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Revealed Comparative Economies of Scope and Development Index
Shuhe Li,Changzhen Gong 서울대학교 경제연구소 1995 Seoul journal of economics Vol.8 No.3
In this note, we attempt to construct some summary statistic to measure economic development and make comparisons across countries. A development index is defined in terms of both "scale" and "scope". "Scale" is measured by output per capita. "Scope" is measured by revealed comparative economies of scope, which in turn is measured by the ratio of the variety of exports over the variety of imports for a country. Using purchasing power parity and the Standard International Trade Classification, we have computed the development index for forty countries.
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Zixu Su,Wei Chen,Changzhen Li,Junyi Yu,Guojiao Gong,Zixin Wang 한국전자통신연구원 2023 ETRI Journal Vol.45 No.5
The application of unmanned aerial vehicles (UAVs) has recently attracted considerable interest in various areas. A three-dimensional multiple-input multiple-output concentric two-hemisphere model is proposed to characterize the scattering environment around a vehicle in an urban UAV-to-vehicle communication scenario. Multipath components of the model consisted of lineof-sight and single-bounced components. This study focused on the key parameters that determine the scatterer distribution. A time-variant process was used to analyze the nonstationarity of the proposed model. Vital statistical properties, such as the space–time–frequency correlation function, Doppler power spectral density, level-crossing rate, average fade duration, and channel capacity, were derived and analyzed. The results indicated that with an increase in the maximum scatter radius, the time correlation and levelcrossing rate decreased, the frequency correlation function had a faster downward trend, and average fade duration increased. In addition, with the increase of concentration parameter, the time correlation, space correlation, and levelcrossing rate increased, average fade duration decreased, and Doppler power spectral density became flatter. The proposed model was compared with current geometry-based stochastic models (GBSMs) and showed good consistency. In addition, we verified the nonstationarity in the temporal and spatial domains of the proposed model. These conclusions can be used as references in the design of more reasonable communication systems.
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