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Two new species of Camellia (Theaceae) from Vietnam
Lieu Thi Nguyen,Ninh Tran,Uematsu CHIYOMI,Katayama HIRONORI,Dung Van Luong,Son Thanh Hoang,Ky Danh NGUYEN,Hung Viet NGUYEN,Toan Canh THAI 한국식물분류학회 2018 식물 분류학회지 Vol.48 No.2
Two new species of Camellia (Theaceae) are described from Vietnam: Camellia vuquangensis Luong, Tran & L. T. Nguyen and Camellia hatinhensis Luong, Tran & L. T. Nguyen. The new taxa were col- lected from Vu Quang National Park in the center of Vietnam. The new finds are morphologically dissimilar to all known Camellia species. Recent Camellia discoveries have increased the number of species recorded in Viet- nam from 50 to 75, making Vietnam a center of diversity and a crucial area for more research into the diversity and distributions of Camellia.
Effect of Extreme Rainfall on Cut Slope Stability
Tran The Viet,Trinh Minh Thu,Giha Lee,Sewook Oh,Nguyen Thi Hai Van 한국지반환경공학회 2015 한국지반환경공학회논문집 Vol.16 No.4
This paper addresses the effects of extreme rainfall on the stability of cut slopes in Yen Bai city, Northern Viet Nam. In this area, natural slopes are excavated to create places for infrastructures and buildings. Cut slopes are usually made without proper site investigations; the design is mostly based on experience. In recent years, many slope failures have occurred along these cuts especially in rainy seasons, resulting in properties damaged and loss of lives. To explain the reason that slope failure often happens during rainy seasons, this research analyzed the influence of extreme rainfalls, initial ground conditions, and soil permeability on the changes of pore water pressure within the typical slope, thereafter determining the impact of these changes on the slope stability factor of safety. The extreme rainfalls were selected based on all of the rainfalls triggering landslide events that have occurred over the period from 1960 to 2009. The factor of safety (FS) was calculated using Bishop’s simplified method. The results show that when the maximum infiltration capacity of the slope top soil is less than the rainfall intensity, slope failures may occur 14 hours after the rain starts. And when this happens, the rainfall duration is the deciding factor that affects the slope FS values. In short, cut slopes in Yen Bai may be stable in normal conditions after the excavation, but under the influence of tropical rain storms, their stability is always questionable.
Bank Dividend Policy and Degree of Total Leverage
TRAN, Dung Viet Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.2
We provide one of the first investigation on the impact of the degree of total leverage to the dividend policy of bank. We use a large sample of US bank holding companies from 2000:Q1 to 2017:Q4 to shed light our research question. Our empirical analysis provides consistent evidence that banks with high degree of total leverage (i.e. banks with a relatively high fixed-to-variables costs) are less likely to pay dividends, and they spend a lower fraction of incomes to pay back shareholders, suggesting a higher conservatism in dividend policy of banks subject to high degree of total leverage. The evidence remains unchanged with alternative econometric approaches, alternative measures of dividend policy and degree of total leverage. We further document that this higher conservatism is strengthened for a sample of banks with low franchise value during the financial crises. Our result suggests that the conservatism in dividend policy of banks with high degree of total leverage seems to be related to the precautionary motives aimed at preserving corporate resources under financial distress. Our study contributes to the literature of cost structure and dividend policy by pointing out that the impacts of the degree of fixed-to-variable expenses to dividend policy are extended to the case of banks.
Experiment on Nearest Level Modulation algorithm for FPGA based Modular Multilevel Converters
Tran Hung Cuong,Pham Viet Phuong,Tran Van Phuong,Tran Trong Minh 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Modular Multilevel Converters (MMC) have many advantages in comparison with conventional multilevel converters in application to high voltage system. However, the control system of MMC requires a large amount of I/O signal ports which cannot be generated by a single digital signal processor (DSP) with maximum I/O port of 24. This paper fucuses on the experimental results of aMMC that uses a Field Programmable Gate Array (FPGA) in which embedge the Nearest Level Modulation (NLM) method and capacitor voltage balancing algorithm. The MMC consists of 12 Sub-Modules (SM) in each phase to generate a 13-level ac output voltage. Applying the NLM method and capacitor voltage balancing algorithm have significantly reduced the switching frequency and produced an ac output voltage with very low harmonic distortion. The experimental results have verified by a laboratory-scale prototype and compared with the simulation results.
Fuzzy analysis for stability of steel frame with fixity factor modeled as triangular fuzzy number
Tran, Thanh Viet,Vu, Quoc Anh,Le, Xuan Huynh Techno-Press 2017 Advances in computational design Vol.2 No.1
This study presents algorithms for determining the fuzzy critical loads of planar steel frame structures with fixity factors of beam - column and column - base connections are modeled as triangular fuzzy numbers. The finite element method with linear elastic semi-rigid connection and Response Surface Method (RSM) in mathematical statistic are applied for problems with symmetric triangular fuzzy numbers. The ${\alpha}$ - level optimization using the Differential Evolution (DE) involving integrated finite element modeling is proposed to apply for problems with any triangular fuzzy numbers. The advantage of the proposed methodologies is demonstrated through some example problems relating to for the twenty - story, four - bay planar steel frames.
Shallow Landslide Assessment Considering the Influence of Vegetation Cover
Viet, Tran The,Lee, Giha,Kim, Minseok Korean Geo-Environmental Society 2016 한국지반환경공학회논문집 Vol.17 No.4
Many researchers have evaluated the influence of vegetation cover on slope stability. However, due to the extensive variety of site conditions and vegetation types, different studies have often provided inconsistent results, especially when evaluating in different regions. Therefore, additional studies need to be conducted to identify the positive impacts of vegetation cover for slope stabilization. This study used the Transient Rainfall Infiltration and Grid-based Regional Slope-stability Model (TRIGRS) to predict the occurrence of landslides in a watershed in Jinbu-Myeon, Pyeongchang-gun, Korea. The influence of vegetation cover was assessed by spatially and temporally comparing the predicted landslides corresponding to multiple trials of cohesion values (which include the role of root cohesion) and real observed landslide scars to back-calculate the contribution of vegetation cover to slope stabilization. The lower bound of cohesion was defined based on the fact that there are no unstable cells in the raster stability map at initial conditions, and the modified success rate was used to evaluate the model performance. In the next step, the most reliable value representing the contribution of vegetation cover in the study area was applied for landslide assessment. The analyzed results showed that the role of vegetation cover could be replaced by increasing the soil cohesion by 3.8 kPa. Without considering the influence of vegetation cover, a large area of the studied watershed is unconditionally unstable in the initial condition. However, when tree root cohesion is taken into account, the model produces more realistic results with about 76.7% of observed unstable cells and 78.6% of observed stable cells being well predicted.