Bimetallic au/ag metal superstructures from macromolecular metal complexes in solid-state

Indexación: Web of Science; Scielo.Novel bimetallic Au/Ag superstructures have been prepared from solid-state pyrolysis of the macromolecular complexes Chitosan(MLn/M'Ln)n y PSP-4-PVPx( MLn/M'Ln)n with MLn = AuCl3 and M'Ln = Ag(CF3SO3)The characterization was made from XRD (X-ray diffraction of powder), SEM and EDS analysis. Morphologies are influenced by both the nature of the polymer and the metal/polymer, molar ratio of the polymer precursor. EDS analysis suggests a core/shell Au/Ag structure for the materials. A probable mechanism of the formation of these superstructures is discussed. Although separated reports of metallic superstructures of Au or Ag have been recently described, the here reported are the first bimetallic Au/Ag. Key words: Superstructures, Macromolecular complexes, metallic Au and Ag, Pyrolysishttp://ref.scielo.org/y6jcg

Multi-state Boson Stars

Motivated by the increasing interest in models which consider scalar fields as viable dark matter candidates, we have constructed a generalization of relativistic Boson Stars (BS) composed of two coexisting states of the scalar field, the ground state and the first excited state. We have studied the dynamical evolution of these Multi-state Boson Stars (MSBS) under radial perturbations, using numerical techniques. We show that stable MSBS can be constructed, when the number of particles in the first excited state, N2, is smaller than the number of particles in the ground state, N1. On the other hand, when N2 > N1, the configurations are initially unstable. However, they evolve and settle down into stable configurations. In the stabilization process, the initially ground state is excited and ends in a first excited state, whereas the initially first excited state ends in a ground state. During this process, both states emit scalar field radiation, decreasing their number of particles. This behavior shows that even though BS in the first excited state are intrinsically unstable under finite perturbations, the configuration resulting from the combination of this state with the ground state produces stable objects. Finally we show in a qualitative way, that stable MSBS could be realistic models of dark matter galactic halos, as they produce rotation curves that are flatter at large radii than the rotation curves produced by BS with only one state.Comment: 14 pages. Extended discussion and new figures added. Conclusions unchanged. Accepted for publication in Physical Review

The role of visual management in collaborative integrated planning and control for engineer-to-order building systems

Visual Management is a key approach in the implementation of Lean Production. It emphasizes the importance of developing easy-to-understand visual devices for sharing knowledge within an organization. Such visual devices can play an important role in mitigating the complexity of engineer-to-order production systems. A major difficulty in managing engineer-to-order prefabricated building systems is the need to integrate planning and control of different processes, such as design, fabrication and assembly on site, in a multiple project environment. This paper reports preliminary findings on the implementation of visual devices for collaborative and integrated planning and control in a Steel Fabricator, which designs, fabricates and assembles steel structures. The aim of this paper is to understand how visual management tools can contribute to improve the effectiveness of planning and control in this environment. A set of visual devices have been used in the planning and control system in this company, including a panel that makes available information about 200 simultaneous contracts in an easy-to-understand way. The implementation of those tools has enhanced the participation of different people in the planning process from operational levels or from the different production units

General-relativistic resistive magnetohydrodynamics in three dimensions: Formulation and tests

We present a new numerical implementation of the general-relativistic resistive magnetohydrodynamics (MHD) equations within the Whisky code. The numerical method adopted exploits the properties of implicit-explicit Runge-Kutta numerical schemes to treat the stiff terms that appear in the equations for large electrical conductivities. Using tests in one, two, and three dimensions, we show that our implementation is robust and recovers the ideal-MHD limit in regimes of very high conductivity. Moreover, the results illustrate that the code is capable of describing scenarios in a very wide range of conductivities. In addition to tests in flat spacetime, we report simulations of magnetized nonrotating relativistic stars, both in the Cowling approximation and in dynamical spacetimes. Finally, because of its astrophysical relevance and because it provides a severe testbed for general-relativistic codes with dynamical electromagnetic fields, we study the collapse of a nonrotating star to a black hole. We show that also in this case our results on the quasinormal mode frequencies of the excited electromagnetic fields in the Schwarzschild background agree with the perturbative studies within 0.7% and 5.6% for the real and the imaginary part of the l=1 mode eigenfrequency, respectively. Finally we provide an estimate of the electromagnetic efficiency of this process.Comment: 22 pages, 19 figure

Structure, Microstructure, and Some Selected Mechanical Properties of Ti-Ni Alloys

Titanium nickel (Ti-Ni) alloys with low nickel (Ni) content can be used as biomaterials because they improve the mechanical properties, corrosion, and wear resistance of commercially pure titanium (Cp-Ti). Among the mechanical properties of a biomaterial, elastic modulus and microhardness are very important, and each varies according to the microstructure and interstitial elements such as oxygen and nitrogen as well as the amount of substitutional element and thermomechanical processing. Heat treatments are used to obtain a homogeneous microstructure, free of internal stresses structural, microstructural, also to retain or change the size of the phases. In this chapter, the preparation, chemical, structural, and microstructural, and mechanical characterization of Ti-Ni alloys are presented. The structural and microstructural characterization showed the predominant presence of α and Ti2Ni phases. There is no clear variation of the microhardness due to the amount of nickel. The dynamic elastic modulus was slightly above the Cp-Ti due to the addition of a new intermetallic phase (Ti2Ni) but did not vary significantly with the amount of Ni

Analysis of the presynaptic signaling mechanisms underlying the inhibition of LTP in rat dentate gyrus by the tyrosine kinase inhibitor, genistein

No abstract

Estilos de aprendizagem de futuros professores e estratégias de ensino da matemática no 1.º ciclo do ensino básico

Considerando que as estratégias de ensino utilizadas pelos professores para ensinarem Matemática influenciam a aprendizagem dos alunos e que os estilos de aprendizagem podem interferir na definição das estratégias de cada professor, nesta reflexão enfatizamos os aspectos defendidos pelos alunos, futuros professores de Matemática da Educação Básica, bem como a relação das estratégias defendidas com os seus estilos de aprendizagem. O principal objectivo desta investigação consiste em identificar os estilos de aprendizagem de uma amostra de futuros professores e averiguar as características que enfatizam para as estratégias de ensino e aprendizagem da Matemática ao nível do 1.º Ciclo do Ensino Básico. Dos resultados da investigação provenientes de uma amostra de alunos do ensino superior, destaca-se que a maioria dos futuros professores da Educação Básica tem como estilo predominante o estilo reflexivo, atendendo à classificação dos estilos de aprendizagem seguida por Alonso, Gallego e Honey (1999). Os indicadores relativos às estratégias de ensino e aprendizagem acerca de competências, actividades, recursos e formas de trabalhar assumem diversos aspectos comuns nos vários estilos de aprendizagem