Tying a knot in a smoke ring sounds like a feat worthy of those enjoying a certain kind of cigarette. But treat smoke as an example of a fluid, and it becomes a physics problem.
Now for the first time a fluid knot has been created – from water rather than smoke. The achievement will allow us to probe what had been theoretical objects, and this might in turn lead to better models of airflow around aircraft wings, or of strange quantum substances like superfluids.
Unlike the knots in your shoelaces, the knots that physicists and mathematicians talk about are closed entanglements that cannot be untied as they have no ends. The simplest of these are the trefoil, a loop that crosses itself three times, and the Hopf link, two linked loops.
The idea of a knot made of fluid first cropped up in the 1860s when the mathematical physicist Lord Kelvin suggested that atoms might be knots in the ether – a mysterious fluid then thought to permeate the entire universe. That idea fell flat, but since then, knots have become central to many aspects of science, from mathematics to biology. And that has led to renewed interest in the idea of a fluid knot.
Mathematicians have shown that just as knots in string can't be untied no matter how much you prod and pull them, fluid knots should also never unravel – even though the particles that make up the fluid will be circulating around. But this non-unravelling property only applies if the knot is made of a theoretical "ideal fluid", one that has no viscosity – in other words, no resistance to flow. How a knot in a real fluid such as smoke or water would evolve is unknown, as is whether these structures exist in nature or in the plumes created by machines such as aircraft.
To investigate, Dustin Kleckner and William Irvine of the University of Chicago, Illinois 3D-printed strips of plastic shaped into a trefoil knot and a Hopf link. Crucially, the strips had a cross section shaped like a wing, or hydrofoil (see picture).
Next, the researchers dragged the knots through water filled with microscopic bubbles. Just as a wing passing through air creates a trailing vortex, the acceleration of the hydrofoils created a knot-shaped vortex that sucked in the bubbles. The result was a knot-shaped flow of moving bubbles – the first fluid knot created in a lab – which the team imaged with lasers.
Once formed, the knots move, rotate and eventually appear to dissipate, though whether the vortices completely unknot, unlike in ideal fluids, or somehow preserve the knottedness but in a more diffuse form remains an open question.
It should be possible to create knotted smoke rings using a similar technique, as a smoke ring is simply a vortex in air containing trapped particles of smoke. However, in water, the rings stick around for longer, making them easier to study.
Kleckner and Irvine are now investigating whether they can make more complicated knots. "We don't think there is a fundamental limit: we're trying to make all sorts of things," says Irvine.
Studying water knots could improve understanding of other kinds of vortices, such as those that come off aircraft wings. "People can do simulations to model these problems, but there's always the issue of knowing whether the simulation is right," says Irvine.
Knotted vortices might also show up naturally, for example in mysterious superfluids. These frictionless quantum fluids have been created in the lab by cooling helium to near absolute zero and are thought to exist inside neutron stars. Creating knots in water provides an easier way to study their quantum cousins, as the lasers used to image the knots would heat up a superfluid, destroying its properties.
Being able to both create and image these knots is impressive, says Mark Dennis at the University of Bristol, UK. "Kelvin spent a long time trying to understand how vortex knots would flow in fluids, and since then experimentalists have tried to realise his idea." Now theory and experiment have come full circle, which should help with further study of both knots and fluids, he says.
SternisheFan writes: "Shaun McGlaun of Slashgear writes:
If you’ve ever studied genetics in school or college, you’ll know that the structure of DNA is a double helix. You likely know that DNA carries all of our genetic code. While traditionally we think of only double helix DNA, scientists from Cambridge University in England have made an interesting discovery.
According to the researchers, a quadruple helix is also present in some cells and is believed to relate to cancer in some ways. According to the researchers, controlling these quadruple helix structures could provide new ways to fight cancer. The scientists believe the quadruple helix may form when the cell has a certain genotype or operates in a certain dysfunctional state.
Scientists have been able to produce quadruple helix material in test tubes for years. The material produced is called the G-quadruplex. The G refers to guanine, which is one of the base pairs that hold DNA together. The new research performed at the University is believed to be the first to firmly pinpoint quadruple helix in human cells.
