Predatory Fish Select for Coordinated Collective Motion in Virtual Prey

Movement in animal groups is highly varied and ranges from seemingly disordered motion in swarms to coordinated aligned motion in flocks and schools. These social interactions are often thought to reduce risk from predators, despite a lack of direct evidence. We investigated risk-related selection for collective motion by allowing real predators ( bluegill sunfish) to hunt mobile virtual prey. By fusing simulated and real animal behavior, we isolated predator effects while controlling for confounding factors. Prey with a tendency to be attracted toward, and to align direction of travel with, near neighbors tended to form mobile coordinated groups and were rarely attacked. These results demonstrate that collective motion could evolve as a response to predation, without prey being able to detect and respond to predators.

Evidence of collective relaxation behavior in the reentrant phase of oxygen-rich LaMnO3

The reentrant low temperature phase of the perovskite manganite LaMnO3+delta (delta=0.22) has been investigated with ac susceptibility and dc magnetization studies. A critical examination of the memory effects in ac susceptibility leads us to the conclusion that the slow dynamics in the system is a consequence of collective relaxation processes resulting from interactions between ferromagnetic clusters, whose presence was indicated in earlier studies. Here, we postulate that the collective behavior is due to the existence of long-range (dipolar) interactions between the large ferromagnetic `superspins'. This is also confirmed by an abnormally large microscopic spin-flip time (similar to 10(-9) s) compared to a canonical spin glass. (C) 2013 Elsevier B.V. All rights reserved.

Collective behavior with heterogeneous controllers

In this paper, we study the collective motion of individually controlled planar particles when they are coupled through heterogeneous controller gains. Two types of collective formations, synchronization and balancing, are described and analyzed under the influence of these heterogeneous controller gains. These formations are characterized by the motion of the centroid of the group of particles. In synchronized formation, the particles and their centroid move in a common direction, while in balanced formation the movement of particles possess a fixed location of the centroid. We show that, by selecting suitable controller gains, these formations can be controlled significantly to obtain not only a desired direction of motion but also a desired location of the centroid. We present the results for N-particles in synchronized formation, while in balanced formation our analysis is confined to two and three particles.

Clusters, asters, and collective oscillations in chemotactic colloids

The creation of synthetic systems that emulate the defining properties of living matter, such as motility, gradient-sensing, signaling, and replication, is a grand challenge of biomimetics. Such imitations of life crucially contain active components that transform chemical energy into directed motion. These artificial realizations of motility point in the direction of a new paradigm in engineering, through the design of emergent behavior by manipulating properties at the scale of the individual components. Catalytic colloidal swimmers are a particularly promising example of such systems. Here we present a comprehensive theoretical description of gradient-sensing of an individual swimmer, leading controllably to chemotactic or anti-chemotactic behavior, and use it to construct a framework for studying their collective behavior. We find that both the positional and the orientational degrees of freedom of the active colloids can exhibit condensation, signaling formation of clusters and asters. The kinetics of catalysis introduces a natural control parameter for the range of the interaction mediated by the diffusing chemical species. For various regimes in parameter space in the long-ranged limit our system displays precise analogs to gravitational collapse, plasma oscillations, and electrostatic screening. We present prescriptions for how to tune the surface properties of the colloids during fabrication to achieve each type of behavior.

Collective eigenstates of emission in an N-entity heterostructure and the evaluation of its Green tensors and self-energy components

Optical emission from emitters strongly interacting among themselves and also with other polarizable matter in close proximity has been approximated by emission from independent emitters. This is primarily due to our inability to evaluate the self-energy matrices and radiative properties of the collective eigenstates of emitters in heterogeneous ensembles. A method to evaluate self-energy matrices that is not limited by the geometry and material composition is presented to understand and exploit such collective excitations. Numerical evaluations using this method are used to highlight the significant differences between independent and the collective modes of emission in nanoscale heterostructures. A set of N Lorentz emitters and other polarizable entities is used to represent the coupled system of a generalized geometry in a volume integral approach. Closed form relations between the Green tensors of entity pairs in free space and their correspondents in a heterostructure are derived concisely. This is made possible for general geometries because the global matrices consisting of all free-space Green dyads are subject to conservation laws. The self-energy matrix can then be assembled using the evaluated Green tensors of the heterostructure, but a decomposition of its components into their radiative and nonradiative decay contributions is nontrivial. The relations to compute the observables of the eigenstates (such as quantum efficiency, power/energy of emission, radiative and nonradiative decay rates) are presented. A note on extension of this method to collective excitations, which also includes strong interactions with a surface in the near-field, is added. (C) 2014 Optical Society of America

