A new project on smart materials

I am the principle investigator on a new project that is being funded by the National Science Foundation to investigate the physics underlying morphing materials. The project brings together a large team of scientists, engineers, surgeons, educators and even artists to study various aspects of photo-mechanical materials, their applications, and how they can be used as an educational tool.

The grant is expected to be awarded in July; and, I look forward to moving into this new research direction -- through I am sure there will be many administrative headaches associated with this project.  So while I am excited by the research, part of me regrets the extra non-science-related burden that this project will bring.  Note that this project was recommended for funding on my birthday!

The work itself is best summarized by the abstract that we submitted to NSF:
 

The three goals of this project are to demonstrate what we call a “photomorphon,” the basic building block of a smart material that changes shape in response to light, to interconnect photomorphons with light in optical fibers, and to use interconnected photomorphons to create novel devices.  Like the transistor, which endows integrated circuits with complex functionality, photomorphons interconnected with light will make photonic circuits with exceptional capabilities.  Each element within such a photomorphon network will be both a sensor and an actuator, making a morphing material that intelligently changes shape in response to external stimuli.  Our approach is to work from the ground up in developing new materials with enhanced photomechanical response, creating photomorphons from the new materials, and integrating these to explore applications enabled by morphing materials. Applications will include tactile haptics and sensors, ultra-smart active textiles, and adaptive stretchable electronics, antennas and mirrors.

The fruits of our work will be the scientific and engineering foundations that enable technologies that are unimaginable today. We are developing a tool-set to build photomorphon networks and to understand how to program them.  As proof-of-principle of a photomorphon device, we are collaborating with physicians to make a light-actuated electrode positioner to be used for deep brain stimulation, which is currently in clinical trials and hold great promise for treatment of neural diseases such as Parkinson’s and Alzheimer’s.   Our focus on using light to bend fibers into arbitrary space curves is an excellent paradigm for exploring the connections with art, and connecting art with soft-matter science in a way that will attract curious and creative young students to explore exciting new research embodying the union of art and science.

The best trip ever

Since this blog is supposed to be a diary, I should occasionally make a real diary entry, so here goes.

The fact that I flew to Finland for a one-day meeting and was away from home a total of 80 hours brings sighs of horror to my friends and colleagues.  For me, it was the perfect trip.

My plane was scheduled to depart from Pullman airport at 11:20am, so as is custom for those of us who live in a small town and a five to ten minute drive from the airport, I planned on leaving home an hour before my flight -- plenty of time.  I always seem to get to the airport too early and end up sitting around, so this time, I decided to watch a 20 minute show on TV with my wife, which would get me to the airport about 45 minutes before my flight.  Having underestimated the length of the show and the time, I ended up getting to the airport about 30 minutes before my flight.

As I entered the terminal, I heard the PA announcement, "the ticket counter is now closed."  Since I was traveling overseas, I needed to check in, so I hectically waved at the guy at the counter to get his attention as he was about to leave the gate area through a secure door.  Luckily, he saw me and checked me in, sternly warning me that I should have been there an hour earlier.

By the time I got through security, the plane was fully boarded, so I was the last one to get on the plane.As an added perk, I got to choose a seat in in a fully open row with, giving me lots of leg space and room for my carry-on in the seat next to mine.  This was very fortunate given that the guy next to my assigned seat was overweight and spilled over into my space.

During the short flight to Seattle, I worked through a section of a book on the mathematical foundations of statistical mechanics.  Being seated at the back of the, I was able to get off the plane first (on these turboprops, they use both the front and back doors to expedite the process).

I got to the underground rail just as a train was arriving, and was at my overseas gate in record time.  Since my layover was less than two hours, I had just enough time to get a burger at a fast food near the gate.  The boarding process started shortly after I was watered and fed.

As usual, I used my optimization strategy to get on the plane quickly to get a spot in the overhead bin for my luggage.  Even so, only one spot remained free above my seat.  I read a bit more until the plane took off.  The guy in the seat next to mine was a pleasant version of me, having planned out his medication protocol to optimize his sleep cycle on the 10-hour flight to Amsterdam.

"Dinner" is typically served early in the trip, so I strategically timed my Ambien dose just at the start of the meal service.  Since much of what is served is carbohydrates, I dug into my private stash of Atkins bars and nuts to supplement the sparse airline offerings.  Next thing I remembered was awakening to a cabin that was coming to life as the flight attendants were bringing out breakfast.

