Dynamical Configurations and Bistability of Helical Nanostructures under External Torque

We study the motion of a ferromagnetic helical nanostructure under the action of a rotating magnetic field. A variety of dynamical configurations were observed that depended strongly on the direction of magnetization and the geometrical parameters, which were also confirmed by a theoretical model, based on the dynamics of a rigid body under Stokes flow. Although motion at low Reynolds numbers is typically deterministic, under certain experimental conditions, the nanostructures showed a surprising bistable behavior, such that the dynamics switched randomly between two configurations, possibly induced by thermal fluctuations. The experimental observations and the theoretical results presented in this letter are general enough to be applicable to any system of ellipsoidal symmetry under external force or torque.Comment: 15 pages, 4 figure

Big-headed marine crocodyliforms and why we must be cautious when using extant species as body length proxies for long-extinct relatives

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Locomotion pattern and foot pressure adjustments during gentle turns in healthy subjects

People suffering from locomotor impairment find turning manoeuvres more challenging than straightahead walking. Turning manoeuvres are estimated to comprise a substantial proportion of steps taken daily, yet research has predominantly focused on straight-line walking, meaning that the basic kinetic, kinematic and foot pressure adaptations required for turning are not as well understood. We investigated how healthy subjects adapt their locomotion patterns to accommodate walking along a gently curved trajectory (radius 2.75 m). Twenty healthy adult participants performed walking tasks at self-selected speeds along straight and curved pathways. For the first time for this mode of turning, plantar pressures were recorded using insole foot pressure sensors while participants’ movements were simultaneously tracked using marker-based 3D motion capture. During the steady-state strides at the apex of the turn, the mean operating point of the inside ankle shifted by 1 degree towards dorsiflexion and that for the outside ankle shifted towards plantarflexion. The largest change in relative joint angle range was an increase in hip rotation in the inside leg (>60%). In addition, the inside foot was subject to a prolonged stance phase and a 10% increase in vertical force in the posteromedial section of the foot compared to straight-line walking. Most of the mechanical change required was therefore generated by the inside leg with hip rotation being a major driver of the gentle turn. This study provides new insight into healthy gait during gentle turns and may help us to understand the mechanics behind some forms of impairment

Movement of Artificial Bacterial Flagella in Heterogeneous Viscous Environments at the Microscale

Swimming microrobots have the potential to be used in medical applications such as targeted drug delivery. The challenges for navigating microrobots in the human body lie not only in the viscosity of body fluids but also in the existence of different types of fibers and cells such as blood cells or protein strands. This paper investigates artificial bacterial flagella (ABFs), which are helical microrobots actuated by an external magnetic field, in methyl cellulose solutions of different concentrations. It can be shown that the microrobots can be propelled in these gel-like heterogeneous solutions and successful swimming was demonstrated in solutions with a viscosity of more than 20 times that of water. Furthermore, results indicate that the existence of fibers can help ABFs swim more effectively, which agrees with previous experimental results reported for natural bacteria

Unmanned aircraft systems as a new source of disturbance for wildlife: A systematic review.

The use of small Unmanned Aircraft Systems (UAS; also known as "drones") for professional and personal-leisure use is increasing enormously. UAS operate at low altitudes (<500 m) and in any terrain, thus they are susceptible to interact with local fauna, generating a new type of anthropogenic disturbance that has not been systematically evaluated. To address this gap, we performed a review of the existent literature about animals' responses to UAS flights and conducted a pooled analysis of the data to determine the probability and intensity of the disturbance, and to identify the factors influencing animals' reactions towards the small aircraft. We found that wildlife reactions depended on both the UAS attributes (flight pattern, engine type and size of aircraft) and the characteristics of animals themselves (type of animal, life-history stage and level of aggregation). Target-oriented flight patterns, larger UAS sizes, and fuel-powered (noisier) engines evoked the strongest reactions in wildlife. Animals during the non-breeding period and in large groups were more likely to show behavioral reactions to UAS, and birds are more prone to react than other taxa. We discuss the implications of these results in the context of wildlife disturbance and suggest guidelines for conservationists, users and manufacturers to minimize the impact of UAS. In addition, we propose that the legal framework needs to be adapted so that appropriate actions can be undertaken when wildlife is negatively affected by these emergent practices

The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation

Background Archosaurs (birds, crocodilians and their extinct relatives including dinosaurs) dominated Mesozoic continental ecosystems from the Late Triassic onwards, and still form a major component of modern ecosystems (>10,000 species). The earliest diverse archosaur faunal assemblages are known from the Middle Triassic (c. 244 Ma), implying that the archosaur radiation began in the Early Triassic (252.3–247.2 Ma). Understanding of this radiation is currently limited by the poor early fossil record of the group in terms of skeletal remains. Methodology/Principal Findings We redescribe the anatomy and stratigraphic position of the type specimen of Ctenosauriscus koeneni (Huene), a sail-backed reptile from the Early Triassic (late Olenekian) Solling Formation of northern Germany that potentially represents the oldest known archosaur. We critically discuss previous biomechanical work on the ‘sail’ of Ctenosauriscus, which is formed by a series of elongated neural spines. In addition, we describe Ctenosauriscus-like postcranial material from the earliest Middle Triassic (early Anisian) Röt Formation of Waldhaus, southwestern Germany. Finally, we review the spatial and temporal distribution of the earliest archosaur fossils and their implications for understanding the dynamics of the archosaur radiation. Conclusions/Significance Comprehensive numerical phylogenetic analyses demonstrate that both Ctenosauriscus and the Waldhaus taxon are members of a monophyletic grouping of poposauroid archosaurs, Ctenosauriscidae, characterised by greatly elongated neural spines in the posterior cervical to anterior caudal vertebrae. The earliest archosaurs, including Ctenosauriscus, appear in the body fossil record just prior to the Olenekian/Anisian boundary (c. 248 Ma), less than 5 million years after the Permian–Triassic mass extinction. These earliest archosaur assemblages are dominated by ctenosauriscids, which were broadly distributed across northern Pangea and which appear to have been the first global radiation of archosaurs

Transfer Mispricing As an Argument for Corporate Social Responsibility

This article presents a case for transfer mispricing as an argument for Corporate Social Responsibility (CSR). The argument builds on the position that in order to compensate for potential loss of brand image and reputation, Multinational Companies (MNCs) would be more socially responsible when they are operating in countries where the legislation and laws in place are not effective at identifying and sanctioning transfer mispricing. We first discuss the dark side of transfer pricing (TP), next we present the nexus between TP and poverty and finally we advance arguments for CSR in transfer mispricing. While acknowledging that TP is a legal accounting practice, we argue that in view of its poverty and underdevelopment externalities, the practice per se should be a solid justification for CSR because it is also associated with schemes that deprive developing countries of capital essential for investments in health, education and development programmes. Therefore CSR owing to TP cannot be limited to a strategic management approach, but should also be considered as some kind of social justice because of associated transfer mispricing practices. We further argue that, CSR by multinational corporations could incite domestic companies to comply more willingly with their tax obligations and/or engage in similar activities. Whereas, traditional advocates of CSR have employed concepts such as reputation, licence-to-operate, sustainability, moral obligation and innovation to make the case for CSR, the present inquiry extends this stream of literature by arguing that TP and its externalities are genuine justifications for CSR. We consolidate our arguments with a case study of Glencore and the mining industry in the Democratic Republic of Congo