• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.713-725
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• 2004

The two-dimensional motion of a freely falling circular cylinder in an infinite fluid is investigated numerically using combined formulation. The effect of vortex shedding on the motion of a freely falling cylinder is clearly seen: as the streamwise velocity of the cylinder increases due to gravity, the periodic vortex shedding induces a periodic motion of the cylinder. This motion in turn affects the flow field, which is manifested by the generation of the angular velocity vector of the cylinder parallel to the cross product of the gravitational acceleration vector and the transverse velocity vector of the cylinder. A correlation of St-Re relationship for a freely falling circular cylinder is drawn from the present results. The Strouhal number for a freely falling circular cylinder is found to be smaller than that for a fixed circular cylinder when the two Reynolds numbers based on the streamwise terminal velocity of a freely failing circular cylinder and the free stream velocity of a fixed one are the same. From "thought experiments", it is shown that the transverse motion of the cylinder plays a crucial role in reducing the Strouhal number and has an effect of reducing the Reynolds number from the viewpoint of the pressure coefficient. The mechanism of this reduction in the Strouhal number is revealed by the fact that the freely falling cylinder experiences a smaller lift force than the fixed one due to the transverse motion resulting in the retardation of the vortex shedding.

• Membrane Journal
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• v.25 no.3
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• pp.276-286
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• 2015

The effects of relaxation and backwashing on fouling in ultrafiltration were investigated using full-scale membrane bioreactors (MBRs) which operated at a constant flux of 30 LMH. This paper also estimated the feasibility of using intermittent aeration strategies for minimizing the hydraulic resistance to filtration in comparison with the continuous aeration for running MBRs. Multiple cycles of filtration (14.5 min each) and relaxation (0.5 min each) were repeated. Similarly, a backwash was conducted by replacing a relaxation after each filtration cycle for the comparative performance test. The attached cake thickness on the membrane rapidly increased, caused by subsequent no aeration leading to easier combining with gel layer and the formation of heterogeneous layer on the membrane surface. During periodic backwashing, it is expected that gel and thin cake layer might sufficiently be removed by heterogeneous layer. After periodic backwashing, subsequent cake layer formation during time of no aeration was rapid than frequent no aeration, acting as a prefilter and preventing further irreversible fouling. Based on the Pearson correlation analysis, overall period fouling (dTMP/min) and average of all cycles (dTMP/min) were strongly correlated with the on-off period of aeration for operating MBRs.

• Sleep Medicine and Psychophysiology
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• v.17 no.2
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• pp.75-84
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• 2010

The cyclic alternating pattern (CAP) is a periodic EEG activity in NREM sleep, characterized by sequences of transient electrocortical events that are distinct from background EEG activities. A CAP cycle consists of two periodic EEG features, phase A and subsequent phase B whose durations are 2-60 s. At least two consecutive CAP cycles are required to define a CAP sequence. The CAP phase A is a phasic EEG event, such as delta bursts, vertex sharp transients, K-complex sequences, polyphasic bursts, K-alpha, intermittent alpha, and arousals. Phase B is repetitive periods of background EEG activity. The absence of CAP more than 60 seconds or an isolated phase A is classified as non-CAP. Phase A activities can be classified into three subtypes (A1, A2, and A3), based on the amounts of high-voltage slow waves (EEG synchrony) and low-amplitude fast rhythms (EEG desynchrony). CAP rate, the percentage of CAP durations in NREM sleep is considered to be a physiologic marker of the NREM sleep instability. In insomnia, the frequent discrepancy between self-reports and polysomnographic findings could be attributed to subtle abnormalities in the sleep tracing, which are overlooked by the conventional scoring methods. The conventional scoring scheme has superiority in analysis of macrostructure of sleep but shows limited power in finding arousals and transient EEG events that are major component of microstructure of sleep. But, it has recently been found that a significant correlation exists between CAP rate and the subjective estimates of the sleep quality in insomniacs and sleep-improving treatments often reduce the amount of CAP. Thus, the extension of conventional sleep measures with the new CAP variables, which appear to be the more sensitive to sleep disturbance, may improve our knowledge on the diagnosis and management of insomnia.

