Tuesday, 31 March 2020

Online seminars during the coronavirus epidemic

My 3yo son, realising that many things are cancelled at the moment, asked me this morning "is working from home cancelled?"  Alas not.  As it looks like we'll all be working from home for at least a couple of months, various schemes seem to have popped up to start research seminars that are given over the newly dominant teleconferencing platform, Zoom.  

The nuclear reaction theory community has started a series of seminars, detailed on https://reactionseminar.github.io. I wasn't aware of it when the first seminar was given, but I plan to attend future seminars.  One will be given by my Surrey colleague Natasha Timofeyuk.  I'm not aware of a similar initiative by the nuclear structure theory community (structure + reactions is a traditional way of dividing up low-energy theoretical nuclear physics, though I sit in both camps).  I would certainly join one if it started, though I'm not quite keen enough to start such a project by myself.

Based at CERN there is a series called Seminar on Precision Physics and Fundamental Symmetries which includes nuclear physics, but is broader than that.  There will be two seminars per week (Tuesday and Thursday at times to suit the speaker) starting today: https://indico.cern.ch/category/12183/.

If anyone knows of any more, please advertise them in the comments below.

That's my son who asked the question in the picture, during one of our daily permitted excursions for exercise.  It was at the weekend when the weather was very cold, and a streak of hailstone is caught in the picture too.

edit: Thanks to JINA-CEE for responding to me tweeting this blogpost.  They point out their online seminars in nuclear astrophysics.  See https://www.jinaweb.org/events and look for the events tagged "IReNA online seminar"

Monday, 30 March 2020

Li-6 as a probe of giant monopole resonances

A new paper appeared on the arXiv this morning (in nucl-ex, cross-posted to nucl-th) titled Reexamination of 6Li scattering as a Probe to Investigate the Isoscalar Giant Resonances in Nuclei.  The Isoscalar Giant Resonances are excitations of nuclei in which the protons and neutrons move together en masse, in phase.  

The two main isoscalar giant resonances, and the two examined in the paper, are the monopole and quadrupole versions.  The Isoscalar Giant Monopole Resonance (ISGMR) is sometimes called the breathing mode, since it can be loosely imagined as a kind of inflating and deflating of the nucleus, though there is no air being pushed inside or breathed out to cause the motion.  The breathing mode is set off when particular kind of particle is sent scattering of the nucleus in such a way that no angular momentum is imparted.  In this case, a nucleus which started off as spherical will retain its spherical shape as it breathes in and out.

The other one of interest here is the Isoscalar Giant Quadrupole Resonance (ISGQR) which gets excited when two units of angular momentum are  transferred to the nucleus by the excitation.  This gives a different shape for the excitation in which the nucleus is squeezed in one direction while expanding in the orthogonal plane -- imagine the Earth squeezing down along the poles and expanding along the equatorial plane as a result, and then bouncing back as it tries to restore its equilibrium shape.

A key interest in making these excitations is that they probe rather generic properties of nuclear matter.  By squeezing a nucleus you can immediately probe the matter all the way through it and try to understand how "stiff" it is - how hard it is to compress.  The answer here has to come from the underlying forces between the nucleons, and we can learn all about that force by exciting these resonances.  

The traditional particle of choice for striking on nuclei to form the ISGMR is the alpha particle.  This works well because alphas only excite isoscalar excitations (those in which the protons and neutrons behave in the same way, unlike isovector excitations in which they act out of phase, and which can strongly mask isoscalar excitations).  A difficulty, though, is that the scattered alpha particles, which have to be observed to deduce how they interacted with the nucleus, have to be measured at very small scattering angles.  In other words, these measured alpha particles are very close to the beam line which is full of alpha particles which did not interact, or even worse, with stray alphas that scatter out of the beam line but not due to the interaction being targetted.   

