• 대기
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• 제28권4호
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• pp.383-392
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• 2018

This study investigates synoptic characteristics of cold surges over South Korea during winter season (December-February). A total of 63 cold events are selected by quantile regression analysis using daily mean temperature observations from 11 KMA stations for 38 years (1979/80-2016/17). Large-scale pressure pattern during the cold surges is well characterized by high over Siberia and low over Aleutian regions, which elucidates cold advection over the Korean peninsula. However, the large-scale pattern cannot successfully explain the observed sudden decrease of temperature during the cold surges. Composite analyses reveal that a synoptic-scale cyclone developing over the northern Japan is a key feature that significantly contribute to the enhancement of cold advection by increasing pressure gradient over the Korean peninsula. Enhanced sensible and latent heat fluxes are observed over the southern ocean of Korea and Japan during the cold surges due to temperature and humidity differences between the near surface and the lower atmosphere over the ocean. The evaporated water vapor transported toward the center of the surface cyclone and condenses in the lower-to-middle troposphere. The released energy likely promotes the development of the surface cyclone by inducing positive PV near the surface of the heating region.

• Investigative Magnetic Resonance Imaging
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• 제26권1호
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• pp.60-65
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• 2022

Gadoxetic acid-enhanced magnetic resonance imaging (MRI) has been widely used to detect and characterize focal hepatic lesions. Because gadoxetic acid is a hepatocyte-specific contrast agent, its patterns during hepatobiliary phase enhancement provide useful information for differential diagnoses of focal hepatic lesions. Hepatic angiomyolipoma (AML) is a rare mesenchymal hepatic neoplasm composed of blood vessels, epithelioid cells, and varying amounts of adipose tissue components. Hepatic AMLs usually show marked hypointensity during the hepatobiliary phase of gadoxetic acid-enhanced MRI as hepatic AMLs are devoid of hepatocytes and fibrotic components. The present study describes a patient with hepatic AML and an atypical imaging feature. This tumor showed hyperintensity during the hepatobiliary phase of gadoxetic acid-enhanced MRI, mimicking hepatocellular tumors such as hepatocellular adenoma. The hepatobiliary hyperintensity of this lesion was likely due to multifocal entrapped hepatocytes resulting from an intrasinusoidal growth pattern of tumor cells and insufficient hepatic parenchymal enhancement during the hepatobiliary phase of gadoxetic acid-enhanced MRI.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.38.3-39
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• 2009

Equatorial Plasma Bubble (herafter, EPB) is a common feature in low-latitude F-region during the night time. Since EPB causes significant impacts on the satellite communication and navigation systems, its accurate forecast is highly demanded by the GNSS users. Thus, further understanding of these features and their configuration is a challenging issue in space weather studies. The day-to-day variability of the plasma bubble activity was investigated by analyzing the TIMED/GUVI, ROCSAT-1, DMSP, and CHAMP satellite data. The pre-reversal enhancement (PRE) is known as the most important single parameter for the onset of plasma bubbles but we do not know yet to what extent the day-to-day variability of the bubble activity can be attributed to the PRE. We obtained the magnitude of the PRE from ROCSAT-1 and the occurrence of bubbles in relation to the PRE was investigated by using the coincident observations of EPBs from TIMED/GUVI, DMSP, and CHAMP. By conducting one-to-one comparison of the PRE characteristics with the EPB occurrence we examined the role of the PRE in the onset of EPBs.

• 한국음향학회지
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• 제16권4호
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• pp.57-63
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• 1997

본 논문에서는 다양한 전화선 채널에서 수집된 한국통신(KT)의 데이터베이스를 이용하여 인식 시스템의 성능을 향상시키기 위한 효율적인 특징벡터 및 전처리방법을 연구하였다. 먼저 잡음 및 주변 환경 변화에 강인한 갓으로 알려져 있는 특징벡터들을 이용한 인식 성능을 비교하고, 가중 켑스트랄 거리측정 방법을 이용하여 인식시스템의 성능 향상을 검증하였다. 실험 결과, KT의 인식 시스템에서 이용하는 LPC 켑스트럼의 경우에 비하여 PLP(Perceptual Linear Prediction)과 MFCC)Mel Frequency Cepstral Coefficient)등에 대하여 인식률이 향상되었다. 켑스트럼간의 거리측정에 있어서는 RPS(Root Power Sums)와 BPL(Band Pass Lifter)과 같은 가중 켑스트랄 거리측정 함수들이 인식성능 향상에 도움을 주었다. 스펙트럼 차감법(Spectral Subtraction)의 적용은 왜곡에 의한 효과가 커서 인식률이 저하되었지만, RASTA(RelAtive SpecTrAl) 처리방법, CMS(Cepstral Mean Subtraction), SBR(Signal Bias Removal)의 적용시에는 인식 성능 향상을 보였다. 특히, CMS 방법은 간편하면서도 높은 인식 성능 향상을 보였다. 마지막으로, CMS의 실시간 구현을 위한 방법들의 인식 성능을 비교하고, 인식 성능 저하를 막기 위한 개선책을 제시하였다.

