Caroline Lambert

Temperature dependence of the resistivity in Au-YBa2Cu3Ox sintered composites

Abstract We combine experimental and numerical techniques to investigate the temperature dependence of the resistivity ρ in metal–superconductor (M─S) Au─YBa2Cu3Ox (Au─YBCO) sintered composites. The experimental data for ρ are studied as a function of the Au volume fraction φ. Below the superconductor critical temperature T < 92 K, a systematic shift of the M─S transition threshold φS is observed as T varies. Up to T = 200 K, the resistivity curves present a maximum. Both the amplitude of the maximum and the corresponding composition vary with T. Our experimental results are well described by a random conductor network model which incorporates porosity and interface resistances. The interface resistance computed from the model is consistent with a simple picture of local modifications of the oxygen concentration at the YBCO─YBCO and Au─YBCO contacts.

Low temperature resistivity of Au-YBa2Cu3O7-delta sintered materials: Influence of porosity and secondary phases

The resistivity rho of sintered Au and YBa2Cu3O7-delta(Au and YBCO) mixed powders is measured at T = 60K, as a function of the gold volume fraction phi . The samples retain zero resistivity up to phi = phi c = 0.62. In the range phi [phi c, 1], the curve rho (phi) is bell-shaped, with a maximum at phi 0.75. Scanning electron microscopy observations suggest that the increase of resistivity can be attributed both to porosity and to secondary phases inducing contact resistances between YBCO and Au grains. A random conductor network model is used to test the relative influence of both parameters. The numerical data show that porosity alone cannot account for the resistivity maximum. Conversely, a peak is indeed observed in the simulations when a substantial interface resistivity is imposed.

IDENTITY AND REFLEXIVITY IN RESEARCH ON WOMEN ACCOUNTANTS.

The article analyzes stories which purport to explain the dearth of women in top management positions in the field of accounting. The four explanations discussed include the lack of experienced candidates, characteristic differences of women from men, organizational obstacles, and prejudice. It is said that none of these separate reasons can wholly account for the scarcity of top-level female executives in accounting. The combination of social with organizational barriers is presented as a more accurate explanation.