Magnetic Field Amplification in Galaxy Clusters and its Simulation

We review the present theoretical and numerical understanding of magnetic field amplification in cosmic large-scale structure, on length scales of galaxy clusters and beyond. Structure formation drives compression and turbulence, which amplify tiny magnetic seed fields to the microGauss values that are observed in the intracluster medium. This process is intimately connected to the properties of turbulence and the microphysics of the intra-cluster medium. Additional roles are played by merger induced shocks that sweep through the intra-cluster medium and motions induced by sloshing cool cores. The accurate simulation of magnetic field amplification in clusters still poses a serious challenge for simulations of cosmological structure formation. We review the current literature on cosmological simulations that include magnetic fields and outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure

Nonthermal phenomena in clusters of galaxies

Recent observations of high energy (> 20 keV) X-ray emission in a few clusters of galaxies broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton scattering of relativistic electrons by the cosmic microwave background (CMB) radiation. Direct evidence for the presence of relativistic electrons in some 50 clusters comes from measurements of extended radio emission in their central regions. We briefly review the main results from observations of extended regions of radio emission, and Faraday rotation measurements of background and cluster radio sources. The main focus of the review are searches for nonthermal X-ray emission conducted with past and currently operating satellites, which yielded appreciable evidence for nonthermal emission components in the spectra of a few clusters. This evidence is clearly not unequivocal, due to substantial observational and systematic uncertainties, in addition to virtually complete lack of spatial information. If indeed the emission has its origin in Compton scattering of relativistic electrons by the CMB, then the mean magnetic field strength and density of relativistic electrons in the cluster can be directly determined. Knowledge of these basic nonthermal quantities is valuable for the detailed description of processes in intracluster gas and for the origin of magnetic fields.Comment: 23 pages, 7 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 5; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

ENXERTIA DE COFFEA ARABICA SOBRE PROGÊNIES DE C. CANEPHORA E DE C. CONGENSIS NO CRESCIMENTO, NUTRIÇÃO MINERAL E PRODUÇÃO GRAFTS OF COFFEA ARABICA ONTO C. CANEPHORA AND C. CONGENSIS AND ITS EFFECTS ON GROWTH, MINERAL NUTRITION AND YIELD

A enxertia de cultivares de Coffea arabica L. sobre Coffea canephora Pierre vem sendo utilizada como alternativa para o cultivo do café em áreas infestadas por nematóides, em vista da resistência de C. canephora a esse patógeno. O objetivo deste trabalho foi estudar no campo, em áreas isentas de nematóides, o desenvolvimento da parte aérea, a nutrição mineral e a produção de cultivares de C. arabica enxertados sobre C. canephora e C. congensis. Em 1986 , instalaram-se experimentos em três regiões cafeeiras paulistas - Campinas, Garça e Mococa - no espaçamento de 3,5 x 2,0 m, com duas plantas por cova. Como porta-enxerto, utilizaram-se duas progênies de C. canephora (Apoatã IAC 2258 e IAC 2286) e uma de C. congensis (IAC Bangelan coleção 5), tolerantes a nematóides e, como enxerto, dois cultivares de C. arabica (Catuaí Vermelho IAC H 2077-2-5-81 e Mundo Novo IAC 515-20). Também se efetuaram auto-enxertias no Catuaí e no Mundo Novo e, como testemunhas, consideraram-se plantas desses cultivares não enxertadas. Os dados mostraram que, mesmo na ausência de nematóides, a utilização de progênies de C. canephora e de C. congensis como porta-enxerto conferiu maior desenvolvimento e produção (médias de cinco anos) aos cultivares de C. arabica, sendo esse efeito mais acentuado no 'Catuaí'. O crescimento sazonal em altura, em todos os tratamentos, foi maior na primavera e no verão e menor no outono e no inverno. De modo geral, a enxertia aumentou o crescimento em altura em todas as estações do ano, principalmente no outono e no inverno. As plantas enxertadas apresentaram maiores teores foliares de potássio e menores de manganês, em relação às não enxertadas. A enxertia não alterou de modo consistente os teores dos demais nutrientes.<br>Grafts of Coffea arabica L. onto C. canephora Pierre have been routinely used in regions infested with nematodes, due to the resistance of C. canephora to these pathogens. In the present work, growth, mineral nutrition and yield of two C. arabica cultivars grafted on C. canephora and C. congensis were evaluated in fields free from nematodes, in three coffee growing regions of São Paulo State, Brazil. Catuaí Vermelho IAC H 2077-2-5-81 and Mundo Novo IAC 515-20 (two cultivars of C. arabica) were grafted on nematode resistant lines Apoatã IAC 2258 and IAC 2286 of C. canephora and on IAC Bangelan colection 5 of C. congensis. Plants not grafted were used as controls, and plants grafted onto their own roots were also evaluated. Grafted cultivars after five years grew better and had higher yield than the ungrafted ones, specially the Catuaí cultivar. Seasonal growth (plant height) was faster during spring and summer, for all treatmentes. In general, grafting increased height throughout the year, mainly during fall and winter seasons. Leaves of grafted plants had higher potassium and lower manganese content than ungrafted ones. Levels of other nutrients were not consistently affected by grafting