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david jon furbish

@davidjonfurbish.bsky.social
194 followers 111 following 434 posts

emeritus professor studying statistical physics of sediment transport & science philosophy essays and ebook preview at: my.vanderbilt.edu/davidjonfurbish author of Fluid Physics in Geology: academic.oup.com/book/40895?login=f…

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david jon furbish @davidjonfurbish.bsky.social · 24/08/2026
Our neighborhood “wild” turkeys like to visit our birdbath — one of their favorite watering spots. Occasionally they will actually try to bathe in it, like the little birds. This mostly just makes a wet feathery mess of things 😂 #wildlife #birds #wildturkey
Three wild turkeys sipping water from a birdbath in grassy lawn
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david jon furbish @davidjonfurbish.bsky.social · 18/08/2026
Rowan’s cool butt markings highlight her natural sashay 😂 #dogs #dogsofbluesky #AustralianShepherd
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david jon furbish @davidjonfurbish.bsky.social · 18/08/2026
These three 6 m stems of Paulownia tomentosa (princess tree or empress tree or foxglove tree) started as small shoots in June. Native to China, the deciduous hardwood princess tree is among the fastest growing in the world, and it invasively thrives in TN.
Pic of three stems of princess tree with large leaves growing in front of gray cabin, with Australian Shepherd standing near the base of the trees
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david jon furbish @davidjonfurbish.bsky.social · 16/06/2026
I usually compose footnotes in a manner befitting their normally intended purpose: to support or elaborate material in the main text. But I also view certain footnotes as opportunities to drop serious snark. Here is one of my favorite recently composed footnotes, with context.
Consider rain splash transport as an example, and recall the one-dimensional entrainment form of the Exner equation...

Focusing on the advective term in (1)...

where D = k E / c_b.  Thus the advective term looks like diffusion as defined mathematically.  Whereas it is correct to say that (2) is a diffusion equation, it is incorrect to say that this equation represents the effects of particle diffusion.  The effects of particle diffusion are described by the last term in (1), a point that we fully examine in Chapter 11.  A similar interpretation applies to soil creep, where (2) arises from the assumption that the vertically integrated soil flux is proportional to the local land-surface slope.

The derivative on the right side of (2) often is referred to as a diffusive term, likely in analogy with a conventional advection--diffusion equation.  This is correct in a mathematical sense, and perhaps intended to refer to the idea that ``diffusive smoothing'' of the function < zeta > occurs according to the mathematical algorithm defined by a diffusion equation.  But in a physical sense related to transport, the derivative on the right side of (2) is actually an advective term.  It looks mathematically diffusive only because the average particle displacement is proportional to the land-surface slope.\footnote{\textcolor{blue}{This point of confusion seems to reflect a broader misunderstanding of the meaning of advection.  The popular, heuristically confused ``stream power model'' of land-surface evolution includes a ``diffusive'' term as in (2) and a term involving the product of the local land-surface slope and the upstream catchment area.  This latter term is often referred to as an advective term, but it has nothing to do with advection.  It is in fact a local sink term.  Moreover, for physical reasons the two terms are not additive as normally assumed.}}
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david jon furbish @davidjonfurbish.bsky.social · 09/06/2026
eBook Preview (continued): Statistical Physics of Sediment Particle Motions and Transport Chapter 7: Master Equations Below is a brief description from my webpage to go with the link. cdn.vanderbilt.edu/t2-my/my-prd...
eBook Preview

Statistical Physics of Rarefied Sediment Particle Motions and Transport: Applications to Hillslopes and Rivers

Chapter 7: Master Equations

Of all the topics covered in the book, the formalism of a master equation quintessentially embodies the power and beauty of the principles and methods of statistical physics as applied to sediment particle systems. Herein we see that a master equation really is what its name says it is --- a universal "truth" describing conservation of probability --- where e.g. the behavior of Brownian particles, sediment particles and the stars of the Milky Way Galaxy are all described by the same equation, the Fokker-Planck equation.  Yes... Brownian particles are like rarefied bed load particles are like stars --- all experiencing velocity proportional (Stokes) friction!

