What Zhang did was to create the world’s most precise value for a subatomic nuclear particle called a neutral pion. It’s a quark and an antiquark comprising a meson. The neutral pion (also known as p0) is the lightest of the mesons, but a player in the strong attractive force that holds the atom’s nucleus together.
And that, in turn, makes it a part of the puzzle Gao and her students have been trying to solve for many years. The prevailing theory about the strong force is called quantum chromodynamics (QCD), and it’s been probed for years by high-energy physics. But Gao, Zhang and their collaborators are trying to study QCD under more normal energy states, a notoriously difficult problem.
Yang Zhang spent six years analyzing and writing up the data from a Primakoff (PrimEx-II) experiment in Hall B at Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, VA. His work was done on equipment supported by both the National Science Foundation and the Department of Energy.
In a Primakoff experiment, a photon beam is directed on a nuclear target, producing neutral pions. In both the PrimEx-I and PrimEx-II experiments at Jefferson Lab, the two photons from the decay of a neutral pionwere subsequently detected in an electromagnetic calorimeter. From that, Zhang extracted the pion’s ‘radiative decay width.’ That decay width is a handy thing to have, because it is directly related to the pion’s life expectancy, and QCD has a direct prediction for it.
Zhang’s hard-won answer: The neutral pion has a radiative decay width of 7.8 electron-volts, give or take. That makes it an important piece of the dauntingly huge puzzle about QCD. Gao and her colleagues will continue to ask the fundamental questions about nature, at the finest but perhaps most profound scale imaginable.
The PrimEx-I and PrimEx-II collaborations were led by Prof. Ashot Gasparian from North Carolina A&T State University. Gao and Zhang joined the collaboration in 2011.
“Precision Measurement of the Neutral Pion Lifetime,” appears in Science May 1. Dr. Yang Zhang is now a quantitative researcher at JPMorgan Chase & Co.
The proton, that little positively-charged nugget inside
an atom, is fractions of a quadrillionth of a meter smaller than anyone thought,
according to new research appearing Nov. 7 in Nature.
In work they hope solves the contentious “proton radius puzzle” that has been roiling some corners of physics in the last decade, a team of scientists including Duke physicist Haiyan Gao have addressed the question of the proton’s radius in a new way and discovered that it is 0.831 femtometers across, which is about 4 percent smaller than the best previous measurement using electrons from accelerators. (Read the paper!)
A single femtometer is 0.000000000000039370 inches
imperial, if that helps, or think of it as a millionth part of a billionth part
of a meter. And the new radius is just 80 percent of that.
But this is a big — and very small — deal for
physicists, because any precise calculation of energy levels in an atom will be
affected by this measure of the proton’s size, said Gao, who is the Henry
Newson professor of physics in Trinity College of Arts & Sciences.
What the physicists actually measured is the radius of
the proton’s charge distribution, but that’s never a smooth, spherical point,
Gao explained. The proton is made of still smaller bits, called quarks, that
have their own charges and those aren’t evenly distributed. Nor does anything
sit still. So it’s kind of a moving target.
One way to measure a proton’s charge radius is to scatter
an electron beam from the nucleus of an atom of hydrogen, which is made of just
one proton and one electron. But the electron must only perturb the proton very
gently to enable researchers to infer the size of the charge involved in the
interaction. Another approach measures the difference between two atomic
hydrogen energy levels. Past results from these two methods have generally
But in 2010, an experiment at the Paul Scherrer Institute replaced the electron in a hydrogen atom with a muon, a much heavier and shorter-lived member of the electron’s particle family. The muon is still negatively charged like an electron, but it’s about 200 times heavier, so it can orbit much closer to the proton. Measuring the difference between muonic hydrogen energy levels, these physicists obtained a proton charge radius that is highly precise, but much smaller than the previously accepted value. And this started the dispute they’ve dubbed the “proton charge radius puzzle.”
To resolve the puzzle, Gao and her collaborators set out
to do a completely new type of electron scattering experiment with a number of
innovations. And they looked at electron scattering from both the proton and
the electron of the hydrogen atom at the same time. They also managed to get
the beam of electrons scattered at near zero degrees, meaning it came almost
straight forward, which enabled the electron beam to “feel” the proton’s charge
response more precisely.
Voila, a 4-percent-smaller proton. “But actually, it’s
much more complicated,” Gao said, in a major understatement.
