10,827 research outputs found

    Observationally-Motivated Analysis of Simulated Galaxies

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    The spatial and temporal relationships between stellar age, kinematics, and chemistry are a fundamental tool for uncovering the physics driving galaxy formation and evolution. Observationally, these trends are derived using carefully selected samples isolated via the application of appropriate magnitude, colour, and gravity selection functions of individual stars; conversely, the analysis of chemodynamical simulations of galaxies has traditionally been restricted to the age, metallicity, and kinematics of `composite' stellar particles comprised of open cluster-mass simple stellar populations. As we enter the Gaia era, it is crucial that this approach changes, with simulations confronting data in a manner which better mimics the methodology employed by observers. Here, we use the \textsc{SynCMD} synthetic stellar populations tool to analyse the metallicity distribution function of a Milky Way-like simulated galaxy, employing an apparent magnitude plus gravity selection function similar to that employed by the RAdial Velocity Experiment (RAVE); we compare such an observationally-motivated approach with that traditionally adopted - i.e., spatial cuts alone - in order to illustrate the point that how one analyses a simulation can be, in some cases, just as important as the underlying sub-grid physics employed.Comment: Accepted for publication in PoS (Proceedings of Science): Nuclei in the Cosmos XIII (Debrecen, Jul 2014); 6 pages; 3 figure

    On characteristic equations, trace identities and Casimir operators of simple Lie algebras

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    Two approaches are developed to exploit, for simple complex or compact real Lie algebras g, the information that stems from the characteristic equations of representation matrices and Casimir operators. These approaches are selected so as to be viable not only for `small' Lie algebras and suitable for treatment by computer algebra. A very large body of new results emerges in the forms, a) of identities of a tensorial nature, involving structure constants etc. of g, b) of trace identities for powers of matrices of the adjoint and defining representations of g, c) of expressions of non-primitive Casimir operators of g in terms of primitive ones. The methods are sufficiently tractable to allow not only explicit proof by hand of the non-primitive nature of the quartic Casimir of g2, f4, e6, but also e.g. of that of the tenth order Casimir of f4.Comment: 39 pages, 8 tables, late

    Two parameter Deformed Multimode Oscillators and q-Symmetric States

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    Two types of the coherent states for two parameter deformed multimode oscillator system are investigated. Moreover, two parameter deformed gl(n)gl(n) algebra and deformed symmetric states are constructed.Comment: LaTeX v1.2, 14 pages with no figure

    Galactic Archaeology and Minimum Spanning Trees

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    Chemical tagging of stellar debris from disrupted open clusters and associations underpins the science cases for next-generation multi-object spectroscopic surveys. As part of the Galactic Archaeology project TraCD (Tracking Cluster Debris), a preliminary attempt at reconstructing the birth clouds of now phase-mixed thin disk debris is undertaken using a parametric minimum spanning tree (MST) approach. Empirically-motivated chemical abundance pattern uncertainties (for a 10-dimensional chemistry-space) are applied to NBODY6-realised stellar associations dissolved into a background sea of field stars, all evolving in a Milky Way potential. We demonstrate that significant population reconstruction degeneracies appear when the abundance uncertainties approach 0.1 dex and the parameterised MST approach is employed; more sophisticated methodologies will be required to ameliorate these degeneracies.Comment: To appear in "Multi-Object Spectroscopy in the Next Decade: Big Questions, Large Surveys and Wide Fields"; Held: Santa Cruz de La Palma, Canary Islands, Spain, 2-6 Mar 2015; ed. I Skillen & S. Trager; ASP Conference Series (Figures now optimised for B&W printing

    Correlation length in cuprates deduced from the impurity-induced magnetization

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    We report a new multi-nuclei based NMR method which allows us to image the staggered polarization induced by nonmagnetic Li impurities in underdoped O6.6 and slightly overdoped O7 YBa2Cu3O6+y above T_C. The spatial extension of the polarization xi_imp approximately follows a Curie law, increasing up to six lattice constants at T=80K at O6.6 in the pseudogap regime. Near optimal doping, the staggered magnetization has the same shape, with xi_imp reduced by a factor 2. xi_imp is argued to reveal the intrinsic magnetic correlation length of the pure system. It is found to display a smooth evolution through the pseudogap regime.Comment: 8 latex pages + 8 figures, to appear in Physical Review B, this resubmitted version is twice longer than the previous one : we detail here our method to determine the impurity-induced magnetizatio

    q-Boson approach to multiparticle correlations

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    An approach is proposed enabling to effectively describe, for relativistic heavy-ion collisions, the observed deviation from unity of the intercept \lambda (measured value corresponding to zero relative momentum {\bf p} of two registered identical pions or kaons) of the two-particle correlation function C(p,K). The approach uses q-deformed oscillators and the related picture of ideal gas of q-bosons. In effect, the intercept \lambda is connected with deformation parameter q. For a fixed value of q, the model predicts specific dependence of \lambda on pair mean momentum {\bf K} so that, when |{\bf K}|\gsim 500 - 600 MeV/c for pions or when |{\bf K}|\gsim 700 - 800 MeV/c for kaons, the intercept \lambda tends to a constant which is less than unity and determined by q. If q is fixed to be the same for pions and kaons, the intercepts \lambda_\pi and \lambda_K essentially differ at small mean momenta {\bf K}, but tend to be equal at {\bf K} large enough (|{\bf K}|\gsim 800MeV/c) where the effect of resonance decays can be neglected. We argue that it is of basic interest to check in the experiments on heavy ion collisions: (i) the exact shape of dependence \lambda = \lambda({\bf K}), and (ii) whether for |{\bf K}| \gsim 800 MeV/c the resulting \lambda_\pi and \lambda_K indeed coincide.Comment: 6 pages, revtex, 4 figures, to be published in Mod. Phys. Lett.

    The Radiation Balance of Snow-Free Surfaces at Poste-de-la-Baleine, Québec, May 30 – June 1, 1970

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    On a mesuré le rayonnement solaire global et le bilan du rayonnement pour des surfaces très variées à Poste-de-la-Baleine, au Québec, du 30 mai au 1er juin 1970, pendant des périodes cycloniques et anticycloniques alternantes. À l'exception d'une surface d'eau libre dans le sud-est de la Baie de James et près des îles Belcher, la glace recouvrait la Baie d'Hudson. Les flux provenant de l'ouest et du sud-ouest s'accompagnaient de temps frais, humide et nuageux. On a trouvé une bonne corrélation linéaire entre le bilan du rayonnement et le rayonnement global, pour toutes les surfaces et pour les temps nuageux, depuis le brouillard jusqu'aux cirrus. Les résultats indiquent que, malgré la réduction du rayonnement solaire par les nuages, environ 72% de l'énergie était disponible en surface pour les processus biologiques et physiques. Il faut noter l'importance du flux de chaleur sensible et l'advection de l'air froid provenant de la Baie.Total insolation and net radiation were measured for a wide variety of surfaces at Poste-de-la-Baleine, Québec, from May 30 to June 1, 1970, during alternating cyclonic and anticyclonic situations. With the exception of open water in southeastem James Bay and in the vicinity of the Belcher Islands, the ice cover was complete over Hudson Bayand westerly and southwesterly flow were associated with cool, wet, cloudy weather. For cloudy conditions, including fog and cirrus, and damp surfaces, a close linear relationship was found to exist between net radiation and total insolation for all surfaces. The results indicated that although the insolation was much reduced by cloud cover, about 72% of the energy was available at the surface for physical and biological processes. The importance of the sensible heat flux is noted, and of the cold advection from the Bay
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