Bonus: This chapter provides the first completely rigorous derivation and explanation of the activity form of the Exner equation --- highlighting its stochastic qualities under rarefied transport conditions --- thus avoiding unphysical consequences of conventional misapplications of the continuum hypothesis.
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david jon furbish @davidjonfurbish.bsky.social · 01/06/2026
eBook Preview (continued): Statistical Physics of Sediment Particle Motions and Transport For anyone interested, I posted revised versions of the Preface and Introduction (Chapter 1) on my webpage. Below is a brief description from my webpage to go with the link. cdn.vanderbilt.edu/t2-my/my-prd...
Posting this preview of material from my next (unfinished) book might be a mistake. But eh... what the hell. It represents real progress in understanding. And given the current state of domestic and world affairs amidst a climate crisis, who knows what doing science will even look like by the time I finish the book?

The linked pdf contains the title page with front material, the Preface, and the Introduction (Chapter 1).  These sections provide a clear idea of the material covered in the book, including its philosophical basis.  Although I originally committed an early version of the book to a well-known university press, I eventually decided instead to prepare it as an ebook, consistent with my views on open access, to be freely accessible to all.  Although it currently exceeds 450 pages without figures, I still have much to do and won't offer a target date.  Completed parts of the book are accessible on my webpage (currently posted versions are a bit dated and do not show recent edits), together with essays on topics that will eventually appear in the book.

The objective of the book is to provide a framework for describing sediment particle motions and transport in a manner that integrates principles and methods of probability with mechanical considerations of particle motions. The book therefore covers the topic of sediment transport in a manner that is mostly unfamiliar to folks in the Earth-surface processes community. Nonetheless, I suspect it will resonate with students and early career people eager for a fresh view of this complex and often confusing topic. To be sure, the book unapologetically breaks from current dogmatic styles of thinking and analysis in the field.
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david jon furbish @davidjonfurbish.bsky.social · 26/04/2026
Rowan especially enjoys romping amidst the bright fresh greenery of springtime in the Tennessee highlands — here on the trail to the creek (gonna look for frogs and turtles!) and on the creek floodplain currently flooded with ferns! #dogs #dogsofbluesky #AustralianShepherd
tri-color Australian Shepherd walking on trail in woods with bright green understory plantstri-color Australian Shepherd standing on creek floodplain amidst bright green ferns within oak-hickory forest
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david jon furbish @davidjonfurbish.bsky.social · 15/04/2026
Rowan… intrepid woof, Dragon Soccer star, enthusiastic hiking companion, fearless creek wader… #dogs #dogsofbluesky #AustralianShepherd
photo of tri-color Australian Shepherd looking to side of camera with blue sky in upper background
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david jon furbish @davidjonfurbish.bsky.social · 15/04/2026
to launch into more advanced foundational topics — kinematics of the particle flux, master equations, advection and diffusion, considerations of entropy, etc. — thence to the second part of the book focused on applications. 3/3
Plots of realizations of a Wiener process $X(t)$ starting at $X(0) = 0$ with (left) $\tau = 0.1$ and (right) $c \tau = 10$ for scaling factor $c = 100$, showing self-similar geometry over different time scales.
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david jon furbish @davidjonfurbish.bsky.social · 08/03/2026
I can’t help myself 😊 A teaser from Chapter 2 — the opening paragraphs of the section on ensemble averaging — for serious-minded students/aficionados of sediment transport I got this section just right cdn.vanderbilt.edu/t2-my/my-prd...
\textbf{2.4.3 Ensemble Averaging}

\noindent The far-reaching significance of ensemble averaging was cemented in physics by the work of \textcolor{blue}{Gibbs (1902)}.  As \textcolor{blue}{Kittel (1958)} notes, ``the scheme introduced by Gibbs... [provides a formal way] to replace \textit{time averages} over a single system by \textit{ensemble} averages, which are averages at a fixed time over all systems in an ensemble.''  With specific reference to the statistical mechanics of gas particles, \textcolor{blue}{Gibbs (1902)} defined an ensemble as ``a great number of independent systems, identical in nature, but differing in phase, that is, in their condition with respect to configuration and velocity.''  For context we briefly outline below the concept of a Gibbs ensemble in relation to gas particles, and then develop this concept more fully in Chapter 9.  A key point of this section is to illustrate that the concept of a Gibbs ensemble as applied in stochastic systems analysis is now much broader than what Gibbs originally envisioned, owing to the clear interpretive value of ensemble averaging.  For our purposes we may define a Gibbs-like ensemble as a great number of independent but nominally identical systems, each evolving independently but in the same probabilistic manner.

