期刊：
Journal of Alloys and Compounds,2024年970:172434 ISSN：0925-8388
通讯作者：
Zeng, G;Zhou, XJ
作者机构：
[Sun, Wei; Zeng, Guang; Yao, Yuan; Deng, Yangchao; Liu, Wenyuan] Cent South Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.;[Zhan, Hongyi] Gen Motors Global Res & Dev, China Sci Lab, Shanghai 201206, Peoples R China.;[Zhou, Xiaojie; Zhou, XJ] Changsha Univ Sci & Technol, Hunan Prov Key Lab Intelligent Mfg Technol High Pe, Changsha 410114, Peoples R China.
通讯机构：
[Zeng, G ; Zhou, XJ ] C;Cent South Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.;Changsha Univ Sci & Technol, Hunan Prov Key Lab Intelligent Mfg Technol High Pe, Changsha 410114, Peoples R China.
关键词：
Mg-Sn based alloy;Dynamic recrystallization;Precipitation;Hot compression
摘要：
The intrinsic correlation between dynamic precipitation and Dynamic Recrystallization (DRX) in a rare earth (RE)-free engineering Mg-4Sn-3Al-1Zn (TAZ431, wt.%) magnesium alloy has been systematically investigated. Hot compression tests were performed on the TAZ431 alloy, in comparison to Mg-3Al-1Zn (AZ31, wt.%) as a reference alloy, with varying temperatures, strain rates, and strain levels (T = 300 -460 degrees C; epsilon = 0.001 -1 s-1; epsilon = 0 to-0.9). Correlative microstructural characterizations including Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electron Backscatter Diffraction (EBSD), were employed to explore the behaviors of precipitation, DRX and intragranular deformation as subjected to hot compression. The results indicate a significant interaction between Mg2Sn dynamic precipitation and the formation of DRXed grains. The TAZ431 alloy with Sn alloying exhibits profuse precipitation and larger DRX fraction within the microstructure, resulting in the increase of modulus and hardness. Nucleation of DRXed grains in the TAZ431 alloy was stimulated by relatively large (over 1 micrometer) undissolved Mg2Sn intermetallic particles. Meanwhile, the precipitation of nano-sized Mg2Sn occurred within DRXed grains and was facilitated by DRX process, consequently hindering the further growth of DRXed grains. The findings here may have implications for alloy design and thermal-mechanical processing of magnesium alloy structural components.
摘要：
This paper shows that the panic index shadow line difference (ULD) can be an effective predictor of oil returns. We use a candlestick chart to plot the investor panic index (VIX) and subtract the lower shadow from the upper shadow to obtain ULD. The in-sample analysis shows that the ULD can significantly and negatively predict oil returns. The out-of-sample results show that the inclusion of ULD, an exogenous regression variable, in the model not only substantially improves the predictive accuracy of oil returns, but also yields good economic benefits when using its predicted values for portfolio investment. All bivariate regression models that include ULD as an exogenous regression variable obtain higher prediction accuracy than univariate regression models, both for in-sample and out-of-sample predictions. All the robustness tests done in this paper show that ULD is a powerful predictor that significantly improves the predictability of oil returns.
摘要：
Hyperspectral images (HSIs) have been widely used for target detection due to their abundant spatial and spectral information. In this article, a shadow-insensitive hyperspectral target detection (HTD) framework based on exposure fusion is proposed, which consists of the following major steps. First, the input HSI is divided into two parts, namely the shadow region and the nonshadow region. Second, total variation-based feature extraction and overexposure operation are performed on the input image to produce two feature images, i.e., the original feature image and the overexposure image. Third, a self-guided constrained energy minimization (SGCEM) detector is performed on the two feature images to detect the targets in shadow and nonshadow regions, respectively. Finally, the detection results obtained on the original feature image and the overexposure image are fused to acquire the final detection result. Extensive experiments conducted on real-world data illustrate that the proposed method can achieve satisfactory results when shadow exists.
摘要：
In order to improve the flame-retardant performance of insulating paper and reduce the fire risk, hydroxyethyl diphosphate and dicyandiamide were used to modify starch to prepare a new starch-based flame retardant (SHPD). The combustion, mechanical, and electrical properties of SHPD treated flame-retardant insulating paper were investigated. The results showed that when the impregnation concentration of SHPD was 25.0%, the limiting oxygen index of the insulating paper was increased from 18.3% to 38.3% and reached the level of UL-94 V-0. The tensile index and burst index of the flame-retardant insulating papers were only 10.17% and 12.5% lower than that of the control insulating paper. The ring crush strength and alternating current breakdown strength in air of the flame-retardant insulating papers were 63.3% and 1.8% higher than that of the control insulating paper. The SHPD flame retardant has a good application prospect in insulating paper.
