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71.
Adaptive evolution of dispersal strategies is one mechanism by which species can respond to rapid environmental changes. However, under rapid anthropogenic fragmentation, the evolution of dispersal may be limited, and species may be unable to adequately adapt to fragmented landscapes. Here, we develop a spatially explicit model to investigate the evolution of dispersal kernels under various combinations of fragmentation dynamics and initial conditions. We also study the consequences of modelling an evolutionary process in which dispersal phenotypes continuously and gradually shift in phenotype space in a manner corresponding to a polygenic underlying genetic architecture. With rapid fragmentation rates, we observed the emergence of long-term transient states in which dispersal strategies are not well suited to fragmented landscapes. We also show that the extent and length of these transient states depend on the pre-fragmentation dispersal strategy of the species, as well as on the rate of the fragmentation process leading to the fragmented landscape. In an increasingly fragmented world, understanding the ability of populations to adapt, and the effects that rapid fragmentation has on the evolution of dispersal, is critical for an informed assessment of species viability in the Anthropocene. 相似文献
72.
《材料科学技术学报》2024,186(19)
The coarse as-cast lamellar microstructure in TiAl alloys is difficult to be broken completely by thermo-mechanical processing.Some remnant lamellar colonies in the deformed microstructure seriously affect the microstructural homogeneity and deteriorate the properties.In this study,it is found that by isother-mal compression at 1230 ℃ and 1250 ℃,the lamellar colonies of Ti-43.5Al-4Nb-1Mo-0.1B(TNM)alloys can be completely broken.This is attributed to the weakened anisotropic deformation behavior of the lamellar colonies due to the isothermal holding treatment before deformation.The deformation behavior at 1230 ℃ was investigated by quasi-in-situ experiments.It is observed that the regions near lamel-lar colony boundaries first undergo dynamic recrystallization at small strain,while the lamellar colonies gradually break down with increasing strain.The adequate fragmentation of lamellar colonies mainly depends on the recrystallization of α lamellae(αL).The isothermal holding at 1230 ℃ leads to an in-crease in the content and thickness of αL,which allows it to assume more deformation and promotes its recrystallization by reaching critical strain.The interrupted γ lamellae(γL)formed by decomposition during isothermal holding facilitates the occurrence of α recrystallization within the lamellar colonies by hindering dislocation movement.In addition,recrystallized γ grains(γR)are gradually dissolved by the formation of α precipitates inside them through the γ → α phase transformation and the subsequent consumption of α precipitates by the recrystallized α grains. 相似文献
73.
74.
《Advanced Materials Interfaces》2018,5(18)
The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin–filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC‐active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol‐ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m−3) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin‐based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin–filler interface. 相似文献
75.
《Concurrency and Computation》2018,30(13)
The performance and efficiency of the distributed database system (DDBS) design are dependent on proper data fragmentation, reallocation, and replication of global relations. In this research, a Cluster Based Distributed and Parallel Database System (CB‐DDBS) architecture over a cloud environment is proposed. The proposed CB‐DDBS architecture processes the client's query requests, which access the clustered DDBS from anywhere. It also allows vertical and horizontal fragmentation, allocation, and replication decisions to be taken statically at the initial stage of the design. In addition, it allows migration and/or replication decisions to be taken by each cluster independently of other clusters using the proposed Optimal Fragment Reallocation and Replication (OFRAR) Algorithm. The proposed CB‐DDBS architecture and the proposed OFRAR Algorithm are tested in both Amazon cloud environment and a simulated environment. Experimental results show that the proposed OFRAR Algorithm efficiently reduces the communication costs for typical access patterns, the overloads of the sites, and the frequency and time spent on fragment migration over the network sites by imposing a stricter condition for fragment reallocation and replication, resulting in a great overall improvement in the DDBS performance. It also shows that the proposed CB‐DDBS architecture results in a significant reduction of the execution time needed for the transactions and for noticing an error. 相似文献
76.
Natalia S Serkhacheva Nikolay I Prokopov Elena V Chernikova Elena Y Kozhunova Inna O Lebedeva Oleg V Borisov 《Polymer International》2019,68(7):1303-1314
Emulsifier‐free batch emulsion polymerization of n‐butyl acrylate and its semi‐batch copolymerization with 2,2,3,3,4,4,5,5‐octafluoropentyl acrylate and 2,2,3,4,4,4‐hexafluorobutyl acrylate both mediated by poly(acrylic acid) containing the trithiocarbonate group in the chain was employed to produce amphiphilic triblock copolymers. The polymerization‐induced self‐assembly of these copolymers in aqueous media gave rise to spherical core–shell particles. Irrespective of the experimental conditions, the polymeric product was characterized by a bimodal molecular weight distribution. The apparent violation of the reversible addition–fragmentation chain transfer polymerization mechanism may be attributed to restricted accessibility of the trithiocarbonate group in the self‐assembled block copolymers for propagating radicals that enter into the particle. Mean‐field theoretical arguments were employed to explain the exclusively spherical morphology of the particles observed in the experiment. © 2019 Society of Chemical Industry 相似文献
77.
Polymer‐grafted inorganic particles (PGIPs) are attractive building blocks for numerous chemical and material applications. Surface‐initiated controlled radical polymerization (SI‐CRP) is the most feasible method to fabricate PGIPs. However, a conventional in‐batch reaction still suffers from several disadvantages, including time‐consuming purification processes, low grafting efficiency, and possible gelation problems. Herein, a facile method is demonstrated to synthesize block copolymer–grafted inorganic particles, that is, poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMEMA)‐b‐poly(N‐isopropylacrylamide) (PNIPAM)–grafted silica micro‐particles using continuous flow chemistry in an environmentally friendly aqueous media. Immobilizing the chain transfer agent and subsequent SI‐CRP can be accomplished sequentially in a continuous flow system, avoiding multi‐step purification processes in between. The chain length (MW) of the grafted polymers is tunable by adjusting the flow time or monomer concentration, and the narrower molar mass dispersity (Ð < 1.4) of the grafted polymers reveals the uniform polymer chains on the particles. Moreover, compared with the in‐batch reaction at the same condition, the continuous system also suppresses possible gelation problems. 相似文献
78.
79.
Jing Sun Lianfang Qiu Fei Wang Yang Yang Lijie Guo 《Materials Science & Technology》2019,35(6):709-715
A distinct modification of eutectic Si was observed in the selective laser melted AlSi10Mg. The eutectic Si particles were modified substantially and demonstrated a nanoscale size, a fibrous morphology with obvious ‘necking effect’. The modification mechanism and the influence of heat treatment on eutectic Si growth were explored. It was suspected that Si experienced the necking effect under a tensile environment due to the large temperature gradient and α-Al erosion during the SLM process. Upon heat treatment, the Si particles were spheroidised and distributed homogeneously. Under the synergistic action of Si crystal fragmentation and the continuous precipitation of saturated Si from the Al matrix, the coarsened and spheroidised eutectic Si were distributed homogeneously in the Al matrix. 相似文献
80.
崩落矿石块度对放矿的影响分析 总被引：3，自引：0，他引：3
从散体力学的角度，分析了矿石块度大小、粗颗粒矿石含量对抗剪强度的影响。通过室内模拟试验，深入研究了放矿过程中崩落矿石块度对放矿规律及放出体大小的影响，得出了矿石块度组成是影响放出体形状和大小的重要因素的结论，对现场生产具有指导意义。 相似文献