Ferromagnetic shape memory alloys with a body-centered-cubic ordered structure in a Ni–Ga–Fe system have been developed. The alloys with the composition range of Ni 27 at. % Ga (20–22 at. %)Fe exhibit a thermoelastic martensitic transformation from a B2 and/or an L21 parent to a martensite phase, with a seven-layer modulated (14M) and a five-layer modulated (10M) structure, in the ferromagnetic state. The parent phase transforms from the B2 to the L21 structure at about 970 K during cooling, and the degree of the L21 order in the parent phase is increased by annealing at 773 K, resulting in the increase of both the martensite starting and the Curie temperatures. The ductility of these alloys is improved by introducing of a small amount of a γ-phase solid solution. Consequently, we can conclude that the present alloys are promising for ferromagnetic shape memory alloys.

No abstract

The martensitic and magnetic transitions of Ni 54 Ga 27 Fe 19 alloy were investigated by differential scanning calorimetry and X-ray powder diffraction and with a vibrating sample magnetometer. The alloy is martensitically transformed from a L2 1 to a martensite phase with a 14M (7R) structure. The ferromagnetic transition is also accompanied by the martensitic transformation from a paramagnetic parent phase to a ferromagnetic martensite phase in the temperature interval between M s (= 293 K) and M f (= 274 K). The Ni-Ga-Fe system is promising as a ferromagnetic shape memory alloy.

The effects of the introduction of the (A1) phase into the (B2) phase on the mechanical and shape memory properties in ferromagnetic Co-Ni-Al shape memory alloys with the þ two-phase structure were investigated by cold-rolling, tensile tests, and bending tests. The mechanical properties were found to be improved with an increase in the volume fraction of the phase, and Co-33 at%Ni-26 at%Al alloy with V ¼ 36% exhibited excellent cold workability with a critical reduction ratio of 40%. Although the degree of shape recovery decreases with an increase in the volume fraction of the phase, it can be enhanced by training. Since two-phase þ Co-Ni-Al alloys have several advantages such as cost efficiency and workability, this alloy system is considered as being a new type of ferromagnetic shape memory alloys (FSMAs).

No abstract

The majority of thymocytes die in the thymus, whereas small populations of T cells that are able to specifically recognize an antigen are considered to survive. Although the thymic selection is thought to have a profound effect on T‐cell receptor (TCR) repertoire, little is known how TCR repertoire is formed during the thymocyte developmental process. We examined TCRα‐ and β‐chain variable regions (TCRAV and TCRBV) repertoire in thymic T‐cell subpopulations from mice bearing different major histocompatibility (MHC) haplotypes. In Balb/c mice, but not C57BL/6, remarkable alterations of the TCR repertoire were observed in mature T‐cell subpopulations as previously reported. In contrast, there were no significant differences of TCRBV repertoire between DN3 (CD25+CD44−) and DN4 (CD25−CD44−), and between DN4 and DP. These results suggest that (1) TCR repertoire of mature T cells was formed mainly under the influence of endogenous superantigens, while MHC haplotypes played the least role; (2) the ‘β‐selection’ process during immature stages had little impact on TCRBV repertoire formation; and (3) TCR repertoire in immature T‐cell subpopulations was extremely similar between different strains of mice. We thus consider that pre‐selection TCR repertoire in immature T cells could be determined by some genetic factors conserved among different strains.

The liver is a major site of generation of extrathymic T cells with unique properties (e.g., expressing intermediate TCR and containing self-reactive clones). We investigated herein whether the levels of extrathymic alpha beta T cells varied in various organs as a function of age. A systematic examination of the number of mononuclear cells in various organs of BALB/c mice revealed that the number of hepatic MNC increased with age whereas the number of thymocytes decreased. These changes were more striking in mice fed under conventional conditions than under specific pathogen-free condition. The age-dependent changes in the number of mononuclear cells in the spleen and lymph nodes were minimal. Although the total proportion of alpha beta T cells in each organ remained constant, the staining patterns of TCR-alpha beta as shown by immunofluorescence profiles varied. The most prominent change was that intermediate TCR-alpha beta cells, which constituted a small population in the liver of young mice, expanded in the liver of older mice. Intermediate TCR cells appeared even in the periphery of older mice. These findings were confirmed by the appearance of extrathymic T cells with other unique properties, e.g., double-negative CD4-8- phenotype and CD44 expression. In athymic nude mice, only intermediate TCR cells were present in the liver and periphery. An age-dependent increase of intermediate TCR cells was also seen in these mice. Taken together with the result of bromodeoxyuridine-injection experiment, which showed an intensive in vivo proliferation of cells in the hepatic sinusoids, extrathymic T cells may differentiate predominantly in the liver and appeared even to the periphery in older mice.

No abstract