David Pesetsky honored by MIT Linguistics colleagues and alumni

More than 100 faculty colleagues, current and former students, and guests gathered at the Stata Center on Feb. 11 for a daylong linguistics workshop organized as a tribute to the research and teaching of MIT linguist David Pesetsky.

Attendees came from as far away as Korea, Russia, and Turkey to honor Pesetsky, the Ferrari P. Ward Professor of Modern Languages and Linguistics and head of MIT’s Department of Linguistics and Philosophy. Pesetsky is noted both for his innovative and critical research on syntactic theory and for his teaching; he is a Margaret MacVicar Faculty Fellow at MIT, an honor awarded to the Institute’s finest teachers and mentors.

Surprise!

Planned in secret over a year and a half as a surprise to mark Pesetsky’s 60th birthday, the event featured panel discussions on two linguistics topics of keen interest to Pesetsky — case and wh-questions — and was rounded out with poster sessions and a celebratory dinner. The event was organized by Claire Halpert PhD ’12, MIT Professor Sabine Iatridou, Hadas Kotek PhD ’14, and Coppe van Urk PhD ’15, with help from Mary Grenham, the administrative officer for MIT Linguistics.

Iatridou offered welcoming remarks to start the day. “We’re here to show you our love and appreciation,” she said. “You have contributed to each and every one of us — with dedication and generosity and enormous linguistic talent — to our thinking, to our work, to our attitude toward doing science in general. Thank you.”

While it’s unclear how Pesetsky was persuaded to pop into the Stata Center on a wintry gray Saturday, it’s certain he was both genuinely surprised and delighted to discover the event had been planned in his honor. “Seeing over three decades of former students, from my very first PhD student from 1986 to students who just finished (and of course many who are still at MIT), all together in the same room — that was overwhelming,” he said. “One of our alums who participated quoted her incredulous spouse as saying that ‘we are in a special line of work if an all-day work conference on a Saturday counts as a really great birthday surprise.’ But that’s exactly how it was.”

A Pesky set

A highlight of the day was the presentation of a Festschrift for Pesetsky — “A Pesky Set: Papers for David Pesetsky” — a collection of 60 linguistic papers contributed by former and current students. “If I understand correctly, it was apparently a magical accident that they numbered exactly 60,” Pesetsky commented, “but it’s no accident that the papers are fantastic, because their authors are some of the best researchers in the field today.”

Halpert, an assistant professor of linguistics at the University of Minnesota, co-edited the book with Kotek, a lecturer in semantics at Yale University, and van Urk, a lecturer in linguistics at Queen Mary University of London. “Our aim with the Festschrift was to celebrate a part of David’s legacy and impact on the field that is perhaps less immediately obvious just from looking at his own research output: the far-reaching effect of his tireless mentorship as a teacher and adviser,” Halpert said.
 
Pesetsky is an “an inspiring teacher and dedicated mentor,” said Kotek, noting that she continues to look to him as a role model now that she is a faculty member herself. “It can be hard to convey to someone just how much they’ve influenced your life, but I hope that this event is a good way for us to start saying ‘thank you!'”

Commenting in advance of the occasion, Institute Professor Emeritus Noam Chomsky, who led the department along with Institute Professor Emeritus Morris Halle during its early years, said the honor for Pesetsky is in some ways the fruition of the dream they had for the department.

“Morris and I sometimes reminisce about the days, 60 years ago, when we mused about what it might be like to develop a linguistics program at MIT, quite a long shot at the time. Looking back over the years, it is immensely gratifying to see how the experiment took its course, and where it has reached today,” Chomsky said.

“It is particularly gratifying to know that the project is now in the very capable hands of David Pesetsky, one of the truly outstanding linguists of the current period, whose original and far-reaching achievements have been enriching the study of language and related disciplines since his student days.”
 

Story by MIT SHASS Communications
Editorial team: Kathryn O’Neill, Emily Hiestand

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The Committee on Animal Care solicits feedback

The Committee on Animal Care (CAC) and the vice president for research welcome any information that would aid our efforts to assure the humane care of research animals used at MIT and the Whitehead Institute for Biomedical Research.

Established to ensure that MIT researchers working with animals comply with federal, state, local and institutional regulations on animal care, the CAC inspects animals, animal facilities, and laboratories, and reviews all research and teaching exercises that involve animals before experiments are performed.

If you have concerns about animal welfare, please contact the Committee on Animal Care (CAC) by calling 617-324-6892, or send your concern in writing to the CAC Office (Room 16-408), or email cacpo@mit.edu. The issue will be forwarded to the chair of the CAC and the attending veterinarian.

You may also contact any of the following:

•       Vice president for research: 617-253-3206, mtz@mit.edu
•       Director of the Division of Comparative Medicine and attending veterinarian: 617-253-1735, jgfox@mit.edu
•       CAC chair: 617-285-5156, helh@med.mit.edu

All concerns about animal welfare will remain confidential. The identity of individuals who contact the CAC with concerns will be treated as confidential, and individuals will be protected against reprisal and discrimination consistent with MIT policies. The Committee on Animal Care will report its findings and actions to correct the issue to the vice president for research, the director of comparative medicine, the individual who reported the concern (if not reported anonymously), and oversight agencies as applicable.

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MIT rates No. 1 in 12 subjects in 2017 QS World University Rankings

MIT has been honored with 12 No. 1 subject rankings in the QS World University Rankings for 2017.

MIT received a No. 1 ranking in the following QS subject areas: Architecture/Built Environment; Linguistics; Computer Science and Information Systems; Chemical Engineering; Civil and Structural Engineering; Electrical and Electronic Engineering; Mechanical, Aeronautical and Manufacturing Engineering; Chemistry; Materials Science; Mathematics; Physics and Astronomy; and Economics.

Additional high-ranking MIT subjects include: Art and Design (No. 2), Biological Sciences (No. 2), Earth and Marine Sciences (No. 5), Environmental Sciences (No. 3), Accounting and Finance (No. 2), Business and Management Studies (No. 4), and Statistics and Operational Research (No. 2).

Quacquarelli Symonds Limited subject rankings, published annually, are designed to help prospective students find the leading schools in their field of interest. Rankings are based on research quality and accomplishments, academic reputation, and graduate employment.

MIT has been ranked as the No. 1 university in the world by QS World University Rankings for five straight years.

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New approach suggests path to emissions-free cement

It’s well known that the production of cement — the world’s leading construction material — is a major source of greenhouse gas emissions, accounting for about 8 percent of all such releases. If cement production were a country, it would be the world’s third-largest emitter.

A team of researchers at MIT has come up with a new way of manufacturing the material that could eliminate these emissions altogether, and could even make some other useful products in the process.

The findings are being reported today in the journal PNAS in a paper by Yet-Ming Chiang, the Kyocera Professor of Materials Science and Engineering at MIT, with postdoc Leah Ellis, graduate student Andres Badel, and others.

“About 1 kilogram of carbon dioxide is released for every kilogram of cement made today,” Chiang says. That adds up to 3 to 4 gigatons (billions of tons) of cement, and of carbon dioxide emissions, produced annually today, and that amount is projected to grow. The number of buildings worldwide is expected to double by 2060, which is equivalent to “building one new New York City every 30 days,” he says. And the commodity is now very cheap to produce: It costs only about 13 cents per kilogram, which he says makes it cheaper than bottled water.

So it’s a real challenge to find ways of reducing the material’s carbon emissions without making it too expensive. Chiang and his team have spent the last year searching for alternative approaches, and hit on the idea of using an electrochemical process to replace the current fossil-fuel-dependent system.

Ordinary Portland cement, the most widely used standard variety, is made by grinding up limestone and then cooking it with sand and clay at high heat, which is produced by burning coal. The process produces carbon dioxide in two different ways: from the burning of the coal, and from gases released from the limestone during the heating. Each of these produces roughly equal contributions to the total emissions. The new process would eliminate or drastically reduce both sources, Chiang says. Though they have demonstrated the basic electrochemical process in the lab, the process will require more work to scale up to industrial scale.