摘要：
Fatigue performances of critical structures are strongly affected by the microstructural (e.g. grain, defect, inclusion, etc.) size effect, and it is thus important to quantify their detrimental effect. In this work, a numerical procedure is constructed to quantify the influence of microstructure on the mechanical and fatigue behaviors of Ni-based superalloy GH4169. Specifically, by combining sub modelling approach with crystal plasticity constitutive model, a dual-scale modelling approach is developed for studying grain-level mechanical behavior of Ni-based superalloy GH4169 notched components. In addition, the dislocation-based Tanaka-Mura-Wu model is applied for fatigue crack initiation life prediction. The Paris law is then utilized for fatigue crack propagation analysis based on the simulated short crack. To study the microstructural size effect on fatigue crack initiation and propagation behaviors, sub-models containing various grain orientation, grain size, defect size/shape are built and analysed. Finally, a series of fatigue tests on notched specimens of Ni-based superalloy GH4169 were carried out for method validation. Results indicate that the established dual-scale modelling approach and fatigue life prediction framework yields good agreement with experimental results.
通讯机构：
[Zhang, L ] H;Hunan City Univ, Coll Civil Engn, Yiyang 413000, Peoples R China.;Hunan Univ Technol, Hunan Engn Res Ctr Struct Safety & Disaster Preven, Yiyang 413000, Peoples R China.
关键词：
boulder and hard rock environment;GPR;wavelet scale energy spectrum;wavelet packet energy;time-frequency characteristics
摘要：
The hard rocks in the stratum can pose safety risks and hinder the progress of urban underground tunnel construction using shield and jacking methods, thereby reducing construction efficiency and increasing construction costs. This paper utilizes wavelet scale energy spectrum, wavelet packet theory and statistical methods to conduct research on the detection of special geological formations such as hard rocks and voids, as well as the analysis of their signal time-frequency characteristics based on the ground-penetrating radar (GPR) technique. On the basis of calibrating the permittivity of different types of rock blocks, we established a forward model for detecting hard rocks and voids, and the simulated signals were analyzed in the time and frequency domains. Subsequently, laboratory experiments were conducted to perform GPR tests on different types of hard rocks in natural and water-saturated states and voids, to explore the time-frequency characteristics, frequency band energy variations, and statistical patterns of typical single-trace signals. The results show that the granite detection signal contains more low-frequency components, the sandstone detection signal contains more medium-low frequency components, while the limestone detection signal contains more medium-high frequency components in their natural state; the signal from the karst cave has relatively more low-frequency components than the signal from the empty cavity. The geometric shape of the rock has no influence on the dominant frequency and time-frequency distribution of its reflection signal. Generally, rocks with higher rebound values (hardness) also exhibit larger variance and standard deviation in frequency band energy. The research has important theoretical significance and practical value for the measurement and assessment of special geological features such as hard rocks and voids in urban underground trenchless construction.
期刊：
Journal of Computational Design and Engineering,2024年11(2):230-252 ISSN：2288-4300
通讯作者：
Lairong Yin
作者机构：
[Peng Zhang; Yuyu Li; Kejun Tang; Lairong Yin; Long Huang; Hongbing Wang] College of Automotive and Mechanical Engineering, Changsha University of Science and Technology , Changsha 410114 Hunan , China
通讯机构：
[Lairong Yin] C;College of Automotive and Mechanical Engineering, Changsha University of Science and Technology , Changsha 410114 Hunan , China
摘要：
Automated tape placement (ATP) is an important automated process adopted for the fabrication of large composite components. Trajectory planning is the key link of ATP, which directly affects the precision and efficiency of the layup process and the quality of final products. Presently, most existing trajectory optimization methods for ATP focus on smooth surfaces. Nevertheless, as commercial CAD/CAM software generally uses NURBS (Non-uniform Rational B-Splines) for modelling, the difficulty of finding the solution and the low efficiency associated with the calculation process are inevitable. The discrete methods provide alternatives for designing layup trajectories, whereas their accuracy is seldom analysed. Furthermore, a path optimization algorithm for eliminating gap problems while preventing wrinkles on discrete models is rarely reported. In this paper, the adjustment of layup trajectories for ATP is considered on triangular meshes. First, the triangular mesh is reconstructed as a Nagata patch to recover the original geometry with good accuracy. Then, a numerical method for tracing desired paths on the Nagata patch set is provided and the computation efficiency is validated. Next, two optimization methodologies are proposed to improve the layup of composite tapes while avoiding wrinkles. Finally, the presented two strategies are examined on a discrete hyperbolic surface and a discrete freeform surface and some of the results are delivered.
