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        • KCI등재

          Methodology of uncertainty analysis prediction based on multi-well data fusion

          Huan Jie Zhang,Kai Wei,Alain P. Tchameni,G. Ben-Kane 한국자원공학회 2018 Geosystem engineering Vol.21 No.3

          During drilling activities, geological parameters of a well to be drilled (target well) can be predicted within a limited interval based on multi-well data fusion which aims at ensuring a drilling safety, enhancement of drilling efficiency, reduction of drilling cost as well as acquiring accurate measurements in respect to Oil and Gas protection layers. This work presents a method of uncertainty analysis prediction of pressures using fusion data (formation pressures) from adjacent multi-well. The Eaton method, effective stress theory, and mathematical confidence interval were the various methods used to establish the formation pressure matrix of the target well. The results revealed that due to the complexity and variability of the formations, data interpretation errors of the geological parameters were inevitable. Therefore, the probability density distribution function was established through stratigraphy, probability statistics, and information diffusion. Moreover, the real value of the wells’ formation pressure (target well) was within the distribution interval of multi-well data fusion. Hence, the developed method cannot only effectively reduce the interval of geological parameter of the target well but also enhance the accuracy of parameters prediction.

        • Risk Factors for Cervical Cancer in Rural Areas of Wuhan China: a Matched Case-control Study

          Zhang, Bin,Zhou, Ai-Fen,Zhu, Chang-Cai,Zhang, Ling,Xiang, Bing,Chen, Zhong,Hu, Rong-Hua,Zhang, Ya-Qi,Qiu, Lin,Zhang, Yi-Ming,Xiong, Chao-Du,Du, Yu-Kai,Shi, Yu-Qin Asian Pacific Organization for Cancer Prevention 2013 Asian Pacific journal of cancer prevention Vol.14 No.12

          Cervical cancer is a serious public health problem in developing countries. We investigated possible risk factors for cervical cancer in rural areas of Wuhan China using a matched case-control study with 33 women diagnosed with cervical cancer and 132 healthy women selected from the same area as matched controls. A questionnaire, which included questions about general demography conditions, environmental and genetic factors, the first sexual intercourse, first marriage age, age at first pregnancy, pregnancy first child's age, female personal health history, social psychological factors, dietary habits, smoking and alcohol status and other living habits was presented to all participants. At the same time, HPV infection of every participant was examined in laboratory testing. Results showed HPV infection (P<0.000, OR=23.4) and pregnancy first child's age (P<0.000, OR=13.1) to be risk factors for cervical cancer. Menopause (P=0.003, OR=0.073) was a protective factor against cervical cancer. However, there was no indication of associations of environmental (drinking water, insecticide, disinfectant) genetic (cancer family history), or life-style factors (smoking status, alcohol status, physical training, sleep quality), including dietary habits (intake of fruit and vegetable, meat, fried food, bean products and pickled food) or social psychological factors with cervical cancer. The results suggest that the risk of cervical cancer in Chinese rural women may be associated with HPV infection, menopause and the pregnancy first child's age.

        • SCIESCOPUSKCI등재

          Performance Analysis of Transmit Diversity in Multiuser Data Networks With Fading Correlation

          Zhang, Kai,Niu, Zhisheng The Korean Institute of Communications and Informa 2008 Journal of communications and networks Vol.10 No.4

          This paper studies the performance of multiuser data networks with transmit diversity under correlated fading channels. Previous work shows that correlated fading reduces the link performance of multiple antenna systems, but how correlated fading affects the throughput of multiuser data networks is still unknown since the throughput depends not only on the link performance but also on the multiuser diversity. We derive the throughput of the multiuser data networks with various transmit diversity schemes under correlated fading channels. The impact of correlated fading on the throughput is investigated. Analytical and simulation results show that, although correlated fading is harmful for link performance, it increases the throughput of the multiuser data networks if the transmit scheme is appropriately selected.

