A Robust Numerical Method for Integration of Point-Vortex Trajectories in Two Dimensions

The venerable 2D point-vortex model plays an important role as a simplified version of many disparate physical systems, including superfluids, Bose-Einstein condensates, certain plasma configurations, and inviscid turbulence. This system is also a veritable mathematical playground, touching upon many different disciplines from topology to dynamic systems theory. Point-vortex dynamics are described by a relatively simple system of nonlinear ODEs which can easily be integrated numerically using an appropriate adaptive time stepping method. As the separation between a pair of vortices relative to all other inter-vortex length scales decreases, however, the computational time required diverges. Accuracy is usually the most discouraging casualty when trying to account for such vortex motion, though the varying energy of this ostensibly Hamiltonian system is a potentially more serious problem. We solve these problems by a series of coordinate transformations: We first transform to action-angle coordinates, which, to lowest order, treat the close pair as a single vortex amongst all others with an internal degree of freedom. We next, and most importantly, apply Lie transform perturbation theory to remove the higher-order correction terms in succession. The overall transformation drastically increases the numerical efficiency and ensures that the total energy remains constant to high accuracy.Comment: 21 pages, 4 figure

Model of surface instabilities induced by stress

We propose a model based on a Ginzburg-Landau approach to study a strain relief mechanism at a free interface of a non-hydrostatically stressed solid, commonly observed in thin-film growth. The evolving instability, known as the Grinfeld instability, is studied numerically in two and three dimensions. Inherent in the description is the proper treatment of nonlinearities. We find these nonlinearities can lead to competitive coarsening of interfacial structures, corresponding to different wavenumbers, as strain is relieved. We suggest ways to experimentally measure this coarsening.Comment: 4 pages (3 figures included

The effect of quantization on the FCIQMC sign problem

The sign problem in Full Configuration Interaction Quantum Monte Carlo (FCIQMC) without annihilation can be understood as an instability of the psi-particle population to the ground state of the matrix obtained by making all off-diagonal elements of the Hamiltonian negative. Such a matrix, and hence the sign problem, is basis dependent. In this paper we discuss the properties of a physically important basis choice: first versus second quantization. For a given choice of single-particle orbitals, we identify the conditions under which the fermion sign problem in the second quantized basis of antisymmetric Slater determinants is identical to the sign problem in the first quantized basis of unsymmetrized Hartree products. We also show that, when the two differ, the fermion sign problem is always less severe in the second quantized basis. This supports the idea that FCIQMC, even in the absence of annihilation, improves the sign problem relative to first quantized methods. Finally, we point out some theoretically interesting classes of Hamiltonians where first and second quantized sign problems differ, and others where they do not.Comment: 4 pages w/ 2 page appendix, 2 figures, 1 tabl

The effect of bedrest on various parameters of physiological function. part v- dietary requirements

Effect of bedrest on various parameters of physiological function - nutritional requiremen

Coupling between tidal mudflats and salt marshes affects marsh morphology

It is generally assumed that coastal salt marshes are capable of adapting to moderately fast rising sea levels although local sediment availability crucially affects this capability. While there is an increasing awareness that local sediment availability is inherently related to sediment dynamics on the adjacent tidal mudflat, our current understanding of the interactions between salt marshes and tidal flats is very limited. To address this knowledge gap, we measured suspended sediment concentrations alongside hydrodynamic, morphological and sediment deposition measurements over a total period of 16weeks in a wave-exposed macro-tidal mudflat-salt marsh system on the UK east coast (Tillingham). Our results show that local sediment supply to the salt marsh is strongly linked to intertidal sediment dynamics and that the vast majority of suspended sediment deposited on the marsh originates from wind-wave induced intertidal sediment resuspension in very close vicinity (5mmyr⁠−1, thereby increasing the slope of the tidal mudflat-salt marsh transition and making the salt marsh susceptible to lateral erosion. Consequently, the marsh edge retreats at a rate of approximately 0.8myr⁠−1. Our study shows that the response of coastal salt marshes to climate change is a function of the coupled tidal mudflat-salt marsh system, rather than their vertical sediment accretion rates alone. Therefore, the idea that salt marsh adaptability relies on local sediment supply needs to be expanded, incorporating the morphology and long-term evolution of the adjacent tidal mudflats.NERC-funded projects Coastal Biodiversity and Ecosystem Services Sustainability (CBESS; grant no: NE/J015423/1) and BLUE-coast (grant no: NE/N015878/1)

New Can Bus Communication Modules for Digitizing Forest Machines Functionalities in the Context of Forestry 4.0

In line with the context of Industry 4.0, forestry, and in particular the entire ecosystem around it, also needs digitalization solutions in order to allow better interaction between all agents that work and live from the forest. It is important for a better management of forest resources allowing productivity gains, more sustainability and resilience. One of the agents that can benefit, but also contribute to better forestry, are machine producers.With digitalization, the machinery is now equipped with new and better sensors that can be used not only for machine operations but also for forest management, through LiDAR (Light Detection And Ranging) or RGB (Red, Green, Blue) cameras for example. On the other hand, there are new needs for predictive maintenance or solutions for remote assistance of machines operating in the forest, typically in isolated areas with great limitations in access to communications. Thinking about these technological challenges, this work seeks to provide answers with communication solutions in forest machines, enabling the digitalization of functionalities, also allowing remote access to machine controllers in order to provide them with connectivity in an IIoT (Industrial Internet of Things) scenarios. New hardware modules designed in partnership and according to the prerequisites of a forest machine manufacturer are presented. These modules are a step towards digitizing the machines and opening up the scalability of new requirements, as well as remote access through additional gateways. The results already obtained in real scenarios show that these modules can be a concrete solution for the current and emerging needs of industrial machine manufacturers.info:eu-repo/semantics/publishedVersio

Effects of aging on identifying emotions conveyed by point-light walkers

M.G. was supported by EC FP7 HBP (grant 604102), PITN-GA-011-290011 (ABC) FP7-ICT-2013-10/ 611909 (KOROIBOT), and by GI 305/4-1 and KA 1258/15-1, and BMBF, FKZ: 01GQ1002A. K.S.P. was supported by a BBSRC New Investigator Grant. A.B.S. and P.J.B. were supported by an operating grant (528206) from the Canadian Institutes for Health Research. The authors also thank Donna Waxman for her valuable help in data collection for all experiments described here.Peer reviewedPostprin