Harvesting Wind Energy for Signal Detection

Wind is free and ubiquitous and can be harnessed in multiple ways. We recently published an article in the Physical Review demonstrating mechanical stochastic resonance in a tabletop experiment that harvests wind energy to amplify weak periodic signals detected via the movement of an inverted pendulum. Unlike earlier mechanical stochastic resonance experiments, where noise was added via electrically driven vibrations, our broad-spectrum noise source is a single flapping flag.

This research results from a novel collaboration between The College of Wooster and Grinnell College over several years and includes six undergraduate coauthors. The first version of the apparatus was created in the Taylor Hall’s shop at Wooster and used wooden wheels and grocery-store syrup for damping! The design evolved over several years, with the final version at Grinnell sporting shiny aluminum U-channels and 3D-printed plastic wheels.

Mechanical Stochastic Resonance

Schematic of the mechanical stochastic resonance apparatus. At lower right, a wind-blown flapping flag delivers noise to the main axle via a slipless pulley. At lower left, a rotary motor delivers a subthreshold sinusoidal signal to the main axle indirectly via a tensioned slipping belt. At upper left, a bistable inverted pendulum rotates back and forth between two stops.

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Sunshine and Water

As promised, I have one more post from my recent research trip to Vienna, Austria.  First, a confession which will act as a bit of a spoiler, I had never heard of supernumerary rainbows until Dr. Leary joined the College and used a picture of one he had seen in Poland on his web page. Ever since then, I have been jealous and longing to see one myself.

One Sunday when I was in Austria, my host Dr. Smoliner and his wife and I went on an excursion east of Vienna to Schloss Hof, a palace built by Prince Eugene of Savoy in the 1720s and later renovated by Empress Maria Theresa.  I love visiting these types of palaces — not just for the buildings themselves but especially for the gardens.

Late fall flowers at Schloss Hof

Late fall flowers at Schloss Hof

It was raining on and off, so we went to see the gardens first, and got caught in the rain.  After drying off a bit, we went through the rooms, which mainly had their window shutters closed to protect the furniture and wall-coverings from sunlight.  As we reached the room in the front corner of the building, the shutters were open to allow views of the Baroque gardens.  I looked out the window to the side of the Schloss and gasped in surprise — out the window was a supernumerary rainbow!

Supernumerary rainbow over Schloss Hof, Austria, 9 October 2016

Supernumerary rainbow over Schloss Hof, Austria, 9 October 2016

The supernumerary part of a supernumerary rainbow is the extra fringes that you can see on the inside part of the bow.  Most of the colors are washed out in the fainter bow, but you can generally see the extra greenish/purple lines.  In my picture, you can mostly just see one extra light green line, especially toward the top of the bow.  You get supernumerary rainbows when the rain droplets are particularly uniform in size.

The sky cleared quickly while we were looking at the rainbow, so our timing was so very lucky!  Here’s the view directly to the front of the Schloss just a moment later.  By the way, the large hill you can see is actually in Slovakia!  The border is a river which you can kind of see in the picture as the line of trees that follow the river.

View toward Slovakia, from Schloss Hof

View toward Slovakia, from Schloss Hof

So, we left Schloss Hof and headed toward a national park on the Danube, because I wanted to see the wetlands (the Auen) around the river.  As we drove, another rainbow appeared and became so bright and vivid that we had to pull off the road to get a picture.

Supernumerary rainbow and double rainbow outside Engelhartstetten, Austria, 9 October 2016

Supernumerary rainbow and double rainbow outside Engelhartstetten, Austria, 9 October 2016

Everybody on the road was stopping, it was so amazing.  A nice Austrian man tried to tell me something that my German was not quite up to at first, but then I realized he was saying the rainbow was so close that you could see that it was in front of the trees at the back of the field.  That is, if you enlarge this picture (just click on it), and look at where the rainbow appears to meet the ground, you can see that the trees are behind the rainbow.  Totally awesome.  And, it’s another supernumerary!  Look towards the top of the bow to see the extra fringes.  Apparently, Thomas Young used the existence of supernumerary rainbows as part of his argument that light was a wave.  The extra fringes cannot be explained by ray optics — you need interference effects.

Finally, we wrapped up the sight-seeing at the Donau-auen park, and the light of the late evening sun was just beautiful.  Sunshine on the water looks so lovely….

