Estimation de la taille de l'instabilité potentielle d'un versant homogène sous sollicitations sismiques par des approches empiriques

International audienceLe séisme est connu comme une catastrophe naturelle particulièrement destructrice et meurtrière. En plus des effets directs spectaculaires bien connus, le séisme déclenche également des instabilités de versants. L'effet de site topographique peut aggraver encore ce phénomène par l'amplification du mouvement sismique au sommet des reliefs. Ce travail propose une méthode de calcul simple, sans recours à des simulations numériques, pour estimer la taille de la zone située près de surface topographique la plus affectée par l'amplification. Cette zone est considérée comme une zone de risque élevé pour le développement d'instabilité de versant. Sa connaissance est indispensable et importante, non seulement dans le domaine de la gestion des risques naturels mais aussi dans le domaine du génie civil. À partir d'études paramétriques portant sur des paramètres géomorphologiques et sismiques, les facteurs influençant la taille de la zone amplifiée sont déterminés. Ces études ont également permis de mettre en évidence le rôle de la fréquence adimensionnelle, rapport de la hauteur de versant à la longueur d'onde du signal sismique appliqué, dans l'évaluation de l'effet de site topographique. Un grand nombre de simulations numériques, en appliquant un signal sismique mono-fréquentiel de type sinusoïdal, est réalisé par la méthode des différences finies sous FLAC 2D. Les résultats obtenus ont permis de définir des relations empiriques pour estimer la hauteur, la largeur et l'aire de la zone d'amplification au sommet du versant. Ces approches empiriques ont également été utilisées dans le cas de signaux sismiques réels et ont donné des résultats proches de ceux obtenus par simulations numériques

Rôle du paramètre "fréquence adimensionnelle" dans l'évaluation de l'effet de site topographique en cas de séisme

International audienceL'effet de site topographique correspond au phénomène où le mouvement sismique est amplifié au sommet des reliefs, lequel peut entraîner des dommages aux ouvrages voire des instabilités de versant. Cette étude vise à montrer la relation entre la fréquence adimensionnelle, qui est le rapport de la hauteur du versant (H) à la longueur d'onde sismique, avec l'effet de site topographique. Au travers de plusieurs simulations numériques, les résultats montrent que dans le cas où les versants ont une même valeur de le fréquence adimensionnelle et une même pente topographique, la distribution des masses amplifiées et non-amplifiées est alors similaire pour tous les cas, quels que soient la hauteur, les caractéristiques géologiques et le signal excité. Dans le domaine du génie civil, la connaissance de la zone affectée par l'amplification au niveau de la surface libre est importante et indispensable pour la conception des structures. Par ailleurs, ce travail apporte aussi une évaluation détaillée du rôle des autres facteurs géomorphologiques. Enfin, suite aux observations des résultats numériques, un autre intérêt de la fréquence adimensionnelle est de permettre une diminution de temps de calcul en réduisant les dimensions du modèle

Evaluation of topography site effect in slope stability under dynamic loading

International audienceThe slope topography site effect is a phenomenon in which the seismic ground motion is amplified at the crest of the slope. This effect can damage structures and can even cause slope instabilities. The aim of this study is to explore the impact of slope geomorphology parameters on topographic site effects. A dimensionless factor, the ratio of the slope height to the seismic wavelength is identified as a critical parameter. Numerical simulations resulting in the seismic response of a uniform slope in an elastic material to excitation of vertically propagating SV waves, allowed defining the effects of these parameters to amplification factors and extension of the affected zones. In civil engineering, the knowledge of zones which will experience amplified excitation is important and essential for the structural design. In particular, the vicinity of the crest is a zone frequently affected by strong amplifications, and in some cases, earthquake-induced landslides may occur. For this reason, graphs derived from the results of numerous numerical analyses, can be useful to predicting the maximum amplification factors, the area as well as the dimension of the amplified zone in the vicinity of the crest

