Brine-driven destruction of clay minerals in Gale crater, Mars.

Mars' sedimentary rock record preserves information on geological (and potential astrobiological) processes that occurred on the planet billions of years ago. The Curiosity rover is exploring the lower reaches of Mount Sharp, in Gale crater on Mars. A traverse from Vera Rubin ridge to Glen Torridon has allowed Curiosity to examine a lateral transect of rock strata laid down in a martian lake ~3.5 billion years ago. We report spatial differences in the mineralogy of time-equivalent sedimentary rocks <400 meters apart. These differences indicate localized infiltration of silica-poor brines, generated during deposition of overlying magnesium sulfate-bearing strata. We propose that destabilization of silicate minerals driven by silica-poor brines (rarely observed on Earth) was widespread on ancient Mars, because sulfate deposits are globally distributed.

Evidence for Multiple Diagenetic Episodes in Ancient Fluvial-Lacustrine Sedimentary Rocks in Gale Crater, Mars.

The Curiosity rover's exploration of rocks and soils in Gale crater has provided diverse geochemical and mineralogical data sets, underscoring the complex geological history of the region. We report the crystalline, clay mineral, and amorphous phase distributions of four Gale crater rocks from an 80-m stratigraphic interval. The mineralogy of the four samples is strongly influenced by aqueous alteration processes, including variations in water chemistries, redox, pH, and temperature. Localized hydrothermal events are evidenced by gray hematite and maturation of amorphous SiO2 to opal-CT. Low-temperature diagenetic events are associated with fluctuating lake levels, evaporative events, and groundwater infiltration. Among all mudstones analyzed in Gale crater, the diversity in diagenetic processes is primarily captured by the mineralogy and X-ray amorphous chemistry of the drilled rocks. Variations indicate a transition from magnetite to hematite and an increase in matrix-associated sulfates suggesting intensifying influence from oxic, diagenetic fluids upsection. Furthermore, diagenetic fluid pathways are shown to be strongly affected by unconformities and sedimentary transitions, as evidenced by the intensity of alteration inferred from the mineralogy of sediments sampled adjacent to stratigraphic contacts.

Designed experiments for classification problems.

This paper presents a new approach to evaluating classification procedures experimentally in human service organizations. Methods of design and analysis are proposed which answer the major objections to designed experiments with human subjects and which are suited to the special character of the classification problem. One important feature of the approach recommended here is the use of EVOP, a methodology originally developed for use in industrial production facilities, which allows methods of experimental design to be applied even where variation must be restricted. It is also shown that constrained mixture designs, rather than ordinary designs such as factorials, form the appropriate class of experimental designs for use in this problem. The example of assignment of prison inmates to minimum and maximum security is used to clarify the presentation and to demonstrate the practical implications of the proposed approach.

Evaluating the National Health Planning and Resources Development Act: learning from experience?

The future of health planning and regulation is tied to past performance in both a political and intellectual sense. Evidence of success or failure to accomplish program goals will structure partisan debate about the future of PL 93-641; and the experience of the past seven years will provide policy analysts with the raw material from which to build more effective technologies of planning and regulation. This paper discusses a number of analytic factors which jeopardize the integrity of both impact assessment and knowledge development. These include the nature of the program's goals, the difficulties of generating reliable forecasts as to what would have occurred in the program's absence, the likelihood of unintended consequences, and the seeming inevitability of having to work with elaborate multivariate models which contain numerous interaction terms. We argue that without careful analysis and cautious interpretation, grand experiments such as PL 93-641 are likely to yield little useful evidence to guide policy adaptation.