April 2011
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Month April 2011

Teaching Thursday: Dimensional Analysis

I have taught and done outreach at all levels, from kindergardners to specialized scientists in post-graduate training. Now, I teach mostly college freshmen and sophomores.

At the university where I teach, many of our students are first-generation: that is, they are the first in their families to attend college. Our estimates are maybe 1/3 or more fit this category. Many come to college not quite prepared for college work. It’s really rewarding for me to show them some tools that bench scientists use every day. I think most scientists take some of their methods for granted, because they become so familiar that we begin to believe we’ve always known how to do them.

For example, when I sit down to calculate what I need for a 1 molar solution of sodium chloride in water, I already have memorized that the molecular weight of NaCl is 58.44 g/mole and I know exactly how to combine that with other numbers to get the amount I need to weigh out.

But I didn’t always know how to do that. It’s something that you get better at with long practice.

A shortcut of sorts that scientists use is something called “Dimensional Analysis”. I learned it as “The Factor-Label Method” but it’s the same thing with either name. You’ve got two goals: 1) make the units work out; 2) keep multiplying by things you know equal 1 until the units do work out.

This video (5:44) shows students how to approach problems using Dimensional Analysis. It’s also available at YouTube.

Dimensional Analysis

Iodine-131 in US Milk: Cause for Concern?

A good friend who trusts my judgment (silly rabbit) has asked me to comment on a recent blog report that screams, “Japan Nuclear Iodine Radiation in San Francisco Milk over 2600% Above EPA Drinking Water Limit”.

Now, I’m as concerned as the next guy (maybe more so) over contamination from the Fukushima reactor accident. But I don’t find reports like this one to be very helpful. Let me count the ways.

1. “Japan Nuclear Iodine Radiation” doesn’t make much sense to me.

2. There is no such thing as “San Francisco Milk”. In point of fact, there aren’t even any dead people in San Francisco, much less dairy farms.

3. “Over 2600%” sounds so much scarier than “over 26 times”.

4. Milk ain’t drinking water.

5. Call me a curmudgeon, but for years I’ve felt the way in which news is delivered is even more important than the content of the news. This blog is littered with ads for radiation treatments, scare headlines, lots of typos and out-and-out misstatements (e.g. I graduated from the University of California, Berkeley and not “University of Berkeley” so I’m pretty sure there is no such institution).

It was a good opportunity for me to go and take a look at the data. Here’s what I found. But first, some background on radiation and why we’re concerned about iodine-131 (also shown as 131I, a shorthand I’ll use here).

When a reactor accident or above-ground nuclear test occurs, a number of radioactive isotopes are given off. Radioactive decay occurs when the number of positively-charged protons and/or the number of non-charged neutrons in the nucleus are more than this structure can support. The picture here shows nuclear fission, but a number of other types of radioactive decay occur that don’t make for as violent a picture.

Seven Deadly Sins Sunday: Gluttony Part 2

Each Sunday, I’m excerpting a chapter of The Seven Deadly Synapses, a book on the neuroscience of sin. In this series, we’re examining the sin of Gluttony.

In part 1 of “Gluttony”, we didn’t get to the scientific part. It was mostly just a warm-up. Now it’s time to figure out how the taste system sends a signal to the brain, and how the digestive system handles food.

 


Gluttony

Part 2

For most of mankind’s history, eating has been the key to staying alive and so has been a human’s main job. Most of a person’s waking hours were devoted to getting calories, processing calories into a healthy and digestible form, and storing calories for future needs. The word “famine” appears 107 times in the King James Version of the Christian Bible (including the passage shown here, that describes a famine so severe that a mother boils and eats her son); “hunger” 60 times; “starve”, “starving”, “starvation”, 19 times. Other religious texts show a similar historical fixation with either metaphorical or real hunger: the word is used 74 times in the Qur’an, and only 18 times in the Upanishads. Gluttony is likely to be a sin mostly because it revels in the flaunting of what mankind has struggled so hard, for so many years, to achieve: nutrition.

