Asymmetric Specimens Research Articles

Biometric Characteristics of the Three-Spined Stickleback (Gastetosteus aculeatus L.) from the Northern Baltic Proper

Three-spined sticklebacks from the northern Baltic proper, caught in 1968 and 1969, were examined with regard to number of plates, body length, head length in relation to body length, and the percental proportions of the forms trachurus, leiurus (=gymnurus), and semiarmatus. A total number of 1791 specimens were examined. It is shown that the number of asymmetric specimens, regarding the number of plates on the right and left side of the body, is higher than numbers shown earlier, and that there is a significant difference in relative head length between females and males, and, that smaller fish displayed proportionally longer heads than adults. Semiarmatus specimens accounted for about 80 per cent of the samples and only 2 leiurus specimens were found.

The occurrence of glissile Shockley loops in field-ion specimens of iridium

Abstract The paper describes observations of faulted loops with Burgers vector of the α/6〈112〉 type in iridium field-ion specimens. The densities observed in some specimens are as high as 1018 loops per cm3. The occurrence of these loops is related to fracture of the specimens and specimen asymmetry. It is suggested that the high shear stresses operating on a field-ion specimen during imaging and evaporation homogeneously nucleate glissile Shockley loops. In some cases the intersection of these loops leads to a crack nucleus and then to fracture. The presence of some image streaks in asymmetric specimens is shown to be related to the presence of faults, produced by shear, intersecting the surface.

Streak contrast in field-ion images from asymmetric specimens

Abstract Among several kinds of image streaking observed in field-ion micrographs a particular type is attributed to asymmetric specimens (Ranganathan et al. 1965). Brandon (1966) has proposed a model for this type of streaking which has been further discussed by Ralph and Bowkett (1966). Electron micrographs of asymmetric specimens show that the streak contrast in the field-ion image is often associated with surface irregularities introduced by the electrochemical specimen preparation.

Streak contrast in field-ion micrographs

Abstract Field-ion micrographs of asymmetric specimens show a particular type of image streaking (Ranganathan et al. 1965). A model of this type of streaking has been proposed (Brandon 1966). This model is considered in the light of the observed nature of streaks in asymmetric images and it is concluded that while the model accounts for some specific streaks it is not generally applicable.