SciBlogs

Archive June 2010

Group intelligence Marcus Wilson Jun 30

No Comments

Last night I half-watched the programme on TVOne about swarms. (I say half-watched because I was mostly listening to it while doing the washing up). It is certainly fascinating how large groups of fairly simply behaving creatures can have a ‘group intelligence.’ This kind of organization of small units into a larger entity is well studied in physics. Ants are particularly fascinating – an individual ant doesn’t possess a great deal of intellectual capacity, but a whole colony seems to have some extra intelligence of its own.  At one point the programme compared an individual ant to a brain cell, and the whole colony to a brain. Like single ants, brain cells on their own aren’t particularly complicated systems – you can describe them with just a few equations (I know – I do that in some of my research). Basically if you poke them with enough current they ‘fire’, and if two cells that touch through a synapse fire at commensurate times, they can either strengthen or weaken that synapse between them. They can also ‘leak’ a bit of current from one cell to a neighbour. All very simple really. But stick lots together and you have a brain. (It could be your brain).

But here’s where we get a problem with the analogy – we humans are conscious (for 16 hours a day, give or take)  - I know I am as I write this, and I assume you are as you read it. But can a colony of ants be conscious?  I find it hard to believe.  What would that mean for the ethics of putting down poison to kill off the colony that’s taken up residence in your house? Are you killing a being with a high-level of consciousness?   Here’s the problem for neuroscientists – what is it about the collection of cells in your brain that results in consciousness? Basically no-one has a clue. There are some ideas discussed, but getting any scientific evidence is going to be tricky. We can certainly say things like how consciousness correlates to the pattern of firing activity, for example the voltages  picked up on the electroencephalogram (electrodes stuck on the scalp), and anaesthetists will often use the electroencephalogram to give them clues as to whether a patient is actually unconscious, but what is it about these firing events that leads to consciousness? Or what is it about consciousness that leads to those firing events? Or what is the unknown process that influences both the firing of cells and consciousness? I don’t know.

What I’m saying here, is that consciousness isn’t necessarily just a by-product of throwing lots of interacting brain cells together and so we should be a bit careful about saying a colony of interacting ants is ‘intelligent’, if that means we get the picture that there is some conscious thinking related to the colony. 

The Blue Brain project, based at Lausanne in Switzerland, is (in simple terms) an attempt to simulate an entire region of a rat brain on a computer. The idea is that the computer simulation will respond in the same way as the rat brain. But will the computer simulation be conscious? I wouldn’t think so.

As another example, think of plants. My colleague Alison Campbell has described some ‘intelligent’ (and quite surprising) plant behaviour. Plants that hunt, plants that communicate with others. Sounds like the triffids are already here.

Patience in experimenting Marcus Wilson Jun 28

No Comments

I’ve spend most of today in our new teaching lab, grappling with a piece of experimental equipment. Over the break between our A and B semesters (i.e. now) we’re moving our 2nd and 3rd year undergraduate physics lab out of one room and into another. It’s a small part of a large plan to use the available space to full advantage, and it means lots of things are moving about at the moment. A bit like moving house, with our deadline being two Monday’s time, when semester starts, and everything has to be up and running.

For the most part, we can move a piece of equipment from one room to another, set it up, and have it work without too much difficulty. But there are three or so pieces of equipment that are a location-sensitive. The one I’ve been working with today is a NMR / MRI machine.  It’s just a baby – not the size you find in hospitals – but it is an excellent teaching tool – one of the best bits of kit I think our third years get to play with.

Rather than have a huge coil to generate a magnetic field (what you need for nuclear magnetic resonance), as happens in the hospital, this machine uses the earth’s magnetic field. Convenient, yes, but a bit awkward too, because the field in the lab isn’t exactly nice and uniform. Walk around the room with a compass, and you’ll see the needle drift several degrees – there is, after all, a whole lot of steel in the building, and that is going to influence the magnetic fields in its vicinity.  Now, to use the NMR in the lab, I need to know what size of the magnetic field (because strength of the field controls the resonant frequency). Although the old lab and the new lab are close by, the strength of the earth’s field in the two of them proved surprisingly different, and it took me a while to get any signal on the machine at all.

