Physics | Duke Research Blog

From the basement, female physicists shaped Duke and German science

December 5th, 2012

By Ashley Yeager

German physicist Hedwig Kohn (April 5, 1887 – 1964) in her laboratory, circa 1912. Image courtesy of: the Jewish Women’s Archive.

Physicist Hedwig Kohn‘s brother was murdered in a Nazi concentration camp in 1941.

Yet, when she trained young German physicists at Duke University a little more than 10 years later, she bore no resentment against them. Those students later returned to Germany and helped educate the country’s students in quantum mechanics.

Kohn fled Nazi Germany with the help of several prominent scientists in 1940, teaching first at the Women’s College in Greensboro, now UNC–Greensboro, and then at Wellesley College in Massachusetts. In 1952, she retired from teaching and accepted a research associate position working with physicist Hertha Sponer at Duke.

“It’s important that Kohn’s and Sponer’s tenure at Duke not be forgotten,” said physicist Brenda Winnewisser, an adjunct professor at The Ohio State University. The women’s lives and their research helped shape the physics department’s early encouragement of women interested in science.

Winnewisser, who earned her Ph.D. in physics at Duke in 1965, spoke briefly about Sponer and mostly about Kohn during a Nov. 28 physics colloquium. During her talk, Winnewisser recounted Kohn’s history, explained how she saved Kohn’s letters and photographs from destruction and described how she is using the archived information to write Kohn’s biography, a book called Hedwig Kohn: A Passion for Physics.

In her lab, which was in the subbasement of the Duke physics building, Kohn measured the absorption features and concentrations of atomic species in flames. The research was a continuation of what she had worked on from 1912 until 1933, when the Nazis stripped her of her privilege to do research and teach because of her being Jewish and female.

Still, the Nazis couldn’t take away the quality or importance of her work, which had a resurgence in citations in the 1960s as researchers began to test rocket designs and study plasmas, Winnewisser said. She added that Kohn also had an “indirect impact on improving quantum mechanics education in Germany after World War II.”

Three of the four physicists Kohn mentored at Duke returned to Germany to teach at prominent universities, bringing with them what they had learned from Kohn about flames, absorption and also quantum mechanics. “Kohn gave them the technical basis for successful careers,” Winnewisser said.

Her biography of Kohn, who died in 1964, is slated for release by Biting Duck Press in the spring of 2014.

Gecko’s stick inspires adhesives and even superheroes

November 9th, 2012

By Ashley Yeager

A single hair on a gecko’s foot has enough “stickiness” to pick up an ant. Credit: Kellar Autumn, Lewis & Clark College.

Sticky feet driving you up the wall?

Well, maybe not. But they are for Cicak, or Gecko-Man. After a few sips of coffee contaminated by a virus-infected gecko, a loser lab scientist suddenly becomes a Malaysian superhero, sticking to walls, using his tongue to scale skyscrapers and even eating bugs.

“Gecko feet are nature’s best adhesion and removal device,” said Lewis & Clark College biologist Kellar Autumn. He gave the keynote speech during the awards ceremony of the third annual Abhijit Mahato photo contest on Nov. 7.

While Autumn riled up the audience with his images and videos of the science behind gecko feet and their inspiration for new adhesives, robots and superheroes, he also used the talk to remind the photographers in the audience that appearance and scientific images can be misleading.

The science of how geckos climb up walls and across ceilings is at least a 200-year-old question, one that even Aristotle tried to answer. In the late 1960s, one scientist took some scanning electron microscope images of gecko feet and thought they revealed suction cups as the mechanism that let geckos scale walls and ceilings. But that idea was wrong.

It wasn’t until Autumn and his collaborators began looking more closely at the creature’s feet in the late nineties and early 2000s that scientists realized it wasn’t suction, but nanometer-scale interactions between a surface and the gecko’s foot hairs, or setae, that let them stick, release and climb. His team took a single gecko foot hair and made the first direct measurement of its adhesive function. Turns out the stickiness in one hair is so strong it can lift the weight of an ant.

The team also discovered that geckos release their feet as they climb by changing the angle of their feet hairs. That means that the contact geometry of setae are more important that any other factor in their ability to climb, Autumn said, adding that the discovery demonstrated “we could make this stuff.”

Tom Cruise climbs a skyscraper with “gecko gloves: in MI:Ghost Protocol. Image courtesy of: Danny Baram.

He showed videos of both the kinematics and kinetics of the way geckos climb and compared and contrasted the physics the creatures use to the human-engineered “nanopimples” and wedge-shaped nanoridges that resemble geckos’ sticky feet. The animal’s foot physics is “different than pretty much everything else out there,” Autumn said, though he did describe several developing projects to try to mimic the animals’ movements.

