• Journal of The Korean Astronomical Society
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• v.48 no.5
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• pp.267-275
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• 2015

Simultaneous time monitoring observations of H₂O and SiO maser lines were performed toward the D-type symbiotic binary system V407 Cyg with the Korean VLBI Network single dish radio telescope. These monitoring observations were carried out from March 2, 2010 (optical phase ϕ = 0.0), 8 days before the nova outburst on March 10, 2010 to June 5, 2014 (ϕ = 2.13). Eight days before the nova outburst, we detected the SiO v = 1, 2, J = 1–0 maser lines which exhibited values of 0.51 K (∼ 6.70 Jy) and 0.71 K (∼ 9.30 Jy), respectively, while after the outburst we could not detect them on April 2 (ϕ = 0.04), May 5 (ϕ = 0.09), May 8 (ϕ = 0.09), or on June 5, 2010 (ϕ = 0.13) within the upper limits of our KVN observations. After restarting our monitoring observations, we detected SiO v = 2, J = 1–0 masers starting on October 20, 2011 (ϕ = 0.83) and detected SiO v = 1, J = 1–0 masers starting on December 22, 2011 (ϕ = 0.92). These results provide clear evidence of the interaction between the shock from the nova outburst and the SiO maser regions of the Mira envelope. The peak emission of SiO v = 1, 2, J = 1–0 masers always occurred at blueshifted velocities with respect to the stellar velocity except for that of SiO v = 1 at one epoch. These phenomena may be related to the redistribution of SiO maser regions after the outburst. The peak velocity variations of SiO masers associated with stellar pulsation phases show an increasing blueshifted trend during our monitoring interval after the outburst.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1269-1274
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• 2011

To cut down the maintenance expenses at branch lines, the foreign developed countries have developed the low-cost signalling on low-density lines. These examples are FFB(FunkFahrBetrieb) Radio based train operation by German railways(Deutsche Bahn AG), ERTMS REGIONAL by Europe and LOCOPROL system using a GPS. Also, Korea is developing Information and Communication Technology based low-cost signalling on low-density lines. The characteristics of this system are directly controled switch and crossing by driver. For the purpose of this paper, we reviewed the business process for switch and crossing control. Specially, we compared and analysed both methods whether the driver takes control over the operation procedures of switch or the control message is carried by the command of the controller. And by utilizing the instrument of UML, I planned the switch according to the control authority and the operation procedures needed for the control of crossing.

• Journal of electromagnetic engineering and science
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• v.12 no.4
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• pp.280-286
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• 2012

The conventionally classified waves are reclassified in this paper, including the waves associated with metamaterial (MTM) transmission lines. Various types of guided waves in periodic structures are analyzed for 1D Composite Right/Left Handed (CRLH) transmission lines (TL). In addition, dispersion diagrams for 1D CRLH, RH, and LH TLs are presented in terms of radiation conditions. We have refined the design equations of the conventional 1D CRLH TL and proposed a condition to realize the desired phase shift and its slope per unit cell. This condition has been applied to the conventional Wilkinson power divider and realized into MTM added $90^{\circ}$ hybrid coupler. Based on the 10 dB return loss and the $90{\pm}10^{\circ}$ phase shift, the bandwidths of the MTM added $90^{\circ}$ hybrid coupler are 82.25% and 103.5% against the conventional 23% and 52.5%, respectively.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.363-365
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• 2002

train radio system used for shinkansen in japan has been 18 years since it was opened in 1982 and grown old. Analogue train radio is short of the number of lines and can't cope with the needs for the new high speed data transmission by 1,200 bps. The construction to renew the Tohoku - Joethu shinkansen train radio system(shinkansen train radio system) with digital method started from 2000 in JREast Digital method makes it possible to improve the quality of radio transmission, reliability of the network and every device, the speed and capacity of transmission and to be more efficient maintenance by introducing the latest IT technology. This paper will consider synchronization between base station. diversity method. software receiver, mobile high speed digital radio system, high reliability LAN introduced as technologies supporting these.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.49.2-49.2
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• 2021

