Experimental study of the beta-delayed proton decays of Er-145,Er-147

The beta-delayed proton decays of Er-145,Er-147 have been studied experimentally using the Ni-58 + Mo-92 reaction at beam energy of 383 MeV. On the basis of a He-jet apparatus coupled with a tape transport system, the beta-delayed proton radioactivities both from the nu s(1/2) ground state and the nu h(11/2) isomer in Er-145,Er-147 were observed by proton-gamma coincidence measurements. By analyzing the time distributions of the 4(+) -> 2(gamma)(+) transitions in the granddaughter nuclei Dy-144,Dy-146, the half-lives of 1.0 +/- 0.3 s and 1.6 +/- 0.2 s have been deduced for the nu h(11/2) isomers in Er-145,Er-147, respectively.

Properties of the beta-Delayed Proton Decay of Er-147

The beta-delayed proton decay of Er-147 is studied experimentally using the Ni-58+Mo-92 reaction at a beam energy of 383 MeV. Based on a He-jet apparatus coupled with a tape transport system, the beta-delayed proton radioactivities both from the nu s(1/2) ground state and the nu h(11/2) isomer in Er-147 are identified by proton-gamma coincidence measurements. By analyzing the time distribution of the 4(+) -> 2(+) gamma transition in the grand-daughter nucleus Dy-146, a half-life of 1.6 +/- 0.2 s is determined for the nu h(11/2) isomer in Er-147. The half-life for the ground state of Er-147 is estimated to be 3.2 +/- 1.2 s.

Microstructure and mechanical properties of slowly cooled Cu47.5Zr47.5Al5

Cu47.5Zr47.5Al5 was prepared by arc melting and solidified in situ by suction casting into 2-5-mm-diameter rods under various cooling rates (200-2000 K/s). The microstructure was investigated along the length of the rods by electron microscopy, differential scanning calorimetry and mechanical properties were investigated under compression. The microstructure of differently prepared specimens consists of macroscopic spherical shape chemically inhomogeneous regions together with a low volume fraction of randomly distributed CuZr B2 phase embedded in a 2-7 nm size clustered "glassy-martensite" matrix. The as-cast specimens show high yield strength (1721 MPa), pronounced work-hardening behavior up to 2116 MPa and large fracture strain up to 12.1-15.1%. The fracture strain decreases with increasing casting diameter. The presence of chemical inhomogenities and nanoscale "glassy-martensite" features are beneficial for improving the inherent ductility of the metallic glass.

Experimental Study on Flow and Sediment Movement in Cavity Circulations

This paper reports a flume experiment of flow and sediment movement in a cavity. The flow velocity, sediment concentration and the mechanism of hydraulic sorting in the circulation flow are discussed. The quantity and patterns of sediment deposition in the circulation area are studied as well.

纳米铜团簇凝结规律的分子动力学研究

Freezing processes of liquid Cu nanoclusters with atoms of 147,309 and 561 are performed by means of molecular dynamics, which show that the structures of the obtained solid nanoclusters at room temperature arc, governed by the cooling rate and the cluste

Oil-Water Two-Phase Flow Inside T-Junction

The oil/water two-phase flow inside T-junctions was numerically simulated with a 3-D two-fluid model, and the turbulence was described using the mixture k - epsilon model. Some experiments of oil/water flow inside a single T-junction were conducted in the laboratory. The results show that the separating performance of T-junction largely depends oil the inlet volumetric fraction and flow patterns. A reasonable agreement is reached between the numerical simulation and the experiments for both the oil fraction distribution and the separation efficiency.

Energy Principle And Nonlinear Electric-Mechanical Behavior Of Ferroelectric Ceramics

Many experimental observations have shown that a single domain in a ferroelectric material switches by progressive movement of domain walls, driven by a combination of electric field and stress. The mechanism of the domain switch involves the following steps: initially, the domain has a uniform spontaneous polarization; new domains with the reverse polarization direction nucleate, mainly at the surface, and grow though the crystal thickness; the new domain expands sideways as a new domain continues to form; finally, the domain switch coalesces to complete the polarization reversal. According to this mechanism, the volume fraction of the domain switching is introduced in the constitutive law of the ferroelectric material and used to study the nonlinear constitutive behavior of a ferroelectric body in this paper. The principle of stationary total potential energy is put forward in which the basic unknown quantities are the displacement u(i), electric displacement D-i and volume fraction rho(I) of the domain switching for the variant I. The mechanical field equation and a new domain switching criterion are obtained from the principle of stationary total potential energy. The domain switching criterion proposed in this paper is an expansion and development of the energy criterion established by Hwang et al. [ 1]. Based on the domain switching criterion, a set of linear algebraic equations for determining the volume fraction rho(I) of domain switching is obtained, in which the coefficients of the linear algebraic equations only contain the unknown strain and electric fields. If the volume fraction rho(I) of domain switching for each domain is prescribed, the unknown displacement and electric potential can be obtained based on the conventional finite element procedure. It is assumed that a domain switches if the reduction in potential energy exceeds a critical energy barrier. According to the experimental results, the energy barrier will strengthen when the volume fraction of the domain switching increases. The external mechanical and electric loads are increased step by step. The volume fraction rho(I) of domain switching for each element obtained from the last loading step is used as input to the constitutive equations. Then the strain and electric fields are calculated based on the conventional finite element procedure. The finite element analysis is carried out on the specimens subjected to uniaxial coupling stress and electric field. Numerical results and available experimental data are compared and discussed. The present theoretic prediction agrees reasonably with the experimental results.

