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      Communications system achieves fastest laser link from space yet

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      In May 2022, the TeraByte InfraRed Delivery (TBIRD) payload onboard a small CubeSat satellite was launched into orbit 300 miles above Earth’s surface. Since then, TBIRD has delivered terabytes of data at record-breaking rates of up to 100 gigabits per second — 100 times faster than the fastest internet speeds in most cities — via an optical communication link to a ground-based receiver in California. This data rate is more than 1,000 times higher than that of the radio-frequency links traditionally used for satellite communication and the highest ever achieved by a laser link from space to ground. And these record-setting speeds were all made possible by a communications payload roughly the size of a tissue box.

      MIT Lincoln Laboratory conceptualized the TBIRD mission in 2014 as a means of providing unprecedented capability to science missions at low cost. Science instruments in space today routinely generate more data than can be returned to Earth over typical space-to-ground communications links. With small, low-cost space and ground terminals, TBIRD can enable scientists from around the world to fully take advantage of laser communications to downlink all the data they could ever dream of.

      Designed and built at Lincoln Laboratory, the TBIRD communications payload was integrated onto a CubeSat manufactured by Terran Orbital as part of NASA’s Pathfinder Technology Demonstrator program. NASA Ames Research Center established this program to develop a CubeSat bus (the “vehicle” that powers and steers the payload) for bringing science and technology demonstrators into orbit more quickly and inexpensively. Weighing approximately 25 pounds and the size of two stacked cereal boxes, the CubeSat was launched into low-Earth orbit (LEO) aboard Space X’s Transporter-5 rideshare mission from Cape Canaveral Space Force Station in Florida in May 2022. The optical ground station is located in Table Mountain, California, where most weather takes place below the mountain’s summit, making this part of the sky relatively clear for laser communication. This ground station leverages the one-meter telescope and adaptive optics (to correct for distortions caused by atmospheric turbulence) at the NASA Jet Propulsion Laboratory Optical Communications Telescope Laboratory, with Lincoln Laboratory providing the TBIRD-specific ground communications hardware.

      “We’ve demonstrated a higher data rate than ever before in a smaller package than ever before,” says Jade Wang, the laboratory’s program manager for the TBIRD payload and ground communications and assistant leader of the Optical and Quantum Communications Technology Group. “While sending data from space using lasers may sound futuristic, the same technical concept is behind the fiber-optic internet we use every day. The difference is that the laser transmissions are taking place in the open atmosphere, rather than in contained fibers.”

      From radio waves to laser light

      Whether video conferencing, gaming, or streaming movies in high definition, you are using high-data-rate links that run across optical fibers made of glass (or sometimes plastic). About the diameter of a strand of human hair, these fibers are bundled into cables, which transmit data via fast-traveling pulses of light from a laser or other source. Fiber-optic communications are paramount to the internet age, in which large amounts of data must be quickly and reliably distributed across the globe every day.

      For satellites, however, a high-speed internet based on laser communications does not yet exist. Since the beginning of spaceflight in the 1950s, missions have relied on radio frequencies to send data to and from space. Compared to radio waves, the infrared light employed in laser communications has a much higher frequency (or shorter wavelength), which allows more data to be packed into each transmission. Laser communications will enable scientists to send 100 to 1,000 times more data than today’s radio-frequency systems — akin to our terrestrial switch from dial-up to high-speed internet.

      From Earth observation to space exploration, many science missions will benefit from this speedup, especially as instrument capabilities advance to capture larger troves of high-resolution data, experiments involve more remote control, and spacecraft voyage further from Earth into deep space.  

      However, laser-based space communication comes with several engineering challenges. Unlike radio waves, laser light forms a narrow beam. For successful data transmission, this narrow beam must be pointed precisely toward a receiver (e.g., telescope) located on the ground. And though laser light can travel long distances in space, laser beams can be distorted because of atmospheric effects and weather conditions. This distortion causes the beam to experience power loss, which can result in data loss.

      For the past 40 years, Lincoln Laboratory been tackling these and related challenges through various programs. At this point, these challenges have been reliably solved, and laser communications is rapidly becoming widely adopted. Industry has begun a proliferation of LEO cross-links using laser communications, with the intent to enhance the existing terrestrial backbone, as well as to provide a potential internet backbone to serve users in rural locations. Last year, NASA launched the Laser Communications Relay Demonstration (LCRD), a two-way optical communications system based on a laboratory design. In upcoming missions, a laboratory-developed laser communications terminal will be launched to the International Space Station, where the terminal will “talk” to LCRD, and support Artemis II, a crewed program that will fly by the moon in advance of a future crewed lunar landing.

      “With the expanding interest and development in space-based laser communications, Lincoln Laboratory continues to push the envelope of what is possible,” says Wang. “TBIRD heralds a new approach with the potential to further increase data rate capabilities; shrink size, weight, and power; and reduce lasercom mission costs.”

      One way that TBIRD aims to reduce these costs is by utilizing commercial off-the-shelf components originally developed for terrestrial fiber-optic networks. However, terrestrial components are not designed to survive the rigors of space, and their operation can be impacted by atmospheric effects. With TBIRD, the laboratory developed solutions to both challenges.

      Commercial components adapted for space

      The TBIRD payload integrates three key commercial off-the-shelf components: a high-rate optical modem, a large high-speed storage drive, and an optical signal amplifier.

      All these hardware components underwent shock and vibration, thermal-vacuum, and radiation testing to inform how the hardware might fare in space, where it would be subject to powerful forces, extreme temperatures, and high radiation levels. When the team first tested the amplifier through a thermal test simulating the space environment, the fibers melted. As Wang explains, in vacuum, no atmosphere exists, so heat gets trapped and cannot be released by convection. The team worked with the vendor to modify the amplifier to release heat through conduction instead.

      To deal with data loss from atmospheric effects, the laboratory developed its own version of Automatic Repeat Request (ARQ), a protocol for controlling errors in data transmission over a communications link. With ARQ, the receiver (in this case, the ground terminal) alerts the sender (satellite) through a low-rate uplink signal to re-transmit any block of data (frame) that has been lost or damaged.