Setting the machine up in its new location is rather like tuning a radio with a poor quality aerial when you don’t know the frequency of the radio station you want, nor do you quite know the direction of the transmitter, in a room with a lot of electrical noise. It takes a lot of patience, looking at different frequencies, until you pick up a little signal in amongst the noise. (This, being a physics lab, is just loaded with electrical noise – that’s another problem).  It’s an example of how, with noisy data, you can still get a ‘signal’, but you need to average over lots and lots of trials to see it. It’s just basic statistics really; the more averages you take (in my case, the more times I sample the data), the easier it is to see a signal buried in the noise, because the noise slowly ‘averages out’ to zero, while the signal doesn’t. But with a weak signal, it takes some time. 

With a lot of patience, I got there – found my NMR signal. Then I could slowly tune up the apparatus to work with that signal, and finally at the end of the afternoon I have it working tolerably well.  But basically it took a day to do it. 

In research, we often need far longer than a day to tune-up our equipment, and a good experimenter will have lots and lots and lots of patience. ( I do not claim for one moment to be one of these – as an undergraduate I chose my papers very carefully to keep practical work to an absolute minimum – and then went on to do a PhD which just involved pen-and-paper and a computer – ironic that I now teach our experimental physics papers). Patience is certainly a virtue for a physicist. 

 

 

The essence of physics Marcus Wilson Jun 24

3 Comments

Exams are looming, and I’ve had a constant stream of students coming to me this week asking me questions.

One question I’ve had has been asked by two students independently, relating to an example calculation done in a text book. The question goes like this: "I’ve been going through this example, and I get the answer 0.159, but the book says its 160. I don’t get it"

To be honest, I’m a bit saddened that students weren’t able to figure this one out for themselves. Experience tells me that when I am a factor of 1000 out, it’s almost always because of an issue with the units – somewhere a ‘milli-something’ or a "kilo-something" has been overlooked. It is what comes from extracting numbers from a question and putting them into the calculator without thinking about what numbers are being used.  And, indeed, if the students had looked at the units the textbook answer was given in, they would have spotted that the book’s 160 mA m-1 is exactly the same as the 0.159 A m-1 the student has. (Here also we have a significant figures issue).

The students’ question says it all.."I get the answer 0.159".  But 0.159 what?  

Units and dimensions are fundamentally key to physics. There’s probably no other area where they are so critical. One could even say that units is what physics is all about. Describing physical quantities. Units are so important that there is a whole area of branch of physics devoted to establishing them in practical terms - metrology – and international committees dedicated to doing such boring (but essential) things as deciding on what one ampere actually means. Without this, physics will fall apart. This is one reason why lecturers like me bleat on about paying attention to the units.

Claims on the electromagnetic spectrum Marcus Wilson Jun 23

No Comments

I wrote a couple of weeks ago about the value of electromagnetic spectrum real-estate. It proved quite topical – as I wrote it I had no idea that Stephen Joyce was about to release an emphatic "no" to requests from the Maori Council for rights to the 4G spectrum (See e.g. the TVNZ coverage of this story).

What’s this about?  Well, when NZ television viewers (which I guess is most of us) are finally forced to throw away their otherwise perfectly good analogue sets in a few years time, and go digital, the frequencies currently used to broadcast the analogue signals (the ’4G’ band) become available for other uses. They’re earmarked for mobile phone and internet, and will be of significant value to the people who have the rights to use them.

So who controls organizations’ rights to use this spectrum (i.e. transmit things)? The government says it is them, and solely them. And I would imagine that’s the way it is in almost all countries with effective governments. A free-for-all of the airwaves doesn’t work; you can’t have two broadcasts on the same frequency in the same region or your receiver will pick up a combination of both, which isn’t likely to be very meaningful.

Apparantly the spectrum has been declared as taonga by the Waitangi Tribunal (implying that there should be some Maori ownership / control of it), but previous governments have refused to recognise this. (N.B. For you non-New Zealanders, taonga, broadly speaking, can be translated as ‘treasure’). In the TVNZ article Joyce is quoted as saying  "Because spectrum was not in use at the time that the treaty was signed [1840] and was not known at the time that the treaty was signed, it’s difficult to argue it was taonga". 

