• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.214-219
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• 1997

We propose a new scheme of high-resolution heterodyne interferometer that employs the two-axial mode He-Ne laser with an inter-mode beat frequency of 600-1000 MHz. An electronic RF-heterodyne circuit lowers the beat frequency down to 5 MHz, so that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nanometer without significant loss of dynamic bandwidth. A thermal control scheme is adopted to stabilize the cavity length with aims to suppress frequency drifts caused by the phenomena of frequency pulling and polarization anisotropy of the two-axial mode laser to a stability level of 2 parts in $10^9$. The two-axial mode HeNe laser yields a high output power of 2.0 mW, whlch allows us to perform multiple measurements of up to 10 machine axes simultaneously.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.6
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• pp.398-402
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• 2018

The following conclusions were obtained after analyzing the data transmission characteristics using two frequencies and studying a system that selects data with a good reception frequency as a priority data. Data transmission and reception using two frequencies were measured at -41 to -51 dBm when the frequency was normal, and data transmitted at 900 MHz was selected as priority data. When priority frequency failure occurred, the frequency reception data of the next rank was automatically adopted, and when the frequency of the next rank was disturbed, the priority frequency search was performed again. The above results show that the use of two frequencies enables more stable data transmission and transmission, and further studies should be continued to expand the transmission and reception distances.

• Journal of electromagnetic engineering and science
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• v.4 no.3
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• pp.113-118
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• 2004

As an application of ring filters, a new and simple method to determine an inherent-ring-resonance frequency is introduced. The ring filter consists of a ring and two short stubs. They are connected at 90$^{\circ}$ and 270$^{\circ}$ points of the ring and the ring filter may be seen in such way that two filters are connected in parallel. Therefore, if the two powers of the two filters are out-of-phase at the output, the power excited at the input can not be delivered. That can be done by making difference in length of the two short stubs, and when a certain condition is satisfied, a frequency exists where all the excited power is reflected. That is the very inherent-ring-resonance frequency. In the lossless case, the return loss with the condition reaches 0 dB at the inherent-ring-resonance frequency but does not with conductor, dielectric losses and so on. Therefore, the effective loss tangent at a frequency of interest may be obtained correctly. To verify the method, two ring filters have been fabricated in microstrip lines and the measured results show good agreement with the predicted ones.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.3
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• pp.197-206
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• 2021

We compared two typical ensemble time scale algorithms; AT1 and Kalman filter. Four commercial atomic clocks composed of two hydrogen masers and two cesium atomic clocks provided measurement data to the algorithms. The allocation of relative weights to the clocks is important to generate a stable ensemble time. A 30 day-average-weight model, which was obtained from the average Allan variance of each clock, was applied to the AT1 algorithm. For the reduced Kalman filter (Kred) algorithm, we gave the same weights to the two hydrogen masers. We also compared the frequency stabilities of the outcome from the algorithms when the frequency offsets and/or the frequency drift offsets estimated by the algorithms were corrected or not corrected by the KRISS-made primary frequency standard, KRISS-F1. We found that the Kred algorithm is more effective to generate a stable ensemble time scale in the long-term, and the algorithm also generates much enhanced short-term stability when the frequency offset is used for the calculation of the Allan deviation instead of the phase offset.

• Bulletin of the Korean Chemical Society
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• v.8 no.4
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• pp.338-340
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• 1987

The single-frequency two-photon absorption tensor is carefully rederived and examined. It is pointed out that the conventionally used tensor, which has been formally deduced from the different-frequency two-photon absorption tensor, can give an incorrect absolute two-photon absorption rate. The identity forbidded selection rule and the polarization ratio expressions are also examined with the new tensor.

