granular material

Love, a Footnote
  1. The KGB Bar off 2nd Avenue in New York’s East Village was a gathering place for the Ukrainian Communist Party, which explains the curious décor but not the frequent readings.
  2. Red is evoked by the longest wavelengths of light discernible to the human eye. Red is long; long and slow. The curtains in the KGB Bar are not so much red as a history of red.
  3. “Podium,” from the Latin, often confused with “lectern.” One stands on a podium. One leans one’s elbows or sets one’s beer, beaded with condensation, on the lectern.
  4. In ventriloquism, the speaker’s voice seems to come from elsewhere. This doesn’t explain why he called his poem “The Ventriloquist.” Maybe something about the poet and the reader, but I don’t like trickery, anyway.
  5. We associate red with heat, energy, and blood, and with emotions associated with heat, energy, and blood—such as anger or love. Ezra Pound makes his ideogram of “red” with four signifiers: rose, cherry, iron rust, flamingo. I would use: bark, blood, cardinal, sex. Sex because, like red, it occurs in long, slow waves.
  6. You sat next to me, though I didn’t know you at the time. It was red, dark and red, and there was so much smoke you could see the air moving around people as they moved.
  7. I love words that can inhabit more than one part of speech, as in a match or to match. The phosphorous smell of a just-lit match. Enough light for two faces to share.
  8. Wallace Stegner’s comment about art as the communication of insight appears in various incarnations in his work, but my favorite is in Angle of Repose. You acted surprised that I had such a thought. I took it as a compliment at the time.
  9. In Plato’s Symposium, Diotima tells Socrates how to experience the ideal form of beauty through love. From our desire to possess one body, we sense eternity.
  10. An “angle of repose” is the slope at which granular materials come to rest at, say, the base of a sheer rock face. In Utah, owing to iron rust, the rocks are often red. The process is long, and slow.
  11. As with “match,” one can be patient, or one can be a patient. I have been both, but never at the same time.
  12. Veselka is a Ukrainian diner in the East Village, near St. Mark’s Church. Very good pierogi. Many of the customers have chic glasses, cases for musical instruments, and dirty hair. I like to sit at the counter.
  13. Sake is produced by multiple fermentations of rice. Sometimes it tastes like heavy moonlight, sometimes it tastes like a neon sign that’s just been turned off. In Japan, sake is drunk from small cups called choku. In certain friends’ Lower East Side apartments in December, it is heated in a microwave and drunk from chipped coffee mugs that say things like “Happy Secretary’s Day” and “#1 Dad,” even though the person who lives there is neither a secretary nor a dad.
  14. Feeling is a way of knowing what you’re going to think about something. Example: I felt the thought, I could want you. Emotion as premonition. It is a mystery. It is the ideal form of beauty.

Rebecca Lindenberg

peter and the starcatcher sentence meme
  • "When I was a boy, I wished I could fly."
  • "What? Girls dream."
  • "Nothing is forever. That's the rule. Everything ends."
  • "And so our story begins."
  • "GOD SAVE HER!"
  • "Orphans! Most useless creatures on earth."
  • "I hate, I hate, I hate grown-ups!"
  • "Can you keep a secret?"
  • "Dodo: a fat, clumsy bird, hence the Latin name, Didus ineptus."
  • "Your eyes're green as the sea... and your hair's wavy, too."
  • "Left me widowed at fort--er, thirty."
  • "He fed me worms!"
  • "I'm the leader!"
  • "If you're so smart, how come you're stuck on this dirt-bucket?"
  • "We have important things to do."
  • "Do you write poems about pie?"
  • "Ever notice, ______, the more you claim leadership the more it eludes you?"
  • "Oh snap!"
  • "Oh, for the wings, for the wings of a dove..."
  • "Life is meant to be horrible!"
  • "The thing we did...against impossible odds."
  • "Parrots have taken over your ship? Well, what genius brought parrots--?"
  • "PIRATES! We've been taken over by pirates!"
  • "When you say sand, do you mean the utterly worthless granular material one associates with the water's edge?"
  • "So, bedtime stories? Not a big priority, okay?"
  • "D'ya want some tea?"
  • "How do you eat this?"
  • "WANT THAT TRUNK!"
  • "LASAGNA!"
  • "Sticky pudding. It's so good...."
  • "We're foreigners--that's what we're for!"
  • "You abused the concept of the theatre collective--it was too much for me."
  • "'What kiss', she says."
  • "My bloomers have stood up to stronger wind than this!"
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In a recent video, Practical Engineering tackles an important and often-overlooked challenge in civil engineering: dam failure. At its simplest, a levee or dam is a wall built to hold back water, and the higher that water is, the greater the pressure at its base. That pressure can drive water to seep between the grains of soil beneath the dam. As you can see in the demo below, seeping water can take a curving path through the soil beneath a dam in order to get to the other side. When too much water makes it into the soil, it pushes grains apart and makes them slip easily; this is known as liquefaction. As the name suggests, the sediment begins behaving like a fluid, quickly leading to a complete failure of the dam as its foundation flows away. With older infrastructure and increased flooding from extreme weather events, this is a serious problem facing many communities. (Video and image credit: Practical Engineering)

