388 research outputs found
Ferromagnetism in two band metals: Combined effect of Coulomb correlation, hybridization and band widths
We study the possibility of ferromagnetism in metals. The metal is described
by two hybridized bands one of which includes Hubbard correlation whereas the
other is uncorrelated. We parametrize the ratio of the band widths and their
centers as well. The original Hamiltonian is transformed in an effective and
simpler one. Only one site retains the full correlation (U) while in the others
acts as an internal field, the self-energy, in the framework of an alloy
analogy approximation. This field, in turn, is self-consistently determined by
imposing the translational invariance of the problem. For several total
electronic occupation numbers (n_{total}) we compare the spin dependent free
energies with the corresponding paramagnetic ones. We present several results
pointing out the mechanism by which the self-consistency introduces a sort of
constraints, for given values of band width and band shift .Comment: 6 pages, 7 figure
Comparing water relations and stomatal regulation of Touriga Nacional and Syrah under mild water stress
Proceedings - IX International Terroir Congress, 2012Aiming to compare the physiological responses of the Portuguese red variety Touriga Nacional (TN) with Syrah (SY),
we studied during the 2007 growing season five-year-old grapevines growing in a commercial non-irrigated vineyard
located at the Lisbon winegrowing region. Predawn (Ypd) and midday (YM) leaf water potential, leaf stomatal
conductance (gs) and photosynthetic rate (A) were periodically measured between fruit set and harvest. Ypd displayed a
decreasing pattern throughout the growing cycle from -0.10 MPa at flowering to -0.44 MPa at harvest. Both varieties
showed similar values except during the two measurements made in August when TN presented significantly higher
values than SY. Ymid also showed a decreasing pattern from the end of June towards harvest date, with significant
differences between varieties being observed during the ripening period, with SY showing lower values than TN. A
measured either at mid-morning and midday presented, for most part of the cases, lower values in SY than in TN,
although the differences were only significant during the ripening period. gs pattern was parallel to A and, in general,
the relative differences between varieties mirrored those reported for A. No significant effect of the variety was detected
on the relationships between A or gs measured at mid-morning and Ypd. However, when analyzing the set of data
collected at midday it was observed that the regression lines of the relationships between A or gs (dependent variables)
and Ypd (independent variable) presented a significantly higher slope in SY as compared to those showed by TN. These
results show that the rate of decrease of A and gs with the decrease of Ypd was lower in TN than in SY suggesting that
the two varieties have different stomatal regulation, with a more “optimistic” behavior in TN
Dynamics of soil and canopy temperature: a conceptual approach for Alentejo vineyards
Context and purpose of the study - Climate change imposes increasing restrictions and risks to
Mediterranean viticulture. Extreme heat and drought stress events are becoming more frequent which puts
in risk sustainability of Mediterranean viticulture. Moreover row crops e.g. grapevine for wine, are
increasingly prone to the impact of more intense/longer exposure time to heat stress. The amplified effects
of soil surface energy reflectance and conductance on soil-atmosphere heat fluxes can be harmful for leaf
and berry physiology. Leaf/canopy temperature is a biophysical variable with both physiological and
agronomic meaning. Improved comprehension of spatial and temporal dynamics of soil and leaf/canopy
temperature (thermal microclimate) in irrigated vineyards can support improved crop and soil monitoring
and management under more extreme and erratic climate conditions. In this work we propose a conceptual
approach to integrate information on major soil-vine-atmosphere interactions under deficit irrigation.
Ultimately a conceptual model based on temperature relations is proposed to support assessment of the
impact of air and soil temperatures on canopy and berry temperatures, leaf senescence and gas exchange.
This model may support Decision Support Systems (DSS) for canopy and soil management and irrigation
scheduling in Mediterranean vineyards. In addition a set of temperatures (e.g. canopy, soil) are proposed to
feed the conceptual models to support the DSSinfo:eu-repo/semantics/publishedVersio
Canopy and soil thermal patterns to support management of irrigated vineyards
Irrigated viticulture expanded fast in Southern European countries such as Portugal to optimize berry yield and quality and to increase vine’s longevity. However, intensive irrigation increases pressure over the local and regional water resources, that are getting scarcer, and increases also management costs. Additionally, row crops such as grapevine, are more vulnerable to heat stress due to the additional effects of soil heat fluxes which can negatively influence canopy and berry thermal condition. Therefore, a better understanding of grapevine responses (diurnal and seasonal) to environmental factors (air temperature, soil water) and agronomic practices (deficit irrigation, soil management) are on demand by the industry.
Ground based thermography was used to monitor the vertical profile of canopy temperature as well as soil temperature patterns along the day and season as means to assess plant water status and predict risks of heat stress damage. As part of the EU-INNOVINE project, field trials were carried in 2013, 2014 and 2015 in Alentejo (South Portugal). We examined the diurnal and seasonal response of two V. vinifera varieties Aragonez (syn. Tempranillo) and Touriga Nacional subjected to sustained deficit irrigation (SDI), and regulated deficit irrigation (RDI, about 50% of the SDI). Diurnal canopy (TC), and soil surface (Tsoil) temperatures were assessed by thermography. Punctual measurements of leaf temperature with thermal couples, leaf water potential and leaf gas exchange were also done.