We landed about 90 minutes later, during which snacked and chatted idly with my row-mate.

Next was the mad dash to my Helsinki flight.  In Amsterdam, one needs to clear immigrations then go through security.  Long lines and missed connections are the norm.  Since I had a one-hour layover, I again applied optimization strategies to minimize the time waiting in lines.  This time it worked out.  As I made it to the secure side, the monitors were flashing "flight closing" and informed us of the estimated walk time to the gate, 17 minutes.  I ran the whole way and got on the plane within 10 minutes of the doors closing.  Again, I had the luxury of choosing an empty row.

I read a bit and dozed off a bit.  In a couple of hours, we were in Helsinki.  It was 1:00pm and sunny with blue skies.  I was able to get from the plane to the curb in 5 minutes, and caught a cab with a pleasant driver with whom I chatted about Finland and the effects of the financial crises on his life.  He seemed pretty infatuated with the US because he felt he had few options for fun in his life, like doing Motocross, a passion that he could not pursue in Finland.

Mounds of snow were to be found near every plowed street and all the rivers that crisis-cross the city were still frozen.  Though there were bike paths and trails all over the place, many people chose to walk on the river, a weird sight for us Americans whose country does not allow its citizens to take such risks.

A view of the frozen river from my room.  Notice the pedestrian near the boat and others further downriver?

I checked in to my hotel and asked for directions to the nearest restaurant, and was routed around the corner to a place two blocks away.  It was 2:00pm, and I was starving.  As is usual for trips to Europe, this is when jet lag starts to take over, peaking at about 5:00pm with an urge to sleep so intense that I have almost fallen asleep while standing, a real trick for an insomniac such as me.  After a delightful steak lunch, I returned to the hotel.

Given that it was a sunny and crisp afternoon, I decided to fight the jet lag by ice skating at a park - a place that I had researched before my trip.  It was about a 10 block walk.  The ice rink was in a very picturesque part of the city, and the whole atmosphere quite happy, filled with tourists and their families.  I believe that one family, with a little girl who was learning to skate, was speaking Italian.  Given my attempts to learn Italian, I tried to eavesdrop, but with no success.  Their extended family included parents, at least one grandparent, aunts and uncles -- all of them excitedly taking photos of their wunderkid who to them was a remarkable skater.  Judging from her skill level, it was probably her first time.  I shouldn't talk because I myself looked like a beginner on the incredibly dull rental skates.  I almost wiped our several times.

The ice skating park in Helsinki.

After an hour of skating, I walked back to the hotel and did some more reading.  Concerned that I would miss my 7:00pm dinner, I set my iPhone alarm for 6:30pm.  It woke me up just in time to change and meet my host in the lobby at 6:45pm.  I was a bit tired, but without the typically intense jet lag.

We walked to a trolly and took it to a wonderful restaurant with lots of huge windows opening up to a square decorated with lots of white lights.

We had a great meal, and quite accidentally left at just the right time to catch the next trolly back to the hotel.  If we had missed this one, we would have had to have waited for an hour for the next one - an unpleasant thought given that it was getting pretty cold.

We were scheduled to start the meeting early.  Luckily, I fell asleep almost as soon as I got into bed and woke up perhaps at 5:00am.  I showered, packed my bags, did some work, ate breakfast, and checked out by 7:30 am.

The panel was comprised of 5 scientists who were evaluating big proposals for centers of excellence.  Our task was to rate four of the proposals in our areas of expertise.  We had each read and pre-ranked the proposals prior to the meeting.  For each proposal, we spent about 45 minutes comparing notes, then hearing a presentation from the principle investigator and his team (about 10 people from each team showed up), followed by questions/answers and then a post discussion to evaluate the interviews.

At the end of the day, we wrote up our final evaluations.  We had worked almost 12 hours straight with only a 45 minute break for lunch.  At 6:00pm, the building's air handler system automatically turned off to save energy, but we were not yet done.  One of the Academy reps opened all the doors to the room to make sure we had enough oxygen.  I thought she was joking, but she was truly concerned.

The meeting room at the Academy of Finland.

