The virtual contact loading method is further developed in this paper tostudy the multi-body contact phenomena within solid and hollow roller bearings. The distributive virtual contact loads are used to simulate the contact constraint forces on each contact surface. The deepest penetration criterion is proposed to select and determine the contact nodes in an orderly way, so as to ensure the local iteration process converged and to increase the computational efficiency. The load distributions within the solid and hollow roller bearings have been studied in more detail and some reasonable results are obtained.
This paper presents a review of high performance damage-resistant seismic resistant structural (DRSRS) systems for the sustainable and resilient city. Firstly, the motivation and the basic principle as well as methodology of the developing DRSRS system are briefly illustrated. Then, the structural detailing and the seismic behaviors of three types of existing DRSRS systems, namely, the replaceable structural element (RSE), rocking seismic resisting structural (RSRS) system, and self-centering seismic resisting structural (SCSRS) system, are summarized in detail. The theoretical and extensive experimental study results indicated that the three existing types of DRSRS system can minimize the postdamage after loading. Types of energy dissipation devices and dampers, as well as fuse sections, can largely enhance the energy dissipation capacity of the proposed structural system. Many numerical and finite element models have been proposed to analyze the dynamic and static cyclic responses of them. The residual deformation after the dynamic response is smaller compared to that following the cyclic response. Then, the current research challenges of DRSRS system are illustrated, and the new research highlights that emerged in recent years are stated. Finally, the conclusions of this paper are summarized; furthermore, the recommendations for the future studies are pointed out at the end of the paper.
Many studies have found that plant invasion can enhance soil organic carbon (SOC) pools, by increasing net primary production (NPP) and/or decreased soil respiration. While most studies have focused on C input, little attention has been paid to plant invasion effects on soil respiration, especially in wetland ecosystems. Our study examined the effects of Spartina alterniflora invasion on soil respiration and C dynamics in the Yangtze River estuary. The estuary was originally occupied by two native plant species: Phragmites australis in the high tide zone and Scirpus mariqueter in the low tide zone. Mean soil respiration rates were 185.8 and 142.3 mg CO2 m−2 h−1 in S. alterniflora and P. australis stands in the high tide zone, and 159.7 and 112.0 mg CO2 m−2 h−1 in S. alterniflora and S. mariqueter stands in the low tide zone, respectively. Aboveground NPP (ANPP), SOC, and microbial biomass were also significantly higher in the S. alterniflora stands than in the two native plant stands. S. alterniflora invasion did not significantly change soil inorganic carbon or pH. Our results indicated that enhanced ANPP by S. alterniflora exceeded invasion-induced C loss through soil respiration. This suggests that S. alterniflora invasion into the Yangtze River estuary could strengthen the net C sink of wetlands in the context of global climate change.
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