Search Results (10,053)

From a public health perspective, it is necessary to improve indoor air quality (IAQ) in schools. This study aims to assess the state of perceived IAQ in Slovenian school classrooms and its association with the selected IAQ factors to improve the understanding of perceived IAQ for designing public health interventions aimed to improve IAQ in schools. A national cross-sectional study was performed in all 454 Slovenian primary schools in the school year 2019/2020. The questionnaires were filled out by the 3rd-grade teachers with the support of the caretakers. Teachers rated the IAQ in the classroom as the worst in winter. We found that the teachers’ perceived IAQ in the classroom is statistically significantly associated with the micro location of the school and some of the IAQ factors. Poor IAQ is associated with reduced manual airing of classrooms due to the thermal comfort of the occupants. Interventions should be aimed at improving occupants’ adaptive behaviors to increase the frequency of natural ventilation in classrooms. Full article

This article explores the influence of lunar regolith and rover structure, such as mast design and material composition, on antenna parameters. It focuses on the distinctive difficulties of communication in the lunar environment, which need specialized antenna solutions. This study specifically examines the performance of antennas on the lunar Rashid rover within the Atlas crater, a landing site on the moon, considering two antenna types: a sleeve dipole antenna and an all-metal patch antenna. Thermal analyses reveal temperatures in the Atlas crater can exceed 80°C during lunar mid-day. The findings highlight the effect of different materials used as thermal coatings for Rashid rover antennas, as well as the influence of rover materials on antenna performance. Furthermore, this study extends to analyze the conductivity and depth of lunar regolith within the Atlas crater. Given the critical role of antennas in wireless communication, understanding how lunar regolith properties affect antenna performance is essential. This research contributes to the creation of a strong communication system for the Rashid rover and future lunar missions by considering the features of the lunar regolith in addition to the rover’s size and material attributes. Full article

Induction heating is a clear, cheap, and highly effective technology used for many industrial and commercial applications. Generally, a time-varying magnetic field produces the required heat in the workpiece with a specially designed coil. The efficiency of the heating process depends highly on the coil design and the geometrical arrangement. A detailed and accurate finite element analysis of the induction heating process usually needs to resolve a coupled thermoelastic–magnetic problem, whose parameters values depend on the solution of another field. The paper deals with a shrink-fitting process design problem: a gear should be assembled with an axe. The interesting part of this case study is given the prescribed low limits for critical stress, the temperature of the gear material, and the heat-treated wearing surfaces. A coupled finite-element-based model and a genetic algorithm-based parameter determination methodology were presented. A thermal imaging-based measurement validated the presented numerical model and parameter determination task. The results show that the proposed methodology can be used to calibrate and validate the numerical model and optimize an induction heating process.. Full article

To satisfy the requirements of five-axis processing quality, this article improves and optimizes the machine tool structure design to produce improved dynamic characteristics. This study focuses on the investigation of five-axis machine tools’ static and dynamic stiffness as well as structural integrity. We also include performance optimization and experimental verification. We use the finite element approach as a structural analysis tool to evaluate and compare the individual parts of the machine created in this study, primarily the saddle, slide table, column, spindle head, and worktable. We discuss the precision of the machine tool model and relative space distortion at each location. To meet the requirements of the actual machine, we optimize the structure of the five-axis machine tool based on the parameters and boundary conditions of each component. The machine’s weight was 15% less than in the original design model, the material it was subjected to was not strained, and the area of the structure where the force was considerably deformed was strengthened. We evaluate the AM machine’s impact resistance to compare the vibrational deformation observed in real time with the analytical findings. During modal analysis, all the order of frequencies were determined to be 97.5, 110.4, 115.6, and 129.6 Hz. The modal test yielded the following orders of frequencies: 104, 118, 125, and 133 Hz. Based on the analytical results, the top three order error percentages are +6.6%, +6.8%, +8.1%, and +2.6%. In ME’scope, the findings of the modal test were compared with the modal assurance criteria (MAC) analysis. According to the static stiffness analysis’s findings, the main shaft and screw have quite substantial major deformations, with a maximum deformation of 33.2 µm. Force flow explore provides the relative deformation amount of 26.98 µm from the rotating base (C) to the tool base, when a force of 1000 N is applied in the X-axis direction, which is more than other relative deformation amounts. We also performed cutting transient analysis, cutting spectrum analysis, steady-state thermal analysis, and analysis of different locations of the machine tool. All of these improvements may effectively increase the stiffness of the machine structure as well improve the machine’s dynamic characteristics and increases its machining accuracy. The topology optimization method checks how the saddle affects the machine’s stability and accuracy. This research will boost smart manufacturing in the machine tool sector, leading to notable advantages and technical innovations. Full article

