Spacetime deployments parametrized by gravitational and electromagnetic fields

On the basis of a "Punctual" Equivalence Principle of the general relativity context, we consider spacetimes with measurements of conformally invariant physical properties. Then, applying the Pfaff theory for PDE to a particular conformally equivariant system of differential equations, we make explicit the dependence of any kind of function describing a "spacetime deployment", on n(n+1) parametrizing functions, denoting by n the spacetime dimension. These functions, appearing in a linear differential Spencer sequence and determining gauge fields of spacetime deformations relatively to a "substrat spacetime", can be consistently ascribed to unified electromagnetic and gravitational fields, at any spacetime dimensions n greater or equal to 4.Comment: 26 pages, LaTeX2e, file macro "suppl.sty", correction in the definition of germs and local ring

Smooth leading edge transition in hypersonic flow

The boundary layer transition along the attachment line of a smooth swept circular cylinder in hypersonic flow is investigated in a blowdown wind tunnel. A wide range of spanwise Mach numbers Me (3.28 to 6.78) is covered with the help of different models at several sweep angles (60 degrees less than or equal to Lambda less than or equal to 80 degrees). The transition is indirectly detected by means of heat flux measurements. The influence of the wall to stagnation temperature ratio is investigated by cooling the model with liquid nitrogen

Josephson Effect through an isotropic magnetic molecule

We investigate the Josephson effect through a molecular quantum dot magnet connected to superconducting leads. The molecule contains a magnetic atom, whose spin is assumed to be isotropic. It is coupled to the electron spin on the dot via exchange coupling. Using the numerical renormalization group method we calculate the Andreev levels and the supercurrent and examine intertwined effect of the exchange coupling, Kondo correlation, and superconductivity on the current. Exchange coupling typically suppresses the Kondo correlation so that the system undergoes a phase transition from 0 to $\pi$ state as the modulus of exchange coupling increases. Antiferromagnetic coupling is found to drive exotic transitions: the reentrance to the $\pi$ state for a small superconducting gap and the restoration of 0 state for large antiferromagnetic exchange coupling. We suggest that the asymmetric dependence of supercurrent on the exchange coupling could be used as to detect its sign in experiments

Phonon-mediated negative differential conductance in molecular quantum dots

Transport through a single molecular conductor is considered, showing negative differential conductance behavior associated with phonon-mediated electron tunneling processes. This theoretical work is motivated by a recent experiment by Leroy et al. using a carbon nanotube contacted by an STM tip [Nature {\bf 432}, 371 (2004)], where negative differential conductance of the breathing mode phonon side peaks could be observed. A peculiarity of this system is that the tunneling couplings which inject electrons and those which collect them on the substrate are highly asymmetrical. A quantum dot model is used, coupling a single electronic level to a local phonon, forming polaron levels. A "half-shuttle" mechanism is also introduced. A quantum kinetic formulation allows to derive rate equations. Assuming asymmetric tunneling rates, and in the absence of the half-shuttle coupling, negative differential conductance is obtained for a wide range of parameters. A detailed explanation of this phenomenon is provided, showing that NDC is maximal for intermediate electron-phonon coupling. In addition, in absence of a gate, the "floating" level results in two distinct lengths for the current plateaus, related to the capacitive couplings at the two junctions. It is shown that the "half-shuttle" mechanism tends to reinforce the negative differential regions, but it cannot trigger this behavior on its own

Adaptive Optics: introduction to the feature issue

This Applied Optics feature issue is a companion to the Journal of the Optical Society of America A feature issue on the same topic. The feature highlights the expansion of adaptive optics to different applications as well as its development to routine applications brought about because of significant advances in component technologies