Extended magnetic reconnection at the Earth's magnetopause from detection of bi-directional jets

Magnetic reconnection is a process that converts magnetic energy into bi-directional plasma jets; it is believed to be the dominant process by which solar-wind energy enters the Earth's magnetosphere. This energy is subsequently dissipated by magnetic storms and aurorae. Previous single-spacecraft observations revealed only single jets at the magnetopause--while the existence of a counter-streaming jet was implicitly assumed, no experimental confirmation was available. Here we report in situ two-spacecraft observations of bi-directional jets at the magnetopause, finding evidence for a stable and extended reconnection line; the latter implies substantial entry of the solar wind into the magnetosphere. We conclude that reconnection is determined by large-scale interactions between the solar wind and the magnetosphere, rather than by local conditions at the magnetopause.

Aggregation During Precipitation from Solution. A Pore Diffusion-Reaction Model for Calcium Oxalate Monohydrate.

We have studied the precipitation of calcium oxalate monohydrate (COM) from supersaturated saline solutions both as an in vitro model of the formation of human kidney stones and more generally as a model of particle-size enlargement during precipitation from solution. In any precipitation system there are two mechanisms for size enlargement: growth, by which is meant the deposition of ionic or molecular species on crystal surfaces, and aggregation, the process by which crystals collide, adhere to each other, and form new, stable particles. In this paper we report batch precipitation experiments conducted at constant initial supersaturation and varying ratios of calcium to oxalate ions. By comparison with a simple diffusion-reaction model we are able to draw substantial inferences on the processes that control aggregation. We conclude that at constant temperature and agitation, the aggregation rate constant depends only on the cementing rate, which in turn depends on the solution composition and an appropriately formulated Thiele modulus only. Thus, for the first time, it is possible to propose and evaluate a physico-chemical model for the kinetics of aggregation during precipitation from solution. Copyright 1998 Academic Press.