• Journal of Institute of Convergence Technology
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• v.3 no.2
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• pp.51-56
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• 2013

This paper describes the atomization characteristics, as well as the velocity and size distribution, of DME spray based on common-rail injection system. To analyze the possibility of using DME fuel as an alternative fuel of diesel, spray atomization characteristics were investigated. For this investigation, two-dimensional phase Doppler analyzer system was used to obtain droplet size and velocity distribution simultaneously. Velocity and droplet size measurements were performed at various injection pressures. Results showed that increasing pressure from 25MPa to 50MPa leads to higher spray droplet velocities and smaller droplet diameter but injection pressure above 40MPa, no signifiant reduction was observed. With the droplet velocity and SMD comparison between diesel and DME fuel, it can be observed that DME has smaller SMD and droplet velocity due to its low surface tension.

• The Journal of Churna Manual Medicine for Spine and Nerves
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• v.4 no.2
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• pp.39-45
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• 2009

Objectives : The aim of this study is to compare the improvement of Low back pain (LBP) depending on male Inpatient's Brachlalankle Pulse Wave Velocity (baPWV), Method : We evaluated 35 LBP inpatients who took pulse wave velocity test during admission at Jaseng hospital from November 2008 to september 2009. We used applanation tonometry method to measure pulse wave velocity and numerical rating scale to measure patient's improvement. Result : At admission, standard deviation of normal group's NRS was $7.44{\pm}1.67$ and high risk group's was $7.57{\pm}2.09$(P=0.678). After 5 days of admission, standard deviation of normal group's NRS was $5.67{\pm}1.94$ and high risk group's was $6.00{\pm}2.17$(P=0.680). After 10 days of admission, standard deviation of normal group's NRS was $4.00{\pm}1.80$ and high risk group's was $4.95{\pm}1.96$(P=0.281). After 15 days of admission, standard deviation of normal group's NRS was $2.89{\pm}1.62$ and high risk group's was $4.10{\pm}1.92$(P=0.124). At discharge, standard deviation of normal group's NRS was $5.11{\pm}1.69$ and high risk group's was $4.86{\pm}2.08$(P=0.504). Comparison between admission and discharge, standard deviation of normal group's NRS was $5.11{\pm}1.69$ and high risk group's was $4.86{\pm}2.08$(P=0.504) Conclusion : Low back patients with high Brachialankle Pulse Wave Velocity, showed slower improvement rate compare to patients within normal rate. But statically, had no significance.

• Structural Engineering and Mechanics
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• v.48 no.4
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• pp.501-518
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• 2013

Apart from thinning of cortical layers, the local bone curvature, varying along bone periphery, modulates ultrasound waves as well, which is however often underestimated or overlooked in clinical quantitative ultrasound (QUS). A dedicated three-dimensional finite element modelling technique for cortical bones was established, for quantitatively exploring and calibrating the effect of local curvature of cortical bone on ultrasound. Using a correlation-based mode extraction technique, high-velocity group (HVG) and low-velocity group (LVG) wave modes in a human radius were examined. Experimental verification using acrylic cylinders and in vitro testing using a porcine femur were accomplished. Results coherently unravelled the cortical curvature exerts evident influence on bone-guided ultrasound when RoC/${\lambda}$ <1 for HVG mode and RoC/${\lambda}$ <2 for LVG mode (RoC/${\lambda}$: the ratio of local bone curvature radius to wavelength); the sensitivity of LVG mode to bone curvature is higher than HVG mode. It has also been demonstrated the local group velocity of an HVG or LVG mode at a particular skeletal site is equivalent to the velocity when propagating in a uniform cylinder having an outer radius identical to the radius of curvature at that site. This study provides a rule of thumb to compensate for the effect of bone curvature in QUS.

• Structural Engineering and Mechanics
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• v.75 no.4
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• pp.435-444
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• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.140-145
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• 2011

In order to analyze the influence of the noise on a cross-well traveltime tomography to detect a small scale low velocity body in a homogeneous medium, the first arrival travel times were computed one a tunnel model by a finite-difference ray tracing scheme. Three different types and four different intensity levels of white noises were added to the computed first arrival travel times, and velocity tomograms were constructed using an iterative inversion method (SIRT). Tomograms with the noise intensity up to 10% of the maximum traveltime delay in the tunnel model, showed the exact location of the tunnel. However, the velocity shown at the tunnel location was not close to air velocity but only slightly less than the velocity of the background medium. The additive random noise showed significantly less degree of influence on the resulting tomogram than the source- and receiver consistent noise.