Panorama of the Danube River between Vienna and Bratislava

Panorama of the Danube River between Vienna and Bratislava

That’s the beautiful blue Danube!  Again, you should click on this image to make it full size.  You should even be able to spot the moon, in the middle of that amazing sky.

Capturing the moment in the national park Donau-auen

Me, capturing the moment in the national park Donau-auen

We wrapped off the day with a good meal and conversation at a very traditional Wiener  heurige at the edge of the Wiener Wald.  It was definitely one of those tremendous days to keep in your memory to cheer you up when things are darker.  When I’m scraping the ice off my windshield this winter, I can just go back in my mind to Schloss Hof and my two supernumerary rainbows!



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A Physicist in Austria

As mentioned in my previous post, I’ve just recently returned from a research trip to Vienna, Austria.  I was there for two and a half weeks, and fortunately, I had plenty of time to see some sights!  I first visited Vienna when I was in college and on a whirlwind tour of Europe (Marburg, Berlin, Prague, Vienna, and Paris, all in two weeks!) with my aunt. It was my favorite city during that tour, and so I’ve created opportunities to return!

I remember visiting Schönbrunn Palace with tired feet on a hot August day back on that first time in Vienna.  Although we didn’t have the energy to explore the gardens that time, Schönbrunn did become one of my favorite places, and I have since explored those gardens thoroughly!  I’m not really a runner, but during my last visit to Vienna in 2013, I ran on the garden paths of Schönbrunn several times, and I finally feel that I’ve seen the full grounds. This visit was colder, but I did manage it one morning, and the view of the Schloss from the Gloriette in the (relatively) early morning was wonderful.  This is the view that Empress Maria Theresa had most mornings for breakfast.

Schloss Schönbrunn, from the Gloriette

Schloss Schönbrunn, from the Gloriette

I took a few excursions out of Vienna on the weekends, including a 2 hour river cruise on the Danube through the Wachau Valley from Melk to Krems (and connecting to Vienna by train).  The entire valley of the Wachau is a world heritage site and has been inhabited by humans for around 30,000 years, since the Paleolithic!  The village of Willendorf, where the famous female figure known as the Venus of Willendorf was found, is here in this valley.  One of my favorite sights on this trip is the ruins of the castle at Dürnstein.  This castle is where Richard the Lionheart was held captive on his way home to England from the Crusades.  That was in 1192!  Without this captivity, we wouldn’t have the stories of Robin Hood or Ivanhoe. Frankly, I’m not sure King Richard was as great as he was made out to be in either of those stories, though.

The ruins at Dürnstein, on the Danube River

The ruins at Dürnstein, on the Danube River

Another excursion took me east of Vienna, to Carnuntum, an excavation and reconstruction of a Roman military installation and city.

Heidentor (Heathen's Gate) outside Carnuntum

Heidentor (Heathen’s Gate) outside Carnuntum

Coliseum at Carnuntum

Coliseum ruins at Carnuntum

A Roman mosaic floor, at Carnuntum

A well-preserved Roman mosaic floor at Carnuntum, with a reconstructed typical Roman room around it

So you can see my little mascot Leo in some of these pictures.  I keep him in my bag and put him in a lot of my pictures — I like the personal character he brings to my otherwise standard tourist shots!

On the Graben

On the Graben


Leo also enjoyed visiting with another lion at a fountain on the Graben, right in the heart of Vienna.

At the opera

At the opera


And he made a visit to the Vienna State Opera to see Puccini’s Tosca.

The last weekend that I was in Austria, we made an excursion to Styria, in southern Austria, and saw some amazing things. It is so different to be shown around a country by a native, rather than just being a tourist.  We were able to see things I would have never found on my own.  Namely, we stayed at a hotel in this amazing castle, south of Graz.

Burg Deutschlandberg

Burg Deutschlandberg

And we went to see the Weltmaschine (World Machine) of Franz Gsellmann.  The Weltmaschine really defies easy characterization, but I would describe it as a type of outsider art.  Gsellmann wanted to be an electrical engineer but was unable to afford school. At his family farm, he gradually built this electrical machine with bells, lights, and many moving parts out of bits and pieces that he collected from flea markets.  There are some videos online, but it is amazing in person.  Imagine all these bits whirring around, quite loudly, with ringing bells and flashing lights.



