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February 2010 Archives

Physicists don't usually have to put too many proposals before ethics committees in their working lives. (For the uninitiated, in simplistic terms an ethics committee is where a proposal for an experiment on/involving animals and/or humans will be discussed, to see if it is 'appropriate'. Universities are full of them, and my biologist / psychologist colleagues know them well.) Compared with other forms of science, physics probably has rather few ethical dilemmas.   But I've had one this week.   I'll be deliberately vague, but hopefuly you should get the picture.

I've been asked by a reputable  journal to review an article (let's call it 'A') as part of the standard peer review process.  What are my thoughts on its content and quality, etc.?   Now, I have a look at the article in question and I find that the authors refer heavily to another article (let's call it 'B'), in a journal that I haven't heard of.   Thanks to the magic of the internet, I quickly retrieve 'B', and have a look at it.  No problems so far, but I'm now interested in finding out a bit more about the mysterious journal in which it is published.

The mighty Google works a treat - not only do I find the journal's website, but, more interesting, up comes a lot of links to blogs where this journal's name is used in the same sentence as 'quack' and 'pseudoscience'.

Now, here's the problem. My job is to review article 'A', not article 'B'.  My review of 'A' should be on the merits of article 'A' alone. Shouldn't it? The fact that the journal where 'B' appears has been discussed in a fairly savage light on many science blogs should not influence my thinking as to whether 'A' is a piece of quality science. (?)  After all, blogs are not necessarily reliable (Says he who is writing a blog) - but they are in a sense 'peer reviewed' - that's what the comments do.

 So, what should I do?  Decline to review the article? But that just passes the problem to someone else. Try to get one bit of my brain to ignore what another bit knows? Tricky one this.

I suppose one thing it shows is how difficult it is for anyone to make a truly independent judgement about anything.  Any background knowledge starts to influence the way you see something. 

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I spent yesterday afternoon in a seminar discussing how my teaching can be analyzed for its effectiveness. One much used word is 'appraisal'.   Students may recognize that as meaning those annoying questionnaires that get thrown in front of them in the last two minutes of the final lecture of the year, in which they need to answer questions on the content of the paper and the performance of the lecturer. There's a vague implication that the university wants to know from its students how they feel about the teaching they have received, but it's not often made clear.

It was very interesting to learn yesterday exactly how different lecturers use the appraisals.  Students might be in for a shock here. It depends very much on the lecturer.  Some lecturers carefully go through every form, pull out the major themes from student comments, think how they can improve and make changes for next year's teaching.  Then, next year, they pick their appraisal questionnaire questions carefully so they can assess whether their changes have been effective.

But some lecturers do nothing with them (other than maybe check their overall score isn't too bad.)   All that time the poor student has spent identifying three ways in which the lecturer could improve, etc - the lecturer may choose not even to read it, let alone do anything about it.

Also, something that struck me this morning, is that the appraisal questionnaires that we gave our students here at Waikato in 2009 are not very much different from those I had to fill out as a student in Cambridge in 1989.   Twenty years have passed since I first sat in lectures and, on the face of it, not much has actually changed in terms of how the quality of teaching is reviewed (or not).  I now wonder what happened to the forms I did back then - did anyone take notice?  

But there is actually, as I'm learning, a huge amount of research on how to evaluate your own teaching effectively.  So why do we seem to focus so much on those questionnaires? 

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There was a short piece on the television news last night about the 'Taser' weapon now being used by the NZ police force.  I always listen carefully to popular media when they discuss electrical things, since there is a quagmire of terminology that is often used incorrectly.   This time, however, I didn't pick-up incorrectly used terms - "50 thousand volts" was mentioned, but fortunately not in the context of 50 thousand volts of current, or 50 thousand volts flowing through it, or a power of 50 thousand volts.  Well done TVNZ.

