Rusty mittens

Just for fun, and because it's winter, I thought I'd look at mitten heaters, specifically the non-reusable type that comes with a warning not to take the plastic off until you're ready to use them. You've probably seen them sold with outdoor recreation stuff, such as camping gear. They're little cloth pockets with a powder inside, and you can stuff them inside your shoes or mittens to help keep warm.

There are a few ingredients in that powder, but only one produces heat. I think the others moderate the speed of the reaction so it lasts about a half hour, instead of getting a lot hotter and only lasting a few minutes.

The source of heat is a multi-step, electrochemical reaction: rust.

Fake snowflakes

You know how they say no two snowflakes are alike?

It turns out that they're so sensitive to the conditions they form in, and are also fragile in a turbulent area, that the odds of two snowflakes growing in precisely the same way and having the exact same collisions breaking pieces off as they go are pretty small.

There are, however, a few main shapes of snowflakes that all snowflakes follow.

Science fiction fans, rejoice!

All I can really say about this is, WOW.

NASA's Kepler team has found loads of planet candidates to date (about 2300) by measuring variations in brightness in the star as the planet orbits. They've confirmed a bunch of them as well, so we know there are other planets out there. And just in case you think 2300 is a low number considering how many stars are in the sky, keep in mind that the Kepler telescope has been staring at a patch of sky about the size of your outstretched hand the entire time. I don't know about you, but I can't even see 2300 stars in that kind of an area, and the Kepler telescope has found that many planet candidates.

Now they've found one in its star's habitable zone - where liquid water can exist.

If you take a look at their news story, they show our solar system with the habitable zone defined - Venus is too close to the sun to be habitable, but Earth and Mars are both in the right area. This is why they've been sending robots to Mars to look for evidence of past water. Past water, because Mars' atmosphere is much too thin to retain enough heat to have present water, but it does have present ice in the form of its polar ice caps (as well as solid CO₂, dry ice).

It remains to be seen whether this planet has an atmosphere which will hold in enough heat to maintain liquid water, but at least its orbit is in the right place for this even to be an option. Composition of some planets' atmospheres (mostly the early Jupiter-sized ones so far) has been studied using infrared absorption spectra, which is a whole level of nifty that I would need to study for a while to understand.

The Voyagers are still going strong

This pair was aptly named. Launched in 1977, the Voyagers are still cruising, still doing science, still sending back photos and data, still occasionally making the news. Just this past summer, they discovered bubbles in the outer edge of the sun's magnetic field, way out at the boundary of the solar system.

The most recent news is more mundane and administrative in one sense, and pretty darn amazing in another sense. The Voyagers have now switched the last set of thrusters to the backup set. Sounds kind of boring, until you realize that this means the longest lasting of the primary set of thrusters lasted for 33 years. Without maintenance. Yeah, try that with your car.

Every time I look at this set of twins, they amaze me. They were designed from the start to be deep space probes; these are the ones who carry the famous golden record (and the needle to play it—yes, it is in fact a phonograph record, only made out of gold instead of vinyl) and took the first ever picture of both the earth and the moon in the same frame. (Links at the bottom of that page to larger versions of the photo.) They're also the only spacecraft ever to have visited Uranus (1986) and Neptune (1989). Everything we know about those two planets beyond distant telescope viewing, we owe to Voyager 2.

Apparently now that they're fully switched to the backup thrusters, they can shut off the heat to the primaries and save power, and expect to get at least another 10 years out of the backup thrusters. Did I mention the backup thrusters weren't maintained for over 30 years either, and they worked fine when NASA turned them on? This just boggles my mind.

I am curious to see what they find when they finally cross out of our sun's area of influence and get into interstellar space, and I really hope their thrusters last that long. (The thrusters in question aren't their drive, they're for aiming the antenna so they can keep talking to Earth.) They just keep on finding new things!

Don't plug the pressure relief valve.

The pressure relief valve is one of my favourite pieces of safety equipment.

In this case, it's just a simple valve that's designed to leak if the pressure gets above a certain point on one side. By letting a small leak happen, you avoid having the pressure get higher than the tank or pipe is designed to handle. If the pressure in a tank gets higher than it's designed to handle, you get stuff like this:

They aren't only on large industrial systems though.