Detail of some of the construction of the Weltmaschine

Detail of some of the construction of the Weltmaschine

Detail of the Weltmaschine

Another Detail of the Weltmaschine

It was an amazing trip, and I haven’t even told you about the cheese cave, the pumpkin seed oil, the Lainzer Tiergarten, or the art at the Albertina!  I do have one more awesome thing to share, but it deserves its own post, so you’ll have to wait and see!  I promise, I’ll get back into physics for that one!

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Wooster Physics in Vienna, Austria!

After several years of being department chair, I am very much enjoying being on research leave this year.  A research leave is an opportunity for Wooster faculty to take a semester or a year just to focus on our research, without any teaching, committee work, or other kinds of administrative work.  It’s a time to meet new people, get new ideas, and learn new things.  I have two major research trips planned this year to expand my perspectives,  and to develop some collaborations.

I recently returned from the first trip — which was to visit my colleague Dr. Jürgen Smoliner at the Institut für Festkörperelektronik of the Technische Universität Wien, or in other words, the Institute for Solid State Electronics at the Vienna University of Technology.  I first visited Dr. Smoliner on my last leave in 2012, when I wanted to get better at the technique of ballistic electron emission microscopy, and it has become a great collaboration for both of us.

Entrance to the main building of TU-Wien, on Karlsplatz in Vienna.

Entrance to the main building of TU-Wien, on Karlsplatz in Vienna.

As an American, one of the things that I most love about visiting Vienna is the history.  (I’ll get more into this in a later post, about not doing physics in Vienna!)  For example, Christian Doppler of the famous Doppler effect was a graduate of TU-Wien!

On this visit, though, there was no Doppler effect involved.  We were doing ballistic electron emission microscopy (BEEM), which is a variation of scanning tunneling microscopy (STM) where there is a very thin additional contact on top of the sample of interest.  Ultimately, the plan was to investigate nickel on gallium arsenide, but there were some technical challenges, so we spent most of the time with the standard test sample of gold on gallium arsenide.

To make the samples, we need to create a layer of gold that is around 8 nm thick — that is, extremely thin!  The gallium arsenide must be absolutely clean first, so it is dipped in hydrochloric acid, and then placed into the vacuum chamber where the gold will be deposited.  We used a thermal evaporation system for the gold, which (funnily enough) is the very first thing I ever learned to do in graduate school!  (Thank you, Dr. Briscoe!)  Unlike my work in grad school, though, we did all of this sample processing in a clean room.

Clean room selfie

Clean room selfie!  That’s Dr. Smoliner with the beard, and also Fabian and Gernot, students who were learning about sample prep and BEEM.

Once the gold layer has been evaporated onto the gallium arsenide, we could make the electrical connections and actually begin making measurements.  In BEEM, we need two electrical connections to the sample — one connection to that thin gold layer, and one connection to the gallium arsenide itself.  In the top view image, you can see the thicker wire (with a little indium gooped on the end to make it sticky) connecting to the top of the sample.  It’s actually touching one of the gold lines on the sample, but that wasn’t visible in the picture.  The thinner gold wire was tucked underneath the round mounting disk in this picture, but for our actual measurements it was moved to the top of the sample.  I took this picture through the eyepiece of an ordinary optical microscope — the coppery-colored disk that the sample is sitting on is actually about 1 cm in diameter.

Top view of the sample and electrical connections

Top view of the sample and electrical connections through an optical microscope.

In the side view picture below, you can see the sample once it was mounted in the STM.  If you look closely, you can see that same thick gold wire, the thin gold wire, and also the STM tip coming down to image the sample.  I was surprised to get this good a picture from an iPhone!  (Thank you, optical physicists who work for Apple!)

Side view of the sample

Side view of the sample and connections, mounted in the STM.

So, like all experimental physics, it takes a good bit of time to get to this point — sample prepared, system working– and then you can actually hope that it will all keep working long enough to get some good data!  We were able to get good data for the gold on gallium arsenide sample, so that was a success!  Also, I needed to test whether my home-built BEEM amplifier was still working, and fortunately, found out that it was.  (There’s a long back story there — short version is that the BEEM current we measure is only on the order of picoamps, so we need a very sensitive, low noise amplifier in order to make this signal measurable.  This exact configuration is not something that is available commercially, so we built it ourselves a few years ago, but had been having trouble and were not sure whether something had happened to the amplifier.  So, I took it along to check out.)

