• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2691-2707
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• 2014

Medium access control is critical in wireless networks for efficient spectrum utilization. In this paper, we introduce a novel collision resolution method based on the technique of known interference cancellation, and propose a new MAC protocol named as CR-MAC, in which AP tries to decode all the collided data packets by combining partial retransmissions and known interference cancellation. As the collided transmissions are fully utilized, less retransmission is required, especially in a crowded network. The NS-2simulation and MATLAB numerical results show that, under various network settings, CR-MAC performs much better than the IEEE 802.11 DCF in terms of the aggregation throughput and the expected packet delay.

• 천문학회보
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• 제38권2호
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• pp.35.2-35.2
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• 2013

I will present a new approach to constrain galaxy physical parameters from the combined interpretation of stellar and nebular emission in wide ranges of observations. This approach relies on a comprehensive library of synthetic spectra, assembled using state-of-the-art models of star formation and chemical enrichment histories, stellar population synthesis, nebular emission and attenuation by dust. We focus on the constraints set by 5-band photometry and low- and medium-resolution spectroscopy at optical rest wavelengths on a few physical parameters characterizing the stars and interstellar medium. Since these parameters cannot be known a priori for any galaxy sample, we assess the accuracy to which they can be retrieved by simulating 'pseudo-observations' using models with known parameters. We find that the combined analysis of stellar and nebular emission in low-resolution (50A FWHM) galaxy spectra provides valuable constraints on all physical parameters. The approach can be extended to the analysis of any type of observation and during this talk i will present some applications to observed galaxies up to redshift 1.5.

• 천문학회보
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• 제41권2호
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• pp.56.2-56.2
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• 2016

We present chemical abundances for about 800 red giant stars in Omega Centauri, based on medium-resolution spectra obtained using Hydra multi-fiber spectrograph at the CTIO 4-m telescope. Our sample covers 14.2 < V < 15.0, and is almost unbiased against colors (and therefore metallicity). The metallicity distribution function (MDF) constructed from our data has an overall shape and local peaks that approximately match those for brighter giant stars in Johnson et al.. We also find that more metal-rich cluster members are more concentrated in the cluster center, which is consistent with previous studies. On the other hand, we find no clear evidence for such a spatial dependence with respect to alpha elemental abundance ([${\alpha}/Fe$]).

• 천문학회보
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• 제36권1호
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• pp.69.2-69.2
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• 2011

We present medium resolution spectra in the near-infrared (IR) band 1.4-1.8 microns at a resolving power of R = 5000-10000 of template stars in G, K, and M types with luminosity classes of III observed by the echelle spectrometer, IRCS, at the SUBARU 8.2 m telescope. Identification of lines in the template star spectra has been completed base on the reference of Arcturus spectrum. We measured equivalent width (EW) of the lines, and analyze the trends of EW through the stellar spectral types.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.792-797
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• 2002

In the following paper two algorithms, suitable for the analysis of panchromatic data as provided by KOMPSAT-1 will be presented. One is a texture analysis which will be used to create a settlement mask based on the variations of gray values. The other is a fusion algorithm which allows the combination of high resolution panchromatic data with medium resolution multispectral data. The procedure developed for this purpose uses the spatial information present in the high resolution image to spatially enhance the low resolution image, while keeping the distortion of the multispectral information to a minimum. This makes it possible to use the fusion results for standard multispecatral classification routines. The procedures presented here can be automated to large extent, making them suitable for a standard processing routine of satellite data.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.636-642
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• 2012

Delay-and-sum (DAS) Planar Beamforming has been a widely used Noise Source Identification Technique for the last decade. It is a quick one shot measurement technique being able to map sources that are larger than the array itself. The spatial resolution is proportional to distance between array and source, and inversely proportional to wavelength, thus the resolution is only good at medium to high frequencies. Improved algorithms using iterative de-convolution techniques offers up to ten times better resolution. The principle behind these techniques is described in this paper, as well as measurement examples from the automotive industry are presented.

• 대기
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• 제18권4호
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• pp.387-395
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• 2008

The impact of horizontal resolution on a regional climate model was investigated by simulating precipitation over the Korean Peninsula. As a regional climate model, the SNURCM(Seoul National University Regional Climate Model) has 21 sigma layers and includes the NCAR CLM(National Center for Atmospheric Research Community Land Model) for land-surface model, the Grell scheme for cumulus convection, the Simple Ice scheme for explicit moisture, and the MRF(Medium-Range Forecast) scheme for PBL(Planetary Boundary Layer) processing. The SNURCM was performed with 20 km resolution for Korea and 60 km resolution for East Asia during a 20-year period (1980-1999). Although the SNURCM systematically underestimated precipitation over the Korean Peninsula, the increase of model resolution simulated more precipitation in the southern region of the Korean Peninsula, and a more accurate distribution of precipitation by reflecting the effect of topography. The increase of precipitation was produced by more detailed terrain data which has a 10 minute terrain in the 20 km resolution model compared to the 30 minute terrain in the 60 km resolution model. The increase in model resolution and more detailed terrain data played an important role in generating more precipitation over the Korean Peninsula. While the high resolution model with the same terrain data resulted in increasing of precipitation over the Korean Peninsula including the adjoining sea, the difference of the terrain data resolution only influenced the precipitation distribution of the mountainous area by increasing the amount of non-convective rain. In conclusion, the regional climate model (SNURCM) with higher resolution simulated more precipitation over the Korean Peninsula by reducing the systematic underestimation of precipitation over the Korean Peninsula.

