Search Results (302)

Environmental assumptions, which are expectations about a system’s operating context, play a critical yet often underexplored role in the emergence of requirements technical debt (RTD). When these assumptions are incorrect, incomplete, or evolve over time, they can compromise the validity of system requirements and lead to costly rework in later stages of development. This paper investigates how environmental assumptions influence the identification of RTD through the analysis of a real-world case study in the domain of small uncrewed aerial systems (sUASs). A structured qualitative analysis of safety-related requirements and their associated assumptions was conducted to examine how deviations in these assumptions can introduce various forms of RTD. This work addresses a gap in the literature by explicitly focusing on the role of environmental assumptions in RTD identification. A classification framework is proposed, highlighting five distinct types of assumption-driven RTD. This framework serves as a foundation for supporting early detection of debt and improving the sustainability and resilience of software-intensive systems. Full article

Background/Objectives: In the twin-screw wet granulation (TSWG) process, accurate measurement of residence time distribution (RTD) is critical, as it characterizes material transport kinetics and mixing behavior. It plays a critical role in evaluating the homogeneity and stability of the granulation process and optimizing process parameters. It is necessary to overcome the limitations arising from the complex and time-consuming procedures of conventional RTD determination methods. Methods: This study proposes a new RTD detection method based on image processing. It uses black dye as a tracer to obtain RTD curve data, and the effects of process parameters such as tracer dosage, screw speed, and feeding rate on the RTD were investigated. Results: The results show that the established method can accurately determine RTD and that the tracer dosage has no significant effect on the detection results. Further analysis revealed that the screw speed is negatively correlated with the mean residence time (MRT). As the speed increases, not only does the MRT shorten, but its distribution also decreases. Similarly, an increase in the feeding rate also leads to a decrease in the MRT and distribution, but it is worth noting that lower feeding rates are beneficial for achieving a state close to mixed flow, while excessively high feeding rates are not conducive to sufficient mixing of materials in the extruder. Conclusions: The RTD detection method provides a reliable parameter basis and theoretical guidance for the in-depth study of the TSWG process and the development of quality control strategies. Full article

Background/Objectives: The objective of this study was to compare muscular strength and neuromuscular activation characteristics between male gymnasts and physical education (PE) students during isometric shoulder extension and flexion tasks. Methods: Thirteen competitive male gymnasts (age: 19.59 ± 1.90 years; body mass: 66.54 ± 6.10 kg; height: 169.38 ± 6.28 cm; mean ± SD) and thirteen male physical education (PE) students (age: 20.96 ± 2.30 years; body mass: 74.00 ± 8.69 kg; height: 174.96 ± 4.93 cm) voluntarily participated in the study. Peak torque (PT), rate of torque development (RTD), RTD normalized to body mass (RTD/BM), and muscle activation assessed via surface electromyography (EMG), normalized to maximal EMG activity (EMG/EMGmax), were evaluated during bilateral isometric shoulder extension and flexion at a joint angle of 45°. Measurements were analyzed across the following time intervals: −50 to 0 ms (pre-tension), 0–30 ms, 0–50 ms, 0–100 ms, and 0–200 ms relative to contraction onset. Custom MATLAB R2024b scripts were used for data processing and visualization. One-way and two-way multivariate analyses of variance (MANOVAs) were conducted to test for group differences. Results: Gymnasts exhibit higher values of PT, PT/BM, RTD, and RTD/BM particularly within the early contraction phases (i.e., 0–50 ms and 0–100 ms) compared to PE students (p < 0.05 to <0.001; η² = 0.04–0.66). Additionally, EMG activity normalized to maximal activation (EMG/EMGmax) was significantly greater in gymnasts during both early and mid-to-late contraction phases (0–100 ms and 0–200 ms), (p < 0.05 to <0.001; η² = 0.04–0.48). Conclusions: These findings highlight gymnasts’ superior explosive neuromuscular capacity. Metrics like RTD, RTD/BM, and EMG offer valuable insights into rapid force production and neural activation, supporting performance monitoring, training optimization, and injury prevention across both athletic and general populations. Full article

