I’m announcing two new global feeds: a redesigned Global Shared Stories and a new feed called Good Reads.
Redesigned Global Shared Stories
Global Shared Stories has been in the sidebar for years, and for years it worked in a way I never liked. It was not the shares of everybody on NewsBlur. It was the shares of the accounts that the @popular account happened to follow, a list I put together by hand a long time ago and rarely touched. If you were on that list and you shared a lot, you decided what everybody else saw. If you shared one story a month and wrote a paragraph about why it mattered, you were drowned out by someone who shared thirty without a word.
So I rebuilt it. Every hour, NewsBlur now gathers every story shared across the whole site in the last few hours, caps each person at three so nobody can flood the pool, drops private blurblogs, and then picks a few worth reading. The picks accumulate, so the river stays deep enough to scroll back through.
The picking is done by Claude Haiku, once an hour, and it is worth being precise about what it does and does not do. It does not go looking for stories. It does not write anything. It only ranks stories that NewsBlur readers already chose to share, and the thing it weighs most heavily is the comment the sharer wrote, because a share with a few sentences attached is a share somebody thought about. It is allowed to pick nothing at all in a quiet hour, and in testing it regularly passes on half of what it is offered. If the API is ever unreachable, a plain heuristic takes over and the river keeps flowing.
Good Reads
The new feed in the sidebar is Good Reads, and it asks a question the other feeds do not: which stories did somebody finish and then do something about?
A story lands in Good Reads when at least two people read it closely, thirty seconds or more, and at least one of them then saved it, shared it, or trained it up. Finishing is not enough. Somebody has to have bothered to act. On top of that, the score is tilted toward feeds with few subscribers, so a story from a site with forty readers can beat a story from a site with forty thousand. That tilt is the whole point. The big sites do not need help getting seen.
Four feeds, four questions
There are now four curated rivers sitting together in the sidebar, and the reason there are four and not one is that they each answer a different question.
Global Shared Stories asks what people chose to hand to someone else. It runs on sharing, a deliberate human act.
Widely Read Stories asks what held the most attention across NewsBlur. It runs on reading time, not clicks, so a headline nobody read cannot buy its way in.
Long Reads asks what was worth an afternoon. Features and essays that readers gave real time to, rather than skimmed.
Good Reads asks what somebody finished and then kept, and leans toward the small sites you have probably never heard of.
Widely Read Stories and Long Reads have been around since April, and I wrote about how they work when they launched. None of the four ranks by clicks, and none of them is trying to keep you scrolling. They are all built out of what NewsBlur readers actually did with their time.
Because it was never obvious from looking at them which was which, each of the four now explains itself in a line at the top of its story list. It scrolls away with the stories, so it is there when you arrive and gone once you are reading.
Your classifiers still apply to all four. If you have trained a tag, an author, or a site, those green and red scores carry through, including on stories from feeds you do not subscribe to. And all four work as dashboard rivers, so you can park any of them next to your regular feeds.
Good Reads and the rebuilt Global Shared Stories are available now on the web. If a story shows up in one of these feeds that clearly should not have, I want to hear about it on the NewsBlur forum.
Researchers thought that what enabled complex fluids to break apart was their elasticity. But a crack in a nonelastic simple fluid has them questioning that idea.
When pulled at 100 millimeters per second, a blend of hydrogen and carbon stretches. At 300 millimeters per second, the fluid breaks.
Thamires Lima, a research professor in chemical engineering at Drexel University, studies the properties of thick, viscous liquids — think honey or molasses, though in a lab you’re more likely to find polypropylene or crude oil. Using a method called extensional rheology, Lima stretches liquids between metal plates to find the force that makes them flow.
A few years ago, she was conducting a test as part of a project in collaboration with the oil and gas company Exxon Mobil when she heard a short, sharp crack. “I thought it was the machine,” Lima said. But the crack came from the fluid that the machine was pulling: a gooey, black blend of hydrogen and carbon. Instead of stretching, the fluid had fractured.
Fractures are known to occur in certain elastic complex fluids, which can act like solids under certain conditions. But Lima was working with a nonelastic simple fluid. Even with almost no elasticity, it snapped apart under stress.
