640 research outputs found
Brane Bremsstrahlung in DBI Inflation
We consider the effect of trapped branes on the evolution of a test brane
whose motion generates DBI inflation along a warped throat. The coupling
between the inflationary brane and a trapped brane leads to the radiation of
non-thermal particles on the trapped brane. We calculate the Gaussian spectrum
of the radiated particles and their backreaction on the DBI motion of the
inflationary brane. Radiation occurs for momenta lower than the speed of the
test brane when crossing the trapped brane. The slowing down effect is either
due to a parametric resonance when the interaction time is small compared to
the Hubble time or a tachyonic resonance when the interaction time is large. In
both cases the motion of the inflationary brane after the interaction is
governed by a chameleonic potential,which tends to slow it down. We find that a
single trapped brane can hardly slow down a DBI inflaton whose fluctuations
lead to the Cosmic Microwave Background spectrum. A more drastic effect is
obtained when the DBI brane encounters a tightly spaced stack of trapped
branes.Comment: 20 pages, 1 figur
Oscillation damping of chiral string loops
Chiral cosmic string loop tends to the stationary (vorton) configuration due
to the energy loss into the gravitational and electromagnetic radiation. We
describe the asymptotic behaviour of near stationary chiral loops and their
fading to vortons. General limits on the gravitational and electromagnetic
energy losses by near stationary chiral loops are found. For these loops we
estimate the oscillation damping time. We present solvable examples of
gravitational radiation energy loss by some chiral loop configurations. The
analytical dependence of string energy with time is found in the case of the
chiral ring with small amplitude radial oscillations.Comment: 10 pages, 2 figures. Accepted for publication in Physical Review
Validation of meteorological and ground-level ozone WRF-CHIMERE simulations in a mountainous grapevine growing area for phytotoxic risk assessment
Ozone is the most damaging phytotoxic air pollutant to crop yield quantity and quality. This study presents the validation of a simulation with the WRF-CHIMERE modelling system in order to assess the risk of phytotoxicity by tropospheric ozone for an important and characteristic Mediterranean crop, i.e. the grapevine. The study region was the Douro wine region in Portugal, which is characterized by a rugged relief and a Mediterranean climate. The simulation covered a reference grapevine growing season in the Northern Hemisphere (from April to September 2017), during which a particular measuring campaign was also carried out. The validation of the meteorological simulations on a daily and hourly time resolution was performed based on data from three weather stations, namely on temperature, global solar radiation, relative humidity, wind speed and direction values. The ozone phytotoxicity was assessed with data from two measuring stations. A specific grapevine growth parameter based on monitored phenological observations was introduced for ozone stomatal uptake assessment. Concerning meteorology, validation statistics were acceptable and within the range of what has been found in other regional climate modelling simulations. Ground-level ozone-based values were calculated for a better assessment of the phytotoxic risk, in particular cumulative standards for vegetation protection. Stomatal flux estimates were within the range of those measured for the local cultivars in the field campaign when there was not severe water stress limitation. Both field and statistically adjusted model values indicate that considerable areas in the Demarcated Douro Region of Portugal can exceed the critical exposure values for vegetation according to current European legislation standards. Moreover, measured and simulated results indicate an ozone impact on grapevine yield and quality in the target region because the exposure- and flux-based indices exceed the criteria based on current open-top-chamber experimental knowledge.The authors acknowledge the national funds from FCT-Science and
Technology Portuguese Foundation for the doctoral grant of D. Blanco-
Ward (SFRH/BD/139193/2018). Thanks are also due for the financial
support to CESAM (UIDB/50017/2020+UIDP/50017/2020), to FCT/
MEC through national funds, and the co-funding by FEDER within the
PT2020 Partnership Agreement and Compete 2020. The authors also
wish to thank the DOUROZONE project (PTDC/AAG-MAA/3335/2014;
POCI-01-0145-FEDER-016778) for financial support through Project