One gripe though, the fact that it is 50 000 volts is only half of the issue. A Van der Graaf generator, as loved by all teachers of physics, (especially those with long hair) will happily get to hundreds of thousands of volts and pose no threat to anyone, other than the odd 'zap' that you wish to inflict on your students.  The point is that the current delivered by a Van der Graaf generator is tiny. Contrast that with the mains supply. It's only 230 volts, but is designed to deliver large quantities of current.  That's fine if the device on the end is your electric kettle or heat pump, but if it's you then you could be in trouble - much more so than getting a controlled shock from a taser.  (Not that I would volunteer to experience the latter.)

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We bought a vegetable juicer recently.   At one end you feed in all those delicious carrots and corguettes that have been growing nicely in the vegetable patch, and at the other end comes out carrot and corguette juice.  Get the right combination of vegetables, and it's a nice drink. (I don't recommend kohlrabi though. Actually, we haven't found anything nice to do with our kohlrabi other than adding it straight to the compost bin - the trouble is we planted rather a lot of it - if anyone has any tips they would be greatly appreciated)

 Our juicer is a 'centrifugal' type.  That means the veggies get ripped apart first of all by a rotating blade with little piranha-teeth on it, then the bits get thrown against a mesh where the centrifugal force squashes the juice out of the veggie-piece. The juice flows through the mesh and then is collected, whereas the bits make their way to the top of the revolving bit (which is wider at the top than the bottom) and are then thrown out and collected elsewhere.   Very efficient, and very viscious.   The warning about not inserting your fingers into the machine is there for good reason.

I'm not sure just how fast the centrifuge bit rotates, but it is certainly beyond the ability for the eye to 'see' the movement - everything just blurs into one. So I would say it is at least 20 times a second, possibly a lot more.   It has a radius of about 5 cm or so.   A little bit of physics calculation tells me the centripetal acceleration of a lump of carrot at the centrifuge rim - namely 4 times pi squared times rotation rate squared times radius.  (The acceleration is equal to the angular rotation rate squared times the radius.)   So we'd have 4 times 3.14 squared times (20 per second) squared times 0.05 metres which comes to about 800 metres per second squared. 

Compare this with the acceleration due to gravity  of about 10 metres per second squared.   The veggie-lump experiences about 80 times this. I suspect this is a conservative estimate.  So it gets squashed very nicely.

N.B.  No apologies made for referring to 'centrifugal'.  See  http://sci.waikato.ac.nz/physicsstop/2008/12/going-around-in-circles.shtml and the xkcd cartoon below.

Centrifugal Force

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Following on from yesterday's discussion of the paper by Gire et al. I'll remark on one little aspect of this study that physics teachers and lecturers need to take note of. (Well, in my opinion they do, and I've got a steadily increasing pile of literature to back me up on this).

One of the questions that was asked of the students was "When I solve a physics problem, I locate an equation that uses the variables given in the problem and plug in the values".  Now, I would say that is not a good approach. No no NO NO NO! That approach yields no understanding to the student about what is going on.  But in the sample group, about 70% of first year physics majors, 80% of second year physics majors, and 90% of first year engineering students agreed with that statement.  The authors describe this worrying result nicely:

The unfavourable responses of year 1 and 2 students are striking because it suggests that students in the first two years of undergraduate study find the plug-and-chug stategy to be productive in solving physics problems

What this tells me is that we (that is, the teachers) are setting the wrong kind of problem, even in second year physics.  (By year 4 only 40% of the students agreed, and there is some comfort to be had that 0% of graduate students thought this approach was the one to take. The message that physics is not about sticking numbers into formulae gets across in the end, but it takes a long time)

When I set assignment and exam problems, I try to do so in a way that assesses the students' knowledge of the underlying concepts, not their ability to choose and manipulate an equation.  But setting this kind of plug-it-in problem is pretty ingrained - for example it permeates many university physics textbooks, and it is hard to prise myself out of that mode of operation. If we ask questions that lend themselves to the 'plug-and-chug' or 'stuffing numbers into formulae' approach, we only have ourselves to blame when our students hit third year without understanding  the physics concepts that we thought we taught them.

