Study on the Formation and Geometries of Rainfall-Induced Landslide Dams

Xuan Khanh Do,Ram Krishna Regmi,Ho Phuong Thao Nguyen,정관수 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.5

Recently, the occurrence of landslide dam problems has been aggravated due to the effects caused by climate change and the further expansion of land use in mountainous areas. Knowledge of landslide dam formation and its geometry is very necessary to accurately evaluate dam stability and hence provide good predictions for disaster preparedness. In previous studies, landslide dam formation was considered as a separate issue; its link with slope failure was ignored, and thus their description and interpretation are still inadequate. Previous models also were limited to evaluate landslide dam shape in 2 dimensions (2D). Through a series of experiments, this study aims to analyze the effect of different slope failure mechanism on the formation of landslide dam. This study also integrated 2D seepage flow model, 2D slope stability model, landslide dam-geometry evaluation model in a single unit and proposed a new method to estimate the landslide dam shape in lateral direction (3D). The experimental results indicated that in the sudden failure, the failed mass can quickly block the river width, making a high impact in regard to dam construction. In retrogressive failure, the shape of dam was formed layers by layers which slowly span to the other side of river and to both up and downstream direction. The results also showed the failed volume and river bottom slope are the two most essential factors that dominate the shape of landslide dam. The simulation results including the failure surface, landslide volume and shape of landslide dam in lateral direction were comparable with those observed from the experiments.

A Study on Rainfall Induced Slope Failures

Xuan Khanh Do,Kwansue Jung,Giha Lee,Ram Krishna Regmi 한국지반환경공학회 2016 한국지반환경공학회논문집 Vol.17 No.5

A rainfall induced slope failure is a common natural hazard in mountainous areas worldwide. Sudden and rapid failures which have a high possibility of occurrence in a steep slope are always the most dangerous due to their suddenness and high velocities. Based on a series of experiments this study aimed to determine a critical angle which could be considered as an approximate threshold for a sudden failure. The experiments were performed using 0.42 ㎜ mean grain size sand in a 200 ㎝ long, 60 ㎝ wide and 50 ㎝ deep rectangular flume. A numerical model was created by integrating a 2D seepage flow model and a 2D slope stability analysis model to predict the failure surface and the time of occurrence. The results showed that, the failure mode for the entire material will be sudden for slopes greater than 67°; in contrast the failure mode becomes retrogressive. There is no clear link between the degree of saturation and the mode of failure. The simulation results in considering matric suction showed good matching with the results obtained from experiment. A subsequent discarding of the matric suction effect in calculating safety factors will result in a deeper predicted failure surface and an incorrect predicted time of occurrence.

A Study on Rainfall Induced Slope Failures: Implications for Various Steep Slope Inclinations

Do, Xuan Khanh,Jung, Kwansue,Lee, Giha,Regmi, Ram Krishna Korean Geo-Environmental Society 2016 한국지반환경공학회논문집 Vol.17 No.5

A rainfall induced slope failure is a common natural hazard in mountainous areas worldwide. Sudden and rapid failures which have a high possibility of occurrence in a steep slope are always the most dangerous due to their suddenness and high velocities. Based on a series of experiments this study aimed to determine a critical angle which could be considered as an approximate threshold for a sudden failure. The experiments were performed using 0.42 mm mean grain size sand in a 200 cm long, 60 cm wide and 50 cm deep rectangular flume. A numerical model was created by integrating a 2D seepage flow model and a 2D slope stability analysis model to predict the failure surface and the time of occurrence. The results showed that, the failure mode for the entire material will be sudden for slopes greater than $67^{\circ}$; in contrast the failure mode becomes retrogressive. There is no clear link between the degree of saturation and the mode of failure. The simulation results in considering matric suction showed good matching with the results obtained from experiment. A subsequent discarding of the matric suction effect in calculating safety factors will result in a deeper predicted failure surface and an incorrect predicted time of occurrence.

