• Journal of The Korean Astronomical Society
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• v.39 no.1
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• pp.9-17
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• 2006

In an attempt to investigate star formation activity and statistical properties of clumps of high Galactic latitude clouds (HLCs), we mapped the Polaris Flare region, PF121.3+25.5, in $^{12}CO\;and\;^{13}CO$ J = 1 - 0 using SRAO 6-m telescope and also observed its 12 $^{13}CO$ peak positions in CS J = 2 - 1 with TRAO 14-m telescope. $^{13}CO$ integrated intensity map shows clearly its clumpy structure and the locations of clumps well agree with $^{12}CO$morphology. CS line is not detected toward the 12 $^{13}CO$ peak positions, so we can conclude there are no dense $(\sim10^4\;cm^{-3})$ in this region. We decomposed 105 clumps from $^{13}CO$ map using GAUSSCLUMPS algorithm. The mass of clumps ranges from $7.8\;M_{\odot}\;to\;7.4{\times}10^{-2}\;M_{\odot}$ with a total mass of $66.4\;M_{\odot}$ The mass spectrum follows a power law, dN/dM ${\propto}\;M^{-\alpha}$ with a power index of ${\alpha}=1.91{\pm}0.13$. The virial masses of clumps are in the range of $10{\sim}100M_{LTE}$ and so these clumps are considered to be gravitationally unbound.

• The KIPS Transactions:PartA
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• v.19A no.4
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• pp.195-204
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• 2012

M-commerce services are rapidly emerging with recent advances in mobile devices and wireless communications. Internet Shopping mall managers provide mobile phone users with their mobile shopping malls for m-commerce. However, these mobile shopping malls usually have their own sites which are not compatible with their Internet shopping malls, thus resulting in inefficiency to manage the two kinds of shopping malls. In this paper, we develop a M-commerce content provider system to effectively bring Internet shopping malls to mobile phones by extracting items only concerned to users from product documents. We then apply and evaluate the system over a specific internet shopping mall site. The results show that the system reduces considerably the amount of data transferred to user's mobile phones compared with using general web browsers.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.72.2-72.2
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• 2010

The extremely metal-poor halo planetary nebula BoBn 1 has been investigated based on IUE archive data, Subaru/HDS spectra, VLT/UVES archive data, and Spitzer/IRS spectra. We have measured a heliocentric radial velocity of $+191.6\pm1.3\;kms^{-1}$ and expansion velocity 2Vexp of $40.5\pm3.3\;kms^{-1}$ from an average over 300 lines. The estimations of C, N, O, and Ne abundances from the optical recombination lines (ORLs) and Kr, Xe, and Ba from the collisional excitation lines (CELs) are also done. We have detected 5 fluorine and several slow neutron capture elements (the s-process). The amounts of [F/H], [Kr/H], and [Xe/H] suggest that BoBn 1 is the most F-rich among F detected PNe and is a heavy s-process element rich PN. The photo-ionization models built with non-LTE theoretical stellar atmospheres indicate that the progenitor was a 1-1.5 $M_\bigstar$ that would evolve into a white dwarf with an $0.62M_{\odot}$ core mass and $0.09M_{\odot}$ ionized nebula. Careful examination implies that BoBn 1 has evolved from a binary and experienced coalescence during the evolution to become a visible PN. The elemental abundances except N could be explained by a binary model composed of $0.75M_{\odot}+1.5M_{\odot}$ stars.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.2
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• pp.181-186
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• 2014

In this paper, we propose an overload control scheme to resolve an overload problem in a random access channel of cellular machine-to-machine (M2M) communication networks. The M2M applications are characterized by small-sized data intermittently transmitted by a massive number of machines. Due to this characteristics, an overload situation in random access channel (RACH) can happen when a large number of devices try to send a signal via the RACH. To address this overload problem, we propose a scheme in which a base station estimates the total load in the network and controls the load by using a p-persistent method based on the estimated load.

• ETRI Journal
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• v.37 no.5
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• pp.856-866
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• 2015

A heterogeneous network (HetNet) is a network topology composed by deploying multiple HetNets under the coverage of macro cells (MCs). It can improve network throughput, extend cell coverage, and offload network traffic; for example, the network traffic of a 5G mobile communications network. A HetNet involves a mix of radio technologies and various cell types working together seamlessly. In a HetNet, coordination between MCs and small cells (SCs) has a positive impact on the performance of the networks contained within, and consequently on the overall user experience. Therefore, to improve user-perceived service quality, HetNets require high-efficiency network protocols and enhanced radio technologies. In this paper, we introduce a 5G HetNet comprised of MCs and both fixed and mobile SCs (mSCs). The featured mSCs can be mounted on a car, bus, or train and have different characteristics to fixed SCs (fSCs). In this paper, we address the technical challenges related to mSCs. In addition, we analyze the network performance under two HetNet scenarios-MCs and fSCs, and MCs and mSCs.

