Solar system

Abstract:

This paper explores the concept of utilizing a long duration stratospheric airship as an astronomical observatory in the sub-millimetre wavelengths. In the first section of the paper, a conceptual description of the airship platform is presented along with the principles of operation of the platform. The results of a computer design code and trajectory simulation code are presented. These codes show that through the use of a modest power and propulsion system, the difficulty of constructing such a such a platform is greatly reduced. Finally, the results of a brief study into the accommodation and optical performance of a Ø3.5m class telescope and photometric and spectrographic instrument similar to the Herschel/SPIRE system within such an airship are presented. This study indicates that while the atmospheric absorption and emission characteristics impose some limitations on the spectrographic and photometric performance of the system in the 200μm to 1000μm band, the overall performance is more than adequate to render the concept viable and complementary to existing and planned ground, airborne and space based observatories.

Abstract:

The performance of the PAW instrumentation on the 60kg Beagle 2 lander for ESA's 2003 Mars Express mission will be described. Beagle 2 will search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilise acquisition and preparation tools to obtain samples from below the surface, and both under and inside rocks. In situ analysis will include examination of samples with an optical microscope, Mossbauer and fluorescent X-ray spectrometers. Extracted samples will be returned to the lander for analysis, in particular a search for organics and a measurement of their isotopic composition. The PAW experiment performance data will be described along with the status of the project.

Abstract:

We examine the decay of passive scalars with small, but nonzero, diffusivity in bounded two-dimensional (2D) domains. The velocity fields responsible for advection are smooth (i.e., they have bounded gradients) and of a single large scale. Moreover, the scale of the velocity field is taken to be similar to the size of the entire domain. The importance of the initial scale of variation of the scalar field with respect to that of the velocity field is strongly emphasized. If these scales are comparable and the velocity field is time periodic, we see the formation of a periodic scalar eigenmode. The eigenmode is numerically realized by means of a deterministic 2D map on a lattice. Analytical justification for the eigenmode is available from theorems in the dynamo literature. Weakening the notion of an eigenmode to mean statistical stationarity, we provide numerical evidence that the eigenmode solution also holds for aperiodic flows (represented by random maps). Turning to the evolution of an initially small scale scalar field, we demonstrate the transition from an evolving (i.e., non-self-similar) probability distribution function (pdf) to a stationary (self-similar) pdf as the scale of variation of the scalar field progresses from being small to being comparable to that of the velocity field (and of the domain). Furthermore, the non-self-similar regime itself consists of two stages. Both stages are examined and the coupling between diffusion and the distribution of the finite time Lyapunov exponents is shown to be responsible for the pdf evolution.