• Tribology and Lubricants
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• v.11 no.5
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• pp.128-135
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• 1995

Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales, ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer, and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of single-crystal silicon, natural diamond, magnetic media (magnetic tapes and disks) and magnetic heads have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurements of atomic-scale friction of a freshly-cleaved highly-oriented pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement has been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is observed on both micro- and macro scales which results from the surface preparation and anisotropy in surface roughness. Microscale friction is generally found to be smaller than the macrofriction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load approaching to the macrofriction at contact stresses higher than the hardness of the softer material. Wear rate for single-crystal silicon is approximately constant for various loads and test durations. However, for magnetic disks with a multilayered thin-film structure, the wear of the diamond like carbon overcoat is catastrophic. Breakdown of thin films can be detected with AFM. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nono scratches. AFM has been modified to obtain load-displacement curves and for nanoindentation hardness measurements with depth of indentation as low as 1 mm. Scratching and indentation on nanoscales are the powerful ways to screen for adhesion and resistance to deformation of ultrathin fdms. Detection of material transfer on a nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thichness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolyers and chemically-bonded lubricant films with a mobile fraction are superior in wear resistance. Finally, AFM has also shown to be useful for nanofabrication/nanomachining. Friction and wear on micro-and nanoscales have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help def'me the regimes for ultra-low friction and near zero wear.

• Parasites, Hosts and Diseases
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• v.33 no.1
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• pp.9-18
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• 1995

The study made an observation on periodicity of oviposition, and the effects of nutrient and salinity in egg un larval development of Aedes togoi, and the results are summarized as follows: The 53.9% mosquitoes of one feeding laid eggs once, 26.9% laid hice and 19.2% laid three times. Autogenous rate of Aedes togoi reared in three different nutrient groups in larval stage was 6.9% in 0.8 mg/larva, 22.5% in 1.6 mg/larva and 44.4% in 2.4 mg/larva. The oviposition rate according to different salinity of the oviposition sites (0%, 0.5%, 1.0%, 2.0% and 4.0%) was 25.2% in distilled water, 36.2% in 0.5% salinity 23.5% in 1.0% salinity and 14.6% in 2.0% salinity. Developing period of the aquatic stage of male Aedes toBoi in $25^{\circ}C$ were shorter (10.73 days) than females (11.85 days). The most effective concentration of salinity for the developing period was 1.0% which took 9.25 days in males and 10.44 days in females. In the developmental status of the follicles according to nutrition in the larval stage, the numbers of follicles of groups fed 0.8 mg, 1.6 mg and 2.4 mg per larva were 180.7, 197.% and 202 respectively. The result of ovary dissection on the 1 with day after emergence, three different nutrition groups were in Christopher's stage IIa mostly; each 71.0%, 61.1% and 39.9% of the total follicles and autogenous females observed.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.2
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• pp.86-94
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• 2000

In order to extract the spatio-temporal characteristics of long-term variability of the net heat flux on the sea surface in the East Asian marginal seas, empirical orthogonal function (EOF) analysis was conducted using data set calculated every 12 hours interval during 1978-1995. Among the first three modes explaining 73% of the total variance, the first mode having high peak at 1 year period indicates high variability area around the Sandong Peninsula and central and northeastern part of the East Sea. In the second mode which has spatial distribution of dipole type at the north and south, the peaks appear at 3.6 year and 2.3 year cycles. Time coefficient of the second EOF is believed to have close relation with the E1 Nino and has out-of-phase variation with NINO3 SST. Lagged correlation between NINO3 SST and time coefficient of the second EOF indicates four month time delay in the NINO3 SST. In the third mode which has opposite sign at the east and west, the periodicity of 6-9 year cycle has relatively clear appearance compared to other two EOFs. Also, high heat loss exceeding 800 W/$m^{2}$ in winter time occured at the south part of the Sandong Peninsula and Vladivostok. It reveals more frequent occurrence of about two times at the Sandong Peninsula than Vladivostok. The event is concentrated in January at Vladivostok, but it occurs primarily in December and January at the Sandong Peninsula.

