452 research outputs found
Data and software for article: Taylor-West, J. J., Balmforth, N. J., and Hogg, A. J. (2024) Lava delta formation: Mathematical modelling and laboratory experiments
No full textExperimental and numerical data and scripts required to reproduce the results of Taylor-West, Balmforth, & Hogg 2024 "Lava delta formation: Mathematical modelling and laboratory experiments". Accepted to JGR: Earth Surfaces. doi:10.1029/2023JF00750
Data and software for article: Taylor-West, J. J., Balmforth, N. J., and Hogg, A. J. (2023) Lava delta formation: Mathematical modelling and laboratory experiments
No full textExperimental and numerical data and scripts required to reproduce the results of Taylor-West, Balmforth, & Hogg 2023 "Lava delta formation: Mathematical modelling and laboratory experiments". Submitted to JGR: Earth Surfaces
Dam breaking by wave-induced erosional incision
No full textWe present an experimental and theoretical study of whether a large
displacement wave can lead to catastrophic erosional incision of a
moraine damming a glacial lake. The laboratory experiments consist of
reservoirs held by barriers of granular materials in a glass tank; the
theoretical model combines the Saint-Venant equations of hydraulic
engineering with an empirical prescription for erosion. The results of
both the laboratory experiments and the numerical simulations indicate
that a single wave is generally unable to break the dam, but a
sufficiently large disturbance in an almost-filled reservoir creates a
seiche that can repeatedly overtop the dam. In such a case, the combined
effect of the multiple erosion events ultimately breaks the dam
A hierarchy of coupled maps
No full textA large number of logistic maps are coupled together as a mathematical metaphor for complex natural systems with hierarchical organization. The elementary maps are first collected into globally coupled lattices. These lattices are then coupled together in a hierarchical way to form a system with many degrees of freedom. We summarize the behavior of the individual blocks, and then explore the dynamics of the hierarchy. We offer some ideas that guide our understanding of this type of system
A shocking display of synchrony
No full textThis article explores the Kuramoto model describing the synchronization of a population of coupled oscillators. Two versions of this model are considered: a discrete version suitable for a population with a finite number of oscillators, and a continuum model found in the limit of an infinite population. When the strength of the coupling between the oscillators exceeds a threshold, the oscillators partially synchronize. We explore the transition in the continuum model, which takes the form of a bifurcation of a discrete mode from a continuous spectrum. We use numerical methods and perturbation theory to study the patterns of synchronization that form beyond transition, and compare with the synchronization predicted by the discrete model. There are similarities with instabilities in ideal plasmas and inviscid fluids, but these are superficial
Dam-breaking seiches
No full textExperimental and theoretical models are used to explore the break of a
moraine dam by catastrophic erosional incision initiated by an
overtopping wave. The experiments are conducted in a rectangular tank
with an erodible barrier made from sand and grit. Theory combines
shallow-water hydrodynamics with an empirical model of erosion. The
models confirm that dams can be broken by a catastrophic incision.
However, the displacement wave does not break the dam in its first
passage but excites a long-lived seiche that repeatedly washes over the
dam. The Cumulative erosion of the downstream face by the overtopping
seiches eventually allows an incipient channel to form, and catastrophic
incision follows. Estimates are presented of the strength of the initial
disturbance required to break the dam, the maximum discharge and the
duration of the runaway incision
Turbulent mixing at a stable density interface : the variation of the buoyancy flux–gradient relation
No full textExperiments conducted on mixing across a stable density interface in a turbulent Taylor–Couette flow show, for the first time, experimental evidence of an increase in mixing efficiency at large Richardson numbers. With increasing buoyancy gradient the buoyancy flux first passes a maximum, then decreases and at large values of the buoyancy gradient the flux increases again. Thus, the curve of buoyancy flux versus buoyancy gradient tends to be N-shaped (rather than simply bell shaped), a behaviour suggested by the model of Balmforth et al. (J. Fluid Mech. vol. 428, 1998, p. 349). The increase in mixing efficiency at large Richardson numbers is attributed to a scale separation of the eddies active in mixing at the interface; when the buoyancy gradient is large mean kinetic energy is injected at scales much smaller than the eddy size fixed by the gap width, thus decreasing the eddy turnover time. Observations show that there is no noticeable change in interface thickness when the mixing efficiency increases; it is the mixing mechanism that changes. The curves of buoyancy flux versus buoyancy gradient also show a large variability for identical experimental conditions. These variations occur at time scales one to two orders of magnitude larger than the eddy turnover time scale
Viscoplastic flow over an inclined surface
No full textWe review viscoplastic flow over inclined surfaces, focusing on constant-flux extrusions from small vents and the slumping of a fixed volume of material. Lubrication theory is used for shallow and slow flows to reduce the governing equations to a nonlinear diffusion-type equation for the local fluid depth; this model is used as the basis for exploration of the problem. Theory is compared to experiments. A number of complications and additional physical effects are discussed that enrich real situations
Tidal Conversion by Supercritical Topography
No full textCalculations are presented of the rate of energy conversion of the barotropic tide into internal gravity waves above topography on the ocean floor. The ocean is treated as infinitely deep, and the topography consists of periodic obstructions; a Green function method is used to construct the scattered wavefield. The calculations extend the previous results of Balmforth et al. for subcritical topography (wherein waves propagate along rays whose slopes exceed that of the topography everywhere), by allowing the obstacles to be arbitrarily steep or supercritical (so waves propagate at shallower angles than the topographic slopes and are scattered both up and down). A complicated pattern is found for the dependence of energy conversion on , the ratio of maximum topographic slope to wave slope, and the ratio of obstacle amplitude and separation. This results from a sequence of constructive and destructive interferences between scattered waves that has implications for computing tidal conversion rates for the global ocean.National Science Foundation (Award 0645529)United States. Office of Naval Research (Grant N00014-0501-0575
Hundreds of variants clustered in genomic loci and biological pathways affect human height
No full textMost common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits(1), but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait(2,3). The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P<0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways
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