The application of gradient-corrected exchange-correlation functionals in total-energy calculations using a plane-wave basis set is discussed. The usual form of the exchange-correlation potential includes gradients whose calculation requires the use of a high-quality representation of the density which is computationally expensive in both memory and time. These problems may be overcome by defining an exchange-correlation potential for the discrete set of grid points consistent with the discretized form of the exchange-correlation energy that is used in Car-Parrinello-type total-energy calculations. This potential can be calculated exactly on the minimum fast-Fourier-transform grid and gives improved convergence and stability as well as computational efficiency.First-principles total-energy calculations based on density-functional theory' have become the major theoretical tool in solid-state physics, surface science, and molecular physics. Pseudopotential calculations using a planewave basis set and a Car-Parrinello approach to energy minimization ' have become increasingly important since this allows use to be made of the fast Fourier transform (FFT). Although the local-density approximation (LDA) to exchange and correlation gives a good description of many solid-state properties, for many applications it appears to be essential to go beyond the LDA by including gradient corrections. This is particularly important where accurate molecular bonding energies are required as in, for example, dissociative chemisorption. For bulk properties the need for gradient corrections is less clear although some improvements over LDA have been reported in calculations for semiconductors and transition metals. Unfortunately, the currently popular generalized gradient approximations (GGA) to the exchange-correlation energy functional (such as that of Perdew and Wang or Becke and Perdew ) give rise to potentials which are rapidly varying functions near to ion cores as has been noted previously in the context of pseudopotential generation. ' Because of this, and in order to calculate the required gradients accurately, a large number of plane waves are needed to represent these exchangecorrelation potentials accurately. In this paper it is pointed out that the exchange-correlation energy is, in practice, invariably approximated. It is shown that it is possible to construct an exchange-correlation potential which is consistent with this approximate form of the exchange-correlation energy and which can be calculated exactly much more efficiently than the conventional exchange-correlation potential.First recall the use of FFT's in Car-Parrinello-type totalenergy calculations. ' This makes use of the fact that the kinetic energy and Hartree energy/potential are easily calculated in reciprocal space (the Hartree potential, for example, becomes a simple product in reciprocal space) while the electron-ion potential energy is easily calculated in real space since the required integrals can be performed exactly as sums over the points of the m...

Since the turn of the century, emerging unmanned aircraft systems (UAS) have found increasingly diverse applications in wildlife science as convenient, very highresolution remote sensing devices. Achieved or conceptualized applications include optical surveying and observation of animals, autonomous wildlife telemetry tracking, and habitat research and monitoring. As the technology continues to progress and interest from the wildlife science community grows, there may yet be much untapped potential for UAS to contribute to the discipline. We present a review of the published primary literature on the application of UAS in wildlife science and related fields. This is followed by a systematic review of the broader wildlife science literature published since the turn of the century to assess where UAS are likely to make important contributions going forward based on the trends that have emerged thus far. UAS, in particular small lightweight models, are generally well suited for collecting data at an intermediate spatial scale between what is easily coverable on the ground and what is economically coverable with conventional aircraft. They are particularly useful for monitoring wildlife and habitats in places that are difficult to access or navigate from the ground, as well as approaching sensitive or aggressive species.Key words: aerial survey, conservation, remotely piloted aircraft system, unmanned aerial vehicle, drone, wildlife monitoring.Résumé : Depuis le début du siècle, les nouveaux systèmes d'aéronefs sans pilote (UAS), en tant qu'appareils de télédétection de haute résolution pratiques, ont donné lieu à de plus en plus d'applications diverses en science de la faune. Les applications réalisées ou conceptualisées comprennent l'inventaire et l'observation optiques des animaux, la localisation autonome de la faune par télémétrie et la recherche et la surveillance des habitats. À mesure que la technologie continue de progresser et que l'intérêt de la part du milieu scientifique du domaine de la faune croît, la contribution des UAS à la discipline pourra augmenter, car il peut y avoir encore beaucoup de potentiel à exploiter. Nous présentons un examen de la littérature primaire publiée portant sur l'application des UAS dans les domaines de la science de la faune et connexes. Un examen systématique de l'ensemble de la littérature de la science de la faune publiée depuis le début du siècle s'ensuit dans le but d'évaluer, d'après les tendances qui ont émergé jusqu'à maintenant, où les UAS vont possiblement faire des contributions à l'avenir. Les UAS, en particulier les petits modèles légers, sont bien adaptés à la collecte de données à une échelle spatiale intermédiaire entre ce qui est facilement saisi sur le terrain et ce qui est saisi à l'aide d'un aéronef traditionnel. Ils sont particulièrement utiles pour la surveillance de la faune et des habitats dans les endroits difficiles à accéder ou à naviguer à partir du sol, ainsi que pour s'approcher des espèces sensibles ou agressives.

No abstract