• ETRI Journal
• /
• v.38 no.5
• /
• pp.952-961
• /
• 2016

In this paper, we study a spectrum sharing network (SSN) where a spectrum sharing device (SSD) coexists with multiple wireless communication systems (WCSs) in the same channel. The SSD can operate with either a duty cycle (DC) channel access mechanism or a listen-before-talk (LBT) channel access mechanism, whereas WCSs operate with an LBT mechanism. An opportunistic channel selection scheme for the SSD in the SSN is first proposed to minimize the outage probability. The optimal data transmission time for the DC-based SSD is derived to further improve the outage probability. We also derive the exact and closed-form outage probability of the proposed channel selection in the SSN by assuming that the number of WCSs operating in each channel is uniformly distributed. The simulation results show that the proposed channel selection scheme outperforms other channel selection schemes. It was also observed that a DC-based SSD with an optimal data transmission time provides a better outage performance than an LBT-based SSD. As the number of available channels increases, the channel selection scheme plays an important role in minimizing the outage probability of the SSNs.

• Bulletin of the Korean Space Science Society
• /
• 2010.04a
• /
• pp.25.1-25.1
• /
• 2010

This talk outlines the current understanding of solar flares, mainly focusing on magnetohydrodynamic (MHD) processes. A flare causes plasma heating, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes related to a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), formation of current-concentrated areas (current sheets) in the corona, and magnetic reconnection proceeding in current sheets that causes shock heating, mass ejection, and particle acceleration. A flare starts with the dissipation of electric currents in the corona, followed by various dynamic processes which affect lower atmospheres such as the chromosphere and photosphere. In order to understand the physical mechanism for producing a flare, theoretical modeling has been developed, in which numerical simulation is a strong tool reproducing the time-dependent, nonlinear evolution of plasma before and after the onset of a flare. In this talk we review various models of a flare proposed so far, explaining key features of these models. We show observed properties of flares, and then discuss the processes of energy build-up, release, and transport, all of which are responsible for producing a flare. We come to a concluding view that flares are the manifestation of recovering and ejecting processes of a global magnetic flux tube in the solar atmosphere, which was disrupted via interaction with convective plasma while it was rising through the convection zone.

• The Journal of the Convergence on Culture Technology
• /
• v.5 no.3
• /
• pp.215-227
• /
• 2019

This study empirically explores the effects of SNS use and the individual differences as the self-esteem on the social connectedness. The study results show that the higher self-esteem, the more use the Instagram and the Kakao Talk, which implies that the individual who has the more pro-social propensity uses the more diverse SNS. In contrast, the twitter shows the opposite pattern compared to the Instagram and Kakao Talk in terms of the SNS use according to the degree of the self-esteem. It also shows that women use the more SNS and the cell phone compared to the men do, whereas men use the more Internet than women do. The study results show that the more SNS use and the higher self-esteem, the higher social connectedness. Among the diverse SNS, only the Instagram shows the statistically positive effect on the social connectedness, which implies that the more the Instagram use, the more active in off-line social meetings.

• Korean journal of communication and information
• /
• v.77
• /
• pp.9-35
• /
• 2016

This research focuses on how political talk shows by Channel A and TV Chosun provoke strong, negative emotions, such as anger or loathing, towards certain parties, politicians and groups only, and tries to explain what's the relation to Korean democracy crisis under the circumstances. Those talk shows by Channel A and TV Chosun, predominantly about anger and loathing towards oppositions, opposition politicians and pro-North Korea people, have contributed to practical exclusion of the citizens from the political process by their imaginary political participation rather than a role as a democratic public sphere, so they have functioned very well in order to sustain the system of Korean democracy as a way of 'the politics of exclusion', and have been retained regardless of their commercial success for the reason. In other words, the Korean democracy has systematically excluded every citizen and amplified ideological conflicts, and in that chaos of excessively produced emotions, has dealt with all the crucial matters using political technology, which is a serious problem. However, for the good of the political power who wants to keep such kind of political system, this became a reason why those Channel A and TV Chosun shows-sensational and politically biased-have survived, and since Channel A and TV Chosun are remarkably functional within the continuance of that political system they can keep being influential in politics.