• Journal of the Korean association of regional geographers
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• v.19 no.3
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• pp.446-453
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• 2013

Festivals using plant phenology is one of the examples can represent the ecosystem services. Changwon Jinhae Gunhangje is typical spring festival using cherry blossoms phenology. This research was done to define relationship between flowering of cherry blossoms and Gunhangje. Phenological data (Julian day) of cherry blossoms and visitor number of Gunhangje from 1987 to 2013 were collected. Differences of Phenological phase of cherry blossoms and duration of Gunhangje was analyzed. Trend analysis was performed to know changes of flowering and budding day of cherry blossoms. Correlations between visitor number of Gunhangje and environmental factors was defined by factor analysis and regression analysis. Results are showed that during the 26 years, periodicity of flowering and budding day was not identified or even identified it was not significant. Environmental factors effect on visitor numbers of Gunhangje were defined as temperature factor, day factor, and precipitation factor. Temperature factor was significantly correlated with visitor numbers of Gunhangje. Though Flowering day of cherry blossoms and festival duration was not matched, however, difference of visitor numbers was not showed. These results suggest that fixed duration of Gunhangje would be more effective to visitors than changing the festival duration following the phenological day changes of cherry blossoms.

• The Journal of Korean Medical History
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• v.15 no.1
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• pp.11-24
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• 2002

First, during Jin and Sui dynasty, It is possible that the theory of the contraindications of needling according to whereabouts of the self-guarding energy and demon, affected considerably to the practise of acupuncture and moxibustion, but the detailed situations are unknown. Only, there are some records of the process about circulation of the self-guarding energy and demon by a periodicity of 30 days in the "The prescriptions of Fan-Wang" by Fan-Wang in Jin dynasty and "Hua Tuo Fa" by a nameless person. But the theory differs form the theory of "Huang Di Xia Mo Jing" in some respect. Also, there is the contraindications of needling to abscesses according to whereabouts of the self-guarding energy and demon by every year in the "Liu Juan Zi Gui Yi Fang". but the book has no specific rule in use. Second, during Tang dynasty there were a vasty development on the contraindications of needling according to whereabouts of the self-guarding energy and demon. In the medical works in Tang dynasty, the contents of the contraindications of needling are included in various periodicities and directions such as 12 regions according to the year, 9 regions according to the year, 9 palaces in the body according to the year, whereabouts of the self-guarding energy and demon according the four seasons, every 10 days, every 12 days, every 30 days, and every dozen hours. Also, during Tang dynasty period, the contraindications of needling according to whereabouts of the self-guarding energy and demon were formulated through several adjustments and modifications by many medical scholars. Third, the period between Jin and Tang dynasty, because of historical situations, the documentary data are insufficient in the study of the recommendations and contraindications on the acupuncture, moxibution, and herb medicine according to the specific days and times. And the detailed informations are unknown. Only but once in Tang dynasty the considerable and theoretical adjustments were performed in the "Qian Jin Yao Fang". In Song dynasty, there were also much theoretical fluctuations in the study of the choice of the favorable or the injurious days and times or directions in the acupuncture, moxibustion and the prescription and processing of herbs. Fourth, contraindications on the acupuncture, moxibution, and herb medicine did not include acute and serious disease among the effect province, only include chronic and not serious disease. If the doctors had treated a surgical patients and abscess patients with deeply attached contraindications on the acupuncture, moxibution, and herb medicine, the patients would have became more serious. So the theory was not used for treatment by doctor.

• Fire Science and Engineering
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• v.34 no.4
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• pp.1-6
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• 2020

In this study, the authors measured voltage and current waveforms in real time during a serial arc discharge. The analysis results of the arc discharge radiation patterns exhibited intermittent discharge, arc growth, creation of a heat generating area, occurrence of plume, and formation of a red heat area, which proceeded in that order. When the serial arc discharge was introduced, the current and voltage waveforms exhibited periodicity as sine waves. It was also observed that a restriking transient voltage occurred when the waveform changed from positive (+) to negative (-) and vice versa. When the discharge proceeded, the amount of heat generated for 1 s and 600 s was approximately 0.317 mJ, and 190 mJ, respectively. The duration of the short circuit was approximately 1.66 ms, and in the case of the voltage waveform, it was evident that the electric potential increased to 49.9 V in the same cycle. Furthermore, when the discharge proceeded, the effective value (RMS value) of the current was approximately 1.72 A with a maximum current of approximately 2.53 A, whereas the effective value of the voltage was approximately 42.8 V with a maximum of approximately 208 V.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.4
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• pp.659-668
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• 2017

