7,995 research outputs found
The two-and three-point correlation functions of the polarized five-year WMAP sky maps
We present the two- and three-point real space correlation functions of the
five-year WMAP sky maps, and compare the observed functions to simulated LCDM
concordance model ensembles. In agreement with previously published results, we
find that the temperature correlation functions are consistent with
expectations. However, the pure polarization correlation functions are
acceptable only for the 33GHz band map; the 41, 61, and 94 GHz band correlation
functions all exhibit significant large-scale excess structures. Further, these
excess structures very closely match the correlation functions of the two
(synchrotron and dust) foreground templates used to correct the WMAP data for
galactic contamination, with a cross-correlation statistically significant at
the 2sigma-3sigma confidence level. The correlation is slightly stronger with
respect to the thermal dust template than with the synchrotron template.Comment: 10 pages, 5 figures, published in ApJ. v2: New title, minor changes
to appendix, and fixed some typos. v3: Matches version published in Ap
A Markov Chain Monte Carlo Algorithm for analysis of low signal-to-noise CMB data
We present a new Monte Carlo Markov Chain algorithm for CMB analysis in the
low signal-to-noise regime. This method builds on and complements the
previously described CMB Gibbs sampler, and effectively solves the low
signal-to-noise inefficiency problem of the direct Gibbs sampler. The new
algorithm is a simple Metropolis-Hastings sampler with a general proposal rule
for the power spectrum, C_l, followed by a particular deterministic rescaling
operation of the sky signal. The acceptance probability for this joint move
depends on the sky map only through the difference of chi-squared between the
original and proposed sky sample, which is close to unity in the low
signal-to-noise regime. The algorithm is completed by alternating this move
with a standard Gibbs move. Together, these two proposals constitute a
computationally efficient algorithm for mapping out the full joint CMB
posterior, both in the high and low signal-to-noise regimes.Comment: Submitted to Ap
CMB likelihood approximation by a Gaussianized Blackwell-Rao estimator
We introduce a new CMB temperature likelihood approximation called the
Gaussianized Blackwell-Rao (GBR) estimator. This estimator is derived by
transforming the observed marginal power spectrum distributions obtained by the
CMB Gibbs sampler into standard univariate Gaussians, and then approximate
their joint transformed distribution by a multivariate Gaussian. The method is
exact for full-sky coverage and uniform noise, and an excellent approximation
for sky cuts and scanning patterns relevant for modern satellite experiments
such as WMAP and Planck. A single evaluation of this estimator between l=2 and
200 takes ~0.2 CPU milliseconds, while for comparison, a single pixel space
likelihood evaluation between l=2 and 30 for a map with ~2500 pixels requires
~20 seconds. We apply this tool to the 5-year WMAP temperature data, and
re-estimate the angular temperature power spectrum, , and likelihood,
L(C_l), for l<=200, and derive new cosmological parameters for the standard
six-parameter LambdaCDM model. Our spectrum is in excellent agreement with the
official WMAP spectrum, but we find slight differences in the derived
cosmological parameters. Most importantly, the spectral index of scalar
perturbations is n_s=0.973 +/- 0.014, 1.9 sigma away from unity and 0.6 sigma
higher than the official WMAP result, n_s = 0.965 +/- 0.014. This suggests that
an exact likelihood treatment is required to higher l's than previously
believed, reinforcing and extending our conclusions from the 3-year WMAP
analysis. In that case, we found that the sub-optimal likelihood approximation
adopted between l=12 and 30 by the WMAP team biased n_s low by 0.4 sigma, while
here we find that the same approximation between l=30 and 200 introduces a bias
of 0.6 sigma in n_s.Comment: 10 pages, 7 figures, submitted to Ap
Nitrogen management on large organic dairy farms
Large dairy herds need much grassland near the farm. Utilisation and losses of nitrogen in such grass-intensive crop rotations can be controlled by management: In grassland, grazing days or fertiliser input can be reduced, and following grassland cultivation, a barley whole crop for silage undersown with Italian ryegrass can reduce leaching to a minimum
Statistical uncertainties and systematic errors in weak lensing mass estimates of galaxy clusters
Upcoming and ongoing large area weak lensing surveys will also discover large
samples of galaxy clusters. Accurate and precise masses of galaxy clusters are
of major importance for cosmology, for example, in establishing well calibrated
observational halo mass functions for comparison with cosmological predictions.
