7,178 research outputs found
Low-temperature thermochronology and thermokinematic modeling of deformation, exhumation, and development of topography in the central Southern Alps, New Zealand
Apatite and zircon (U-Th)/He and fission track ages were obtained from ridge transects across the central Southern Alps, New Zealand. Interpretation of local profiles is difficult because relationships between ages and topography or local faults are complex and the data contain large uncertainties, with poor reproducibility between sample duplicates. Data do form regional patterns, however, consistent with theoretical systematics and corroborating previous observations: young Neogene ages occur immediately southeast of the Alpine Fault (the main plate boundary structure on which rocks are exhumed); partially reset ages occur in the central Southern Alps; and older Mesozoic ages occur further toward the southeast. Zircon apparent ages are older than apatite apparent ages for the equivalent method. Three-dimensional thermokinematic modeling of plate convergence incorporates advection of the upper Pacific plate along a low-angle detachment then up an Alpine Fault ramp, adopting a generally accepted tectonic scenario for the Southern Alps. The modeling incorporates heat flow, evolving topography, and the detailed kinetics of different thermochronometric systems and explains both complex local variations and regional patterns. Inclusion of the effects of radiation damage on He diffusion in detrital apatite is shown to have dramatic effects on results. Geometric and velocity parameters are tuned to fit model ages to observed data. Best fit is achieved at 9 mm a−1 plate convergence, with Pacific plate delamination on a gentle 10°SE dipping detachment and more rapid uplift on a 45–60° dipping Alpine Fault ramp from 15 km depth. Thermokinematic modeling suggests dip-slip motion on reverse faults within the Southern Alps should be highest ∼22 km from the Alpine Fault and much lower toward the southeast
Deformation of a free interface pierced by a tilted cylinder
We investigate the interaction between an infinite cylinder and a free
fluid-fluid interface governed only by its surface tension. We study the
deformation of an initially flat interface when it is deformed by the presence
of a cylindrical object, tilted at an arbitrary angle, that the interface
"totally wets". Our simulations predict all significant quantities such as the
interface shape, the position of the contact line, and the force exerted by the
interface on the cylinder. These results are compared with an experimental
study of the penetration of a soap film by a cylindrical liquid jet. This
dynamic situation exhibits all the characteristics of a totally wetting
interface. We show that whatever the inclination, the force is always
perpendicular to the plane of the interface, and its amplitude diverges as the
inclination angle increases. Such results should bring new insights in both
fluid and solid mechanics, from animal locomotion to surface
micro-processing.-processing.Comment: 6 pages, 5 figure
A genetic algorithm optimization framework for the characterization of hyper-viscoelastic materials:application to human articular cartilage
This study aims to develop an automated framework for the characterization of materials which are both hyper-elastic and viscoelastic. This has been evaluated using human articular cartilage (AC). AC (26 tissue samples from 5 femoral heads) underwent dynamic mechanical analysis with a frequency sweep from 1 to 90 Hz. The conversion from a frequency- to time-domain hyper-viscoelastic material model was approximated using a modular framework design where finite element analysis was automated, and a genetic algorithm and interior point technique were employed to solve and optimize the material approximations. Three orders of approximation for the Prony series were evaluated at N = 1, 3 and 5 for 20 and 50 iterations of a genetic cycle. This was repeated for 30 simulations of six combinations of the above all with randomly generated initialization points. There was a difference between N = 1 and N = 3/5 of approximately ~5% in terms of the error estimated. During unloading the opposite was seen with a 10% error difference between N = 5 and 1. A reduction of ~1% parameter error was found when the number of generations increased from 20 to 50. In conclusion, the framework has proved effective in characterizing human AC
When is a surface foam-phobic or foam-philic?
By integrating the Young-Laplace equation, including the effects of gravity,
we have calculated the equilibrium shape of the two-dimensional Plateau borders
along which a vertical soap film contacts two flat, horizontal solid substrates
of given wettability. We show that the Plateau borders, where most of a foam's
liquid resides, can only exist if the values of the Bond number and
of the liquid contact angle lie within certain domains in
space: under these conditions the substrate is
foam-philic. For values outside these domains, the substrate cannot support a
soap film and is foam-phobic. In other words, on a substrate of a given
wettability, only Plateau borders of a certain range of sizes can form. For
given , the top Plateau border can never have greater
width or cross-sectional area than the bottom one. Moreover, the top Plateau
border cannot exist in a steady state for contact angles above 90. Our
conclusions are validated by comparison with both experimental and numerical
(Surface Evolver) data. We conjecture that these results will hold, with slight
modifications, for non-planar soap films and bubbles. Our results are also
relevant to the motion of bubbles and foams in channels, where the friction
force of the substrate on the Plateau borders plays an important role.Comment: 20 pages, 14 figure
What is the shape of an air bubble on a liquid surface?
We have calculated the equilibrium shape of the axially symmetric meniscus along which a spherical bubble contacts a flat liquid surface, by analytically integrating the Young-Laplace equation in the presence of gravity, in the limit of large Bond numbers. This method has the advantage that it provides semi-analytical expressions for key geometrical properties of the bubble in terms of the Bond number. Results are in good overall agreement with experimental data and are consistent with fully numerical (Surface Evolver) calculations. In particular, we are able to describe how the bubble shape changes from hemispherical, with a shallow flat bottom, to lenticular, with a deeper, curved bottom, as the Bond number is decreased
Long-term exposure to air pollution and cognitive function in older adults: a systematic review and meta-analysis
Topological and geometrical disorder correlate robustly in two-dimensional foams
A 2D foam can be characterised by its distribution of bubble areas, and of
number of sides. Both distributions have an average and a width (standard
deviation). There are therefore at least two very different ways to
characterise the disorder. The former is a geometrical measurement, while the
latter is purely topological. We discuss the common points and differences
between both quantities. We measure them in a foam which is sheared, so that
bubbles move past each other and the foam is "shuffled" (a notion we discuss).
Both quantities are strongly correlated; in this case (only) it thus becomes
sufficient to use either one or the other to characterize the foam disorder. We
suggest applications to the analysis of other systems, including biological
tissues
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