• 한국정밀공학회지
• /
• 제16권5호통권98호
• /
• pp.48-57
• /
• 1999

Applications of thresholding technique are based on the assumption that object and background pixels in a digital image can be distinguished by their gray level values. For the segmentation of more complex images, it is necessary to resort to multiple threshold selection techniques. This paper describes a new method for multiple threshold selection of gray level images which are not clearly distinguishable from the background. The proposed method consists of three main stages. In the first stage, a probability distribution function for a gray level histogram of an image is derived. Cluster points are defined according to the probability distribution function. In the second stage, fuzzy partition matrix of the probability distribution function is generated through the fuzzy clustering process. Finally, elements of the fuzzy partition matrix are classified as clusters according to gray level values by using max-membership method. Boundary values of classified clusters are selected as multiple threshold. In order to verify the performance of the developed algorithm, automatic inspection process of ball grid array is presented.

• Earthquakes and Structures
• /
• 제9권5호
• /
• pp.957-981
• /
• 2015

Earthquakes occur as a cluster in many regions around the world where complex fault systems exist. The repeated shaking usually induces accumulative damage to affected structures. Damage accumulation in structural systems increases their level of degradation in stiffness and also reduces their strength. Many existing analytical tools of modeling RC structures lack the salient damage features that account for stiffness and strength degradation resulting from repeated earthquake loading. Therefore, these tools are inadequate to study the response of structures in regions prone to multiple earthquakes hazard. The objective of this paper is twofold: (a) develop a tool that contains appropriate damage features for the numerical analysis of RC structures subjected to more than one earthquake; and (b) conduct a parametric study that investigates the effects of multiple earthquakes on the response of RC moment resisting frame systems. For this purpose, macroscopic constitutive models of concrete and steel materials that contain the aforementioned damage features and are capable of accurately capturing materials degrading behavior, are selected and implemented into fiber-based finite element software. Furthermore, finite element models that utilize the implemented concrete and steel stress-strain hysteresis are developed. The models are then subjected to selected sets of earthquake sequences. The results presented in this study clearly indicate that the response of degrading structural systems is appreciably influenced by strong-motion sequences in a manner that cannot be predicted from simple analysis. It also confirms that the effects of multiple earthquakes on earthquake safety can be very considerable.

• 천문학회지
• /
• 제54권3호
• /
• pp.103-112
• /
• 2021

The intracluster medium (ICM) is expected to experience on average about three passages of weak shocks with low sonic Mach numbers, M ≲ 3, during the formation of galaxy clusters. Both protons and electrons could be accelerated to become high energy cosmic rays (CRs) at such ICM shocks via diffusive shock acceleration (DSA). We examine the effects of DSA by multiple shocks on the spectrum of accelerated CRs by including in situ injection/acceleration at each shock, followed by repeated re-acceleration at successive shocks in the test-particle regime. For simplicity, the accelerated particles are assumed to undergo adiabatic decompression without energy loss and escape from the system, before they encounter subsequent shocks. We show that in general the CR spectrum is flattened by multiple shock passages, compared to a single episode of DSA, and that the acceleration efficiency increases with successive shock passages. However, the decompression due to the expansion of shocks into the cluster outskirts may reduce the amplification and flattening of the CR spectrum by multiple shock passages. The final CR spectrum behind the last shock is determined by the accumulated effects of repeated re-acceleration by all previous shocks, but it is relatively insensitive to the ordering of the shock Mach numbers. Thus multiple passages of shocks may cause the slope of the CR spectrum to deviate from the canonical DSA power-law slope of the current shock.

• 전자공학회논문지
• /
• 제52권3호
• /
• pp.213-220
• /
• 2015

저렴한 다수의 센서들로 구성되는 WSN(Wireless Sensor Network)은 운용 특성상 한 번 배치되면 전원의 교체가 불가능하기에 효율적인 에너지 관리는 중요한 문제이다. 에너지 효율성을 위한 방법 중 네트워크를 몇 개의 클러스터로 나누고 모든 센서들을 클러스터 헤드와 멤버 노드로 구분하는 클러스터링은 에너지 효율적인 WSN을 위한 매우 좋은 라우팅 기법이다. 최초의 클러스터 기반 라우팅 프로토콜인 LEACH는 정해진 확률에 따라 랜덤하게 클러스터 헤드를 선출한다. 하지만 선출된 헤드의 네트워크 내 분포가 적절하지 못 한 경우 클러스터 헤드들의 균일한 에너지 소비를 보장할 수 없고 이로 인해 시간에 따른 생존 노드 수 성능이 많이 감소할 수 있다. 이러한 점에 착안하여 논 본문에서는 클러스터 헤드 선택 시 모든 노드의 잔존 에너지를 비교한 뒤 최대 잔존 에너지를 갖는 노드를 헤드로 선택하는 방법을 제안한다. 노드 간 잔존 에너지 차이를 감소시켜 헤드였던 노드가 더욱 오랫동안 멤버 노드로서 역할을 할 수 있고 이로 인해 더욱 향상된 네트워크 생존 기간과 더 많은 데이터가 기지국으로 도착함을 확인할 수 있었다.

