A Study on the Visual Character of the Eames House

학위논문(석사) --서울대학교 대학원 :건축학과,2007.Maste

무선 인지 네트워크에서 임의 접속 방식에 관한 성능 분석

학위논문(박사) - 한국과학기술원 : 수리과학과, 2013.2, [ vi, 55 p. ]Spectral resource demand has greatly increased in the last two decades due to newly emerging wireless services and products and accordingly all usable spectrum resources have been already allocated. However, recent actual measurements have shown that most of the allocated spectrum resources are underutilized. This discrepancy between allocation and usage leads to the introduction of cognitive radio (CR) networks. The CR concept represents a significant paradigm change in wireless spectrum utilization and regulation, i.e., from exclusive use of spectrum by licensed users (,called primary users) to dynamic spectrum access for unlicensed users (,called secondary users). The high potential of CR has attracted considerable efforts for more efficient spectrum management policies and techniques. In this dissertation, we consider random channel access policies in a CR networks under various environments. Secondary users in a CR network stochastically determine whether to access a channel at each slot by using the access probability and then active secondary users select the channel among primary channels consulting the information on the network. Main results of this dissertation can be categorized into two subjects. The first one is developing the analytical models for the performances of users in a CR network. We analyze the queueing performance and throughput of an arbitrary SU under a various scenarios. And we obtain the optimal APs that maximizing the performance of an SU and provide an insight on how to optimally design in a CR network when SUs adopt random channel access policy. In Chapter 2, we consider a time slotted cognitive radio network under Rayleigh fading where multiple secondary users (SUs) contend for spectrum usage over available primary users’ channels. We analyze the performance of a channel access policy where each SU stochastically determines whether to access a wireless channel or not based on a given access probability. In the analysis, we...한국과학기술원 : 수리과학과

Varying appearances of cholangiocarcinoma: radiologic-pathologic correlation

Intrahepatic cholangiocarcinoma is the second most common primary hepatic tumor. Various risk factors have been reported for intrahepatic cholangiocarcinoma, and the radiologic and pathologic findings of this disease entity may differ depending on the underlying risk factors. Intrahepatic cholangiocarcinoma can be classified into three types on the basis of gross morphologic features: mass-forming (the most common), periductal infiltrating, and intraductal growth. At computed tomography (CT), mass-forming intrahepatic cholangiocarcinoma usually appears as a homogeneous low-attenuation mass with irregular peripheral enhancement and can be accompanied by capsular retraction, satellite nodules, and peripheral intrahepatic duct dilatation. Periductal infiltrating cholangiocarcinoma is characterized by growth along the dilated or narrowed bile duct without mass formation. At CT and magnetic resonance imaging, diffuse periductal thickening and increased enhancement can be seen with a dilated or irregularly narrowed intrahepatic duct. Intraductal cholangiocarcinoma may manifest with various imaging patterns, including diffuse and marked ductectasia either with or without a grossly visible papillary mass, an intraductal polypoid mass within localized ductal dilatation, intraductal castlike lesions within a mildly dilated duct, and a focal stricture-like lesion with mild proximal ductal dilatation. Awareness of the underlying risk factors and morphologic characteristics of intrahepatic cholangiocarcinoma is important for accurate diagnosis and for differentiation from other hepatic tumorous and nontumorous lesions.ope

Differentiation of benign and malignant solid pseudopapillary neoplasms of the pancreas

OBJECTIVE: The aim of this study was to investigate differential imaging features between benign and malignant solid pseudopapillary neoplasms (SPN) of the pancreas on computed tomographic and magnetic resonance imagings. METHODS: Between January 2001 and January 2007, we identified 30 patients with confirmed SPN by surgery. The computed tomographic and magnetic resonance images were reviewed by 3 radiologists in consensus. Each tumor was analyzed for the following categories: location of tumor, tumor margin, proportion of solid component, morphology of capsule, growth pattern, calcification, and presence of upstream pancreatic ductal dilatation. RESULTS: Benign SPN usually had oval/round or smoothly lobulated margins, and malignant SPN more commonly had focal lobulated margins (P = 0.027). Presence of complete encapsulation was more frequently seen in benign SPN, whereas focal discontinuity of capsule was more commonly seen in malignant SPN (P = 0.005). There was no statistical difference between benign and malignant tumors in other imaging findings. CONCLUSIONS: A focal lobulated margin and a focal discontinuity of the capsule may suggest malignant SPN, whereas a round or smoothly lobulated margin and a complete encapsulation were more commonly seen in benign SPN.ope