Avoiding the rating bounce : why rating agencies are slow to react to new information

Rating agencies state that they take a rating action only when it is unlikely to be reversed shortly afterwards. Based on a formal representation of the rating process, I show that such a policy provides a good explanation for the empirical evidence: Rating changes occur relatively seldom, exhibit serial dependence, and lag changes in the issuers’ default risk. In terms of informational losses, avoiding rating reversals can be more harmful than monitoring credit quality only twice per year

On the distribution of class groups of number fields

We propose a modification of the predictions of the Cohen--Lenstra heuristic for class groups of number fields in the case where roots of unity are present in the base field. As evidence for this modified formula we provide a large set of computational data which show close agreement.Comment: 14 pages. To appear in Experimental Mat

Optical Mineralogy

This resource is a 43 page pdf document on the principals of optical mineralogy. Topics include light, the polarizing light microscope, the refractive index, optical classes and indicatrix theory, the relationship of optical properties to crystal chemistry, and advanced methods in optical mineralogy. The website features both text and figures. Educational levels: Graduate or professional, Undergraduate lower division, Undergraduate upper division

Use of DNA-based genetic markers in plant breeding

Genetic markers have been used since the beginnings of plant breeding, but the concept of linkage and recently the availability of molecular markers have offered new and powerful tools that can help to perform the traditional tasks of selection or that can change the traditional breeding process. Markers can either be used in a descriptive manner to identify varieties, to study the ‘micro-evolution’ of composite crosses or variety mixtures or to analyse the breeding progress retrospectively in order to learn from the past. The operative use of markers in plant breeding is connected to the selection of parental lines and progeny lines. The possible implementation of these processes stretches from the introgression of specific chromosome fragments to ‘marker-based idiotype breeding’