• 천문학회보
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• 제41권2호
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• pp.41.1-41.1
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• 2016

The Galactic center, Sagittarius A* (Sgr A*), is the closest supermassive black hole and emits synchrotron radiation. It provides great opportunity to study the origin of mm/sub-mm emission. Currently, two competing models have been suggested as a jet base and a radiatively inecient accretion flow (RIAF). To unveil the properties, the extremely high resolution(${\sim}10{\mu}as$) corresponding to the projected Schwarzschild radius of ~0.1AU is necessary. With KVN, a jet model can be tested by multi- frequency simultaneous observations because the optically thick surface in a jet (i.e. radio core) moves toward the center at a higher frequency. We conducted 8 observations with KVN at 43/86GHz in 2015, and found that the measured positional shift to the reference calibrator, J1744-3116, was ~0.3 mas to the south of Sgr A* using the source frequency phase referencing (SFPR) at Q/W bands for the first time. With the result, in the future, we will attempt to measure the variation of source position shifts that can constrain the direction of approaching jets and the variability of black hole activity of Sgr A*.

• 센서학회지
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• 제24권3호
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• pp.169-174
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• 2015

In this study, we developed a system to detect the various defects in the metallic objects using the phenomenon that the defects cause the changes of the natural resonant frequencies. Our system consists of a FFT Amp, an Auto Impact Hammer, a Hammer controller and a PC. Auto Impact Hammer creates vibrations in the metallic objects when tapped on the surface. These vibrational signals are converted to the voltage signals by an acceleration sensor attached to the metallic part surface. These analog voltage signals were fed into an ADC (analog-digital converter) and an FFT (fast fourier transform) conversion in the FFT Amp to obtain the digital data in the frequency domain. Labview graphical program was used to process the digital data from th FFT amp to display the spectrum. We compared those spectra with the standard spectrum to find the shifts in the resonant frequencies of the metal parts, and thus detecting the defects. We used PCB's acceleration sensor and TI's TMS320F28335 DSP (digital signal processor) to obtain the resolution of 2.93 Hz and to analyze the frequencies up to 44 kHz.

• 한국가시화정보학회지
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• 제18권1호
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• pp.26-37
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• 2020

Magnetic resonance thermometry (MRT) is a technique capable of measuring three-dimensional mean temperature fields by utilizing temperature-dependent shifts in proton resonance frequency. In this study, experimental verification of the technique is obtained by measuring 3D temperature fields within fully developed turbulent pipe flow, using 3T and 7T MRI scanners. The effect of the proton resonance frequency (PRF) thermal constant is examined in detail.

• 대기
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• 제33권4호
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• pp.399-411
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• 2023

This study compares the three detection algorithms of East Asian summer atmospheric rivers (ARs). The algorithms developed by Guan and Waliser (GW15), Park et al. (P21), and Tian et al. (T23) are particularly compared in terms of the AR frequency, the number of AR events, and the AR duration for the period of 2016-2020. All three algorithms show similar spatio-temporal distributions of AR frequency, centered along the edge of the North Pacific high. The maximum AR frequency gradually shifts northward in early summer as the edge of the North Pacific High expands, and retreats in late summer. However, the detailed pattern and the maximum value differ among the algorithms. When the AR frequency is decomposed into the number of AR events and the AR duration, the AR frequencies detected by GW15 and P21 are equally explained by both factors. However, the number of AR events primarily determine the AR frequency in T23. This difference occurs as T23 utilizes the machine learning algorithm applied to moisture field while GW15 and P21 apply the threshold value to moisture transport field. When evaluating AR-related precipitation, the ARs detected by P21 show the closest relationship with total precipitation in East Asia by up to 60%. These results indicate that AR detection in the East Asian summer is sensitive to the choice of the detection algorithm and can be optimized for the target region.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.340-341
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• 2012

In this work, we investigated the effects of temperature stress on flatband voltage (VFB) shifts of HfO2-SiO2 double gate dielectrics devices. Fig. 1 shows a high frequency C-V of the device when a positive bias for 10 min and a subsequent negative bias for 10 min were applied at room temperature (300 K). Fig. 2 shows the corresponding plot when the same positive and negative biases were applied at a higher temperature (473.15 K). These measurements are based on the BTS (bias temperature stress) about mobile charge in the gate oxides. These results indicate that the positive bias stress makes no difference, whereas the negative bias stress produces a significant difference; that is, the VFB value increased from ${\Delta}0.51$ V (300 K, Fig. 1) to ${\Delta}14.45$ V (473.15 K, Fig. 2). To explain these differences, we propose a mechanism on the basis of oxygen vacancy in HfO2. It is well-known that the oxygen vacancy in the p-type MOS-Cap is located within 1 eV below the bottom of the HfO2 conduction band (Fig. 3). In addition, this oxygen vacancy can easily trap the electron. When heated at 473.15 K, the electron is excited to a higher energy level from the original level (Fig. 4). As a result, the electron has sufficient energy to readily cross over the oxide barrier. The probability of trap about oxygen vacancy becomes very higher at 473.15 K, and therefore the VFB shift value becomes considerably larger.

