Sunday, 18 April 2021

A couple of new papers: On fission, and nuclear sizes

 I haven't mentioned here about a couple of new papers I have been involved with which have appeared over the last month:

• First is a paper on nuclear fission (here in Physical Review C, here open access arXiv version).  The work was done primarily by a PhD student in Beijing, but I contributed a little with discussions, expertise in the code and interpretation of results.  In it we try to understand what goes on microscopically (at the level of individual neutrons and protons) when fission takes place.  We go beyond some previous work (e.g. that of my previous PhD student here and here). Through random fluctuations we see reproduction of the different final products that appear in the distribution of fission products.

• Next is a paper on the isotope shift across shell gaps (here in Journal of Physics G, here open access arXiv version). This is work done by an extended group of collaborators, and again I contributed discussion, interpretation, suggestion of which calculations to do, with the lead authors doing those calculations.  It also builds on some work I did with the same PhD student as the fission work, published here.  I think the nicest thing about this paper is the showing how the underlying mechanism of the isotope shift (change in radius of nuclei as one adds neutrons) can be described in complementary ways by two somewhat disparate theories which each have their own language and mindset for thinking about nuclear structure.  It is also neat in that the idea of understanding how the size of nuclei change as you add more neutrons is in the (science) news right now thanks to the recent results from NASA's NICER telescope on the properties of neutron stars.

Here's a pretty picture from the fission paper representing how different fission events progress through different paths of shape of the fissioning nucleus:



Tuesday, 13 April 2021

Conference week

 I mentioned earlier that I had a couple of conference coming up, happening in the same week.  This is the week:  There is the joint IoP Astroparticle Physics, High Energy Particle Physics, and Nuclear Physics Groups' conference (website: http://appheppnp2021.iopconfs.org/home, Twitter hashtag: #EdiIOP2021) and the YQIS Young Quantum Information Scientists' conference (website: https://indico.frib.msu.edu/event/31/).

With the IoP conference being in the UK and the YQIS conference in the US, I could in principle attend the IoP conference and the the YQIS meeting with only a small amount of overlapping time.  In practice, with childcare responsibilities that's not very practical, but everything is being recoreded, and I am trying to make a sensible combined programme of talks that I want to see and then arranging which ones I am able to watch live, and which I will watch after the fact.  This ability to watch pre-recorded lectures is just what many of our students are now finding useful in our taught undergraduate classes. 

Yesterday, when the conferences started, was a Monday, meaning my day for looking after my youngest children, so I wasn't planning on doing much live participation, though it also happened to be the day when my own talk was scheduled at the IoP conference, so I arranged to have the boys looked after for that time and gave the talk.  I perhaps could have strapped the baby to a sling and walked around while giving the talk, but it turned out to be easier to arrange a little time swap with my partner in childcare duties. 

Today, having cycled all the kids to school / nursery, I am able to attend the live sessions, which means that I have started with Jim Hough's talk on gravitational waves (screenshot below).  It's amazing how we have been able to observe so many events of merging black holes over the last few years, coming from a situation not so long ago when black holes were suspected to exist, but not definitively observed, even indirectly.  

I think it's a bit of a shame that the conference is set up using Zoom's webinar mode, in which I can't see who else is in the audience, can't send them a quick message to say hi, or do any of the other 'conferring' that I would do at a conference.  I know there is a formally-arranged coffee break as part of the schedule, but I don't quite get the point of limiting our ability to interact with other attendees.

Here is a snapshot from Prof. Hough's talk.  Right now there is a talk I'd like to listen to about the FAIR laboratory and the work going on / planned there, but the speaker's audio has a strange bass echo that makes it unlistenable to me.



Tuesday, 30 March 2021

A talk in Athens on Zoom

 I gave a talk on Zoom this morning to a group based in Athens, Greece.  I didn't have to, or didn't get to, go to Athens for the talk, and was just sitting in my daughter's bedroom where I have a desk set up for home working.  It's my first talk of this year, and I talked about some calcualtions I have been doing on octupole vibrations in nuclei around lead-208.  I started work on them during the first lockdown, and have not looked at them too much in the last six months, but I would like to get them into a shape suitable for publication - which mainly means polishing off one last aspect of the calculation, and then deciding how best to present the "story" to the wider world.

It's nice to be able to give a talk to people in Athens without the time-consuming, carbon-consuming air travel to Greece, but I do slightly miss the whole experience of visiting another research group, joining them for discussions, joining them for lunch ... 

I'm not sure I have anything very Greek in the house for lunch.  It'll probably be a peanut butter and banana sandwich.

I at least did get a lesson on how to pronounce Greek letters properly.  I have always said "Phi" and "Psi" to rhyme with pie, but the proper (Greek) way is to rhyme with tree.  Well, I'll see if I can switch over to the right way in future.

