SciBlogs

Archive February 2011

[withdrawn] Some weblinks Marcus Wilson Feb 28

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This post has been withdrawn. 

If it ain’t broke, don’t fix it Marcus Wilson Feb 24

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With teaching semester almost upon us, here’s a thought for you university lecturers out there.

I’ve been at a teaching workshop this afternoon, where we’ve been discussing how teaching and research can link together – i.e. that they are not two completely inseparable activities, as we often think.  There were a number of presenters (I was one – I felt really flattered and somewhat of a fraud talking about this subject) and one point that came up was how different people and departments approach the idea of ‘experimenting’ on students.

You can’t improve the way you teach (or the way you do anything) if you’re not prepared to change something and see how it goes. "You can teach for twenty years, or you can teach for one year twenty times", as one saying goes. But some in the group described how some departments can be very reluctant to let lecturers change anything.  "But what if it doesn’t work?" – they say – "then the students will be worse off. You’ll have harmed their education. If it ain’t broke, why are you thinking about fixing it?"

That’s a fair response if the course and the way you teach it genuinely ‘ain’t broke’.  But how do you know that it ‘ain’t broke?’. I suspect that many people who wheel that line out don’t actually know how effective the teaching in question actually is.  Until you do (and a good score on course appraisals does NOT equal good teaching) you really can’t make any informed choice about whether to leave something alone or to change it.   Remember, not changing anything is a choice of action in just the same way that changing something is a choice.  To those who think it’s unethical to use your students as guinea pigs by trying a different teaching strategy I would ask whether it ethical to deny your students better teaching when it could be available to them. I mean, what would you think if Graham Henry refused to try out any new players because they might not be as good in an All Black jersey as the current ones?

Unless you are prepared to make the effort to find out how good your teaching really is, and to try out schemes that could improve the areas where improvement is required, you will be no better a teacher this year than you were the year before, or the year before that, or the one before that… And it will be your students who suffer most.

Slowdown in activity Marcus Wilson Feb 22

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[Somehow the original version of this has been garbled by some bit of computer software somewhere. Hopefully this version makes sense.  My thoughts and prayers for those in Christchurch and their loved ones]

My apologies in advance for what will be reduced blogging in the next three or four months. The following statistics show the story:

2008:  Teaching, 40%; Research, 36%, Other 24%

2009: Teaching, 42%, Research, 35%, Other 24% 

2010: Teaching, 44%, Research 32%, Other 24%

In the last few years, I’ve kept records of how many hours I’ve spend doing various tasks at work. For example, I can say just how many hours I’ve spent, for example, teaching my contribution to the third year electromagnetic waves paper, and running Cafe Scientifique (which, incidently, starts tonight). So, with a few clicks of a mouse, I can prepare some statistics like the ones above. The boundaries of these areas are a little bit blurred, but they give a general picture of what’s going on.

It’s pretty normal to hear the complaint around these corridors of ‘too much admin to do’, but, in my case at least (and remember a sample size of one doesn’t lead to very good statistics) its not the adminstrative work that has increased. Rather, it’s the time spent on teaching that has increased, and that has come at the expense of research. Some of the increase for 2010 I think is a result of my study for the Post Graduate Certificate in Tertiary Teaching, which has encouraged me to spend more time on my teaching.

I can be reasonably confident that 2011 will see a continuation of this trend, with a teaching semester starting that will be busier than the last three years. Therefore, I’m afraid, I suspect my blog-post-rate (or whatever the correct geeky term is for it) is about to diminish.

Uses of Liquid Nitrogen Marcus Wilson Feb 17

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I went to the doctor yesterday and he attacked me with liquid nitrogen.  To be more specific, I had a wart ‘frozen’ off.  Now, I had some similar treatment years ago, in which the doctor used a container of the stuff surrounded by polystyrene foam, and open to the air. Rather like what we use in the lab sometimes. He dipped in what looked like cotton wool buds, and applied those to the wart. Ouch.

This time I when the doctor disappeared out of the room to get the nitrogen, I was expecting him to come back carrying something similar. But instead, he entered holding a very snazzy shiny metallic thermos flask with a spray nozzle on a stalk. It was a case of point the nozzle at the target and spray. Ouch again.  It looked awfully space-age, much more elegant than a container in polystyrene. I want one.

