Archive for Physics

Talking About Undergraduate Physics Research…

Posted in Education, The Universe and Stuff with tags , , , , , , , on July 2, 2014 by telescoper

One of the courses we offer in the School of Physics & Astronomy here at the University of Sussex is the integrated Masters in Physics with a Research Placement. Aimed at high-flying students with ambitions to become research physicists, this programme includes a paid research placement as a Junior Research Associate each summer vacation for the duration of the course; that means between Years 1 & 2, Years 2 & 3 and Years 3 & 4 . This course has proved extremely attractive to a large number of very talented students and it exemplifies the way the Department of Physics & Astronomy integrates world-class research with its teaching in a uniquely successful and imaginative way.

Some time ago I blogged about  some very good news about one of our undergraduate researchers, Talitha Bromwich, who is about to graduate from her MPhys degree, after which she will be heading to Oxford to start her PhD DPhil; she is pictured below with her supervisor Dr Simon Peeters:

Talitha Bromwich with her JRA supervisor Dr Simon Peeters at 'Posters in Parliament' event 25 Feb 14

Talitha spent last summer working on the DEAP3600 dark-matter detector after being selected for the University’s Junior Research Associate scheme. Her project won first prize at the University’s JRA poster exhibition last October, and she was then chosen to present her findings – alongside undergraduate researchers from 22 other universities – in Westminster yesterday as part of the annual Posters in Parliament exhibition, organized under the auspices of the British Conference of Undergraduate Research (BCUR).

A judging panel – consisting of Ben Wallace MP, Conservative MP for Wyre and Preston North; Sean Coughlan, Education Correspondent for the BBC; and Professor Julio Rivera, President of the US Council of Undergraduate Research; and Katherine Harrington of the Higher Education Academy – decided to award Talitha’s project First Prize in this extremely prestigious competition.

We held a small drinks party in the School of Mathematical and Physical Sciences to congratulate Talitha on her success. Here are a couple of pictures of that occasion:

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From left to right you see Simon Peeters, myself, Talitha and Prof. Michael Farthing (the Vice Chancellor of the University of Sussex); the winning poster is in the background. Here’s me presenting a little gift:

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More recently still, the MPS Elves have made a little video featuring Talitha talking about her research placement:

We take undergraduate research very seriously here at the University of Sussex, and are now extending the Research Placement scheme to Mathematics. Many Departments talk about how important it is that their teaching is based on state-of-the-art research, but here at Sussex we don’t just talk about research to undergraduates – we let them do it!

 

The Cake Equation

Posted in The Universe and Stuff with tags , , , on May 31, 2014 by telescoper

Yesterday being the last Friday of the month of May it was time for another tea-and-cake event in the School of Mathematical and Physical Sciences. These provide an opportunity for staff to get together and chat while demolishing a specially-themed cake. The cakes themselves are organized by the inestimable Miss Lemon and I never know what the theme is before the goods arrive, so I have to ad lib a short introduction (for just a minute, without repetition, hesitation, deviation or repetition) before cutting the cake.

As you will observe, this time the (Lemon Drizzle) cake was decorated with the Dirac Equation (which I consider to be the most beautiful equation in physics)..

Examination Times

Posted in Biographical, Education with tags , , , , , on May 19, 2014 by telescoper

After a gloriously sunny weekend, it’s now a gloriously sunny Monday. There always seems to be good weather when students are revising for, or actually taking, their examinations. It’s Mother Nature’s special torture. The bus I was on this morning went past a large crowd of students waiting outside the Sports Hall in the bright sunshine for some examination or other.  The sight did remind me that I usually post something about examinations at this time of year, so here’s a lazy rehash of my previous offerings on the subject.

My feelings about examinations agree pretty much with those of  William Wordsworth, who studied at the same University as me, as expressed in this quotation from The Prelude:

Of College labours, of the Lecturer’s room
All studded round, as thick as chairs could stand,
With loyal students, faithful to their books,
Half-and-half idlers, hardy recusants,
And honest dunces–of important days,
Examinations, when the man was weighed
As in a balance! of excessive hopes,
Tremblings withal and commendable fears,
Small jealousies, and triumphs good or bad–
Let others that know more speak as they know.
Such glory was but little sought by me,
And little won.

