Search Results (26)

Trajectory planning for morphing gliding reentry vehicles is a nonconvex optimization problem driven by nonlinearity, parameter uncertainty, and multiple constraints. No-fly zones (NFZs) are a critical constraint because their rapid movement and expansion hinder the real-time generation of optimal flight trajectories and wing morphing strategies. Therefore, this study proposes an innovative online trajectory optimization method based on sequential convex optimization integrated with a deep neural network (DNN). The proposed method first uses the Radau pseudospectral method to discretize continuous dynamics and convert the non-convex trajectory planning problem into a relaxed convex subproblem. The subproblem is reformulated as an augmented Lagrangian function through linearization and is iteratively solved using the interior-point method. Finally, the DNN learns the mapping between flight states and optimal control variables (angle of attack rate, bank angle rate, and wing sweep angle rate) to rapidly generate control variables. Different from the time-consuming offline optimization method, the proposed model only requires 0.4 ms to predict three groups of control variables, with the predicted control errors remaining below 2.25%. This method efficiently provides high-precision and stable reentry trajectories and morphing strategies for gliding reentry vehicles. Thus, the proposed method achieves synchronous flight path and wing deformation optimization and demonstrates strong robustness under time-varying mission conditions. Full article

Low tensile strength (brittleness) is a significant drawback of lightweight aggregate concrete, as it significantly limits its application. The parameters can be improved by using dispersed reinforcement. For the purpose of the study, two fractions of high-strength lightweight aggregate were used. It was produced by sintering waste material from power plants and cogeneration plants (e.g., fly ash). Hook-shaped steel fibres were used as the reinforcement. The presented tension test results apply to lightweight fibre-reinforced concrete, i.e., flexural tensile strength, splitting tensile strength and residual flexural tensile strength compared to lightweight non-reinforced concrete. It also refers to the analysis of fibre distribution using computer tomography and the microstructure of the fibre–cement slurry contact zone. The test results revealed that steel fibres are distributed correctly in lightweight concrete, creating effective reinforcement for the brittle cement matrix. The experimental work was supported by numerical simulations based on the Finite Element Method (FEM). A lightweight concrete structure with volumetric content and steel fibre distribution identical to those used in the experiment was modelled. This way, the numerical simulations were verified. The confirmation of the numerical model’s reliability shall help engineers develop the material’s strength at the product design stage. The optimisation shall be possible owing to the easy application of the fibres’ variable configuration, given their share and orientation. As a result of combining experimental tests with numerical simulations, the paper evaluates the influence of steel fibres on the strength of lightweight concrete. Ansys Workbench software was used to model a three-point bending test on lightweight concrete beams. A Menetrey–Willam constitutive model was selected to represent the mechanical behaviour of fibre-reinforced concrete; the model assumed material hardening/softening. Simulations yielded numerical responses similar to the experimental results, confirming the model’s ability to capture the fibre reinforcement’s influence on the forms of destruction. Full article

For the complex problems of multi-aircraft cooperative game guidance with No-Fly Zone (NFZ) avoidance and cross-task constraint propagation, a deep deterministic policy gradient algorithm with temporal awareness and priority cooperative optimization (TP-MADDPG) is proposed. Based on the three-body cooperative guidance, a new coupled guidance task is formed by adding the NFZ avoidance constraint. At the same time, considering the constraint compatibility problem in dynamic task switching, the cooperative aircraft are modeled as independent agents with differentiated policy networks. First, a nonlinear kinematic model of the three-body game constructed by Evader–Pursuer–Defender is established. And four complex constraint conditions, namely homing guidance, NFZ avoidance, collision avoidance, and cooperative guidance, are modeled separately. Secondly, the Long Short-Term Memory-based (LSTM) Actor–Critic framework is proposed to dynamically capture the evolution patterns of adversarial scenarios by mining hidden correlations in historical state-action sequences. This enables smooth policy transitions between the cooperative guidance phase and subsequent homing guidance phase, effectively addressing the challenges of environmental non-stationarity and temporal task dependencies. Then, a priority-driven adaptive sampling mechanism is proposed along with a heterogeneous roles cooperative reward function to specifically address credit assignment imbalance and sparse reward problems, respectively. The sampling mechanism capitalizes on the efficient retrieval properties of SumTree data structures while integrating bias correction techniques to expedite policy gradient convergence. The reward function utilizes the reward shaping method to formulate cooperative reward components that explicitly capture behavioral correlations among agents. Finally, simulations show that the proposed method significantly outperforms multi-agent reinforcement learning baselines, effectively improving the performance of cooperative game guidance under complex constraints. Full article

