Maria Holland

What Do You Do Here?

In Uncategorized on June 29, 2015 at 9:13 pm

Now that I’ve finally got my computer set up and am working, perhaps I should talk a little about why I’m in Beijing?  

The official abstract for my NSF EAPSI grant is: 

EAPSI: Investigation of the wrinkling and buckling behavior of layered soft materials, with applications in the developing brain.

During the third trimester of gestation, the human brain evolves from having a mostly smooth surface to the characteristic ’wrinkled’ appearance of the adult brain. How does this happen, and why does it sometimes go wrong? The mechanics community has been interested in these questions for decades, attempting to model the brain as a thin, stiff, growing layer (gray matter) attached to a thicker, softer layer (white matter). Recent mechanical tests, however, have revealed that gray matter is actually slightly less stiff than the underlying white matter, challenging many prior models and assumptions. Through collaboration with Dr. Feng Xi-Qiao of Tsinghua University in Beijing, China, an expert in the wrinkling and buckling of soft films, this project will explore the behavior of thin growing layers on substrates of a similar stiffness. This research will lead to a greater understanding of brain development in light of these recent findings.

For a stiff growing layer on a soft substrate, the formation of sinusoidal waves is expected, while the growth of a soft layer on a stiffer substrate will lead to creases with pinched valleys. The transition between waves and creases happens gradually in the region of interest for brain tissue. Using both analytical and numerical approaches, this research will explore the behavior of soft layered materials with stiffness ratios close to unity. Numerical simulations will be performed in the finite element software Abaqus, using the built-in linear perturbation analysis as well as user-defined material models that simulate volumetric growth.

This was written for lay people (especially the first paragraph) so I’m assuming this is all crystal clear to you, right?

If not . . . Okay, so I’m a mechanical engineer, and I study the brain.  Yeah, it’s weird.  My field, more specifically, is solid mechanics, which is the study of how solids respond to forces (as opposed to fluid mechanics, which is the study of how fluids react to forces).  Even more specifically, I do computational (as opposed to experimental) solid mechanics, which means I make mathematical or computer models of objects in order to predict how they will respond to forces.  Even more specifically, I do computational biomechanics, so the objects I study are biological systems.  And, for one level of specificity beyond that, the group I work in at Stanford focuses on biological systems that grow (add mass) or remodel (change their physical properties).

During my undergraduate degree in mechanical engineering, I spent four years studying the behavior of engineering materials, like steel and concrete.  These are super important, as we build houses and bridges out of them and stuff.  They’re also fairly simple (well, at least in hindsight).  Under normal conditions, their behavior is well-known and reliable.  

Picture an ordinary steel pipe.  If you compress it (squeeze it from both ends), it will get shorter, exhibiting a linear elastic response.  “Linear” means that if you doubled the load on it (squeezed twice as hard), it would deform twice as much (shorten by twice as much).  “Elastic” means that if you unloaded it (stopped squeezing), it would return to its original length immediately.  Not that you would probably notice – under normal loading conditions steel exhibits small strain deformation, meaning that its length would change so little that we can assume its new length is approximately the same as its original length.  It is also “homogeneous”, meaning that if you cut it into shorter pipes, each of them would behave identically because the material is the same everywhere.  And finally, it is “isotropic”, meaning that if you cut square out of this steel, you could compress it from side to side or from top to bottom, and it would behave the same.

But, I study the brain.  Many biological materials, including the brain, differ from engineering materials in a few major ways.  They are generally not linear, elastic, small-strain, homogeneous, or isotropic.  Instead, they are usually “nonlinear”, meaning that as you compress or stretch them, it may get easier or harder to do so.  They may be “viscoelastic”, which means their response depends on how fast you compress or stretch them (like Silly Putty), or “plastic”, which means they don’t return to their original shape when unloaded (think of a paper clip).  Or both!  They can exhibit large strains.  Squeeze some of the skin on your arm together – if you can reduce the distance between your fingers by half, that’s 50% strain, waaay larger than the 0.02% strain range that engineering materials operate in.  They’re usually “inhomogenous” – your bones, for instance, have different densities throughout, in order to bear the weight of your body most efficiently.  And they’re often “anisotropic” – muscles are a great example of a fibrous tissue, with muscle fibers running along their length because the direction in which they contract.  Finally, biological materials can grow, or add mass.  Steel doesn’t do this – if you have some quantity of steel now, you’ll have the same quantity of steel a year from now.  

