave with a large nonlinear effect. The porosity of 30% is most effective for the reduction of the maximum pressure gradient of the compression wave front. The present calculation results are in a good agreement with experimental ones obtained previously.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.4036-4043
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• 1996

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.105-108
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• 1986

Ultrasound(50KHz) accelerated the reduction reaction of aromatic nitro group to aromatic amino group in high yield with mild condition using iron, hydrazine hydrate and activated carbon under room temperature and atmospheric pressure. The activated carbon has been used as a mixing material to highly active metals. However, aromatic nitro group does not reduce at all only with iron-hydrazine witliout adding activated carbon even under ultrasonic irradiation. We also discovered that the conversion yield from nitro group to amino group is directly proportional to the amount of activated carbon.

• Korean Journal of Materials Research
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• v.19 no.3
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• pp.169-173
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• 2009

In chemistry, the study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems. In the area of chemical kinetics, it has been observed that ultrasound can greatly enhance chemical reactivity in a number of systems by as much as a million-fold. Nano-technology is a super microscopic technology in which structures of 100 nanometers or smaller can be investigated. This technology has been used to develop $TiO_2$ materials and $TiO_2$ devices of that size. Thus far, electrochemistry methods and photochemistry methods have generally been used to create $TiO_2$ nano-size particles. However, these methods are complicated and create pollutants as a by-product. In the present study, nano-scale silver particles (5 nm) were prepared in a sonochemistry method. Sonochemistry deals with mechanical energy that is provided by the collapse of cavitation bubbles that form in solutions during exposure to ultrasound. $TiO_2$ powders 25 nm in size doped with Ag were formed using an ultrasonic sound technique. The experimental results showed the high possibility of removing pollution through the action of a photocatalyst. This powder synthesis technique can be considered as an environmentally friendly powder-forming processing owing to its energy saving characteristics.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.3
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• pp.242-247
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• 2008

As an absolute positioning system, iGS is designed based on ultrasonic signals whose speed can be formulated clearly in terms of time and room temperature, which is utilized for a mobile robot localization. The iGS is composed of an RFID receiver and an ultra-sonic transmitter, where an RFID is designated to synchronize the transmitter and receiver of the ultrasonic signal. The traveling time of the ultrasonic signal has been used to calculate the distance between the iGS system and a beacon which is located at a pre-determined location. This paper suggests an effective operation method of iGS to estimate position of the mobile robot working in unstructured environment. To expand recognition range and to improve accuracy of the system, two strategies are proposed: utilization of beacons belonging to neighboring blocks and removal of the environment-reflected ultrasonic signals. As the results, the ubiquitous localization system based on iGS as a pseudo-satellite system has been developed successfully with a low cost, a high update rate, and relatively high precision.