• Publications of The Korean Astronomical Society
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• v.13 no.1 s.14
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• pp.149-166
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• 1998

The structure and environments of the molecular clouds near the SNR $HB3(G132.7\pm1.3)$ are studied. The molecular complex which is located at the southern rim of HB3 was proposed by former investigators as the one interacting with HB3. This complex region of $2^{\circ}\times2^{\circ}\;at\;l=133^{\circ}$ has been observed at $^{12}CO,\;^{13}CO,\;J=1-0\;at\;a\;1'$, resolution with the 14-m radio telescope at Taeduk Radio Astronomy Observatory. We have reached to the following four conclusions. The possibility that these molecular complex and HB3 are interacting with each other cannot be supported with any of our data. The morphologies of the two show no similarities. Neither particular features for the interaction are found in the CO lines. The hypothetical 'Molecular wall' which was expected to exist on the northwestern rim of HB3 as a cause for the noncircular morphology of HB3 is turned out to be nonexistent in CO. The molecular complex which resembles a 'bar' at a low resolution is now resolved into a U-shaped shell. It seems that the U-shape is consist of two independent components. No peculiarities, such as unseen masses or bright stars capable of forming HlI regions, are found within the U-shape region. The total mass included in the complex is estimated to be $M_{total}\;=\;2.9\~8.4\times10^5\;M_\bigodot$, which is in good agreement with previous observations within errors. Considering about 12 clumps distinguishable within the complex, the total mass implies that masses of each of clumps are on the order of $10^4\;M_\bigodot$, which makes these good objects for further studies in relation to star-formation. Especially the clumps associated with W3 are worthy for more high resolution observations for better understanding of astrophysical phenomenon ongoing in them.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.9
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• pp.1051-1057
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• 2008

In this paper, we analyzed the characteristics of the EM wave absorber which was fabricated by using flake sendust (soft metal magnetic powder). The flake sendust was made of 3 different granularity by attrition mill. First, we have fabricated 3 kind of EM wave absorbers using the flake sendust and CPE(Chlorinated Polyethylene) and measured the S-parameters of the EM wave absorber. The complex relative permittivity and permeability were calculated from the measured data and the variations according to a change of granularity were researched. As a result, it was confirmed that the EM wave absorber using flake sendust with the $140{\mu}m$ average granularity has outstanding absorption ability in high frequency range(C band) for the reduction of eddy current loss(increase of permeability) and the increase of space charge polarization(increase of permittivity).

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.45-48
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• 2011

The electrodeless fluorescent lamp is relatively new luminaire and has been known as the high energy saving lamp which has long life and environment-friendly. But these kind of lamps have some risks to cause harmful radio interference unavoidably due to its own inductive characteristics. In this paper we measured the radio disturbance characteristics of the induction lamp with the operating frequency at 250 kHz, and compared the values with the limits of relevant standards. Finally we have estimated the interference protection distance between the induction lamps and some services around their operating frequencies, and considered the desirable future scopes and limits of the applications for these kind of lamps.

• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.72-77
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• 2011

Spectrum sensing is a critical functionality of CR network; it allow secondary user to detect spectral holes and to opportunistically use under-utilized frequency bands without causing harmful interference to primary use. Recently, wideband service has been increase for processing abundance of data traffic. So CR network needs a realizable implementation design of spectrum sensing for wideband. To get high resolution performance of wideband sensing must precede algorithm processing for reliability signal detection. By the way, the performance of spectrum sensing can be degraded due to fading and shadowing. In order to overcome this problem, we propose system model of wideband sensing scheme on energy detected collaborative technique. we divide wideband into narrowbands and use narrowbands to detect signal excepting some narrowbands including bad channel through the CSI. And we simulate and analyze in terms of detection probability with various SNR.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.6
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• pp.759-767
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• 2020

This paper proposes a new Recurrent neural network (RNN) based spectrum sensing technique for cognitive radio communications. The proposed technique determines the existence of primary user's signal without any prior information of the primary users. The method performs high-speed sampling by considering the whole sensing bandwidth and then converts the signal into frequency spectrum via fast Fourier transform (FFT). This spectrum signal is cut in sensing channel bandwidth and entered into the RNN to determine the channel vacancy. The performance of the proposed technique is verified through computer simulations. According to the results, the proposed one is superior to more than 2 [dB] than the existing threshold-based technique and has similar performance to that of the existing Convolutional neural network (CNN) based method. In addition, experiments are carried out in indoor environments and the results show that the proposed technique performs more than 4 [dB] better than both the conventional threshold-based and the CNN based methods.