• 한국방송∙미디어공학회:학술대회논문집
• /
• 한국방송공학회 2008년도 추계학술대회
• /
• pp.103-105
• /
• 2008

차세대 양방향데이터방송 (BIFS: BInary Format for Scenes) 서비스에서는 하향링크(downlink) 데이터 전송률에 상응하는 높은 상향링크(uplink) 데이터 전송률이 요구되고 있다. 이에 무선 전송 채널의 한정된 자원 환경 속에서 상향링크 전송용량 증대를 위한 주파수 효율성 제고 기술의 필요성이 대두되고 있다. 본 논문에서는 차세대 양방향데이터방송을 위한 다중 모바일(mobile) 사용자의 클러스터(cluster) 기반 상향링크 협동 다이버시티(cooperative diversity) 기법을 제안한다. 제안된 기법은 하나의 단일 안테나(single antenna) 방송 기지국과 다수의 단일 안테나 모바일 사용자가 있는 상향링크 시분할다중접속 (TDMA: Time Division Multiple Access) 시스템에서 데이터 지연허용(delay-tolerant)에 따라 클러스터를 구성하고 제곱 다이버시티 차수(square diversity order)의 협동 프로토콜(cooperative protocol)을 통해 높은 공간다이버시티 이득(spatial diversity gain)을 얻는다. 또한, 비대칭(asymmetric) 무선 채널 환경에서 공정성(fairness)을 보장한다.

• International Journal of Costume and Fashion
• /
• 제12권1호
• /
• pp.29-48
• /
• 2012

The purpose of this study was to examine the relationship between consumer spatial behavior and consumer characteristics based on trade area selection criteria 469 female consumers who lived in the two new towns near Seoul, Bundang and Ilsan, participated in the study by completing questionnaires. Data were analyzed by using cluster analysis, ANOVA, Duncan's multiple range test, chi-square analysis, etc. The findings of the empirical research were as follows: 1. Five groups were identified by cluster analysis based on trade area selection criteria of clothing price-oriented group, time convenience-oriented group, shopping convenience-oriented group, variety/entertainment-oriented group, and passive shopping group. 2. Each group differed in spatial behavior such as clothing shopping area, the visiting frequency, and spatial movement type. 3. Each group showed differences in fashion involvement and demographic characteristics(age, marital status, education, occupation and social status).

• 한국균학회지
• /
• 제27권5호
• /
• pp.328-336
• /
• 1999

Isozyme comparisons of mycelial extracts from Pleurotus ostreatus were undertaken using isoelectric focusing. Enzyme isozyme patterns were Used to describe the extent of geographical diversity and degree of intraspecific variation in these extracts. A total of 77 bands were resolved from six different enzymes. Cluster analyses were performed using the zymograms for esterase (EST), glucose phosphate isomerase (GPI), leucine aminopeptidase (LAP), malate dehydrogenase(MDH), peroxidase (POX), and phosphoglucomutase (pGM). EST gave multiple banding patterns, while less variability was observed for GPI, MDH, and PGM. Cluster analyses demonstrated that strains of P. ostreatus from geographically different origins are genetically divergent, supporting the idea that there is little or no gene flow between these geographically distant population groups.

• Journal of Communications and Networks
• /
• 제18권5호
• /
• pp.773-783
• /
• 2016

Both coordinated multi-point transmission and frequency reuse are effective approaches to mitigate inter-cell interference and improve network coverage. The motivation of this work is to explore the manner to effectively utilize the spectrum resource by reasonably combining cooperation and frequency reuse. The $Mat{\acute{e}}rn$ cluster process, which is appropriate to model networks with hot spots, is used to model the spatial distribution of base stations. Two cooperative mechanisms, coherent and non-coherent joint transmission (JT), are analyzed and compared. We also evaluate the effect of multiple antennas and imperfect channel state information. The simulation reveals that the proposed approach to combine cooperation and frequency reuse is effective to improve the network coverage for users located at both the center and the boundary of the cooperative region.

• 조명전기설비학회논문지
• /
• 제27권10호
• /
• pp.50-58
• /
• 2013

In Wireless Sensor Network, clustering scheme is used to prolong the lifetime of WSN by efficient usage of energy of sensor. In the distributed clustering protocol just like LEACH, every sensor in a network plays a cluster head role once during each epoch. So the FND is prolonged. But, even though every sensor plays a head role, the energy consumed by each sensor is different because the energy consumed increases according to the distance to the Base Station by the way of multiple increase. In this paper, we propose a mechanism to select a head depending on the distance to Base Station, which extends the timing of FND occurrence by 68% compared to the LEACH and makes network stable.

• 천문학회지
• /
• 제33권3호
• /
• pp.137-142
• /
• 2000

CN and CH band strengths for ten new bright giants in the globular cluster M15 have been measured from archival spectra obtained with the Multiple Mirror Telescope. Using published indices for other bright M15 giants, a CN-CH band strength anticorrelation is found for bright red giants. However, stars that do not follow the CN-CH anticorrelation are also found. They seem to show a positive correlation between the two indices. Among them, all the AGB and HB stars of the sample are included. Stars I-38 and X6, which are located near the RGB fiducial line in the CMD, have low measured CH(G) indices compared with other RGB stars. Stars IV-38, S4, and S1, which are all near the RGB tip, have strong measured CH(G) indices. Therefore, most of their evolutionary states are suspected to be different from those of a normal single RGB star.