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Graphene and Quantum Hall Effect Could Help Redefine Metrics
eldavojohn writes "The National Physical Laboratory has published research in Nature that could lead to redefining two of our most commonly used metrics. There's been a lot of trouble stemming from defining an exact Kilogram as some lump of platinum-iridium sitting in a glass case somewhere, so the proposal was put forth to study the quantum hall effect with different materials. Enter the Nobel prize winning, super strong, silicon usurping graphene. NPL now says you can add quantum resistance metrology to the list of graphene's many conquests as they say the quantum hall effect in graphene is 'very robust and easy to measure.' With this at their disposal, the Kilogram may be redefined in terms of h, the Planck constant, and the Ampere may be redefined in terms of e, the electron charge (alias Elementary charge or the charge of a proton). You can find the full paper here."
...that the ampere was already defined in terms of the charge of the electron.
It even won a Nobel prize.
SECOND POST! Both kg and A may be redefined in terms of h and e.
When was the last time someone redefined a pound?
The Kruger Dunning explains most post on
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The SI base unit is the Ampere. The Coulomb is a derived unit (Ampere-seconds).
Which is definitely silly - the base unit is charge flow, and the derived unit is charge?
To a Lisp hacker, XML is S-expressions in drag.
The gift that keeps on giving.
vos nescitis quicquam, nec cogitatis quia expedit nobis ut unus moriatur homo pro populo et non tota gens pereat.
1) Can bitcoins be minted from graphene?
2) How does this affect the Packt constant?
Right now the accuracy with which the kilogram can be measured is about 1 part per 1E8. The paper mentions a noise of around 1 part per 1.6E11. That's over 1,000 times better. That certainly suggests that this method will be sufficiently "better" to be used as the new standard.
I, for one, welcome our incredibly accurate overlords.
Great warrior...hrmph! Wars not make one great.
The US Dollar.
Set your phasers on "funky"!
It even won a Nobel prize.
They only awarded that because it wasn't George Bush.
"Yay, inanimate carbon, errr, sheet!
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
That's not true..
And the award goes to... this inanimate carbon sheet!
I'm glad to see that we can finally dump that silly imperial system and get to a set of eminently sensible standards and measures that aren't obscure and/or arbitrary.
Because when I want to buy meat, I certainly first think "how will this pile of hamburger relate to the Planck constant?"
-Styopa
How much I pay for my baggage at the airport?
Eventually Scotty will come up with a way around it at Kirk's behest.
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Isotropically pure diamonds, either all C-12 or all C-13, have 50% higher thermal conductivity then isotropically mixed diamonds. http://en.wikipedia.org/wiki/Isotopically_pure_diamond When using graphene for this kind of measurement, do they also use a single isotope of carbon? Does it make any difference if the carbon used in not isotropically pure?
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I had always assumed that a meter is based on the speed of light (so relativistic effects can change the size of the meter, have fun with that). And that 1/10 of a meter is a decimeter (deci means 1/10th). And if you form a cube whose sides are 1 decimeter, you get a volume that is 1 liter. And if that liter volume is filled with pure water at 0 degrees Celsius (the temperature at which water freezes, but in the liquid rather than the solid state), and weigh that water, it weighs 1 kilogram. I always thought this is how metric units of measure were created. Temperature was Celsius, with water being the arbitrary stuff used as reference, and where it freezes is 0C and where it boils is 100C and there are no offsets. Fahrenheit arbitrarily uses water too, but they have 180 degrees between boiling and freezing (I suppose its easy to have 180 marks on a half circle), except they have this weird 32 degree offset (I don't remember why), so that water is declared to freeze at 0+32 rather than 0, and boil at 180+32=212 (again, I don't know why). Using whole numbers, Fahrenheit is 1.8 times as accurate as the Celsius. When you use a single digit decimal with Celsius, its 5.5 times as accurate as Fahrenheit.
And if that liter volume is filled with pure water at 0 degrees Celsius (the temperature at which water freezes, but in the liquid rather than the solid state), and weigh that water, it weighs 1 kilogram.
This was the definition for about five or so years in the eighteenth century.
One Horsepower is the power of a big white dead horse kept at the headquarters of the International Bureau of Weights and Measures in Paris
0 degrees Fahrenheit was the freezing point of a particular brine, which was the lowest freezing point liquid material available at the time.
One: meter. Originally, the meter was suppose to be 1/40,000 of the circumference of the earth as measured from poll-to-poll and back. They actually tried to measure this, with surveyors and crap, and they were a bit off on it. Now, yes, it is based on the distance light travels in a vacuum in a specific (very short) amount of time, although it is still very close to that original (inaccurate) measurement. However, you don't need to "worry" about relativistic effects: any measuring device you apply will shrink in the same proportion as what is being measured (because the difference is only visible to an observer in a different reference frame.)
Two: kilogram. They originally did it by a cubic centimeter (which is why the base unit name was the gram) not a cubic decimeter; when the changed to cubic decimeter/liter though they didn't redefine gram, they just said they were defining the KILOgram. And yes, it was at zero degrees, but it was also--unspecified but assumed--at one atmosphere of pressure. Later, it was changed to be at 4 degrees, since that's when water is at its most-dense (again, at 1 atm.) and that's the mass that the reference mass was based on, but since then the reference mass is the ONLY thing the measure is based on. Which is handy, because (as you've surely guessed) the value would change at different pressures (or if the definition of a meter changed) but is bad because you can't just describe a kilogram; you have to physically use the reference mass.
Three: Fahrenheit. Fahrenheit also used water, yes, but it was salt water (he was interested in international shipping, which goes through oceans, which are full of salt water). Salt water freezes at 0 F and boils at 100 F; nothing to do with degrees in a circle.
Now, bonus question: why is the pressure measurement "1mm of water" not equal to 1/10th of the pressure measurement "1cm of water"?
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I hope the Plank Constant is not found to vary over the life of the universe, as alpha has been conjectured to.
I am a little surprised that the several spheres of silicon scattered around the world hadn't already redefined kg standard. I saw one of those balls 10 years ago, and understood then that the work was almost complete - the deviations from a perfect sphere were negligible, radius well determined, and purity excellent.
I'm also a little surprised that these versions of the kg standard need exist at all. I thought it was exactly 1L of water. Which is exactly 10cm*10cm*10cm of water. And a metre is exactly the distance light travels in 1299,792,458 of a second (it had formerly been 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom).
I guess "water" isn't sufficiently well defined or reproducible.
Salt water does not boil at 100 Fahrenheit at any normal pressure.
BP of fresh/sweet water is 212, salt increases that (Raoult's Law).
Beyond redefinition of the meter, a matter-based unit of mass is
sensitive to the isotope ratio of the matter used e.g; deuterated (heavy) water
Were that I say, pancakes?
Redefining the kilogram with the Planck constant doesn't help with accuracy, since the Planck constant itself is known to the precision of 5e-8 only. So, in effect, the determination to the accuracy of 1e-8 isn't a major improvement. Just think of 1e-8 in terms of the prototype kilogram. 1e-8 means that the mass of the prototype (1000 g) can be fixed to within 0.01 mg, which is really a lot. This is an amount that can be measured by hand, without using any fancy and expensive machine. Our university department has a regular, everyone-and-their-dog-has-one, off-the-shelf, scientific garden variety, scale, which measures to this precision, five decimals to the gram. To put this in context, I use a four-decimal scale for everyday weighing in small-scale work; I usually avoid the five-decimal scale because it's prone to annoying hunting behavior (it "dances around" the correct value) more than the more robust four-decimal scale. In effect, it's just passing the buck if you define the kilogram based on the Planck constant.