No abstract

Spin-wave resonance has been observed at 9 GHz in thin films of Ni-Co alloys containing between 0 and 40% CO at temperatures between 4.2 K and room temperature.The dispersion relationship, critical angle, linewidth and annealing results suggest that the surface spins are pinned by a surface layer about l00A thick. The exchange stiffness constant D is found to have a value about a quarter of that obtained by other methods, namely approximately 100 meV A2.

We consider the polarization of unstable type-IIB D0-branes in the presence of a background five-form field strength. This phenomenon is studied from the point of view of the leading terms in the non-abelian Born Infeld action of the unstable D0-branes. The equations have SO(4) invariant solutions describing a non-commutative 3-sphere, which becomes a classical 3-sphere in the large-N limit. We discuss the interpretation of these solutions as spherical D3-branes. The tachyon plays a tantalizingly geometrical role in relating the fuzzy S 3 geometry to that of a fuzzy S 4 .

The possible applications of double phase conjugation effect (DPC) such as optical computing, image processing and so on attracted investigators last few years. The realization of DPC was successfully fulfilled in photorefractive crystalls [1]. Meanwhile DPC in nonlocal responce media is seemed to be desirable due to considerable nonlinearities of some of such media. In addition these media are more available. However, when reflected waves were otained in experiments they were not phase conjugated [2]. In this work we treat conditions of phase conjugated wave generation in nonlocal responce medium.

Illinois 601 15. USC M S . received 14th M a y 1970Ahtract. Starting from bare-ion pseudopotentials, net crystal potentials are evalutiied in direct space by (a) the usual linear screening technique and (b) the Thomas-Fermi method. For the metals considered (Na and AI), the potentials are quite similar, crossing outside the cores and never differing by more than 0.02 a.u. in the case of Na nor by more than 0.2 a.u. in the case of Al. The similarity of the results based on (a) and (b) suggest the use of the pseudopotential concept in conjunction with the rather general method (b) under conditions when (a) is questionable, that is whenever the zeroth order uniform electron gas solution is a poor physical approximation to the actual system under study (specific examples being molecules, insulating solids and interfaces).Methods (a) and (bj both yield shallower wells than those most often used as input information in band structure calculations and obtained by superposing atomic data.