Attack of the Killer Dust Bunnies

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I was waylaid by dust bunnies yesterday. It started in the lab; I was exposing the fresh layer of sticky mats as I usually do, and noticed that the air disturbance (quite a flourish if you want to get the sheet up in one motion) had sent some dust bunnies scurrying. I tracked them down and captured them with an unused section of the mat, but they really shouldn’t be in the lab at all — that’s what the mats are for. We don’t let the cleaning crew in, because of safety issues and the potential for damage. But the mats have proven to be stronger than the floor, and the tile has been failing, so there are areas that have been mat-less for a while, and that has helped the bunnies thrive. I bought some frames (non-skid backing rather than adhesive) for the mats, so the mats can be reintroduced. Open season on dust bunnies! My colleague that signed the receipt for the mat frames said, “Mat frames. Cool!” Sure. He’s the one playing with the pulsed laser.

So I get home, and there’s a dreaded “Can’t connect to the internet” error on the computer. So I went searching for the likely suspects — cycle power on the modem and router, and then recheck all of the connections. Which requires some crawling around in places that have more dust bunnies! I had to wield the bunny-buster to ensure I got out alive. Turns out my phone jack had died, so no more DSL from there. I had to move the model and router to another room, and now I’m relying on wireless (and had some trouble with the router. Obviously an ally of the bunnies)

Run Away!

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Time-Lapse Video: Retreating Glacier

This remarkable image sequence captures a series of massive calving events at Columbia Glacier near Valdez, Alaska. Composed of 436 frames taken between May and September of 2007, it shows the glacier rapidly retreating by about half a mile (1.6 kilometers), a volume loss of some 0.4 cubic miles (1.67 cubic kilometers) of ice or 400 billion gallons (1.5 trillion liters) of water.

Yelling for a Good Reason

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The issue that helped instigate the issue in the previous post was How long would you have to yell to heat a cup of coffee?, which Zz had linked to.

The analysis is fine up until this point

The average human yells at about 80 decibels, which carries along with it about .001 watts of energy

The 0 dB reference for sound energy is 10-12 Watts, so 8 orders of magnitude higher is not a milliWatt. They get this right a little later on.

The average person whispers at about 40 decibels, which translates out to about 10-8 (sic) watts.

Go up by 40 dB, and you get 4 orders of magnitude in power, or 10-4 Watts. But I also read that “loud speech” is equated to 90 dB, not 80 dB, so I’m not sure where the error truly lies. If the power in Watts is what they wanted to use then their answer is fine, but if they really meant 80 dB then the answer is too small by a factor of 10.

When I first saw this problem, it was in the form of a claim that it would take 8 years of yelling, and that fits if you yell at somewhere around 83 dB. The point is that sound doesn’t carry much energy, which is one reason behind Nick’s calculation about how the Electrons per Song on an iPod has been decreasing, and how it’s possible that you can run one for 10 hours on a 3.7 V battery with only 73 mAh of capacity. That’s just 2.7 Joules, but even at 110 dB, this would only represent 1 Joule of sound energy during that span.

On the Job

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How Physics Can Solve Crime And Help To Cure Cancer

Zapperz has a nice little rant, after linking to a story that presents an order-of-magnitude solution to some trivial situation.

I also received a rather nasty and profanity-laced “comment” to the blog, which basically asked why us “MF’s” are wasting out time and not using our brains to cure cancer

Short answer: Chill, bro. “We” (meaning some physicists) are, but OOM calculations are only the beginning of such issues, whereas they were the end of the “how much energy does it take to do X” problem.

Not too Bitter, not too Sweet

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No bitterness rule

Advice on deciding on whether or not one should go to grad school. Striving to be realistic, without flavoring it too much in either direction.

[Y]ou should know the basic facts of grad school experience: most experiments do NOT produce useful results, but that shouldn’t stop you from trying. You are not guaranteed an academic job after your PhD – or any job in specific geographic area or any specific type of the job. You will be making minimum wage-like salaries for ~5-7 years, and even though postdocs get paid more, it is not much more. But for this time you will have the company of like-minded people who are extremely smart, you will learn a lot, and since you live only once, grad school will certainly provide a unique experience that will shape your outlook on life.

“You will make a lot of money” isn’t on the list of what happens afterward, either. (It certainly can happen, but it probably won’t). But what the PhD helps enable is the opportunity to work on interesting problems. So if the whole “hanging out with smart people” angle appeals to you, it’s certainly something to consider.

Cans in a Blanket

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Rhett asks a straightforward question over at Dot Physics, in A blanket and cold stuff

Suppose you put take two identical cans of soda out of the fridge and place them on the floor in the middle of a room. One can you leave alone and one can you cover with a wool blanket. After an hour, you come back and check on the two cans of soda. Which will be warmer?

The reason I think it’s a great question is that it plays on a common misconception about thermodynamics, and it reminds me of a joke, and a related story.

The joke is about a person declaring that a thermos (which we often call a Dewar) is the smartest thing in the world. When it’s pointed out that all it does is keep hot things hot and cold things cold, the response is, “How does it know?”

Well, some years ago we were giving a tour of our lab to an Admiral (or Sneetch. I have taken to calling military lab visitors Sneetches, a Dr. Seuss creature. The high-ranking ones have stars upon thars) We mentioned the vacuum system, and the Admiral mentioned the lines from the joke — it keeps hot things hot and cold things cold, how does it know? My colleague was so focused in on explaining things, he didn’t recognize the joke, and started explaining the physics of heat transfer: a vacuum is a really good barrier to nonradiative heat transfer. I mentioned that it was a joke before he went in for a second round of explanation.

But the misconception — that blankets heat things up, rather than act as a barrier to heat transfer, is what is pointed out in this example.

No More Breadbox

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I’ve mentioned before that I’m bigger than a breadbox. But that description will have to change. It’s not that I’m appreciably smaller (though I have lost some mass from running a net energy deficit the last several lunar cycles), it’s that I now have a much geekier description to use.

A colleague has been setting up a pulsed laser system, in anticipation of getting into frequency combs for optical time transfer using fibers as well as eventually doing optical clocks. And, frankly, he dropped the ball. He got the system running and announced it had a pulse, but neglected to shout “Give my creature life!” or “It … is … ALIVE!” at any stage of the work. Anyway, we were watching him tweak the system and were looking at the signal on an oscilloscope, and got to the point where we wanted a much larger bandwidth, so we started looking for the spectrum analyzer.

“Where is it?”
“I think it’s in the lab. I saw it around here somewhere.”

[Group members begin to fan out]

“Oh, there it is, behind Tom.”

I had been blocking the view of it. Ergo, I can now be described as being “bigger than a spectrum analyzer.”