Microscopic examination of NpNn dominance in the evolution of nuclear structure

The proton-neutron interaction in determining the evolution of nuclear structure has been studied by using the Brillouin-Wigner perturbation expansion. The particle-hole and particle-particle p-n interactions are unifiedly described in the theory. The obtained formulas of level energies and excitation energies scaled in the small- and large-NpNn limits can well explain the linearity of the extracted proton-neutron interaction energies and the attenuation of the 2(1)(+) excitation energies against the valence nucleon product NpNn for five mass regions from A = 100-200.

Well-width dependence of in-plane optical anisotropy in (001) GaAs/AlGaAs quantum wells induced by in-plane uniaxial strain and interface asymmetry

The well-width dependence of in-plane optical anisotropy (IPOA) in (001) GaAs/AlxGa1-xAs quantum wells induced by in-plane uniaxial strain and interface asymmetry has been studied comprehensively. Theoretical calculations show that the IPOA induced by in-plane uniaxial strain and interface asymmetry exhibits much different well-width dependence. The strain-induced IPOA is inversely proportional to the energy spacing between heavy- and light-hole subbands, so it increases with the well width. However, the interface-related IPOA is mainly determined by the probability that the heavy- and light-holes appear at the interfaces, so it decreases with the well width. Reflectance difference spectroscopy has been carried out to measure the IPOA of (001) GaAs/AlxGa1-xAs quantum wells with different well widths. Strain- and interface-induced IPOA have been distinguished by using a stress apparatus, and good agreement with the theoretical prediction is obtained. The anisotropic interface potential parameters are also determined. In addition, the energy shift between the interface- and strain-induced 1H1E reflectance difference (RD) structures, and the deviation of the 1L1E RD signal away from the prediction of the calculation model have been discussed.

Determination of the values of hole-mixing coefficients due to interface and electric field in GaAs/AlxGa1-xAs superlattices

Numerical calculations within the envelope function framework have been performed to analyze the relations between the magnitude of in-plane optical anisotropy and the values of the additional hole-mixing coefficients due to interface and electric field in (001) symmetric GaAs/AlxGa1-xAs superlattices for light propagating along the [001] direction. It is found that the heavy- and light-hole states are mixed independently by interface and electric field. The numeric results demonstrate that the line shape of the in-plane anisotropic spectrum is determined by the ratio of the two hole-mixing coefficients. Theoretical analysis shows that with the help of simple calculation of the anisotropy at k=0, reliable values of the hole-mixing coefficients can be determined by reflectance-difference spectroscopy (IDS) technique, demanding no tedious fitting of experimental curves. The in-plane optical anisotropy measured by RDS provides a new method of getting the information on buried interfaces through the Value of the hole-mixing coefficient due to interface.

Energy and entropy radiated by a black hole embedded in a de Sitter braneworld

We study the Hawking radiation of a (4+n)-dimensional Schwarzschild black hole imbedded in space-time with a positive cosmological constant. The greybody and energy emission rates of scalars, fermions, bosons, and gravitons are calculated in the full range of energy. Valuable information on the dimensions and curvature of space-time is revealed. Furthermore, we investigate the entropy radiated and lost by black holes. We find their ratio near 1 in favor of the Bekenstein's conjecture.

Fabrication of a metal particle array based on a self-assembled template from a two-armed polymer

A two-armed polymer with a crown ether core self-assembles to produce macroporous films with pores perpendicularly reaching through the film down to the substrate. A possible assembling mechanism is discussed. The pore size can be conveniently adjusted by changing the solution concentration. These through-hole macroporous films provide a template for fabricating an array of Cu nanoparticle aggregates.

