Wikipedia:Reference desk/Archives/Science/2016 December 21

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December 21

Interesting effect I've noticed.

So, I was watching EverythingApplePro's video on him testing out the taser case and when he tazed the Nokia (bottom part), his microphone started going weird. First time, it was making static, then after that, it would cut out completely.

Do any of you know what's happening? Some people are assuming it's making some sort of EMP wave. CyanoTex (talk) 11:00, 21 December 2016 (UTC)

You should give a link rather than assuming people will be happy to go to the trouble of googling your terms and searching for something like what you describe. I didn't do that but I wouldn't be surprised if a piece of electronics went wrong when exposed to the shock of the taser. Yes it would make a small EMP beside the spark. When working with electronics one should always be careful to sit down, not shuffle one's feet, and use a wrist band and a conductive pad. Basically not expose it to high voltage gradients which could burn out something, and especially not go and taser the stuff with even tiny sparks. Dmcq (talk) 11:22, 21 December 2016 (UTC)

@Dmcq: I apologize for not giving a link as youtu.be links are blacklisted here. Here it is regardless. https://www.youtube.com/watch?v=ad53oSMB8hw CyanoTex (talk) 17:18, 21 December 2016 (UTC)

Tallest mountains prior to those in the Himalayan Plateau? (and after)

At some point millions of years ago, the tallest mountains were not in the Himalayan Plateau, as the Himalayas did not even exist prior to the Indian Plate with the Eurasian Plate. In what mountain chain would have contained the hightest mountain prior to the mountains in the Himalayas taking the crown? Secondly, is any information available as to when/which mountain chain will overtake the Himalayn peaks and how far in the future? From current Plate tectonic movement, I would expect either the mountains caused by the collision of African and Europe as the Mediterranean is closed *or* the collision caused as Australia moves north.Naraht (talk) 17:53, 21 December 2016 (UTC)

There is a theory that once a mountain range gets much above the snowline then tectonic uplift can no longer outgrow galcial erosion. [1][2] If true, the Himalayas are about as tall as it is possible for a mountain range to get. SpinningSpark 19:18, 21 December 2016 (UTC)

It is not really possible to get accurate height information for past orogenies but the Taconic Mountains are a candidate for getting to Himalaya-like heights in the Taconic orogeny about 480 mya and the Adirondack Mountains are perhaps also a possible candidate about a billion years ago. SpinningSpark 19:32, 21 December 2016 (UTC)

Would that mean that for equal tectonic forces, that equatorial mountains would be able to be higher due to a higher snowline? And what mountains were at snowline levels when the Himalayas got there?Naraht (talk) 20:02, 21 December 2016 (UTC)

The theoretical limit on a mountain height is set by the yield strength of the rock and by the gravity of the planet [3], [4] and the tallest mountains on Earth are fairly close to that limit. If you factor the glacial erosion in, the estimate of how tall the mountains can get is reduced [5] but not drastically. Dr Dima (talk) 00:07, 22 December 2016 (UTC)

These calculations are about the base-to-peak height of the mountain, but since the we've been talking about the Himalayas rather than Hawaii, the question is about maximum height above sea level. If the mountain sits on top of a plateau like the Himalayan Plateau, we also need to estimate the highest possible plateau above sea level, add that to the calculated base-to-peak maximum, and adjust the result for the weight of the mountain depressing the plateau "foundation" under it. --69.159.60.210 (talk) 00:36, 22 December 2016 (UTC)

Gamma rays causing interference on professional video recording?

I've just finished watching a programme on BBC4 about the sliding into place of the Chernobyl New Safe Confinement arch to cover the original sarcophagus. At http://www.bbc.co.uk/programmes/b08650s6 (is this available outside the UK?). In the light of the immensity of the engineering my question seem a very trivial one. I noticed that whenever the video (contemporary and high quality) was from inside the hall containing the reactor there was a slight speckling of white dots flashing on the TV screen (about 7:00 into the programme, for example). Like the "snow" I remember from the days of analogue television but very much smaller dots. We were told there was such a high level of gamma radiation present that people could still only be there for a matter of seconds. Would the gamma radiation be causing the interference? Thincat (talk) 22:38, 21 December 2016 (UTC)

Having watched the same (excellent) documentary, I noticed the same thing. Just for the record, IPlayer is not available outside the UK. The interference is indeed due to radiation, found this nice overview of responses of imaging sensors to radiation (seems to be a school project, a rather cool one!). It's not surprising, gamma radiation is just photons after all, same as visible light. Possibly interesting side note, in microscope imaging we sometimes see similar things, when doing live imaging at low intensity. This is generally considered to be due to cosmic rays. Not sure if anyone has ever proved this. Fgf10 (talk) 23:33, 21 December 2016 (UTC)

• Ionizing radiation causes atoms to release electrons. When this occurs inside a component inside an integrated circuit, it can result in a spurious signal. Radiation-tolerant circuitry must go to considerable effort to mitigate this. The individual pixels within an IC video sensor (an Active pixel sensor or a CCD) are specifically designed to be very sensitive to electrons generated by the photoelectric effect, so they are also extremely sensitive to ionizing radiation. I speculate that the effect will be exactly what you saw: individual pixels will saturate (totally "on") for one sample time. I know nothing about the current state of the art, but I speculate that this can be mitigated either in the time domain (sample at 3 times the video frame rate) or in the spatial domain (use three collimated cameras) to "vote the affected pixel out of the image. -Arch dude (talk) 03:56, 22 December 2016 (UTC)

Agree: Also some of the bright pixel 'pops' in low light imaging might also be due to some extent to electrical circuit noise. Can happen when amplifying very weak signals because the amplifier amplifies the noise too. Fortunately, a human viewer can learn to ignore them. If they do become too distracting however, one can always write an algorithm to compare the average pixel value. If the value rises (say) beyond average Δ (delta) then substitute 'black' or average . In the early days of experimental television broadcasting, 'snow' would often appear on the screen if someone drove by in a motor vehicle that had no suppression on its ignition system (spark plugs and all that) or you switch a light or the vacuum cleaner on which can also cause saturate (totally "on") as mentioned above. By simply inverting the broadcast luminance signal. The bright pops became black pops which were not noticeable. Only two percent of the speckles that appear on a TV screen when not receiving any signal is recognized to be cosmic background radiation. But then you have to factor in, that everything is radio active, including the imaging equipment.--Aspro (talk) 21:18, 22 December 2016 (UTC)

To add anecdotal evidence, I have seen the same effect in some other recording from the damaged Chernobyl reactor hall, so you are likely correct. This was years ago; it definitely wasn't the same program. --47.138.163.230 (talk) 06:11, 22 December 2016 (UTC)

It might be worth pointing out that this is very DIFFERENT to cosmic microwave background. CMB is non ionizing radiation picked up by the device's antenna, basically like a weak TV signal, and then "displayed" on the screen (when there is no "strong" signal to drown it out) . It's totally different to ionizing radiation hitting the "sensor" and spuriously "firing" the sensor. Possibly related, tho not really well understood is Cosmic ray visual phenomena. Vespine (talk) 01:51, 23 December 2016 (UTC)

• Thank you for these helpful answers. I had been wondering whether the cameras' electronics could have been shielded better from the radiation but I can see that the image sensor is inevitably unshielded. Thincat (talk) 13:39, 23 December 2016 (UTC)