Links for December 2016

Late, alas. Also: there have been a couple of complaints about the spam filter for comments on this blog, and I’m trying to track down the issue. The filter is supposed to tell you what’s wrong and help you successfully post the comment. If you’ve been unable to get past the filter, or if it’s just too much of a hassle even when you can get past it, please let me know so I can try to fix this.

  • Europe’s Galileo satellite navigation system recently went online, although without yet a complete constellation. In just a few years, there will be a full four independent navigations from great powers: the EU, the US (GPS), Russia (GLONASS), and China (BeiDou). Devices are already being built to use all four systems at once. Everyone wins through the increased redundancy and satellite count.
  • Design of the Solo cup.
  • I highly recommend this semi-technical talk on ARC fusion reactor design by Dennis Whyte.

    (Video DownloadHelper allows downloading video off YouTube.)

    Proposed in 2014 by Whyte and collaborators, ARC is a newer but only under-development alternative to traditional Tokamak-style reactor, where rare earth barium copper oxide (ReBCo) superconductors play a crucial role. Whyte argues that the key hold-up on fusion reactors is their absolute size, which necessitate large-scale, lumbering international collaboration. ReBCo superconductors are the key technical advance allowing smaller magnetic confinement. The parameters of these designs scale extremely well with increased magnetic field. Significant downsides include increased vessel pressure and pulsed operation because of intrinsic limitations on neutrons shielding.The fusion fuel is deuterium and tritium, which is most amenable choice of reactant on the fusion slope of the nuclei binding energy curve. Since the latter is so scarce, it will be produced on site (just as with the ITER fuel cycle) using neutrons ejected from plasma, which collide with Lithium place in the surrounding “blanket” (tritium breeding). Lithium is much more abundant than tritium, and (like deuterium) can eventually be extracted from sea water. Here are more details on the tritium breeding budget. a  

  • I wasn’t paying attention back in June when this depressing report on the National Ignition Facility was released:

    More than three years after the deadline passed for obtaining a sustained, high-energy-yield nuclear fusion reaction at the National Ignition Facility (NIF), the US Department of Energy is still unsure whether the $3.5 billion laser can ever attain that milestone. Much as it did in 2012, the agency has established a new, less ambitious goal for NIF several years hence: to determine whether the machine can ever achieve its eponymous goal, and if not, why not.

    “The question is if the NIF will be able to reach ignition in its current configuration and not when it will occur,” states a May report prepared by DOE’s National Nuclear Security Administration (NNSA). The reassessment of progress toward ignition at the Lawrence Livermore National Laboratory facility was conducted three years after the NNSA suspended its formal two-year-long ignition campaign in September 2012. Ignition, the threshold at which more energy results from a fusion reaction than is required to spark it, is an essential determinant in whether inertial confinement fusion (ICF) could ever become a source of fusion power….

    In a new plan for the ICF program, the NNSA establishes a goal, with a deadline of 2020, to “determine the efficacy of reaching ignition on NIF.” That contrasts sharply with the virtual assurances of ignition that were made by proponents in 2009, when NIF began operating.