Incidentally, the NZQA scholarship physics exam is a great example of setting questions that probe a student's understanding of physics, rather than their ability to pick equations of a rack. If you are thinking about doing this exam - and agree with the statement "When I solve a physics problem, I locate an equation that uses the variables given in the problem and plug in the values" you will be in for a very big shock. 

 

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As part of my reading for the Postgraduate Certificate in Tertiary Teaching (henceforth known as the PGCert(TT) )  I've come across this article by Gire et al. on how physics students think.   The study looked at how closely the physics-thought-processes of undergraduate and graduate students aligned with the physics-thought-processes of practising physicists.    In other words, do students studying physics think like physicists?

To do this the authors studied students taking physics at university (be they physics majors or doing physics as part of another programme, e.g. engineering students),  and asked them a set of agree/disagree questions that exposed how they thought. For example: "When I solve a physics problem, I locate an equation that uses the variables given in the problem and plug in the values"; "In physics, it is important to make sense out of formulas before I can use them correctly"; and 'There are times I solve a physics problem more than one way to help my understanding".   I would answer these questions: disagree; agree; agree; in that order.

Now, there are a couple of interesting findings from this work. First of all, students who enter first year wanting to major in physics enter the classroom substantially more expert in their thinking than those wanting to study engineering. Perhaps that's not surprising - those who think like a physicist want to study physics. Secondly, students maintain this level of expertise through 2nd and 3rd year (show no improvement or loss), but improvements are significant once students reach 4th year (in this study the physics degree in question was done over four years) and there are further improvements for graduate students. 

 This prompts some questions - are the first three years in this degree doing very much for the students, and are there problems with the way physics is taught to engineering students?  These have significance for the way I teach - my second-year solid state physics class after Easter will mostly contain engineering students, not physicists, but they are being taught by a physicist (me). Should I change the way I teach to account for this? And how?

Gire, E., Jones, B. and Price, E. (2009) Characterizing the epistemological development of physics majors. Physical Review Special Topics - Physics Education Research 5, 010103. 

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I've spent most of the morning grappling with a bit of troublesome mathematics.  I can tell that I've had enough, because I'm starting to see greek letters tango with roman ones across the computer screen before raising themselves to inappropriate powers and differentiate themselves into oblivion, and graphs of noisy data that are beginning to look suspiciously like Mt Pirongia...I think a change of topic is called for for the afternoon.

pirongia_change.jpgFortunately, there is our first Cafe Scientifique of the year tonight, in which my university colleague Adrian Pittari will be talking about pyroclastic flows from some of the world's more exciting volcanic eruptions (well, exciting if you viewed them from an appropriate distance). Should keep my mind off the maths for a while.

 (P.S. The pink line is not REAL data - I made it up to give me something relatively mindless to do over lunchtime)

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It was nice to hear this morning that someone actually has won the America's cup, and there is now the prospect of getting back to some proper racing again instead of slugging it out in a courtroom. In the end it was superior technology, rather than a superior legal team, that won the day for Oracle. (Though the two may not be entirely unconnected.) Oracle simply had the fastest boat - and no amount of skill by Alinghi could overcome that advantage.

It's another example of how sport is more and more dominated by science and technology. Gone are the days where the winning was down to superior strength or skill, now it is down to having the best equipment, whether it is the rugby jersey that an opponent can't grab hold of, a slippery swimsuit, or a correctly tensioned tennis racket.  OK - I exaggerate - you can't expect me to beat Roger Federer simply by giving me a good racket to play with - but give Federer a 1950's racket and I bet most of the other top players would knock him off his pedestal relatively easily.  (There's an intruiging thought - someone could sabotage his rackets - might be the only chance anyone has of beating him in the near future....)

 Of course, the best equipment costs money (especially in sailing, where the cost of the boat can on occasion exceed the cost of your lawyers) which is just one of the reasons why sport is such big business. 

Sometimes sports rules have to change (or be interpreted on the hoof) to cope with changing technology. (Anyone remember Dennis Lillee's aluminium cricket bat?) It's not just for the players - the introduction of video replays in sports like rugby and cricket was invetiable given the mockery they made of some umpiring decisions - and the use of Hawkeye in tennis is a step forward in my opinion.   

