Time-Dependent Magnons from First Principles

We propose an efficient and non-perturbative scheme to compute magnetic excitations for extended systems employing the framework of time-dependent density functional theory. Within our approach, we drive the system out of equilibrium using an ultrashort magnetic kick perpendicular to the ground-state magnetization of the material. The dynamical properties of the system are obtained by propagating the time-dependent Kohn–Sham equations in real time, and the analysis of the time-dependent magnetization reveals the transverse magnetic excitation spectrum of the magnet. We illustrate the performance of the method by computing the magnetization dynamics, obtained from a real-time propagation, for iron, cobalt, and nickel and compare them to known results obtained using the linear-response formulation of time-dependent density functional theory. Moreover, we point out that our time-dependent approach is not limited to the linear-response regime, and we present the first results for nonlinear magnetic excitations from first principles in iron

Introduction to the CoNLL-2001 Shared Task: Clause Identification

We describe the CoNLL-2001 shared task: dividing text into clauses. We give background information on the data sets, present a general overview of the systems that have taken part in the shared task and briefly discuss their performance

Ultrafast modification of Hubbard UU in a strongly correlated material: ab initio high-harmonic generation in NiO

Engineering effective electronic parameters is a major focus in condensed matter physics. Their dynamical modulation opens the possibility of creating and controlling physical properties in systems driven out of equilibrium. In this work, we demonstrate that the Hubbard $U$, the on-site Coulomb repulsion in strongly correlated materials, can be modified on femtosecond time scales by a strong nonresonant laser excitation in the prototypical charge transfer insulator NiO. Using our recently developed time-dependent density functional theory plus self-consistent $U$ (TDDFT+U) method, we demonstrate the importance of a dynamically modulated $U$ in the description of the high-harmonic generation of NiO. Our study opens the door to novel ways of modifying effective interactions in strongly correlated materials via laser driving, which may lead to new control paradigms for field-induced phase transitions and perhaps laser-induced Mott insulation in charge-transfer materials

High-harmonic generation from few layer hexagonal boron nitride: evolution from the monolayer to the bulk response

Two-dimensional materials offer a versatile platform to study high-harmonic generation (HHG), encompassing as limiting cases bulk-like and atomic-like harmonic generation [Tancogne-Dejean and Rubio, Science Advance \textbf{4}, eaao5207 (2018)]. Understanding the high-harmonic response of few-layer semiconducting systems is important, and might open up possible technological applications. Using extensive first-principle calculations within a time-dependent density functional theory framework, we show how the in-plane and out-of-plane nonlinear non-perturbative response of two-dimensional materials evolve from the monolayer to the bulk. We illustrate this phenomenon for the case of multilayer hexagonal BN layered systems. Whereas the in-plane HHG is found not to be strongly altered by the stacking of the layers, we found that the out-of-plane response is strongly affected by the number of layers considered. This is explained by the interplay between the induced electric field by electron-electron interactions and the interlayer delocalization of the wave-functions contributing most to the HHG signal. The gliding of a bilayer is also found to affect the high-harmonic emission. Our results will have important ramifications for the experimental study of monolayer and few-layer two-dimensional materials beyond the case of hexagonal BN studied here as the result we found arew generic and applicable to all 2D semiconducting multilayer systems

Self-consistent DFT+U method for real-space time-dependent density functional theory calculations

We implemented various DFT+U schemes, including the ACBN0 self-consistent density-functional version of the DFT+U method [Phys. Rev. X 5, 011006 (2015)] within the massively parallel real-space time-dependent density functional theory (TDDFT) code Octopus. We further extended the method to the case of the calculation of response functions with real-time TDDFT+U and to the description of non-collinear spin systems. The implementation is tested by investigating the ground-state and optical properties of various transition metal oxides, bulk topological insulators, and molecules. Our results are found to be in good agreement with previously published results for both the electronic band structure and structural properties. The self consistent calculated values of U and J are also in good agreement with the values commonly used in the literature. We found that the time-dependent extension of the self-consistent DFT+U method yields improved optical properties when compared to the empirical TDDFT+U scheme. This work thus opens a different theoretical framework to address the non equilibrium properties of correlated systems

Où est Dieu dans le terrain?