In appealing to a Gibbs-like ensemble, we often are referring to a set of imagined systems that are nominally identical to a real prototype system.  In this case the number of imagined systems may be arbitrarily large.  In certain situations, as outlined in examples below, we can identify an ensemble consisting of real systems, although the ensemble size might be small relative to an imagined large ensemble.  Nonetheless, this situation lends realism to the idea of an \textit{ensemble distribution} and ensemble averaging.
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david jon furbish @davidjonfurbish.bsky.social · 04/03/2026
Rowan is the happiest woof in the world when she is romping and sniffing in the woods… and a creek just makes the adventure nearly perfect #dogs #dogsofbluesky #AustralianShepherd
pic of tri-color Australian Shepherd (Rowan) standing in a rocky creek with mossy banks in an oak-hickory wooded area

Rowan is looking back at the camera
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david jon furbish @davidjonfurbish.bsky.social · 03/03/2026
more generally...
A Brief History of Humanity

Religion got there first before science and helped hardwire the capacity for willful ignorance, greed and cruelty. So whereas we learned that with knowledge, rationality and empathy we are capable of achieving a healthy and just world, evidently we prefer to destroy this one pale blue dot and its life in the name of fantasy. One grand religious shitshow.

The end.

djf 03.03.26
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david jon furbish @davidjonfurbish.bsky.social · 01/03/2026
All along the watchtower The [woof] began to howl “Please don’t interrupt me, Big Woof! With springtime approaching, I’m trying to explain the new rules to the squirrels and the owls out there in the woods!” #dogs #dogsofbluesky #AustralianShepherd
pic of tri-color Australian Shepherd (Rowan) standing on a wooden deck overlooking oak-hickory wooded area visible through mesh beneath deck rails. Rowan is looking at the camera as though interrupted by my voice.
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david jon furbish @davidjonfurbish.bsky.social · 28/02/2026
eBook Preview (continued): Statistical Physics of Sediment Particle Motions and Transport Chapter 2: Probabilistic Concepts I Chapter 3: Probabilistic Concepts II Oh gosh! Nuts and bolts! These chapters illustrate how the principles and methods... 1/n cdn.vanderbilt.edu/t2-my/my-prd...
Figure 3.1: Contour plot (lower left) of joint probability density function $f_{x,y} (x,y)$ (upper right) together with marginal distributions $f_x(x)$ and $f_y(y)$.  The integral of $f_{x,y}(x,y)$ over $y$ within the slice of width $\mathrm d x$ gives the probability $f_x(x) \mathrm d x$.
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david jon furbish @davidjonfurbish.bsky.social · 18/02/2026
post from Mastodon regarding AI generated material
I'm so tired. People, I am not interested in reading *blogs* generated with claude, gemini or chatgpt. No, not even ones proofread by AI. Do it yourself. I do not wish to even accidentally click on "one-shotted" dummy projects. Don't show me your AI-generated analysis of anything. Above all, I do not wish to see images/artwork someone prompt created.

I value real content, with all its good and bad quirks, from actual human beings. 

Somebody please normalize auto-tagging of AI generated content across all formats - text, images and code so I can blanket ban them from my personal computer.

