1,488 research outputs found
Parga, and the Ionian islands; comprehending a refutation of the mis-statements of the Quarterly Review and of Lieut.- Gen. Sir Thomas Maitland, on the subject; with a report of the trial between that officer and the author.
No full textPreface: Bosset, C.P.(de)Appendix.Dedication:Content description: TitleIllustration: (Maps ,)Pagination: PP26+530PVolumes: 1Text Genre:ProseIllustration: (χάρτες ,
Hydrodynamic induced deformation of and orientation of a microscopic elastic filament
No full textWe describe simulations of an elastic filament immersed in a fluid and subjected to a body force. The coupling between the fluid flow and the friction that the filament experiences induces bending and alignment perpendicular to the force. With increasing force there are four shape regimes, ranging from slight distortion to an unsteady tumbling motion. We also find marginally stable structures. The instability of these shapes and the alignment are explained by induced bending and nonlocal hydrodynamic interactions. These effects are experimentally relevant for stiff microfilaments
Cooperativity and hydrodynamic interactions in externally driven semiflexible filaments
No full textWe describe a simple simulation method that describes the hydrodynamics of semiflexible filaments immersed in a low Reynolds number fluid and analyze how multiple body cooperativity emerges due to the presence of hydrodynamic interactions (HI). We study the sedimentation of ensembles of filaments under an external force and also consider the propulsion of filaments subject to simple periodic driving. In both cases the dynamics shows qualitative differences due to the presence of HI. For sedimentation, the effects include cooperative velocity and instabilities that can be understood from the interplay of deformations due to flexibility and hydrodynamic forces. The motion of swimmers is more complex, and shows both positive and negative cooperation depending on distance, frequency of drive, and flexibility
An ashy septingentenarian: the Kaharoa tephra turns 700 (with notes on its volcanological, archaeological, and historical importance)
No full textMost of us are aware of the basaltic Tarawera eruption on 10th June 1886: the high toll on life (~120 people), landscape devastation, and loss of the Pink and White Terraces. But this was not the first time that Mt Tarawera produced an eruption of importance both to volcanology and human history. This edition of the GSNZ Newsletter marks the 700th anniversary of the Kaharoa eruption – its septingentenary to be precise – which occurred at Mt Tarawera in the winter of 1314 AD (± 12 years) (Hogg et al. 2003) (Fig. 1). The importance of the Kaharoa eruption is at least threefold. (1) It is the most recent rhyolite eruption in New Zealand, and the largest New Zealand eruption volumetrically of the last millennium. (2) The Kaharoa tephra is an important marker horizon in late Holocene stratigraphy and geoarchaeology (Lowe et al. 1998, 2000), and in particular helps to constrain the timing of settlement of early Polynesians in North Island (Newnham et al. 1998; Hogg et al. 2003; Lowe 2011). (3) There is a link between the soils that developed on the Kaharoa tephra, the animal ‘wasting’ disease known as ‘bush sickness’, and the birth of a government soil survey group as an independent organisation (Tonkin 2012)
A simulation study of the dynamics of a driven filament in an Aristotelian fluid
No full textWe describe a method, based on techniques used in molecular dynamics, for simulating the inertialess dynamics of an elastic filament immersed in a fluid. The model is used to study the "one-armed swimmer". That is, a flexible appendage externally perturbed at one extremity. For small-amplitude motion our simulations confirm theoretical predictions that, for a filament of given length and stiffness, there is a driving frequency that is optimal for both speed and efficiency. However, we find that to calculate absolute values of the swimming speed we need to slightly modify existing theoretical approaches. For the more relevant case of large-amplitude motion we find that while the basic picture remains the same, the dependence of the swimming speed on both frequency and amplitude is substantially modified. For large-amplitudes we show that the one-armed swimmer is comparatively neither inefficient nor slow. This begs the question, why are there little or no one-armed swimmers in nature
Short-time dynamics of colloidal suspensions
No full textWe report numerical simulations of the velocity autocorrelation function (VACF) for tagged particle motion in a colloidal suspension. We find that the asymptotic decay follows the theoretical expression for the VACF of an isolated particle, but with the suspension viscosity replacing the pure fluid viscosity (at long times the suspension behaves, so far as a tagged particle is concerned, like a fluid with the suspension viscosity—as an ‘‘effective fluid’’). While physically appealing, this observation is hard to reconcile with a recent theoretical prediction that at long times the VACF in a suspension should be the same as the VACF at infinite dilution. It also differs, in a rather subtle manner, from a scaling rule which has been used in the analysis of experimental and computer simulation results. From the scaling behavior of the VACF we conclude that effective fluid behavior only occurs on a time scale somewhat longer than the time taken for transverse momentum to diffuse a particle radius. This contrasts with the findings of earlier workers who concluded that effective fluid behavior is already observed at much shorter times
Do hydrodynamic dispersion coefficients exist?
No full textWe have calculated dispersion coefficients for tracer particles in a fluid flowing through a porous medium consisting of randomly packed spheres. At high Péclet numbers, where the motion of the tracer is determined largely by convection, we found evidence that the dispersion coefficient is diverging and that the dispersion process is anomalous. A transient region of anomalous dispersion has been predicted theoretically. However, our simulations suggest that, rather than being transient, this effect persists. We argue that our findings are consistent with the available experimental data
The influence of time-dependent hydrodynamics on polymer centre-of-mass motion
No full textWe describe simulations of isolated ideal polymer chains consisting of N monomers. The solvent is simulated using a dissipative ideal gas maintained at a set temperature by a Lowe-Andersen thermostat. By choosing a particular ratio of the Kuhn length to the monomer hydrodynamic radius, long-polymer scaling of the diffusion coefficient holds even for chains composed of a few beads. However, this requires that the model capture the hydrodynamics correctly on length scales equivalent to a typical solvent particle separation. It does. The decay of the centre-of-mass velocity autocorrelation function, C(t), for short chains scales rapidly to a function independent of N, so we can determine the long-polymer limit of the function. At long times it decays with an algebraic long-time tail of the form C(t) ?t?3/2. This is consistent with the predictions of theories that take into account the time dependence of the intra-polymer hydrodynamic interactions. We argue that the scaling of the decay implies that the intra-polymer hydrodynamic interactions propagate on a surprisingly rapid time scale.Applied Science
Sedimentation of pairs of hydrodynamically interacting semiflexible filaments
No full textWe describe the effect of hydrodynamic interactions in the sedimentation of a pair of inextensible semiflexible filaments under a uniform constant force at low Reynolds numbers. We have analyzed the different regimes and the morphology of such polymers in simple geometries, which allow us to highlight the peculiarities of the interplay between elastic and hydrodynamic stresses. Cooperative and symmetry breaking effects associated to the geometry of the fibers gives rise to characteristic motion which give them distinct properties from rigid and elastic filaments
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