Einstein metrics and quaternionic Kähler manifolds

The research is partially suported by a grant from the Natural Sciences and Engineering Research Council of Canada     

A dihydroxo-bridged Fe(II)-Fe(III) complex: a new member of the diiron diamond core family

The first structurally characterized Fe(II)-Fe(III) complex containing a M2(mu-OH)2 diamond core is a Robin and Day class II mixed-valence complex.     

Mechanisms of selenium-mediated protection from photocarcinogenesis and cell death are not solely p53-dependent

Recent studies published in Oncogene and Proc. Natl. Acad. Sci. USA ascribe a role for selenium, acting through wild type p53, in protecting skin cells in culture from ultraviolet radiation-induced death. While selenium clearly protects cells against ultraviolet radiation-induced death, data that we present and discuss in this letter shows that wild type p53 is not required for such protection. Moreover the non-physiologically high levels of selenium used in some studies leads us to question the relevance of such effects for selenium-induced photoprotection.     

ELDONET--a decade of monitoring solar radiation on five continents

The European light dosimeter network (ELDONET) comprises more than 40 stations in 24 countries on 5 continents. The present report compares solar radiation data in the photosynthetic active radiation, UV-A (315-400 nm) and UV-B (280-315 nm) wavelength ranges for 17 stations at different latitudes on the northern and southern hemispheres for up to 10 years of monitoring. While the maximal irradiances on clear days follow a latitudinal gradient due to the cosine dependence on the solar angle, the total doses strongly depend on the local climate and atmospheric conditions as well as the day-length distribution over the year. UV-B irradiances and doses are strongly influenced by the total column ozone, which is recorded for all covered stations.     

Single P and As dopants in the Si(001) surface

Using first-principles density functional theory, we discuss doping of the Si(001) surface by a single substitutional phosphorus or arsenic atom. We show that there are two competing atomic structures for isolated Si-P and Si-As heterodimers, and that the donor electron is delocalized over the surface. We also show that the Si atom dangling bond of one of these heterodimer structures can be progressively charged by additional electrons. It is predicted that surface charge accumulation as a result of tip-induced band bending leads to structural and electronic changes of the Si-P and Si-As heterodimers which could be observed experimentally. Scanning tunneling microscopy (STM) measurements of the Si-P heterodimer on a n-type Si(001) surface reveal structural characteristics and a bias-voltage dependent appearance, consistent with these predictions. STM measurements for the As:Si(001) system are predicted to exhibit similar behavior to P:Si(001).     

Reaction and subsequent transformation of anionic acetylide-carbene complexes using the Ph3PAu+ fragment

The metallated Fischer-type carbene complexes (CO)(5)M=C(NMe(2))C[triple bond]CLi (M = Cr, W) react with Ph(3)PAuNO(3) to form the beta-substituted products (CO)(5)M=C(NMe(2))C[triple bond]CAuPPh(3). In solution these products isomerise by formal metal fragment exchange to furnish Ph(3)PAuC(=NMe(2))C[triple bond]CM(CO)(5). A preliminary kinetic investigation by means of (1)H-NMR spectroscopy indicates an unusual and complicated reaction mechanism. Model DFT calculations predict small energy differences between the products before and after the metal fragment exchange.