• Journal of Communications and Networks
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• v.10 no.3
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• pp.253-257
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• 2008

In this paper, the performance of generic orthogonal space-time block codes (OSTBCs) introduced by Alamouti [2], Tarokh [3], and Su and Xia [11] is analyzed. We first define one-dimensional component symbol error function (ODSEF) from the exact expression of the pairwise error probability of an OSTBC. Utilizing the ODSEF and the bit error probability (BEP) expression for quadrature amplitude modulation (QAM) introduced by Cho and Yoon [9], the exact closed-form expressions for the BEP of linear OSTBCs with QAM in quasi-static Rayleigh fading channel are derived. We also derive the exact closed-form of the BEP for some OSTBCs which have at least one message symbol transmitted with unequal power via all transmit antennas.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.71.1-71.1
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• 2014

To investigate physical properties of Solar pores, we use SDO/HMI data from 2010 to 2013. For this, we select single and isolated pores from the active region (Axx, Bxo, Bxi and Bxc-type) listed in Solar Region Summary. Pore is defined by connected pixels satisfying the intensity threshold from pixel of minimum intensity. We try to obtain area, intensity, magnetic field, and Doppler velocity of pores from HMI data. After removing the effects of orbital motion of the SDO satellite and differential rotation of the Sun, we identify that significant daily variations of Doppler velocity with non-zero ordinates still remain in the umbral region, and the artifact is quite dependent on the strength of magnetic field and radial component of velocity of SDO satellite. In this study we develope empirical model to remove the artifact. A preliminary result on the elimination of the artifact will be presented.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.763-767
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• 2004

A possible and practical engine system research method is proposed. Varieties of objectives of the engine component and system technology developments are fulfilled by the small scale rig and engine demonstration. Some research applications of small jet engines in National Aerospace Laboratory of Japan (NAL) are presented together with historical overview.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.11a
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• pp.347-350
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• 2011

This paper propose a statistical color model of background extraction base on Hue-Saturation-Value(HSV) color space, instead of the traditional RGB space, and shows that it provides a better use of the color information. HSV color space corresponds closely to the human perception of color and it has revealed more accuracy to distinguish shadows [3] [4]. The key feature of this segmentation method is based on processing hue component of color in HSV color space on image area. The HSV color model is used, its color components are efficiently analyzed and treated separately so that the proposed algorithm can adapt to different environmental illumination condition and shadows. Polar and linear statistical operations are used to calculate the background from the video frames. The experimental results show that the proposed background subtraction method can automatically segment video objects robustly and accurately in various illuminating and shadow environments.

• Honam Mathematical Journal
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• v.46 no.2
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• pp.237-248
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• 2024

In this manuscript, the hypersurfaces of non-flat Riemannian 4-space forms are considered. A hypersurface of a 4-dimensional Riemannian space form defined by an isometric immersion 𝐱 : M³ → 𝕄⁴(c) is said to be biconservative if it satisfies the equation (∆²𝐱 )^⊤ = 0, where ∆ is the Laplace operator on M³ and ⊤ stands for the tangent component of vectors. We study an extended version of biconservativity condition on the hypersurfaces of the Riemannian standard 4-space forms. The C-biconservativity condition is obtained by substituting the Cheng-Yau operator C instead of ∆. We prove that C-biconservative hypersurfaces of Riemannian 4-space forms (with some additional conditions) have constant scalar curvature.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.34.4-35
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• 2008

The significant I&T process gain represented by reduction in overall budget expenditure can be obtained from the use of efficient alignment technique for large space optical systems. Such process gain tends to increase rapidly with an increase in aperture and/or in number of optical elements within the system. However, in practice, the alignment of multiple optical components tends to be rather difficult task because of the multiple coupling effects among the elements within the target system. In order to understand and hence identify the complex interplay of the wavefront coupling effects from the alignment process, the original differential wavefront sampling(DWS) method was presented elsewhere in recent years. DWS uses partial differential of the wavefront of optical component and perturbation value of the optical component against a particular alignment factor. The straightforward application of DWS for an off-axis optical system revealed that it tends to give incorrect estimation of the given misalignment state. In this study, we added off-axis correction terms to the original DWS algorithm and investigated its alignment performance. The performance simulation result for a Korsch type space optical system shows that the modified DWS is capable of bringing the misaligned system into the target alignment tolerance only after 3 iterations. It also shows that this new improved algorithm can be used to estimate the source misalignment as well. We are planning to apply this method for the alignment of a 800mm Korsch type telescope in the near future. We discuss the computational technique, simulation results and implications in details.

