Anyone who’s got any business to do with physics or math – from relatively low level like homework, to higher level calculations – knows the occasional frustration of having to solve a physical equation involving constants.

Wolfram Alpha usually is the best solution, but it can be a bit tedious and complicated, and to use it right, I find you need to search for the values of the constants or the way Wolfram Alpha expects them to be written.

This means that sometimes a relatively simple equation can turn into an annoying research of the Wolfram Alpha documentation.

There are a few good calculators online (Google.com being one of them, on a crunch) but not many that help you make your way through the (many) physical constants that might be used in various calculations.

Now, however, there is one more added to the list that helps you solve these type of equations easily and without much fuss, guessing the constants you mean and solving the equations neatly and quickly: Fermion, by Mark Danovich.

Fermion displays a list of constants at the bottom of the page so you can see their values and the way the calculator expects to read them. More than that – and what I think makes the calculator truly worthwhile – the system pops up a list with the constants you may mean. Did you mean ‘e’ as in the mass of the electron or the charge of it? Pick the right constant, and use it properly for your calculation.

Brilliantly simple. Truly helpful. It’s funny, I really like Wolfram Alpha for it’s power, and I use Mathematica and Matlab quite often for the same (but extended) reason, but sometimes they are a total overkill. A simple calculation can transform into quite a bit of wasted time of digging through the manuals or declaring all the constants on your own to begin with.

For these sort of calculations, Fermion rules.

Check it out, it’s totally worth it.

EDIT: Mark notified me that the calculator also allows for unit conversion inside the calculation, which is quite helpful as well.

For instance, to use the speed of light ‘c’ in a calculation using feet per second rather than the defined meters per second, just type “c{ft}” and the system converts automatically. Rawkin’!

There’s a useful YouTube video explaining the entire system.

I don’t know what about you, but I have a box I keep my change in. I’ve bene thinking for a while what I can do with that change – buy a boat, rent a jetski, get a trip on those cool X-Planes that go up to space, etc etc. Big plans for small money, I know, but.. I’ll keep on dreaming.

Now, though, you too have something to do with your extra nickels and pennies you keep safe for future plans: You can do science with them! Yay!

So, this experiment is very simple and fun, and I wanted to do it a bit different than what you probably already know (and what I ended up doing eventually in the video). When I was roaming around the internet looking for more ideas and information, I saw this picture and decided I should try it out (even though I had no doubt, in this case).

Okay, so maybe I went a bit too far with my love for fun: after all, who knew those ice boxes fight back. I didn’t.

But we can learn a lot from this experiment, as well as this experience. We will start with the scientific principles. Then, we’ll go on to my flying metal clips. Pooooiiing.

What you need?

• Pennies.
• Nickels.
• Salt water (just mix water with about 2 table spoons of salt)
• Tissue paper.
• Voltmeter or LED or small light bulb – anything that will prove to you that there is voltage in this spare change tower.
• Depending on your tower-building skills, you may need copper wires.

What do you do?

To create a difference in potentials (which will lead to the existence of voltage and ‘power up’ your lightbulb/LED/voltmeter) you need to create a small tower, alternating a penny, a tissue paper soaked with saltwater and a nickel.

Penny -> saltwater -> Nickel -> saltwater -> Penny -> saltwater -> Nickel … and so on.

Easy!

Note: Make sure you have access to the bottom of the pile. By the time I finished building my little spare-change tower I found out I can’t reach the bottom of the pile to check for voltage, and had to squeeze in another bit of copper wire. If you need one, get it, but if you “play” it right (like, put the first penny sticking out a little) you can do it without any wires at all.

What’s going on?

When we put table salt in water we create a mixture that is electrically conductive. The saltwater mixture is an electrolyte. An electrolyte is a substance that has free ions and conducts electricity.

The electrolyte reacts with different metals, allowing for an exchange of electrons from the metal to the solution. But different metals react differently. A Nickel is made of approximately 75% Copper and 25% Nickel. A Penny has about 97% Zinc and 3% Copper. The difference between the metals causes a difference in reactions to the electrolyte.

This difference creates a difference in electrical potential, which is voltage. And it can light up your lightbulb, your LED or show the difference on a voltmeter.

A bit of History

This experiment, or something very close to it, was done by Alessandro Volta, who created the first cell battery.

In his experiment, he alternated plates of Zinc with plates of Copper, with an electrolyte substance between them (He used either saltwater or sulfuric acid), and created the first cell battery.

