3,878 research outputs found
Quantifying the impact of model inaccuracy in climate change impact assessment studies using an agro-hydrological model
Numerical simulation models are frequently applied to assess the impact of climate change on hydrology and agriculture. A common hypothesis is that unavoidable model errors are reflected in the reference situation as well as in the climate change situation so that by comparing reference to scenario model errors will level out. For a polder in The Netherlands an innovative procedure has been introduced, referred to as the Model-Scenario-Ratio (MSR), to express model inaccuracy on climate change impact assessment studies based on simulation models comparing a reference situation to a climate change situation. The SWAP (Soil Water Atmosphere Plant) model was used for the case study and the reference situation was compared to two climate change scenarios. MSR values close to 1, indicating that impact assessment is mainly a function of the scenario itself rather than of the quality of the model, were found for most indicators evaluated. A climate change scenario with enhanced drought conditions and indicators based on threshold values showed lower MSR values, indicating that model accuracy is an important component of the climate change impact assessment. It was concluded that the MSR approach can be applied easily and will lead to more robust impact assessment analyses
Climate Research Wageningen UR : Projects, researchers and expertise
Wageningen UR focuses not only on the global climate system but also on regional and local climate phenomena, taking both scientific and social aspects into account in an integral way. Wageningen UR wants to play an effective role in the transition to a world that is both climate neutral and climate proof. Our strength is using the limited space available in our delta, in a climate-proof manner, thus providing opportunities for among others agriculture, horticulture, aquaculture, recreation and living
Three-micron spectra of AGB stars and supergiants in nearby galaxies
The dependence of stellar molecular bands on the metallicity is studied using
infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and
M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and
in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for
oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB
stars. The equivalent width of acetylene is found to be high even at low
metallicity. The high C2H2 abundance can be explained with a high
carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast,
the HCN equivalent width is low: fewer than half of the extra-galactic carbon
stars show the 3.5micron HCN band, and only a few LMC stars show high HCN
equivalent width. HCN abundances are limited by both nitrogen and carbon
elemental abundances. The amount of synthesized nitrogen depends on the initial
mass, and stars with high luminosity (i.e. high initial mass) could have a high
HCN abundance. CH bands are found in both the extra-galactic and Galactic
carbon stars. None of the oxygen-rich LMC stars show SiO bands, except one
possible detection in a low quality spectrum. The limits on the equivalent
widths of the SiO bands are below the expectation of up to 30angstrom for LMC
metallicity. Several possible explanations are discussed. The observations
imply that LMC and SMC carbon stars could reach mass-loss rates as high as
their Galactic counterparts, because there are more carbon atoms available and
more carbonaceous dust can be formed. On the other hand, the lack of SiO
suggests less dust and lower mass-loss rates in low-metallicity oxygen-rich
stars. The effect on the ISM dust enrichment is discussed.Comment: accepted for A&
Ultralong-range order in the Fermi-Hubbard model with long-range interactions
We use the dual boson approach to reveal the phase diagram of the
Fermi-Hubbard model with long-range dipole-dipole interactions. By using a
large-scale finite-temperature calculation on a square lattice
we demonstrate the existence of a novel phase, possessing an `ultralong-range'
order. The fingerprint of this phase -- the density correlation function --
features a non-trivial behavior on a scale of tens of the lattice sites. We
study the properties and the stability of the ultralong-range ordered phase,
and show that it is accessible in modern experiments with ultracold polar
molecules and magnetic atoms
Very Large Telescope three micron spectra of dust-enshrouded red giants in the Large Magellanic Cloud
We present ESO/VLT spectra in the 2.9--4.1 micron range for a large sample of
infrared stars in the Large Magellanic Cloud (LMC), selected on the basis of
MSX and 2MASS colours to be extremely dust-enshrouded AGB star candidates. Out
of 30 targets, 28 are positively identified as carbon stars, significantly
adding to the known population of optically invisible carbon stars in the LMC.
We also present spectra for six IR-bright stars in or near three clusters in
the LMC, identifying four of them as carbon stars and two as oxygen-rich
supergiants. We analyse the molecular bands of C2H2 at 3.1 and 3.8 micron, HCN
at 3.57 micron, and sharp absorption features in the 3.70--3.78 micron region
that we attribute to C2H2. There is evidence for a generally high abundance of
C2H2 in LMC carbon stars, suggestive of high carbon-to-oxygen abundance ratios
at the low metallicity in the LMC. The low initial metallicity is also likely
to have resulted in less abundant HCN and CS. The sample of IR carbon stars
exhibits a range in C2H2:HCN abundance ratio. We do not find strong
correlations between the properties of the molecular atmosphere and
circumstellar dust envelope, but the observed differences in the strengths and
shapes of the absorption bands can be explained by differences in excitation
temperature. High mass-loss rates and strong pulsation would then be seen to be
associated with a large scale height of the molecular atmosphere.Comment: Accepted for publication in Astronomy and Astrophysics. 20 pages.
Figure 11 is degraded for posting on astro-p
Two-particle correlations and the metal-insulator transition: Iterated Perturbation Theory revisited
Recent advances in many-body physics have made it possible to study
correlated electron systems at the two-particle level. In Dynamical Mean-Field
theory, it has been shown that the metal-insulator phase diagram is closely
related to the eigenstructure of the susceptibility. So far, this situation has
been studied using accurate but numerically expensive solvers. Here, the
Iterated Perturbation Theory (IPT) approximation is used instead. Its
simplicity makes it possible to obtain analytical results for the two-particle
vertex and the DMFT Jacobian. The limited computational cost also enables a
detailed comparison of analytical expressions for the response functions to
results obtained using finite differences. At the same time, the approximate
nature of IPT precludes an interpretation of the metal-insulator transition in
terms of a Landau free energy functional.Comment: Revised versio
- …