• ETRI Journal
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• v.41 no.4
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• pp.536-548
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• 2019

In this study, an electronically steerable parasitic array radiator (ESPAR) antenna via analog radio frequency (RF) switches for a single RF chain MIMO system is presented. The proposed antenna elements are spaced at ${\lambda}/64$, and the antenna size is miniaturized via a dielectric radome. The optimum reactance load value is calculated via the beamforming load search algorithm. A switch simplifies the design and implementation of the reactance loads and does not require additional complex antenna matching circuits. The measured impedance bandwidth of the proposed ESPAR antenna is 1,500 MHz (1.75 GHz-3.25 GHz). The proposed antenna exhibits a beam pattern that is reconfigurable at 2.48 GHz due to changes in the reactance value, and the measured peak antenna gain is 4.8 dBi. The reception performance is measured by using a $4{\times}4$ BPSK signal. The measured average SNR is 17 dB when using the proposed ESPAR antenna as a transmitter, and the average SNR is 16.7 dB when using a four-conventional monopole antenna.

• The KIPS Transactions:PartD
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• v.13D no.4 s.107
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• pp.455-462
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• 2006

Recently, the filtering approach using vector approximation such as VA-file[1] or LPC-file[2] have been proposed to support similarity search in high dimensional data space. This approach filters out many irrelevant vectors by calculating the approximate distance from a query vector using the compact approximations of vectors in database. Accordingly, the total elapsed time for similarity search is reduced because the disk I/O time is eliminated by reading the compact approximations instead of original vectors. However, the search time of the VA-file or LPC-file is not much lessened compared to the brute-force search because it requires a lot of computations for calculating the approximate distance. This paper proposes a new bitmap index structure in order to minimize the calculating time. To improve the calculating speed, a specific value of an object is saved in a bit pattern that shows a spatial position of the feature vector on a data space, and the calculation for a distance between objects is performed by the XOR bit calculation that is much faster than the real vector calculation. According to the experiment, the method that this paper suggests has shortened the total searching time to the extent of about one fourth of the sequential searching time, and to the utmost two times of the existing methods by shortening the great deal of calculating time, although this method has a longer data reading time compared to the existing vector approximation based approach. Consequently, it can be confirmed that we can improve even more the searching performance by shortening the calculating time for filtering of the existing vector approximation methods when the database speed is fast enough.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.71.1-71.1
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• 2021

We perform disk-halo decomposition of the Large Magellanic Cloud (LMC) using a novel HI velocity field extraction method, aimed at better deriving its HI kinematics and thus mass distribution in the galaxy including both baryons and dark matter. We decompose all the line-of-sight velocity profiles of the combined HI data cube of the LMC, taken from the Australia Telescope Compact Array (ATCA) and Parkes radio telescopes with an optimal number of Gaussian components. For this, we use a novel tool, the so-called BAYGAUD which performs profile decomposition based on Bayesian MCMC techniques. From this, we disentangle turbulent non-ordered HI gas motions from the decomposed gas components, and produce an HI bulk velocity field which better follows the global circular rotation of the galaxy. From a 2D tilted-ring analysis of the HI bulk velocity field, we derive the rotation curve of the LMC after correcting for its transverse, nutation and precession motions. The dynamical contributions of baryons like stars and gaseous components which are derived using the Spitzer 3.6 micron image and the HI data are then subtracted from the total kinematics of the LMC. Here, we present the bulk HI rotation curve, the mass models of stars and gaseous components, and the resulting dark matter density profile of the LMC.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.41.3-42
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• 2016

New CCD photometric observations of GX Aur have been made between 2004 and 2015. Our light curves are the first ever compiled and display the variable O'Connell effect. The light variations are satisfactorily modeled by including time-varying cool-spots on the component stars. Our light curve synthesis indicates that the eclipsing pair is an A-type contact binary with parameters of i = 81.1 deg, ${\Delta}T=36K$, q = 0.950 and f = 46%. Including our 25 timing measurements, a total of 83 times of minimum light spanning about 66 yr were used for a period study. It was found that the orbital period of GX Aur has varied due to two periodic oscillations superposed on an upward-opening parabolic variation. The long-term period increase rate is deduced as $+9.636{\times}10^{-10}d\;yr^{-1}$, which can be produced as a mass transfer from the secondary star to the primary at a rate of $3.136{\times}10^{-6}M_{\odot}\;yr^{-1}$, among the largest rates for contact systems. The periods and semi-amplitudes of the two periodic variations are about $P_3=8.7yr$ and $P_4=21.2yr$, and $K_3=0.011d$ and $K_4=0.017d$, respectively. The most reasonable explanation for both cycles is a pair of light-travel-time effects driven by the possible existence of an unseen third and fourth components with projected masses of $M_3=0.91M_{\odot}$ and $M_4=1.09M_{\odot}$ in eccentric orbits of $e_3=0.13$ and $e_4=0.73$. Because no third light was detected in the light curve synthesis, each circumbinary object could be a compact star or a binary itself.

