Interaction of Close-in Planets with the Magnetosphere of their Host Stars I: Diffusion, Ohmic Dissipation of Time Dependent Field, Planetary Inflation, and Mass Loss

The unanticipated discovery of the first close-in planet around 51 Peg has rekindled the notion that shortly after their formation outside the snow line, some planets may have migrated to the proximity of their host stars because of their tidal interaction with their nascent disks. If these planets indeed migrated to their present-day location, their survival would require a halting mechanism in the proximity of their host stars. Most T Tauri stars have strong magnetic fields which can clear out a cavity in the innermost regions of their circumstellar disks and impose magnetic induction on the nearby young planets. Here we consider the possibility that a magnetic coupling between young stars and planets could quench the planet's orbital evolution. After a brief discussion of the complexity of the full problem, we focus our discussion on evaluating the permeation and ohmic dissipation of the time dependent component of the stellar magnetic field in the planet's interior. Adopting a model first introduced by C. G. Campbell for interacting binary stars, we determine the modulation of the planetary response to the tilted magnetic field of a non-synchronously spinning star. We first compute the conductivity in the young planets, which indicates that the stellar field can penetrate well into the planet's envelope in a synodic period. For various orbital configurations, we show that the energy dissipation rate inside the planet is sufficient to induce short-period planets to inflate. This process results in mass loss via Roche lobe overflow and in the halting of the planet's orbital migration.Comment: 47 pages, 12 figure

Microwave scattering and emission properties of large impact craters on the surface of Venus

Many of the impact craters on Venus imaged by the Magellan synthetic aperture radar (SAR) have interior floors with oblique incidence angle backscatter cross sections 2 to 16 times (3 dB to 12 dB) greater than the average scattering properties of the planet's surface. Such high backscatter cross sections are indicative of a high degree of wavelength-scale surface roughness and/or a high intrinsic reflectivity of the material forming the crater floors. Fifty-three of these (radar) bright floored craters are associated with 93 percent of the parabolic-shaped radar-dark features found in the Magellan SAR and emissivity data, features that are thought to be among the youngest on the surface of Venus. It was suggested by Campbell et al. that either the bright floors of the parabolic feature parent craters are indicative of a young impact and the floor properties are modified with time to a lower backscatter cross section or that they result from some property of the surface or subsurface material at the point of impact or from the properties of the impacting object. As a continuation of earlier work we have examined all craters with diameters greater than 30 km (except 6 that were outside the available data) so both the backscatter cross section and emissivity of the crater floors could be estimated from the Magellan data

Self-recording portable soil penetrometer

A lightweight portable penetrometer for testing soil characteristics is described. The penetrometer is composed of a handle, data recording, and probe components detachably joined together. The data recording component has an easily removed recording drum which rotates according to the downward force applied on the handle, and a stylus means for marking the drum along its height according to the penetration depth of probe into the soil

Artificial neural network prediction of weld distortion rectification using a travelling induction coil

An experimental investigation has been carried out to determine the applicability of an induction heating process with a travelling induction coil for the rectification of angular welding distortion. The results obtained from experimentation have been used to create artificial neural network models with the ability to predict the welding induced distortion and the distortion rectification achieved using a travelling induction coil. The experimental results have shown the ability to reduce the angular distortion for 8 mm and 10 mm thick DH36 steel plate and effectively eliminate the distortion on 6 mm thick plate. Results for 6 mm plate also show the existence of a critical induction coil travel speed at which maximum corrective bending occurs. Artificial neural networks have demonstrated the ability to predict the final distortion of the plate after both welding and induction heating. The models have also been used as a tool to determine the optimum speed to minimise the resulting distortion of steel plate after being subjected to both welding and induction heating processes

Resistive flow in a weakly interacting Bose-Einstein condensate

We report the direct observation of resistive flow through a weak link in a weakly interacting atomic Bose-Einstein condensate. Two weak links separate our ring-shaped superfluid atomtronic circuit into two distinct regions, a source and a drain. Motion of these weak links allows for creation of controlled flow between the source and the drain. At a critical value of the weak link velocity, we observe a transition from superfluid flow to superfluid plus resistive flow. Working in the hydrodynamic limit, we observe a conductivity that is 4 orders of magnitude larger than previously reported conductivities for a Bose-Einstein condensate with a tunnel junction. Good agreement with zero-temperature Gross-Pitaevskii simulations and a phenomenological model based on phase slips indicate that the creation of excitations plays an important role in the resulting conductivity. Our measurements of resistive flow elucidate the microscopic origin of the dissipation and pave the way for more complex atomtronic devices.Comment: Version published in PR

Landau-Ginsberg Theory of Quark Confinement

We describe the SU(3) deconfinement transition using Landau-Ginsberg theory. Drawing on perturbation theory and symmetry principles, we construct the free energy as a function of temperature and the Polyakov loop. Once the two adjustable parameters of the model are fixed, the pressure p, energy epsilon and Polyakov loop expectation value P_F are calculable functions of temperature. An excellent fit to the continuum extrapolation of lattice thermodynamics data can be achieved. In an extended form of the model, the glueball potential is responsible for breaking scale invariance at low temperatures. Three parameters are required, but the glueball mass and the gluon condensate are calculable functions of temperature, along with p, epsilon and P_F.Comment: Lattice99(Finite Temperature and Density) <= added keywords only change in revised version, sorry; 3 pages, LaTeX with espcrc2.sty and epsf.tex. Talk presented at Lattice99, Pisa, 29 June - 3 July 1999, to appear in Nucl. Phys. B (Proc.Suppl.