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Monday, August 19th, 2019
| Time | Event |
| 10:20a | Boosting computing power for the future of particle physics A new machine learning technology tested by an international team of scientists including MIT Assistant Professor Philip Harris and postdoc Dylan Rankin, both of the Laboratory for Nuclear Science, can spot specific particle signatures among an ocean of Large Hadron Collider (LHC) data in the blink of an eye. Sophisticated and swift, the new system provides a glimpse into the game-changing role machine learning will play in future discoveries in particle physics as data sets get bigger and more complex. The LHC creates some 40 million collisions every second. With such vast amounts of data to sift through, it takes powerful computers to identify those collisions that may be of interests to scientists, whether, perhaps, a hint of dark matter or a Higgs particle. Now, scientists at Fermilab, CERN, MIT, the University of Washington, and elsewhere have tested a machine-learning system that speeds processing by 30 to 175 times compared to existing methods. Such methods currently process less than one image per second. In contrast, the new machine-learning system can review up to 600 images per second. During its training period, the system learned to pick out one specific type of postcollision particle pattern. “The collision patterns we are identifying, top quarks, are one of the fundamental particles we probe at the Large Hadron Collider,” says Harris, who is a member of the MIT Department of Physics. “It’s very important we analyze as much data as possible. Every piece of data carries interesting information about how particles interact.” Those data will be pouring in as never before after the current LHC upgrades are complete; by 2026, the 17-mile particle accelerator is expected to produce 20 times as much data as it does currently. To make matters even more pressing, future images will also be taken at higher resolutions than they are now. In all, scientists and engineers estimate the LHC will need more than 10 times the computing power it currently has. “The challenge of future running,” says Harris, “becomes ever harder as our calculations become more accurate and we probe ever-more-precise effects.” Researchers on the project trained their new system to identify images of top quarks, the most massive type of elementary particle, some 180 times heavier than a proton. “With the machine-learning architectures available to us, we are able to get high-grade scientific-quality results, comparable to the best top-quark identification algorithms in the world,” Harris explains. “Implementing core algorithms at high speed gives us the flexibility to enhance LHC computing in the critical moments where it is most needed.” |
| 10:59a | A new way to deliver drugs with pinpoint targeting Most pharmaceuticals must either be ingested or injected into the body to do their work. Either way, it takes some time for them to reach their intended targets, and they also tend to spread out to other areas of the body. Now, researchers at MIT and elsewhere have developed a system to deliver medical treatments that can be released at precise times, minimally-invasively, and that ultimately could also deliver those drugs to specifically targeted areas such as a specific group of neurons in the brain. The new approach is based on the use of tiny magnetic particles enclosed within a tiny hollow bubble of lipids (fatty molecules) filled with water, known as a liposome. The drug of choice is encapsulated within these bubbles, and can be released by applying a magnetic field to heat up the particles, allowing the drug to escape from the liposome and into the surrounding tissue. The findings are reported today in the journal Nature Nanotechnology in a paper by MIT postdoc Siyuan Rao, Associate Professor Polina Anikeeva, and 14 others at MIT, Stanford University, Harvard University, and the Swiss Federal Institute of Technology in Zurich. “We wanted a system that could deliver a drug with temporal precision, and could eventually target a particular location,” Anikeeva explains. “And if we don’t want it to be invasive, we need to find a non-invasive way to trigger the release.” Magnetic fields, which can easily penetrate through the body — as demonstrated by detailed internal images produced by magnetic resonance imaging, or MRI — were a natural choice. The hard part was finding materials that could be triggered to heat up by using a very weak magnetic field (about one-hundredth the strength of that used for MRI), in order to prevent damage to the drug or surrounding tissues, Rao says. Rao came up with the idea of taking magnetic nanoparticles, which had already been shown to be capable of