Reply Comment: Comparison of Approaches to Classical Signature Change

We contrast the two approaches to ``classical" signature change used by Hayward with the one used by us (Hellaby and Dray). There is (as yet) no rigorous derivation of appropriate distributional field equations. Hayward's distributional approach is based on a postulated modified form of the field equations. We make an alternative postulate. We point out an important difference between two possible philosophies of signature change --- ours is strictly classical, while Hayward's Lagrangian approach adopts what amounts to an imaginary proper ``time" on one side of the signature change, as is explicitly done in quantum cosmology. We also explain why we chose to use the Darmois-Israel type junction conditions, rather than the Lichnerowicz type junction conditions favoured by Hayward. We show that the difference in results is entirely explained by the difference in philosophy (imaginary versus real Euclidean ``time"), and not by the difference in approach to junction conditions (Lichnerowicz with specific coordinates versus Darmois with general coordinates).Comment: 10 pages, latex, no figures. Replying to - "Comment on `Failure of Standard Conservation Laws at a Classical Change of Signature'", S.A. Hayward, Phys. Rev. D52, 7331-7332 (1995) (gr-qc/9606045

Note on Signature Change and Colombeau Theory

Recent work alludes to various `controversies' associated with signature change in general relativity. As we have argued previously, these are in fact disagreements about the (often unstated) assumptions underlying various possible approaches. The choice between approaches remains open.Comment: REVTex, 3 pages; to appear in GR

(13)C NMR investigation of the superconductor MgCNi_3 up to 800K

We report (13)C NMR characterization of the new superconductor MgCNi_3 (He et al., Nature (411), 54 (2001)). We found that both the uniform spin susceptibility and the spin fluctuations show a strong enhancement with decreasing temperature, and saturate below ~50K and ~20K respectively. The nuclear spin-lattice relaxation rate 1/(13)T_1T exhibits typical behaviour for isotropic s-wave superconductivity with a coherence peak below Tc=7.0K that grows with decreasing magnetic field.Comment: Accepted for publication in Physical Review Letter

BOUNDARY CONDITIONS FOR THE SCALAR FIELD IN THE PRESENCE OF SIGNATURE CHANGE

We show that, contrary to recent criticism, our previous work yields a reasonable class of solutions for the massless scalar field in the presence of signature change.Comment: 11 pages, Plain Tex, no figure

Challenge

This is my last Challenge article as I retire from active duty in the Navy as of 1 September. It has been 43 years since I raised my right hand and took the oath to enlist in the Navy. It is a strange quirk of fate that it all began here in Newport, for I arrived here for recruit training on the old Fall River liner Priscilla. It will all end here almost a half a century later

President\u27s Notes: Challenge!

The past is not dead. It survives in many forms taken for granted — in laws, customs, institutions, and beliefs. Though often intangible, these provide an environment real as the physical world

A Statement By The President of the Naval War College Upon Assumption of Command

Because the Naval War College is a graduate institution, it is not, and should not be, simply an establishment which exists to dis­seminate facts and preconceived ideas. It is, and must continue to be, an institution which is dynamic and sensitive to the rapidly changing world scene

Challenge

It is recognized throughout the Navy that many officers may not have the opportunity to attend a Naval War College resident course because of career requirements or high priority operational assignments, Concurrently, a burgeoning demand for professional excellence makes this advanced education essential