• Progress in Superconductivity
• /
• v.13 no.2
• /
• pp.97-104
• /
• 2011

In the dielectric resonator method, which has been widely used for measuring the microwave surface resistance of superconductors, accuracies in the geometrical factors (G-factors) affect the uncertainty in the measured surface resistance. We compare the G-factors of short-ended sapphire resonator as obtained by using field analysis with those by using computer simulations: The former is obtained by using the analytic expressions for the electric and the magnetic field components inside the resonator, and the latter by using computer software. The G-factors as obtained by using the latter appear to be closer to those obtained by using the former as the resonator space is divided into larger number of sub-space, i.e., a tighter mesh, with a difference of ~8 % observed for a mesh of 14400 sub-spaces reduced to ~2 % for 114996 sub-spaces. Variations in the relative uncertainty in the surface resistance of typical $YBa_2Cu_3O_{7-\delta}$ superconductor films with those in the G-factors are studied, which provides an upper limit of the relative uncertainty in the G-factors required for realizing the target uncertainty in the surface resistance. These results could be useful in estimating the optimum number of meshes for obtaining the G-factors through computer simulations.

• Journal of Astronomy and Space Sciences
• /
• v.11 no.1
• /
• pp.71-80
• /
• 1994

It is generally known that the measurement of the ionospheric total electron content(TEC) by GPS can more accurately monitor the broader area of the ionosphere than other current methods. \Ve measured the TEC along a slant path considering the arrival time differences of P-code which is transmitted from GPS satellites with the modulation on two L-band carrier frequencies, L1 (1574.42MHz) and L2 (1227.60MHz). Under the assumptions that the ionosphere is uniformly distributed and its average height is 350km, we transformed the slant TEC to the vertical TEC at the point that the line-of-sight direction to GPS satellite cut across the average height of the ionosphere. Because there is no dual frequency P-code GPS receiver in Korea, we used the data observed at the TAIW GPS station ($N25^{\circ},E121.5^{\circ}$) in Taiwan which is one of the core stations in International GPS and Geodynamics Services (IGS). The TEC values obtained in this work showed a typical daily variation of the ionosphere which is high in the daytime and low in the nighttime. Our results are found to be consistent with the SOLAR-DAILY data of NOAA and the Klobuchar's model for the ionospheric correction of GPS. In addition, in the cornparision with SOLAR-DAILY data, we estimated the precision of our TEC measurement as 2 TEC.

• Journal of Navigation and Port Research
• /
• v.43 no.6
• /
• pp.429-436
• /
• 2019

The eLoran system is considered the best alternative because the vulnerability of satellite navigation systems cannot be resolved as perfect. Thus, South Korea is in the process of establishing a testbed of the eLoran system in the West Sea. To provide resilient navigation services to all waters, additional eLoran transmitters are required. However, it is difficult to establish eLoran transmitters because of various practical reasons. Instead, the positioning with NDGNSS/AIS source can expand the coverage and its algorithm with applying continuous waves is under development. Using the already operating NDGNSS reference station and the AIS base station, it is possible to operate the navigation system with higher accuracy than before. Thus, it is crucial to predict the performance when each system is integrated. In this paper, we have developed a simulation tool that can predict the performance of terrestrial integrated navigation system using the eLoran system, maritime NDGNSS station and the AIS station. The esitmated phase error of the received signal is calculated with the Cramer-Rao Lower Bound factoring the transmission power and the atmospheric noise according to the transmission frequency distributed by the ITU. Additionally, the simulation results are more accurate by estimating the annual mean atmospheric noise of the 300 kHz signal through the DGPS signal information collected from the maritime NDGNSS station. This approach can further increase the reliability of simulation results.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.36 no.5
• /
• pp.891-901
• /
• 2016

