Quantum Conductance in Silver Nanowires: correlation between atomic structure and transport properties

We have analyzed the atomic arrangements and quantum conductance of silver nanowires generated by mechanical elongation. The surface properties of Ag induce unexpected structural properties, as for example, predominance of high aspect ratio rod-like wires. The structural behavior was used to understand the Ag quantum conductance data and the proposed correlation was confirmed by means of theoretical calculations. These results emphasize that the conductance of metal point contacts is determined by the preferred atomic structures and, that atomistic descriptions are essential to interpret the quantum transport behavior of metal nanostructures.Comment: 4 pages, 4 figure

The role of structural evolution on the quantum conductance behavior of gold nanowires during stretching

Gold nanowires generated by mechanical stretching have been shown to adopt only three kinds of configurations where their atomic arrangements adjust such that either the [100], [111] or [110] zone axes lie parallel to the elongation direction. We have analyzed the relationship between structural rearrangements and electronic transport behavior during the elongation of Au nanowires for each of the three possibilities. We have used two independent experiments to tackle this problem, high resolution transmission high resolution electron microscopy to observe the atomic structure and a mechanically controlled break junction to measure the transport properties. We have estimated the conductance of nanowires using a theoretical method based on the extended H\"uckel theory that takes into account the atom species and their positions. Aided by these calculations, we have consistently connected both sets of experimental results and modeled the evolution process of gold nanowires whose conductance lies within the first and third conductance quanta. We have also presented evidence that carbon acts as a contaminant, lowering the conductance of one-atom-thick wires.Comment: 10 page

Enraizamento de estacas caulinares de kiwi (Actinidia chinensis Planch cv Abbott) tratadas com auxinas e boro

This study was carried out to evaluate the effects of some synthetical auxins and boron trade formulations in the rooting of stem cuttings of some kiwi (Actinidia chinensis Planch) varieties. The experiment was carried out in a misty nebulization chamber in the Botany Department, Bioscience Institute, UNESP, Botucatu -SP. The stem cuttings had two nodes and two leaves cut in half, the basal cut was performed nearly a node and the apical one in the next upper node. The auxin effect in Actinidia chinensis Planch rooting stems was observed through seven different treatments: T1 H(2)0); T2 (NAA 300 ppm); T3 (IBA 300 ppm); T4 (NAA 300 ppm + B); T5 (IBA 300 ppm + B); T6 (NAA 0,5%-talc) and T7 (IBA 0,5%-talc), applied to the stem bases. After these treatments, the stems were placed in suitable rooting dishes, with pure vermiculite in a misty nebulization chamber for 120 days until collection. The evaluation of auxin and boric acid effects in kiwi stem cuttings was made based on the following observations: 1. the percentage of rooted stem cuttings; 2. reductor sugar and total sugar analyses (in g/100 g of dry matter); and 3. tryptophan analyses (in µg/100 mg of dry matter). The results showed that the winter and autumn seasons are the best for rooting of Actinidia chinensis Planch, stem cuttings. The use of auxins in the cuttings showed positive results too and the higher contents of reductor and total sugars, increased rooting percentage.O trabalho teve como finalidade, estudar o efeito de várias auxinas sintéticas em formulações comerciais e do boro, sobre o enraizamento de estacas caulinares de kiwi (Actinidia chinensis Planch, cv Abbott.). As estacas utilizadas continham dois nós e duas folhas cortadas ao meio, com aproximadamente 10 cm de comprimento, onde o corte basal em bisel foi realizado logo abaixo de um nó e o apical acima do outro nó. O efeito das auxinas, sobre o enraizamento de estacas caulinares de kiwi foi verificado mediante os seguintes tratamentos, aplicados sobre as bases das estacas: T1 H(2)0); T2 (NAA 300 ppm); T3 (IBA 300 ppm); T4 (NAA 300 ppm + B); T5 (IBA 300 ppm + B); T6 (NAA 0,5%-pó) e T7 (IBA 0,5%-pó). Após o tratamento das estacas, estas foram plantadas em bandejas de enraizamento, contendo vermiculita pura e colocadas em câmara de nebulização, onde permaneceram por 120 dias, até a sua coleta. Para a avaliação do efeito de auxinas e do ácido bórico, sobre o enraizamento de estacas caulinares de kiwi, foram realizadas as seguintes observações: 1. porcentagem de estacas enraizadas; 2. análise de açúcares redutores e açúcares totais (em g/100 g de matéria seca); 3. análise de triptofano (em µg/100 mg de matéria seca). Os resultados obtidos no processo de enraizamento de estacas caulinares de kiwi (Actinidia chinensis Planch.) variedade Abbott, levou a concluir que o inverno e outono foram as melhores épocas de coleta dos ramos de auxinas para a confecção das estacas. O processo de enraizamento foi ainda incrementado com a aplicação exógena na base das estacas, sendo que o alto teor de açúcares redutores e totais beneficiou a maior porcentagem de enraizamento

