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February 2012 Archives

One of the strange things about blogging is that you are carrying out a (usually) one-way conversation with unknown people. Now, I know there are several people who read this blog regularly who will comment regularly, and although I have never met many of them I feel I am 'getting to know them'. I also know there must be many people who read the blog regularly and don't comment at all - or very sparingly. It was very curious to meet a couple at the NZ Institute of Physics conference last year - they read my name tag and instantly knew who I was, and let me know that they are PhysicsStop followers, though I didn't know them from Adam.   It was hard to know how to react!

So, then, its kind of strange to put this on a blog, but for those who don't know, the next big event in my life is penciled-in for the third week in June, when I become a father for the first time. Very exciting stuff, and I'm sure the child will be a source of great blog-fodder in the years to come (and a source of other stuff too, some no-doubt pretty yukky), as he or she develops into a physicist. (I wish.) I guess my entry-rate might take a dip about then (or maybe it will rise!) - but you'll know why.




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There's just one more week of 'freedom' before the teaching deluge starts next Monday. As many people have pointed out to me, this is really, really late in the year, and I must have enjoyed a really long summer holiday with nothing to do. I wish. Not being semester time doesn't mean that an academic spends all day at the beach.

One of the things I've been racing through this summer is finishing a piece of research and associated journal article.  It was submitted recently to a very well-renowned journal, and today I got the feedback on it from the reviewers.

Firstly, I should point out that this is a journal where the editor, or a sub-editor, sifts the articles received for significance and relevance, before sending out to reviewers. So a good percentage never get to 'review'. The fact that this piece of work got through this first stage already is some positive feedback on it.

The article went to three reviewers. The first, broadly speaking, liked it, and raised just a few minor points. The second has come back with various awkward but reasonable questions, and its clear he or she hasn't yet filed it in that small cylindrical filing cabinet that inhabits the corner of every room. Unfortunately, however, the third one indicates that it is worth its weight in Greek government bonds (Not exactly the words used, but that's the basic impression given.)

Hmm. Such a mixed combination of good and bad in a review isn't actually all that unusual. It's part of doing science. Other people look at your work, ask you awkward questions; you then address these with the result that the finished article is better and the work is more robust. It doesn't guarantee that it is correct, but it does ensure that it is of quality. I've clearly got a bit of work to do, and I don't think I've got time before the students arrive back (which may mean it has to wait till Easter) but that's what doing science involves. So although peer review can be brutal, and my first reaction is to despair, it won't be my final reaction. I like to think that peer-review is to science what democracy is to politics - the worst possible way of doing things except for all the others.




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I've often commented on the failure of students to apply common sense when calculating physical quantitites. For example, perhaps I ask them to calculate or estimate the pressure exerted by a car tyre on the road (with the car attached to the tyre) and they punch their figures into a calculator and get 10.4 pascals. (For those that aren't familiar with the physics needed here, just note that ten pascals is WAY too low - for example, atmospheric pressure is about 100 kilo (thousand) pascals.)

What's happened is that the students have made a mistake somewhere - perhaps they've hit 'divide' rather than 'multiply' on their calculator, or neglected to account for 'mega' meaning 'a million'. That happens occasionally and is excusable. What isn't excusable is when the incorrect answer is written down without a thought towards common sense. Just a tiny bit of thought will tell a physicist that the pressure exerted is much higher than 10 pascals, which is what you'd get by spreading out a kilogram mass of something over a metre sqaured of surface. An experienced physicist such as myself would never make such a blunder.

Well...except...Umm...maybe...just occasionally.  Currently, my church (not MY church, but you know what I mean) is considering various renovations, and I've been involved with looking at the options and prices etc. One of the things we'd like to do is to remove the pews and replace them with nice, new, comfortable chairs. The chairs that our pastor is eyeing up are 80 dollars each - when you multiply that by two-hundred-and-something we get a total price of about 18 thousand dollars. It ain't cheap. Anyway, on Monday night I was putting together some powerpoint slides for the congregation on the renovation and how to fund it, etc, and, with the numbers, eighty, eighteen, and thousand sloshing around in my head I wrote down $80k as the price it would be. Understandable, maybe, to make that mistake (particularly after a hard day at work doing general administrative stuff), but not excusable to write it down without thinking. Eighty thousand dollars for some chairs is just a little steep. Fortunately I sent my slides to some others for checking first, before it resulted in major embarrassment.


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Breaking news...(ish)...Well, only a few hours old...

Maybe the faster-than-light neutrinos are caused by a dodgy connection.

Einstein can sleep easy again.


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This morning I was over in Tauranga giving a talk to the Continuing Education group (i.e. 'older' people) on the CERN - Gran Sasso neutrino experiment. (For those interested, you should be able to download the full paper on this work  here.) My philosophy is that no piece of work is too difficult to explain to the general public - by which I mean anyone between the ages of 3 and about 103 - though this one taxed me a bit more than most.

