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- 摘要：Let
- 摘要：To identify the dominant factors governing groundwater pollution and to apportion their sources， a representative industrial area in Shishan Town， one of the major manufacturing hubs in Foshan City， was selected as the study area. A total of 135 groundwater samples were collected. Hydrochemical classification combined with a Positive Matrix Factorization （PMF） model was employed to preliminarily identify the dominant controlling factors and potential pollution sources in groundwater. Pollution zone classification and source apportionment were then performed based on a Self-Organizing Map （SOM） neural network. The results showed that the study area can be divided into three hydrochemical zones： Zone Ⅰ encompasses the area around the historical landfill and Changhongling Industrial Park in the central part of the study area； Zone Ⅱ is the interlaced zone of farmland and low-intensity industrial areas in the northern and western parts； and Zone Ⅲ is the former lead-acid battery dismantling industrial area in the eastern part. The results indicate that： 1） Average concentrations of Mn， Fe， Al， and Ni in groundwater of the study area exceed the Class Ⅳ limit values of the Chinese National Groundwater Quality Standard. Heavy metal distributions exhibit pronounced spatial heterogeneity strongly influenced by anthropogenic activities. The PMF model suggests that pollution sources contribute 78.6% of the observed pollution. 2） Hydrochemical patterns in Zone Ⅰ are Cl·HCO₃-Ca·Na and Cl-Na； those in Zone Ⅱ are HCO₃-Ca and HCO₃·Cl-Ca； and the hydrochemical type in Zone Ⅲ is SO₄-type. 3） Hydrochemical zoning results derived from SOM cluster analysis and hydrochemical analysis are consistent. The hydrochemical patterns of groundwater in Zone Ⅰ and Zone Ⅲ exhibit the most significant differences， while the differences between Zone Ⅰ and Zone Ⅱ are relatively minor.No direct hydrochemical correlation was found between the excessive Ni concentrations in Zone Ⅲ and Zone Ⅰ. The excessive Ni concentration in the groundwater of Zone Ⅰ may be associated with historical landfilling， reflecting a point source pollution.关键词：groundwater pollution;hydrochemical classification;positive matrix factorization model（PMF）;self-organizing map（SOM）;source apportionment;Pearl River Delta16|232|0更新时间：2026-04-03
- 摘要：Vegetation dynamics are driven by multiple factors and are particularly sensitive to climate in arid and semi-arid regions. The Tianshan Mountains， as the largest mountain range in the world’s arid regions， have undergone significant vegetation changes， yet the drivers behind these changes and their relative contributions remain insufficiently understood. To address this， we used Theil-Sen median trend analysis and Mann-Kendall test to analyze interannual and seasonal spatiotemporal patterns from 1982 to 2021， and applied a Geodetector model to quantify the effects of natural factors on the normalized difference vegetation index （NDVI）. Results revealed an overall increasing trend in NDVI （slope 0.001 6 a-1）， indicating a marked greening， with localized degradation in the northern part of the central Tianshan. The spatial distribution of vegetation was primarily shaped by interactions among elevation， precipitation， and temperature， as well as between these factors and other environmental variables （e.g.，VDP）. The impact of climatic factors on vegetation change has increased significantly over the period. This study provides a scientific basis for informing ecological security and sustainable development in the Tianshan.关键词：climate change;vegetation;normalized difference vegetation index （NDVI）;Tianshan Mountains;geodetector17|160|0更新时间：2026-04-03
- 摘要：The shape of sand particles affects the physical and mechanical properties of sand， thereby influencing its engineering behavior. To investigate the influence of soil particle shape on its internal structure and particle motion characteristics， the creep process of sands with different particle shapes under varying stresses was simulated based on the discrete element method in the study. The results reveal that the micro-scopic of non-spherical particles to creep is quite different from that of spherical particles. The flatter particle shape leads to higher sample strength and more volumetric contraction. The particle shape affects the distribution of contact force during creep， which makes it more comparable to the distribution of contact force in the shearing process. In terms of particle alignment， the flatter the particles， the more they tend to be distributed in the direction perpendicular to the major external loading （i.e.， the horizontal direction） during creep. During shearing， particle shape changes the contribution of internal particle contact motion to overall specimen deformation normal contact deformation produces dilatancy while tangential contact deformation generates contraction， contrary to its contribution in spherical particle motion. The contribution of inter-particle contact motion to the volumetric strain during creep is closely related to the strain characteristics at the onset of creep. In other words， the contribution of the interparticle contact motion in creep depends on the initial state of creep and is a continuation of the deformation from that state. This study provides a theoretical basis for predicting long-term stability and deformation in geotechnical foundations.关键词：particle shape;creep deformation;internal structure of soil;particle motion characteristic9|164|0更新时间：2026-04-03
