Mid-infrared images of beta Pictoris and the possible role of planetesimal collisions in the central disk

When viewed in optical starlight scattered by dust, the nearly edge-on debris disk surrounding the A5V star beta Pictoris (distance 19.3 pc; ref. 1) extends farther than 1,450 au from the star. Its large-scale complexity has been well characterized, but the detailed structure of the disk's central approximately 200-au region has remained elusive. This region is of special interest, because planets may have formed there during the star's 10-20-million-year lifetime, perhaps resulting in both the observed tilt of 4.6 degrees relative to the large-scale main disk and the partial clearing of the innermost dust. A peculiarity of the central disk (also possibly related to the presence of planets) is the asymmetry in the brightness of the 'wings', in which the southwestern wing is brighter and more extended at 12 microm than the northeastern wing. Here we present thermal infrared images of the central disk that imply that the brightness asymmetry results from the presence of a bright clump composed of particles that may differ in size from dust elsewhere in the disk. We suggest that this clump results from the collisional grinding of resonantly trapped planetesimals or the cataclysmic break-up of a planetesimal.     

An integrated view of the chemistry and mineralogy of martian soils

The mineralogical and elemental compositions of the martian soil are indicators of chemical and physical weathering processes. Using data from the Mars Exploration Rovers, we show that bright dust deposits on opposite sides of the planet are part of a global unit and not dominated by the composition of local rocks. Dark soil deposits at both sites have similar basaltic mineralogies, and could reflect either a global component or the general similarity in the compositions of the rocks from which they were derived. Increased levels of bromine are consistent with mobilization of soluble salts by thin films of liquid water, but the presence of olivine in analysed soil samples indicates that the extent of aqueous alteration of soils has been limited. Nickel abundances are enhanced at the immediate surface and indicate that the upper few millimetres of soil could contain up to one per cent meteoritic material.     

Bitterbrush ( Purshia tridentata Pursh) growth in relation to browsing

The objectives of this study were to compare vegetative and reproductive growth characters of bitterbrush ( Purshia tridentata Pursh) stands as they relate to browsing levels. Growth characters were measured on 10 ecologically diverse stands in southwestern Montana on which browsing ranged from 0% to 60% of all current annual long shoot (LS) growth. Bitterbrush plants exhibited both twig-level and plant-level responses to browsing. Total bud density per plant was similar for browsed and unbrowsed sites, but differed ( P P P P P < 0.05). Our data suggest that long-term unbrowsed plants should not be used as a standard for comparison with normally browsed plants.     

High-energy colliders and the rise of the standard model

Over the past quarter of a century, experiments at high-energy particle colliders have established the standard model as the precise theory of particle interactions up to the 100 GeV scale. A series of important experimental discoveries and measurements have filled in most of the missing pieces and tested the predictions of the standard model with great precision.     

Philosophical Differences: The Case of Architects' Reluctance to Use Strategic Planning Software

A briefing workshop was run in an effort to involve its participants in choosing a strategic direction, and eventual form, for a proposed facility. The workshop was an action research, participative process that sought to improve final design by preconsultation with some relevant stakeholders. This paper will specifically focus on our attempt to use strategic planning software at an early stage of such a workshop. It discusses and illustrates the difficulties of importing a new technique into an established, professional setting where activities and roles may be expressed, or assumed, on the basis of previous experience. More exactly, although we hoped to use our software to analyze and explore participants' design styles, and so predict their likely choice of design option, the architects present undermined such analyzes by playing a role rather than telling the software what they really thought about the various strategic choices. Hence it was, in some ways, a waste of time using our software. We speculate below whether such undermining might be symptomatic of deep philosophical differences between the workshop organizers, planners, and architects. We also examine whether such differences bode ill for the future of architecture.     

Evidence for magmatic evolution and diversity on Mars from infrared observations

Compositional mapping of Mars at the 100-metre scale with the Mars Odyssey Thermal Emission Imaging System (THEMIS) has revealed a wide diversity of igneous materials. Volcanic evolution produced compositions from low-silica basalts to high-silica dacite in the Syrtis Major caldera. The existence of dacite demonstrates that highly evolved lavas have been produced, at least locally, by magma evolution through fractional crystallization. Olivine basalts are observed on crater floors and in layers exposed in canyon walls up to 4.5 km beneath the surface. This vertical distribution suggests that olivine-rich lavas were emplaced at various times throughout the formation of the upper crust, with their growing inventory suggesting that such ultramafic (picritic) basalts may be relatively common. Quartz-bearing granitoid rocks have also been discovered, demonstrating that extreme differentiation has occurred. These observations show that the martian crust, while dominated by basalt, contains a diversity of igneous materials whose range in composition from picritic basalts to granitoids rivals that found on the Earth.     

Variation in bitterbrush ( Purshia tridentata Pursh) crude protein in southwestern Montana

The objective of this study was to determine if crude protein varies significantly during late summer and midwinter among stands of bitterbrush ( Purshia tridentata Pursh) in southwestern Montana. A secondary objective was to determine if leaves, when present, contribute significant additional protein in the region. Nine sites with different environmental conditions within a radius of 14.5 km were studied. Bitterbrush leaves and leaders collected in August 1990 and 1991 and February 1991 were used for crude protein and leaf-to-leader ratio determinations. Crude protein differed ( P < 0.001) among sites for both leaves and leaders on individual collection dates. Crude protein in leaves was nearly twice the level found in leaders. Because few leaves were present in February, they increased crude protein in total foliage by only 0.3% over twigs alone. February crude protein levels averaged 6.8% for total foliage, which is below the estimated requirement for wintering deer.