Effect of Rapid or slow release nitrogen supply and cover crop/weed management on crop yield, pest incidence and fruit quality in intensive organic apple production

Apple is the commercially most important top fruit crop grown in the European Union. In spring 2001 one-year-old trees of the apple variety ‘Ingrid Marie’ were established in an organic production system with 3.0 m between the tree rows. Each plot consisted of three semi-plots at planting distances 0.6m (5555 trees ha-1), 0.9 m (3333 trees ha –1) and 1.2 m (2777 trees ha-1). Tree growth, soil moisture, soil-, leaf- and branch analysis, diseases, fruit production, outer and inner fruit quality were measured. The healthiest trees with the best coloured fruits were produced on trees grown in weed. But the yield was so low that production was not economical. A high production combined with trees less infected with fruit tree canker and with a satisfactory colouring was produced on trees grown in intensive production system of 5555 trees per ha with no nitrogen supply

Combined production of broilers and fruits

Combined production of broilers and fruit trees is a subject often discussed in organic fruit production in Denmark. Very little research has been carried out on this type of production system. In organic production in Denmark, nearly no pesticides are allowed, so the need for alternative pest control is large. Apple sawfly (Hoplocampa testudinea) and pear midge (Contarinia pyrivora) cause big crop losses in apples and pears respectively, in unsprayed organic fruit production. Both insects infest fruitlets and cause these to drop prematurely after which the pests pupate in the topsoil. In the present experiment a research orchard with the varieties ‘Discovery’ and ‘Conference’ were used as outdoor area for broilers to minimise the population of sawflies and pear midges, and to reduce the need for weeding and manuring. The trees were kept unsprayed. Fruit yield and fruit quality were assessed at harvest. White sticky traps were placed in the test area in order to measure the occurrence of sawfly over time. The infestation of pear midge was investigated counting the infested fruitlets in clusters on trees at the centre of the plots. The catch of apple sawflies was reduced in the combined apple and broiler production, but no significant effect on the yield or the fruit quality was seen. Experiences from on-farm research show that combining fruit and egg-production is one way to reduce the problem with apple sawfly, but poultry alone is not a sufficient way of controlling sawflies. The welfare and health of the broilers were excellent under fruit trees

Optical Hall conductivity in bulk and nanostructured graphene beyond the Dirac approximation

We present a perturbative method for calculating the optical Hall conductivity in a tight-binding framework based on the Kubo formalism. The method involves diagonalization only of the Hamiltonian in absence of the magnetic field, and thus avoids the computational problems usually arising due to the huge magnetic unit cells required to maintain translational invariance in presence of a Peierls phase. A recipe for applying the method to numerical calculations of the magneto-optical response is presented. We apply the formalism to the case of ordinary and gapped graphene in a next-nearest neighbour tight-binding model as well as graphene antidot lattices. In both case, we find unique signatures in the Hall response, that are not captured in continuum (Dirac) approximations. These include a non-zero optical Hall conductivity even when the chemical potential is at the Dirac point energy. Numerical results suggest that this effect should be measurable in experiments.Comment: 7 pages, 4 figures, accepted in Physical Review

Convex Multivariable Trace Functions

For any densely defined, lower semi-continuous trace \tau on a C*-algebra A with mutually commuting C*-subalgebras A_1, A_2, ... A_n, and a convex function f of n variables, we give a short proof of the fact that the function (x_1, x_2, ..., x_n) --> \tau (f(x_1, x_2, ..., x_n)) is convex on the space \bigoplus_{i=1}^n (A_i)_{self-adjoint}. If furthermore the function f is log-convex or root-convex, so is the corresponding trace function. We also introduce a generalization of log-convexity and root-convexity called \ell-convexity, show how it applies to traces, and give a few examples. In particular we show that the trace of an operator mean is always dominated by the corresponding mean of the trace values.Comment: 13 pages, AMS TeX, Some remarks and results adde

Selfdual spaces with complex structures, Einstein-Weyl geometry and geodesics

We study the Jones and Tod correspondence between selfdual conformal 4-manifolds with a conformal vector field and abelian monopoles on Einstein-Weyl 3-manifolds, and prove that invariant complex structures correspond to shear-free geodesic congruences. Such congruences exist in abundance and so provide a tool for constructing interesting selfdual geometries with symmetry, unifying the theories of scalar-flat Kahler metrics and hypercomplex structures with symmetry. We also show that in the presence of such a congruence, the Einstein-Weyl equation is equivalent to a pair of coupled monopole equations, and we solve these equations in a special case. The new Einstein-Weyl spaces, which we call Einstein-Weyl ``with a geodesic symmetry'', give rise to hypercomplex structures with two commuting triholomorphic vector fields.Comment: 30 pages, 7 figures, to appear in Ann. Inst. Fourier. 50 (2000

Optical second harmonic generation from Wannier excitons

Excitonic effects in the linear optical response of semiconductors are well-known and the subject of countless experimental and theoretical studies. For the technologically important second order nonlinear response, however, description of excitonic effects has proved to be difficult. In this work, a simplified three-band Wannier exciton model of cubic semiconductors is applied and a closed form expression for the complex second harmonic response function including broadening is derived. Our calculated spectra are found to be in excellent agreement with the measured response near the band edge. In addition, a very substantial enhancement of the nonlinear response is predicted for the transparency region

Optical properties of graphene antidot lattices

Undoped graphene is semi-metallic and thus not suitable for many electronic and optoelectronic applications requiring gapped semiconductor materials. However, a periodic array of holes (antidot lattice) renders graphene semiconducting with a controllable band gap. Using atomistic modelling, we demonstrate that this artificial nanomaterial is a dipole-allowed direct gap semiconductor with a very pronounced optical absorption edge. Hence, optical infrared spectroscopy should be an ideal probe of the electronic structure. To address realistic experimental situations, we include effects due to disorder and the presence of a substrate in the analysis.Comment: 11 pages, 9 figures, accepted for publication in Phys. Rev.

Monitoring Leverage

We discuss how leverage can be monitored for institutions, individuals, and assets. While traditionally the interest rate has been regarded as the important feature of a loan, we argue that leverage is sometimes even more important. Monitoring leverage provides information about how risk builds up during booms as leverage rises and how crises start when leverage on new loans sharply declines. Leverage data is also a crucial input for crisis management and lending facilities. Leverage at the asset level can be monitored by down payments or margin requirement or and haircuts, giving a model-free measure that can be observed directly, in contrast to other measures of systemic risk that require complex estimation. Asset leverage is a fundamental measure of systemic risk and so is important in itself, but it is also the building block out of which measures of institutional leverage and household leverage can be most accurately and informatively constructed.Leverage, Loan to value, Margins, Haircuts, Monitor, Regulate, Leverage on new loans, Asset leverage, Investor leverage

Predatory Trading

This paper studies predatory trading: trading that induces and/or exploits other investors' need to reduce their positions. We show that if one trader needs to sell, others also sell and subsequently buy back the asset. This leads to price overshooting, and a reduced liquidation value for the distressed trader. Hence, the market is illiquid when liquidity is most needed. Further, a trader prots from triggering another trader's crisis, and the crisis can spill over across traders and across assetsasset pricing