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  1. Standard member RBHILL
    Acts 13:48
    19 Jun '14 14:47 / 1 edit
    People falsely accused of starting fires:
    http://www.today.com/video/today/55451431
  2. Standard member DeepThought
    Losing the Thread
    20 Jun '14 17:32
    Originally posted by RBHILL
    People falsely accused of starting fires:
    http://www.today.com/video/today/55451431
    Well yes. I'd make the point that he was prosecuted on the basis of that evidence alone, which is surprising. I wonder how many tests they did to establish their claim that a V-shaped burn mark is only associated with the presence of an accelerant.

    There have been people convicted of killing their children in the U.K. after a second cot death. The basis for the prosecutions was an expert opinion where the "expert" said it couldn't be cot death due to the chances being so low. He'd got the probability by squaring the chances of one cot death - thereby falling for the birthday fallacy.

    Bad methodology does this.
  3. Standard member Grampy Bobby
    Boston Lad
    07 Aug '14 05:52
    People's lack of knowledge of Science

    An area I lack knowledge in is the Van Allen Belts in the earth's upper atmosphere. What function do they perform?
  4. 07 Aug '14 07:04
    Originally posted by Grampy Bobby
    An area I lack knowledge in is the Van Allen Belts in the earth's upper atmosphere. What function do they perform?
    Start here:
    http://en.wikipedia.org/wiki/Van_Allen_radiation_belt

    It is unwise to treat natural phenomena as performing a function as it can lead to confusion. Rather simply ask: what are they and what do we know so far about what happens in them and what effects do they have?
  5. Standard member sonhouse
    Fast and Curious
    07 Aug '14 11:18 / 1 edit
    Originally posted by Grampy Bobby
    [b]People's lack of knowledge of Science

    An area I lack knowledge in is the Van Allen Belts in the earth's upper atmosphere. What function do they perform?[/b]
    The apparent function they perform is to keep orbiting manned vehicles from taking up long term residence at the altitudes where the radiation belt resides.

    The ISS has to use orbits much lower than the Van Allen belts or they would be fried with radiation, a LOT of radiation.

    That has the effect of requiring a lot of fuel onboard to periodically fire rockets to raise them back up to the operating altitude because even though the air is extremely thin at that altitude, about 230 miles up, there IS air there and the solar panels presents a huge surface area to that air, and they are going a good 18,000 miles per hour, about 5 miles per second. So the solar panels and the whole ISS is constantly being slowed down, not much, but enough that over the course of a few months the loss of kinetic energy and therefore orbital velocity means the orbit gets lower and lower, maybe a foot a day, just a guess. That means every now and again they have to fire rockets to speed them up a few miles per hour to get back to the former altitude.

    So if it were not for the Van Allen belt, they could orbit higher up, and be at an altitude where the residual air is even thinner and reducing the amount of fuel needed per year for any such maneuvering to keep altitude.

    So it is an inhibitor to going to the altitude they would like to have an orbiting space station reside.

    But I wouldn't call that a function, I would call it an effect. Posing that effect as a function would be to imply some kind of intelligence behind the radiation belts. That would be like wondering what is the function of sunspots.
  6. Standard member Grampy Bobby
    Boston Lad
    08 Aug '14 17:18
    Originally posted by sonhouse
    The apparent function they perform is to keep orbiting manned vehicles from taking up long term residence at the altitudes where the radiation belt resides.

    The ISS has to use orbits much lower than the Van Allen belts or they would be fried with radiation, a LOT of radiation.

