http://www.evanmlerner.com/work daily 1.0 2022-12-27 https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1451146958789-5UDQ3EG5O53HAZ3PW8B6/clams-center-inset.jpg Work - Research From Penn and UCSB Shows How Giant Clams Harness the Sun Evolution in extreme environments has produced life forms with amazing abilities and traits. Beneath the waves, many creatures sport iridescent structures that rival what materials scientists can make in the laboratory. A team of researchers from the University of Pennsylvania and the University of California, Santa Barbara, has now shown how giant clams use these structures to thrive, operating as exceedingly efficient, living greenhouses that grow symbiotic algae as a source of food. This understanding could have implications for alternative energy research, paving the way for new types of solar panels or improved reactors for growing biofuel. The study was led by Alison Sweeney, assistant professor in the Department of Physics and Astronomy in Penn’s School of Arts & Sciences, and Daniel Morse, professor emeritus in UCSB’s Department of Molecular, Cellular and Developmental Biology and Director of its Marine Biotechnology Center. The team also includes lead author Amanda Holt, a postdoctoral researcher formerly at UCSB and now at Penn, as well as Sanaz Vahidinia of NASA’s Ames Research Center and Yakir Luc Gagnon of Duke University. It was published in the Journal of the Royal Society Interface. “Many mollusks, like squid, octopuses, snails and cuttlefish,” Sweeney said, “have iridescent structures, but almost all use them for camouflage or for signaling to mates. We knew giant clams weren’t doing either of those things, so we wanted to know what they were using them for.” While the true purpose of these iridescent structures, cells known as iridocytes, was not known, the team had a strong hypothesis. Like neighboring coral, giant clams are home to symbiotic algae that grow within their flesh. These algae convert the abundant sunlight of the clams’ equatorial home into a source of nutrition but are not particularly efficient in the intense sunlight found on tropical reefs; sunlight at the latitude where these clams live is so intense that it can disrupt the algae’s photosynthesis, paradoxically reducing their ability to generate energy. The team members began their study hypothesizing that the clams’ iridocytes were being used to maximize the usefulness of the light that reaches the algae within their bodies. They were first confounded by the relationship between these iridescent structures and the single-celled plants, until they realized that they had an incomplete picture of their geometry. When they made more precise cross sections of the clams, they found that the algae were organized into pillars, with a layer of iridocytes at the top. “When we saw the complete picture, we understood that the pillars are oriented exactly the wrong way if you want to catch sunlight,” Sweeney said. “That’s where the iridocytes come into play.” The team relied on Amanda Holt and Sanaz Vahidinia to model exactly what was happening to the light once it passed through the iridocytes; the degree of disorder within these cells bore a resemblance to structures Vahidinia studies at NASA: the dust of Saturn’s rings. Their analysis suggested that the iridocytes would scatter many wavelengths of light in a cone-like distribution pointing deeper into the clam. Red and blue wavelengths, the most useful to the algae, spread the widest, impacting the sides of the pillars in which the single-celled plants were stacked. To test this model, the team constructed fiber optic probes with spherical tips the size of an individual alga. Threaded through a section of clam flesh alongside the native algae, this spherical probe was able to detect the angled light scattered by the iridocytes, whereas a flat-tipped probe, only able to sense light shining straight down, detected nothing. “We see that, at any vertical position within the clam tissue, the light comes in at just about the highest rate at which these algae can make use of photons most efficiently,” Sweeney said. “The entire system is scaled so the algae absorb light exactly at the rate where they are happiest.” “This provides a gentle, uniform illumination to the vertical pillars consisting of the millions of symbiotic algae that provide nutrients to their animal host by photosynthesis,” said Morse. “The combined effect of the deeper penetration of sunlight — reaching more algae that grow densely in the 3-dimensional volume of tissue — and the “step-down” reduction in light intensity — preventing the inhibition of photosynthesis from excessive irradiation — enables the host to support a much larger population of active algae producing food than possible without the reflective cells.” Mimicking the micron-scale structures within the clam’s iridocytes and algal pillars could lead to new approaches for boosting the efficiency of photovoltaic cells without having to precisely engineer structures on the nanoscale. Other alternative energy strategies might adopt lessons from the clams in a more direct way: current bioreactors are inefficient because they must constantly stir the algae to keep them exposed to light as they grow and take up more and more space. Adopting the geometry of the iridocytes and algal pillars within the clams would be a way of circumventing that issue. “The clam has to make every square inch count when it comes to efficiency,” Sweeney said. “Likewise, all of our alternatives are very expensive when it comes to surface area, so it makes sense to try to solve that problem the way evolution has.” The research was supported by the Army Research Office and the Office of Naval Research. https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1466024527141-1TUR2Q7HMDJ8EUGP6ZHK/Hogan+Longshot.png Work