We present the results of long-term simultaneous monitoring observations (~ 12 years) of H²O (22 GHz) maser and several vibrationally excited lines of SiO J = 1-0, 2-1, 3-2 masers (43, 86, 129 GHz) carried out with the 21-m antennas of the Korean VLBI Network (KVN) toward a sample of three AGB stars (RT Vir, RR Aql, IRC-10151) that are believed to be semiregular variable star, Mira variable star, and OH/IR star, respectively, according to a sequential evolutionary phase of AGB star. A total 10 transitions were observed, of which we detected H²O, SiO 𝝊 = 1 and 2, J = 1-0, SiO 𝝊 = 1, J = 2-1 and J = 3-2 maser lines in all three target objects, depending on the observational epochs. In this study, we scrutinize the evolutionary traits of each target object based on the maser line profiles, flux/velocity variations, and phase lags with the optical light curves. The IRAS two color diagram and the infrared spectral energy distributions (SEDs) in the wavelength range from 1.2 to 240 ㎛ of three observed sources were also analyzed.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.6
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• pp.9-14
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• 2008

Intentional city bands and public radio frequencies could reduce the internet transmission speed on the wired lines because AM and HF band are overlapping on the xDSL up and down data steam by way of the wired transmission lines. We were designed the adaptive common mode rejection circuit with 2 way amplifier against public radio frequency. Specially our circuits were applied for power and signal lines. We could reduced the common mode rejection up to 30dB and increased the up stream speed around 1.8 times using a our developed equipments. Also it could expanded the transmission distance up to 1.7 times than old lines.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.4
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• pp.151-155
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• 2006

HVAC transmission lines must be designed to satisfy environmental regulations. Therefore it is necessary to pre-evaluate environmental problems for transmission line designer using prediction program. In this study, environmental design software, TLCALC(Transmission Line CALCulation) for transmission lines was developed as a comprehensive window program. It has 6 modules that are audible noise, radio noise, television noise, magnetic field, electric field and conductor surface gradient. TLCALC solved a few problems in use of the existing foreign tools and took several advantages as follows; (1) It is a common tool that solves calculating limitations of foreign formulas, (2) It has wide application ranges and enhances accuracy of prediction. (3) It can be applied to almost transmission line configurations in Korea. (4) Experienced designers can get the results of calculation within about 15 minutes. Because the use of TLCALC is easy and practical, this program will be usefully applied to the environmental friendly design and construction of transmission lines. In the future, it is expected that public complaints and social environmental cost will be reduced by the use of TLCALC.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.71.2-71.2
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• 2021

Using multi-epoch spectra of active galactic nuclei (AGN) obtained from the Sloan Digital Sky Survey, we identify 16 spectrally variable sources, for which the spectral shapes of broad emission lines significantly vary with a time scale of yrs. Out of them, 3 AGNs are already known as changing-look (CL) AGNs by previous studies. 6 AGNs are newly identified as CL AGNs from our study. A majority of these AGNs are relatively faint and their variability in the continuum is small, which may explain their non-detection in the previous studies. 7 sources are known as binary AGN candidates based on the systematic velocity offset between broad emission lines and narrow emission lines. For those sources and 3 CL AGNs, we find that the peak of broad emission lines had been shifted up to a few thousands km/s for ~10 years, implying that those can be promising candidates for pc-scale binary AGNs or recoiling black holes. We plan to conduct multiwavelength follow-up studies to nail down the physical origin of the velocity shift.

• Publications of The Korean Astronomical Society
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• v.15 no.1
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• pp.35-60
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• 2000

We have analyzed the frequency sharing in the range of 71-275 GHz, which was adopted as a main topic of the WARC-2000 at the previous conference WARC-97. Though the technology of the active services has not been fully developed in this frequncy range, the heavy usage of this technology is expected in foreseeable future. To protect the passive services from spurious and out-of-band emissions of active services, realignment of the spectrum between 71 GHz and 275 GHz is strongly required. In addition, some effort should be made to allocate special bands for the radio astronomy service.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.6 s.109
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• pp.529-537
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• 2006

Multi-layer PCBs are of ien used In compact microwave circuit design as density of PCB layout is increased. In this paper, the crosstalk between coupled lines connected with vias in a 4-layer PCB is investigated theoretically based on the circiuit-concept approach. Coupled lines connected with vias in a 4-layer PCB are divided into three sections, which are coupled microstrip lines and upper via section, center via section, and lower via and coupled microstrip lines section, respectively. Each section is represented by ABCD matrix. By cascading these three ABCD matrices crosstalk between coupled lines connected with vias in a 4-layer PCB is approximately calculated. The validity of this theoretical approach is verified by comparing the calculated results with the simulated ones using HFSS.