First of all, the new approach could eliminate the use of fossil fuels for the heating process, substituting electricity generated from clean, renewable sources. “In many geographies renewable electricity is the lowest-cost electricity we have today, and its cost is still dropping,” Chiang says. In addition, the new process produces the same cement product. The team realized that trying to gain acceptance for a new type of cement — something that many research groups have pursued in different ways — would be an uphill battle, considering how widely used the material is around the world and how reluctant builders can be to try new, relatively untested materials.

The new process centers on the use of an electrolyzer, something that many people have encountered as part of high school chemistry classes, where a battery is hooked up to two electrodes in a glass of water, producing bubbles of oxygen from one electrode and bubbles of hydrogen from the other as the electricity splits the water molecules into their constituent atoms. Importantly, the electrolyzer’s oxygen-evolving electrode produces acid, while the hydrogen-evolving electrode produces a base.

In the new process, the pulverized limestone is dissolved in the acid at one electrode and high-purity carbon dioxide is released, while calcium hydroxide, generally known as lime, precipitates out as a solid at the other. The calcium hydroxide can then be processed in another step to produce the cement, which is mostly calcium silicate.

The carbon dioxide, in the form of a pure, concentrated stream, can then be easily sequestered, harnessed to produce value-added products such as a liquid fuel to replace gasoline, or used for applications such as oil recovery or even in carbonated beverages and dry ice. The result is that no carbon dioxide is released to the environment from the entire process, Chiang says. By contrast, the carbon dioxide emitted from conventional cement plants is highly contaminated with nitrogen oxides, sulfur oxides, carbon monoxide and other material that make it impractical to “scrub” to make the carbon dioxide usable.

Calculations show that the hydrogen and oxygen also emitted in the process could be recombined, for example in a fuel cell, or burned to produce enough energy to fuel the whole rest of the process, Ellis says, producing nothing but water vapor.

In a demonstration of the basic chemical reactions used in the new process, electrolysis takes place in neutral water. Dyes show how acid (pink) and base (purple) are produced at the positive and negative electrodes. A variation of this process can be used to convert calcium carbonate (CaCO3) into calcium hydroxide (Ca(OH)2), which can then be used to make Portland cement without producing any greenhouse gas emissions. Cement production currently causes 8 percent of global carbon emissions.

In their laboratory demonstration, the team carried out the key electrochemical steps required, producing lime from the calcium carbonate, but on a small scale. The process looks a bit like shaking a snow-globe, as it produces a flurry of suspended white particles inside the glass container as the lime precipitates out of the solution.

While the technology is simple and could, in principle, be easily scaled up, a typical cement plant today produces about 700,000 tons of the material per year. “How do you penetrate an industry like that and get a foot in the door?” asks Ellis, the paper’s lead author. One approach, she says, is to try to replace just one part of the process at a time, rather than the whole system at once, and “in a stepwise fashion” gradually add other parts.

The initial proposed system the team came up with is “not because we necessarily think we have the exact strategy” for the best possible approach, Chiang says, “but to get people in the electrochemical sector to start thinking more about this,” and come up with new ideas. “It’s an important first step, but not yet a fully developed solution.”

The research was partly supported by the Skolkovo Institute of Science and Technology.

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Global agreements

Many linguistics scholars regard the world’s languages as being fundamentally similar. Yes, the characters, words, and rules vary. But underneath it all, enough similar structures exist to form what MIT scholars call universal grammar, a capacity for language that all humans share.

To see how linguists find similariites that can elude the rest of us, consider a language operation called “allocutive agreement.” This is a variation of standard subject-verb agreement. Normally, a verb ending simply agrees with the subject of a sentence, so that in English we say, “You go,” but also, “She goes.”

Allocutive agreement throws a twist into this procedure: Even a third-person verb ending, such as “she goes,” changes depending on the social status of the person being spoken to. This happens in Basque, for one. It also occurs in Japanese, says MIT linguist Shigeru Miyagawa, even though Japanese has long been thought not to deploy agreement at all. But in fact, Miyagawa asserts, the same principles of formality appear in Japanese, if you know where to look.

“It goes a long way toward the idea that there’s agreement in every language,” says Miyagawa, a professor of linguistics and the Kochi-Manjiro Professor of Japanese Language and Culture at MIT. “In Japanese this politeness system has exactly the same distribution as the Basque allocutive system.”

Now Miyagawa has published a book — “Agreement Beyond Phi,” out today from the MIT Press — that explores some of these unexpected structural similarities among languages. The book has a second aim, as well: Miyagawa would like to orient the search for universal linguistic principles around a greater diversity of languages. (The title, incidentally, refers to agreement systems that are not found in Indo-European languages.)

Because English is the native language of so many great linguists, he observes, there is a tendency to regard it as a template for other languages. But drawing more heavily on additional languages, Miyagawa thinks, could lead to new insights about the specific contents of our universal language capacity; he cites the work of MIT linguist Norvin Richards as an example of this kind of work.

“Given the prominence of Indo-European languages, especially English, in linguistic theory, one sometimes gets the impression that if something happens in English it’s due to universal grammar, but if something happens in Japanese, it’s because it’s Japanese,” Miyagawa says.

Not mere formalities

To see why allocutive agreement seems like such a compelling example to Miyagawa, take a very brief look at how it works.

The best-known examples of addressing people formally come from Indo-European languages such as French, in which second-person subject-verb agreement changes in a simple way, depending on the social status of the person being addressed. Consider the phrase, “You speak.” To a peer or friend, you would use the informal version, “Tu parles.” But to a teacher or an older stranger you would likely use the more formal agreement, “Vous parlez.”

What happens in Basque and Japanese is a bit more complicated, however, since both informal and formal modes of address are employed even when speaking about other people. For instance, in Basque, consider a phrase Miyagawa dissects in the book, “Peter worked.” To a male friend, you would say, “Peter lan egin dik.” But to someone with higher social status, you would say, “Peter lan egin dizu.” The verb ending — the verb is last word in this sentence — changes even though it remains in the third person.

And while Japanese grammar differs in many ways from Basque grammar, Miyagawa contends in the new book that Japanese “politeness marking” follows the same rules. The sentence “Taro said that Hanako will come,” for example, includes the politeness marking “mas” when being spoken in a formal setting. In Japanese, transliterated in English characters, this becomes: “Taroo-wa hanako-ga ki-mas-u to itta.” But for the same sentence, when spoken to a peer, the “mas” disappears.

This kind of agreement, Miyagawa notes, is something he proposed in a 2010 book — titled, “Why Agree? Why Move?” — but did not observe until about 2012.

“I found in Basque the prediction I made in 2010 but couldn’t substantiate then,” Miyagawa says. “It’s exactly the same agreement system.”

Strikingly, Basque and Japanese seem to have very different origins. And Basque — although spoken in the Basque region that lies in between France and Spain — is not an Indo-European language. Indeed, linguists are not certain how to account for the origins of Basque. The presence of allocative agreement in both tongues, then, suggests a deep and unexpected universality among the kinds of linguistic rules that can occur.

Unpredictable

Miyagawa acknowledges he cannot predict precisely how his colleagues in linguistics will react to the book’s agenda, but says he has gotten a positive reception when presenting its concepts at conferences.

Certainly, some linguists have been very receptive to Miyagawa’s arguments. Johan Rooryck, a professor of French linguistics at Leiden University in the Netherlands, has said that Miyagawa’s new book “makes an elegant and compelling case for this exciting perspective.”

Miyagawa himself stresses that the point of the research is not to upend the conceptual foundations of universal grammar — as codified by MIT linguist Noam Chomsky and many others — but to expand the range of comparisons available to linguists. Beyond English, Japanese, and Basque, the book also draws on similarities found in Dinka (spoken in Sudan) and Jingpo (spoken in China and Burma), among other languages.

The book, he says, “is heavily influenced by the insights of the previous work, [and is] standing on the shoulders of some of the great minds, of Chomsky and many others.”

But when linguists look at more and more languages, Miyagawa adds, “You start to discover things you never noticed before.”

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MIT engineers develop “blackest black” material to date

With apologies to “Spinal Tap,” it appears that black can, indeed, get more black.