- 摘要：This paper proposes an interface-traction-based equilibrium finite element method combined with dual analysis theory to achieve high-precision stress solutions and strict a posteriori error estimation for finite sliding contact problems. First， the principle of minimum complementary energy for contact problems is derived within the framework of finite sliding. By introducing contact constraints， the problem is transformed into a quadratic programming problem. Subsequently，an traction-based equilibrium element is constructed using the macro-element technique and substituted into the principle of minimum complementary energy. Consequently，a high-precision equilibrium stress field that strictly satisfies the equilibrium equations is obtained. By combining the equilibrium stress field obtained from this method with the compatible displacement field from standard finite elements， the constitutive relation error （CRE） for contact problems can be derived and calculated. It is proven that this CRE serves as a strict upper bound for the discretization error. Finally， the proposed method is numerically verified through typical multi-body contact benchmarks， demonstrating its effectiveness in terms of solution accuracy， convergence， and discretization error estimation.关键词：finite-slip contact problem;equilibrium finite element;complementary energy principle;local search algorithm;dual analysis19|145|0更新时间：2026-04-02
- 摘要：To address the performance degradation of fault diagnosis in spacecraft attitude control systems under conditions of scarce fault samples and imbalanced data distribution， this paper proposes a fault diagnosis method integrating time-series image encoding and deep learning. First， a Wasserstein Generative Adversarial Network with gradient penalty （WGAN-GP） is employed to augment fault time-series samples and balance the training set distribution. Subsequently， three encoding methods—Gramian Angular Summation Field， Markov Transition Field， and Recurrence Plot—are utilized to convert time-series signals into two-dimensional images. Then， a two-dimensional convolutional neural network is constructed to extract and classify fault features. Experimental results demonstrate that the proposed method significantly improves diagnostic accuracy under varying sample imbalance ratios， validating its effectiveness and robustness in imbalanced sample scenarios.关键词：spacecraft attitude control system;fault diagnosis;time-series image encoding;generative adversarial network;convolutional neural network36|95|0更新时间：2026-04-02
- 摘要：The accuracy of medium and long-term orbit predictions for LEO spacecraft is susceptible to uncertainties in the space environment and on-orbit configuration changes.The traditional prediction methods are limited by errors in atmospheric density models，the inadequate applicability of drag coefficients，and the lack of detailed modeling of the variation in effective windward area due to configuration changes.This paper proposes a medium and long-term orbit prediction method for large morphing spacecraft.This method introduces pseudo-drag coefficient to uniformly model the multiple uncertainties related to atmospheric drag as a learnable time-varying parameter.It constructs a prediction framework that integrates high-precision dynamic orbit model with data-driven techniques.Furthermore，a correction model for the pseudo-drag coefficient is established to explicitly characterize the quantitative relationship between changes in the windward area and the pseudo-drag coefficient. Simulation experiments conducted on a large morphing spacecraft demonstrate that， under multiple morphing scenarios，the proposed method achieves significantly lower orbit prediction errors than traditional method，effectively enhancing the accuracy and adaptability of medium and long-term prediction.关键词：large spacecraft;orbit prediction;drag coefficient;windward area5|8|0更新时间：2026-04-02