      “If the signal drops out, data can be re-transmitted, but if done inefficiently — meaning you spend all your time sending repeat data instead of new data — you can lose a lot of throughput,” explains TBIRD system engineer Curt Schieler, a technical staff member in Wang’s group. “With our ARQ protocol, the receiver tells the payload which frames it received correctly, so the payload knows which ones to re-transmit.”

      Another aspect of TBIRD that is new is its lack of a gimbal, a mechanism for pointing the narrow laser beam. Instead, TBIRD relies on a laboratory-developed error-signaling concept for precision body pointing of the spacecraft. Error signals are provided to the CubeSat bus so it knows how exactly to point the body of the entire satellite toward the ground station. Without a gimbal, the payload can be even further miniaturized.

      “We intended to demonstrate a low-cost technology capable of quickly downlinking a large volume of data from LEO to Earth, in support of science missions,” says Wang. “In just a few weeks of operations, we have already accomplished this goal, achieving unprecedented transmission rates of up to 100 gigabits per second. Next, we plan to exercise additional features of the TBIRD system, including increasing rates to 200 gigabits per second, enabling the downlink of more than 2 terabytes of data — equivalent to 1,000 high-definition movies — in a single five-minute pass over a ground station.”

      Lincoln Laboratory developed the TBIRD mission and technology in partnership with NASA Goddard Space Flight Center. More

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      3 Questions: Why cybersecurity is on the agenda for corporate boards of directors

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      Organizations of every size and in every industry are vulnerable to cybersecurity risks — a dynamic landscape of threats and vulnerabilities and a corresponding overload of possible mitigating controls. MIT Senior Lecturer Keri Pearlson, who is also the executive director of the research consortium Cybersecurity at MIT Sloan (CAMS) and an instructor for the new MIT Sloan Executive Education course Cybersecurity Governance for the Board of Directors, knows how business can get ahead of this risk. Here, she describes the current threat and explores how boards can mitigate their risk against cybercrime.

      Q: What does the current state of cyberattacks mean for businesses in 2023?

      A: Last year we were discussing how the pandemic heightened fear, uncertainty, doubt and chaos, opening new doors for malicious actors to do their cyber mischief in our organizations and our families. We saw an increase in ransomware and other cyber attacks, and we saw an increase in concern from operating executives and board of directors wondering how to keep the organization secure. Since then, we have seen a continued escalation of cyber incidents, many of which no longer make the headlines unless they are wildly unique, damaging, or different than previous incidents. For every new technology that cybersecurity professionals invent, it’s only a matter of time until malicious actors find a way around it. New leadership approaches are needed for 2023 as we move into the next phase of securing our organizations.

      In great part, this means ensuring deep cybersecurity competencies on our boards of directors. Cyber risk is so significant that a responsible board can no longer ignore it or just delegate it to risk management experts. In fact, an organization’s board of directors holds a uniquely vital role in safeguarding data and systems for the future because of their fiduciary responsibility to shareholders and their responsibility to oversee and mitigate business risk.

      As these cyber threats increase, and as companies bolster their cybersecurity budgets accordingly, the regulatory community is also advancing new requirements of companies. In March of this year, the SEC issued a proposed rule titled Cybersecurity Risk Management, Strategy, Governance, and Incident Disclosure. In it, the SEC describes its intention to require public companies to disclose whether their boards have members with cybersecurity expertise. Specifically, registrants will be required to disclose whether the entire board, a specific board member, or a board committee is responsible for the oversight of cyber risks; the processes by which the board is informed about cyber risks, and the frequency of its discussions on this topic; and whether and how the board or specified board committee considers cyber risks as part of its business strategy, risk management, and financial oversight.

      Q: How can boards help their organizations mitigate cyber risk?

      A: According to the studies I’ve conducted with my CAMS colleagues, most organizations focus on cyber protection rather than cyber resilience, and we believe that is a mistake. A company that invests only in protection is not managing the risk associated with getting up and running again in the event of a cyber incident, and they are not going to be able to respond appropriately to new regulations, either. Resiliency means having a practical plan for recovery and business continuation.

      Certainly, protection is part of the resilience equation, but if the pandemic taught us anything, it taught us that resilience is the ability to weather an attack and recover quickly with minimal impact to our operations. The ultimate goal of a cyber-resilient organization would be zero disruption from a cyber breach — no impact on operations, finances, technologies, supply chain or reputation. Board members should ask, What would it take for this to be the case? And they should ensure that executives and managers have made proper and appropriate preparations to respond and recover.

      Being a knowledgeable board member does not mean becoming a cybersecurity expert, but it does mean understanding basic concepts, risks, frameworks, and approaches. And it means having the ability to assess whether management appropriately comprehends related threats, has an appropriate cyber strategy, and can measure its effectiveness. Board members today require focused training on these critical areas to carry out their mission. Unfortunately, many enterprises fail to leverage their boards of directors in this capacity or prepare board members to actively contribute to strategy, protocols, and emergency action plans.

      Alongside my CAMS colleagues Stuart Madnick and Kevin Powers, I’m teaching a new  MIT Sloan Executive Education course, Cybersecurity Governance for the Board of Directors, designed to help organizations and their boards get up to speed. Participants will explore the board’s role in cybersecurity, as well as breach planning, response, and mitigation. And we will discuss the impact and requirements of the many new regulations coming forward, not just from the SEC, but also White House, Congress, and most states and countries around the world, which are imposing more high-level responsibilities on companies.

      Q: What are some examples of how companies, and specifically boards of directors, have successfully upped their cybersecurity game?

      A: To ensure boardroom skills reflect the patterns of the marketplace, companies such as FedEx, Hasbro, PNC, and UPS have transformed their approach to governing cyber risk, starting with board cyber expertise. In companies like these, building resiliency started with a clear plan — from the boardroom — built on business and economic analysis.

      In one company we looked at, the CEO realized his board was not well versed in the business context or financial exposure risk from a cyber attack, so he hired a third-party consulting firm to conduct a cybersecurity maturity assessment. The company CISO presented the results of the report to the enterprise risk management subcommittee, creating a productive dialogue around the business and financial impact of different investments in cybersecurity.  