I await with interest to see what as-yet-undeveloped technology will be commonplace in next twenty or thirty years' time.

 

 

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This year, I've finally decided (more accurately, finally got around to doing it) to undertake a Postgraduate Certificate in Tertiary Teaching.  In plain English, that means do some training that actually prepares me to teach at university. "What?" I hear you say - "You mean you haven't got any qualification to teach at university?".  Nope. And the same is true of most lecturers, in most universities. They are appointed because they are good at their research, and it is just assumed that if you stick them in front of a class of students the students will somehow come out better off. And, as every student or ex-student (i.e. me) knows, sometimes it happens, and sometimes it doesn't.

Anyway, as part of the PGCert (Tertiary Teaching), I'm thinking about ways that I can know whether or not (probably the latter) my students have understood what I have been teaching. A brief look at the literature shows that there are numerous ways of doing this in the context of physics.  Very crudely, you can test your class before you teach something, and test them again afterwards.  The improvement equals their learning.

Or does it?  First of all, learning, if not exercised, diminishes over time.   Test them a week after you taught it, and their performance may be good. Give them a similar test at the end of the semester, or in the next semester, or in two years' time, and the scores will be lower. However, the learning doesn't usually decay to zero - usually something sticks for good.

But the thing that grabbed me on reading this recent paper by Sayre and Heckler is the effect of 'interference' by a similar, but different topic.  After learning about the topic of interest (in this case electric fields) the students do well in a short test.  But a couple of weeks later, they do poorly, not because of the passing of time, but because, at that time, they are being taught another topic that they are confusing with the first (in this case electric potential). Tested again later on, when the confusing interfering topic has been taken away, their performance has risen again.

So it's not all that easy to assess whether learning has taken place.  With this example, have the students REALLY learned about electric fields properly? One could perhaps argue that, if the learning had been deep enough, their understanding would not have been confused by a related, but different, topic.   One could perhaps test them yet again, on both electric fields and electric potential, at a still later date, and see if the confusion has remained.  What I thought would be a very simple procedure suddenly gets rather complicated.

Sayre, E. C. and Heckler, A. F. (2009) Peaks and decays of student knowledge in an introductory E&M [electricity and magnetism] course, is the effect of 'interference'. Physical Review Special Topics - Education Research, 5, 013101  

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I keep a list in a notebook about possible things I could write a blog entry about. When I see something in the media, or something happens at work, anything to prompt me to think about a particular area of physics really, and I scribble it down and may choose to inflict it upon the world at a later date. For example, I thought I got a good one a couple of weeks ago when I learned about an impending mass-overdose on homeopathic medicine as a protest against it being stocked by chemists in the UK.  Then I discovered it had been extensively covered on about six thousand science blogs already.  I didn't add to that list. (In case you are interested, and have somehow escaped reading about it, have a look at the campaign website on http://www.1023.org.uk/ )

On my list is 'dynamic equilibrium'.   I put in on there after writing my blog entry about feeling 'cold' radiating off something - it's a very much related topic, and an important one in physics and chemistry (and I think probably biology too), but I haven't got around to talking about it.  I'll give you a physics-coloured example.

We say things are in equilibrium when thing appear to stay the same. For example, the telephone in my office is in thermal equilibrium with the air in my office. That is, the temperature of the phone is the same as the temperature of the air (roughly speaking). But that's not to say that nothing is happening.  Two objects will always exchange heat with each other - if they touch then through conduction, if there is a fluid involved then through convection, and if there is a line-of-sight between them through radiation.  So the air is transferring heat to the telephone. Likewise, the telephone is transferring heat back to the air. But the rates of transfer are equal. Consequently the telephone gains as much heat as it loses, and its temperature stays the same

Migration is another example. The population of a particular town might stay the same from one year to the next, but the people in it do not.  People are born, people die, people move away, and people arrive, but the number being born and immigrating equals the number  dying or emigrating. Overall, the town may not show any changes at all (the 'equilibrium' bit), but the components that make it up (the people) are constantly changing (the 'dynamic' bit). 