- 摘要：In pressurized water reactors，these rods are commonly constrained by spacer grids，forming a multi-span beam configuration characterized by multiple elastic supports. Concurrently，the flow channels housing the fuel rods experience turbulence induced by axial flow interacting with the spacer grids，leading to increased excitation forces on the fuel rod surfaces compared to pure axial flow conditions. Based on the transfer matrix method（TMM） and the anisotropy of fuel rod stiffness， a multi-elastic constraint model of fuel rod bending vibration was established.. Additionally，the mode superposition method（MSM） is utilized to simulate and investigate the vibration response of fuel rods subjected to axial flow by applying segmented harmonic excitations. A comparative assessment of various elastic constraint failure scenarios is also performed. Finally，the method’s accuracy is verified.关键词：vibration characteristic;multiple constraints;fuel rod;TMM;MSM21|68|0更新时间：2026-04-02
- 摘要：Investigating the niche characteristics of rare and endangered plant populations is crucial to understanding their endangered status and enhancing protection efficiency. Based on data from 166 20 m×20 m quadrats， this study examined the niche characteristics of 21 rare and endangered woody plant species in Guanshan National Nature Reserve， Jiangxi Province. The niche breadth of these 21 species was assessed using the Levins and Shannon indices， and their resource utilization differentiation was studied using the Schoener's niche similarity proportion （Cik） and Pianka's niche overlap index （Oik）. The results indicate that： 1） The species with the largest niche breadth was Tapiscia sinensis， followed by Taxus wallichiana var. mairei， Michelia chapensis， and Toona ciliata， while the species with the smallest niche breadth was Hibiscus paramutabilis. Linear regression analysis showed a significant positive correlation between niche breadth and importance value， and a significant negative correlation with the coefficient of variation of importance value. 2） Rare and endangered plants in Guanshan displayed considerable differences in resource utilization， with both the niche similarity proportion （Cik） and niche overlap index （Oik） being relatively low. The maximum values of Cik and Oik were observed for the species pair Toona ciliata and Amentotaxus argotaenia （Cik：0.44， Oik：0.53）， reflecting their similar resource utilization. 3） Linear regression analysis showed a significant positive correlation between the Oik and Cik values of species pairs and the mean niche breadth of the pairs， indicating that species with wider niche breadths have a higher probability of occupying similar ecological niches. These findings provide a scientific basis for optimizing the allocation of conservation and management resources and designing targeted conservation plans in the nature reserve.关键词：rare and endangered plant;ecological niche characteristic;species conservation10|67|0更新时间：2026-04-01
- 摘要：To achieve high-value utilization of titanium-bearing blast furnace slag（TBBFS），this study employed high-calcium content TBBFS as a calcium source，oxalic acid as an acid activator，and borax as a retarder to prepare slag-based calcium oxalate cement（COC）via an acid-base reaction. The effects of the mass ratio of TBBFS to oxalic acid［m（TBBFS）/m（OA）］and the retarder dosage on the mechanical properties and hydration process of COC were systematically investigated.The results showed that at a m（TBBFS）/m（OA） ratio of 6 and a retarder dosage of 0.5%，the prepared COC exhibited an initial setting time of 11.32 min and compressive strength of 27.05 MPa （28 d），demonstrating both favorable workability and mechanical performance.The main hydration products were identified as CaC2O4·2H2O and amorphous silicic acid/silica. The hardening mechanism involves a multi-step synergistic phase-formation process.First， the acidic environment created by the dissolution of oxalic acid promotes the release of Ca2+ and SiO42- ions from calcium silicate.These ions then react with oxalate（C2O42-） and hydrogen ions（H+） to form the primary binding phase（CaC2O4·2H2O）， while the resulting amorphous silicic acid or silica gel contributes to toughening and pore-filling.Meanwhile， chemically inert calcium titanate（CaTiO3）particles are uniformly distributed throughout the matrix，functioning as reinforcing micro-aggregates.This hierarchical composite structure achieves a synergistic enhancement in strength，toughness，and durability through the orderly formation and cooperative interaction of different phases at the microscale.关键词：Titania-rich blast furnace slag（TBBFS）;calcium oxalate cement;acid-base cement;hardening mechanism21|39|0更新时间：2026-04-01
