A reader shares a report from SciTechDaily: MIT mathematicians and engineers have developed a mathematical model that predicts how stable a knot is, based on several key properties, including the number of crossings involved and the direction in which the rope segments twist as the knot is pulled tight. "These subtle differences between knots critically determine whether a knot is strong or not," says Jorn Dunkel, associate professor of mathematics at MIT. "With this model, you should be able to look at two knots that are almost identical, and be able to say which is the better one." "Empirical knowledge refined over centuries has crystallized out what the best knots are," adds Mathias Kolle, the Rockwell International Career Development Associate Professor at MIT. "And now the model shows why."
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In comparing the diagrams of knots of various strengths, the researchers were able to identify general "counting rules," or characteristics that determine a knot's stability. Basically, a knot is stronger if it has more strand crossings, as well as more "twist fluctuations" -- changes in the direction of rotation from one strand segment to another. For instance, if a fiber segment is rotated to the left at one crossing and rotated to the right at a neighboring crossing as a knot is pulled tight, this creates a twist fluctuation and thus opposing friction, which adds stability to a knot. If, however, the segment is rotated in the same direction at two neighboring crossing, there is no twist fluctuation, and the strand is more likely to rotate and slip, producing a weaker knot. They also found that a knot can be made stronger if it has more "circulations," which they define as a region in a knot where two parallel strands loop against each other in opposite directions, like a circular flow.

By taking into account these simple counting rules, the team was able to explain why a reef knot, for instance, is stronger than a granny knot. While the two are almost identical, the reef knot has a higher number of twist fluctuations, making it a more stable configuration. Likewise, the zeppelin knot, because of its slightly higher circulations and twist fluctuations, is stronger, though possibly harder to untie, than the Alpine butterfly -- a knot that is commonly used in climbing. The findings have been published in the journal Science.

An anonymous reader quotes a report from TechCrunch: "We want to miniaturize accelerator technology in a way that makes it a more accessible research tool," explained project lead Jelena Vuckovic in a Stanford news release. But this wasn't designed like a traditional particle accelerator like the Large Hadron Collider or one at collaborator SLAC's National Accelerator Laboratory. Instead of engineering it from the bottom up, they fed their requirements to an "inverse design algorithm" that produced the kind of energy pattern they needed from the infrared radiation emitters they wanted to use. That's partly because infrared radiation has a much shorter wavelength than something like microwaves, meaning the mechanisms themselves can be made much smaller -- perhaps too small to adequately design the ordinary way. The algorithm's solution to the team's requirements led to an unusual structure that looks more like a Rorschach test than a particle accelerator. But these blobs and channels are precisely contoured to guide infrared laser light pulse in such a way that they push electrons along the center up to a significant proportion of the speed of light.

The resulting "accelerator on a chip" is only a few dozen microns across, making it comfortably smaller than a human hair and more than possible to stack a few on the head of a pin. A couple thousand of them, really. And it will take a couple thousand to get the electrons up to the energy levels needed to be useful -- but don't worry, that's all part of the plan. The chips are fully integrated but can be put in a series easily to create longer assemblies that produce larger powers. These won't be rivaling macro-size accelerators like SLAC's or the Large Hadron Collider, but they could be much more useful for research and clinical applications where planet-destroying power levels aren't required. For instance, a chip-sized electron accelerator might be able to direct radiation into a tumor surgically rather than through the skin. The findings have been published in the journal Science.

By the end of August 2019, the entire pig population of China had dropped by about 40 percent. China accounted for more than half of the global pig population in 2018, and the epidemic there alone has killed nearly one-quarter of all the world's pigs. From a report: By late September, the disease had cost economic losses of one trillion yuan (about $141 billion), according to Li Defa, dean of the College of Animal Science and Technology at China Agricultural University in Beijing. Qiu Huaji, a leading Chinese expert on porcine infectious diseases, has said that African swine fever has been no less devastating "than a war" -- in terms of "its effects on the national interest and people's livelihoods and its political, economic and social impact." "We lost hundreds of thousands of yuan," my sister-in-law bemoaned, several tens of thousands of dollars. "Haven't you been compensated by the government for the dead pigs?" I asked. "Only 100 yuan per head," less than $15, she said, "That didn't help."

