Unravelling the competitive effect of microstructural features on the fracture toughness and tensile properties of near beta titanium alloys

The competitive effect of microstructural features including primaryα(α_(p)),secondaryα(α_(s)),grain boundaryα(α_(GB)) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes.The relative effect of β grain size and STA(solution treatment and ageing)processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method.These results were further explained via correlating microstructure with the fracture toughness and tensile properties.It was found that large numbers of fine as precipitates and continuous α_(s) played greater roles than other features,resulting in a high strength and very low ductility(<2%)of STA process samples.The β grain size had a negative correlation with fracture toughness.In the samples prepared by BASCA( β anneal slow cooling and ageing)process,improved ductility and fracture toughness were obtained due to a lower density ofα;precipitates,a basket-weave structure and zigzag morphology of α_(GB).For this heat treatment,an increase in prior β grain size had an observable positive effect on fracture toughness.The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained.It was shown that the microstructure obtained from different processes after β solution has complex effect on mechanical properties.This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties.A novel table was proposed to quasi-quantitatively unravel these competitive effects.

Deposition mechanism of nano-structured single-layered C_(36) film on a diamond (100) crystal plane

The Brenner-LJ potential is adopted to describe the interaction between C36 clusters and diamond surface, and the deposition mechanism of multi-C36 clusters on the diamond surface is also studied by using the method of molecular dynamics simulation. The simulation results show that the competition effects of two interactions, i.e. the interaction between cluster and cluster and the interaction between cluster and crystal plane, are studied, and then the influence of these competition effects on C36 cluster deposition is analysed. The finding is that when an incident energy is appropriately chosen, C36 clusters can be chemically adsorbed and deposited steadily on the diamond surface in the form of single-layer, and in the deposition process the multi-C36 clusters present a phenomenon of energy transmission. The experimental result shows that at a temperature of 300K, in order to deposit C36 clusters into a steady nanostructured single-layered film, the optimal incident energy is between 10 and 18 eV, if the incident energy is larger than 18 eV, the C36 clusters will be deposited into an island nano-structured film.

Barrier or easy-flow channel: The role of grain boundary acting on vortex motion in type-Ⅱ superconductors

Grain boundaries(GBs),as extremely anisotropic pinning defects,have a strong impact on vortex motion in type-Ⅱsuperconductors,and further on the macro level dominates the superconductivity for example the critical current density.Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion,while an easy-flow channel just under some certain conditions.In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works,in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-Ⅱsuperconductors.The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel,and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions.Such the competition effect essentially depends on the attributes of both the GB(described by the GB strength and angleθ)and no-GB pining regions(by the relative disorder strengthα_(p)/α_(v)).Specifically,for a YBa_(2)Cu_(3)O_(7-x)(YBCO)sample,to obtain a clear knowledge of vortex motion in GB region,we visualized the three typical trajectories of vortices during the three vortex movement stages.Further,in order to understand how GB results in the macro current-carrying property,corresponding to the current-voltage relation of the YBCO conductor,we obtained the average velocity v_(y) of vortices varying with their driving force,which is nearly identical with the previous observations.

Effects of soil substrate heterogeneity and moisture on interspecific competition between Alternanthera philoxeroides and four native species

