The correlation of length spectra of two hyperbolic surfaces

We derive an asymptotic formula for the number of free homotopy classes on a closed surface which have (approximately) the same length with respect to two different hyperbolic structures on the surface. The growth rate in the asymptotic formula is described in terms of the thermodynamic formalism for the geodesic flow.     

The absorption,magnetic circular dichroism and emission of Eu2+ in cubic elpasolites

The absorption, magnetic circular dichroism (MCD) and emission/excitation spectra of some $\text{4?}{}^7\text{→4?}{}^6\text{5d}$ transitions in Eu²⁺ in several hexachloro and hexabromoelpasolites have been measured. Data were collected between 5 and 300 K and up to energies of 42,000 cm^?1. The absorption and MCD were satisfactorily interpreted using a coupling scheme that treats the d-electron crystal field as being much greater than the f-electron spin orbit coupling and essentially ignores other interactions.     

Surface phenotypes in T-cell leukaemia are determined by oncogenic retroviruses

Spontaneous thymic leukaemia in experimental mice is the result of a complex series of genetically controlled events. An important step in this process involves the production by thymocytes of recombinant polytropic retroviruses (MCF viruses). These leukaemogenic agents arise by recombination of genes from the env regions of endogenous precursor viruses. Sequences in these regions encode the envelope glycoprotein gp70 (ref. 6). Thus far, each cloned isolate of recombinant virus from AKR and HRS/J mice has been found to possess unique oligonucleotide sequences in its env region, as well as clone-specific peptides in its gp70 (refs 7,8). Therefore, the polytropic viruses of these leukaemia-susceptible mice are extremely diverse. These findings suggest that random recombination of env genes gives rise to leukaemogenic polytropic viruses. McGrath and Weissman have proposed that thymocytes with cell surface receptors for the gp70 of a particular leukaemogenic virus are the target cells for malignant transformation by that specific virus. In view of the diversity of polytropic viral gp70, their hypothesis would predict extensive phenotypic diversity among spontaneous thymic leukaemias. In contrast, leukaemias induced by a particular leukaemogenic recombinant virus would always have the same phenotype. Here we verify these predictions experimentally.