It's not as racist as it sounds. Some researchers have created what is supposed to be the blackest substance ever made, as in it absorbs 99.9 percent of the light that hits it. It's a collection of carbon nanotubes stacked next to each other. There is a picture of it in the link (picture #3). It's blacker than the blackness standard currently used by N.I.S.T. The theory is that this might be useful in solar energy production or stealth applications. Cool stuff.
Franny's not impressed. She says she made one of these years ago. Of course you use nanotubes. It's the teeniness that does it. The light can't get through. 'Cuz the teeniness. And the carbon. I love pregnant scientists.
Showing posts with label physics. Show all posts
Showing posts with label physics. Show all posts
Tuesday, January 15, 2008
Friday, October 5, 2007
Mass Metrology: A small taste of Dave's job
From time to time, I hear, "So what exactly do you do anyway?" For some reason, metrology and calibration are unusual concepts for most people. My sister heard metrology, and wondered why I wanted to be a weatherman. The details of what I do really don't matter that much to most people. The world keeps on ticking as long as people like me are out doing our thing. Yeah, Dave, but what is your "thing"?
Don't worry if your eyes glaze over while reading this and you don't finish. I'm sure you'll be in the majority. I just present it in case anyone is interested in the arcane science of what I do.
I'm a small part of a large system linking measurement devices all over the world back to standard measurements somewhere. That's metrology, or the sturdy of precision measurements. Calibration is just the comparison of one measurement device back to something that is traceable through an unbroken chain of comparisons to one of those standards. Most measurements in this country are traced back to the National Institute of Standards and Technology (NIST), a part of the Commerce Department. NIST laboratories maintain the U.S. national standard for thousands of things. Some are basic measurements like the second or the meter and some are more obscure such as standard Columbia River beach sand or whatever.
I'm more concerned with the basic measurements. NIST has extensive experimental apparatus that can determine with a great deal of precision exactly how long a meter is using light speed and how long a second is using atomic fluctuations. Most basic units are defined this way. There is an accepted standard that the distance light travels in a certain fraction of a second equals one meter. Everybody agrees on that definition, so anyone can find the meter depending only the ability to isolate the fraction of a second and measure how far the light went.
It used to be that all measurements were based on artifacts, or specific things that defined a yard or a foot or what ever. In the beginning, the myth goes that a yard was the distance between the king's thumb and his nose. Someone decided that something more specific might be useful since different places had different kings, so he decided to use a particular stick that was about the right length. He then could make copies of that stick and pass them around so everybody was using the same yard. However, over time, this method begins to fail as the specific artifacts are used and damaged. You end up with a bunch of sticks that are something like a yard, but none of them are exact anymore and none of them completely agree with each other, which kind of defeats the purpose. So over the years, most units have been defined in terms of physical properties of certain materials, properties that will theoretically never change. Therefore everyone who can set up experiments to measure those properties can recreate the units as precisely as they can measure them.
The sole exception to this method is mass. Up until around 1800, the kilogram was defined as the mass of one cubic decimeter of water. A cubic decimeter was used instead of a liter because length is a base unit, while volume is derived based on length. However, since water can change due to temperature and pressure, a better method was needed. Again, like the stick, someone made a prototype kilogram, which was from that point considered the de facto definition of a kilogram. However, nobody has yet come up with a proper physical property measurement for mass to replace this old method of measurement.
The current, most exact kilogram was made in the 1880's, as were the various copies of it scattered around the world. The primary kilogram prototype (pictured above, inside concentric bell jars) is in France and the U.S. top kilogram (pictured below) is at NIST. The primary kilogram is kept sealed and locked in a vault almost all of the time. It is brought out once in a great while (maybe once every decade or two) for comparison with the various national standards. Other than that, it never gets touched. The U.S. national kilogram is then compared occasionally by NIST against several copies they use for checks against other weights. My company has a master set of weights that are sent to NIST every five years for comparison against that second tier of weights. Those are then compared against our other weights once a year and against another set that is used for customer weight calibrations. I then take my weights and calibrate balances and scales used in the world. We even work on other metrology balances that are used for further weight checks. The idea is to handle the sets closer to NIST as little as possible in order to keep them from changing too much between calibrations. There is a certain amount of uncertainty in each comparison, which increases for each step away from the prototype. If your weights change beyond that uncertainty, then you throw the work you've been doing into question. That's bad.