 

To find food, and eat it, and to balance surfeit with famine, is the responsibility of a few thousand nerve cells in a pinky-end-sized hunk of brain called the hypothalamus. Just like the thermostat in your house keeps the household temperature close to where you want it to be, the hypothalamus is responsible for your body’s balancing acts, the processes and feedback loops that physiologists call “homeostatic mechanisms”. Like Goldilocks, we want our bodies to be “just right”. not too cold, not too hot; not too thin, not too fat; not too much breath, not too little. How the hypothalamus causes us mischief is the root of our story.

Oscar® Winning Neuroscientists

A classic method for earning a quick sawbuck is to bet someone that you can find the word “Wisconsin” on a US $5 bill. You’ll need a magnifying glass, but there it is, around the top of the Lincoln Memorial.

If you’re bored with that bet, or if you just want a change of pace, bet someone you can name two Academy Award winners who have published papers in neuroscience.

Colin Firth and Natalie Herschlag, Neuroscientists (and actors)

As Mind Hacks has already pointed out, both Natalie Portman (neé Hershlag) and Colin Firth (neé Firth) have played a prominent enough role in recent neuroscience research to merit mentions as fifth and third authors, respectively, on neuroscience research papers.

The Kanai et al. paper, on which Firth is an author, has already been covered in this blog. The story of how Firth (and fellow BBC radio host Tom Feilden) came to be co-authors with Kanai and Geraint Rees has been explained in the Neurocritic blog.

Firth originally commissioned Kanai and Rees to scan the brains of two British politicians, one liberal (Labour), one conservative.

Teaching Thursday: Mean T Cells

Every Thursday, I plan to post an “explainer”, a short video or screencast that will explain some scientific concept. The first few of these will come from my teaching vaults. After a while, I’ll run out of videos and need to make new ones, but for now, I’ll go with what I have laying around.

This week’s Teaching Thursday video is a two-fer. My students have always struggled with understanding the immune system, and the interplay between its cells.

T-cytotoxic, T-helper, T-helper, T-regulator

Back in graduate school, my major advisor was probably one of the worst human beings on earth but one of the best teachers. (I have found that teaching ability is often inversely proportional to human kindness.) He would personalize brain cells. Each one had a personality, and a backstory, so that attending his class was like having a particularly lurid soap opera plot explained to you.

It was in this spirit that I created these videos.

What if we reimagined the cells of the immune system as boys (B cells) and girls (T cells)? B cells just spit out their antibodies and leave. T cells use specialized signaling chemicals called cytokines to coordinate the immune attack.

The movie “Mean Girls” is about the interplay between young women in a high school environment, which is a lot like the immune system. That’s the basic premise I started with. That gave me a chance to throw in some random facts about the immune system based on scenes in the movie.

There’s some other little tidbits in there that I had fun with. For example, there is evidence (reviewed in Sheril Kirshenbaum’s The Science of Kissing) that one of the functions of kissing is to compare the genetically determined cell surface proteins called “major histocompatibility complex proteins” or “human leukocyte antigens”. If the match is close, then you may be kissing your sister and you should stop. If there is no match, then you are may form a child with a stronger immune system that can attack a broader variety of invaders.

There are two movies:

The first is simply the trailer for “Mean Girls” narrated to explain what it means when re-explained as a story about the immune system.

Mean T Cells Trailer

The second is a little longer and consists of re-edited movie scenes with an explanation of an immune system concept accompanying each one.

Mean T Cells

 

To Sleep, Perchance to Cause a Midair Collision

Recent incidents with air traffic controllers have pointed up the hazards of shift work and the supremacy of the circadian rhythm. In one recent case, an air ambulance was forced to land at 2 a.m. without local air traffic controller guidance at Reno-Tahoe International Airport.

These recent incidents have pointed up the existence and causes of what medical science calls Shift Work Sleep Disorder, or SWSD. It’s not clear how many people are affected by SWSD, but it’s probably a fairly significant chunk of the 15% of Americans who perform night-shift work.

Lead (battery) balloon

When I was 19, I dropped out of school for a time and took a job working in a plant that melted down lead plates from car batteries and turned them into lead ingots. The lead ingots were then sold back to AC Delco and other manufacturers of lead-acid batteries.