A Study on Optimal Design of Permanent Magnet Synchronous Motor for High-Speed Railway Vehicle Application

Vu-Khanh Tran(칸 뷰 트란),Yon-Do Chun(전연도),Pil-Wan Han(한필완),Jae-Gil Lee(이재길),Paul Sarbajit(폴 살바짓),Xuan-Truong Luong(루엉 쒄 트엉) 대한전기학회 2022 대한전기학회 학술대회 논문집 Vol.2022 No.7

Violation of Bans on Tobacco Advertising and Promotion at Points of Sale in Viet Nam: Trend from 2009 - 2015

Le, Thi Thanh Huong,Tran, Khanh Long,Phung, Xuan Son,Do, Phuc Huyen,Phan, Thuy Linh,Nguyen, Ngoc Bich,Nguyen, Xuan Lam,Le, Vu Anh,Tran, Thi Tuyet-Hanh Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.no.sup1

Comprehensive bans on tobacco advertising and promotion were introduced through tobacco control legislation in Viet Nam, but it has been established that violations of the bans are very common. This study was conducted to explore the trend in violations of bans on tobacco advertising and promotion at points of sale in Viet Nam in the past six years and to explore any differences in the violation situations before and after the Law on Tobacco Control came into effect on 1st May 2013. Quantitative data were collected through observation of violations of the bans on tobacco advertising and promotion at points of sale in 10 provinces throughout Viet Nam in four survey rounds (2009, 2010, 2011, and 2015). Variation in violation prevalence over time was examined by chi-square test using a Bonferini method. Binary logistic regression was employed to identify the factors that may have influences on different types of violation. A level of significance of p<0.05 was used for all tests in this article. The most common form of violation was the display of more than one pack/one carton of a cigarette brand. Violation of bans on tobacco advertising increased while violations on promotion ban and on displaying tobacco decreased through time. Some factors associated with the tobacco advertising and promotion bans included surveyed years, types of points of sale, regions and areas where the points of sale were located. The enforcement of the bans did not improve even after the issuance and the enactment of the Law on Tobacco Control. This suggests that the monitoring and enforcement of bans on tobacco advertising and promotion at points of sale should be strengthened. Penalties should be strictly applied for violators as indicated in the current tobacco control legislation.

Factors Affecting Mobile Payment Acceptance and Intention: A Case Study of Hospitality Customers in Vietnam

Dinh Tram Anh PHAN,Thi Thuy Ngan NGUYEN,Thi Khanh Nhi NGUYEN,Tran Thien An NGUYEN,Van Si Dan PHAN,Ngoc Phuong Thao HO,Kim Xuan DO,Trong Luan NGUYEN 한국유통과학회 2022 The Journal of Asian Finance, Economics and Busine Vol.9 No.5

The outbreak of the COVID-19 pandemic has had a significant impact on the Vietnamese economy. In the midst of a complex disease that compelled people to limit their interaction, customers’ shopping habits shifted from “offline” to “online” transactions. Mobile payments have also grown in popularity. The goal of this study is to figure out what factors influence the use of mobile payments by hotel clients in Can Tho after COVID-19. The research team also examines how those factors influence customers’ willingness to use mobile payment and makes recommendations to better the current situation. Primary data was collected from 227 persons using online surveys and processed with SPSS software for this study. To analyze the correlation relationship between the elements determining the intention to use, the Cronbach alpha, EFA, Correlation, and Regression methods used to assess the scale are applied. Perceived Trustworthiness, Perceived Usefulness, and Perceived Ease of Use all have positive effects on customers’ propensity to use, according to the findings. Perceived Security, on the other hand, has no bearing. The findings of this study have significant theoretical and practical implications for the development of mobile payment services in Can Tho, particularly following the implementation of COVID-19.

Erbium-Doped Silicon-Rich Oxide Waveguides Fabricated by Using an Electro-Chemical Method

Pham Van Hoi,Bui Huy,Tran Thi Cham,Ha Xuan Vinh,Do Khanh Van 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3

In this article, we describe and electro-chemical method for fabricating erbium-doped silicon-rich oxide (SRO) waveguides. The porosity, the Er-ion concentration and the refractive index can be controlled by varying the current density (continuous or pulsed currents) during the production process. The refractive index difference between the core and the cladding layers and the profile of the SRO waveguides were tested by using an m-line spectrometer and Field-emission scanning electron microscope (FE-SEM). The photo-luminescent (PL) emission of Er-ions at 1550 nm in the SRO waveguides could be obtained even when the excitation wavelength was away from the resonance absorption band of the Er-ions. This result revealed that Er-ions are possibly excited from the ground state 4I15/2 to the first excited state 4I13/2 by energy transfer from excited Si nanocrystallites. The Er-doped SRO waveguides can be applied to optoelectronic devices compatible with Si-based integrated circuit technology.