88 research outputs found
A Hamiltonian Formulation for Long Internal Waves
A novel canonical Hamiltonian formalism is developed for long internal waves
in a rotating environment. This includes the effects of background vorticity
and shear on the waves. By restricting consideration to flows in hydrostatic
balance, superimposed on a horizontally uniform background of vertical shear
and vorticity, a particularly simple Hamiltonian structure arises, which can be
thought of as describing a nonlinearly coupled infinite collection of shallow
water systems. The kinetic equation describing the time evolution of the
spectral energy of internal waves is subsequently derived, and a stationary
Kolmogorov solution is found in the high frequency limit. This is surprisingly
close to the Garrett--Munk spectrum of oceanic internal waves
Time-temperature dependent fracture toughness of PMMA
A toughness-biased Ree-Eyring relationship gives a good description of fracture toughness data of PMMA over a range of temperatures (283 to 353 K) and crack velocities (10 −5 to 1 m sec −1 ). Fracture toughness was measured by Gurney's sector method. The activation energy associated with the equation supports earlier work which suggests that, in the same temperature and velocity range, cracking in PMMA is controlled by craze growth, which is governed by secondary ( β ) molecular processes. Unstable cracking at moderate velocities (10 −2 to 1 m sec −1 ) seems to be produced by an isothermal/adiabatic transformation; an analysis for the onset of instability is given. At temperatures below 283 K, changes in toughness behaviour are seen, and below 243 K no stable cracking at all was obtained. A discussion is given of various methods of characterizing resistance to cracking, and methods of transforming R (à , T ) and K (à , T ) data are compared.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44668/1/10853_2004_Article_BF00540829.pd
Fractographic study of transverse cracks in a fibre composite
Transverse fracture of unidirectional fibre composites was studied in a model glass/epoxy composite in which 1 mm-diameter rods had been used in place of fibres. The fracture surface resulting from transverse cracking in this model system was studied by scanning electron microscopy (SEM). The interaction of the crack with the epoxy matrix resin and the glass rods was the following: Cracks in the resin appeared to have effected a debonding at the glassmatrix interface before reaching the glass. The debonding then propagated along the interface and induced secondary cracks ahead of the primary debonding crack. The confluence of the secondary and primary cracks resulted in sharp ridges being formed on the matrix resin surface, produced by plastic deformation of the rigid epoxy resin. These appeared as a field of parabolic marks. Considering the brittleness of the resin, the amount of plastic deformation indicated by the ridges was astonishing. As the debonding continued around the glass rod, a transverse corrugated texture developed on the resin surface, again produced by plastic deformation. Finally, the cracks reentered the matrix from small patches of polymer adhering especially strongly to the glass surface. The overall fracture energy of transverse cracking of unidirectional fibre composites is suggested to consist, therefore, of the following elements in addition to crack propagation in the matrix resin: (a) the glass-resin debonding before the incoming cracks reach the glass, (b) the initiation of secondary cracks or debonds at the interface, (c) the plastic deformation in generating the ridges on the rigid resin surface, appearing both as the paraboloids and the transverse corrugation, and (d) cracking of the matrix reinitiated at the opposite side of the glass. The use of an enlarged glass reinforcement in this study provided a more direct observation of the properties of transverse crack propagation in composite materials than would have been possible with the small, roughly 10 μ m fibres.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44691/1/10853_2005_Article_BF01111915.pd
Stress analysis near the tip of a curvilinear interfacial crack between a rigid spherical inclusion and a polymer matrix
The effect of carbon nanotubes on the fracture toughness and fatigue performance of a thermosetting epoxy polymer
Regulation of electrolyte transport with IL-1β in rabbit distal colon
Interletrkin-1β levels are elevated in inflammatory bowel disease. In this study the mechanism by which interleukin-1β affects electrolyte transport in the rabbit distal colon, was investigated. Interleukin-1β caused a delayed increase in short-circuit current (Isc) which was attributed to protein synthesis since the effect was inhibited by cycloheximide. The interleukin-1β induced increase in Isc was not affected by amiloride treatment but was completely inhibited by bumetanide or in chloride-free buffer and by indomethacin. Prostaglandin E2 levels increased in tissue treated with interleukin-1β, but this increase was reversed by cycloheximide. These data suggest that interleukin-1β causes its effect via a yet to be identified second messenger, by increasing chloride secretion through a prostaglandin E2 mediated mechanism
Interaction between short subcritical length fibres and polymer matrix. An approximate adhesion evaluation
Changes in expression of neuronal and glial glutamate transporters in rat hippocampus following kainate-induced seizure activity
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Time-Dependent Propagation of Tsunami-Generated Acoustic-Gravity Waves in the Atmosphere
Abstract
Tsunami-generated linear acoustic–gravity waves in the atmosphere with altitude-dependent vertical stratification and horizontal background winds are studied with the long-term goal of real-time tsunami warning. The initial-value problem is examined using Fourier–Laplace transforms to investigate the time dependence and to compare the cases of anelastic and compressible atmospheres. The approach includes formulating the linear propagation of acoustic–gravity waves in the vertical, solving the vertical displacement of waves and pressure perturbations numerically as a set of coupled ODEs in the Fourier–Laplace domain, and employing den Iseger’s algorithm to carry out a fast and accurate numerical inverse Laplace transform. Results are presented for three cases with different atmospheric and tsunami profiles. Horizontal background winds enhance wave advection in the horizontal but hinder the vertical transmission of internal waves through the whole atmosphere. The effect of compressibility is significant. The rescaled vertical displacement of internal waves at 100-km altitude shows an arrival at the early stage of wave development due to the acoustic branch that is not present in the anelastic case. The long-term displacement also shows an O(1) difference between the compressible and anelastic results for the cases with uniform and realistic stratification. Compressibility hence affects both the speed and amplitude of energy transmitted to the upper atmosphere because of fast acoustic waves
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