Here's a snapshot my host took, on a very equationy slide.  Normally I do not go into as much mathematical detail as this, but I wanted to how how "simple" the theory was.  Hopefully the words I used to accompany it conveyed that okay.  Just looking at equations without context is never simple.



Thursday, 25 March 2021

Vaccinated!

 Today I got a text message saying that I was now eligible for a Covid vaccination. I followed the link in the text message and less than an hour later I had received the first dose of the Oxford-Astrazenica vaccine

So far, I don't think I've felt any side effects though I've had some Lemsip just in case. I feel very lucky to have had it done



Wednesday, 24 March 2021

Picking a new reference manager

Around 12 years ago I tried out a new reference management piece of software caled Mendeley.  It is a reference manager, and it keeps a database of papers that I want to keep somewhere to be able to read.  It superseded an unstructured directory of pdf files on my computer, with a hand written html index page, which itself supserseded a pile of printed-out papers in my office.

At one point I was apparently the main user of Mendeley at the University of Surrey, as the Mendeley people actually got in touch with me to ask if I would help spread the word at the University.  (I said no, not because I didn't necessarily want to help either them or my colleagues, but more because I didn't think the model of me giving some kind of presentation to my peers to promote a product was likely to work, and this was, as I remember, what was suggested).

To some extent its function mirrored its predecessor methods, in that they provided a means for me to think that I had done something useful with papers, while not actually reading them.  A bit like how I used to record stuff off the telly onto video without ever actually watching it.  But I actually do read some fraction of the papers I have stored on Mendeley.  I installed a Mendeley app on the Android tablet I have via work, and find being able to read papers on it from my Mendeley library very useful.  

The other useful things in Mendeley are that it will automatically generate Bibtex output for refererencing when writing papers, and that I can create shared groups with other people, so I have (for example) recently set up a shared group with my PhD student and his co-supervisor to have a shared group of papers on interest in his project.  We can all drop papers there when we come across one and then discuss it in our next meeting.

In 2013 Elsevier bought Mendeley.  Since then, it has changed its focus, which has included removing features.  The most recently-removed feature is the removal of the mobile apps, so it no longer works on my tablet (or my phone, where I didn't use it so much as the screen is not so conducive to reading pdfs, but it was still useful there).  In principle, I can access it via the web interface, though not when offline - a situation that is not uncommon with my tablet.  In practice, the web interface is broken in a couple of ways.  Here is what it looks like right now on the desktop computer that I am composing this blogpost on:

It has been saying that since I logged in earlier today.  I suppose I can expect that sort of bug to get fixed at some point.  Here's how it looks on my tablet:

My Mendeley account used to be associated with my University email, but I had to get in touch with them only a few weeks ago to get them to change that, as Elsevier had automatically assigned my University account to an Elsevier-Mendely account that was not linked to my original pre-Elsevier Mendely library.  Still, on the tablet, unless I keep finding the right cookie to delete every time I want to log on, Mendeley will not even let me type in the username/email address I want to use, it will just tell me that "it looks like I am signing on with my Elsevier account".  Sigh.

So, though I can possibly navigate and fix these problems, except for offline reading on mobile devices, I suppose I will be ditching Mendeley.  

A quick search of Twitter, which features a few people complaining about the deleted features, suggests that most people are moving to Zotero.  That looks promising enough, but there are no mobile apps for it.  So... I'm not quite sure what the best way to proceed is.  Right now I think the front runner might just be to copy all my pdfs to a directory on OneDrive and open them from there.  It at least seems to function (not without some annoyances) from everywhere. 

Anyone got any better ideas?
 


Tuesday, 9 March 2021

Time-dependent methods articles published as ebook

I think I've already plugged enough times on this blog the series of articles I've co-edited in a special Research Topic in the journal Frontiers in Physics.  

Perhaps this will be the last mention, because the final aspect of it has just been published, which is a free e-book, in pdf and epub format.  You can download it from the main page for the Research Topic.  The main thing it does is to collect the articles in a single document, along with the editorial which I suppose would never be read as a stand-along piece of work. 

The whole e-book has its own doi (10.3389/978-2-88966-567-9) and ISBN (978-2-88966-567-9) so is, I suppose, its own entity apart from just the separate files. There is a generic Frontiers-style front page of tessellating shapes.   Here is the header of it below. 



RIP David Brink 1930–2021

I read the sad news yesterday that David Brink died in the early hours yesterday morning.  

David Brink made a significant impact into the theory of nuclear physics starting from his DPhil thesis from Oxford in 1955.  It is still highly-cited today as the source of the Brink-Axel hypothesis (along with a development from Peter Axel in 1961) which states that each excited state of a nucleus should have a giant dipole resonance associated with it, with a structure largely independent of the details of the excited state.

