River channel morphology plays a critical role in riverine ecosystems, society and the entire basin. However, quantifying river channel morphological changes and identifying sediment deposition hotspots are poorly understood in mountain river systems. This study utilized multi-temporal satellite images to assess the river channel morphological dynamics and sedimentation over the past 30 years (1990-2020) in Tamor River of the Central Himalaya, Nepal. Geospatial and statistical techniques were employed for a detailed analysis of the 10 divided river reaches for six subperiods. Over 30 years, the midstream section experienced significant changes in channel width, area and mid-channel bar, whereas both upstream and downstream sections displayed minimal morphological variation. Across all river sections, the erosion area (12.75%) slightly exceeded the deposition area (11.33%). The river centerline and thalweg exhibited a consistent pattern of asymmetric migration, dominated by a maximum rightward centerline migration of 301.47 m, compared to 250.59 m leftward in the middle reaches. Results showed that the notable sediment deposition hotspots concentrated along the right bank of the sinuous bends of the downstream reaches. The most pronounced channel instability occurred from 1995 to 2005, driven by intense precipitation and extreme flood events. These findings provide a strong foundation for infrastructure planning and engineering measures to mitigate river disasters, especially in Himalayan River systems.
Lakes in the middle and lower reaches of the Yangtze River (MLY) are important freshwater ecological zones in China; investigating organic matter (OM) sources can deepen our understanding of regional carbon cycling and human effects on carbon storage. We compiled sediment core data from previous studies to determine the proportion of OM originating from endogenous sources and exogenous sources using a Bayesian mixing model supported by measurements of TOC, TN, C/N ratio, delta 13C, and delta 15N from five lakes (Lake Tai, Lake Cao, Lake Poyang, Lake Longgan, and Lake Changshou) in the MLY. Most C/N ratios ranged from 5 to 12, suggesting that sediment OM came from both autochthonous and allochthonous sources. Some ratios exceeded 12, indicating a strong terrestrial input. We used delta 13C and C/N ratios for qualitative analysis. The results indicated that soil OM, algae, aquatic vascular plants, domestic sewage, and C-3 plants influenced sediment OM in the MLY lakes. Subsequently, we employed a Bayesian mixing model to estimate the contributions of autochthonous and allochthonous sources. Domestic sewage (29.2%) and soil OM (28.5%) were the main sources. Aquatic vascular plants (16.7%), algae (14.1%), and terrestrial C-3 plants (11.6%) served as secondary sources. These findings suggest that the lake ecosystems in the MLY are mainly affected by severe soil erosion and pollution from domestic sewage. Rapid urbanization in the basin has altered land-use patterns in surrounding areas, increasing soil erosion and intensifying organic pollution from industrial wastewater and nutrient runoff from domestic sewage.
Nonlinear structural analysis serves as a fundamental tool for accurately predicting structural bearing capacity and ultimate strength. The incremental-iterative solution scheme represents the prevailing methodology for tracing nonlinear load-displacement responses and is implemented in most commercial finite element software. To enhance the robustness and computational efficiency of existing schemes, this paper first revisits the incremental-iterative framework, providing a detailed analysis that clarifies the distinct roles of the load increment factor in the predictor and corrector phases. Subsequently, a novel framework of updated orthogonal iterative schemes (UOIS) is established. Within this framework, the current generalized stiffness parameter (CGSP) and a cumulative indicator Si are introduced in the predictor phase to adaptively control the magnitude and sign of the load increment, respectively. In the corrector phase, four enhanced orthogonal iteration strategies are formulated. Furthermore, to improve computational efficiency, a novel acceleration strategy is proposed, which embeds a secant prediction operator in the predictor phase, thereby circumventing the costly assembly and inversion of the tangent stiffness matrix. The results demonstrate that: (1) compared to the conventional generalized stiffness parameter (GSP), the proposed CGSP exhibits superior stability in tracking stiffness variations, offering a more reliable indicator for adaptive step-size control; (2) the cumulative indicator Si reliably identifies load limit points and accurately distinguishes between loading and unloading regimes; (3) the UOIS framework demonstrates strong convergence in tracing complex equilibrium paths with multiple critical points and exhibits significantly superior robustness under large increment sizes compared to the generalized displacement control method (GDCM); and (4) the secant-prediction acceleration strategy achieves substantial improvements in computational efficiency without compromising solution accuracy.
The vibration reduction performance of metaconcrete is primarily attributed to the bandgap characteristics of its cells. The width and number of bandgaps determine the operational frequency range and the effectiveness of vibration reduction in metaconcrete. To address this, a dual-resonant metaconcrete is proposed in this paper. Specifically, a metal shell and a flexible soft coating are added to the exterior of the original soft coating of the resonant aggregate, transforming the resonant aggregate from a single-degree-of-freedom system into a two-degree-of-freedom system. This design further broadens the operational frequency range of metaconcrete and enhances its vibration reduction performance. In this study, an analytical model of a metaconcrete cell containing dual-resonant aggregates was established. Subsequently, the finite-element method was used to analyze the band structure, vibration modes, and energy distribution characteristics, with a focus on the bandgap characteristics of dual-resonant metaconcrete cell. To further refine the analysis, bandgap influencing factors were selected using the equivalent model method, and the influence of design parameters on the bandgap was investigated. Building upon this, an analytical model of a dual-resonant metaconcrete, composed of 12 longitudinally arranged cells, was developed. Finally, the frequency response function, time-domain characteristics, and energy flow properties of the dual-resonant metaconcrete were analyzed. The results showed that the proposed dual-resonant metaconcrete cell can generate two bandgaps, with the starting and cutoff frequencies of these bandgaps determined by the vibration modes of Resonator I, Resonator II, and the matrix. Furthermore, the elastic modulus, Poisson's ratio, and thickness of the soft coating were identified as the key factors influencing the bandgap characteristics. The vibration reduction performance of the dual-resonant metaconcrete was demonstrated within both bandgaps. When the excitation frequency was within the bandgap, the vibration directions of the resonators and the matrix were opposite, and the superposition of these reverse vibrations resulted in a reduction of vibration at the output end. Energy was continuously converted between the kinetic energy of the resonator and the elastic strain energy of the soft coating. Under these conditions, the dual-resonant metaconcrete was shown to behave similarly to a filter, exhibiting significant filtering characteristics and energy localization. As a result, the propagation of elastic waves was shielded, achieving effective attenuation.
It is known in control theory that the problem how an interconnection of ISS (abbreviation of input-to-state stability) subsystems remains ISS leads to a cycle condition, which is a set of inequalities involving the composition of unbounded Kamke functions. In this paper we convert the problem on those inequalities to functional equations and obtain 𝒦_∞ solutions by finding fixed points in a complete metric space or a locally convex topological linear space. We also give 𝒦_∞ solutions by piecewise construction. Our results can be applied to discussing ISS of interconnection.
