Monday, February 3rd, 2020

Time	Event
10:30a	A smart surface for smart devices We’ve heard it for years: 5G is coming.  And yet, while high-speed 5G internet has indeed slowly been rolling out in a smattering of countries across the globe, many barriers remain that have prevented widespread adoption. One issue is that we can’t get faster internet speeds without more efficient ways of delivering wireless signals. The general trend has been to simply add antennas to either the transmitter (i.e., Wi-Fi access points and cell towers) or the receiver (such as a phone or laptop). But that’s grown difficult to do as companies increasingly produce smaller and smaller devices, including a new wave of “internet of things” systems. Researchers from MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) looked at the problem recently and wondered if people have had things completely backwards this whole time. Rather than focusing on the transmitters and receivers, what if we could amplify the signal by adding antennas to an external surface in the environment itself? That’s the idea behind the CSAIL team's new system RFocus, a software-controlled “smart surface” that uses more than 3,000 antennas to maximize the strength of the signal at the receiver. Tests showed that RFocus could improve the average signal strength by a factor of almost 10. Practically speaking, the platform is also very cost-effective, with each antenna costing only a few cents. While the system could serve as another form of WiFi range extender, the researchers say its most valuable use could be in the network-connected homes and factories of the future.  For example, imagine a warehouse with hundreds of sensors for monitoring machines and inventory. MIT Professor Hari Balakrishnan says that systems for that type of scale would normally be prohibitively expensive and/or power-intensive, but could be possible with a low-power interconnected system that uses an approach like RFocus. “The core goal here was to explore whether we can use elements in the environment and arrange them to direct the signal in a way that we can actually control,” says Balakrishnan, senior author on a new paper about RFocus that will be presented next month at the USENIX Symposium on Networked Systems Design and Implementation (NSDI) in Santa Clara, California. “If you want to have wireless devices that transmit at the lowest possible power, but give you a good signal, this seems to be one extremely promising way to do it.” RFocus is a two-dimensional surface composed of thousands of antennas that can each either let the signal through or reflect it. The state of the elements is set by a software controller that the team developed with the goal of maximizing the signal strength at a receiver.  “The biggest challenge was determining how to configure the antennas to maximize signal strength without using any additional sensors, since the signals we measure are very weak,”  says PhD student Venkat Arun, lead author of the new paper alongside Balakrishnan. “We ended up with a technique that is surprisingly robust.” The researchers aren’t the first to explore the possibility of improving internet speeds using the external environment. A team at Princeton University led by Professor Kyle Jamieson proposed a similar scheme for the specific situation of people using computers on either side of a wall. Balakrishnan says that the goal with RFocus was to develop an even more low-cost approach that could be used in a wider range of scenarios.  “Smart surfaces give us literally thousands of antennas to play around with,” says Jamieson, who was not involved in the RFocus project. “The best way of controlling all these antennas, and navigating the massive search space that results when you imagine all the possible antenna configurations, are just two really challenging open problems.” (Comment on this)
10:59a	New electrode design may lead to more powerful batteries New research by engineers at MIT and elsewhere could lead to batteries that can pack more power per pound and last longer, based on the long-sought goal of using pure lithium metal as one of the battery’s two electrodes, the anode.   The new electrode concept comes from the laboratory of Ju Li, the Battelle Energy Alliance Professor of Nuclear Science and Engineering and professor of materials science and engineering. It is described today in the journal Nature, in a paper co-authored by Yuming Chen and Ziqiang Wang at MIT, along with 11 others at MIT and in Hong Kong, Florida, and Texas. The design is part of a concept for developing safe all-solid-state batteries, dispensing with the liquid or polymer gel usually used as the electrolyte material between the battery’s two electrodes. An electrolyte allows lithium ions to travel back and forth during the charging and discharging cycles of the battery, and an all-solid version could be safer than liquid electrolytes, which have high volatilility and have been the source of explosions in lithium batteries. “There has been a lot of work on solid-state batteries, with lithium metal electrodes and solid electrolytes,” Li says, but these efforts have faced a number of issues. One of the biggest problems is that when the battery is charged up, atoms accumulate inside the lithium metal, causing it to expand. The metal then shrinks again during discharge, as the battery is used. These repeated changes in the metal’s dimensions, somewhat like the process of inhaling and exhaling, make it difficult for the solids to maintain constant contact, and tend to cause the solid electrolyte to fracture or detach. Another problem is that none of the proposed solid electrolytes are truly chemically stable while in contact with the highly reactive lithium metal, and they tend to degrade over time. Most attempts to overcome these problems have focused on designing solid electrolyte materials that are absolutely stable against lithium metal, which turns out to be difficult.  