Thermal Energy Storage (TES) technologies improve solar power dispatchability by addressing the important challenge of energy intermittency. Sensible heat energy storage technology using materials based on Ordinary Portland Cement (OPC) is the simplest and most economical. However, the operation of these materials is limited to temperatures below 400 °C due to the structural degradation of OPC at this temperature. This paper investigates the design and development of inorganic polymers based on Construction and Demolition Waste (CDW) as a sustainable, low-cost, and environmentally friendly alternative to OPC-based materials for high-temperature sensible TES applications. Based on the ternary systems Na₂O-SiO₂-Al₂O₃ and K₂O-SiO₂-Al₂O₃, representative compositions of CDW-based inorganic polymers were theoretically designed and evaluated using the thermochemical software FactSage 7.0. The experimental verification of the theoretically designed inorganic polymers confirmed that they can withstand temperatures higher than 500 and up to 700 °C. The optimized materials developed compressive strength around 20 MPa, which was improved with temperatures up to 500 °C and then decreased. Moreover, they presented thermal capacities from 600 to 1090 J kg⁻¹ °C ⁻¹, thermal diffusivity in the range of 4.7–5.6 × 10⁻⁷ m² s⁻¹, and thermal conductivity from 0.6 to 1 W m⁻¹ °C⁻¹. These properties render the developed inorganic polymers significant candidates for TES applications. Full article

To address the stability problem related to grid-connected modular multilevel converter high voltage direct current (MMC HVDC) connected to weak alternative current (AC) systems, the short-circuit ratio (SCR) that affects the stability of the system was analyzed first. Short-circuit ratios with SCR values greater than 1.3 were obtained, and the system could still operate stably. By applying the theoretical equations of classical circuits, it has been theoretically proven that for the constant active power and constant AC voltage control modes on the weak system side, after the flexible direct current enters the weak system mode, the power must be reduced to ensure the stable operation of the system. Combined with the actual situation of the north channel of the Chongqing–Hubei back-to-back MMC HVDC project, which is connected to the weak system mode, measures such as the optimization of the control mode and the improvement of control functions in the weak system mode were proposed, and simulation calculations and real time digital simulator (RTDS) simulation verifications were carried out. These control strategies have been applied to the Chongqing–Hubei MMC HVDC project, and on-site verification tests have been conducted to ensure stable operation in the weak system mode. Full article

The behavior of molten steel within a tundish plays a crucial role in achieving uniform temperature and chemical composition, enhancing the removal efficiency of non-metallic inclusions, and reducing the wear of refractory linings. These aspects are key for ensuring the production of steel with superior quality. In multi-strand delta-type tundishes, such as the six-strand configuration, flow dynamics become particularly challenging. Key considerations include strand-specific residence times, the uniform distribution of steel flow, and the mitigation of refractory degradation. This paper presents a detailed numerical analysis aimed at designing an optimally shaped impact pad. The effectiveness of each proposed design was assessed through a tracer-based visualization of flow behavior and the evaluation of residence time distribution (RTD) curves. RTD curves were created in isothermal conditions, while the calculations of the temperature fields of steel in the tundish were made in non-isothermal conditions. The results of the simulations were verified by a real plant trial test and indicate that the use of the “SPHERIC-K4” impact pad can greatly enhance the flow characteristics of liquid steel during the continuous casting process. These improvements include preventing the erosion of the tundish refractory lining, improving the distribution of residence times between individual casting strands, and adjusting the proportions of the mixing zones. Full article

