Diffusion a la Chocolate Lava Cake

By Ashley Yeager

Note: This is the second post in a four-part, monthly series that will give readers recipes to try in their kitchen and learn a little chemistry and physics along the way. Read the first post here.

Making chocolate lava cakes demonstrates the diffusion of heat. Credit: Ashley Yeager, Duke.

Between bites of hot lava cake and vanilla ice cream, freshmen taking Chemistry and Physics of Cooking talk about diffusion. Their conversation isn’t so esoteric that an outsider wouldn’t understand.

Instead, it’s a simple chat about how long to cook a cake based on how heat moves.

Understanding diffusion is a way to make sense of cooking times, says chemistry and physics professor Patrick Charbonneau, who is leading the class along with chef Justine de Valicourt.

Diffusion of matter is how particles in a liquid, gas or solid intermingle and move from a region of higher concentration to one of lower concentration.

Heat diffusion describes how hot particles warm up cooler particles around them, which allows the inside of a dish to cook, even though only the outside is heated.

Before turning his students loose in a kitchen in Smith Warehouse to eat a product of this process, Charbonneau and his teaching fellows had the group work through the equations that describe diffusion.

“Solving the diffusion equations of heat gives you a first estimate of how long to bake a cake or cook a turkey,” Charbonneau says. The cooking time for lava cake is especially critical in order to get the outside it to bake, while the inside remains gooey, de Valicourt adds.

In class, the students calculated that to make a muffin-sized lava cake with ingredients at room temperature in an oven at 400°F (204°C) would take about 10 minutes. In the lab, they found that the calculation was fairly accurate, but for a more exact estimate of cooking time, they needed to factor in the temperature of melted chocolate chips in their recipe.

“Still, with the cooking time being not so mysterious, it’s one fewer thing left to chance,” Charbonneau says, adding, “then you can be more creative with the recipe in other ways.”

He and de Valicourt, who have partnered with the Alicia Foundation to offer the Chemistry and Physics of Cooking class, have provided the following recipe for experimenting with diffusion and hot lava cake.

Hot Lava Cake –

Ingredients:
60g (1/3 c) dark chocolate chips
60 g (1/2 stick) butter
60 g (1/4 c) sugar
3 eggs (or 2 egg and 45mL (3tbs) coconut milk)
30 g (1/4 c) flour
small pinch salt
Non-stick cooking spray

Materials:
1 bowl (bain-marie)*
4 ramekin dishes or 1 muffin tin
2 medium bowls
1 scale (if weighing ingredients)
1 sieve
1 cooking thermometer (optional)

* You can make a bain-marie by placing a bowl over a saucepan of simmering water.

Instructions:

1. Preheat the oven to 400°F/204°C.
2. Melt chocolate and butter on bain-marie. Stir. Do not boil the water or the chocolate could burn.
3. Combine eggs and sugar (and coconut milk) in a medium bowl and whisk until bubbly.
4. Combine flour and salt in another bowl and pass it through the sieve.
5. With one person whisking and another pouring, slowly add the chocolate mixture to the egg mixture.
6. Add the flour and salt to the wet ingredients and whisk well.
7. Spray ramekins or muffin tin with non-stick cooking spray.
8. Fill the ramekins or muffin tin a little more than halfway full.
9. Place the ramekins or tin in the oven on the middle rack.
10. Bake until the cakes start growing. The interior of the lava cake should be around 158-176°F/70-80°C and the outside around 203-212°F/95-100°C – ie until the edges of the cake are set, but the center is still a liquid – about 7 to 10 minutes (less for smaller cakes).

Close Encounters of the Twitter Kind

By Ashley Yeager

Astrophysicist Katie Mack and other researchers are starting to join Twitter to do better science. Image courtesy of: mediabistro.com

Before launching into dark matter’s effects on particle physics in the early universe, astrophysicist Katie Mack of the University of Melbourne in Australia took a little detour Wednesday to talk about Twitter.

The social media tool is helping her “do better science and learn about new science,” she said during her Jan. 30 seminar at Duke.

