Time-Resolved Exciton Wave Functions from Time-Dependent Density-Functional Theory

Time-dependent density-functional theory (TDDFT) is a computationally efficient first-principles approach for calculating optical spectra in insulators and semiconductors including excitonic effects. We show how exciton wave functions can be obtained from TDDFT via the Kohn–Sham transition density matrix, both in the frequency-dependent linear-response regime and in real-time propagation. The method is illustrated using one-dimensional model solids. In particular, we show that our approach provides insight into the formation and dissociation of excitons in real time. This opens the door to time-resolved studies of exciton dynamics in materials by means of real-time TDDFT

Exchange torque in noncollinear spin density functional theory with a semilocal exchange functional

We present a new semilocal exchange energy functional for spin density functional theory (SDFT) based on a short-range expansion of the spin-resolved exchange hole. Our exchange functional is directly derived for noncollinear magnetism, U(1) and SU(2) gauge invariant, and gives rise to nonvanishing exchange torques. The functional is tested for frustrated antiferromagnetic chromium clusters and shown to perform favorably compared to the far more expensive Slater potential and optimized effective potential for exact exchange. This provides a path forward for functional development in noncollinear SDFT and the ab initio study of magnetic materials in and out of equilibrium

Le goutte à goutte enterré : une solution innovante pour irriguer sous conditions restrictives en eau

La mise en oeuvre de techniques d'irrigation innovantes telles que le goutte à goutte enterré est la solution adoptée par la plupart des pays confrontés aux problèmes de pénurie d'eau en raison de sa très bonne efficience. De plus en plus de régions françaises étant soumises à des restrictions d'eau, sa possible utilisation pour irriguer les grandes cultures est à l'ordre du jour

Effect of cropping strategies on irrigation water productivity of durum wheat

The interest of irrigation for durum wheat is often questionable because of possible spring rainfalls in the SE of France. In this study cropping strategies i.e. plant density (PD), sowing date and irrigation management were analysed for improving irrigation water productivity (IWP). An experiment was carried out for calibrating and validating PILOTE model. An adaptation of the potential harvest index to PD was implemented in PILOTE. The latter satisfactory simulates different model outputs with coefficients of efficiency greater than 0.97. The model was employed for simulating the impact of cropping strategies on IWP for a long climatic series. According to model simulations, the necessity of irrigation is questionable under our conditions. IWP was notably lower under high PD than under low PD for the same sowing date. Under low PD and without irrigation it would be possible to obtain a yield similar to that obtained under high PD with irrigation

Gestion opérationnelle des transports d’eau dans les canaux et les rivières

Après une présentation générale historique des canaux d'irrigation, de leur importance stratégique et des évolutions récentes, nous définissons de manière plus précise les systèmes hydrauliques à surface libre auxquels nous nous intéressons dans cet article. Nous présentons leurs spécificités qui rendent leur gestion essentielle mais délicate. Nous précisons ensuite ce que nous appelons concrètement "gestion", avec différentes nuances, dont la gestion opérationnelle, et nous utilisons des concepts issus de la gestion industrielle pour mieux l'analyser. Enfin, parmi ces concepts nous détaillons celui des "machines" permettant de mettre en ½uvre cette gestion opérationnelle. / After a historical overview of irrigation canals, their strategic importance and recent trends, we define more precisely the free surface hydraulic systems we analyse in this article. We see that they have features that make their management difficult but essential. Then, we define more precisely what we call "management", with different levels, including "operational management", and we use concepts from production management to better analyze it. Finally, we detail one of these concepts: the "devices" used to implement the operational management

Invasive North American bullfrogs transmit lethal fungus Batrachochytrium dendrobatidis infections to native amphibian host species

Invasive species can be a threat to native species in several ways, including transmitting lethal infections caused by the parasites they carry. However, invasive species may also be plagued by novel and lethal infections they acquire when invading, making inferences regarding the ability of an invasive host to vector disease difficult from field observations of infection and disease. This is the case for the pathogenic fungus Batrachochytrium dendrobatidis (Bd) in Europe and one invasive host species, the North American bullfrog Lithobates catesbeianus, hypothesized to be responsible for vectoring lethal infection to European native amphibians. We tested this hypothesis experimentally using the alpine newt Ichthyosaura alpestris as our model native host. Our results show that infected bullfrog tadpoles are effective vectors of Bd. Native adult newts co-housed with experimentally infected bullfrog tadpoles became Bd infected (molecular and histological tests). Moreover, the exposed adult newts suffered mortality while the majority of infected bullfrog tadpoles survived until metamorphosis. Invasive species can be a threat to native species in several ways, including transmitting lethal infections caused by the parasites they carry. However, invasive species may also be plagued by novel and lethal infections they acquire when invading, making inferences regarding the ability of an invasive host to vector disease difficult from field observations of infection and disease. This is the case for the pathogenic fungus Batrachochytrium dendrobatidis (Bd) in Europe and one invasive host species, the North American bullfrog Lithobates catesbeianus, hypothesized to be responsible for vectoring lethal infection to European native amphibians. We tested this hypothesis experimentally using the alpine newt Ichthyosaura alpestris as our model native host. Our results show that infected bullfrog tadpoles are effective vectors of Bd. Native adult newts co-housed with experimentally infected bullfrog tadpoles became Bd infected (molecular and histological tests). Moreover, the exposed adult newts suffered mortality while the majority of infected bullfrog tadpoles survived until metamorphosis. These results cannot resolve the historical role of alien species in establishing the distribution of Bd across Europe or other regions in the world where this species was introduced, but they show its potential role as a Bd reservoir capable of transmitting lethal infections to native amphibians. Finally, our results also suggest that the removal of infected bullfrogs from aquatic environments may serve to reduce the availability of Bd in European amphibian communities, offering another justification for bullfrog eradication programmes that are currently underway or may be considere

Caterpillars and fungal pathogens: two co-occurring parasites of an ant-plant mutualism

In mutualisms, each interacting species obtains resources from its partner that it would obtain less efficiently if alone, and so derives a net fitness benefit. In exchange for shelter (domatia) and food, mutualistic plant-ants protect their host myrmecophytes from herbivores, encroaching vines and fungal pathogens. Although selective filters enable myrmecophytes to host those ant species most favorable to their fitness, some insects can by-pass these filters, exploiting the rewards supplied whilst providing nothing in return. This is the case in French Guiana for Cecropia obtusa (Cecropiaceae) as Pseudocabima guianalis caterpillars (Lepidoptera, Pyralidae) can colonize saplings before the installation of their mutualistic Azteca ants. The caterpillars shelter in the domatia and feed on food bodies (FBs) whose production increases as a result. They delay colonization by ants by weaving a silk shield above the youngest trichilium, where the FBs are produced, blocking access to them. This probable temporal priority effect also allows female moths to lay new eggs on trees that already shelter caterpillars, and so to occupy the niche longer and exploit Cecropia resources before colonization by ants. However, once incipient ant colonies are able to develop, they prevent further colonization by the caterpillars. Although no higher herbivory rates were noted, these caterpillars are ineffective in protecting their host trees from a pathogenic fungus, Fusarium moniliforme (Deuteromycetes), that develops on the trichilium in the absence of mutualistic ants. Therefore, the Cecropia treelets can be parasitized by two often overlooked species: the caterpillars that shelter in the domatia and feed on FBs, delaying colonization by mutualistic ants, and the fungal pathogen that develops on old trichilia. The cost of greater FB production plus the presence of the pathogenic fungus likely affect tree growth