2,345 research outputs found
Euclidean Supersymmetry, Twisting and Topological Sigma Models
We discuss two dimensional N-extended supersymmetry in Euclidean signature
and its R-symmetry. For N=2, the R-symmetry is SO(2)\times SO(1,1), so that
only an A-twist is possible. To formulate a B-twist, or to construct Euclidean
N=2 models with H-flux so that the target geometry is generalised Kahler, it is
necessary to work with a complexification of the sigma models. These issues are
related to the obstructions to the existence of non-trivial twisted chiral
superfields in Euclidean superspace.Comment: 8 page
Leaf morphoanatomy of four red grapevine cultivars grown under the same terroir
XII Congreso Internacional TerroirThis study compare leaf morphoanatomical characteristics of four red cultivars - âTouriga
Nacionalâ, âTrindadeiraâ, âCabernet Sauvignonâ and âSyrahâ -, grown side by side at the same terroir. The
analyzed leaf traits, under light and scanning electron microscopy, showed large variability among genotypes.
âTrincadeiraâ has the biggest single leaf area and âCabernet Sauvignonâ the smallest one. âTouriga Nacionalâ
showed the lowest leaf dry weight and âTrincadeiraâ the highest one, nonetheless there was no significantly
differences in leaf dry mass per area and in leaf density. Leaf dry mass per area was positively correlated with
leaf density but showed no correlation with leaf thickness. The French genotypes presented higher thickness of
the leaf anatomical traits than the two Portuguese ones. âTrincadeiraâ showed significantly highest stomata
density while the other cultivars showed no significant differences among them. The analyses of the three types
of stomata revealed that âTrincadeiraâ has the lower percentage of raised above and the highest percentage of
sunken stomata while âCabernet Sauvignonâ showed the opposite behaviour. The hairs on the lower surface
presented a similar woolly aspect in all cultivars. The possible role of leaf morphoanatomical characteristics in
determining the cultivars adaptation to abiotic stresses is suggested and discussedinfo:eu-repo/semantics/publishedVersio
Anatomia da folha de cultivares brancas de videira com distinta origem geogrĂĄfica
This study aims to compare the leaf morphoanatomical characteristics of seven Vitis vinifera subsp. vinifera white cultivars with different
geographical origin, grown side by side at the same âterroirâ. The leaf morphoanatomical traits analyzed under light and scanning electron
microscopy (SEM) showed large variability among genotypes. Significant differences between cultivars were observed in single leaf area, specific
leaf area, leaf density and in the thickness of cuticle, upper and lower epidermal cells and mesophyll. Leaf dry mass per area presented a
significant positive correlation with leaf density but showed no correlation with leaf thickness, results that can be explained by the quite different
mesophyll structure, epidermal cells and cuticle thickness. âAlvarinhoâ, âEncruzadoâ, âMacabeuâ and âViosinhoâ were the cultivars with the
highest thickness of cuticle and mesophyll tissues. Under SEM magnification three types of stomata were identified: sunken, at the same level and
raised above, with the same level type presenting the higher percentage in all cultivars. Stomata density presented significant differences between
cultivars, with âMacabeuâ showing the highest value and âAlvarinhoâ and âArintoâ the lowest ones. The hairs on the lower surface presented a
similar woolly aspect in all cultivars. Calcium oxalate crystals, raphids and druses were visible and widely distributed in the parenchyma tissues.
The observed differences in leaf traits among genotypes suggest a major role of leaf anatomy in determining grapevine capacity for coping with
different environmental conditionsinfo:eu-repo/semantics/publishedVersio
Overcoming the challenge of bunch occlusion by leaves for vineyard yield estimation using image analysis
Accurate yield estimation is of utmost importance for the entire grape and wine production chain,
yet it remains an extremely challenging process due to high spatial and temporal variability in
vineyards. Recent research has focused on using image analysis for vineyard yield estimation,
with one of the major obstacles being the high degree of occlusion of bunches by leaves. This
work uses canopy features obtained from 2D images (canopy porosity and visible bunch area)
as proxies for estimating the proportion of occluded bunches by leaves to enable automatic
yield estimation on non-disturbed canopies. Data was collected from three grapevine varieties,
and images were captured from 1 m segments at two phenological stages (veraison and full
maturation) in non-defoliated and partially defoliated vines. Visible bunches (bunch exposure;
BE) varied between 16 and 64 %. This percentage was estimated using a multiple regression
model that includes canopy porosity and visible bunch area as predictors, yielding a R2 between
0.70 and 0.84 on a training set composed of 70 % of all data, showing an explanatory power
10 to 43 % higher than when using the predictors individually. A model based on the combined
data set (all varieties and phenological stages) was selected for BE estimation, achieving a R2 =
0.80 on the validation set. This model did not show validation metrics differences when applied
on data collected at veraison or full maturation, suggesting that BE can be accurately estimated
at any stage. Bunch exposure was then used to estimate total bunch area (tBA), showing low
errors (< 10 %) except for the variety Arinto, which presents specific morphological traits such
as large leaves and bunches. Finally, yield estimation computed from estimated tBA presented
a very low error (0.2 %) on the validation data set with pooled data. However, when performed
on every single variety, the simplified approach of area-to-mass conversion was less accurate
for the variety Syrah. The method demonstrated in this work is an important step towards a fully
automated non-invasive yield estimation approach, as it offers a solution to estimate bunches
that are not visible to imaging sensorsinfo:eu-repo/semantics/publishedVersio
Yield components detection and image-based indicators for non-invasive grapevine yield prediction at different phenological phases
Forecasting vineyard yield with accuracy is one of the most important trends of research in viticulture today.