Instead, Li and his team adopted an unusual design that utilizes two additional classes of solids, “mixed ionic-electronic conductors” (MIEC) and “electron and Li-ion insulators” (ELI), which are absolutely chemically stable in contact with lithium metal. The researchers developed a three-dimensional nanoarchitecture in the form of a honeycomb-like array of hexagonal MIEC tubes, partially infused with the solid lithium metal to form one electrode of the battery, but with extra space left inside each tube. When the lithium expands in the charging process, it flows into the empty space in the interior of the tubes, moving like a liquid even though it retains its solid crystalline structure. This flow, entirely confined inside the honeycomb structure, relieves the pressure from the expansion caused by charging, but without changing the electrode’s outer dimensions or the boundary between the electrode and electrolyte. The other material, the ELI, serves as a crucial mechanical binder between the MIEC walls and the solid electrolyte layer. “We designed this structure that gives us three-dimensional electrodes, like a honeycomb,” Li says. The void spaces in each tube of the structure allow the lithium to “creep backward” into the tubes, “and that way, it doesn’t build up stress to crack the solid electrolyte.” The expanding and contracting lithium inside these tubes moves in and out, sort of like a car engine’s pistons inside their cylinders. Because these structures are built at nanoscale dimensions (the tubes are about 100 to 300 nanometers in diameter, and tens of microns in height), the result is like “an engine with 10 billion pistons, with lithium metal as the working fluid,” Li says. Because the walls of these honeycomb-like structures are made of chemically stable MIEC, the lithium never loses electrical contact with the material, Li says. Thus, the whole solid battery can remain mechanically and chemically stable as it goes through its cycles of use. The team has proved the concept experimentally, putting a test device through 100 cycles of charging and discharging without producing any fracturing of the solids. Reversible Li metal plating and stripping in a carbon tubule with an inner diameter of 100nm. Courtesy of the researchers. Li says that though many other groups are working on what they call solid batteries, most of those systems actually work better with some liquid electrolyte mixed with the solid electrolyte material. “But in our case,” he says, “it’s truly all solid. There is no liquid or gel in it of any kind.”   The new system could lead to safe anodes that weigh only a quarter as much as their conventional counterparts in lithium-ion batteries, for the same amount of storage capacity. If combined with new concepts for lightweight versions of the other electrode, the cathode, this work could lead to substantial reductions in the overall weight of lithium-ion batteries. For example, the team hopes it could lead to cellphones that could be charged just once every three days, without making the phones any heavier or bulkier. One new concept for a lighter cathode was described by another team led by Li, in a paper that appeared last month in the journal Nature Energy, co-authored by MIT postdoc Zhi Zhu and graduate student Daiwei Yu. The material would reduce the use of nickel and cobalt, which are expensive and toxic and used in present-day cathodes. The new cathode does not rely only on the capacity contribution from these transition-metals in battery cycling. Instead, it would rely more on the redox capacity of oxygen, which is much lighter and more abundant. But in this process the oxygen ions become more mobile, which can cause them to escape from the cathode particles. The researchers used a high-temperature surface treatment with molten salt to produce a protective surface layer on particles of manganese- and lithium-rich metal-oxide, so the amount of oxygen loss is drastically reduced. Even though the surface layer is very thin, just 5 to 20 nanometers thick on a 400 nanometer-wide particle, it provides good protection for the underlying material. “It’s almost like immunization,” Li says, against the destructive effects of oxygen loss in batteries used at room temperature. The present versions provide at least a 50 percent improvement in the amount of energy that can be stored for a given weight, with much better cycling stability. The team has only built small lab-scale devices so far, but “I expect this can be scaled up very quickly,” Li says. The materials needed, mostly manganese, are significantly cheaper than the nickel or cobalt used by other systems, so these cathodes could cost as little as a fifth as much as the conventional versions. The research teams included researchers from MIT, Hong Kong Polytechnic University, the University of Central Florida, the University of Texas at Austin, and Brookhaven National Laboratories in Upton, New York. The work was supported by the National Science Foundation. (Comment on this)