    That has the effect of requiring a lot of fuel onboard to periodically fi ...[text shortened]... gence behind the radiation belts. That would be like wondering what is the function of sunspots.
    Do these belts in any way affect the temperature of the earth's immediate atmosphere or content of the air we breathe?
  7. 08 Aug '14 18:00
    Originally posted by Grampy Bobby
    Do these belts in any way affect the temperature of the earth's immediate atmosphere or content of the air we breathe?
    Not in any significant way.
  8. Standard member sonhouse
    Fast and Curious
    08 Aug '14 18:23
    Originally posted by twhitehead
    Not in any significant way.
    Like he said, pretty close to zero interaction with the atmosphere, but there still is stuff up there, better vacuum than I get at work, right now 9 E-8 torr, a very good vacuum for industrial purposes but the vacuum up there is like minus 14 torr or so, a million times better a vacuum than we can make in standard industrial uses. Don't quote me but I think the big boys, like at Cern don't get much better than E-12 maybe E-13 level, which is still 100 times more populated than up there a few hundred miles high. And they manage to do cutting edge physics at that level so the vacuum up 500 miles to 1000 miles up, which is prime Van Allen territory, there is much less stuff there and if anything, the stuff from the lower atmosphere would tend to contaminate IT, not vice versa.
  9. Standard member Grampy Bobby
    Boston Lad
    08 Aug '14 19:03
    Originally posted by sonhouse
    Like he said, pretty close to zero interaction with the atmosphere, but there still is stuff up there, better vacuum than I get at work, right now 9 E-8 torr, a very good vacuum for industrial purposes but the vacuum up there is like minus 14 torr or so, a million times better a vacuum than we can make in standard industrial uses. Don't quote me but I think ...[text shortened]... d if anything, the stuff from the lower atmosphere would tend to contaminate IT, not vice versa.
    What does this "minus 14 torr or so, a million times better a vacuum than we can make in standard industrial uses." suck?
  10. Standard member Grampy Bobby
    Boston Lad
    08 Aug '14 19:05
    Originally posted by twhitehead
    Not in any significant way.
    What then does "affect the temperature of the earth's immediate atmosphere or content of the air we breathe"?
  11. 08 Aug '14 19:39
    Originally posted by Grampy Bobby
    What then does "affect the temperature of the earth's immediate atmosphere or content of the air we breathe"?
    A lot of things. Most notably, the sun and plants. The sun is responsible for practically all the heat, and plants for the oxygen we breathe. But obviously there is a lot more to it than that. Without knowing what specifically you are interested in, I can't really help. You could look up 'climate', and 'atmosphere' on wikipedia.
  12. Standard member sonhouse
    Fast and Curious
    08 Aug '14 20:35 / 2 edits
    Originally posted by Grampy Bobby
    What does this "minus 14 torr or so, a million times better a vacuum than we can make in standard industrial uses." suck?
    Yeah, the way industrial vacuum goes, there is a level of vacuum that goes from zero to about about 30 inches of mercury, that's where in a column of mercury where it is in a u shaped tube say three feet high on both necks, and you put mercury in it and pump down one side of the tube while the other side is open to atmosphere, the more you pump out the one side the more the mercury moves from where it was level between the two tubes to higher up on the side that is being pumped.

    That movement though, ends when the level changes by about 30 inches because atmospheric pressure pushing down on the open end pushed the mercury up the side with the vacuum but only up to a point. Doesn't matter how much better the vacuum gets (how much less air is left on that side) the mercury will refuse to move any more than that 30 inches or so because Earth's atmosphere can't push any harder than that.

    On Venus, however, the pressure there is almost a thousand times that of Earth, just like biblical hell, 1500 pounds per square inch and a thousand degrees...

    So there, if you had the same set up, the tube would have to be thirty THOUSAND inches high because that is how hard Venus' atmosphere would push down on a column of mercury when the other side is sucked out.

    Conversely, if that same setup was on the moon, no matter how good your vacuum is on the side you are pumping out, the mercury won't move at all since the vacuum on the other side is already WAY better than anything we can achieve on Earth.

    Get that part?

    Now, that is the level of vacuum used to hold down stuff like wafers to a chuck or the high end vinyl record players that have a vacuum to suck down the vinyl record flat.

    That's the first level of vacuum and is easy to get with cheap pumps.

    The next level is where you start to think about atmosphere pressure in terms of Torr (the name of an early atmosphere scientist).

    One atmosphere is 760 torr and that 30 inches of mercury thing would be getting down to MAYBE 1 torr.