We were done by 7:30pm.  I asked for my host to call a cab to the airport, which was waiting for me right outside the building as we exited.  I bid my farewell to my colleges, and got in the cab.  Thirty minutes later, I was at the airport hotel.  I had dinner after checking in.  The service was rather slow, so I got back to my room at 9:30pm and requested a 4:00am wake-up call.  By the time I got to bed it was after 10:00pm, but I fell asleep immediately and was wide awake by 3:00am, so I got up, showered and packed.  On my way to the breakfast, I stopped at the front desk to cancel my wake-up call.  (several years ago, I did not cancel a wake-up call and found security banging on our door as we were coming back from breakfast).

I checked out and walked to the airport under covered pathways surrounded by the dark early morning and producing vapor in the crisp early-morning air with every breath, the silence broken by my roller wells and those of other passengers in the distance.  I checked in and started my long voyage home.  Being exhausted, I dozed off here and there, but took no sleeping aids.  All the connections went smoothly, and I was home in time for dinner on Tuesday evening.

I went to bed and got up at the next morning at the normal time (about 6:30am), and eventually made my way to work and taught my morning class.  It was the perfect trip! I had no down time to contemplate the miseries of travel, and was back without missing a beat.

A refreshing review of our new paper on a model of self healing

There are times when one of my less stellar papers, in my opinion, gets accepted for publication without trouble; and, at other times, what I think are very significant papers have lots of trouble.  Perhaps this is a matter of taste, or perhaps papers that are outside the norm are misunderstood and therefore rejected.

As a case in point, I was invited to submit a paper to a special issue of a journal dedicated to self-healing polymers.  The focus of this special issue is on polymers that are made to self heal after mechanical cracking by incorporating tiny reserves of monomer that runs into cracks as they form, thus filling them and repairing the material.

Our work is very different, so I thought that our invitation was an effort by the editors to broaden the scope of the journal.  However, we were shocked to find that our paper was rejected without review based on the assessment that the work was "incremental."  We responded to the editors, reminding them that we were invited to write the paper.  The next email informed us that the editors had made an error,and that the paper would go out for review.

Two reviewers responded and one of them recommended that our paper be rejected on the grounds that the work was incremental.  However, the editor gave us the opportunity to respond.

In the meantime, we had found data at the extremes that were inconsistent with our model.  We fixed the model with one simple change in the underlying assumptions, and the new model fit all of our data. (This in itself is a very interesting story which I will report on later.) We revised the manuscript to include the new data and resubmitted it.

The editors sought an opinion from a forth reviewer.  An excerpt from his/her comments, follow,"One of the reviewers evidently commented that this work is incremental. However, I don’t agree. The authors are clearly refining their model, and this is an entirely new set of data and observations. The authors search for a better physical understanding will naturally require a significant amount of investigation, and it is helpful to the community to see the work as it unfolds, not wait 25 years for a definitive explain‐all paper that may never appear."

We, of course, agree with this reviewer, and are glad that this paper came to a happy ending, especially in light of the fact that I believe that our new results provide important insights that are taking us a step closer to understanding a new phenomena. 

The new version was accepted with minor revisions suggested, which we made.  The paper was then accepted and the page proofs arrived a couple weeks ago.  We fixed minor typos and now the paper is in the queue for publication in the early summer.  I ust learned today that the electronic version is already available online.  It's ironic that we were even invited to provide an artistic rendition of a figure that might be used as a cover photo.  What a difference a revision makes!  From incremental to cover story material with the change of one variable!

For the interested reader, below is the introductory paragraph, which describes our work and how it differs from the norm, "Structural damage and degradation of a polymer is usually associated with cracking. Mitigating damage or developing methods to promote healing in polymeric materials after cracking is an active area of research motivated by its practical utility. White and coworkers reported on a structural polymeric material with the ability to autonomically self-repair cracks. Such polymers incorporate a microencapsulated healing agent that is released in the cracking process with polymerization being triggered by contact of a catalyst with the healing agent, thus bonding the crack faces. White observed as much as 75% recovery in toughness. 

"Our work presented here is different in two regards. First, the sample is a dye-doped polymer rather than a neat polymer and the degradation process is through optically induced burning, so chemical changes are induced rather than solely mechanical/structural damage – though cracking can accompany burning. The dopant molecules thus mediate the phenomena. The degree of damage is observed using optical techniques, the simplest of which is the detection of a color change. Secondly, the healing process is a microscopic one, originating at a molecular level that we believe involves a cooperative process of aggregates of molecules. The polymers of interest to our work have applications as optical materials where photodegradation is a common cause of optical and optoelectronic device failures, either as catastrophic failure or a slow deterioration of performance."