All of this stuff makes biological materials more difficult (and more interesting?) than engineering materials.  Just like engineering materials, however, biological materials respond to their mechanical environment – the forces they experience acting upon them.  I’m studying the development of the brain, trying to understand what influence mechanical forces have on the development of the wrinkled shape of our brain.  

NewImage

A lot of things in computational mechanics start very simply.  Very much like the joke, “assume a spherical cow”, all of my work this summer will likely be on rectangular brains.  This allows us to focus on what we think are the essential characteristics of the brain, at least from a mechanics point of view – there are two materials (a thin layer of gray matter laying on a thicker layer of white matter) and they are connected to each other as they grow.  

Over the last ~30 years of people studying the brain, we thought the thin gray matter layer was stiffer than the white matter.  These equations are fairly easy to solve (on rectangular brains, at least!), especially when the gray matter is a lot stiffer.  When the top layer grows or is compressed (mechanically, the two loadings are the same), the results look something like this, with regular sinusoidal waves.  

>1

But last year, some colleages of mine tested animal brains – literally, got them from a slaughterhouse and poked them with a very sensitive machine to see how stiff they were.  They found two things: First of all, brain is less soft than Jello!  More importantly (although probably less likely to be shared as a fun anecdote at your next dinner party), the white and gray matter are pretty much equally stiff; if anything, the white matter is stiffer.

(My dad asked me why it’s so hard to measure the stiffness of the brain – “Come on, it’s 2015!” he said.  Things like steel or aluminum or even wood are easy to test because you can cut perfect shapes, and you can grab on and pull them easily.  It’s much harder to cut a nice cube or bar out of a slowly disintegrating fresh brain, and harder still to stretch or squish it in some measurable, repeatable way.)

Given this, there are a lot of past assumptions that need to be reevaluated.  For layered materials with an “inverse” stiffness ratio (where the substrate is stiffer than the thin layer), you see patterns more like this, with creases developing under loading:

<1

These two behaviors transition into each other gradually, looking something like this in between:

=1

The brain lies somewhere around here.  My project this summer is to increase our understanding of the behavior of layered materials with inverse stiffness ratios (the 2nd and 3rd pictures), which I would then apply to my research on brain folding.

Bo Li, one of the professors I’m working with, found a paper that’s similar to what we’re hoping to do – they investigated both wrinkles (the first picture) and creases (the second picture) but in a single material, whereas we are looking at two layers of different materials.  I spent the day working through the first part of the paper, making sure I understand what they did and looking for the parts that we will have to change for our purposes.  It was nice to have a very concrete task and get a glimpse of an outcome similar to what we’re hoping for.  

 

It kind of rained today, which was nice for two reasons.  First of all, the sky had a legitimate reason for being gray, and actually had some cloud-like texture to it instead of its usual appearance, which has all the variety of a concrete wall.  Secondly, rain usually brings cleaner air.  (Which, I can’t help thinking, means that the rain is washing the pollution out of the sky.  It’s a wonder the raindrops don’t burn my skin!)  Look at what happened after Friday night’s storm: 

Screenshot 2015 06 27 16 40 40

Too bad we weren’t outside from 10pm to 1am, when the air was so nice!  I’m hopeful that today’s improvement will last a bit longer . . . 

This evening, I tried to Skype with my Dad but the hotel internet is terrible in the evenings.  It’s kind of absurd to me that I have Skyped with my parents from all over the world, including a “small” Chinese city five years ago, but here in the capital of China in 2015 it’s just too much.  

Today I learned: 

My N100 mask keeps out scents significantly better than my N95 mask.  I bike by a large, open garbage dump on my way to work, and the smell makes me almost throw up every single time I pass it.  I’ve been trying to hold my breath, but I can’t hold it for long enough.  The N100 mask worked well enough that I think I’ll start wearing it, even though it’s too big for my face.  

Chinese Catholic Art

In Uncategorized on June 28, 2015 at 10:52 am

I was woken up by one of the most disturbing texts I’ve ever received, from an EAPSI colleague in Shanghai:

I woke up in the midle of the night to a woman screaming.  Look outside my window to see a man beating up a woman.  I go to the front desk and ask them to call the police.  They call the police and the police “don’t want to get involved”.  Amazing.

I went to 北堂 again today.  I had the route figured out and, feeling healthy, had a bit more pep in my step, so I made good time.  I got to the church at least 10 minutes before Mass started, and was able to stake out a good spot near the front.  This is important because I don’t think the music is in hymnals, just on two screens near the front, which I couldn’t read last time.

