265 research outputs found
Seasonal changes in berry fluorescence induced by different levels of uv-radiation
Plant stress is usually diagnosed via physiological measurements on leaves such as water potential,
photosynthetic rate or chlorophyll fluorescence. Since stress in the case of grapevines is of concern with respect
to the quality of the fruit, we attempted to use one of the above mentioned techniques, chlorophyll fluorescence,
directly on the fruit itself in order to investigate stress responses in vivo. Berry fluorescence was measured in an
experiment with different levels of UV-B and UV-A radiation in the field in 2000 in Geisenheim with the variety
Riesling. UV radiation has been shown to affect chlorophyll and was thus likely to show differences in
fluorescence signals. Berry fluorescence was measured periodically between veraison and harvest on darkadapted
berries (20min). For each berry, a light response curve was recorded followed by a recovery phase in the
dark. The maximum quantum yield of PSII (qY) was determined after a saturation pulse at each light intensity.
The qY decreased exponentially with increasing light intensity. The response level of the quantum yield of PSII
decreased during ripening indicating a loss in chlorophyll and/or PSII capacity for all treatments. Effects of the
different levels of UV-radiation on the light curve were only detected at the end of the ripening period, with
higher quantum yield values recorded for the treatments protected against UV-A and UV-A+UV-B. Similar
results were obtained after recovery in the dark. Changes in fluorescence signals were accompanied by a visual
change in berry colour indicating changes in skin pigmentation, which may also have some effect on fruit
qualityinfo:eu-repo/semantics/publishedVersio
Validation of an empirical model for grapevine leaf area estimation with data from simplified pruning systems
The performance of a mathematical model developed for non-destructive estimation of primary leaf area
per shoot of Tempranillo grapevines, was tested using independent datasets from two vineyards with simplified
pruning techniques. The first dataset was collected in Portugal on Cabernet Sauvignon grapevines subjected to
mechanical hedge pruning and the second one in Germany on minimal pruned Riesling grapevines. For both
datasets the model presented a very good fit between observed and estimated values with the error increasing with
the increase in leaf area per shoot. The mean absolute percent error for all systems was lower or equal to 10% with
lower absolute values (7.7%) for the Riesling dataset. Both linear regression between observed (dependent variable)
and estimated (independent variable) leaf area had high and significant R2 with an intercept not significantly
different from zero. Fitted lines were not significantly different from 1 for Cabernet Sauvignon, but slightly yet
significantly different from 1 for Riesling fitted line (1.03), indicating that the model underestimated the leaf area
per shoot. The good results obtained with this validation test show that the model can be used to accurately predict
primary leaf area per shoot independent of variety, training system and climatic conditionsinfo:eu-repo/semantics/publishedVersio
Water in a warmer world – is atmospheric evaporative demand changing in viticultural areas?
The predicted developments in climate are region-specific and adaptation can only be successful considering the regional characteristics with its diverse technical, environmental, economic and social implications. One of the key concerns for many regions is the availability of water through precipitation, the distribution of precipitation throughout the year, and possible changes in evaporative demand of the atmosphere and thus water use. From rising temperatures it is mostly assumed that water holding capacity of the atmosphere will increase in the future as a function of the Clausius-Clapeyron law, which predicts an increase in the saturation vapour pressure of the atmosphere of 6–7% per degree Celsius. As a consequence, a simultaneous increase in potential evapotranspiration (ETp, the amount of water that could potentially be evaporated from soils and transpired by plants due to changes in climatic factors such as temperature, vapour pressure deficit, radiation and wind speed) is assumed in many cases, which would alter soil and plant water relations. However, the same underlying principles also predict an increase in precipitation by 1–2% per degree warming. Additionally, model predictions for many regions forecast altered precipitation patterns and thus in combination with the possibility of increased ETp, farmers around the world fear an increase in the likelyhood of water deficit and a reduction in the availability of water for irrigation. Contrary to expectations, there have been reports on a reduction in evaporative demand worldwide despite increasing temperatures. In many cases this has been related to a decrease in solar radiation observed for many areas on earth including wine growing regions in Europe until the beginning of the 80th (global dimming) of the last century. However, since then, solar radiation has increased again, but ETp did not always follow and a worldwide decrease in wind speed and pan evaporation has been observed. In order to evaluate different grape growing regions with respect to observed changes on precipitation patterns and ETp, the data of