Purpose: This study evaluates and compares the effect of printing layer thickness (LT) and post-polymerization time (PPT) on the flexural strength and hardness of three 3D-printed resins after thermal aging. Methods: A bar shape (64 × 10 × 3.3 mm) and a disc shape (15 × 2 mm) were designed for flexural strength and hardness testing, respectively. ASIGA, NextDent, and FormLabs 3D-printed resins were used to print specimens with different LTs (25 µm, 50 µm, and 100 µm). Each thickness group was post-polymerized (PP) for different times (15, 30, 60, and 90 min). All printed specimens were thermally cycled (5000 cycles) and then tested, measuring the flexural strength and hardness using a universal testing machine and Vickers hardness tester, respectively. The data were analyzed using ANOVA and a post hoc Tukey’s test (α = 0.05). Results: A PPT of 90 min showed the highest flexural strength. In comparisons of the LTs, 25 µm and 50 µm significantly increased flexural strength compared with 100 µm, which showed the lowest value for each PPT. The hardness increased as the PPT increased for all materials. In our LT comparison, 25 µm and 50 µm significantly increased the hardness for NextDent and FormLabs resins, while only 25 µm showed high hardness compared with 50 µm and 100 µm for ASIGA. Conclusion: Both parameters (LT and PPT) impact flexural strength and hardness. Increased PPT with the minimum LT is recommended. Full article

Eu/Tb metal–organic frameworks (Eu/Tb-MOFs), exhibiting Eu³⁺ and Tb³⁺ emissions, stand out as some of the most fascinating luminescent thermometers. As the relative thermal sensitivity model is limited to its lack of precision for fitting ratio of Eu³⁺ and Tb³⁺ emissions, accurately predicting the sensing performance of Eu/Tb-MOFs remains a significant challenge. Herein, we report a series of luminescent Eu/Tb-MOF thermometers, Eu_xTb_1−xL, with excellent thermal sensitivity around physiological levels, achieved through the tuning energy transfer from ligands to Eu³⁺ and Tb³⁺ and between the Ln ions. It was found that the singlet lowest-energy excited state (S₁) of the ligand and the higher triplet energy level (T_n) are crucial in the energy transfer processes of ligand→Tb³⁺ and ligand→Eu³⁺. This enables Eu_xTb_1−xL to serve as an effective platform for exploring the impact of these energy transfer processes on the temperature-sensing properties of luminescent Eu/Tb-MOF thermometers. The relative thermal sensitivity is comparable to that of dual-center MOF-based luminescent thermometers operating at physiological levels. This study provides valuable insights into the design of new Eu/Tb thermometers and the accurate prediction of their sensing performance. Full article

Research on occupant behavior is a crucial aspect of building energy-saving research. Among them, the shading adjustment behavior in buildings, which occurs frequently during building usage, significantly impacts building energy consumption. Due to the randomness of shading adjustment behavior and the complexity of its motivations, interdisciplinary research is required in this field. In order to better analyze the driving factors of shading adjustment behavior and thus provide a reference for promoting building energy-saving technologies and strategies, this paper employs novel methods for research. We establish a structural equation model based on social cognitive theory, then design a questionnaire and collect data. We utilize structural equation modeling to examine the interrelationships between different dimensions. We ultimately determine the connections between different driving factors of shading adjustment behavior. The results show that whether in the behavior of activating or deactivating shading, environmental factors have a positive correlation with personal factors, and both environmental and personal factors significantly influence shading adjustment behavior. Furthermore, within environmental factors, social environmental factors also significantly affect shading adjustment behavior. Lastly, comparing the behaviors of activating and deactivating shading, the impacts of light and thermal environmental factors on shading adjustment behavior show certain differences. Full article