This is a plead for help I never thought I'll have to make.
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david jon furbish @davidjonfurbish.bsky.social · 15/02/2026
“Before you say anything snarky, Big Woof, I definitely earned this pillow! Doing yard work is hard! Chasing and dragging sticks ain’t easy, and those sticks don’t just chew themselves!” #dogs #dogsofbluesky #AustralianShepherd
Tri-color Australian Shepherd laying on a couch with her head on a big yellow pillow
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david jon furbish @davidjonfurbish.bsky.social · 14/02/2026
for sure, guys like getting flowers here are mine ☺️
pic of vase on wooden table containing mostly red carnations plus white flowers
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david jon furbish @davidjonfurbish.bsky.social · 13/02/2026
Our high-tree-density part of south Nashville suffered extensive damage to trees from the ice storm, w/ loss of power for nearly 2 wks. Most power/data lines are restored, but the cleanup has just started. Meanwhile, Rowan thinks yard work & stick chewing w/ Chief woof and Big woof is great fun.
Pic of side of road at intersection with power/data line on the ground next to stop signPic of piles of tree logs and branches lining the side of a road in the neighborhood. Some of these piles are tens of meters long and 3-4 meters high, and have LARGE logs along with the slashPic of several piles of logs and branches lining the side of the road below our house. Foreground pile is one of several we have startedPic of Rowan the intrepid woof standing in the front lawn near a wheel barrow checking out other woofs and hoomans doing yard work in the neighborhood
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david jon furbish @davidjonfurbish.bsky.social · 11/02/2026
A recent journal article reminded me that deterministic descriptions of sediment transport have led to some "famous" but decidedly flawed results that many uncritically cite as fact. To wit, here is an excerpt from my (unfinished) ebook under the heading, "The Algebra and Calculus of Expectations."
Here we note that deterministic descriptions of sediment particle motions and transport often mix deterministic quantities with random variables and manipulate these according to the ordinary rules of algebra, not recognizing or acknowledging that the algebra of random variables is unlike the algebra of ordinary variables, nor properly averaging the algebraic expressions involved.  As a consequence it is difficult to decipher the mechanical meaning and implications of such descriptions, as they can involve hidden or missing information, or algebraic relations among quantities that do not correctly represent the physical situation.  Numerous examples exist in the literature.  Here are brief summaries of three.

Deterministic formulations of the onset of individual bed load particle motions have appealed to the ratio $R_F = F_\mathrm{L} / F_\mathrm{D}$ of the lift force and the drag force, $F_\mathrm{L}$ and $F_\mathrm{D}$, acting on a stationary particle.  Within a strictly laminar flow the lift $F_\mathrm{L}$ and drag $F_\mathrm{D}$ are fixed, and the ratio $R_F$ is therefore fixed.  In this situation the forces, and the ratio $R_F$, may be treated as deterministic quantities.  Within a turbulent flow the lift and drag forces on a stationary particle fluctuate (e.g. \textcolor{blue}{Schmeeckle et al., 2007}),\footnote{Likewise the lift and drag forces on a moving particle fluctuate (\textcolor{red}{e.g. REFS}).} and these forces must be viewed as random variables.  In turn, the ratio $R_F = F_\mathrm{L} / F_\mathrm{D}$ is a random variable.  Now, whereas it is possible to form the ratio $R_F^* = \langle F_\mathrm{L} \rangle / \langle F_\mathrm{D} \rangle$ of the averages $\langle F_\mathrm{L} \rangle$ and $\langle F_\mathrm{D} \rangle$, this ratio differs from the expected value $\langle R_F \rangle$.  In fact, $\langle R_F \rangle = \langle F_\mathrm{L} / F_\mathrm{D} \rangle$.  Moreover, whereas the ratio $R_F^*$ is likely to be well-defined, the expected value $\…
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david jon furbish @davidjonfurbish.bsky.social · 28/01/2026
Winter storm conditions in Nashville w/ continued freezing and power outages are grim. Needed to use crampons, for sure, just to take Rowan outside for her constitutionals, dodging downed trees and power lines everywhere. We did 2 days/nights w/ fireplace and camp stove before making our way south.
pic of sun shining through ice covered tree, and surrounding area of trees, all ice covered. Damage to trees in the area of Nashville is extensivepic of ice covered road with downed trees blocking parts/much of road. This is a “major” road in this part of Nashville. It was not passable, and we backed out to go a different route
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david jon furbish @davidjonfurbish.bsky.social · 19/01/2026
the English language meets Cantor’s continuum hypothesis lol
cartoon from @snail.and.snail with two snails conversing:

English is difficult. When do we use “many” and when do we use “much”?

