二硫化モリブデンを用いた電界効果トランジスタチャンネル表面における固気および固液反応と電気特性変化に関する研究

要約のみTohoku University米田忠弘課

Multi-Cell Random Beamforming: Achievable Rate and Degrees of Freedom Region

Random beamforming (RBF) is a practically favourable transmission scheme for multiuser multi-antenna downlink systems since it requires only partial channel state information (CSI) at the transmitter. Under the conventional single-cell setup, RBF is known to achieve the optimal sum-capacity scaling law as the number of users goes to infinity, thanks to the multiuser diversity enabled transmission scheduling that virtually eliminates the intra-cell interference. In this paper, we extend the study of RBF to a more practical multi-cell downlink system with single-antenna receivers subject to the additional inter-cell interference (ICI). First, we consider the case of finite signal-to-noise ratio (SNR) at each receiver. We derive a closed-form expression of the achievable sum-rate with the multi-cell RBF, based upon which we show an asymptotic sum-rate scaling law as the number of users goes to infinity. Next, we consider the high-SNR regime and for tractable analysis assume that the number of users in each cell scales in a certain order with the per-cell SNR. Under this setup, we characterize the achievable degrees of freedom (DoF) for the single-cell case with RBF. Then we extend the analysis to the multi-cell RBF case by characterizing the DoF region. It is shown that the DoF region characterization provides useful guideline on how to design a cooperative multi-cell RBF system to achieve optimal throughput tradeoffs among different cells. Furthermore, our results reveal that the multi-cell RBF scheme achieves the "interference-free DoF" region upper bound for the multi-cell system, provided that the per-cell number of users has a sufficiently large scaling order with the SNR. Our result thus confirms the optimality of multi-cell RBF in this regime even without the complete CSI at the transmitter, as compared to other full-CSI requiring transmission schemes such as interference alignment.Comment: 28 pages, 6 figures, to appear in IEEE Transactions of Signal Processing. This work was presented in part at IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Kyoto, Japan, March 25-30, 2012. The authors are with the Department of Electrical and Computer Engineering, National University of Singapore (emails: {hieudn, elezhang, elehht}@nus.edu.sg

Private Sector Corruption in Vietnam: From Legislation to its Impact on the Economy

Purpose: The objective of this study was to analyze Vietnamese legal legislation regarding corruption in the private sector, identify its current shortcomings, and assess its impact on the Vietnamese economy since its adoption in 2018.   Theoretical framework: There have been many studies to assess corruption in Vietnam in many aspects, including the overview of corruption in Vietnam, the influence of corruption on economic development, and the consequences of corruption. However, there is still much to investigate and learn about the impact of the current provisions on corruption in the private sector on Vietnam’s economy.   Design/methodology/approach:  The study uses secondary data from the Provincial Competitiveness Index Report (PCI Vietnam) issued by the Vietnam Chamber of Commerce and Industry (VCCI) in collaboration with the United States Agency for International Development (USAID). Besides, the article analyzes Vietnam's Corruption Control Index (CCI), which is assessed annually by the World Bank (WB). At the same time, the authors refer to the data on Vietnam's GDP and make a comparison with the CC index to  clarify the article’s objective. The authors also use a qualitative method by analyzing previous studies to assess the corruption in the private sector in Vietnam, the rules of law concerning private corruption, and its impact on the economy.   Findings:  Vietnam has had specific legislative achievements in criminalizing private corruption in the 2015 Criminal Law and promulgating anti-corruption provisions in the 2018 Anti-Corruption Law. These regulations had a positive impact on Vietnam's economy. However, corruption in the private sector in Vietnam is quite severe, especially bribery in business.   Research, Practical & Social implications:  We suggest future research of in-depth analysis of the causes and effects of specific kinds of corruption acts in the private sector.   Originality/value:  The results indicate that the new provisions on corruption in the private sector since it was adopted have positively affected the development of Vietnam's economy and the fight against corruption

PRIVATE EQUITY: ITS ROLE IN PORTFOLIO OPTIMIZATION

Alternative investments have increasingly been used to complement a traditional portfolio of stocks and bonds. Among them, Private Equity is found to be able to provide diversification benefits and higher expected returns. This study uses the traditional mean-variance portfolio optimization process with several inputs: “equilibrium” returns for the traditional assets as a neutral starting point generated by the Black-Litterman model; and a range of expected returns of private equity fund types. We find that private equity funds in earlier stages are more suitable for investors seeking higher expected returns and with higher levels of risk appetite, while private equity in later stages are more suitable for investors with lower risk appetite, seeking for more modest levels of returns. In both cases, it is notable that the portfolio gains efficiency after the inclusion of private equity. The diversification benefits from low correlations are also observed

Magnitude of Annual Soil Loss from a Hilly Cultivated Slope in Northern Vietnam and Evaluation of Factors Controlling Water Erosion

A soil erosion experiment was conducted in northern Vietnam over three rainy seasons to clarify the magnitude of soil loss and factors controlling water erosion. The plot had a low (8%) or medium (14.5%) slope with land-cover of cassava or morning glory or being bare. Annual soil loss (177 to 2,361 g/m2) was a tolerable level in all low-slope plots but was not in some medium-slope plots. The effects of slope gradient and seasonal rainfall on the mean daily soil loss of the season were confirmed, but the effect of land-cover was not, owing to the small canopy cover ratio or leaf area index during the season. The very high annual soil loss (>2,200 g/m2) observed in the first year of some medium-slope plots was the site-specific effect from initial land preparation. Since the site-specific effect was large, the preparation must be done carefully on the slope