being heated by placing them in a magnetic field, and packing them into these spheres called liposomes. These are like little bubbles of lipids, which naturally form a spherical double layer surrounding a water droplet. When placed inside a high-frequency but low-strength magnetic field, the nanoparticles heat up, warming the lipids and making them undergo a transition from solid to liquid, which makes the layer more porous — just enough to let some of the drug molecules escape into the surrounding areas. When the magnetic field is switched off, the lipids re-solidify, preventing further releases. Over time, this process can be repeated, thus releasing doses of the enclosed drug at precisely controlled intervals. The drug carriers were engineered to be stable inside the body at the normal body temperature of 37 degrees Celsius, but able to release their payload of drugs at a temperature of 42 degrees. “So we have a magnetic switch for drug delivery,” and that amount of heat is small enough “so that you don’t cause thermal damage to tissues,” says Anikeeva, who holds appointments in the departments of Materials Science and Engineering and the Brain and Cognitive Sciences. In principle, this technique could also be used to guide the particles to specific, pinpoint locations in the body, using gradients of magnetic fields to push them along, but that aspect of the work is an ongoing project. For now, the researchers have been injecting the particles directly into the target locations, and using the magnetic fields to control the timing of drug releases. “The technology will allow us to address the spatial aspect,” Anikeeva says, but that has not yet been demonstrated. This could enable very precise treatments for a wide variety of conditions, she says. “Many brain disorders are characterized by erroneous activity of certain cells. When neurons are too active or not active enough, that manifests as a disorder, such as Parkinson’s, or depression, or epilepsy.” If a medical team wanted to deliver a drug to a specific patch of neurons and at a particular time, such as when an onset of symptoms is detected, without subjecting the rest of the brain to that drug, this system “could give us a very precise way to treat those conditions,” she says. Rao says that making these nanoparticle-activated liposomes is actually quite a simple process. “We can prepare the liposomes with the particles within minutes in the lab,” she says, and the process should be “very easy to scale up” for manufacturing. And the system is broadly applicable for drug delivery: “we can encapsulate any water-soluble drug,” and with some adaptations, other drugs as well, she says. One key to developing this system was perfecting and calibrating a way of making liposomes of a highly uniform size and composition. This involves mixing a water base with the fatty acid lipid molecules and magnetic nanoparticles and homogenizing them under precisely controlled conditions. Anikeeva compares it to shaking a bottle of salad dressing to get the oil and vinegar mixed, but controlling the timing, direction and strength of the shaking to ensure a precise mixing. Anikeeva says that while her team has focused on neurological disorders, as that is their specialty, the drug delivery system is actually quite general and could be applied to almost any part of the body, for example to deliver cancer drugs, or even to deliver painkillers directly to an affected area instead of delivering them systemically and affecting the whole body. “This could deliver it to where it’s needed, and not deliver it continuously,” but only as needed. Because the magnetic particles themselves are similar to those already in widespread use as contrast agents for MRI scans, the regulatory approval process for their use may be simplified, as their biological compatibility has largely been proven. The team included researchers in MIT’s departments of Materials Science and Engineering and Brain and Cognitive Sciences, as well as the McGovern Institute for Brain Research, the Simons Center for Social Brain, and the Research Laboratory of Electronics; the Harvard University Department of Chemistry and Chemical Biology and the John A. Paulsen School of Engineering and Applied Sciences; Stanford University; and the Swiss Federal Institute of Technology in Zurich. The work was supported by the Simons Postdoctoral Fellowship, the U.S. Defense Advanced Research Projects Agency, the Bose Research Grant, and the National Institutes of Health. |