• Journal of The Korean Society of Grassland and Forage Science
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• v.16 no.1
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• pp.17-26
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• 1996

This experiment was carried out to investigate the effects of endophyte staWendophyte-free and -infect) and cutting frequency(3, 4, 5 and 6 timeslyear) on the forage quality of tall fescue(Festuca crnrtzdit~crcerr Schreb.) at the Experimental Field of Grassland and Forage Crops Division. National Livestock Research Institute, Suweon, from 1993 to 1994. 'Ihe results obtained are summarized as follows: CP content of tall fexue was increased with endophyte-free and cutting frequency for two varieties. Crude protein yield(CPY) of tall fescue in 1993 was increased with endophyte-free and cutting frequency for two varieties(P<0.05). In 1994, however. CPY of endophyte-free tall fescue was slightly lower than that of endophyte-infected tall fescue and the higher CPY was observed when tall fescue was harvested 6 times per year. NDF content of tall fescue was not different between endophyte-infected and -free. NDF was decreased with cutting frequency for two varieties in 1993, however. it was not influenced by the endophyte and cutting frequency in 1994. ADF content of tall fescue was not different between endophyte-infected and -free. and it was decreased with cutting frequency for two varieties. IVDMD was not influenced by endophyte, however, it was increased with cutting frequency for two varieties. Based on the results of this experiment, it is suggested that a slight increase in forage quality could be obtained from endophyte-free tall fescue and the quality was increased with frequent cutting.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3391-3396
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• 2012

Two-dimensional infrared (2D-IR) spectroscopy can probe the fast structural evolution of molecules under thermal equilibrium. Vibrational frequency fluctuation caused by structural evolution produced the time-dependent line shape change in 2D-IR spectrum. A variety of methods has been used to connect the evolution of 2D-IR spectrum with Frequency-Frequency Correlation Function (FFCF), which connects the experimental observables to a molecular level description. Here, a new method to extract FFCF from 2D-IR spectra is described. The experimental observable is the time-dependent frequency shift of maximum peak position in the slice spectrum of 2D-IR, which is taken along the excitation frequency axis. The direct relation between the 2D-IR peak shift and FFCF is proved analytically. Observing the 2D-IR peak shift does not need the full 2D-IR spectrum which covers 0-1 and 1-2 bands. Thus data collection time to determine FFCF can be reduced significantly, which helps the detection of transient species.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.7 no.1
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• pp.23-27
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• 2009

Purpose : The purpose of this study was to examine the effects of different medium frequency currents on afferent fibers. Methods : Thirty healthy volunteers who had no known history of neurological disorders were equally assigned to one of three groups; 2500Hz, 4000Hz, and control and each group was applied to the left wrist in palmer cutaneous branch of radial nerve by different medium frequency currents for 15 min. We measured the changes of thresholds for tactile, two-point discrimination, and thresholds for pain. Results : The results showed that the medium frequency currents stimulation increased thresholds for tactile, two-point discrimination, and thresholds for pain. However, there is no statistically significant difference between group 2500Hz and group 4000Hz. Conclusion : This may explain thresholds for tactile, two-point discrimination, and thresholds for pain plain medium frequency currents stimulation inhibits the excitability of afferent fibers, but the effect of the frequency difference within medium frequency currents is not demonstrated.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.2
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• pp.122-129
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• 2009

Frequency is an important operating parameter of a power system. It is essential that the frequency of a power system be maintained very close to its nominal frequency. And frequency measurement devices have need to measure a fast and accurate of frequency using voltage signals. This paper proposes a comparative study of frequency estimation techniques using the high speed FIR filter based algorithm, the DFT filter based algorithm using phasor angle between two phasors, and positive sequence component based algorithm using the half angle between two successive positions of phasor. The discussed three techniques have been formed through numerical manipulation of a discrete system. The proposed techniques have been tested using signals obtained from selected power system model using ATP simulation package. Some test results are shown in this paper.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.195-201
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• 2002

We propose a new scheme of high-resolution heterodyne interferometer that employs the two-axial mode He-Ne laser with an inter-mode beat frequency of 600~1000 MHz. An electronic RF-heterodyne circuit lowers the beat frequency down to 5 MHz, so that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nanometer without significant loss of dynamic bandwidth. A thermal control scheme is adopted to stabilize the cavity length with ainus to suppress frequency drifts caused by the phenomena of frequency pulling and polarization anisotropy of the two-axial made laser to a stability level of 2 parts in $10^9$. The two-axial mode HeNe laser yields a high output power of 2.0 mW, which allows us to perform multiple measurements of up to 10 machine axes simultaneously.