Narrow Overlap Research Articles

Pratylenchus Pinguicaudatus N. Sp. (Pratylenchinae: Nematoda) With a Key To the Genus Pratylenchus

Pratylenchus pinguicaudatus n. sp., associated with wheat at Rothamsted, is distinguished from other Pratylenchus species by having three head annules, no males, a long narrow oesophageal overlap and a broadly rounded smooth tail tip. A key is given separating 36 species in the genus.

Change in Fermi Surfaces of Graphite by Dilute Acceptor Doping

The effect of doping graphite single crystals with the acceptor boron was studied in the dilute range from ≲0.1 pprn to 0.5% by measurements of the Hall effect and de Haas - van Alphen effect. The transition from a mixed electron and hole conduction in the narrow band overlap region (0.035 eV) to that of a single hole conduction produces a peak in the Hall coefficient that shifts to a lower boron concentration with a decrease in temperature. The increase in hole concentration is accompanied by a rapid decrease in mobility, demonstrating the importance of collision broadening. Preliminary de Haas - van Alphen results tentatively identify the major electron and hole Fermi surfaces by means of the period shift with increasing acceptor concentration. A new, very small ellipsoid-like Fermi surface was discovered. It is aligned along the hexagonal axis, having an anisotropy ratio of 9 with orbital masses of about 0.0023 m0 for H || C and 0.017 m0 for H | C. Analysis strongly indicates that this surface contains minority holes. Three of these surfaces are considered to be aligned symmetrically like outriggers about the major hole surface, producing a total of six in the Brillouin zone. A comparison is made with the cyclotron resonance results and a possible interpretation of these minority Fermi surfaces is presented using the Slonczewski-Weia band model.

Some peculiarities of spatially and sexually restricted gene exchange in the Erebia tyndarus group.

The butterfly genus Erebia contains about 70 species widely distributed in mountainous areas of the Holarctic region. Their occasional restriction to small areas, often in close proximity to each other, makes this genus a suitable subject for studies of relationships between the geographical and genetical isolation of populations. However, till now, its advantages in this respect remained unexplored. In this paper a short review of my studies of the Erebia tyndarus group will be given, especially in connection with restricted gene exchange in the zones of contact or narrow overlap belts between very closely related units, where some unexplained relationships were found. Likewise unexpected genetical relationships were also detected between widely separated groups which, owing to their allopatry and slight morphological differences, are difficult to estimate taxonomically, a common trouble with the systematics of allopatric populations.