Plasmon-mediated emergence of collective emission and enhanced quantum efficiency in quantum dot films

We present experimental and theoretical results on monolayer colloidal cadmium selenide quantum dot films embedded with tiny gold nanoparticles. By varying the density of the embedded gold nanoparticles, we were able to engineer a plasmon-mediated crossover from emission quenching to enhancement regime at interparticle distances for which only quenching of emission is expected. This crossover and a nonmonotonic variation of photoluminescence intensity and decay rate, in experiments, is explained in terms of a model for plasmon-mediated collective emission of quantum emitters which points to the emergence of a new regime in plasmon-exciton interactions. The presented methodology to achieve enhancement in optical quantum efficiency for optimal doping of gold nanoparticles in such ultrathin high-density quantum dot films can be beneficial for new-generation displays and photodetectors.

Stabilization of Collective Motion in Synchronized, Balanced and Splay Phase Arrangements on a Desired Circle

This paper proposes a design methodology to stabilize collective circular motion of a group of N-identical agents moving at unit speed around individual circles of different radii and different centers. The collective circular motion studied in this paper is characterized by the clockwise rotation of all agents around a common circle of desired radius as well as center, which is fixed. Our interest is to achieve those collective circular motions in which the phases of the agents are arranged either in synchronized, in balanced or in splay formation. In synchronized formation, the agents and their centroid move in a common direction while in balanced formation, the movement of the agents ensures a fixed location of the centroid. The splay state is a special case of balanced formation, in which the phases are separated by multiples of 2 pi/N. We derive the feedback controls and prove the asymptotic stability of the desired collective circular motion by using Lyapunov theory and the LaSalle's Invariance principle.

Organization dependent collective magnetic properties of secondary nanostructures with differential spatial ordering and magnetic easy axis orientation

Achieving control on the formation of different organization states of magnetic nanoparticles is crucial to harness their organization dependent physical properties in desired ways. In this study, three organization states of iron oxide nanoparticles (gamma-Fe2O3), defining as (i) assembly (ii) network aggregate and (iii) cluster, have been developed by simply changing the solvent evaporation conditions. All three systems have retained the same phase and polydispersity of primary particles. Magnetic measurements show that the partial alignment of the easy axes of the particles in the network system due to the stacking aggregation morphology can result in significant enhancement of the coercivity and remanence values, while the opposite is obtained for the cluster system due to the random orientation of easy axes. Partial alignment in the aggregate system also results in noticeable non -monotonic field dependence of ZFC peak temperature (TpeaB). The lowest value of the blocking temperature (TB) for the cluster system is related to the lowering of the effective anisotropy due to the strongest demagnetizing effect. FC (Field cooled) memory effect was observed to be decreasing with the increasing strength of dipolar interaction of organization states. Therefore, the stacking aggregation and the cluster formation are two interesting ways of magnetic nanoparticles organization for modulating collective magnetic properties significantly, which can have renewed application potentials from recording devices to biomedicine. (C) 2016 Elsevier B.V. All rights reserved.

An analysis of collective damage for short fatigue cracks based on equilibrium of crack numerical density

Collective damage of short fatigue cracks was analyzed in the light of equilibrium of crack numerical density. With the estimation of crack growth rate and crack nucleation rate, the solution of the equilibrium equation was studied to reveal the distinct feature of saturation distribution for crack numerical density. The critical time that characterized the transition of short and long-crack regimes was estimated, in which the influences of grain size and grain-boundary obstacle effect were investigated. Furthermore, the total number of cracks and the first order of damage moment were discussed.

Simulations and Experiments of Stochastic Characteristics for Collective Short Fatigue Cracks in Steels

Stochastic characteristics prevail in the process of short fatigue crack progression. This paper presents a method taking into account the balance of crack number density to describe the stochastic behaviour of short crack collective evolution. The results from the simulation illustrate the stochastic development of short cracks. The experiments on two types of steels show the random distribution for collective short cracks with the number of cracks and the maximum crack length as a function of different locations on specimen surface. The experiments also give the variation of total number of short cracks with fatigue cycles. The test results are consistent with numerical simulations.

