Subsurface water and clay mineral formation during the early history of Mars.

Clay minerals, recently discovered to be widespread in Mars's Noachian terrains, indicate long-duration interaction between water and rock over 3.7 billion years ago. Analysis of how they formed should indicate what environmental conditions prevailed on early Mars. If clays formed near the surface by weathering, as is common on Earth, their presence would indicate past surface conditions warmer and wetter than at present. However, available data instead indicate substantial Martian clay formation by hydrothermal groundwater circulation and a Noachian rock record dominated by evidence of subsurface waters. Cold, arid conditions with only transient surface water may have characterized Mars's surface for over 4 billion years, since the early-Noachian period, and the longest-duration aqueous, potentially habitable environments may have been in the subsurface.

Deep, subsurface microflora after excavation respiration and biomass and its potential role in degradation of fossil organic matter.

Three types of Miocene claystones (amorphous, lamellar, and transitional) were aseptically sampled from depths of 30 m and 150 m below the soil surface. Respiration of these sediments was measured under conditions that prevented inoculation by other microorganisms not indigenous to the claystones in situ. Microbial respiration was higher in lamellar than amorphous claystones and was not affected by sampling depth. During cultivation, microbial biomass (as indicated by PLFA) significantly increased. Microbial biomass after cultivation was significantly higher in sediments from 30 m than from 150 m depth. Both microbial respiration and biomass increased after glucose addition.

Microbiological characterisation of southern African medicinal and cosmetic clays.

The effects of traditionally used medicinal and cosmetic clays in southern Africa on selected microorganisms were studied using microbiological media. The clay pH, microchemical composition, kind of associated microorganisms and antimicrobial activity of clays against test microorganisms were determined. The clays contained varying numbers of microorganisms which ranged from 0 up to 105 CFU/g. Clay pH ranged from 2.3-8.9. Neither Escherichia coli, nor other faecal coliforms were detected. Clays of pH value of <4 displayed antimicrobial activities. Clays which were active against test microorganisms had Na(2)O, Al(2)O(3), SiO(2), SO(3), CuO or Cl(2)O as major components. Microbial activity of clays was attributed mainly to low pH but cations such as Cu, Al, S or Cl and various anions might have contributed to the microbicidal effects. No antimicrobial activity was established for many of the clays commonly used in the treatment of common ailments of microbial origin.

[The classification of ceramics according to its chemical nature and its method of production]. / Classification des céramiques selon la nature chimique et le procédé de mise en oeuvre.

Nowadays, we find on the market a huge amount of design and manufactured system that allows the realisation of all-ceramics restorations, using different ceramics. The purpose of this article is suggesting a classification of mostly used ceramics and a few laboratory process used in our university.