        • KCI등재

          Impossible Differential Cryptanalysis on DVB-CSA

          ( Kai Zhang ),( Jie Guan ),( Bin Hu ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.4

          The Digital Video Broadcasting-Common Scrambling Algorithm is an ETSI-designated algorithm designed for protecting MPEG-2 signal streams, and it is universally used. Its structure is a typical hybrid symmetric cipher which contains stream part and block part within a symmetric cipher, although the entropy is 64 bits, there haven`t any effective cryptanalytic results up to now. This paper studies the security level of CSA against impossible differential cryptanalysis, a 20-round impossible differential for the block cipher part is proposed and a flaw in the cipher structure is revealed. When we attack the block cipher part alone, to recover 16 bits of the initial key, the data complexity of the attack is O(2<sup>44.5</sup>), computational complexity is O(2<sup>22.7</sup>) and memory complexity is O(2<sup>10.5</sup>) when we attack CSA-BC reduced to 21 rounds. According to the structure flaw, an attack on CSA with block cipher part reduced to 21 rounds is proposed, the computational complexity is O(2<sup>21.7</sup>), data complexity is O(2<sup>43.5</sup>) and memory complexity is O(2<sup>10.5</sup>), we can recover 8 bits of the key accordingly. Taking both the block cipher part and stream cipher part of CSA into consideration, it is currently the best result on CSA which is accessible as far as we know.

        • KCI등재

          The Correlation Research between Lifestyle Changes and Evolution of Residential Communities - Based on a Survey of Shanghai, China

          Zhang, Kai Architectural Institute of Korea 2020 Architectural research Vol.22 No.1

          From 1990s to the present, in China, residential communities has developed rapidly in terms of government policies and living environments. With economic development, dwelling commercialization and socialization gradually reshaped the housing distribution system and local government management in Chinese urban area. After this process, dwellings were endowed with commodity attributes, which were planned and designed depending on residents' requirements of life. During the 30 years of social transformation, Chinese citizens' lifestyle also had huge changes. In this period, the forms of residential area improved constantly to keep pace with social development. This study aims to research the features of contemporary communities and survey citizens' lifestyle changes to find the reasons of the evolution of communities. Moreover, in this paper, there is a clear explanation of the reasons why gated communities are popular in Chinese urban area. In addition, comprehensive data analysis is derived from a questionnaire administered in Shanghai, China. In this part, the questionnaire surveys what factors about lifestyle influence the transformation of living environments and residential buildings. The results of survey show that residents have housing preferences dependent on their lifestyles, and their daily needs related with environmental features.

        • KCI등재

          The Correlation Research between Lifestyle Changes and Evolution of Residential Communities - Based on a Survey of Shanghai, China

          Kai Zhang 대한건축학회 2020 Architectural research Vol.22 No.1

          From 1990s to the present, in China, residential communities has developed rapidly in terms of government policies and living environments. With economic development, dwelling commercialization and socialization gradually reshaped the housing distribution system and local government management in Chinese urban area. After this process, dwellings were endowed with commodity attributes, which were planned and designed depending on residents’ requirements of life. During the 30 years of social transformation, Chinese citizens’ lifestyle also had huge changes. In this period, the forms of residential area improved constantly to keep pace with social development. This study aims to research the features of contemporary communities and survey citizens’ lifestyle changes to find the reasons of the evolution of communities. Moreover, in this paper, there is a clear explanation of the reasons why gated communities are popular in Chinese urban area. In addition, comprehensive data analysis is derived from a questionnaire administered in Shanghai, China. In this part, the questionnaire surveys what factors about lifestyle influence the transformation of living environments and residential buildings. The results of survey show that residents have housing preferences dependent on their lifestyles, and their daily needs related with environmental features.

        • KCI등재
        • SCIESCOPUSKCI등재

          Performance Improvement Strategy for Parallel-operated Virtual Synchronous Generators in Microgrids

          Zhang, Hui,Zhang, Ruixue,Sun, Kai,Feng, Wei The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.2

          The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

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