New collaboration aims to strengthen orthotic and prosthetic care in Sierra Leone

MIT’s K. Lisa Yang Center for Bionics has entered into a collaboration with the government of Sierra Leone to strengthen the capabilities and services of that country’s orthotic and prosthetic (O&P) sector. Tens of thousands of people in Sierra Leone need orthotic braces and artificial limbs, but access to such specialized medical care in this African nation is limited.

The agreement between MIT, the Center for Bionics, and Sierra Leone’s Ministry of Health and Sanitation (MoHS) provides a detailed memorandum of understanding (MOU) and intentions that will begin as a four-year program. The collaborators aim to strengthen Sierra Leone’s O&P sector through six key objectives: data collection and clinic operations, education, supply chain, infrastructure, new technologies, and mobile delivery of services.

Project objectives include:

• data collection and clinic operations: collect comprehensive data on epidemiology, need, utilization, and access for O&P services across the country;
• education: create an inclusive education and training program for the people of Sierra Leone, to enable sustainable and independent operation of O&P services;
• supply chain: establish supply chains for prosthetic and orthotic components, parts, and materials for fabrication of devices;
• infrastructure: prepare infrastructure (e.g., physical space, sufficient water, power, and internet) to support increased production and services;
• new technologies: develop and translate innovative technologies with potential to improve O&P clinic operations and management, patient mobility, and the design or fabrication of devices; and
• mobile delivery: support outreach services and mobile delivery of care for patients in rural and difficult-to-reach areas.

Working together, MIT’s bionics center and Sierra Leone’s MoHS aim to sustainably double the production and distribution of O&P services at Sierra Leone’s National Rehabilitation Centre and Bo Clinics over the next four years.

The team of MIT scientists who will implement this novel collaboration is led by Hugh Herr, MIT professor of media arts and sciences. Herr, himself a double amputee, serves as co-director of the K. Lisa Yang Center for Bionics and heads the renowned Biomechatronics research group at the MIT Media Lab.

“From educational services to supply chain to new technology, this important MOU with the government of Sierra Leone will enable the center to develop a broad, integrative approach to the orthotic and prosthetic sector within Sierra Leone, strengthening services and restoring much-needed care to its citizens,” notes Herr.

Sierra Leone’s Honorable Minister of Health Austin Demby also states: “As the Ministry of Health and Sanitation continues to galvanize efforts towards the attainment of universal health coverage through the life stages approach, this collaboration will foster access, innovation, and capacity-building in the Orthotic and Prosthetic division. The ministry is pleased to work with and learn from MIT over the next four years in building resilient health systems, especially for vulnerable groups.”

“Our team at MIT brings together expertise across disciplines from global health systems to engineering and design,” adds Francesca Riccio-Ackerman, the graduate student lead for the MIT Sierra Leone project. “This allows us to craft an innovative strategy with Sierra Leone’s Ministry of Health and Sanitation. Together we aim to improve available orthotic and prosthetic care for people with disabilities.”

de MIT News https://ift.tt/pO3QTMu

Why lung cancer doesn’t respond well to immunotherapy

Immunotherapy — drug treatment that stimulates the immune system to attack tumors — works well against some types of cancer, but it has shown mixed success against lung cancer.

A new study from MIT helps to shed light on why the immune system mounts such a lackluster response to lung cancer, even after treatment with immunotherapy drugs. In a study of mice, the researchers found that bacteria naturally found in the lungs help to create an environment that suppresses T-cell activation in the lymph nodes near the lungs.

The researchers did not find that kind of immune-suppressive environment in lymph nodes near tumors growing near the skin of mice. They hope that their findings could help lead to the development of new ways to rev up the immune response to lung tumors.

“There is a functional difference between the T-cell responses that are mounted in the different lymph nodes. We’re hoping to identify a way to counteract that suppressive response, so that we can reactivate the lung-tumor-targeting T cells,” says Stefani Spranger, the Howard S. and Linda B. Stern Career Development Assistant Professor of Biology, a member of MIT’s Koch Institute for Integrative Cancer Research, and the senior author of the new study.

MIT graduate student Maria Zagorulya is the lead author of the paper, which appears today in the journal Immunity.

Failure to attack

For many years, scientists have known that cancer cells can send out immunosuppressive signals, which leads to a phenomenon known as T-cell exhaustion. The goal of cancer immunotherapy is to rejuvenate those T cells so they can begin attacking tumors again.

One type of drug commonly used for immunotherapy involves checkpoint inhibitors, which remove the brakes on exhausted T cells and help reactivate them. This approach has worked well with cancers such as melanoma, but not as well with lung cancer.

Spranger’s recent work has offered one possible explanation for this: She found that some T cells stop working even before they reach a tumor, because of a failure to become activated early in their development. In a 2021 paper, she identified populations of dysfunctional T cells that can be distinguished from normal T cells by a pattern of gene expression that prevents them from attacking cancer cells when they enter a tumor.

“Despite the fact that these T cells are proliferating, and they’re infiltrating the tumor, they were never licensed to kill,” Spranger says.

In the new study, her team delved further into this activation failure, which occurs in the lymph nodes, which filter fluids that drain from nearby tissues. The lymph nodes are where “killer T cells” encounter dendritic cells, which present antigens (tumor proteins) and help to activate the T cells.

To explore why some killer T cells fail to be properly activated, Spranger’s team studied mice that had tumors implanted either in the lungs or in the flank. All of the tumors were genetically identical.

The researchers found that T cells in lymph nodes that drain from the lung tumors did encounter dendritic cells and recognize the tumor antigens displayed by those cells. However, these T cells failed to become fully activated, as a result of inhibition by another population of T cells called regulatory T cells.

These regulatory T cells became strongly activated in lymph nodes that drain from the lungs, but not in lymph nodes near tumors located in the flank, the researchers found. Regulatory T cells are normally responsible for making sure that the immune system doesn’t attack the body’s own cells. However, the researchers found that these T cells also interfere with dendritic cells’ ability to activate killer T cells that target lung tumors.

The researchers also discovered how these regulatory T cells suppress dendritic cells: by removing stimulatory proteins from the surface of dendritic cells, which prevents them from being able to turn on killer-T-cell activity.

Microbial influence

Further studies revealed that the activation of regulatory T cells is driven by high levels of interferon gamma in the lymph nodes that drain from the lungs. This signaling molecule is produced in response to the presence of commensal bacterial — bacteria that normally live in the lungs without causing infection.

The researchers have not yet identified the types of bacteria that induce this response or the cells that produce the interferon gamma, but they showed that when they treated mice with an antibody that blocks interferon gamma, they could restore killer T cells’ activity.

Interferon gamma has a variety of effects on immune signaling, and blocking it can dampen the overall immune response against a tumor, so using it to stimulate killer T cells would not be a good strategy to use in patients, Spranger says. Her lab is now exploring other ways to help stimulate the killer T cell response, such as inhibiting the regulatory T cells that suppress the killer-T-cell response or blocking the signals from the commensal bacteria, once the researchers identify them.

The research was funded by a Pew-Stewart Scholarship, the Koch Institute Frontier Research program, the Ludwig Center at the Koch Institute, and an MIT School of Science Fellowship in Cancer Research.

de MIT News https://ift.tt/lnthViW

Sparse, small, but diverse neural connections help make perception reliable, efficient

The brain’s cerebral cortex produces perception based on the sensory information it’s fed through a region called the thalamus.

“How the thalamus communicates with the cortex in a fundamental feature of how the brain interprets the world,” says Elly Nedivi, the William R. and Linda R. Young Professor in The Picower Institute for Learning and Memory at MIT. Despite the importance of thalamic input to the cortex, neuroscientists have struggled to understand how it works so well given the relative paucity of observed connections, or “synapses,” between the two regions.

To help close this knowledge gap, Nedivi assembled a collaboration within and beyond MIT to apply several innovative methods. In a new study described in Nature Neuroscience, the team reports that thalamic inputs into superficial layers of the cortex are not only rare, but also surprisingly weak, and quite diverse in their distribution patterns. Despite this, they are reliable and efficient representatives of information in the aggregate, and their diversity is what underlies these advantages.

Essentially, by meticulously mapping every thalamic synapse on 15 neurons in layer 2/3 of the visual cortex in mice and then modeling how that input affected each neuron’s processing of visual information, the team found that wide variations in the number and arrangement of thalamic synapses made them differentially sensitive to visual stimulus features. While individual neurons therefore couldn’t reliably interpret all aspects of the stimulus, a small population of them could together reliably and efficiently assemble the overall picture.

“It seems this heterogeneity is not a bug; it’s a feature that provides not only a cost benefit, but also confers flexibility and robustness to perturbation” says Nedivi, corresponding author of the study and a member of MIT’s faculty in the departments of Biology and Brain and Cognitive Sciences.

Aygul Balcioglu, the research scientist in Nedivi’s lab who led the work, adds that the research has created a way for neuroscientists to track all the many individual inputs a cell receives as that input is happening.

“Thousands of information inputs pour into a single brain cell. The brain cell then interprets all that information before it communicates its own response to the next brain cell,” Balcioglu says. “What is new, and we feel exciting, is we can now reliably describe the identity and the characteristics of those inputs, as different inputs and characteristics convey different information to a given brain cell. Our techniques give us the ability to describe in living animals where in the structure of the single cell what kind of information gets incorporated. This was not possible until now.”

"MAP"ping and modeling

Nedivi and Balcioglu’s team chose layer 2/3 of the cortex because this layer is where there is relatively high flexibility, or “plasticity,” even in the adult brain. Yet, thalamic innervation there has rarely been characterized. Moreover, Nedivi says, even though the model organism for the study was mice, those layers are the ones that have thickened the most over the course of evolution, and therefore play especially important roles in the human cortex.

Precisely mapping all the thalamic innervation onto entire neurons in living, perceiving mice is so daunting it’s never been done.

To get started, the team used a technique established in Nedivi’s lab that enables observing whole cortical neurons under a two-photon microscope using three different color tags in the same cell simultaneously, except in this case they used one of the colors to label thalamic inputs contacting the labeled cortical neurons. Wherever the color of those thalamic inputs overlapped with the color labeling excitatory synapses on the cortical neurons, that revealed the location of putative thalamic inputs onto the cortical neurons.

Two-photon microscopes offer deep looks into living tissues, but their resolution is not sufficient to confirm that the overlapping labels are indeed synaptic contacts. To confirm their first indications of thalamic inputs, the team turned to a technique called MAP invented in the Picower Institute lab of MIT chemical engineering Associate Professor Kwanghun Chung. MAP physically enlarges tissue in the lab, effectively increasing the resolution of standard microscopes. Rebecca Gillani, a postdoc in the Nedivi lab, with help from Taeyun Ku, a Chung Lab postdoc, was able to combine the new labeling and MAP to definitely resolve, count, map, and even measure the size of all thalamic-cortical synapses onto entire neurons.

The analysis revealed that the thalamic inputs were rather small (typically presumed to also be weak and maybe temporary), and accounted for between 2 and 10 percent of the excitatory synapses on individual visual cortex neurons. The variance in thalamic synapse numbers was not just at a cellular level, but also across different “dendrite” branches of individual cells, accounting for anywhere between zero and nearly half the synapses on a given branch.

“Wisdom of the crowd”

These facts presented Nedivi’s team with a conundrum. If the thalamic inputs were weak, sparse, and widely varying, not only across neurons but even across each neuron’s dendrites, then how good could they be for reliable information transfer?

To help solve the riddle, Nedivi turned to colleague Idan Segev, a professor at Hebrew University in Jerusalem specializing in computational neuroscience. Segev and his student Michael Doron used the Nedivi lab’s detailed anatomical measurements and physiological information from the Allen Brain Atlas to create a biophysically faithful model of the cortical neurons.

Segev’s model showed that when the cells were fed visual information (the simulated signals of watching a grating go past the eyes) their electrical responses varied based on how their thalamic input varied. Some cells perked up more than others in response to different aspects of the visual information, such as contrast or shape, but no single cell revealed much about the overall picture. But with about 20 cells together, the whole visual input could be decoded from their combined activity — a so-called “wisdom of the crowd.”

Notably, Segev compared the performance of cells with the weak, sparse, and varying input akin to what Nedivi’s lab measured, to the performance of a group of cells that all acted like the best single cell of the lot. Up to about 5,000 total synapses, the “best” cell group delivered more informative results, but after that level the small, weak, and diverse group actually performed better. In the race to represent the total visual input with at least 90 percent accuracy, the small, weak, and diverse group reached that level with about 6,700 synapses, while the “best” cell group needed more than 7,900.

“Thus heterogeneity imparts a cost reduction in terms of the number of synapses required for accurate readout of visual features,” the authors wrote.

Nedivi says the study raises tantalizing implications regarding how thalamic input into the cortex works. One, she says, is that given the small size of thalamic synapses they are likely to exhibit significant “plasticity.” Another is that the surprising benefit of diversity may be a general feature, not just a special case for visual input in layer 2/ 3. Further studies, however, are needed to know for sure.

In addition to Nedivi, Balcioglu, Gillani, Ku, Chung, Segev and Doron, other authors are Kendyll Burnell and Alev Erisir.

The National Eye Institute of the National Institutes of Health, the Office of Naval Research, and the JPB Foundation funded the study.

de MIT News https://ift.tt/UkKclM0

Why 1968 still matters

“The whole world is watching,” protestors famously chanted outside the 1968 Democratic National Convention in Chicago, as police beat them.

That might not have been literally true, but it was close enough. The convention was the top-rated telecast for all of 1968 in the U.S., with 90 percent of U.S. households tuning in for an average of 9.5 hours. Many viewers had a strong reaction to the chaotic events being broadcast. And a majority of those who wrote letters afterward to the three national television networks — ABC, CBS, and NBC — expressed unhappiness with the things they had just witnessed.

These people were not angry about the use of force against the protestors, however. As MIT Professor Heather Hendershot chronicles in a new book, many Americans were upset with the news coverage because they deemed it too sympathetic to the protestors.

“It just took the Chicago Convention to make us really blast you for your prejudiced and one-sided coverage,” one airline pilot wrote to famed CBS news anchor Walter Cronkite, asking why the network would reward “filthy, screaming minority groups with free TV coverage and at the same time subject millions of true American citizens with such sickening acts?”

Hendershot explores these events in a new book, “When the News Broke: Chicago 1968 and the Polarizing of America,” published by the University of Chicago Press. In it, Hendershot chronicles the turmoil on the streets and inside the convention hall, and shows that the convention was a key inflection point in the relationship between politics and media. Right-wingers had accused mainstream news organizations of unfair coverage during Barry Goldwater’s presidential campaign of 1964, but following the 1968 Chicago convention, such accusations would take root among a wider swath of people and become an ongoing feature of contemporary culture wars and political polarization.

“This is a really important moment, but there have been no deep analyses of it as a media event, and the fallout afterward,” Hendershot says. “It’s a turning point for the idea of ‘liberal media bias’ taking hold as a nationalized sort of discourse. It’s important to be thinking about what’s regarded as a Golden Age of news coverage and how that came to be destabilized after the convention.”

Inside and out

Hendershot’s research has often focused on media and conservative politics in the postwar era. “When the News Broke” grew out of related research Hendershot was conducting, and took flight as a project after she rewatched the entirety of the 1968 Democratic National Convention as it was originally telecast.

As the book makes clear, changes in perceptions of news coverage were related to the very real changes the country was experiencing at the time. The civil rights movement, as well as Richard Nixon’s adoption of the Southern Strategy and a “law and order” theme for his 1968 campaign as the Republican Party nominee, had begun to bring more polarization to the level of party politics.

To be sure, there were plenty of battles unfolding within the Democratic Party, which came into focus at the 1968 convention. Hendershot’s book devotes a chapter to each of the four days of the convention and contains a wealth of detail about events inside the convention hall, where the Democratic coalition was having disputes over its party platform, delegate selection — and the nominee. Hubert Humphrey, President Lyndon Johnson’s vice president, beat out both antiwar candidate Sen. Eugene McCarthy and underdog Sen. George McGovern.

“I also switch the narrative to talk about what was really happening inside the hall,” Hendershot says.

At the same time, 10,000 people had descended on Chicago in 1968 to protest from the left — an amalgam of antiwar protesters, Yippies, and other groups. There were about 12,000 police officers on duty, along with 5,000 members of the national guard and an estimated 1,000 Secret Service and FBI agents. Some protestors did shout foul language and throw objects at the police, including bags of human excrement. The police responded with force, broadcast on the networks. And that did create a clear ideological conflict in which largely lefty protestors were pitted against the law-and-order police forces.

“A lot of Americans felt that just showing this police brutality was showing a bias against the police, and what the networks had done was tell the story wrong, and not show how protestors provoked the brutality, and implicitly or explicitly deserved to be beaten by the police,” Hendershot says.

That was very much Chicago Mayor Richard Daley’s view — and Nixon’s response, too.

“Police can be a little rough,” Nixon told President Johnson in a phone call soon after the convention. “Some of those guys are pretty tough. But on the other hand, nobody was pointing out the provocation” the police faced from protestors, he said.

All of which created a vexing situation for the Democratic Party. The protesters were attacking them from the left, and a Democratic Party mayor supported the physical response, but under the circumstances, it was easy for Republicans to identify with the law-and-order response.

“Daley agreed with the right wing and the mainstream Americans who felt the police had used an appropriate amount of violence in Chicago, or should have used more,” Hendershot says. “Daley said there was media bias [in the convention coverage], conservatives said there was bias. Daley helped the Republicans win [in November]. He didn’t mean to, but he helped Nixon. He kept the story alive.”

Then and now

As Hendershot explains in the book, this emphasis that there was something not just incomplete but biased about the news coverage was fairly new. It was also not necessarily merited, based on the media coverage of fast-moving events under difficult circumstances — including an electricians’ strike that Daley leveraged to limit the media’s ability to use equipment.

“Most people thought, the media makes mistakes sometimes, but you could be a conservative or Republican, or a liberal, and feel they [the media] were very neutral,” Hendershot says. “And after the convention there was an idea that they’re not neutral. That was incorrect. They had done a very good job being neutral. They had made some mistakes, but they actually told the story pretty well.”

Moreover, as Hendershot writes, “Completely ignoring the streets would have been unconscionable, but showing anything in the streets would make the networks vulnerable to attack from those ‘law and order’ Americans who were repulsed and angered by longhairs and antiwar protestors. The ferocity of this inevitable anger caught the networks by surprise.”

Importantly, having found an opening, Nixon spent his years in office cultivating the notion of media bias against him — often through Vice President Spiro Agnew’s public speeches.

“Attacks on the ‘liberal media’ would become one important piece of the culture wars that have raged ever since,” Hendershot writes.

For that matter, Hendershot suggests that such attacks helped Nixon during Watergate, when the news networks seemed less than fully aggressive in pursuing the story, with CBS even paring back its Watergate coverage at one point following White House complaints.

Even so, Hendershot notes, matters have moved to a new extreme today, with claims from many quarters that factual reported news is simply fake, with no attempt to demonstrate such assertions. False claims about the 2020 presidential election, for instance, have flourished despite no evidence supporting them.

“What’s fascinating for me, when you compare it to today, is the idea of news people being told they could have done a better job. There’s still something to the idea that news people can tell a proper story,” Hendershot says. “Today people say what you’re showing never happened, it’s fake news.”

Other scholars have praised Hendershot’s new book. Ann Marie Lipinski of Harvard University has said that “When the News Broke” contains “a deeply researched argument for how four turbulent days planted the seeds of public distrust in media that are still bearing bitter fruit. It is a fascinating look back at a dramatic American summer on which the sun has still not set.” 

For her part, Hendershot says she welcomes a wide variety of readers of any background — very much including those who were not present at the time.

“I really wanted to make it a story that would resonate and be meaningful for younger people, and not just older people who already have an idea of what Chicago 1968 was,” she says. Indeed, as Hendershot notes, by quoting James Baldwin at the end of the book: “History is not the past. It is the present. We carry our history with us. We are our history.”

de MIT News https://ift.tt/DAT7OFh

World Wide Web Consortium is now a public-interest nonprofit organization

The World Wide Web Consortium (W3C), which leads development of the technical standards and guidelines to ensure that the web remains open, accessible, and interoperable, officially launched as a public-interest nonprofit organization as of Jan. 1. After 28 years of being hosted collectively at MIT and three other international host organizations, the crusaders for web standards have become their own entity. 

Many diverse brains make up and contribute to the community collective that is W3C, cultivating and setting global standards for building websites, browsers, and devices. Some of W3C's greatest hits involve making public standards for the technologies that underlie the web, such as HTML, CSS, and XML, which are so ubiquitous, they’re practically ingrained in the fabric of our daily lives — every time we use a computer or smartphone. The organization has created more than 460 web standards since 1994, gathering minds from software and hardware worlds, research centers, universities, and public administrators. 

W3C was first hosted and nurtured at the MIT Laboratory for Computer Science (LCS). In 1989, the organization was invited to MIT’s Computer Science & Artificial Intelligence Laboratory (CSAIL, formerly LCS) by its director, Michael Dertouzos, ushered in by Sir Tim Berners-Lee, known as the inventor of the World Wide Web, at the European Organization for Nuclear Research (CERN). He had written the first web browser and server, introducing a language for creating webpages (HTML), a communications protocol (HTTP), and a naming scheme (URLs). Albert Vezza, then associate director of the MIT LCS, would serve as chair. The crew was beginning to form. 

So how did W3C end up in Frank Gehry’s Stata Center? Around the time of W3C's inception, the buzz around the "internet," "browsers," and the "web" was so loud it was nearly deafening. And while open-source software now forms the basis for innovation in the world, Berners-Lee was an early champion; he opened up the browser source code in 1993 for the public, helping kick off the internet bonanza of the 1990s. With the humming in mind, Berners-Lee needed to secure a home for the newly formed consortium in 1994. Enter the "hosted" model. Enter MIT. 

As their footprint began to overflow, more hosts were in order, alongside Berners-Lee’s early intentions for that footprint to be global. The French Institute for Research in Computer Science and Automation then became a host in 1995 (the ERCIM EEIG took over the European hosting since 2003), followed by Keio University in Japan in 1996, Beihang University in China in 2013, with a sprinkling of regional offices all over the world. W3C, effectively, was like the web — all around us. 

The nascent industry that was "the internet" was breaking out into the mainstream in the 1990s. With Marc Andreessen’s Mosaic-turned-Netscape Navigator 2.0 taking over home computers by storm, Berners-Lee and W3C’s first chairperson, Jean-François Abramatic, believed a fusion of minds to govern international standards was imperative to scale the web — and it needed to be developed with the masses in mind. In that pursuit, they put out guidelines to streamline and standardize the technical quality and compatibility of technologies created over the web to avoid outdated technologies and inconsistency in the display of web pages. 

Some of W3C's best-known standards let us see, use, and store data efficiently, including "Cascading Style Sheets" or CSS, which details how HyperText Markup Language (HTML) elements are displayed on screens, paper, and other media, for example. HTML itself is the standard web markup language that's arguably the celebrity of the bunch. Another essential standard, similar to HTML, is "Extensible Markup Language," or XML, a language created to provide rules to define any data. 

These standards have fused the marrow that is the backbone of the web. This infrastructure has created space to overlay and inject humanity and beauty into the online space through visual formats. "WebRTC" helps facilitate real-time communication for video and audio calls that’s consistent across different browsers and devices, for countless conversations proliferating over Zoom and the like. Enjoy reading online? The consortium's work also underpins the digital ecosystem of e-books, newspapers, and journals in countless languages. 

If you think remembering your passwords is annoying or fear "phishing" attacks, W3C has helped your passwords work across different browsers and devices. Our most sought-after currency — data — is more usable thanks to W3C's Linked Data, a set of best practices for publishing structured data on the web. Security technologies protect users' privacy and ensure better web safety. Finally, with the proliferation of connected devices that collect and share data, they've built technologies to better assimilate the web with the internet of things.

To make the web a level playing field and neutral playground, it needed to be accessible to everyone — including those who are deaf, blind, or have physical ailments, spurring guidelines to make the web more comprehensible for those with disabilities. From its inception, Berners-Lee believed another crucial tentacle of a truly worldwide web was making the organization global in its nature and internationalizing all web-related activities and technologies so content can be easily adapted for users from any culture, region, or language. 

With all of this in place, perhaps the best insurance policy came in the form of what has been described by The Boston Globe as Berners-Lee’s "greatest act of all" in being something he "didn't do:" require fees for patents. Instead, a royalty-free patent policy was created so that people who use patents covering technologies in their standards don't have to pay royalties or fees. Other standards development organizations have since copied this over the years since it was developed in the early 2000s. 

Over the past six years, W3C has also become home to a few shiny gold statues. They've nabbed three Emmys, one for pioneering work in television experience, a second for captions, and a third for WebFonts.

"W3C has an impressive and accomplished history, and I am optimistic as they transition into their next chapter with a solid foundation. We celebrate the vision and efforts of all those based at the host institutions, including MIT CSAIL, and across the world to date," says Daniela Rus, director of CSAIL and the Andrew (1956) and Erna Viterbi Professor of Electrical Engineering and Computer Science, who has served on the board of directors for the new W3C, Inc. "W3C has developed many building blocks of the modern web, including HTML, CSS, and XML, as well as the Web Accessibility Initiative (WAI), which aims to make the web accessible to people with disabilities. W3C has fostered extraordinary contributions in technologies and standards that enable an open, accessible, and fair web — from WebRTC to WebAuth and WebPayments; to making the web beautiful with WebFonts, CSS, and more. We're eager to see how they continue to shape the web of the future."

de MIT News https://ift.tt/3qDCmn5

Engineers invent vertical, full-color microscopic LEDs

Take apart your laptop screen, and at its heart you’ll find a plate patterned with pixels of red, green, and blue LEDs, arranged end to end like a meticulous Lite Brite display. When electrically powered, the LEDs together can produce every shade in the rainbow to generate full-color displays. Over the years, the size of individual pixels has shrunk, enabling many more of them to be packed into devices to produce sharper, higher-resolution digital displays.

But much like computer transistors, LEDs are reaching a limit to how small they can be while also performing effectively. This limit is especially noticeable in close-range displays such as augmented and virtual reality devices, where limited pixel density results in a “screen door effect” such that users perceive stripes in the space between pixels.

Now, MIT engineers have developed a new way to make sharper, defect-free displays. Instead of replacing red, green, and blue light-emitting diodes side by side in a horizontal patchwork, the team has invented a way to stack the diodes to create vertical, multicolored pixels.

Each stacked pixel can generate the full commercial range of colors and measures about 4 microns wide. The microscopic pixels, or “micro-LEDs,” can be packed to a density of 5,000 pixels per inch.

“This is the smallest micro-LED pixel, and the highest pixel density reported in the journals,” says Jeehwan Kim, associate professor of mechanical engineering at MIT. “We show that vertical pixellation is the way to go for higher-resolution displays in a smaller footprint.”

“For virtual reality, right now there is a limit to how real they can look,” adds Jiho Shin, a postdoc in Kim’s research group. “With our vertical micro-LEDs, you could have a completely immersive experience and wouldn’t be able to distinguish virtual from reality.”

The team’s results are published today in the journal Nature. Kim and Shin’s co-authors include members of Kim’s lab, researchers around MIT, and collaborators from Georgia Tech Europe, Sejong University, and multiple universities in the U.S, France, and Korea.

Placing pixels

Today’s digital displays are lit through organic light-emitting diodes (OLEDs) — plastic diodes that emit light in response to an electric current. OLEDs are the leading digital display technology, but the diodes can degrade over time, resulting in permanent burn-in effects on screens. The technology is also reaching a limit to the size the diodes can be shrunk, limiting their sharpness and resolution.

For next-generation display technology, researchers are exploring inorganic micro-LEDs — diodes that are one-hundredth the size of conventional LEDs and are made from inorganic, single-crystalline semiconducting materials. Micro-LEDs could perform better, require less energy, and last longer than OLEDs.

But micro-LED fabrication requires extreme accuracy, as microscopic pixels of red, green, and blue need to first be grown separately on wafers, then precisely placed on a plate, in exact alignment with each other in order to properly reflect and produce various colors and shades. Achieving such microscopic precision is a difficult task, and entire devices need to be scrapped if pixels are found to be out of place.

“This pick-and-place fabrication is very likely to misalign pixels in a very small scale,” Kim says. “If you have a misalignment, you have to throw that material away, otherwise it could ruin a display.”

Color stack

The MIT team has come up with a potentially less wasteful way to fabricate micro-LEDs that doesn’t require precise, pixel-by-pixel alignment. The technique is an entirely different, vertical LED approach, in contrast to the conventional, horizontal pixel arrangement.

Kim’s group specializes in developing techniques to fabricate pure, ultrathin, high-performance membranes, with a view toward engineering smaller, thinner, more flexible and functional electronics. The team previously developed a method to grow and peel away perfect, two-dimensional, single-crystalline material from wafers of silicon and other surfaces — an approach they call 2D material-based layer transfer, or 2DLT.

In the current study, the researchers employed this same approach to grow ultrathin membranes of red, green, and blue LEDs. They then peeled the entire LED membranes away from their base wafers, and stacked them together to make a layer cake of red, green, and blue membranes. They could then carve the cake into patterns of tiny, vertical pixels, each as small as 4 microns wide.

“In conventional displays, each R, G, and B pixel is arranged laterally, which limits how small you can create each pixel,” Shin notes. “Because we are stacking all three pixels vertically, in theory we could reduce the pixel area by a third.”

As a demonstration, the team fabricated a vertical LED pixel, and showed that by altering the voltage applied to each of the pixel’s red, green, and blue membranes, they could produce various colors in a single pixel.

“If you have a higher current to red, and weaker to blue, the pixel would appear pink, and so on,” Shin says. “We’re able to create all the mixed colors, and our display can cover close to the commercial color space that’s available.”

The team plans to improve the operation of the vertical pixels. So far, they have shown they can stimulate an individual structure to produce the full spectrum of colors. They will work toward making an array of many vertical micro-LED pixels.

“You need a system to control 25 million LEDs separately,” Shin says. “Here, we’ve only partially demonstrated that. The active matrix operation is something we’ll need to further develop.”

“For now, we have shown to the community that we can grow, peel, and stack ultrathin LEDs,” Kim says. “This is the ultimate solution for small displays like smart watches and virtual reality devices, where you would want highly densified pixels to make lively, vivid images.”

This research was supported, in part, by the U.S. National Science Foundation, the U.S. Defense Advanced Research Projects Agency (DARPA), the U.S. Air Force Research Laboratory, the U.S. Department of Energy, LG Electronics, Rohm Semiconductor, the French National Research Agency, and the National Research Foundation in Korea.

de MIT News https://ift.tt/TLW8m96

Physicists observe rare resonance in molecules for the first time

If she hits just the right pitch, a singer can shatter a wine glass. The reason is resonance. While the glass may vibrate slightly in response to most acoustic tones, a pitch that resonates with the material’s own natural frequency can send its vibrations into overdrive, causing the glass to shatter.

Resonance also occurs at the much smaller scale of atoms and molecules. When particles chemically react, it’s partly due to specific conditions that resonate with particles in a way that drives them to chemically link. But atoms and molecules are constantly in motion, inhabiting a blur of vibrating and rotating states. Picking out the exact resonating state that ultimately triggers molecules to react has been nearly impossible.

MIT physicists may have cracked part of this mystery with a new study appearing today in the journal Nature. The team reports that they have for the first time observed a resonance in colliding ultracold molecules.

They found that a cloud of super-cooled sodium-lithium (NaLi) molecules disappeared 100 times faster than normal when exposed to a very specific magnetic field. The molecules’ rapid disappearance is a sign that the magnetic field tuned the particles into a resonance, driving them to react more quickly than they normally would.

The findings shed light on the mysterious forces that drive molecules to chemically react. They also suggest that scientists could one day harness particles’ natural resonances to steer and control certain chemical reactions.

“This is the very first time a resonance between two ultracold molecules has ever been seen,” says study author Wolfgang Ketterle, the John D. MacArthur Professor of Physics at MIT. “There were suggestions that molecules are so complicated that they are like a dense forest, where you would not be able to recognize a single resonance. But we found one big tree standing out, by a factor of 100. We observed something completely unexpected.”

Ketterle’s co-authors include lead author and MIT graduate student Juliana Park, graduate student Yu-Kun Lu, former MIT postdoc Alan Jamison, who is currently at the University of Waterloo, and Timur Tscherbul at the University of Nevada.

A middle mystery

Within a cloud of molecules, collisions occur constantly. Particles may ping off each other like frenetic billiard balls or stick together in a brief yet crucial state known as an “intermediate complex” that then sets off a reaction to transform the particles into a new chemical structure.

“When two molecules collide, most of the time they don’t make it to that intermediate state,” says Jamison. “But when they’re in resonance, the rate of going to that state goes up dramatically.”

“The intermediate complex is the mystery behind all of chemistry,” Ketterle adds. “Usually, the reactants and the products of a chemical reaction are known, but not how one leads to the other. Knowing something about the resonance of molecules can give us a fingerprint of this mysterious middle state.”

Ketterle’s group has looked for signs of resonance in atoms and molecules that are super-cooled, to temperatures just above absolute zero. Such ultracold conditions inhibit the particles’ random, temperature-driven motion, giving scientists a better chance of recognizing any subtler signs of resonance. 

In 1998, Ketterle made the first ever observation of such resonances in ultracold atoms. He observed that, when a very specific magnetic field was applied to super-cooled sodium atoms, the field enhanced the way the atoms scattered off each other, in an effect known as a Feshbach resonance. Since then, he and others have looked for similar resonances in collisions involving both atoms and molecules.

“Molecules are much more complicated than atoms,” says Ketterle. “They have so many different vibrational and rotational states. Therefore, it was not clear if molecules would show resonances at all.”

Needle in a haystack

Several years ago, Jamison, who at the time was a postdoc in Ketterle’s lab, proposed a similar experiment to see whether signs of resonance could be observed in a mixture of atoms and molecules cooled down to a millionth of a degree above absolute zero. By varying an external magnetic field, they found they could indeed pick up several resonances amid sodium atoms and sodium-lithium molecules, which they reported last year.

Then, as the team reports in the current study, graduate student Park took a closer look at the data.

“She discovered that one of those resonances did not involve atoms,” Ketterle says. “She blew away the atoms with laser light, and one resonance was still there, very sharp, and only involved molecules.”

Park found that the molecules seemed to disappear — a sign that the particles underwent a chemical reaction — much more quickly than they normally would, when they were exposed to a very specific magnetic field.

In their original experiment, Jamison and colleagues applied a magnetic field that they varied over a wide, 1,000-Gaussian range. Park found that molecules of sodium-lithium suddenly disappeared, 100 times faster than normal, within a tiny sliver of this magnetic range, at about 25 milli-Gaussian. That’s equivalent to the width of a human hair compared to a meter-long stick.

“It takes careful measurements to find the needle in this haystack,” Park says. “But we used a systematic strategy to zoom in on this new resonance.”

In the end, the team observed a strong signal that this particular field resonated with the molecules. The effect enhanced the particles’ chance of binding in a brief, intermediate complex that then triggered a reaction that made the molecules disappear.

Overall, the discovery provides a deeper understanding of molecular dynamics and chemistry. While the team does not anticipate scientists being able to stimulate resonance, and steer reactions, at the level of organic chemistry, it could one day be possible to do so at the quantum scale.

“One of the main themes of quantum science is studying systems of increasing complexity, especially when quantum control is potentially in the offing,” says John Doyle, professor of physics at Harvard University, who was not involved in the group’s research. “These kind of resonances, first seen in simple atoms and then more complicated ones, led to amazing advances in atomic physics. Now that this is seen in molecules, we should first understand it in detail, and then let the imagination wander and think what it might be good for, perhaps constructing larger ultracold molecules, perhaps studying interesting states of matter.”

This research was supported, in part, by the National Science Foundation, and the U.S. Air Force Office of Scientific Research.

de MIT News https://ift.tt/Rb85NHX