The talk materialized from a tweet she had posted a few days ago about attending ScienceOnline, an annual, Raleigh-based conference for scientists and communicators talking and writing about science on the Internet.

Duke physicist Mark Kruse, who joined Twitter in October after the 2012 Council for the Advancement of Science Writers meeting, saw Mack’s tweet about coming to the Triangle and then contacted her to see if she would like to speak about her research.

She said yes, obviously, and explained during her talk that the invitation, as well as the other networking she has done on Twitter, got her to thinking about why all physicists (and scientists) should use the site.

@AstroKatie shares her top reasons scientists should be on Twitter. Credit: Katie Mack, U. of Melbourne.

Here is a paraphrased list of her top five reasons:

1. You can see what scientific breakthroughs people are getting excited about.
2. You can keep track of science discoveries outside of your field.
3. You can share your work with a broader audience.
4. You can connect with other scientists in and outside your field, building your professional network.
5. You can connect and share your work with the public.

Clearly Mack’s invitation to speak at Duke illustrates her third point about Twitter. Now, she said, she looks forward to attending her first ScienceOnline meeting to build on those points and learn new ways of using the tool to connect with other scientists and science enthusiasts.

You can follow Mack at @astrokatie, Kruse at @markckruse and ScienceOnline at @ScienceOnline (or #scio13) if you’re already on Twitter.

And, if you’re a Duke researcher not yet on Twitter but want to be, check it out here, then contact the university’s news office if you’ve got questions.

Cooking up chemistry with candy

By Ashley Yeager

Note: This is the first in a four-part, monthly series that will give readers recipes that they can try in their kitchen and also learn a little chemistry and physics along the way.

Making sucre à la crème (left) and soft toffee (right) illustrates the fundamental principles of changing a liquid to a solid. Credit: Ashley Yeager, Duke.

A dozen freshmen pull on pieces of fresh, soft toffee, popping the candy into their mouths and licking it from their teeth as chef Justine de Valicourt talks about making the treats in a tiny kitchen on the second floor of Smith Warehouse.

Eating toffee and other sweets doesn’t usually spark a discussion about chemistry. But, as the students learn, the core of the eating experience is entirely about chemistry and some physics too, says professor Patrick Charbonneau.

He is leading a freshman seminar, called the Chemistry and Physics of Cooking, and in this particular class, he, de Valicourt and a team of teaching assistants work with the students to explore phase transitions – such as the change of liquid water to ice – by making two traditional Québécois desserts, sucre à la crème and soft toffee.

Both desserts have the same ingredients — maple syrup, butter and cooking cream. But, the experience of eating them is entirely different. One, the toffee, is stretchy, chewy and sticky, while the other, the sucre à la crème, is more crumbly and smooth.

The way the sugar molecules in solution cool down into a solid structure is what determines the final texture of a candy or chocolate, Charbonneau says.

During the lab, the students cool one mixture of syrup, butter and cream quickly and then whisk it. The stirring motion forces the sugar molecules to bump into each other, creating seeds of crystallization, which continue to grow and eventually clump together to give the sucre à la crème its solid, crumbly texture.

The students mix and heat the ingredients, then let them cool slowly, leaving the candy to set for at least three hours. Not whisked or stirred, it solidifies without forming too many large crystals, giving it a glassier appearance and a stickier, chewy texture, a signature feature of toffee.

Making these candies is pretty basic, easy enough that anyone could try it in a home kitchen, Charbonneau says, adding that he and de Valicourt have provided the recipes as a way to reach beyond the classroom and give more than just their students an introduction to cooking and, of course, the chemistry behind it too.

Sucre à la crème –

Ingredients:
1 can of maple syrup (540mL)
45 ml (3 tbsp.) of butter (plus some to grease the mold)
250 ml (1 cup) of cooking cream 35%

Materials:
1 medium saucepan
1 candy thermometer
1 wooden spoon
1 square mold
1 whisk
1 bucket of cold water

Instructions:

1. Put all ingredients in the saucepan. Stir.
2. Heat on the stove to 118°C (244°F) – 120°C (248°F). Be careful not to touch the bottom of the pan with the thermometer, which will give an incorrect reading.
3. Put the saucepan in the bucket of cold water and let the mixture cool down to 55°C (131°F) – 60°C (140°F) in the center. Do not stir the mixture.
4. Once cooled in the water, whisk the mixture to make a creamy pale paste. Pour in the mold and cut it before it gets too hard.
5. Let it rest 30 min in the fridge.