He made important contributions across nuclear structure and reaction theory, and it is his work applying the Skyrme interaction using the Hartree-Fock procedure that has influenced my research the most.  His paper with Dominique Vautherin (in Phys Rev C) is one which my PhD students all have to work through in order to understand the basis of the methods I use in much of my own research.  The paper has been cited over 2,000 times (according to the ISI database) and I might account for about 1% of those citations. 

I did know David Brink personally, and most of my interaction dates back a bit before I really interacted closely with his nuclear physics research work.  I think I can recount the sum of my memories of him without making an overly-long blog post.

Applying to Oxford

From secondary school I applied to Oxford to study Physics and Philosophy.  My school (a local comprehensive in Essex) had no particular links to Oxford, or much recent history of sending pupils there (I was the only applicant from my year) but they did at least encourage me to apply.  On getting to the stage in my education to potentially apply to university,  I had little or no idea about universities in general and that it made some kind of sense to go to as "good" a university as you could.  I was thinking of probably applying to polytechnics via PCAS though in the end I didn't, partly because I plumped for physics as a subject to study and that were mostly offered only by universities which one applied to via UCCA in those days.  Anyway, I was not particularly aware that Oxford was considered a top university, but went to some open days at the suggestion of my school, as I did also to Cambridge.  The open days were college-based, and I looked at more modern colleges - I remember going to St Cats and St Anne's - thinking that might be the right kind of place for a neophyte like me.  I liked the visits very much and decided to apply

In the end I applied to St Cats.  I was called up to one of the teachers at school one day to say that St Cats had got in touch to say that while they do in principle accept students for physics and philsophy, they were not going to take any this year, so I'd be better changing to another college, and they suggested Balliol, which was the principal phys-phil college (them taking more than any other college).  So, my application was amended to Balliol and I was called up for interview there in December 1991, having sat the entrance exams at school shortly before that. 

I went to Oxford for interviews wearing my standard attire of the time, which involved my favourite jumper with holes all down one of the arms, and a duffel coat which was a bit less ragged, but not quite elegant either.  I remember being slightly surprised when lots of the other applicants turned up in suits, even to the parts of the process in which we were just hanging out in college, accommodated for a night or two (or more depending if other colleges called us up for interview that week, which did happen).  There was one other girl I met, Vicky Whitford, also up for physics, who was dressed in cool grungy clothes, but who then transformed into a very smart uniform for the time of her interview itself.  I just didn't think to take any smart clothes with me.  Not that I had any apart from my school uniform.

Anyway - I mention the clothes partly because being the only one with no smart clothes was something I remember from the time, but also because I remember my interviewers having to remind me to pick up my coat, hanging on the back of the office door when I left with a series of unintentially comedic lines like "Oh, don't forget your coat!" to "we wouldn't want to be left with it here" and "not that it isn't a nice coat.  It is a nice coat ..." and so on.  At least it covered up the tatty jumper!  The office I was in for that interview was David Brink's office, above the Senior Common Room.  In the interview were me, David Brink, David Wark, Jonathan Hodby (those three there for physics) and Bill Newton-Smith (for philosophy).  I don't remember all the questions I was asked in what I remember as quite a short interview (about 20 minutes).  I do remember that David Brink showed me a postcard and asked me what, physically, was wrong with the picture.  It was a Japanese style print with a mountain in the background and a lake in the foreground.  There was a reflection of the mountain in the lake, but it was off to one side.  I saw what was wrong, and struggled to articulate it in the language of a physicist, and in the end David prompted me by asking what is particular about an incident light ray, a reflected light ray, and the normal to the surface at which it is reflected and I said the right thing - that they are all in the same plane. 

As an Undergraduate at Oxford

I was duly accepted to Balliol and spent three years there studying physics (I switched from phys-phil to just physics during the first year).  Around the beginning of the first term David Brink invited all the new physics + phys-phil students to his house for a little party, which I took to be a tradition of his.  We all navigated together to his house somewhere down Cowley Rd (an unknown part of town to us who had just arrived as Undergraduates, but I think I remember the address as being on Divinity Rd).  I remember meeting his wife Verena there, I think the only time I did meet her, and somehow coping with the small talk.  My abiding memory, though, is the communal unspoken sense of not knowing what to do when it was clearly time we should be leaving because it was late.  In the end, I piped up and said I think it was time I was heading back and there seemed to be a sense of relief that somebody had said it.  Indeed, one of the other phys-phil students (Clare Brown) thanked me for it!  Funny how these are the memories that abide from that time.

