Friday, 1 October 2021

Back in the lecture theatre

It's the end of week 1 of the first semester of the new academic year.  I teach two modules this semester: Modern Computational Techniques and Special Relativity.  I had the first face-to-face sessions in both classes yesterday, and it was nice - and weird - to be back on campus, teaching students.  I did have a similar level of face-to-face teaching for at least part of semester 1 last year.  That stopped at the beginning of December and it has been 10 months since I've last regularly gone onto campus or seen students face to face. 

My modules are third year undergraduate modules, though the Special Relativity one can also be taken by students on one year taught masters' programmes.  I think it is probably right to say that I met none of the students I saw this week face to face before.  Quite a few of them I have interacted with online and it was nice to see them in person.  In particular, one student I supervised for an EPSRC-funded summer project this year is taking both my modules.  We had interacted a lot over the summer via Teams and Zoom, and yesterday we met in person for the first time.  "You're taller than I was expecting" he said to me. "You too!" I said in return.  We are both around the same height (195cm) and I suppose used to most other people being at least a little shorter than us.

Week 1 of semester has also been #BikeToSchoolWeek so I took a photo of my youngest three on the back of our bikes as my partner and I were about to set off on the school run.  It's bike to school week every week for us, but I hope posting a nice picture to Twitter (and here) will make a few people think that maybe it's a possibility for them, too, and make the environment of our town a bit nicer for all.  I don't know if it's the colder weather causing it, but the traffic fumes of all the vehicles dropping their kids off at the schools this morning seemed even worse than normal.

Tuesday, 21 September 2021

RIP Sir Clive Sinclair


Last week brought the sad news of the death of Clive Sinclair.  He had a huge impact on my life through the computers he invented with his Sinclair Research company.  

I was 8 years old when we got our first computer - a Sinclair ZX Spectrum.  It had 48k of memory, and cost £175.  The photo shows me holding it in my hand (picture taken last week).  It makes it look very small!  I had no idea what a computer was when my dad told me we were getting one, and I asked about playing games on it.  He explained that yes you could play games, but you have to tell it how, or program it first.  I remember wondering if that meant that latent inside it was a more-or-less fully-formed version of Space Invaders that somehow needed unlocking. Of course, it's not quite like that, but I was completely fascinated by the computer and what could be created inside it.  It came with a big manual of how to program it with the built-in Basic interpreter.  I went through a lot of that manual, and typed in lots of programs from books and magazines and learnt the rudiments of programming.  

As I grew older, I mainly just played games on it, often with friends from school - and my weekends were spent cycling to a friend's house to play on their computer or have them come to mine to do the same.  The ability to use a computer to create worlds in one's imagination seemed to me easily to rival that of any other medium.  It was also a very cultural phenomenon at the time, at least to my peers and me.  We had ridiculous rivalry between computers with a kind of understanding of what owning each one meant.  The Spectrum was in some sense at the lowest end of the technical pecking order, and it had social associations with its mass-market appeal and vast base of games, while better-off parents with good intentions for their children would get the recommended BBC computer for their children, and there was a kind of (middle) class-related badge to having one.  The Commodore 64, much better technically than the spectrum, American, and with an ample supply of games signified a better-off family with the populist strain that the Spectrum embodied.