Aeolian sand is abundant in arid deserts, but its high replacement in cement-stabilized bases can reduce strength and raise cracking risk. Strain localization and crack evolution are also poorly quantified. This study aimed to optimize the early age performance of cement-fly ash stabilized aeolian sand gravel (CFSAG) and clarify its failure mechanism. A Box–Behnken response surface methodology varied the cement content, cement-to-fly ash ratio, coarse aggregate gradation, and aeolian sand content. The 7-d unconfined compressive strength (UCS) and splitting tensile strength (STS) were tested. Digital image correlation (DIC) recorded full-field strains and crack metrics in compression and splitting. SEM–EDS was used to interpret microstructural changes. The aeolian sand content dominated UCS, whereas the cement content and cement-to-fly ash ratio mainly controlled STS. Factor interactions were non-negligible and supported the joint optimization of the two strength indices. DIC identified a crack propagation threshold near 0.9 P_max in splitting. Excess aeolian sand (>50%) caused earlier localization, more cracks, and wider openings. In the appropriate amount of aeolian sand mixtures, hydration products filled voids and improved paste continuity. SEM–EDS indicated that excessive fines increased porosity and weakened the interfacial transition zone. Overall, the combined RSM–DIC–SEM approach links mix design with deformation and microstructure evidence. It provides practical guidance to balance strength and cracking resistance at early ages for cement-stabilized bases in desert highway engineering. Full article

DNA metabarcoding data obtained by next generation sequencing (NGS) has been used to identify species in mixed biological samples, such as DNA from the gut content of invertebrates that feed on vertebrates (invertebrate-derived DNA, iDNA). This investigation employed DNA metabarcoding approach to determine vertebrate hosts of female phlebotomine sand flies, blood-feeding leishmaniasis vectors. We evaluated performance across three mitochondrial markers: a mammal-specific mini-barcode (16S rRNA), a pan-vertebrate mini-barcode (12S rRNA), and a standard CytB barcode region. Phlebotomine sand flies collections occurred in the Cacao Region of Southeastern Bahia, Brazil, an American Tegumentary Leishmaniasis (ATL) endemic zone. Our analysis examined iDNA from forty female specimens pooled in thirteen samples of seven sand fly species, including confirmed ATL vectors. Metabarcoding-derived operational taxonomic units (OTUs) underwent taxonomic assignment through comparison with GenBank NCBI^® reference databases. Results identified twenty vertebrate OTUs: primates (four OTUs), rodents (four), ungulates (five), marsupials (one), plus a domestic dog and a chicken. Notably, non-mammalian taxa, including reptiles (one OTU) and amphibians (three), were detected. The iDNA metabarcoding approach allowed us to accurately sample the diversity of phlebotomine sandflies’ bloodmeals in a single specimen of a non-engorged female sand fly with mixed feeding. Full article

This study explores an integrated strategy combining gypsum activation and pressurized flue gas heat curing (FHC) to enhance the interfacial transition zone (ITZ) in concrete incorporating over 80% circulating fluidized bed fly ash (CFBFA)-based artificial coarse aggregates. The inherently weak ITZ, characterized by low bonding strength and high porosity, remains a major limitation to the mechanical performance of CFBFA-based concrete. Gypsum promotes the formation of ettringite (AFt) and facilitates the development of a dense CaCO₃ shell through enhanced carbonation. Their synergistic effect improves microstructural homogeneity and reduces crack connectivity at the interface. A novel grayscale image-based double-peak gradient method is developed for non-contact, quantitative measurement of ITZ thickness, revealing a strong inverse correlation (R² = 0.87) between ITZ thickness and compressive strength. Microstructural analyses confirm that the dual treatment significantly refines the ITZ, resulting in denser aggregate interiors, improved matrix continuity, and more structurally integrated interfaces. The failure mode correspondingly shifts from interface-dominated fracture to composite-controlled behavior. These findings demonstrate the effectiveness of the FHC–gypsum approach in tailoring ITZ morphology and enhancing mechanical integrity, offering a viable pathway for high-performance, low-carbon cementitious composites utilizing industrial by-products. Full article