The paper, then, uses lithium-6 (3 protons, 3 neutrons) to scatter off the target nucleus and cause the excitation.  The benefit here is that Li-6 breaks up easily into an alpha particle and a deuteron, and the interaction with the target nucleus will often cause this to happen.  One can then look for the alpha particles coming off, which are no longer contaminated by beam alphas (since the beam is now lithium).  The cost is a more complicated analysis of the scattering process and the possibility of different excitations of the target nucleus.  From the paper, though, the results seem very nice.  Here is a plot of the excitation of carbon-12, showing the tiny error bars:

 There is some structure to the peak.  Even ignoring what is happening below ~13 Mev, there appears to be one main peak and at further peaks in the shoulders - at least one prominent one in the higher-energy side.  This could be due to all sorts of things, but with carbon-12 not being spherical (it is oblate deformed, like the Earth) then there should a strong coupling to the ISGQR when the ISGMR is excited, and that is likely what dominates the structure.

Monday, 23 March 2020

Working from home

Today is day one of working from home for me.  The University stopped its face-to-face teaching at the end of last week, and now although the University is still open, there is little justification for going in.  I have contemplated walking in – it's about 15 minute walk for me – and chances are I could get in to my office and shut the door without bumping in to anyone, but for now I'm attempting home working.  

The hardest parts are (1) having my partner and 3 youngest children here and (2) there not being as good a desk or other working space as I have at work.  (1) is hard because I have to resist the temptation to spend the whole day helping with childcare, but at least being here I can help for little bits during the day in short breaks which I couldn't do if I was in the office.  It's just hard to strike the right balance.  I am still full-time at work and have the various associated obligations that go with that.  With a bit of time and practice, I'm sure I'll get there.  For (2) I might need to invest in a better office-type chair to sit in, or to clear some space at the dining-room table.  Our house is in a kind of chaotic state thanks to having builders in building an extension (started last September, end date hopefully another 3 months).  There's only a partial roof on our house, and the dining room in particular is the dumping-place for everything that had to be moved somewhere.  Still, the environment is not too bad for working.

The University have just launched a new VPN program for us to use.  It's unfortunate that their planned roll-out and replacement of the old VPN co-incided with the Coronavirus pandemic, but there you go.  In fact, the VPN only has some minor use for me for accessing those of the University websites which are only available on campus (some management/teaching ones are, some aren't).  The most useful aid to home-working, which the VPN doesn't do as standard is to run a SOCKS5 proxy so that I can make all my web-browsing happen through a machine at work.  It doesn't actually help me access some work-based websites because it doesn't change the DNS to resolve internal-only addresses, but it lets me access journals and other professional websites from a University IP address - something the split tunnel VPN doesn't do.  

Here are some brief instructions for setting up a SOCKS5 proxy from a Unix-based machine (e.g. linux or Mac OSX):

• Use Firefox and install the Proxy Toggle add-on.  Set up its preferences to look like this:

• Open a terminal and type ssh -N -D 1337 -q myname@machine.my.uni.edu except that you should replace myname@machine.my.uni.edu by a machine at your University that you can ssh into.

• Turn on proxy browsing in your Firefox by clicking on the icon that's been added to the toolbar.  It should look like this:

when the SOCKS5 proxy is not active and this:
when it is active.

When you are done, you can quit the ssh command with ctrl-c and switch the proxy back to the off position. 

Friday, 20 March 2020

Coronavirus 20th March

Today is the last day that the University is operating roughly as normal, at least in terms of teaching undergraduates.  We've been teaching as normal this week, and from next week everything is to be done remotely.  For me, this is relatively easy, as this is my light teaching semester, when I only have project supervision to do.  Today is also the last day my middle two children are at school (oldest already been off since beginning of week and youngest is only a few months old, so no school for him anyway).

I'm all set up with a University-issue headset, and I've done my first meeting with the Zoom teleconferencing software, so I feel more or less able to go with working from home.  The difficult thing will be getting anything done while in the same house as my family, with young children.  We'll just have to see how that goes. 

My parents made it home from Spain in a mad dash last weekend.  They had gone their for a 1-month holiday on the car ferry via Bilbao.  They drove back over the period of 2 days getting through France just before the borders within Europe were generally shut (though they might still have let people through to return to their homes, I think).  It's a relief that they are at home.

The FaceBook group I set up in the nearby roads has had lots of people join it.  For now no-one has requested help with things like getting groceries, but I expect that will change if things carry on like they do, with more and more people being asked to self-isolate at home. 