Still, he said, he’s convinced that “had geckos not evolved their sticky feet, humans would not have invented adhesive nanostructures.” And, there’s no way we’d have gecko gloves or could even think of gecko band-aides and the other cool applications of gecko-feet science, he said.

Citations:

“Adhesive force of a single gecko foot-hair.” Autumn, K., et. al. (2000). Nature 405, 681-685.

“Evidence for van der Waals adhesion in gecko setae.” Autumn, K., et. al. (2002). Proc. Natl. Acad. Sci. USA 99, 12252-12256.

“Evidence for self-cleaning in gecko setae.” Hansen, W. and Autumn, K. (2005). Proc. Nat. Acad. Sci. U. S. A. 102, 385-389.

Refereed physics for Twitter and Facebook, maybe

October 19th, 2012

By Ashley Yeager

These library stacks of science journals are going out of style as more publishers opt for online-only, open access formats. Credit: UCSF.

When journal publishers send peer-reviewed tweets, they’ll have truly entered the digital age. They’re not there yet, but that doesn’t mean they’re not trying, said Gene Sprouse, editor-and-chief of the American Physical Society(APS) and a physics professor at Stony Brook University.

Sprouse, speaking at an Oct. 17 physics colloquium, described how the Internet is changing the way scientists share their research. They used to submit papers to journals, have their ideas vetted by other scientists, and then see their arguments and data in print — or not. He said it has been this way since the 1660s when the first journal, Philosophical Transactions, was first published.

But with online journals available right on researchers’ desktop and open-access digital archives, such as arXiv.org, journal editors, like those at the helm of magazines and newspapers, are trying to figure out how to shift print publications online while still making a profit.

“Eventually print journals will disappear,” Sprouse said, explaining that sans paper, authors and publishers could include new types of content like movies and active graphics in their articles. But even with new media features, “what physicists want is rapid acceptance of their paper into a prestigious journal with no hassles during peer review. They want attention for their work, and they want it widely distributed.”

To meet those demands in the new media landscape, APS has developed a Creative Commons license for authors to share their articles on their personal web sites and encourages them to publish pre-prints in online digital archives, such as arXiv.org.

Hoping to merge the prestige of the “baby Nature” journals – Nature Photonics, Nature Optics, Nature Physics, etc. – with the open-access model of the Public Library of Science, or PLOS, journals, the society has also created Physical Review X.

It’s the society’s first online-only, fully open-access journal. The one-year-old publication, which charges authors $1,500 per accepted article, is already comparable in prestige to APS’s other leading journal, Physical Review Letters. The difference is that now authors have an open-access journal to submit to at APS, which is important as more funders push researchers to submit to that type of publication, Sprouse said.

The society isn’t ignoring Twitter and Facebook either. When asked when the society would post the first refereed physics tweet, Sprouse said he couldn’t really say because he personally doesn’t use social media. But, APS, he added quickly, is working on its social media strategy and would “welcome any advice from those of you exploring that realm.”

Packing for Proteins

September 27th, 2012

This artist's rendering shows a ribbon diagram of the protein T4 phage lysozyme. Image courtesy of Ohio State.

By Ashley Yeager

If you ask vacationers about packing, they’ll probably tell you about over-stuffed suitcases and inflatable beach toys. But if you ask Yale physicist Corey O’Hern, he’ll tell you packing is about pockets, proteins and geometry.

“You may not believe it or may not have heard about it, but I’m going to argue that just geometry is important for understanding protein structure,” and “that makes protein structure look like a packing problem,” O’Hern said at a Sept. 26 physics colloquium. The protein packing problem and solving it could have implications for drug design.

O’Hern first learned about packing problems in physics as an undergraduate at Duke in the early 1990s. Working with Duke physicist Bob Behringer, he tried to explain how corn and coffee beans get jammed in their dispensers. O’Hern continued this type of work as a graduate student at the University of Pennsylvania and then earned a faculty post as a theorist in Yale’s engineering and applied science department.

“I didn’t believe in fate until I went to Yale and learned about Fred Richards. Now I do,” O’Hern said, explaining that the Yale biophysicist was interested in the structure of proteins and the “interior packing,” or arrangement, of their amino acids. O’Hern said Richards thought of proteins as a jigsaw puzzle and tried to figure out how the weird pieces fit together.

To better understand a protein’s geometry, Richards would trace water molecules over the surface of its amino acids. He thought that the inner folds of proteins were “well-packed” because the strong attractions of the atoms in those areas. “I don’t completely believe Richards’ results,” but the work “made me feel destined to get in on the research,” O’Hern said.