      Another organization focused their board on the alignment of their cybersecurity program and operational risk. The CISO, chief risk officer, and board collaborated to understand the exposure of the organization from a risk perspective, resulting in optimizing their cyber insurance policy to mitigate the newly understood risk.

      One important takeaway from these examples is the importance of using the language of risk, resiliency, and reputation to bridge the gaps between technical cybersecurity needs and the oversight responsibilities executed by boards. Boards need to understand the financial exposure resulting from cyber risk, not just the technical components typically found in cyber presentations.

      Cyber risk is not going away. It’s escalating and becoming more sophisticated every day. Getting your board “on board” is key to meeting new guidelines, providing sufficient oversight to cybersecurity plans, and making organizations more resilient. More

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      Busy GPUs: Sampling and pipelining method speeds up deep learning on large graphs

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      Graphs, a potentially extensive web of nodes connected by edges, can be used to express and interrogate relationships between data, like social connections, financial transactions, traffic, energy grids, and molecular interactions. As researchers collect more data and build out these graphical pictures, researchers will need faster and more efficient methods, as well as more computational power, to conduct deep learning on them, in the way of graph neural networks (GNN).  

      Now, a new method, called SALIENT (SAmpling, sLIcing, and data movemeNT), developed by researchers at MIT and IBM Research, improves the training and inference performance by addressing three key bottlenecks in computation. This dramatically cuts down on the runtime of GNNs on large datasets, which, for example, contain on the scale of 100 million nodes and 1 billion edges. Further, the team found that the technique scales well when computational power is added from one to 16 graphical processing units (GPUs). The work was presented at the Fifth Conference on Machine Learning and Systems.

      “We started to look at the challenges current systems experienced when scaling state-of-the-art machine learning techniques for graphs to really big datasets. It turned out there was a lot of work to be done, because a lot of the existing systems were achieving good performance primarily on smaller datasets that fit into GPU memory,” says Tim Kaler, the lead author and a postdoc in the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL).

      By vast datasets, experts mean scales like the entire Bitcoin network, where certain patterns and data relationships could spell out trends or foul play. “There are nearly a billion Bitcoin transactions on the blockchain, and if we want to identify illicit activities inside such a joint network, then we are facing a graph of such a scale,” says co-author Jie Chen, senior research scientist and manager of IBM Research and the MIT-IBM Watson AI Lab. “We want to build a system that is able to handle that kind of graph and allows processing to be as efficient as possible, because every day we want to keep up with the pace of the new data that are generated.”

      Kaler and Chen’s co-authors include Nickolas Stathas MEng ’21 of Jump Trading, who developed SALIENT as part of his graduate work; former MIT-IBM Watson AI Lab intern and MIT graduate student Anne Ouyang; MIT CSAIL postdoc Alexandros-Stavros Iliopoulos; MIT CSAIL Research Scientist Tao B. Schardl; and Charles E. Leiserson, the Edwin Sibley Webster Professor of Electrical Engineering at MIT and a researcher with the MIT-IBM Watson AI Lab.     

      For this problem, the team took a systems-oriented approach in developing their method: SALIENT, says Kaler. To do this, the researchers implemented what they saw as important, basic optimizations of components that fit into existing machine-learning frameworks, such as PyTorch Geometric and the deep graph library (DGL), which are interfaces for building a machine-learning model. Stathas says the process is like swapping out engines to build a faster car. Their method was designed to fit into existing GNN architectures, so that domain experts could easily apply this work to their specified fields to expedite model training and tease out insights during inference faster. The trick, the team determined, was to keep all of the hardware (CPUs, data links, and GPUs) busy at all times: while the CPU samples the graph and prepares mini-batches of data that will then be transferred through the data link, the more critical GPU is working to train the machine-learning model or conduct inference. 

      The researchers began by analyzing the performance of a commonly used machine-learning library for GNNs (PyTorch Geometric), which showed a startlingly low utilization of available GPU resources. Applying simple optimizations, the researchers improved GPU utilization from 10 to 30 percent, resulting in a 1.4 to two times performance improvement relative to public benchmark codes. This fast baseline code could execute one complete pass over a large training dataset through the algorithm (an epoch) in 50.4 seconds.                          

      Seeking further performance improvements, the researchers set out to examine the bottlenecks that occur at the beginning of the data pipeline: the algorithms for graph sampling and mini-batch preparation. Unlike other neural networks, GNNs perform a neighborhood aggregation operation, which computes information about a node using information present in other nearby nodes in the graph — for example, in a social network graph, information from friends of friends of a user. As the number of layers in the GNN increase, the number of nodes the network has to reach out to for information can explode, exceeding the limits of a computer. Neighborhood sampling algorithms help by selecting a smaller random subset of nodes to gather; however, the researchers found that current implementations of this were too slow to keep up with the processing speed of modern GPUs. In response, they identified a mix of data structures, algorithmic optimizations, and so forth that improved sampling speed, ultimately improving the sampling operation alone by about three times, taking the per-epoch runtime from 50.4 to 34.6 seconds. They also found that sampling, at an appropriate rate, can be done during inference, improving overall energy efficiency and performance, a point that had been overlooked in the literature, the team notes.      

      In previous systems, this sampling step was a multi-process approach, creating extra data and unnecessary data movement between the processes. The researchers made their SALIENT method more nimble by creating a single process with lightweight threads that kept the data on the CPU in shared memory. Further, SALIENT takes advantage of a cache of modern processors, says Stathas, parallelizing feature slicing, which extracts relevant information from nodes of interest and their surrounding neighbors and edges, within the shared memory of the CPU core cache. This again reduced the overall per-epoch runtime from 34.6 to 27.8 seconds.

      The last bottleneck the researchers addressed was to pipeline mini-batch data transfers between the CPU and GPU using a prefetching step, which would prepare data just before it’s needed. The team calculated that this would maximize bandwidth usage in the data link and bring the method up to perfect utilization; however, they only saw around 90 percent. They identified and fixed a performance bug in a popular PyTorch library that caused unnecessary round-trip communications between the CPU and GPU. With this bug fixed, the team achieved a 16.5 second per-epoch runtime with SALIENT.

