33,034 research outputs found
The Role of the 1994-95 Coffee Boom in Uganda's Recovery
This paper reports a CGE analysis that explores the consequences of the 1994-95 rise in the international price of coffee for Uganda´s economy. Evidence is found for a small effect on medium-term growth and poverty reduction. Aid dependence is among the reasons why this effect is not found to be larger. Major beneficiary groups are not only the farmers to which the windfall initially accrued but also urban wage earners and the urban self-employed
Bias, redshift space distortions and primordial nongaussianity of nonlinear transformations: application to Lyman alpha forest
On large scales a nonlinear transformation of matter density field can be
viewed as a biased tracer of the density field itself. A nonlinear
transformation also modifies the redshift space distortions in the same limit,
giving rise to a velocity bias. In models with primordial nongaussianity a
nonlinear transformation generates a scale dependent bias on large scales. We
derive analytic expressions for these for a general nonlinear transformation.
These biases can be expressed entirely in terms of the one point distribution
function (PDF) of the final field and the parameters of the transformation. Our
analysis allows one to devise nonlinear transformations with nearly arbitrary
bias properties, which can be used to increase the signal in the large scale
clustering limit. We apply the results to the ionizing equilibrium model of
Lyman-alpha forest, in which Lyman-alpha flux F is related to the density
perturbation delta via a nonlinear transformation. Velocity bias can be
expressed as an average over the Lyman-alpha flux PDF. At z=2.4 we predict the
velocity bias of -0.1, compared to the observed value of -0.13 +/- 0.03. Bias
and primordial nongaussianity bias depend on the parameters of the
transformation. Measurements of bias can thus be used to constrain these
parameters, and for reasonable values of the ionizing background intensity we
can match the predictions to observations. Matching to the observed values we
predict the ratio of primordial nongaussianity bias to bias to have the
opposite sign and lower magnitude than the corresponding values for the highly
biased galaxies, but this depends on the model parameters and can also vanish
or change the sign.Comment: 18 pages, 1 figur
Broken Symmetry as a Stabilizing Remnant
The Goldberger-Wise mechanism enables one to stabilize the length of the
warped extra dimension employed in Randall-Sundrum models. In this work we
generalize this mechanism to models with multiple warped throats sharing a
common ultraviolet brane. For independent throats this generalization is
straight forward. If the throats possess a discrete interchange symmetry like
Z_n the stabilizing dynamics may respect the symmetry, resulting in equal
throat lengths, or they may break it. In the latter case the ground state of an
initially symmetric configuration is a stabilized asymmetric configuration in
which the throat lengths differ. We focus on two- (three-) throat setups with a
Z_2 (Z_3) interchange symmetry and present stabilization dynamics suitable for
either breaking or maintaining the symmetry. Though admitting more general
application, our results are relevant for existing models in the literature,
including the two throat model with Kaluza-Klein parity and the three throat
model of flavor based on a broken Z_3 symmetry.Comment: 23 pages; v2 minor cosmetic chang
Estimating the number of injecting drug users in scotland's HCV-diagnosed population using capture-recapture methods
How to measure redshift-space distortions without sample variance
We show how to use multiple tracers of large-scale density with different
biases to measure the redshift-space distortion parameter
beta=f/b=(dlnD/dlna)/b (where D is the growth rate and a the expansion factor),
to a much better precision than one could achieve with a single tracer, to an
arbitrary precision in the low noise limit. In combination with the power
spectrum of the tracers this allows a much more precise measurement of the
bias-free velocity divergence power spectrum, f^2 P_m - in fact, in the low
noise limit f^2 P_m can be measured as well as would be possible if velocity
divergence was observed directly, with rms improvement factor ~[5.2(beta^2+2
beta+2)/beta^2]^0.5 (e.g., ~10 times better than a single tracer for beta=0.4).
This would allow a high precision determination of f D as a function of
redshift with an error as low as 0.1%. We find up to two orders of magnitude
improvement in Figure of Merit for the Dark Energy equation of state relative
to Stage II, a factor of several better than other proposed Stage IV Dark
Energy surveys. The ratio b_2/b_1 will be determined with an even greater
precision than beta, producing, when measured as a function of scale, an
exquisitely sensitive probe of the onset of non-linear bias. We also extend in
more detail previous work on the use of the same technique to measure
non-Gaussianity. Currently planned redshift surveys are typically designed with
signal to noise of unity on scales of interest, and are not optimized for this
technique. Our results suggest that this strategy may need to be revisited as
there are large gains to be achieved from surveys with higher number densities
of galaxies.Comment: 22 pages, 13 figure
Modelling the alumina abundance of oxygen-rich evolved stars in the Large Magellanic Cloud
In order to determine the composition of the dust in the circumstellar
envelopes of oxygen-rich asymptotic giant branch (AGB) stars we have computed a
grid of modust radiative-transfer models for a range of dust compositions,
mass-loss rates, dust shell inner radii and stellar parameters. We compare the
resulting colours with the observed oxygen-rich AGB stars from the SAGE-Spec
Large Magellanic Cloud (LMC) sample, finding good overall agreement for stars
with a mid-infrared excess. We use these models to fit a sample of 37 O-rich
AGB stars in the LMC with optically thin circumstellar envelopes, for which
535-m Spitzer infrared spectrograph (IRS) spectra and broadband
photometry from the optical to the mid-infrared are available. From the
modelling, we find mass-loss rates in the range to
M, and we show that a grain
mixture consisting primarily of amorphous silicates, with contributions from
amorphous alumina and metallic iron provides a good fit to the observed
spectra. Furthermore, we show from dust models that the AKARI [11][15]
versus [3.2][7] colour-colour diagram, is able to determine the fractional
abundance of alumina in O-rich AGB stars.Comment: 22 pages, 17 figures, accepted MNRA
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