Category Archives: Body

Pink and Green

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Pink, green

There is no spoon green dot. It’s an afterimage from seeing the pink.

Things to add — if you look away, you’ll see green afterimages. Also, if you stare at any of the pink dots for a while, they (or the rest) will still tend to disappear. When you stare at one point, images can fade, especially if they are dim and away from the point at which you are looking, which is a problem in astronomy — you’re looking at a dim star, and it has a tendency to just disappear. This, I’ve learned, is called Troxler’s fading (the wikipedia page uses this illusion as an example). We normally don’t experience this, because we tend to move our eyes a few times per second.

Update: The “pink, green” link is dead, so try this one : Lilac chaser

Those Who Can, Do. Those Who Can't, Explain.

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Usain Bolt: The Science of Running Really Fast

Even without knowing the times, you can see that this is a special run. The first few seconds are fairly average, and as expected the acceleration trails off after around 40m, but then he just keeps going. Bolt covers 60-80m faster than 40-60m, somehow increasing his acceleration, and takes 80-100m at the same speed, with no significant deceleration.

Energy: It's Nothing to Snicker At

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Of Car Crashes and Snickers Bars

Pop quiz, hotshot. Using the caloric energy content of a candy bar (e.g. Snickers, at 250 food calories), what is the kinetic energy of a two-ton behemoth SUV traveling at about 70 mph? A first-order approximation is fine — no need to worry about more than one significant digit.

Got it? Think of your number and then proceed to the analysis.
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Which One's Pink?

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Color and Reality. Another take on color vs. the brain’s interpretation of color, discussed (OK, linked to) previously in Color on the Brain

We were all taught about Sir Isaac Newton who discovered that a glass prism can split white light apart into its constituent colors.

While we consider this rather trivial today, at the time you’d be laughed out of the room if you suggested this somehow illustrated a fundamental property of light and color. The popular theory of the day was that color was a mixture of light and dark, and that prisms simply colored light. Color went from bright red (white light with the smallest amount of “dark” added) to dark blue (white light with the most amount of “dark” added before it turned black).

Evidence of Things Not Seen

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Until you do a CAT scan.

NYT: Autopsies of War Dead Reveal Ways to Save Others

Col. Howard T. Harcke, a 71-year-old Marine Corps radiologist who delayed retirement to read CT scans at Dover, noticed something peculiar in late 2005. The emergency treatment for a collapsed lung involves inserting a needle and tube into the chest cavity to relieve pressure and allow the lung to reinflate. But in one case, Colonel Harcke could see from a scan that the tube was too short to reach the chest cavity. Then he saw another case, and another, and half a dozen more.

In an interview, Colonel Harcke said it was impossible to tell whether anyone had died because the tubes were too short; all had other severe injuries. But a collapsed lung can be life-threatening, so proper treatment is essential.

Colonel Harcke pulled 100 scans from the archives and used them to calculate the average thickness of the chest wall in American troops; he found that the standard tubing, five centimeters long, was too short for 50 percent of the troops. If the tubing was lengthened to eight centimeters, it would be long enough for 99 percent.

“Soldiers are bigger and stronger now,” Colonel Harcke said.

The findings were presented to the Army Surgeon General, who in August 2006 ordered that the kits given to combat medics be changed to include only the longer tubing.

This reminds me of a story, possibly apocryphal, of a study done in WWII. The army wanted more armor on bombers to protect them, but needed to be selective about where it was placed, lest the speed and/or range suffer too much. And they didn’t really want to take planes in production to test them, since they were all needed in battle. So some people analyzed the damage pattern of planes that returned from missions. They assumed that anti-aircraft bursts were basically random, so the pattern of damage from returning aircraft indicated non-critical harm, and were areas that didn’t need reinforcing — it was the gaps in the pattern which indicated the fatal hits. and that was where additional armor would do the most good.

Braaiiins

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Darpa: Heat + Energy = Brains. Now Make Us Some.

The idea behind Darpa’s latest venture, called “Physical Intelligence” (PI) is to prove, mathematically, that the human mind is nothing more than parts and energy. In other words, all brain activities — reasoning, emoting, processing sights and smells — derive from physical mechanisms at work, acting according to the principles of “thermodynamics in open systems.” Thermodynamics is founded on the conversion of energy into work and heat within a system (which could be anything from a test-tube solution to a planet). The processes can be summed up in formalized equations and laws, which are then used to describe how systems react to changes in their surroundings.

Forty Winks

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What is How to Measure Sleep?

As we sleep, our brains pass through a series of stages, like shifting between gears in a car. The most famous is REM sleep, characterized by fluttering eye movements. But other categories include light sleep (stage S1), stable sleep (S2), slow-wave sleep (SS), and even being awake (W), each identified by a signature from polysomnography (PSG), in which electrodes record from the scalp, eyelids, and heart.

Look Deep into My Eyes

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So that’s what the bottoms of limpid pools look like. Scary eh?

Eye exam the other day. (My eyeglasses problem happened after I scheduled this, but before the exam. Come to think of it, I chipped a tooth right after making my dentist appointment. Note to self: do NOT schedule a urology visit.)

Retina scan from the doc’s new toy. I’d gotten scans before, from laser-safety examinations. They don’t actually make it any safer to work around lasers, they just give you a baseline so you can assess the amount of damage of you look into the big scary laser. The previous ones required dilation, which means you can’t drive (or do much of anything, really) for several hours. This one didn’t.

retina-scan1

I just hope this doesn’t compromise the security of the Genesis Project.