| 11:00a | Rocky, Earth-sized exoplanet is missing an atmosphere Astronomers at MIT, Harvard University, and elsewhere have searched a rocky, Earth-sized exoplanet for signs of an atmosphere — and found none. Atmospheres have previously been detected on planets much larger than our own, including several hot-Jupiters and sub-Neptunes, all of which are primarily made of ice and gas. But this is the first time scientists have been able to nail down whether an Earth-sized, terrestrial planet outside our solar system has an atmosphere. The planet in question, LHS 3844b, was discovered in 2018 by NASA’s Transiting Exoplanet Survey Satellite, TESS, and was measured to be about 1.3 times larger than Earth. The planet zips around its star in just 11 hours, making it one of the fastest orbiting exoplanets known. The star itself is a small, cool M-dwarf that resides just 49 light-years from Earth. In a paper published today in Nature, the team reports that LHS 3844b likely has neither a thick, Venus-like atmosphere nor a thin, Earth-like atmosphere. Instead, the planet is probably more similar to Mercury — a blistering, bare rock. If an atmosphere ever existed, the researchers say the star’s radiation likely blasted it away early in the planet’s formation. “We basically found a hot planet with no gases around it,” says co-author Daniel Koll, a postdoc in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “This is the first time we’ve known anything in detail about the atmosphere of a planet around these M-dwarfs, which are the most common type of star, making LHS 3844b the most common type of rocky planet in the galaxy.” Could any form of life manage to take hold in such a barren wasteland? Koll and his colleagues say it’s extremely unlikely, as the lack of an atmosphere would instantly cook off any organisms on the planet’s surface. But that doesn’t mean other terrestrial exoplanets are similarly without cover. “We never thought this particular planet would be hospitable for life,” says lead author Laura Kreidberg, a researcher at the Harvard Center for Astrophysics. “It’s more a question of whether this whole category of planets around smaller stars has atmospheres or not. And our technique is a robust way of assessing whether an atmosphere is present or not.” Kreidberg and Koll’s co-authors from MIT include Jason Dittmann, Ian Crossfield, David Berardo, Xueying “Sherry” Guo, George Ricker, Sara Seager, and Roland Vanderspek, along with colleagues from Harvard, the University of Texas at Austin, the Jet Propulsion Laboratory, Caltech, Stanford University, the University of Maryland, and Vanderbilt University. Faces exposed In 2018, LHS 3844b was among the first crop of extrasolar worlds confirmed by TESS, an MIT-developed satellite that monitors thousands of the closest, brightest stars, for transits — periodic dips in starlight that could signal a planet orbiting in front of the star, momentarily blocking its light. Kreidberg and her team flagged LHS 3844b as an ideal laboratory, as its star is bright and nearby, and therefore a source against which scientists could study the planet in detail. As LHS 3844b is extremely close to its star, and thus incredibly hot, Kreidberg and Koll reasoned that it should give off enough heat to reveal clues as to whether it hosts an atmosphere.
Cartoon illustrating the brightness measured over time (white line) corresponding to a tidally locked planet orbiting its parent star. The brightness increases as the planet’s hot dayside rotates into view. Image: Laura Kreidberg LHS 3844b is a tidally locked planet, meaning that it has a permanent day side and night side to its star, just as the moon always shows the same face to the Earth. If an atmosphere exists, it would circulate heat around the entire planet, and the heat emitted by both the day and night sides would be roughly the same. In the absence of an atmosphere, the day side would be considerably hotter than the night side. As the planet orbits its star, an observer can see various faces of that planet. As it comes out from behind its star, the planet’s day side is exposed. Then, as it circles in front of the star, the planet swivels to show its night side, before coming back around to expose its day side before crossing behind the star again. The researchers figured that if they could measure the heat given off by the planet’s various faces during its orbit, they could determine the temperature difference between the day side and night side, and ultimately, whether the planet has an atmosphere. To test this idea, the team used NASA’s Spitzer Space Telescope, an instrument that measures infrared radiation, or heat, and pointed the telescope at LHS 3844b for 100 hours, capturing about 10 orbits of the planet in total. They measured the heat given off by the planet’s various faces throughout each orbit. “This has been done a lot for planets closer in size to Jupiter, but this is the very first time that this measurement has ever been made for a terrestrial planet around an M dwarf star,” Koll says. “Somewhere