• The Journal of the Korea Contents Association
• /
• v.17 no.1
• /
• pp.567-584
• /
• 2017

This study investigated formats and structure of meanings for the TV talk shows with North Korean defectors. The authors selected of Channel A and of TV Chosun as research subjects. As results of this study, it was found that the former dealt with heavy issues about North Korea, expressed positive perspectives on North Korea and fantasic expectations about South Korea, and produced superior dicourse of South Korea. On the other hand, the latter one dealt with light and sensational items about North Korea, employed dialogues about critics and disappointments on South Korea, and produced problematic discourse about South Korea. The former produced a kind of converged discourse structure to create superior ideology of South Korea, while the latter produced a kind of dichotomous discourse structure to create frustrating ideology. In short, through this study, it turned out that North Korean defectors suffered from their confused identities, unclear self identities, and minority positions in the South Korean society.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1992.07a
• /
• pp.17-17
• /
• 1992

In this talk, our recent progress in experiment study on microscopic surface phonons has been reviewed. After the brief introduction concerning the concept of surface phonons, exprimental apparatus of HREELS and the principle of the measurment for surface phonon dispersions, I show the experimental data of some solide surfaces. The following points are discussed ; (1) lattice dynamical analysis of the phonon dispersions of some transi tion metal carbide (100) surfaces indicates the large changes in the force constant near the surface, which is consistent wi th a rippled structure of a topmost layer. (2) the phonon dispersions of a graphite overlayer show the modified phonon structure, which indicates that the thickness of the overlayer is one atomic layer, and in addition, the electronic structure is also modified. (3) The phonon structure of $LaB_6$ (100) surface is discussed. Lastly I telJ about new technology of extreme high vaccum less than $10^{-10}$ Pa.EX> Pa.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.59.2-59.2
• /
• 2019

In this talk, I will explain the implications of a rapid appearance of dark energy between the redshifts ($z$) of one and two on the expansion rate and growth of perturbations. Using both Gaussian process regression and a parametric model, I show that this is the preferred solution to the current set of low-redshift ($z<3$) distance measurements if $H_0=73~\rm km\,s^{-1}\,Mpc^{-1}$ to within 1\% and the high-redshift expansion history is unchanged from the $\Lambda$CDM inference by the Planck satellite. Dark energy was effectively non-existent around $z=2$, but its density is close to the $\Lambda$CDM model value today, with an equation of state greater than $-1$ at $z<0.5$. If sources of clustering other than matter are negligible, we show that this expansion history leads to slower growth of perturbations at $z<1$, compared to $\Lambda$CDM, that is measurable by upcoming surveys and can alleviate the $\sigma_8$ tension between the Planck CMB temperature and low-redshift probes of the large-scale structure.

• Asia pacific journal of information systems
• /
• v.28 no.1
• /
• pp.36-60
• /
• 2018

As an increasing number of people gained access to social network services (SNS), organizations started to use SNS as a channel for marketing and promotional purposes. The online advertising market has significant growth potential. Brand engagement is a key motive for online advertising, but how SNS users engage with brands, particularly in terms of the promotion of organizations, is poorly understood. This study uses customer value theory to examine brand engagement of users in terms of promoting companies in the context of Korean SNS marketing. This study identifies the antecedents of brand engagement based on customer value theory. Our findings show the significance of three factors of SNS marketing, namely, price discount, relationship support, and convenience, on brand engagement. We further show the consequences of brand engagement, namely, purchase decisions and word-of-mouth activities. These findings help advance customer value theory and offer practical insights into the use of information systems and marketing in the context of SNS.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.28 no.3
• /
• pp.177-185
• /
• 2017

In this paper, we proposed a concept of interference load to analyze the performance of spectrum sharing technologies in unlicensed frequency bands. The interference load can quantitatively compare the technical properties of various spectrum sharing technologies, such as frequency hopping(FH), duty cycle(DC), listen-before-talk(LBT). Therefore, it can help to evaluate whether a local regulation about spectrum sharing is reasonably established or not. In order to verify the suggested concept, we applied it to 2.4 GHz frequency bands. Also, we demonstrated a real-time test-bed. Two bit error rate(BER) curves for FH with 10 random channels and DC of 10 %, show such good agreement that our proposed concept is expected to be widely used to assess various spectrum sharing technologies.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.1A
• /
• pp.58-65
• /
• 2002

This paper deals with a delay problem in the endpoint detection of double-talk detection algorithm using correlation coefficient in the acoustic echo canceller. In case that past power is much bigger than current power like at the end of double-talking period, the power, estimated using forgetting factor, decreases slowly to cause a delay problem in the endpoint detection. In this paper, two methods are proposed to solve this problem. One is that the current power is periodically replaced by a new average power and the other is that the past power in recursive equation is periodically removed or replaced by other values. The simulation results show that proposed methods outperform conventional method in the endpoint of double-talking periods without increasing the computational burden much more.