My job was to maintain the efficiency of the blast furnace by climbing two stories to its top, where there was a small hole about twice the diameter of a pencil. I’d stick a hollow metal rod inside. On the cooler end of the rod was a hand pump and a toy balloon for collecting the gases. Then I’d bring the balloon back to the lab, rushing so that the entire thing didn’t leak, and run the gases through a chromatograph, an instrument that separated the gases by size. I’d report this to the engineers in the morning. These data would tell the engineers, who wore white hardhats, whether the furnace needed more air, or more fuel, to burn efficiently.

Seven Deadly Sins Sunday: Gluttony Part 1

Every Sunday, I’ll print an excerpt from the upcoming book Seven Deadly Sins. Because alliteration is a virtue, not a sin, I’m calling this feature “Seven Deadly Sins Sunday”. Other days of the week will be devoted to other things, but on Sunday we’ll examine the neuroscience of sin.

Everyone wants to read about Lust, but that’s a cheap shot and I want to keep you wanting more, not sated after the first few Sunday posts. So I’m going to start with gluttony. (I mixed a little Lust in just to keep your interest.)

 


Gluttony

Brain science is a big field. With so much scientific real estate to cover, there are not one, but several Holy Grails. You could define the Holy Grail of Neuroscience many different ways. Maybe it’s a rare piece of scientific evidence that makes all the other pieces of the puzzle fall into place. Maybe it’s the chance laboratory finding that helps billions of humans lead healthier lives. Maybe it’s a secret that makes you rich beyond your wildest imagination. I’m sure neuroscientists would disagree on which of these is the most desirable, but if I got to choose, I’d go for all three at once — I’d figure out how to make people eat only healthy foods, and only the food they need. I’d slay gluttony.

Searching for the Holy Grail of Neuroscience will likely involve Killer Rabbits.

Liberally Thinking: Red Brain, Blue Brain

I was at a dinner party, held at a huge mansion lit with gaslamps. We were in one of the most conservative neighborhoods in one of the most conservative states in the union. But this was a party filled with liberals, and the whole enterprise had a feel like we were teenagers who had taken over someone’s parent’s house while they were away on a European vacation.

Sandra Irby had a conversational point to make, an amuse bouche for the group of a half-dozen of us huddled around a Louis XVI coffee table. “I know stupid conservatives, and I know smart conservatives.”

We all nodded at the “smart conservatives” part. Some of my best friends could put William Buckley to shame in the brains (and political orientation) department.

“But I don’t know any stupid liberals. Do you?”

“Teddy Kennedy,” I offered, citing his fatal error at Chappaquiddick.

Edward Kennedy leaves court at Edgartown, surrounded by state troopers. Source: AP.

 

Welcome to Seven Deadly Synapses

I’m Jim Hutchins. You can find out more about me at the “About” page.

I’ve started this blog after a successful experience commenting at Nate Silver’s fivethirtyeight.com blog and, after he moved to the New York Times, on an independent site called logarchism.com. I recommend both of those blogs if your interests tend more to politics than science or ethics. I will still comment on those sites under the username Monotreme. Like a spiny echidna, I’m a bit unclassifiable and exotic.

In the next few months, I’ll be working on a book project I call Seven Deadly Synapses. What can modern neuroscience tell us about the Seven Deadly Sins? How does neuroscience fit into the 1600-year history of the Seven Deadly Sins? Can we link Dante and Damasio?

Or, in the poetry of Rubén Darío (“Los Motivos del Lobo“),

Mas empecé a ver que en todas las casas
estaban la Envidia, la Saña, la Ira,
y en todos los rostros ardían las brasas
de odio, de lujuria, de infamia y mentira.

As the wolf exposes himself to human behavior and frailty, he laments:

But I began to see that in all the houses
There dwelled Envy, Spite, Ire,
And that in all the faces blazed the embers
Of hatred, lechery, infamy, and lies.

(Thanks to Nereyda Hesterberg for introducing me to Darío’s poetry and helping with the translation.)

If Darío’s wolf were a lupine neuroscientist, what would he see? What are the brain mechanisms — anatomy, chemistry, physiology — underlying envy, spite and ire? What is the evolutionary advantage, if any, to these invidious behaviors?