The team of scientists were able to produce specific antibody proteins designed to track down and find to regions of human DNA rich in the quadruplex structure. The antibodies were tagged with a florescence marker so the emergence of the structures in the cell could be tracked and imaged. The researchers were able to determine that most frequent occurrence of the quadruple helix DNA arose during the “S-phase” when a cell copies DNA prior to dividing. The G-quadruplex could be implemented in the development of some cancers according to the researchers and they believe that it could be possible to make synthetic molecules that contain the structure and block the runaway cell proliferation that cause tumors.
“The existence of these structures may be loaded when the cell has a certain genotype or a certain dysfunctional state,” said Prof Shankar Balasubramanian from Cambridge’s department of chemistry.
“We need to prove that; but if that is the case, targeting them with synthetic molecules could be an interesting way of selectively targeting those cells that have this dysfunction,” he told BBC News."
SternisheFan writes: ArsTechnica' John Timmons writes:
Over the past decades, researchers have made significant progress in cooling objects closer to absolute zero, the temperature at which all molecular motion reaches its minimum. This has allowed them to study unusual states of matter, like Bose-Einstein condensates, which behave quite differently from the materials we're familiar with. But absolute zero is as low as a temperature can get, and we can't actually reach it, so progress will ultimately be limited.
As thermodynamics defines temperature, it's theoretically possible to have a negative value. Yesterday, a team of German researchers reported that they were actually able to produce a system with exactly that. They found that the negative temperature system was stable for hundreds of milliseconds, raising the prospect that we can study a radically different type of material.
SternisheFan writes: Dr. Rita Levi-Montalcini discovered chemical tools the body uses to direct cell growth and build nerve networks. By BENEDICT CAREY of The New York Times: December 30, 2012 Dr. Rita Levi-Montalcini, a Nobel Prize-winning neurologist who discovered critical chemical tools that the body uses to direct cell growth and build nerve networks, opening the way for the study of how those processes can go wrong in diseases like dementia and cancer, died on Sunday at her home in Rome. She was 103. Her death was announced by Mayor Gianni Alemanno of Rome.
“I don’t use these words easily, but her work revolutionized the study of neural development, from how we think about it to how we intervene,” said Dr. Gerald D. Fishbach, a neuroscientist and professor emeritus at Columbia.
Scientists had virtually no idea how embryo cells built a latticework of intricate connections to other cells when Dr. Levi-Montalcini began studying chicken embryos in the bedroom of her house in Turin, Italy, during World War II. After years of obsessive study, much of it at Washington University in St. Louis with Dr. Viktor Hamburger, she found a protein that, when released by cells, attracted nerve growth from nearby developing cells.
In the early 1950s, she and Dr. Stanley Cohen, a biochemist also at Washington University, isolated and described the chemical, known as nerve growth factor — and in the process altered the study of cell growth and development. Scientists soon realized that the protein gave them a new way to study and understand disorders of neural growth, like cancer, or of degeneration, like Alzheimer’s disease, and to potentially develop therapies.
In the years after the discovery, Dr. Levi-Montalcini, Dr. Cohen and others described a large family of such growth-promoting agents, each of which worked to regulate the growth of specific cells. One, called epidermal growth factor and discovered by Dr. Cohen, plays a central role in breast cancer; in part by studying its behavior, scientists developed drugs to combat the abnormal growth.
In 1986, Dr. Levi-Montalcini and Dr. Cohen shared the Nobel Prize in Physiology or Medicine for their work.
Dr. Cohen, now an emeritus professor at Vanderbilt University, said Dr. Levi-Montalcini possessed a rare combination of intuition and passion, as well as biological knowledge. “She had this feeling for what was happening biologically,” he said. “She was an intuitive observer, and she saw that something was making these nerve connections grow and was determined to find out what it was.”
SternisheFan writes: "The Huffington Post's Cara Santa Maria has an alternate take on a story that's been written about by many science sites of late, whether our 'reality' could really just be a computer simulation.
