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21
Radio Show & Podcast Feedback / Training the next generation
« Last post by thedoc on Today at 12:40:20 »
University students gain hands-on experience of a new DNA sequencing technology
Read a transcript of the interview by clicking here
or Listen to it now or [download as MP3]
22
Radio Show & Podcast Feedback / New hope for epilepsy
« Last post by thedoc on Today at 12:40:20 »
Drugs that block the hormone oestrogen have the potential to treat seizures
Read a transcript of the interview by clicking here
or Listen to it now or [download as MP3]
23
Radio Show & Podcast Feedback / Going global
« Last post by thedoc on Today at 12:40:20 »
Genetics reveals how an 11,000 year-old dog cancer has spread around the world
Read a transcript of the interview by clicking here
or Listen to it now or [download as MP3]
24
Radio Show & Podcast Feedback / Schistosome Stem Cells
« Last post by thedoc on Today at 12:40:20 »
How stem cells help parasitic worms to thrive in their host
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25
Quote from: kdd2018
When water is being used for hydraulic fracking can it cause an earthquake?
Yes - it is thought that the water can lubricate fault lines, allowing the pent-up energy to be dissipated in an earthquake.

Is this bad? The earthquake would have happened sooner or later. If it is sooner, earthquaes at 2 or less on the Richter scale aren't felt by humans. And if it were later, it would be after more geological stress had built up, and it would be more destructive. So are a number of very small earthquakes better than one large and destructive earthquake? Our legal system is not set up to decide such questions (and the Italian legal system is not set up to deal with entirely natural earthquakes).

Quote
I have heard that man-made earthquakes are created more often by waste water injection
When oil and gas wells start to dry up, water is often injected under pressure into obsolete wells. Since oil and gas float on top of the water, this increases flow into the wells that are still operational.

This can cause slips on fault lines, just like fracking.

Quote
What is the difference between the water used in fracking and waste water?
Water used in fracking contains a "proppant", used to "prop open" the cracks in the sedimentary layers. The proppant consists mostly of sand (which is what rocks are mostly made of), although there have been concerns about other additives.

I don't think the differences in the water are significant - it is mostly the injection of fluid under pressure that leads to the earthquakes.
See: https://en.wikipedia.org/wiki/Environmental_impact_of_hydraulic_fracturing#Seismicity
26
    Quote from: Alan McDougall
    What about the Lagrange points between the moon and earth?
    These Lagrangian points are fixed in the Earth-Moon system, ie they rotate once around the Earth every time the Moon rotates around the Earth, ie once every 27.3 days.
    • This also means that the satellite is invisible half of the time, from any given point on Earth.
    • And when you can see it, you need a tracking dish to track it across the sky, which is more expensive and more likely to malfunction.
    • It is about 10 times farther away from the Earth than geosynchronous orbit (nearer the Moon at 380,000km, compared to geosynchronous orbit at 35,000km)
    • This means that transmitters have to be about 100 times more powerful (due to the inverse square law)
    • Communication delays are about 10 times greater; interactive voice communications becomes impossible (it takes a bit of effort even via geosynchronous satellite).
    • Internet browsing is already slow from geosynchronous orbit; it would be 10 times worse at Lunar Lagrange points.
    • There are 5 Lagrangian points, of which one is on the other side of the Moon. This gives 4 satellite locations visible from Earth, compared to the 180 satellite slots at 2 degrees separation for geosynchronous satellites sharing the same frequency bands.

    For effective communications, a 24-hour orbit is very much preferred, compared to a Lunar Lagrangian point, since the geosynchronous satellite sits in a fixed position in the sky, as seen from Earth's surface.

    Quote
    if an object were placed there it would be far more stable situation, than any geocentric orbit
    Of the 5 Lagrangian points, only 2 are stable (ie at L4 and L5, a satellite will stay there, provided the cyclic gravitational tugs of the Sun and Jupiter don't build up an oscillation that gets too large).

    For the other Lagrangian points, if the satellite drifts away from the precise point, it will accelerate away from that point. However, a number of satellites have been positioned at (or orbiting around) various Lagrangian points - they just need to use fuel for station-keeping, to keep them in the right location. Not so different from satellites in geosynchronous orbit.

    See:
    https://en.wikipedia.org/wiki/Lagrangian_point
    https://en.wikipedia.org/wiki/List_of_objects_at_Lagrangian_points
    https://en.wikipedia.org/wiki/List_of_satellites_in_geosynchronous_orbit[/list]
    27
    There is no center of the Universe.
    28
    Physics, Astronomy & Cosmology / Re: What is absolute nothingness?
    « Last post by Flatland on Today at 11:30:14 »
    What is absolute nothingness?

    As an example of what I mean by this question, lets suppose the universe is everything that exists, then shrink it down back to the singularity and imagine, if possible that the singularity vanishing from existence.

    Absolute nothingness (You cannot say nothing is left, or you have nothing left, because the word "IS" and LEFT and HAVE, denote that you have a something.)

    Maybe we could use "Absolute nothingness= Total Absence of Everything? 

    An infinite totally empty void is not nothing, it is three dimentional empty space!

    Can one describe a negation like this in words?

    Alan

    The closes analogy I can think of is death.  Total absolute none existence.
    29
    Quote
    what is a vanishing spray?
    It is used by referees to temporarily mark football fields for the duration of one play (perhaps 1 minute).

    See: https://en.wikipedia.org/wiki/Vanishing_spray

    Quote
    a spray paint that vanishes
    A spray paint that was highly visible would need a lot of liquid, containing some filler which is highly visible. Paints typically use fillers like titanium dioxide (lead oxide having been banned due to toxicity).

    But to get this highly visible filler to become transparent is quite a challenge! And it must not kill the grass, or leave a slippery patch on the grass (that could cause a later accident).

    I think the foaminess is the secret to being highly visible when first sprayed, and yet disappearing into a damp spot on the grass in a minute or so. The foam contains very little liquid - it is mostly gas, which dissipates into the atmosphere as the bubbles collapse.
    30
    I had a chat to a friend working in Australia's National Measurement Institute.
    • NMI use commercial Cesium clocks; these cost about $US70,000, and need refurbishment after 10 years for about $US30,000.
    • You can obtain Rubidum atomic clocks for $1,000 - $2000 (and even cheaper, second-hand).
    • There are now commercial trapped ion clocks. But the international standard is currently based on Cesium clocks.
    • Transfer of time reference around the nation and international is done by both ends of the transfer observing the same individual GPS satellites, while they are visible in both locations. This is more accurate than the normal GPS-based time reference, which is an average of the time provided by a group of satellites - but each location will see a different set of GPS satellites.
    • For time transfer to the other side of the Earth, both laboratories can't observe the same GPS satellite at the same time, so it is done in two hops, using an intermediate laboratory with a Cesium clock.
    • Most of our computers and smartphones have their time set by Network Time Protocol (NTP), and some NTP servers are synchronized by this method.

    For a specialist time-keeping interest group, see: http://www.leapsecond.com/time-nuts.htm
    In case you want your own atomic clock at home, apparently they have instructions for obtaining your own Rubidium clock on the cheap by resurrecting defunct Rubidium tubes!
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