Using the Biocheck.UGent™ scoring tool in Irish farrow-to-finish pig farms : Assessing biosecurity and its relation to productive performance

Background: Biosecurity is one of the main factors affecting disease occurrence and antimicrobial use, and it is associated with performance in pig production. However, the importance of specific measures could vary depending on the (national) context. The aim of this study was to describe the biosecurity status in a cohort of Irish pig farms, to investigate which of those biosecurity aspects are more relevant by using the Biocheck.UGent™ scoring system, and to study the impact of such aspects on farm performance. Results: External biosecurity score was high compared to most countries due to the characteristics of the Irish pig sector (i.e. purchasing only semen and breeding gilts on farm). The internal biosecurity score was lower and had greater variability among farms than other EU countries. Using multivariable linear regression, the biosecurity practices explained 8, 23, and 16% of variability in piglet mortality, finisher mortality, and average daily gain, respectively. Three clusters of farms were defined based on their biosecurity scores (0 to 100) using principal components and hierarchical clustering analysis. Scores for clusters 1, 2 and 3 were (mean ± SD) 38 ± 7.6, 61 ± 7.0 and 66 ± 9.8 for internal and 73 ± 5.1, 74 ± 5.3 and 86 ± 4.5 for external biosecurity. Cluster 3 had lower piglet mortality (P = 0.022) and higher average daily gain (P = 0.037) when compared to cluster 2. Conclusions: Irish farms follow European tendencies with internal biosecurity posing as the biggest liability. Our results suggest that practices related to the environment and region, feed, water and equipment supply, and the management of the different stages, need to be addressed in lower performing farms to improve productive performance. Further studies on the economic impact of these biosecurity practices including complementary data on herd health, gilt rearing, piglet management, vaccination and feeding strategies are needed

Carbon footprint of apple and pear : orchards, storage and distribution

Apple and pear represent 51% of fresh fruit orchards in Portugal. This paper presents a life-cycle (LC) greenhouse gas (GHG) assessment (so-called carbon footprint) of 3 apple and 1 pear Portuguese production systems. An LC model and inventory were implemented, encompassing the farm stage (cultivation of fruit trees in orchards), storage and distribution (transport to retail). The functional unit considered in this study was 1 kg of distributed fruit (at retail). Four different LC inventories for orchards were implemented based on data collected from three farms. Inventory data from two storage companies were also gathered. The main results show that the GHG emissions of apple and pear ranged between 192 and 229 gCO2eq kgfruit-1. The GHG emissions (direct and indirect) from the cultivation phase ranged from 36% to 60% of total emissions. Fruit storage, which lasted for as much as 8-10 months, was also responsible for significant emissions due to high energy requirements

