Long-term evolution of massive star explosions

We examine simulations of core-collapse supernovae in spherical symmetry. Our model is based on general relativistic radiation hydrodynamics with three-flavor Boltzmann neutrino transport. We discuss the different supernova phases, including the long-term evolution up to 20 seconds after the onset of explosion during which the neutrino fluxes and mean energies decrease continuously. In addition, the spectra of all flavors become increasingly similar, indicating the change from charged- to neutral-current dominance. Furthermore, it has been shown recently by several groups independently, based on sophisticated supernova models, that collective neutrino flavor oscillations are suppressed during the early mass-accretion dominated post-bounce evolution. Here we focus on the possibility of collective flavor flips between electron and non-electron flavors during the later, on the order of seconds, evolution after the onset of an explosion with possible application for the nucleosynthesis of heavy elements.Comment: 12 pages, 7 figures, conference proceeding, HANSE 2011 worksho

Long-term Evolution of Sunspot Magnetic Fields

Independent of the normal solar cycle, a decrease in the sunspot magnetic field strength has been observed using the Zeeman-split 1564.8nm Fe I spectral line at the NSO Kitt Peak McMath-Pierce telescope. Corresponding changes in sunspot brightness and the strength of molecular absorption lines were also seen. This trend was seen to continue in observations of the first sunspots of the new solar Cycle 24, and extrapolating a linear fit to this trend would lead to only half the number of spots in Cycle 24 compared to Cycle 23, and imply virtually no sunspots in Cycle 25. We examined synoptic observations from the NSO Kitt Peak Vacuum Telescope and initially (with 4000 spots) found a change in sunspot brightness which roughly agreed with the infrared observations. A more detailed examination (with 13,000 spots) of both spot brightness and line-of-sight magnetic flux reveals that the relationship of the sunspot magnetic fields with spot brightness and size remain constant during the solar cycle. There are only small temporal variations in the spot brightness, size, and line-of-sight flux seen in this larger sample. Because of the apparent disagreement between the two data sets, we discuss how the infrared spectral line provides a uniquely direct measurement of the magnetic fields in sunspots

3GPP Long Term Evolution: Architecture, Protocols and Interfaces

The evolution of wireless networks is a continuous phenomenon. Some key trends in this changing process include: reduced latency, increased performance with substantial reduction in costs, and seamless mobility. Long Term Evolution (LTE) is based on an evolved architecture that makes it a candidate of choice for next generation wireless mobile networks. This paper provides an overview of both the core and access networks of LTE. Functional details of the associated protocols and interfaces are also presented

Long-term evolution of isolated N-body sytems

We report results of N-body simulations of isolated star clusters, performed up to the point where the clusters are nearly completely dissolved. Our main focus is on the post-collapse evolution of these clusters. We find that after core collapse, isolated clusters evolve along nearly a single sequence of models whose properties are independent of the initial density profile and particle number. Due to the slower expansion of high-N clusters, relaxation times become almost independent of the particle number after several core collapse times, at least for the particle range of our study. As a result, the dissolution times of isolated clusters exhibit a surprisingly weak dependence on N. We find that most stars escape due to encounters between single stars inside the half-mass radius of the cluster. Encounters with binaries take place mostly in the cluster core and account for roughly 15% of all escapers. Encounters between single stars at intermediate radii are also responsible for the build up of a radial anisotropic velocity distribution in the halo. For clusters undergoing core oscillations, escape due to binary stars is efficient only when the cluster center is in a contracted phase. Our simulations show that it takes about 10^5 N-body time units until the global anisotropy reaches its maximum value. The anisotropy increases with particle number and it seems conceivable that isolated star clusters become vulnerable to radial orbit instabilities for large enough N. However, no indication for the onset of such instabilities was seen in our runs.Comment: 14 pages, 20 figures, MNRAS in press, V2: Order of authors changed in author-fiel

Long Term Evolution of Massive Black Hole Binaries

The long-term evolution of massive black hole binaries at the centers of galaxies is studied in a variety of physical regimes, with the aim of resolving the ``final parsec problem,'' i.e., how black hole binaries manage to shrink to separations at which emission of gravity waves becomes efficient. A binary ejects stars by the gravitational slingshot and carves out a loss cone in the host galaxy. Continued decay of the binary requires a refilling of the loss cone. We show that the standard treatment of loss cone refilling, derived for collisionally relaxed systems like globular clusters, can substantially underestimate the refilling rates in galactic nuclei. We derive expressions for non-equilibrium loss-cone dynamics and calculate time scales for the decay of massive black hole binaries following galaxy mergers, obtaining significantly higher decay rates than heretofore. Even in the absence of two-body relaxation, decay of binaries can persist due to repeated ejection of stars returning to the nucleus on eccentric orbits. We show that this recycling of stars leads to a gradual, approximately logarithmic dependence of the binary binding energy on time. We derive an expression for the loss cone refilling induced by the Brownian motion of a black hole binary. We also show that numerical N-body experiments are not well suited to probe these mechanisms over long times due to spurious relaxation.Comment: Replaced to match the accepted version, ApJ, 596 (2003