Forced Motion of Solitons in the Field of a Pumping Wave

Exact solutions of the Landau – Lifshitz equation are found for a ferromagnet with the easy-axis anisotropy. These solutions describe the interaction of a nonlinear magnetization wave of arbitrary amplitude with solitons, such as breathers, solitary domains and domain walls. The change of the internal structure and physical parameters of the solitons caused by their interaction with the magnetization wave is analyzed. The conditions for the destruction of the solitons by the wave are obtained.

ASSEMBLY OF GAP JUNCTIONS DURING AMPHIBIAN NEURULATION

Sequential thin-section, tracer (K-pyroantimonate, lanthanum, ruthenium red, and horseradish peroxidase), and freeze-fracture studies were conducted on embryos and larvae of Rana pipiens to determine the steps involved in gap junction assembly during neurulation. The zonulae occludentes, which join contiguous neuroepithelial cells, fragment into solitary domains as the neural groove deepens. These plaque-like contacts also become permeable to a variety of tracers at this juncture. Where the ridges of these domains intersect, numerous 85-Å participles apparently pile up against tight junctional remnants, creating arrays recognizable as gap junctions. With neural fold closure, the remaining tight junctional elements disappear and are replaced by macular gap junctions. Well below the junctional complex, gap junctions form independent of any visible, preexisting structure. Small, variegated clusters, containing 4–30 particles located in flat, particle-free regions, characterize this area. The number of particles within these arrays increases and they subsequently blend together into a polygonally packed aggregate resembling a gap junction. The assembly process in both apical and basal regions conforms with the concept of translational movement of particles within a fluid plasma membrane.