• Journal of the Korean Vacuum Society
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• v.15 no.6
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• pp.581-586
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• 2006

We have generated the argon plasma in the diode chamber based on the established coaxial electrode type and investigated the emitted visible light for emission spectroscopy. We applied various voltages $2\sim3.5kV$ to the device by 0.5kV, and obtained the emission spectrum data for the focused plasma in the diode chamber on the argon pressure of 330 mTorr. The Ar I and Ar II emission line are observed. The electron temperature and ion density have been measured by the Boltzmann plot and Saha equation from assumption of local thermodynamic equilibrium (LTE) The Ar I and Ar II ion densities have been calculated to be $\sim10^{15}/cc\;and\;~10^{13}/cc$, respectively, from Saha equation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.7
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• pp.2389-2413
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• 2015

High data rates in long-term evolution (LTE) networks can affect the mobility of networks and their performance. The speed and motion of user equipment (UE) can compromise seamless connectivity. However, a proper handover (HO) decision can maintain quality of service (QoS) and increase system throughput. While this may lead to an increase in complexity and operational costs, self-optimization can enhance network performance by improving resource utilization and user experience and by reducing operational and capital expenditure. In this study, we propose the self-optimization of HO parameters based on fuzzy logic control (FLC) and multiple preparation (MP), which we name FuzAMP. Fuzzy logic control can be used to control self-optimized HO parameters, such as the HO margin and time-to-trigger (TTT) based on multiple criteria, viz HO ping pong (HOPP), HO failure (HOF) and UE speeds. A MP approach is adopted to overcome the hard HO (HHO) drawbacks, such as the large delay and unreliable procedures caused by the break-before-make process. The results of this study show that the proposed method significantly reduces HOF, HOPP, and packet loss ratio (PLR) at various UE speeds compared to the HHO and the enhanced weighted performance HO parameter optimization (EWPHPO) algorithms.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.82.2-82.2
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• 2012

We present Herschel-PACS observations of L1448-MM, a Class 0 protostar with a prominent outflow, part of the DIGIT Key Program (PI: N. Evans). We detect numerous emission lines including CO and $H_2O$ rotational transitions, OH transitions, and [OI] forbidden transitions at wavelengths from 55 to 210 ${\mu}m$. The $H_2O$, [OI], mid-J CO (J < 23), and OH emission distributes along the outflow direction although high-J CO and other OH emission peaks at the central spatial pixel. According to our simple excitation analysis, CO seems to have two temperature components of warm and hot, which might be attributed to the PDR and shock, respectively. After exploring a wide range of physical conditions with a non-LTE LVG code, RADEX, we found that either shock alone or the combination of PDR and shock can explain the observations. The relative fraction of observed line luminosities suggest that L1448-MM is shielded from the UV radiation because $H_2O$ and CO are the dominant coolants rather than OH and [OI]. In addition, our observed fluxes match better with C-shock models rather than J-shocks. The non-LTE LVG model supports that the IR pumping process is important for OH transitions because the OH line ratios are fitted much better when the dust thermal continuum is included.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.12
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• pp.4819-4834
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• 2015

The spectral efficiency of cellular networks can be improved when proximate users engage in device-to-device (D2D) communications to communicate directly without going through a base station. However, D2D communications that are not properly designed may generate interference with existing cellular networks. In this paper, we study resource allocation and power control to minimize the probability of an outage and maximize the overall network throughput. We investigate three power control-based schemes: the Partial Co-channel based Overlap Resource Power Control (PC.OVER), Fractional Frequency Reuse based Overlap Resource Power Control (FFR.OVER) and Fractional Frequency Reuse based Adaptive Power Control (FFR.APC) and also compare their performance. In PC.OVER, a certain portion of the total bandwidth is dedicated to the D2D. The FFR.OVER and FFR.APC schemes combine the FFR techniques and the power control mechanism. In FFR, the entire frequency band is partitioned into two parts, including a central and edge sub-bands. Macrocell users (mUEs) transmit using uniform power in the inner and outer regions of the cell, and in all three schemes, the D2D receivers (D2DRs) transmit with low power when more than one D2DRs share a resource block (RB) with the macrocells. For PC.OVER and FFR.OVER, the power of the D2DRs is reduced to its minimum, and for the FFR.APC scheme, the transmission power of the D2DRs is iteratively adjusted to satisfy the signal to interference ratio (SIR) threshold. The three schemes exhibit a significant improvement in the overall system capacity as well as in the probability of a user outage when compared to a conventional scheme.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.3
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• pp.21-28
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• 2016

We propose an adaptive scheme of a differential codebook for temporally correlated channels. And the codeword entries of the propose codebook are selected among the set of M-PSK constellations - the values of M proposed in this paper are 8, 16, or 32. Firstly, we analyze mathematically how the optimal spherical cap radius of the proposed codebook is tracked. Then, we explain the practical implementation of the proposed adaptive method. Practically, some candidate differential codebooks we propose in this paper can be switched according to the temporal correlation coefficients of wireless channels in the proposed scheme. Monte-Carlo simulations demonstrate that the achievable throughput performance employing the proposed codebook is always superior to those of the differential codebooks employing M-PSK constellations and non-adaptive differential codebooks with the same amount of feedback information.