Carbon fabric reinforced polyetherketoneketone (CFF/PEKK) composites have garnered significant attention from researchers due to their superior properties and have been successfully applied in various engineering fields. Environmental conditions are known to directly influence the mechanical properties and service life of composites; however, limited literature exists on the mechanical behavior of CFF/PEKK composites under different environmental conditions. This study elucidates the correlation between the bending and shear behaviors of CFF/PEKK composites and environmental factors, thereby offering robust data support for engineering applications. In this work, CFF/PEKK composite laminates with a fiber volume fraction of 55 vol% were fabricated and subjected to saturated moisture absorption treatments at 70 °C. The moisture absorption characteristics of the material were investigated. The bending and shear properties of CFF/PEKK composites were characterized under three environmental conditions: −55 °C dry state (CTD), room temperature dry state (RTD), and 70 °C wet state (ETW). Failure modes and mechanisms of composite specimens were also analyzed. The equilibrium moisture absorption rate of CFF/PEKK composites is approximately 0.27%. Hygrothermal aging resulted in noticeable fiber pull-out in mechanical specimens, indicating damage to the interfacial performance of the composites. Furthermore, no cracks or delamination were observed. Results indicate that in the CTD condition, the bending strength and shear strength of CFF/PEKK composites are higher compared to those in the RTD condition, while the modulus remains relatively unaffected. In the ETW condition, both bending and shear properties exhibit a significant decline, with the most pronounced reduction observed in interlaminar shear strength. No significant differences in failure modes were noted across different environmental conditions. Full article

This study explored the feasibility of applying transcritical CO₂ in an artificial ground freezing method. By carrying out indoor modeling tests, the temperature field evolution law and the development characteristics of the freezing front during the freezing process of transcritical CO₂ in a sand layer were analyzed, and the freezing effect of transcritical CO₂ was compared with that of traditional alcohol. The theoretical solution of the freezing temperature field was derived, and the accuracy of the theoretical analytical solution was verified by test results. The results showed that the freezing efficiency of transcritical CO₂ was significantly higher than that of alcohol. After 6 h of freezing, the temperature range of the measuring point (C1–C7/C10–C16) can reach −28 °C–3.5 °C, and the freezing front radius exceeded 60 mm. The temperature range of the alcohol measuring point (J1–J7/J10–J16) was only −12.6 °C–8.8 °C, and it took 24 h to achieve the same radius. The test data were in good agreement with the theoretically predicted values, verifying the rationality of the theoretical formula. Freezing temperature T_d had a significant influence on the calculation results of freezing front radius. After transcritical CO₂ freezing for 24 h, the difference in the freezing front radius R(T_d = −2) reached 8.02 mm when the freezing temperature T_d was −2 °C and 0 °C. The difference in the freezing front radius caused by the freezing temperature T_d was concentrated in the range of 1.5–8.1 mm, and the difference in the effect on different types of refrigerants was small. The research results not only confirm the feasibility of the application of transcritical CO₂ in the freezing method but also provide test data and experience for engineering applications, which promotes the innovation and development of freezing method technology. Full article

Constructed wetlands (CWs) are a sustainable, nature-based solution for wastewater treatment, where pollutants are removed through contact with microorganisms attached to substrates and plant roots. Efficient hydraulic performance is critical for CWs, since poor hydraulic performance can reduce treatment efficiency by altering the actual residence time relative to the design value. Two methods to evaluate the Residence Time Distribution (RTD) within the CW system are the tracer method and numerical modelling. This study provides a comprehensive review of experimental methodologies and numerical models used to investigate hydraulic processes in CWs, outlining available techniques to assist researchers in selecting the most suitable approach based on their research needs and wetland characteristics. For experimental procedures, this review focuses on the selection of tracers, indicators for hydraulic performance assessment, and water quality responses to changing hydrological conditions. The advantages and disadvantages of existing numerical models, their suitability, and future research direction are also discussed. Understanding these methodologies and their application is crucial for advancing our knowledge of the hydraulic features of CWs and improving their design and operation. Ultimately, improving hydraulic performance through appropriate experimental and modelling techniques supports the sustainable development and operation of CW systems for long-term wastewater treatment applications. Full article