MIT engineers report today that they have cooked up a material that is 10 times blacker than anything that has previously been reported. The material is made from vertically aligned carbon nanotubes, or CNTs — microscopic filaments of carbon, like a fuzzy forest of tiny trees, that the team grew on a surface of chlorine-etched aluminum foil. The foil captures at least 99.995 percent* of any incoming light, making it the blackest material on record.

The researchers have published their findings today in the journal ACS-Applied Materials and Interfaces. They are also showcasing the cloak-like material as part of a new exhibit today at the New York Stock Exchange, titled “The Redemption of Vanity.”

The artwork, a collaboration between Brian Wardle, professor of aeronautics and astronautics at MIT, and his group, and MIT Center for Art, Science, and Technology artist-in-residence Diemut Strebe, features a 16.78-carat natural yellow diamond from LJ West Diamonds, estimated to be worth $2 million, which the team coated with the new, ultrablack CNT material. The effect is arresting: The gem, normally brilliantly faceted, appears as a flat, black void.

Wardle says the CNT material, aside from making an artistic statement, may also be of practical use, for instance in optical blinders that reduce unwanted glare, to help space telescopes spot orbiting exoplanets.

“There are optical and space science applications for very black materials, and of course, artists have been interested in black, going back well before the Renaissance,” Wardle says. “Our material is 10 times blacker than anything that’s ever been reported, but I think the blackest black is a constantly moving target. Someone will find a blacker material, and eventually we’ll understand all the underlying mechanisms, and will be able to properly engineer the ultimate black.”

Wardle’s co-author on the paper is former MIT postdoc Kehang Cui, now a professor at Shanghai Jiao Tong University.

Into the void

Wardle and Cui didn’t intend to engineer an ultrablack material. Instead, they were experimenting with ways to grow carbon nanotubes on electrically conducting materials such as aluminum, to boost their electrical and thermal properties.

But in attempting to grow CNTs on aluminum, Cui ran up against a barrier, literally: an ever-present layer of oxide that coats aluminum when it is exposed to air. This oxide layer acts as an insulator, blocking rather than conducting electricity and heat. As he cast about for ways to remove aluminum’s oxide layer, Cui found a solution in salt, or sodium chloride.

At the time, Wardle’s group was using salt and other pantry products, such as baking soda and detergent, to grow carbon nanotubes. In their tests with salt, Cui noticed that chloride ions were eating away at aluminum’s surface and dissolving its oxide layer.

“This etching process is common for many metals,” Cui says. “For instance, ships suffer from corrosion of chlorine-based ocean water. Now we’re using this process to our advantage.”

Cui found that if he soaked aluminum foil in saltwater, he could remove the oxide layer. He then transferred the foil to an oxygen-free environment to prevent reoxidation, and finally, placed the etched aluminum in an oven, where the group carried out techniques to grow carbon nanotubes via a process called chemical vapor deposition.

By removing the oxide layer, the researchers were able to grow carbon nanotubes on aluminum, at much lower temperatures than they otherwise would, by about 100 degrees Celsius. They also saw that the combination of CNTs on aluminum significantly enhanced the material’s thermal and electrical properties — a finding that they expected.

What surprised them was the material’s color.

“I remember noticing how black it was before growing carbon nanotubes on it, and then after growth, it looked even darker,” Cui recalls. “So I thought I should measure the optical reflectance of the sample.

“Our group does not usually focus on optical properties of materials, but this work was going on at the same time as our art-science collaborations with Diemut, so art influenced science in this case,” says Wardle.

Wardle and Cui, who have applied for a patent on the technology, are making the new CNT process freely available to any artist to use for a noncommercial art project.

“Built to take abuse”

Cui measured the amount of light reflected by the material, not just from directly overhead, but also from every other possible angle. The results showed that the material absorbed at least 99.995 percent of incoming light, from every angle. In other words, it reflected 10 times less light than all other superblack materials, including Vantablack. If the material contained bumps or ridges, or features of any kind, no matter what angle it was viewed from, these features would be invisible, obscured in a void of black.  

The researchers aren’t entirely sure of the mechanism contributing to the material’s opacity, but they suspect that it may have something to do with the combination of etched aluminum, which is somewhat blackened, with the carbon nanotubes. Scientists believe that forests of carbon nanotubes can trap and convert most incoming light to heat, reflecting very little of it back out as light, thereby giving CNTs a particularly black shade.

“CNT forests of different varieties are known to be extremely black, but there is a lack of mechanistic understanding as to why this material is the blackest. That needs further study,” Wardle says.

The material is already gaining interest in the aerospace community. Astrophysicist and Nobel laureate John Mather, who was not involved in the research, is exploring the possibility of using Wardle’s material as the basis for a star shade — a massive black shade that would shield a space telescope from stray light.

“Optical instruments like cameras and telescopes have to get rid of unwanted glare, so you can see what you want to see,” Mather says. “Would you like to see an Earth orbiting another star? We need something very black. … And this black has to be tough to withstand a rocket launch. Old versions were fragile forests of fur, but these are more like pot scrubbers — built to take abuse.”

*An earlier version of this story stated that the new material captures more than 99.96 percent of incoming light. That number has been updated to be more precise; the material absorbs at least 99.995 of incoming light.

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Articles of faith

If you have the chance, listen to a toddler use the words “a” and “the” before a noun. Can you detect a pattern? Is he or she using those two words correctly?

And one more question: When kids start using language, how much of their know-how is intrinsic, and how much is acquired by listening to others speak?

Now a study co-authored by an MIT professor uses a new approach to shed more light on this matter — a central issue in the area of language acquisition.

The results suggest that experience is an important component of early-childhood language usage although it doesn’t necessarily account for all of a child’s language facility. Moreover, the extent to which a child learns grammar by listening appears to change over time, with a large increase occurring around age 2 and a leveling off taking place in subsequent years.

“In this view, adult-like, rule-based [linguistic] development is the end-product of a construction of knowledge,” says Roger Levy, an MIT professor and co-author of a new paper summarizing the study. Or, as the paper states, the findings are consistent with the idea that children “lack rich grammatical knowledge at the outset of language learning but rapidly begin to generalize on the basis of structural regularities in their input.”

The paper, “The Emergence of an Abstract Grammatical Category in Children’s Early Speech,” appears in the latest issue of Psychological Science. The authors are Levy, a professor in MIT’s Department of Brain and Cognitive Sciences; Stephan Meylann of the University of California at Berkeley; Michael Frank of Stanford University; and Brandon Roy of Stanford and the MIT Media Lab.

Learning curve

Studying how children use terms such as “a dog” or “the dog” correctly can be a productive approach to language acquisition, since children use the articles “a” and “the” relatively early in their lives and tend to use them correctly. Again, though: Is that understanding of grammar innate or acquired?

Some previous studies have examined this specific question by using an “overlap score,” that is, the proportion of nouns that children use with both “a” and “the,” out of all the nouns they use. When children use both terms correctly, it indicates they understand the grammatical difference between indefinite and definite articles, as opposed to cases where they may (incorrectly) think only one or the other is assigned to a particular noun.

One potential drawback to this approach, however, is that the overlap score might change over time simply because a child might hear more article-noun pairings, without fully recognizing the grammatical distinction between articles.

By contrast, the current study builds a statistical model of language use that incorporates not only child language use but adult language use recorded around children, from a variety of sources. Some of these are publicly available copora of recordings of children and caregivers; others are records of individual children; and one source is the “Speechome” experiment conducted by Deb Roy of the MIT Media Lab, which features recordings of over 70 percent of his child’s waking hours.

The Speechome data, as the paper notes, provides some of the strongest evidence yet that “children’s syntactic productivity changes over development” — that younger children learn grammar from hearing it, and do so at different rates during different phases of early childhood.

“I think the method starts to get us traction on the problem,” Levy says. “We saw this as an opportunity both to use more comprehensive data and to develop new analytic techniques.”

A work in progress

Still, as the authors note, a second conclusion of the paper is that more basic data about language development is needed. As the paper notes, much of the available information is not comprehensive enough, and thus “likely not sufficient to yield precise developmental conclusions.”

And as Levy readily acknowledges, developing an airtight hypothesis about grammar acquisition is always likely to be a challenge.

“We’re never going to have an absolute complete record of everything a child has ever heard,” Levy says.