• Geophysics and Geophysical Exploration
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• v.6 no.3
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• pp.153-159
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• 2003

Using reciprocity theorem, one direction aperture of seismogram can be extended to full aperture seismogram. Modified seismogram is applied to reverse time migration only to acquire improved migration image. In this paper, we tested reverse time migration with the Marmousi velocity data to examine efficiency of modified seismogram. And linearly increasing velocity model is selected and examined for a case where velocity data is insufficient. When true velocity is applied, using modified seismogram enhances the reverse time migration image more than using original seismogram. In the case of using linearly increasing velocity model, migration image is distorted. So low frequency source is brought in migration process. Reverse time migration image with low frequency source and linearly increasing velocity model is improved when modified seismogram is used. From the result of study, seismogram modification by reciprocity theorem is useful and migration image can be enhanced.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.40.4-41
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• 2010

Using magnetic field and plasma moment data obtained by THEMIS satellites(A, D, and E), we selected 203 fast flow events accompanied by dipolarization in the near-Earth region( X(GSM) = -7 ~ -12 RE) and statistically examined their properties. It was found that most of the fast flows show the maximum velocity between 1 minute before dipolarization onset and 2 minutes after onset and proceed earthward and duskward. We also found that only the flows with low velocity of less than 400 km/s are observed at X > -8 RE, while the high velocity flows(as well as low velocity flows) are observed at the further tailward region(X < -8 RE). And most of the tailward flows are slow regardless of distance at X(GSM) = -7 ~ -12 RE. On the other hand, if we consider the fast flow as a bubble (Pontius and Wolf, 1990), the entropy parameter, PV5/3 is an important factor to describe the plasma sheet dynamics. Thus we investigated the relationship between the flow velocity and the amount of change in PV5/3 before and after dipolarization onset and found out that the dipolarizations with more depleted entropy parameter tend to show higher flow velocity. Also we examined how the magnetic field at geosynchronous orbit responds to the fast flow accompanied by dipolarization in the near-earth plasma sheet, using the measurements from GOES 11 and 12 statellites. We found that most of the fast flows do not reach geosynchronous orbit as suggested by Ohtani et al. (2006).

• Ocean and Polar Research
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• v.44 no.4
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• pp.287-296
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• 2022

High-frequency (HF) radar measures sea surface currents from the radio waves transmitted and received by antenna on land. Since the data quality of HF radar measurements sensitively depend on the radio wave environment around antenna, Antenna Pattern Measurements (APM) plays an important role in evaluating the accuracy of measured surface currents. In this study, APM was performed by selecting the times when the background noise level around antenna was high and low, and radial data were generated by applying the ideal pattern and measured pattern. The measured antenna pattern for each case was verified with the current velocity data collected by drifters. The radial velocity to which the ideal pattern was applied was not affected by the background noise level around antenna. However, the radial velocity obtained with APM in the period of high background noise was significantly lower in quality than the radial velocity in a low noise environment. It is recomended that APM be carried out in consideration of the radio wave environment around antenna, and that the applied result be compared and verified with the current velocity measurements by drifters. If it is difficult to re-measure APM, we suggest using radial velocity in generating total vector with the ideal pattern through comparative verification, rather than poorly measured patterns, for better data quality.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.53-60
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• 2009

Construction of a tunnel induces rock masses damage around the tunnel. The degree of damage produced on rock masses will affect on the mechanical and hydraulic behaviors of the rock masses. In this paper, P wave velocity measured by cross-hole test was used to assess rock masses damage around the test tunnel. Initiation of source signal was carried out using mechanical impact at the source installed borehole. In consequence, the generated P wave signal was low noise and apparent wave form, which allows accurate pick-up of first arrival time. From the test, the region where rock damage is expected shows relatively low P wave velocity. In addition, with multiple points of P wave velocity measurement along each cross-hole, two dimensional P wave tomography was obtained. The tomography provides apparent view of the rock damage behind the tunnel. The measured P wave velocity was correlated with features of rock masses, porosity and Q value.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.3
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• pp.179-184
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• 2017

Recently, traffic accidents and damage on the highway have increased because of overloaded vehicles. The existing overload-detecting system has a low accuracy rate. An overload-detecting system using a weigh-in-motion (WIM) system has been developed to solve this problem. The WIM system can be used to detect overloaded vehicles by measuring the weight of the vehicles. The WIM system is divided into high-speed and low-speed types. The inaccuracy rate in the low-speed WIM system results mainly from the low response rate of the sensor when the velocity is moving at more than 20 km/h. In this study, a low-speed overload-detecting pad with a hydraulic structure using a WIM system was developed to make the system more accurate. The structural and formal analysis was carried out by using a finite element method (FEM) in order to analyze the structural stability and the extrusion velocity of the system. In addition, a static load test was performed to confirm the linearity and accuracy of the pad.