Turbulence and galactic structure

Interstellar turbulence is driven over a wide range of scales by processes including spiral arm instabilities and supernovae, and it affects the rate and morphology of star formation, energy dissipation, and angular momentum transfer in galaxy disks. Star formation is initiated on large scales by gravitational instabilities which control the overall rate through the long dynamical time corresponding to the average ISM density. Stars form at much higher densities than average, however, and at much faster rates locally, so the slow average rate arises because the fraction of the gas mass that forms stars at any one time is low, ~10^{-4}. This low fraction is determined by turbulence compression, and is apparently independent of specific cloud formation processes which all operate at lower densities. Turbulence compression also accounts for the formation of most stars in clusters, along with the cluster mass spectrum, and it gives a hierarchical distribution to the positions of these clusters and to star-forming regions in general. Turbulent motions appear to be very fast in irregular galaxies at high redshift, possibly having speeds equal to several tenths of the rotation speed in view of the morphology of chain galaxies and their face-on counterparts. The origin of this turbulence is not evident, but some of it could come from accretion onto the disk. Such high turbulence could help drive an early epoch of gas inflow through viscous torques in galaxies where spiral arms and bars are weak. Such evolution may lead to bulge or bar formation, or to bar re-formation if a previous bar dissolved. We show evidence that the bar fraction is about constant with redshift out to z~1, and model the formation and destruction rates of bars required to achieve this constancy.Comment: in: Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork strikes a New Note, Eds., K. Freeman, D. Block, I. Puerari, R. Groess, Dordrecht: Kluwer, in press (presented at a conference in South Africa, June 7-12, 2004). 19 pgs, 5 figure

Zircon to scheelite phase transition induced by pressure and magnetism in TbCrO4

7 páginas, 6 figuras, 3 tablas.-- PACS number(s): 75.25.-j, 62.50.-p, 61.66.Fn, 75.30.Cr.-- et al.The scheelite form of the TbCrO4 oxide has been obtained by treating TbCrO4-zircon at 4 GPa and 823 K. X-ray and neutron diffraction data reveal that the high-pressure polymorph of TbCrO4 crystallizes with tetragonal symmetry space group I41/a and lattice parameters a=5.036 74(10) Å and c=11.3734(4) Å. Although bisdisphenoids [TbO8] and tetrahedra [CrO4] are present in both scheelite and zircon polymorphs, the remarkable changes observed in both polyhedra appear to support the reconstructive model for the zircon-scheelite first-order phase transition. Specific heat and neutron diffraction measurements confirm the antiferromagnetic ordering previously proposed from magnetic susceptibility measurements, in which both Tb3+ and Cr5+ sublattices are involved. The magnetic structure has been determined and can be described on the basis of the coincidence between the chemical and magnetic cells, k=(0,0,0), where the magnetic moments of the Tb3+ and Cr5+ cations are antiferromagnetically aligned along the c axis of the structure, with TN=29 K. Their values at 2 K are 8.97(3)μB and 1.089(9)μB, respectively.The authors are grateful to Spanish MICINN and FEDER for financial support under Research Projects No. MAT2007- 63497 and No. MAT2007-61621, CONSOLIDER-Ingenio 2010 (Grant No. CSD 2007-00010).Peer reviewe

Leadership of the nurse: an integrative literature review Liderazgo del enfermero: una revisión integradora de la literatura Liderança do enfermeiro: uma revisão integrativa da literatura

This Integrative Literature Review, sought to evidence and discuss the main characteristics of the concept of leadership and of the nurse leader, as well as their contributions to the practice of nursing and health from nursing scientific publications indexed in the database Medical Literature Analysis and Retrieval System Online (MEDLINE) and published between 1998 and 2008. Following the inclusion criteria, a total of 36 studies were selected for analysis, of these 89% (33 articles) were published in foreign journals and 11% (3) published in national journals. The profiles of nursing leaders encountered were the authentic and the authoritative, with the leadership evidenced as an organizational tool that combines communication, interpersonal relationships, planning, the commitment to success and the resolvability of conflicts. Education is presented as fundamental for the formation of leaders, relating directly the valorization of academic titles with the improvement of this competence.<br>Se trata de una Revisión Integradora de la literatura, que buscó evidenciar y discutir las principales características del concepto de liderazgo y del enfermero líder, así como sus contribuciones para la práctica en enfermería y salud, a partir de publicaciones científicas de enfermería indexadas en la base de datos Medical Literature and Retrivial System on Line (MEDLINE) entre 1998 y 2008. Siguiendo los criterios de inclusión, se totalizó 36 estudios seleccionados para análisis, de los cuales 89% (33 artículos) fueron publicados en periódicos extranjeros y 11% (3) publicados en periódicos nacionales. Los perfiles de enfermeros líderes encontrados fueron el autoritario y el auténtico, siendo el liderazgo evidenciado como una herramienta organizacional que articula comunicación, relaciones interpersonales, planificación, el compromiso con el éxito y la resolutividad de conflictos. La educación se presenta como fundamental para la formación de líderes, relacionando directamente la valorización de la titulación académica con el perfeccionamiento de esa competencia.<br>Trata-se de revisão integrativa da literatura, que buscou evidenciar e discutir as principais características do conceito de liderança e do enfermeiro líder, bem como suas contribuições para a prática em enfermagem e saúde, a partir de publicações científicas de enfermagem indexadas na base de dados Medical Literature and Retrivial System on Line (MEDLINE), entre 1998 e 2008. Seguindo os critérios de inclusão, totalizaram-se 36 estudos selecionados para análise, dos quais 89% (33 artigos) foram publicados em periódicos estrangeiros e 11% (3) publicados em periódicos nacionais. Os perfis de enfermeiros líderes encontrados foram o autoritário e o autêntico, sendo a liderança evidenciada como ferramenta organizacional que articula comunicação, relações interpessoais, planejamento, o compromisso com o êxito e a resolutividade de conflitos. A educação apresenta-se como fundamental para a formação de líderes, relacionando diretamente a valorização da titulação acadêmica ao aperfeiçoamento dessa competência