This type of battery, however, is short-lived. The voltage stops when the chemical reaction creates hydrogen bubbles that (initially help the procedure, but) later form a sort of ‘barrier’ to one of the metal electrodes. It is also not very safe (and not necessarily due to what you’ve wittnessed in the video) because sulfuric acid is quite dangerous, even when diluted.

But it was certainly the start for the batteries we have today, that operate on the exact same principle!

What happened in my first try?

Okay, so you’ve seen the video and you’re laughing. Great. Glad I could brighten your day with my mishaps. But now what? Does that mean you can’t do it? Probably not. The method of connecting the “electrodes” (spare change) to the walls of the ice box should work just fine, as long as you have enough time to mess with it. I was fighting against the clock, as the sun was setting and the lighting in my apartment is quite poor when dark.

But take your time, try this method out, and let me know if you got it, it seems like fun!

About Experimental Errors

We’re talked before about experimental errors, but I think this experiment (and the “blooper” that accompanied it) is a good chance to state one, very important, issue about science and experimentation:

Mistakes are very important.

We learn from our mistakes. It sounds so repetitive, I know, you’ve heard it from your kindergarden teacher a billion times, but it’s true, and it’s even truer for science. Experimental errors should be examined and analyzed. It may be the equipment, it may be the settings, it may be that it’s not an error at all but a brand new discovery you are going to win the Nobel prize for.

Mistakes happen. The important thing is to understand why they happen.

This is also why true scientists (in true labs) never settle for a single experiment. The experiments are always repeated, over and over, but multiple people. Then, they are analyzed – mistakes and all – and summarized. Then, other scientists from other labs look at the experiment and result and try to repeat them too. If the experiment can be repeated with similar (or same) results, then it is probably actually indicative. If other scientists cannot repeat the experiment, there is a big problem with the suggested conclusion.

This is part of the scientific method.

In my videos I am showing you simple demonstrations of scientific phenomena. This is, by no means, a replacement for actual scientific experiments in labs. I will probably never be able to get actual significat results that affect the scientific community (or the way we live and think) by recording a once-performed experiment at my house. But that’s also not my intended purpose.

I don’t mean to give you “new” radical answers, I mean to give a taste of waht science is about, and how you can check these principles and prove them for yourselves at your own home without going to a fancy lab, or spending lots of time for a PhD. Not that PhDs aren’t important..

Take these videos as examples of what and how things are done, and what the scientific method is all about. Other than being fun (and sometimes funny), these experiments can show you that if you can reach a relatively accurate conclusion at your own home, then true laboratories doing the same (or similar) experiments with much better and more accurate equipment can get much better and more accurate results. But at least now you know how they do it.

More References

• The Amazing Meeting 6: http://www.randi.org/joom/component/option,com_registrationpro/Itemid,33/func,details/did,1/
• James Randi Educational Foundation: http://www.randi.org/

• Alessandro Volta: http://en.wikipedia.org/wiki/Alessandro_Volta
• A Cent (Penny): http://en.wikipedia.org/wiki/Cent_(United_States_coin)
• A Nickel: http://en.wikipedia.org/wiki/Nickel_(United_States_coin)
• How batteries work: http://en.wikipedia.org/wiki/Battery_%28electricity%29#How_batteries_work
• This experiment at the US Mint (Dept of Treasury) site: http://www.usmint.gov/kids/teachers/lessonPlans/viewLP.cfm?lessonPlanId=138
• This experiment in “Make Magazine”: http://blog.makezine.com/archive/2006/11/pennypowered_le.html

Notice: This experiment is incomplete, and unclear. There were several attempts to correctly state the situation, but at the moment, a new re-make is planned to explain exactly and thoroughly what is happening to create this phenomenon.

Well, this is going to be sweet, short and to the point: Fire in closed spaces can really suck.

Ha, I was dying to use that pun for a while now, and here I had the chance. This experiment is a really short and sweet one, and can join your mental arsenal of “party tricks” for the partying geeks. It can really impress anyone, and from now on – you are going to know what makes this happen.

Ready?

Air is a fascinating thing, but sometimes it can be an obstacle. We will see that in future experiments, where the existence of air (or, more precisely, of oxygen) can hinder an experiment and render it unexperimentable. … Right. I think I need a dictionary replacement.

Warning!

In case this isn’t completely clear, I am going to point out that since we are dealing with a live and exposed flame, the use of any high-percentage alcohol is absolutely not recommended.

I hope that is obvious, but in case it’s not – ALCOHOL IS FLAMMABLE. SO IS GASOLINE. Don’t do something very stupid, don’t use flammable liquids in this experiment!

