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davidjonfurbish.bsky.social
david jon furbish
@davidjonfurbish.bsky.social
130 followers 79 following 290 posts
granddad and emeritus professor studying statistical physics of sediment transport & science philosophy

essays on these topics: https://my.vanderbilt.edu/davidjonfurbish/

author of Fluid Physics in Geology: https://academic.oup.com/book/40895?login=false
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davidjonfurbish.bsky.social
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 me pic of underside of toy stuffed dragon showing white belly and green tail, with stitches closing the (previous) tear between the butt and tail
October 15, 2025 at 8:16 PM
davidjonfurbish.bsky.social
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
October 2, 2025 at 6:49 PM
davidjonfurbish.bsky.social
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 paws tri-color Australian Shepherd laying in grassy lawn with toy stuffed dragon between her front paws
September 21, 2025 at 2:10 PM
davidjonfurbish.bsky.social
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
September 3, 2025 at 3:53 PM
davidjonfurbish.bsky.social
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.
August 14, 2025 at 7:17 PM
davidjonfurbish.bsky.social
“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
August 7, 2025 at 11:33 AM
davidjonfurbish.bsky.social
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.}
August 1, 2025 at 11:04 PM
davidjonfurbish.bsky.social
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
July 22, 2025 at 8:40 PM
davidjonfurbish.bsky.social
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
July 18, 2025 at 6:22 PM
davidjonfurbish.bsky.social
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
June 13, 2025 at 12:06 AM
davidjonfurbish.bsky.social
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 boardwalk Boardwalk next to small river, on a sunny day with tree shadows on boardwalk
May 30, 2025 at 8:28 PM
davidjonfurbish.bsky.social
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
May 14, 2025 at 7:20 PM
davidjonfurbish.bsky.social
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
May 13, 2025 at 2:55 PM
davidjonfurbish.bsky.social
🙄
🥱🥱
😴😴😴
so-called stream power erosion model with diffusion-like term that is purported to describe evolution of the land-surface elevation h
April 30, 2025 at 10:28 PM
davidjonfurbish.bsky.social
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 bowls adult Golden Retriever dog sitting in green grass looking at camera
April 22, 2025 at 10:07 PM
davidjonfurbish.bsky.social
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.
April 11, 2025 at 4:29 PM
davidjonfurbish.bsky.social
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.
April 11, 2025 at 3:39 PM
davidjonfurbish.bsky.social
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.
March 28, 2025 at 7:10 PM
davidjonfurbish.bsky.social
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
March 18, 2025 at 8:57 PM
davidjonfurbish.bsky.social
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.
March 2, 2025 at 10:33 PM
davidjonfurbish.bsky.social
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.
February 12, 2025 at 2:58 AM
davidjonfurbish.bsky.social
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.
January 17, 2025 at 3:54 PM
davidjonfurbish.bsky.social
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.
January 16, 2025 at 1:39 AM