La souffrance émotionnelle des personnels d’intervention : résultats préliminaires de l’étude sur la santé et la qualité de vie au travail dans les métiers du secteur de l’aide et du soin à domicile

Resumen: La prolongación de la edad y el aumento de la expectativa de vida han hecho surgir nuevas necesidades de atención para las personas ancianas y ello ha inducido a la ampliación de las prestaciones de servicios a domicilio. En este sentido, el trabajo de estos profesionales de intervención a domicilio, así como sus misiones, están en plena mutación. Es un sector con dificultades, debido a la dificultad de reclutar un personal especializado y al absentismo inquietante. Después de un análisis sobre el estado de este sector de la profesión en el que se establece la diferencia entre el enfoque físico y el psicológico sobre la salud, nuestra reflexión se centra en los riesgos psicosociales de esta población de profesionales. Se presentan los resultados preliminares de la investigación realizada con una muestra de 38 personas que ejercían laboralmente en este sector. Emerge la expresión de un sufrimiento emocional, en la que el aislamiento de los participantes es uno de los factores que caracterizan los oficios identificados con una fuerte dimensión relacional con personas vulnerables. La dimensión asistencial del trabajo se presenta como fuente de satisfacción del oficio pero, a su vez, puede conducir a una dificultad de gestionar acontecimientos no previstos

Collective evolution characteristics and computer simulation of short fatigue cracks

Fatigue testing was conducted using a kind of triangular isostress specimen to obtain the short-fatigue-crack behaviour of a weld low-carbon steel. The experimental results show that short cracks continuously initiate at slip bands within ferrite grain domains and the crack number per unit area gradually increases with increasing number of fatigue cycles. The dispersed short cracks possess an orientation preference, which is associated with the crystalline orientation of the relevant slip system. Based on the observed collective characteristics, computer modelling was carried out to simulate the evolution process of initiation, propagation and coalescence of short cracks. The simulation provides progressive displays which imitate the appearance of experimental observations. The results of simulation indicate that the crack path possesses a stable value of fractal dimension whereas the critical value of percolation covers a wide datum band, suggesting that the collective evolution process of short cracks is sensitive to the pattern of crack site distribution.

L'aristocratie negriere, ou, reflexions philosophiques et historiques sur l'esclavage et l'affranchissement des noirs : par M. L'Abbé Sibire : ancien ami des Africains; et leur premier Missionnaire dans le royaume de Loango

Sibire foi o primeiro missionário do Reino de Loango, antigo estado africano, fundado provavelmente em 1485 pelo povo Vili. O reino de Loango tornou-se independente entre os séculos XVIl e XVIII, e em 1885 dividiu-se entre o Estado do Congo, Portugal e França . Sibire considerava-se grande amigo dos africanos. A obra ‘L'aristocratie negriere, ou, Réflexions philosophiques et hisloriques sur l'esclavage et l'affranchissemenl des noirs’ é composta de duas partes: a primeira traz a transcrição de um discurso proferido por Sibire na Assembleia Nacional africana; a segunda relata o conteúdo de uma carta dirigida aos colonos, negros, europeus, negociantes e agricultores. O tema dominante em toda a obra é o repúdio à escravidão e a defesa da liberdade do ser humano

Voisinage et hábitat dans les communautés des Pyrénées Occidentales entre le XV et le XVIIIe siècles : de la croissance au blocage

Publicado dentro de la colección «Méridiennes» (ISSN: 1950-0130)

Histoire philosophique et politique : des établissemens et du commerce des européens dans les deux Indes

Guillaume Raynal, historiador e filósofo francês, nasceu em Saint-Geniez-en Rouergue em 11 de abril de 1713 e morreu em Choillot, em 6 de março de 1796. Estudou no Colégio dos Jesuítas de Pézenas, distinguindo-se como pregador e professor. Abandonou o hábito jesuita para se dedicar à filosofia e à história, publicando numerosos artigos no Mercure de France. Tendo sido alvo de um mandado de prisão, refugiou-se na Prússia e mais tarde na Rússia; retornou à França em 1787. ‘Histoire philosofique et politique’ foi publicada simultaneamente pelo mesmo editor em duas impressões, contendo cinco volumes a primeira e dez volumes a segunda. Foi uma das obras que mais ínfluenciou o movimento da Revolução Francesa, tendo o autor utilizado opiniões e, eventualmente, a colaboração de Diderot e Holbach, entre outros contemporâneos. Proibido na França e ai queimado em 1781, este importante trabalho de Raynal teve mais de trinta edições num periodo de vinte anos e foi traduzido para quase todos os idiomas europeus. Segundo Borba de Moraes, ‘esta edição de Genebra é a melhor e mais bela’. Na impressão de dez volumes existentes na Biblioteca da Câmara, a seção referente ao Brasil encontra-se no volume 5.