3599 – Promoting the Scientific Production and the Technological
Development, and Thematic Networks (3599-PPCDT) – and through
FEDER. Thanks are also given to SOGRAPE VINHOS S.A. for facilitating
the collection of surface O3 data and sharing meteorological data at one
of their vineyard fields.info:eu-repo/semantics/publishedVersio
Preheating After Modular Inflation
We study (p)reheating in modular (closed string) inflationary scenarios, with
a special emphasis on Kahler moduli/Roulette models. It is usually assumed that
reheating in such models occurs through perturbative decays. However, we find
that there are very strong non-perturbative preheating decay channels related
to the particular shape of the inflaton potential (which is highly nonlinear
and has a very steep minimum). Preheating after modular inflation, proceeding
through a combination of tachyonic instability and broad-band parametric
resonance, is perhaps the most violent example of preheating after inflation
known in the literature. Further, we consider the subsequent transfer of energy
to the standard model sector in scenarios where the standard model particles
are confined to a D7-brane wrapping the inflationary blow-up cycle of the
compactification manifold or, more interestingly, a non-inflationary blow up
cycle. We explicitly identify the decay channels of the inflaton in these two
scenarios. We also consider the case where the inflationary cycle shrinks to
the string scale at the end of inflation; here a field theoretical treatment of
reheating is insufficient and one must turn instead to a stringy description.
We estimate the decay rate of the inflaton and the reheat temperature for
various scenarios.Comment: 34 pages, 10 figures. Accepted for publication in JCA
Cosmic D-Strings and Vortons in Supergravity
Recent developments in string inspired models of inflation suggest that
D-strings are formed at the end of inflation. Within the supergravity model of
D-strings there are 2(n-1) chiral fermion zero modes for a D-string of winding
n. Using the bounds on the relic vorton density, we show that D-strings with
winding number n>1 are more strongly constrained than cosmic strings arising in
cosmological phase transitions. The D-string tension of such vortons, if they
survive until the present, has to satisfy 8\pi G_N \mu \lesssim p 10^{-26}
where p is the intercommutation probability. Similarly, D-strings coupled with
spectator fermions carry currents and also need to respect the above bound.
D-strings with n=1 do not carry currents and evade the bound. We discuss the
coupling of D-strings to supersymmetry breaking. When a single U(1) gauge group
is present, we show that there is an incompatibility between spontaneous
supersymmetry breaking and cosmic D-strings. We propose an alternative
mechanism for supersymmetry breaking, which includes an additional U(1), and
might alleviate the problem. We conjecture what effect this would have on the
fermion zero modes.Comment: 11 page
Climate change potential effects on grapevine bioclimatic indices: a case study for the Portuguese demarcated Douro Region (Portugal)
In this work, bioclimatic parameters and indices relevant to the grapevine are estimated for the years 2000 (recent-pat), 2049 (medium-term future) and 2097 (long-term future), based on very high resolution (1 km × 1 km) MPI-WRF RCP8.5 climate simulations. The selected parameters and indices are the mean temperature during the grapevine growing season period (April to October, Tgs), the cumulative rainfall during the grapevine growing season period (Pgs), the Winkler index (WI), the Huglin heliothermic index (HI), the night cold index (CI) and the dryness index (DI). In general, a significant increase in mean temperature during the grapevine growing season period is observed, together with a significant decrease in precipitation. The recent-past WI is associated with the production of high-quality wines; the higher values predicted for the future represent intensive production of wines of intermediate quality. The HI shows the passage of a grapevine growing region considered as temperate-warm to a warm category of higher helio-thermicity. The recent-past CI indicates very cool conditions (associated with quality wines), while in the future there is a tendency for temperate or warmer nights. Finally, DI indicates an increase in water stress considered already high under the recent-past climate conditions. These results point to an increased climatic stress on the Douro region wine production and increased vulnerability of its vine varieties, providing evidence to support strategies aimed to preserve the high-quality wines in the region and their typicality in a sustainable way.The authors wish to thank the financial support of the
