Surface Effects on the Mechanical Elongation of AuCu Nanowires: De-alloying and the Formation of Mixed Suspended Atomic Chains

We report here an atomistic study of the mechanical deformation of AuxCu(1-x) atomic-size wires (NWs) by means of high resolution transmission electron microscopy (HRTEM) experiments. Molecular dynamics simulations were also carried out in order to obtain deeper insights on the dynamical properties of stretched NWs. The mechanical properties are significantly dependent on the chemical composition that evolves in time at the junction; some structures exhibit a remarkable de-alloying behavior. Also, our results represent the first experimental realization of mixed linear atomic chains (LACs) among transition and noble metals; in particular, surface energies induce chemical gradients on NW surfaces that can be exploited to control the relative LAC compositions (different number of gold and copper atoms). The implications of these results for nanocatalysis and spin transport of one-atom-thick metal wires are addressed.Comment: Accepted to Journal of Applied Physics (JAP

Cooking pasta with Lie groups

We extend the (gauged) Skyrme model to the case in which the global isospin group (which usually is taken to be SU(N)) is a generic compact connected Lie group G. We analyze the corresponding field equations in (3+1) dimensions from a group theory point of view. Several solutions can be constructed analytically and are determined by the embeddings of three dimensional simple Lie groups into G, in a generic irreducible representation. These solutions represent the so-called nuclear pasta state configurations of nuclear matter at low energy. We employ the Dynkin explicit classification of all three dimensional Lie subgroups of exceptional Lie group to classify all such solutions in the case G is an exceptional simple Lie group, and give all ingredients to construct them explicitly. As an example, we construct the explicit solutions for G=G2. We then extend our ansatz to include the minimal coupling of the Skyrme field to a U(1) gauge field. We extend the definition of the topological charge to this case and then concentrate our attention to the electromagnetic case. After imposing a \u201cfree force condition\u201d on the gauge field, the complete set of coupled field equations corresponding to the gauged Skyrme model minimally coupled to an Abelian gauge field is reduced to just one linear ODE keeping alive the topological charge. We discuss the cases in which such ODE belongs to the (Whittaker-)Hill and Mathieu types

Mechanical Deformation Of Nanoscale Metal Rods: When Size And Shape Matter.

Face centered cubic metals deform mainly by propagating partial dislocations generating planar fault ribbons. How do metals deform if the size is smaller than the fault ribbons? We studied the elongation of Au and Pt nanorods by in situ electron microscopy and ab initio calculations. Planar fault activation barriers are so low that, for each temperature, a minimal rod size is required to become active for releasing elastic energy. Surface effects dominate deformation energetics; system size and shape determine the preferred fault gliding directions which induce different tensile and compressive behavior.10605550

O estudo da Agroecologia como disciplina dentro dos cursos tradicionais de Engenharia Agronômica

O presente trabalho pretende entender as dificuldades em ministrar a Agroecologia como disciplina dentro de cursos tradicionais de Engenharia Agronômica. Como objetivo pretendido neste estudo está a caracterização de como a Agroecologia é vista dentro de um currículo tradicionais pelos acadêmicos, como ela é trabalhada pelo professor dentro desta ótica tradicional de agricultura voltada ao agronegócio e as dificuldades encontradas em trabalhar a disciplina dentro de uma visão curricular ainda tradicional. Este trabalho tem como importância entender como seria a melhor forma de trabalhar a disciplina dentro de um modelo tradicional de Engenharia Agronômica. A metodologia usada foi o estudo de caso da disciplina de Agroecologia do Instituto Federal do Paraná (IFPR) do curso de Engenharia Agronômica do Campus Palmas (PR) ministrada para duas turmas. Conclui-se que os alunos tem uma ideia equivocada do que é Agroecologia e muitas dúvidas sobre o assunto e muitos deles não creem que seja possível se ter uma agricultura que tenha como pilares a Agroecologia.This work intends to understand the difficulties of ministering to Agroecology as a discipline within traditional courses of Agricultural Engineering. As intended goal in this study is the characterization of how Agroecology is seen within a traditional curriculum for academic, as it is worked by the teacher under this perception of traditional agriculture and agribusiness focused on the difficulties encountered in working discipline within a curricular vision yet traditional. This work is important to understand how would be the best way of working discipline within a traditional model of Agronomy. The methodology used was the case study of Agroecology discipline of the Federal Institute of Paraná (IFPR) the course of the Agronomic Engineering Campus Palmas (PR) given to two groups. It was concluded that students have a mistaken idea of what Agroecology and many questions about it and many of them do not believe it is possible to have an agriculture that has as pillars Agroecology.Eje A5: Sistemas de conocimientoFacultad de Ciencias Agrarias y Forestale