      “Our work showed, I think, that the devil is in the details,” says Kaler. “When you pay close attention to the details that impact performance when training a graph neural network, you can resolve a huge number of performance issues. With our solutions, we ended up being completely bottlenecked by GPU computation, which is the ideal goal of such a system.”

      SALIENT’s speed was evaluated on three standard datasets ogbn-arxiv, ogbn-products, and ogbn-papers100M, as well as in multi-machine settings, with different levels of fanout (amount of data that the CPU would prepare for the GPU), and across several architectures, including the most recent state-of-the-art one, GraphSAGE-RI. In each setting, SALIENT outperformed PyTorch Geometric, most notably on the large ogbn-papers100M dataset, containing 100 million nodes and over a billion edges Here, it was three times faster, running on one GPU, than the optimized baseline that was originally created for this work; with 16 GPUs, SALIENT was an additional eight times faster. 

      While other systems had slightly different hardware and experimental setups, so it wasn’t always a direct comparison, SALIENT still outperformed them. Among systems that achieved similar accuracy, representative performance numbers include 99 seconds using one GPU and 32 CPUs, and 13 seconds using 1,536 CPUs. In contrast, SALIENT’s runtime using one GPU and 20 CPUs was 16.5 seconds and was just two seconds with 16 GPUs and 320 CPUs. “If you look at the bottom-line numbers that prior work reports, our 16 GPU runtime (two seconds) is an order of magnitude faster than other numbers that have been reported previously on this dataset,” says Kaler. The researchers attributed their performance improvements, in part, to their approach of optimizing their code for a single machine before moving to the distributed setting. Stathas says that the lesson here is that for your money, “it makes more sense to use the hardware you have efficiently, and to its extreme, before you start scaling up to multiple computers,” which can provide significant savings on cost and carbon emissions that can come with model training.

      This new capacity will now allow researchers to tackle and dig deeper into bigger and bigger graphs. For example, the Bitcoin network that was mentioned earlier contained 100,000 nodes; the SALIENT system can capably handle a graph 1,000 times (or three orders of magnitude) larger.

      “In the future, we would be looking at not just running this graph neural network training system on the existing algorithms that we implemented for classifying or predicting the properties of each node, but we also want to do more in-depth tasks, such as identifying common patterns in a graph (subgraph patterns), [which] may be actually interesting for indicating financial crimes,” says Chen. “We also want to identify nodes in a graph that are similar in a sense that they possibly would be corresponding to the same bad actor in a financial crime. These tasks would require developing additional algorithms, and possibly also neural network architectures.”

      This research was supported by the MIT-IBM Watson AI Lab and in part by the U.S. Air Force Research Laboratory and the U.S. Air Force Artificial Intelligence Accelerator. More

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      Breaking the scaling limits of analog computing

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      As machine-learning models become larger and more complex, they require faster and more energy-efficient hardware to perform computations. Conventional digital computers are struggling to keep up.

      An analog optical neural network could perform the same tasks as a digital one, such as image classification or speech recognition, but because computations are performed using light instead of electrical signals, optical neural networks can run many times faster while consuming less energy.

      However, these analog devices are prone to hardware errors that can make computations less precise. Microscopic imperfections in hardware components are one cause of these errors. In an optical neural network that has many connected components, errors can quickly accumulate.

      Even with error-correction techniques, due to fundamental properties of the devices that make up an optical neural network, some amount of error is unavoidable. A network that is large enough to be implemented in the real world would be far too imprecise to be effective.

      MIT researchers have overcome this hurdle and found a way to effectively scale an optical neural network. By adding a tiny hardware component to the optical switches that form the network’s architecture, they can reduce even the uncorrectable errors that would otherwise accumulate in the device.

      Their work could enable a super-fast, energy-efficient, analog neural network that can function with the same accuracy as a digital one. With this technique, as an optical circuit becomes larger, the amount of error in its computations actually decreases.  

      “This is remarkable, as it runs counter to the intuition of analog systems, where larger circuits are supposed to have higher errors, so that errors set a limit on scalability. This present paper allows us to address the scalability question of these systems with an unambiguous ‘yes,’” says lead author Ryan Hamerly, a visiting scientist in the MIT Research Laboratory for Electronics (RLE) and Quantum Photonics Laboratory and senior scientist at NTT Research.

      Hamerly’s co-authors are graduate student Saumil Bandyopadhyay and senior author Dirk Englund, an associate professor in the MIT Department of Electrical Engineering and Computer Science (EECS), leader of the Quantum Photonics Laboratory, and member of the RLE. The research is published today in Nature Communications.

      Multiplying with light

      An optical neural network is composed of many connected components that function like reprogrammable, tunable mirrors. These tunable mirrors are called Mach-Zehnder Inferometers (MZI). Neural network data are encoded into light, which is fired into the optical neural network from a laser.

      A typical MZI contains two mirrors and two beam splitters. Light enters the top of an MZI, where it is split into two parts which interfere with each other before being recombined by the second beam splitter and then reflected out the bottom to the next MZI in the array. Researchers can leverage the interference of these optical signals to perform complex linear algebra operations, known as matrix multiplication, which is how neural networks process data.

      But errors that can occur in each MZI quickly accumulate as light moves from one device to the next. One can avoid some errors by identifying them in advance and tuning the MZIs so earlier errors are cancelled out by later devices in the array.

      “It is a very simple algorithm if you know what the errors are. But these errors are notoriously difficult to ascertain because you only have access to the inputs and outputs of your chip,” says Hamerly. “This motivated us to look at whether it is possible to create calibration-free error correction.”

      Hamerly and his collaborators previously demonstrated a mathematical technique that went a step further. They could successfully infer the errors and correctly tune the MZIs accordingly, but even this didn’t remove all the error.

      Due to the fundamental nature of an MZI, there are instances where it is impossible to tune a device so all light flows out the bottom port to the next MZI. If the device loses a fraction of light at each step and the array is very large, by the end there will only be a tiny bit of power left.

      “Even with error correction, there is a fundamental limit to how good a chip can be. MZIs are physically unable to realize certain settings they need to be configured to,” he says.