That’s reasonable enough, but one could also argue that just because people didn’t know of the existence of something doesn’t mean it didn’t exist.  If a new oil-field were discovered on Maori-owned land somewhere, one could expect a very reasonable claim to be made by the owners on the contents.  In 1840, no-one knew that this entity (‘the spectrum’) existed (Hmm.. could debate that one, I mean people knew that the visible spectrum wasn’t all there was and that infra-red existed), let alone the potential value of it, but it was still there. Maybe not as a treasure (can you treasure something you don’t know exists?) but certainly as something of value.

One could counter that by saying that the government is duty bound to act in the best interests of its citizens (ha ha, yeah, right)  including Maori, and, in this case, proper development of the 4G band should ensure massive benefit to the country. Since NZ is on the edge of nowhere, a good internet etc is likely to be more useful to NZ than it is to many other countries. And I would like to think that the government is in the best position to deliver on that.

The more I think about it the more thorny this one is.

 

Why conventional astronomy is rubbish Marcus Wilson Jun 21

No Comments

My father-in-law sent me this link at the weekend. It’s to a book published in 1914 (that’s nineteen fourteen, not sixteen fourteen, or nine fourteen), describing how children of the day are being taught lies with regard to the shape and movement of the earth in the solar system.

Does the Earth Rotate? No.  By William Edgell.

http://web.archive.org/web/20080122142029/http://www.litotes.demon.co.uk/dTeR/doesTheEarthRotate.html

It is quite, quite hilarious. It illustrates how, once a person has got an idea in their head (in this case that the Earth is flat and motionless), they will hold to it tenaciously and will distort and misinterpret data that would tell them otherwise, if only they were prepared to look at it at face value.

Edgell makes some wonderfully fanciful interpretations of phenomena that would otherwise tell him that the earth is curved. The fact that ships disappear over the horizon, hull first, is pretty strong evidence of earth curvature. Edgell dismisses this effect as due to sea mist that is thickest closest to the sea surface and therefore obscures the hull first. Funny how he makes no mention of the fact that this phenomenon is most clearly seen on a very clear day, when there is no mist.

New Zealand gets mentioned a lot, presumably because it is at the opposite side of the globe (if you hold to that wrong interpretation) to England. Edgell notes that this fallacious understanding would imply that kiwis are upside down, and asks the reader to think whether this is reasonable.

But the most interesting thing I can see is Edgell’s comment that in New Zealand the pole star subtends an angle of 40 degrees to the horizon. Now, I have lived in NZ for six years or so, and I can say that I have never, ever, ever seen the pole star from here. For good reason. And I don’t expect ever to do so. I can only think that he has misinterpreted a comment from an astronomer about the pole star in New Zealand being 40 degrees below the horizon. (Which is why I’m never likely to see it here.) He has clearly never travelled to New Zealand, or the equator, or, from the sounds of things, very far at all, or he might have noticed just how the stars change.

But, hey, that doesn’t stop you being an expert in world geography, does it?

I wonder if Mr Edgell ever changed his mind later on?

It never works when you need it to Marcus Wilson Jun 18

No Comments

A couple of weeks ago my wife mistook an old glass jug of ours for a pyrex one and poured boiling water in it. The result was quite pretty, with a jigsaw of cracks across the jug rendering it incapable of holding any fluid ever again, boiling or otherwise.

That’s thermal expansion for you. Glass is a failry poor thermal conductor (in this context, anyway); the heat stays on the inside and the inside expands more quickly than the outside and the glass can’t cope with the stresses this induces. Crack.

Last week, a colleague of mine did this as a demonstration in our annual Osborne Physics and Engineering Lectures to local schools.  He chose the cheapest, lowest quality glass he could find from a well-known low-price store. He prepared it beforehand by putting it into ice to get it really cold. But would it break when the boiling water went in? No. Not in front of an audience of several hundred children.

It’s always the way – when you demonstrate things live they never quite work the way they should. But that’s what makes doing this kind of thing fun, and unanticipated failures add to the audience experience. However, during the lecture in question, we did see the successful destruction of several household objects all in the name of materials science, and that was exciting.

 

The context doesn’t change the laws of physics Marcus Wilson Jun 16

2 Comments

No, I didn’t stay up to watch the New Zealand v Slovakia game last night. Based on the grand sample size of one match each, NZ is as good as England. Not sure who that compliments / insults, though for you UK readers (I know there are some), the public reaction here to a 1-1 draw is somewhat more positive than it will have been back in Blighty on Saturday night. Total delerium would be one way of putting it – anyone would think that NZ has won the whole tournament, rather than just a point.

