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John Cuthber

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Everything posted by John Cuthber

  1. Water is pretty nearly transparent to visible light- as used by plants. So plankton a few metres down are not troubled by the absorption of light by water; they are, however shadowed because the plankton above them soak up the light. A thin layer of concentrated plankton will absorb the same fraction of the light as a thick layer of dilute plankton. https://en.wikipedia.org/wiki/Beer–Lambert_law But supply of nutrients may be easier in a less crowded environment. Of course, there's also other stuff in the water which absorbs lioo.
  2. If I wanted to implement that I would need an amplifier with a well defined gain "A". In practical terms, I'd do that with an op amp and two resistors. In order not to load the rest of the system, those resistors would need to be reasonably large. What's the effect of those large resistors (with correspondingly large noise voltages) on the overall performance of the circuit?
  3. In the presence of air, those acids attack copper. To some extent the copper sulphate and common salt also does. Sodium hydroxide will dissolve aluminum, but not copper. It is, however, more corrosive to skin.
  4. Are we talking about the one whose banner says "Lifting Global Consciousness Raising Our Vibration and Expanding Our Capacity to Love"? Because I don't see any science behind the use of the word "vibration" (or, indeed, anything else they do).
  5. Sufficiently large DC voltages can be detected - because people's hair stands on end as in the pic here https://spectrumscientifics.wordpress.com/2016/08/16/making-electricity-van-de-graaff-generators-and-tesla-coils/ However, the idea that a small battery would produce a notable effect is unlikely at best.
  6. You missed the fact that the same "mechanical" failures will still happen. Having a remote driver doesn't stop the brakes failing You just add more things that can go wrong, so the odds of something going wrong get worse.
  7. Your idea should work fine. My first thought would have been to remove the aluminium by dissolving it in sodium hydroxide solution. Either option may damage any patination. Also, in either case, wash the piece thoroughly after treatment before letting it dry.
  8. Somewhere is "technically a desert" if it doesn't rain or snow much. Nothing to do with nutrients. "Why aren't the oceans covered in floating seaweed?" Much of it is, but they are rather small. https://en.wikipedia.org/wiki/Phytoplankton#/media/File:Plankton_satellite_image.jpg from https://en.wikipedia.org/wiki/Phytoplankton
  9. I believe that people can, and do, achieve all those things. It's called "driving". It's important to recall that a self driving car doesn't need to be perfect- it needs to be better than a (typical) human. The most interesting issue (to me) is a moral one. You need to persuade people to buy a car which will be programmed to kill them in certain circumstances. Another interesting issue (already raised) if it goes wrong, who is responsible? The driver? The manufacturer? The programmer?
  10. There is plenty of anecdotal evidence that this happens with humans too. The NHS information on fertility says "It's a good idea to see your GP if you haven't conceived after a year of trying."
  11. I flatter myself that anyone is interested but... I repeated the experiment but, at 14:50, I moved the cell into a ziploc bag + placed it in a bag full of ice. 08:50 1.59114 1.59114 10:15 1.5911 1.59105 11:00 1.59109 1.59103 15:35 1.59337 1.59329 16:45 1.59378 1.5937 18:35 1.59377 1.59369 19:10 1.59376 1.59369 20:35 1.59373 1.59365 As far as I can tell, that pretty much nails it. The cell voltage is higher for lower temperatures. Also, a torch cell in a bag in a bunch of ice turns out to be a pretty stable reference voltage- albeit one that isn't very predictable. A reference stable to a few tens of parts per million would be good enough for the OP's experiment. If I get bored, I might look at how well it works driving some sort of load.
  12. Well, here's the data, including that from later in the day 12:40 1.59115 1.59121 12:52 1.59114 1.59118 13:40 1.59112 1.59113 14:15 1.5911 1.59108 15:56 1.59101 1.59095 16:45 1.5909 1.59083 17:55 1.59081 1.59073 19:25 1.59086 1.59077 20:30 1.59089 1.59081 22:00 1.59093 1.59085 And, as I said, I suspect that temperature makes a difference. It's plausible that one meter is better "lagged" than the other so there's a delay between them. Neither meter is properly calibrated, but that hardly matters here. I may get round to thermostating a torch battery.
  13. I presume you didn't search for it. Yeast produces an enzyme which destroys hydrogen peroxide. https://en.wikipedia.org/wiki/Catalase
  14. So... OK I got bored + wondered how stable a torch battery is. I measured the voltage on my two bench multimeters over the afternoon. They both claim GOhm input impedances so they aren't drawing much current. 12:40 1.59115 1.59121 12:52 1.59114 1.59118 13:40 1.59112 1.59113 14:15 1.59110 1.59108 15:56 1.59101 1.59095 16:45 1.59090 1.59083 17:55 1.59081 1.59073 I guess the biggest effect is a change in temperature as the room warms up over the course of the day.
  15. What's the point of having a dress code stricter than business casual?
  16. LOL anyway, re. "what root psychological cause is there in the rise of atheism in the 20th century free world?" Why assume it is psychological? Why couldn't it be as simple as The more things we find a real explanation for, the less we need a sky fairy to explain.
  17. Over the duration of a typical school experiment I suspect that a torch battery might be good enough. (A slightly used Hg cell will give you 1.35V- reliable to 3 sig fig over the course of a few years.) Logically, you can set up two "sets" of whatever the experiment is; change one, and measure the difference. If the first one isn't stable enough then the experiment's meaningless anyway.
  18. That's unequivocally true, but I wonder if the OP can make use of it.
  19. Is there a distinction between these two statements? "I think that man is a thief because he is black" and "I think that man is a thief because I saw him stealing". I think there is; I think the first is bias and the second is observation. This seems to me to be a reasonable way of expressing an experimentally determined fact https://www.businessinsider.com/study-watching-fox-news-makes-you-less-informed-than-watching-no-news-at-all-2012-5?r=US&IR=T
  20. My unicorn existed for precisely zero seconds.
  21. No, because (in principle) there is no upper limit to their energy and so the diffraction angles get impractically small. https://en.wikipedia.org/wiki/Ultra-high-energy_gamma_ray
  22. I'm guessing that "direct" measurement of frequencies means counting the number of times it goes up and down in a second. As far as I know you can't do that much beyond the microwave regions (maybe mm wave?). I'm not sure if tehOP counts this as "direct" or not. https://en.wikipedia.org/wiki/Frequency_comb#Applications
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