That one was a little bitty (5 gallon, according to the public safety notice I found it on) hot water tank that exploded. A full size hot water tank does a lot more damage, such as done by this 80 gallon commercial hot water tank installed for a school cafeteria. Did I mention you don't ever plug the pressure relief valve? It's there for a reason.

And because it involves explosions, mythbusters naturally did a couple of episodes to find out if a hot water tank really does launch itself like a rocket and if it really can punch through the 2nd floor then the roof of a 2-story house.

So yeah, if your hot water tank has a dripping valve, don't plug it—call the repairman and put a bucket under it until then.

The reverse of a pressure relief is a vacuum relief, which lets air into tanks that you're emptying. Like this one:

Gravitational assumptions

I was working on some fluid flow at work the other day, and while trying to determine whether I could use gravity flow between a series of tanks or whether I had to put a pump in there somewhere, I wondered how a chemical plant built in microgravity would work.

Fluids or solids move because they have potential energy. (Once they're moving they also have kinetic energy.) So what kind of potential energy could, say, a pipe full of water have, if it didn't have gravitational potential and thus couldn't do any kind of gravity flow?

The first thing I thought of was pressure; this is how pumps overcome gravity and lift liquids uphill. Absent gravity, building up pressure at one end of a pipe would push the fluid toward the other, lower pressure end.

Mortality

Here's a pair of medical terms I have often seen together. One of them I thought I had a moderately good understanding of the meaning, and the other I wasn't really sure exactly what it meant.

As with my previous post in this series, the same comment applies: If a medical doctor happens to read this and notices that I have something wrong, I would be thrilled to get a correction. I'm not a doctor and I'm writing this for other not-doctors; while I'm ok with simplification I don't want to be wrong.

Now, for my pair of terms: mortality is the former; it means how many people die. (Rather appropriate for a Hallowe'en post!) But it's also more than that; it is, specifically, the number of deaths in a given group over a given time period, and what the group and time period is has to be defined. The restrictions make sense, once I stopped to think about it: ultimately, the mortality of humans is 100% - everybody dies of something, at some point. But if you look at the mortality of a disease, or a type of accident, then the group is restricted to the people who have that disease or that injury, and the time is restricted to the time of the study, and the mortality is less than 100%. Something else kills the other people in the study at some other time, not covered by the study.

Acid and oxygen

Acid rock drainage is one of the big environmental problems facing hard rock mines, because it keeps going for decades after the mine is closed and abandoned, poisoning everything downstream with the toxic metals leached from the rock. It's a natural process that occurs wherever rock is exposed to oxygen and water; metal sulphides are oxidized by the oxygen to dissolved metal and sulphuric acid. Exposed rock is eventually consumed until there is little to no unreacted metal or sulphide accessible to oxygen.

However, as the process requires oxygen, it couldn't happen until the earth's atmosphere actually had oxygen in it. I haven't yet found a definitive description of what exactly the earth's atmospheric composition was before the change, but the difference between chemistry with and without oxygen is pretty clear, as oxygen is highly reactive and tends to get into everything. For one, the acid rock drainage I mentioned above. Another indication is the type of iron minerals deposited—with or without oxygen, and how much oxygen. As iron combines very easily with oxygen, if you find an iron deposit without any oxygen there's a good chance no oxygen was available to it at the time it was formed.

Research

I've been following the Science Based Medicine blog for a while now (even though I'm not a doctor) and one of the things I realized is that medical research is a whole lot more complicated than, say, chemistry. In the sort of trials I might do, if you put the same ingredients in a jar, you'll get the same results every time. In medical trials, this isn't the case, because human bodies are a whole lot more complicated than even a jar full of a hundred different chemicals. I sort of already knew this, but some of the articles on SBM have really made this clear to me.

Another thing I realized is that there is a lot of vocabulary around these trials which I only partially understood. So, here is my attempt at explaining this stuff more completely to myself. And, as it says in my sidebar, "I thought I'd share."

(If a medical doctor happens to read this and notices that I have something wrong, I would be thrilled to get a correction. I'm not a doctor and I'm writing this for other not-doctors; while I'm ok with simplification I don't want to be wrong.)

The first one I'm going to cover is clinical trials.

Happy Thanksgiving

I'll be back next week with something. This weekend is for overeating and visiting family, not working and writing.