In this study, long-term rainfall data of more than 300 years including the paleoclimatic rainfall data from Chuk Woo Kee (1777-1907), the modern observed rainfall data (1908-2015), and the climate change scenario (2016-2099), which were provided by KMA (Korea Meteorological Agency), was used to analyze the statistical characteristics of the extreme drought in the Seoul., Annual average rainfall showed an increasing trend over a entire period, and Wavelet transform analysis of SPI (Standardized Precipitation Index) which is meteorological drought index, showed 64 to 80 months (5-6 Year) of drought periods for Chuk Woo Kee and KMA data, 96 to 128 months (8 to 10 years) of drought period for climate change data. The dry spell analysis showed that the drought occurrence frequency in the ancient period was high, but frequency was gradually decreased in the modern and future periods. In addition, through the analysis of the drought magnitude, 1901 was the extreme drought year in Seoul, and 1899-1907 was the worst consecutive 9 years long term drought in Seoul.

• Journal of the Korean Geotechnical Society
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• v.34 no.1
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• pp.5-16
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• 2018

In this study, seismic performance of geotechnical seismic isolation system capable of primary seismic isolation in the ground was evaluated. 1-G shaking table test was used to assess the performance of Teflon or steel slag as geotechnical seismic isolation systems installed beneath superstructure foundation. Response acceleration and response spectra were analyzed considering different input motions. The results were compared with those of fixed foundation structure without seismic isolation system. The steel slag-type seismic isolation system showed significant reduction in acceleration. The teflon-type seismic isolation system did not show significant effects on acceleration reduction in low-to-moderate seismicity condition, but it did show better effects in case of strong seismic condition. As input motion was transferred to the upper mass, the response spectrum of the fixed foundation structure was amplified in the short period range. In contrast, the response spectrum of the structure with seismic isolation using teflon or steel slag amplified in the long period range. It is found that the change of periodicity and the friction characteristics between isolation materials and foundations affected acceleration reduction.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.239-245
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• 2014

Finite element modeling of composite structures may be cumbersome due to complex distributions of reinforcements. In this paper, an efficient scheme is proposed that can generate periodic meshes for the composite structures. Regular meshes with hexahedral finite elements are first prepared, and the elements are then trimmed to fit external surfaces of reinforcements in the composite structures. The trimmed hexahedral finite elements located at interfaces between the matrix and the reinforcements correspond to polyhedral finite elements, which allow an arbitrary number of nodes and faces in the elements. Because the trimming process is consistently conducted by means of consistent algorithms, the elements of the reinforcements are automatically compatible with those of the matrices. With the additional consideration of periodicity of reinforcements in a representative volume element(RVE), the proposed scheme provides periodic meshes in an efficient manner, which are compatible for each pair of periodic boundaries of the RVE. Therefore, periodic boundary conditions for the RVE are enforced straightforwardly. Numerical examples demonstrate the effectiveness of the proposed scheme for finite element modeling of complex composite structures.

• Journal of Korea Water Resources Association
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• v.45 no.1
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• pp.75-89
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• 2012

This study attempted to analyze statistical characteristics of historical drought of Korea through trend, periodicity and drought spell analysis by using the drought indices. Standard Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) were calculated using weather data of 59 weather stations under Korea Meteorological Administration (KMA). As a result of analysis, SP13 and SP16 showed trend of drier spring, drier winter and wetter summer in all basin of Korea. However, SPI12 and PDSI showed different trends with shorter duration drought indices. In case of wavelet transform analysis for drought periodicities, in a band of 1~2 years or below 6 years showed significant spectrum. SP13 showed strongest power spectrum near the band of 1~2 year variance, and SPI12 and PDSI showed 6 years periodicities. The results from drought spell showed that Nakdong River Basin, Geum River Basin and Youngsan River Basin were appeared as severe drought vulnerable area of Korea.