  • “Formation of a debris disk after the tidal disruption of a star by a supermassive black hole”:
  • GiveWell responds about their stance on population ethics.
  • Bird feet are skinny and poorly insulated, but necessarily have blood flow. In order to reduce heat loss through their feet, the warm arterial blood coming from their heart interweaves with cold veinal blood coming from the feet in a countercurrent heat exchanger known as the rete mirabile. The heat exchange due to convection is thereby mostly eliminated, leaving only the (much slower) conduction process.
  • There is data on everything: Architects and laymen systematically differ on the aesthetic qualities of exposed concrete.
  • Pointed criticism of the stringy Breakthrough prizes from Peter Woits. However, as Woit notes, it doesn’t apply to another (minor) winner, PI’s own Asimina Arvanitaki!
  • Also, see these particularly good links from Woit.
  • Because of recent developments in safety tech, the front seats are now as safe or safer than the rear seats in the car for adults. Children under 13, and especially under 9, are still safest in the back. This applies to cars made after 2006.
  • Microsoft is going to sell a billion dollars worth of the Surface Hub, a touch-screen TV designed for meetings and conference calls. (HN discussion.)
  • Ice skating treadmill:
  • Scott Aaronson and Sabine Hossenfelder discuss the 2017 Edge Questions.
  • According to Planet Earth II, the highest density of nesting Peregrine Falcons of anywhere in the world is in New York City, and the highest density of Leopards is in the city of Mumbai.
  • The existence of spaced repetition shows how dysfunctional educational systems (both public and private) are at making evidence-based improvements. If a method with such a clear overwhelming advantage at the stated goal isn’t incorporated by schools, what hope is there that they’ll make improvements where the evidence is hazier? Michael Nielsen concurs: “One of the most cited papers in the area is Frank Dempster’s paper about the failure of educational systems to adopt spaced repetition… Although the paper was was written almost 30 years, little has changed.”
  • Also by way of Nielsen: “Proofs and Refutations” by Imre Lakatos is a socratic dialog illustrating how the edifice of mathematics, which appears to be a rigid structure of theorems and proofs, is built through a back-and-forth interaction of definitions, counterexamples, and re-definitions. First part available as a PDF.
  • Robin Hanson gives a good (conditional) defense of hyperspecialization in academia.
  • Some data on the prevalence of cheaper hidden-city tickets.
  • Three decade time-lapse of the Earth:
  • As you might expect, tonal languages need fewer syllables per word.
  • Related: there are new pretty pictures of ITER, which uses legacy superconductors.
  • Also related: this Nature Communications article on Germany’s stellarator. Very accessible to non-specialists. H/t Paul Blackburn, who says:

    It’s been a year since Germany’s Wendelstein 7-X experimental fusion reactor achieved first Helium plasma. Since then they’ve moved to Hydrogen, and very recently confirmed that the shape of the magnetic inside matches its designed shape to within one part in 100,000. That’s insane.

    Click through to the (very readable, extremely fascinating) article in Nature Communications to start your Saturday learning… Note the picture (picture, not rendering) of the visualization of magnetic field lines.

    Something I had not realized, but personally found extremely interesting, is that the tools of chaos theory (Kolmogorov–Arnold–Moser theorem) have been applied to modeling the magnetic field-plasma interaction.

  • Japan’s ISS resupply mission includes a half-mile tether testing an idea for cleaning up space junk.
  • Ultrasonic brain surgery.
  • Cassini’s new orbit is polar, allowing for some great shots of the hexagonal pole.
  • Incidentally, here’s a time-lapse movie from Juno, which is still stuck in its early 53-day orbit:
  • Electronically diagnose genetic syndromes:

    Of the more than 7,000 known genetic syndromes, Face2Gene estimates that up to half have a distinct facial pattern that can be learned and used for diagnosis.

    H/t Tyler Cowen.

  • Robert Geroch’s advice on giving physics talks:

    As a general rule, one chooses for his subject the broadest and most general version that he can feel comfortable with. This almost always involves broadening the scope of what one really wants to say.

    and

    You should intend that every single mark on a figure will be fully understood by the audience. (If
    they don’t understand something, leave it off the figure.)

    H/t Itay Yavin.

  • Video of a lava flow slowly destroying parts of a village over several days.
  • Rah Sarah Constantin on “Fact posts”.

Footnotes

(↵ returns to text)

  1. The fusion fuel is deuterium and tritium, which is most amenable choice of reactant on the fusion slope of the nuclei binding energy curve. Since the latter is so scarce, it will be produced on site (just as with the ITER fuel cycle) using neutrons ejected from plasma, which collide with Lithium place in the surrounding “blanket” (tritium breeding). Lithium is much more abundant than tritium, and (like deuterium) can eventually be extracted from sea water. Here are more details on the tritium breeding budget.
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2 Comments

  1. Jess, Happy 2017!

    The youtube link to the Earth time-lapse is broken.

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