A spectroscopic study of the globular Cluster NGC 4147

Indexación: Web of ScienceWe present the abundance analysis for a sample of 18 red giant branch stars in the metal-poor globular cluster NGC 4147 based on medium- and high-resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Y, Ba, and Eu. We find a metallicity of [Fe/H] = -1.84 +/- 0.02 and an alpha-enhancement of +0.38 +/- 0.05 (errors on the mean), typical of halo globular clusters in this metallicity regime. A significant spread is observed in the abundances of light elements C, N, O, Na, and Al. In particular, we found an Na-O anticorrelation and Na-Al correlation. The cluster contains only similar to 15 per cent of stars that belong to the first generation (Na-poor and O-rich). This implies that it suffered a severe mass-loss during its lifetime. Its [Ca/Fe] and [Ti/Fe] mean values agree better with the Galactic halo trend than with the trend of extragalactic environments at the cluster metallicity. This possibly suggests that NGC 4147 is a genuine Galactic object at odd with what claimed by some author that proposed the cluster to be member of the Sagittarius dwarf galaxy. An antirelation between the light s-process element Y and Na may also be present.https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stw114

Measurements of heavy ion beam losses from collimation

The collimation efficiency for Pb ion beams in the LHC is predicted to be lower than requirements. Nuclear fragmentation and electromagnetic dissociation in the primary collimators create fragments with a wide range of Z/A ratios, which are not intercepted by the secondary collimators but lost where the dispersion has grown sufficiently large. In this article we present measurements and simulations of loss patterns generated by a prototype LHC collimator in the CERN SPS. Measurements were performed at two different energies and angles of the collimator. We also compare with proton loss maps and find a qualitative difference between Pb ions and protons, with the maximum loss rate observed at different places in the ring. This behavior was predicted by simulations and provides a valuable benchmark of our understanding of ion beam losses caused by collimation.Comment: 12 pages, 20 figure

Chromatic LHC Optics Effects on Collimation Phase Space Cuts

The different levels of LHC collimators must be set up by respecting a strict setting hierarchy in order to guarantee the required performance and protection during the different operational machine stages. Two different subsystems establish betatron and momentum collimation for the LHC. Collimator betatronic phase space cuts are defined for a central on-momentum particle. However, due to the chromatic features of the LHC optics and energy deviations of particles, the different phase space cuts become coupled. Starting from the basic equation of the transverse beam dynamics, the influence of off-momentum beta-beat and dispersion on the effective collimator settings has been calculated. The results are presented, defining the allowed phase space regions from LHC collimation. The impacts on collimation-related setting tolerances and the choice of an optimized LHC optics are discussed

Pan-Africanism: a contorted delirium or a pseudonationalist paradigm? Revivalist critique

This essaic-article goes against established conventions that there is anything ethno-cultural (and hence national) about the so-called African tribes. Drawing largely from the culture history of precolonial/prepolitical Africans—that is, the Bantu/Cushitic-Ethiopians (Azanians)—the author has demonstrated vividly that far from being distinct ethno-culture national communities, the so-called tribes of African states are better considered subculture groups, whose regional culture practices erstwhile paid tribute to their nation’s main culture center in Karnak. For example, using the culture symbols and practices of some local groups and linking them to the predynastic and dynastic Pharaonic periods, I argued that there is compelling evidence against qualifying Africa’s tribes as distinct ethno-culture national entities. In genuine culture context, I stressed that the Ritual of Resurrection and its twin culture process of the mummification of deceased indigenous Pharaohs tend to suggest that the object of the Bantu/Cushitic-Ethiopians national culture was life (in its eternal manifestation) and then resurrection later, and that there are recurring (culturally sanctioned) ethical examples among the culture custodians of these subculture groups that generally pay tribute to the overarching culture norm. Furthermore, the fact that the Ritual of Resurrection began in the Delta region and ended at the Sources of the Nile, where the spirit of the deceased indigenous Pharaohs was introduced into the spiritual world of their ancestors, contradicts conventional perceptions that ancient Egypt was a distinct national community isolated from precolonial/prepolitical Africa/Azania

Beam Commissioning Plan For LHC Collimation

The Large Hadron Collider extends the present state-of-the-art in stored beam energy by 2-3 orders of magnitude. A sophisticated system of collimators is implemented along the 27 km ring and mainly in two dedicated cleaning insertions, to intercept and absorb unavoidable beam losses which could induce quenches in the superconducting (sc) magnets. 88 collimators for the two beams are initially installed for the so called Phase 1. An optimized strategy for the commissioning of this considerable number of collimators has been defined. This optimized strategy maximizes cleaning efficiency and tolerances available for operation, while minimizing the required beam time for collimator setup and ensuring at all times the required passive machine protection. It is shown that operational tolerances from collimation can initially be significantly relaxed

LHC Cleaning Efficiency with Imperfections

The performance reach of the LHC depends on the magnitude of beam losses and the achievable cleaning efficiency of its collimation system. The ideal performance reach for the nominal Phase 1 collimation system is reviewed. However, unavoidable imperfections affect any accelerator and can further deteriorate the collimation performance. Multiple static machine and collimator imperfections were included in the LHC tracking simulations. Error models for collimator jaw flatness, collimator setup accuracy, the LHC orbit and the LHC aperture were set up, based to the maximum extent possible on measurements and results of experimental beam tests. It is shown that combined “realistic” imperfections can reduce the LHC cleaning efficiency by about a factor 11 on average