DOUROZONE project (PTDC/AAG-MAA/3335/2014; POCI-
01-0145-FEDER-016778) through the Project 3599 – Promoting
the scientific production and the technological development,
and thematic networks (3599-PPCDT) and through
FEDER, and the national funds from FCT-Science and
Technology Portuguese Foundation for the doctoral grants of Blanco-Ward, D. (SFRH/BD/139193/2018) and Silveira, C. (SFRH/BD/112343/2015). Thanks, are also due for the financial
support to CESAM (UID/AMB/50017 - POCI-01-0145-FEDER-
007638), to FCT/MEC through national funds (PIDDAC), and
the co-funding by the FEDER, within the PT2020 Partnership
Agreement and Compete 2020.info:eu-repo/semantics/publishedVersio
Grapevine bioclimatic indices in relation to climate change: a case study in the Portuguese Douro Demarcated Region
Climate change is of major relevance to wine production as most of the wine-growing regions of the world, in
particular the Douro region, are located within relatively narrow latitudinal bands with average growing season temperatures limited to 13-21ÂşC. This study focuses on the temporal variability of three grapevine bioclimatic indices, which are commonly used as part of the Geoviticulture Multicriteria Climatic Classification System (MCC) to classify the climate of wine producing regions worldwide. Dynamical downscaling of MPI-ESM-LR global data forced with RCP8.5 climatic scenario is performed with the Weather Research and Forecast (WRF) model to a regional scale including the Douro valley of Portugal for recent-past (1986-2005) and future periods (2046-2065; 2081-2100). Results indicate significant shifts towards warmer and dryer conditions during
the growing season and higher night temperatures during the grape ripening period. An assessment on the statistical significance of the differences between the recent-past and the future scenarios and the potential impact on wine production in the study area is performed. These results will provide evidence for future strategies aimed to preserve the high-quality wines in the region and their typicality in a sustainable way.The authors wish to thank the financial support of the
DOUROZONE project (PTDC/AAG-MAA/3335/2014; POCI-
01-0145-FEDER-016778) through the Project 3599 –
Promoting the scientific production and the technological
development, and thematic networks (3599-PPCDT) and
through FEDER, and the national funds from FCT – Science
and Technology Portuguese Foundation for the doc grant of C.
Silveira (SFRH/BD/112343/2015).info:eu-repo/semantics/publishedVersio
Analysis of climate change indices in relation to wine production: a case study in the Douro region (Portugal)
Climate change is of major relevance to wine production as most of the wine-growing regions of
the world, in particular the Douro region, are located within relatively narrow latitudinal bands with average
growing season temperatures limited to 13–21◦C. This study focuses on the incidence of climate variables and
indices that are relevant both for climate change detection and for grape production with particular emphasis
on extreme events (e.g. cold waves, storms, heat waves). Dynamical downscaling ofMPI-ESM-LR global data
forced with RCP8.5 climatic scenario is performed with the Weather Research and Forecast (WRF) model to
a regional scale including the Douro valley of Portugal for recent-past (1986–2005) and future periods (2046–
2065; 2081–2100). The number, duration and intensity of events are superimposed over critical phenological
phases of the vine (dormancy, bud burst, flowering, v´eraison, and maturity) in order to assess their positive
or negative implications on wine production in the region. An assessment on the statistical significance of
climatic indices, their differences between the recent-past and the future scenarios and the potential impact
on wine production is performed. Preliminary results indicate increased climatic stress on the Douro region
wine production and increased vulnerability of its vine varieties. These results will provide evidence for future
strategies aimed to preserve the high-quality wines in the region and their typicality in a sustainable way.The authors wish to thank the financial support of the DOUROZONE project (PTDC/AAG-MAA/3335/2014; POCI- 01-0145-FEDER-016778) through the Project 3599 – Promoting the scientific production and the technological development, and thematic networks (3599-PPCDT) and through FEDER.info:eu-repo/semantics/publishedVersio
