http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/952 Volume 13, Number 1, June 2025 Sun, 26 Apr 2026 00:26:05 GMT 2026-04-26T00:26:05Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/964 The Influence of Silt Layer Orientation on Slope Stability in Shale Formations Alam, AKM Badrul; Fujii, Yoshiaki; Li, Zhixue; Hasan Dipu, Nahid; Tajib–Ul–Islam, Md.; Ahmed Razo, Shakil Shale rock masses often include silt layers, impacting slope stability in construction and mining. Analyzing their interaction is crucial for long-term stability. This study used an elasto-plastic model, incorporating the stress transfer method and Coulomb's criterion. It computed stress distribution, assessed failure potential, and identified vulnerable regions. A shale rock mass ranging from 14.75 to 16.75 meter thick, with silt layers varying from 0.36 to 0.5 meter thick was considered in the model. It examined four silt layer conditions: horizontal (SilHL), vertical (SilVL), in-facing (SilIN), and out-facing slope (SilOUT). Mechanical parameters like Uniaxial Compressive Strength (UCS), Tensile Strength (TS),andYoung’s modulus (E) were adjusted for varied scenarios: UCS (0.5 to 5 MPa), and E(6 to 60 MPa), keeping UCS/TS = 5 for all the conditions. In the elasto-plastic analysis, overall reductions of 20%, 40%, 60%, 80%, and 90% in E, UCS and TS were evaluated, taking into consideration the temporal degradation. The findings for SilHL indicate that: (i) when the E, UCS, and TS of the silt layer and shale were equivalent, significant structural failure occurred at 60% reduction, with pronounced collapse at 80% and complete failure at 90%; (ii) a lower Ein the silt layer with equivalent strength to shale showed no significant differences; (iii) reductions in both Eand UCS for the silt layer also revealed no notable differences. For SilVL, the results were similar, with (i) consistent effects as SilHL; (ii) slippage occurring with a lower Efor the silt layer; and (iii) bitension failure and toppling observed when the silt layer's strength was one-tenth that of shale. In SilIN, similar patterns emerged, with slippage and tension failures noted under reduced Eand UCS conditions. For SilOUT, results mirrored SilHL, with tension failures and divergence in failure patterns under reduced Eand UCS. The results of this study indicate that slope failure scenarios involving shale with a silt layer can be effectively simulated using the elasto-plastic method, particularly by incorporating reductions in strength and Young’s modulus. Furthermore, these findings highlight the critical need for additional research on specific slope configurations to refine design methodologies and enhance stability assessments within the context of the elasto-plastic model. Sun, 01 Jun 2025 00:00:00 GMT http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/964 2025-06-01T00:00:00Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/963 Aerodynamic Characteristics and Flow Patterns of Square Cylinders with Rounded Facets Biswas, Nripendranath This study experimentally investigates the effect of facet widthon the static pressure distribution around a single square cylinder with rounded facets. Experiments are conducted in an open-circuit wind tunnel at a Reynolds number of 5.4 × 10⁴, based on the side dimension of the cylinder subjected to a uniform flow velocity of 13.6 m/s. Five different dimensionless facet widthsare systematically introduced to assess their influence on pressure distribution at varyinganglesof attack. Static pressure measurements are collected around the perimeter of the cylinder, and the resulting data are processed through numerical integration to determine the corresponding drag coefficients. The results demonstrate that incorporating facets significantly modifies the aerodynamic characteristics of the cylinder by reducing the drag coefficient comparedto that of a sharp-edged configuration. The drag reduction is primarily attributed to delayed flow separation and a decreasein the size of the wake region. However, beyond a critical facet width, further increases produce only marginal improvements, indicating the presence of an optimal range for facet dimensions. This research demonstrates that facet modification is an effective and practical approach for controlling aerodynamic drag in bluff bodies. The findings offer valuable insights for optimizing structural designs subjected to wind loads, highlighting potential applications in civil engineering fields such as building design, bridge construction, and tower development. By deepening the understanding of how minor geometric alterations can impact flow behaviour, this work contributes to the development of safer, more efficient, and