Generalized Farey trees, transfer Operators and phase transitions

We consider a family of Markov maps on the unit interval, interpolating between the tent map and the Farey map. The latter map is not uniformly expanding. Each map being composed of two fractional linear transformations, the family generalizes many particular properties which for the case of the Farey map have been successfully exploited in number theory. We analyze the dynamics through the spectral analysis of generalized transfer operators. Application of the thermodynamic formalism to the family reveals first and second order phase transitions and unusual properties like positivity of the interaction function.Comment: 39 pages, 10 figure

Glycoprotein gene truncation in avian metapneumovirus subtype C isolates from the United States

The length of the published glycoprotein (G) gene sequences of avian metapneumovirus subtype-C (aMPV-C) isolated from domestic turkeys and wild birds in the United States (1996–2003) remains controversial. To explore the G gene size variation in aMPV-C by the year of isolation and cell culture passage levels, we examined 21 turkey isolates of aMPV-C at different cell culture passages. The early domestic turkey isolates of aMPV-C (aMPV/CO/1996, aMPV/MN/1a-b, and 2a-b/97) had a G gene of 1,798 nucleotides (nt) that coded for a predicted protein of 585 amino acids (aa) and showed >97% nt similarity with that of aMPV-C isolated from Canada geese. This large G gene got truncated upon serial passages in Vero cell cultures by deletion of 1,015 nt near the end of the open reading frame. The recent domestic turkey isolates of aMPV-C lacked the large G gene but instead had a small G gene of 783 nt, irrespective of cell culture passage levels. In some cultures, both large and small genes were detected, indicating the existence of a mixed population of the virus. Apparently, serial passage of aMPV-C in cell cultures and natural passage in turkeys in the field led to truncation of the G gene, which may be a mechanism of virus evolution for survival in a new host or environment

Exploring the smallest terrestrial planet: Dawn at Vesta

The Dawn mission is designed to map Vesta and Ceres from polar orbit for close to one year each. The ion-propelled Dawn spacecraft is illustrated in Figure 1. Dawn carries a framing camera with clear and color filters, a visible and infrared mapping spectrometer, a gamma ray and neutron spectrometer, and obtains radiometric data on the gravity field. The camera obtains stereo imagery from which a global shape and topography model are derived. The mapping spectrometer determines the mineral composition of the surface and the gamma and neutron spectrometer determines the elemental composition. As Dawn approaches Vesta, as illustrated in Figure 2, it measures the rotational characteristics of the body to determine the orientation of the rotation axis. This in turn determines when solar illumination reaches the north pole and when mapping can be completed. As shown in Figure 3, there are three science orbits: Survey at a radial distance of 3000 km and a period of 69 hr; high-altitude mapping at a radial distance of 950 km and a period of 12.3 hr; and low-altitude mapping at a radius of 465 km and a period of 4 hours. Vesta is the ultimate source of the HED meteorites from which much has been learned about their parent body. By the time of this presentation we will have surveyed the region around Vesta for moons, determined a much more accurate mass and rotation axis for Vesta, and have preliminary information on surface features and composition from the survey orbit