The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk
We study the relationship between age, metallicity, and alpha-enhancement of
FGK stars in the Galactic disk. The results are based upon the analysis of
high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore
the limitations of the observed dataset, i.e. the accuracy of stellar
parameters and the selection effects that are caused by the photometric target
preselection. We find that the colour and magnitude cuts in the survey suppress
old metal-rich stars and young metal-poor stars. This suppression may be as
high as 97% in some regions of the age-metallicity relationship. The dataset
consists of 144 stars with a wide range of ages from 0.5 Gyr to 13.5 Gyr,
Galactocentric distances from 6 kpc to 9.5 kpc, and vertical distances from the
plane 0 < |Z| < 1.5 kpc. On this basis, we find that i) the observed
age-metallicity relation is nearly flat in the range of ages between 0 Gyr and
8 Gyr; ii) at ages older than 9 Gyr, we see a decrease in [Fe/H] and a clear
absence of metal-rich stars; this cannot be explained by the survey selection
functions; iii) there is a significant scatter of [Fe/H] at any age; and iv)
[Mg/Fe] increases with age, but the dispersion of [Mg/Fe] at ages > 9 Gyr is
not as small as advocated by some other studies. In agreement with earlier
work, we find that radial abundance gradients change as a function of vertical
distance from the plane. The [Mg/Fe] gradient steepens and becomes negative. In
addition, we show that the inner disk is not only more alpha-rich compared to
the outer disk, but also older, as traced independently by the ages and Mg
abundances of stars.Comment: accepted for publication in A&
Climate change impact on a wine-producing region using a dynamical downscaling approach: Climate parameters, bioclimatic indices and extreme indices
Climate change is of major relevance to wine production as most of the winegrowing
regions of the world are located within relatively narrow latitudinal bands
with average growing-season temperatures (GSTs) limited to 13–21 C. This study
focuses on the incidence of climate variables and indices that are relevant both for
climate change assessment and for grape production, with emphasis on grapevine
bioclimatic indices and extreme events (e.g., cold waves, storms, heatwaves).
Dynamical downscaling of European Reanalysis-Interim and Max Planck Institute
Earth System low-resolution global simulations forced with a Representative Concentration
Pathway 8.5 (RCP8.5) greenhouse gas emission scenario was performed
with the Weather Research and Forecast (WRF) model to a regional scale including
the Douro Valley of Portugal for recent-past (1986–2005) and future periods
(2046–2065, 2081–2100). The number, duration and intensity of events were superimposed
over critical phenological phases estimated by using a specific local
grapevine varietal phenological model in order to assess their positive or negative
implications for wine production in the region. An assessment of the relevance of
climate parameters and indices and their progression in recent-past and future climate
scenarios with regard to the potential impact on wine production was performed.
Results indicate a positive relation between higher growing-season heat
accumulations and greater vintage yields. A moderate incidence of very hot days
(daily maximum temperature above 35 C) and drought from pre-véraison phenological
conditions have a positive association with vintage ratings. However, the
mid- and long-term WRF-MPI RCP8.5 future climate scenarios reveal shifts to
warmer and drier conditions, with the mean GST not remaining within range for
quality wine production in the long-term future climate scenario. These results indicate
potential impacts that suggest a range of strategies to maintain wine production
and quality in the region.The authors wish to thank the DOUROZONE project
(PTDC/AAG-MAA/3335/2014; POCI-01-0145-FEDER-
016778) for financial support through Project 3599 – Promoting
the Scientific Production and the Technological
Development, and Thematic Networks (3599-PPCDT) – and
through FEDER, and the national funds from FCT-Science
and Technology Portuguese Foundation for the doctoral
grant of D. Blanco-Ward (SFRH/BD/139193/2018). Thanks
are also due for the financial support to CESAM
(UID/AMB/50017 - POCI-01-0145-FEDER-007638), to
FCT/MEC through national funds, and the co-funding by
FEDER within the PT2020 Partnership Agreement and
Compete 2020.info:eu-repo/semantics/publishedVersio
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