O estudo da Agroecologia como disciplina dentro dos cursos tradicionais de Engenharia Agronômica

O presente trabalho pretende entender as dificuldades em ministrar a Agroecologia como disciplina dentro de cursos tradicionais de Engenharia Agronômica. Como objetivo pretendido neste estudo está a caracterização de como a Agroecologia é vista dentro de um currículo tradicionais pelos acadêmicos, como ela é trabalhada pelo professor dentro desta ótica tradicional de agricultura voltada ao agronegócio e as dificuldades encontradas em trabalhar a disciplina dentro de uma visão curricular ainda tradicional. Este trabalho tem como importância entender como seria a melhor forma de trabalhar a disciplina dentro de um modelo tradicional de Engenharia Agronômica. A metodologia usada foi o estudo de caso da disciplina de Agroecologia do Instituto Federal do Paraná (IFPR) do curso de Engenharia Agronômica do Campus Palmas (PR) ministrada para duas turmas. Conclui-se que os alunos tem uma ideia equivocada do que é Agroecologia e muitas dúvidas sobre o assunto e muitos deles não creem que seja possível se ter uma agricultura que tenha como pilares a Agroecologia.This work intends to understand the difficulties of ministering to Agroecology as a discipline within traditional courses of Agricultural Engineering. As intended goal in this study is the characterization of how Agroecology is seen within a traditional curriculum for academic, as it is worked by the teacher under this perception of traditional agriculture and agribusiness focused on the difficulties encountered in working discipline within a curricular vision yet traditional. This work is important to understand how would be the best way of working discipline within a traditional model of Agronomy. The methodology used was the case study of Agroecology discipline of the Federal Institute of Paraná (IFPR) the course of the Agronomic Engineering Campus Palmas (PR) given to two groups. It was concluded that students have a mistaken idea of what Agroecology and many questions about it and many of them do not believe it is possible to have an agriculture that has as pillars Agroecology.Eje A5: Sistemas de conocimientoFacultad de Ciencias Agrarias y Forestale

The SAMI Galaxy Survey: Stellar population radial gradients in early-type galaxies

We study the internal radial gradients of the stellar populations in a sample comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney- AAO Multi-object Integral field spectrograph) Galaxy Survey. We stack the spectra of individual spaxels in radial bins, and derive basic stellar population properties: total metallicity ([Z/H]), [Mg/Fe], [C/Fe] and age. The radial gradient ($\nabla$) and central value of the fits (evaluated at R$_e$/4) are compared against a set of six possible drivers of the trends. We find that velocity dispersion ($\sigma$) - or, equivalently gravitational potential - is the dominant driver of the chemical composition gradients. Surface mass density is also correlated with the trends, especially with stellar age. The decrease of $\nabla$[Mg/Fe] with increasing $\sigma$ is contrasted by a rather shallow dependence of $\nabla$[Z/H] with $\sigma$ (although this radial gradient is overall rather steep). This result, along with a shallow age slope at the massive end, imposes stringent constraints on the progenitors of the populations that contribute to the formation of the outer envelopes of ETGs. The SAMI sample is split between a 'field' sample and a cluster sample. Only weak environment-related differences are found, most notably a stronger dependence of central total metallicity ([Z/H]$_{e4}$) with $\sigma$, along with a marginal trend of $\nabla$[Z/H] to steepen in cluster galaxies, a result that is not followed by [Mg/Fe]. The results presented here serve as constraints on numerical models of the formation and evolution of ETGs.Comment: 14 pages, 9 figures, 3 tables. Submitted to MNRA

The complete and fully assembled genome sequence of Aeromonas salmonicida subsp. pectinolytica and its comparative analysis with other Aeromonas species: investigation of the mobilome in environmental and pathogenic strains.