(Thanks to RedShiftScience for pointing out people might not find this obvious.)

Corrections!

Before I go on to corrections, let me say a word about getting things wrong: Human beings are usually emotional entities, and as such, we tend to take things personally. Science is supposed to be empirical, void from emotions. How do you connect the two? Using the scientific method.

There is no shame in getting things wrong. We are only humans.

The best thing about science and experimentation is to have other people think about things, analyze them, and criticize your work. I not only enjoy that, I think it’s a necessary part of science.

In my video, I explained a few things incompletely, and some even seemed to have come across bluntly wrong (aaa! matter is not created out of nothing, and it does not disappear! in failing to mention that, I sounded like this experiment defies the laws of thermodynamics!). So, I am hereby correcting, adding and subtracting to what I said. I tried to do that well in this post — and then Shane Killian — who noticed this error first – posted a video reply.

So now I can just post it here instead of doing it all over again. Cheers, Shane, GREAT job, and thanks a lot for the correction!

Don’t ever be afraid to try just because you’re afraid to make a mistake.

What is a Vacuum?

A vacuum is a volume of space with no matter in it, and a zero atmospheric pressure. That is the formal definition. That said, there are no places in nature that have absolute vacuum.

We tend to call “Outer Space” a vacuum, but in reality, it is filled with particles, which makes it have some sort of matter, which means it’s not a complete vacuum. But it’s close enough.

Since a vacuum is supposed to have 0 atmospheric pressure (or as close as possible), it “sucks” into it anything that has a different – and higher – pressure. This is due to the tendency to have a balance of pressures — different pressures will try to balance one another, so the lower pressure environment will “suck” matter from the higher pressure environment until both environment are at a balance.

That’s why you see people get sucked out of the airlock in sci-fi movies. It’s one of those things movies got right.

In our experiment, we lowered the pressure and created a semi-vacuum inside the glass, and in turn, it sucked up the liquid around it. Or, more specifically -

What’s going on here?

With this cool little party trick, we are creating a “semi” vacuum inside the clear glass by consuming the oxygen inside it. When the fire consumes the oxygen molecules, it “vacates” a place for – well – whatever else. The pressure inside the glass rises, and since it isn’t sealed, it sucks whatever it is standing on

CORRECTION: The pressure inside the glass increases as the fire heats up the molecules. Oxygen is being “consumed” by the fire, that produces Carbon Dioxide (the matter itself remains, no matter is mysteriously ‘vanishing’ or ‘created’ out of nothing!). But now, the pressures are different and therefore the water outside the glass are pushed inwards — the lower pressure of the INSIDE ‘sucks in’ the liquid around it under the pressure stabilizes.

Thanks to Shane Killian for the correction.

If I were to use a jar and sealed it well while the candle inside fed on the oxygen, the cap would have been “sucked” into the jar mouth, and the jar would have been sealed. Since I am not using a cap, but rather putting the glass on top of liquid (that can “pass through” the edge of the cup), the liquid is sucked inside the glass and stays there, until I release the pressure and allow air in.

This is a really sweet, cool and short experiment, but the best thing about it is that it will help us produce home-style vacuum setting for other experiments. And so, it’s good to know.

Plus, it’s fun. And edible. Woo hoo.

Practical Applications

• First, this is a cool and easy way of creating home-made semi-vacuum setting, for whatever other experiment you will need. We’ll use this in the future.
• Here’s a cool practical trick to preserve food for you to consider, though it isn’t precisely the same method, it uses a similar point: If you cook something and wish to save some for later in sealed jars, the best way of doing that is seal the jar while the food is still hot. Once sealed, whatever air inside the jar is trapped, and when the food cools, the air compresses and tightens the jar cap so that it is relatively sealed from the outside. Food will last longer this way, but you will have a bit of a harder time opening the jar.
• Impress people in parties, collect on bets, and dazzle your dates. What else do you want?

Resources:

• Another video with the same point: http://www.metacafe.com/watch/334272/physics_experiment_liquid_suction/
• And another: http://www.metacafe.com/watch/540641/bored_try_this_easy_experiment/
• Vacuum: http://en.wikipedia.org/wiki/Vacuum
• The Human Body in Space (Vacuum): http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

The human body is an incredible machine. Though far from being perfect, we have evolved to what we are today through a process that took millions of years of mutation and natural selection.

There is one little piece of us, though, that holds the secret to our existence, and the history of our species: The DNA.

