New prototype Petri dishes let ordinary scientists in on the advanced technology.
- Acoustic tweezers allow bioparticles and cells to be precisely manipulated without touching them.
- Sound waves grab and move very tiny objects as desired.
- Previously available only in expensive and complex devices, acoustic tweezers have now been built into Petri dishes.
When a tweezer is not a tweezer<p>To understand how the "tweezers" work, it's important to know that they're tweezers only in that they grab objects so that they can be manipulated. That's the extent of their similarity to household tweezers: Acoustic tweezers are not small hand-held devices to pinch with. They're much more high-tech than that. <a href="https://en.wikipedia.org/wiki/Acoustic_tweezers" target="_blank">Acoustic tweezers</a> use pairs of sound waves directed at the object to be manipulated. (NASA has an <a href="https://www.nasa.gov/specials/X59/science-of-sound.html" target="_blank">excellent pair of short videos</a> explaining how sound waves work.)</p><p>In an acoustic tweezer, sound waves directed toward each other push an object into the location at which the waves meet, called a "trapping node." Once the object is trapped there, the node's position can be repositioned as desired by adjusting the strength, or amplitude, of the sound waves. As the node moves, so does the object trapped within it.</p><p>Acoustic tweezers provide a touch-free, gentle and non-destructive means of holding on to and manipulating even very tiny objects — a single cell or particle, for example. Using multiple sound waves emitted from opposite each other, and above and below, objects can be moved in three dimensions. This allows scientists to mix objects together with tremendous precision and to construct two-dimensional and three-dimensional structures from trapped objects. </p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzk5MjAyOC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY1MDY2Mjg4Mn0.5cMqhSjZa6eo8ISWnY37j3R9UtMsEHV9qGAh2EC53i4/img.jpg?width=980" id="fb16a" class="rm-shortcode" data-rm-shortcode-id="2acb472e02638d001a5e0ccdc9c8b6e8" data-rm-shortcode-name="rebelmouse-image" alt="graphic explaining how sound waves move objects" />
Graphic explaining how sound waves move objects
Credit: Big Think
How the prototypes work<p>The researchers present three different prototypes in their paper. They all employ small <a href="https://en.wikipedia.org/wiki/Piezoelectricity" target="_blank">piezoelectric</a> <a href="https://blog.teufelaudio.com/transducers/" target="_blank">sound transducers</a> affixed to the edges and/or below Petri dishes. These transducers convert electrical energy into sound waves and can move objects in Petri dishes in pretty much any direction.</p><ul><li>The first prototype has four transducers arrayed around the four quadrants of a Petri dish, allowing the tweezers to move targeted objects laterally.</li><li>The second model uses a tilted sound transducer beneath the Petri dish that creates a whirlpool in its center capable of capturing, concentrating, and mixing the contents of a dish.</li><li>The third design fits two transducers beneath the dish together like a zipper, forming a holographic IDT (interdigital transducer.) This highly configurable arrangement generates high-frequency beam-like waves from below the dish. They can be programmed as 3D focused or vortex beams, for example, allowing them to perform a range of object manipulations.</li></ul><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzk5MjExOS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyODA1ODkzM30.ypFFEBKMYg0iBNvAQ3aiF07-UK8OM8nACZTQTM9unds/img.jpg?width=980" id="120f9" class="rm-shortcode" data-rm-shortcode-id="dc8c535494b9830e1a1a594d8495b2c1" data-rm-shortcode-name="rebelmouse-image" />
Credit: Tian, et al./Scientific Advances
Moving forward<p>The primary purpose of this study was to work out how to implement already available acoustic tweezers in more compact, practical form for researchers, according to Huang.</p><p>As the paper notes: "Although previous acoustic tweezers have been demonstrated for the manipulation of cells, most of them require customized microfluidic channels/chambers, which usually require time-consuming and costly steps for fabrication and sterilization and hence are not frequently used in biological and biomedical laboratories." The authors' aim, says the paper, was to develop "acoustic tweezer devices that can directly manipulate bioparticles in the most common laboratory cell culture plate, the Petri dish."</p><p>The authors' next goal is to further catalogue the capabilities of their prototypes, in particular their configurable third design. Down the road, they hope, will be development of a device that combines all three types of functionality provided by the prototypes in a single device.</p>
Dust sticking to things on the moon is a serious problem researchers are trying to solve.