He now looks at how tightly animo acid molecules fit together in certain regions of the protein, T4 phage lysozyme. To study its packing properties, O’Hern simulates the energy and entropy in the pockets, or cavities, of the lysozyme’s inner folds. His early results suggest that the most stable forms of the protein have the most entropy, or randomness, among the amino acids in the pockets.

That way of packing is definitely counter-intuitive, O’Hern said. He’s still working on how the results are possible and, in a broader sense, how they could affect packing and folding of drugs to improve their effectiveness.

Taking a ‘DiVE’ into Neutrinos

September 21st, 2012

Physicists can now analyze neutrino events, such as this one, in 3D. Courtesy: Berkeley Lab.

By Ashley Yeager

Using a virtual, 3D environment, scientists are getting their closest look yet at neutrinos’ interactions with matter.

Neutrinos are subatomic particles that “interact with matter only very rarely, maybe once in your body in your entire lifetime,” said Duke physicist Kate Scholberg during a Sept. 21 talk, which the Visualization Technology Group hosted.

Scholberg explained that to study neutrino interactions, scientists use large, underground detectors, which may only record one event per day. That might not seem significant. But, as Scholberg explained, scientists need to observe the events to determine how the universe developed with more matter than anti-matter, a phenomenon that allows life to exist.

Typically, Scholberg and her colleagues analyze neutrino interactions from their Japan-based detector Super-K in a two-dimensional computer program. Recently, however, Scholberg “stepped” into the Duke immersive Virtual Environment, or DiVE, a six-sided, cave-like, virtual-reality theater programed with data from Super-K.

Inside, Scholberg got her first look at neutrinos interactions in 3D. She was able to see a representation of Super-K and thousands of its light detectors. She could also see data from a recent neutrino event and was able to walk around the detector simulation and visualize the neutrino interaction from all sides. The software had even traced out the “sonic boom” of light, which looks like a circle in two-dimensions and a cone or ring in three-dimensions, given off after a neutrino event.

“This is what I’ve imagined happens a million times after an interaction,” Scholberg said, showing a video of her experience in the DiVE. “It’s entirely different seeing it in 3D,” she said, adding that the drawing of the cone shape of a Cherenkov ring has never been done in a neutrino event display before.

Benjamin Izatt a student at the University of California, Berkeley was the mastermind who developed the 3D neutrino simulation, called Super-KAVE. He designed it to help Duke physicists explain their neutrino research to the public.

But, Scholberg said, the tool may also help her and her collaborators at Super-K better understand complex neutrino interactions and sort out where the particles’ rings and cones overlap. She added that in future simulations, “we may also be able to see particles and interact with the particles, which would be not only fun, but helpful.”

A second crack at the nature of glass

August 13th, 2012

By Ashley Yeager

Glassblowers shape molten silica before the glass transitions from liquid to a more solid structure. Credit: handblownglass.com.

Patrick Charbonneau and his collaborators have taken another crack at understanding the nature of glass. Their latest simulations show that a key assumption of theoretical chemists and physicists to explain the molecular structure of glass is wrong.

Glass forms when liquids are slowly compressed or super-cooled, but don’t crystallize the way cooled water turns to ice. The liquidy pre-cursors to glass, like molten silica, do become hard like a solid, but the atoms in the material don’t organize themselves into a perfect crystal pattern.

The result is a substance that is as hard as a solid but has the molecular arrangement of a liquid — a phenomenon that scientists can’t quite explain, yet.

Previous theories assumed that at the transition point between a liquid and glass, the material’s atoms become caged by each other in a “simple” Gaussian shape. This same shape describes the distribution of people’s height in the U.S. and is known as a bell-shaped curve.

But new simulations, described online Aug. 13 in PNAS, suggest this assumption is wrong. The simulations model the interactions of glass particles in multiple dimensions and show the shape of the particle cage is much more complex than a Gaussian distribution.

The discovery is a “paradigm shift in the sense that so many people have been having the same, wrong, conception for so long, and they should now revisit that basic assumption,” says Charbonneau, a theoretical chemist at Duke. “The assumption was actually constraining how they thought about the problem.”

Even with a new shine on the way scientists think about glass, it is not clear how close or far the theorists are from writing an accurate description of what happens at the liquid-glass transition. But “the path to get there seems clearer than it has been in a long time,” Charbonneau says.

The next step in the research is to understand the relationship between glassy states of matter and those that are jammed, like pieces of cereal wedged in a grain hopper. Charbonneau and collaborators are already at work about how to study the connections between the two forms of matter.