Understanding the Intention to Use the Grab Service in Ho Chi Minh City

The primary objective of this study was to identify the factors that influence Grab’s intention to use its services in Ho Chi Minh City and assess the impact of these factors. The ultimate goal was to provide appropriate recommendations to enhance Grab’s services. The study involved 200 participants from Ho Chi Minh City. To achieve this objective, a quantitative research method was employed, and several analytical techniques were used, including reliability testing using Cronbach’s Alpha coefficient, exploratory factor analysis, correlation analysis, and regression. The analysis results revealed three factors that significantly influence the intention to use Grab services, ranked in descending order of influence: (1) Perceived Usefulness, (2) Price Value, and (3) Alternative Vehicles. These factors play a significant role in shaping customers’ intentions to use Grab’s services. The study acknowledges its limitations and suggests future research directions for similar studies to further explore and refine the understanding of customer behavior in the ride-hailing industry. Keywords: intention, service quality, perceived usefulness, prive value, alternative vehicle

Micro-Thermoelectric Generators: Material Synthesis, Device Fabrication, and Application Demonstration

Micro-thermoelectric generator (TEG) possesses a great potential for powering wireless Internet of Things (IoT) sensing systems due to its capability of harvesting thermal energy into usable electricity. Herein, this work reviews the progress in recent studies on the micro-TEG, including material synthesis, device fabrication, and application demonstration. Thermoelectric materials are synthesized by the electrochemical deposition method. Three kinds of high-performance thermoelectric materials, including thick bulk-like thermoelectric material, Pt nanoparticles embedded in a thermoelectric material, and Ni-doped thermoelectric material, are presented. Besides the material synthesis, novel fabrication methods for micro-TEG can also help increase its output power and power density significantly. Two fabrication processes, micro/nano fabrication technology and assembly technology, are investigated to produce high-performance micro-TEG. Moreover, the fabircated micro-TEG as a power source for portable and wearable electronic devices has been demonstrated successfully

Optimal User Pairing Approach for NOMA-based Cell-free Massive MIMO Systems

This study investigates a non-orthogonal multiple access (NOMA)-assisted cell-free massive multiple-input multiple-output (MIMO) system, considering the impact of both individual and linear-combination channel estimations. To make the best use of NOMA as an enabler for cell-free massive MIMO systems, user pairing should be employed effectively. Random user pairing naturally leads to a non-optimal solution, whereas an exhaustive search approach is unfavorable for practical systems owing to the high complexity. In this study, we propose an optimal user pairing strategy to group users that jointly optimize the minimum downlink rate per user and power allocation at an acceptable cost of complexity. To address this problem, we first relax the binary variables to continuous variables and then develop an iterative algorithm based on the inner approximation method, yielding at least one locally optimal solution. Numerical results show that the proposed user pairing algorithm outperforms existing counterparts, such as conventional beamforming, random pairing, far pairing, and close-pairing strategies, while it can be performed dynamically, that is, two arbitrary users satisfying the formulated problem can be paired regardless of geographical distance. Finally, our approach demonstrates that the combination channel estimation-based NOMA-assisted cell-free massive MIMO achieves the best result in terms of the downlink rate per user when associated with the proposed algorithm

Women’s involvement in coffee agroforestry value-chains: Financial training, Village Savings and Loans Associations, and Decision power in Northwest Vietnam

Globally, in the coffee sector and smallholder agriculture in developing countries, there is a distinct gender gap in key factors that enable women’s active participation in and contribution to the coffee value chain and in farm and domestic decisions, such as decisions over credit, agricultural inputs, and training opportunities and division of labor and time. This study assesses Village Savings and Loans Associations (VSLA) impacts and related training on gender equality and women’s access to coffee markets in an ongoing coffee- project in northwest Vietnam. All 169 women in this survey received gender equality and finance training, with one group being members of a VSLA and taking out small loans. With Women’s Empowerment in Agriculture Index (WEAI), women rated their perception of their decision-making power over a range of 18 tasks related to household and agricultural responsibilities and use of income and social activities over 18 months. There were significant improvements in decision-making power in categories with previously low participation and increased sharing of domestic responsibilities. The categories with the biggest gains were decision-making over large purchases and use of income, especially for VSLA-members who sought out market information before engaging with potential coffee buyers and enhanced their negotiating abilities to arrange more favorable outcomes successfully. These results indicate that active gender and finance training translated to real changes in gender dynamics, and membership of a VSLA also helped women improve their financial literacy and improve their negotiating abilities. Husbands to women in the study also began to reconsider gender roles and shift towards equal sharing of responsibility and decision- making with their wives. Based on this study, we recommend (1) implementing gender and finance training and enabling access to loans for women as a means for their inclusion in agriculture value chains, and (2) engaging the whole household in gender training in order for all family members to be receptive to adjustments in the gender division of responsibility, labor and decision-making. The results indicate the conditions under which women can benefit from activities involving agroforestry systems that also enhance carbon sequestration for climate change mitigation compared to coffee monoculture