The work was done at the Department of Energy’s Thomas
Jefferson National Accelerator Facility in Newport News, Virginia, using new
equipment supported by both the National Science Foundation and the Department
of Energy, and some parts that were purpose-built for this experiment. “To
solve the argument, we needed a new approach,” Gao said.
Gao said she has been interested in this question for nearly
20 years, ever since she became aware of two different values for the proton’s
charge radius, both from electron scattering experiments. “Each one claimed about 1 percent
uncertainty, but they disagreed by several percent,” she said.
And as always in modern physics, had the answer not
worked out so neatly, it might have called into question parts of the Standard
Model of particle physics. But alas, not this time.
“This is particularly important for a number of reasons,”
Gao said. The proton is a fundamental building block of visible matter, and the
energy level of hydrogen is a basic unit of measure that all physicists rely
The new measure may also help advance new insights into
quantum chromodynamics (QCD), the theory of strong interaction in quarks and
gluons, Gao said. “We really don’t understand how QCD works.”
“This is a very, very big deal,” she said. “The field is
very excited about it. And I should add that this experiment would not have
been so successful without the heroic contributions from our highly talented
and hardworking graduate students and postdocs from Duke.”
This work was funded in part by the U. S. National Science Foundation (NSF MRI PHY-1229153) and by the U.S. Department of Energy (Contract No. DE-FG02-03ER41231), including contract No. DE-AC05-06OR23177 under which Jefferson Science Associates, LLC operates Thomas Jefferson National Accelerator Facility.
CITATION: “A Small Proton Charge Radius from An Electron-Proton Scattering Experiment,” W. Xiong, A. Gasparian, H. Gao, et al. Nature, Nov. 7, 2019. DOI: 10.1038/s41586-019-1721-2 (ONLINE)
Just about every day, there’s a new headline about this or
that factor possibly contributing to Alzheimer’s Disease. Is it genetics,
lifestyle, diet, chemical exposures, something else?
The sophisticated answer is that it’s probably ALL of those things working together in a very complicated formula, says Alexander Kulminski, an associate research professor in the Social Science Research Institute. And it’s time to study it that way, he and his colleague, Caleb Finch at the Andrus Gerontology Center at the University of Southern California, argue in a recent paper that appears in the journal Alzheimer’s and Dementia, published by the Alzheimer’s Association.
“Life is not simple,” Kulminski says. “We need to combine
“We propose the ‘AD Exposome’ to address major gaps in
understanding environmental contributions to the genetic and non-genetic risk
of AD and related dementias,” they write in their paper. “A systems approach is
needed to understand the multiple brain-body interactions during
The analysis would focus on three domains, Kulminski says:
macro-level external factors like rural v. urban, pollutant exposures,
socio-economcs; individual external factors like diet and infections; and internal
factors like individual microbiomes, fat deposits, and hormones.
That’s a lot of data, often in disparate, broadly scattered
studies. But Kulminski, who came to Duke as a physicist and mathematician, is
confident modern statistics and computers could start to pull it together to
make a more coherent picture. “Twenty years ago, we couldn’t share. Now the way
forward is consortia,” Kulminski said.
The vision they outline in their paper would bring together
longitudinal population data with genome-wide association studies,
environment-wide association studies and anything else that would help the
Alzheimer’s research community flesh out this picture.
And then, ideally, the insights of such research
would lead to ways to “prevent, rather than cure” the cognitive declines of the
disease, Kulminsky says. Which just
happens to be the NIH’s goal for 2025.
is increasingly asking artificial intelligence machines to help us search and interpret
huge collections of data, and it’s making a difference.
But unfortunately, polymer chemistry — the study of large, complex molecules — has been hampered in this effort because it lacks a crisp, coherent language to describe molecules that are not tidy and orderly.
Think nylon. Teflon. Silicone. Polyester. These and other polymers are what the chemists call “stochastic,” they’re assembled from predictable building blocks and follow a finite set of attachment rules, but can be very different in the details from one strand to the next, even within the same polymer formulation.
old stick and ball models and shorthand chemical notations aren’t adequate for a
long molecule that can best be described as a series of probabilities that one
kind of piece might be in a given spot, or not.