11:00a	Chemists unveil the structure of an influenza B protein A team of MIT chemists has discovered the structure of a key influenza protein, a finding that could help researchers design drugs that block the protein and prevent the virus from spreading. The protein, known as BM2, is a proton channel that controls acidity within the virus, helping it to release its genetic material inside infected cells. “If you can block this proton channel, you have a way to inhibit influenza infection,” says Mei Hong, an MIT professor of chemistry and senior author of the study. “Having the atomic-resolution structure for this protein is exactly what medicinal chemists and pharmaceutical scientists need to start designing small molecules that can block it.” MIT graduate student Venkata Mandala is the lead author of the paper, which appears today in Nature Structural and Molecular Biology. Other authors include graduate students Alexander Loftis and Alexander Shcherbakov and associate professor of chemistry Bradley Pentelute. Atomic-scale resolution There are three classes of influenza virus — A, B, and C — and each of them produces a different version of the M2 protein. M2 is an ion channel that carries protons through the virus’s outer membrane, known as the lipid envelope. These protons usually flow into the virus, making the interior more acidic. This acidity helps the virus to merge its lipid envelope with the membrane of a cellular compartment called an endosome, allowing it to release its DNA into the infected cell. Until now, most structural studies of the M2 protein have focused on the version of M2 found in influenza A, which is usually the most common form, especially earlier in the flu season. In this study, the researchers focused on the version of M2 found in influenza B viruses, which usually dominate in March and April. However, in contrast to previous patterns of seasonal flu infections, this winter, influenza B has been unusually dominant, accounting for 67 percent of all flu cases reported to the U.S. Centers for Disease Control since last September. The A and B versions of M2 vary significantly in their amino acid sequences, so Hong and her colleagues set out to study what structural differences these proteins might have, and how those differences influence their functions. One key difference is that the BM2 channel can allow protons to flow in either direction, whereas the AM2 channel only allows protons to flow into the viral envelope. To investigate the structure of BM2, the researchers embedded it into a lipid bilayer, similar to a cell membrane, and then used nuclear magnetic resonance (NMR) spectroscopy to analyze the structure with atomic-scale resolution. Very few ion channels have been studied at such high resolution because of the difficulty of studying proteins embedded within membranes. However, Hong has previously developed several NMR techniques that allow her to obtain accurate structural information from membrane-embedded proteins, including their orientation and the distances between atoms of the protein. This model depicts an M2 protein channel embedded in the viral envelope of an influenza B virus. Credit: Venkata Shiva Mandala The M2 channel is made of four helices that run parallel to each other through the membrane, and Hong found that the alignment of these helices changes slightly depending on the pH of the environment outside the viral envelope. When the pH is high, the helices are tilted by about 14 degrees, and the channel is closed. When the pH goes down, the helices increase their tilt to about 20 degrees, opening up like a pair of scissors. This scissoring motion creates more space between the helices and allows more water to get into the channel. MIT chemists created this model of how the four helical proteins that make up the BM2 channel tilt when the channel is open. Credit: Venkata Shiva Mandala Previous studies have found that as water flows into the M2 channel, the amino acid histidine grabs protons from the water in the top half of the channel and passes them to water molecules in the lower half of the channel, which then deliver the excess protons into the virion.   Unlike the AM2 channel, the BM2 channel has an extra histidine at the virion-facing end of the channel, which the MIT team believes to explain why protons can flow in either direction through the channel. More study is needed to determine what kind of advantage this may provide for influenza B viruses, the researchers say. Blocking the channel Now that chemists know the structure of both the open and closed states of the BM2 channel at atomic resolution, they can try to come up with ways to block it. There is precedent for this type of drug development: Amantadine and rimantadine, both used to treat influenza A, work by wedging themselves into the AM2 channel pore and cutting off the flow of protons. However, these drugs do not affect the BM2 channel. Hong’s research group is now investigating another one of BM2’s functions, which is generating curvature in lipid membranes in order to allow progeny viruses to be released from cells. Preliminary studies suggest that a portion of the protein that sticks out from the membrane forms a structure called a beta sheet that plays a role in inducing the membrane to curve inward. The research was funded by the National Institutes of Health. (Comment on this)

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