University of Transport and Communications

In the air conditioning and refrigeration market, air conditioners using mechanical compressors have become very common, leading to a significant increase in electricity consumption and contributing to the power crisis that many countries are facing. The emergence and development of absorption chillers in general, and absorption chillers without using liquid pumps in particular, provide effective cooling capabilities, energy savings, and environmental friendliness through the reuse of waste energy at low temperatures. However, improving the efficiency of absorption chillers without using liquid pumps remains a challenging problem. This paper delves into the study of the heat transfer characteristics of the thermosiphon desorber (in absorption chillers without using liquid pumps). The mass flow rate of the hot water supplied to the desorber device is varied, combined with different heights of the riser tubes (zV = 0.25 m and zV = 0.7 m). A model is formulated by simultaneously solving mass, energy, and momentum equations to calculate the heat transfer coefficient for single-phase and two-phase flows. Subsequently, an assessment is made of the heat flow and pressure drop in the riser tube of the thermosiphon desorber.

Recently, freight transportation systems have garnered attention as a key driver of sustainability. Accordingly, various measures and initiatives are being implemented, along with the development of diverse conceptual solutions. However, the feasibility of measures and initiatives is influenced by factors like resources, policymakers’ perspectives, interests, demand, trade-offs, and consensus. This study develops a new hybrid MCDM model that combines the Fuzzy Analytical Hierarchy Process (FAHP), Entropy, and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methods to select the preferred urban freight transport measures, benefiting both decision-makers and participants. The results indicate that the measure “Ring roads for through traffic” is ranked as the most critical choice, with a final score of 0.785, followed by the measure “Multimodal/Intermodal freight transport center” (relative closeness (RC) = 0.771) and “Real-time information system” (RC = 0.750). However, there is a difference in the results between excluding and including the participation of logistics companies. The priority of measure selection varies significantly when the freight industry’s opinions are not considered. These findings emphasize the necessity of engaging decision-makers at all levels in a fully participatory process to address the urgent need for strong actions aimed at achieving a sustainable urban transport system.

Vietnam, like other East Asian nations, is rapidly aging. Older adults—like much of the population—are motorcycle-dependent. However, age presents a barrier: motorcycles can become harder to use later in life. This may prompt some older adults to shift to buses. To support and encourage this shift, Hanoi introduced free bus passes for people aged 60 and above in 2019. This is the first large-scale study to evaluate the impacts of that policy. More than half a million people have signed up for free passes—but are they actually using them? And is eliminating fares enough to boost public transport use among older adults? Drawing on a representative survey of nearly 1000 older bus passengers in Hanoi, this study uses logit and linear regression models to examine two variables: the frequency of current bus use and the intention to continue using buses. The analysis indicates that about one-third of free pass holders in Hanoi use buses regularly. Beyond that, the study offers insights into who is more likely to use a free pass and why. Crucially, price alone is not enough to encourage older adults to ride the bus. Other factors—including safety, accessibility, and service quality—also matter greatly.

Maritime search and rescue (SAR) operations are challenged by vast search areas, poor visibility, and the time-critical nature of victim survival, particularly in dynamic coastal areas. This study presents an intelligent unmanned aerial vehicle (UAV) framework for real-time detection, tracking, and prioritization of people in distress at sea. Unlike existing UAV-based SAR systems that rely on visual sensing or offline human intervention, the proposed framework integrates RGB-thermal multimodal sensing and posture recognition to enhance victim prioritization and survivability estimation. Visual-thermal data support human posture detection, inference of physiological indicators, and autonomous UAV navigation. Metadata are transmitted to a ground control station to enable adaptive altitude control, trajectory rejoining, and multi-target prioritization. Field-inspired experiments in Quang Ninh Province, Vietnam demonstrated robust real-time performance, achieving 23 FPS with detection accuracy up to 84% for swimming subjects and over 50% for drowning postures. These findings demonstrate that Edge-AI-enabled UAVs can serve as a practical and efficient solution for maritime SAR, reducing response times and improving mission outcomes.

Introduction: Adopting government financial policies, such as a fare-free one, contributes to creating inclusive public transportation. However, their impact on bus satisfaction, which can significantly improve the well-being of older users, has been underexplored. This article investigates the satisfaction of bus passengers who are 60+ years old and use bus services freely to travel in Hanoi (Vietnam), a motorcycle-dependent megacity. Data and method: Our study relied on a representative sample of 526 older persons using bus services at least once per week. The Partial Least Squares Structural Equation Modelling (PLSSEM) was applied to analyze the data for empirically investigating complex relationships among safety and security concerns, service quality, perceived fare-free policy, socio-demographics, and bus satisfaction. Results: The results suggested that bus satisfaction was deterred by safety and security concerns but facilitated by perceived fare-free policy and service quality. The positive effect of perceived fare-free policy ((3 = 0.233) was much weaker than service quality's ((3 = 0.425). Interestingly, perceived fare-free policy negatively moderated the positive link between service quality and satisfaction. In this sense, an older passenger with a greater appreciation of the fare-free policy tended to acknowledge less the role of service quality in forming their satisfaction. The multigroup analysis demonstrated a heterogeneity of the relationships between latent variables and satisfaction among gender-based groups. Conclusions: This study empirically demonstrates the critical role of the fare-free policy in contributing to bus satisfaction among older passengers; however, enterprises and policy-makers should not overlook the importance of making the bus service more age-friendly through solutions and campaigns tailored based on gender.