• Korean Journal of Cognitive Science
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• v.23 no.3
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• pp.295-322
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• 2012

In this paper, we cluster similar word senses applying vector space model and HAL (Hyperspace Analog to Language). HAL measures corelation among words through a certain size of context (Lund and Burgess 1996). The similarity measurement between a word pair is cosine similarity based on the vector space model, which reduces distortion of space between high frequency words and low frequency words (Salton et al. 1975, Widdows 2004). We use PCA (Principal Component Analysis) and SVD (Singular Value Decomposition) to reduce a large amount of dimensions caused by similarity matrix. For sense similarity clustering, we adopt supervised and non-supervised learning methods. For non-supervised method, we use clustering. For supervised method, we use SVM (Support Vector Machine), Naive Bayes Classifier, and Maximum Entropy Method.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.116.1-116.1
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• 2012

When an interplanetary (IP) shock passes over the Earth's magnetosphere, the geosynchronous magnetic field strength near the noon is always enhanced, while the geosynchronous magnetic field near the midnight decreases or increases. In order to understand what determines the positive or negative magnetic field response at nightside geosynchronous orbit to sudden increases in the solar wind dynamic pressure, we have examined 120 IP shock-associated sudden commencements (SC) using magnetic field data from the GOES spacecraft near the midnight (MLT = 2200~0200) and found the following magnetic field perturbation characteristics. (1) There is a strong seasonal dependence of geosynchronous magnetic field perturbations during the passage of IP shocks. That is, the SC-associated geosynchronous magnetic field near the midnight increases (a positive response) in summer and decreases (a negative response) in winter. (2) These field perturbations are dominated by the radial magnetic field component rather than the north-south magnetic field component at nightside geosynchronous orbit. (3) The magnetic elevation angles corresponding to positive and negative responses decrease and increase, respectively. These field perturbation properties can be explained by the location of the cross-tail current enhancement during SC interval with respect to geosynchronous spacecraft position.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.39.1-39.1
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• 2010

We have investigated interplanetary (IP) structures of 82 intense geomagnetic storms (Dst $\leq$ -100 nT) that occurred from 1998 to 2006. According to their interplanetary origins, we classified them as four groups: 20 sMC events (IP shock and MC), 19 SH events (sheath field), 12 SH+MC events (Sheath field and MC), and 8 nonMC events (non-MC type ICME). For each group, we examined the relationships between Dst index and solar/IP parameters, namely, direction parameter (DP), CME speed ($V_{CME}$), solar wind speed ($V_{SW}$), minimum of IMF $B_z$ component($Bz_{min}$), and maximum of $E_y$ component ($Ey_{max}$).We found that the relationships strongly depend on their IP source. Our main results can be summarized as follows: 1) The correlation between Dst and DP is the best for the SH+MC events (r = -0.61). 2) The relationship between Dst and $V_{CME}$ gives the best correlation for the sMC events (r = -0.56). 3) There is the best correlation between Dst and $V_{SW}$ for the sMC events (r = -0.61), while there is a very weak correlation (r=-0.17) for the SH events. 4) The relationship between Dst and $Bz_{min}$ gives the best correlation (r = -0.87) for the SH+MC events. 5) The correlation between Dst and $Ey_{max}$ is the best for the SH+MC events (r = -0.87). Summing up, the sMC and SH+MC events give us good correlations, but the SH events, weak correlations. From this study, we suggest that this tendency should be caused by the characteristics of IMF southward components, e.g., smooth field rotations for the MC events and highly IMF fluctuations for the SH events.

• Korean Institute of Interior Design Journal
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• v.26 no.5
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• pp.83-92
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• 2017

This research is about the characteristics of the saccades that occurring in the process of observing the spatial. The size of the saccades is the visual activity for acquiring the information, and the search trace that left by the spatial visitor. Reviewed over the saccade through the analysis of observation process that appeared in the eye-tracking experiment of sports store from the department store, the saccade is defined as the sight movement in the process of finding a component to view in the spatial. If some spatial component induces saccade, and able to know which specific component acquired through the saccade, then the designer will have a clue which able to provide the spatial desired by the consumer. The results of analyzing the process in the deriving the spatial component and saccade characteristic from industrial space, can be summarised as follows. The first, the average fixed number of [IN].[OUT] zone appeared similarly, and it leads to knowing that the time used for attention with one frequency is about 0.3 seconds. Second, there were more saccades toward [$IN{\rightarrow}OUT$] (13 persons, 76.5%) than [$OUT{\rightarrow}IN$] (4 persons, 23.5%). The Los Angeles area has lots of interesting things to watch, so it able to thinks to begins with small saccade and then occur to bigger saccade activity to find new interests shortly after [OUT] saccade. Third, according to time range changes, keep eyes on the characteristics of saccade, [IN].[OUT] frequency has slightly decreased the changes of viewing time, but there was no significant change in an average number of observations. This means that the frequency and the number of observations are decreased together. Therefore, it can be seen that the amount of information to be acquired (frequency) is decreased (count) as the observation time elapses.