Sticky situation<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzU5OTA1Mi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY1MDAyMzU0MH0.lfYLUy2mETdXOgEGdyEHPUJD2aXqab9qB-WoMp94ldk/img.jpg?width=980" id="a045b" class="rm-shortcode" data-rm-shortcode-id="40f701f33214c9cfdb248d88a49d0ca9" data-rm-shortcode-name="rebelmouse-image" />
Microscopic view of man-made "moon dust"
Credit: IMPACT lab/CU Boulder<p>Lunar dust is not much like the stuff settling on the surfaces of your home. For one thing, Wang reports, "Lunar dust is very jagged and abrasive, like broken shards of glass."</p><p>The reason that it's so stubbornly sticky is that it carries an electric charge not unlike that of a sock you've just removed from the dryer. The charge results from being continually exposed to the Sun's radiation as the dust sits on the lunar surface unprotected by an atmosphere like ours. The moon does have very thin atmosphere that contains odd gases such as sodium and potassium, <a href="https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html" target="_blank">says NASA</a>, but it isn't thick enough to afford much protection from radiation.</p>
Overload of electrons<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="ea957f6f96e5b4796909ee398cc65658"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/-aHHWAeda6o?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>The researchers explored the idea of shooting a beam of electrons at lunar dust to fill the spaces between its particles with negative charges that could push the particles further apart, away from each other and also off a surface to which they might be adhering. Says Wang, "The charges become so large that they repel each other, and then dust ejects off of the surface."<br></p><p>To test their concept, the researchers acquired <a href="https://www.nasa.gov/sites/default/files/atoms/files/nasa_tm_2010_216446_simuserg.pdf" target="_blank">lunar regolith stimulant</a> from NASA, a substance formulated on Earth that's designed to replicate lunar dust. They placed objects of various materials that had been coated with the stuff in a vacuum chamber and fired electron beams at them. (The video above shows the dust's response.)</p><p>Speaking of the behavior of the electron-blasted dust on a number of tested surfaces, including spacesuit fabric and glass, "It literally jumps off," says lead author <a href="https://www.mendeley.com/authors/57218515747/" target="_blank" rel="noopener noreferrer">Benjamin Farr</a>. However, the finest-grained regolith, the kind that gets stuck in brushes, remained unperturbed by the electrons. Overall, the electrons cleaned off about 75 percent to 85 percent of the dust. "It worked pretty well, but not well enough that we're done," says Farr. Looking forward, the team is exploring ways in which the electron beam's cleaning power can be increased.</p><p>This is not the first attempt at using electrons to clean up lunar dust. For example, NASA has explored using <a href="https://www.seeker.com/space/exploration/new-spacesuit-system-could-repel-destructive-moon-dust" target="_blank">nanotube electrode networks</a> in spacesuits to keep dust off. <a href="https://www.nasa.gov/feature/goddard/2019/nasa-s-coating-technology-could-help-resolve-lunar-dust-challenge" target="_blank" rel="noopener noreferrer">To keep regolith off other materials</a>, NASA is also considered combining charge-dissipating indium tin oxide with paint that could then be applied to otherwise dust-collecting surfaces.</p><p>The CU Boulder team anticipates one day hanging up a spacesuit in a room or compartment where it can be bombarded with electrons for cleaning. Even more convenient would be facilities where "You could just walk into an electron beam shower to remove fine dust," says study coauthor <a href="https://www.colorado.edu/physics/mihaly-horanyi" target="_blank">Mihály Horányi</a> of CU Boulder's <a href="https://www.colorado.edu/physics/" target="_blank" rel="noopener noreferrer">Department of Physics</a>.</p>
Ever wonder how soft hair can dull a steel razor? So did scientists at MIT.
- Steel is fifty times harder than hair, yet shaving razors dull in a hurry.
- A new study finds much of this is caused by hair cracking razors at points of imperfection.
- The findings may lead to new ways of making razors that last longer.
An extremely magnified image of a razor blade cutting hair.