Really, the important thing for physics is although macroscopically (on a large scale) things might appear to be constant, look on a small enough scale and they are not.

 

 

 

 

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I was reading this weekend in January's physicsworld some curiously contrasting articles on the state of physics funding in various countries. The UK has recently announced some serious cutbacks to their international collaborative projects, in an attempt to claw back 40 million pounds that was mis-spent a couple of years ago following an accounting error.  Whoops. For example, there will be the complete withdrawal by the UK from my favourite Large Hadron Collider experiment, ALICE.

Meanwhile, Japan's physicists are nervous after some major budget slashing by its government. There are fears that major research facilities there, such as the Spring-8 synchrotron in Hyogo, will be under the knife, perhaps to fund the new government's ambitious election promises.

However, across the Pacific, in the US, things are looking a bit rosier, at least if you work in the 'right' bits of physics. The National Science Foundation will get a 7% increase on its budget, and NASA a 5% increase. And just across the channel from the UK, France is dishing out a 35 billion euros stimulus package to its university and industy research programmes.

And in the same issue, there's an article looking at where the 'top' 158 physicists in the world began their research, and where they are now.  Of these, 30% were born in the US, but 67% of them are based there now. And those based in the US have about a 16% higher 'h-index' (a measure of a scientist's research output) than those based elsewhere.

For what it's worth, I've also done up a quick count of the job adverts in the back of the magazine. It (if you haven't guessed) is a UK magazine, and out of 13 adverts for jobs, four of them are based in the UK, and nine elsewhere in Europe.

I'm not sure what conclusion I should come to from these ramblings (safest not to come to any conclusion given the selectivity of my data source), though it does indicate what most physicists know already - if you want to do well in physics research, you have to be mobile. And particularly mobile in the direction of the United States of America.

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In an earlier post I made the outrageous claim that three is a working approximation to infinity. If you thought that was ambitious, have a read of the following extract from an abstract that I discovered this morning while doing a bit of literature searching as part of my research. It's a great insight into the mind of a theoretical physicist.

 The present work studies the effect of additive noise on two high-dimensional systems. The first system under study is two-dimensional, evolves close to the deterministic stability threshold and exhibits an additive noise-induced shift of the control parameter when driving one variable by uncorrelated Gaussian noise...

Reference:   Hutt, A.  Additive noise may change the stability of nonlinear systems. Europhysics Letters, 84(3), 34003. (2008).  DOI 10.1209/0295-5075/84/34003

Did you spot the implication?   The author is implying that a two-dimensional system is high-dimensional.  In other words, two is a big number. Now, I don't know about you, but I live quite happily in three dimensions. This large number of dimensions doesn't cause me any problems. But, when it comes to analyzing how systems behave, there is actually a massive increase in the diversity of behaviour when we move from a one-dimensional system to a two-dimensional system. (By a one-dimensional system, I mean one that needs just one variable to descibe it, and a two-dimensional system is one that needs two variables to describe it. In this sense a pendulum is a two-dimensional system. To describe its state you need to know the bob's position and velocity.)  Two dimensions are pretty diverse, really.  The pendulum can sit still and just hang under gravity, or it can do its characteristic swing back and forth, but that's not all. If you whirl it to start with it can go round and round in circles, or, if you start it pointing vertically upwards and ignore friction, it will drop (but which way?), swing round, and end up back exactly where it started.

The physicist, and perhaps more so the mathematician, will then make great strides forward, and happily move from two to three, four, ten and even infinite dimensional systems, which are just further examples of high dimensional systems.  Visualizing what's happening becomes a bit tricky, but, in practice, once you've got used to the idea, there is not a lot of difference between two and ten.

