Sand Ripples and Dunes
Annual Review of Fluid Mechanics
An erodible bed sheared by a fluid flow, gas or liquid, is generally unstable, and bed forms grow. This review discusses the following issues, in light of the recent literature: What are the relevant dynamical mechanisms controlling the emergence of bed forms? Do they form by linear instability or nonlinear processes such as pattern coarsening? What determines their timescales and length scales, so different in air and water? What are the similarities and differences between aeolian and subaqueous patterns? What is the influence of the mode of transport: bed load, saltation, or suspension? Can bed forms emerge under any hydrodynamical regime, laminar and turbulent? Guided by these questions, we propose a unified description of bed-form growth and saturation, emphasizing the hydrodynamical regime in the inner layer and the relaxation phenomena associated with particle transport.
When I Heard the Learn’d Astronomer
BY WALT WHITMAN
When I heard the learn’d astronomer,
When the proofs, the figures, were ranged in columns before me,
When I was shown the charts and diagrams, to add, divide, and measure them,
When I sitting heard the astronomer where he lectured with much applause in the lecture-room,
How soon unaccountable I became tired and sick,
Till rising and gliding out I wander’d off by myself,
In the mystical moist night-air, and from time to time,
Look’d up in perfect silence at the stars.
Good Morning Gloucester 
Great shot and very contemplative poetry ~ thanks, xxx
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Reminds me of grad school, both the science and the poetry, but mostly of my distraction by the debate over whether or not Whitman was trying to say that there’s more to life than science. Great post, great photo.
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I too love Whitman and what he is saying here, but I also understand and identify with the nameless engineer and why he’s curious about the mechanism behind the phenomenon. Seems to me that he expresses his wonder in another language, even if we hear it as stultifying compared to the poetry. Thanks for the wonderful shot and the encouragement to think about it in different ways.
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Agreed, Greg. Beauty affects each of us differently. There’s a wonderful book called “Dialogues with Scientists and Sages” (http://www.amazon.com/Dialogues-Scientists-Sages-Science-Mysticism/dp/0710206550) that illustrates how spiritual leaders, such as the Dalai Lama and physicist, such as David Bohm (great friends, BTW) both feel as if they are searching for — and discovering — the same thing.
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Love it, gave me a lot to think about and marvel at!
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i do mess these and watching the crabs run down the ridges was fun too as a young lad thanks:-)
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Great commrnttary ,(as usuaal)…”I always wondered…”
However my left brain is still intrigued by the Hydrological fluid physics, and probably still trumps the right brain. Now that you have awakened that left side, I’m doomed to follow up.
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