Thermal cities represent a valuable example of cultural heritage as an expression of territorial relationships, reflecting the interplay between the physical characteristics of the landscape and human creativity. Their cultural value was recognized with the inscription of 11 spa towns in the UNESCO World Heritage List in 2021. However, since the late 20th century, shifting economic and social conditions have led to a widespread crisis in thermal tourism, resulting in abandonment and degradation. So far, this issue has been primarily addressed through tourism and economic models, largely neglecting the landscape perspective. This article, instead, argues that a landscape-based approach is essential for understanding the complexity of the problem and for providing sustainable solutions. The paper seeks to answer two research questions: (i) the first concerns the role of landscape design within the conservation framework of thermal heritage; (ii) the second addresses the creation of new values and opportunities, investigating how landscape design can support a sustainable and context-sensitive transformation of thermal cities. The study adopts the Research-through-Design (RTD) methodology and takes advantage of the landscape design proposal developed for Montecatini Terme, in Italy, as an opportunity to explore the broader issue of rethinking traditional spa towns in crisis. As a result of this design and research experience, it is argued that landscape design plays a crucial role in establishing an integrated system capable of supporting the sustainable development of spa towns and recommendations for decision-makers are provided. Full article

With the widespread application of RTD-fluxgate sensors in UAV aeromagnetic measurements, improving sensor sensitivity is essential for aeromagnetic gradient detection. The excitation waveform is one of the key factors affecting sensitivity. Under sinusoidal excitation, the output model shows poor linearity, and the time-difference expression needs to consider coercivity. Additionally, when triangular and trapezoidal waves are used, sensitivity improvement is limited. To address these issues, this paper proposed using a sawtooth wave as the excitation waveform for RTD-fluxgate sensors. The expressions for output time difference $\Delta T$ and sensitivity $S$ were derived, and the sensor’s output characteristics under different excitations were compared. It was found that the time-difference expression under sawtooth wave excitation was independent of coercivity. The simulation results showed that under identical frequency and amplitude conditions, the time difference $\Delta T$ produced by sawtooth wave excitation was 2 times that of the triangular wave and 3.3 times that of the trapezoidal wave, significantly enhancing sensitivity. This excitation waveform offers advantages, providing new technical support for UAV aeromagnetic gradient detection and demonstrating broad application potential. Full article

Owing to its superior mechanical properties and recyclability, the carbon fabric/polyetheretherketone (CFF/PEEK) composite has seen increasing application in engineering domains. However, studies examining the impact of hygrothermal aging on its performance remain relatively limited in the existing literature. To investigate its durability in hygrothermal environments, this study fabricated CFF/PEEK composites with a fiber volume fraction of 55 vol% and subjected them to equilibrium hygroscopic treatment at 70 °C. The hygroscopic behavior of polyetheretherketone (PEEK) resin and CFF/PEEK composites, along with their tensile and compressive properties under dry conditions at room temperature (RTD) and wet conditions at 70 °C (ETW), were systematically evaluated. The results indicated that both PEEK resin and CFF/PEEK composites exhibited Fickian diffusion behavior during the initial stages of aging but diverged in later stages. The equilibrium moisture absorption rates were approximately 0.32% for PEEK resin and 0.19% for CFF/PEEK composites. After aging at 70 °C, the strength of both materials decreased significantly, while the modulus showed only minor changes. Under ETW conditions, the tensile strength retention rate of PEEK resin was 74.92%, and the compressive strength retention rate was 81.85%. For the CFF/PEEK composites, the tensile strength retention rate was approximately 85%, and the compressive strength retention rate was about 95%. The typical failure modes of CFF/PEEK composites did not exhibit notable differences between tensile and compressive specimens after hygrothermal aging. Resin debonding was observed in the moisture-absorbed composite specimens, while no microcracks or delamination were detected. The degradation of mechanical properties is predominantly attributed to the deterioration of the resin matrix and interface characteristics, which are caused by water molecule intrusion and the adverse effects of wet strain mismatch between the resin and fibers. Full article