Anyway, that’s a sidetrack. Today I visited one of the local Hamilton schools following a request from a teacher to help his top students do some preparation for the scholarship physics exam. Before I went, I did a bit of preparation by looking at the previous year’s exam paper and the examiners’ comments on it. As usual, there are a few themes that I have read before.

The first one is ‘read the question’. I’ve mentioned this a lot before, but really, for those of you sitting exams (any kind of exam) it is the most important thing you can do. What I mean is read the question properly, and answer the question that has actually been asked, not the question that you would like to have been asked, or the one that you think should be asked.

Another one is that students seemed to get into a flap about the laws of physics when confronted with a context they hadn’t seen before. No, the examiners didn’t use the phrase ‘in a flap’, that’s my colloquial paraphrasing, meaning that students, when seeing something that looked new, forgot their physics principles. 

An example – conservation of momentum applies wherever you are (so long as their are no external forces). It doesn’t matter if your collision is between equal mass frictionless pucks on an air table (a familiar context to physicists) or two cars on a road resulting in debris strewn over tens of metres, conservation of momentum is going to be appropriate. The situation may be unfamiliar, but the laws of physics don’t change, and still apply. The trick is to see how to apply them to the particular situation you have. It’s not always easy, and takes a bit of practice.

So here’s an example question , for would-be scholarship examinees. Estimate the force that Winston Reid applied to the ball in his stunning header last night. In the spirit of Dan Meyer, I give no details about the velocity of Shane Smeltz’s cross, the mass of the new football, the distance of Reid from the goal, etc.  That’s for you to estimate. But I remind you that, as always,  normal laws of physics apply. 

What shall I blog about today? Marcus Wilson Jun 15

No Comments

Don’t ask that question. There I was, last night, leaving work, thinking that I had nothing to put on a physics blog, when I turned the key in my car ignition to find an engine that was struggling to give me any power. After going a kilometre or so, it was clear it wasn’t a problem with the automatic choke, and I pulled over and called the AA.

It was, of course, a problem that they see frequently – I note it’s on the AA top ten list of reasons for callouts. A degraded high-tension lead. That’s the lead that supplies a spark plug its high voltage – but this one had a tiny hole in it that was giving a short circuit to the cylinder head, meaning the spark plug wasn’t getting enough voltage across it to spark (and consequently, the fuel in the cylinder wasn’t igniting).  So the AA man did a temporary fix with a bit of insulation tape and I got home without incident. Just need to get some new leads now.

Anyway, that reminded me of how the car electrical system works. It’s a pretty neat concept, that allows you to go from a 12 volt d.c. (direct current) battery to many thousands of volts over the spark plugs. The easy way of transforming voltage is to start with an a.c. supply – that’s why the mains supply to our homes is a.c. (alternating current). Transformers, consisting of two coils with different numbers of turns, step up or down the voltage according to the turns on the two coils.  The changing current through the primary gives a changing magnetic flux through the secondary, this changing flux puts a voltage on the secondary.

But how do you do it with a d.c. supply? Nothing is alternating Put a constant current through the primary and there is no voltage on the secondary. The answer is to switch your current on and off. If you put current through a primary solenoid, then switch it off, the lines of magnetic flux will collapse, and cut that solenoid (and a concentric secondary), creating a voltage on the secondary by Faraday’s law of electromagnetic induction. If there are lots of turns on the secondary solenoid, it can give a sizeable voltage for a short period of time. It is this voltage that is fed to the spark plugs, allowing them to spark. Or, in the case of my car last night, not.

A simple application of a capacitor controls the collapse of current so that there is no spark across the switch (in the distributer) supplying current to the primary solenoid.  

All quite simple, really, and that might be one reason why a temporary fix (insulating tape) is actually possible.

This is a nice reference on the electrical system for a car http://www.jetav8r.com/Vision/Ignition/CDI.html

 

 

What equation do I need? Marcus Wilson Jun 10

No Comments

With A-semester exams looming, the students here at Waikato are becoming a little more focused on their work. That inevitably means that I get more of them coming to me after a lecture, or knocking on the door of my office. And that is good.