To put the precision into context, I have Class 1 weights (the best available) ranging from 20 kilograms (about 45 lb.) down to 1 milligram (a tiny piece of foil you would overlook if you didn't know about it). For the smaller of these weights, say below about 200 grams, I know the exact weight down 8 digits beyond the decimal point, with the uncertainty (different for each one) showing up in the 5th or 6th place. This means that I know the values of my weights to at least 7 significant figures. This is important since the best balance (precision scale) I work with has 20,000,000 divisions (2 grams to 0.1 micrograms, or 0.0000001 grams). For reference, the main prototype is known to about 10 significant figures.
The problem with all this is that the prototype kilograms are suffering the same fate as the sticks, despite all the care put into their handling. The main prototype has lost approximately 30 micrograms over the last century. That means that if you assume that it was once 1.000000000 kilogram when it was made, it is now 0.999999970 kilogram. Seems pretty insignificant doesn't it? It is, for now at least. There are almost no instruments in the world good enough to see that difference. However, the kilograms will get worse and instruments will get better, especially as we continue to try and probe further into the atom and deeper into space. Eventually, this definition will fail to be good enough.
So what to do about it? There are two options that scientists are pursuing right now.
The first is basically making a better kilogram prototype. A group of Australian scientists is working on just that. They are trying to make a perfect sphere of silicon (pictured below) that is exactly one kilogram. The atomic weight of silicon is known quite well as is it's crystalline structure. It's quite possible to grow a very large perfect crystal of silicon. That's how computer chips are made. Then you apply a little math. You can figure out how many atoms of silicon you need to make a kilogram based on its atomic weight, and knowing the crystalline structure, you can figure out how big a sphere needs to be to contain the proper number of atoms. The hard part is now to make a perfectly round sphere of exactly the right diameter (using length, which is known very well). By the time they are done with this thing, it will essentially be the roundest thing ever made. This is basically just making another prototype, which will have the same issues as the current one. Unlike the current one, however, someone in the future can do the same thing again and come up with an identical, or maybe even better version, limited only by measurement and machining capability.
The second option is the watt balance. It is designed to use electrical properties, which are known very well, to determine the mass of an oscillating body. The math is very intensive. This type of device exists. NIST is working very hard on this method of mass determination. In the long run, something like this will likely take the place of having an artifact that must be compared back to. However, for the moment the uncertainty of doing it this way is still higher than using the current shrinking French kilogram.
Most of this is mainly academic. We are many centuries away from these variations causing the common man any trouble. A half a pound of deli ham and a gallon of gas will still be the same things as far as you will be able to tell. This becomes a problem only at the edge of research and possibly into some VERY exacting manufacturing, although I can't think of an example. Nothing you could afford anyway.
There. I obviously find this interesting, and I assume that if you made it this far, it must at least hold passing amusement for you. Let me know if I left anything too muddy or if something doesn't make sense.
Don't worry if your eyes glaze over while reading this and you don't finish. I'm sure you'll be in the majority. I just present it in case anyone is interested in the arcane science of what I do.
I'm a small part of a large system linking measurement devices all over the world back to standard measurements somewhere. That's metrology, or the sturdy of precision measurements. Calibration is just the comparison of one measurement device back to something that is traceable through an unbroken chain of comparisons to one of those standards. Most measurements in this country are traced back to the National Institute of Standards and Technology (NIST), a part of the Commerce Department. NIST laboratories maintain the U.S. national standard for thousands of things. Some are basic measurements like the second or the meter and some are more obscure such as standard Columbia River beach sand or whatever.
I'm more concerned with the basic measurements. NIST has extensive experimental apparatus that can determine with a great deal of precision exactly how long a meter is using light speed and how long a second is using atomic fluctuations. Most basic units are defined this way. There is an accepted standard that the distance light travels in a certain fraction of a second equals one meter. Everybody agrees on that definition, so anyone can find the meter depending only the ability to isolate the fraction of a second and measure how far the light went.
It used to be that all measurements were based on artifacts, or specific things that defined a yard or a foot or what ever. In the beginning, the myth goes that a yard was the distance between the king's thumb and his nose. Someone decided that something more specific might be useful since different places had different kings, so he decided to use a particular stick that was about the right length. He then could make copies of that stick and pass them around so everybody was using the same yard. However, over time, this method begins to fail as the specific artifacts are used and damaged. You end up with a bunch of sticks that are something like a yard, but none of them are exact anymore and none of them completely agree with each other, which kind of defeats the purpose. So over the years, most units have been defined in terms of physical properties of certain materials, properties that will theoretically never change. Therefore everyone who can set up experiments to measure those properties can recreate the units as precisely as they can measure them.