摘要：
High-temperature titanium alloys' thermal stability and creep resistance are significant during service in high temperatures. This study systematically investigated the thermal stability and mechanical properties of Ti-6.5A1-2.5Sn-9Zr-0.5Mo-1Nb-1W-0.3Si- x Sc ( x , 0-0.5 wt.%) at 650 degrees C. The lamellar secondary alpha phase is refined and the formation of Sc2 O3 is increased with the increasing scandium ( Sc ) additions, which improves the strength of the alloy, while excessive Sc2 O3 becomes the crack source and deteriorates the plasticity. The oxygen content in the matrix is reduced by the interaction between Sc and oxygen, inhibiting the growth of the Ti3 Al phase and improving the thermal stability of the alloy. Meanwhile, Sc accelerates the dissolution of the residual ,B phase and precipitation of fine, diffusely distributed ellipsoidal silicides, which strongly prevents dislocation movement. The enhancement of creep resistance for the Sc -containing alloy is attributed to the refined lamellar secondary alpha phases, Sc2 O3 particles, Ti3 Al phase, and silicides, especially the precipitated silicides. Eventually, the 0.3Sc alloy shows optimal thermal stability (the plasticity loss rate 17.3%) and creep resistance (steady-state creep rate 4.4 x 10-7 s-1 ). The investigation results provide new insights into the mechanism and thermal stability improvement in high-temperature titanium alloys modified by rare earth (RE).(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
关键词：
Asphalt pavement;Photocatalytic coating;Nanometer titanium dioxide;Quantum dot;Tail gas degradation
摘要：
To address the escalating issue of vehicular exhaust pollution, the application of photocatalyst materials on road surfaces for rapid degradation of exhaust gas has gained significant attention in pavement engineering. However, poor visible light response and low separation efficiency of photogenerated charge carriers limit the practical application of nanometer titanium dioxide (nano-TiO2) photocatalyst on road surfaces. In this study, tungsten oxide (WO3) and tungsten sulfide (WS2) quantum dots (QDs) were introduced into graphene oxide (GO)/TiO2 nanocomposites through a sol-gel process to form ternary heterojunction structures. Characterization results revealed that the QDs modified GO/TiO2 composites exhibited enhanced light absorption, electrical conductivity and surface area. Photocatalytic degradation tests of model vehicle exhaust pollutants showed that the GO/WS2 QDs/TiO2 and GO/WO3 QDs/TiO2 coatings achieved over 70 % degradation rate of nitrogen oxides within 120 min under visible light irradiation, outperforming bare TiO2 and binary GO/TiO2. Mechanism studies suggested that the ternary heterojunction facilitated efficient separation of photogenerated charge carriers at multi-phase interfaces. Additionally, the photocatalytic coating demonstrated good durability after simulated traffic loading, maintaining a 60 % degradation rate of nitrogen oxides even after 20,000 rolling cycles. This work provides a promising solution for sustainable environmental remediation on road surfaces.
摘要：
Developing robust and efficient nonprecious metal-based electrocatalysts toward hydrogen evolution reaction (HER) is a big challenge for green and sustainable energy since insufficient catalytic activity and poor stability of current catalysts cannot meet the application requirements. This work reports a freestanding HER electrode FeNiCuAlMo prepared by arc-melting and chemical dealloying methods. The HER performance firstly improves and then declines with the increase of dealloying time. When the dealloying time is 3 h, the electrode shows optimal catalytic performance. The fabricated electrode is composed of AlMo3 and Al5CuMo2, where micro-sized AlMo3 particles are embedded in cellular dendritic Al5CuMo2. Impressively, it displays excellent HER performance, including a small overpotential of 173 mV at a current density of 500 mA/cm2 and outstanding long-term stability for 100 h of continuous hydrogen evolution at 1000 mA/cm2 in an alkaline electrolyte without obvious attenuation. The intrinsic activity of the electrodes combined intermetallic compounds with hierarchical porous structure provides several effects, including enhanced massive active sites, electrolyte access, electron transport, and fast gas release that contribute jointly to enhancing HER activities. The micro-sized AlMo3 particles provide robust framework for the dendritic Al5CuMo2 active sites center, allowing the exposure of enough active sites and simultaneously maintaining good stability. The highly stable and active electrocatalytic HER property makes it as a promising candidate for practical hydrogen production.