That makes it much harder to interpret the cognitive process leading to either correct or incorrect uses of, say, articles such as “a” and “the.” After all, if a child uses the phrase “a bus” correctly, it still might only be because that child has heard the phrase before and likes the way it sounds, not because he or she grasped the underlying grammar.

“Those things are very hard to tease apart, but that’s what we’re trying to do,” Levy says. “This is only really an initial step.”

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Scientists detect tones in the ringing of a newborn black hole for the first time

If Albert Einstein’s theory of general relativity holds true, then a black hole, born from the cosmically quaking collisions of two massive black holes, should itself “ring” in the aftermath, producing gravitational waves much like a struck bell reverbates sound waves. Einstein predicted that the particular pitch and decay of these gravitational waves should be a direct signature of the newly formed black hole’s mass and spin.

Now, physicists from MIT and elsewhere have studied the ringing of an infant black hole, and found that the pattern of this ringing does, in fact, predict the black hole’s mass and spin — more evidence that Einstein was right all along.

The findings, published today in Physical Review Letters, also favor the idea that black holes lack any sort of “hair” — a metaphor referring to the idea that black holes, according to Einstein’s theory, should exhibit just three observable properties: mass, spin, and electric charge. All other characteristics, which the physicist John Wheeler termed “hair,” should be swallowed up by the black hole itself, and would therefore be unobservable.

The team’s findings today support the idea that black holes are, in fact, hairless. The researchers were able to identify the pattern of a black hole’s ringing, and, using Einstein’s equations, calculated the mass and spin that the black hole should have, given its ringing pattern. These calculations matched measurements of the black hole’s mass and spin made previously by others.

If the team’s calculations deviated significantly from the measurements, it would have suggested that the black hole’s ringing encodes properties other than mass, spin, and electric charge — tantalizing evidence of physics beyond what Einstein’s theory can explain. But as it turns out, the black hole’s ringing pattern is a direct signature of its mass and spin, giving support to the notion that black holes are bald-faced giants, lacking any extraneous, hair-like properties.

“We all expect general relativity to be correct, but this is the first time we have confirmed it in this way,” says the study’s lead author, Maximiliano Isi, a NASA Einstein Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. “This is the first experimental measurement that succeeds in directly testing the no-hair theorem. It doesn’t mean black holes couldn’t have hair. It means the picture of black holes with no hair lives for one more day.”

A chirp, decoded

On Sept. 14, 2015, scientists made the first-ever detection of gravitational waves — infinitesimal ripples in space-time, emanating from distant, violent cosmic phenomena. The detection, named GW150914, was made by LIGO, the Laser Interferometer Gravitational-wave Observatory. Once scientists cleared away the noise and zoomed in on the signal, they observed a waveform that quickly crescendoed before fading away. When they translated the signal into sound, they heard something resembling a “chirp.”

Scientists determined that the gravitational waves were set off by the rapid inspiraling of two massive black holes. The peak of the signal — the loudest part of the chirp — linked to the very moment when the black holes collided, merging into a single, new black hole. While this infant black hole gave off gravitational waves of its own, its signature ringing, physicists assumed, would be too faint to decipher amid the clamor of the initial collision. Thus, traces of this ringing were only identified some time after the peak, where the signal was too faint to study in detail.

Isi and his colleagues, however, found a way to extract the black hole’s reverberation from the moments immediately after the signal’s peak. In previous work led by Isi’s co-author, Matthew Giesler of Caltech, the team showed through simulations that such a signal, and particularly the portion right after the peak, contains “overtones” — a family of loud, short-lived tones. When they reanalyzed the signal, taking overtones into account, the researchers discovered that they could successfully isolate a ringing pattern that was specific to a newly formed black hole.

In the team’s new paper, the researchers applied this technique to actual data from the GW150914 detection, concentrating on the last few milliseconds of the signal, immediately following the chirp’s peak. Taking into account the signal’s overtones, they were able to discern a ringing coming from the new, infant black hole. Specifically, they identified two distinct tones, each with a pitch and decay rate that they were able to measure.

“We detect an overall gravitational wave signal that’s made up of multiple frequencies, which fade away at different rates, like the different pitches that make up a sound,” Isi says. “Each frequency or tone corresponds to a vibrational frequency of the new black hole.”

Listening beyond Einstein

Einstein’s theory of general relativity predicts that the pitch and decay of a black hole’s gravitational waves should be a direct product of its mass and spin. That is, a black hole of a given mass and spin can only produce tones of a certain pitch and decay. As a test of Einstein’s theory, the team used the equations of general relativity to calculate the newly formed black hole’s mass and spin, given the pitch and decay of the two tones they detected.

They found their calculations matched with measurements of the black hole’s mass and spin previously made by others. Isi says the results demonstrate that researchers can, in fact, use the very loudest, most detectable parts of a gravitational wave signal to discern a new black hole’s ringing, where before, scientists assumed that this ringing could only be detected within the much fainter end of the gravitational wave signal, and identifying many tones would require much more sensitive instruments than what currently exist.

“This is exciting for the community because it shows these kinds of studies are possible now, not in 20 years,” Isi says.

As LIGO improves its resolution, and more sensitive instruments come online in the future, researchers will be able to use the group’s methods to “hear” the ringing of other newly born black holes. And if they happen to pick up tones that don’t quite match up with Einstein’s predictions, that could be an even more exciting prospect.

“In the future, we’ll have better detectors on Earth and in space, and will be able to see not just two, but tens of modes, and pin down their properties precisely,” Isi says. “If these are not black holes as Einstein predicts, if they are more exotic objects like wormholes or boson stars, they may not ring in the same way, and we’ll have a chance of seeing them.”

This research was supported, in part, by NASA, the Sherman Fairchild Foundation, the Simons Foundation, and the National Science Foundation.

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QS ranks MIT the world’s No. 1 university for 2017-18

MIT has been ranked as the top university in the world in the latest QS World University Rankings. This marks the sixth straight year in which the Institute has been ranked in the No. 1 position.

The full 2017-18 rankings — published by Quacquarelli Symonds, an organization specializing in education and study abroad — can be found at topuniversities.com. The QS rankings were based on academic reputation, employer reputation, citations per faculty, student-to-faculty ratio, proportion of international faculty, and proportion of international students. MIT earned a perfect overall score of 100.

MIT was also ranked the world’s top university in 12 of 46 disciplines ranked by QS, as announced in March of this year.

MIT received a No. 1 ranking in the following QS subject areas: Architecture/Built Environment; Linguistics; Computer Science and Information Systems; Chemical Engineering; Civil and Structural Engineering; Electrical and Electronic Engineering; Mechanical, Aeronautical and Manufacturing Engineering; Chemistry; Materials Science; Mathematics; Physics and Astronomy; and Economics.

The Institute also ranked among the top five institutions worldwide in another seven QS disciplines: Art and Design (No. 2), Biological Sciences (No. 2), Earth and Marine Sciences (No. 5), Environmental Sciences (No. 3), Accounting and Finance (No. 2), Business and Management Studies (No. 4), and Statistics and Operational Research (No. 2).

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Objects can now change colors like a chameleon

The color-changing capabilities of chameleons have long bewildered willing observers. The philosopher Aristotle himself was long mystified by these adaptive creatures. But while humans can’t yet camouflage much beyond a green outfit to match grass, inanimate objects are another story. 

A team from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) has brought us closer to this chameleon reality, by way of a new system that uses reprogrammable ink to let objects change colors when exposed to ultraviolet (UV) and visible light sources. 

Dubbed “PhotoChromeleon,” the system uses a mix of photochromic dyes that can be sprayed or painted onto the surface of any object to change its color — a fully reversible process that can be repeated infinitely. 

PhotoChromeleon can be used to customize anything from a phone case to a car, or shoes that need an update. The color remains, even when used in natural environments.

“This special type of dye could enable a whole myriad of customization options that could improve manufacturing efficiency and reduce overall waste,” says CSAIL postdoc Yuhua Jin, the lead author on a new paper about the project. “Users could personalize their belongings and appearance on a daily basis, without the need to buy the same object multiple times in different colors and styles.”