By comparing test blasting data experimented in three layered-structure polymorphic grounds to a geological profile, influence of blast vibration with respect to uncontrollable ground characteristics was analyzed. Inefficient blast have been performed without sufficient verifications or confirmations because insufficiencies with regard to experiments and data of blasting engineering on the layered structures to be irregularly repeated clinker layer consisted of volcanic clastic zones. It is difficult to quantify N values of clinkers within test blasting region because they have diverse ranges, or coverages. An absolute value of attenuation coefficient N in a field, estimated by blasting vibration predictive equation (SRSD), are lesser than criteria of a design instruction, meaning that vibrations caused by blast can spread far away, and the vibrational characteristics of blasting test No.1, indicating relatively small values, inferred by the geological profile, pressures of gas by the explosion may be lost into a widely distributed clinker layers by penetrating holes resulted from blast into vicinity of clinker layers located in bottom of soft rock layers at the moment of blast. As a result, amounts of spalling rocks are decreased by almost half. Also, ranges of primary frequencies in the fields are identified as similar to those of natural frequency of typical structures.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.33 no.4
• /
• pp.225-235
• /
• 2020

Ultrasonic investigation of damage detection has been widely used for non-destructive testing of various concrete structures. This study focuses on damage detection analysis with the aid of wave propagation in two-phase composite concrete with aggregate (inclusion) and mortar (matrix). To fabricate a realistic simulation model containing a variety of irregular aggregate shapes, the mesh generation technique using an image processing technique was proposed. Initially, the domains and boundaries of the aggregates were extracted from the digital image of a typical concrete cut-section. This enables two different domains: aggregates and mortar in heterogeneous concrete sections, and applied the grids onto these domains to discretize the model. Subsequently, finite element meshes are generated in terms of spatial and temporal requirements of the model size. For improved analysis results, all meshes are designed to be quadrilateral type, and an additional process is conducted to improve the mesh quality. With this simulation model, wave propagation analyses were conducted with a central frequency of 75 kHz of the Mexican hat incident wave. Several void damages, such as needle-shaped cracks and void-shaped holes, were artificially introduced in the model. Finally, various formats of internal damage were detected by implementing energy mapping based signal processing.

• Journal of the Korean earth science society
• /
• v.32 no.6
• /
• pp.674-686
• /
• 2011

Choosing a seismic source and geophone type including a coupling method can be the most important factor in shallow seismic surveys. We studied the characteristics of seismic signals by analyzing 6 different seismic data sets that collected from several sources and geophone conditions. Geophones attached to weight plate (1.8 kg) can be easily and economically installed on the paved road where geophones with spikes would cause the coupling problem. In addition, experiments in this study revealed that a small handy hammer can be used as a seismic source by striking the paved road to generate the seismic signals within 200 ms two-way travel time. Attaching weight plates to geophones may change the geophone response curve which generally depends on the geophone mass, but the change seems not to give significant differences in the first arrival of refracted wave and in the pattern of reflection events. Consequently, using weight plates on paved roads can be an efficient and cost-saving method in the near-surface high-resolution seismic surveys.

• Journal of the Korean Electrochemical Society
• /
• v.4 no.1
• /
• pp.14-20
• /
• 2001

The Langmuir adsorption isotherms of the under-potentially deposited hydrogen (UPD H) and the over-potentially deposited hydrogen (OPD H) at the single crystal Pt(100)/0.5 M $H_2SO_4$ and 0.5 M LiOH aqueous electrolyte interfaces have been studied using the phase-shift method. The phase-shift profile $({-\varphi}\;vs.\;E)$ for the optimum intermediate frequency can be used as a useful method to estimate the Langmuir adsorption isotherm $(\theta\;vs.\;E)$ at the interfaces. The equilibrium constant (K) for the OPD H and the standard free energy $({\Delta}G_{ads})$ of the OPD H at the Pt(100)/0.5M $H_2SO_4$ aqueous electrolyte interface are $1.5\times10^{-4}$ and 21.8 kJ/mol, respectively. At the Pt(100)/0.5 LiOH aqueous electrolyte interface, K transits from 1.9(UPD H) to $6.8\times10^{-6}$(OPD H) depending on the cathode potential (E) and vice versa. Similarly, ${\Delta}G_{ads}$ transits -1.6 kJ/mol (UPD H) to 29.5 kJ/mol (OPD H) depending on E and vice versa. The transition of K and ${\Delta}G_{ads}$ is attributed to the two distinct adsorption sites of the UPD H and OPD H on the Pt(100) surface. The UPD H and the OPD H at the Pt(100) interfaces are the independent processes depending on the H adsorption sites rather than the sequential processes for the cathodic $H_2$ evolution reactions.