摘要：
Abstract Reducing the burden of social security contributions for firms, unleashing their vitality, and enhancing their total factor productivity (TFP) are crucial measures in China's pursuit of sustainable and high‐value‐added growth. This article utilizes three reductions in the corporate pension insurance contribution ratio in China as a quasi‐natural experiment to construct a treatment intensity DID (Difference‐in‐Differences) model. By utilizing data from listed companies between 2013 and 2020, this study empirically examines the impact of reducing the pension insurance contribution ratio on firms’ TFP while identifying the underlying mechanisms. The findings of the study are as follows: First, the policy exhibits a significant positive effect on corporate TFP in China. Second, this policy's contribution primarily stems from stimulating firms to increase their employment of highly skilled labour, elevating wages for ordinary employees, and enhancing firm investment efficiency. Lastly, the analysis of heterogeneity demonstrates that the policy's positive effect is more pronounced among non‐state‐owned enterprises, small and medium‐sized enterprises, and labour‐intensive enterprises. This study provides empirical evidence for evaluating the contribution reduction policy and serves as a policy reference for endeavours to deepen the reform of the pension insurance system and enhance pension insurance fund budget management.
摘要：
Recommendation systems have been effectively utilized in various fields, but their internal decision-making methods are still largely unknown. This opaque decision-making method can greatly affect users’ trust in the recommendation system. Therefore, finding a way to explain the reasons for model decisions has become an urgent task. Previous studies often used LSTM and other models to generate recommendation explanations and explain the reasons for recommendations in text form. However, traditional methods cannot effectively use the ID information of users and items, and the text generated is highly repetitive. To solve this problem, this paper uses the method of prompt learning combined with a graph encoder to design a recommendation explanation generation model. In order to narrow the semantic gap between the ID information of users and items and natural language and capture high-level interaction information, this paper designs a graph encoder based on user similarity to learn the interactive semantic information of user and item IDs, and to construct a continuous prompt. Then, the discrete prompt composed of discrete features of users and items is combined with the continuous prompt to construct a hybrid prompt to input into the pre-trained model to generate the recommended explanation. This paper experiments on three publicly available datasets and compares them with several state-of-the-art methods to demonstrate the personalization and text quality of the generated explanations.
摘要：
The dry separate curing of duck egg yolks was carried out by ultrasonic synergize NaCl (sodium chloride) and NaCl alone. The mechanism of the amelioration of salted egg yolk quality by ultrasonic synergistic NaCl dry-curing was studied. The quality variations of the salted egg yolks were analyzed for the same curing time and NaCl content achieved by ultrasonic synergistic NaCl curing and NaCl curing alone. The results showed that under the same salting time, the NaCl content, oil exudation and chewiness of U48-SEY (ultrasonic for 48h-salted egg yolk) were higher than those in SEY (salted egg yolk). At the same NaCl content, the oil exudation and chewiness of U44-SEY (ultrasonic for 44h-salted egg yolk) were still significantly increased. Compared to SEY, the soluble protein content and H(0) of U44-SEY and U48-SEY were augmented. Scanning electron microscopy (SEM) indicated that the polyhedral particles in the salted egg yolks prepared by ultrasonic synergistic NaCl dry-curing were closely aligned and evenly distributed, and the salted egg yolks were sandier. Structural analysis revealed that the secondary and tertiary structures of egg yolk protein were changed although the ultrasonic synergistic NaCl dry-curing did not cause the fragmentation or aggregation of the peptide chain structure. The above results suggested that ultrasonic not only perfected the quality of salted egg yolk by promoting NaCl penetration, but also modified the structures of egg yolk protein by the action of ultrasonic itself, which prominently improved the quality of salted egg yolks.
通讯机构：
[Gu, K ] C;Changsha Univ Sci & Technol, Sch Comp & Commun Engn, Changsha 410114, Peoples R China.