"Have you ever wondered whether all this--you, your life, the universe--is just a sophisticated computer simulation? Martin Savage, a physicist at the University of Washington, thinks we can't discount the idea. In fact, he and two colleagues (Silas Beane and Zohreh Davoudi) published a paper in November 2012 exploring the possibility. I spoke to him about why he thinks we may be the byproduct of some sophisticated computer code. As we spoke, I noticed he used the word they a lot, when referencing the proposed simulators. I couldn't help but ask, "who is they?" His answer will blow your mind. To hear what he had to say, watch the video..." "... or read the script...""
SternisheFan writes: The BBC reports: The University of Utah researchers used instruments to measure the forces and acceleration when martial artists hit a punch bag. They found that the structure of the fist provides support that increases the ability of the knuckles to transmit "punching" force. Details have been published in the Journal of Experimental Biology. "We asked the question: 'can you strike harder with a fist than with an open palm?'," co-author David Carrier told BBC News.
"We were surprised because the fist strikes were not more forceful than the strikes with the palm. In terms of the work on the bag there is really no difference." Of course, the surface that strikes the target with a fist is smaller, so there is more stress from a fist strike. "The force per area is higher in a fist strike and that is what causes localised tissue damage," said Prof Carrier. "There is a performance advantage in that regard. But the real focus of the study was whether the proportions of the human hand allow buttressing (support)." The team found that making a clenched fist did indeed provide protective buttressing for the delicate bones of the hand. Making a fist increased the stiffness of the second meta-carpo-phalangeal, or MCP, joint (these joints are the knuckles visible when the hand is clenched as a fist) by a factor of four. It also doubled the ability of the proximal phalanges (the bones of the fingers that articulate with the MCP joints) to transmit a punching force
SternisheFan writes: Physicists propose experiment to test hypothesis that reality is just a computer simulation.
Originally published: Dec 14 2012 — 5:00pm
By: Joel N. Shurkin, ISNS Contributor
(ISNS) — What if everything — all of us, the world, the universe — was not real? What if everything we are, know and do was really just someone's computer simulation? The notion that our reality was some kid on a couch in the far future playing with a computer game like a gigantic Sim City, or Civilization, and we are his characters, isn't new. But a group of physicists now thinks they know of a way to test the concept. Three of them propose to test reality by simulating the simulators.
Martin Savage, professor of physics at the University of Washington, Zohreh Davoudi, one of his graduate students, and Silas Beane of the University of New Hampshire, would like to see whether they can find traces of simulation in cosmic rays. The work was uploaded in arXiv, an online archive for drafts of academic research papers.
The notion that reality is something other than we think it is goes far back in philosophy, including Plato and his Parable of the Cave, which claimed reality was merely shadows of real objects on a cave wall. Sixteenth-century philosopher-mathematician René Descartes thought he proved reality with his famous "I think, therefore, I am," which proposed that he was real and his thoughts had a reality.
Then, in 2003, a British philosopher, Nick Bostrom of the University of Oxford, published a paper that had the philosophy and computer science departments buzzing.
Bostrom suggested three possibilities: "The chances that a species at our current level of development can avoid going extinct before becoming technologically mature is negligibly small," "almost no technologically mature civilizations are interested in running computer simulations of minds like ours,” or we are "almost certainly" a simulation.
All three could be equally possible, he wrote, but if the first two are false, the third must be true. "There will be a
SternisheFan writes: —Volcanic activity in modern-day India, not an asteroid, may have killed the dinosaurs, according to a new study. Tens of thousands of years of lava flow from the Deccan Traps , a volcanic region near Mumbai in present-day India, may have spewed poisonous levels of sulfur and carbon dioxide into the atmosphere and caused the mass extinction through the resulting global warming and ocean acidification, the research suggests. The findings, presented Wednesday (Dec. 5) here at the annual meeting of the American Geophysical Union , are the latest volley in an ongoing debate over whether an asteroid or volcanism killed off the dinosaurs about 65 million years ago in the mass die-off known as the K-T extinction.
SternisheFan writes: What should the future of our space program be? The National Research Council had unpleasant medicine for NASA in its just-released report on the vision and direction of the agency. A panel of 12 independent experts concluded, among other things, that the program lacks clear direction from the White House and Congress about what its goals should be, and that NASA cannot do everything it aims to without more money. More cash is an unlikely prospect in the current economic climate, the panel also said. So the government and the agency have to decide what they want NASA to focus on. The report made for “rather grim reading,” one space policy expert, Scott Pace of George Washington University, told The Times.
