分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-08-23
摘要: Sink strength is a fundamental quantity in modeling the microstructure evolution of irradiated materials by the mean-field approaches. The analytical expressions for different sinks have been extensively studied. The Object Kinetic Monte Carlo (OKMC) simulations were subsequently performed to corroborate the expressions and to guide the development of analytical theories. Although a general agreement was found between the theory and simulation, there are still some discrepancies in the case of the small spherical sinks and the dislocation lines. In this work, OKMC simulations were performed to study the sink strength of spherical sinks and dislocation lines. Our results revealed the origins of discrepancies between the theory and simulation for small sinks, high volume fraction sinks and periodically distributed dislocation lines. The theoretical corrections were also proposed accordingly. These corrections can extend the capabilities of mean-field approaches to properly reproduce the defect evolution of irradiated materials, and provide a better insight into the experimental phenomena, such as the defect cluster nucleation, the irradiation-induced swelling and the blistering.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Vinyl-functionalized thermosensitive Pluronic F127 micelles have been used as multifunctional cross-links for the synthesis of super tough, highly resilient and thermores- ponsive nanomicelle (NM) hydrogels. Pluronic F127 diacrylate (F127DA) with vinyl groups on both ends self- assembled in aqueous solution into micelles. Such micelles served as multifunctional macro-cross-links to copolymerize with acrylamide (AAm) monomers, generating novel NM hydrogels with extraordinary tensile and compressive proper- ties, without using any chemical cross-linkers. Uniaxial tensile tests demonstrated a fracture strain above 2265%, an ultimate stress of 276 kPa, and a fracture energy of 2.34 MJ/m3. Under compression tests, these hydrogels did not fracture up to 98% strain and 62 MPa stress. Cyclic compressive loading−unloading tests at 90% strain showed no decay of the hyseteresis energy, indicating an unprecedented fatigue resistance.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: The composite NdFeB magnets with blending melt-spun flakes and Fe fine powders were prepared by the hot-pressed and hot-deformed route. Characterizations of the hot-deformed NdFeB magnets affected by the doped Fe powders were tested. The doped Fe powders decrease the hot-deformed pressure when the strain is between 15 and 50%. XRD patterns show that the doped Fe powders have little influence on the c-axis alignment of hot-deformed NdFeB magnets in the press direction. The Br and the (BH)max get improved when the doped Fe powders are less than 3 wt%. The doped Fe of hot-deformed NdFeB magnets exists in the elongated state and the spherical state surrounded by the Nd-rich phase. With the Fe fraction increasing, the potential of magnet moves to the positive direction and the diameter of the Nyquist arc becomes larger, which indicate that the corrosion resistance improved effectively. The bending strength was enhanced by the elongated α-Fe phase embedded in the matrix 2:14:1 phase.
提交时间: 2017-05-02
摘要: The flexural strength reliability of bulk metallic glasses [BMGs] plates is analyzed using Weibull statistics. The Weibull modulus [m] and characteristic strength [sigma[0]] of the Zr48Cu45Al7 BMG are 34 and 2630 MPa, respectively, which are much higher t
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: In this study, highly cross-linked and completely imidized polyimide aerogels were prepared from polyimide containing trimethoxysilane side groups, which was obtained as the condensation product of polyimide containing acid chloride side groups and 3-aminopropyltrimethoxysilane. After adding water and acid catalyst, the trimethoxysilane side groups hydrolyzed and condensed one another, and a continuous increase in the complex viscosities of the polyimide solutions with time was observed. The formed polyimide gels were dried by freeze-drying from tert-butyl alcohol to obtain polyimide aerogels, which consisted of a three-dimensional network of polyimide fibers tangled together. By varying the solution concentration of the polyimide containing trimethoxysilane side groups, polyimide aerogels with different densities (ranging from 0.19 to 0.42 g/cm3) were obtained. The resulting polyimide aerogels had small pore diameter (ranging from 20.7 to 58.3 nm), high surface area (ranging from 310 to 344 m2/g), high 5% weight loss temperature in air (at about 440 °C), and an excellent mechanical property. In addition, the glass transition temperature (349 °C) of the polyimide aerogels was much higher than that (210 °C) of the corresponding linear polyimide. So, even after being heated at 300 °C for 30 min, the porous structure of the polyimide aerogels was not completely destroyed.
分类: 生物学 >> 植物学 提交时间: 2019-01-17 合作期刊: 《干旱区科学》
摘要: Vegetation roots contribute to soil fixation and reinforcement, thus improving soil resistance against erosion. Generally, the amount of soil fixation presented by roots mainly depends on root density and tensile strength. In the present study, we conducted the research in order to further understand the biotechnical properties of Haloxylon persicum and also to quantify its role in increasing soil cohesion in arid lands of Iran. Ten H. persicum shrubs were randomly selected for root distribution and strength investigations, in which five samples were set on flat terrain and other five samples on a moderate slope terrain. The profile trench method was used to assess the root area ratio (RAR) as the index of root density and distribution. Two profiles were dug around each sample, up and downslope for sloped treatment and north and south sides for flat treatment. The results showed that RAR increased with increasing soil depth and significantly decreased in 40–50 cm layers of downhill (0.320%) and 50–60 cm for uphill (0.210%). The minimum values for the northward and southward profiles were 0.003% and 0.003%, respectively, while the maximum values were 0.260% and 0.040%, respectively. The relationship between the diameter of root samples and root tensile strength followed a negative power function, but tensile force increased with increasing root diameter following a positive power function. The pattern of increased cohesion changes in soil profile was relatively similar to RAR curves. The maximum increased cohesion due to the presence of roots in uphill and downhill sides were 0.470 and 1.400 kPa, respectively. In the flat treatment, the maximum increased cohesions were 0.570 and 0.610 kPa in northward and southward profiles, respectively. The analysis of variance showed that wind and slope induced stresses did not have any significant effect on the amount of increased cohesion of H. persicum. The findings served to develop knowledge about biotechnical properties of H. persicum root system that can assist in assessing the efficiency of afforestation and restoration measures for erosion control in arid lands.
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-05-09
摘要: Multi-stimuli responsive hydrogels are synthesized using self-assembled nanomicelles of Pluronic F127 diacrylate triblock copolymer as non- covalent macro-crosslinkers to in situ copolymerize with acrylamide and methyl chloride quaternized N,N-dimethylamino ethylacrylate mono- mers, generating positively charged hydrogels. These hydrogels showed high strength, toughness, and outstanding fatigue resistance, and are reversibly responsive to changes in pH and ionic strength.