INTRODUCTIONIndividuals of the Antarctic krill Euphausia superba Dana assemble in spring into dense formations (estimated 20,000 m3) which swim for long distances and at considerable speed (estimated 20 cm s−1) to search for patches of phytoplankton (Hamner, 1984). Recruitment to schools and maintenance of a defined position in a travelling formation, a remarkable social behaviour, requires some kind of communication system between individuals.Vision, as a sophisticated image-processing system, habituating strongly with time, appears inappropriate for the task of continuously monitoring position in the formation. This is not in contradiction of the fact that the prominent eyes of Euphausia orient the shrimp with respect to the axis of light coming from above, and direct the photophores 180° away from light (Land, 1980). The function of the photophores is only partially explained (e.g. predator avoidance by counter-shading, Grinnell et al., 1988), their role in formation swimming being doubtful because they are reportedly active only during dawn and dusk. Of course the eyes help Euphausia to assemble in schools and to evade predators (Strand & Hamner, 1990) as well as fishing nets (Everson & Bone, 1986a,b), but a simple mechanical reflex seems more suitable to control individual position in the formation.

The point defects in β-iron disilicide (β-FeSi2) have been investigated by electron paramagnetic resonance (EPR) along with the thermoelectric properties. The samples used are FeSix (1.9≤x≤2.8) ceramics sintered with FeSix micrograins processed in SiH4-plasma and nonprocessed. EPR detects (1) several S=1/2 signals and (2) a multiplet signal. An S=1/2 signal with orthorhombic g factors (g1=2.061, g2=2.047, g3=2.024) is detected in all n-type specimens, and ascribed to unpaired electrons of donors associated with iron vacancies. The other S=1/2 signals are detected in both n-type and p-type specimens. The centers responsible for these signals are considered to exist in an oxidized intergrain region of the ceramics. The EPR intensity of the multiplet signal due to the closed-pair of a high spin Fe3+ ion (S=5/2) and an S=1/2 center is reduced by SiH4-plasma treatments. SiH4-plasma processing of FeSix micrograins prior to sintering changes the Seebeck coefficient sign and magnitude, depending upon the condition of plasma processing. This Seebeck change is explained in terms of the introduction of silicon- and/or iron-vacancies. SiH4-plasma processing increases the electrical conductivity of nearly stoichiometric specimens and reduces the EPR intensity of the multiplet signal. A possible model for the increased conductivity is discussed using an energy band model for the ceramic grains and grain boundaries. We consider that the change of the thermoelectric properties by SiH4-plasma processing is mainly due to the modification of defects in and near the ceramic intergrain region.

To assess development changes in kinetic properties of the cardiac sodium current, whole-cell voltage-clamp experiments were conducted using 3-, 10-, and 17-day-old embryonic chick ventricular heart cells. Experimental data were quantified according to the Hodgkin-Huxley model. While the Na current density, as examined by the maximal conductance, drastically increased (six- to seven-fold) with development, other current - voltage parameters remained unchanged. Whereas the activation time constant and the steady-state activation characteristics were comparable among the three age groups, the voltage dependence of the inactivation time constant and the steady-state inactivation underwent a shift in the voltage dependence toward negative potentials during embryonic development. Consequently, the steady-state (window current) conductance, which was sufficient to induce automatic activity in the young embryos, was progressively reduced with age.

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