Biogas nutrient management in organic cropping - not only a nitrogen issue

Nutrient imbalance, mainly due to low K and high Ca and/or Mg concentrations, was a plausible explanation for low growth response to digestate fertilisation by beetroot following harvested grass-clover biogas ley. To derive the full benefit of a transition to a biogas nutrient management (BG) system, extra nutrients except for N may need to be added, especially if digestate supply is divided between many crop positions in the rotation. This is probably of extra importance on sandy soils such as that used in this experiment

Nonlocal density functionals and the linear response of the homogeneous electron gas

The known and usable truly nonlocal functionals for exchange-correlation energy of the inhomogeneous electron gas are the ADA (average density approximation) and the WDA (weighted density approximation). ADA, by design, yields the correct linear response function of the uniform electron gas. WDA is constructed so that it is exact in the limit of one-electron systems. We derive an expression for the linear response of the uniform gas in the WDA, and calculate it for several flavors of WDA. We then compare the results with the Monte-Carlo data on the exchange-correlation local field correction, and identify the weak points of conventional WDA in the homogeneous limit. We suggest how the WDA can be modified to improve the response function. The resulting approximation is a good one in both opposite limits, and should be useful for practical nonlocal density functional calculations.Comment: 4 pages, two eps figures embedde

Ability to Pay in New Zealand's Tax System

This article begins with a review of tax distribution principles and theory to provide a framework to which the position and interpretation of the ability to pay principle can be related. In the next three sections the author describes how the income tax base, the wealth tax and the income support system correspond with the ability to pay principle. Finally, the author looks upon new equity trends in taxation from a New Zealand perspective

Metal-insulator transitions: Influence of lattice structure, Jahn-Teller effect, and Hund's rule coupling

We study the influence of the lattice structure, the Jahn-Teller effect and the Hund's rule coupling on a metal-insulator transition in AnC60 (A= K, Rb). The difference in lattice structure favors A3C60 (fcc) being a metal and A4C60 (bct) being an insulator, and the coupling to Hg Jahn-Teller phonons favors A4C60 being nonmagnetic. The coupling to Hg (Ag) phonons decreases (increases) the value Uc of the Coulomb integral at which the metal-insulator transition occurs. There is an important partial cancellation between the Jahn-Teller effect and the Hund's rule coupling.Comment: 4 pages, RevTeX, 3 eps figure, additional material available at http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene

Electron self-energy in A3C60 (A=K, Rb): Effects of t1u plasmon in GW approximation

The electron self-energy of the t1u states in A3C60 (A=K, Rb) is calculated using the so-called GW approximation. The calculation is performed within a model which considers the t1u charge carrier plasmon at 0.5 eV and takes into account scattering of the electrons within the t1u band. A moderate reduction (35 %) of the t1u band width is obtained.Comment: 4 pages, revtex, 1 figure more information at http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene

Mott Transition in Degenerate Hubbard Models: Application to Doped Fullerenes

The Mott-Hubbard transition is studied for a Hubbard model with orbital degeneracy N, using a diffusion Monte-Carlo method. Based on general arguments, we conjecture that the Mott-Hubbard transition takes place for U/W \propto \sqrt{N}, where U is the Coulomb interaction and W is the band width. This is supported by exact diagonalization and Monte-Carlo calculations. Realistic parameters for the doped fullerenes lead to the conclusion that stoichiometric A_3 C_60 (A=K, Rb) are near the Mott-Hubbard transition, in a correlated metallic state.Comment: 4 pages, revtex, 1 eps figure included, to be published in Phys.Rev.B Rapid Com

Mott-Hubbard insulators for systems with orbital degeneracy

We study how the electron hopping reduces the Mott-Hubbard band gap in the limit of a large Coulomb interaction U and as a function of the orbital degeneracy N. The results support the conclusion that the hopping contribution grows as roughly \sqrt{N}W, where W is the one-particle band width, but in certain models a crossover to a \sim NW behavior is found for a sufficiently large N.Comment: 7 pages, revtex, 6 figures more information at http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene

The effect of child labor on mathematics and language achievement in Latin America

The authors use a unique data set on language, and mathematics test scores for third, and fourth graders in eleven different Latin American countries, to determine whether child labor raises or lowers school achievement. Their findings are amazingly consistent across countries. In every country, child labor lowers performance on tests of language and mathematics proficiency, even when controlling for school and household attributes. The magnitude of the effect is similar to the percentage reduction in adult wages from child labor reported by Ilahi, Sedlacek and Orazem. The adverse impact of child labor on test performance is larger when children work regularly, rather than occasionally. Even modest levels of child labor at early ages cause adverse consequences for the development of cognitive abilities. These findings strongly refute the presumptions that child labor may be neutral, or complementary to academic performance, provided that the child remains enrolled in school. Instead, child labor consistently makes a year of education less productive in the generation of human capital.