Direct structure inversion from exit waves: Part I: Theory and simulations

In order to interpret the amplitude and phase of the exit wave in terms of mass and position of the atoms, one has to “invert” the dynamic scattering of the electrons in the object so as to obtain a starting structure which can then be used as a “seed” for further quantitative structure refinement. This is especially challenging in case of a zone axis condition when the interaction of the electrons with the atom column is very strong. Based on the channelling theory we will show that the channelling map not only yields a circle on the Argand plot but also a circular “defocus curve” for every column. The former gives the number of atoms in each column, while the latter provides the defocus value for each column, which reveals the surface roughness at the exit plane with single atom sensitivity.     

Mechanical testing machine stiffness : Part II—Application to data reduction

It is shown how mechanical testing machine stiffness can be used in the reduction of load-time. data to stress and strain, for constant crosshead-speed machines and for constant strain-rate machines. This technique, of explicitly calculating values of machine stiffness and using these values in data reduction, is compared to the frequently used method of measuring offset times, from the initial slope line of the load-time trace, and using these times to calculate points on a stress-strain curve. The differences between the two methods are small unless the change of machine stiffness during a test may be determined. When this is possible—and tests can nearly always be conducted so that it is possible—the technique in this work is superior to earlier, approximate methods. It is superior in accuracy of data reduction and in the fact that strain rates for all data points are more accurately calculated.