- 摘要：To investigate the chemical constituents of mulberry branches and their inhibitory activity against phosphodiesterase 4（PDE4）， various chromatographic techniques including normal phase silica gel， reversed phase silica gel， and gel were comprehensively utilized for the separation and purification of mulberry branches. The structures of the compounds were identified through spectral data such as NMR and MS， combined with literature comparison. Using tritiated 3'，5'-cyclic adenosine monophosphate（3H-cAMP） as the substrate， the PDE4 inhibitory activity of the compounds was determined in vitro using liquid scintillation counting. The results showed that eight compounds were isolated and identified from the ethyl acetate fraction of the mulberry branch ethanol extract， namely： Morusin（1）， Mornigrol E（2）， Mornigrol F（3）， Kuwanon C（4）， Moracin M-3'-O-β-D-glucopyranoside（5），cis-oxyreseratrol-4-O-β-D-glucopyranoside（6）， Steppogenin（7）， and Dihydromorin（8）. Compound 6 was isolated from mulberry plants for the first time. The isopentenyl flavonoids 1， 3， and 4 exhibited good PDE4 inhibitory activity， with half-inhibitory concentrations（IC50） values of（1.02±0.20），（0.50±0.07）， and（0.38±0.06） μmol/L， respectively， indicating their potential as lead compounds for PDE4 inhibitors.关键词：Ramulus Mori;chemical constituents;phosphodiesterase-4;inhibitor24|76|0更新时间：2026-04-01
- 摘要：In the field of stock price prediction， there often exists complex interrelationships among multiple variables in multivariate time series， simultaneously influenced by various factors， which increases the difficulty of accurate prediction. To address this challenge， we propose an innovative hybrid preprocessing technique. Firstly， we utilize Empirical Wavelet Transform （EWT） to simultaneously extract the low-frequency and high-frequency components of time series. Subsequently， we introduce Dynamic Time Warping （DTW） and Differential Dynamic Time Warping （DDTW） to measure the similarity between different components， effectively identifying correlated patterns and similarities in stock price time series. In further analysis， we employ a sliding window approach for high-frequency components and conduct Principal Component Analysis （PCA）， while directly applying PCA to low-frequency components. Finally， we apply these methods to multiple neural network prediction models and observe significant improvements in model performance and prediction accuracy.关键词：stock price prediction;empirical wavelet transform;dynamic time warping;principal component analysis;neural network126|274|0更新时间：2026-03-06
- 摘要：In this paper， we study a class of nonlinear elliptic equation
- 摘要：By using Fourier transforms and based on group representations and characteristic theory， the eigenvalues of the Cayley graph on the direct product group of double cyclic groups and cyclic groups are explicitly given， and a closed-form formula for the Kirchhoff index of the graph is established. Meanwhile， two examples are presented to illustrate the applicability of our obtained theoretical results.关键词：Kirchhoff index;Cayley graph;representation of groups;characters of groups64|199|0更新时间：2026-03-06
- 摘要：In the fields of signal processing and algebraic analysis， quaternions and their transformation theory have attracted extensive attention due to their unique mathematical properties. This paper studies the right-sided quaternion linear canonical transform （QLCT）. Firstly， it introduces the basic concepts of quaternion algebra， including the representation of quaternions， operation rules， conjugation， and norm； and provides the definition of QLCT. Secondly， based on the parity of the signal， it proposes the decomposition method of even and odd components of the QLCT， deeply explores the relevant properties of this transformation， and provides proofs. Finally， taking gaussian signals as an example， simulation experiments are conducted to verify the theoretical derivation and demonstrate the characteristics of each component of the quaternion-valued signal and its QLCT transformation.关键词：quaternions;quaternion linear canonical transform;gaussian signal122|228|0更新时间：2026-03-06
- 摘要：Transmission eigenvalue problem of internal inverse scattering in inhomogeneous media with fully coated boundary conditions is investigated. First，a fourth-order nonlinear transmission eigenvalue problem is established. Second， an equivalent mixed formulation with auxiliary variables is proposed to transform the nonlinear problem into a linear eigenvalue problem. Appropriate operators are constructed using the Riesz representation theorem and the Rellich compactness theorem. Then， the compactness and coerciveness of operators are proven through the Brezzi theory， Cauchy convergence criterion， and Poincaré inequality. Subsequently， finite element discretization is performed. It is demonstrated that optimal convergence rates for transmission eigenvalues can be achieved on both convex and non-convex domains. A sparse generalized eigenvalue problem is derived， which significantly reduces matrix size by compressing nearly all ∞ eigenvalues with huge multiplicities while preserving sparsity.关键词：inverse scattering;transmission eigenvalue;finite element method;generalized eigenvalue130|210|0更新时间：2026-01-29
