Coercivity of single-domain nickel wires

The coercivity H_c of compacts of thin (0.1?5 μ diameter) nickel wires embedded in a silver matrix has been measured as a function of the effective wire radius d_eff. H_c increases linearly with 1/d_eff², in agreement with Aharoni's theory of magnetization reversal by curling. From the slope, δH_{c/gd (deff^?2)}, upper and lower bounds for the exchange constant A of Nickel have been derived (77K): 1.5 × 10^?11 Wsec/m ? 3.0 × 10^?11 Wsec/m.     

Eine topologische Kennzeichnung des Ordnungsduals eines Vektorverbandes

Ohne Zusammenfassung     

Detection of lueders' lines by means of brittle coating

Use is made of an improvement of Durelli, Kobayashi and Hofer's method¹ for the detection of Lueders' lines by means of brittle coating. The precision of the method is evaluated by using Fry's etching method in comparison. The propagation of Lueders' lines by increments in notched tensile bars is shown. From a comparison with information contained in literature as regards the propagation of Lueders' lines, it results that the well-known theories of elasticity and plasticity predict the propagation of the Lueders' lines in a qualitatively correct way only in special cases. The technical importance of applying the described brittlecoating method is pointed out.