It seems to me a great a pity that our system of education – both at School and University – places such a great emphasis on examination and assessment to the detriment of real learning. On previous occasions, before I moved to the University of Sussex, I’ve bemoaned the role that modularisation has played in this process, especially in my own discipline of physics.

Don’t get me wrong. I’m not opposed to modularisation in principle. I just think the way modules are used in many British universities fails to develop any understanding of the interconnection between different aspects of the subject. That’s an educational disaster because what is most exciting and compelling about physics is its essential unity. Splitting it into little boxes, taught on their own with no relationship to the other boxes, provides us with no scope to nurture the kind of lateral thinking that is key to the way physicists attempt to solve problems. The small size of many module makes the syllabus very “bitty” and fragmented. No sooner have you started to explore something at a proper level than the module is over. More advanced modules, following perhaps the following year, have to recap a large fraction of the earlier modules so there isn’t time to go as deep as one would like even over the whole curriculum.

In most UK universities (including Sussex), tudents take 120 “credits” in a year, split into two semesters. In many institutions, these are split into 10-credit modules with an examination at the end of each semester; there are two semesters per year. Laboratories, projects, and other continuously-assessed work do not involve a written examination, so the system means that a typical  student will have 5 written examination papers in January and another 5 in May. Each paper is usually of two hours’ duration.

Such an arrangement means a heavy ratio of assessment to education, one that has risen sharply over the last decades,  with the undeniable result that academic standards in physics have fallen across the sector. The system encourages students to think of modules as little bit-sized bits of education to be consumed and then forgotten. Instead of learning to rely on their brains to solve problems, students tend to approach learning by memorising chunks of their notes and regurgitating them in the exam. I find it very sad when students ask me what derivations they should memorize to prepare for examinations. A brain is so much more than a memory device. What we should be doing is giving students the confidence to think for themselves and use their intellect to its full potential rather than encouraging rote learning.

You can contrast this diet of examinations with the regime when I was an undergraduate. My entire degree result was based on six three-hour written examinations taken at the end of my final year, rather than something like 30 examinations taken over 3 years. Moreover, my finals were all in a three-day period. Morning and afternoon exams for three consecutive days is an ordeal I wouldn’t wish on anyone so I’m not saying the old days were better, but I do think we’ve gone far too far to the opposite extreme. The one good thing about the system I went through was that there was no possibility of passing examinations on memory alone. Since they were so close together there was no way of mugging up anything in between them. I only got through  by figuring things out in the exam room.

I think the system we have here at the University of Sussex is much better than I’ve experienced elsewhere. For a start the basic module size is 15 credits. This means that students are usually only doing four things in parallel, and they consequently have fewer examinations, especially since they also take laboratory classes and other modules which don’t have a set examination at the end. There’s also a sizeable continuously assessed component (30%) for most modules so it doesn’t all rest on one paper. Unusually compared with the rest of the University, Physics students don’t have many examinations in the January mid-year examination period either. Although there’s still in my view too much emphasis on assessment and too little on the joy of finding things out, it’s much less pronounced than elsewhere. Maybe that’s one of the reasons why the Department of Physics & Astronomy does so consistently well in the National Student Survey?

We also have modules called Skills in Physics which focus on developing the problem-solving skills I mentioned above; these are taught through a mixture of lectures and small-group tutorials. I don’t know what the students think of these sessions, but I always enjoy them because the problems set for each session are generally a bit wacky, some of them being very testing. In fact I’d say that I’m very impressed at the technical level of the modules in the Department of Physics & Astronomy generally. I’ve been teaching Green’s Functions, Conformal Transformations and the Calculus of Variations to second-year students this semester. Those topics weren’t on the syllabus at all in my previous institution!