Sinclair as a businessman seemed at once both astute and reckless as he quickly turned great success into failure and the company - at least the computer part of it - was bought out by technically and socially humdrum rival Amstrad who brought out a souped-up "Spectrum +2" which we got to replace our original Spectrum.  I still used that computer to exclusively play games on, and gaming was my main motivation for getting a Commodore Amiga when I was something like 14 years old.  My Dad had said, when I got it, that he hoped I would do more than just play games on it, and in fact I did really start getting to grips with a lot of how it worked and how to program it.  It came with AmigaBasic, but I wanted something a bit more powerful.  Unfortunately commerical compilers for languages like C on the Amiga were quite expensive.  The affordable option, because the technology was much simpler, was to get a machine code assembler which required one to directly program at the level of the CPU's native instruction set, but at least did not involve the "hand-assembly" of converting the maching op-codes into numbers.  So it was that one of the first languages I really wrote complete codes that I shared was 68k assembler.  That became my go-to language for doing anything, and with the library routines of the Amiga's operating system to assist, one could write quite sophisticated things in a modest amount of machine code.  I used to solve mathematics problems from my GCSE class on it, and sometimes submit answers alongside computer code.  I have no idea what my teachers made of it, but I suppose I assumed that if I could understand it, so could / should they.  I was never told to stop, and did the same in my GCSE "Technology" exam, which I now see would have flummoxed the examiner, who graciously erred on the side of giving me a high mark.

I remember very little of 68k machine code now, but have been programming in one language or another since about that time, and it is a significant part of my work as a physics lecturer and researcher..  It all started with that Spectrum, though, and even if I ended up using it for playing games on, I did get the seeds of programming at that time, and thought of using typed computer language instructions as a perfectly natural way of getting computers to do what you want them to.

Tuesday, 31 August 2021

In Oxford as a tourist

Over the weekend, we visited Oxford as a family on a purely non-academic visit.  I spent several years of my life studying there quite a long time ago (arriving in 1992) and I've only been back on a few occasions which mainly involved going only to the physics department for work reasons.  

This weekend we visited some friends who have just moved to Oxford.  It was strange going to parts of town I hadn't been to in so many years, and it brought back many memories.  I've always had a keen affinity with the fact that the etymology of the word nostalgia is a negative medical condition, like neuralgia, and being thrown back to memories of my past is usually an experience with at best mixed emotions.  But, actually, I found it enjoyable, being there with three of my children, answering their questions about my time there and some of the landmarks.  30 years is nothing to the buildings of central Oxford.

Visiting friends who lived out towards Headington - a perfectly manageable walk from the city centre - made me realise what a small ambit I had of the city when I studied there.  My world was centred round my college life. both study and social, and the half hour walk to South Park or beyond was too distant to really contemplate.  I'm sure there were students there for whom that wasn't the case, but my psychogeographical memory of Oxford is rooted very much in the life of an 18 year old who has just arrived, blinking, at University, and very different from the 47 year old man with a family, visiting some friends in a city they have moved to.  

Despite walking past it most days for a couple of years, I never visited the botanical gardens in Oxford when I lived there.  I went there this weekend, and enjoyed it very much.  Here's a picture of me, with Kit (my youngest) in a sling, in the botanical gardens, with Magdalen tower in the background.


Thursday, 1 July 2021

The Pad in Madison, and my late Uncle

I have, in the past, made a few posts with obituaries, or at least reminiscenes, about nuclear physicists who have died.  Here is one about a relative of mine who died earlier this week, who has perhaps a rather tangential link to nuclear physics.

To the extent that I have knowledge of my family tree, I am not aware of any origins outside the British Isles, but my dad's sister Jean did leave the UK for Los Angeles where she married an American man by the name of Murray Winer.  He died earlier this week (on 28th June).  It's been some years since I last saw him - in fact, it must have been when I attended the Nuclear Structure conference in Berkeley in 2010 - when I also went with my partner to a conference in her field in San Diego first and we made out way up to the Bay Area stopping in with my aunt and uncle in Lake Temecula, where they lived at the time. 

As a young child, my summer holidays were in places like Aberdeen (camping - the first and only time, as my mother refused to camp again after that), Berwick-upon-Tweed, Lythm St Annes, and then later to places on the south coast when we moved from Scotland to England.   After my aunt moved to LA, when I was around 9 or 10 we started to go on overseas holidays and managed to alternate going to stay with her and Murray in LA.  For me these were wonderful and memorable holidays.  I got to go to theme parks like Disneyland, Magic Mountain, Knott's Berry Farm, places like Sea World, Universal Studies - as well as to the beach, and many other tourist places, all while staying with family.  I knew Murray, then, in the context of my aunt's husband, in LA, where he worked in car sales.