Thursday, 19 March 2020

Nuclear Fission Dynamics in our Frontiers special topic

The next article published in our special topic on advances in time-dependent methods in nuclear structure and reactions in Frotiers in Physics is "Nuclear Fission Dynamics: Past, Present, Needs, and Future" by Aurel Bulgac, Jin Shi, and Ionel Stetcu.  The reference is Front. Phys. 8, 63 (2020) doi:10.3389/fphy.2020.00063.

It's a broad-ranging discussion of how the process of fission works from a microsopic point of view (microscopic meaning at the level of individual nucleons and their quantum wave functions).  The take home message is that the adiabatic approximation that is frequently applied does not work for the last stages of fission where the rearragement of the nuclear shape is too fast for the nucleus to continuously relax into the ground state associated with its instantaneous shape.  

There are lots of nice figures included which makes it easy for me to include one in the blog post.  This is part of their Figure 7 showing a typical density plot of the point in the fission process in which the nucleus (in this case fermium-258) splits into two.  One sees the importance of not assuming spatial symmetry, which is an approximation often made.

Sunday, 15 March 2020

Coronavirus 15th March

Here are some photos from my nearby branch of Waitrose:

They show where the pasta usually is, where the toilet rolls usually are, and where the baby wipes normally would be.  Panic buying has hit Guildford.  It's a bit dispiriting to see, and to realise that at the first sign of a social difficulty, in the form of the effects of people having to self-isolate because of the Coronavirus, is that people go and take more from the supermarkets than they need, thus depriving others.  There were a couple of things on my shopping list that I couldn't get (Lemsip, baby wipes (and I actually have a baby that needs wiping)) but I'll manage without, and will probably be able to pick them up when they are re-stocked.  But still, a bit sad.

It's Monday tomorrow, and my flexible working arrangement mean that I work compressed hours, which involves me staying at home on Mondays to spend time with my #1 son.  As a bonus, my #2 daughter's school has just (at 23:15) emailed to say it will be closed tomorrow because a staff member has developed symptoms consistent with Coronavirus infection.  Aside from looking after kids, my other plan is to make and distribute leaflets to all the houses in my block to set up a network where people who need help shopping (for example) because they are self-isolating get the help.  Hopefully it will not much be needed, but it would be awful if it were needed and it wasn't there.

On the plus-side, Waitrose had loads of half kilo "Essential" tiramisu, and on special offer too:

Friday, 13 March 2020

Affected by Coronavirus

The World Health Organisation has declared that the incidence of the coronavirus is enough to count as a pandemic, and the UK is one of the countries affected.  The University of Surrey has just announced that next week will be our last week of regular teaching activities.  After that we will be switching to all-online teaching and examining activities.  The campus is not yet planning to shut down, so going in to work is supposed to carry on as normal for now.

Had the coronavirus pandemic not come about, I would have just return a couple of days ago from a meeting in Beijing, but that was cancelled several weeks ago.  Yesterday the Institute of Physics announced the cancellation of all their meetings coming up, which includes the annual Nuclear Physics Conference which they sponsor.  I was due to talk in that, but it's not going ahead.  Before that, is a meeting in Jyväskylä, Finland, which is now almost certain to be changed in some way (cancelled, moved, or performed online).  It's all rather dramatic.  But of course, these small aspects of my work are nothing compared with the consequences of the disease.

On a more personal level, this year very unusually my family was going to come with me on my work trips.  Unusually because my partner is on maternity leave and this gives her the time to travel with me, as well as meaning I can carry on sharing the care of our children when I get home from work even when travelling.  With the Edinburgh conference cancelled it looks like we will be losing quite a bit of money on the travel costs (unless we go anyway, I guess), and the same may well happen yet to a meeting we are all supposed to be going to in Japan in May.  My parents are in Spain for a month-long holiday.  Where they are, all bars, cafes and restaurants have just been shut down, so it is well that they are in a self-catered apartment.  But worrying for them (and me), as their age makes them more at danger from the virus.  They have yet to learn whether the ferry they have booked to get them home will still be running.

Oh, and tomorrow night's school quiz run by my daughter's school Parent-Teacher-Association has been cancelled.  Gah!