442 research outputs found
Assessment of the environmental and economic performance of agroforestry along a European gradient
Poste
Modelling environmental benefits of silvoarable agroforestry in Europe
Increased adoption of silvoarable agroforestry (SAF) systems in Europe, by integrating trees and arable crops on the same land, could offer a
range of environmental benefits compared with conventional agricultural systems. Soil erosion, nitrogen leaching, carbon sequestration and
landscape biodiversity were chosen as indicators to assess a stratified random sample of 19 landscape test sites in the Mediterranean and
Atlantic regions of Europe. At each site, the effect of introducing agroforestry was examined at plot-scale by simulating the growth of one of
five tree species (hybrid walnut Juglans spp., wild cherry Prunus avium L., poplar Populus spp., holm oak Quercus ilex L. subsp. ilex and stone
pine Pinus pinea L.) at two tree densities (50 and 113 trees ha 1) in combination with up to five crops (wheat Triticum spp., sunflower
Helianthus annuus L., oilseed rape Brassica napus L., grain maize and silage maize Zea mays L.). At landscape-scale, the effect of introducing
agroforestry on 10 or 50% of the agricultural area, on either the best or worst quality land, was examined. Across the 19 landscape test sites,
SAF had a positive impact on the four indicators with the strongest effects when introduced on the best quality land. The computer simulations
showed that SAF could significantly reduce erosion by up to 65% when combined with contouring practices at medium (>0.5 and
3 t ha 1 a 1) erosion sites. Nitrogen leaching could be reduced by up to 28% in areas where leaching is currently
estimated high (>100 kg N h 1 a 1), but this was dependent on tree density.With agroforestry, predicted mean carbon sequestration through
immobilization in trees, over a 60-year period, ranged from 0.1 to 3.0 t C h 1 a 1 (5–179 t C h 1) depending on tree species and location.
Landscape biodiversity was increased by introducing SAF by an average factor of 2.6. The implications of this potential for environmental
benefits at European-scale are discussed
Kahler Moduli Inflation
We show that under general conditions there is at least one natural
inflationary direction for the Kahler moduli of type IIB flux
compactifications. This requires a Calabi-Yau which has h^{2,1}>h^{1,1}>2 and
for which the structure of the scalar potential is as in the recently found
exponentially large volume compactifications. We also need - although these
conditions may be relaxed - at least one Kahler modulus whose only
non-vanishing triple-intersection is with itself and which appears by itself in
the non-perturbative superpotential. Slow-roll inflation then occurs without a
fine tuning of parameters, evading the eta problem of F-term inflation. In
order to obtain COBE-normalised density perturbations, the stabilised volume of
the Calabi-Yau must be O(10^5-10^7) in string units, and the inflationary scale
M_{infl} ~ 10^{13} GeV. We find a robust model independent prediction for the
spectral index of 1 - 2/N_e = 0.960 - 0.967, depending on the number of
efoldings.Comment: 17 pages, 1 figure; v2. references adde
Integrating environmental and economic performance to assess modern silvoarable agroforestry in Europe
AnalysisThe environmental and economic performance of silvoarable agroforestry in Europe is
highly variable. Multi-criteria analysis, using the PROMETHEE outranking approach, was
used to evaluate the integrated performance of silvoarable agroforestry on hypothetical
farms in nineteen landscape test sites in Spain, France, and The Netherlands. The
silvoarable scenarios allocated a proportion of the hypothetical farms (10 or 50%) to
silvoarable agroforestry at two different tree densities (50 or 113 trees ha−1) on two different
qualities of land (best or worst quality land). The status quo (conventional arable farming)
was also assessed for comparison. The criteria used in the evaluation (soil erosion, nitrogen
leaching, carbon sequestration, landscape biodiversity, and infinite net present value) were
assessed at each landscape test site; infinite net present value was assessed under six levels
of government support. In France, the analysis showed, assuming equal weighting between
environmental and economic performance, that silvoarable agroforestry was preferable to
conventional arable farming. The best results were observed when agroforestry was
implemented on 50% of the highest quality land on the farm; the effect of tree density (50–
113 trees ha−1) was small. By contrast, in Spain and The Netherlands, the consistently
greater profitability of conventional arable agriculture relative to the agroforestry
alternatives made overall performance of agroforestry systems dependent on the
proportion of the farm planted, and the tree density and land quality used
Axionic D3-D7 Inflation
We study the motion of a D3 brane moving within a Type IIB string vacuum
compactified to 4D on K3 x T_2/Z_2 in the presence of D7 and O7 planes. We work
within the effective 4D supergravity describing how the mobile D3 interacts
with the lightest bulk moduli of the compactification, including the effects of
modulus-stabilizing fluxes. We seek inflationary solutions to the resulting
equations, performing our search numerically in order to avoid resorting to
approximate parameterizations of the low-energy potential. We consider
uplifting from D-terms and from the supersymmetry-breaking effects of anti-D3
branes. We find examples of slow-roll inflation (with anti-brane uplifting)
with the mobile D3 moving along the toroidal directions, falling towards a
D7-O7 stack starting from the antipodal point. The inflaton turns out to be a
linear combination of the brane position and the axionic partner of the K3
volume modulus, and the similarity of the potential along the inflaton
direction with that of racetrack inflation leads to the prediction n_s \le 0.95
for the spectral index. The slow roll is insensitive to most of the features of
the effective superpotential, and requires a one-in-10^4 tuning to ensure that
the torus is close to square in shape. We also consider D-term inflation with
the D3 close to the attractive D7, but find that for a broad (but not
exhaustive) class of parameters the conditions for slow roll tend to
destabilize the bulk moduli. In contrast to the axionic case, the best
inflationary example of this kind requires the delicate adjustment of potential
parameters (much more than the part-per-mille level), and gives inflation only
at an inflection point of the potential (and so suffers from additional
fine-tuning of initial conditions to avoid an overshoot problem).Comment: 29 pages, 5 figure
Fibre Inflation: Observable Gravity Waves from IIB String Compactifications
We introduce a simple string model of inflation, in which the inflaton field
can take trans-Planckian values while driving a period of slow-roll inflation.