out there” From their measurements, the researchers calculated that the dayside is a toasty 1,000 kelvins, or about 1,340 degrees Fahrenheit, whereas the nightside plummets to as low as 0 K, or -460 F. The drastic temperature difference indicates that the planet does not have a thick, Venus-like atmosphere that would distribute heat evenly around the entire planet. The team simulated various scenarios involving thinner atmospheres of different compositions, but they found that none produced a heat distribution that matched their observations, indicating that the planet also does not host a thin, Earth-like atmosphere. There was one scenario in which an extremely thin atmosphere, similar to that of Mars, could produce the planet’s drastic heat difference. However, the team found that it was unlikely that such a thin atmosphere could remain stable, as the star’s radiation would quickly blast away any trace gases surrounding the planet. The researchers have concluded that LHS 3844b is essentially a super-hot, bare rock. But what type of rock could it be? In one last step, the team looked to identify its composition by measuring the reflectivity of the planet’s surface. As we know on Earth, different minerals reflect light to various degrees — basalt, which is black, solidified lava, reflects very little light, whereas lighter-colored rocks like granite, containing minerals such as quartz, have a higher reflectivity. The team measured the ratio of the star’s brightness with that of the planet’s in order to calculate the planet’s reflectivity. “We can see a granite-like surface is ruled out by our data, whereas a dark material like a lava field in Hawaii, or the lunar mare, or like the surface of Mercury, is consistent with our observations,” Kreidberg says. While the group concluded there is an absence of any atmosphere — and, therefore, life — on LHS 3844b, they say this may not be the case for similar terrestrial exoplanets orbiting cool M-dwarfs. They hope to apply their technique to other rocky exoplanets, including ones that are further out from their stars and have a better chance of retaining an atmosphere. “Atmospheres help protect life and shield it from ultraviolet radiation,” Kreidberg says. “I would be thrilled to detect an atmosphere on a planet, even if it’s a little too hot or too cold, because that would tell us, yes, some terrestrial exoplanets can have atmospheres, and probably somewhere out there, there’s going to be one that’s the right temperature, that has been able to keep liquid water.” |
| 1:00p | Watching electrons using extreme ultraviolet light A new technique developed by a team at MIT can map the complete electronic band structure of materials at high resolution. This capability is usually exclusive to large synchrotron facilities, but now it is available as a tabletop laser-based setup at MIT. This technique, which uses extreme ultraviolet (XUV) laser pulses to measure the dynamics of electrons via angle-resolved photoemission spectroscopy (ARPES), is called time-resolved XUV ARPES. Unlike the synchrotron-based setup, this laser-based setup further provides a time-resolved feature to watch the electrons inside a material on a very fast, femtosecond (quadrillionth of a second) timescale. Comparing this fast technique on a time and distance scale, while light can travel from the moon to the Earth in roughly one second, it can only travel as far as the thickness of a single sheet of regular copy paper in one femtosecond. The MIT team evaluated their instrument resolution using four exemplary materials representing a wide spectrum of quantum materials: a topological Weyl semimetal, a high-critical-temperature superconductor, a layered semiconductor, and a charge density wave system. The technique is described in a paper appearing in the journal Nature Communications, authored by MIT physicists Edbert Jarvis Sie PhD ’17, former postdoc Timm Rohwer, Changmin Lee PhD ’18, and MIT physics Professor Nuh Gedik. A central goal of modern condensed-matter physics is to discover novel phases of matter and exert control over their intrinsic quantum properties. Such behaviors are rooted in the way the energy of electrons changes as a function of their momentum inside different materials. This relationship is known as the electronic band structure of materials and can be measured using photoemission spectroscopy. This technique uses light with high photon energy to knock the electrons away from the material surface — a process formerly known as the photoelectric effect, for which Albert Einstein received the Nobel Prize in Physics in 1921. Nowadays, the speed and direction of the outgoing electrons can be measured in an angle-resolved manner to determine the energy and momentum relationship inside the material. The