10.59 It's Wolfgang Bauer with Supernova Dynamics via Kinetic Theory.
11.00 I'm still smarting from Wolfgang Bauer's outrageous elbowing of me in yesterday's football game. A clear red card offence.
11.01 Michigan State University is located on a map for us, and the virtues of Michigans summer are extolled.
11.03 Element abundances are shown. A quick recap on the Big Bang nucleosynthesis gives us the relevant timescales and temperatures for nucleon and nuclei freeze-out. At 1s, n/p = 0.22. At 100s, temperature has fallen below 10^9K, nucleons can bond into alpha particles, which vacuum up all the free neutrons.
11.08 Bauer preempts my blog by declaring the one valuable piece of information I am going to get from this talk - He/H = 23% from the Big Bang. That's my work done for today then!
11.09 Ok, I'll press on a little longer and see if I can glean any other information.
11.10 The end point of massive star evolution is run through. Iron core is tipped over the Chandrasekhar limit as the Silicon shell burining deposits more iron. Collapse then ensues.
11.11 The great problem of supernova simulations - they don't explode! (Mostly). Problem is, the realistic simulation of a supernova is an extraordinarily comlicated computational problem. The neutrino flow is especially difficult to include in a self-consistent way and the effects of rotation require multi-dimensional simulation which is obviously much more difficult.
11.16 Limited success with Burrows 2D simulation and Fryers 3D simulation. One big problem is the coupling to Boltzmann equations for neutrino flow which is not done self-consistently.
11.17 Bauer diplomatically avoids stating his opinion of Burrows' acoustic mechanism. Is he talking about his mouth?
11.18 My blog is preempted again by asking the question: where does the 6D phase space transport equation come from? (We're talking nuclear collision simulations now).
11.19 He begins to answer with Many Body Theory in a nutshell. The above equation results from a Wigner transform. So now you know.
11.21 So where does this equation come from?
11.21 + 30 secs. After some details, we're left with 6 differential equations in time for each test particle. But - for a supernova simulation is the number of test particles not a little larger than for heavy ion collisions?
11.23 Ah, yes - this is now addressed. We use 10 million test particles. Each test particle is a moon's worth of baryons. Wow.
11.24 By the way, the great advantage of this method is that it allows a natural (and hence relatively simple) coupling to the neutrino transport equations (also Boltzmann based).
11.29 Some computational details later, we get to some simulations. Woosley and Weaver provide the progenitor core. They have a batch of them in the fridge - they'll send you one if you ask nicely.
11.30 Results from a single processor. BKD EoS is used. A large number of small time steps (10^-5 s) are required because of the interplay of micro- and macroscopic forces.
11.31 I feel some animations coming on. Here we go...
11.34 Lots of dots are moving in front of my eyes. Is this the animation or the Skol from last night?
11.35 We're up to rebound - at a central density of 0.2 nuclear matter density. That's incredibly small (compared to standard modeling)! No uniform nuclear matter in the core at bounce. Very Interesting.
11.38 Summary - new explosion mechanism - neutrino heating and opacity change. The shockwave originates 50km above the neutron star surface. Most interesting to me is the low core density at bounce. I repeat 0.2 TIMES NUCLEAR MATTER DENSITY! (c.f. 2-3 times nuclear matter density as is commonly accepted).
11.45 Excuse the lack of coverage of the questions - I've got my hand up for a question, so typing is inhibited.
11.50 I ask if he has plans to apply his method to an ONeMG core collapse. Answer: No - he has too much on his plate. But he agrees to send me his code so I can do it. That's in writing now - it's binding.
11.52 My voice sounds funny through a microphone.
11.55 Next up is Paulo Gomes with "Fusion enhancement/suppression and irreversibility in reactions induced by weakly bound nuclei". Now say that three times quickly.
11.57 The basic question: in heavy ion collisions, does break up couple to fusion and enhance cross sections or compete with it and suppress them?
11.58 Where is fusion decided - when the Coulomb barrier is breached, or a little way outside? Not sure I understand, given the quantum mechanical nature of barrier penetration.
12.03 Experimental details now.
12.08 The slides are going by apace. I have to admit I'm struggling to keep up. I'm having visions of flan.
12.10 Raabe et al in Nature report that 6He's halo does not enhance fusion probability. The title is misleading - it should read the breakup of 6He's halo.
12.12 At the rick of incurring the wrath of experimentalists, those are some comically large error bars.
12.13 Ok, so we want to compare data on collisions involving stongly and weakly bound projectiles on the same target. Irrelevent differences should be eliminated in the data reduction.
12.16 A long discussion on methods to do this results in a Renormalized Experimental Fusion Function, a Universal Fusion Function and Wong functions. Add them to the Jargon page on the Wiki!
12.19 Finally, by comparing the Renormalized Experimental Fusion Function with the Universal Fusion Function, we get to the breakup effects we're looking for.
12.22 If systems don't follow the expected systematic (which I missed), we are shown three options
1 - Something interesting going on
2 - The experiment is wrong
3 - The calculations are wrong
I think that pretty much covers all of physics.
12.24 Bottom line (for a layman in this field like me) - they've come up with a method of comparing data to theory in examining the collisions involving strongly bound and weakly bound (e.g. halo) nuclei. The conclusions are extensive, and my humble typing skills (I'm up to four fingers now) can's keep up.
12.29 Wolfgang Bauer asks my question from 11.58! I'm so excited I miss the answer.
12.31 So hungry.
12.33 My brain is suddenly being swamped with signals from my stomach. Can't think straight.
12.35 It's lunch! You've been great, and I'll be back later.
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Totally excellent summary of what I said. ... all, except one statement: "A clear red card offence"! What are you, Italian?
ReplyDeleteyes, he is an Italian who thinks is a German. He does not even understand that this is what makes him so successful!
ReplyDeleteMy secret is out. I am a German named Fabio who was discovered washed up on the shores of a west Lancashire Victorian tourist resort.
ReplyDeleteJust read through this post - the ends of a couple of paragrpahs seem to have gone astray, so I've edited them back in. Also corrected a couple of typos.
ReplyDeleteI was there (the session, not the match) and it happenned exactly like Will said it did. If he continues like this he'll become the Newton of nuclear physics blogging - mabye he already is!
ReplyDeleteOne thing Will skipped was Wolfgang Bauer's comment that he's +sure+ the heavy elements were synthezied in supernovae. But Gail McGlaughin said in her talk that she could imagine two sites where the r-process could occur (supernovae and black hole-neutron star mergers). Is this a controversial question?