In the last decade or so, a considerable amount of interest has been shown in the studies of the optical systems in the presence of various orders of spherical aberrations. Barakat [ 11 has derived formulae for the evaluation of the modulation transfer function (MTF) of a circular aperture in the presence of rotationally symmetrical aberrations. Barakat and Morello [2] have given methods for calculating the MTF for various orders of spherical aberration. Barakat and Houston [3] have studied the MTF of a slit aperture in the presence of optimum balanced third and fifth order spherical aberration. Barakat 141 has given numerical results for the MTF of a circular aperture in the presence of fifth order spherical aberration. The case of an annular aperture in the presence of third and fifth order spherical aberration has been treated by Barakat and Houston [5]. The MTF of the systems in the presence of seventh order spherical aberration corresponding to Strehl criterion has been studied by Keprt [6]-[8].
The technique of neutron polarisation analysis has been used to examine the broad 'central' peak in paramagnetic praseodymium. Measurements over the temperature range 1.2-25 K show that these peaks, observed at reciprocal space positions (Ql, 0,2m + 1) with Ql = 0.11 SI^, are entirely magnetic in character. The relationship between these shortrange magnetic correlations and the long-range antiferromagnetic ordering process is discussed.
The arrangement of atoms in a β-tin crystal lattice is studied. Interplanar spacings between lattice planes and the minimum atomic distances in glide are calculated. Geometrical approaches are carried out on the stacking of lattice planes and the atomic arrangement of jogs which are produced by intersection of dislocations or emission of vacancies. The results are discussed in connection with the reported slip systems and the observed phenomena in plastic deformation. Elastic interaction between a slip and a forest dislocation is studied, and the force exerted on each part of the slip dislocation and the total force are calculated for every combination of relative locations and Burgers vectors of both dislocations.
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