4.6 billion year old aragonite and its implications for understanding the geological record of Ca-carbonate

Owing to its diagenetic instability, aragonite is rare in the geological record and almost entirely absent from pre-carboniferous sedimentary rocks. The former presence of this mineral in older deposits has to be inferred from petrographic, chemical or isotopic proxies. Crystals of aragonite that formed around 4563 million years ago occur in carbonaceous chondrite meteorites, showing that under certain conditions, the orthorhombic polymorph of Ca-carbonate can survive essentially indefinitely. Together with other carbonate minerals, phyllosilicates and sulphides, this aragonite formed by low-temperature water-mediated alteration of anhydrous minerals and glass in the interior of the meteorite’s parent asteroid(s). The survival of aragonite for such a long time can be attributed to the loss of free water by its incorporation into phyllosilicates, and to the very low permeability of the fine-grained and organic-rich rock matrix that prevented the ingress of fresh solutions via intergranular flow. By analogy with these meteorites, terrestrial aragonite is likely to survive where it has been similarly isolated from liquid water, particularly in organic-rich mudrocks, and such deposits may provide important new evidence for deducing the original mineralogy of skeletal and non-skeletal carbonates in deep-time

Recent trends in corporate leverage

Corporations - Finance ; Flow of funds ; Debt

The increasing importance of retailers' inventories

Although inventory--sales (IS) ratios and inventory volatility have declined somewhat since the early 1980s, little evidence supports the view that declining IS ratios are associated with declines in inventory investment volatility. In the retail sector, IS ratios have risen and inventory investment volatility has, at best, not increased, pointing to a more significant role in future cyclical fluctuations.Inventories ; Investments ; Retail trade

Inventories and output volatility

Analyzing disaggregate data on inventories and sales from the U.S. manufacturing and trade sector between 1960 and 1997 yields four main findings. First, I find that IS ratios are somewhat lower after 1984: 1 among durable goods manufacturers and durable goods retailers outside the motor vehicle industry. Second, I find that industries which have lowered their IS ratios tend to be those in which the variance of output relative to sale has declined. Third, by decomposing the variance of output into its components, I find that the variance of sales is less important, and the variance of inventory investment is more important, after 1984:1 than in earlier years for the overall manufacturing and trade sector. Finally, the evidence suggests that industries where IS ratios fell are those where inventory investment volatility played a smaller role in output volatility in the later period.Inventories

Following the Mobile Student: Can We Develop the Capacity for a Comprehensive Database to Assess Student Progression?

Presents a study of state-level databases on postsecondary student retention and completion rates and the feasibility of tracking students across state lines. Outlines challenges and recommendations, including establishing a common reporting standard

A Process Model of Risk Communication: The Case of Global Climate Change

The authors describe a survey of public media use as it relates to different stages of awareness and concern regarding risk issues

Exploring Thermal Processing of the Mildly Aqueously Altered Cm2 Eet 96029 Using Sulphide Mineralogy and Carbon Structure [abstract]

No abstract available

Coordination polymers and isomerism; a study using silver(I) and a ∏-stacked ligand

The ligand 2,5-bis(2-pyridylmethylsulfanylmethyl)pyrazine (L) was prepared by the base coupling of 2-(sulfanylmethyl)pyridine and 2,5-bis(chloromethyl)pyrazine. This new ligand was treated with AgClO₄ in a 1 1 metal-to-ligand ratio and with AgNO₃in a 2 1 metal-to-ligand ratio to give coordination polymers. The crystal structures of {[Ag(L)]ClO₄}∞ ( 1) and {[Ag₂(L)](NO₃)₂}∞ ( 2) were determined. The Ag(I) ions in the one-dimensional polymeric chains of 1 adopted square-pyramidal geometries with the pyridine and pyrazine N donors coordinated in an extremely bent fashion. The structure of 2 revealed two isomeric polymer chains in the one crystal forming a single supramolecular array. The isomeric polymers differed in the donor atoms about the Ag(I) ions and in the arrangement of adjacent ligands along the chain. A feature of both structures was that L adopted a three-layer ∏-stacked arrangement