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Pasto, Colombia

Bertin M.C.,Federal University of ABC | Pimentel B.M.,Sao Paulo State University | Valcarcel C.E.,Sao Paulo State University | Zambrano G.E.R.,University Nario
Classical and Quantum Gravity | Year: 2011

In this work, we study the theory of linearized gravity via the Hamilton-Jacobi formalism. We make a brief review of this theory and its Lagrangian description, as well as a review of the Hamilton-Jacobi approach for singular systems. Then, we apply this formalism to analyze the constraint structure of the linearized gravity in instant- and front-form dynamics. © 2011 IOP Publishing Ltd. Source

Insuasty H.,University Nario | Castro E.,University Nario | Sanchez E.,University Nario | Cobo J.,University of Jaen | Glidewell C.,University of St. Andrews
Acta Crystallographica Section C: Crystal Structure Communications | Year: 2010

In O-ethyl N-benzoylthiocarbamate, C10H11NO 2S, the molecules are linked into sheets by a combination of two-centre N-H⋯O and C-H⋯S hydrogen bonds and a three-centre C-H⋯(O,S) hydrogen bond. A combination of two-centre N-H⋯O and C-H⋯O hydrogen bonds links the molecules of O-ethyl N-(4-methyl-benzoyl) thiocarbamate, C11H13NO2S, into chains of rings, which are linked into sheets by an aromatic π-π stacking interaction. In O,S-diethyl N-(4-methylbenzoyl)imidothiocarbonate, C 13H17NO2S, pairs of molecules are linked into centrosymmetric dimers by pairs of symmetry-related C-H⋯π(arene) hydrogen bonds, while the molecules of O,S-diethyl N-(4-chloro-benzoyl) imidothiocarbonate, C12H14ClNO2S, are linked by a single C-H⋯O hydrogen bond into simple chains, pairs of which are linked by an aromatic π-π stacking interaction to form a ladder-type structure. © 2010 International Union of Crystallography. Source

Mera J.,University Nario | Doria J.,National University of Colombia | Crdoba C.,University Nario | Paredes O.,University Nario | And 4 more authors.
Physica B: Condensed Matter | Year: 2010

Zn0.9Mn0.1O thin films were prepared by pulsed laser deposition (PLD) on c-Al2O3(0 0 0 1) substrates. The polymeric precursor method was used to synthesize the powders from which the ablation targets were fabricated. Zn0.9Mn0.1O films ablated from these targets showed excellent epitaxial growth with a full-width at half-maximum (FWHM) ∼0.07°. Probably, the purity offered by the soft chemistry methods to prepare ceramic-type polycrystalline compounds with nanometric particle size plays an important role in achieving high-quality films of novel oxides as Mn-doped ZnO. Interestingly, the Zn0.9Mn 0.1O films displayed well-defined magnetic hysteresis loops both at room temperature and 5 K, which points out to the presence of ferromagnetic order in the films. Nevertheless, the mechanism leading to room temperature ferromagnetism in the Mn-doped ZnO is not fully established. Probably, unpaired electron spins responsible for ferromagnetism in the films have their origin in the oxygen vacancies, especially on the surfaces of the oxide nanoparticles. The oxygen deficiency would result from thin film growth conditions as the studied samples were grown in low-pressure oxygen atmosphere (1×10-4 mbar). © 2010 Elsevier B.V. All rights reserved. Source

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