• 한국측량학회지
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• 제31권6_2호
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• pp.585-592
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• 2013

CBIR is an effective tool to search and extract image contents in a large remote sensing image database queried by an operator or end user. However, as imaging principles are different by sensors, their visual representation thus varies among image modality type. Considering images of various modalities archived in the database, image modality difference has to be tackled for the successful CBIR implementation. However, this topic has been seldom dealt with and thus still poses a practical challenge. This study suggests a cross modality CBIR (termed as the CM-CBIR) method that transforms given query feature vector by a supervised procedure in order to link between modalities. This procedure leverages the skill of analyst in training steps after which the transformed query vector is created for the use of searching in target images with different modalities. Current initial results show the potential of the proposed CM-CBIR method by delivering the image content of interest from different modality images. Despite its retrieval capability is outperformed by that of same modality CBIR (abbreviated as the SM-CBIR), the lack of retrieval performance can be compensated by employing the user's relevancy feedback, a conventional technique for retrieval enhancement.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권6호
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• pp.2730-2747
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• 2016

Due to the limitation of the bandwidth resource and capture resolution of depth cameras, low resolution depth maps should be up-sampled to high resolution so that they can correspond to their texture images. In this paper, a novel depth map up-sampling algorithm is proposed by exploiting the fractal internal self-referential feature. Fractal parameters which are extracted from a depth map, describe the internal self-referential feature of the depth map, do not introduce inherent scale and just retain the relational information of the depth map, i.e., fractal transforms provide a resolution-independent description for depth maps and could up-sample depth maps to an arbitrary high resolution. Then, an enhancement method is also proposed to further improve the performance of the up-sampled depth map. The experimental results demonstrate that better quality of synthesized views is achieved both on objective and subjective performance. Most important of all, arbitrary resolution depth maps can be obtained with the aid of the proposed scheme.

• 한국수학사학회지
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• 제18권2호
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• pp.23-30
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• 2005

직관은 참된 지식을 발견하는 도구이며 문제해결 과정에서 번뜩이는 아이디어가 발현되는 것으로 받아들여진다. 직관에 의해 우리는 자명한 사실을 즉각적으로 인식하며, 수학적 사실을 발견하는 힘을 부여받는다. 따라서 직관은 논리와 더불어 수학교육에서 강조해야 할 중요한 주제이다. 인 글에서는 수학 교수$\cdot$학습에서 직관적 사고력의 신장을 위해 직관에 대한 체계적인 연구가 필요함을 인식하고, 이를 위해 수리철학의 역사와 수학적 발견의 역사에서 직관에 대하여 알아보았다.

• 한국정밀공학회지
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• 제15권12호
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• pp.226-235
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• 1998

This study proposes the analysis and evaluation of method of time series of ultrasonic signal using the chaotic feature extraction for ultrasonic pattern recognition. The features are extracted from time series data for analysis of weld defects quantitatively. For this purpose, analysis objectives in this study are fractal dimension, Lyapunov exponent, and strange attractor on hyperspace. The Lyapunov exponent is a measure of rate in which phase space diverges nearby trajectories. Chaotic trajectories have at least one positive Lyapunov exponent, and the fractal dimension appears as a metric space such as the phase space trajectory of a dynamical system. In experiment, fractal(correlation) dimensions and Lyapunov exponents show the mean value of 4.663, and 0.093 relatively in case of learning, while the mean value of 4.926, and 0.090 in case of testing in slag inclusion(weld defects) are shown. Therefore, the proposed chaotic feature extraction can be enhancement of precision rate for ultrasonic pattern recognition in defecting signals of weld zone, such as slag inclusion.

• 대한지리학회지
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• 제40권4호
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• pp.441-453
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• 2005

본 연구의 목적은 지형자료에 대한 계층화 알고리즘을 개발하여 하계망을 일반화하고자 하였다. 하계망은 계층적인 구조를 갖기 때문에 일반화를 위해 선형사상들에 대한 지형자료의 계층화가 요구된다. 하계망 일반화의 절차는 하계망의 계층화, 차수별 선택과 제거, 그리고 알고리즘 적용으로 진행하였다. 계층화는 하계망의 고도에 따른 방향 결정, Stroke Segment 서열화. Strahler 차수화로 진행하였으며, 선형사상의 선택과 제거는 지리자료의 질의를 통해 차수와 선의 길이를 기준으로 처리하였다 개선된 Simoo 알고리즘은 선형사상의 곡률을 낮추고 완만화에 효과적이었다 연구결과는 공간적으로 다양한 계층구조를 갖는 사상들에 대한 일반화를 개선할 수 있을 것으로 기대된다.

• 대한원격탐사학회지
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• 제27권3호
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• pp.359-367
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• 2011

A suitable pan-sharpening method has to be chosen with respect to the used spectral characteristic of the multispectral bands and the intended application. The research on pan-sharpening algorithm in improving the accuracy of image classification has been reported. For a classification, preserving the spectral information is important. Other applications such as road detection depend on a sharp and detailed display of the scene. Various criteria applied to scenes with different characteristics should be used to compare the pan-sharpening methods. The pan-sharpening methods in our research comprise rather common techniques like Brovey, IHS(Intensity Hue Saturation) transform, and PCA(Principal Component Analysis), and more complex approaches, including wavelet transformation. The extraction of matching pairs was performed through SIFT descriptor and Canny edge detector. The experiments showed that pan-sharpening techniques for spatial enhancement were effective for extracting point and linear features. As a result of the validation it clearly emphasized that a suitable pan-sharpening method has to be chosen with respect to the used spectral characteristic of the multispectral bands and the intended application. In future it is necessary to design hybrid pan-sharpening for the updating of features and land-use class of a map.