The talk went well - I got some interesting questions and some good feedback - and even learnt a couple of new neutrino jokes. This is the best of them:

The bartender says "Sorry, we don't serve neutrinos here". A  neutrino walks into a bar.

On an almost unrelated note, I thought I'd share this is an example of really bad design. I've recently received a new work computer (hooray!) and for the last two weeks it's sat in a docking station on my desk at work, since I haven't had cause to take it elsewhere. Last night, in preparation for my Tauranga talk, I tried to remove it from the docking station. That was easier said than done. After pressing buttons, sliding sliders, rotating sideways and peering between the gap between the computer and the docking station for clues, I eventually struck it lucky and the computer popped out. Then, lo and behold, I see the instructions on how to release the computer from the docking station - they were on a sticky label attached to the docking station such that they were obscured by the computer when it was attached.

In other words, I had to remove the computer in order to read the instructions on how to remove it. Who decided to put the instructions there?

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Unfortunately I didn't get to the cricket last night - I wasn't feeling well - and missed Richard Levi's demonstration of how to hit sixes Would have been fun to see.

It occurred to me at the weekend that I've managed to avoid the rain in the last week. While its poured down in Cambridge, I've been at work in Hamilton - and Hamilton has managed to get a soaking outside normal work hours while I've been in Cambridge or elsewhere. Sooner or later the thunder is going to catch up with me. In the meantime, I'm not complaining.

That's one of the features of this kind of weather pattern - you just don't know where the storms are going to pop up. The met-service people can tell us that they will pop up, and someplace is going to get drenched,  but just where and when is anyone's guess. The atmosphere is 'unstable' - and that word means something very specific in physics. Specifically, the equilibrium state, where the heat, moisture, airflow etc  is shared out equally over an area (i.e. everywhere in Waikato, say, is a similar temperature and humidity) isn't going to stay like that. If we start with the equilibrium state, and change it slightly, it encourages further changes to occur. So we end up with pockets of rising air, leading to rain clouds forming, and pockets of falling air, which give us dry conditions, rather than all the air sitting still. 

There are many examples of unstable that we can see - for example, the ridges on metalled roads, patterns in sand on a beach, and bunching of buses along bus routes so that you really do wait ages for one and then three come at once.  In our work on computer modelling of the cortex, we can also see spatial and temporal (time-varying) instabilities in the firing rates of collections of neurons. This can lead to patches of a cortex having greater activity than other patches (i.e. the equilibrium state, with activity shared out equally over all areas of the cortex, doesn't occur) which is similar to what is seen in practice - for example with electroencephalography and MRI.

So when something has an equilibrium position, we have to be careful as it doesn't mean that the equilibrium will be the state that the system takes.

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Tuesday evening was a very enjoyable night spent at the NZ versus Zimbabwe Twenty20 cricket at Seddon Park in Hamilton.

I got to watch the New Zealand fast bowlers serve up boundary-fodder for the aptly-named  Hamilton Masakadza and Brendan Taylor, who didn't disappoint, wafting Mills and Bates and co over the square-leg boundary with monotonous regularity.  The Black-Caps will certainly need to teach their bowlers what a good length is before Sunday's match against South Africa, or the Hamilton fans won't be going away happy.

Watching the batsmen was a reminder that against a fast bowler you don't need to hit a cricket ball hard to get it to clear the boundary - you just need to hit it on the right place on the bat at the right moment. The ball comes at you with plenty of momentum - your job is to exploit it. If you get an almost elastic collision with the bat (and that depends on where on the bat the ball hits) then it will come away with the same velocity - maybe a bit more if you put in a little effort -  and you can divert it over whichever boundary is most appropriate. Not hitting the ball hard but still sending it rocketing to the boundary is a skill that Sachin Tendulkar really is a master at.

The change in momentum of the ball is equal to the impulse the bat provides to it - that's the force times the time of the collision. Since momentum and forces are vector quantities, to hit the ball back over the bowler's head requires more force than pulling it over or behind square-leg - since you are diverting its direction a lot more with the former. If you bowl too short, on a leg stump line,  particularly if you are bowling fast, then the latter is just too easy for a good batsmen, and the sixes will start mounting.

I'm looking forward to seeing the South African batsmen at work.



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Friday's Herald, page 15. In an article on Lake Vostok, the location of this mass of water is described as "3.8 km beneath the surface, about 1300 km east of the South Pole". Go figure.

Unfortunately the online version is somewhat trimmed down and misses this plainly ridiculous piece of information.  

Google Earth tells me it's 77 degrees south, 105 degrees east.

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I've been to a couple of really good seminars this week - one by Waikato's own Noeline Wright, from the Faculty of Education, and another from John Gilbert, a Science Educator at King's College London. Although the focus of the two talks was different, they both touched on a similar theme, namely that one of the best things you can do for your students is to teach them how to ascertain the quality of any information they might access.