Just how cold is the spray, though? The contents will be under  pressure, and, releasing this pressure is going to cause them to cool very rapidly.  Just what temperature it gets down to will depend a bit on the rate of flow of fluid and the temperature and pressure in the flask, and how the nitrogen mixes with the air on its journey to the skin, but I suspect it is really quite low indeed. Computational fluid dynamics software can probably do the calculations for me.  I wouldn’t have wanted to touch the end of the nozzle immediately afterwards, however.

I note that there are some interesting applications of the sprayer described on the internet, many of them involving unwelcome insects.

Physics discoveries Marcus Wilson Feb 15

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I’ve been thinking a bit more about the comment I made yesterday that there used to be a time that physics discoveries were made by people but now we just need to build a machine to do it (the LHC). 

The major science discoveries, almost by definition, are unexpected and can be very serendipitous. The discoverer wasn’t out there looking for something new per se, but, through some lucky sequence of events, it presented itself to him  (and, unfortunately, most physics discoveries are still ‘him’ not ‘her’). Three examples spring to mind: Oersted’s discovery that an electric current produces a magnetic field, Becquerel’s discovery of radioactivity, and Geiger/Marsden/Rutherford’s discovery that an atom has a nucleus.

In Oersted’s case, so the story goes, he was giving a lecture (1820) on this new ‘electricity’ thing, and just happend to have a compass sitting on his bench. He saw that when the current was switched on, the compass needle moved. The skill of the physicist here was to realize that this phenomenon was something that should be investigated further, which Oersted duly did, to great success.

In Becquerel’s case (1896), he found that unexposed photographic plates had somehow become exposed. Rather than waving this away and thinking that somehow light must have leaked in, he tracked it down to the fluorescent uranium salts that he was preparing to experiment on. Yes, Becquerel got lucky, but it was his careful experimenting afterwards that resulted in him recognizing that something ‘new’ was happening.

One could argue that the discovery of the atomic nucleus was less down to luck – after all, Geiger and Marsden were carrying out an experiment (in 1909) to look at the properties of alpha particles (i.e. discover ‘new’ knowledge about this particle) - but what they got was completely unexpected. Again, careful consideration and analysis of the phenomenon by Rutherford led him to conclude that the positive charge in the atom must be concentrated in a nucleus – a previously unknown piece of physics.

None of these steps forward in physics was ‘expected’ (though in Oersted’s case there was already some suspiscion of a link between electricity and magnetism). Yes, to some extent, these physicists created their own luck, and certainly exercised skill in recognizing and interpreting what they saw, but, fundamentally, they weren’t expecting to see something sensational. Contrast this with the LHC, where something entirely new (but, of course, we don’t quite know what yet) is anticipated.   A machine to do physics for us.

What’s CERN twittering about? Marcus Wilson Feb 14

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A quick skim of CERN’s Twitter site, www.twitter.com/cern tells me that the LHC is going to be pootling on for the next two years at 3.5 TeV per beam, before it is prepared for running at 7 TeV, starting hopefully in 2014

"…[This] gives the LHC’s experiments a good chance of finding new physics in the next two years…"

There used to be a time when new physics was discovered by people. Now, it seems, all we need to do is build a machine to do it for us.  (By ‘new physics’, they mean things like finding the elusive Higgs Boson, or dark matter, or something else that we just don’t know about yet.)

A less high-impact story, but just as interesting, is that the ‘anti-hydrogen’ research group at CERN has just won an award for their work.  Anti-hydrogen is the simplest atom of anti-matter, made up of a single anti-proton and an anti-electron (positron). Anti-hydrogen behaves, as far as anyone can tell, pretty much like normal hydrogen, but with the annoying drawback that it is a touch tricky to contain (what with positrons disappearing when they come close to an electron). So simply studying anti-hydrogen is a major achievement in iteself.   As of November last year, the ALPHA group had trapped 38 anti-hydrogen atoms for 170 milliseconds – not long but long enough to start doing useful measurements on them. (Rest assured that the ‘Angels and Demons’ scenario is a long way off yet.)

Any subtle differences in the properties of anti-hydrogen compared to hydrogen (e.g. in its energy levels) may help solve that mysterious question as to why there is so much more matter in the universe than antimatter.

The sock monster Marcus Wilson Feb 12

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As I’m sure is the case in your house, socks go missing on a regular basis. You’re sure that every night a PAIR of socks goes into the linen basket, and that when the washing is done ALL its contents go in the machine, but, once things are dried and ready to go back in the drawers and wardrobes, some sock somewhere will be missing its partner.

