Free Energy Calculation of Al-Li-Mg Alloy from Electron Level
Based on Thomas-Fermi model£¬the calculation method of free energy for atom cluster with electric field had been found. The change trend of free energy of Al-Li-Mg alloy under the effect of electric field had been calculated systemically and quantitatively. And following results had been given: mostly the free energy of Al3Li andMg5Al8 at aging temperature is lower than that of free energy at solid solution temperature, but once the negative electric field increased to certain degree there will be opposite result. At aging temperature, the free energy ofAl3Li and Mg5Al8 are lower than that of Al-2.14wt.%Li andAl-2.6wt.%Mg. And comparing with 1420 alloy, the electric field promotes the precipitation of Al3Li and restrains the precipitation of Mg5Al8.
The effect of an electric field on the mechanical properties and microstructure of Al–Li alloy containing Ce
Abstract The influence of an electric field on the tensile properties and microstructure of Al–Li alloy containing Ce is investigated. The ductility of the alloy is improved, but the strength has no change under the effect of an electric field (electric field treatment). Scanning Electron Microscopy (SEM) and TEM results show that the fracture mode is changed by the applied electric field; the subgrains become larger with the increase of the strength of the electric field, the volume fraction of δ ′ phase increases and its distribution is more random with an electric filed. The relation between the mechanical properties, and the microstructure of those alloys is analyzed. On the basis of experiment results, the mechanism of the effect of an electric field is discussed.
The Limits of Vulnerability in Explaining Fear of Crime: A Comparative Neighborhood Analysis
Recent research on the fear of crime in the United States has focused on the sources of fear. Many of these studies have identified neighborhood-level variables that are related to fear, but most have examined the differences in fear among individual residents of one or more cities. There has been substantially less research on the differences in the sources of fear among residents of different areas within a single city. This article examines the causes of fear through a comparative analysis of three different neighborhoods in San Francisco. An analysis of covariance model is used to assess the importance of differences in the sources of fear that may be associated with an individual's neighborhood of residence. The findings demonstrate that age, as a measure of physical vulnerability previously associated with fear among individuals, is not related to fear in neighborhoods where residents express the greatest general concern about crime. It is concluded that in those urban areas where crime problems are regular features of the neighborhood environment, measures of physical vulnerability are less important in predicting differences in fear among individuals.