• Journal of The Korean Astronomical Society
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• v.56 no.1
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• pp.1-9
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• 2023

The Crab nebula is widely used as a polarization angle calibrator for single-dish radio observations because of its brightness, high degree of linear polarization, and well-known polarization angle over a wide frequency range. However, the Crab nebula cannot be directly used as a polarization angle calibrator for single-dish observations with the Korean VLBI Network (KVN), because the beam size of the telescopes is smaller than the size of the nebula. To determine the polarization angle of the Crab nebula as seen by KVN, we use 3C 286, a compact polarized extragalactic radio source whose polarization angle is well-known, as a reference target. We observed both the Crab nebula and 3C 286 with the KVN from 2017 to 2021 and find that the polarization angles at the total intensity peak of the Crab nebula (equatorial coordinates (J2000) R.A. = 05^h34^m32.3804^s and Dec = 22°00'44.0982'') are 154.2° ± 0.3°, 151.0° ± 0.2°, 150.0° ± 1.0°, and 151.3° ± 1.1° at 22, 43, 86, and 94 GHz, respectively. We also find that the polarization angles at the pulsar position (RA = 05^h34^m31.971^s and Dec = 22°00'52.06'') are 154.4° ±0.4°, 150.7° ±0.4°, and 149.0° ± 1.0° for the KVN at 22, 43, and 86 GHz. At 129 GHz, we suggest to use the values 149.0° ± 1.6° at the total intensity peak and 150.2° ± 2.0° at the pulsar position obtained with the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-meter Telescope. Based on our study, both positions within the Crab nebula can be used as polarization angle calibrators for the KVN single-dish observations.

• Journal of electromagnetic engineering and science
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• v.18 no.1
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• pp.20-28
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• 2018

The time synchronization of each sub-unit of a pulsed generator is important to generate an output high-power radio frequency (RF) signal. To obtain the time synchronization between an input RF signal fed by an external source and an electron beam produced by an electric pulse generator, the influence of different charging voltages on a delay and a rise time of the output pulse waveform in the electric pulse generator should be carefully considered. This paper aims to study the timing characteristics of the delay and the rise time as a function of different charging voltages with a peak value of less than -35 kV in the high-voltage pulse generator, including a trigger generator (TG) and a pulse-forming line (PFL). The simulation has been carried out to estimate characteristics in the time domain, in addition to their output high-voltage amplitude. Experimental results compared with those obtained by simulation indicate that the delay of the output pulses of the TG and PFL, which are made by controlling the external triggering signal with respect to different charging voltages, is getting longer as the charging voltage is increasing, and their rise times are inversely proportional to the amplitude of the charging voltage.

• Korean Journal of Human Ecology
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• v.18 no.6
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• pp.1323-1336
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• 2009

This study examined the attitude and education need for food safety of high school students. Data were collected from 297 high school students in Gyeongbuk province through a self-administered questionnaire on December, 2008. Frequency, t tests, one-way analysis of variance, Duncan's multiple range tests, and chi-square tests were conducted using SPSS V. 14.0. Many respondents answered that the foods produced and distributed in Korea were not safe enough. Over a third of the respondents replied that the produced and distributed foods were not safe because of unsanitary food processing. They pointed out food additives threatened food safety the most, which was followed by heavy metal contamination, and endocrine disruptors. Most respondents mentioned difficulties in acquiring information concerning food safety, and obtained information from the media, such as TV and radio. The respondents required a high level of education regarding food safety, and preferred movie clips and broadcasting media the most. Finally, they pointed out food-related government organizations to be the most efficient educational institution for food safety.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.5
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• pp.489-498
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• 2003

Recently to introduce new services of ultra-high speed wireless access and systems beyond the 3rd generation mobile communication, 5 GHz band has been highly interested. As a way of getting the required frequency, it is considered that microwave relay bands below 6 GHz, which shows a slow decrease in demand and less cost-effectiveness, should be moved to other bands above 6 GHz. In this paper, as a tool for analyzing microwave link design and its service quality, the outage prediction based upon Vigants & Barnett＇s model is reviewed. To show outage and availability calculation, simulations are performed for the operating 4 GHz radio sites, and some results and features regarding frequency movement to 6.7 as well as 8 GHz are also discussed in terms of diversity techniques, bit error rate, and availability As the results, it is confirmed that only the diversity techniques of space or space and frequency can satisfy the annual objective of availability irrespective of frequency movement.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.12
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• pp.1315-1320
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• 2015

In this paper Communication data link equipment on a high speed-hopping method to use the frequency resources efficiently for the frequency environment is introduced such as sensing techniques, using the same frequency band by using the received two-channel technique and the receive filter bank unit applied to be shared with other equipment such as radar and so on. The real-time measurement and analysis were operated for measurement the frequency environment of the operating band in advance. and primarily equipment to develop is analyzed how the interference effect to the radar minimize the operation of radar equipment. In reverse, to use the same frequency band the methods such as frequency sharing techniques are presented in this paper. Finally, by design of the main items of the RF transceiver NF, transmission output, and a simulation of the IMD, such as whether the key is verified prior to meet specifications.