Tens of thousands of Australians are fleeing their homes as hundreds of fires rage across the continent's southeast coast. And yes, climate change is almost certainly to blame for the extent of the disaster. From a report: With more than a thousand buildings destroyed and 17 deaths since October, it already ranks as one of the worst fire seasons in Australia's history -- and summer there has barely begun. What's driving the fires? Summer wildfires are common in Australia, but climate change is making them worse. Spring rainfall has declined in recent decades, even as temperatures rise, extreme heat events become more common, and droughts turn more severe, according to a 2018 report by Australia's Bureau of Meteorology. Those forces have contributed to a greater number of days with "very high fire dangers," and helped extend the fire season into spring.

Music is an ideal medium for interstellar communication. From a report: Each summer for the past 25 years, tens of thousands of people have flocked to Barcelona, Spain, to witness Sonar, a three-day festival dedicated to electronic music, art, and design. To celebrate Sonar's 25th anniversary in 2018, the festival partnered with the Catalonia Institute for Space Studies and the nonprofit METI International to send a series of interstellar messages to Luyten's star, a red dwarf about 12 light-years from Earth. Although red dwarfs are the most common stellar objects in our galaxy, Luyten's star is remarkable for hosting GJ237b, the closest potentially habitable planet outside of our own solar system. No one knows for sure whether GJ237b hosts life, intelligent or otherwise, but if ET does call the planet home, Sonar wants to rock its socks off. Over the course of several nights in late 2017 and early 2018, a radar system in Tromso, Norway, blasted a custom message from Sonar toward GJ237b. Like any good correspondence, the message began with a greeting: In this case, the first 33 prime numbers repeated on two alternating radio frequencies functioned as a stand-in for "hello."

This was followed by a brief tutorial that the message designers hoped would teach ET to extract the music written by Sonar-affiliated musicians and embedded in the message. [...] The Sonar messages are unique insofar as they are the only interstellar transmissions to use songs designed by musicians specifically for communicating with ET. That the messages include a substantial information content places them firmly in the tradition of messaging extraterrestrial intelligences, or METI, a term coined by the Russian radio astronomer Alexander Zaitsev to differentiate the practice from other modes of interstellar communication. The Search for Extraterrestrial Intelligence, or SETI, is focused on listening for ET signals rather than sending them, and "active SETI" is about creating beacons that lack information but signal to alien intelligences that we exist.

A computer made from strands of DNA in a test tube can calculate the square root of numbers up to 900. New Scientist reports: Chunlei Guo at the University of Rochester in New York state and colleagues developed a computer that uses 32 strands of DNA to store and process information. It can calculate the square root of square numbers 1, 4, 9, 16, 25 and so on up to 900. The DNA computer uses a process known as hybridization, which occurs when two strands of DNA attach together to form double-stranded DNA.

To start, the team encodes a number onto the DNA using a combination of ten building blocks. Each combination represents a different number up to 900, and is attached to a fluorescence marker. The team then controls hybridization in such a way that it changes the overall fluorescent signal so that it corresponds to the square root of the original number. The number can then be deduced from the color. The DNA computer could help to develop more complex computing circuits, says Guo. Guo believes DNA computers may one day replace traditional computers for complex computations. The findings have been published in the journal Small.

Doctor Stephan Moll, a blood-clot expert from the University of North Carolina, helped develop a treatment plan for a NASA astronaut who discovered a blood clot in the jugular vein partway through a long-term mission on the International Space Station. CNET reports: NASA hasn't revealed the crew member's name or when the incident happened, though the astronaut discovered the clot two months into a six-month mission while getting a neck ultrasound for a research study. Moll and a NASA medical team chose to treat the clot with blood thinners. The limited on-board supply of medicine required carefully meting out the dose until a fresh cargo shipment arrived from Earth.

The astronaut went through about 40 days of injections before switching to an oral pill. The NASA crew member discontinued the pills shortly before returning to Earth and required no follow-up treatment for the clot. Moll co-authored a case study on the clot published in the The New England Journal of Medicine on Thursday.