A Numerical Investigation of a Two-Layer Frontal

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Dynamical modeling of collective behavior from pigeon flight data: flock cohesion and dispersion

Several models of flocking have been promoted based on simulations with qualitatively naturalistic behavior. In this paper we provide the first direct application of computational modeling methods to infer flocking behavior from experimental field data. We show that this approach is able to infer general rules for interaction, or lack of interaction, among members of a flock or, more generally, any community. Using experimental field measurements of homing pigeons in flight we demonstrate the existence of a basic distance dependent attraction/repulsion relationship and show that this rule is sufficient to explain collective behavior observed in nature. Positional data of individuals over time are used as input data to a computational algorithm capable of building complex nonlinear functions that can represent the system behavior. Topological nearest neighbor interactions are considered to characterize the components within this model. The efficacy of this method is demonstrated with simulated noisy data generated from the classical (two dimensional) Vicsek model. When applied to experimental data from homing pigeon flights we show that the more complex three dimensional models are capable of predicting and simulating trajectories, as well as exhibiting realistic collective dynamics. The simulations of the reconstructed models are used to extract properties of the collective behavior in pigeons, and how it is affected by changing the initial conditions of the system. Our results demonstrate that this approach may be applied to construct models capable of simulating trajectories and collective dynamics using experimental field measurements of herd movement. From these models, the behavior of the individual agents (animals) may be inferred

Critical Social Justice: The Moral Imperative for Critical Perspectives in Nursing

There is increasing urgency to enact critical perspectives in the profession of nursing, with a resurgence of the political, a deliberative focus on social change, and a growing uneasiness with remaining neutral in the face of such pressing need. This analysis starts with a brief overview of critical perspectives, underscoring nursing’s complex positioning at the interface of witnessing peoples’ suffering, and the structural change necessary to address its root causes. Although witnessing may imply watching, or even bystanding, here it refers to historical and cultural meanings of witnessing as standing alongside in solidarity and action throughout the struggle for justice—bearing witness as a moral and a political obligation. Moral bystanding is described as a foundational barrier to achieving the moral imperative of critical perspectives. We conclude with pathways for cultivating and enacting a critical gaze, and a call for moral courage to systematically integrate critical perspectives in nursing. Throughout the discussion, we draw upon the work of nurse ethicists to provide important links about enacting critical perspectives as part of the moral foundation of nursing. Our intention is not to provide an analysis of the moral contexts of nursing, but rather to situate critical perspectives within the moral territory of social change, synthesizing key ideas that have direct salience for critical social justice in nursing. Keywords: critical perspectives in nursing, critical social justice in nursing, moral bystanding, social change   &nbsp

On the duality between interaction responses and mutual positions in flocking and schooling.

Recent research in animal behaviour has contributed to determine how alignment, turning responses, and changes of speed mediate flocking and schooling interactions in different animal species. Here, we propose a complementary approach to the analysis of flocking phenomena, based on the idea that animals occupy preferential, anysotropic positions with respect to their neighbours, and devote a large amount of their interaction responses to maintaining their mutual positions. We test our approach by deriving the apparent alignment and attraction responses from simulated trajectories of animals moving side by side, or one in front of the other. We show that the anisotropic positioning of individuals, in combination with noise, is sufficient to reproduce several aspects of the movement responses observed in real animal groups. This anisotropy at the level of interactions should be considered explicitly in future models of flocking and schooling. By making a distinction between interaction responses involved in maintaining a preferred flock configuration, and interaction responses directed at changing it, our work provides a frame to discriminate movement interactions that signal directional conflict from interactions underlying consensual group motion

Surface photochemistry of the herbicide napropamide. The role of the media and environmental factors in directing the fates of intermediates

The photochemical behaviour of the herbicide napropamide is studied on cellulose and silica surfaces, using steady-state and laser-flash diffuse ectance techniques. The results are used to probe how the reaction sites of the host matrices influence the photo-reactive pathways. Napropamide undergoes reaction when irradiated with UV (lamps) or visible (sunlight) radiation on both solid supports. The nature of the intermediates and final products depend strongly on the presence or absence of molecular oxygen. The triplet state of napropamide adsorbed on cellulose is detected by both time-resolved luminescence and transient absorption spectroscopies. The triplet sate was not observed on silica, but transients which include the participation of molecular oxygen are detected during. ash photolysis studies. The keto intermediates of the photo-Claisen rearrangement products are observed on both solids. Substituted 1-naphthols from photo-Claisen reactions and 1-naphthol are among the main reaction products. 1,4-Naphthoquinone is a major photoproduct in the presence of molecular oxygen and is expected to be prevalent when napropamide undergoes photodegradation in the environment (i. e., after being applied to plants and fields)

Effects of anisotropic interactions on the structure of animal groups

This paper proposes an agent-based model which reproduces different structures of animal groups. The shape and structure of the group is the effect of simple interaction rules among individuals: each animal deploys itself depending on the position of a limited number of close group mates. The proposed model is shown to produce clustered formations, as well as lines and V-like formations. The key factors which trigger the onset of different patterns are argued to be the relative strength of attraction and repulsion forces and, most important, the anisotropy in their application.Comment: 22 pages, 9 figures. Submitted. v1-v4: revised presentation; extended simulations; included technical results. v5: added a few clarification

Active Brownian Particles. From Individual to Collective Stochastic Dynamics

We review theoretical models of individual motility as well as collective dynamics and pattern formation of active particles. We focus on simple models of active dynamics with a particular emphasis on nonlinear and stochastic dynamics of such self-propelled entities in the framework of statistical mechanics. Examples of such active units in complex physico-chemical and biological systems are chemically powered nano-rods, localized patterns in reaction-diffusion system, motile cells or macroscopic animals. Based on the description of individual motion of point-like active particles by stochastic differential equations, we discuss different velocity-dependent friction functions, the impact of various types of fluctuations and calculate characteristic observables such as stationary velocity distributions or diffusion coefficients. Finally, we consider not only the free and confined individual active dynamics but also different types of interaction between active particles. The resulting collective dynamical behavior of large assemblies and aggregates of active units is discussed and an overview over some recent results on spatiotemporal pattern formation in such systems is given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte

Enhancing community-driven initiatives in urban water supply in Ghana

Despite the notable contributions of community-driven initiatives to improve access to urban water supply in Ghana, no conscious effort has been made to harness the full potential of their involvement in improving urban water supply. Drawing on ongoing research on improving urban water and sanitation provision through information and action driven locally, this paper examines community-driven initiatives towards improve access to water supply in urban Ghana. The discussions reveals that while the role of communitybased water providers remain unrecognised in the absence of support from governments and financial institutions, they are vital to millions of poor urban households who cannot access water through the formal network. The paper calls for promoting and supporting community-driven initiatives so that in the absence of universal pipe coverage, they can operate efficiently under a light regulatory regime that ensures fair prices and a viable service delivery