• 한국병원경영학회지
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• 제21권3호
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• pp.11-21
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• 2016

The purpose of this study is to investigate the degree of difficulty and turnover of nurses working in the field and to derive clinical work activation and supply policy improvements. Data was collected from December, 2014 to January, 2015, from 23 hospitals, and participants were 3,887 nurses working in the field, Survey details : the difficulty of the clinical work of nurses working in hospitals, turnover intentions status and policy proposals for clinical research work enabled General characteristics, difficulties in clinical working, turnover intention and clinical work plan activation are frequency analysis. The difference between each of the variables in accordance with the general characteristics are one-way ANOVA analysis, Correlation analysis of the variables is also a Pearson correlation coefficients. 'difficulties in clinical working' was a statistically significant difference depending on the type of hospital, nursing class, number of beds, location, age, position, employment, gender, working form, working department, salary, career, and degree level. 'turnover intention' was a statistically significant difference depending on nursing rate, number of beds, region, age, position, sex, shifts, departments, annual income, and career. 'policy recommendation' was a statistically significant difference depending on type of hospital, nursing rate, age, position, employ, shifts, departments, annual income, degree level and career 'difficulties in clinical working' is 'turnover intention' (p<.001), 'policy recommendations' (p<.001) and had a significant positive correlation. and 'turnover intention' had a "policy recommendation" significant positive correlation with the relationship (p<.001) The most difficulties point of the nurses working in the field are the environment, such as shift, urgent and dangerous. Major policy proposals are improve treatment such as wages, and welfare.

• Safety and Health at Work
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• 제6권2호
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• pp.104-113
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• 2015

Background: Given the long hours on the road involving multiple and interacting work stressors (i.e., delivery pressures, irregular shifts, ergonomic hazards), commercial drivers face a plethora of health and safety risks. Researchers goal was to determine whether and to what extent long-haul trucker work schedules influence sleep duration and quality. Methods: Survey and biometric data collected from male long-haul truck drivers at a major truckstop in central North Carolina over a six month period. Results: Daily hours worked (mean = 11 hours, 55 minutes) and frequency of working over government-mandated daily HOS regulations (23.8% "frequently or always") were statistically significant predictors of sleep duration. Miles driven per week (mean = 2,812.61), irregular daily hours worked (63.8%), and frequency of working over the daily hour limit (23.8% "frequently or always") were statistically significant predictors of sleep quality. Conclusion: Implications of findings suggest a comprehensive review of the regulations and operational conditions for commercial motor vehicle drivers be undertaken.

• The Plant Pathology Journal
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• 제22권1호
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• pp.1-6
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• 2006

The population shifts of Monilinia fructicola isolates which were resistant to the fungicide benzimidazoles were investigated in four regions of Korea from 1998 to 2000. The isolation frequency of benzimidazole-resistant isolates ranged from 18.8% to 29.6% in Chongdo and from $22.0\%$ to $26.8\%$ in Gyeongsan during the same period. However, the frequency of benzimidazoleresistant isolates was less than $4.0\%$ in Chochiwon and Youngduk during the same period. Benzimidazoleresistant isolates showed cross-resistance among benzimidazoles. On the other hand, none of the isolates showed cross-resistance to diethofencarb and carbendazim. Regardless of the year, the benzimidazole-resistant isolates of $EC_{50}$ higher than 500 $\mug%$ a.i./ml were isolated more frequently in mid and late season than in early season. In an orchard of Gyeongsan that had not been exposed to any fungicides for several years, the population of benzimidazole-resistant isolate had persisted without much fluctuation for three years. These results suggest that benzimidazole resistance of M. fructicola is becoming a problem in controlling brown rot and blossom blight of peach in regions like Chongdo and Gyeongsan.

• Safety and Health at Work
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• 제8권2호
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• pp.212-219
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• 2017

Background: Low back pain (LBP) is a major problem for office workers. Individuals adopting poor postures during prolonged sitting have a considerably increased risk of experiencing LBP. This study aimed to investigate seat pressure distribution characteristics, i.e., average pressure, peak pressure ratio, frequency of postural shift, and body perceived discomfort (BPD), during 1 hour of sitting among office workers with and without chronic LBP. Methods: Forty-six participants (chronic LBP = 23, control = 23) typed a standardized text passage at a computer work station for an hour. A seat pressure mat device was used to collect the seat pressure distribution data. Body discomfort was assessed using the Body Perceived Discomfort scale. Results: Office workers with chronic LBP sat significantly more asymmetrically than their healthy counterparts. During 1-hour sitting, all workers appeared to assume slumped sitting postures after 20 minutes of sitting. Healthy workers had significantly more frequent postural shifts than chronic LBP workers during prolonged sitting. Conclusion: Different sitting characteristics between healthy and chronic LBP participants during 1 hour of sitting were found, including symmetry of sitting posture and frequency of postural shift. Further research should examine the roles of these sitting characteristics on the development of LBP.

• Asian Pacific Journal of Cancer Prevention
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• 제13권7호
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• pp.3423-3426
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• 2012

Background: The objective of this study was to measure the antibody content of NuTu-19 ovarian cancer cells in serum samples using a quartz crystal microbalance (QCM) immunosensor. Materials and Methods: NuTu-19 cells were first cultured onto the electrode surfaces of crystals in Dulbecco's modified Eagle medium, and then specified amounts of immunized serum samples of immunized rabbit were also added. The change in mass caused by specific adsorbtion of antibodies of NuTu-19 to the surfaces of the crystals was detected. Results: The change in resonance frequency of crystals caused by immobilization of NuTu-19 cells was from 83 to 429Hz. The antibody content of NuTu-19 detected was 341ng/ul. The frequency shifts were linearly dependent on the amount of antibody mass in the range of 69 to 340ng. The positive detection rate and the negative detection rate were 80% and 100%, respectively. Conclusion: This immunoassay provides a viable alternative to other early ovarian cancer detection methods and is particularly suited for health screening of the general population.