EFFICIENT CONTROL OF ACCELERATOR MAPS

Recently, the Hamiltonian Control Theory was used in [Boreux et al., 2012] to increase the dynamic aperture of a ring particle accelerator having a localized thin sextupole magnet. In this paper, these results are extended by proving that a simplified version of the obtained general control term leads to significant improvements of the dynamic aperture of the uncontrolled model. In addition, the dynamics of flat beams based on the same accelerator model can be significantly improved by a reduced controlled term applied in only one degree of freedom.

BIFURCATIONS IN DYNAMICS OF SHEPHERD SYSTEMS

A small moon orbiting near the edge of a ring of particles can act as a "shepherd", keeping errant ring particles from drifting away and keeping the ring boundary sharp. This phenomenon was predicted before it was observed [Goldreich & Tremaine, 1979] and has been successfully modeled by many authors, see [Murray & Dermott, 1999]. In this paper we focus on the bifurcations that occur in the motion of a ring particle as the mass of the moon and the distance between orbits of the moon and the particle are adjusted.

A nuclear cap-binding complex binds Balbiani ring pre-mRNA cotranscriptionally and accompanies the ribonucleoprotein particle during nuclear export.

In vertebrates, a nuclear cap-binding complex (CBC) formed by two cap- binding proteins, CBP20 and CBP80, is involved in several steps of RNA metabolism, including pre-mRNA splicing and nuclear export of some RNA polymerase II-transcribed U snRNAs. The CBC is highly conserved, and antibodies against human CBP20 cross-react with the CBP20 counterpart in the dipteran Chironomus tentans. Using immunoelectron microscopy, the in situ association of CBP20 with a specific pre-mRNP particle, the Balbiani ring particle, has been analyzed at different stages of pre-mRNA synthesis, maturation, and nucleo-cytoplasmic transport. We demonstrate that CBP20 binds to the nascent pre-mRNA shortly after transcription initiation, stays in the RNP particles after splicing has been completed, and remains attached to the 5' domain during translocation of the RNP through the nuclear pore complex (NPC). The rapid association of CBP20 with nascent RNA transcripts in situ is consistent with the role of CBC in splicing, and the retention of CBC on the RNP during translocation through the NPC supports its proposed involvement in RNA export.