Before LA, though, Murray lived in Madison, Wisconsin where he opened a coffee house called The Pad.  I was vaguely aware that it had some connections with the likes of Bob Dylan, who played there while Murray was managing the place.   I don't know exactly where in Madison it was, but presumably a cool place to hang out like this would be near enough the University to draw business from it, and in a newspaper story from 1997 that Murray's son in law posted on facebook (below), it mentions that it was frequented by 'university professors [and] students' as well as musicians, beatniks and poets.  The University of Wisconsin, Madison then as now had people doing nuclear physics research, so it is just possible that people I know now, also met my uncle in the 1960s.   The person I thought of was our emeritus professor Ron Johnson at Surrey, who I knew was a postdoc in Madison sometime around the 1960s between his PhD in Manchester and his permanent position in Surrey.  I asked him if he had any memory of The Pad, but he told me that though he was there at around the right time (1963-4), hanging out in such places was not his thing.

Do any readers have links with the University of Wisonsin Madison from around this time, and remember a place called The Pad?  I'd be very interested to hear.

Below is the newspaper clipping I mentioned above, along with a picture of Murray taken some time within the last 10 years, and later than the time I last saw him.  RIP Murray.

Tuesday, 8 June 2021

Papers 064304 and 064305

By something of a coincidence, I have two papers appearing consecutively in Physical Review C this month.  An unplanned coincidence because one was submitted in April, accepted in May and published in June, while the other was submitted in January, accepted in April, and published in June.  

The older (published last Friday) paper also has a longer history:  It is work done by my PhD student Matthew Barton.  Matthew finished his PhD in 2018 and this paper was part of it.  His thesis was on the use of the time-dependent density matrix (TDDM) method to look at beyond mean-field aspects of nuclear dynamics with a goal (initially) of understanding fission processes.  Previous implementations of the (rather computationally intensive) TDDM method involved a few approximations which we thought we could overcome.  Although we did sort-of overcome them, we only did partially, in the sense that the result was too time-consuming to apply to fission.  One of the approximations we got rid of was to not assume that an uncorrelated ground state was good enough to start studies of collective motion from.  It seemed sensible, especially with fission as a goal, to start from as close to the right state as possible. 

This means running the time-dependent calculation in such a way as to turn on part of the interaction at the beginning of the simulation time so that the generation of the starting point ground state for the 'real' calculation occurs as the nuclear interaction is turned on.  It uses the Gell-Mann Low theorem to build up the ground state correlations.  In the end just this part of the calculation was quite a heroic effort and had not been done before in the same level of consistency we had done it.  Even though it was a sub-project of Matthew's thesis, we thought it worth publishing, and eventually got round to writing it up in time for a submission at the beginning of this year.

The paper is published as Matthew Barton, Paul Stevenson, and Arnau Rios, Phys. Rev. C 103, 064304 (2021) doi: 10.1103/PhysRevC.103.064304

Here's a figure from the paper showing the Gell-Mann Low theorem in action, turning on the correlation part of the formalism to build up a more complicated wave function and finding a lower energy state than the inial configuration which was itself a variational minimum within the space of uncorrelated wave functions

The newer paper's history (or at least my involvement with it) dates back to October last year when my colleague at Surrey, (Emeritus) Prof Phil Walker got in touch to ask me a question about state mixing and how it might change the wave functions of K-isomers.  State mixing is a bit like the correlations of the TDDM paper above, in the sense that we are trying to 'mix' or 'correlate' some functions that we have calcualted based on a model to make them more like nature has them.  Nature has already done the mixing or correlation.  As a statement, I cringe slightly when I write things like that, as if there is something somehow natural that they should be thought of as uncorrelated and nature then mixes them.  It's a language we use in nuclear physics, and in physics in general, that implies an event - states are mixed, symmetry is broken etc, when the action of mixing or breaking is only done in our theories so that we better reproduce what nature is.  Anyway - there is some logic to thinking this way, because sometimes natures produces unmixed states or unbroken symmetries and we can use those as a way to understand the more complicated cases. 