Citation:
“Dimensional study of the caging order parameter at the glass transition.” 2012. Charbonneau, P., et al. PNAS Early Edition. DOI: 10.1073/pnas.1211825109

Reading between the lines of light

August 10th, 2012

By Ashley Yeager

Harry Potter's invisibility cloak is not exactly what scientists have in mind for their light tricks. Credit: Warner Brothers.

The way we understand light is largely based on how we see it. To our eyes, light is like a stream of particles.

Scientists usually study these particle streams by measuring their wavelengths and how they interact with objects. But over the last decade, researchers have begun to realize that light particles can interact with objects within wavelengths too.

Now, scientists are looking inside wavelengths to control and manipulate light, which is transforming the traditional field of optics, according to Duke engineer David Smith and his colleagues.

They describe the changes to the field of optics in a review article appearing online Aug. 2 in Science, and they describe how, at a tenth or even a hundredth of the wavelength of visible light, the classic picture of how we see breaks down.

In this regime, streams of light particles can bend away from an object, essentially tricking the eye into thinking the object is not there. As a result, scientists can no longer think of light in terms of particle streams. Instead, they must think of it as a manipulation of electric and magnetic field lines.

Thinking of light this way, Smith and other scientists are beginning to understand how they can hide one object within another and even harvest energy. The new understanding “will be the design tool of choice” as scientists continue to play with the forces between electrically charged particles, the authors argue.

Citation:

“Transformation Optics and Subwavelength Control of Light.” Pendry, J., et. al. 2012. Science 337: 549-552.
DOI: 10.1126/science.1220600

Hot particles appear in Science

July 19th, 2012

By Ashley Yeager

Protons and neutrons "melt" to produce a plasma of freely interacting quarks and gluons. Credit: RHIC/BNL.

On July 20, readers of the journal Science are in for quite a treat — a clear, concise explanation of what matter looked like in the early universe and how scientists study it.

Science has “published very few articles in this field, as is generally the case in nuclear and particle physics, so it was a nice surprise when they invited us to write the piece,” said Duke theoretical physicist, Berndt Mueller, a co-author of the review article.

Subatomic scientists rarely try to present their latest discoveries in widely accessible terms, which may be why the journal does not run many articles related to nuclear physics, he said.

In the piece, Mueller and his co-author, Barbara Jacak, an experimental physicist at Stony Brook University, describe the most recent discoveries and remaining questions about matter in the early universe, a primordial soup called the quark-gluon plasma.

One of the most puzzling questions for physicists in this field how the subatomic particles that make matter — quarks and gluons — behave when they are “liberated,” or broken apart, as they were in the early phase of the cosmos. “We now know, thanks to the experiments at the Relativistic Heavy Ion Collider (RHIC), that they behave completely differently than theorists thought, but we only know some aspects, many others remain to be explored,” Mueller said.

The “big” question is what structure the primordial soup of quarks and gluons takes at extremely high temperatures‚ beyond two trillion degrees Celsius. “We don’t know. It’s somehow made up of quarks and gluons. It’s like saying that liquid water is made up of the elements hydrogen and oxygen, but not knowing that they form water, or H2O molecules, and that those again cluster in teaming little molecular clusters,” Mueller said.

Gold particles collide, forming a soup of quarks and gluons. Click the image to watch a more-detailed video about the quark-gluon soup.Credit: RHIC/BNL.

Answering the structure question may also help to better explain how some atoms at the opposite extreme of the temperature scale‚ a minute fraction of a degree above absolute zero, act as a nearly perfect fluid, flowing almost without resistance, just as the quark-gluon plasma does. The answer could also offer ways to comprehend black holes, string theory, and extra dimensions.

To make those connections, the authors argue that physicists will need to explore how quark matter evolves over a range of energies, temperatures and densities. They can use the Large Hadron Collider (LHC) in Europe to probe the universe’s primordial soup at the highest range of energies. But RHIC seems to be able to operate at the energy “sweet spot” for exploring the transition from ordinary matter to the quark-gluon plasma.

The scientists will talk more about future plans and research at RHIC and LHC at the Quark Matter 2012 conference in Washington, D.C. on August 12-18, which the Duke nuclear theory group helped to organize. Jacak, the leader of a 500-member international collaboration performing experiments at RHIC and a member of the National Academy of Sciences, will be at Duke on Sept. 5 to give a talk about hot nuclear matter research.

Citation: The Exploration of Hot Nuclear Matter. Jacak, B., and Mueller, B. 2012. Science. 337: 310-314.
DOI: 10.1126/science.1215901