“Many” is for nouns that are countable, like apples.  “Much is for nouns that are not countable, like water.

So we should say “many rational numbers” and “much real numbers”?
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david jon furbish @davidjonfurbish.bsky.social · 29/12/2025
When Rowan was a puppy she enrolled in several self-guided courses. After excelling in Basic Couch Use 101, she then took Principles of Pillowing 101, and Advanced Pillowing 240. Scored well in both. A genuine autodidact. 😊 #dogs #dogsofbluesky #AustralianShepherd
tri-color Australian Shepherd comfortably laying in sunlight on a couch with a pillow beneath her head
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david jon furbish @davidjonfurbish.bsky.social · 13/12/2025
For those interested in sediment transport in rivers: We've all stared at log-log plots involving a gazillion data points of bed load transport rate versus shear stress and noticed that the residual variance about some selected empirical flux-stress function typically spans... 1/3
Plot of (top) 50 realizations (black lines) of particle number N(t) versus time t showing increasing variance with t about expected value (yellow line) and +/- 2 standard deviations (red lines); and (bottom) 50 realizations (black lines) of time-averaged particle number flux q_{nx} versus averaging interval Delta t showing convergence to ensemble expected value <q_{nx}> (yellow line) with +/- 2 standard deviations (red lines).  Plots are generated with Poisson rate lambda = 1 s^{-1}, and mimic measured times series of coarse gravel transport in flume experiments. See preview of Chapter 6: Kinematics of the Particle Flux, for further explanation.Plot of 14 experimental realizations of the number flux q_{nx} with (black line) expected flux <q_{nx}> for D = 11.3-16 mm particles. The expected value <q_{nx}> is estimated as the time average of the full time series. Similar results occur for other sizes in the gravel mixture.
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david jon furbish @davidjonfurbish.bsky.social · 11/12/2025
Sometimes Rowan forgets to look, but today she responsibly and capably checked for trolls under all the bridges — and she’s not shy about chasing them out! #dogs #dogsofbluesky #AustralianShepherd
tri-color Australian Shepherd wading in small creek looking under a wooden plank bridge for a footpath in an oak-hickory forest
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david jon furbish @davidjonfurbish.bsky.social · 08/12/2025
Rowan the intrepid woof couldn’t find any frogs along the edge of the pond this time of year, so instead she decided to study waves. Seems to like fluid mechanics as much as aquatic biology. 😊 #dogs #dogsofbluesky #AustralianShepherd
tri-color Australian Shepherd wading in a shallow pond, seeming to examine the water waves that she created in front of her
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david jon furbish @davidjonfurbish.bsky.social · 05/12/2025
Happy birthday to Rowan the Intrepid Woof! 5 years! Rowan insisted that we do a special romp in the woods this afternoon for her birthday — you know, to make sure we sniffed all possible interesting sniffable things that we might have missed this morning! #dogs #AustralianShepherd #dogsofbluesky
tri-color Australian Shepherd standing on leafy forest floor near large hole in the ground, with head turned to look behind hertri-color Australian Shepherd sitting on leafy forest floor looking at camera
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david jon furbish @davidjonfurbish.bsky.social · 02/12/2025
Towards the Forest Canopy linocut artwork by Gail Kellett www.gailkellett.com.au/artworks/
linocut artwork of trees looking upward toward the canopy with blue sky background
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david jon furbish @davidjonfurbish.bsky.social · 15/10/2025
Oh gosh our befriended dragon Icarus was seriously injured in a game of Dragon Soccer! Fortunately the Chief Woof does excellent dragon surgery (generally a dangerous business) and fixed Icarus’s noise-maker innards and the laceration. Look at those beautiful butt/tail stitches! All better 😊
pic of toy stuffed dragon resting on my knees and Rowan (tri-color Australian Shepherd) in front of my knees looking at the dragon and mepic of underside of toy stuffed dragon showing white belly and green tail, with stitches closing the (previous) tear between the butt and tail