We investigate the level of statistical uncertainties and sources of systematic
errors expected for weak lensing mass estimates. Future surveys that will cover
large areas on the sky, such as Euclid or LSST and to lesser extent DES, will
provide the largest weak lensing cluster samples with the lowest level of
statistical noise regarding ensembles of galaxy clusters. However, the expected
low level of statistical uncertainties requires us to scrutinize various
sources of systematic errors. In particular, we investigate the bias due to
cluster member galaxies which are erroneously treated as background source
galaxies due to wrongly assigned photometric redshifts. We find that this
effect is significant when referring to stacks of galaxy clusters. Finally, we
study the bias due to miscentring, i.e., the displacement between any
observationally defined cluster centre and the true minimum of its
gravitational potential. The impact of this bias might be significant with
respect to the statistical uncertainties. However, complementary future
missions such as eROSITA will allow us to define stringent priors on
miscentring parameters which will mitigate this bias significantly.Comment: 14 pages, 7 figures; accepted for publication in MNRA
Productivity and N-leaching in organic dairy grass-arable crop rotations
Increasing size of organic dairy farms makes grazing of all cropped land inexpedient due to long distance to the milking facilities. We investigated nutrient dynamics and feed production in two dairy crop rotations with differences in proportion of grazing and cutting. One six year crop rotation represents close to the farm buildings (barley undersown with grass-clover - 4 years of grass-clover - spring barley/catch crop) and another represents further away (barley undersown with grass-clover, 2 years of grass-clover -barley/catch crop - maize/catch crop - lupin/catch crop). In each of the crop rotations was made five treatments concerning grazing/cutting strategy and manure application. Results shows that herbage production was high in year 1-4 of grass-clover. Nitrate leaching in the crop rotations were highest in grazed and manured 2-4 years old grasslands, but also following maize and lupin considerable losses occurred despite the presence of catch crops. Following grassland cultivation, a barley silage crop undersown with Italian ryegrass reduced leaching to a minimum
Herbs in grasslands
Ongoing experiments have shown that herbs can constitute a significant proportion of the sward and that management affects the composition. However, the competitive strength and feeding value of the different herb species varied highly
Yield effects of grazing and red clover in white clover/grass mixtures
In white clover/ryegrass mixtures grazing in one year significantly increases the yield in the next, compared to cutting. Red clover is a good supplement to the mixture as it performs well under cutting regime, while white clover takes over during grazing. Overall, inclusion of red clover in the mixture contributes to a more robust sward and
increased flexibility in utilizatio
Herbs in high producing organic grasslands – effect of management
In many organic grasslands herbs are established due to their expected beneficial properties for nutritive value and biodiversity. However, knowledge about grassland herbs is limited. Three mixtures were therefore established at different grazing/cutting and fertilization managements to examine the growth potential and feeding value. The competitiveness of the different species varied greatly. Chicory, plantain and caraway were competitive in mixtures with traditional grassland species. Lotus and salad burnet were weak competitors and chervil and sainfoin were very weak. The feeding value was also highly variable. Caraway had high digestibility of organic matter, also compared with the traditional grassland species, whereas plantain and salad burnet had lowest digestibility. The management, grazing, cutting, slurry and sward age, affected the proportion of the herb species. The proportion of caraway increased at cutting, slurry application and sward age. The proportion of plantain also increased at cutting but decreased at slurry application and sward age. The proportion of chicory increased with slurry application and decreased with sward age independently of cutting/grazing. The experiment showed that inclusion of herbs in the sward increased the biodiversity, made the herbage mass more diverse without affecting the dry matter yield
Residual effects of cutting and grazing on grass/clover growth
The residual effect of cutting and grazing during the growing season was investigated in the spring and summer growth in an organic crop rotation with 1-4 year-old grass-clover mixtures of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) either with or without red clover (Trifolium pratense L.) and with and without slurry. The white clover mixtures had significantly higher yields in spring and summer in swards that were previously grazed compared to previously cut swards, when slurry was applied. The percentage of white clover in spring was considerably reduced by previous grazing and this caused the yield response of slurry application to be highest following grazing. A similar effect on the clover content was not found in the summer growth. With the inclusion of red clover in the sward the effect of previous management on spring yield disappeared. Red clover was very abundant under the cutting regime, while the contents were declining with grazing
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