Now, to try to limit this problem I have an odd-sock box. When I find a sock without a partner, it gets checked against the contents of the odd-sock box, to see if it’s a match. If it is, then great, we have recovered a pair; if it’s not, then it goes in the box. And so the contents of the odd sock box sometimes increase in number, and sometimes decrease.  But mostly  the contents increase.

One would of thought that if there are (say) ten odd socks in the odd-sock box, then there are ten rogue socks scattered around the house somewhere. Let’s face it, socks only ENTER the house in pairs (I’m fairly certain on this point) and only LEAVE it again in pairs, so by the law of continuity the total contents of the house should remain pairable. So where are they? I further hypothesize then that the chances of me finding a rogue sock (e.g. under a bed, on top of a bookcase, under the cat bowl etc) should be directly proportional to the number of rogue socks there are – the more rogue socks, the greater the chance of stumbling on one.  Moreover, the rate of loss of socks, I suggest, is roughly constant – after all, I tend to put the same number of socks on my feet every day, so why would I be more likely to lose one one day as opposed to the next.

So we can construct a differential equation for the number of rogue socks in the house – the rate of increase of rogue socks is equal to a constant (for the loss part) minus another constant times the total number lost (for the re-discovery) part. A bit of maths tells me then that I would expect the number of rogue socks to eventually reach a limit, when the rate of loss equals the rate of discovery, and approach that limit exponentially, rather like the voltage across a charging capacitor.

Alas, experimental data suggests that there is no sign of such a limit being reached. The contents of the odd-sock box seems to be growing linearly.

My new hypothesis, which I shall need to test, is that we have a  sock eating monster in the house. Evidence for this hypothesis, I admit, is currently thin, but it would certainly explain why the cat suddenly leaps two feet in the air without warning (on being startled by the sock monster), or, in the middle of the night, runs up and down the corridor several times (being chased by the sock monster).    Unfortunately, there’s also the nagging question  of why the sock monster hasn’t learned to raid the sock box when it feels a bit peckish, but let’s ignore that one.  

Next step is to construct a sock-monster trap (at least the bait will be easy to procure) and wait…

 

The bed of nails Marcus Wilson Feb 10

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http://www.youtube.com/watch?v=hG7lGZqWFpM

You may have seen a bed of nails demonstrated. You may even have done it yourself. I’ve laid on a bed of nails before (it’s not desperately comfortable but it doesn’t hurt) though what this video does is a bit beyond what I think I’d like to try.

So why is it possible?  It really comes down to pressure. Just how much force goes through each nail, and over what area is it spread? You’ll find that there are a lot of nails on a bed of nails, so, if you divide your weight by that number you’ll get a measure of how much force each has to support.

You could easily end up with your weight distributed on a thousand or so nails. If you have a mass of say 65 kg, or weigh 650 N, that gives a force of around 0.65 N on each nail. Call it a newton for the sake of round figures. However, what’s more important is the area over which the pressure is spread. Your skin will deform around the point of the nail, and so the area over which the nail acts might be larger than you think. But let’s say its about a millimetre by a millimetre, which is a millionth of a metre squared. That gives a pressure of about 1 N divided by a millionth of a metre squared, or about a million pascals.  That’s not so big when you remember that air pressure is about a hundred thousand pascals – it’s only ten times this.

Think also about the pressure on your feet when you stand on tiptoe – or when you run – when the whole of your weight is supported by a small area of a single foot. A rough estimate gives me a similar sort of pressure to what the bed of nails will do.  Your skin doesn’t get ripped to shreds when you run, so then you wouldn’t expect it to on the bed of nails.   And I can vouch for that.

So, if you get the opportunity, try one – it’s fun.

Pseudo-science in high places Marcus Wilson Feb 08

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Why has our prime minister taken to wearing an ‘energy-enhancing’ bracelet?

Fashionable – maybe (I saw someone wearing one at university today – not someone in the science faculty I should add); Demonstrating a sound knowledge of science and its potential to address the world’s big issues  - nope.

You readers in Wellington – get round to the Beehive now and tell him where he should put it.

I do hope that  the new Science and Innovation Minister doesn’t follow his boss’s lead or I shall know for sure that this country is doomed.

 

Science Faction – a great story Marcus Wilson Feb 04

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Have a read of this great short story by Jennifer Ouellette.  The Scholar and the Caliph, on www.physicsworld.com.

Note the scientific method at work – "I will make myself the enemy of all I have read, attack the old ideas from every angle and dismantle all that do not pass my tests until only the truth remains".

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