https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1672182001135-W6Z8TOWMYK8C78W05ATO/85BF241E-8923-452D-ADFC-EFA57ACD93BE.jpeg Work https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1451155759136-AEZB0G0PZLTIV7CGVR4W/image-asset.png Work - Metamaterials: What They Are and Why They're Important https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1451155876080-JS037MMSM5JQDZCMG62S/image-asset.png Work - RHex the Parkour Robot https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1451156158179-PYRTS5OOB0N27F4BMEMO/image-asset.png Work - Robot Quadrotors Perform James Bond Theme https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1451228374742-ZEZS2R2J4M84GVPWAUFY/image-asset.png Work - Creative Students Get Their Hack on at PennApps On Friday, Sept. 4, nearly 2,000 of the world’s top young computer scientists and engineers assembled in the bowl of the Wells Fargo Center. They were awaiting the start of PennApps, the world’s largest collegiate hackathon. In the opening ceremony, Vijay Kumar, the Nemirovsky Family Dean of the School of Engineering and Applied Science, put a fine point on the purpose of the event. “Hacking is the noblest form of research,” Kumar said. Though it conjures images of cybercrime, for engineers, “hacking” is the embodiment of the ingenuity it takes to solve a problem. Over the next 36 hours, PennApps contestants vied against one another to make the best possible pieces of software and hardware—and were also teaching and learning from their peers. While the crucible of a competition featuring more than $60,000 in prizes is a motivator, students, including hundreds of high-schoolers, come to PennApps to push the boundaries of what they can do with computers. “Whether you win the grand prize or just make your first working program and put it on the App Store, both of those are equally gratifying,” says Pranav Vishnu Ramabhadran, PennApps’ director. Ramabhadran, a senior in the Jerome Fisher Program in Management and Technology, a dual degree program with the Engineering and Wharton schools, is carrying the torch for PennApps, an organization founded in 2009. The student group has hosted 11 such competitions in the past. The hackathon has evolved significantly since it launched with just 17 teams, which were all from Penn. This year’s program, PennApps XII, featured hundreds of groups, hailing from around the nation, India, Denmark, Singapore, Australia, and more. The weekend’s proceedings—from teams’ travel costs, to catering, to the space itself—were entirely made possible though sponsorships arranged by the students behind PennApps. Foremost among these sponsors was Comcast, the owner of the Wells Fargo Center, which was eager to show its arena’s new technical capabilities and scout rising talent. As part of their recruiting efforts, other sponsors were happy to lend or donate their hardware as testing platforms, and PennApps provided a parts library, plus soldiering and 3D-printing stations, to help contestants build their own. Still, many contestants’ suitcases were stuffed, not with clothes, but the chips and wires necessary to realize their ideas. Sponsors also incentivized participants with a series of prize categories for using their technology. Apple watches, Microsoft tablets, and more fungible rewards, like bitcoins or gift cards, were in play. New this year was the inclusion of routes, or thematic categories contestants could enter their projects into. The top “Health” hack was a program that could help detect skin cancer by taking a picture of a mole, while the top “Civic” hack provided an easier way of filling out various government forms. Runners-up for the best overall hack included a tool for measuring a person’s gait and a search engine designed for codebases. The grand prize winning team, Fifth Sense, developed an assistive device that connects to smartphones and allows input and output in braille. Carnegie Mellon sophomores Edward Ahn, Cyrus Tabrizi, Rajat Mehndiratta, and Vasu Agrawal also took home prizes in two other categories, including best “Hardware” hack. It was this combination of ingenuity and problem solving that impressed the panel of judges—made up of representatives from local tech and venture capital firms—and is sending the team on to an invite-only hackathon at Facebook headquarters. It also embodies the envelope-pushing spirit of PennApps. “Hacking is really taking the best of what you have around you and making something new,” says PennApp’s Ramabhadran. “It’s taking the normal stuff and doing something unconventional with it.” https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1462736072666-33VD2XEMYKZJ66ROWWMA/IMG_3589.JPG Work https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1462738886668-UCQR4ZKZBC2K0HB4SZVT/Morales%2BAFM.jpg Work http://www.evanmlerner.com/artists daily 0.75 2015-12-26 https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1451138380391-E9D6VDBCFLV04KHIRCKA/Photon+Spin+Device+FULL+.jpg Releases - Penn Researchers Discover New Chiral Property of Silicon, With Photonic Applications By encoding information in photons via their spin, “photonic” computers could be orders of magnitude faster and efficient than their current-day counterparts. Likewise, encoding information in the spin of electrons, rather than just their quantity, could make “spintronic” computers with similar advantages. University of Pennsylvania engineers and physicists have now discovered a property of silicon that combines aspects of all of these desirable qualities. In a study published in Science, they have demonstrated a silicon-based photonic device that is sensitive to the spin of the photons in a laser shined on one of its electrodes. Light that is polarized clockwise causes current to flow in one direction, while counter-clockwise polarized light makes it flow in the other direction. This property was hiding