• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.43.1-43.1
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• 2010

A novel method to characterize the topology of the early-universe intergalactic medium during the epoch of cosmic reionization is presented. The 21-cm radiation background from high redshift is analyzed through calculation of the 2-dimensional (2D) genus. The radiative transfer of hydrogen-ionizing photons and ionization-rate equations are calculated in a suite of numerical simulations under various input parameters. The 2D genus is calculated from the mock 21-cm images of high-redshift universe. We construct the 2D genus curve by varying the threshold differential brightness temperature, and compare this to the 2D genus curve of the underlying density field. We find that (1) the 2D genus curve reflects the evolutionary track of cosmic reionization and (2) the 2D genus curve can discriminate between certain reionization scenarios and thus indirectly probe the properties of radiation-sources. Choosing the right beam shape of a radio antenna is found crucial for this analysis. Square Kilometer Array (SKA) is found to be a suitable apparatus for this analysis in terms of sensitivity, even though some deterioration of the data for this purpose is unavoidable under the planned size of the antenna core.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.56.1-56.1
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• 2017

When turbulent motions perturb magnetic field lines and produce magnetic fluctuations, the perturbations leave imprints of turbulence statistics on magnetic field. Observation of synchrotron radiation is one of the easiest ways to study turbulent magnetic field. Therefore, we study statistical properties of synchrotron polarization emitted from media with magnetohydrodynamic (MHD) turbulence, using both synthetic and MHD turbulence simulation data. First, we obtain the spatial spectrum and its derivative with respect to wavelength of synchrotron polarization arising from both synchrotron radiation and Faraday rotation. The study of spatial spectrum shows how the spectrum is affected by Faraday rotation and how we can recover the statistics of underlying turbulent magnetic field as well as turbulent density of electrons from interferometric observations that incorporate the effects of noise and finite telescopic beam size. Second, we study quadrupole ratio to quantitatively describe the degree of anisotropy introduced by magnetic field in the presence of MHD turbulence. We consider the case that the synchrotron emission and Faraday rotation are spatially separated, as well as the situation that the sources of the synchrotron radiation and thermal electrons causing Faraday rotation exist in the same region. In this study, we demonstrate that the spectrum and quadrupole ratio of synchrotron polarization can be very informative tools to get detailed information about the statistical properties of MHD turbulence from radio observations of diffuse synchrotron polarization.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.38.2-38.2
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• 2017

We present the observational study toward the multiple outflows around $LkH{\alpha}$ 234 star formation region. The high-resolution, near-IR spectral mapping using the Immersion Grating Infrared Spectrograph (IGRINS) allowed us to distinguish at least four separate outflows with the molecular hydrogen ($H_2$) and forbidden iron ([Fe II]) emission lines. The outflow associated with the radio continuum source VLA 3B is detected in both H2 and [Fe II] emission, while the outflows driven by MM 1, VLA 2 sources were only detected in $H_2$, indicating the different physical conditions of outflows. We confirm the axis of VLA 3B jet, the position angle of ${\sim}240^{\circ}$. We firstly identified the redshifted, near-IR H2 outflow associated with VLA 2, which is coincident with the previous detections of $H_2O$ masers. From the $H_2$ line ratios, we interpret the gas properties of the shock excited blue- and redshifted components, and UV excited surrounding photodissociation region. We also discuss the origin of the high-velocity (|VLSR| > $150km\;s^{-1}$) $H_2$ emission.

• Journal of The Korean Astronomical Society
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• v.50 no.6
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• pp.185-190
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• 2017

We present observations of $HCO^+$ 1-0 absorption lines toward two extragalactic compact radio sources, NRAO 150 and BL Lac with the Korean VLBI Network in order to investigate their time variation over 20 years by Galactic foreground clouds. It is found that the line shape of $-17kms^{-1}$ component changed marginally during 1993-1998 period and has remained unaltered thereafter for NRAO 150. Its behavior is different from that of $H_2CO$ $1_{10}-1_{11}$, suggesting chemical differentiation on ~ 20 AU scale, the smallest ever seen. On the other hand, BL Lac exhibits little temporal variation for the $HCO^+$ and $H_2CO$ lines. Our observation also suggests that Korea VLBI Network performs reliably in the spectrum mode in that the shapes of the new $HCO^+$ 1-0 spectra are in good agreement with the previous ones to an accuracy of a few percent except the time varying component toward NRAO 150.

• Applied Science and Convergence Technology
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• v.23 no.6
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• pp.357-365
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• 2014

A non-invasive method for ion energy distribution measurement at a RF biased surface is proposed for monitoring the property of ion bombardments in capacitively coupled plasma sources. To obtain the ion energy distribution, the measured electrode voltage is analyzed based on the circuit model which is developed with the linearized sheath capacitance on the assumption that the RF driven sheath behaves like a simple diode for a bias power whose frequency is much lower than the ion plasma frequency. The method is verified by comparing the ion energy distribution function obtained from the proposed model with the experimental result taken from the ion energy analyzer in a dual cathode capacitively coupled plasma source driven by a 100 MHz source power and a 400 kHz bias power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11A
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• pp.1085-1090
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• 2010

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geolocation, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional mobile wireless systems sharing the frequency bands such as Cellular CDMA and Korean PCS. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a direct-sequence spread-spectrum UWB source and an impulse radio UWB source, to a Cellular CDMA and K-PCS digital transmission system. The average frame error rate degradation of each system arc presented. From these experimental results, we show that in all practical cases UWB system can coexist with Cellular CDMA and K-PCS terminal without causing any dangerous interference.

