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

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

Nitrate leaching in grazed grasslands of different composition and age

In a field experiment at Research Centre Foulum a suction cup technique was used to investigate nitrate leaching from grassland depending on composition (grass-clover or perennial ryegrass), management (grazing or cutting) and age of the swards. In 1997-2001 was investigated the successive nitrate leaching from 4-7 year old grazed grass-clover and ryegrass with cut plots of similar age and spring barley as reference. In 2000-2001 the simultaneous nitrate leaching from newly established swards, swards grazed for 1 and 7 years and swards cut for 7 years was investigated. In the newly established swards nitrate leaching from grass-clover and ryegrass were similar but at increasing sward age nitrate leaching from the fertilized ryegrass increased dramatically compared to a constant low level from the unfertilized grass-clover. Apparently, the clover component of grass-clover was able to equalize differences in soil nitrogen availability in swards of different age. The results of N2 fixation studies in swards of different age in 2001 will be used in the interpretation of the nitrate leaching data

Management affects nitrate leaching from organic farms

Management decisions significantly affect nitrate-N leaching (N-leaching) from comparable organic fields. The main concern is field management during autumn and themanagement of grass leys. After ploughing-in fertility building crops, like grass-clover leys, effective catch crops are important during autumn and winter for at least two years on sandy soils. On farms with grazing animals the occurrence of “hot spots” should be avoided. These hot spots develop with uneven concentrations of animal manure combined with limited N-uptake in the ley. Management measures to minimize N-leachingmay conflicts with the farmers aim to produce high quality feed and/or to combat yield limiting perennial weeds. It may also conflict with the organic regulations for the grazing period of cows

Nitrate leaching from silage maize

During the last 20 years the area with maize in Denmark has increased dramatically and reached 163,000 ha in 2008. Silage maize is easy to grow, is a suitable fodder for cows and goes well with grass-clover in the diet. This means that silage maize is often found in crop rotations with grass-clover on sandy soils in western Denmark. The ploughing in of grass-clover fields poses a serious risk of increased nitrate leaching on a coarse sandy soil, even when carried out in spring. With increased maize cropping, there is therefore a need for strategies to reduce nitrate leaching after ploughing of grass-clover.In the ICROFS project, OrgGrass, we examined the effect of catch crop and slurry application on nitrate leaching from maize after a spring-ploughed grass-clover

The fields of uniformly accelerated charges in de Sitter spacetime

The scalar and electromagnetic fields of charges uniformly accelerated in de Sitter spacetime are constructed. They represent the generalization of the Born solutions describing fields of two particles with hyperbolic motion in flat spacetime. In the limit Lambda -> 0, the Born solutions are retrieved. Since in the de Sitter universe the infinities I^+- are spacelike, the radiative properties of the fields depend on the way in which a given point of I^+- is approached. The fields must involve both retarded and advanced effects: Purely retarded fields do not satisfy the constraints at the past infinity I^-.Comment: 5 pages, 3 figures, RevTeX; Slightly expanded version of the paper published in Physical Review Letters. (The published version can be generated from the same TeX source.); problem with the postscript fixe

Biomass production and N2-fixation in seven grass-legume mixtures

Inclusion of forage legumes in low-input grassland mixtures improves biomass production and soil fertility trough addition of nitrogen (N) from N2-fixation. The impacts of different mixture of legumes and companion grasses on the N production of the forage mixture have rarely been investigated under comparable soil and climatic conditions. We conducted a field experiment on a sandy soil at two nitrogen levels with seven two-species grassland mixtures: alfalfa (Medicago sativa), bird’s-foot trefoil (Lotus corniculatus), red clover (Trifolium pratense), or white clover (Trifolium repens) in mixture with perennial ryegrass (Lolium perenne), and white clover in mixture with meadow fescue (Festuca pratensis), timothy (Phleum pratense), or hybrid ryegrass (Lolium hybridum). Red clover and alfalfa fixed 400-500 kg N ha-1 and bird ’s-foot trefoil just above 100 kg N ha-1 in aboveground biomass. The white clover N fixation was affected by the companion grass species and ranged from 150 to 175 kg N ha-1. Fertilization had different effects on N2-fixation among the legumes, but also significant effects on white clover N2-fixation depending on the companion grass species

Grassland carbon sequestration and emissions following cultivation in a mixed crop rotation

Grasslands are potential carbon sinks to reduce unprecedented increase in atmospheric CO2. Effect of age (1 to 4-yr-old) and management (slurry, grazing multispecies mixture) of a grass phase mixed crop rotation on carbon sequestration and emissions upon cultivation was compared with 17-yr-old grassland and a pea field as reference. Aboveground and root biomass were determined and soils were incubated to study CO2 emissions after soil disturbance. Aboveground biomass was highest in 1-yr-old grassland with slurry application and lowest in 4-yr-old grassland without slurry application. Root biomass was highest in 4-yr-old grassland, but all 1 to 4-yr-old grasslands were in between the pea field (0.81±0.094 g kg-1 soil) and the 17-yr-old grassland (3.17±0.22 g kg-1 soil). Grazed grasslands had significantly higher root biomass than cut grasslands. There was no significant difference in the CO2 emissions within 1 to 4-yr-old grasslands. Only the 17-yr-old grassland showed markedly higher CO2 emissions (4.9 ± 1.1 g CO2 kg-1 soil). Differences in aboveground and root biomass did not affect CO2 emissions, and slurry application did not either. The substantial increase in root biomass with age but indifference in CO2 emissions across the age and management in temporary grasslands, thus, indicates potential for long-term sequestration of soil C

Many-Body Expanded Full Configuration Interaction. I. Weakly Correlated Regime

Over the course of the past few decades, the field of computational chemistry has managed to manifest itself as a key complement to more traditional lab-oriented chemistry. This is particularly true in the wake of the recent renaissance of full configuration interaction (FCI)-level methodologies, albeit only if these can prove themselves sufficiently robust and versatile to be routinely applied to a variety of chemical problems of interest. In the present series of works, performance and feature enhancements of one such avenue towards FCI-level results for medium to large one-electron basis sets, the recently introduced many-body expanded full configuration interaction (MBE-FCI) formalism [J. Phys. Chem. Lett., 8, 4633 (2017)], will be presented. Specifically, in this opening part of the series, the capabilities of the MBE-FCI method in producing near-exact ground state energies for weakly correlated molecules of any spin multiplicity will be demonstrated.Comment: 38 pages, 7 tables, 3 figures, 1 SI attached as an ancillary fil

Many-Body Expanded Full Configuration Interaction. II. Strongly Correlated Regime

In this second part of our series on the recently proposed many-body expanded full configuration interaction (MBE-FCI) method, we introduce the concept of multideterminantal expansion references. Through theoretical arguments and numerical validations, the use of this class of starting points is shown to result in a focussed compression of the MBE decomposition of the FCI energy, thus allowing chemical problems dominated by strong correlation to be addressed by the method. The general applicability and performance enhancements of MBE-FCI are verified for standard stress tests such as the bond dissociations in H$_2$O, N$_2$, C$_2$, and a linear H$_{10}$ chain. Furthermore, the benefits of employing a multideterminantal expansion reference in accelerating calculations of high accuracy are discussed, with an emphasis on calculations in extended basis sets. As an illustration of this latter quality of the MBE-FCI method, results for H$_2$O and C$_2$ in basis sets ranging from double- to pentuple-$\zeta$ quality are presented, demonstrating near-ideal parallel scaling on up to almost $25000$ processing units.Comment: 41 pages, 4 tables, 10 figures, 1 SI attached as an ancillary fil