collective interaction between electrons in these materials often goes beyond textbook predictions. One method to study such non-conventional interactions is by promoting the electrons to higher energy levels and watching how they relax back to the ground state. This is called a "pump-and-probe" method, which basically is the same method people use in their everyday lives to perceive new objects around them. For example, anyone can drop a pebble on the surface of water and watch how the ripples decay to observe the surface tension and acoustics of water. The difference in the MIT setup is that the researchers use infrared light pulses to “pump” the electrons to the excited state and the XUV light pulses to “probe” the photoemitted electrons after a time delay. Time- and angle-resolved photoemission spectroscopy (trARPES) captures movies of the electronic band structure of the solid with femtosecond time resolution. This technique provides invaluable insights into the electron dynamics, which is crucial to understand the properties of the materials. However, it has been difficult to access high-momenta electrons with narrow energy resolution via laser-based ARPES, severely constraining the type of phenomena that can be studied with this technique. The newly developed XUV trARPES setup at MIT, which is approximately 10 feet long, can generate a femtosecond extreme ultraviolet light source at high energy resolution. “XUV will be quickly absorbed by air, so we house the optics in vacuum,” Sie says. “Every component from the light source to the sample chamber is projected on the computer drawing on a millimeter precision.” This technique enables full access to the electronic band structure of all materials with unprecedentedly narrow energy resolution on femtosecond timescales. “To demonstrate the resolution of our setup, it is not sufficient to measure the resolution of the light source alone,” Sie says. “We must verify the true resolutions from real photoemission measurements using a wide range of materials — the results are very satisfying!” The final assembly of the MIT setup comprises several emerging instruments that are being developed concurrently in industry: femtosecond XUV light source (XUUS) from KMLabs, XUV monochromator (OP-XCT) from McPherson, and angle-resolved time-of-flight (ARToF) electron analyzer from Scienta Omicron. “We believe that this technique has the potential to push the boundary of condensed matter physics,” Gedik says, “so we worked with relevant companies to achieve this spearheading capability.” The MIT setup can accurately measure the energy of electrons with high momenta. “The combination of time-of-flight electron analyzer and XUV femtosecond light source gives us the ability to measure the complete band structure of almost all materials,” Rohwer says, “Unlike some other setups, we don’t have to repeatedly tilt the sample to map the band structure — and this saves us a lot of time!” Another significant advance is the ability to change the photon energy. “Photoemission intensity often varies significantly with the photon energy used in the experiment. This is because the photoemission cross section depends on the orbital character of the elements forming the solid,” Lee says. “The photon energy tunability provided by our setup is extremely useful in enhancing the photoemission counts of particular bands that we are interested in.” Stanford Institute for Materials and Energy Science Staff Scientist Patrick S. Kirchmann, an expert in ARPES techniques, says, “As a practitioner I believe that trARPES is profoundly useful. Any quantum material, topological insulator, or superconductivity question profits from understanding the band structure in non-equilibrium. The basic idea of trARPES is simple: By detecting the emission angle and energy of photoemitted electrons, we can record the electronic band structure. Done after exciting the sample with light, we can record changes of the band structure that provide us with ‘electron movies,’ which are filmed at frame rates of their natural femtosecond time scale.” Commenting on the Gedik research group’s new findings at MIT, Kirchmann says, “The work of Sie and Gedik sets a new standard by achieving 30 meV [milli-electron-volt] bandwidth while maintaining 200 femtosecond time resolution. By incorporating exchangeable gratings in their setup, it will also be possible to change that partitioning of the time-bandwidth product. These achievements will enable long-needed high-definition studies of quantum materials with high enough energy resolution to provide profound insights." The work was supported by the U.S. Department of Energy, Army Research Office, and the Gordon and Betty Moore Foundation. |
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