      So, the team developed a new type of MZI. The researchers added an additional beam splitter to the end of the device, calling it a 3-MZI because it has three beam splitters instead of two. Due to the way this additional beam splitter mixes the light, it becomes much easier for an MZI to reach the setting it needs to send all light from out through its bottom port.

      Importantly, the additional beam splitter is only a few micrometers in size and is a passive component, so it doesn’t require any extra wiring. Adding additional beam splitters doesn’t significantly change the size of the chip.

      Bigger chip, fewer errors

      When the researchers conducted simulations to test their architecture, they found that it can eliminate much of the uncorrectable error that hampers accuracy. And as the optical neural network becomes larger, the amount of error in the device actually drops — the opposite of what happens in a device with standard MZIs.

      Using 3-MZIs, they could potentially create a device big enough for commercial uses with error that has been reduced by a factor of 20, Hamerly says.

      The researchers also developed a variant of the MZI design specifically for correlated errors. These occur due to manufacturing imperfections — if the thickness of a chip is slightly wrong, the MZIs may all be off by about the same amount, so the errors are all about the same. They found a way to change the configuration of an MZI to make it robust to these types of errors. This technique also increased the bandwidth of the optical neural network so it can run three times faster.

      Now that they have showcased these techniques using simulations, Hamerly and his collaborators plan to test these approaches on physical hardware and continue driving toward an optical neural network they can effectively deploy in the real world.

      This research is funded, in part, by a National Science Foundation graduate research fellowship and the U.S. Air Force Office of Scientific Research. More

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      MIT Policy Hackathon produces new solutions for technology policy challenges

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      Almost three years ago, the Covid-19 pandemic changed the world. Many are still looking to uncover a “new normal.”

      “Instead of going back to normal, [there’s a new generation that] wants to build back something different, something better,” says Jorge Sandoval, a second-year graduate student in MIT’s Technology and Policy Program (TPP) at the Institute for Data, Systems and Society (IDSS). “How do we communicate this mindset to others, that the world cannot be the same as before?”

      This was the inspiration behind “A New (Re)generation,” this year’s theme for the IDSS-student-run MIT Policy Hackathon, which Sandoval helped to organize as the event chair. The Policy Hackathon is a weekend-long, interdisciplinary competition that brings together participants from around the globe to explore potential solutions to some of society’s greatest challenges. 

      Unlike other competitions of its kind, Sandoval says MIT’s event emphasizes a humanistic approach. “The idea of our hackathon is to promote applications of technology that are humanistic or human-centered,” he says. “We take the opportunity to examine aspects of technology in the spaces where they tend to interact with society and people, an opportunity most technical competitions don’t offer because their primary focus is on the technology.”

      The competition started with 50 teams spread across four challenge categories. This year’s categories included Internet and Cybersecurity, Environmental Justice, Logistics, and Housing and City Planning. While some people come into the challenge with friends, Sandoval said most teams form organically during an online networking meeting hosted by MIT.

      “We encourage people to pair up with others outside of their country and to form teams of different diverse backgrounds and ages,” Sandoval says. “We try to give people who are often not invited to the decision-making table the opportunity to be a policymaker, bringing in those with backgrounds in not only law, policy, or politics, but also medicine, and people who have careers in engineering or experience working in nonprofits.”

      Once an in-person event, the Policy Hackathon has gone through its own regeneration process these past three years, according to Sandoval. After going entirely online during the pandemic’s height, last year they successfully hosted the first hybrid version of the event, which served as their model again this year.

      “The hybrid version of the event gives us the opportunity to allow people to connect in a way that is lost if it is only online, while also keeping the wide range of accessibility, allowing people to join from anywhere in the world, regardless of nationality or income, to provide their input,” Sandoval says.

      For Swetha Tadisina, an undergraduate computer science major at Lafayette College and participant in the internet and cybersecurity category, the hackathon was a unique opportunity to meet and work with people much more advanced in their careers. “I was surprised how such a diverse team that had never met before was able to work so efficiently and creatively,” Tadisina says.

      Erika Spangler, a public high school teacher from Massachusetts and member of the environmental justice category’s winning team, says that while each member of “Team Slime Mold” came to the table with a different set of skills, they managed to be in sync from the start — even working across the nine-and-a-half-hour time difference the four-person team faced when working with policy advocate Shruti Nandy from Calcutta, India.

      “We divided the project into data, policy, and research and trusted each other’s expertise,” Spangler says, “Despite having separate areas of focus, we made sure to have regular check-ins to problem-solve and cross-pollinate ideas.”

      During the 48-hour period, her team proposed the creation of an algorithm to identify high-quality brownfields that could be cleaned up and used as sites for building renewable energy. Their corresponding policy sought to mandate additional requirements for renewable energy businesses seeking tax credits from the Inflation Reduction Act.

      “Their policy memo had the most in-depth technical assessment, including deep dives in a few key cities to show the impact of their proposed approach for site selection at a very granular level,” says Amanda Levin, director of policy analysis for the Natural Resources Defense Council (NRDC). Levin acted as both a judge and challenge provider for the environmental justice category.

      “They also presented their policy recommendations in the memo in a well-thought-out way, clearly noting the relevant actor,” she adds. This clarity around what can be done, and who would be responsible for those actions, is highly valuable for those in policy.”

      Levin says the NRDC, one of the largest environmental nonprofits in the United States, provided five “challenge questions,” making it clear that teams did not need to address all of them. She notes that this gave teams significant leeway, bringing a wide variety of recommendations to the table. 

      “As a challenge partner, the work put together by all the teams is already being used to help inform discussions about the implementation of the Inflation Reduction Act,” Levin says. “Being able to tap into the collective intelligence of the hackathon helped uncover new perspectives and policy solutions that can help make an impact in addressing the important policy challenges we face today.”

      While having partners with experience in data science and policy definitely helped, fellow Team Slime Mold member Sara Sheffels, a PhD candidate in MIT’s biomaterials program, says she was surprised how much her experiences outside of science and policy were relevant to the challenge: “My experience organizing MIT’s Graduate Student Union shaped my ideas about more meaningful community involvement in renewables projects on brownfields. It is not meaningful to merely educate people about the importance of renewables or ask them to sign off on a pre-planned project without addressing their other needs.”