Anyway, my Theoretical Physics paper is next week (on 28th May) so I’ll find out if the students managed to learn anything despite having such a lousy lecturer. Which reminds me, I must get the rest of their revision notes onto the Study Direct website…

A Sticky Physics Problem

Posted in Cute Problems with tags , , on May 1, 2014 by telescoper

As I often do when I’m too busy to write anything strenuous I thought I’d post something from my back catalogue of physics problems. I don’t remember where this one comes from but I think you’ll find it interesting…

Oil of viscosity η and density ρ flows downhill in a flat shallow channel of width w which is sloped at an angle θ. The oil is everywhere of the same depth, d, where d<<w. The effect of viscosity on the side walls can be assumed to be negligible.

If x is a coordinate that represents the vertical position within the flow (i.e. x=0 at the bottom and x=d at the top), write down a differential equation for the velocity within the flow  v(x) as a function of x. Use physical arguments to derive appropriate boundary conditions at x=0 and x=d and use these to solve the equation, thereby determining an explicit form for v(x). Hence determine the volume flow rate in terms of η, ρ, θ, d and w as well as the acceleration due to gravity, g.

As usual, answers through the comments box please!

 

Promoting Women in Physics at Sussex

Posted in Education, The Universe and Stuff with tags , , , , , on April 28, 2014 by telescoper

At the end of a very busy day of meetings I suddenly remembered that I forgot to pass on a nice bit of news about the Department of Physics & Astronomy at the University of Sussex.

It doesn’t seem very long ago at all that I announced the promotion of its first ever female Professor of Physics in the Department, Prof. Antonella de Santo. In fact it was in July last year. Well, just before the Easter break I was delighted at the promotion panel’s decision  to appoint the second female Professor in the Department. The successful candidate this time was Clauda Eberlein, who has been promoted to a Chair in Theoretical Physics with immediate effect.

I’ve already posted about how the proportion of female undergraduates studying physics as been stuck at around the 20% mark for a decade despite strenuous efforts to widen participation. A recent (2012) study by the Institute of Physics contains a wealth of statistical information about staff in Physics departments, which I encourage people to read if they’re interested in the overall issue with equality and diversity in physics. Here I’ll just pull out the figure (based on a 2010 survey) that out of a total of 650 Professors of Physics (and/or Astronomy) in the UK, just 5.5% were female. At that date about 20 physics departments had no female professors at all; that would have included Sussex, of course.

The first ever female Professor of Physics in the United Kingdom was Daphne Jackson, a nuclear physicist, who took up her Chair at the University of Surrey way back in 1971. It’s interesting to note that when Daphne Jackson studied physics as an undergraduate at Imperial College she was one of only two women among the 88 undergraduates in her year.

Congratulations to Claudia on her promotion, but the news doesn’t end there. Claudia will actually be taking over as Head of the Department of Physics & Astronomy in January 2015. She is currently Director of Teaching and Learning for the School of Mathematical and Physical Sciences and will take up her new role when the current Head of Physics & Astronomy, Philip Harris, stands down, having served his term in admirable fashion. Anyway, when Claudia takes up her post as Head of Department she will join an elite band of female physicists to have been appointed to such a role. Does anyone out there know how many other women have headed a Physics department?

 

 

 

 

Who was the Bringer of the Lines from Pauli?

Posted in History, The Universe and Stuff with tags , , , , on April 13, 2014 by telescoper

Part of the entertainment at last night’s Physics & Astronomy Ball was a marvellously entertaining and informative after-dinner speech by particle physicist David Wark. David had to leave before the evening ended in order to get a taxi to Heathrow and thence a flight to Japan, so he missed out on the dancing and general merriment. I may get time tomorrow to write a bit more about the Ball itself, including the fact that I received an award from the students! For the time being, though, I’ll just pass on a fascinating snippet that David Wark, an expert on neutrinos, mentioned in his speech.