• Economic and Environmental Geology
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• v.39 no.3 s.178
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• pp.269-284
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• 2006

Aquifer responses to the river stage fluctuations were analyzed between the groundwater level and the river stage in an alluvial aquifer. The auto-correlation and cross-correlation as a time series analysis were applied. Study site is a floodplain in the Mangyeong river. Groundwater levels in each depth representing the silt and sand(SS), gravel and sand(GS), and weathered zone(WZ) layer were monitored. The groundwater levels were more sensitive to the river stage fluctuations than rainfall. Since the river stages are influenced by the gate operations downstream and tide, show periodic patterns, and the correlation coefficients with rainfall is low. Cross-correlation function between groundwater level in each depth do not show any delay time, then response time is very short to each depth. Cross-correlation analysis were performed to estimate the response time of groundwater levels to river stage fluctuations. Groundwater levels respond to the river stage within 30 minutes to 1 hour in wells near the stream. Short time lag between groundwater level and river stage indicates the quick response. A different response time imply the hydraulic inhomogeneity of the site, and a probable high permeability zone between river and aquifer can be inferred. Mangyeong-river in study site is a gaining stream normally, and river stage rising by gate operation or floods makes river water flow into groundwater. The auto-correlation and cross-correlation functions as a time series analysis can be a good tool to interpret the aquifer responses to stream stage fluctuation

• Journal of dental hygiene science
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• v.10 no.5
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• pp.329-334
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• 2010

This study was performed to identify the relationship between scaling behaviors and knowledge about scaling and oral health belief of worker, and to provide baseline data for developing industry oral health policy. The survey had conducted self-administered questionnaires by 326 workers in Gyeongsan and Yeongcheon areas in Gyeongbuk province. Their scaling behaviors, knowledge and oral health belief were measured. The results were as follow; The average score of knowledge about scaling was 6.44. The average oral health belief was 2.72. In detail, 'usefulness' was 3.24 as the highest and 'seriousness' was 2.25 as the lowest. The periodic scaling and scaling cycle were associated with 'seriousness' and 'barrier' as positive correlation(p<.05, .01). On the other hand, they were associated with knowledge and 'usefulness' as negative correlation(p<.01). Meanwhile, scaling motive showed positive correlation with 'cue of action'(p<.01), showed negative correlation with knowledge(p<.01). In the correlation between knowledge about scaling and oral health belief, knowledge showed negative correlation with 'barrier'(p<.01) and showed positive correlation with 'usefulness'(p<.01). Finally, we need to advertise and manage the importance of scaling politically and makes people do the voluntary scaling in six-month intervals in order to keep the periodontal health of worker.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.35 no.1
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• pp.55-62
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• 2017

The SRP (Solar Radiation Pressure) model has always been an issue in the dynamic GPS (Global Positioning System) orbit determination. The widely used CODE (Center for Orbit Determination in Europe) model and its variants have nine parameters to estimate the solar radiation pressure from the Sun and to absorb the remaining forces. However, these parameters show a very high correlation with each other and, therefore, only several of them are estimated at most of the IGS (International GNSS Service) analysis centers. In this study, we attempted to numerically verify the correlation between the parameters. For this purpose, a bi-directional, multi-step numerical integrator was developed. The correlation between the SRP parameters was analyzed in terms of post-fit residuals of the orbit. The integrated orbit was fitted to the IGS final orbit as external observations. On top of the parametric analysis of the SRP parameters, we also verified the capabilities of orbit prediction at later time epochs. As a secondary criterion for orbit quality, the positional discontinuity of the daily arcs was also analyzed. The resulting post-fit RMSE (Root-Mean-Squared Error) shows a level of 4.8 mm on average and there is no significant difference between block types. Since the once-per-revolution parameters in the Y-axis are highly correlated with those in the B-axis, the periodic terms in the D- and Y-axis are constrained to zero in order to resolve the correlations. The 6-hr predicted orbit based on the previous day yields about 3 cm or less compared to the IGS final orbit for a week, and reaches up to 6 cm for 24 hours (except for one day). The mean positional discontinuity at the boundary of two 1-day arcs is on the level of 1.4 cm for all non-eclipsing satellites. The developed orbit integrator shows a high performance in statistics of RMSE and positional discontinuity, as well as the separations of the dynamic parameters. In further research, additional verification of the reference frame for the estimated orbit using SLR is necessary to confirm the consistency of the orbit frames.