Conventional methods for yield forecasting are manual, require a lot of labour and resources and are often
destructive. Recently, image-analysis approaches have been explored to address this issue. Many of these
approaches encompass cameras deployed on ground platforms that collect images in proximal range, on-the-go. As
the platform moves, yield components and other image-based indicators are detected and counted to perform yield
estimations. However, in most situations, when image acquisition is done in non-disturbed canopies, a high fraction
of yield components is occluded. The present workâs goal is twofold. Firstly, to evaluate yield componentsâ
visibility in natural conditions throughout the grapevineâs phenological stages. Secondly, to explore single bunch
images taken in lab conditions to obtain the best visible bunch attributes to use as yield indicators.
In three vineyard plots of red (Syrah) and white varieties (Arinto and Encruzado), several canopy 1 m segments
were imaged using the robotic platform Vinbot. Images were collected from winter bud stage until harvest and yield
components were counted in the images as well as in the field. At pea-sized berries, veraison and full maturation
stages, a bunch sample was collected and brought to lab conditions for detailed assessments at a bunch scale.
At early stages, all varieties showed good visibility of spurs and shoots, however, the number of shoots was only
highly and significantly correlated with the yield for the variety Syrah. Inflorescence and bunch occlusion reached
high percentages, above 50 %. In lab conditions, among the several bunch attributes studied, bunch volume and
bunch projected area showed the highest correlation coefficients with yield. In field conditions, using non-defoliated
vines, the bunch projected area of visible bunches presented high and significant correlation coefficients with yield,
regardless of the fruitâs occlusion.
Our results show that counting yield components with image analysis in non-defoliated vines may be insufficient for
accurate yield estimation. On the other hand, using bunch projected area as a predictor can be the best option to
achieve that goal, even with high levels of occlusioninfo:eu-repo/semantics/publishedVersio
Nonlinear atom optics and bright gap soliton generation in finite optical lattices
We theoretically investigate the transmission dynamics of coherent matter
wave pulses across finite optical lattices in both the linear and the nonlinear
regimes. The shape and the intensity of the transmitted pulse are found to
strongly depend on the parameters of the incident pulse, in particular its
velocity and density: a clear physical picture for the main features observed
in the numerical simulations is given in terms of the atomic band dispersion in
the periodic potential of the optical lattice. Signatures of nonlinear effects
due the atom-atom interaction are discussed in detail, such as atom optical
limiting and atom optical bistability. For positive scattering lengths, matter
waves propagating close to the top of the valence band are shown to be subject
to modulational instability. A new scheme for the experimental generation of
narrow bright gap solitons from a wide Bose-Einstein condensate is proposed:
the modulational instability is seeded in a controlled way starting from the
strongly modulated density profile of a standing matter wave and the solitonic
nature of the generated pulses is checked from their shape and their
collisional properties
Tempranillo physiological and agronomical responses to heat and drought stress â perspectives on its vulnerability under climate change scenarios
With the aim to characterize the ability of Tempranillo grapevines, one of the most widely
used varieties in Spain and Portugal, to withstand drought and heat stress, ecophysiological
and agronomical data from irrigation experiments conducted in the hot and dry region of
Alentejo, south of Portugal, are presented.
The impact of different irrigation treatments on physiological parameters (leaf water
potential, photosynthesis, and stomatal conductance) and water use efficiency are showed.
Leaf senescence observed in non-irrigated and deficit irrigated plants and its consequences on
cluster exposure and berry temperature are compared with those of fully irrigated plants. The
consequences on berry ripening and juice composition are discussed in order to evaluate the
vulnerability of Tempranillo to the expected global climatic changeinfo:eu-repo/semantics/publishedVersio
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