in plain sight; it is a function of the geometric relationship between the pattern of atoms on the surface of silicon nanowires and how electrodes placed on those wires intersect them. The interaction between the semiconducting silicon and the metallic electrodes produces an electric field at an angle that breaks the mirror symmetry that silicon typically exhibits. This chiral property is what sends electrons in one direction or the other down the nanowire depending on the polarity of the light that hits the electrodes. The study was led by Ritesh Agarwal, a professor in the Department of Materials Science and Engineering in Penn’s School of Engineering and Applied Science, and Sajal Dhara, a postdoctoral researcher in Agarwal’s lab. They collaborated with Eugene Mele, a professor in the Department of Physics and Astronomy in Penn’s School of Arts & Sciences. “Whenever you change a symmetry, you can do new things,” said Agarwal. “In this case, we have demonstrated how to make a photodetector sensitive to a photon’s spin. All photonic computers need photodetectors, but they currently only use the quantity of photons to encode information. This sensitivity to photon spin would be an extra degree of freedom, meaning you could encode additional information on each photon. “Typically, materials with heavy elements show this property due to their spins strongly interacting with electron’s orbital motion, but we have demonstrated this effect on the surface of silicon, originating only from the electron’s orbital motion” Agarwal and Dhara reached out to Mele due to his work on topological insulators. He, along with fellow Penn physicist Charles Kane, laid the foundation for this new a class of materials, which are electrical insulators on their interiors but conduct electricity on their surfaces. Agarwal’s group was working on various materials that exhibit topological effects, but as a check on their methods, Mele suggested trying their experiments with silicon as well. As a light, highly symmetric material, silicon was not thought to be able to exhibit these properties. “We expected the control experiment to give a null result, instead we discovered something new about nanomaterials,” Mele said. Silicon is the heart of computer industry, so finding ways of producing these types of effects in that element is preferable to learning how to work with the heavier, rarer elements that naturally exhibit them. Once it was clear that silicon was capable of having chiral properties, the researchers set out to find out the atomic mechanisms behind it. “The effect was coming from the surface of the nanowire,” Dhara said. “The way most silicon nanowires are grown, the atoms are bound in zigzag chains that go along the surface, not down into the wire.” These zigzag patterns are such that placing a mirror on top of them would produce an image that could be superimposed on the original. This is why silicon is not intrinsically chiral. However, when metal electrodes are placed on the wire in the typical perpendicular fashion, they intersect the direction of the chains at a slight angle. “When you have any metal and any semiconductor in contact, you’ll get an electric field at the interface, and it’s this field that is breaking the mirror symmetry in the silicon chains," Dhara said. Because the direction of the electric field does not exactly match the direction of the zigzag chains, there are angles where the silicon is asymmetric. This means it can exhibit chiral properties. Shining a circularly polarized laser at the point on the nanowire where metal and semiconductor meet produces a current, and the spin of the photons in that laser determines the direction of the current’s flow. Dhara and Agarwal are currently working on ways to get planar silicon to exhibit these properties using the same mechanism. The research was supported by the U.S. Army Research Office, the Department of Energy and the National Science Foundation through Penn’s Materials Research Science and Engineering Center. https://images.squarespace-cdn.com/content/v1/567e9c3b5a5668eee105b109/1451145148599-731CU4B8JS4BK7PBB2TR/image-asset.jpeg Releases - Penn, University of California and Army Research Lab Show How Brain’s Wiring Leads to Cognitive Control How does the brain determine which direction to let its thoughts fly? Looking for the mechanisms behind cognitive control of thought, researchers at the University of Pennsylvania, University of California and United States Army Research Laboratory have used brain scans to shed new light on this question. By using structural imaging techniques to convert brain scans into “wiring diagrams” of connections between brain regions, the researchers used the structure of these neural networks to reveal the fundamental rules that govern which parts of the brain are most able to exert “cognitive control” over thoughts and actions. Earlier research has long placed the frontal cortex as the core of this cognitive control network, which allows people to stay focused on one task or switch to a radically different one. This study is the first to provide a mechanistic explanation for how the frontal cortex accomplishes this feat, exerting control over trillions of individual neurons. The work, published in Nature Communications, weds cutting-edge neuroscience with the emerging field of network science, which is often used to study social systems. It applies control theory, a field traditionally used to study electrical and mechanical systems, to show that being on the “outskirts” of the brain is necessary for the frontal cortex to dynamically control the direction of thoughts and goal-directed behavior. This fundamental understanding of how the brain controls its activity could help lead to better interventions for medical conditions associated with reduced cognitive control, such as autism, schizophrenia or