So what should NASA's mission be? Do scientists and the public care about sending astronauts to an asteroid by 2025? Is it realistic to send astronauts to Mars in the 2030s? Are we focusing too much on Mars? Opinions on that vary, as our article noted. Here's an interview with space exploration enthusiast Bill Nye (of “Science Guy” fame), the chief executive of The Planetary Society.
SternisheFan writes: A self-controlled swimming robot has completed a journey from San Francisco to Australia. The record-breaking 9,000 nautical mile (16,668km) trip took the PacX Wave Glider just over a year to achieve. Liquid Robotics, the US company behind the project, collected data about the Pacific Ocean's temperature, salinity and ecosystem from the drone. The company said its success demonstrated that such technology could "survive the high seas". The robot is called Papa Mau in honour of the late Micronesian navigator Pius "Mau" Piailug, who had a reputation for finding ways to navigate the seas without using traditional equipment. "During Papa Mau's journey, [it] weathered gale-force storms, fended off sharks, spent more than 365 days at sea, skirted around the Great Barrier Reef, and finally battled and surfed the east Australian current to reach his final destination in Hervey Bay, near Bundaberg, Queensland," the company said in a statement. Some of the data it gathered about the abundance of phytoplankton -plant-like organisms that convert carbon dioxide into oxygen and provide food for other sea life -could already be monitored by satellite. However, the company suggested that its equipment offered more detail, providing a useful tool for climate model scientists.
SternisheFan writes: Hubble images of six of the starburst galaxies first found by ESA’s Herschel Space Observatory (Keck data shown below each in blue) Many of the brightest, most actively star-forming galaxies in the Universe were actually undetectable by Earth-based observatories, hidden from view by thick clouds of opaque dust and gas. Thanks to ESA’s Herschel space observatory, which views the Universe in infrared, an enormous amount of these “starburst” galaxies have recently been uncovered, allowing astronomers to measure their distances with the twin telescopes of Hawaii’s W.M. Keck Observatory. What they found is quite surprising: at least 767 previously unknown galaxies, many of them generating new stars at incredible rates. Although nearly invisible at optical wavelengths these newly-found galaxies shine brightly in far-infrared, making them visible to Herschel, which can peer through even the densest dust clouds. Once astronomers knew where the galaxies are located, they were able to target them with Hubble and, most importantly, the two 10-meter Keck telescopes —the two largest optical telescopes in the world. By gathering literally hundreds of hours of spectral data on the galaxies with the Keck telescopes, estimates of their distances could be determined as well as their temperatures and how often new stars are born within them. “While some of the galaxies are nearby, most are very distant; we even found galaxies that are so far that their light has taken 12 billion years to travel here, so we are seeing them when the Universe was only a ninth of its current age,” said Dr. Caitlin Casey, Hubble fellow at the UH Manoa Institute for Astronomy and lead scientist on the survey. “Now that we have a pretty good idea of how important this type of galaxy is in forming huge numbers of stars in the Universe, the next step is to figure out why and how they formed.”
SternisheFan writes: The structure of the universe and the laws that govern its growth may be more similar than previously thought to the structure and growth of the human brain and other complex networks, such as the Internet or a social network of trust relationships between people, according to a new study. “By no means do we claim that the universe is a global brain or a computer,” said Dmitri Krioukov, co-author of the paper, published by the Cooperative Association for Internet Data Analysis (CAIDA), based at the San Diego Supercomputer Center (SDSC) at the University of California, San Diego.“But the discovered equivalence between the growth of the universe and complex networks strongly suggests that unexpectedly similar laws govern the dynamics of these very different complex systems,” Krioukov noted
Having the ability to predict – let alone trying to control – the dynamics of complex networks remains a central challenge throughout network science. Structural and dynamical similarities among different real networks suggest that some universal laws might be in action, although the nature and common origin of such laws remain elusive By performing complex supercomputer simulations of the universe and using a variety of other calculations, researchers have now proven that the causal network representing the large-scale structure of space and time in our accelerating universe is a graph that shows remarkable similarity to many complex networks such as the Internet, social, or even biological networks. These findings have key implications for both network science and cosmology,” said Krioukov.