The final paragraph in the conclusion succinctly states what we believe is cool about our work, as follows, "The concept that a material would exhibit such complex behavior without intentional design by the experimenter is an interesting one. Though self-healing is a process with great practical utility, it is intriguing that nature has been kind enough to provide an inherently smart material system that appears to behave in a way contrary to most others; it mediates recovery in a world in which irreversible damage is the norm. Further advances in understanding the physics underlying this phenomena will surely enable new applications that require materials to withstand high light intensities; and, may lead to new physics.

Now the next battle...

Monopoles, electric dipoles, and the inverse square potential

Research is a fulfilling enterprise, especially when it takes us on an unexpected path that leads to new insights even when others may have crossed the same path.

A couple years ago on Christmas eve, I was toying with a calculation based on my realization that a potential of the form V(x) = x^q captures all of the interesting toy models of quantum mechanics such as the harmonic oscillator (q=2), the particle in a box (q = ∞), and the hydrogen atom (q= -1). I wanted to derive a general analytical expression for the energy spectrum as a function of q so that I could analyze the nonlinear-optical properties of all such systems. To my delight, I was able to get such an expression using a mathematical trick. I was am certain that I was not the first to do so, but I nevertheless felt satisfied.

A plot of my results showed a removable singularity at q=0, which corresponds to a free particle that has no bound states (bound states are needed for my calculation of the nonlinear-optical properties), and a divergence at q = -2. I dutifully wrote up the results and left them sitting on my computer for a couple years. The work was given new life when I handed it over to new graduate student.

After working on the problem for a summer and part of a semester, he found a huge literature on the x^-2 potential, the location of the divergence in my plot. It turns out that this potential has all sorts of interesting mathematical problems. It has a continuum of bound states -- very unusual and in fact an impossibility; and, the wave functions and their duals do not span the same space -- a peculiar state of affairs. The known fix, as the student found in the literature, is to exclude a small region near x = 0 and then solve the problem in the limit as this small region tends to zero. Doing so fixes the problems by essentially removing the point-like properties of the dipole. 

The x^-2 potential describes the influence of an electric dipole moment on a point charge. Certainly nature must reconcile these funny mathematical difficulties given that dipoles and point charges exist. But how?

Nature is very clever by not allowing true point electric dipoles to exist.  Instead, all dipoles are extended dipoles where the potential deviates from x^-2 at close range, thus removing the pathological behavior. In fact, this may be the reason why an ideal point dipole is not observed in any particle. If it existed, serious paradoxes would ensue.

The electron has a very tiny electric dipole moment beyond the limits of measurability with today's technology, and arises from the CP-violating part of the CKM matrix in the standard model. The moment is tiny because CP violation involves quarks that are created as virtual particles, interact with the electron, and then are annihilated. As a result, the dipole moment is not a point dipole but is due to a sea of virtual quarks. All elementary particles have only small electric dipole moments with an extended charged cloud, so nature avoids potential pathologies by forbidding point dipoles.

Magnetic dipoles, which are a consequence of moving charges through spin and orbital angular momentum, are a different story. Spin angular momentum does not originate from spread out charge that spins in physical space.The spin anguar momentum lives in its own space so the associated magnetic dipole moment is pointlike, and will lead to pathologies when interacting with a magnetic monopole. Nature has apparently avoided such problems by forbidding the existence of magnetic monopoles. While there are theories that allow for magnetic monopoles, searches for them have come up short and I don't think they will be found.

In summary, the interaction of a point dipole that interacts with a point charge leads to all kinds of pathologies that can only be resolved by demanding that the dipole be an extended object that avoids being a true x^-2 potential. Nature seems to have solved the problem by allowing point electric charges but no point electric dipoles. Magnetic point dipoles, on the other hand exist; but, there are no magnetic monopoles with which they can interact.  The symmetry between the electric and magnetic parts of Maxwell's equations is broken to avoid unphysical behavior.

I cannot claim to be the first person to have this idea and wouldn't be surprised if this argument is common knowledge. Or, my argument may be faulty.  This does not make my musings any less exciting to me. I continue to be in awe of the power of physics, which allows us to ponder domains that are far removed from our daily experiences. My job not only allows me to think of such things, but encourages it; it is indeed a wonderful life

In studying the complex ramifications of the simple x^-2 potential when applied to nonlinear optics leads to insights into why point electric dipoles and magnetic monopoles can't exist.  How can I sleep tonight!

