Friday, January 30, 2009

Mandelbrot Bear

This is too awesome not to make (or buy...please, someone start selling these) for your child:

Friday, January 2, 2009

How Does Soap Work?

I started pondering this question when I read this "10 Germ Myths" story at ABC News. In particular it discusses the myth that anti-bacterial soap keeps your hands cleaner than regular soap. It turns out to be a myth and one that is perpetuated by the lack of understanding of what one is attempting to accomplish when they wash their hands.

Now, I plead ignorance here: I never really thought too much about bacteria and my hands. I simply followed the mantra taught by all parents: wash your hands with soap and warm water to stay clean and healthy. Staying healthy implies I am getting rid of germs (bacteria and/or viruses) and thus preventing the spread of some infection. Therefore, you would think that anti-bacterial soap would help in preventing this infection by reducing the number of pathogens on my hands. It turns out that the US Food and Drug Administration has questioned this notion for some time now.

So, what happens when you wash your hands? Well, germs aside for the moment, the goal of washing your hands is to get clean. Getting clean means getting rid of dirt and grease, which is generally hydrophobic, which means it doesn't play well with water. Therefore, simply running your hands under water will not work well. It may wash away some of the loose debris, but dirt that is caked onto your greasy little hands will stay right where it is.

Something different needs to be added to this equation. You may think, "Hey, if dirt is hydrophobic, then it must like to mix with oil. Let's wash our hands with oil!" Your first thought is correct. Most things that are hydrophobic, like oil itself, do mix well with oil (lipophilic). But if you washed your hands with oil you are just compounding your original problem. How are you going to get all that oil off of your hands now?

If only there were a chemical that both liked water (hydrophilic) and liked oil (hydrophobic) at the same time. Well, let me introduce you to my friend SOAP. You can make soap by heating up some fat with some alkali/base such as Sodium Hydroxide, NaOH, or as fans of Fight Club (or soap making) call it: Lye. What results from the saponification process is a long hydrocarbon chain with a Carboxylate head, i.e. CH3-(CH2)14-CO2-Na. The Sodium ion will dissolve off in water creating a negatively charged head. These soap molecules are known as amphiphilic -- they are both hydrophilic and lipophilic.

When a bunch of amphiphilic molecules meet, they form a micelle, which is a ball of with the hydrophilic heads on the surface and all of the hydrophoibic tails in the center of the ball. This is due to the interaction of the negatively charged head with water, which is a polar molecule, and dispersion forces between the long hydrocarbon tails.

This micelle makes the quintessential emulsifier: something that can aid in mixing two immiscible liquids -- usually oil and water. When cooks think of emulsifiers, they think of the egg yolk in their mayonaisse or honey and/or mustard in their salad dressings. For soap, though, the micelle arrangement is perfect. It allows the dirt/grease to get trapped in the center of the micelle with the lipophilic tails. At the same time, the Carboxylate head keeps the center from mixing with the water (and repels other micelles, since they are all negatively charged surfaces) and keeps the dirt suspended in such a way that it can easily get rinsed away off of your hands and down the drain.

Back to Bacteria. This is a leap of faith on my part here, because I am not sure, but I assume the same process can encapsulate bacteria and wash it away. What I do know is that regular soap does nothing to kill bacteria, you are just washing it away.

Anti-bacterial soap, on the other hand, does contain chemicals mixed in with the soap that can kill bacteria. However, the aforementioned studies seem to indicate that using these soaps does not decrease the rate of infection. This is most likely due to the fact that most anti-bacterial chemicals need to be left on the skin for at least two minutes to work. When is the last time you rubbed Dial all over your hands for more than two minutes without rinsing? That's what I thought. In fact, using anti-bacterial soaps has the potential to create "super-bugs" that are resilient to said anti-bacterials (such as Triclosan) and creating a problem much worse than having dirty hands.

Alcohol gels, on the other hand, are better at killing bacteria, considered an acceptable substitute to washing with soap and water by the CDC, and will not result in the potential evolution of a resiliant super-bug. The alcohol concentration needs to be >60% to do its job properly (its job being to dehydrate bacteria to kill it), so soaps that contain alcohol don't contain a high enough concentration to be "anti-bacterial," especially if you rub your hands under the water immediately. Also, keep in mind that these alcohol gels kill bacteria, but they don't "clean" your hands in the "dirt and grease" sense of the word. You need soap and water for that.

One final thought: We learned that soap does not kill bacteria. So, the next time you are in a public bathroom (or at a friends house) and you see that white bar of soap, think to yourself: how many people have wiped their E. coli ridden butts and then used that soap? And then start carrying around some Purell.

Monday, December 29, 2008

40 Weeks

Maybe this is common knowledge to people that are already parents, but I was shocked to find out that pregnancies are counted from the end of the woman's last period. That means being "1 week pregnant" (not that anyone says that) is not pregnant. Conception generally happens 14 days (2 weeks) after the last period. Thus, by the time you find out you are pregnant, you are already 4 weeks in, but the embryo is only 2 weeks old.

So, full-term is basically a 38 week old fetus. Which makes the premature babies that survive after only 25 weeks gestation even more mind-boggling because the fetus is just 23 weeks old.

Saturday, December 27, 2008

The McGurk Effect

What you see really is what you get.

Or at least that is what The McGurk Effect says.  The effect was first published by (you guessed it) McGurk (and MacDonald, who presumably feels a little bitter about the whole naming thing) in 1976 in the prestigious journal, Nature.  It was one of those quirkily named articles that you know the authors spent way too much time thinking of: Hearing Lips and Seeing Voices.  

The basic idea is that seeing someone talk helps you understand what they are saying.  When you can't see someones lips, it makes comprehending their speech more difficult.  I personally know this is true because if I am having a conversation in a loud place (like the local public house), I rely heavily on the speaker's visual cues to understand what they are saying.  The McGurk Effect takes this notion to the extreme -- hearing "Sound A" when a person aurally says "Sound B", but their mouth makes the motions of "Sound A."  So, like I said: What you see is what you get.  You can fool your own brain with the video of this on YouTube.

I learned about this in the context of the show Scientific American Frontiers with Alan Alda on PBS (a quite wonderful show, I might add, that I always find entertaining and educational whenever I manage to see it).  It was an episode entitled Cars That Think, and The McGurk Effect was mentioned in the context of a voice recognition feature for a car that was being deveoped by IBM.   It turns out that voice recognition still sort of sucks -- you already know this if you have ever been on the phone with one of those bloody automated phone systems that thinks it can understand you.  The show quoted something like 80% accuracy (a bit generous, methinks) for standard voice recognition.  But if you add in the capability of analyzing lip movement, they claimed that the accuracy became essentially 100%.

I enjoy these sort of tricks your mind plays on you as a result of the way your brain typically processes information in hopes of helping you.  The most common example that comes to mind are optical illusions.  But I feel like The McGurk Effect is a more extraordinary example because your senses actually conflict with one another and force your brain to choose an interpretation -- a sort of battle of the senses.  It is interesting that in interpretting the spoken word, something most closely associated with hearing, that your brain chooses to believe the visual information.