Ca isotope fractionation on the Earth and other solar system materials

What mechanisms of flow control do animals use to enhance hydrodynamic performance? Animals are capable of manipulating flow around the body and appendages both passively and actively. Passive mechanisms rely on structural and morphological components of the body (i.e., humpback whale tubercles, riblets). Active flow control mechanisms use appendage or body musculature to directly generate wake flow structures or stiffen fins against external hydrodynamic loads. Fish can actively control fin curvature, displacement, and area. The vortex wake shed by the tail differs between eel-like fishes and fishes with a discrete narrowing of the body in front of the tail, and three-dimensional effects may play a major role in determining wake structure in most fishes.

http://www.people.fas.harvard.edu/~glauder/reprints_unzipped/FishLauder2006.pdf

Passive and Active Flow Control by Swimming Fishes and Mammals

The viscoelastic properties of (mostly carbon black) filled elastomers are reviewed with emphasis on the strain-dependence of the complex dynamic modulus (Payne effect) Considerable progress has been made in the past in relating the typical dynamical behavior at low strain amplitudes to a cyclic breakdown and reagglomeration of physical filler-filler bonds in typical clusters of varying size, including the infinite filler network Common features between the phenomenological agglomeration/deagglomeration Kraus approach and very recent semi-microscopical networking approaches (two aggregate VTG model, links-nodes-blobs model, kinetical cluster-cluster aggregation) are discussed All semi-microscopical models contain the assumption of geometrical arrangements of sub-units (aggregates) in particular filler network structures, resulting for example from percolation or kinetical cluster-cluster aggregation These concepts predict some features of the Payne effect that are independent of the specific types of filler These features are in good agreement with experimental studies For example, the shape exponent m of the storage modulus, G′, drop with increasing deformation is determined by the structure of the cluster network Another example is a scaling relation predicting a specific power law behavior of the elastic modulus as a function of the filler volume fraction The exponent reflects the characteristic structure of the fractal filler clusters and of the corresponding filler network The existing concepts of the filler network breakdown and reformation appear to be adequate in describing the deformation-dependence of dynamic mechanical properties of filled rubbers The different approaches suggest in a common manner that there is a change of filler structure with increasing dynamic strain However, in all cases additional assumptions are made about the accompanying energy dissipation process, imparting higher hysteresis to the filled rubber This process may be slippage of entanglements (slip-links) in the transition layer between bound rubber layer and mobile rubber phase, and/or partially release of elastically ‘dead’ immobilized rubber trapped within the filler network or agglomerates

Recent Advances in the Theory of Filler Networking in Elastomers

In vitro degradation of resin-dentin bonds analyzed by microtensile bond test, scanning and transmission electron microscopy.

The effect of different storage methods on the mechanical properties of trabecular bone

Dynamic mechanical measurements during the life to death transition in animal tissues1

The viscoelastic responses of intervertebral disks taken from the cervical regions of the spinal columns of several adult, male, mongrel dogs have been determined. The results are presented in terms of a mean complex shear compliance,Jd*=J′d−iJ″d, for the disk structures when these are subjected to small-amplitude audiofrequency vibrations (25–5000 Hz) while surrounded by normal salt solution, both at room temperatures and at 98·6°F (37.0°C) (in vitro). Values of the general compliance levels decrease with time after sacrifice, and an abrupt transition in the 100-Hz compliance-time curves at 5·5 hours after death is attributed to the completion of rigor mortis (at room temperature). Comparisons of the broad compliance-frequency disk spectra with those of five synthetic polymeric materials, including a silicone rubber, are presented and suggestions for materials suitable to be used in disk prosthesis are made. Such materials must have values of both elastic compliance (J′) and viscous compliance (J″) which are close to the corresponding living disk compliances. A brief discussion of the characteristic sharp resonance dispersions or fine structure observed in the disk spectra is also presented along with suggestions for future measurements. Finally, the idea is advanced that a composite synthetic structure with a stiff, outer ring of low compliance and a very compliant inner core might most satisfactorily mimic the viscoelastic behaviour of a normal intervertebral diskin vivo.

Viscoelastic response of intervertebral disks at audiofrequencies

Starting with the idea that wave mechanics should be useful in dealing with mechanical properties of solids, a connection between particle waves and deformation in crystals is developed. The connection is one in which Planck's constant h plays a prominent part. According to the view described, nonelastic deformation in crystals arises through the propagation of internally generated particle momentum waves with the de Broglie wavelength λ = h/mvi. Here, m and vi are the mass and velocity, respectively, of certain, initially field‐free atoms that exist because of lattice defects in the crystal. The particle waves in question are not the probability waves of contemporary, orthodox quantum theory which satisfy the Schrodinger equation. Instead, real‐property waves governed by a new differential equation are proposed. Solutions to this equation for both finite and infinite lattices lead to frequency‐wave vector conditions from which a number of interesting results follow. These include the occurrence of charac...

Particle Waves and Audiofrequency Modes in Crystals

Experimental observations of mechanical resonance dispersion in solids will be reviewed. Results of complex shear compliance measurements on single crystals, polycrystalline metals, and crystalline polymers will be presented. A theoretical explanation for the existence of the resonances on an atomic basis will be adduced. The theory allows the calculation of the critical shear stress or yield strengths for crystalline materials which deform by plastic flow or alternatively predicts the breaking stress for materials exhibiting brittle fracture. Good agreement with experimental values is obtained.

Edwin R. Fitzgerald

Papers

Dynamic mechanical measurements during the life to death transition in animal tissues1

Viscoelastic response of intervertebral disks at audiofrequencies

Particle Waves and Audiofrequency Modes in Crystals

Mechanical Resonance Dispersion and Plastic Flow in Crystalline Solids

Blubber and compliant coatings for drag reduction in water II. Matched shear impedance for compliant layer drag reduction