Polymer chemists searching for new materials for medical treatments or plastics that won’t become an environmental burden have been somewhat hampered by using a written language that looks like long strings of consonants, equal signs, brackets, carets and parentheses. It’s also somewhat equivocal, so the polymer Nylon-6-6 ends up written like this:
And when we get to something called ‘concatenation
syntax,’ matters only get worse.
Stephen Craig, the William T. Miller Professor of Chemistry, has been a polymer chemist for almost two decades and he says the notation language above has some utility for polymers. But Craig, who now heads the National Science Foundation’s Center for the Chemistry of Molecularly Optimized Networks (MONET), and his MONET colleagues thought they could do better.
“Once you have that insight about how a polymer is grown,
you need to define some symbols that say there’s a probability of this kind of
structure occurring here, or some other structure occurring at that spot,”
Craig says. “And then it’s reducing that to practice and sort of defining a set
Now he and his MONET colleagues at MIT and Northwestern University have done just that, resulting in a new language – BigSMILES – that’s an adaptation of the existing language called SMILES (simplified molecular-input line-entry system). They they think it can reduce this hugely combinatorial problem of describing polymers down to something even a dumb computer can understand.
And that, Craig says, should enable computers to do all the stuff they’re good at – searching huge datasets for patterns and finding needles in haystacks.
The initial heavy lifting was done by MONET members Prof. Brad Olsen and his co-worker Tzyy-Shyang Lin at MIT who conceived of the idea and developed the set of symbols and the syntax together. Now polymers and their constituent building blocks and variety of linkages might be described like this:
certainly not the best reading material for us and it would be terribly difficult
to read aloud, but it becomes child’s play for a computer.
of MONET spent a couple of weeks trying to stump the new language with the
weirdest polymers they could imagine, which turned up the need for a few more
parts to the ‘alphabet.’ But by and large, it holds up, Craig says. They also threw
a huge database of polymers at it and it translated them with ease.
“One of the things I’m excited about
is how the data entry might eventually be tied directly to the synthetic
methods used to make a particular polymer,” Craig says. “There’s an opportunity
to actually capture and process more information about the molecules than is
typically available from standard characterizations. If that can be done,
it will enable all sorts of discoveries.”
BigSMILES was introduced to the
polymer community by an article in ACS Central Science
last week, and the MONET team is eager to see the response.
“Can other people use it and does it work for
everything?” Craig asks. “Because polymer structure space is effectively
infinite.” Which is just the kind of thing you need Big Data and machine
learning to address.
“This is an area where the
intersection of chemistry and data science can have a huge impact,” Craig says.
The technical-sounding category of “light-driven
charge-transfer reactions,” becomes more familiar to non-physicists when you just
call it photosynthesis or solar electricity.
When a molecule (in a leaf or solar cell) is hit by an
energetic photon of light, it first absorbs the little meteor’s energy, generating
what chemists call an excited state. This excited state then almost immediately
(like trillionths of a second) shuttles an electron away to a charge acceptor
to lower its energy. That transference of charge is what drives plant life and
The energy of the excited state plays an important role in
determining solar energy conversion efficiency. That is, the more of that
photon’s energy that can be retained in the charge-separated state, the better.
For most solar-electric devices, the excited state rapidly loses energy,
resulting in less efficient devices.
But what if there were a way to create even more energetic
excited states from that incoming photon?
Using a very efficient photosynthesizing bacterium as their inspiration,
a team of Duke chemists that included graduate students Nick Polizzi and Ting
Jiang, and faculty members David Beratan and Michael Therien, synthesized a
“supermolecule” to help address this question.
“Nick and Ting discovered a really cool trick about electron
transfer that we might be able to adapt to improving solar cells,” said Michael
Therien, the William R. Kenan, Jr. Professor of Chemistry. “Biology figured
this out eons ago,” he said.
“When molecules absorb light, they have more energy,” Therien said. “One of the things that these molecular excited states do is that they move charge. Generally speaking, most solar energy conversion structures that chemists design feature molecules that push electron density in the direction they want charge to move when a photon is absorbed. The solar-fueled microbe, Rhodobacter sphaeroides, however, does the opposite. What Nick and Ting demonstrated is that this could also be a winning strategy for solar cells.”
The chemists devised a clever synthetic molecule that shows the advantages of an excited state that pushes electron density in the direction opposite to where charge flows. In effect, this allows more of the energy harvested from a photon to be used in a solar cell.