G. Roscioli<p>Lead author Gianluca Roscioli grew his facial hair out for three days before <a href="https://www.smithsonianmag.com/smart-news/why-razors-are-dull-within-weeks-according-science-180975534/" target="_blank">shaving</a>. He then brought his razors into the lab to examine them under an electron microscope. While the team expected to see even dulling on the blade edge, they instead noticed strange C-shaped chips missing. Intrigued, they attached a camera to the microscope so they could record the blade cutting the <a href="https://www.sciencemag.org/news/2020/08/your-hair-can-crack-steel-when-it-hits-right-spot" target="_blank">hair</a>. At the same time, they investigated the properties of the razors at the microscopic level.</p><p>This apparatus revealed that, when the razor blade hit the hairs at non-perpendicular angles, small cracks formed. These tended to develop in boundary areas between where the steel was harder and where it was softer due to differences in the properties at each location caused by the manufacturing <a href="https://www.newscientist.com/article/2251202-we-just-figured-out-why-shaving-soft-hair-blunts-steel-razor-blades/" target="_blank">process</a>. Over time, these cracks grew into chips. While these chips are too small to see with the naked eye, they were large enough to reduce the blade's effectiveness.</p><p>Roscioli told <a href="https://www.smithsonianmag.com/smart-news/why-razors-are-dull-within-weeks-according-science-180975534/" target="_blank" rel="noopener noreferrer dofollow">NPR</a>, "The size of the chips are about 1/10 of the diameter of a human hair."</p><p>The chips can be caused by hair of any thickness and appear to be unavoidable in blades with standard imperfections. </p><p>The finding surprised other scientists, who also quickly accepted the explanation. Professor Suveen Mathaudhu of UC Riverside explained to <a href="https://www.npr.org/2020/08/06/898577234/cutting-edge-research-shows-how-hair-dulls-razor-blades" target="_blank" rel="noopener noreferrer dofollow">NPR</a> that he had expected a larger role in the dulling process to be played by corrosion but that the findings made a great deal of sense. Other scientists expressed how impressed they were by the quality of the images and the difficulty of the study. </p>
How can we possibly use this information?<div class="rm-shortcode" data-media_id="ELqsmO1M" data-player_id="FvQKszTI" data-rm-shortcode-id="2295233989512b59279237452c0e0076"> <div id="botr_ELqsmO1M_FvQKszTI_div" class="jwplayer-media" data-jwplayer-video-src="https://content.jwplatform.com/players/ELqsmO1M-FvQKszTI.js"> <img src="https://cdn.jwplayer.com/thumbs/ELqsmO1M-1920.jpg" class="jwplayer-media-preview" /> </div> <script src="https://content.jwplatform.com/players/ELqsmO1M-FvQKszTI.js"></script> </div> <p>The study determined that part of the reason for this chipping is the imperfections in the steel used to make the blades, specifically the lack of uniformity in the composition of the steel at the microscopic level. At least partly, these imperfections are due to the nature of the production process and can be reduced through alternative methods. This study's research team is also working on a new material with more structural uniformity as a possible solution.</p><p>These findings may one day lead to longer-lasting razor blades. Given that Americans throw out two billion blades each <a href="https://www.usatoday.com/story/news/nation/2019/08/07/landfill-waste-how-prevent-disposable-razor-plastic-pollution/1943345001/" target="_blank">year</a>, such a discovery's environmental impact would be tremendous.</p>
A clever new study definitively measures how long it takes for quantum particles to pass through a barrier.
- Quantum particles can tunnel through seemingly impassable barriers, popping up on the other side.
- Quantum tunneling is not a new discovery, but there's a lot that scientists don't know.
- By super-cooling rubidium particles, researchers use their spinning as a magnetic timer.
When it comes to weird behavior, there's nothing quite like the quantum world. On top of that world-class head scratcher entanglement, there's also quantum tunneling — the mysterious process in which particles somehow find their way through what should be impenetrable barriers.
Exactly why or even how quantum tunneling happens is unknown: Do particles just pop over to the other side instantaneously in the same way entangled particles interact? Or do they progressively tunnel through? Previous research has been conflicting.
That quantum tunneling occurs has not been a matter of debate since it was discovered in the 1920s. When IBM famously wrote their name on a nickel substrate using 35 xenon atoms, they used a scanning probe microscopes to see what they were doing. And tunnel diodes are fast-switching semiconductors that derive their negative resistance from quantum tunneling.
"Quantum tunneling is one of the most puzzling of quantum phenomena," says Aephraim Steinberg of the Quantum Information Science Program at Canadian Institute for Advanced Research in Toronto to Live Science. Speaking with Scientific American he explains, "It's as though the particle dug a tunnel under the hill and appeared on the other."