• MALSORI
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• no.29_30
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• pp.61-94
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• 1995

The aim of this paper is to describe the linguistic differences of two Koreas with a special emphasis on the phonetic aspect of Seoul and Pyongyang speech. The sources of the North Korean speech material used in the study are 1) the Pyongyang radio and TV broadcasts, 2) interviews of north Korean defectors and 3) speech material of north Korean scholars collected by the writer in london, Warsaw, France and China between 1989 and 1994. The most noticeable phonetic differences of Seoul and Pyongyang speech are abstracted as follows: 1) The vowels /이/, /에/ and /애/ are higher and fronter in Pyongyang speech than in Seoul speech. 2) The vowels /우/ and /으/ of Pyongyang speech are somewhat fronter than the corresponding vowels of Seoul speech. 3) The Pyongyang vowels /으/ and if are produced with rounded lips compared to the corresponding Seoul vowels. 4) The Pyongyang vowel /h) is much lower in tongue position and at the same time somewhat fronter than the corresponding Seoul vowel. 5) The consonants /r ,i ,n / are pronounced in Pyongyang as alveolar affricates or something close to them whereas they are pronounced in Seoul as post-alveolar affricates. 6) Unlike in Seoul speech there is a very strong tendency in Pyongyang speech to reduce aspiration feature in consonant seouences such as /ㅂ+ㅎ/, /ㄷ+ㅎ/, /ㄱ+ㅎ/. 7) /ㄴ/ and /ㄹ/(flap) freely occur word-initially in Pyongyang speech whereas they are restricted in Seoul speech. 8) Unlike in Seoul speech the phonemic contrast of long and short vowels are generally not functional in Pyongyang speech. Thus the vowels pronounced long in Seoul speech are usually pronounced short in Pyongyang speech.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.2
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• pp.480-497
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• 2012

As a new business concept, machine-to-machine (M2M) communications are born from original telemetry technology with the intrinsic features of automatic data transmissions and measurement from remote sources typically by cable or radio. M2M includes a number of technologies that need to be combined in a compatible manner to enable its deployment over a broad market of consumer electronics. In order to provide better understanding for this emerging concept, the correlations among M2M, wireless sensor networks, cyber-physical systems (CPS), and internet of things are first analyzed in this paper. Then, the basic M2M architecture is introduced and the key elements of the architecture are presented. Furthermore, the progress of global M2M standardization is reviewed, and some representative applications (i.e., smart home, smart grid and health care) are given to show that the M2M technologies are gradually utilized to benefit people's life. Finally, a novel M2M system integrating intelligent road with unmanned vehicle is proposed in the form of CPS, and an example of cyber-transportation systems for improving road safety and efficiency are introduced.

• Journal of the Korean Society of Safety
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• v.22 no.3 s.81
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• pp.13-21
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• 2007

Personal and static sampling for formaldehyde, wood dust and noise monitoring, in accordance to the equipment running on the day, were carried out throughout wood panel manufacturing process. Even though the exposure level of formaldehyde and wood dust were below than exposure criteria, but the personal protective equipment(PPE) for those should be worn to everyone in the process because of its potential characteristics like carcinogenicity. Also a few local air extraction system above the cutting, grinding sections and organic blending room should be required. Most of the exposures of noise exposure were exceeded permitted exposure criteria, in case of Hopper operators, exposed to maximally 94dB(A) as LAeq 8hr, therefore active controls like PPE, monitoring, isolation etc. are necessary. The main sources of noise were caused on compressed air of the machinery, radio sound and operation noise like running machines, conveying, cutting, sawing, moving vehicles, storing and so on. For the comparison of control criteria in each country, the permitted exposure standards for above hazardous materials and noise in Korea, ACGIH and Australia were discussed. We have recognized that the Korean criteria should be discussed urgently to give the right information to employee and modified, if it is necessary.

• Korean Journal of Human Ecology
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• v.10 no.1
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• pp.71-80
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• 2007

This study was carried out to investigate dietary habits and nutrition knowledge of teachers, who are in charge of actual education of nutrition knowledge and dietary habits for students, of the elementary schools. Five hundred male and female teachers, who attended the programs for teacher's qualification of 1st and 2nd grades and function education during summer vacations, were surveyed using of questionnaire at Jeollabuk-do Educational Training Institute. A lot of teachers have had undesirable dietary habits. The most frequently(65.4%) used sources of nutrition knowledge were mass media such as TV, radio, magazines and newspapers, About 93% of teachers recognized nutrition education for the students, and 75.6% of them answered that their dietary habits may have an influence on students' dietary habits. Or, teachers' nutrition knowledge level was found to be low in general. The improvement of dietary habits and their nutrition knowledge of the teachers are very important because their dietary habits and nutrition knowledge have an influence on formation of students' dietary habits.