At Oxford, a key part of the education was in tutorials and every week I had to attempt and submit problems in physics and philosophy to be discussed in tutorials, and some of these were with David Brink.  In these tutorials, David gave the impression of being somewhat of a scatty professor, but it was only an impression.  If there was a problem that the students were stuck on, he'd look at it.  Say "ah" repeatedly in a way that sounded like it indeed was a sticky problem, rub his hands up and down his thighs as if a bit of help with blood circulation would help things, and then, when it looked like he might have forgotten how to speak, or might possibly have passed away (I thought him old, but he was only early 60s then) he would come out with the most impressive resolution of the problem, which was just perfect in terms of communicating to undergraduates like me, as well as so obviously being correct. 

The tutorials were in his office above the Senior Common Room - the staff room for the fellows of the college.  I didn't know at first that this was the purpose of the big room below his office, but what I did know is that up next to his office was a door out onto a flat roof which usually seemed to be kept unlocked.   One night, then, after drinking with a group in the college bar, I somehow thought of suggesting we go up to this roof, and so we did. One of the College porters came to get us.   I don't remember his name, but he was the stern Scottish one, and he let it be known that we were in serious trouble for trying to break into the Senior Common Room.  As he led us through the quad in dim evening light, Iain Corby from the year above me, who had a reputation as a conservative sort, suggested we run away.  This seemed very wise since in the low light, the ability of one man to lead a large bunch of students across the grass did indeed seem rather limited, so I walked, or ran, off, leaving the porter to take some fraction of the group to the lodge.   My name was, however, given in as one of the perpetrators of this great crime and I did receive some ticking off later.

I think David Brink left Balliol on extended leave after my first year to take up a position in ECT* (European Centre for Theoretical Nuclear Physics) in Italy as director of the institution, so I did not have him as a tutor beyond my first year.

Postgrad and later

I stayed on at Oxford to do a DPhil in theoretical nuclear physics.  It was David Brink's subject, though I don't think I realised that when I embarked on my D.Phil (and indeed, David was still away in Trento, Italy).  My choice of nuclear physics came from having enjoyed the optional paper in my final year - a combined nuclear and particle physics paper, if I remember rightly - and that in part because I enjoyed learning from the particular tutor who taught it.  It was not necessarily the most sensible choice, since it was a subject on the wane in Oxford.  They had already made a deliberate decision that particle physics was the future where nuclear physics was the past, and all the experimental effort was shifted to particle physics, with a few of the older theorists (like Peter Hodgson and Brian Buck) still keeping on with nuclear physics.  I, in fact, joined a mostly experimental group working in the condensed matter department which really did nuclear physics, but which was physically sited in the building which had access to the low temperature facilities needed for their work.  The group was run by Nick and Jirina Stone, with Jirina being a theorist who became my supervisor.  

I spent much of my postgraduate student time in Oak Ridge, Tennessee, as I was funded and co-supervised from there, and didn't see much of David Brink.  I do remember meeting him once or twice when back in Oxford both during my DPhil and after, but perhaps the largest role he directly played in my life then was to be my internal examiner for my viva.  Although I remember what question he asked in my undergraduate admission interview, I don't remember what he asked in my DPhil exam.  I only remember one question, from the other examiner, Ted Barnes, which asked me to compare nuclei to metals.  I suppose that was the question I struggled with most and hence remember still now!  I think, more importantly than passing my thesis, David helped behind the scenes supporting my early career with references and reviews to help me get established at Surrey and in the UK community as a young researcher. 

The last time I saw David was, I think, when he came to Surrey to give a seminar, which according to my email records might have been in January 2008.  That would make sense as I recall he was talking about a paper he published in 2007 with Stancu.  This revisited old work the pair had done together (also with Hubert Flocard) in 1977 on the tensor part of the Skyrme interaction.  It had just been rediscovered by others and a mass of new interest in the topic had caused a flourishing of new results.  

More recently another Brink and Stancu paper was published, in 2018, following up on the subject. This was nearly his last research paper, with another (with Angela Bonaccorso) coming later in 2018.  I don't know if there are any others to be finished up and published by co-authors, but even 2018 is an amazing 62 years after his first paper was published, a single-author paper on the shell-model applied to Pb-208.  That paper, I suppose, was just a diversion from his main PhD work.

and finally

well, I said this could be a fairly short post recounting my interactions with David.  In the end, it was not so short.  David Brink was involved in my life as a physicist either directly or through his work since I first met him in 1991, 30 years ago, which is after all not a short time. 

These were my personal reminiscences.  In the email announcing his death his close friend and collaborator Angela Bonaccorso linked to a paper she wrote about David in 2006 where one can more written about him.  No doubt more obituaries will follow, including a full article in the Royal Society's Biographical Memoirs journal, since all FRSs get an extensive obituary there.  I look forward to reading that when it comes.

I don't think I have a picture of David of my own.  Taking pictures of my University lecturers was not something which occurred to me, though there may well be one somewhere of PhD viva day.  Here is a picture I found online from the website of the same meeting where Angela presented the paper just linked to: