The determination of the ground-state energy of an antiferromagnetic lattice by means of a renormalization procedure

An approximate value for the ground-state energy of an antiferromagnetic lattice of spins one-half is determined by means of a repeated renormalization procedure in which the lattice is divided into cells with an effective interaction. This effective interaction is determined on the basis of the spin-hamiltonian formalism

A (3+1) resonance enhanced multiphoton ionization study of the C 1S+ and E 1P states of CO: polarization dependence used to probe electronic excitation routes and electronic character

The three-photon excitations of the C 1 + and E 1 states have been investigated with resonance enhanced multiphoton ionization spectroscopy as a function of the polarization of the excitation light. From the observed polarization dependence the contributions of the various excitation routes have been determined, and the electronic character of these states has been analyzed. The results indicate that the v=0 and 1 vibrational levels of the E 1 state have slightly different electronic characters. The Journal of Chemical Physics is copyrighted by The American Institute of Physics

Modelconcepten voor de interactie tussen verzadigd grondwater en oppervlaktewater

Uitgaande van de 3 kernbegrippen drainageflux, lekflux en voedingsflux is getracht een koppeling te vinden tussen het topsysteem en het diepe grondwater. Op weg naar deze koppeling zijn een aantal aannames gedaa

The costs and benefits of biological control of invasive alien plants in South Africa

This paper provides a brief review of the environmental and economic costs of invasive alien plants in South Africa as a background to assessments of returns on investment in weed biological control. The understanding of impacts and their economic costs is far from perfect, but estimates indicate that some costs (of lost water, grazing and biodiversity) are currently about R6.5 billion per annum (about 0.3 % of South Africa’s GDP of around R2000 billion: R7=about US$1), and could rise to >5%ofGDPif invasive plants are allowed to reach their full potential. By comparing the costs of biological control research and implementation to the benefits of restored ecosystem services, or avoided costs, and avoided ongoing control costs, biological control has been shown to be extremely beneficial in economic terms: estimated benefit:cost ratios ranged from 8:1 up to 3726:1. Currently, spending on biological control is far lower than on other forms of control (about 5 % and 14 % of that spent on mechanical and chemical control, respectively), despite the significantly better returns on investment from biological control. In aggregate these assessments indicate that higher levels of spending on biological control research would generate extremely attractive returns on investment.Centre of Excellence for Invasion Biolog

Bundling arrows: improving translational CNS drug development by integrated PK/PD-metabolomics

Diseases of the Central Nervous System (CNS) affect millions of people worldwide, with the number of people affected quickly growing. Unfortunately, the successful development of CNS-acting drugs is less than 10%, and this is attributed to the complexity of the CNS, unexpected side effects, difficulties in penetrating the blood-brain barrier and lack of biomarkers. Areas covered: Herein, the authors first review how pharmacokinetic/pharmacodynamic (PK/PD) models are designed to predict the dose-dependent time course of effect, and how they are used to translate drug effects from animal to man. Then, the authors discuss how pharmacometabolomics gives insight into system-wide pharmacological effects and why it is a promising method to study interspecies differences. Finally, the authors advocate the application of PK/PD-metabolomics modeling to advance translational CNS drug development by discussing its opportunities and challenges. Expert opinion: It is envisioned that PK/PD-metabolomics will increase our understanding of CNS drug effects and improve translational CNS drug development, thereby increasing success rates. The successful future development of this concept will require multi-level and longitudinal biomarker evaluation over a large dose range, multi-tissue biomarker evaluation, and the generation of a proof of principle by application to multiple CNS drugs in multiple species. INTRODUCTIONArticle / Letter to editorLeiden Academic Centre for Drug Researc

Bepaling van freatische lekweerstanden in het NHI fase 1+

Dit artikel beschrijft een methode om op basis van GIS-bestanden de drainage relaties tussen het grondwater en de aanwezige oppervlaktewaterstelsels te berekenen voor vierkante elementen (bijvoorbeeld MODFLOW cellen). In de hier beschreven methode worden lijnvormige drainage stelsels omgezet naar representatieve parameters per vierkant

De parameterisatie van de interactie tussen grondwater en oppervlaktewater voor landelijke en regionale grondwatermodellering

Alterra, RIVM en RIZA richtten de Ad hoc Werkgroep Concensus Hydrologie op, waarbij de interactie tussen grond- en oppervlaktewater centraal staa