“Nick and Ting’s work shows that there are huge advantages
to pushing electron density in the exact opposite direction where you want
charge to flow,” Therien said in his top-floor office of the French Family
Science Center. “The biggest advantage of an excited state that pushes charge the
wrong way is it stops a really critical pathway for excited state relaxation.”
“So, in many ways it’s a Rube Goldberg Like conception,”
Therien said. “It is a design strategy that’s been maybe staring us in the face
for several years, but no one’s connected the dots like Nick and Ting have
In a July 2
commentary for the Proceedings of the National Academy of Sciences, Bowling
Green State University chemist and photoscientist Malcom D.E. Forbes calls this
work “a great leap forward,” and says it “should be regarded as one of the most
beautiful experiments in physical chemistry in the 21st century.”
CITATION: “Engineering Opposite Electronic Polarization of
Singlet and Triplet States Increases the Yield of High-Energy Photoproducts,”
Nicholas Polizzi, Ting Jiang, David Beratan, Michael Therien. Proceedings of
the National Academy of Sciences, June 10, 2019. DOI: 10.1073/pnas.1901752116
It’s one of those things that seems so simple and elegant that you’re left asking yourself, “Geez, why didn’t I think of that?”
Say you were trying to help people lose weight, prep for a surgery or take their meds every day. They’re probably holding a smartphone in at least one of their hands — all you need to do is enlist that ever-present device they’re staring at to bug them!
So, for example, have the health app send a robo-text twice a day to check in: “Did you weigh yourself?” Set up a group chat where their friends all know what they’re trying to accomplish: “We’re running today at 5, right?”
This is a screenshot of a Pattern Health app for pre-operative patients.
It’s even possible to make them pinky-swear a promise to their phone that they will do something positive toward the goal, like walking or skipping desert that day. And if they don’t? The app has their permission to lock them out of all their apps for a period of time.
Seriously, people agree to this and it works.
Two app developers on this frontier of personalized, portable “mHealth” told a lunchtime session sponsored by the Duke Mobile App Gateway on Thursday that patients not only willingly play along with these behavioral modification apps, their behaviors change for the better.
The idea of using phones for health behavior came to pediatric hematologist Nirmish Shah MD one day while he attempted to talk to a 16-year-old sickle cell disease patient as she snapped selfies of herself with the doctor. Her mom and toddler sister nearby both had their noses to screens as well. “I need to change how I do this,” Shah thought to himself.
Pediatric hematologist Nirmish Shah MD is director of Duke’s sickle cell transition program.
Twenty health apps later, he’s running phase II clinical trials of phone-based interventions for young sickle cell patients that encourage them to stay on their medication schedule and ask them often about their pain levels.
One tactic that seems to work pretty well is to ask his patients to send in selfie videos as they take their meds each day. The catch? The female patients send a minute or so of chatty footage a day. The teenage boys average 13 seconds, and they’re grumpy about it.
Clearly, different activities may be needed for different patient populations, Shah said.
While it’s still early days for these approaches, we do have a lot of behavioral science on what could help, said Aline Holzwarth, a principal of the Center for Advanced Hindsight and head of behavioral science for a Durham health app startup called Pattern Health.
Aline Holzwarth is a principal in the Center for Advanced Hindsight.
“It’s not enough to simply inform people to eat better,” Holzwarth said. The app has to secure a commitment from the user, make them set small goals and then ask how they did, enlist the help of social pressures, and then dole out rewards and punishments as needed.
Pattern Health’s app says “You need to do this, please pick a time when you will.” Followed by a reward or a consequence.
Thursday’s session, “Using Behavioral Science to Drive Digital Health Engagement and Outcomes, was the penultimate session of the annual Duke Digital Health Week. Except for the Hurricane Florence washout on Monday, the week has been a tremendous success this year, said Katie McMillan, the associate director of the App Gateway.
‘Population Health’ is the basis of a new department in the School of Medicine, a byword for a lot of new activity across campus , and on Tuesday the subject of a half-day symposium that attempted to bring all this energy together.
For now, population health means a lot of different things to a lot of different people.
The half-day symposium drew an overflow crowd of faculty and staff. (photo – Colin Huth)
“We’re still struggling with a good definition of what population health is,” said keynote speaker Clay Johnston, MD, PhD, dean of the new Dell School of Medicine in Austin, Texas. Smoking cessation programs are something most everyone would agree is taking care of the population outside of the clinic. But improved water quality? Where does that fit?