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Every time I blink I seem to get another email from a science journal that I haven't heard of inviting me to contribute to their most prestiguous publication.  It's all very flattering to get emails telling me that as a world leader in organic chemistry research I am invited to contribute to their well-read journal, but I am beginning to wonder about the validity of the science-journal based system of documenting and disseminating scientific research.   (NB In case you are wondering, I am NOT a world leader in organic chemistry research, but send out the email to enough people and you'll hit one who is...)

When I was a PhD student in the early 1990's (cue soppy nostalgic violin music)  I spent a lot of time in the library looking at journal articles.  Every month, a publication called 'physics abstracts' would appear in the physics library in Bristol - a huge thick thing that contained short summaries of research that was published in physics journals that month. It was nicely indexed by way of topic, and I could browse through it pulling out articles that might be relevant to my research. I'd then go and get the journal volumes off the shelf, find those articles (or maybe have the librarian order them for me from another library) and read them. Some of them would be useful, others not, but in this way I kept up to date with relevant work.

Now, I don't leave the office.  I can search the library catalogues, pull off PDFs of relevant articles, check which subsequent articles cite them, all without leaving the comfort of my office chair. The University of Waikato library has a fantastic new extension to it but I am yet to see the inside of it - I just haven't had cause to actually go down there to consult something that is not available online.

All that is great, but it has led to an absolute explosion in information. The ISI Web of Science, a popular tool for searching publications, looks at about 10,000  journals.  That's a huge number. I dread to think how large that 'physics abstracts' publication would be now. Finding a piece of relevant work can be like looking for a needle in a haystack of irrelevant information. I am forced to wonder just how many of these journals actually contribute significantly to the advancement of science.  How much work is never read, and how much gets repeated in several places across the world because the various groups are unaware of each other's existence? This is where conferences can be very advantageous - by putting people who are working on similar things together, in one place, it is much easier to become aware of who in the world is researching what.

More information is not necessarily better, but more information is what we are getting.

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According to the fount of all knowledge  -  Wikipedia ;-)    - the only three countries not to have adopted the System Internationale units are Burma/Myanmar, Liberia and the United States of America. 

I can't help thinking that there is something deeply significant about those three countries falling into the same group, but I can't quite put my finger on it.

One of my big thick first year university physics text books has in large red writing on the back cover - "Not for sale in the United States".  I assume this is because of the SI unit issue.  I also assume it will be hard to find this book in a bookshop in Monrovia, though I haven't tried looking for it there.

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As any physics student knows (or should know), units are important things. By 'unit' I mean a measure of the kind of quantity you are dealing with. So if it's mass, then a kilogram, a gram, an ounce, etc are all units;  if it's distance, then kilometres, light-years, feet are all units.   Units are essential - it's not very helpful to say that the distance from Hamilton to Auckland is 130. If I had a dollar for every time I've had to yell 'UNITS' at a student  who has missed them out, I'd be ... well, maybe not a millionaire, but at least able to affford one more cup of coffee a week during term time.

 Units are very useful too.  Last week I was trudging through some pretty intense algebra for some of  my research work. The potential for mistakes is huge, and it's difficult to be sure you get the right answer out at the end. (It's research, which means, amongst other things, you can't go and look up the right answer in a text book - it's up to you to work through it, and to know that you have worked through it correctly.) Units help in this process because when you have an equation, the units (more formally, the dimensions) must balance. Here's a rather trivial example. 

The distance a ball falls when in free fall is given by the equation s = g t^2 / 2 (g times t squared, then divided by 2). Here, distance is denoted by 's', time by 't', the acceleration due to gravity by 'g'. Let's check the units. On the right-hand side, 'g' is an acceleration, so would carry the SI unit of metres per second squared.  't' is a time, so would carry the unit of seconds (in SI). And 2 is just 2. No unit there. So on the right hand side we have

metres per second squared, times seconds squared

which is of course just metres.  And that matches the unit of the left hand side, which is a distance. That example isn't too taxing, but when you get nasty equations that need manipulating and solving it is a very good check that things are reasonable. (Of course it can't be used to spot all mistakes - if I'd written s = g t^2 / 3, this method wouldn't have picked up a problem.)

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