Ti-V System Research Articles

Phase transformations in the Ti-V system under high pressure up to 25 GPa

Polycrystalline samples of pure Ti and Ti-V alloys containing 2.8, 7.6, 11.4, 20, 25, 35, 40 and 50 atomic percent V were investigated up to ~ 25 GPa at ambient temperature using a diamond anvil pressure cell and X-ray diffraction techniques. The X-ray data show that for alloys with less than ~ 30% V, the hexagonal ω phase is more stable under high pressure conditions than the h.c.p. α phase and the b.c.c. β phase. For alloys with higher V content (> ~ 30%), however, no ω phase was detected. The transformation pressure for the α → ω + α transition decreases gradually with increasing V content whereas for the β → ω + β transition, it increases exponentially. The pressure-induced ω phase obtained in the Ti-V system has an axial ratio c o a o of 0.6105 ± 0.0015, which is about 0.3% lower than the value (0.612) reported for thermally treated ω phases. The pressure-induced ω phase has a smaller volume than the corresponding β and a phases. Thus the relationships a ω = √2 a β and c ω = ( √3 2 ) a β , which hold very well for thermal ω phases, do not hold for the pressure-induced ω phase.

Ti-V系における2相分離

Ti-V系における2相分離

The Tiv System of Election

The Tiv System of Election

A Genealogical Charter

Opening ParagraphThe Tiv of Northern Nigeria, who number some 800,000, believe that they are all descended from one man, Tiv, through some 14 to 17 generations of known ancestors (Fig. 1). These ancestors are constantly named in casual conversation and in discussion of serious affairs. To understand things Tiv one must know Tiv genealogies. By genealogical reference a Tiv traces ties of kinship and marriage, claims a place to live and farm, argues his case in a moot, conducts matters of magic and ritual, and decides against whom he will fight on any given occasion. Genealogies are the key to Tiv social organization. Tiv political structure is based on a lineage system: a system of segmented groups in which each segment (save the maximal) is included in a segment of a higher order but of the same kind, and each segment (save the minimal) includes segments of a lower order but of the same kind. The Tiv system has an almost one to one correlation between lineage and territorial segments. Both are called ‘those of X’, the eponymous ancestor; thus Mbaduku (those of Aduku) describes both the lineage segment (ipaven, pl. uipaven) and the discrete territory which they inhabit (tar, pl. utar).