      “I wanted to test my limits, gain exposure, and expand my world,” Tadisina adds. “The exposure, friendships, and experiences you gain in such a short period of time are incredible.”

      For Willy R. Vasquez, an electrical and computer engineering PhD student at the University of Texas, the hackathon is not to be missed. “If you’re interested in the intersection of tech, society, and policy, then this is a must-do experience.” More

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      Celebrating open data

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      The inaugural MIT Prize for Open Data, which included a $2,500 cash prize, was recently awarded to 10 individual and group research projects. Presented jointly by the School of Science and the MIT Libraries, the prize recognizes MIT-affiliated researchers who make their data openly accessible and reusable by others. The prize winners and 16 honorable mention recipients were honored at the Open Data @ MIT event held Oct. 28 at Hayden Library. 

      “By making data open, researchers create opportunities for novel uses of their data and for new insights to be gleaned,” says Chris Bourg, director of MIT Libraries. “Open data accelerates scholarly progress and discovery, advances equity in scholarly participation, and increases transparency, replicability, and trust in science.” 

      Recognizing shared values

      Spearheaded by Bourg and Rebecca Saxe, associate dean of the School of Science and John W. Jarve (1978) Professor of Brain and Cognitive Sciences, the MIT Prize for Open Data was launched to highlight the value of open data at MIT and to encourage the next generation of researchers. Nominations were solicited from across the Institute, with a focus on trainees: research technicians, undergraduate or graduate students, or postdocs.

      “By launching an MIT-wide prize and event, we aimed to create visibility for the scholars who create, use, and advocate for open data,” says Saxe. “Highlighting this research and creating opportunities for networking would also help open-data advocates across campus find each other.” 

      Recognizing researchers who share data was also one of the recommendations of the Ad Hoc Task Force on Open Access to MIT’s Research, which Bourg co-chaired with Hal Abelson, Class of 1922 Professor, Department of Electrical Engineering and Computer Science. An annual award was one of the strategies put forth by the task force to further the Institute’s mission to disseminate the fruits of its research and scholarship as widely as possible.

      Strong competition

      Winners and honorable mentions were chosen from more than 70 nominees, representing all five schools, the MIT Schwarzman College of Computing, and several research centers across MIT. A committee composed of faculty, staff, and a graduate student made the selections:

      Yunsie Chung, graduate student in the Department of Chemical Engineering, won for SolProp, the largest open-source dataset with temperature-dependent solubility values of organic compounds. 
      Matthew Groh, graduate student, MIT Media Lab, accepted on behalf of the team behind the Fitzpatrick 17k dataset, an open dataset consisting of nearly 17,000 images of skin disease alongside skin disease and skin tone annotations. 
      Tom Pollard, research scientist at the Institute for Medical Engineering and Science, accepted on behalf of the PhysioNet team. This data-sharing platform enables thousands of clinical and machine-learning research studies each year and allows researchers to share sensitive resources that would not be possible through typical data sharing platforms. 
      Joseph Replogle, graduate student with the Whitehead Institute for Biomedical Research, was recognized for the Genome-wide Perturb-seq dataset, the largest publicly available, single-cell transcriptional dataset collected to date. 
      Pedro Reynolds-Cuéllar, graduate student with the MIT Media Lab/Art, Culture, and Technology, and Diana Duarte, co-founder at Diversa, won for Retos, an open-data platform for detailed documentation and sharing of local innovations from under-resourced settings. 
      Maanas Sharma, an undergraduate student, led States of Emergency, a nationwide project analyzing and grading the responses of prison systems to Covid-19 using data scraped from public databases and manually collected data. 
      Djuna von Maydell, graduate student in the Department of Brain and Cognitive Sciences, created the first publicly available dataset of single-cell gene expression from postmortem human brain tissue of patients who are carriers of APOE4, the major Alzheimer’s disease risk gene. 
      Raechel Walker, graduate researcher in the MIT Media Lab, and her collaborators created a Data Activism Curriculum for high school students through the Mayor’s Summer Youth Employment Program in Cambridge, Massachusetts. Students learned how to use data science to recognize, mitigate, and advocate for people who are disproportionately impacted by systemic inequality. 
      Suyeol Yun, graduate student in the Department of Political Science, was recognized for DeepWTO, a project creating open data for use in legal natural language processing research using cases from the World Trade Organization. 
      Jonathan Zheng, graduate student in the Department of Chemical Engineering, won for an open IUPAC dataset for acid dissociation constants, or “pKas,” physicochemical properties that govern how acidic a chemical is in a solution.
      A full list of winners and honorable mentions is available on the Open Data @ MIT website.

      A campus-wide celebration

      Awards were presented at a celebratory event held in the Nexus in Hayden Library during International Open Access Week. School of Science Dean Nergis Mavalvala kicked off the program by describing the long and proud history of open scholarship at MIT, citing the Institute-wide faculty open access policy and the launch of the open-source digital repository DSpace. “When I was a graduate student, we were trying to figure out how to share our theses during the days of the nascent internet,” she said, “With DSpace, MIT was figuring it out for us.” 

      The centerpiece of the program was a series of five-minute presentations from the prize winners on their research. Presenters detailed the ways they created, used, or advocated for open data, and the value that openness brings to their respective fields. Winner Djuna von Maydell, a graduate student in Professor Li-Huei Tsai’s lab who studies the genetic causes of neurodegeneration, underscored why it is important to share data, particularly data obtained from postmortem human brains. 

      “This is data generated from human brains, so every data point stems from a living, breathing human being, who presumably made this donation in the hope that we would use it to advance knowledge and uncover truth,” von Maydell said. “To maximize the probability of that happening, we have to make it available to the scientific community.” 