The sole exception to this method is mass. Up until around 1800, the kilogram was defined as the mass of one cubic decimeter of water. A cubic decimeter was used instead of a liter because length is a base unit, while volume is derived based on length. However, since water can change due to temperature and pressure, a better method was needed. Again, like the stick, someone made a prototype kilogram, which was from that point considered the de facto definition of a kilogram. However, nobody has yet come up with a proper physical property measurement for mass to replace this old method of measurement.
The current, most exact kilogram was made in the 1880's, as were the various copies of it scattered around the world. The primary kilogram prototype (pictured above, inside concentric bell jars) is in France and the U.S. top kilogram (pictured below) is at NIST. The primary kilogram is kept sealed and locked in a vault almost all of the time. It is brought out once in a great while (maybe once every decade or two) for comparison with the various national standards. Other than that, it never gets touched. The U.S. national kilogram is then compared occasionally by NIST against several copies they use for checks against other weights. My company has a master set of weights that are sent to NIST every five years for comparison against that second tier of weights. Those are then compared against our other weights once a year and against another set that is used for customer weight calibrations. I then take my weights and calibrate balances and scales used in the world. We even work on other metrology balances that are used for further weight checks. The idea is to handle the sets closer to NIST as little as possible in order to keep them from changing too much between calibrations. There is a certain amount of uncertainty in each comparison, which increases for each step away from the prototype. If your weights change beyond that uncertainty, then you throw the work you've been doing into question. That's bad.
To put the precision into context, I have Class 1 weights (the best available) ranging from 20 kilograms (about 45 lb.) down to 1 milligram (a tiny piece of foil you would overlook if you didn't know about it). For the smaller of these weights, say below about 200 grams, I know the exact weight down 8 digits beyond the decimal point, with the uncertainty (different for each one) showing up in the 5th or 6th place. This means that I know the values of my weights to at least 7 significant figures. This is important since the best balance (precision scale) I work with has 20,000,000 divisions (2 grams to 0.1 micrograms, or 0.0000001 grams). For reference, the main prototype is known to about 10 significant figures.
The problem with all this is that the prototype kilograms are suffering the same fate as the sticks, despite all the care put into their handling. The main prototype has lost approximately 30 micrograms over the last century. That means that if you assume that it was once 1.000000000 kilogram when it was made, it is now 0.999999970 kilogram. Seems pretty insignificant doesn't it? It is, for now at least. There are almost no instruments in the world good enough to see that difference. However, the kilograms will get worse and instruments will get better, especially as we continue to try and probe further into the atom and deeper into space. Eventually, this definition will fail to be good enough.
So what to do about it? There are two options that scientists are pursuing right now.
The first is basically making a better kilogram prototype. A group of Australian scientists is working on just that. They are trying to make a perfect sphere of silicon (pictured below) that is exactly one kilogram. The atomic weight of silicon is known quite well as is it's crystalline structure. It's quite possible to grow a very large perfect crystal of silicon. That's how computer chips are made. Then you apply a little math. You can figure out how many atoms of silicon you need to make a kilogram based on its atomic weight, and knowing the crystalline structure, you can figure out how big a sphere needs to be to contain the proper number of atoms. The hard part is now to make a perfectly round sphere of exactly the right diameter (using length, which is known very well). By the time they are done with this thing, it will essentially be the roundest thing ever made. This is basically just making another prototype, which will have the same issues as the current one. Unlike the current one, however, someone in the future can do the same thing again and come up with an identical, or maybe even better version, limited only by measurement and machining capability.
The second option is the watt balance. It is designed to use electrical properties, which are known very well, to determine the mass of an oscillating body. The math is very intensive. This type of device exists. NIST is working very hard on this method of mass determination. In the long run, something like this will likely take the place of having an artifact that must be compared back to. However, for the moment the uncertainty of doing it this way is still higher than using the current shrinking French kilogram.
Most of this is mainly academic. We are many centuries away from these variations causing the common man any trouble. A half a pound of deli ham and a gallon of gas will still be the same things as far as you will be able to tell. This becomes a problem only at the edge of research and possibly into some VERY exacting manufacturing, although I can't think of an example. Nothing you could afford anyway.
