A probabilistic assessment of climate change impacts on yield and nitrogen leaching from winter wheat in Denmark

Climate change will impact agricultural production both directly and indirectly, but uncertainties related to likely impacts constrain current political decision making on adaptation. This analysis focuses on a methodology for applying probabilistic climate change projections to assess modelled wheat yields and nitrate leaching from arable land in Denmark. The probabilistic projections describe a range of possible changes in temperature and precipitation. Two methodologies to apply climate projections in impact models were tested. Method A was a straightforward correction of temperature and precipitation, where the same correction was applied to the baseline weather data for all days in the year, and method B used seasonal changes in precipitation and temperature to correct the baseline weather data. Based on climate change projections for the time span 2000 to 2100 and two soil types, the mean impact and the uncertainty of the climate change projections were analysed. Combining probability density functions of climate change projections with crop model simulations, the uncertainty and trends in nitrogen (N) leaching and grain yields with climate change were quantified. The uncertainty of climate change projections was the dominating source of uncertainty in the projections of yield and N leaching, whereas the methodology to seasonally apply climate change projections had a minor effect. For most conditions, the probability of large yield reductions and large N leaching losses tracked trends in mean yields and mean N leaching. The impacts of the uncertainty in climate change were higher for loamy sandy soil than for sandy soils due to generally higher yield levels for loamy sandy soils. There were large differences between soil types in response to climate change, illustrating the importance of including soil information for regional studies of climate change impacts on cropping systems

Subsoil loosening eliminated plough pan but had variable effect on crop yield

Subsoil compaction is a widespread problem on Danish arable soils and especially in form of plough pan compaction. Subsoil compaction may reduce crop yield and quality, increase negative environmental impact (e.g. in form of increased nitrogen leaching), and reduce soil workability and traffic ability of the soil. Danish Institute of Agricultural Sciences has in a DARCOF project investigated the effect of subsoil loosening. The investigations were carried out in an organic crop rotation experiment at two sandy loams: Flakkebjerg (13% clay) and Foulum (8% clay)

Mekanisk jordløsning fjernede pløjesål men gav varierende effekt på udbyttet

Pakning af underjorden forekommer på en stor del af den dyrkede jord. Særligt er en rodhæmmende pløjesål et udbredt problem. Pakning af underjorden forringer kvantitet og kvalitet af afgrøderne, kan give problemer med færdsel på jorden under våde forhold og har negativ effekt på miljøet fx i form af øget risiko for N udvaskning. Danmarks JordbrugsForskning har i et FØJO-projekt undersøgt effekten af at løsne den rodhæmmende pløjesål i de økologiske sædskifteforsøg på Flakkebjerg og Foulum

Confinement effects from interacting chromo-magnetic and axion fields

We study a non-Abelian gauge theory with a pseudo scalar coupling \phi \epsilon ^{\mu \nu \alpha \beta} F_{\mu \nu}^a F_{\alpha \beta}^a in the case where a constant chromo-electric, or chromo-magnetic, strength expectation value is present. We compute the interaction potential within the framework of gauge-invariant, path-dependent, variables formalism. While in the case of a constant chromo-electric field strength expectation value the static potential remains Coulombic, in the case of a constant chromo-magnetic field strength the potential energy is the sum of a Coulombic and a linear potentials, leading to the confinement of static charges.Comment: 12 pages, no figures, published versio

On the Grothendieck Theorem for jointly completely bounded bilinear forms

We show how the proof of the Grothendieck Theorem for jointly completely bounded bilinear forms on C*-algebras by Haagerup and Musat can be modified in such a way that the method of proof is essentially C*-algebraic. To this purpose, we use Cuntz algebras rather than type III factors. Furthermore, we show that the best constant in Blecher's inequality is strictly greater than one.Comment: 9 pages, minor change

Wilson Loops and QCD/String Scattering Amplitudes

We generalize modern ideas about the duality between Wilson loops and scattering amplitudes in ${\cal N}=4$ SYM to large $N$ QCD by deriving a general relation between QCD meson scattering amplitudes and Wilson loops. We then investigate properties of the open-string disk amplitude integrated over reparametrizations. When the Wilson loop is approximated by the area behavior, we find that the QCD scattering amplitude is a convolution of the standard Koba-Nielsen integrand and a kernel. As usual poles originate from the first factor, whereas no (momentum dependent) poles can arise from the kernel. We show that the kernel becomes a constant when the number of external particles becomes large. The usual Veneziano amplitude then emerges in the kinematical regime where the Wilson loop can be reliably approximated by the area behavior. In this case we obtain a direct duality between Wilson loops and scattering amplitudes when spatial variables and momenta are interchanged, in analogy with the $\cal N$=4 SYM case.Comment: 39pp., Latex, no figures; v2: typos corrected; v3: final, to appear in PR

Nucleation of quark matter bubbles in neutron stars

The thermal nucleation of quark matter bubbles inside neutron stars is examined for various temperatures which the star may realistically encounter during its lifetime. It is found that for a bag constant less than a critical value, a very large part of the star will be converted into the quark phase within a fraction of a second. Depending on the equation of state for neutron star matter and strange quark matter, all or some of the outer parts of the star may subsequently be converted by a slower burning or a detonation.Comment: 13 pages, REVTeX, Phys.Rev.D (in press), IFA 93-32. 5 figures (not included) available upon request from [email protected]