65,870 research outputs found

    NLTE analysis of Sr lines in spectra of late-type stars with new R-matrix atomic data

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    We investigate statistical equilibrium of neutral and singly-ionized strontium in late-type stellar atmospheres. Particular attention is given to the completeness of the model atom, which includes new energy levels, transition probabilities, photoionization and electron-impact excitation cross-sections computed with the R-matrix method. The NLTE model is applied to the analysis of Sr I and Sr II lines in the spectra of the Sun, Procyon, Arcturus, and HD 122563, showing a significant improvement in the ionization balance compared to LTE line formation calculations, which predict abundance discrepancies of up to 0.5 dex. The solar Sr abundance is log A = 2.93 \pm 0.04 dex, in agreement with the meteorites. A grid of NLTE abundance corrections for Sr I and Sr II lines covering a large range of stellar parameters is presented.Comment: 11 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

    Disconnections in US and EU Agricultural Policy and Trade Negotiations: A Transaction Cost Politics Approach

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    This article investigates aspects of the institutions and decision making processes in the United States and the European Union that affect the coordination of domestic farm programs and trade negotiations for agriculture in each entity. We explore how current institutions and processes contribute to a level of incoherence - or lack of coordination - between domestic farm programs and trade negotiations in the United States. Constructs from transaction cost politics with an emphasis on the decision to delegate authority from the principal to an agent are used to understand how institutional processes affect the coordination of domestic legislation.This article investigates aspects of the institutions and decision making processes in the United States and the European Union that affect the coordination of domestic farm programs and trade negotiations for agriculture in each entity. We explore how current institutions and processes contribute to a level of incoherence - or lack of coordination - between domestic farm programs and trade negotiations in the United States. Constructs from transaction cost politics with an emphasis on the decision to delegate authority from the principal to an agent are used to understand how institutional processes affect the coordination of domestic legislation., Agribusiness, Agricultural and Food Policy, Agricultural Finance, Crop Production/Industries, Farm Management, Political Economy,

    Dislocation subgrain structures and modeling the plastic hardening of metallic single crystals

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    A single crystal plasticity theory for insertion into finite element simulation is formulated using sequential laminates to model subgrain dislocation structures. It is known that local models do not adequately account for latent hardening, as latent hardening is not only a material property, but a nonlocal property (e.g. grain size and shape). The addition of the nonlocal energy from the formation of subgrain structure dislocation walls and the boundary layer misfits provide both latent and self-hardening of a crystal slip. Latent hardening occurs as the formation of new dislocation walls limits motion of new mobile dislocations, thus hardening future slip systems. Self-hardening is accomplished by an evolution of the subgrain structure length scale. The substructure length scale is computed by minimizing the nonlocal energy. The minimization of the nonlocal energy is a competition between the dislocation wall energy and the boundary layer energies. The nonlocal terms are also directly minimized within the subgrain model as they affect deformation response. The geometrical relationship between the dislocation walls and slip planes affecting the dislocation mean free path is taken into account, giving a first-order approximation to shape effects. A coplanar slip model is developed due to requirements while modeling the subgrain structure. This subgrain structure plasticity model is noteworthy as all material parameters are experimentally determined rather than fit. The model also has an inherit path dependence due to the formation of the subgrain structures. Validation is accomplished by comparison with single crystal tension test results

    Observational constraint on the fourth derivative of the inflaton potential

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    We consider the flow-equations for the 3 slow-roll parameters n_S (scalar spectral index), r (tensor to scalar ratio), and dn_S/dlnk (running of the spectral index). We show that the combination of these flow-equations with the observational bounds from cosmic microwave background and large scale structure allows one to put a lower bound on the fourth derivative of the inflationary potential, M_P^4(V''''/V) > -0.02.Comment: 3 pages, 3 figure

    A comparative study of two 47 Tuc giant stars with different s-process enrichment

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    Here we aim to understand the origin of 47 Tuc's La-rich star Lee 4710. We report abundances for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, and Eu, and present a detailed abundance analysis of two 47 Tuc stars with similar stellar parameters but different slow neutron-capture (s-)process enrichment. Star Lee 4710 has the highest known La abundance ratio in this cluster ([La/Fe] = 1.14), and star Lee 4626 is known to have normal s-process abundances (e.g., [Ba/Eu]<0<0). The nucleosynthetic pattern of elements with Z≳\gtrsim56 for star Lee 4710 agrees with the predicted yields of a 1.3M⊙1.3M_{\odot} asymptotic giant branch (AGB) star. Therefore, Lee 4710 may have been enriched by mass transfer from a more massive AGB companion, which is compatible with its location far away from the center of this relatively metal-rich ([Fe/H]∼−0.7\sim-0.7) globular cluster. A further analysis comparing the abundance pattern of Lee 4710 with data available in the literature reveals that nine out of the ∼200\sim200 47 Tuc stars previously studied show strong s-process enhancements that point towards later enrichment by more massive AGB stars.Comment: ApJL in press. 6 pages, 4 figure

    The QCD Critical End Point in the Context of the Polyakov--Nambu--Jona-Lasinio Model

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    We investigate the phase diagram of the so-called Polyakov--Nambu--Jona-Lasinio model at finite temperature and nonzero chemical potential with three quark flavors. Chiral and deconfinement phase transitions are discussed, and the relevant order-like parameters are analyzed. A special attention is payed to the critical end point (CEP): the influence of the strangeness on the location of the CEP is studied; also the strength of the flavor-mixing interaction alters the CEP location, once when it becomes weaker the CEP moves to low temperatures and can even disappear.Comment: Prepared for Strangeness in Quark Matter 2011, Sept. 18--24, Cracow, Polan

    Exploring the role of model parameters and regularization procedures in the thermodynamics of the PNJL model

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    The equation of state and the critical behavior around the critical end point are studied in the context of the Polyakov--Nambu--Jona--Lasinio model. We prove that a convenient choice of the model parameters is crucial to get the correct description of isentropic trajectories. The physical relevance of the effects of the regularization procedure is insured by the agreement with general thermodynamic requirements. The results are compared with simple thermodynamic expectations and lattice data.Comment: Talk given at XIII International Conference on Hadron Spectroscopy (Hadron 2009), Tallahassee, Florida, USA, 29 Nov - 4 Dec, 200

    How parameters and regularization affect the PNJL model phase diagram and thermodynamic quantities

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    We explore the phase diagram and the critical behavior of QCD thermodynamic quantities in the context of the so-called Polyakov--Nambu--Jona-Lasinio model. We show that this improved field theoretical model is a successful candidate for studying the equation of state and the critical behavior around the critical end point. We argue that a convenient choice of the model parameters is crucial to get the correct description of isentropic trajectories. The effects of the regularization procedure in several thermodynamic quantities is also analyzed. The results are compared with simple thermodynamic expectations and lattice data.Comment: 27 pages, 7 figures, 4 tables; PRD versio
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