While at TU-Wien, I also taught a brief graduate seminar on BEEM of nanostructures (aka, Ballistische Elektronenmikroskopie auf Nanostrukturen). It was fun teaching at a very different level than I am used to.  And, one of the students taking the course suggested that BEEM might be a good tool to look at some of the samples that his group studies, so it could very well end up in a new collaboration!

Billboard showing the new ZMNS building

Billboard showing the new ZMNS building

The people that I was working with are all in the ZMNS at TU-Wien, which is the Center for Micro and Nano Structures.  The university is currently building a new building (actually, starting with the base of an extremely *old* building) for ZMNS which will have a new and larger clean room.  So, I am looking forward to checking that out on my next visit to Vienna!

Stay tuned for posts on what else there is to do in Vienna besides physics!


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Raptor Interplanetary Transport Engine

Why has SpaceX chosen methane to fuel its Raptor rocket engine? Robert Goddard’s first rockets used liquid oxygen Oor LOX and gasoline. The Saturn V moon rocket first stage used LOX and refined kerosene. The Saturn V second stage used LOX and hydrogen that burn to water in my favorite chemical reaction, 2H2 + O2 → 2H2O. Methane CH4, gasoline (a C7H16 to C11H24 blend), and kerosene (a C12H26 to C15H32 blend) are all linear hydrocarbons CnH2n+2 that burn to carbon dioxide and water (and residual carbon if the burning is incomplete).

Hydrolox is most efficient but requires huge tanks (due to hydrogen’s low density), which must be cooled to just a few degrees above absolute zero. Kerolox is less efficient but needs smaller tanks (due to kerosene’s high density), which can be at normal temperature and pressure. Methalox is a compromise. But unlike kerolox, methalox does not coke the engines with residual carbon that makes reuse more difficult. Also, to improve efficiency, SpaceX will densify the oxygen and methane by cooling them to just above their freezing points (rather than just below their boiling points).

However, the real advantage of methalox is that it can be manufactured from carbon dioxide and water by CO2 + 2H2O → CH4 + 2O2 on Mars.

Raptor rocket engine powered by supercooled liquid methane and oxygen or methalox

Raptor rocket engine powered by supercooled liquid methane and oxygen or methalox

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Maggie Lankford `16: National Finalist for Top Award in Undergraduate Physics Research!

I’m excited to report that Maggie Lankford, who graduated summa cum laude this year as a Wooster physics major, has been selected as a finalist for the American Physical Society’s LeRoy Apker Award– known as the preeminent honor for undergraduate physics research in the United States!  Maggie received this recognition for work reported in her Senior Independent Study thesis, entitled “The Production and Manipulation of Nonseparable Spin-Orbit Modes of Light Under Hong-Ou-Mandel Interference Conditions.”


Maggie with the apparatus she helped to design and build.

In short, Maggie built a device which produced novel structures of light (photons), in which two of the light’s degrees of freedom–polarization and spatial intensity distribution–could not be characterized or described without direct reference to one another.  Her thesis also demonstrated that this setup is capable of imparting such structures onto pairs of photons that are simultaneously exhibiting quantum interference, which is a key component in a number of quantum computing protocols.  If you’d like to know more, just click this link to our open-access publication, which recently appeared in the research journal Optics Express. 


Maggie presented her work last June at a poster session at the Quantum Electronics and Laser Science conference in San Jose, CA (see photo above).  Then in August, she gave an oral presentation on her research before the Apker Award selection committee in Washington, D.C., along with the six other finalists from other institutions including MIT, Kenyon and Dartmouth.  Two winners – one from a Ph.D. granting institution and one from a non-Ph.D. granting institution – will be announced in October.  She is the third Wooster physics graduate to be named as an Apker finalist.

Maggie’s Apker recognition has been reported by the American Physical Society Newsletter and Wooster News.  A quote from Maggie from one of these articles sums up her research nicely: “We developed this new apparatus … made a mathematical model of it, then built it, then used it to generate this new type of pattern of light that can be used for information processing or for communicating between two parties.”

This is what I love about being a tabletop experimental physicist– a field in which it is still possible for a small group of scientists to hatch an original idea, work out the relevant predictions from first principles, design and build the associated experiment, and carry it on to completion!