In the case of this paper we have some excited state of nuclei which either look like quite pure simple wave function which can be written down as 'unmixed' configuration, but that get mixed with other ones if there is a chance near-degeneracy between states with the same quantum numbers.  Then the wave functions of each state gets mixed together.   The effects of two state mixing is widely understood (by afficionados) to mix together the values of angular momentum projection (known as K in the context of nuclear isomers), changing the decay rates of the states compared to if there were no mixing.  Phil had come to me to see if I could help him understand whether a three-way mixing might be causing what appeared to be quite an anomalous decay rate for a particular isomeric state in Ta-179.  I helped by doing the three-state mixing calculation, but Phil did all the "understanding".  Anyway, his hunch was right, and the calcualtion should this really nicely. 

Here's a picture of the effect of the extra mixing caused by the third state:

The paper is P. M. Walker and P. D. Stevenson, Phys. Rev. C 103, 064305 (2021) doi: 10.1103/PhysRevC.103.064305

I owe my current position to Phil Walker, by the way, as it was he who first employed me as a post-doc at Surrey.  Thanks Phil!  Glad to still be collaborating with you.

Wednesday, 26 May 2021

Bull Sessions

 My colleague Jim Al-Khalili, who exceeds my 21 years in the Department of Physics at the University of Surrey asked a question about the term "Bull Sessions" on Twitter a couple of days ago:

I first heard the term, I think, after arriving at Surrey, when I found that the nuclear group had these informal talks in which lots of discussion was intended, called "Bull Sessions".  Usually they were based on talks from researchers in the group, and differed in style from the kind of more formal invited seminar from a visiting speaker.

You can follow the replies to Jim's tweet to see what other people know about the term.  I was slightly surprised to learn the following in the Oxford English Dictionary, which mentions the phrase, dating it back to at least 1920.  It appears unrelated to the animal, or the papal bull, but is related to the sense of bull meaning "Trivial, insincere, or untruthful talk or writing; nonsense" from which bullshit derives.  So, in that sense, it means an informal discussion.  It's a US term, originally.

The etymology of bull in this sense is listed as unknown according to the OED, but lists some similar sounding and meaning words in Old French, Modern Icelandic and Middle English which might (I suppose one is supposed to infer) be related. 

Interesting!  I don't know how it got into the Surrey group, but my guess is that possibly Ron Johnson brought it back from the US after doing a postdoc there and becoming head of the Surrey group (as well as one of Jim's PhD supervisors).

Tuesday, 25 May 2021

RIP Steven Moszkowski 1927–2020


I just heard the news that Steven Moszkowski died in December.  I heard of his death from my PhD supervisor, Jirina Stone, who has been working with him in recent years (with a highly-cited paper co-authored by Moszkowski, Jirina Stone, and her husband Nick Stone published in 2014).  I met Steven once, as far as I can remember, but I knew his name for his work on effective interactions for use in nuclear structure calculations - particularly the surface delta interaction (SDI).  I was reminded of him recently when a final year project student I've been working with this semester was working on a solvable model of octupole states in lead-208, as worked out by Piet van Isacker.  It made use of this SDI interaction, since although it is not a fundamental nucleon-nucleon interaction, still captures enough of the correct physics to be very useful, and is conceptually and mathematically simple.

Like my meetings with many of the older generation of nuclear physicists, I felt a bit inadequate to collaborate with them, and have clearly now missed my opportunity.  As I say, I only met Moszkowski one time (that I recall).  From the short memorial page to him at his institution, UCLA, it sounds like there were a lot of interesting stories he could have told me.  RIP, Steven.