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  1. SongDog

    COVID From 60 Minutes an Epidemiological View Of What Vaccination Level Is Needed

    Influenzas circulate and mutate in many wild and domesticated specie, not just humans. As a result, new variants arise frequently in swine, birds, even camels. AFAIK, we don’t yet see a similar behaviour for coronaviruses.
  2. SongDog

    Floating a cruise ship in a bucket of water

    It will if you do it right. Capacitance can be measured to exquisite sensitivity by counting individual electrons with a SQUID (vide Rod Harris-Lowe).
  3. SongDog

    B Exploiting radiocarbon dating for FTL communication

    Well, there's only one observer, the terrestrial one. In the observed frame, the distant Starshot sample should age slower. Consider a simple binary message: If life is detected, measure the first half of memory. Otherwise measure the second half. In the terrestrial wafer, does the remote...
  4. SongDog

    B Exploiting radiocarbon dating for FTL communication

    [Mentors' note: This thread was split from] Empirical test: If one wished to implement a controlled experiment of this sort, start with separating stocks of pure C12 and pure C14 with a mass spectrometer. Use the C12 to...
  5. SongDog

    B Long term sustainable energy bounds

    "Is there an upper bound on the amount of sustainable energy/unit time that could ever be made useful to mankind?" That depends. Are you assuming it must be used on Earth? If so, we can start by considering how much sunlight intersects our disc. Earth has a polar circumference of about 4E7...
  6. SongDog

    B Why does GPS require an accurate clock?

    Have a look at and you'll see that rapid signal acquisition depends on having the receiver's clock within approx. 1.023 microsecond of the clock used for the received signal. A 32ns/day drift, over a month, would exceed that. Equivalently, so would an...
  7. SongDog

    Has anyone ever dealt with limescale in a bathroom sink?

    The process described by @Mark Harder is now done automagically in modern water conditioners. Once a month or so you dump a 20kg or 40kg sack of conditioner salt into a holding tank, and software does the rest. When brine is needed, water fills the holding tank long enough to saturate with NaCl...
  8. SongDog

    Are charged batteries heavier?

    @CWatters, you might want to re-read that Wikipedia entry more closely.
  9. SongDog

    Why doesn't a magnetically levitating conductor oscillate?

    In the DC limit, Lenz' law tells us that the EMF goes to zero. At nonzero frequencies the induced EMF is proportional to (and opposing) the rate of flux change, so lower frequencies would require higher currents to maintain the same peak lifting force. However, with ordinary...
  10. SongDog

    Do carriers move across a p-n junction at 0 K?

    Ask instead how the behavior changes as the carrier kinetic energy approaches zero: what is the limiting case?
  11. SongDog

    Lightbulb burnout

    Sounds like a bog-standard grossly inefficient "warm white" 2700K 300W at 120V incandescent like Philips 38941-1 listed on page 138 of It appears the "300W" is closer to 282W (perhaps...
  12. SongDog

    Laser interaction with ions

    Continue on straight? In a fibre? They normally are made with a radially graduated index of refraction to self-focus along the central axis, aren't they?
  13. SongDog

    SNR Vs bandwidth limitations

    Yes, SNR and usable bandwidth are interrelated. You want to read up on "signal detection theory".
  14. SongDog

    Most efficient way to rotate a cylinder using a motor?

    Just tilt the drum, like a cement mixer. Even 20-30 degrees tilt should do fine. Feed it from the raised end, not the side of the cylinder. Empty with a shovel from the same hole, or tip the whole thing back to dump it.
  15. SongDog

    Most efficient way to rotate a cylinder using a motor?

    Let's rather say one rotation per day. Haste makes waste. It's just a composter! Now we're looking at ~40 mW. This could easily be provided by one or two square inches of solar cell, perhaps scavenged from garden lighting. No need for a battery: if it only turns on sunny days, so what...
  16. SongDog

    Most efficient way to rotate a cylinder using a motor?

    Used bicycle parts are cheap or even free at a small-town dump. You don't need high speeds, one or two rotations per day is a lot for composting. Keep the rotation rate that low and you can get by on just milliwatts with lots of mechanical advantage. Then you can use a small solar panel to drive...
  17. SongDog

    Ice vs. Teflon : coefficent of friction

    Application areas: Skis, snowboards, skates, bobsled, luge, iceboats, avalanches, snowblowers, icebreaker hulls, river-bridge foundations, roofing, automotive exterior finishes, etc all concern interfaces to (and within) ice and snow. Traditional Inuit dogsleds use a smooth coating of ice on the...
  18. SongDog

    How does the eye detect the angle of incidence?

    In simple terms, for a perfect lens, the azimuth and elevation on the retina of the points which are illuminated with images of your two cubes are simply a scalar multiple of the angles on which they were incident upon the centre of the lens. The scalar multiple is a function of the lense shape...
  19. SongDog

    Hot water (energy conversion)

    Interesting case. Too deep to siphon, too impure to use directly for domestic hot water. Since it has to be pumped out anyhow, there may be geothermal uses, but I suspect it's best applied to pre-heat a working fluid going to some other superheater (e.g. solar). I assume it's presently being...