Aims Clonal plant species have the potential for high relative performance in heterogeneous environments,and this might increase the com-petitive ability and invasiveness of introduced clonal plant species.It was hypothesized that clonal species whose performance responds more to heterogeneity of a resource have higher competitive ability in habitats where this resource is more heterogeneous and that this relationship is stronger when other resources are less limiting.Methods To test these hypotheses,the perennial clonal herb Alternanthera philoxeroides,which is invasive in China,was grown alone or with each of four clonal perennial,co-occurring herbs native to China,i.e.Alternanthera sessilis,Cynodon dactylon,Hemarthria altissima and Wedelia chinensis.Plants were given homogeneous or het-erogeneous soil substrate crossed with low and high levels of soil moisture.Important Findings Effects of heterogeneity on the accumulation of mass and ramets and on competitive effect and response of A.philoxeroides differed between native species and interacted with effects of soil moisture.A.philoxeroides reduced the final total mass or ramet number of the native species except A.sessilis,and the negative competitive effects on H.altissima and C.dactylon were more pronounced in heterogeneous than in homogeneous soil.Competitive response of A.philoxeroides was more negative to A.sessilis than to the other native species.Across native species,the competitive response of A.philoxeroides was more negative in heterogeneous than in homo-geneous soils at low moisture level,but the reverse was true at high moisture level.Results do not consistently support either hypoth-esis,but do suggest that competitive ability can be partly explained by individual species traits such as size,and that some competi-tive effects and responses are emergent properties of interspecific interactions.

Compensatory effects between Pinus massoniana and broadleaved tree species

Aims Evaluation of the interaction intensity between Masson pine(Pinus massoniana)and broadleaved trees will facilitate selecting tree combinations suitable for reforestation in abandoned sites in subtropical areas.Methods Pinus massoniana and seven broadleaved trees species were grown either in monoculture or in two-species mixture.Biomass of tree species was measured and inter-specific interactions were estimated using log response ratio.Test of homogeneity of variances was performed to compare the stability of biomass in the monoculture of the broadleaved trees with that in the mixture.Important Findings Our results showed that the direction and intensity of interactions between P.massoniana and the broadleaved trees varied from year to year and the identity of the broadleaved species.Facilitative interactions were found between Camellia oleifera,Rhus chinensis and P.massoniana.Pinus massoniana had competitive effects on Lithocarpus glaber,Cyclobalanopsis glauca and Elaeocarpus japonicus.Significantly negative relations were found between biomass of P.massoniana and the broadleaved trees in the third year of the experiment,and the compensatory effects between P.massoniana and the broadleaved trees may be involved in stability maintenance in the multi-species forests in the subtropical area.The results of homogeneity test of variances also showed that the biomass per pot in the mixture had significantly lower variances than that in the monoculture,suggesting that total biomass is more stable in the mixture than the monoculture.

Structure of National Science and Technology Competitiveness: A Methodological and Empirical Study

This paper clearly defines the concepts of the national competitiveness,the national S&T competitiveness,and the national S&T competitiveness structure.It develops an evaluation framework with three dimensions:the national S&T competitive potential,the national S&T competitive strength and the national S&T competitive effectiveness.This paper proposes a structure analysis method and depicts the national S&T competitiveness structure of 35 countries in an empirical research.Apart from the definitions and the structure analysis method,this paper mainly draws the following conclusions:(1)In the one-dimensional national S&T competitiveness structure,the top 5 countries were all developed countries in 2015,while the developing countries generally performed better than developed countries considering the average annual growth rate of the national S&T competitiveness index.The 35 countries are clustered into 4 categories using the two-dimensional structure analysis method.For example,based on the ranking of the national S&T competitive strength index and the national S&T competitive effectiveness index of the 35 countries in 2015,the 35 countries are clustered into four categories:high-strength and higheffectiveness,low-strength and high-effectiveness,low-strength and low-effectiveness,and high-strength and low-effectiveness.(2)To a large extent,there is a significant correlation between the national S&T competitiveness index score and the GDP per capita value.And to a certain extent,there is some correlation between the national S&T competitiveness index score and the GDP value.Moreover,under the background of strength and effectiveness combination,or under the background of strength and potential combination,the national S&T competitiveness structure and GDP or GDP per capita show significant relationship.

Holes in Fossil Shells Show Effects of Competition and Evolution

化石能够或多或少地反映出当时生物及其生存环境的状况,这为人类了解生命的历史和地球上生态环境变迁的历史提供了重要的线索。一代又一代的科学家通过对不断发现的越来越多的生物化石的研究,根据它们形态特征上的异同来了解各门类生物之间的亲缘关系。