Despite its significant thermal requirements, melon is a vegetable species that holds the potential for expanding the crop range in temperate climate regions. The selection of appropriate varieties and agronomic practices facilitates its cultivation in these regions. This experiment, employing a randomized block design, was conducted from 2019 to 2021, and this study evaluated the response of three melon varieties—‘Seledyn F1’, ‘Melba’, and ‘Malaga F1’ (factor I)—to various mulching materials (factor II): black polyethylene film (PE), black polypropylene nonwoven (PP), biodegradable film (Fbio), and giant miscanthus straw. Control plots were left unmulched. Melon seeds were sown on 15 April, and seedlings were transplanted on 31 May at a spacing of 100 × 80 cm. This study assessed yield, fruit number, individual fruit weight, and vertical and horizontal fruit diameters. Under optimal conditions, the varieties Seledyn F1 and Malaga F1 produced fruits with the highest individual mass. The application of synthetic mulches led to a two-fold increase in fruit yield compared to unmulched plots, with a 23.7% increase in fruit number. On average, the largest fruits were obtained with PE mulch. Melons grown on Fbio mulch yielded, on average, 40% less and produced 18.8% fewer fruits compared to those grown with PE mulch. Full article

Molecularly imprinted polymers (MIPs) are a growing highlight in polymer chemistry. They are chemically and thermally stable, may be used in a variety of environments, and fulfill a wide range of applications. Computer-aided studies of MIPs often involve the use of computational techniques to design, analyze, and optimize the production of MIPs. Limited information is available on the computational study of interactions between the epinephrine (EPI) MIP and its target molecule. A rational design for EPI-MIP preparation was performed in this study. First, density functional theory (DFT) and molecular dynamic (MD) simulation were used for the screening of functional monomers suitable for the design of MIPs of EPI in the presence of a crosslinker and a solvent environment. Among the tested functional monomers, acrylic acid (AA) was the most appropriate monomer for EPI-MIP formulation. The trends observed for five out of six DFT functionals assessed confirmed AA as the suitable monomer. The theoretical optimal molar ratio was 1:4 EPI:AA in the presence of ethylene glycol dimethacrylate (EGDMA) and acetonitrile. The effect of temperature was analyzed at this ratio of EPI:AA on mean square displacement, X-ray diffraction, density distribution, specific volume, radius of gyration, and equilibrium energies. The stability observed for all these parameters is much better, ranging from 338 to 353 K. This temperature may determine the processing and operating temperature range of EPI-MIP development using AA as a functional monomer. For cost-effectiveness and to reduce time used to prepare MIPs in the laboratory, these results could serve as a useful template for designing and developing EPI-MIPs. Full article

In the context of rapid growth in renewable energy installations and increasingly severe consumption issues, this paper designs a 100% green electricity supplied zero-carbon integrated energy station. It aims to analyze its configuration focusing on the following three core features: zero carbon emissions, 100% green electricity supply, and a centralized–distributed system structure. It discusses equipment selection and provides models for configuring upstream green electricity resources, power generation, energy storage, transformer, and energy conversion. The study examines the synergy between lithium-ion battery storage and modular molten salt thermal storage, along with the virtual energy storage characteristics formed by thermal load inertia, supported by mathematical models. Based on the data from a green electricity system in an Eastern Chinese city and typical load profiles, the paper validates a specific configuration for a 100% green electricity supplied zero-carbon integrated energy station, confirming model accuracy and calculating the required scale of upstream green electricity resources. It proves that establishing an electro-thermal storage synergy system is crucial for addressing the significant fluctuations in renewable energy output. It also argues that leveraging thermal load inertia to create virtual storage can reduce the investment in energy storage system construction. Full article

The design of composites offers extensive opportunities for controlling parameters and utilizing diverse materials, including those sourced from recycling or waste streams. In this study, biocomposites were developed using high-density polyethylene (HDPE) and pomace derived from oilseed plants such as evening primrose, gold of pleasure, rapeseed, and sunflower seeds, mixed in a 1:1 ratio. These biocomposites were evaluated for their structural, mechanical, morphological, and thermal properties, as well as their vulnerability to overgrowth by cellulolytic fungi. The results indicate that incorporating plant waste into HDPE reduces thermal stability while increasing water absorption and thickness swelling. Additionally, the biocomposites showed enhanced fungal growth, which may improve their biodegradability. Notably, the PE_EP composite, derived from evening primrose pomace, did not show significant differences in surface roughness and MOE parameters compared to pure polyethylene. In the case of PE_R composite, an increase in MOE was observed while maintaining the MOR parameter compared to pure PE. Although generally the mechanical properties of composites were lower compared to pure polyethylene, the findings suggest that with further optimization, oil plant pomace can be a valuable raw material for producing biocomposites suitable for various industrial applications, thereby contributing to sustainability and effective waste recycling. Full article