Very few of us become scientists, even amongst those who do science in the last couple of years at school, but all of us will have to make decisions based on information that's available, and many of these decisions will have some kind of science base to them (e.g. do I try this new medication?, will replacing my car save me fuel costs?, what benefit will insulating my roof actually give me?...)

There is a huge, exponentially growing lot of information that is readily accessible to most people. Some is of real quality, other stuff is just trash. How do I know which website to trust and which to have a good laugh at?  Experience that Noeline and John have had suggests that secondary school students, and even first year university students, don't have the skills to distinguish the two. We're talking skills like identifying who is writing the information (e.g. are they trying to sell you something?), what agendas are being pushed?, what evidence is  presented for the claims? what other information is out there? Given these skills will be way more useful to everyone than, for example, being able to solve Schrodinger's equation in a quadratic potential - and that's true for physics students as well as the general population - why don't we actually teach it?

You should be frightened by this: people such as these first year students will form our government in 30 years time. Imagine a cabinet of ministers whose primary port of call for information is Wikipedia. (The thought does occur that certain members of the current cabinet probably get their briefings from Wikipediea, but I shan't follow that line of thinking any further...)

Noeline showed some amusing but in some cases shocking examples of websites that the students don't  'see though' and can accept as gospel truth without any real thought. This is an amusing 'spoof' example, but there are plenty out there that are seriously pushing some dodgy agenda (e.g. holocaust deniers) and some that are just out to get your money.

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This story from Yahoo is hilarious - about a policeman who chased himself for 20 minutes. In a nutshell, a CCTV operator sees a man acting suspiciously, unaware that it is in fact a plain clothes policeman. He radios through to the police, who pass the message on to their nearest policeman to the scene, who is, of course, the man himself. And off he goes, to find this suspiscious man, unaware that it's himself, guided by messages relayed from the CCTV operator.

WIth a bit of physics experience, I can see how the chase would unfold. The officer is in Smith Street, say, but he gets a call on the radio to go to nearbyJones Street. That's because there's been a bit of a delay getting the message to him - Jones Street was where he was two minutes ago. When he gets to Jones Street, and sees nothing, he gets told that, actually, the man is in Smith Street - again, where he was two minutes ago. Back to Smith Street he goes, to be told that he should be in Jones Street, and so it continues.

I don't know that's exactly how it went, but it's plausible. The thing that's controlling the behaviour here is the fact that the feedback is delayed. When this happens it can often lead to oscillation (e.g. Smith to Jones to Smith to Jones...) It's something that has to be thought about in control systems of aircraft, for example. If the aerilons respond too slowly and too severely to small fluctuations in an aircraft's roll, the aircraft can start oscillating. Not a good situation to be in. There's ways of analyzing just how stable a system will be when it receives feedback, and it's a key analysis to be done in many situations. The CCTV one is a comical one of little significance, but, in many modern systems full of electronics, the systems engineer needs to have done his or her job properly or you could be in trouble. 

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A couple of weeks ago I found this brief article in the newspaper about Vesna Vulovic, who perhaps holds the record for the longest non-fatal fall - a staggering 10 km after a midair explosion on a plane in 1972. I say 'perhaps' because the circumstances of the fall are disputed - it is possible that the plane, rather than being at cruising altitude, was attempting an emergency landing and was only 800 m above the ground when it was mistakenly shot down by a Czechoslovak fighter.

Unfortunately Vulovic herself is no help in determining the circumstances since, unsurprisingly considering her considerable injuries, she remembers nothing of the flight.

So the Guinness Book of Records no longer records her feat, and her status as a heroine is in question; so says the article.

Now, hang on a minute shall we? It appears that the  Independent newspaper is suggesting that surviving a fall of 800 metres is a trivial occurrence. I beg to differ on that one. A little bit of physics application would say that surviving the impact from an 800 m fall is every bit as remarkable as surviving the impact of a 10 km fall. Eight hundred metres is not a trivial height - it is plenty of distance for one to obtain ninety-odd percent of  terminal velocity - that is for the force of gravity pulling you downwards to be balanced by the force of air resistance pushing upwards. Once you are at terminal velocity, your impact speed will be the same, whether you fall 1 km, 5 km or 20 km.

There are other factors to consider, however. At 10 km it would be decidedly chilly, especially in Eastern Europe in January. The windchill as you fall at 200 km an hour bear imaging.  Air pressure is much lower, too, meaning that conditions are against you. But in terms of impact alone, there would be no difference.

It's also worth bringing out the old statistic about cat falls - above a certain height (I forget how much, it's a few storeys I think) the cats survival rate increases with height fallen because they have longer to prepare themselves for the landing - though I think this statistic and interpretation is disputed. But the point is that above a certain height, and it's much lower for the pussy cat than it is for the human, the height doesn't add anything to the impact.

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