With the rapid growth of user service demands, space–air–ground integrated networks (SAGINs) face challenges such as limited resources, complex connectivity, diverse service requirements, and no-fly zone (NFZ) constraints. To address these issues, this paper proposes a joint optimization approach under NFZ constraints, maximizing system utility by simultaneously optimizing user association, unmanned aerial vehicle (UAV) trajectory, and slice resource allocation. Due to the problem’s non-convexity, it is decomposed into three subproblems: user association, UAV trajectory optimization, and slice resource allocation. To solve them efficiently, we design the iterative SAC-MS algorithm, which combines matching game theory for user association, sequential convex approximation (SCA) for UAV trajectory, and soft actor–critic (SAC) reinforcement learning for slice resource allocation. Simulation results show that SAC-MS outperforms TD3-MS, DDPG-MS, DQN-MS, and hard slicing, improving system utility by 10.53%, 13.17%, 31.25%, and 45.38%, respectively. Full article

The incorporation of fly ash into concrete reduces cement consumption by 10–30%, lowers CO₂ emissions by 30–50%, cuts costs by 15–25%, and enhances durability, thus reducing maintenance expenses. However, the predictive model for the elastic modulus of fly ash concrete subjected to calcium leaching is still lacking. Regarding the theoretical method, the content of calcium hydroxide and calcium silicate hydrate in fly ash–cement systems is quantitatively calculated according to the hydration reaction relationship between cement, fly ash, and water, and then the porosity of the fly ash–cement matrix and interface transition zone (ITZ) after calcium leaching can be obtained. Based on the theory of two-phase composite spheres and the non-uniform ITZ model, the prediction method for the elastic modulus of leached fly ash concrete can be constructed, which comprehensively considers key parameters such as fly ash content, non-uniform characteristics of the ITZ, and the water–binder ratio (w/b). Additionally, the corresponding experimental investigation is also designed to study the variation regulation of the leaching depth, leaching extent, and elastic modulus of fly ash concrete with leaching time. The prediction method for the elastic modulus of leached fly ash concrete is validated via self-designed experimental methods and third-party experiments. This study further delves into the specific effects of w/b, aggregate volume fraction (f_a), fly ash content, and ITZ thickness (h_ITZ) on the elastic modulus of leached concrete (E). The research findings indicate that an appropriate amount of fly ash can effectively enhance the leaching resistance of concrete. For a leaching degree of 10.0%, 30.0%, and 50.0%, E at w/b = 0.40 exceeds that of w/b = 0.60 by 26.71%, 28.43%, and 30.28%, respectively; E at h_ITZ = 10 μm exceeds that of h_ITZ = 50 μm by 16.96%, 15.80%, and 15.11%, respectively; and E at f_a = 65% is 39.82%, 43.15%, and 46.12% higher, respectively, than that of concrete with f_a = 45%. Furthermore, a linear correlation exists between the elastic modulus and the degree of leaching. The prediction method for the elastic modulus offers a theoretical foundation for in-depth exploration of the durability of leached mineral admixture concrete and its scientific application in practical engineering. Full article

