131 research outputs found

    GENOTYPE X ENVIRONMENT INTERACTION IN GRAPES RIPENING METABOLIC TRAITS

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    Objectives of the first part of research program were the effect of some environmental and physiological aspects on the intensity of flavonoid synthesis. The trial was carried out during the 2011 growing season in the commercial vineyard of the Plantaze, Podgorica (Montenegro). Two grapevine cultivars were compared: Vranac and Cabernet Sauvignon. The following experimental treatments were compared: early leaf removal (flowering time), cluster thinning (veraison time) and combination of both treatments. The early defoliation reduced yield per vine in Cabernet Sauvignon and Vranac. In Cabernet Sauvignon defoliation initially delayed berry growth. In cultivar Vranac defoliation did not modify the berry growth and berry weight. In the treatments \u201cdefoliated-thinned\u201d is observed reduction of the cluster weight, berry weight and berry number per cluster. Early defoliation and cluster thinning in both varieties raised the concentration of anthocyanins and proanthocyanidins. The enhanced contents of these compounds per berry in variety Vranac is the result of increased synthesis. The objective of second study was to improve the knowledge of the eco-physiological basis of the genotype x environmental interaction. The experimental plan included the study of the Sangiovese grapes, a variety by a particular responsiveness to changing environmental conditions, and Cabernet Sauvignon grapes, a so called international cultivar characterized by more stable features. It was operated within the framework of Appellations of Origin Bolgheri (Tuscany coast), Montalcino (Tuscany Apennines) and Misano (Romagna coast). The experiment was conducted during two growing seasons (2011-2012) through grape development and ripening from fruit set to ripe stage. Since carotenoids are the precursors to C13-norisoprenoid aroma compounds in wine, relationship between carotenoid and norisoprenoid levels in grapes was investigated. In the first phase of berry ripening, before veraison, sites with greater global solar radiation (Montalcino and Bolgheri) showed positive correlation with the intensity of total carotenoids accumulation. Location Montalcino was also characterized by a greater water stress. Correlation between carotenoids accumulation prior to veraison and accumulation of norisoprenoids were not observed. Sangiovese showed a greater reactivity to the environment compared to Cabernet Sauvignon. The norisoprenoids levels in variety Sangiovese largely varied between different years and sites. The synthesis of norisoprenoids appears to be more related to the specific ecophysiological conditions that occur during maturation, rather than to the carotenoids content at veraison

    Diffusion of Pt dimers on Pt(111)

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    We report the results of a density-functional study of the diffusion of Pt dimers on the (111) surface of Pt. The calculated activation energy of 0.37 eV is in {\em exact} agreement with the recent experiment of Kyuno {\em et al.} \protect{[}Surf. Sci. {\bf 397}, 191 (1998)\protect{]}. Our calculations establish that the dimers are mobile at temperatures of interest for adatom diffusion, and thus contribute to mass transport. They also indicate that the diffusion path for dimers consists of a sequence of one-atom and (concerted) two-atom jumps.Comment: Pour pages postscript formatted, including one figure; submitted to Physical Review B; other papers of interest can be found at url http://www.centrcn.umontreal.ca/~lewi

    Implication of the overlap representation for modelling generalized parton distributions

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    Based on a field theoretically inspired model of light-cone wave functions, we derive valence-like generalized parton distributions and their double distributions from the wave function overlap in the parton number conserved s-channel. The parton number changing contributions in the t-channel are restored from duality. In our construction constraints of positivity and polynomiality are simultaneously satisfied and it also implies a model dependent relation between generalized parton distributions and transverse momentum dependent parton distribution functions. The model predicts that the t-behavior of resulting hadronic amplitudes depends on the Bjorken variable x_Bj. We also propose an improved ansatz for double distributions that embeds this property.Comment: 15 pages, 8 eps figure

    Island diffusion on metal fcc(100) surfaces

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    We present Monte Carlo simulations for the size and temperature dependence of the diffusion coefficient of adatom islands on the Cu(100) surface. We show that the scaling exponent for the size dependence is not a constant but a decreasing function of the island size and approaches unity for very large islands. This is due to a crossover from periphery dominated mass transport to a regime where vacancies diffuse inside the island. The effective scaling exponents are in good agreement with theory and experiments.Comment: 13 pages, 2 figures, to be published in Phys. Rev. Let

    Changing shapes in the nanoworld

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    What are the mechanisms leading to the shape relaxation of three dimensional crystallites ? Kinetic Monte Carlo simulations of fcc clusters show that the usual theories of equilibration, via atomic surface diffusion driven by curvature, are verified only at high temperatures. Below the roughening temperature, the relaxation is much slower, kinetics being governed by the nucleation of a critical germ on a facet. We show that the energy barrier for this step linearly increases with the size of the crystallite, leading to an exponential dependence of the relaxation time.Comment: 4 pages, 5 figures. Accepted by Phys Rev Let

    The effects of early leaf removal and cluster thinning treatments on berry growth and grape composition in cultivars Vranac and Cabernet Sauvignon

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    Background: The aim of the present work was to investigate the effect of early leaf removal and cluster thinning treatments in the Mediterranean climate on berry growth and how these two techniques affect phenolic profile (especially proathocyanidins) and color characteristics for later wine production. The study was conducted in 2011 in Podgorica, Montenegro. Two grapevine cultivars were selected to compare different ability in flavonoid accumulation: Vranac, with moderate accumulation and Cabernet Sauvignon, usually showing very good accumulation of polyphenols. Four treatments were compared: only leaf removal, only cluster thinning, leaf removal combined with cluster thinning, and no treatment that was used for control (control set). Results: Early defoliation reduced the yield in both varieties. In Cabernet Sauvignon, defoliation initially delayed berry growth, but at the end, defoliation slightly affected almost all yield parameters (cluster weight, berry weight, and number of berries per cluster), while in cultivar Vranac, defoliation did not modify the berry growth and berry weight. In both varieties, cluster thinning did not affect the berry weight. In the treatments where both defoliation and cluster thinning was applied, a reduction of the cluster weight, berry weight, and berry numbers per cluster was observed. Cabernet Sauvignon showed a greater reactivity to the applied techniques, while Vranac was less reactive. At harvest, no damaged bunches (caused by sunburn) were found in defoliated treatment. Conclusions: It can be concluded that for both varieties, early defoliation and cluster thinning lead to better soluble solids accumulation than in the control set. The treatments lead to raised concentration of anthocyanins and proanthocyanidins in both varieties. It is confirmed that the highest content of anthocyanins and proanthocyanidins was in the skin extracts of the grapes where both treatments were applied. This is followed by the treatment where only defoliation was applied. The enhanced contents of these compounds per berry in grape variety Vranac are the result of increased synthesis, while in Cabernet sauvignon variety, increased content was due to the less berry weight. The best wine characteristics (alcohol, color intensity, color hue, total anthocyanins, total polyphenols) were found in products, where defoliation was applied

    A contiuum model for low temperature relaxation of crystal steps

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    High and low temperature relaxation of crystal steps are described in a unified picture, using a continuum model based on a modified expression of the step free energy. Results are in agreement with experiments and Monte Carlo simulations of step fluctuations and monolayer cluster diffusion and relaxation. In an extended model where mass exchange with neighboring terraces is allowed, step transparency and a low temperature regime for unstable step meandering are found.Comment: Submitted to Phys.Rev.Let
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