Search Results - (Author, Cooperation:D. Stefanescu)

2015-11-07

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1365-2478

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

Physics

The authors generalize a method expounded in a previous paper (1971, Geoph. Prosp. 18, 786-799) to the case of a local conductivity σ(M) of the infinite medium satisfying the relation 〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00168025:GPR246:GPR_246_mu1"/〉 where the Ri's are the distances from the point M to n fixed points Si (i= 1,. n), k is a positive real constant and Ci, Cii are constants ensuring the condition α 〉 O.The sub-surface conductivity distributions (half-spaces) complying with (1) provide a wide variety of conducting structures, which can fit quite successfully the rather complicated distributions of conductivity occurring in natural ore bodies.An exact algebraic calculation of the apparent resistivity for these grounds, valid for any dc electrical prospecting devices (Wenner, Schlumberger, dipole, etc.) leads to a set of simultaneous linear equations, with a matrix which is invariant with respect to the position of the quadrupole being used. This greatly simplifies the numerical computation.We also present some examples of cross sections for the real and apparent resistivity obtained by this method.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The problem of maintaining the oxygen stoichiometry of the Y1Ba2Cu3Ox (the so-called 123) compound at the desired level of x=6.0±0.1 when fabricating superconducting wires using the powder-in-tube method is addressed. A solution to this problem appears to be incorporating an unstable oxide like Ag2O in the core material, such that it acts as an in situ oxygen donor during the final sintering or annealing stage. Moreover, the segregation of Ag at the grain boundaries of the 123 grains and at the porosities seems to be a possible reason for the considerable improvement of the critical current density Jc of these wires. The effect of processing parameters, like different sintering temperatures and addition of various percentages of either Ag or Ag2O, is presented. Finally, in order to test conservation of superconductive properties during handling, the wires were subjected to different degrees of bending, and the subsequent effect on superconducting transition temperature, Tc and Jc, is reported.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A fabrication technique for producing bulk and irregular-shaped aluminum/high Tc superconductor composites by traditional powder metallurgy method is reported. During the course of fabrication, the oxygen stoichiometry can be maintained at the desired level in order to retain superconductivity by addition of certain metal oxides or metal carbonates with low oxidation tendency, e.g., Ag2O, Ag2CO3, and CdO. Moreover, replacement of oxygen with fluorine is also possible by addition of certain unstable fluorides like AgF. Superconductivity measurements of Al/YBa2Cu3Ox random composites with additions of different oxygen or fluorine donors show a similiar or improved Tc in comparison to the pure 123 compound. The concept of oxygen/fluorine donor can also be used in other fabrication techniques of metal/123 composites to stabilize the oxygen/fluorine stoichiometry.

Electronic Resource

0165-4608

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Medicine

Electronic Resource

0165-4608

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Medicine

Electronic Resource