SternisheFan writes: (CNN) -A toy helicopter controlled by nothing but brainwaves could be available to the public just in time to hover under this year's Christmas tree. Currently touted on crowd-funding website Kickstarter --where it has already exceeded its pledge goal twice over --the Orbit comes equipped with an electroencephalography (EEG) headset, capable of reading electrical activity along the scalp. "As you focus your mind on something --whether it be a math equation or the lyrics of a song --your brain produces electric signals," explains Steve Cattelotti, CEO and co-founder of Puzzlebox, the San Francisco-based company behind the project. "The headset monitors those signals and converts them into flight commands," he says.
There are future plans to enable multi-directional control, but in its present incarnation signals sent from the brain can only be used to lift the helicopter off the ground. "When you concentrate, up it goes; when you mentally relax, it comes back down again," explains Cattelotti. Aside from its obvious entertainment value, Puzzlebox are pitching the Orbit as an educational toy that will help improve concentration and relaxation skills. According to Cattelotti, the art of keeping mentally focused is inherently difficult to master. "If you're learning how to ride a bike, there's a very obvious, physical indication when you improve --you stop falling off," says the 34-year-old computer science graduate. "It's much harder to know when you're concentrating properly and, to a lesser extent, relaxing, because there is little scope for accurate, real-time feedback." http://www.dailymail.co.uk/news/article-2237982/Just-time-Christmas-The-brain-powered-helicopter-offering-genuine-blue-sky-thinking.html
SternisheFan writes: Sophisticated bladelets suggest that humans passed on their technological skill down the generations
A haul of stone blades from a cave in South Africa suggests that early humans were already masters of complex technology more than 70,000 years ago .
The tiny blades — no more than about 3 centimetres long on average — were probably used as tips for throwable spears, or as spiky additions to club-like weapons, says Curtis Marean, an archaeologist at Arizona State University in Tempe who led the team that found the bladelets.
Twenty-seven such blades, called microliths by archaeologists, were found in layers of sand and soil dating as far back as 71,000 years ago and representing a timespan of about 11,000 years, showing how long humans were manufacturing the blades.
Clever crafters The find lends credence to the idea that early humans were capable of passing on their clever ideas to the next generation of artisans, creating complex technologies that endured over time. John Shea, a palaeoanthropologist at Stony Brook University in New York, says that it also suggests that “previous hypotheses that 'early' Homo sapiens differed from 'modern' ones in these respects are probably wrong”.
SternisheFan writes: By Ian Steadman, Wired UK:
Most of the stars that will ever exist have already been born, according to the most comprehensive survey of the age of the night sky.
An international team of astronomers used three telescopes —the UK Infrared Telescope and the Subaru Telescope, both in Hawaii, and Chile’s Very Large Telescope — to study trends in star formation, from the earliest days of the universe. Extrapolating their findings has revealed that half of all the stars that have ever existed were created between 9 and 11 billion years ago, with the other half created in the years since. That means that rate at which new stars are born has dropped off massively, to the extent that (if this trend continues) 95 percent of all the stars that this universe will ever see have already been born. Several studies have looked at specific time “epochs”, but the different methods used by each study has restricted the ability to compare their findings and discern a fuller model of how stars have evolved over the course of the entire universe’s lifespan.
We do know that many stars around today — including our own — likely formed out of the dust left over from earlier, bigger stars going supernova in the early years of the universe. The problem was figuring out exactly how many stars the universe used to give birth to relative to how many are born in later years, as it seemed that at some point there was a steep drop off in the creation of new stars. The telescopes searched for alpha particles emitted by Hydrogen atoms (commonly found in star formation, appearing as a bright red light) throughout huge patches of sky. Snapshots were taken of the look of the universe at defined different points in time, when it was 2, 4, 6 and 9 billion years old — a sample that’s 10 times as large as any previous similar study.
The results showed clearly that half of all the stars that have ever existed in the universe were created more than 9 billion years ago, with the remaining half coming into existence since then.