Non-local symmetries of first-order equations

It is shown how one can transform scalar first-order ordinarydifferential equations which admit non-local symmetries of theexponential type to integrable equations admitting canonicalexponential non-local symmetries. As examples we invoke theAbel equation of the second kind, the Riccati equation and naturalgeneralizations of these. Moreover, our method describes howa double reduction of order for a second-order ordinary differentialequation which admits a two-dimensional Lie algebra of generatorsof point symmetries can be affected if the second-order equationis first reduced in order once by a symmetry which does notspan an ideal of the two-dimensional Lie algebra.     

Magnon excitation by spin injection in thin Fe/Cr/Fe films

The technique of Brillouin light scattering is used to observe strong excitation of magnons in antiferromagnetically coupled trilayers of Fe/Cr/Fe at room temperature. The magnons are driven out of equilibrium by a microwave current applied in the trilayer through point contacts. The magnitude of the scattering intensity is investigated as a function of the magnon wave number and applied magnetic field. Confirming recent theoretical predictions, the observations provide strong evidence of electronic spin injection in the rf driving field.     

Particle size analysis: A comparison of various methods ii

In previous work, the relative performance of various methods used to characterize the particle size distribution of powders composed of fine irregularly shaped particles was assessed. It was found that methods employing Fraunhofer diffraction theory were inferior with respect to particle counting methods. Furthermore, calculated particle size distributions varied considerably between manufactures of Fraunhofer devices. It is well known that the Mie optical model can also be used to analyze the data collected by laser diffraction instruments. Here, we have compared particle size distributions collected using two Laser diffraction instruments to those determined by the Aerosizer. In our earlier work the Aerosizer was shown to produce results nearly identical to those determined by image analysis. The results of this study indicate that the use of the Mie optical model does not correct for deficiencies previously noted for laser diffraction methods. Considerable variation exists between the results obtained on laser diffraction instruments manufactured by different companies. Our earlier recommendation to use extreme caution when employing laser diffraction instruments to characterize fine powders continues to be supported in the present work.     

New Approach to the Study of Particle-Surface Adhesion Using Atomic Force Microscopy

The colloidal probe technique is commonly employed to determine the adhesion force between a particle and a solid surface. Characterization of the adhesion of a particle across a surface can be as important, if not more so, as the determination of an average value for the adhesion. Unfortunately, the measurement of the variation in adhesion can be difficult at best. A new approach for studying particle-surface adhesion based on the force-volume technique is presented. Upon combining the force-volume technique with a colloidal probe, not only is it possible to determine the average adhesion force, but an image of the spatial variation of the adhesion can also be obtained. This method is envisioned to have great potential for examining and analyzing the adhesion behavior in complex natural and technological systems. Copyright 2000 Academic Press.