This paper reviews sintered silver (s-Ag) die-attach materials for wide band gap (WBG) semiconductor packaging. WBG devices that die-attach with s-Ag have attracted a lot of attention owing to their low energy loss and high temperature operation capabilities. For their practical operation, a reliability design should be established based on the failure of physics of the s-Ag die layer. This paper first focuses on the material characteristics of the s-Ag and tensile mechanical properties. Then, the s-Ag die-attach reliability is assessed with high-temperature storage, power cycling, and thermal shock tests. Each fracture mode was discussed by considering both the fracture surface analysis results and its mechanical properties. Finally, the effective reliability design parameters of the s-Ag die layer are introduced. Full article

During liquid hydrogen bunkering into a cryogenic tank, boil-off losses occur due to the high thermal gradient between liquid hydrogen and the warm surface of the tank. This leads to gaseous hydrogen release. Such losses constitute a significant drawback in using hydrogen as a fuel for maritime applications where bunkering operations are regularly carried out, thereby constituting a significant loss along the liquid hydrogen pathway. Due to the inherently low temperature of liquid hydrogen, boil-off losses are always present. Some boil-off losses cannot be eliminated because they are thermodynamically constrained or intrinsic to the system’s design. Boil-off recovery methods can be implemented to capture the boil-off; however, those solutions come with an additional cost and system complexities. Hence, this paper investigates the feasibility of minimizing boil-off losses during the first bunkering of liquid hydrogen or refilling of liquid hydrogen in an empty cryogenic tank by first precooling the cryogenic tank surface to decrease the thermal gradient between the liquid hydrogen and the tank surface/wall. In this paper, different media for precooling a cryogenic tank are evaluated to assess the boil-off reduction potential and the associated costs in order to identify the most suitable solution. The assessment has been carried out based on analytical formulation. Full article

Heterogeneous CO₂ hydrogenation catalytic reactions, as the strategies for CO₂ emission reduction and green carbon resource recycling, play important roles in alleviating global warming and energy shortages. Among these strategies, photothermal CO₂ hydrogenation technology has become one of the hot catalytic technologies by virtue of the synergistic advantages of thermal catalysis and photocatalysis. And it has attracted more and more researchers’ attentions. Various kinds of effective photothermal catalysts have been gradually discovered, and nickel-based catalysts have been widely studied for their advantages of low cost, high catalytic activity, abundant reserves and thermal stability. In this review, the applications of nickel-based catalysts in photothermal CO₂ hydrogenation are summarized. Finally, through a good understanding of the above applications, future modification strategies and design directions of nickel-based catalysts for improving their photothermal CO₂ hydrogenation activities are proposed. Full article

Graphene foam composite is a promising candidate for advanced thermal management applications due to its excellent mechanical strength, high thermal conductivity, ultra-high porosity and huge specific surface area. In this study, a three-dimensional physical model was developed in accordance with the dodecahedral structure of graphene foam composite. A comprehensive numerical simulation was carried out to investigate the fluid flow and convective heat transfer in open-cell graphene foam composite by using ANSYS Fluent 2021 R1 commercial software. Research results show that, as porosity increases, the pressure gradient for graphene foam composite with circular and triangular cross-section struts is reduced by 65% and by 77%, respectively. At a given porosity of 0.904, when the inlet velocity increases from 1 m/s to 5 m/s, the pressure gradient is increased by 11.3 times and 13.8 times, and the convective heat transfer coefficient is increased by 54.5% and 43% for graphene foam composite with circular and triangular cross-section struts, respectively. Due to the irregularity of the skeleton distribution, the pressure drop in Y direction is the highest among the three directions, which is 8.7% and 17.4% higher than that in the Z and X directions at the inlet velocity of 5 m/s, respectively. The convective heat transfer coefficient in the Y direction is significantly lower than that along the X and Z directions. Furthermore, triangular cross-section struts induce a greater pressure drop but offer less effective heat transfer compared to circular struts. The research findings may provide critical insights into the design and optimization of graphene foam composites, and promote their potential for efficient thermal management and gas/liquid purification in engineering applications. Full article