Tuesday, 30 June 2020

Nuclear soliton review

The latest article in the special topic I am co-editing in Frontiers in Physics appeared today.  It is called "Solitons in Nuclear Time-Dependent Density Functional Theory" and is by Yoritaka Iwata, from Kansei University, Osaka.

It follows on from some of his previous work (including a paper in New Journal of Physics I co-authored with him), combining a review of why one might expect soliton behaviour in nuclei, some existing results, and a new more thorough exploration of relevant parameter space.

The basis of the idea is that the time-dependent density functional theory which describes nuclear systems appears as a non-linear Schrödinger equation which formally is equivalent to the canonical equation with which solitons are described.  Depending, then, on details of the nuclear interaction, and on the boundary conditions – the specific nuclear interaction being explored – one may find soliton solutions.

One particular confounding factor with the existence of solitons in nuclear reactions is the relative speed of the waves which equilibrate the charge and those which move matter.  If neutrons and protons are exchanged too quickly in reactions, then solitons are not possible.  This is something highlighted in Iwata's previous papers, and a hot topic in understanding heavy-ion reactions, with a recent paper in Physical Review Letters studying the same thing from a more nuclear physics (rather than mathematical/solitonic) perspective. 

Here's a picture from the paper (their Figure 4) showing a collisions around the boundary where charge equilibration is important:

Monday, 15 June 2020

The Surrey Alumnus and The Spy

Some nights, as I go to bed, if I am not falling asleep as my head hits the pillow, I pick up a book on the history of MI5, the British security service.  It's enjoyable bedtime reading, and a mighty tome which I am about 3/4 of the way through.  The book proceeds chronologically, and I'm currently around the 1970s.  This was perhaps a quieter time for spying than the days of the Profumo scandal or the Cambridge Five, at least in terms of international intrigue involving the Soviets, but I've just come across a spy that I had not heard of, that has some local interest to me.

Though I was an undergraduate at an Oxford college, I was never recruited as a spy, and if anyone tried, I totally misread it.  Now I have been at the University of Surrey for 20 years, it turns out that one of the ex-undergraduates here, from the earliest days of the University in the late '60s became a spy.  Michael John Smith studied electronic engineering at Surrey, and came to MI5s attention as someone who got involved in the activities of the Communist Party of Great Britain (CPGP).  He worked, after graduation, as an electronic engineer at EMI where he had clearance to work on technology contracts for Britain's nuclear bomb.  Apparently his security clearance was granted thanks to a mix-up in his rather common name, and the fact that there was another Michael John Smith enrolled in the Surrey branch of the CPGB.  He duly worked on radar fuses for Britain's free-falling nuclear bomb, and was able to pass documents on to the KGB.  Eventually, the clerical error at the security service was spotted, and his clearance was revoked.  His Soviet handlers had made sure he stopped taking the Morning Star, and switch to the Telegraph, join a local tennis club, and stop association with the CPGB;  still, they were suspicious that so soon after this preparation he was able to pass them such secrets, and they thought that the information about the radar-activated fuses, complete with details of the frequency used, and hence how to jam them, might have been fake plants from the British.  Not so. 

Eventually, Smith was arrested, and sentenced to 25 years in 1993, reduced to 20 on appeal.  I wonder where he is now.  Retired, and living round the corner from me, perhaps.  

The image at the top is from Britain's free-fall nuclear bomb WE.177, now at the Imperial War Museum North (presumably without the warhead inside).

Tuesday, 9 June 2020

Cycling near the speed of light in Nature

As mentioned in my last post, a paper written by a BSc project student and me has just appeared in Proc Roy Soc A, and was due to be mentioned in Nature.  Duly the Nature "research highlight" has appeared.

Here's a video the student made for the project (but which we did not include in the paper)

Friday, 5 June 2020

A paper on relativity, and a book on instantons: The week in Lockdown Guildford.

I've lost count of which week of lockdown it is, but I do know that it's Week 13 in the University calendar, which means two more weeks of semester to go and then it is the long vacation - or "the summer semester" depending how you reckon it.  I have two MSc projects to supervise over summer, so I have some direct teaching to do, as well as plenty of preparation for my autumn semester modules. 

This week I have been marking Final Year Project reports from various students on our BSc programmes, covering various different topics.  It's been interesting to see what they have been up to in their projects, and as marking goes, they are enjoyably varied – more so than 50 exam scripts answering the same questions, though the similarity in that case has its own benefits. 

This week also sees the publication (here) of a work done in a Final Year Project last year, by a student (Evan Cryer-Jenkins) working with me on a topic in Special Relativity - namely on the visual appearance of fast-moving objects.  There are well known optical distortion effects that arise in Special Relativity thanks to a combination of length contraction, and the finite speed of light meaning that light has to leave different parts of an extended object at different times in order to arrive at ones eye at the same time.  Evan, in this project looked at how such a distortion would appear to a two-eyed observer (or to two spatially-separated cameras) and how the two different images would not be able to be focused to a single image.  In a way it's similar to looking at an object through a glass of water - each eye will see a fixed shape distorted in to two different shapes because of the different optical path taken to reach each eye.  We also looked at what one might be able to infer (the distance and speed of the object) from the absolute and relative distortions.

We submitted the paper not much less than a year ago.  The first referee reports came back giving us hope for acceptance if we made a few changes, and responded to the referees' points.  The journal (Proceedings of the Royal Society) told us that a resubmission would be treated as a new submission, and so the published version is listed as being submitted in October.  They are also quite on the slow side at doing things at that journal, not helped by the Coronavirus situation.  Anyway - the paper was published this week.  The same day, a journalist from Nature got in touch asking about the paper in order to run a story on it.  That never happens to my nuclear physics research.

I also got, in the post, the fruits of my labour commenting on a book proposal for Cambridge University Press.  This was a book on instantons which can be used to describe quantum tunnelling processes.  I harbour a desire to use the technique to understand tunnelling in nuclear fission.  If, after some effort at understanding the book, and further effort with implementing the calculations, running the code, processing and understanding the output, I may be able to write that up and see it published for all to see.  I won't expect a journalist to get in touch with me, though.  Perhaps I should think more often of writing for such a general journal as Proc Roy Soc A.

The picture shows me reading the book about instantons.  Well, pretending to read, but activating the PhotoBooth app on my computer to take the picture.