PhotoChromeleon builds off of the team’s previous system, “ColorMod,” which uses a 3-D printer to fabricate items that can change their color. Frustrated by some of the limitations of this project, such as small color scheme and low-resolution results, the team decided to investigate potential updates. 

With ColorMod, each pixel on an object needed to be printed, so the resolution of each tiny little square was somewhat grainy. As far as colors, each pixel of the object could only have two states: transparent and its own color. So, a blue dye could only go from blue to transparent when activated, and a yellow dye could only show yellow.  

But with PhotoChromeleon’s ink, you can create anything from a zebra pattern to a sweeping landscape to multicolored fire flames, with a larger host of colors.  

The team created the ink by mixing cyan, magenta, and yellow (CMY) photochromic dyes into a single sprayable solution, eliminating the need to painstakingly 3-D print individual pixels. By understanding how each dye interacts with different wavelengths, the team was able to control each color channel through activating and deactivating with the corresponding light sources. 

Specifically, they used three different lights with different wavelengths to eliminate each primary color separately. For example, if you use a blue light, it would mostly be absorbed by the yellow dye and be deactivated, and magenta and cyan would remain, resulting in blue. If you use a green light, magenta would mostly absorb it and be deactivated, and then both yellow and cyan would remain, resulting in green.

After coating an object using the solution, the user simply places the object inside a box with a projector and UV light. The UV light saturates the colors from transparent to full saturation, and the projector desaturates the colors as needed. Once the light has activated the colors, the new pattern appears. But if you aren’t satisfied with the design, all you have to do is use the UV light to erase it, and you can start over. 

They also developed a user interface to automatically process designs and patterns that go onto desired items. The user can load up their blueprint, and the program generates the mapping onto the object before the light works its magic. 

The team tested the system on a car model, a phone case, a shoe, and a little (toy) chameleon. Depending on the shape and orientation of the object, the process took anywhere from 15 to 40 minutes, and the patterns all had high resolutions and could be successfully erased when desired. 

“By giving users the autonomy to individualize their items, countless resources could be preserved, and the opportunities to creatively change your favorite possessions are boundless,” says MIT Professor Stefanie Mueller.   

While PhotoChromeleon opens up a much larger color gamut, not all colors were represented in the photochromic dyes. For example, there was no great match for magenta or cyan, so the team had to estimate to the closest dye. They plan to expand on this by collaborating with material scientists to create improved dyes. 

“We believe incorporation of novel, multi-photochromic inks into traditional materials can add value to Ford products by reducing the cost and time required for fabricating automotive parts,” says Alper Kiziltas, technical specialist of sustainable and emerging materials at Ford Motor Co. (Ford has been working with MIT on the ColorMod 3-D technology through an alliance collaboration.) “This ink could reduce the number of steps required for producing a multicolor part, or improve the durability of the color from weathering or UV degradation. One day, we might even be able to personalize our vehicles on a whim.”

Jin and Mueller co-authored the paper alongside CSAIL postdocs Isabel Qamar and Michael Wessely. MIT undergraduates Aradhana Adhikari and Katarina Bulovic also contributed, as well as former MIT postdoc Parinya Punpongsanon.

Adhikari received the Morais and Rosenblum Best UROP Award for her contributions to the project.

Ford Motor Co. provided financial support, and permission to publish was granted by the Ford Research and Innovation Center.

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Robot learns to follow orders like Alexa

Despite what you might see in movies, today’s robots are still very limited in what they can do. They can be great for many repetitive tasks, but their inability to understand the nuances of human language makes them mostly useless for more complicated requests.

For example, if you put a specific tool in a toolbox and ask a robot to “pick it up,” it would be completely lost. Picking it up means being able to see and identify objects, understand commands, recognize that the “it” in question is the tool you put down, go back in time to remember the moment when you put down the tool, and distinguish the tool you put down from other ones of similar shapes and sizes.

Recently researchers from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) have gotten closer to making this type of request easier: In a new paper, they present an Alexa-like system that allows robots to understand a wide range of commands that require contextual knowledge about objects and their environments. They’ve dubbed the system “ComText,” for “commands in context.”

The toolbox situation above was among the types of tasks that ComText can handle. If you tell the system that “the tool I put down is my tool,” it adds that fact to its knowledge base. You can then update the robot with more information about other objects and have it execute a range of tasks like picking up different sets of objects based on different commands.

“Where humans understand the world as a collection of objects and people and abstract concepts, machines view it as pixels, point-clouds, and 3-D maps generated from sensors,” says CSAIL postdoc Rohan Paul, one of the lead authors of the paper. “This semantic gap means that, for robots to understand what we want them to do, they need a much richer representation of what we do and say.”

The team tested ComText on Baxter, a two-armed humanoid robot developed for Rethink Robotics by former CSAIL director Rodney Brooks.

The project was co-led by research scientist Andrei Barbu, alongside research scientist Sue Felshin, senior research scientist Boris Katz, and Professor Nicholas Roy. They presented the paper at last week’s International Joint Conference on Artificial Intelligence (IJCAI) in Australia.

How it works

Things like dates, birthdays, and facts are forms of “declarative memory.” There are two kinds of declarative memory: semantic memory, which is based on general facts like the “sky is blue,” and episodic memory, which is based on personal facts, like remembering what happened at a party.

Most approaches to robot learning have focused only on semantic memory, which obviously leaves a big knowledge gap about events or facts that may be relevant context for future actions. ComText, meanwhile, can observe a range of visuals and natural language to glean “episodic memory” about an object’s size, shape, position, type and even if it belongs to somebody. From this knowledge base, it can then reason, infer meaning and respond to commands.

“The main contribution is this idea that robots should have different kinds of memory, just like people,” says Barbu. “We have the first mathematical formulation to address this issue, and we’re exploring how these two types of memory play and work off of each other.”

With ComText, Baxter was successful in executing the right command about 90 percent of the time. In the future, the team hopes to enable robots to understand more complicated information, such as multi-step commands, the intent of actions, and using properties about objects to interact with them more naturally.

For example, if you tell a robot that one box on a table has crackers, and one box has sugar, and then ask the robot to “pick up the snack,” the hope is that the robot could deduce that sugar is a raw material and therefore unlikely to be somebody’s “snack.”

By creating much less constrained interactions, this line of research could enable better communications for a range of robotic systems, from self-driving cars to household helpers.

“This work is a nice step towards building robots that can interact much more naturally with people,” says Luke Zettlemoyer, an associate professor of computer science at the University of Washington who was not involved in the research. “In particular, it will help robots better understand the names that are used to identify objects in the world, and interpret instructions that use those names to better do what users ask.”

The work was funded, in part, by the Toyota Research Institute, the National Science Foundation, the Robotics Collaborative Technology Alliance of the U.S. Army, and the Air Force Research Laboratory.

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How to make a book last for millennia

First discovered in 1947 by Bedouin shepherds looking for a lost sheep, the ancient Hebrew texts known as the Dead Sea Scrolls are some of the most well-preserved ancient written materials ever found. Now, a study by researchers at MIT and elsewhere elucidates a unique ancient technology for parchment making and provides new insights into possible methods to better preserve these precious historical documents.

The study focused on one scroll in particular, known as the Temple Scroll, among the roughly 900 full or partial scrolls found in the years since that first discovery. The scrolls were found in jars hidden in 11 caves on the steep hillsides just north of the Dead Sea, in the region around the ancient settlement of Qumran, which was destroyed by the Romans about 2,000 years ago. It is thought that, to protect their religious and cultural heritage from the invaders, members of a sect called the Essenes hid their precious documents in the caves, often buried under a few feet of debris and bat guano to help foil looters.

The Temple Scroll is one of the largest (almost 25 feet long) and best-preserved of all the scrolls, even though its material is the thinnest of all of them (one-tenth of a millimeter, or roughly 1/250 of an inch thick). It also has the clearest, whitest writing surface of all the scrolls. These properties led Admir Masic, the Esther and Harold E. Edgerton Career Development Assistant Professor of Civil and Environmental Engineering and a Department of Materials Science and Engineering faculty fellow in archaeological materials, and his collaborators to wonder how the parchment was made.

The results of that study, carried out with former doctoral student Roman Schuetz (now at Israel’s Weizmann Institute of Science), MIT graduate student Janille Maragh, James Weaver from the Wyss Institute at Harvard University, and Ira Rabin from the Federal Institute of Materials Research and Testing and Hamburg University in Germany, were published today in the journal Science Advances. They found that the parchment was processed in an unusual way, using a mixture of salts found in evaporites — the material left from the evaporation of brines — but one that was different from the typical composition found on other parchments.

“The Temple Scroll is probably the most beautiful and best-preserved scroll,” Masic says. “We had the privilege of studying fragments from the Israeli museum in Jerusalem called the Shrine of the Book,” which was built specifically to house the Dead Sea Scrolls. One relatively large fragment from that scroll was the main subject of the new paper. The fragment, measuring about 2.5 centimeters (1 inch) across was investigated using a variety of specialized tools developed by researchers to map, in high resolution, the detailed chemical composition of relatively large objects under a microscope.

“We were able to perform large-area, submicron-scale, noninvasive characterization of the fragment,” Masic says — an integrated approach that he and Weaver have developed for the characterization of both biological and nonbiological materials. “These methods allow us to maintain the materials of interest under more environmentally friendly conditions, while we collect hundreds of thousands of different elemental and chemical spectra across the surface of the sample, mapping out its compositional variability in extreme detail,” Weaver says.

That fragment, which has escaped any treatment since its discovery that might have altered its properties, “allowed us to look deeply into its original composition, revealing the presence of some elements at completely unexpectedly high concentrations,” Masic says.

The elements they discovered included sulfur, sodium, and calcium in different proportions, spread across the surface of the parchment.

Parchment is made from animal skins that have had all hair and fatty residues removed by soaking them in a lime solution (from the Middle Ages onward) or through enzymatic and other treatments (in antiquity), scraping them clean, and then stretching them tight in a frame to dry. When dried, sometimes the surface was further prepared by rubbing with salts, as was apparently the case with the Temple Scroll.

The team has not yet been able to assess where the unusual combination of salts on the Temple Scroll’s surface came from, Masic says. But it’s clear that this unusual coating, on which the text was written, helped to give this parchment its unusually bright white surface, and perhaps contributed to its state of preservation, he says. And the coating’s elemental composition does not match that of the Dead Sea water itself, so it must have been from an evaporite deposit found somewhere else — whether nearby or far away, the researchers can’t yet say.

The unique composition of that surface layer demonstrates that the production process for that parchment was significantly different from that of other scrolls in the region, Masic says: “This work exemplifies exactly what my lab is trying to do — to use modern analytical tools to uncover secrets of the ancient world.”

Understanding the details of this ancient technology could help provide insights into the culture and society of that time and place, which played a central role in the history of both Judaism and Christianity. Among other things, an understanding of the parchment production and its chemistry could also help to identify forgeries of supposedly ancient writings.

According to Rabin, an expert in Dead Sea Scroll materials, “This study has far-reaching implications beyond the Dead Sea Scrolls. For example, it shows that at the dawn of parchment making in the Middle East, several techniques were in use, which is in stark contrast to the single technique used in the Middle Ages. The study also shows how to identify the initial treatments, thus providing historians and conservators with a new set of analytical tools for classification of the Dead Sea Scrolls and other ancient parchments.”

This information could indeed be crucial in guiding the development of new preservation strategies for these ancient manuscripts. Unfortunately, it appears that much of the damage seen in the scrolls today arose not from their 2,000-plus years in the caves, but from efforts to soften the scrolls in order to unroll and read them immediately after their initial discovery, Masic says.

Adding to these existing concerns, the new data now clearly demonstrate that these unique mineral coatings are also highly hygroscopic — they readily absorb any moisture in the air, and then might quickly begin to degrade the underlying material. These new results thus further emphasize the need to store the parchments in a controlled humidity environment at all times. “There could be an unanticipated sensitivity to even small-scale changes in humidity,” he says. “The point is that we now have evidence for the presence of salts that might accelerate their degradation. … These are aspects of preservation that must be taken into account.”

“For conservation issues and programs, this work is very important,” says Elisabetta Boaretto, director of the Kimmel Center for Archaeological Science at the Weizmann Institute of Science in Israel, who was not associated with this work. She says, “It indicates that you have to know very well the document needing to be preserved, and the preservation has to be tailored to the document’s chemistry and its physical state.”

Boaretto adds that this team’s study of the unusual mineral layer on the parchment “is fundamental for future work in preservation, but most importantly to understand how these documents have been prepared in antiquity. This work certainly sets a standard for other researchers in this field.”

The work was partly supported by DFG, the German Research Foundation.

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American Sign Language at MIT

On Aug. 15, 25 MIT students and staff members were engaged in a lively lecture and discussion in Building 66 — but the room was completely silent. The teacher, Carol Zurek, wrote a word on the board and gestured to the class to repeat her movements.

The students practiced the motion, incorporating them into their existing American Sign Language (ASL) vocabulary.

The class was organized by the American Sign Language and Deaf Culture Club at MIT and offered free to members of the MIT community. This fall, the club is hosting non-credit, level one and level two courses, supported by the MindHandHeart Innovation Fund and Graduate Student Life Grants.

The club was officially formed in 2016, though MIT has offered ASL classes organized by the group of students and staff since 2014, with support from the Media Lab. The interest level in the courses has been impressive, with nearly 80 people signing up for classes that are capped at 25 students.

“I think the interest speaks to the MIT community wanting to be open and inclusive,” said Barbara Johnson, a staff member in MIT Information Systems and Technology (IS&T) who spearheaded the effort to bring ASL classes to MIT and is deaf. “The goals of the club are to spread awareness of Deaf culture and ASL as a language, and to get people to see deafness as another component of diversity.”

The classes are structured in six week and eight week sessions and meet for approximately 90 minutes. Students use a book to guide them through learning vocabulary and basic conversational skills, and the instructor prompts students to engage in structured role playing.

“The keystone of the class is that voices are off,” Johnson says. “This can be quite a jolt for some people — figuring out how to communicate using a visual language.”

ASL Club president Gustavo Goretkin, a PhD student at the Computer Science and Artificial Intelligence Laboratory, says this is one of the most rewarding aspects of the class. “You might be conversing with a student and may even consider them a friend, but you’ll go months without hearing their voice,” he says. “It’s a very special and unique layer of connection to have with a person.”

Kristy Johnson, a PhD student in the Media Lab and a founding officer in the club, also appreciates the community she has found through the ASL Club.

“I have two kids and live off campus,” she explains. “So it’s been great for me to have an outlet that promotes so much engagement and connection. You have to really pay attention when you’re learning ASL. You have to look the other person in the eyes and focus on what they’re saying. You can’t be distracted or on your phone.”

Johnson was inspired to sign up for the classes in order to better communicate with her son and because of her general interest in languages.

“I use sign language extensively with my son, who has autism as well as many other special needs,” she says. “He responds much more consistently to signing than he ever does to spoken speech. I also use it with my daughter, who just turned one.”

Learning ASL has also influenced Johnson’s research at the Media Lab.

“It’s valuable to be able to communicate with lots of different people and types of learners,” she says. “The more you become aware of these different abilities, both through people like my son and through members of the Deaf community, the more we can invent for and with that community. If MIT wants to stay at the forefront of innovation, we have to be innovating for everybody.”

In addition to the ASL classes, the club plans to host social events in the fall, including lunchtime practice sessions and field trips. Looking to the future, the group hopes that ASL will become a more permanent fixture on campus and that MIT will offer for-credit courses.

To get a glimpse of the ASL Club in action, check out their video that was awarded first place in the MindHandHeart “Heart at MIT” video contest. To learn more and register for classes, visit the ASL Club website.

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Creating new opportunities from nanoscale materials

A hundred years ago, “2d” meant a two-penny, or 1-inch, nail. Today, “2-D” encompasses a broad range of atomically thin flat materials, many with exotic properties not found in the bulk equivalents of the same materials, with graphene — the single-atom-thick form of carbon — perhaps the most prominent. While many researchers at MIT and elsewhere are exploring two-dimensional materials and their special properties, Frances M. Ross, the Ellen Swallow Richards Professor in Materials Science and Engineering, is interested in what happens when these 2-D materials and ordinary 3-D materials come together.

“We’re interested in the interface between a 2-D material and a 3-D material because every 2-D material that you want to use in an application, such as an electronic device, still has to talk to the outside world, which is three-dimensional,” Ross says.

“We’re at an interesting time because there are immense developments in instrumentation for electron microscopy, and there is great interest in materials with very precisely controlled structures and properties, and these two things cross in a fascinating way,” says Ross. 

“The opportunities are very exciting,” Ross says. “We’re going to be really improving the characterization capabilities here at MIT.” Ross specializes in examining how nanoscale materials grow and react in both gases and liquid media, by recording movies using electron microscopy. Microscopy of reactions in liquids is particularly useful for understanding the mechanisms of electrochemical reactions that govern the performance of catalysts, batteries, fuel cells, and other important technologies. “In the case of liquid phase microscopy, you can also look at corrosion where things dissolve away, while in gases you can look at how individual crystals grow or how materials react with, say, oxygen,” she says.

Ross joined the Department of Materials Science and Engineering (DMSE) faculty last year, moving from the nanoscale materials analysis department at the IBM Thomas J. Watson Research Center. “I learned a tremendous amount from my IBM colleagues and hope to extend our research in material design and growth in new directions,” she says.

Recording movies

During a recent visit to her lab, Ross explained an experimental setup donated to MIT by IBM. An ultra-high vacuum evaporator system arrived first, to be attached later directly onto a specially designed transmission electron microscope. “This gives powerful possibilities,” Ross explains. “We can put a sample in the vacuum, clean it, do all sorts of things to it such as heating and adding other materials, then transfer it under vacuum into the microscope, where we can do more experiments while we record images. So we can, for example, deposit silicon or germanium, or evaporate metals, while the sample is in the microscope and the electron beam is shining through it, and we are recording a movie of the process.”

While waiting this spring for the transmission electron microscope to be set up, members of Ross’ seven-member research group, including materials science and engineering postdoc Shu Fen Tan and graduate student Kate Reidy, made and studied a variety of self-assembled structures. The evaporator system was housed temporarily on the fifth-level prototyping space of MIT.nano while Ross’s lab was being readied in Building 13. “MIT.nano had the resources and space; we were happy to be able to help,” says Anna Osherov, MIT.nano assistant director of user services.

“All of us are interested in this grand challenge of materials science, which is: ‘How do you make a material with the properties you want and, in particular, how do you use nanoscale dimensions to tweak the properties, and create new properties, that you can’t get from bulk materials?’” Ross says.

Using the ultra-high vacuum system, graduate student Kate Reidy formed structures of gold and niobium on several 2-D materials. “Gold loves to grow into little triangles,” Ross notes. “We’ve been talking to people in physics and materials science about which combinations of materials are the most important to them in terms of controlling the structures and the interfaces between the components in order to give some improvement in the properties of the material,” she notes.

Shu Fen Tan synthesized nickel-platinum nanoparticles and examined them using another technique, liquid cell electron microscopy. She could arrange for only the nickel to dissolve, leaving behind spiky skeletons of platinum. “Inside the liquid cell, we are able to see this whole process at high spatial and temporal resolutions,” Tan says. She explains that platinum is a noble metal and less reactive than nickel, so under the right conditions the nickel participates in an electrochemical dissolution reaction and the platinum is left behind.

Platinum is a well-known catalyst in organic chemistry and fuel cell materials, Tan notes, but it is also expensive, so finding combinations with less-expensive materials such as nickel is desirable.

“This is an example of the range of materials reactions you can image in the electron microscope using the liquid cell technique,” Ross says. “You can grow materials; you can etch them away; you can look at, for example, bubble formation and fluid motion.”

A particularly important application of this technique is to study cycling of battery materials. “Obviously, I can’t put an AA battery in here, but you could set up the important materials inside this very small liquid cell and then you can cycle it back and forth and ask, if I charge and discharge it 10 times, what happens? It does not work just as well as before — how does it fail?” Ross asks. “Some kind of failure analysis and all the intermediate stages of charging and discharging can be observed in the liquid cell.”

“Microscopy experiments where you see every step of a reaction give you a much better chance of understanding what’s going on,” Ross says.

Moiré patterns

Graduate student Reidy is interested in how to control the growth of gold on 2-D materials such as graphene, tungsten diselenide, and molybdenum disulfide. When she deposited gold on “dirty” graphene, blobs of gold collected around the impurities. But when Reidy grew gold on graphene that had been heated and cleaned of impurities, she found perfect triangles of gold. Depositing gold on both the top and bottom sides of clean graphene, Reidy saw in the microscope features known as moiré patterns, which are caused when the overlapping crystal structures are out of alignment.

The gold triangles may be useful as photonic and plasmonic structures. “We think this could be important for a lot of applications, and it is always interesting for us to see what happens,” Reidy says. She is planning to extend her clean growth method to form 3-D metal crystals on stacked 2-D materials with various rotation angles and other mixed-layer structures. Reidy is interested in the properties of graphene and hexagonal boron nitride (hBN), as well as two materials that are semiconducting in their 2-D single-layer form, molybdenum disulfide (MoS2) and tungsten diselenide (WSe2). “One aspect that’s very interesting in the 2-D materials community is the contacts between 2-D materials and 3-D metals,” Reidy says. “If they want to make a semiconducting device or a device with graphene, the contact could be ohmic for the graphene case or a Schottky contact for the semiconducting case, and the interface between these materials is really, really important.”

“You can also imagine devices using the graphene just as a spacer layer between two other materials,” Ross adds.

For device makers, Reidy says it is sometimes important to have a 3-D material grow with its atomic arrangement aligned perfectly with the atomic arrangement in the 2-D layer beneath. This is called epitaxial growth. Describing an image of gold grown together with silver on graphene, Reidy explains, “We found that silver doesn’t grow epitaxially, it doesn’t make those perfect single crystals on graphene that we wanted to make, but by first depositing the gold and then depositing silver around it, we can almost force silver to go into an epitaxial shape because it wants to conform to what its gold neighbors are doing.”

Electron microscope images can also show imperfections in a crystal such as rippling or bending, Reidy notes. “One of the great things about electron microscopy is that it is very sensitive to changes in the arrangement of the atoms,” Ross says. “You could have a perfect crystal and it would all look the same shade of gray, but if you have a local change in the structure, even a subtle change, electron microscopy can pick it up. Even if the change is just within the top few layers of atoms without affecting the rest of the material beneath, the image will show distinctive features that allow us to work out what’s going on.”

Reidy also is exploring the possibilities of combining niobium — a metal that is superconducting at low temperatures — with a 2-D topological insulator, bismuth telluride. Topological insulators have fascinating properties whose discovery resulted in the Nobel Prize in Physics in 2016. “If you deposit niobium on top of bismuth telluride, with a very good interface, you can make superconducting junctions. We’ve been looking into niobium deposition, and rather than triangles we see structures that are more dendritic looking,” Reidy says. Dendritic structures look like the frost patterns formed on the inside of windows in winter, or the feathery patterns of some ferns. Changing the temperature and other conditions during the deposition of niobium can change the patterns that the material takes.

All the researchers are eager for new electron microscopes to arrive at MIT.nano to give further insights into the behavior of these materials. “Many things will happen within the next year, things are ramping up already, and I have great people to work with. One new microscope is being installed now in MIT.nano and another will arrive next year. The whole community will see the benefits of improved microscopy characterization capabilities here,” Ross says.

MIT.nano’s Osherov notes that two cryogenic transmission electron microscopes (cryo-TEM) are installed and running. “Our goal is to establish a unique microscopy-centered community. We encourage and hope to facilitate a cross-pollination between the cryo-EM researchers, primarily focused on biological applications and ‘soft’ material, as well as other research communities across campus,” she says. The latest addition of a scanning transmission electron microscope with enhanced analytical capabilities (ultrahigh energy resolution monochromator, 4-D STEM detector, Super-X EDS detector, tomography, and several in situ holders) brought in by John Chipman Associate Professor of Materials Science and Engineering James M. LeBeau, once installed, will substantially enhance the microscopy capabilities of the MIT campus. “We consider Professor Ross to be an immense resource for advising us in how to shape the in situ approach to measurements using the advanced instrumentation that will be shared and available to all the researchers within the MIT community and beyond,” Osherov says.