“We have an intense focus on doctors and their tools,” Johnston said. Our healthcare system is optimized for maximum efficiency in fee-for-service care, that is, getting the most revenue out of the most transactions. “But most of health is outside the clinic,” Johnston said.
Perhaps as a result, the United States pays much more for health care, but lives less well, he said. “We are noticeably off the curve,” when compared to health care costs and outcomes in other countries.
This graphic from a handout shared at the conference shows how population health spans the entire university.
As an example of what might be achieved in population health with some re-thinking and a shift in resources, the Dell School went after the issue of joint pain with input from their engineering and business schools. Rather than diagnosing people toward an orthopedic surgery – for which there was a waitlist of about 14 months – their system worked with patients on alternatives, such as weight loss, physical therapy and behavioral changes before surgery. The 14-month backlog was gone in just three months. Surgeries still happen, of course, but not if they can be comfortably delayed or avoided.
“Payment for prevention needs serious work,” Johnston said. “You need to get people to buy into it,” but in diabetes or depression for example, employers should stand to gain a lot from having healthier employees who miss fewer days, he said.
Health Affairs Chancellor Eugene Washington commented several times, calling the discussion “very interesting and very valuable.” (photo -Colin Huth)
Other examples flowed freely the rest of the afternoon. Duke is testing virtual ‘telemedicine’ appointments versus office visits. Evidence-based prenatal care is being applied to try to avoid expensive neonatal ICU care. Primary care and Emergency Department physicians are being equipped with an app that helps them steer sickle cell patients to appropriate care resources so that they might avoid expensive ED visits.
Family practitioner Eugenie Komives, MD, is part of a team using artificial intelligence and machine learning to try to predict which patients are most likely to be hospitalized in the next six months. That prediction, in turn, can guide primary care physicians and care managers to pay special attention to these patients to help them avoid the hospital. The system is constantly being evaluated, she added. “We don’t want to be doing this if it doesn’t work.”
Community health measures like walkability and grocery stores are being mapped for Durham County on a site called Durham Neighborhood Compass, said Michelle Lyn, MBA, chief of the division of community health. The aim is not only to see where improvements can be made, but to democratize population health information and put it in peoples’ hands. “(Community members) will have ideas we never could have thought of,” Lyn said. “We will be able to see change across our neighborhoods and community.”
Patient input is key to population health, agreed several speakers. “I don’t think we’ve heard them enough,” said Paula Tanabe, PhD, an associate professor of nursing and medicine who studies pain and sickle cell disease. “We need a bigger patient voice.”
Health Affairs Chancellor and Duke Health CEO Eugene Washington, MD, has made population health one of the themes of his leadership. “We really take seriously this notion of shaping the future of population health,” he said in his introductory remarks. “When I think of the future, I think about how well-positioned we are to have impact on the lives of the community we serve.”
“I, as an organizer of this, didn’t know about half of these projects today!” Curtis said. “There’s so much going on at an organic level that the challenge to us is to identify what’s going on and figure out how to go forward at scale.”
In the first week of February, students, experts and conservationists from across the country were brought together for the second annual Duke Blueprint symposium. Focused around the theme of “Nature and Progress,” this conference hoped to harness the power of diversity and interdisciplinary collaboration to develop solutions to some of the world’s most pressing environmental challenges.
Scott Loarie spoke at Duke’s Mary Duke Biddle Trent Semans Center.
One of the most exciting parts of this symposium’s first night was without a doubt its all-star cast of keynote speakers. The experiences and advice each of these researchers had to offer were far too diverse for any single blog post to capture, but one particularly interesting presentation (full video below) was that of National Geographic fellow Scott Loarie—co-director of the game-changing iNaturalist app.
iNat, as Loarie explained, is a collaborative citizen scientist network with aspirations of developing a comprehensive mapping of all terrestrial life. Any time they go outside, users of this app can photograph and upload pictures of any wildlife they encounter. A network of scientists and experts from around the world then helps the users identify their finds, generating data points on an interactive, user-generated map of various species’ ranges.
