Mechanics of a Plant in Fluid Flow

Plants live in constantly moving fluid, whether air or water. In response to the loads associated with fluid motion, plants bend and twist, often with great amplitude. These large deformations are not found in traditional engineering application and thus necessitate new specialised scientific developments. Studying Fluid-Structure Interactions (FSI) in botany, forestry and agricultural science is crucial to the optimisation of biomass production for food, energy, and construction materials. FSI are also central in the study of the ecological adaptation of plants to their environment. This review paper surveys the mechanics of FSI on individual plants. We present a short refresher on fluids mechanics then dive in the statics and dynamics of plant-fluid interactions. For every phenomenon considered, we present the appropriate dimensionless numbers to characterise the problem, discuss the implications of these phenomena on biological processes, and propose future research avenues. We cover the concept of reconfiguration while considering poroelasticity, torsion, chirality, buoyancy, and skin friction. We also cover the dynamical phenomena of wave action, flutter, and vortex-induced vibrations.Comment: 26 pages, 8 figure

Dirac Particles in a Gravitational Field

The semiclassical approximation for the Hamiltonian of Dirac particles interacting with an arbitrary gravitational field is investigated. The time dependence of the metrics leads to new contributions to the in-band energy operator in comparison to previous works on the static case. In particular we find a new coupling term between the linear momentum and the spin, as well as couplings which contribute to the breaking of the particle - antiparticle symmetry

Spirited Imperialism: The Formation and Command of the First Canadian Expeditionary Force in South Africa

This article explores the role played by Chamberlain, Minto and Hutton in shaping the organizational and command structure of the Canadian expeditionary force that deployed to South Africa. In 1899, the war raised not only the vital question about the kind of imperial war Canada ought to participate in, but also the form of that participation. As this article demonstrates, the British politician, the colonial administrator and the general saw the war as an opportunity to advance their specific agenda, strongly fuelled by imperialist sentiments. In doing so, the ideas that shaped their actions between July and October 1899 provided the base for a succession of seemingly unrelated decisions that had a substantial influence on Canada’s contribution and on the command arrangements in South Africa. The Canadian soldiers who sailed to South Africa were, for the first time, grouped in a national military formation commanded by a Canadian officer, setting a precedent for the country’s participation in future conflicts

Bosons Doubling

It is shown that next-nearest-neighbor interactions may lead to unusual paramagnetic or ferromagnetic phases which physical content is radically different from the standard phases. Actually there are several particles described by the same quantum field in a manner similar to the species doubling of the lattice fermions. We prove the renormalizability of the theory at the one loop level.Comment: 12 page

Buckling of a beam extruded into highly viscous fluid

Inspired by microscopic paramecies which use trichocyst extrusion to propel themselves away from thermal aggressions, we propose a macroscopic experiment to study the stability of a slender beam extruded in a highly viscous fluid. Piano wires were extruded axially at constant speed in a tank filled with corn syrup. The force necessary to extrude the wire was measured to increase linearly at first until the compressive viscous force causes the wire to buckle. A numerical model, coupling a lengthening elastica formulation with resistive force theory, predicts a similar behaviour. The model is used to study the dynamics at large time when the beam is highly deformed. It is found that at large time, a large deformation regime exists in which the force necessary to extrude the beam at constant speed becomes constant and length-independent. With a proper dimensional analysis, the beam can be shown to buckle at a critical length based on the extrusion speed, the bending rigidity and the dynamic viscosity of the fluid. Hypothesising that the trichocysts of paramercies must be sized to maximise their thrust per unit volume as well as avoid buckling instabilities, we predict that their bending rigidity must be about $3\times 10^{-9}~\mathrm{N\cdot \mu m^2}$. The verification of this prediction is left for future work.Comment: Accepted for publication in PRE on November 18 2014, 7 pages, 6 figure

Extreme vacuum technology including cryosorption, diffusion pump and pressure calibration studies Summary technical report, 1 Feb. 1965 - 1 Mar. 1966

Cryosorption, diffusion pump, and pressure calibration studies in extreme vacuum science and technology application progra

Study of low pressure application of the orbitron

Evaluation of low pressure performance of orbitron ionization gaug

Modification of nuclear transitions in stellar plasma by electronic processes: K-isomers in 176Lu and 180Ta under s-process conditions

The influence of the stellar plasma on the production and destruction of K-isomers is studied for the examples 176Lu and 180Ta. Individual electromagnetic transitions are enhanced predominantly by nuclear excitation by electron capture, whereas the other mechanisms of electron scattering and nuclear excitation by electron transition give only minor contributions. It is found that individual transitions can be enhanced significantly for low transition energies below 100 keV. Transitions with higher energies above 200 keV are practically not affected. Although one low-energy transition in 180Ta is enhanced by up to a factor of 10, the stellar transition rates from low-K to high-K states via so-called intermediate states in 176Lu and 180Ta do not change significantly under s-process conditions. The s-process nucleosynthesis of 176Lu and 180Ta remains essentially unchanged.Comment: 10 pages, 10 figures, Phys. Rev. C, accepte

From Feynman Proof of Maxwell Equations to Noncommutative Quantum Mechanics

In 1990, Dyson published a proof due to Feynman of the Maxwell equations assuming only the commutation relations between position and velocity. With this minimal assumption, Feynman never supposed the existence of Hamiltonian or Lagrangian formalism. In the present communication, we review the study of a relativistic particle using ``Feynman brackets.'' We show that Poincar\'e's magnetic angular momentum and Dirac magnetic monopole are the consequences of the structure of the Lorentz Lie algebra defined by the Feynman's brackets. Then, we extend these ideas to the dual momentum space by considering noncommutative quantum mechanics. In this context, we show that the noncommutativity of the coordinates is responsible for a new effect called the spin Hall effect. We also show its relation with the Berry phase notion. As a practical application, we found an unusual spin-orbit contribution of a nonrelativistic particle that could be experimentally tested. Another practical application is the Berry phase effect on the propagation of light in inhomogeneous media.Comment: Presented at the 3rd Feynman Festival (Collage Park, Maryland, U.S.A., August 2006

Special treatment reduces helium permeation of glass in vacuum systems

Internal surfaces of the glass component of a vacuum system are exposed to cesium in gaseous form to reduce helium permeation. The cesium gas is derived from decomposition of cesium nitrate through heating. Several minutes of exposure of the internal surfaces of the glass vessel are sufficient to complete the treatment