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david jon furbish @davidjonfurbish.bsky.social · 02/10/2025
decided to use my 30-year-old unabridged Webster LLM and noticed we inherited several of our daughters’ not-so-LLMs (“only” ~70,000 parameters) don’t recall ever seeing any of these hallucinate 🤓😂
large hardbound Webster dictionary on table with three small paperback dictionaries placed on an open page of the Webster
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david jon furbish @davidjonfurbish.bsky.social · 21/09/2025
Rowan caught another dragon for our Dragon Soccer game! The dragon was initially annoyed — and still gets a bit touchy about not being able to fly with too much dog spit on its wings — but now seems to enjoy playing with us! #dogs #dogsofbluesky #AustralianShepherd
tri-color Australian Shepherd in dog down position in grassy lawn with toy stuffed dragon between her front pawstri-color Australian Shepherd laying in grassy lawn with toy stuffed dragon between her front paws
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david jon furbish @davidjonfurbish.bsky.social · 03/09/2025
Rowan and I are NOT doom scrolling on my iPad. We’re watching cool dog agility videos and checking out the stuffed animals toys on the webpage of our locally owned pet supply store. We’re getting ready to go hide in the mountains/woods for a week or so. #dogs #dogsofbluesky #AustralianShepherd
tri-color Australian Shepherd (Rowan) laying on my shoulders as we look at my iPad together on the couch
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david jon furbish @davidjonfurbish.bsky.social · 14/08/2025
for fun, here is another snippet from something I'm currently writing, which concerns the statistical physics of sediment transport although focused on transport of soil particles by rain splash, the idea equally applies to other transport processes, including bed load transport in rivers
Moreover, the ingredients of [expressions of the soil particle flux] are in principle well defined, and the simple linear forms of these expressions appear to hold no surprises.  Stated another way, rain splash transport is perhaps the ``tamest'' surface transport process imaginable --- the ``simplest of all geomorphic processes'' (Dunne et al., 2010, p. 15).  It is therefore an ideal example to examine the probabilistic consequences of rarefied transport conditions for comparison with a conventional deterministic (continuum-like) description of a process that is fundamentally noise driven.  Indeed, like the process of radioactive decay and its measurement, an explanation of rain splash transport requires a probabilistic description; no other possibility exists.
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david jon furbish @davidjonfurbish.bsky.social · 07/08/2025
“Hey Big Woof, I brought my dragon, did you bring the soccer balls for our game of Dragon Soccer?” #dogs #dogsofbluesky #AustralianShepherd
photo of tri-colored Australian Shepherd standing in grassy field looking upward at camera with toy stuffed dragon on the ground at her feet
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david jon furbish @davidjonfurbish.bsky.social · 02/08/2025
my colleague @cstark.bsky.social recently reminded me of a cool word: polemical so for fun, here is one of my favorite footnotes in something I'm currently writing... which concerns the statistical physics of sediment transport
...the motions of natural angular particles down rough inclined surfaces under the influence of gravity, negligibly influenced by the surrounding fluid.  This topic serves to highlight the statistical mechanics of particle disentrainment in which, following entrainment, the cessation of motion within any downslope interval is probabilistic.  A description of the energetics of particle--surface collisions during downslope movement yields a well-defined distribution of particle travel distances whose form and parametric values reflect a balance between the particle kinetic energy gained from gravitational potential energy and the extraction of kinetic energy by collisions.  The analysis illustrates why the notion of a deterministic threshold for cessation of motion is an illusion, with implications transferable to bed load transport.\footnote{Similarly, particle entrainment is probabilistic, and the notion of a so-called critical shear stress marking the onset of bed load transport is an empirical expedient --- an illusion of mechanics.}