aerodynamically stable structures exposed to atmospheric winds. Sun, 01 Jun 2025 00:00:00 GMT http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/963 2025-06-01T00:00:00Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/962 Correlation Analysis of Rate of TEC Index and Spread F over North American Ionosondes Rafi, Mehdi Hasan; Mostafa, Md Golam This study investigates the diurnal, seasonal, and latitudinal variations of Spread F and theRate of TEC Index (ROTI) over North America during the high solar activity period of 2014. Using GNSS-based ROTI measurements and Digisonde ionograms from multiple stations, we systematically analyze the relationship between Spread F occurrences and ROTI enhancements. The analysis incorporated Diurnal and seasonal variations to determine dominant trends and potential drivingmechanisms, such as medium-scale traveling ionospheric disturbances (MSTIDs) and polarization electric fields. Seasonal and latitudinal variations of Spread F occurrences and ROTI fluctuations are found to be strongly linked to MSTIDs and geomagnetic activity. A clear seasonal dependence was observedat the stations situated under the transitional and mid-latitude regions of the ionosphere. The maximum irregularity occurred in April for transitional region stations and in Novemberfor mid-latitudinal stations. Additionally, Spread F and ROTI exhibit similar diurnal and seasonal trends, with maximum irregularity occurrences during nighttime (20:00–02:00 LT). A distinct seasonal dependence is observed, with transitional region stations peaking in winter and mid-latitude stations in summer. Notably, spread Fwas consistently associated with notable ROTI values (>0.15 TECU/min), suggesting gravity waves and polarization electric fields as driving mechanisms. Through detailed case studies, we demonstrated that MSTIDs, likely driven by gravity wave dynamics, play a crucial role in generating plasma irregularities, which in turn enhance ROTI values and contribute to Spread F formation. Under quiet geomagnetic conditions, these irregularities exhibit a strong daytime preference. Conversely, during disturbed geomagnetic conditions (e.g., the geomagnetic storm), the spatial extent of ionospheric irregularities increased significantly, affecting both transitionaland mid-latitude stations for both daytime and nighttime.By demonstrating a persistent relationship between Spread F and ROTI, this study advances ionospheric modelling efforts and supports the development of improved space weather forecasting techniques, crucial for GNSS-based navigation and communication systems. Sun, 01 Jun 2025 00:00:00 GMT http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/962 2025-06-01T00:00:00Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/961 System Usability and Design Evaluation of AI Chatbots: A Comparative Analysis of ChatGPT, Google Bard, and Bing Chat Mustafina, Sumaiya Nuha; Khan, Nusrat Kaniz; Islam, Muhammad Nazrul; Siddiqua Nusrat, Fatema; Akhtaruzzaman, M. Artificial intelligence (AI) has brought significant advancements in technology while the chatbots like ChatGPT, Google Bard, and Bing Chat are some of its remarkable innovations. These chatbots are helping users with diverse backgrounds by generating ideas, providing resources, and overall knowledge management. We acknowledge that these chatbots are still in their experimental stages of use. Evaluating the usability and user experience of chatbots becomes crucial to make them more usable, accessible, and intuitive to end users around the globe. Thus, the objectives of this research are to make a comparative usability analysis of AI-generated chatbots: Google Bard, ChatGPT, and BingChat. To achieve these goals, firstly, the System Usability Score (SUS) through questionnaire surveys and secondly, Heuristic Evaluation (HE) through expert observation were used. Through HE, we investigated characteristics of design, user engagement, and some other specific usability lacking along with a severity score that suggests both urgent and gradual usability improvement action. As an outcome, this study found that the SUS evaluation provided a comprehensive view of user satisfaction. Google Bard and Bing Chat received lower SUSscores, while ChatGPT demonstrated comparatively better usability, with a SUS score above 70. Again, a comparative usability analysis of AI-generated chatbots (ChatGPT, Google Bardand Bing Chat) reveals that, while all these applications suffer from a notable number of usability problems, ChatGPT demonstrates better usability performance compared to Google Bard and BingChat. Sun, 01 Jun 2025 00:00:00 GMT http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/961 2025-06-01T00:00:00Z