This paper investigates nine PVA fiber-reinforced cementitious composites with varying fiber content (1–2.5%) and types (oil-coated and non-coated). The experimental compositions utilize locally available cement, high volumes of fly ash, silica fume, PVA fibers, and a superplasticizer, entirely omitting natural aggregates. Key parameters evaluated include bulk density, compressive strength, secant modulus of elasticity, flexural tensile strength, fracture energy, and structural design applicability. The results show that FRCs without natural aggregates achieves significantly lower densities (1500–1720 kg/m³). Compressive strength is influenced by matrix density, with the highest value recorded at 30.98 MPa. The high fly ash content reduces the secant modulus of elasticity, while flexural tensile strength follows a similar pattern to compressive strength. Oil-coated fibers generally lower fracture energy, except for the 1.5% PVA content, where the 2.5% composition performs best. All specimens exhibit tension softening rather than the strain-hardening behavior of ECCs. Structural design equations were developed, though experimental validation is necessary. The 2.5% PVA composition increases the compression zone height by 7% while requiring 2% more reinforcement. As a sustainable alternative to conventional concrete, the composites offer promising mechanical properties and structural viability for construction applications. Full article

The challenging terrain and deep ravines that characterize mountainous regions often result in slower path planning and suboptimal flight paths for unmanned aerial vehicles (UAVs) when traditional meta-heuristic optimization algorithms are employed. This study proposes a novel Improved Enhanced Snake Optimizer (IESO) for three-dimensional path planning and tested it in a simulated rugged mountainous terrain with obstacles and a restricted “no-fly zone”. The initialization process in the enhanced snake optimizer is refined by integrating the Chebyshev chaotic map. Additionally, a non-monotonic factor is introduced to modulate the “temperature”. This temperature controls the freedom of movement within the solution space. Furthermore, a boundary condition is incorporated into the dynamic opposition learning mechanism. These modifications collectively reduce the likelihood of population convergence to local optima during optimization. The feasibility of IESO is validated through time complexity and global convergence analyses. Comparative simulation experiments benchmarked IESO against five state-of-the-art biologically inspired optimization algorithms across test functions and path-planning simulated scenarios. Experimental results show that compared with five commonly used algorithms, the IESO algorithm improves the quality of flight trajectory planning by nearly 30% on average. Particularly when compared to the original SO algorithm, IESO demonstrates performance enhancement exceeding 36%, proving its superiority in UAV path planning over complex terrain. Full article

Obstacle avoidance is crucial for the successful completion of UAV missions. Static and dynamic obstacles, such as trees, buildings, flying birds, or other UAVs, can threaten these missions. As a result, safe path planning is essential, particularly for missions involving multiple UAVs. Collision-free paths can be designed in either 2D or 3D environments, depending on the scenario. This study provides an overview of recent advancements in obstacle avoidance and path planning for UAVs. These methods are compared based on various criteria, including avoidance techniques, obstacle types, the environment explored, sensor equipment, map types, and path statuses. Additionally, this paper includes a process addressing obstacle detection and avoidance and reviews the evolution of obstacle detection and avoidance (ODA) techniques in UAVs over the past decade. Full article

The coal gangue coarse-aggregate content in ordinary concrete should not be too large. In order to further improve the utilization rate of coal gangue coarse aggregate, this study used the principle of “strong wrapped weak” to prepare high-performance concrete. This study considered four factors, namely, water–binder (W/B) ratios, non-spontaneous combustion coal gangue (NCCG) coarse-aggregate contents, fly ash–slag mass ratios, and silica fume coating to prepare high-performance concrete. The workability, mechanical, and durability properties were studied, and the changes in the interfacial transition zone (ITZ) of concrete before and after sulfate attack and freeze–thaw cycles were analyzed based on the SEM test. The life prediction of NCCG coarse-aggregate high-performance concrete was carried out based on the grey system GM(1,1) prediction model. The results show that the NCCG coarse-aggregate contents have the greatest effect on compressive strength, sulfate resistance, and frost resistance. The W/B ratio has the greatest effect on the anti-carbonization properties. Fly ash–slag mixing can obtain better durability. Considering the effect on the design service life of high-performance concrete, NCCG coarse aggregate is used to prepare high-performance concrete in North China, and the recommended content is 60%; in the Northwest and Northeast regions, the recommended content is 45%. This study provides a basis for the preparation of high-performance concrete with NCCG coarse aggregate. Full article