One of the most common questions I get, usually in relation to an assignment, or a past exam paper, is ‘What equation do I need to solve this?’. I have slowly come to the conclusion (by slow, I mean six years) that when a student says this he actually means the following:

1. I don’t understand this

2. But I don’t mind that I don’t understand, I just need to know what to do to answer the question (and pass the assignment, exam etc.)

It’s the second one that is interesting. Any person can put numbers into an equation and come up with an answer, but it doesn’t necessarily add to their understanding. But unfortunately it can add to their ability to pass examinations, which is what drives students. And giving students that understanding  is part of what teaching a Bachelor of Science degree is about. Without it, a student cannot hope to apply learning to new situations. Remember, that is what real scientists (e.g. physicists) do. No-one gets a science job that involves putting numbers into well established formulae. For example, our graduate profile for a BSc degree says a BSc graduate should have

 "Skills, knowledge and attributes needed to contribute directly and constructively to specific aspects of the building of a science based knowledge economy in New Zealand"
 
That is what I need to be building in my students – the ability to do just this. It is the scientist who will drive the economy forward and solve the world’s major problems. Will our BSc graduates be able to embark down this path? Sure, a lot of science learning occurs after a BSc, but a BSc shows that someone is reasonably compentent in their use of science, enough to contribute positively. How can you contribute positively if you don’t care that you don’t understand something. (point 2 above).
 
If we produce BSc graduates who are skilled in putting numbers into formulae and nothing else we are devaluing the BSc, denying the country good scientists (and therefore harming the economy) and short-changing the tax payer who gives the majority of the money to the universities to educate students. So when I get asked ‘What equation do I need’ I need to stop and think? – What does the student really want, and is it in his best interests (and the country’s) to give him that?

N.B. I could also say the point is that we, the teachers, need to set decent assignments, that mean stuffing-numbers-into-formulae isn’t sufficient to pass.

Lots of flashing LEDs Marcus Wilson Jun 08

1 Comment

A sure-fire way to increase the value of any piece of electronic equipment is to add some superfluous flashing red, yellow and green LEDs to it. (Light Emitting Diode.) They serve no use, but their presence is somehow comforting (especially in sci-fi films) and gives the impression that the equipment is busy doing something useful.

There was a time however when this task wasn’t so easy. In the early days of LEDs, you could have any colour you wanted, so long as it was red. We’ve been looking at LEDs (more specifically, diodes in general) in one of my classes recently. The colour is determined by the band gap of the material from which the diode is made. What’s a band gap?  Well, in a semiconductor, just like any other substance, electrons can’t have any-old-energy. They have to sit in very specific energy levels. In a solid, these levels form bands of permitted energies. A semiconductor has two bands that are close in energy, but are distinct; the lower band, called the valence band, is mostly occupied by electrons, and the upper, called the conduction band, is mostly unoccupied. The material can conduct electricity because electrons can move in the conduction band, and also ‘holes’ (where there are states not occupied by electrons) can also move in the valence band.

In an LED, light is emitted when an electron drops from the conduction band into a hole in the valence band. The wavelength of light is very specific – depending on the size of the bandgap. Large bandgap materials give higher frequencies (frequency is proportional to the energy drop through E=hf where h is Planck’s constant) and so have shorter wavelengths. (9 June 2010 – Whoops, I said longer wavelength in my original post – now it’s correct)

That was the problem with developing blue LEDs.  Blue is short-wavelength visible light, and so a blue LED would need a material with a large bandgap. Developing such a material that was also cheap, robust, easily workable etc wasn’t an easy undertaking. By contrast, the long wavelength red LED was much easier.

I had a suggestion from a student that you could just turn a red LED to a blue one by putting it in a blue piece of plastic. I’m afraid this won’t work. Blue plastic looks blue because it absorbs the red and green light from a white light source. Since a red LED produces red light, if you put it in blue plastic we would just find that the red would be absorbed, and nothing would escape. You wouldn’t get any light out at all.

However, there is a way that you can shift the colour of an LED, namely changing the temperature, as this movie demonstrates.

http://www.youtube.com/watch?v=yNaYYhogGTk&feature=related

Network-wide options by YD - Freelance Wordpress Developer