“Nobody expected that this would be possible in this kind of simple fluid because viscosity usually just rearranges the molecules,” said Arnold Mathijssen, a fluid physicist at the University of Pennsylvania. “You don’t expect it to crack. But it does, so I think that’s what’s really surprising.”
A Brittle Break
Lima stretched the liquid again and again to prove that the unexpected crack wasn’t a one-off. “Every time that she measured it, the material would break,” said Nicolas J. Alvarez, the professor of chemical engineering at Drexel University whose lab led the research. “It makes a loud pop. I mean, like you just took a rubber band and pulled it and stretched it and it snapped.”
Convinced the snap wasn’t a fluke, Lima and Alvarez used high-speed cameras to look at the phenomenon more closely. They realized that the break was essentially a “brittle fracture,” the kind you might see when you drop a dish made of glass or porcelain.
Brittle fractures happen to brittle solids, which have elasticity. Apply some stress to glass or porcelain and it deforms a very tiny bit, and then — if you don’t push it past its breaking point — it springs back to normal once the stress is removed. However, solids are never perfect. In most cases, a brittle solid will have a teeny, tiny defect — a crack at the scale of tens of nanometers. Once the solid is stressed past a critical point, it becomes energetically more favorable for the solid to grow the crack than to elastically store the stress. At that point, the crack grows catastrophically, rapidly breaking the solid apart.
Some complex fluids, called viscoelastic liquids, also have elasticity. For example, polymer melts — melted versions of the polymers in plastics — are made up of long chains of molecules, which become entangled with one another and increase the material’s elastic component.
In a 2016 Physical Review Letters paper, Alvarez and colleagues showed that complex fluids like melted polystyrene can fracture in the same way that solids sometimes do. “We just thought elasticity was something that was a prerequisite for such solid type of breaking, right?” Alvarez said. As a result, they theorized that elasticity was related to the fracture of liquids as well.
But the hydrocarbon blend that Lima was working with was a simple fluid. Simple fluids don’t store much elastic energy. And when they are pushed or pulled past their limits, they don’t usually bend or break — they flow.
So perhaps the old theory about what makes a liquid fracture is wrong. “If there is no elasticity in a problem, then how can you think about initiation or growth of a crack?” said Brato Chakrabarti, a physicist who works on fluid mechanics at the International Center for Theoretical Sciences in Bengaluru, India.
The cracking of the hydrocarbon blend made the researchers look back at the papers of Daniel D. Joseph, a mechanical engineer at the University of Minnesota. In 1995 and 1998, Joseph suggested that any liquid, regardless of how elastic it is, could fracture under a sufficient amount of tearing stress.
Alvarez wonders if the breaking point of a liquid is related not to a property like elasticity, but to something more fundamental to the liquid’s structure. “Maybe, just maybe, the thing that causes [certain] fluids to break … [is] somehow related to this cohesive energy that holds the molecules together,” he said.
A Burst Bubble
Simple fluids do have a way of relieving stress, no breaking required: They form intermolecular voids (bubbles) in a process called cavitation.
If the blades of a propeller spin rapidly in a simple fluid, for example, the fluid on one side of the blade can slosh much faster than the fluid on the other, leading to a drop in pressure on that side. This drop can cause the liquid to cavitate. Engineers work to avoid this, because once those bubbles collapse, they generate shock waves that can damage propellers and pumps.
In his papers in the ’90s, Joseph predicted that cavitation would allow simple fluids to fracture.
“If you think about what holds a fluid together, it’s cohesiveness, or the intermolecular interactions between the molecules,” Alvarez said. If you pull those molecules apart, you can create a bubble. Usually, viscous liquids stay cohesive when bubbles form, by changing shape around them. But if enough bubbles form in quick succession, they could theoretically crack a liquid like a pane of glass.
At Drexel, the researchers found that once a crack nucleates inside a simple fluid, it propagates extremely fast, precisely because the fluid is not elastic. “If you can get that nucleation event of the crack to begin, because there is no elasticity in the material, that crack can propagate as fast as physics will allow it,” Alvarez said.
In previous work on complex fluids, the Drexel researchers found that cracks in melted polystyrene propagate at approximately 0.07 meters per second. In their new study, Lima and colleagues showed that cracks propagate far more rapidly in the simple liquids they studied, reaching velocities of approximately 500 to 1,500 meters per second.