There. I obviously find this interesting, and I assume that if you made it this far, it must at least hold passing amusement for you. Let me know if I left anything too muddy or if something doesn't make sense.
Saturday, April 21, 2007
Science With Franny
This is Franny's idea. Most times, Franny finds science and how-things-work of only passable interest, at least when I talk about them. However, once in a while, and usually laying in bed almost asleep, I'll hear something like, "Do rocks have cells?" Actually, that was a question that she apparently asked a friend during biology class in high school, but it's a good example of the kind of stuff that comes up. Anyway, I dare say I have a more extensive science education (and interest) than she does (although in her defense, she does know a lot more than she lets on), and since I'm am also a known nerd, I am obliged to come up with answers or explanations for these sometimes ridiculous issues. Occasionally, these conversations even end up making me think about things in new ways and make connections I hadn't considered before. For me the topic is usually done by the time I fall asleep, but Franny usually at least pretends my explanations were interesting and has several times said that I should blog about them in case someone else is wondering about the rock/cells debate. So here goes. This is science related stuff that was interesting to Franny at least once. (This particular batch of stuff all came up last night.)
Recently, Franny spilled some oil from an oil lamp onto a bathmat. She blotted up most of it and then threw it into the wash. She showed it to me at this point and the spot where the oil had been had melted/dissolved/deformed and looked like a 4 inch wide brain poking out of the bottom of the mat. Anyway I mentioned to her that washing oil soaked things is discouraged and drying them is a big no-no. As the warning on our machine says, drying "anything that has ever had any type of oil on it (even cooking oils)" can cause "death, explosion, or fire." The mat never made it into the dryer thank goodness, and by the time she had blotted up the stain, it probably didn't have much left on it anyway, but I'm glad we didn't test the theory. The problem is that oil becomes much more volatile at higher temperature and presents a fire or explosion hazard due to all the motors and relays and such that can make sparks. It's even worse if you have a gas dryer, for obvious reasons. When Franny and I were moving to Portland, we stopped in Worland, Wyoming, which is exactly in the middle of nowhere and is where my mother spent some years growing up. Anyway, we specifically stopped to do some laundry and I was amused by the signs saying "No Roughnecks". You might think that's a redneck joke, but roughnecks are the guys that work on the oil rigs. Since they are often drenched in oil, this is exactly the issue the signs were about. Most things are not designed for use in environments where explosive conditions exist, and most electrical items have some potential for making tiny sparks during use. Some things are designed as explosion-proof, including some of the scales that I work on, since they sometimes need to be used in places with flammable gases or powders. (I do work in some hazardous environments occasionally, but the only time I've ever had to worry about this type of thing was in a flour mill of all places. I had to get some guys to stop welding because a pipe had developed a leak and was spewing a cloud of flour through the room. They understood just fine, but I still got flour all over everything, included my up-until-then precision weights. What fun to clean.)
We also got to talking about a gift card to Ritz Camera that we have and what she might buy with it. I mentioned a wide-angle attachment for her camera, and I was surprised to find out that despite here excellent photography background, she didn't know what I was talking about. The focal length of a lens determines how much of your field of vision appears on the imaging surface of the camera (either the film or digital chip). Most of you have probably seen this when adjusting the zoom on your camera. You may not have known it, but you were adjusting the focal length of the camera and thus changing how much of what was in front of you would make up the picture. Most people have used a zoom to get more detail about a portion of a scene, but most cameras can only shorten the focal length to a certain point. A wide angle lens or attachment shortens the effective focal length further and allows more of the scene to be in the picture. This isn't much good if you want more detail, but it helps if you are trying to photograph something relatively big and getting further away from it is impractical.
I can't remember what prompted it, but Franny mentioned that she didn't really understand radio waves. I noted that they were basically the same as lots of other things: microwaves, infrared light, visible light, ultraviolet light, x-rays, gamma rays, and I believe cosmic rays too. She said that those didn't make much sense either. We got into a discussion about photons and what they were. A photon is sort of a wave in that it acts like a wave when interacting with other light waves and in the way it can be manipulated, and sort of a particle in that it does not require anything else to propagate it and it comes in discreet, although very tiny amounts. It's not really a particle though in that it has no mass and is moving, ironically, at the speed of light, which particles can't do without infinite energy. It's not really a wave either, in that it has momentum and in large enough quantity, can push things. It can be affected by gravity, as in bending around star or getting stuck in black holes. One thing I couldn't remember last night was whether you could affect any of this with magnetism. I feel like you can, but I couldn't come up with an example. It was late, so the discussion didn't get into much more detail than that.