Density functional method for nonequilibrium electron transport

We describe an ab initio method for calculating the electronic structure, electronic transport, and forces acting on the atoms, for atomic scale systems connected to semi-infinite electrodes and with an applied voltage bias. Our method is based on the density functional theory (DFT) as implemented in the well tested Siesta approach (which uses non-local norm-conserving pseudopotentials to describe the effect of the core electrons, and linear combination of finite-range numerical atomic orbitals to describe the valence states). We fully deal with the atomistic structure of the whole system, treating both the contact and the electrodes on the same footing. The effect of the finite bias (including selfconsistency and the solution of the electrostatic problem) is taken into account using nonequilibrium Green's functions. We relate the nonequilibrium Green's function expressions to the more transparent scheme involving the scattering states. As an illustration, the method is applied to three systems where we are able to compare our results to earlier ab initio DFT calculations or experiments, and we point out differences between this method and existing schemes. The systems considered are: (1) single atom carbon wires connected to aluminum electrodes with extended or finite cross section, (2) single atom gold wires, and finally (3) large carbon nanotube systems with point defects.Comment: 18 pages, 23 figure

Production of fructo-oligosaccharides by Aspergillus ibericus and their chemical characterization

A great demand for prebiotics is driving the search for new sources of fructo-oligosaccharides (FOS) producers and for FOS with differentiated functionalities. In the present work, FOS production by a new isolated strain of Aspergillus ibericus was evaluated. The temperature of fermentation and initial pH were optimized in shaken flask to yield a maximal FOS production, through a central composite experimental design. FOS were produced in a one-step bioprocess using the whole cells of the microorganism. The model (R2 = 0.918) predicted a yield of 0.56, experimentally 0.53 ± 0.03 gFOS.ginitial sucrose1 was obtained (37.0 °C and a pH of 6.2). A yield of 0.64 ± 0.02 gFOS.ginitial sucrose1 was obtained in the bioreactor, at 38 h, with a content of 118 ± 4 g.L1 in FOS and a purity of 56 ± 3%. The chemical structure of the FOS produced by A. ibericus was determined by HPLC and NMR. FOS were identified as 1-kestose, nystose, and 1F-fructofuranosylnystose. In conclusion, A. ibericus was found to be a good alternative FOS producer.Clarisse Nobre acknowledges the Portuguese Foundation forScience and Technology (FCT) for her Post-Doc Grant [ref. SFRH/BPD/87498/ 2012] and the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124FEDER-027462), the strategic funding of UID/BIO/04469/2013 unit, COMPETE 2020 (POCI-01-0145-FEDER-006684), BioTecNorte operation(NORTE-01-0145-FEDER-000004) and the project MultiBiorefinery (POCI-01-0145-FEDER-016403) funded by European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte.info:eu-repo/semantics/publishedVersio

Conformal linear gravity in de Sitter space II

From the group theoretical point of view, it is proved that the theory of linear conformal gravity should be written in terms of a tensor field of rank-3 and mixed symmetry [Binegar, et al, Phys. Rev. D 27, (1983) 2249]. We obtained such a field equation in de Sitter space [Takook, et al, J. Math. Phys. 51, (2010) 032503]. In this paper, a proper solution to this equation is obtained as a product of a generalized polarization tensor and a massless scalar field and then the conformally invariant two-point function is calculated. This two-point function is de Sitter invariant and free of any pathological large-distance behavior.Comment: 16 pages, no figure, published versio

Higher spin quaternion waves in the Klein-Gordon theory

Electromagnetic interactions are discussed in the context of the Klein-Gordon fermion equation. The Mott scattering amplitude is derived in leading order perturbation theory and the result of the Dirac theory is reproduced except for an overall factor of sixteen. The discrepancy is not resolved as the study points into another direction. The vertex structures involved in the scattering calculations indicate the relevance of a modified Klein-Gordon equation, which takes into account the number of polarization states of the considered quantum field. In this equation the d'Alembertian is acting on quaternion-like plane waves, which can be generalized to representations of arbitrary spin. The method provides the same relation between mass and spin that has been found previously by Majorana, Gelfand, and Yaglom in infinite spin theories