• Journal of The Korean Astronomical Society
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• v.55 no.1
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• pp.1-9
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• 2022

We present the photometric properties of V608 Cas from detailed studies of light curves and eclipse timings. The light curve synthesis indicates that the eclipsing pair is an overcontact binary with parameters of ∆T = 155 K, q = 0.328, and f = 26%. We detected the third light ℓ₃, which corresponds to about 8% and 5% of the total systemic light in V and R bands, respectively. Including our 6 timing measurements, a total of 38 times of minimum light were used for a period study. It was found that the orbital period of V608 Cas has varied in some combination of an upward parabola and two periodic variations. The continuous period increase with a rate of +3.99 × 10^-7 d yr^-1 can be interpreted as a mass transfer from the secondary component to the primary star at a rate of 1.51 × 10^-7 M_⊙ yr^-1. The periods and semi-amplitudes of the two periodic variations are about P₃ = 16.0 yr and P₄ = 26.3 yr, and K₃ = 0.0341 d and K₄ = 0.0305 d, respectively. The most likely explanation of both cycles is a pair of light-traveling time effects operated by the possible presence of third and fourth components with estimated masses of M₃ = 2.20 M_⊙ and M₄ = 1.27 M_⊙ in eccentric orbits of e₃ = 0.66 and e₄ = 0.52. Because the contribution of ℓ₃ is very low compared to the estimated masses of two circumbinary objects, they can be inferred as very faint compact objects.

• Bulletin of the Korean Mathematical Society
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• v.34 no.2
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• pp.155-171
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• 1997

Let $M^n$ be a connected subminifold of a Euclidean space $E^m$, equipped with the induced metric. Denoty by $\Delta$ the Laplacian operator of $M^n$ and by x the position vector. A well-known T. Takahashi's theorem [13] says that $\delta x = \lambda x$ for some constant $\lambda$ if and only if $M^n$ is either minimal subminifold of $E^m$ or minimal submanifold in a hypersphere of $E^m$. In [9], O. Garay studied the hypersurfaces $M^n$ in $E^{n+1}$ satisfying $\delta x = Dx$, where D is a diagonal matrix, and he classified such hypersurfaces. Garay's condition can be seen as a generalization of T.

• Communications of the Korean Mathematical Society
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• v.9 no.3
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• pp.547-564
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• 1994

Let X be a real Banach space. We consider the existence of solutions of the abstract nonlinear functional evolution equation : $$ (E) \frac{du(t)}{dt} + A(t)u(t) + F(u)(t) \ni h(t), $$ $$ u(s) = x_o \in D(A(s)), 0 \leq s \leq t \leq T, $$ where u : $[s, T] \to x$ is an unknown function, ${A(t) : 0 \leq t \leq T}$ is a given family of nonlinear (possibly multivalued) operators in X, and $F : C([s, t];X) \to L^{\infty}([s, X];X)$ and $h : [s, T] \to X$ are given functions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.110-116
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• 2012

This paper proposes a new diversity antenna which is the base of MIMO, tunable and reconfigurable antennas. The antenna has a small size and high inter-antenna isolation resulting from the compact radiating element comprising a meandered line and an open-loop combined in one limited uniplanar space and a modified T-shaped decoupling structure, respectively. In a WiMAX band, the radiating element and the entire antenna are $0.092{\lambda}$ and $0.2216{\lambda}$ in size, which shows effective size-reduction and the gain and efficiency of the proposed antenna attached to the ground of a handheld device are 3.7dBi and 56% acceptable to the industrial standard.

• Electronics and Telecommunications Trends
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• v.37 no.3
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• pp.41-51
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• 2022

This article presents an overview of the key technologies in the communications payload of broadband LEO satellite communications systems. In recent years, new developments have been realized for LEO satellite communications. SpaceX's Starlink, a technology leader in this field, offers premium services with satellites carrying in-house developed communications payloads. OneWeb, Amazon, Telesat, and Boeing are also developing LEO satellite communications payloads. The communications payload consists of user link antennas, inter-satellite link communications equipment, feeder link antennas, and a digital processor. Highly sophisticated technologies of compact active phased array antennas for generating multiple hopping beams and light laser communication equipment for ultra-high-speed inter-satellite communication will be applied to next- generation payloads.

• The Journal of the Korea Contents Association
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• v.17 no.6
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• pp.71-80
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• 2017

The standards for achievement levels for building blocks in elementary geometry class is to enhance spatial cognitive ability through practices describing shape patterns of building blocks observed from different directions. However, most of building block in the textbook is described from only one perspective. Even worse, some examples in the textbook are almost impossible to observe in the real world. Contrary to this, simulated views by Wings3D has shown that each box may look quite differently from different angles let alone the size of each box. Using Wings3D, it is also very easy to build different types of building blocks with various levels of difficulty in the virtual space. Based on these results, in this study, 3D visualization SW is suggested as a potential pedagogical tool for the elementary geometry class to help kids perceive objects in space more precisely. We have shown that 3D visualization SW such as Wings3D could be a powerful, compact 3D SW for most of subjects which are covered in elementary geometry education. Wings3D has another advantage of economic open source SW fully compatible with school PCs.