seven wine-growing areas in five countries in the Northern and Southern hemisphere across a large climatic trans-sect were analyzed (Rheingau, Germany, Burgundy, Rhone Valley, France, Napa Valley, USA, Adelaide Hills, Tasmania, Australia, Marlborough, New Zealand) were analyzed. Precipitation patterns differed vastly between locations and showed very different trends over observation periods ranging from 23 to 60 years. The ETp has increased continuously in only two of the seven wine growing areas (Rheingau and Marlborough). In most other areas, ETp has been stable during winter and summer for at least 22 years (Rhone Valley, Napa Valley, Tasmania), sometimes much longer (45 years Adelaide Hills), and has been declining in Burgundy after a period of strong increase for the last 13 years. The potential underlying factors are discussed in relation to observed shifts in precipitation patterns
Influence de différents niveaux de rayonnement UV sur la physiologie, le taux de pigments et la composition des baies, cépage Riesling
Changes in the stratospheric ozone concentration causes UV-radiation to increase. The response to UV-B radiation on the organ and cellular level is mainly an increase in the formation of UV-absorbing compounds meant to decrease UV-radiation penetration into the tissue. Some key enzymes involved in flavonoid biosynthesis and the phenyl-propanoid pathway have been shown to be up-regulated by UV-radiation, as are levels of key antioxidants glutathione and ascorbate, whereas carotenoid pigment formation and the incorporation of nitrogen into amino acids can be inhibited. Since components such as flavonoids, amino acids and carotenoids are important constituents of grapes with a marked effect on flavour development, some influence of altered UV-radiation can be expected. We investigated these possible effects under field conditions by selectively attenuating various portions of the light spectrum in the UV-part with polyester and di- and tri-acetate films and exposing the entire canopy or parts thereof to these conditions during berry development. We evaluated skin pigment composition using a non-destructive spectro-photometric technique. There was a strong UV-induced shift towards the formation of red and brown pigment components without affecting sugar levels. Chlorophyll degradation in the berry skin proceeded faster in the high UV-radiation treatments and this could be assessed for non-destructively by measuring berry fluorescence. Amino acid concentration was reduced under high levels of UV-B radiation and both the total bound glycosidic secondary metabolites and phenolics were increased. There were some effects noticeable on fermentation velocity and the retention of free and bound aromatic components in the wineinfo:eu-repo/semantics/publishedVersio
High-Intensity and High-Brightness Source of Moderated Positrons Using a Brilliant gamma Beam
Presently large efforts are conducted towards the development of highly
brilliant gamma beams via Compton back scattering of photons from a
high-brilliance electron beam, either on the basis of a normal-conducting
electron linac or a (superconducting) Energy Recovery Linac (ERL). Particularly
ERL's provide an extremely brilliant electron beam, thus enabling to generate
highest-quality gamma beams. A 2.5 MeV gamma beam with an envisaged intensity
of 10^15 s^-1, as ultimately envisaged for an ERL-based gamma-beam facility,
narrow band width (10^-3), and extremely low emittance (10^-4 mm^2 mrad^2)
offers the possibility to produce a high-intensity bright polarized positron
beam. Pair production in a face-on irradiated W converter foil (200 micron
thick, 10 mm long) would lead to the emission of 2 x 10^13 (fast) positrons per
second, which is four orders of magnitude higher compared to strong radioactive
^22Na sources conventionally used in the laboratory.Using a stack of converter
foils and subsequent positron moderation, a high-intensity low-energy beam of
moderated positrons can be produced. Two different source setups are presented:
a high-brightness positron beam with a diameter as low as 0.2 mm, and a
high-intensity beam of 3 x 10^11 moderated positrons per second. Hence,
profiting from an improved moderation efficiency, the envisaged positron
intensity would exceed that of present high-intensity positron sources by a
factor of 100.Comment: 9 pages, 3 figure
The metallic state in disordered quasi-one-dimensional conductors
The unusual metallic state in conjugated polymers and single-walled carbon
nanotubes is studied by dielectric spectroscopy (8--600 GHz). We have found an
intriguing correlation between scattering time and plasma frequency. This
relation excludes percolation models of the metallic state. Instead, the
carrier dynamics can be understood in terms of the low density of delocalized
states around the Fermi level, which arises from the competion between
disorder-induced localization and interchain-interactions-induced
delocalization.Comment: 4 pages including 4 figure
Concentration Dependence of Superconductivity and Order-Disorder Transition in the Hexagonal Rubidium Tungsten Bronze RbxWO3. Interfacial and bulk properties
We revisited the problem of the stability of the superconducting state in
RbxWO3 and identified the main causes of the contradictory data previously
published. We have shown that the ordering of the Rb vacancies in the
nonstoichiometric compounds have a major detrimental effect on the