This leads naturally to a realisation of large field inflation, inasmuch as the
inflationary epoch is well described by the single-field scalar potential . Remarkably, for a broad class of vacua
all adjustable parameters enter only through the overall coefficient , and
in particular do not enter into the slow-roll parameters. Consequently these
are determined purely by the number of \e-foldings, , and so are not
independent: . This implies similar
relations among observables like the primordial scalar-to-tensor amplitude,
, and the scalar spectral tilt, : . is
itself more model-dependent since it depends partly on the post-inflationary
reheat history. In a simple reheating scenario a reheating temperature of
GeV gives , corresponding to and , within reach of future observations. The model is
an example of a class that arises naturally in the context of type IIB string
compactifications with large-volume moduli stabilisation, and takes advantage
of the generic existence there of Kahler moduli whose dominant appearance in
the scalar potential arises from string loop corrections to the Kahler
potential. The inflaton field is a combination of Kahler moduli of a K3-fibered
Calabi-Yau manifold. We believe there are likely to be a great number of models
in this class -- `high-fibre models' -- in which the inflaton starts off far
enough up the fibre to produce observably large primordial gravity waves.Comment: Extended calculations beyond the leading approximations, including
numerical integrations of multi-field evolution; Display an example with ; Simplify the discussion of large fields; Corrected minor errors and
typos; Added references; 41 pages LaTeX, 25 figure
The Universal Kaehler Modulus in Warped Compactifications
We construct the effective theory of the universal Kaehler modulus in warped
compactifications using the Hamiltonian formulation of general relativity. The
spacetime dependent 10d solution is constructed at the linear level for both
the volume modulus and its axionic partner, and nontrivial cancellations of
warping effects are found in the dimensional reduction. Our main result is that
the Kaehler potential is not corrected by warping, up to an overall shift in
the background value of the volume modulus. We extend the analysis beyond the
linearized approximation by computing the fully backreacted 10d metric
corresponding to a finite volume modulus fluctuation. Also, we discuss the
behavior of the modulus in strongly warped regions and show that there are no
mixings with light Kaluza-Klein modes. These results are important for the
phenomenology and cosmology of flux compactifications.Comment: 28 pages, 1 figure; v2. corrected typos, added refs & minor
clarification
Modelling the economics of agroforestry at field- and farm-scale
This report (Deliverable 6.18) assesses the economics of agroforestry systems at field- and farm-scales and compares them with alternative land uses such as arable cropping, pasture and forestry. This analysis is undertaken in terms of financial profitability (e.g. from a farmer perspective) and economic benefits (e.g. from a societal perspective)N/
Warped Spectroscopy: Localization of Frozen Bulk Modes
We study the 10D equation of motion of dilaton-axion fluctuations in type IIB
string compactifications with three-form flux, taking warping into account.
Using simplified models with physics comparable to actual compactifications, we
argue that the lightest mode localizes in long warped throats and takes a mass
of order the warped string scale. Also, Gukov-Vafa-Witten superpotential is
valid for the lightest mass mode; however, the mass is similar to the
Kaluza-Klein scale, so the dilaton-axion should be integrated out of the
effective theory in this long throat regime (leaving a constant
superpotential). On the other hand, there is a large hierarchy between
flux-induced and KK mass scales for moderate or weak warping. This hierarchy
agrees with arguments given for trivial warping. Along the way, we also
estimate the effect of the other 10D supergravity equations of motion on the
dilaton-axion fluctuation, since these equations act as constraints. We argue
that they give negligible corrections to the simplest approximation.Comment: 24pp + appendices, 6 figs, JHEP3 class; v2. corrected reference; v3.
added clarifications; v4. corrected typo
- …