Space Experimental Investigation On Thermocapillary Migration Of Bubbles

Results from a space experiment on bubble thermocapillary migration conducted on board the Chinese 22nd recoverable satellite were presented. Considering the temperature field in the cell was disturbed by the accumulated bubbles, the temperature gradient was corrected firstly with the help of the temperature measurement data at six points and numerical simulation. Marangoni number (Ma) of single bubble migrating in the space experiment ranged from 98.04 to 9288, exceeding that in the previous experiment data. The experiment data including the track and the velocity of two bubble thermocapillary migration showed that a smaller bubble would move slower as it was passed by a larger one, and the smaller one would even rest in a short time when the size ratio was large enough.

Anisotropic Deformation Of Polystyrene Particles By Mev Au Ion Irradiation

MeV An irradiation leads to a shape change of polystyrene (PS) and SiO2 particles from spherical to ellipsoidal, with an aspect ratio that can be precisely controlled by the ion fluence. Sub-micrometer PS and SiO2 particles were deposited on copper substrates and irradiated with Au ions at 230 K, using an ion energy and fluence ranging from 2 to 10 MeV and 1 x 10(14) ions/cm(2) to 1 x 10(15) ions/cm(2). The mechanisms of anisotropic deformation of PS and SiO2 particles are different because of their distinct physical and chemical properties. At the start of irradiation, the volume of PS particles decrease, then the aspect ratio increases with fluence, whereas for SiO2 particles the volume remains constant. (C) 2008 Elsevier B.V. All rights reserved.

FexSi grown with mass-analyzed low-energy dual ion beam deposition

Heavily iron-implanted silicon was prepared by mass-analyzed low-energy dual ion beam deposition technique. Auger electron spectroscopy depth profiles indicate that iron ions are shallowly implanted into the single-crystal silicon substrate and formed 35 nm thick FexSi films. X-ray diffraction measurements show that as-implanted sample is amorphous and the structure of crystal is partially restored after as-implanted sample was annealed at 400degreesC. There are no new phases formed. Carrier concentration depth profile of annealed sample was measured by Electrochemical C-V method and indicated that FexSi film shows n-type conductivity while silicon substrate is p-type. The p-n junction is formed between FexSi film and silicon substrate showing rectifying effect. (C) 2003 Elsevier B.V. All rights reserved.

受拉铝板对连续波CO_2激光的热机械响应

本文对受拉伸载荷的铝合金板被强连续波CO_2激光照射时的热机械响应进行了报导。介绍联合加载实验装置,实验方法和实验结果。对试件的断裂过程以及断裂前的应力应变分布进行了讨论。

平晶型激光错位干涉仪及其在流场测量中的应用

仪器的原理是将一束激光经扩束后通过被测系统,然后在平晶前后表面反射而获得干涉图.仪器防振性能好,可以方便地对横向与纵向尺寸都较大的流场进行测量,光源亮度高,结构简单,调整使用方便,有希望在流场测量特别是超声速流场测量中获得广泛的应用.

An anisotropic elastic-plastic constitutive model for single and polycrystalline metals .1. Theoretical developments

An anisotropic elastic-plastic constitutive model for single and polycrystalline metals is proposed. The anisotropic hardening of single crystals, at first, is discussed with the viewpoint of yield surface and a new formulation of it is proposed. Then, a model for the anisotropic hardening of polycrystals is suggested by increasing the number of slip systems and incorporating the interaction of all slip systems. The interaction of grains through grain boundaries is shown to be similar to, and incorporated into, the interaction of slip systems in grains. The numerical predictions and their comparisons with experiments will follow in Part II of this paper.

Mixed-mode fracture mechanisms near the fatigue threshold of aisi-316 stainless-steel

Near threshold, mixed mode (I and II), fatigue crack growth occurs mainly by two mechanisms, coplanar (or shear) mode and branch (or tensile) mode. For a constant ratio of ΔK_I/ΔK_II the shear mode growth shows a self-arrest character and it would only start again when ΔK_I and ΔK_II are increased. Both shear crack growth and the early stages of tensile crack growth, are of a crystallographic nature; the fatigue crack proceeds along slip planes or grain boundaries. The appearance of the fracture surfaces suggest that the mechanism of crack extension is by developing slip band microcracks which join up to form a macrocrack. This process is thought to be assisted by the nature of the plastic deformation within the reversed plastic zone where high back stresses are set up by dislocation pile-ups against grain boundaries. The interaction of the crack tip stress field with that of the dislocation pile-ups leads to the formation of slip band microcracks and subsequent crack extension. The change from shear mode to tensile mode growth probably occurs when the maximum tensile stress and the microcrack density in the maximum tensile plane direction attain critical values.

三维链网模型及其参数标定

提出一种材料模型，由三维空间取向的平行弹簧束作为构架，讨论了按空间取向进行离散的方式。实现立体角划分的最优化。构造了由一维构元组成的三维链网体胞，给出了体胞几何，物理参数的标定方法。证明该体胞能精确模拟Pisson比从0-1／2的材料行为，突破了已往模型0-1/3限制。探讨了模型简化问题，实现了模拟精度高而计算费用低的统一，举例论述了该模型模拟短纤维增强复合材料的独特优点。