Adventures of a tidally induced bar

Using N-body simulations, we study the properties of a bar induced in a discy dwarf galaxy as a result of tidal interaction with the Milky Way. The bar forms at the first pericentre passage and survives until the end of the evolution at 10 Gyr. Fourier decomposition of the bar reveals that only even modes are significant and preserve a hierarchy so that the bar mode is always the strongest. They show a characteristic profile with a maximum, similar to simulated bars forming in isolated galaxies and observed bars in real galaxies. We adopt the maximum of the bar mode as a measure of the bar strength and we estimate the bar length by comparing the density profiles along the bar and perpendicular to it. The bar strength and the bar length decrease with time, mainly at pericentres, as a result of tidal torques acting at those times and not to secular evolution. The pattern speed of the bar varies significantly on a time-scale of 1 Gyr and is controlled by the orientation of the tidal torque from the Milky Way. The bar is never tidally locked, but we discover a hint of a 5/2 orbital resonance between the third and fourth pericentre passage. The speed of the bar decreases in the long run so that the bar changes from initially rather fast to slow in the later stages. The boxy/peanut shape is present for some time and its occurrence is preceded by a short period of buckling instability

Classification of Low Dimensional Lie Super-Bialgebras

A thorough analysis of Lie super-bialgebra structures on Lie super-algebras osp(1|2) and super-e(2) is presented. Combined technique of computer algebraic computations and a subsequent identification of equivalent structures is applied. In all the cases Poisson-Lie brackets on supergroups are found. Possibility of quantizing them in order to obtain quantum groups is discussed. It turns out to be straightforward for all but one structures for super-E(2) group.Comment: 15 pages, LaTe

Metrópolis de Fritz Lang

Abstract not availabl

Towards Data Mining in Large and Fully Distributed Peer-To-Peer Overlay Networks

The Internet, which is becoming a more and more dynamic, extremely heterogeneous network has recently became a platform for huge fully distributed peer-to-peer overlay networks containing millions of nodes typically for the purpose of information dissemination and file sharing. This paper targets the problem of analyzing data which are scattered over a such huge and dynamic set of nodes, where each node is storing possibly very little data but where the total amount of data is immense due to the large number of nodes. We present distributed algorithms for effectively calculating basic statistics of data using the recently introduced newscast model of computation and we demonstrate how to implement basic data mining algorithms based on these techniques. We will argue that the suggested techniques are efficient, robust and scalable and that they preserve the privacy of data

Lie Bialgebra Structures for Centrally Extended Two- Dimensional Galilei Algebra and their Lie-Poisson Counterparts

All bialgebra structures for centrally extended Galilei algebra are classified. The corresponding Lie-Poisson structures on centrally extended Galilei group are found.Comment: Eq. (11) changed, 15 pages, LaTeX fil

DNA Translocation through Graphene Nanopores

Nanopores -- nanosized holes that can transport ions and molecules -- are very promising devices for genomic screening, in particular DNA sequencing. Both solid-state and biological pores suffer from the drawback, however, that the channel constituting the pore is long, viz. 10-100 times the distance between two bases in a DNA molecule (0.5 nm for single-stranded DNA). Here, we demonstrate that it is possible to realize and use ultrathin nanopores fabricated in graphene monolayers for single-molecule DNA translocation. The pores are obtained by placing a graphene flake over a microsize hole in a silicon nitride membrane and drilling a nanosize hole in the graphene using an electron beam. As individual DNA molecules translocate through the pore, characteristic temporary conductance changes are observed in the ionic current through the nanopore, setting the stage for future genomic screening

Risk perceptions, sexual attitudes, and sexual behavior after HPV vaccination in 11-12 year-old girls

OBJECTIVES: Among 11-12 year-old girls who received the human papillomavirus (HPV) vaccine, we explored, over the subsequent 30 months: (1) trajectories of knowledge about HPV/HPV vaccines and vaccine-related risk perceptions; (2) whether knowledge and risk perceptions impacted sexual attitudes and sexual experience; (3) whether mothers, clinicians, and media influenced girls' risk perceptions, attitudes, and behavior. METHODS: Girls and mothers (n=25dyads) completed separate, semi-structured interviews within 2 days of, and 6, 18, and 30 months after, their first HPV vaccine dose. Knowledge, risk perceptions related to HPV and other sexually transmitted infections (STIs), and attitudes about sexual behaviors were assessed. Sexual experience was assessed at girls' 30 month interviews. Clinicians completed interviews at baseline. Transcribed interviews were analyzed using framework analysis. RESULTS: Girls' baseline knowledge was poor but often improved with time. Most girls (n=18) developed accurate risk perceptions about HPV but only half (n=12) developed accurate risk perceptions about other STIs by 30 months. The vast majority of girls thought that safer sex was still important, regardless of knowledge, risk perceptions, or sexual experience. Girls whose HPV knowledge was high at baseline or increased over time tended to articulate accurate risk perceptions; those who were able to articulate accurate risk perceptions tended to report not having initiated sexual activity. Girls whose mothers demonstrated higher knowledge and/or communication about HPV vaccination tended to articulate accurate risk perceptions, whereas clinicians and media exposure did not appear to influence risk perceptions. CONCLUSIONS: Higher knowledge about HPV vaccines among mothers and girls was linked with more accurate risk perceptions among girls. Clinicians may play an important role in providing education about HPV vaccines to mothers and girls