Application of SSOR-PCGM with improved iteration format in FEM simulation of massive concrete

In this study, for the purpose of improving the efficiency and accuracy of numerical simulation of massive concrete, the symmetric successive over relaxation-preconditioned conjugate gradient method （SSOR-PCGM） with an improved iteration format was derived and applied to solution of large sparse symmetric positive definite linear equations in the computational process of the finite element analysis. A three-dimensional simulation program for massive concrete was developed based on SSOR-PCGM with an improved iteration format. Then, the programs based on the direct method and SSOR-PCGM with an improved iteration format were used for computation of the Guandi roller compacted concrete （RCC） gravity dam and an elastic cube under free expansion. The comparison and analysis of the computational results show that SSOR-PCGM with the improved iteration format occupies much less physical memory and can solve larger-scale problems with much less computing time and flexible control of accuracy.

Alien plant species coexist over time with native ones in Chilean Mediterranean grasslands

Aims Alien species are commonly considered as harmful weeds capa-ble of decreasing native biodiversity and threatening ecosystems.Despite this assumption,little is known about the long-term patterns of the native-alien relationships associated with human disturbed managed landscapes.This study aims to elucidate the commu-nity dynamics associated with a successional gradient in chilean Mediterranean grasslands,considering both native and alien species.Methods Species richness(natives and aliens separately)and life-form(annu-als and perennials)were recorded in four chilean post-agricultural grazed grasslands each covering a broad successional gradient(from 1 to 40 years since crop abandonment).A detrended correspondence analysis(DcA),mixed model effects analyses and cor-relation tests were conducted to assess how this temporal gradient influenced natives and aliens through community dynamics.Important Findings Our results show different life-form patterns between natives and aliens over time.Aliens were mainly represented by annuals(especially ruderals and weeds),which were established at the beginning of succession.Annual aliens also predominated at mid-successional stages,but in old grasslands native species were slightly more representative than alien ones within the community.In the late successional states,positive or no correlations at all between alien and native species richness suggested the absence of competition between both species groups,as a result of differ-ent strategies in occupation of the space.community dynamics over time constitute a net gain in biodiversity,increasing natives and maintaining a general alien pool,allowing the coexistence of both.Biotic interactions including facilitation and/or tolerance processes might be occurring in chilean post-agricultural grasslands,a fact that contradicts the accepted idea of the alien species as contenders.