Formation of electron holes and particle energization during magnetic reconnection

Three-dimensional particle simulations of magnetic reconnection reveal the development of turbulence driven by intense electron beams that form near the magnetic x-line and separatrices. The turbulence collapses into localized three-dimensional nonlinear structures in which the electron density is depleted. The predicted structure of these electron holes compares favorably with satellite observations at Earth's magnetopause. The birth and death of these electron holes and their associated intense electric fields lead to strong electron scattering and energization, whose understanding is critical to explaining why magnetic explosions in space release energy so quickly and produce such a large number of energetic electrons.     

Chemical and biological microstructures as probed by dynamic processes

The dynamic process of electronic energy transfer is shown to be an important tool for probing the microstructure of molecular systems, particularly those in which donors and acceptors occupy specifically labeled sites of spatially confining host matrices. Special attention is given to analyzing the temporal behavior of the direct energy transfer reaction for systems in which the dipolar coupling is between a donor and randomly distributed acceptors. This dynamic process is dependent on two competing lengths when the donor and acceptor distribution is determined by the microstructure of the confining system: Rp, the dominant length characterizing the size of the confinement, and R0, which scales the strength of the dipolar coupling. When energy transfer processes are viewed in the context of these two competing lengths, a picture emerges of the microstructure of the confinement that is consistent with and corroborated by other structural probes.     

The cretaceous-tertiary transition

The fossil sequences from cores across the Cretaceous-Tertiary boundary show a, range of transition times and transition time intervals depending on the fossil indicators and the location of the site. These variations, together with the pattern of iridium distribution with depth at some sites, differences in total amounts of iridium, variations in noble metal abundances normalized to extraterrestrial concentrations, the depositional effects that might be expected in a reducing environment, and the clay mineralogy of the boundary layer clays, put into question the interpretation that an extraterrestrial event was the cause of the faunal changes and the iridium anomaly in the vicinity of the Cretaceous-Tertiary transition. It seems more likely that an explanation for the changes during the transition will come from continued examination of the great variety of terrestrial events that took place at that time, including extensive volcanism, major regression of the sea from the land, geochemical changes, and paleoclimatic and paleoceanographic changes.     

CO2 snow depth and subsurface water-ice abundance in the northern hemisphere of Mars

Observations of seasonal variations of neutron flux from the high-energy neutron detector (HEND) on Mars Odyssey combined with direct measurements of the thickness of condensed carbon dioxide by the Mars Orbiter Laser Altimeter (MOLA) on Mars Global Surveyor show a latitudinal dependence of northern winter deposition of carbon dioxide. The observations are also consistent with a shallow substrate consisting of a layer with water ice overlain by a layer of drier soil. The lower ice-rich layer contains between 50 and 75 weight % water, indicating that the shallow subsurface at northern polar latitudes on Mars is even more water rich than that in the south.     

The scanning ion-conductance microscope

A scanning ion-conductance microscope (SICM) has been developed that can image the topography of nonconducting surfaces that are covered with electrolytes. The probe of the SICM is an electrolyte-filled micropipette. The flow of ions through the opening of the pipette is blocked at short distances between the probe and the surface, thus, limiting the ion conductance. A feedback mechanism can be used to maintain a given conductance and in turn determine the distance to the surface. The SICM can also sample and image the local ion currents above the surfaces. To illustrate its potential for imaging ion currents through channels in membranes, a topographic image of a membrane filter with 0.80-micrometer pores and an image of the ion currents flowing through such pores are presented.     

High-pressure and high-temperature experiments on core-mantle segregation in the accreting Earth

The abundances of siderophile elements in the Earth's silicate mantle are too high for the mantle to have been in equilibrium with iron in the core if equilibrium occurred at low pressures and temperatures. It has been proposed that this problem may be solved if equilibrium occurred at high pressures and temperatures. Experimental determination of the distribution of siderophile elements between liquid metal and liquid silicate at 100 kilobar and 2000 degrees C demonstrates that it is unlikely that siderophile element abundances were established by simple metal-silicate equilibrium, which indicates that the segregation of the core from the mantle was a complex process.