Ambien Rambling II - Your face contains an impressive geography of regions.

I previously posted one of my Ambien-induced ramblings as recorded by my wife.  A much more interesting and complex example of an Ambien rambling took place a few years ago while I was reading in bed.  My wife was apparently falling asleep after taking an Ambien when quite unexpectedly, she sat up and stretched her neck in my direction, placing her head between me and my book.  Her head swaying like a newborn's, she playfully inspected my face, tracing out its contours with her index finger.  "Your face contains an impressive geography of regions," she  informed me.  As if overcome by a stroke of genius, she rolled over and comandeered a notebook and a red pen that she often used for grading.

She proceeded with her narrative, carefully recording each word as she spoke.  When done, she rolled over and fell asleep.  As time passed, my wife used the notebook to jot down ideas, ripping out pages for shopping lists, etc.  While the notebook remained in the bedroom, over time, it thinned out and got used up.  Sadly, the Ambien rambling eventually got separated from the notebook and was lost.

For years, I searched for it.

This past week, we visited out family in Philadelphia, and once again we used Ambien to fight the jet lag.  Our last night in Philadelphia, we took an Ambien at 9:15 pm so that we could get some sleep before getting up at 4:00 am for the early flight.  When we woke up to our phone alarm, Pat was horrified to find that she had sent a text message to our friend,

"Change dinner time on Monday to 7 pm please."

She had no memory of sending the text, but was understandably embarrassed.  She quickly sent an apologetic text message explaining the circumstances.

This incident once again reminded me of the poetic rambling from years past.  Just this morning, my wife was reorganizing a dresser.  As she removed a drawer stuffed with clothing, a piece of paper floated to the floor.  It was the infamous Ambien rambling.  It is reproduced verbatim below. Even under the influence of Ambien, my wife's penmanship is perfect.

"Your face contains an impressive geography of regions. The central nasal range dominates the visual landscape.

"As you speak, the little creatures in your eyes listen and they respond by speaking back. It’s surprising, but they’ve been exposed to the whole vocabulary, just as you. 

"She’s a tender little creature like a small colorful caterpillar – fluffy, but strong enough to stand up with ease. When you would talk she would stand in your eye socket (careful not to get her feet wet in tearducts) and talk back to you. She was your very own, mythical whispering eye."

Ambien Ramblings

Me: "I'm happy I'm not in the state one-one-prime."

Pat: "What's that?"

Me: "That's where I don't know what I'm doing and the next adjacent state is an oscillation parameter of the first."

 --  A conversation I had with Pat after taking an Ambien.

Pat just found a notebook where she recorded our conversation.  Too busy these days to write, through I have lots of material to report.  Next time...

Errors and Creativity

In any deep and complex endeavor, it is easy to make mistakes.  Even after intense scrutiny, errors in logic and reasoning can be difficult to catch.  However, when properly harnessed, errors can lead to new and interesting ideas.

Recently, a bright junior colleague made a mistake in a calculation, and I am sure that he was down on himself over the whole thing;  so, I wrote him the following email (which I have modified slightly for you).  After rereading it, I thought it would be good general advice to all students who are struggling with work at the boundaries of the unknown where mistakes are common.

Dear Student,

Do not be hard on yourself about such errors.  We all make them.  When you have been around long enough to have made all the simple errors, you move on to the more complex ones.  As you mature, you will make these transitions over and over again.  The two of us are similar in the sense that we perhaps make more errors than the average physicist.  This can become a strength if you use it to your advantage.
 
I believe that the tendency to make mistakes is associated with creativity. Mistakes take us into new territories that others may never imagine.  Often, it's a mistake that leads me in new directions that brings me into uncharted domains.  When my colleagues question me about how I ever even thought of doing X, I can't explain it.  Now that I think about it, I should answer that it was a string of errors that led me to X.  These random meanderings avoid the huge walls that block the straighter paths.

The key is to work hard and tirelessly in the pursuit of entertaining lots of new ideas, be slow to publish so that you can catch your mistakes before they become public, and allow yourself times of unrestrained creativity but temper those times with disciplined thought.  And most importantly, do not get caught up in mathematics without thinking about the physical consequences.  It is the physics that is the most fulfilling and the best guide through your intellectual hardships.