    But that is only the beginning of vacuum levels.

    Now more complex mechanical pumps can go down a thousand times lower, to around 1/1000 th of a torr, called in the trade, one millitorr.

    Now that represents the second level.

    The third level which uses a variety of different kinds of high vacuum pumps, google that for more info, it would take me several pages just to list the different technologies that do that job.

    But from 1 milltorr you go down to micro torr level, where 1 E -6 (one millionth of a torr) is starting to be useful for industrial purposes.

    My machine gets down one to two orders of magnitude lower yet, one of them into the -8 range, one hundred millionth of a torr.
    Another machine is in the - 7 range, on tenth of a millionth of torr, ten times worse vacuum but still way good enough for most industries.

    Now there is a third level much lower than that using a bunch of techniques I won't bore you with but the big guys at CERN and so forth, go WAY lower than I do here at work, more like one TRILLIONTH of a torr, down in the -13 or so level.

    That is about as good as we can get here on Earth. If they open the doors to space on a chamber in the ISS, they can get instant -15 or better vacuum. I don't know if they are actually doing experiments like that but it is funny, just open a door and you get vacuum levels way way better than any we can do with on Earth, same as on the moon.

    My machine running on the moon wouldn't even need a vacuum pump, instead it would need to be sealed up so the levels we use when it operates won't just get totally sucked out but the incredible vacuum on the moon

    The best vacuums for R&D labs and some production outfits go down to the -12 level for a process called "Molecular Beam Epitaxy" where they build up layers basically atom by atom and that takes a very good level of vacuum.

    My machine is WAY to dirty for that kind of job, when it runs, it is in the millitorr range and my high vac pump has to be throttled back to allow those higher pressures to exist in the main chamber, otherwise that level would just gum up the pump and the pump would try to keep the vacuum level in the -5 or -6 range (-5 is worse than -6) where we run argon gas into the system a thousand times thicker than that, -3 level.

    So that's the skinny on high vacuum, hope it doesn't give you a headache
  13. Standard member Grampy Bobby
    Boston Lad
    08 Aug '14 20:57 / 1 edit
    Originally posted by twhitehead
    A lot of things. Most notably, the sun and plants. The sun is responsible for practically all the heat, and plants for the oxygen we breathe. But obviously there is a lot more to it than that. Without knowing what specifically you are interested in, I can't really help. You could look up 'climate', and 'atmosphere' on wikipedia.
    twhitehead, my interest in this context is learning what mechanisms [for lack of a better word] make earth habitable.
  14. Standard member Grampy Bobby
    Boston Lad
    08 Aug '14 21:00
    Originally posted by sonhouse
    Yeah, the way industrial vacuum goes, there is a level of vacuum that goes from zero to about about 30 inches of mercury, that's where in a column of mercury where it is in a u shaped tube say three feet high on both necks, and you put mercury in it and pump down one side of the tube while the other side is open to atmosphere, the more you pump out the one ...[text shortened]... n that, -3 level.

    So that's the skinny on high vacuum, hope it doesn't give you a headache
    Please realize that I'll have to ponder your reply since my frame of reference for technical terminology is limited. Thanks.
  15. 09 Aug '14 08:07
    Originally posted by Grampy Bobby
    twhitehead, my interest in this context is learning what mechanisms [for lack of a better word] make earth habitable.
    The most important factor, is the distance of the earth from the sun. It has to be within the Goldilocks zone. There are three planets within that zone, Venus, Earth and Mars.
    Then there is the requirement that the planet be large enough to retain an atmosphere.
    The magnetic field also helps.
    Then there is the composition of the atmosphere.
    I would suggest you start with a course on climate. Try one of these:
    http://forecast.uchicago.edu/moodle/
    http://www.conted.ox.ac.uk/F850-5
    http://www.exeter.ac.uk/climatechangecourse/
    http://www.uncclearn.org/knowledge-platforms
    http://www.openculture.com/2012/01/global_warming_a_free_course_from_uchicago_explains_climate_change.html

    Or search for "free course climate science" for more.