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When we watch sands running through an hourglass, we think their flow rate is constant. In other words, the same number of grains falls through the neck at the beginning and the end. In many practical granular flows, like those through industrial hoppers (left), this is not the case. Instead, emptying those containers involves a surge near the end where the discharge rate is higher.

The surge is related to the interstitial fluid – the air, water, or other fluid in the space between the grains. On the right, you see an experiment in which brown grains submerged in green-dyed water are emptied. The dark layer is dyed water initially at the top of the grains. As the container drains, that dyed layer moves down more rapidly than the grains; this indicates that the interstitial fluid is actually being pumped by the draining of the grains. Researchers think this is an important factor affecting the final surge. (Image credits: hopper - T. Cizauskas; discharge graph - J. Koivisto and D. Durian, source; research credit: J. Koivisto and D. Durian; submitted by Marc A)

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A drop of water that impacts a flat post will form a liquid sheet that eventually breaks apart into droplets when surface tension can no longer hold the water together against the power of momentum flinging the water outward. But what happens if that initial drop of water is filled with particles? Initially, the particle-laden drop’s impact is similar to the water’s – it strikes the post and expands radially in a sheet that is uniformly filled with particles. But then the particles begin to cluster due to capillary attraction, which causes particles at a fluid interface to clump up. You’ve seen the same effect in a bowl of Cheerios, when the floating O’s start to group up in little rafts. The clumping creates holes in the sheet which rapidly expand until the liquid breaks apart into many particle-filled droplets. To see more great high-speed footage and comparisons, check out the full video.  (Image credit and submission: A. Sauret et al., source)

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Sand dunes form with a gentle incline facing the wind and a steeper slip face pointing away from the wind. Most slip faces are angled at about 30 to 34 degrees–called the angle of repose. The shape is determined by the dune’s ability to support its own weight; add more sand and it will cascade down the slip face in a miniature avalanche. Similarly, if you disturb sand on the slip face by digging a hole at the base, you get the cascading collapse seen in this video. By removing sand, the dune’s equilibrium is broken and it can no longer support its weight. This makes sand flow down the slip face until enough is shifted that the dune can support itself. Being a granular material, the sand itself appears to flow much like a fluid, with waves, ripples and all. (Video credit: M. Meier; submitted by Boris M.)

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Many of us have played with sand art–the rotating frames filled with water, sand, and air. In this video, Shanks FX demonstrates some of the realistic and surrealistic landscapes you can create using this toy. It also makes for a neat fluid dynamics demonstration. The buoyancy of the trapped air bubbles lets the sand sift slowly down instead of falling immediately. And the sand descends in a variety of ways–sometimes laminar columns and other times wilder turbulent plumes. (Video credit and submission: Shanks FX/PBS Digital Studios)

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Researchers develop exoskeleton device for walking efficiency - Check it out!

Science Now 33-In this week’s episode we learn about an app to detect depression, walking efficiency, how babies learn from surprise and finally we explore how high-tech tools are helping researcher better understand how granular materials like snow and sand behave.

