The binding energy of hydrogenic impurites in a quantum well wire has been calculated as a function of the width of the quantum well wire and the location of the impurity with respect to the axis of the wire. The calculations have been preformed using a variational wave function which takes into account the confinement of the carriers in the wire. For the confining potential used in our calculations, we have used the models of either an infinite potential well or a finite potential well whose depth is detemined by the discontinuity of the band gas in the quantum well wire and the cladding. For the infinite potential well model, the binding energy continues to increase as the radius of the wire decreases while in the finite potential well model, the binding energy reaches a peak value as the wire radius decreases and then decreases to a value characteristic of the cladding. The binding energy also depends upon the location of the impurity in the wire and is a maximum when the impurity is located on the axis of the wire.

No abstract

No abstract

Insectivorous bat embryos (Tadarida and Myotis) ranging from 6- to 16-mm C-R length were examined for the presence of the nervus terminalis. These embryos have no vomeronasal nerve with which the nervus terminalis could be confused. The nerve and associated ganglion cells first appear in the 7-mm embryo. As the embryo ages, a gradual increase in nerve size and ganglion cell numbers occurs. In the 13-mm embryo, nerve size and ganglion cell numbers are reduced, and in older embryos both nerve and cells are absent, as in the adult. The ganglion cells arise as clusters from the nasal septal epithelium. The largest number of cell clusters occurs in the 10.5-mm embryo. Their number then decreases and none are present in embryos of 13-mm and longer. These cells migrate centrally along the course of the nerve which accompanies the olfactory nerve from the nasal cavity roof to a level just caudal to the olfactory bulb, where the nervus terminalis turns dorsalward along the medial telencephalic wall surface. Except in the youngest and oldest embryos the nervus terminalis, where present, divides into two or three branches to pierce the hemispheric wall, one usually entering the region of the nucleus olfactorious anterior, and the other(s), the region of the medial septal nucleus. In some cases, several ganglion cells are present along the intrahemispheric course of the nerve fibers. All ganglion cells resemble those in various sensory ganglia, and so, are probably also sensory neurons.

The ontogenetic development of the nucleus ambiguus was studied in a series of human embryos and fetuses ranging from 3 to 12.5 weeks of menstrual age (4 to 66 mm crown-rump length). They were prepared by Nissl and silver methods. Nucleus ambiguus neuroblasts, whose neurites extend towards and into the IXth and rostral Xth nerve roots, appear in the medial motor column of 4-6-week-old embryos (4.25-11 mm). These cells then migrate laterally (6.5 weeks, 14 mm) to a position near the dorsal motor nucleus of X. At 7 weeks (15 mm), nucleus ambiguus cells begin their migration, which progresses rostrocaudally, into their definitive ventrolateral position. The basic pattern of organization of the nucleus is established in its rostral region at 8 weeks (22.2-24 mm) and extends into its caudal region by 9 weeks (32 mm), when its nearly adult organization is evident. Cells having the characteristics of mature neurons first appear rostrally in the nucleus during the 8.5-9-week period (24.5-32 mm), gradually increase in number, and constitute the entire nucleus at 12.5 weeks (65.5 mm). Definitive neuronal subgroups first appear at 10 weeks (37.5 mm) in the large rostral nuclear region. These features suggest that the human nucleus ambiguus develops along a rostrocaudal temporospatial gradient. Evidence indicates that function of nucleus ambiguus neurons, manifested by fetal reflex swallowing, occurs after the cells migrate into their definitive position, establish the definitive nuclear pattern, and exhibit mature characteristics.