Evaluating Non-Price Water Demand Policies During Severe Droughts

Western states and provinces live under constant drought threat. When and how to time restrictions on outdoor watering are crucial management issues. The effectiveness of various policies is assessed using experience from Colorado during a severe drought.Environmental Economics and Policy,

EVALUATING NON-PRICE WATER DEMAND POLICIES DURING SEVERE DROUGHTS

This research examines how differing frequencies of water use restrictions affected per-capita water demand in three medium-sized municipalities along the Front Range of Colorado during the 2002 drought. Preliminary results indicate that while one- or two-day per week watering restrictions limit per capita water use, voluntary restrictions may actually promote overuse of water as consumers prepare for more stringent restrictions.Resource /Energy Economics and Policy,

Impact des successions culturales (y compris intercultures) sur l'utilisation de produits phytosanitaires

Impact of crop sequences (including intercropping) on the use of pesticides. Crop sequences and the introduction of catch crops influence the development of agricultural pests (weeds, pests and diseases). This paper gives an overview of the problems that may arise for farmers in practice. Adaptation of crop interventions is often based on the use of plant protection products in the following crop, and these changes serve to solve problems that have been previously generated. Nevertheless, the poorly reasoned introduction of a catch crop can cause unwanted effects in terms of pest management and in relation to the protection of water resources

Assessment of atomic charge models for gas-phase computations on polypeptides

The concept of the atomic charge is extensively used to model the electrostatic properties of proteins. Atomic charges are not only the basis for the electrostatic energy term in biomolecular force fields but are also derived from quantum mechanical computations on protein fragments to get more insight into their electronic structure. Unfortunately there are many atomic charge schemes which lead to significantly different results, and it is not trivial to determine which scheme is most suitable for biomolecular studies. Therefore, we present an extensive methodological benchmark using a selection of atomic charge schemes [Mulliken, natural, restrained electrostatic potential, Hirshfeld-I, electronegativity equalization method (EEM), and split-charge equilibration (SQE)] applied to two sets of penta-alanine conformers. Our analysis clearly shows that Hirshfeld-I charges offer the best compromise between transferability (robustness with respect to conformational changes) and the ability to reproduce electrostatic properties of the penta-alanine. The benchmark also considers two charge equilibration models (EEM and SQE), which both clearly fail to describe the locally charged moieties in the zwitterionic form of penta-alanine. This issue is analyzed in detail because charge equilibration models are computationally much more attractive than the Hirshfeld-I scheme. Based on the latter analysis, a straightforward extension of the SQE model is proposed, SQE+Q0, that is suitable to describe biological systems bearing many locally charged functional groups

A combined experimental-numerical study to tensile behaviour of limestone

In this paper, a combined experimental-computational study of double-edge notched stone specimen subject to cyclic tensile loading is presented. In the experimental part, the load-deformation response and the local displacement field are recorded. Both experimental results are used to validate a numerical model for the description of fracture within finite elements. The model uses displacement discontinuities to model cracks. These discontinuities are implemented using the partition of unity property of finite element shape functions. In the discontinuity, a combined damage-plasticity cohesive law is used. Numerical simulations are compared with experimental observations

Reactivity of three-membered heterocyclic rings with respect to sodium methoxide

Aziridines can be ‘activated’ or ‘non-activated’, depending on whether their N-substituent is an electron-withdrawing group or an electron-donating group, respectively. Activated aziridines are much more susceptible to ring opening than non-activated aziridines and epoxides are even more reactive. The difference in reactivity between activated 2-(bromomethyl)-1-tosylaziridines, non-activated 1-benzyl-2-(bromomethyl)aziridines and epibromohydrins with respect to sodium methoxide was comparatively analysed by means of DFT calculations, such as BMK, MPW1K and MPWB95 [1]. Nucleophilic substitution reactions are known to be influenced by the solvent environment. Therefore, the gas-phase results were extended towards a discrete solvent approach. The solvent effect was taken into account by inspecting the convergence behaviour of the energy of solvation in terms of a systematically increasing number of solvent molecules. To model each of the reactive profiles of the various substrates, a supermolecule model was used with five explicit methanol molecules. Solvation has significantly changed the landscape of the energy profiles, which nicely shows the necessity of taking into account explicit solvation molecules to obtain the correct reaction profiles. The barriers for direct displacement of bromide by methoxide in methanol are comparable for all three heterocyclic species under study. However, ring opening is only feasible for the epoxide and the activated aziridine and not for the non-activated aziridine

A new approach to local hardness

The applicability of the local hardness as defined by the derivative of the chemical potential with respect to the electron density is undermined by an essential ambiguity arising from this definition. Further, the local quantity defined in this way does not integrate to the (global) hardness - in contrast with the local softness, which integrates to the softness. It has also been shown recently that with the conventional formulae, the largest values of local hardness do not necessarily correspond to the hardest regions of a molecule. Here, in an attempt to fix these drawbacks, we propose a new approach to define and evaluate the local hardness. We define a local chemical potential, utilizing the fact that the chemical potential emerges as the additive constant term in the number-conserving functional derivative of the energy density functional. Then, differentiation of this local chemical potential with respect to the number of electrons leads to a local hardness that integrates to the hardness, and possesses a favourable property; namely, within any given electron system, it is in a local inverse relation with the Fukui function, which is known to be a proper indicator of local softness in the case of soft systems. Numerical tests for a few selected molecules and a detailed analysis, comparing the new definition of local hardness with the previous ones, show promising results.Comment: 30 pages (including 6 figures, 1 table

Relativistic effects on the Fukui function

The extent of relativistic effects on the Fukui function, which describes local reactivity trends within conceptual density functional theory (DFT), and frontier orbital densities has been analysed on the basis of three benchmark molecules containing the heavy elements: Au, Pb, and Bi. Various approximate relativistic approaches have been tested and compared with the four-component fully relativistic reference. Scalar relativistic effects, as described by the scalar zeroth-order regular approximation methodology and effective core potential calculations, already provide a large part of the relativistic corrections. Inclusion of spin-orbit coupling effects improves the results, especially for the heavy p-block compounds. We thus expect that future conceptual DFT-based reactivity studies on heavy-element molecules can rely on one of the approximate relativistic methodologie

A discrete model for cyclic mode I loading

AbstractThe cyclic behaviour of a double-edge notched specimen loaded in tension is studied. Cracks in the material are modelled by displacement discontinuities that can propagate during computation. Within these discontinuities, a cohesive zone model is used. The model assumes an additive split of the inelastic jump into a recoverable and an unrecoverable part. The influence of model parameters and discretisation is studied and the results have been compared with experimental data