dementia. Danielle Bassett, the Skirkanich Assistant Professor of Innovation in Penn’s School of Engineering and Applied Science, is senior author on the study. Shi Gu, a graduate student in the School of Arts & Sciences’ Applied Mathematics and Computational Science program, was the lead author. They collaborated with Fabio Pasqualetti, a control theorist at the University of California, Riverside. The research also featured work from the Scott Grafton, Matthew Cieslak and Michael Miller of the University of California, Santa Barbara, along with researchers at the Army Research Laboratory, including Jean Vettel, Alfred Yu and joint ARL-Penn scientists Qawi Telesford and Ari Kahn, and a researcher at the Moss Rehabilitation Research Institute, John Medaglia. “Surprisingly,” Bassett said, “our results suggest that the human brain resembles a flock of birds. The flock comes to a consensus about which way to fly based on how close the birds are to one another and in what formation. Birds that fly at specific places in the flock can drive changes in the flock's direction, being leaders in a so-called multi-agent system. “Similarly, particular regions of your brain are predisposed to control your thoughts based on where they lie in relation to other regions.” Cognitive psychologists and neuroscientists have long known that the frontal cortex is heavily involved in cognitive control. It is most active in experimental subjects asked to do tasks that require executive function, and damage to that region of the brain, through disease or injury, often results in loss of that function. The researchers were interested in developing a more fundamental understanding of how that region of the brain interacts with others to allow for executive function. Starting with detailed brain scans that show how neurons are physically connected to one another with one-millimeter precision, the scientists used a mathematical technique drawn from control theory in engineering. “We need a basic theory of how the brain controls itself, and to get there we suggest treating the brain as an engineering system,” Bassett said. “Cognitive control is a lot like engineering control: you model the system’s dynamics by identifying key points. If I push on that one piece or pull this lever, I can offer a prediction of how it's going to affect other parts of the network.” By applying control theory equations to the “wiring diagrams” generated from brain scans, the researchers showed that the geographical and functional differences between regions of the brain are linked. "In fact,” Pasqualetti said, “we believe that the human brain responds to internal and external stimuli with principles akin to large-scale dynamical network systems, such as power systems and robotic networks, and that a few carefully selected locations may be preferentially located to optimally guide complex functions." While the analysis cannot say whether the frontal cortex’s location or its role evolved first, it suggests that part of the frontal cortex’s ability to control executive function depends on its distance from other parts of the brain network. “The regions on the outskirts can perform a very specific kind of control,” Bassett said. “They can move the system to distant states, like switching from working at your job to playing with your kids. Regions that are most interconnected, and therefore more internal to the network, are very good at moving the brain into nearby states, like from writing someone an email to talking to them on the phone. What’s particularly interesting is, if we look at where those inner nodes are, they're all in ‘default mode' regions, which are the regions that are active when you are resting. This makes sense, because if you were engineering an optimal system, you would want to put its baseline somewhere where it can get to most of the places it has to go pretty easily.” This type of holistic understanding of the relationship between brain regions’ location and their roles is necessary for tailoring better treatments for people who have lost executive function due to disease or injury. “We're very interested in controlling brain networks with techniques like optogenetics, transcranial magnetic or direct-current stimulation, deep brain stimulation or even neurofeedback,” Bassett said, “but the problem has been that there is little theoretical basis to determine how these stimulations affect the dynamics of the whole brain. In most cases, stimulation is applied via trial and error. This research helps to build up an understanding of the impact of stimulation in one region on cognition as a whole.” Future research will test whether “wiring” differences between people predict their performance on cognitive tasks. It will also underpin work on therapeutic and adaptive technologies that capitalize on brain networks’ unique advantages over their computerized counterparts. “Humans can recognize millions of objects in milliseconds,” said ARL’s Jean Vettel, “but computer vision research has limited success after decades of research on autonomous agents. Our focus on brain networks aims to capture the time-evolving nature of global brain dynamics so we can predict fluctuations in human performance. We can then build neurotechnologies that can image the brain and allow us to gain access to covert mental events and build systems that can adapt to us humans, helping us more when we are tired and less when we are alert." The research was supported by the Alfred P. Sloan Foundation, U.S. Army Research Office by contract W911NF-10-2-0022 and through its Institute for Collaborative Biotechnologies grant W911NF-09-0001, National Science Foundation through awards BCS-1441502 and BCS-1430279 and Public Health Service through grant NS44393. http://www.evanmlerner.com/contact daily 0.75 2016-02-13 http://www.evanmlerner.com/resume daily 0.75 2022-12-27