TC values were above the optimal temperature for leaf photosynthesis during part of the day light period (11:00-14:00h to 17:00h), especially under stressful atmospheric conditions (high VPD, high Tair) and under regulated deficit irrigation. Tsoil was on average about 10-15°C higher than TC. We found strong correlation between TC (derived from thermography) and major physiological traits (leaf water potential and leaf gas exchange). Our results suggest that Tc can be explored as a simple but robust non-intrusive thermal indicator of grapevine performance and also as a parameter to feed grapevine growth models and to estimate heat and water fluxes in irrigated vineyardsinfo:eu-repo/semantics/publishedVersio
Can soil water content be used as a predictor of predawn leaf water potential for deficit irrigation scheduling? A case study at Alentejo wine region
Context and purpose of the study: Water and heat stress impose new challenges to irrigation management
in the Mediterranean areas. This reality has a major impact on the vineyard ecosystem, particularly on the
scarce water resources of the Alentejo region (South Portugal). To mitigate this problem, irrigation
management should focus on optimizing yield and fruit quality per volume of water applied. This work aims
to discuss the use of predawn leaf water potential and soil water status relationships as a decision tool for
irrigation management taking as basis data from a field trial where two deficit irrigation strategies were
comparedinfo:eu-repo/semantics/publishedVersio
Is early defoliation a sustainable management practice for mediterranean vineyards? case studies at the portuguese Lisbon winegrowing region
Context and purpose of the study - Recently early defoliation (ED) has been tested in several highyielding
grapevine varieties and sites aiming at reducing cluster compactness and hence, regulating yield
and susceptibility to botrytis bunch rot infection. The reported results have been generally positive,
encouraging growers to use this canopy management technique as an alternative for replacing the
conventional time-consuming cluster thinning and, simultaneously, as a sustainable practice to reduce
the use of fungicides. However, ED increases berry sunburn risks and/or can induce carry-over effects on
vigor and node fruitfulness as shown in the two case studies reported in this work.
Material and methods- Two ED experiments were set up at a commercial vineyard located in the Lisbon
winegrowing region with the varieties Aragonez, syn. Tempranillo (2013-2015) and Semillon (2018). In
both experiments the ED treatment was compared with the non-defoliated (ND; control) using a
randomized complete block design with 4 replicates per treatment. The ED treatment consisted of the
removal of 5-6 basal leaves and any laterals at pre-flowering. Vegetative (leaf area and pruning weight)
and reproductive components (%fruit-set, cluster number, cluster weight, yield) and berry composition
were assessedinfo:eu-repo/semantics/publishedVersio
Cross effect of Coulomb correlation and hybridization in the occurrence of ferromagnetism in two shifted band transition metals
In this work we discuss the occurrence of ferromagnetism in transition-like
metals. The metal is represented by two hybridized() and shifted
) bands one of which includes Hubbard correlation whereas the
other is uncorrelated. The starting point is to transform the original
Hamiltonian into an effective one. Only one site retains the full correlation
(U) while in the others the correlations are represented by an effective field,
the self-energy(single-site approximation). This field is self-consistently
determined by imposing the translational invariance of the problem. Thereby one
gets an exchange split quasi-particle density of states and then an
electron-spin polarization for some values of the parameters , being the ratio of the effective masses of the two bands
and of the occupation number .Comment: 4 pages, 10 figure
Tempranillo physiological and agronomical responses to heat and drought stress – 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
Can Mediterranean terroirs withstand climate change ? Case studies at the Alentejo portuguese winegrowing region
XII Congreso Internacional TerroirClimate change introduced new challenges to vinegrowers in the Mediterranean areas such as the
hot and dry winegrowing region of Alentejo, south Portugal. Warmer and drier conditions are harmful for
grape yield and berry quality attributes and for vine’s longevity, mainly when optimal thresholds are
exceeded. Therefore winegrowers are forced to move from rainfed to irrigated production systems making
Alentejo’ wine production strongly based on available water resources for irrigation. This work aims to
review and discuss ecophysiological and agronomical data obtained in irrigation trials set up at different
terroirs of Alentejo. In the last four decades, classical bioclimatic temperature-based indices showed a
significantly positive trend, while the dryness index present a negative trend over time. Furthermore,
ecophysiological data collected in deficit irrigation experiments are reviewed and discussed, focusing on the
effects of drought and heat stress on vigour, yield and berry composition. Emphasis is given on the indirect
effects of leaf senescence on cluster exposure and consequences on berry temperature and composition. In
order to promote the sustainability and quality of wine production in these hot and dry terroirs short- to longterm
adaptation measures are suggested. The limitations and risks of using deficit irrigation during heat
waves are also underlinedinfo:eu-repo/semantics/publishedVersio
Effects of soil management and deficit irrigation strategies on physiological and agronomical responses of Aragonez field-grown grapevines
The use of irrigation in Mediterranean viticulture is now a common practice in intensive grapevine production to improve quality
of production. The negative effects of water deficits on grape berry development are well known but the underlying mechanisms
remain not fully understood. To avoid the unfavourable impacts of mechanization on the soil structure and biology some farmers
are using cover crops on their vineyards. Within this frame we have compared the traditional soil tillage with a high level of
mechanization with other system where we maintained a permanent soil cover between the rows. In both soil systems we
tested three different irrigation treatments, deficit irrigation (DI - 40% of evapotranspiration (ETc)); regulated deficit irrigation
(RDI); partial root drying (PRD) while in the soil cover treatment we also studied the full irrigation (FI) and the non irrigation (NI)
treatments. Compared to soil tillage the resident vegetation reduced soil water content during late Spring, before irrigation
started, inducing a significant reduction on vine vegetative growth berry weight and yield. Among irrigation strategies only RDI
treatment showed a significant reduction in the lateral leaf area development, berry weight and yield when compared to PRD
and DI treatments which presented similar values. No significant differences were observed in berry composition either for the
two floor management practices or for the three irrigation strategiesinfo:eu-repo/semantics/publishedVersio
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