Electron-optical imaging instruments like Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) use specially designed solenoid electromagnets for focusing of electron beam probe. Indicators of imaging performance of these instruments, like spatial resolution, have strong correlation with focal characteristics of the magnetic lenses which in turn have been shown to be functions of the spatial distribution of axial magnetic field generated by them. Owing to complicated design of practical lenses, empirical mathematical expressions are deemed convenient for use in physics based calculations of their focal properties. So, degree of closeness of such models to the actual field distribution determines accuracy of the calculations. Mathematical models proposed by Glaser[1] and Ramberg[1] have historically been put into extensive use. In this paper the authors discuss one such model with secant-hyperbolic type magnetic field distribution function, and present a comparison among these models, with results from finite element based field simulations as reference.
A composite of copper powder reinforced with SiCp (0-10 wt%) in which aluminum powder of ( 2 wt%) was added for improving wettability of the ceramie phase. . The composite mixture was prepared by mixing with a ball mill for one hour to ensure a homogenous distribution on the composite .Gteen compacts pressed at (350MPa) a steel mold of (12mm)diameter were then sintered at (900 °C) for two hours in an electric furnace, in argon atmosphere . Optical microscopy, Density, porosity content and Vicker's hardness test were then conducted for the sintered samples.Obviously, it was concluded that there was enhancement of the physical and mechanical (hardness) properties of the sintered compacts with increasing the SiC content.
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