# Tag Info

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From Roemer and Light Speed: The orbital period of Io is now known to be 1.769 Earth days. The satellite is eclipsed by Jupiter once every orbit, as seen from the Earth. By timing these eclipses over many years, Roemer noticed something peculiar. The time interval between successive eclipses became steadily shorter as the Earth in its orbit moved toward ...

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The energy shifts of transitions including the s-orbitals of various isotopes of hydrogen are dependent on the proton's charge radius and are a surprisingly sensitive tool for this kind of thing. Recently this has been checked with muonic hydrogen, with surprising results. Paper at http://dx.doi.org/10.1126/science.1230016, and references therein. Related ...

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It is correct if not equivalent in most contexts. For example, if you have a cuboid tank for water, $m^3$ would be the unit used to denote its volume, $m$ the depth of water. Then, when you try to denote the ratio of volume of water to depth with the unit $m^3/m$, you suddenly realize what you are trying to mean is equivalent to its horizontal ...

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Ever since Einstein formulated relativity we describe spacetime as a manifold equipped with a metric. Then we can use all the machinery of differential geometry to calculate properties of our spacetime. In particular, volume is defined using the volume element, $dV$, and we get volumes by integrating $dV$. For a flat space with Cartesian coordinates the ...

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https://en.wikipedia.org/wiki/Optical_fiber states that a rule of thumb is that the speed of light in an optical fiber is 200,000 kilometers per second. https://en.wikipedia.org/wiki/Fibre_Channel states the fibre channel networks run at 2,4,8 and 16 gigabits per second. ...

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It depends on the packaging: it's highly variable. But by far the most common one is defined by the Synchronous Digital Hierarchy standard or the almost identical American SONET standard. This is pretty much standard on all optical trunk networking. The data for this answer and your question will almost certainly have passed through an SDH link for the ...

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Con: There are 3 naturally occurring isotopes of silicon, so isotopic purification would be required after elemental purification. I'm unsure about how hard it is to maintain pure silicon. Isotopically, beryllium would be better (100% $^9$Be, naturally), but I don't know about its reactivity, either. Carbon has two naturally occurring isotopes, but we know ...

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The object of making the silicon sphere was not to define the kilogram by the mass of sphere, but redefine Avogadro's constant in terms of the number of silicon atoms. Then use the fixed Avogadro's constant to fix the kilogram. Avogadro's constant was defined as the number of atoms in 12 grams of carbon atoms. You can read up on the Avogadro project here ...

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