• 대한수학회논문집
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• 제16권3호
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• pp.445-458
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• 2001

The shape and the distribution of material construction of the scatterer may be obtained from its scattered fields by the iterative inversion in the spectral domain. The illposedness, the resolution, and the uniqueness of the inversion are the key problems in the inversion and inter-related. The illposedness is shown to be caused by the evanescent modes which carries and amplifies exponentially the measurement errors in the back-propagation of the measured scattered fields. By filtering out all the evanescent modes in the cost functional defined as the squared difference between the measured and the calculated spatial spectrum of the scattered fields from the iteratively chosen medium parameters of the scatterer, one may regularize the illposedness of the inversion in the expense of the resolution. There exist many local minima of the cost functional for the inversion of the large and the high-contrast scatterer and the hybrid algorithm combining the genetic algorithm and the Levenberg-Marquardt algorithm is shown to find efficiently its global minimum. The resolution of reconstruction obtained by keeping all the propating modes and filtering out the evanescent modes for the regularization becomes 0.5 wavelength. The super resolution may be obtained by keeping the evanescent modes when the measurement error and instance, respectively, are small and near.

• 한국콘텐츠학회논문지
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• 제10권1호
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• pp.192-201
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• 2010

본 연구에서는 영상 콘텐츠의 표현밀도를 화면의 해상도와 피사체와의 거리감으로 정의하고, 표현밀도가 보는 이에게 미치는 감정의 변화를 살펴보고자 하였다. 부산지역 대학교에 재학 중인 학생 61명에게 HDTV방송화면에서 캡처한 영상이미지를 제시하고, 즐거움, 흥분, 통제 3가지 차원의 감정측정을 위해 SAM평가를 실시하였다. 서로 다른 해상도에 대한 비교결과 저해상도보다 고해상도의 콘텐츠 이미지를 볼 때 즐거운, 흥분되는, 통제되지 않는 방향으로 나타났다. 또한 해상도가 연속해서 동일할 때보다 변화가 있을 때 감정 변화 폭이 크게 나타났는데, 고해상도를 보다가 저해상도 이미지를 볼 때 감정이 유쾌하지 않은, 차분해지는 경향을 볼 수 있었다. 그러나 통제 감정에 대해서는 유의미한 결과가 나타나지 않았다. 또한 피사체와의 거리감에 대해 근거리, 중거리, 원거리를 사후다중비교 결과 근거리의 경우 다른 경우들 보다 즐거운, 흥분되는, 통제되지 않는 감정의 값이 더 높아졌다. 다변량 검증결과 해상도와 거리감에 대한 즐거움과 흥분 감정차원은 정의 상관관계를 가지고 있는 것으로 나타났다.

• 한국정보통신학회논문지
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• 제20권12호
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• pp.2259-2266
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• 2016

최근 꾸준히 증가하는 무선랜 셀 및 단말의 증가로 제한된 공간 내에 매우 많은 무선랜 접속이 발생하는 밀집 무선랜 환경이 도래하고 있다. 본 논문은 이러한 밀집 무선랜 환경에서 수많은 단말의 접속으로 인한 기존 매체접속제어 프로토콜의 성능 저하를 막기 위하여 새로운 분산 매체접속제어 프로토콜을 제안한다. 제안하는 프로토콜은 하나의 collision detection (CD) 단계만을 사용하는 기존 carrier sense multiple access with collision resolution (CSMA/CR) 프로토콜을 확장하여 여러 개의 CD 단계를 사용하여 높은 확률로 충돌을 해소한다. 각 CD 단계마다 충돌 검출 여부를 확인하는데 충돌이 검출되지 않은 CD 단계가 연속적으로 발생하여 임계치를 넘으면 CD 단계를 멈추는 방식으로 동작한다. 따라서 제안 방안은 접속하는 단말 수에 따라 적응적으로 CD 단계의 개수를 조절하여 다수의 CD 단계의 사용에 의한 전송 오버헤드를 줄이면서 충돌 해결 확률을 높일 수 있다. 모의실험 결과 제안하는 적응형 CSMA/CR 프로토콜은 단말 수에 따라 가변적으로 CD 단계를 운영하며 고정 개수의 CD 단계를 사용하는 기존 CSMA/CR 프로토콜보다 향상된 처리율을 보여준다.