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david jon furbish @davidjonfurbish.bsky.social · 22/07/2025
lol Rowan was rather annoyed with me that I posted her less-than-graceful dock dive without explanation… and insisted that we make things right so… here it is… her fearlessly and properly executed dock dive (and splash!) with precise tennis ball fetch! 😂 #dogs #dogsofbluesky #AustralianShepherd
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david jon furbish @davidjonfurbish.bsky.social · 18/07/2025
Rowan would chase her ball into the lake for hours if I let her lol she’s a bit shy and maybe less than graceful with her dock dive this time #dogs #dogsofbluesky #AustralianShepherd
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david jon furbish @davidjonfurbish.bsky.social · 13/06/2025
Rowan really enjoys playing catch and release, although the frogs and turtles become rather annoyed by it all, particularly if the release part of the game is not immediate. #AustralianShepherd
Pic of tri-colored Australian Shepherd standing in shallow clear water creek, looking down into the water
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david jon furbish @davidjonfurbish.bsky.social · 30/05/2025
A special part of one of my favorite bike trails — along the Little Harpeth River, Tennessee
Pic overlooking bicycle handlebars on boardwalk next to small river, on a sunny day with tree shadows on boardwalkBoardwalk next to small river, on a sunny day with tree shadows on boardwalk
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david jon furbish @davidjonfurbish.bsky.social · 14/05/2025
Rowan and the big woof couch chillin’ after a rowdy game of Dragon Soccer
Tri-color Australian Shepherd resting on shoulders of guy sitting on couch
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david jon furbish @davidjonfurbish.bsky.social · 13/05/2025
Mini rant! (The full rant currently is about five pages.) Bagnold's pioneering work on the transport of sand by wind is generally outstanding. His work on bed load transport in rivers? Not so much. His 1966 formulation of bed load transport is mechanically ill-conceived. 1/n
Equation for the bed load work rate as presented by R. A. Bagnold in his 1966 USGS Professional Paper 422-I
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david jon furbish @davidjonfurbish.bsky.social · 30/04/2025
🙄 🥱🥱 😴😴😴
so-called stream power erosion model with diffusion-like term that is purported to describe evolution of the land-surface elevation h
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david jon furbish @davidjonfurbish.bsky.social · 22/04/2025
puppy sploot! 😂 and playful but dignified nearly 13 years later my daughter’s beloved Rory #GoldenRetriever
Golden Retriever puppy snoozing in sploot position on floor next to food and water bowlsadult Golden Retriever dog sitting in green grass looking at camera
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david jon furbish @davidjonfurbish.bsky.social · 11/04/2025
It's definitely time for a Rowan the intrepid woof pic! "Big Woof, are you please gonna stop looking at your iPad and take me outside to play in the creek and get all wet and muddy lookin' for frogs and stuff?" #AustralianShepherd
Image of tri-colored Australian Shepherd with her head resting on the side of a couch looking at the camera with longing brown eyes.
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david jon furbish @davidjonfurbish.bsky.social · 11/04/2025
Sediment transport research is now steadily moving beyond its legacy of heuristic engineering masquerading as physics. Here is key perspective on framing the topic in a manner that refocuses on clarifying the essential physics of transport at the outset.
I have repeatedly pointed out in journal articles and in essays that, possibly except for dense granular creep/flow, sediment transport on hillslopes and in rivers occurs under rarefied conditions. Transport does not satisfy the continuum hypothesis as is conventionally assumed or asserted. From a theoretical point of view the clearest defensible starting point is to view rarefied transport in terms of the phase transitions involved. To wit:

In its barest essence, rarefied sediment transport consists of phase transitions of a granular material: the sublimation (entrainment) and deposition (disentrainment) of the material, where intervening particle motions are directionally biased owing to gravity or fluid forces. This phenomenon occurs at the interface between a granular solid that contains interstitial fluid, and a fluid that intermittently contains the sublimated solid, where individual particles reside only briefly in a state of motion close to the interface. In this view of things the physics of the phase transitions becomes central in describing transport, where the stochastic process of entrainment regulates the availability of particles and the stochastic process of disentrainment modulates the bias of the particle motions via particle--surface interactions. Importantly, these phase transitions do not constitute a continuum behavior.

This point of view acknowledges all attributes of particle motions, start to stop. It highlights that any rigorous kinematic definitions of the particle flux and its divergence necessarily start with a (probabilistic) nonlocal formulation of particle motions. Moreover, this point of view highlights the statistical mechanics of particle--surface interactions in explanations of motions at small scales, and it points to the dominant role of entrainment (i.e. particle availability) in setting transport rates when viewed at large space and time scales, where uncertainties in the factors controlling transport unavoidably increase.
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david jon furbish @davidjonfurbish.bsky.social · 28/03/2025
On this matter, here is an excerpt -- a teaser -- from material I am writing that highlights key aspects of sediment transport, with far reaching implications for approaching theoretical (statistical physics) descriptions of transport at different time scales. 2/2
In its barest essence, rarefied sediment transport consists of a phase transition -- the sublimation (entrainment) and deposition (disentrainment) of a granular material, where transport then refers to the biased motion of the particles when not frozen owing to gravity or fluid forces. This phenomenon occurs at the interface between a granular solid that contains interstitial fluid, and a fluid that intermittently contains the sublimated solid, where individual particles reside only briefly in a state of motion close to the interface. In this view of things the physics of the phase transition becomes central in describing transport, where the stochastic process of entrainment regulates the availability of particles and the stochastic process of disentrainment modulates via particle-surface interactions the bias of the particle motions. Importantly, this phase transition is not a continuum behavior.
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david jon furbish @davidjonfurbish.bsky.social · 18/03/2025
a brief time out during a game of dragon soccer in the front yard… then we gotta put fresh water in the bird bath
tri-color Australian Shepherd standing alert on grassy lawn in afternoon sunlight
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david jon furbish @davidjonfurbish.bsky.social · 02/03/2025
Please see my response in the attachment.
To answer your question, one sees this both as assertions and as being implied ("subliminal").

Here is context, maybe more than you need or want, with specific reference to the broad, essential topic of sediment transport. Because of the complexity of the physics involved in many transport processes (e.g. multiple phases, coupled particle-fluid behavior, etc.), much of the "theoretical framework" actually consists of semi-empirical heuristic engineering that masquerades as physics. This is for quirky historical (epistemic) reasons of the 21st century wherein the Earth/environmental scientists, mostly lacking the background and training to offer critical input/pushback, essentially allowed the engineers to dictate the style of thinking and the trajectory of research. The engineers, with surprisingly little physics beyond basic fluid mechanics (or only hydraulics), mostly aimed at answering problems in an engineering manner rather than trying to achieve a deeper understanding of how transport works. A quick example: Most conventional formulations of sediment transport (e.g. bed load transport in rivers) assume particle motions satisfy continuum conditions. But except possibly for dense granular creep/flow, sediment transport has nothing to do with continuum behavior. And only during the past couple of decades have researchers refocused on developing a clearer understanding of the physics of transport, notably shifting the conversation toward the principles and methods of statistical physics, with explicit attention to uncertainty.

With this context, numerical simulations of, say, riverbed dynamics in response to flow and sediment transport typically involve coupling some form of the shallow-water equations with empirical transport formulae, all in an entirely deterministic manner. These often involve only perfunctory (or no) calibration/validation/etc. with experimental measurements, and rarely address in any formal manner the uncertainties involved in the problem.
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david jon furbish @davidjonfurbish.bsky.social · 12/02/2025
Rowan enjoys hanging out on her couch perch above (and on) my shoulders while I'm reading, knowing that I will occasionally reach back and give her plenty of scratches.
Tri-colored Australian Shepherd resting on the back of a couch above my shoulders as I sit reading.
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david jon furbish @davidjonfurbish.bsky.social · 17/01/2025
An Aussie who excels at Dragon Soccer requires lots of calories and sleep. To wit: serious bone chewing… serious couch snoozing…
Australian Shepherd in downward dog position on a mat holding a bone in her paws while looking at camera.Australian Shepherd sleeping on her back on a couch next to a pillow.
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david jon furbish @davidjonfurbish.bsky.social · 16/01/2025
As a point of reference, meet Rowan the intrepid woof. Together we invented the game of Dragon Soccer involving two soccer balls and a stuffed dragon. The rules are complicated… and fluid. But it seems that whoever controls the dragon controls the game. I’ll be posting numerous pics of Rowan.
Tri-colored Australian Shepherd standing in a grassy field, sunbeams on her back, anxious for me to play with her.
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