The only thing I caught from the homily today was that “we all have our own crosses to bear”. I did find myself wondering what people in the pews were hearing back home, and praying for my country.  A lot of “I’m so sorry, Father”s.  

I’ve written a lot about the Church in China in the past, and most of it holds true here in Beijing.  The main new thing I’ve noticed is the fairly regular occurence of priests or members of the congregation taking Hosts back from people who try to walk away with It.  I think I saw this once in Xiamen, and it was very confusing to me at the time; I only later realized what must have happened.  Maybe we get more tourists at the Beijing cathedrals, who don’t know what’s going on but want to get the snack that everyone else is getting?  I’m not sure, but I’ve seen this happen at least once at each of the Sunday Masses I’ve been to so far.  I am really impressed and gratified by the sharpness of their observation, and their courage in confronting people (gently); as an Extraordinary Minister of Holy Communion at my home parish, I know it’s a difficult task for many reasons.  

Last week, I took a taxi home immediately because I wasn’t feeling well, but this week I took the time to look around.  I visited each of the side altars, and was struck by two of them in particular:

IMG 2184

IMG 2186

They’re both images of Mary with the child Jesus, but with Asian features and dress.  These aren’t great pictures, but I also bought several prints of each at the religious goods store.  Plus a book on The Art of the Catholic Church in China!

I took my time walking back to the subway as well, and stopped for noodles on the way.  

In the evening, I got a few friends to go to the U-Center for fish.  This was a great choice.  We got one big fish with potatoes and broccoli, plus rice and tea, for the four of us for 100元.  And afterwards I splurged on a kumquat-lemon drink from Coco which was all that I had hoped for, and more.

Today I learned:

You can see a forecast of the pollution at http://aqicn.org/city/beijing/.  The next two days are supposed to be more of the same.  I haven’t seen a hint of blue in the sky since last Sunday.  

Location and Identity

In Uncategorized on June 27, 2015 at 10:41 am

I went shopping with the other Beijing EAPSI women today.  We’re going to a 4th of July party at the US embassy on Thursday, and the guys got suits made so . . . the stakes have been raised.  We actually had a decent amount of success – one time I even had to tell the shopkeeper that a dress was too big!  This had never happened to me before in China.

I bought a few dresses and some cute cards.  They had pretty scenes on them, along with “recipes”:

Travel recipe
there are a lot of things that we canlearn through
traveling to different places experience
culture and your information

Reading recipe
in today’s world,
training and learning do 
not stop when
we finish schoolthey
must nowcontinue
throughout our working lives

Shopping recipe
use a shopping list
you also need to think about what you
can afford to have

Sleep recipe:
i spread my wings and i’ll learn how to fly
wanna feel the warm breeze
sleep under a palm tree

The last one was my favorite, because it is literally some of the lyrics from “Breakaway” by Kelly Clarkson.

About halfway through, I started noticing my own behavior and seeing in it a mirror of the behavior I see around me.  Chinese people are beyond generous with the people in their ‘inner circle’ (family, friends, colleagues, etc.), but people on the outside of this circle are really not extended any basic courtesy.  I think in the time I’ve spent here, I’ve internalized this attitude more than I’m comfortable with.  In Chinese, it’s easier for me to be demanding, dismissive, curt.  Even five years later, it’s an easier skin to slip into than I realized.  

It’s a difficult question for me, how to find a balance between assimilation and authenticity?  If I could, I would remove any trace of an accent in my Chinese, remove any indication of my American-ness.  There’s much that I admire in Chinese culture and want to make “mine”, most especially the incredible generosity among friends.  I have enough relativism in me to know that Chinese behavior towards strangers is “rude according to Americans”, not “rude”, but . . . I’m an American.  Should my behavior be governed by identity or location?  A bit of both, no?  I don’t quite know what the test is, but I think it comes down to a comparison of values.  When it comes to food, for instance, I go with location: my gastronomical repertoire has increased markedly because I value “accepting gifts graciously” over “Americans don’t eat that”.  And in public transportation, “getting on a bus at some point this week” does outweigh my American belief in “queueing patiently”.

In dealing with shopkeepers, it’s something like “acting less obviously foreign” vs. “recognizing the people I’m interacting with as human”.  The former (besides being a hopeless cause) is simply not worth sacrificing the latter.  

So I started to make a conscious effort to look people in the eyes, smile, say ‘thank you’.  I know that it’s super American to say thank you so much, but I can’t hide my foreignness in my outward appearance, and maybe I shouldn’t try to hide some aspects of my culture any more than the color of my skin and hair or the shape of my face. 

Follow

Get every new post delivered to your Inbox.