Little drinking straws

“Sometimes you know more or less what you are going to see during a growth experiment, but very often there’s something that you don’t expect,” Ross says. She shows an example of zinc oxide nanowires that were grown using a germanium catalyst. Some of the long crystals have a hole through their centers, creating structures which are like little drinking straws, circular outside but with a hexagonally shaped interior. “This is a single crystal of zinc oxide, and the interesting question for us is why do the experimental conditions create these facets inside, while the outside is smooth?” Ross asks. “Metal oxide nanostructures have so many different applications, and each new structure can show different properties. In particular, by going to the nanoscale you get access to a diverse set of properties.”

“Ultimately, we’d like to develop techniques for growing well-defined structures out of metal oxides, especially if we can control the composition at each location on the structure,” Ross says. A key to this approach is self-assembly, where the material builds itself into the structure you want without having to individually tweak each component. “Self-assembly works very well for certain materials but the problem is that there’s always some uncertainty, some randomness or fluctuations. There’s poor control over the exact structures that you get. So the idea is to try to understand self-assembly well enough to be able to control it and get the properties that you want,” Ross says.

“We have to understand how the atoms end up where they are, then use that self-assembly ability of atoms to make a structure we want. The way to understand how things self-assemble is to watch them do it, and that requires movies with high spatial resolution and good time resolution,” Ross explains. Electron microscopy can be used to acquire structural and compositional information and can even measure strain fields or electric and magnetic fields. “Imagine recording all of these things, but in a movie where you are also controlling how materials grow within the microscope. Once you have made a movie of something happening, you analyze all the steps of the growth process and use that to understand which physical principles were the key ones that determined how the structure nucleated and evolved and ended up the way it does.”

Future directions

Ross hopes to bring in a unique high-resolution, high vacuum TEM with capabilities to image materials growth and other dynamic processes. She intends to develop new capabilities for both water-based and gas-based environments. This custom microscope is still in the planning stages but will be situated in one of the rooms in the Imaging Suite in MIT.nano.

“Professor Ross is a pioneer in this field,” Osherov says. “The majority of TEM studies to-date have been static, rather than dynamic. With static measurements you are observing a sample at one particular snapshot in time, so you don’t gain any information about how it was formed. Using dynamic measurements, you can look at the atoms hopping from state to state until they find the final position. The ability to observe self-assembling processes and growth in real time provides valuable mechanistic insights. We’re looking forward to bringing these advanced capabilities to MIT.nano.” she says.

“Once a certain technique is disseminated to the public, it brings attention,” Osherov says. “When results are published, researchers expand their vision of experimental design based on available state-of-the-art capabilities, leading to many new experiments that will be focused on dynamic applications.”

Rooms in MIT.nano feature the quietest space on the MIT campus, designed to reduce vibrations and electromagnetic interference to as low a level as possible. “There is space available for Professor Ross to continue her research and to develop it further,” Osherov says. “The ability of in situ monitoring the formation of matter and interfaces will find applications in multiple fields across campus, and lead to a further push of the conventional electron microscopy limits.”

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Comparing primate vocalizations

The utterances of Old World monkeys, some of our primate cousins, may be more sophisticated than previously realized — but even so, they display constraints that reinforce the singularity of human language, according to a new study co-authored by an MIT linguist. 

The study reinterprets evidence about primate language and concludes that Old World monkeys can combine two items in a language sequence. And yet, their ability to combine items together seems to stop at two. The monkeys are not able to recombine language items in the same open-ended manner as humans, whose languages generate an infinite variety of sequences.

“We are saying the two systems are fundamentally different,” says Shigeru Miyagawa, an MIT linguist and co-author of a new paper detailing the study’s findings.

That might seem apparent. But the study’s precise claim — that even if other primates can combine terms, they cannot do so in the way humans do — emphasizes the profound gulf in cognitive ability between humans and some of our closest relatives.

“If what we’re saying in this paper is right, there’s a big break between two [items in a sentence], and [the potential for] infinity,” Miyagawa adds. “There is no three, there is no four, there is no five. Two and infinity. And that is the break between a nonhuman primate and human primates.”

The paper, “Systems underlying human and Old World monkey communications: One, two, or infinite,” is published today in the journal Frontiers in Psychology. The authors are Miyagawa, who is a professor of linguistics at MIT; and Esther Clarke, an expert in primate vocalization who is a member of the Behavior, Ecology, and Evolution Research (BEER) Center at Durham University in the U.K.

To conduct the study, Miyagawa and Clarke re-evaluated recordings of Old World monkeys, a family of primates with over 100 species, including baboons, macaques, and the probiscis monkey.

The language of some of these species has been studied fairly extensively. Research starting in the 1960s, for example, established that vervet monkeys have specific calls when they see leopards, eagles, and snakes, all of which requires different kinds of evasive action. Similarly, tamarin monkeys have one alarm call to warn of aerial predators and one to warn of ground-based predators.

In other cases, though, Old World monkeys seem capable of combining calls to create new messages. The putty-nosed monkey of West Africa, for example, has a general alarm call, which scientists call “pyow,” and a specific alarm call warning of eagles, which is “hack.” Sometimes these monkeys combine them in “pyow-hack” sequences of varying length, a third message that is used to spur group movement.

However, even these latter “pyow-hack” sequences start with “pyow” and end with “hack”; the terms are never alternated. Although these sequences vary in length and consequently can sound a bit different from each other, Miyagawa and Clarke break with some other analysts and think there is no “combinatorial operation” at work with putty-nosed monkey language, unlike the process through which humans rearrange terms. It is only the length of the “pyow-hack” sequence that indicates how far the monkeys will relocate.

“The putty-nose monkey’s expression is complex, but the important thing is the overall length, which predicts behavior and predicts how far they travel,” Miyagawa says. “They start with ‘pyow’ and end up with ‘hack.’ They never go back to ‘pyow.’ Never.”

As a result, Miyagawa adds, “Yes, those calls are made up of two items. Looking at the data very carefully it is apparent. The other thing that is apparent is that they cannot combine more than two things. We decided there is a whole different system here,” compared to human language.

Similarly, Campbell’s monkey, also of West Africa, deploys calls that might be interpreted as evidence of human-style combination of language items, but which Miyagawa and Clarke believe are actually a simpler system. The monkeys make sounds rendered as “hok,” for an eagle alarm, and “krak,” for a leopard alarm. To each, they add an “-oo” suffix to turn those utterances into generalized aerial alarms and land alarms.

However, that does not mean the Campbell’s monkey has developed a suffix as a kind of linguistic building block that could be part of a more open-ended, larger system of speech, the researchers conclude. Instead, its use is restricted to a small set of fixed utterances, none of which have more than two basic items in them.

“It’s not the human system,” Miyagawa says. In the paper, Miyagawa and Clarke contend that the monkeys’ ability to combine these terms means they are merely deploying a “dual-compartment frame” which lacks the capacity for greater complexity.

Miyagawa also notes that when the Old World monkeys speak, they seem to use a part of the brain known as the frontal operculum. Human language is heavily associated with Broca’s area, a part of the brain that seems to support more complex operations.

If the interpretation of Old World monkey language that Miyagawa and Clarke put forward here holds up, then humans’ ability to harness Broca’s area for language may specifically have enabled them to recombine language elements as other primates cannot — by enabling us to link more than two items together in speech. 

“It seems like a huge leap,” Miyagawa says. “But it may have been a tiny [physiological] change that turned into this huge leap.”

As Miyagawa acknowledges, the new findings are interpretative, and the evolutionary history of human language acquisition is necessarily uncertain in many regards. His own operating conception of how humans combine language elements follows strongly from Noam Chomsky’s idea that we use a system called “Merge,” which contains principles that not all linguists accept.

Still, Miyagawa suggests, further analysis of the differences between human language and the language of other primates can help us better grasp how our unique language skills evolved, perhaps 100,000 years ago.

“There’s been all this effort to teach monkeys human language that didn’t succeed,” Miyagawa notes. “But that doesn’t mean we can’t learn from them.”

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