superconducting temperature Tc.The order-disorder transition is first order
only near x = 0.25, where it cannot be quenched effectively and Tc is reduced
below 1K. We found that the high Tc's which were sometimes deduced from
resistivity measurements, and attributed to compounds with .25 < x < .30, are
to be ascribed to interfacial superconductivity which generates spectacular
non-linear effects. We also clarified the effect of acid etching and set more
precisely the low-rubidium-content boundary of the hexagonal phase.This work
makes clear that Tc would increase continuously (from 2 K to 5.5 K) as we
approach this boundary (x = 0.20), if no ordering would take place - as its is
approximately the case in CsxWO3. This behaviour is reminiscent of the
tetragonal tungsten bronze NaxWO3 and asks the same question : what mechanism
is responsible for this large increase of Tc despite the considerable
associated reduction of the electron density of state ? By reviewing the other
available data on these bronzes we conclude that the theoretical models which
are able to answer this question are probably those where the instability of
the lattice plays a major role and, particularly, the model which call upon
local structural excitations (LSE), associated with the missing alkali atoms.Comment: To be published in Physical Review
Physiological responses and production of 'Syrah' vines as a function of training systems
Plant architecture and its interaction with agricultural practices and environmental constraints is determinant for grapevine canopy structure, which is related to carbon assimilation, bud fertility and fruit quality. In this context, this study evaluated the performance of field-grown 'Syrah' grapevines conducted by two management systems: Vertical Shoot Position (VSP) or a modified Geneva Double Curtain (GDC), in Pirapora, state of Minas Gerais, Brazil, during the winters of 2007 and 2008. The evaluations of leaf area, water relations and net CO2 assimilation were made at the end of the ripening period. Yield per vine and per hectare were estimated and mean berry weight and diameter, total soluble solids, pH and titratable acidity were evaluated during berry ripening. The grapevines trained in VSP had higher water status as compared to GDC, shown by differences in pre-dawn leaf water potential (ψpd) and stem water potential (ψstem). However, the CO2 assimilation was similar in both training systems. Fruit exposure was higher in VSP than in GDC, which contributed to increasing berry temperature. At harvest, the berries in GDC reached values near to 23 ºBrix whereas berries in VSP showed values near 21 ºBrix
Comprehensive analysis of epigenetic clocks reveals associations between disproportionate biological ageing and hippocampal volume
The concept of age acceleration, the difference between biological age and chronological age, is of growing interest, particularly with respect to age-related disorders, such as Alzheimer’s Disease (AD). Whilst studies have reported associations with AD risk and related phenotypes, there remains a lack of consensus on these associations. Here we aimed to comprehensively investigate the relationship between five recognised measures of age acceleration, based on DNA methylation patterns (DNAm age), and cross-sectional and longitudinal cognition and AD-related neuroimaging phenotypes (volumetric MRI and Amyloid-β PET) in the Australian Imaging, Biomarkers and Lifestyle (AIBL) and the Alzheimer’s Disease Neuroimaging Initiative (ADNI). Significant associations were observed between age acceleration using the Hannum epigenetic clock and cross-sectional hippocampal volume in AIBL and replicated in ADNI. In AIBL, several other findings were observed cross-sectionally, including a significant association between hippocampal volume and the Hannum and Phenoage epigenetic clocks. Further, significant associations were also observed between hippocampal volume and the Zhang and Phenoage epigenetic clocks within Amyloid-β positive individuals. However, these were not validated within the ADNI cohort. No associations between age acceleration and other Alzheimer’s disease-related phenotypes, including measures of cognition or brain Amyloid-β burden, were observed, and there was no association with longitudinal change in any phenotype. This study presents a link between age acceleration, as determined using DNA methylation, and hippocampal volume that was statistically significant across two highly characterised cohorts. The results presented in this study contribute to a growing literature that supports the role of epigenetic modifications in ageing and AD-related phenotypes
Combination of searches for Higgs boson pairs in pp collisions at \sqrts = 13 TeV with the ATLAS detector
This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb(-1) of proton-proton collision data at a centre-of-mass energy root s = 13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the b (b) over barb (b) over bar, b (b) over barW(+)W(-), b (b) over bar tau(+)tau(-), W+W-W+W-, b (b) over bar gamma gamma and W+W-gamma gamma final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (kappa(lambda)) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to -5.0 < kappa(lambda) < 12.0 (-5.8 < kappa(lambda) < 12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model. For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.135103</p
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