“That has something to do with the way that the material is able to dissipate energy,” Alvarez said. According to one hypothesis, in a complex fluid, energy is absorbed by the long chains of molecules as they break. But in a simple fluid, “there’s really nothing to slow that crack down,” he said.
This seems to affect the shape of the crack, which in complex fluids looks like the horn of a trumpet and in simple fluids looks like a crack moving through glass, the researchers found.
How To Crack a Liquid
Surprisingly, despite their different ways of cracking, both the complex fluids and the simple fluids that researchers tested tended to fracture at the same critical measure of stress: 2 megapascals. The researchers varied the temperature of the hydrocarbon blend — a simple fluid — to change its viscosity and found that only the least viscous liquid they tested failed to fracture. The team observed that the critical stress level at which liquids fracture is proportional to their viscosity times the strain rate (how quickly they are being pulled or stretched apart and how the diameter of the liquid is changing).
The machine had a limit — albeit a high one — to how quickly it could move: 500 millimeters per second. “There are very few instruments comparable to ours,” Lima said. Lima thinks that potentially, if they had a machine that could pull on the liquids faster, they could fracture less viscous liquids like honey or even water.
In the future, Lima wants to use a more transparent liquid so she can capture the crack as it forms. She would also like to try freezing the surface of the liquid as soon as it snaps and to probe it using a high-resolution microscope that scans surfaces at a nanometer scale.
Alvarez is keen to explore simple fluids in the context of spinning materials into fibers — which can have applications in engineering and medicine. Fractures in fluids could also have implications for inkjet printing, brain injury protection, and soft robotics.
But Alvarez is most excited to learn what it means for a simple fluid to fracture in the first place. “[It’s] different than what we’ve been thinking about in the literature for a very long time,” he said.
How do you speed up computational Python code? A common, and useful,
starting point is:
Pick a good algorithm.
Use a compiled language to write a Python extension.
Maybe add parallelism so you can use multiple CPU cores.
But what if you need more speed? Consider the following real problem,
one of the steps in scikit-learn’s gradient histogram boosting
algorithm:
You have a large array of floating point numbers.
You want to assign them to the integer range 0-254, spread out evenly.
scikit-learn implements this by splitting up the full range of float
values into 255 buckets, creating a sorted array of bucket boundaries,
and then using binary search to choose the appropriate bucket for each
value. The binary search is implemented in a compiled language, and it
can run in parallel on multiple cores.
Recently, as part of my work at
Quansight, and inspired by
twoposts
by Paul Khuong, I sped up this implementation significantly. How? By
making sure the code wasn’t fighting against the CPU.
In this article I’m going to walk you through that speed-up,
demonstrated on a simplified example. Then I’m going to demonstrate a
series of additional optimizations, with the final version running 6×
faster than the original one.
It’s worth knowing that I will be speeding through mentions of many
different low-level hardware topics: instruction-level parallelism,
branch (mis)prediction, memory caches, SIMD, and more. This is only one
article, it can only briefly introduce you to what’s possible, it can’t
function as an in-depth tutorial. So I’ll talk about how you can learn
more about these topics at the end of the article.
The Ferrari Luce will start at €550,000 in Italy, but US pricing hasn’t been announced. | Image: Ferrari
After months of teasers, Ferrari is offering the first full view of its Luce electric vehicle. The Luce is notable not just for being Ferrari's first EV, but for being designed in collaboration with Jony Ive and Mark Newson at their collective LoveFrom. It's also going to be Ferrari's second four-door car and its first five-seat one.
We already knew Ive and Newson were working on the Luce's interiors, which were shown off earlier this year. Now Ferrari says LoveFrom was allowed to "define the design direction of the project from the outset," inside and out.
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Global Shared Stories asks what people chose to hand to someone else. It runs on sharing, a deliberate human act.
Widely Read Stories asks what held the most attention across NewsBlur. It runs on reading time, not clicks, so a headline nobody read cannot buy its way in.
Long Reads asks what was worth an afternoon. Features and essays that readers gave real time to, rather than skimmed.
Good Reads asks what somebody finished and then kept, and leans toward the small sites you have probably never heard of.