Soft toffee –

Ingredients:
1 can of maple syrup (540mL)
45 ml (3 tbsp.) of butter (plus some to grease the mold)
250 ml of cooking cream 35%

Materials:
1 medium saucepan
1 candy thermometer
1 wooden spoon
1 square mold

Instructions:
1. Put all ingredients in the saucepan. Stir.
2. Heat on the stove to 118°C (244°F) – 120°C (248°F). Be careful not to touch the bottom of the pan with the thermometer, which will give an incorrect reading.
3. Pour into the greased mold, let it cool down slowly, without disturbing it for 3-8 hours.

Not Swimming with Spinners

By Ashley Yeager

Spinner dolphins swimming just off the bow of a boat. Image courtesy of Dave Johnston, Duke.

Waianae, HI – Pet a dolphin for me, my sister texted as I stepped onto a catamaran in West Oahu. I didn’t have the heart to tell her that is exactly what I would NOT be doing, under any circumstances.

I have to admit that a little later, as a pod of wild spinner dolphins undulated just ahead of the bow of our boat, it was really hard not to reach out and try to touch one of them.

It was almost as if getting closer to the creatures as they slid through the water would free us, if only for a moment, from our artificial world of buildings, cars, computers and cell phones. But, in reality, interacting with spinners can’t take us away from our hyper-connected world, and chasing and touching the dolphins is not good for them either.

“If you try to play with spinners during the day, it’s like a stranger coming into your bedroom in the middle of the night and trying to wake you up,” says Nicholas School marine biologist Dave Johnston. He comes to Hawaii a few times each year to take photographs and other data on the islands’ spinner dolphins to learn more about their behaviors, population size and the bays they are swimming in during the day.

Spinner dolphins — Stenella longirostris – swim into shallow bays off Hawaii’s coast during the day to rest, turning off half of their brain at a time as they sleep. With one half on and one half off, they can still swim to the surface to breathe and ultimately recharge for the next night’s hunt.

But lots of vacationing people swimming and sailing in the bays aren’t thinking of the dolphins’ schedule and rest, they are only wanting to get closer to the wild animals. And the dolphins, much like humans, are curious. They’re going to check you out if you’re in their space, just like you would if you hear a strange noise in your room while your trying to sleep, our guides from Hawaii Nautical tell us as we cruise out of Waianae Harbor on West Oahu.

We sail for a bit and then come upon a pod of spinner dolphins resting off our port side. Everybody bunches to the front of the boat to get as close as they can to the animals. Our guides remind us of the dolphins’ sleep cycle and explain that the tour company follows the NOAA-sponsored Dolphin SMART program.

SMART stands for: Staying back from the dolphins; Moving away if they seem disturbed; Always keep a boat engine in neutral if you are near a pod; Refraining from feeding or touching them; and Teaching others to be dolphin SMART. Needless to say, we didn’t swim with or touch the dolphins. Sorry sis. Instead, we sailed a bit more, snorkeled with some sea turtles, not touching them of course, and then sailed back toward the harbor.

On the way back, we spotted another pod of spinners, and even more inspiring, we simply watched the animals. They were enjoying their rest, undisturbed in their home — something we all crave and appreciate when we can get it.

Deeper voice still wins, even in “feminine” leadership roles

By Ashley Yeager

Deeper voices get votes even in PTA and school board elections. Credit: Barton Stabler, gettyimages.com

A lower pitched voice gets more votes — even in elections for stereotypically feminine roles, such as for president of the Parent-Teacher Association or member of the School Board, a new Duke study shows.

“These findings are somewhat surprising,” said University of Miami political scientist Casey Klofstad, co-author on the study. He explained that since women typically hold these kinds of leadership positions, people might assume that voters would prefer leaders with more feminine voices.