- 摘要：The study aimed to explore new methods for revealing latent fingerprints by using amino-functionalized poly （p-phenylene vinylene） fluorescentnanoparticles （PPV-brPEI NPs） as the research object. The results showed that the drop method using PPV-brPEI NPs yields the clearest fingerprints， and the number of consecutive fingerprint impressions （1~5 times）， the force applied（0.2~0.7 N）， and the age of the fingerprint（1~12 d） have little effect on the revelation effect. PPV-brPEI NPs can clearly reveal the morphological and detailed features of fingerprints on several difficult substrates such as coins， rough phone cases， and tape surfaces. Compared with traditional powder methods and 502 fuming methods， this method has advantages in eliminating the interference of uneven surfaces， complex patterns， and adhesion on fingerprint revelation. However， PPV-brPEI NPs have an inhibitory effect on DNA detection. All together suggested that PPV-brPEI NPs have certain advantages in revealing oily latent fingerprints， especially on difficult substrates such as rough and complex backgrounds and sticky surfaces， with good revelation effects. It can provide a solution to the problem of fingerprint revelation on difficult substrates. At the same time， the inhibitory effect of this reagent on DNA detection also suggested subsequent reagent improvement in the future.关键词：PPV-brPEI NPs;fingerprint revelation;difficult substrate;DNA detection;forensic science114|252|0更新时间：2026-01-21
- 摘要：The study investigated reaction mechanisms of gallic acid （GA） with hydroxyl radicals and hydroxyl radical-water clusters （OH and OH·H2O） in a physiological environment （aqueous phase at 310.15 K and 1.013×105 Pa） using the M06-2X method of density functional theory combined with the SMD solvation model from the self-consistent reaction field theory. The reactions between GA and OH proceed via three channels： hydrogen abstraction by OH， OH addition to carbon， and single electron transfer from GA to OH. Calculations show that for the hydrogen abstraction channel， the reaction where OH （or OH·H2O） abstracts the hydroxyl hydrogen is the most favorable. Both are barrierless processes accompanied by significant exothermic effects. For the addition channel， the addition of OH （or OH·H2O） to the aromatic ring carbon is the most favorable， with free energy barriers ranging from 24.4 to 58.8 kJ/mol， exhibiting significant exothermic effects. The single electron transfer process from GA to OH and OH·H2O is thermodynamically unfavorable and cannot occur. The results indicate that GA can eliminate OH radicals via hydrogen abstraction and addition reactions， demonstrating that gallic acid can serve as an effective hydroxyl radical scavenger.关键词：gallic acid;hydroxyl radical;density functional theory;self-consistent reaction field theory;transition state;electron transfer;free energy barrier79|124|0更新时间：2026-01-21
- 摘要：An off-grid sparse Bayesian method for underwater acoustic signals using nested arrays is proposed. The method integrates Toeplitz reconstruction and eigenvalue-weighted denoising. It constructs a full-rank covariance matrix through virtual array mapping and reconstruction，then applies eigenvalue weighting to the signal subspace to suppress noise while preserving essential information. And off-grid sparse representation model is solved by Bayesian learning for maximum a posteriori estimation. Simulation and sea trial results demonstrate that the method can estimate up to 11 sources using only 6 physical sensor elements. It maintains high resolution and stability even in scenarios with a low number of snapshots and multiple closely spaced targets. Furthermore，at a signal-to-noise ratio（SNR） of
- 摘要：Finite-element-based digital image correlation（FE-DIC） is widely used for non-contact， full-field deformation measurement. The accuracy of this method is substantially affected by several factors， including mesh size， image noise， element type， and the spatial complexity of the actual displacement field. In this study， both theoretical analyses and numerical simulations were conducted to systematically examine the influence of these factors on the measurement performance of FE-DIC. The results demonstrate the existence of an optimal mesh size that minimizes the displacement measurement error. The amplitude of image noise not only directly degrades the measurement accuracy but also shifts the optimal mesh size. Moreover， higher-order elements exhibit enhanced capability in representing complex displacement fields， albeit with increased sensitivity to image noise. In addition， fine meshes are required in regions with highly nonuniform deformation to accurately capture local deformation characteristics. A uniaxial tensile test on an aluminum plate was performed， validating the effectiveness of the obtained conclusions in practical strain measurements.关键词：optical deformation measurement;digital image correlation;finite element method;measurement error27|13|0更新时间：2026-01-21
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