Accelerating Future Transhumanism, AI, nanotech, the Singularity, and extinction risk.

1. 

   DB
   October 30th, 2007 - 05:13

   I am not aware of any current treatments that make use of artery cleaning biopowered microrobots. Can you provide a source for more information?

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2. 

   Michael Anissimov
   October 30th, 2007 - 07:44

   Here.

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3. 

   Richard Jones
   October 30th, 2007 - 13:17

   “My thought is, “that’s it?” Scaling laws should enable molecular motors with thousands or even millions of times the power density of an auto engine.”

   I think this business of scaling laws for motors needs a bit more thought. Firstly, one should say that for heat engines – like auto engines – scaling laws very much don’t help you when you go small. A heat engine needs to sustain a temperature difference between a hot reservoir and a cold reservoir, and the law of thermal diffusivity tells us that the time we can sustain a given temperature difference scales as the length squared, so as you make a heat engine smaller you have to run it faster and faster until (before you get to the nanoscale) you exceed a maximum frequency which scales like the speed of sound divided by the size.

   This is why biological molecular motors are not heat engines at all, but isothermal motors driven, not by temperature differences, but by chemical potential differences. Essentially they operate by rectifying Brownian motion, so this means the relevant energy scale is set by kT. For this reasons power densities don’t get to be much more than the one described (why they come out at roughly the order of magnitude of an auto engine probably is more than coincidence but I’d need to think about that more).

   I think the scaling you refer to comes from Drexler’s electrostatic motor design. This is fine (apart from the difficulties actually building one described in my old post “6 challenges”), but it’s not really fair to compare the power density of an electric motor with, say a petrol engine. In an electric motor you’ve still got to get the electrical power to the motor, so there will be Ohmic losses in the wiring (scaling, of course, as the inverse size squared), and you’ve still got to find a source for the electricity. Maybe you’ll use a fuel cell, in which case you will probably be limited by how fast you can supply the cell with fuel (again, with very unhelpful size scaling for flow rates and viscous losses that come from the Poiseuille formula). Finally, as I describe elsewhere I am deeply sceptical that you will be able to run a mechanical device at high power densities without leaking energy into vibrational modes (this leakage looks very obvious on the animations posted on http://machine-phase.blogspot.com/).

   Sorry to reply at length but I thought I would try and cheer you up with a technical discussion after all that pesky cultural studies stuff.

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4. 

   Michael Anissimov
   October 30th, 2007 - 13:40

   Thanks Richard. This clears things up a bit! Of course I’ve read your “6 challenges” post and think it makes many important points. I do see the vibration you’re talking about in the Machine Phase animations, and look forward to NanoEngineer being released to the public so that more people can run simulations and look at the issues in closer detail.

   I thought it was suspicious that a biological motor would have similar power density to an auto engine, hence my comment. I am getting the power density estimate from the electrostatic motor numbers. Question: what do you think lowering the temperature to only a few K could accomplish for nanoscale robotics? Could the Ohmic losses be circumvented by using superconducting circuitry? Could resonant vibrations be at least partially avoided by decreasing the temperature?

   It does cheer me up to understand this, thanks.

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5. 

   Richard Jones
   October 31st, 2007 - 09:58

   Decreasing the temperature is always going to be good for MNT. Superconductivity doesn’t necessarily save the day for getting your electricity around without losses, though – remember that superconductors have a critical current density above which they revert to being normal conductors, so you’ll hit this problem as you try to decrease size and increase power density.

   I looked up a very handy review article about biological motors, which gives the following power density values: (all in ergs s-1 g-1)
   Actin polymerization 1e9
   Microtubule polymerization 5e8
   Myosin II 2e8
   Kinesin 7e7
   Vorticellid spasmoneme 4e7
   Typical passenger car engine 3e6
   Striated muscle 2e6
   Bacterial flagellar motor 1e6
   Thyone acrosomal reaction 1e5
   Limulus acrosome reaction 1e4
   Eukaryotic flagellum 3e2

   It’s a bigger range than I would have guessed. I think this must be because, though the energy per power stroke is constrained to be of order kT, the effective frequency can change over quite a few orders of magnitude.

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6. 

   Ines Baile
   September 2nd, 2010 - 17:40

   The 3 phase electric power is common way of alternating current transmission and it is a type of polyphase system and is the normal way used by electric power distribution grids to distribute power. That looks like the right 3 phase alternator I’ve been looking for.

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7. 

   Manual Guide
   October 24th, 2010 - 04:17

   Canon 300d customer handbook. I only subscribed to a used Canon 300D, and also it didn’t come using a textbook. Is here anyplace I could could download it? Or maybe a web site with tips?

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