It is well known that the neutrino was first postulated by Wolfgang Pauli in 1930 to account measurements that suggested that energy and momentum were not conserved in beta decay. What is perhaps less well known – it was certainly new to me until I heard about it last night – is that Pauli’s proposal is described in famous letter, addressed rather charmingly to “Radioactive Ladies and Gentlemen” of Tübingen from his base the ETH in Zürich. Part of the letter is reproduced here:

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The opening phrases of the letter “Wie der überbringer dieser Zeilen den ich huldvollst anzuhören bitte…” is a polite request that the recipient(s) listen to the “bearer of these lines”. Presumably, Pauli being unable to visit Tübingen himself, he sent someone else along with the letter and that person gave some sort of seminar or informal presentation of the idea.

The mystery is that despite the obvious importance of this episode for the history of physics, nobody seems to know who the “bearer of the lines” from Pauli actually was. In his speech David Wark said he had been trying for 15 years to identify the individual, without success.

Anyone out there in Internetshire got any ideas?

Equations in Physics

Posted in Education with tags , , on April 10, 2014 by telescoper

Just so you know that our education system is safe in the hands of Michael Gove I thought I would pass on a couple of examples from the latest official guidance on subject content for GCSE Combined Science. These are both from Appendix 1, entitled Equations in Physics.

Example one:

kinetic energy = 0.5 x mass x (acceleration)2

Example two:

(final velocity)- (initial velocity)= 2 x acceleration x time

Neither of these is even dimensionally correct!

Such sloppiness from the Department of Education is really unforgivable. Has anyone else spotted any similar howlers elsewhere in the document?  If so please let me know via the comments box…

UPDATE: Monday 14th April. Apparently these errors in the document have now been corrected, but still…

 

 

A Problem of Capacitors

Posted in Cute Problems, The Universe and Stuff with tags , , on April 3, 2014 by telescoper

Time for another entry in the Cute Problems  category. I’ve been teaching a course module  in theoretical physics this term so here’s one that my students should find a doddle…

A spherical capacitor consists of an outer conducting sphere of fixed radius b and a concentric inner conducting sphere whose radius a can be varied. The space between the spheres is filled with air which has a breakdown electric field strength E0. What are the greatest achievable values for (i) the potential difference between the spheres, and (ii) the electrostatic energy stored in the capacitor?

Answers via the comments box please.

Day Trip to Harwell

Posted in Education, Science Politics with tags , , , on April 1, 2014 by telescoper

Only time for a quick post as I’ve just got back from a visit to the Rutherford Appleton Laboratory which is located at Harwell (in the heart of the Midlands).

I was there to find out about the Science and Technology Facilities Council‘s Apprenticeship scheme, as we are planning to introduce a similar scheme at the University of Sussex and needed some advice about how to set it up. I hope to write more about that in due course.

Anyway, it was a very informative and useful visit with the added bonus that we also got an impromptu guided tour of the Diamond Light Source (and its associated workshops where some of the current STFC apprentices are employed). The Diamond Light Source is actually shut down at the moment so various upgrades can be performed, and we were therefore allowed up close to where the beam lines are. That was very interesting indeed, especially when I saw that special devices are apparently deployed to counteract the effects of Cold Dark Matter..

Some B-Mode Background

Posted in Astrohype, Science Politics, The Universe and Stuff with tags , , , , , , , , , , , on March 15, 2014 by telescoper

Well, in case you hadn’t noticed, the cosmology rumour mill has gone into overdrive this weekend primarily concerning the possibility that an experiment known as BICEP (an acronym formed from Background Imaging of Cosmic Extragalactic Polarization). These rumours have been circulating since it was announced last week that the Harvard-Smithsonian Center for Astrophysics (CfA) will host a press conference  on Monday, March 17th, to announce “a major discovery”. The grapevine is full of possibilities, but it seems fairly clear that the “major discovery” is related to one of the most exciting challenges facing the current generation of cosmologists, namely to locate in the pattern of fluctuations in the cosmic microwave background evidence for the primordial gravitational waves predicted by models of the Universe that involve inflation.