If you didn't know I was a nerd before, I've certainly confirmed it now. Much of my science is remembered from college chemistry and physics, so it may be remembered incorrectly or just plain wrong. Please leave a comment if you'd like to make any additions or corrections. I assume I got something wrong, or at least incomplete anyway. And Franny, if I mischaracterized anything you said, hey, it was late.
Recently, Franny spilled some oil from an oil lamp onto a bathmat. She blotted up most of it and then threw it into the wash. She showed it to me at this point and the spot where the oil had been had melted/dissolved/deformed and looked like a 4 inch wide brain poking out of the bottom of the mat. Anyway I mentioned to her that washing oil soaked things is discouraged and drying them is a big no-no. As the warning on our machine says, drying "anything that has ever had any type of oil on it (even cooking oils)" can cause "death, explosion, or fire." The mat never made it into the dryer thank goodness, and by the time she had blotted up the stain, it probably didn't have much left on it anyway, but I'm glad we didn't test the theory. The problem is that oil becomes much more volatile at higher temperature and presents a fire or explosion hazard due to all the motors and relays and such that can make sparks. It's even worse if you have a gas dryer, for obvious reasons. When Franny and I were moving to Portland, we stopped in Worland, Wyoming, which is exactly in the middle of nowhere and is where my mother spent some years growing up. Anyway, we specifically stopped to do some laundry and I was amused by the signs saying "No Roughnecks". You might think that's a redneck joke, but roughnecks are the guys that work on the oil rigs. Since they are often drenched in oil, this is exactly the issue the signs were about. Most things are not designed for use in environments where explosive conditions exist, and most electrical items have some potential for making tiny sparks during use. Some things are designed as explosion-proof, including some of the scales that I work on, since they sometimes need to be used in places with flammable gases or powders. (I do work in some hazardous environments occasionally, but the only time I've ever had to worry about this type of thing was in a flour mill of all places. I had to get some guys to stop welding because a pipe had developed a leak and was spewing a cloud of flour through the room. They understood just fine, but I still got flour all over everything, included my up-until-then precision weights. What fun to clean.)
We also got to talking about a gift card to Ritz Camera that we have and what she might buy with it. I mentioned a wide-angle attachment for her camera, and I was surprised to find out that despite here excellent photography background, she didn't know what I was talking about. The focal length of a lens determines how much of your field of vision appears on the imaging surface of the camera (either the film or digital chip). Most of you have probably seen this when adjusting the zoom on your camera. You may not have known it, but you were adjusting the focal length of the camera and thus changing how much of what was in front of you would make up the picture. Most people have used a zoom to get more detail about a portion of a scene, but most cameras can only shorten the focal length to a certain point. A wide angle lens or attachment shortens the effective focal length further and allows more of the scene to be in the picture. This isn't much good if you want more detail, but it helps if you are trying to photograph something relatively big and getting further away from it is impractical.
I can't remember what prompted it, but Franny mentioned that she didn't really understand radio waves. I noted that they were basically the same as lots of other things: microwaves, infrared light, visible light, ultraviolet light, x-rays, gamma rays, and I believe cosmic rays too. She said that those didn't make much sense either. We got into a discussion about photons and what they were. A photon is sort of a wave in that it acts like a wave when interacting with other light waves and in the way it can be manipulated, and sort of a particle in that it does not require anything else to propagate it and it comes in discreet, although very tiny amounts. It's not really a particle though in that it has no mass and is moving, ironically, at the speed of light, which particles can't do without infinite energy. It's not really a wave either, in that it has momentum and in large enough quantity, can push things. It can be affected by gravity, as in bending around star or getting stuck in black holes. One thing I couldn't remember last night was whether you could affect any of this with magnetism. I feel like you can, but I couldn't come up with an example. It was late, so the discussion didn't get into much more detail than that.
If you didn't know I was a nerd before, I've certainly confirmed it now. Much of my science is remembered from college chemistry and physics, so it may be remembered incorrectly or just plain wrong. Please leave a comment if you'd like to make any additions or corrections. I assume I got something wrong, or at least incomplete anyway. And Franny, if I mischaracterized anything you said, hey, it was late.
Subscribe to:
Posts (Atom)