By: National Science Foundation.

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Soil liquefaction is a rather unsettling process in which apparently solid ground begins moving in a fluid-like way after agitation. It occurs in loose sediments when the spaces between individual particles become nearly saturated with water. This can happen, for example, after heavy rains or in a place with inadequate drainage. Such cases are typically very localized, though, and require some significant agitation of the surface, like pressing with heavy machinery or jumping in a single spot. Soil liquefaction becomes a greater danger, however, in an earthquake. Even in a dry area, the earth’s shaking can force groundwater up into the surface sediment and vibrate the soil sufficiently to liquify it, causing whole buildings to sink or tip and wreaking havoc on manmade infrastructure. (Video credit: jokulhlaups)

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Hourglasses are pretty common, but you’ve probably never given much thought to the way they flow. An hourglass designer has to carefully select the sizing of the neck and the grains. Choosing a neck that’s too small relative to the grain size will result in frequent clogs but choosing too large a neck will make setting the timing difficult. Interestingly, it doesn’t matter whether the hourglass is filled with air or with water–the same principle holds. 

Where this knowledge becomes especially useful, though, is when dealing with crowds. We’ve all experienced the frustration of being in a large crowd trying to fit through a small exit. Paradoxically, the fastest way to get a large number of particles (or sheep or people) through a narrow opening is to slow each individual down. This can either be done by instructing everyone to slow down or by forcing that same result by placing an obstacle immediately before the exit. The reduction in speed reduces clogging, which means everyone gets through faster! (Video credit: A. Marin et al.)

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Granular materials like sand are sometimes very fluid-like in their behaviors. The high-speed video above shows a ball bearing being dropped into packed sand. Many features of the splash are fluid-like; the initial impact creates a spreading crownlike splash, followed by a strong upward jet that eventually collapses back into the medium. At the same time, many of the impact characteristics are decidedly non-fluidic. Sand has no surface tension, so both the crown and the jet readily break up into small particles. The granular jet is very narrow and energetic, reaching heights greater than the impacter’s drop height. Interestingly, the column begins collapsing on its lower end before the jet even reaches its highest peak. This may be due to the lower energy of the sand particles that were ejected later in the crater formation process. (Video credit: J. Verschuur, B. van Capelleveen, R. Lammerink and T. Nguyen)

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Sometimes the similarity between fluid flow and granular flows is quite striking. This video shows a stream of sand falling down a tube and impacting a rod. (Note: the view is rotated 90 degrees counter-clockwise, so down points to the right.) As the sand strikes the rod, it’s deflected into a conical sheet, very much like a water bell. There are even ripple-like instabilities that form in the granular sheet, though they move differently than in a liquid due to the sand’s lack of surface tension. (Video credit: S. Nagel et al.)

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When a fluid is vibrated, instabilities can form along its surface. With a sufficient amplitude, voids form inside the fluid and their collapse leads to a jet that shoots out from the fluid. A very different process leads to air cavities forming in a vibrated granular medium, but the jets produced are remarkably similar, as seen in this video. (Video credit: M. Sandtke et al.)

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In a stream of falling liquid, surface tension instabilities cause the fluid to break up into droplets. This video shows a similar experiment with a stream of glass beads, a granular material. The whole system is housed under a vacuum to eliminate the effects of air drag on the stream, and a camera rides alongside the stream to track the evolution of the falling material in a Lagrangian fashion. As with a liquid stream, we see the granular flow develop undulations as it falls, ultimately breaking up into clusters of beads. The authors suggest that nanoscale surface roughness and van der Waals forces may be responsible for the clustering behavior in the absence of surface tension. (Video credit: J. Royer et al.)

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The recently released music video for Jack White’s “High Ball Stepper” is a fantastic marriage of science and art. The audio is paired with visuals based around vibration effects using both granular materials and fluids. There are many examples of Faraday waves, the rippling patterns formed when a fluid interface becomes unstable under vibration. There are also cymatic patterns and even finger-like protrusions formed by when shear-thickening non-Newtonian fluids get agitated. (Video credit: J. White, B. Swank and J. Cathcart; submitted by Mike and Marius)