Non-structural carbohydrates (NSCs), comprising soluble sugars (SS) and starch (ST), are essential for plant growth and development. The distribution of SS and ST concentration across various organs fluctuates throughout time due to the changes in root morphology in plants, ultimately demonstrating multiple strategies for adapting to seasonal environmental variations. The purpose of this investigation was to explore the seasonal dynamic patterns of root morphology in Pinus yunnanensis, with particular emphasis on specific root length (SRL), specific root surface area (SRA), root tissue density (RTD), and average diameter (AD). This study also aimed to investigate the seasonal fluctuation patterns of NSC. The SRL, SRA, RTD, and AD in both first-order and second-order seedlings had analogous fluctuation patterns from March to December. Although the SRL, SRA, RTD, and AD of third-order seedlings exhibited minor differences from the preceding orders, the overall variance patterns corresponded with those of the first two seedling groups. Consequently, the seasonal fluctuations in SS, ST, and NSC levels in various seedling orders exhibited patterns similar to root morphological characteristics. The SRL, SRA, and AD of three seedling orders exhibited a significant correlation with SS, ST, and NSC, confirming the link between NSC concentration and root morphology. The responses of SS, ST, and NSC in various organs of P. yunnanensis seedlings to root morphological characteristics further substantiated the correlation between the variations in NSC across different organs and root morphological traits. Full article

Nitrogen (N) enrichment significantly impacts temperate forest ecosystems, but we lack a comprehensive understanding of the responses of root morphological characteristics, soil microbial communities, and soil multifunctionality concurrently to varying degrees of N enrichment, particularly when exceeding a threefold localized N input in temperate forests. Therefore, we selected four forest communities in China’s temperate forests and experimented with localized N addition to the dominant tree species in each forest community through the root bag method (three N addition treatments were set up: N1, fourfold soil total N; N2, sixfold soil total N; and CK, control). The results showed that (1) N enrichment treatments significantly improved soil multifunctionality and modified root morphological characteristics, leading to increases in RD (root diameter) and RTD (root tissue density) but decreases in SRL (specific root length) and SRA (specific root area). (2) N enrichment treatments also substantially changed microbial community composition and functional taxa. The relative abundance of eutrophic bacteria increased, while that of oligotrophic bacteria and saprotrophic fungi decreased. (3) The microbial α-diversity index decreased, and the microbial co-occurrence networks became less complex and more vulnerable under N enrichment treatments. (4) Soil multifunctionality and the microbial alpha diversity index had a substantial negative correlation. (5) NH₄⁺-N and NO₃⁻-N contents were the key factors affecting microbial dominance phyla, as well as the bacterial Shannon index and the fungal Chao1 index. (6) In addition, soil properties (except NH₄⁺-N and NO₃⁻-N), soil enzyme activities, root morphological characteristics, and the microbial Chao1 index were significantly different among tree species. In summary, N enrichment significantly alters root morphological characteristics and improves soil multifunctionality. Concurrently, it reduced microbial α-diversity, increased the abundance of eutrophic bacteria, and decreased saprophytic fungi, leading to a less complex and more vulnerable microbial community. This study provided important data and insights for a comprehensive study of the repertoire of responses to nitrogen enrichment in temperate forest ecosystems. Full article

The increasing demand for critical metals essential for renewable energy technologies necessitates efficient and environmentally sustainable extraction methods. Ilmenite (FeTiO₃) and similar ore deposits serve as abundant sources of primary elements while also incorporating a suite of strategically significant trace elements, including REEs and Hf, among others. Mixer–settler units are extensively utilized in metal purification processes. It is important to develop approaches for tracking the metal’s extraction process online and optimizing flow dynamics. One widely adopted technique for evaluating the flow dynamics of the various components is the residence time distribution (RTD) measurement, which provides insights into the hydrodynamic behavior of process reactors. This study explored the application of radiotracer techniques for online monitoring of solvent extraction processes in hydrometallurgy, focusing on Hf recovery. A mixer–settler system was employed using di(2-ethylhexyl) phosphoric acid (D2EHPA) as the extractant and the 1M HNO₃ aqueous phase of Ti ore. The radiotracer ¹⁸¹Hf was synthesized via neutron activation and introduced into the system to track phase distribution and RTD. Real-time monitoring revealed over 95% extraction efficiency within 133 min (8000 s). The RTD studies validated system performance using perfect mixers in series and axial dispersion models. The calculated mean residence time of 100 min (6000 s) closely aligned with the theoretical 104 min (6240 s), confirming the model accuracy. The findings demonstrate the viability of radiotracers in monitoring solvent extraction, offering real-time insights into flow dynamics and extraction efficiency. Full article