Anyway, I thought I’d add a bit of background on here to help those interested make sense of whatever is announced on Monday evening.

Looking only at the temperature variation across the sky, it is not possible to distinguish between tensor  (gravitational wave) and scalar (density wave) contributions  (both of which are predicted to be excited during the inflationary epoch).  However, scattering of photons off electrons is expected to leave the radiation slightly polarized (at the level of a few percent). This gives us additional information in the form of the  polarization angle at each point on the sky and this extra clue should, in principle, enable us to disentangle the tensor and scalar components.

The polarization signal can be decomposed into two basic types depending on whether the pattern has  odd or even parity, as shown in the nice diagram (from a paper by James Bartlett)

The top row shows the E-mode (which look the same when reflected in a mirror and can be produced by either scalar or tensor modes) and the bottom shows the B-mode (which have a definite handedness that changes when mirror-reflected and which can’t be generated by scalar modes because they can’t have odd parity).

The B-mode is therefore (at least in principle)  a clean diagnostic of the presence of gravitational waves in the early Universe. Unfortunately, however, the B-mode is predicted to be very small, about 100 times smaller than the E-mode, and foreground contamination is likely to be a very serious issue for any experiment trying to detect it. To be convinced that what is being measured is cosmological rather than some sort of contaminant one would have to see the signal repeated across a range of different wavelengths.

Moreover, primordial gravitational waves are not the only way that a cosmological B-mode signal could be generated. Less than a year ago, a paper appeared on the arXiv by Hanson et al. from SPTpol, an experiment which aims to measure the polarization of the cosmic microwave background using the South Pole Telescope. The principal result of this paper was to demonstrate a convincing detection of the so-called “B-mode” of polarization from gravitational lensing of the microwave background photons as they pass through the gravitational field generated by the matter distributed through the Universe. Gravitational lensing can produce the same kind of shearing effect that gravitational waves generate, so it’s important to separate this “line-of-sight” effect from truly primordial signals.

So we wait with bated breath to see exactly what is announced on Monday. In particular, it will be extremely interesting to see whether the new results from BICEP are consistent with the recently published conclusions from Planck. Although Planck has not yet released the analysis of its own polarization data, analysis of the temperature fluctuations yields a (somewhat model-dependent) conclusion that the ratio of tensor to scalar contributions to the CMB pattern is no more than about 11 per cent, usually phrased in the terms, i.e. R<0.11. A quick (and possibly inaccurate) back-of-the-envelope calculation using the published expected sensitivity of BICEP suggests that if they have made a detection it might be above that limit. That would be really interesting because it might indicate that something is going on which is not consistent with the standard framework. The limits on R arising from temperature studies alone assume that both scalar and tensor perturbations are generated by a relatively simple inflationary model belonging to a class in which there is a direct relationship between the relative amplitudes of the two modes (and the shape of the perturbation spectrum). So far everything we have learned from CMB analysis is broadly consistent with this simplifying assumption being correct. Are we about to see evidence that the early Universe was more complex than we thought? We'll just have to wait and see…

Incidentally, once upon a time there was a British experiment called Clover (involving the Universities of  Cardiff, Oxford, Cambridge and Manchester) which was designed to detect the primordial B-mode signal from its vantage point in Chile. I won’t describe it in more detail here, for reasons which will become obvious.

The chance to get involved in a high-profile cosmological experiment was one of the reasons I moved to Cardiff in 2007, and I was looking forward to seeing the data arriving for analysis. Although I’m primarily a theorist, I have some experience in advanced statistical methods that might have been useful in analysing the output.  Unfortunately, however, none of that actually happened. Because of its budget crisis, and despite the fact that it had spent a large amount (£4.5M) on it already,  STFC decided to withdraw the funding needed to complete it (£2.5M)  and cancelled the Clover experiment. Had it gone ahead it would probably have had two years’ data in the bag by now.

It wasn’t clear that Clover would have won the race to detect the B-mode cosmological polarization, but it’s a real shame it was withdrawn as a non-starter. C’est la vie.

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