• Journal of the Korean Geophysical Society
• /
• v.3 no.1
• /
• pp.25-36
• /
• 2000

3-D Spectrograms for 22 events are drawn to discern about whether those are earthquakes or explosions. Generally, in case of explosions relative to the case of earthquakes, amplitude of P phase is more dominantly shown. According to the results on logarithm of spectral ratio of P (Pn, Pg)/Lg after removing free-surface effects from 3-D (U-D, N-S, E-W) seismogram, $-1.2{\sim}-0.9$ is shown for earthquakes and $-0.7{\sim}-0.1$ if shown for explosions. This result is consistent with previous researches (Kim Park, 1997) that -0.6 of spectral ratio between P and Lg after taking logarithm may be the criterion for the discrimination between earthquakes and explosions in Korea. In addition, Complexity is applied to two events as another discrimination method. The value of Complexity of explosion is much smaller than that of earthquake. This may be due to well-developed P-wave in explosion compared to that in earthquake. This result is in accordance with that of 3-D Spectrogram.

• Economic and Environmental Geology
• /
• v.14 no.2
• /
• pp.93-102
• /
• 1981

Studies of model potential fields continued upward and downward show differences depending on the method of continuation. Beginning with a magnetic field computed over a buried vertical cylinder, the field was continued to various levels by a method introduced by Henderson (Lagrangian interpolation) and by a spectral method (frequency domain analysis). Resultant fields show (1) no significant differences in upward continued values, (2) in downward continuation, accurate values are obtained with the spectral method over the central part of the anomaly, and (3) accurate values are obtained with Henderson's method on the flanks of the anomaly, while oscillations usually characterize the spectral method in this region. Essentially the same observations are made for derivative calculations. Field oscillations are empirically predicted at levels continued to approximately two-thirds of the depth of the source. Our spectral computer program output yields marked oscillations at one-half of the depth of the source. Henderson's method shows no oscillations at this depth and only minor oscillations at the top of the body (some negative values appear on the flanks of the anomaly). The Henderson output is a smooth field even if continued below the top of the body. These results suggest that the presence of oscillations cannot be used to identify the top of a buried source without careful consideration of the method used to continue the field. Use of the derivative to outline and isolate anomalies must similarly include consideration of the method of calculation.

• Journal of IKEEE
• /
• v.24 no.3
• /
• pp.754-765
• /
• 2020

Currently, Intelligent femoral prostheses that support the corresponding mode in walking and specific movements are being studied. Certain controls such as upstairs, sitting, and standing require a technique to classify control commands based on the user's intention because the mode must be changed before the operation. Therefore, in this paper, we propose a technique that can classify various control commands based on the user's intention in the intelligent thigh prosthesis system. If it is determined that the EMG signal needs to be compensated, the proposed technique compensates the EMG signal using the correlation between the strength and frequency components of the normal EMG signal and the muscle volume estimated by the pressure sensor. Through the experiment, it was confirmed that the user's intention was accurately detected even in the situation where muscle fatigue was accumulated. Improved intention detection techniques allow five control modes to be distinguished based on the number of muscle contractions within a given period of time. The results of the experiment confirmed that 97.5% accuracy was achieved through muscle tone compensation even if the strength of the muscle signal was different from normal due to muscle fatigue after exercise.