Steinberg is a co-author of a study just published in the journal Nature that presents a series of clever experiments that allowed researchers to measure the amount of time it takes tunneling particles to find their way through a barrier. "And it is fantastic that we're now able to actually study it in this way."
Frozen rubidium atoms
Image source: Viktoriia Debopre/Shutterstock/Big Think
One of the difficulties in ascertaining the time it takes for tunneling to occur is knowing precisely when it's begun and when it's finished. The authors of the new study solved this by devising a system based on particles' precession.
Subatomic particles all have magnetic qualities and they spin, or "precess," like a top when they encounter an external magnetic field. With this in mind, the authors of the study decided to construct a barrier with a magnetic field, causing any particles passing through it to precess as they did so. They wouldn't precess before entering the field or after, so by observing and timing the duration of the particles' precession, the researchers could definitively identify the length of time it took them to tunnel through the barrier.
To construct their barrier, the scientists cooled about 8,000 rubidium atoms to a billionth of a degree above absolute zero. In this state, they form a Bose-Einstein condensate, AKA the fifth-known form of matter. When in this state, atoms slow down and can be clumped together rather than flying around independently at high speeds. (We've written before about a Bose-Einstein experiment in space.)
Using a laser, the researchers pushed about 2,000 rubidium atoms together in a barrier about 1.3 micrometers thick, endowing it with a pseudo-magnetic field. Compared to a single rubidium atom, this is a very thick wall, comparable to a half a mile deep if you yourself were a foot thick.
With the wall prepared, a second laser nudged individual rubidium atoms toward it. Most of the atoms simply bounced off the barrier, but about 3 percent of them went right through as hoped. Precise measurement of their precession produced the result: It took them 0.61 milliseconds to get through.
Reactions to the study
Scientists not involved in the research find its results compelling.
"This is a beautiful experiment," remarked Igor Litvinyuk of Griffith University in Australia. "Just to do it is a heroic effort." Drew Alton of Augustana University in South Dakota tells Live Science, "The experiment is a breathtaking technical achievement."
What makes the researchers' results so exceptional is their unambiguity. Says Chad Orzel at Union College in New York, "Their experiment is ingeniously constructed to make it difficult to interpret as anything other than what they say." He calls the research, "one of the best examples you'll see of a thought experiment made real." Litvinyuk agrees: "I see no holes in this."
As for the researchers themselves, enhancements to their experimental apparatus are underway to help them learn more. "We're working on a new measurement where we make the barrier thicker," Steinberg said. In addition, there's also the interesting question of whether or not that 0.61-millisecond trip occurs at a steady rate: "It will be very interesting to see if the atoms' speed is constant or not."
Proteus could someday be used to create extremely strong and lightweight armor and locks.
- The material's strength comes from the unique arrangement of the ceramic spheres and aluminum of which it's composed.
- This arrangement is found in some biological structures, such as fish scales.
- Proteus is currently awaiting a patent.
Stefan Szyniszewski et al.<p>The team created Proteus by arranging microscopic ceramic spheres in a highly compressible aluminum matrix of foam. When something like an angle grinder cuts into Proteus, the structure promotes a series of forward- and backward-moving vibrations. This movement excites the ceramic spheres, causing them to break down into particles. Then, these particles fill gaps in the foam matrix, making it even harder to cut through the material.</p>
Stefan Szyniszewski et al.<p style="margin-left: 20px;">"Essentially cutting our material is like cutting through a jelly filled with nuggets" lead author Stefan Szyniszewski, assistant professor of applied mechanics in Durham's Department of Engineering, told <a href="https://newatlas.com/materials/proteus-non-cuttable-bike-lock-armor/" target="_blank">New Atlas</a>. "If you get through the jelly you hit the nuggets and the material will vibrate in such a way that it destroys the cutting disc or drill bit."</p><p style="margin-left: 20px;">"The ceramics embedded in this flexible material are also made of very fine particles which stiffen and resist the angle grinder or drill when you're cutting at speed in the same way that a sandbag would resist and stop a bullet at high speed."</p><p>A video demonstration shows an angle grinder making a slight cut into the surface of the material, but not penetrating much farther. In a study published in <a href="https://www.nature.com/articles/s41598-020-65976-0" target="_blank">Nature Scientific Reports</a>, the researchers said that's because the blade didn't make enough contact with the ceramic spheres to produce vibrations strong enough to stop the cutting.</p>