La question de départ porte sur la manière dont géographie peut rendre compte de la religion et du fait religieux dans le terrain, sur la présence de la divinité dans ce dernier, comment elle peut la localiser et en déterminer une spatialité. Plus généralement, nous nous inscrivons pleinement dans un questionnement sur la nature des objets auxquels le géographe est confronté en situation de terrain. Les objets de la croyance et de la religion apparaissent d'autant plus difficiles à appréhender qu'ils relèvent d'une adhésion qui préexiste à leur apparition (« je vois parce que je crois »), mettant à mal les principes de neutralité scientifique ou d'athéisme méthodologique pourtant de rigueur. La question porte finalement sur la nature des comptes-rendus du géographe après l'expérience du terrain ? De quoi parle-t-il dès lors qu'il aborde le thème du fait religieux ?Notre projet de communication porte sur deux façons d'aborder les relations existant entre le terrain et la géographie : analyser les rapports que celle-ci entretient avec les sciences connexes, notamment la sociologie et l'anthropologie, sur le thème du fait religieux, d'une part, interroger les manières par lesquelles la géographie appréhende le fait religieux en situation de terrain, d'autre part. Ces deux questionnements sont intimement liés puisque l'approche spatiale de la religion et du fait religieux par la discipline géographique a considérablement évolué ces dernières années, en se nourrissant des apports des sociologues et des anthropologues. Plus largement, on constate un regain d'intérêt des sciences sociales pour ce thème de la religion. Cette évolution se comprend dans le double contexte de réactivation des pratiques religieuses et de la mondialisation des biens religieux mettant peu à peu en place un espace religieux mondial à travers lequel les ressources religieuses circulent et s'échangent. Il s'agit donc de discuter l'apport des autres sciences humaines et sociales à la géographie et de voir comment cette dernière parvient à proposer des approches originales de la religion. En second lieu, il s'agit de se demander dans quelle mesure il est légitime de parler d'un « terrain religieux » spécifique à la géographie, au sens où le fait religieux abordé par le géographe ne serait pas le même que celui du sociologue ou de l'anthropologue. La thèse que nous soutenons est que ce « terrain religieux » est bien réel dans la mesure où le fait religieux s'exprime dans et par l'espace. Cette approche spatiale de la religion est d'autant plus juste qu'elle s'affirme au moment même où des auteurs mettent en avant l'idée de pratiques religieuses parfaitement déterritorialisées, s'appuyant désormais sur les réseaux de télécommunication, à commencer par Internet.Afin d'interroger la pertinence de cette notion de « terrain religieux » nous mettrons l'accent sur l'exemple des Eglises évangéliques et pentecôtistes qui connaissent actuellement un succès grandissant à l'échelle de la planète. Nous montrerons en particulier comment ces dernières proposent au géographe un redoutable défi dans la mesure où elles recourent largement à des catégories spatiales, en tant que ressource pratique et élément de leurs propres doctrines. Par ailleurs, en insistant sur la présence effective de Dieu sur la Terre, ces dernières invitent à penser la localisation de Dieu dans des lieux et des espaces particuliers

Une Propriété de Certaines Parties d'un Monoöde Libre

Une propriété de certaines parties d'un monoïde libre permet de répondre à une question posée par Eggan

Methods for Film Coating Electrospun Fibers

Electrospinning uses high voltages to form polymer nanofiber membranes. These membranes have potential for use in filtration, tissue engineering, drug delivery, and catalysis. The nonwoven fiber mat is malleable but has a low tensile strength compared to a solid film of the same polymer. Joining the fibers with a thin film is desired to balance the strength and flexibility. Three methods of producing a film on fiber membrane were tested. The techniques are spraying then melting, spin coating, and dip coating. Electrospinning setup conditions, solvent ratios, damage to fibers, and spin coating speeds were determined. Research was abruptly stopped and optimal dip coating conditions weren’t found. Final characterization of the membranes was also not completed. What was completed will facilitate similar work with electrospinning or finishing this experiment. Using a gas permeable film coating or varying the membrane area covered by film will build off of this research and make it more applicable

Prey Capture Behavior in an Arboreal African Ponerine Ant

I studied the predatory behavior of Platythyrea conradti, an arboreal ponerine ant, whereas most species in this subfamily are ground-dwelling. The workers, which hunt solitarily only around dusk, are able to capture a wide range of prey, including termites and agile, nocturnal insects as well as diurnal insects that are inactive at that moment of the Nyctemeron, resting on tree branches or under leaves. Prey are captured very rapidly, and the antennal palpation used by ground-dwelling ponerine species is reduced to a simple contact; stinging occurs immediately thereafter. The venom has an instant, violent effect as even large prey (up to 30 times the weight of a worker) never struggled after being stung. Only small prey are not stung. Workers retrieve their prey, even large items, singly. To capture termite workers and soldiers defending their nest entrances, ant workers crouch and fold their antennae backward. In their role as guards, the termites face the crouching ants and end up by rolling onto their backs, their legs batting the air. This is likely due to volatile secretions produced by the ants' mandibular gland. The same behavior is used against competing ants, including territorially-dominant arboreal species that retreat further and further away, so that the P. conradti finally drive them from large, sugary food sources

Methods for Film Coating Electrospun Fibers

Electrospinning uses high voltages to form polymer nanofiber membranes. These membranes have potential for use in filtration, tissue engineering, drug delivery, and catalysis. The nonwoven fiber mat is malleable but has a low tensile strength compared to a solid film of the same polymer. Joining the fibers with a thin film is desired to balance the strength and flexibility. Three methods of producing a film on fiber membrane were tested. The techniques are spraying then melting, spin coating, and dip coating. Electrospinning setup conditions, solvent ratios, damage to fibers, and spin coating speeds were determined. Research was abruptly stopped and optimal dip coating conditions weren’t found. Final characterization of the membranes was also not completed. What was completed will facilitate similar work with electrospinning or finishing this experiment. Using a gas permeable film coating or varying the membrane area covered by film will build off of this research and make it more applicable