Analysis of inverted base pavements with thin-asphalt layers

Inverted base pavements are flexible pavement structures built by placing a top quality compacted granular aggregate base between a rigid cement-treated base and a thin-asphalt surface layer. The proximity of the granular base to the load makes its behaviour critical to the pavement response. Three-dimensional finite-element simulations are conducted to assess the mechanical performance of different inverted base pavement structures, with emphasis placed on pavements that feature thin-asphalt surface layers. A nonlinear constitutive model captures the anisotropic stress-dependent stiffness of the granular base. Results show that the stress distribution within inverted base pavements is markedly different from that of conventional pavements due to the stiffness contrast between successive layers. Thin-asphalt layers deform more uniformly and experience lower tension than thick layers. However, in the presence of combined shear and vertical contact loads, the benefits of a membrane response in thin asphalt concrete layers may be overwhelmed by the increased tensile strain at the load edge. The transition from beam to membrane asphalt response depends on the relative stiffness between the asphalt layer and the aggregate base. In most cases, the transition takes place at an asphalt layer thickness between 25 mm and 50 mm.     

2197铝锂合金的组织和性能

通过力学性能测试和显微组织观察研究了2197合金组织和性能之间的关系。结果表明,2197合金具有中等强度,小的各向异性,强的热稳定性。该合金在T8状态下能获得最佳的强度和塑性配合,在T6峰时效状态以析出少量δ′相、θ′相和T_1相联合强化为主。在2197合金的相组成中,T_1相析出数量不占主导地位,Al_6Mn弥散质点的析出有利于减小各向异性。2197合金中Li含量较低,使其呈现较强的热稳定性。     

超热电子能谱分布各向异性的实验研究

报道了100 TW超短脉冲钛宝石激光装置上飞秒激光-固体靶相互作用中超热电子的能谱测量,获得了各向异性分布的超热电子能谱.靶前激光反射方向超热电子能谱和靶前法线方向超热电子能谱类似,呈单温类Maxwell分布;而靶后激光传播方向超热电子能谱出现高能尾部;靶前法线方向超热电子的产额比靶后激光传播方向和靶前激光反射方向要高得多.对以上形成的原因进行了分析.     

Effect of Rare Earth Elements on Anisotropy and Microstructure of AI-Li Alloy 2195 Sheets

For the purpose of decreasing the applied limitation resulting from the anisotropic mechanical property of Al-Li alloy 2195, this study employed a complex heat treatment process, involving the pre-tension, thermo-infiltration of the rare earth element Ce, solution treatment, and artificial aging technology. The results indicate that the infiltration of rare earth element Ce benefits the abatement of anisotropy of Al-Li alloy 2195 sheet, in contrast with that of the normal heat treatment process. The gradient of the Vickers-hardness decreases at least 50% through the thickness, and the tensile strength in the rolling direction also increases significantly. If Ce was infiltrated into the alloy under the optimum pre-deformation, the yield strength （σ0.2） increased by 30 MPa while the tensile strength （σb） enhanced by 25 MPa compared to the rare earth free samples. Meanwhile, the fractography illustrated that the fracture surface of the sample became more desirable.     

[110]晶向近本征硅单晶双光子吸收各向异性

以沿[110]晶向切割的近本征硅单晶为样品,通过研究样品对连续波固体激光器所产生的1.3μm的近红外光的双光子吸收所诱导的光电流对入射光偏振方向的依赖关系,研究了双光子吸收的各向异性.测得了硅单晶对该波长的光的三阶极化率张量χ(3)的各向异性系数为-0.25,两个独立分量的比值χxxxx/χxxyy的幅度为2.4,并基于前期工作所得的χxxyy的结果,进而确定了另一分量χxxxx的值大约为1.49×10-19m2/V2.     

Texture and anisotropy of mechanical properties of spray-formed alloy tool steels

The initial texture and anisotropy of alloyed tool steel specimens are studied by constructing pole figures and conducting compression tests. Scattered initial axial crystallographic growth texture and weak anisotropy of yield stress and ultimate strength are established. A relationship between deformability and texture is determined. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 26–31, 2007.     

Single-crystal growth and anisotropic electrical properties of (La1?xCax)2CaCu2O6

Large single crystals of (La_1–x Ca _x )₂CaCu₂O₆ were synthesized by the travelling solvent floating zone (TSFZ) technique. The dimension of the grown boules was typically 4 mm×30 mm long with thec-axis perpendicular to the growth direction. After oxygen loading at 1080°C in 400 atm of O₂, they became superconductive with a sharp transition at around 50 K. The resistivity was metallic both along thec-axis and within theab-plane, with an anisotropy ratio of ²( _c/ _ab ) 50 which is almost independent of temperature. Details of the crystal growth, heat treatment procedures, and the results of electrical and magnetic property measurements are presented.     

香豆胶衍生物的化学结构及稳定性研究

将市售商品溶于水,用异丙醇沉析提纯,溶于0.1 mol/L NaNO3纯水溶液中,经0.5μm滤膜过滤后用水相凝胶渗透色谱法(GPC)测定,测得香豆胶(FG)、羟丙基香豆胶(HPFG)、阳离子香豆胶(CFG)的数均、重均相对分子质量Mn、Mw分别为:1.19×105、3.36×105,8.52×104、2.85×105,9.33×104、2.87×105。用甘露聚糖链在碱性条件下醚化时发生降解,解释两种改性FG的相对分子质量较FG低而多分散性(Mw/Mn)较FG高的测试结果。认为商品FG的1%水溶液黏度(1300 mPa.s)高于商品HPFG和CFG(分别为705和610 mPa.s)的原因是前者相对分子质量较高且残渣含量也较高(~10%,后二者为1%~2%)。HPFG的取代度为0.12,根据文献发表的13C-NMR数据确认HPFG分子链上羟丙基取代位置为C6。讨论了香豆胶(半乳甘露聚糖)的化学结构。热重分析法测定的热稳定性,HPFG高于CFG,CFG又高于FG。图6表3参13。