Effects of salinity and alkalinity on growth and survival of all-male giant freshwater prawn (Macrobrachium rosenbergii De Man, 1879) juveniles

All-male giant freshwater prawns (AMGFPs) have been a popular crop cultivated in the Mekong Delta, Vietnam, due to their proven production efficiency compared to all-female or mixed-sex prawn cultures. However, the crucial water quality factors impacting AMGFP aquaculture efficiency have yet to be elaborately investigated. Two separate experiments were randomly arranged with three replicates to evaluate the effects of salinity or alkalinity on the growth and survival of AMGFP juveniles during the grow-out period. The results show that the prawn survival rate in the salinity range of 0–15‰ varied from 66.1 to 74.8％ and in a salinity range of 0–5‰ was relatively low compared to the range of 10-15‰; however, the difference was not significant among salinities after 90 days of culture (p > 0.05). All the prawn growth performance parameters significantly decreased with increasing salinities of 0, 5, 10, and 15‰ after 30, 60, and 90 days of culture (p 0.05), and both were significantly higher than those at salinities of 10 and 15‰ (p < 0.05) after 90 days of culture. In addition, the survival rate reached 82.5–84.4％ and did not significantly differ among alkalinities of 80, 100, 120, 140, and 160 mgCaCO3 L−1. However, the growth performance parameters and yield of AMGFPs at an alkalinity of 160 mg L−1 were significantly higher than those at lower alkalinities (80, 100, 120, and 140 mg CaCO3 L−1) after 90 days of culture. Therefore, it is recommended that a salinity range of 0–5‰ and alkalinity of 160 mgCaCO3 L−1 is optimal for the growth-out culture of AMGFP juveniles

PSSA- INTERNATIONAL SOLUTION TO PROTECT THE BIODIVERSITY IN HA LONG BAY - CAT BA MARINE AREA

A Particularly Sensitive Sea Area (PSSA) is an important management tool for biodiversity protection of a marine area. At the time of designation of a Particularly Sensitive Sea Area, an associated protective measure, which meets the requirements of the appropriate legal instrument establishing such measure, must have been approved or adopted by IMO to prevent, reduce, or eliminate the threat or identified vulnerability. Information on each of the Particularly Sensitive Sea Areas (PSSAs) that has been designated by IMO is available on the nautical chart. The Vietnam’s coastal zones and islands are the isolated oceanic habitat of extremely rich marine life in very good condition which is important to the maintenance and dispersal of the marine life of the western tropical Pacific. Vietnam coastal areas are very high risk areas affected by maritime activities, particularly international shipping, therefore in the future identification of some Particularly Sensitive Sea Areas (PSSAs) is necessary. The first Particularly Sensitive Sea Area for Vietnam in Ha Long - Cat Ba was initially proposed in this paper

3D-Stereoscopic Immersive Analytics Projects at Monash University and University of Konstanz

Immersive Analytics investigates how novel interaction and display technologies may support analytical reasoning and decision making. The Immersive Analytics initiative of Monash University started early 2014. Over the last few years, a number of projects have been developed or extended in this context to meet the requirements of semi- or full-immersive stereoscopic environments. Different technologies are used for this purpose: CAVE2™ (a 330 degree large-scale visualization environment which can be used for educative and scientific group presentations, analyses and discussions), stereoscopic Powerwalls (miniCAVEs, representing a segment of the CAVE2 and used for development and communication), Fishtanks, and/or HMDs (such as Oculus, VIVE, and mobile HMD approaches). Apart from CAVE2™ all systems are or will be employed on both the Monash University and the University of Konstanz side, especially to investigate collaborative Immersive Analytics. In addition, sensiLab extends most of the previous approaches by involving all senses, 3D visualization is combined with multi-sensory feedback, 3D printing, robotics in a scientific-artistic-creative environment