Size-dependent inelastic behavior of particle-reinforced metal-matrix composites

The strengthening behavior of particle-reinforced metal-matrix composites (MMCp) is primarily attributed to the dislocation strengthening effect and the load-transfer effect. To account for these two effects in a unified way, a new hybrid approach is developed in this paper by incorporating the geometrically necessary dislocation strengthening effect into the incremental micromechanical scheme. By making use of this hybrid approach, the particle-size-dependent inelastic deformation behavior of MMCp is given. Some comparisons with the available experimental results demonstrate that the present approach is satisfactory.

Dynamic properties and asymmetry of tension and compression of metal matrix composites under impact loading

The mechanical behaviors of 2124, Al-5Cu, Al-Li and 6061 alloys reinforced by silicon carbide particulates, together with 15%SiCw/6061 alloy, were studied under the quasi-static and impact loading conditions, using the split Hopkinson tension/compression bars and Instron universal testing machine. The effect of strain rate on the ultra tensile strength (UTS), the hardening modulus and the failure strain was investigated. At the same time, the SEM observations of dynamic fracture surfaces of various MMC materials showed some distinguished microstructures and patterns. Some new characteristics of asymmetry of mechanical behaviors of MMCs under tension and compression loading were also presented and explained in details, and they could be considered as marks to indicate, to some degree, the mechanism of controlling damage and failure of MMCs under impact loading. The development of new constitutive laws about MMCs under impact loading should benefit from these experimental results and theoretical analysis.

Effect of Particle Size on the Formation of Adiabatic Shear Band In Particle Reinforced Metal Matrix Composites

In this paper, the effect of particle size on the formation of adiabatic shear band in 2024 All matrix composites reinforced with 15% volume fraction of 3.5, 10 and 20 mum SiC particles was investigated by making use of split Hopkinson pressure bar (SHPB). The results have demonstrated that the onset of adiabatic shear banding in the composites strongly depends on the particle size and adiabatic shear banding is more readily observed in the composite reinforced with small particles than that in the composite with large particles. This size dependency phenomenon can be characterized by the strain gradient effect. Instability analysis reveals that high strain gradient is a strong driving force for the formation of adiabatic shear banding in particle reinforced metal matrix composites (MMCp).

Strain Regularity and Stiffness Tensor of Reinforcers in Dense Particle Reinforced Composites

针对高体积份数、随机分布、等轴状颗粒增强复合材料 ,研究了材料的应变分布规律 ,给出了基体和增强体应变平均值与材料微观结构参数之间的定量关系。结果表明 ,除应变平均值外 ,应变涨落是影响刚度张量的另一个重要因素 ,研究了应变涨落与材料微观结构参数之间的关系 ,并推导出了复合材料的刚度张量。与实验结果和以往的理论比较 ,预测结果与实验结果吻合良好

Elastic-plastic constitutive relation of particle reinforced composites

In this paper, a systematic approach is proposed to obtain the macroscopic elastic-plastic constitutive relation of particle reinforced composites (PRC). The strain energy density of PRC is analyzed based on the cell model, and Che analytical formula for the macro-constitutive relation of PRC is obtained. The strength effects of volume fraction of the particle and the strain hardening exponent of matrix material on the macro-constitutive relation are investigated, the relation curve of strain versus stress of PRC is calculated in detail. The present results are consistent; with the results given in the existing references.

Real-Time Measurement on Deformation Fields of Hole-Excavated Samples under Impact Tension

In this paper, the real-time deformation fields are observed in two different kinds of hole-excavated dog-bone samples loaded by an SHTB, including single hole sample and dual holes sample with the aperture size of 0.8mm. The testing system consists of a high-speed camera, a He-Ne laser, a frame grabber and a synchronization device with the controlling accuracy of I microsecond. Both the single hole expanding process and the interaction of the two holes are recorded with the time interval of 10 mu s. The observed images on the sample surface are analyzed by newly developed software based on digital correlation theory and a modified image processing method. The 2-D displacement fields in plane are obtained with a resolution of 50 mu m and an accuracy of 0.5 mu m. Experimental results obtained in this paper are proofed, by compared with FEM numerical simulations.