• Journal of the Korean Society of Physical Medicine
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• v.11 no.2
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• pp.13-16
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• 2016

PURPOSE: The Fukuda test can be used at home and in school to diagnose scoliosis at an early stage and prevent serious curvature of the spine. This study aimed to use the Fukuda test to detect scoliosis. An additional aim was to invoke the national interest in imbalanced postures and habits, which result in scoliosis, by providing data obtained in periodic assessments. METHODS: The study consisted of 35 idiopathic scoliosis patients (22 in right lumbar spinal region and 13 in the left lumbar spinal region). The distance of displacement and angle of displacement were measured following the Fukuda test. A correlation analysis was then used to examine the distance of displacement and angles of displacement and rotation with regard to the direction of the curve in scoliosis. RESULTS: There was a significant negative correlation (p<0.00) between the direction of the curve in scoliosis and the angle of displacement, but there was no correlation between the cobb's angle and distance of displacement or between the cobb's angle and angle of rotation. CONCLUSION: The Fukuda test did not capture changes in spinal curvature such as the cobb's angle, or subsequent changes in the muscles. Thus, the Fukuda test is not suited to examining the direction or status of the thoracic curve in scoliosis patients. Simple methods to objectively measure scoliosis need to be developed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.7
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• pp.917-927
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• 2018

High blood pressure causes various cardiovascular diseases and is associated with mortality. Periodic self-monitoring and recording of blood pressure is very helpful in preventing the occurrence of secondary diseases caused by hypertension. However, existing cuff-type blood pressure monitors have many limitations. As an alternative of that, a method of estimating the blood pressure by measuring the velocity change of the blood flow using the photo plethysmography is widely known. However, photo plethysmography have a low correlation with blood flow. So, we will propose an algorithm for estimating blood pressure using the relationship between velocity change of blood flow measured by magnetic field instead of photo plethysmography and electrocardiogram. For this purpose, First, we analyzed the correlation between photo plethysmography and magneto plethysmography. the correlation between MPG and PPG was r = 0.9449. Second, we compared estimated blood pressure and measured blood pressure. In the four experiment each result was r = 0.5737, r = 0.7863, r = 0.5669, and r = 0.7445.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.451-454
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• 1997

It has been reported that sudden cardiac death and ventricular tachycardia occur after treatment of tetralogy of fallot(TOF). It is regarded that ventricular arrythmia is the main source or the sudden cardiac death, but it is not verified. It is likely that TOF has effect on the heart rate variability because of the ventricular arrythmia. We study how complex and periodic heart rate dynamics change in the normal children (n=13) and TOF children (n=13) throughout 24 hours. We recorded 24-hour holter ECG, and segmented each ECG data into 1 hour length. We analyze each HR time series, and quantify the overall complexity of each HR time series by its correlation dimension. We also calculate the power spectrum of HR, and obtain low-frequency component (0.03-0.15Hz) and high-frequency component (0.15-0.4Hz). We compare the results between normal and TOF groups throughout 24 hours. TOF group have lower correlation dimension ($4.055{\pm}0.4134$ vs. $4.9310{\pm}0.2054$, p<0.05) than the normal group, even though there are no significant differences in the low($0.9864{\pm}0.5598$ vs. $1.5560{\pm}0.8325$, p<0.05) and high($1.1168{\pm}0.1.1448$ vs. $0.9271{\pm}0.6528$, p<0.05) frequency components. It can be concluded that HR time series of TOF group are more regular than that of normal group, and that correlation dimension reveals a nonlinear characteristics of HR time series which is not determined in the frequency domain.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.58-65
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• 2016

Recent frequent occurrence of urban sinkhole serves as a momentum of the periodic inspection of sewer pipelines. Sewer inspection using a CCTV device needs a lot of time and efforts. Many of previous studies which reduce the laborious tasks are mainly interested in the developments of image processing S/W and inspection H/W. However there has been no attempt to find meaningful information from the existing CCTV images stored by the sewer maintenance manager. This study adopts a cross-correlation based image processing method and extracts location data of sewer inspection device from CCTV images. As a result of the analysis of time-location relation, it shows strong correlation between the device's stand times and the sewer damages. In case of using this method to investigate sewer inspection CCTV images, it will save the investigator's efforts and improve the sewer maintenance efficiency and reliability.