      MIT community members who would like to learn more about making their research data open can consult MIT Libraries’ Data Services team.  More

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      Urbanization: No fast lane to transformation

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      Accra, Ghana, “is a city I’ve come to know as well as any place in the U.S,” says Associate Professor Noah Nathan, who has conducted research there over the past 15 years. The booming capital of 4 million is an ideal laboratory for investigating the rapid urbanization of nations in Africa and beyond, believes Nathan, who joined the MIT Department of Political Science in July.

      “Accra is vibrant and exciting, with gleaming glass office buildings, shopping centers, and an emerging middle class,” he says. “But at the same time there is enormous poverty, with slums and a mixing pot of ethnic groups.” Cities like Accra that have emerged in developing countries around the world are “hybrid spaces” that provoke a multitude of questions for Nathan.

      “Rich and poor are in incredibly close proximity and I want to know how this dramatic inequality can be sustainable, and what politics looks like with such ethnic and class diversity living side-by-side,” he says.

      With his singular approach to data collection and deep understanding of Accra, its neighborhoods, and increasingly, its built environment, Nathan is generating a body of scholarship on the political impacts of urbanization throughout the global South.

      A trap in the urban transition

      Nathan’s early studies of Accra challenged common expectations about how urbanization shifts political behavior.

      “Modernization theory states that as people become more ‘modern’ and move to cities, ethnicity fades and class becomes the dominant dynamic in political behavior,” explains Nathan. “It predicts that the process of urbanization transforms the relationship between politicians and voters, and elections become more ideologically and policy oriented,” says Nathan.  

      But in Accra, the heart of one of the fastest-growing economies in the developing world, Nathan found “a type of politics stuck in an old equilibrium, hard to dislodge, and not updated by newly wealthy voters,” he says. Using census data revealing the demographic composition of every neighborhood in Accra, Nathan determined that there were many enclaves in which forms of patronage politics and ethnic competition persist. He conducted sample surveys and collected polling-station level results on residents’ voting across the city. “I was able to merge spatial data on where people lived and their answers to survey questions, and determine how different neighborhoods voted,” says Nathan.

      Among his findings: Ethnic politics were thriving in many parts of Accra, and many middle-class voters were withdrawing from politics entirely in reaction to the well-established practice of patronage rather than pressuring politicians to change their approach. “They decided it was better to look out for themselves,” he explains.

      In Nathan’s 2019 book, “Electoral Politics and Africa’s Urban Transition: Class and Ethnicity in Ghana,” he described this situation as a trap. “As the wealthy exit from the state, politicians double down on patronage politics with poor voters, which the middle class views as further evidence of corruption,” he explains. The wealthier citizens “want more public goods, and big policy reforms, such as changes in the health-care and tax systems, while poor voters focus on immediate needs such as jobs, homes, better schools in their communities.”

      In Ghana and other developing countries where the state’s capacity is limited, politicians can’t deliver on the broad-scale changes desired by the middle class. Motivated by their own political survival, they continue dealing with poor voters as clients, trading services for votes. “I connect urban politics in Ghana to the early 20th-century urban machines in the United States, run by party bosses,” says Nathan.

      This may prove sobering news for many engaged with the developing world. “There’s enormous enthusiasm among foreign aid organizations, in the popular press and policy circles, for the idea that urbanization will usher in big, radical political change,” notes Nathan. “But these kinds of transformations will only come about with structural change such as civil service reforms and nonpartisan welfare programs that can push politicians beyond just delivering targeted services to poor voters.”

      Falling in love with Ghana

      For most of his youth, Nathan was a committed jazz saxophonist, toying with going professional. But he had long cultivated another fascination as well. “I was a huge fan of ‘The West Wing’ in middle school” and got into American politics through that,” he says. He volunteered in Hillary Clinton’s 2008 primary campaign during college, but soon realized work in politics was “both more boring and not as idealistic” as he’d hoped.

      As an undergraduate at Harvard University, where he concentrated in government, he “signed up for African history on a lark — because American high schools didn’t teach anything on the subject — and I loved it,” Nathan says. He took another African history course, and then found his way to classes taught by Harvard political scientist Robert H. Bates PhD ’69 that focused on the political economy of development, ethnic conflict, and state failure in Africa. In the summer before his senior year, he served as a research assistant for one of his professors in Ghana, and then stayed longer, hoping to map out a senior thesis on ethnic conflict.

      “Once I got to Ghana, I was fascinated by the place — the dynamism of this rapidly transforming society,” he recalls. “Growing up in the U.S., there are a lot of stereotypes about the developing world, and I quickly realized how much more complicated everything is.”

      These initial experiences living in Ghana shaped Nathan’s ideas for what became his doctoral dissertation at Harvard and first book on the ethnic and class dynamics driving the nation’s politics. His frequent return visits to that country sparked a wealth of research that built on and branched out from this work.

      One set of studies examines the historical development of Ghana’s rural north in its colonial and post-colonial periods, the center of ethnic conflict in the 1990s. These are communities “where the state delivers few resources, doesn’t seem to do much, yet figures as a central actor in people’s lives,” he says.

      Part of this region had been a German colony, and the other part was originally under British rule, and Nathan compared the political trajectories of these two areas, focusing on differences in early state efforts to impose new forms of local political leadership and gradually build a formal education system.

      “The colonial legacy in the British areas was elite families who came to dominate, entrenching themselves and creating political dynasties and economic inequality,” says Nathan. But similar ethnic groups exposed to different state policies in the original German colony were not riven with the same class inequalities, and enjoy better access to government services today. “This research is changing how we think about state weakness in the developing world, how we tend to see the emergence of inequality where societal elites come into power,” he says. The results of Nathan’s research will be published in a forthcoming book, “The Scarce State: Inequality and Political Power in the Hinterland.”

      Politics of built spaces

      At MIT, Nathan is pivoting to a fresh new framing for questions on urbanization. Wielding a public source map of cities around the world, he is scrutinizing the geometry of street grids in 1,000 of sub-Saharan Africa’s largest cities “to think about urban order,” he says. Digitizing historical street maps of African cities from the Library of Congress’s map collection, he can look at how these cities were built and evolved physically. “When cities emerge based on grids, rather than tangles, they are more legible to governments,” he says. “This means that it’s easier to find people, easier to govern, tax, repress, and politically mobilize them.”  