Unmanned Aerial Vehicles (UAVs) have emerged as a compelling alternative to manned operations, offering the capability to navigate hazardous environments without risks for human operators. Despite their potential, optimizing UAV missions in complex and unstructured environments remains a pivotal challenge. Path planning becomes a crucial aspect to increase mission efficiency, although it is inherently complex due to various factors such as obstacles, no-fly zones, non-cooperative aircraft, and flight mechanics limitations. This paper presents a path-planning technique for fixed-wing unmanned aerial vehicles (UAVs) based on the Theta* algorithm. The approach introduces innovative features, such as the use of Euler spiral, or clothoids, to serve as connection arcs between nodes, mitigating trajectory discontinuities. The design of clothoids can be linked to the aircraft performance model, establishing a connection between curvature constraints and the specific characteristics of the vehicle. Furthermore, to lower the computational burden, the implementation of an adaptive exploration distance and a vision cone was considered, reducing the number of explored solutions. This methodology ensures a seamless and optimized flight path for fixed-wing UAVs operating in static environments, showcasing a noteworthy improvement in trajectory smoothness. The proposed methodology has been numerically evaluated in several complex test cases as well as in a real urban scenario to prove its effectiveness. Full article

Fly ash from coal represents the foremost waste product of fossil fuel combustion. These waste materials are most widely utilised in the cement and concrete industries, but the extent of their use is insufficient. This study investigated the physical, mineralogical, and morphological characteristics of non-treated and mechanically activated fly ash. The possibility of enhancing the hydration rate of the fresh cement paste by replacing part of the cement with non-treated and mechanically activated fly ash, and the hardened cement paste’s structure and early compressive strength performance, were evaluated. At the first stage of the study, up to 20% mass of cement was replaced by untreated and mechanically activated fly ash to understand the impact of the mechanical activation on the hydration course; rheological properties, such as spread and setting time; hydration products; mechanical properties; and microstructure of fresh and hardened cement paste. The results show that a higher amount of untreated fly ash significantly prolongs the cement hydration process, decreases hydration temperature, deteriorates the structure and decreases compressive strength. Mechanical activation caused the breakdown of large porous aggregates in fly ash, enhancing the physical properties and reactivity of fly ash particles. Due to increased fineness and pozzolanic activity by up to 15%, mechanically activated fly ash shortens the time of maximum exothermic temperature and increases this temperature by up to 16%. Due to nanosized particles and higher pozzolanic activity, mechanically activated fly ash facilitates a denser structure, improves the contact zone between the cement matrix, and increases compressive strength up to 30%. Full article

Coal gasification coarse slag (CGCS) is a by-product of coal gasification. Despite its abundance, CGCS is mostly used in boiler blending, stacking, and landfill. Large-scale industrial applications of CGCS can be environment-friendly and cost saving. In this study, the application of CGCS as a substitute for river sand (RS) with different replacement ratios in ultra-high performance concrete (UHPC) was investigated. The effects of CGCS replacement ratios on the fluidity and mechanical properties of specimens were examined, and the effect mechanisms were explored on the basis of hydration products and the multi-scale (millimetre-scale and micrometre-scale) microstructure analysis obtained through X-ray diffraction (XRD), scanning electron microscopy, and X-ray energy-dispersive spectroscopy. With an increase in the CGCS replacement ratio, the water–binder ratio (w/b), flexural strength, and compressive strength decreased. Specimens containing CGCS of ≤25% can satisfy the strength requirement of non-structural UHPC, with flexure strength of 29 MPa and compressive strength of 111 MPa at day 28. According to the XRD results and multi-scale microstructure analysis, amorphous glass beads in CGCS positively influenced ettringite generation due to the pozzolanic activity. Porous carbon particles in CGCS showed strong interfacial bonding with cement slurry due to internal hydration; this bonding was conducive to improving the mechanical strength. However, CGCS hindered hydration in the later curing stage, leading to an increase in the unreacted cement and agglomeration of fly ash; in addition, at a CGCS replacement ratio of up to 50%, an apparent interfacial transition zone structure was observed, which was the main contributor to mechanical strength deterioration. Full article