“We found the opposite, that the preference for leaders with more masculine voices generally still holds,” he said. The results, which appear Dec. 12 in PLoS ONE, however, suggest that women may want men with more feminine qualities to take feminine leadership positions.

“The selection of leaders is arguably one of the most important decisions we make,” said Duke biologist Rindy Anderson, lead author on the study. “It is worth considering that voice pitch, a physically-determined trait that may or may not be related to leadership capacity, influences how we select our leaders,” she said.

In the experiment, she and Klofstad recorded people saying, “I urge you to vote for me this November,” and then altered the recordings to create high and low-pitched versions of each voice. The scientists then held hypothetical elections by asking people to choose, based solely on voice pitch, which candidate they would prefer when voting for president of the PTA or for a position on the School Board.

The results show that women did not distinguish between men with higher-or lower-pitched voices for the two feminine leadership roles. This finding contradicts the team’s previous study, which identified women’s strong preference for men with more masculine voices when voting for candidates who were “running against each other in an election,” rather than for a specific leadership position. The new finding suggests that the strong preference women had in the previous experiment is more relaxed within the more specific context of feminine leadership roles.

“Another possibility is that women are less sensitive to this vocal cue within the context of this specific domain of leadership. It is also possible that some women might actually prefer male leaders with more feminine voices for feminine leadership roles,” Klofstad said.

The scientists need to do more work to understand what is happening to women’s preferences in this situation, he said, adding that he and Anderson also want to know whether people with lower voices are truly more competent leaders.

“We need to test whether voice pitch actually signals anything about leadership capacity,” Klofstad said. He and Anderson are now designing those experiments.

Citation: “Preference for Leaders with Masculine Voices Holds in the Case of Feminine Leadership Roles.” Anderson, R. and Klofstad, C. 2012. PLOS ONE. 7(12): e51216. doi:10.1371/journal.pone.0051216.

Higgs Hunters Seeing Double

By Ashley Yeager

An stuffed animal artist’s conception of the Higgs boson. Credit: The Particle Zoo.

Scientists searching for the Higgs boson on the ATLAS experiment at the Large Hadron Collider near Geneva are reporting small discrepancies from the two main channels they use to look for the particle.

With these channels – the decay of a Higgs to two light particles (photons) or to two Z bosons – the scientists determined the mass of the Higgs-like particle to be roughly 125 GeV, about 125 times the mass of the proton.

They announced complimentary results from both channels in July 2012, and since then have been crunching more data to support the findings. The scientists gave updates on their work Dec. 13 at CERN.

“It’s turned out that for ATLAS the Zed-Zed channel and gamma-gamma channel differ quite a bit, by about 3 GeV, for the respective masses of the Higgs particle from which they decay,” says Duke physicist Mark Kruse, who is analyzing data from the ATLAS experiment. “It doesn’t sound like much, but the probability they could differ by this much or more is only about 0.5 percent.”

“This is probably not a big deal,” he says, noting that the new results explain why the ATLAS team was not ready to report the separate mass measurements at the November 2012 Hadron Collider Physics Symposium in Kyoto, Japan.

Kruse says there could be several reasons for the discrepancy. It could just be a statistical fluke. Or, there could be a subtle problem with one or both of the measurements. “There is a lot that goes into these analyses and it is not always possible at this stage to be absolutely certain every detail has been done perfectly,” Kruse says.

The more dramatic scenario is that these results could be due to two different Higgs-like particles.

Kruse, however, thinks the two Higgs-like particle answer is highly unlikely, especially if scientists using the CMS experiment at LHC do not report the same discrepancy. CMS scientists have not yet released their new “two photon” result.

The ATLAS result is most likely due to a statistical fluctuation. Right now, though, the team has only crunched about half the data from the collisions. Of course, scientists will only know more once they have analyzed the full ATLAS dataset a couple of months from now, Kruse adds, suggesting that there is still the possibly for more Higgs mania to come.

From the basement, female physicists shaped Duke and German science

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

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.