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Summer Research Program 2016

We had a fun and productive summer research program again this summer!  We were fortunate last fall to be awarded an REU site grant from the National Science Foundation, so that enabled us to enlarge the program from the size that it has been for the last few years.  We have a very long history of summer research, but this was one of our biggest programs ever, with five faculty and 14 students!


Figuring out the size of the solar system at BWISER

Figuring out the size of the solar system at BWISER

The outreach program for BWISER is always a hit with both the BWISER campers and the summer research students.  The group doing the “Lightyears in the Movies” demo had the students put on caps with various solar system objects (the sun, the moon, Pluto, etc) and try to stand at scale distances apart.  We have a complicated program where the BWISER campers rotate through seven different demonstrations, learning about light and sound waves, and are completely wowed by the end of two hours.


Ice cream social for all summer research students

Ice cream social for all summer research students


In addition to our weekly picnics, and infamous pie festival, we also had a delicious ice cream social for not just the REU students but all the summer research students on campus.  I’m pretty sure the professors had as much fun dishing up the ice cream as possible.



The finale for the program was the poster session where all the REU students presented their work to family, friends, and colleagues.  Due to the size of the program, we held the poster session upstairs in the Taylor atrium for the first time, and it was a lovely sunlit space for the event.


We had a great turn-out with lots of interested people asking questions about the research each of the students did.  It never fails to amaze me how much the students learn and accomplish during the 10 week program!

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First Deep Space Walk

In 1971 during Apollo 15’s return from Earth’s moon, astronaut Al Worden performed the first deep space walk nearly 200 000 miles from Earth to recover external service module film canisters that had mapped the lunar surface. Worden was able to pause and orient himself to simultaneously see both Earth and moon as disks against the blackness of space, the first human to do so. Looking back toward the command module, he saw astronaut Jim Irwin waiting in the open hatch against the colossal moon — but did not have a camera to record the breathtaking view, the iconic photograph that never was. Fortunately, back on Earth Worden was able to collaborate with artist Pierre Mion for National Geographic magazine to reconstruct the vista. Deep space walks may occur again next decade from NASA’s Orion spacecraft.

The first deep space walk, by Al Worden reflected in Jim Irwin's visor, during Apollo 15 in 1971, as painted by Pierre Mion

The first deep space walk, by Al Worden reflected in Jim Irwin’s visor, during 1971’s Apollo 15 mission to the moon, as painted by Pierre Mion for National Geographic magazine

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Found in a Box

I recently ascended to Czar of Physics. (Oops — I mistyped Chair and it autocompleted to Czar!) It’s not my first year as Czar, but this time, during the handover from the previous Czar, I inherited a small cardboard box. Inside I found a stack of old Wooster ΣΠΣ membership cards. (ΣΠΣ is Greek for SPS and signifies the SPS honor society; SPS is an initialism for the Society of Physics Students.) The two cards in the accompanying photograph are especially interesting. Karl modestly lists his position as president of the Massachusetts Institute of Technology. His brother Arthur reports being a professor at the University of Chicago but doesn’t mention the Nobel Prize he won four years earlier for scattering light from electrons. The Compton effect helped convince physicists of the wave-particle duality of matter and subsume classical mechanics in quantum mechanics.

Wooster Compton brothers sigma pi sigma membership cards

Some Wooster Sigma Pi Sigma membership cards; click for a larger view

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If Apple Designed Buildings…

When Steve Jobs phoned Pritzker Prize architect Norman Foster in 2009 for help designing Apple’s new Cupertino California campus, he said “Don’t think of me as your client; think of me as one of your team”. The design that evolved from that collaboration features an unprecedented annular building over a mile in circumference enclosing an orchard and park. The roof is covered with solar panels and the basement is underground parking for thousands of cars. The inner and outer walls are giant uninterrupted curved panes of glass. From inside, one can always see outside to the park-like surroundings.  A thousand bikes help people get around the campus.

The combined ceiling-and-floor “void slabs” are factory-made hollow polished concrete forms. The awnings block the direct rays of the high summer sun for cooling but transmit the direct rays of the low winter sun for heating. Mirrored undersides (added after the cross sectional illustration below was created) provide indirect illumination. The new campus is powered by 100% renewable energy, and the HVAC system is only for backup. Apple Campus 2 opens in early 2017.

Apple Campus 2 partial cross section

Apple Campus 2 main building partial cross section illustrates over a mile of uninterrupted curved glass with awnings and empty spaces to passively control natural light and temperature.

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