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Vegetation restoration is the primary strategy employed for the purification and restoration of habitats in the Zhegao River wetlands. To investigate the changing characteristics of soil microbial biomass carbon/nitrogen (MBC/MBN) and soil enzyme activities in wetlands undergoing different vegetation restoration treatments, those involving reed and willow restoration were studied in 2014 (WR8) and 2021 (WR1), with a native vegetation wetland (NW) used as a control. This study examined changes in the MBC/MBN, sucrase (Suc), urease (Ure), and acid phosphatase (Acp) in these wetlands. The results indicated that during the restoration of Zhegao River wetlands, reed vegetation had a stronger positive effect on soil properties after one year of restoration than that of willow vegetation. After eight years, the effects of willow vegetation restoration were greater than those of reed vegetation restoration. The activities of MBC, MBN, Suc, Ure, and Acp in the reed and willow wetland soils for different years of vegetation restoration decreased with greater soil depth. Thus, reeds and willows have distinct contributions toward enhancing the ecological service functions of the Zhegao River wetlands for different restoration years, which provides a scientific basis for the selection and protection of ecological wetland restoration. [ABSTRACT FROM AUTHOR]

The Gibbs phenomenon in Fourier series has long been recognized as a drawback in its applications, in particular when it is used to represent a function having discontinuities. One category, namely, intrinsic discontinuities, could be derived from the nature of the physical problems. Another, namely, inherent discontinuities, is created undesirably through the employment of Fourier series. To alleviate these drawbacks, two techniques are developed. The first aims at eliminating the inherent discontinuities. The size of the original domain [0, l] is first doubled with a virtual function [[Psi].sub.0] defined over the neighboring domain [-l, 0]. The augmented domain [-l, l] is then further extended periodically. The virtual function [[Psi].sub.0](y) is chosen so that continuities are achieved at y = 0, [+ or -] l, [+ or -] 2l,.... Consequently, no Gibbs phenomena will occur at the boundaries. The second aims at reproducing the intrinsic discontinuities in the representation function by incorporating piecewise cubic polynomials into the Fourier base function. The enlarged basis function, namely, the Gibbs-phenomenon-free-Fourier-series function, is able to represent accurately any specific boundary conditions and interior intrinsic discontinuous conditions. Examples of vibration and buckling analysis of complex beams show that the present method is versatile, accurate, and efficient.

Explosive devices represent a significant threat to military and civilian structures. Specific design procedures have to be followed to account for this and ensure buildings will have the capacity to resist the imposed pressures. Shrapnel can also be produced during explosions and the resulting impacts can weaken the structure, reducing its capacity to resist the blast pressure wave and potentially causing failures to occur. Experiments were performed by the Defence Science and Technology Agency (DSTA) of Singapore to study this combined loading phenomenon. Slabs were placed on the ground and loaded with approximately 9 kg TNT charges at a standoff distance of 2.1 m. Spherical steel ball bearings were used to reproduce the shrapnel loading. Loading and damage characteristics were recorded from the experiments. A finite element analysis (FEA) model was then created which could simulate the effect of combined shrapnel impacts and blast pressure waves in reinforced concrete slabs, so that its results could be compared to experimental data from the blast tests. Quarter models of the experimental concrete slabs were built using LS-Dyna. Material models available in the software were employed to represent all the main components, taking into account projectile deformations. The penetration depth and damage areas measured were then compared to the experimental data and an analytical solution to validate the models. [ABSTRACT FROM AUTHOR]

In this paper, the boundary finite element method (BFEM) is applied to dynamic fluid-structure interaction problems. The BFEM is employed to model the infinite fluid medium, while the structure is modeled by the finite element method (FEM). The relationship between the fluid pressure and the fluid velocity corresponding to the scattered wave is derived from the acoustic modeling. The BFEM is suitable for both finite and infinite domains, and it has advantages over other numerical methods. The resulting system of equations is symmetric and has no singularity problems. Two numerical examples are presented to validate the accuracy and efficiency of BFEM-FEM coupling for fluid-structure interaction problems. [ABSTRACT FROM AUTHOR]

To investigate the joint effect on shock wave propagation and attenuation in jointed rock masses, a small-scale field explosion test is analyzed numerically by using the three-dimensional discrete element method (3D DEM) and the three-dimensional finite difference method (3D FDM). Results show that rock joints act as a kind of filter through which only low frequency shock waves are allowed to pass. This indicates that high frequency shock waves do no harm to far-field structures when they have to travel across joint sets with specific spacing. Results also reveal that the orientation of the joint sets can remarkably affect the amplitude and frequency composition of shock waves. Furthermore, as a discontinuous numerical method, 3D DEM can capture the main features of shock waves, and most importantly, it can simulate the 3D effect of rock joints. It can be concluded that in modelling 3D shock wave propagation and attenuation in jointed rock masses, 3D DEM has unique advantages over 2D modeling, 3D FDM, and even field testing. [ABSTRACT FROM AUTHOR]

This paper presents the derivation of the governing equations for the stability of vibration of an integrated system comprising a moving train and the railway track. The train consists of a convoy of articulated two-axle wagons. The equations are applicable to any arbitrary number of axles at arbitrary spacing. Each axle is modelled as a mass–spring–damper vibration unit. The railway track is an infinitely long Euler beam subjected to an axial compressive force and rests on a visco-elastic foundation. The governing equations for the integrated system are coupled differential equations, which can be transformed to algebraic equations by Fourier and Laplace transforms. Subsequent inverse Fourier transform and contour integration yield the instability equation. Critical parameter is identified. It follows by parametric studies on the instability of vibration due to different train configurations. Illustrative examples for trains having up to 20 wagons or 40 axles are given. [Copyright &y& Elsevier]