Due to the predominant usage of short-read sequencing to date, most bacterial genome sequences reported in the last years remain at the draft level. This precludes certain types of analyses, such as the in-depth analysis of genome plasticity. Here we report the finalized genome sequence of the environmental strain Aeromonas salmonicida subsp. pectinolytica 34mel, for which only a draft genome with 253 contigs is currently available. Successful completion of the transposon-rich genome critically depended on the PacBio long read sequencing technology. Using finalized genome sequences of A. salmonicida subsp. pectinolytica and other Aeromonads, we report the detailed analysis of the transposon composition of these bacterial species. Mobilome evolution is exemplified by a complex transposon, which has shifted from pathogenicity-related to environmental-related gene content in A. salmonicida subsp. pectinolytica 34mel. Obtaining the complete, circular genome of A. salmonicida subsp. pectinolytica allowed us to perform an in-depth analysis of its mobilome. We demonstrate the mobilome-dependent evolution of this strain's genetic profile from pathogenic to environmental

WD 1856 b: a close giant planet around a white dwarf that could have survived a common-envelope phase

The discovery of a giant planet candidate orbiting the white dwarf WD 1856+534 with an orbital period of 1.4 d poses the questions of how the planet reached its current position. We here reconstruct the evolutionary history of the system assuming common envelope evolution as the main mechanism that brought the planet to its current position. We find that common envelope evolution can explain the present configuration if it was initiated when the host star was on the AGB, the separation of the planet at the onset of mass transfer was in the range 1.69-2.35 au, and if in addition to the orbital energy of the surviving planet either recombination energy stored in the envelope or another source of additional energy contributed to expelling the envelope. We also discuss the evolution of the planet prior to and following common envelope evolution. Finally, we find that if the system formed through common envelope evolution, its total age is in agreement with its membership to the Galactic thin disc. We therefore conclude that common envelope evolution is at least as likely as alternative formation scenarios previously suggested such as planet-planet scattering or Kozai-Lidov oscillations.Comment: 7 pages, 3 figures, 2 tables; accepted for publication in MNRA

Determinação do teor de metilxantinas e análise da variabilidade genética de seis variedades populares de erva-mate.

Os objetivos deste estudo foram determinar os conteúdos de metilxantinas e cafeína em folhas maduras de seis “variedades” populares de erva-mate (Ilex paraguariensis St. Hil. Aquifoliaceae) e avaliar a distância genética entre estas diferentes “variedades” por meio de marcadores RAPD (Random Amplified Polimorphic DNA). A concentração de metilxantinas foi determinada por espectrofotometria UV e a de cafeína por cromatografia gasosa. Foram estudadas seis “variedades” de erva-mate: nativa, folha grande, folha brilhosa, talo-roxo e folha cobre (consideradas variedades botânicas Ilex paraguariensis var. paraguariensis) e a “variedade” peluda (considerada variedade botânica Ilex paraguariensis var. vestita). A “variedade” folha cobre apresentou o maior conteúdo de metilxantinas (1,65 g%) e de cafeína (1,29 g%). A “variedade” peluda mostrou o menor teor de metilxantinas (0,25 g%) e de cafeína (0,06 g%). A diferença entre a quantidade de metilxantinas e cafeína deve-se provavelmente ao conteúdo das outras metilxantinas presentes na erva-mate, como a teobromina e a teofilina. Estas diferenças não foram observadas através de marcadores RAPD. De acordo com as análises do polimorfismo gerado pelo marcador RAPD, foram formados dois grupos distintos, os quais mostraram 58% de similaridade entre eles, utilizando o coeficiente de Jaccard. Um dos grupos incluiu as “variedades” folha cobre, peluda e nativa e o outro as “variedades” folha grande, brilhosa e talo roxo.bitstream/item/16992/1/Boletim_de_pesquisa08.pd

Intrinsic Stability Of The Smallest Possible Silver Nanotube.

Recently, Lagos et al. [Nature Nanotech. 4, 149 (2009)] reported the discovery of the smallest possible Ag nanotube with a square cross section. Ab initio density functional theory calculations strongly support that the stability of these hollow structures is structurally intrinsic and not the result of contamination by light atoms. We also report the first experimental observation of the theoretically predicted corrugation of the hollow structure. Quantum conductance calculations predict a unique signature of 3.6 G0 for this new family of nanotubes.10606550