Simple, right? Multiply that by 500,000 users worldwide, though, and it’s easy to see why researchers like Loarie are excited by the possibilities an app like this can offer. The software first went live in 2008, and since then its user base has roughly doubled each year. This has meant the generation of over 8 million data points of 150,000 different species, including one-third of all known vertebrate species and 40% of all known species of mammal. Every day, the app catalogues around 15 new species.
“We’re slowly ticking away at the tree of life,” Loarie said.
Through iNaturalist, researchers are able to analyze and connect to data in ways never before thought possible. Changes to environments and species’ distributions can be observed or modeled in real time and with unheard-of collaborative opportunities.
To demonstrate the power of this connectedness, Loarie recalled one instance of a citizen scientist in Vietnam who took a picture of a snail. This species had never been captured, never been photographed, hadn’t been observed in over a century. One of iNat’s users recognized it anyway. How? He’d seen it in one of the journals from Captain James Cook’s 18th-century voyage to circumnavigate the globe.
It’s this kind of interconnectivity that demonstrates not just the potential of apps like iNaturalist, but also the power of collaboration and the possibilities symposia like Duke Blueprint offer. Bridging gaps, tearing down boundaries, building up bonds—these are the heart of conservationism’s future. Nature and Progress, working together, pulling us forward into a brighter world.
For their recent retreat, Regeneration Next tried something a little different for the time-honored poster session.
Rather than simply un-tubing that poster they took to the American Association of Whatever a few months ago, presenters were asked to DRAW their poster fresh and hot on a plain sheet of white paper in 15 minutes, using nothing more than an idea and a couple of markers.
“People are always nervous about something they haven’t tried before,” said Regeneration Next Executive Director Sharlini Sankaran. “There was a lot of anxiety about the new format and how they would explain their research without charts and graphs.”
There was palpable poster panic as the retreat moved to the wide open fifth floor of the Trent Semans Center in the late afternoon. Administrative coordinator Tiffany Casey had spread out a rainbow of brand-new sharpies and the moveable bulletin boards stood in neat, numbered ranks with plain white sheets of giant post-it paper.
After some nervous laughter and a few attempts at color-swapping, the trainees and junior faculty got down to drawing their science on the wobbly tackboards.
And then, it worked! It totally worked. “I think I saw a lot more interactivity and conversation,” Sankaran said.
A fist-full of colorful sharpies gave Valentina Cigliola a colorful launching point for some good conversations about spinal cord repair, rather than just standing there mutely while visitors read and read and read.
Louis-Jan Pilaz used the entire height of the giant post-it notes to draw a beautifully detailed neuron, with labeled parts explaining how the RNA-binding protein FMRP does some neat tricks during development of the cortex.
Delisa Clay’s schematics of fruitfly cells having too many chromosomes made it easier to explain. Well, that and maybe a glass of wine.
Jamie Garcia used her cell-by-cell familiarity with the zebrafish to make a bold, clear illustration of notochord development and the fish’s amazing powers of self-repair.
Don’t you think Lihua Wang’s schematic of experimental results is so much more clear than a bunch of panels of tiny text and bar charts?
In the post-retreat survey, Sankaran said people either absolutely loved the draw-your-poster or hated it, but the Love group was much larger.
“Those who hated it felt they couldn’t represent data accurately with hand-drawn charts and graphs,” Sankaran said. “Or that their artistic skills were ‘being judged’.”
A few folks also pointed out that the drawing approach might work against people with a disability of some sort – a concern Sankaran said they will try to address next time.
There WILL be a next time, she added. “I had a few trainees come up to me to say they weren’t sure how it was going to go, but then they said they had fun!”
Post and pix by Karl Leif Bates, whose hand-drawn poster on working with the news office contained no data and was largely ignored.
This year’s listing of the world’s most-cited researchers is out from Clarivate Analytics, and Duke has 34 names on the list of 3,400 researchers from 21 fields of science and social science.
Having your publication cited in a paper written by other scientists is a sign that your work is significant and advances the field. The highly-cited list includes the top 1 percent of scientists cited by others in the years 2005 to 2015.
“Citations by other scientists are an acknowledgement that the work our faculty has published is significant to their fields,” said Vice Provost for Research Lawrence Carin. “In research, we often talk about ‘standing on the shoulders of giants,’ as a way to explain how one person’s work builds on another’s. For Duke to have so many of our people in the top 1 percent indicates that they are leading their fields and their work is indeed something upon which others can build.”