关键词：
Malicious vehicle detection;Internet of Vehicles;graph attention;gated recurrent unit;reputation
摘要：
Internet of vehicles (IoVs) is an important information exchange platform for intelligent transportation systems (ITSs) to provide traffic services. However, the appearance of malicious vehicles in IoVs can damage the security and stability of ITSs, which may provide false traffic data to cause serious traffic accidents. Also, many existing cryptography-based malicious vehicle detection scheme can only be used to resist some external attacks, while some internal malicious vehicles are easy to use their legal identities to provide false traffic data for other honest vehicles. In this paper, we propose a malicious vehicle detection scheme based on spatio-temporal features of traffic flow under cloud-fog computing-based IoVs. In our scheme, a traffic subarea division method based on spatial correlation degrees of road intersections is proposed to divide the urban road network into multiple traffic subareas. Based on the divided traffic subareas, an improved subarea-based graph attention model is proposed to extract the spatial features of traffic flow by the fog server. Then a gated recurrent unit method with attention mechanism is constructed to extract the temporal features of traffic flow by the cloud server, and a short-term traffic flow prediction model is built on the extracted spatio-temporal features of traffic flow. Further, a reputation calculation mechanism is established to score each vehicle by the fog server according to the verification of the traffic data uploaded by the vehicle and the traffic data predicted by our constructed prediction model, which is used to judge whether the vehicle is malicious according to its reputation score. Related experimental results show our scheme is effective and efficient to detect malicious vehicles under cloud-fog computing-based IoVs.
作者机构：
[Weiguo Mao] College of Materials Science and Engineering, Changsha University of Science & Technology, Changsha, P.R. China;[Qingsong Ma; Kuanhong Zeng] Science and Technology on Advanced Ceramic Fibers &Composites Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, P.R. China;[Wei Zhang] College of Materials Science and Engineering, Changsha University of Science & Technology, Changsha, P.R. China<&wdkj&>Science and Technology on Advanced Ceramic Fibers &Composites Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, P.R. China
通讯机构：
[Qingsong Ma] S;[Weiguo Mao] C;Science and Technology on Advanced Ceramic Fibers &Composites Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, P.R. China<&wdkj&>College of Materials Science and Engineering, Changsha University of Science & Technology, Changsha, P.R. China
关键词：
C/Mullite composites;Sintering characteristic of sol;Mechanical properties;Thermal stability
摘要：
C/Mullite composites were fabricated through sol impregnation-drying-heating (SIDH) route using the sol with a high solid content in our previous work, and the composites showed desirable performance. However, it was found that thermal stress caused by sintering shrinkage of mullite matrix is one of the main factors leading to the performance regression of the composites. In present study, the sintering characteristic of Al2O3-SiO2 sol was modified to reduce the thermal stress caused by the sintering shrinkage of mullite matrix, optimizing the performance of the composites. The results showed that the sintering shrinkage of mullite matrix was reduced about 25% after heat treatment at 1600ºC by modifying the sintering characteristic of sol, resulting in that the thermal stress caused by sintering shrinkage of mullite matrix was reduced effectively. Therefore, the strength, modulus and fracture work of the composites were increased by about 19.4%, 24.5% and 24.9% to 318.4 MPa, 62.0 GPa and 6958 J/m2, respectively. Furthermore, thermal stability of the composites was also improved obviously in Ar and vacuum environment.
摘要：
The natural aluminosilicate nanoclay mineral (ANM) has found extensive application in photocatalysis due to its cost-effectiveness, excellent stability, and unique surface properties. The distinctive ANMs surface not only alters the surface characteristics of loaded photocatalysts and regulates the microenvironment of photochemical reactions but also actively participates as a photocatalyst itself, thereby making the roles of ANMs surfaces in photocatalytic reactions highly intricate. This review aims to highlight recent advancements in comprehending the influence of ANMs surfaces on photocatalysis. We commence by summarizing the structural features of ANMs surfaces as traditional supports, functional supports, and photocatalysts. Emphasis is placed on elucidating how the aluminosilicate structure, photochemical activity, and asymmetric structure impact the process of photocatalytic reactions. Particular attention is given to exploring the asymmetric photochemical activity exhibited by ANMs and its consequential unique structural effects. Finally, we summarize challenges faced and future developments pertaining to heterostructure design, enhancement mechanisms, and photochemical applications for ANMs in photocatalysis.