      Nathan has begun to demonstrate that in the post-colonial period, “cities that were built under authoritarian regimes tend to be most legible, with even low-capacity regimes trying to impose control and make them gridded.” Democratic governments, he says, “lead to more tangled and chaotic built environments, with people doing what they want.” He also draws comparisons to how state policies shaped urban growth in the United States, with local and federal governments exerting control over neighborhood development, leading to redlining and segregation in many cities.

      Nathan’s interests naturally pull him toward the MIT Governance Lab and Global Diversity Lab. “I’m hoping to dive into both,” he says. “One big attraction of the department is the really interesting research that’s being done on developing countries.”  He also plans to use the stature he has built over many years of research in Africa to help “open doors” to African researchers and students, who may not always get the same kind of access to institutions and data that he has had. “I’m hoping to build connections to researchers in the global South,” he says. More

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      Can your phone tell if a bridge is in good shape?

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      Want to know if the Golden Gate Bridge is holding up well? There could be an app for that.

      A new study involving MIT researchers shows that mobile phones placed in vehicles, equipped with special software, can collect useful structural integrity data while crossing bridges. In so doing, they could become a less expensive alternative to sets of sensors attached to bridges themselves.

      “The core finding is that information about structural health of bridges can be extracted from smartphone-collected accelerometer data,” says Carlo Ratti, director of the MIT Sensable City Laboratory and co-author of a new paper summarizing the study’s findings.

      The research was conducted, in part, on the Golden Gate Bridge itself. The study showed that mobile devices can capture the same kind of information about bridge vibrations that stationary sensors compile. The researchers also estimate that, depending on the age of a road bridge, mobile-device monitoring could add from 15 percent to 30 percent more years to the structure’s lifespan.

      “These results suggest that massive and inexpensive datasets collected by smartphones could play an important role in monitoring the health of existing transportation infrastructure,” the authors write in their new paper.

      The study, “Crowdsourcing Bridge Vital Signs with Smartphone Vehicle Trips,” is being published in Communications Engineering.

      The authors are Thomas J. Matarazzo, an assistant professor of civil and mechanical engineering at the United States Military Academy at West Point; Daniel Kondor, a postdoc at the Complexity Science Hub in Vienna; Sebastiano Milardo, a researcher at the Senseable City Lab; Soheil S. Eshkevari, a senior research scientist at DiDi Labs and a former member of Senseable City Lab; Paolo Santi, principal research scientist at the Senseable City Lab and research director at the Italian National Research Council; Shamim N. Pakzad, a professor and chair of the Department of Civil and Environmental Engineering at Lehigh University; Markus J. Buehler, the Jerry McAfee Professor in Engineering and professor of civil and environmental engineering and of mechanical engineering at MIT; and Ratti, who is also professor of the practice in MIT’s Department of Urban Studies and Planning.

      Bridges naturally vibrate, and to study the essential “modal frequencies” of those vibrations in many directions, engineers typically place sensors, such as accelerometers, on bridges themselves. Changes in the modal frequencies over time may indicate changes in a bridge’s structural integrity.

      To conduct the study, the researchers developed an Android-based mobile phone application to collect accelerometer data when the devices were placed in vehicles passing over the bridge. They could then see how well those data matched up with data record by sensors on bridges themselves, to see if the mobile-phone method worked.

      “In our work, we designed a methodology for extracting modal vibration frequencies from noisy data collected from smartphones,” Santi says. “As data from multiple trips over a bridge are recorded, noise generated by engine, suspension and traffic vibrations, [and] asphalt, tend to cancel out, while the underlying dominant frequencies emerge.”

      In the case of the Golden Gate Bridge, the researchers drove over the bridge 102 times with their devices running, and the team used 72 trips by Uber drivers with activated phones as well. The team then compared the resulting data to that from a group of 240 sensors that had been placed on the Golden Gate Bridge for three months.

      The outcome was that the data from the phones converged with that from the bridge’s sensors; for 10 particular types of low-frequency vibrations engineers measure on the bridge, there was a close match, and in five cases, there was no discrepancy between the methods at all.

      “We were able to show that many of these frequencies correspond very accurately to the prominent modal frequencies of the bridge,” Santi says.  

      However, only 1 percent of all bridges in the U.S. are suspension bridges. About 41 percent are much smaller concrete span bridges. So, the researchers also examined how well their method would fare in that setting.

      To do so, they studied a bridge in Ciampino, Italy, comparing 280 vehicle trips over the bridge to six sensors that had been placed on the bridge for seven months. Here, the researchers were also encouraged by the findings, though they found up to a 2.3 percent divergence between methods for certain modal frequencies over all 280 trips, and a 5.5 percent divergence over a smaller sample. That suggests a larger volume of trips could yield more useful data.

      “Our initial results suggest that only a [modest amount] of trips over the span of a few weeks are sufficient to obtain useful information about bridge modal frequencies,” Santi says.

      Looking at the method as a whole, Buehler observes, “Vibrational signatures are emerging as a powerful tool to assess properties of large and complex systems, ranging from viral properties of pathogens to structural integrity of bridges as shown in this study. It’s a universal signal found widely in the natural and built environment that we’re just now beginning to explore as a diagnostic and generative tool in engineering.”

      As Ratti acknowledges, there are ways to refine and expand the research, including accounting for the effects of the smartphone mount in the vehicle, the influence of the vehicle type on the data, and more.

      “We still have work to do, but we believe that our approach could be scaled up easily — all the way to the level of an entire country,” Ratti says. “It might not reach the accuracy that one can get using fixed sensors installed on a bridge, but it could become a very interesting early-warning system. Small anomalies could then suggest when to carry out further analyses.”

      The researchers received support from Anas S.p.A., Allianz, Brose, Cisco, Dover Corporation, Ford, the Amsterdam Institute for Advanced Metropolitan Solutions, the Fraunhofer Institute, the former Kuwait-MIT Center for Natural Resources and the Environment, Lab Campus, RATP, Singapore–MIT Alliance for Research and Technology (SMART), SNCF Gares & Connexions, UBER, and the U.S. Department of Defense High-Performance Computing Modernization Program. More