Consequences of advances in agricultural technologies for the distribution of segetal plant communities and species in the Republic of Bashkortostan
G. R. Khasanovaa, *, M. V. Lebedevab, **, B. M. Mirkinc, and L. G. Naumovad, *** aBashkir State Agrarian University, Ufa, 450001 Russia bBotanical Garden-Institute, Ufa Scientific Center, Russian Academy of Sciences, Ufa, 450080 Russia cUfa Institute of Biology, Russian Academy of Sciences, 450054 Russia dBashkir State Pedagogical University, Ufa, 450000 Russia *e-mail: gulnazrim@yandex.ru **e-mail: lebedevamv@mail.ru ***е-mail: leniza.gumerovna@yandex.ru Received May 12, 2016
Сегетальная флора некоторых регионов России: характеристика таксономической структуры
The authors’ data on the weed species composition in 8 geographic regions of the Russian Federation were laid at the basis of this survey. The segetal flora comprised weeds of cereals, root crops, and perennial grasses. The composition and taxonomic structure of weed species were analyzed. The total number of weedy plants encompassed 686 plant species. The level of regional weed species diversity was positively related to the area planted. Altai Territory, Udmurtia, and Rostov Province had the greatest weed species diversity, with more than 300 species, while Vologda Province had the lowest diversity (193 species). Most species-rich plant families (Asteraceae Dumort., Poaceae Barnhart, Fabaceae Lindl., Brassicaceae Burnet), genera (Potentila L., Artemisia L., Veronica L., Chenopodium L., Silene L., Trifolium L.), their subsequences, contributions of singlespecies families (17–39%) and genera (57–74%) were relatively stable systematic structure indicators. Only 18% of the species were common for all the regions. In each region there were region-specific groups of species. Weed species compositions in geographically close regions – the European part of Russia and the Urals – showed the greatest similarity. As for geographically distant regions (Altai Territory and Rostov Province), their weedy species compositions were distant and contained large groups of region-specific species.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.