My main interest is usually physics and astronomy, but I have always been fascinated by that double-helix molecule and its meaning, both philosophically and realistically; since the beginning of Genetics the human race have progressed exponentially. It’s just, simply, amazing.

So when the “rogues” of “The Skeptic’s Guide to the Universe” Podcast debated the history of DNA discoveries, I decided it is time for some biology experiment.

I am about to show you how to extract your own DNA from your own bodies in your own kitchen. Yourselves.

It’s aliiiiiiiiiive!

The Experiment

This experiment allows you to extract DNA matter from cells from your mouth, and is very similar to what Friedrich Miescher discovered. His discovery was from pus, and this one is from your mouth. Physiology can be funny like that.

What do you need?

For this experiment,you will need the following tools:

• Two beakers.
• A glass or a cup. You can use one from the previous experiment.
• Liquid soap (NOT antibacterial. You shouldn’t use those at all anyways).
• 2 test tubes or clean and clear bottles. I used “travel-size”empty plastic bottles for the experiment. These work, just make sure they are properly cleaned with distilled water.
• Distilled water.
• Rubbing Alcohol.
• Sodium Chloride. Well, Salt.
  Sodium Chloride is a nice and fancy way of saying “Salt”. You don’t need anything other than table salt, or cooking salt, but for fun, I suggest going to your nearest pharmacy and try to ask for a small amount of Sodium Chloride.
  I did, and the nice lady replied it is a prescription drug. Worth the chuckling, I promise.
• Glass rod (I used wood, because I didn’t have glass, but wood isn’t as good at all.. try to get a glass rod).
• Anything that can be used to measure the liquids. The more accurate your solutions are formed, the better your results would be.
• Drinking water. Preferably bottled water, to avoid varying amounts of chloride or other contaminants.

The Process

You can find the process I used for this experiment in the repository of About.com biology expert, but here’s a short summary:

1. Solution #1 (Negative-charge Ions to bond the DNA molecules together): 8% Sodium Chloride + 92% Distilled Water.
2. Solution #2 (Breaking apart the cell membranes and “freeing” the DNA from the nucleus): 25% Liquid Soap + 75% Distilled Water.
3. Wash your mouth thoroughly; you want DNA from the cells in your cheek and not from whatever animal (or fruit) you ate for lunch. Make sure your mouth is CLEAN.
4. Swirl about 10ml of water in your mouth. Use the bottled water and NOT the distilled water! If you want a larger amount of cells, do it a bit ‘stronger’. Do that for about 30 seconds.
5. Spit the water into the cup. You have just gathered a bit of cells from your own body, congratulations.
6. Take 1ml of Solution #1 (Sodium Chloride) and add it into an empty, clean bottle (or test tube).
7. Add the cell-water mix you just spit out into the same bottle (or test tube).
8. Add 1ml of Solution #2 (Liquid Soap) into the same bottle (or test tube).
9. Close the cap or seal with a test tube stopper.
10. Twirl, swirl, and turn the bottle upside down and right side up gently. Do not shake. You’re not 007.
11. Add 5ml of Rubbing Alcohol into the bottle while tilting it slightly so the alcohol ends up floating on top of your mixed solutions.
12. Wait for about 5 minutes.
13. Watch. If you want, you can do what I did and move the DNA strand from the solution bottle to a clear bottle that contains alcohol only. I keep my little creation next to my computer screen.
    Make sure you do it very gently.

What’s happening?

Well, DNA exists inside the nucleus of a cell. So to see it, you need to first let it out of its confinement. But that isn’t enough – DNA molecules are positive charge, so they reject one another. In order to see the strand, we need to make sure a bunch of these molecules bond together. Finally, DNA melts in water but not in alcohol – we will use that to “trap” the strand so we can look at it.

So, here’s the summary:

1. Soap has detergent in it, that dissolves the membranes (the “skin” of the cell) and releases the DNA from the nucleus.
2. Sodium Chloride is negatively charged, so it bonds the DNA strands together to create a long strand we can see in the naked eye.
   Correction:
   Okay, I got this wrong again, so ailboles was kind enough to explain it and give links, too!:DNA is a negatively charged molecule. It is the positive ions (in the Sodium Chloride solution) that interact with the DNA (see http://ppge.ucdavis.edu/Equipment/Protocols/thymus_dna_extraction_03.pdf under the section, “Answers to Student Activity” number 5)
   
   Well, that makes more sense. Thanks again to ailboles for taking the time and effort to explain this again!
3. Alcohol “traps” the strand, because it doesn’t break apart in alcohol, only in water.

There you have it. Your own DNA in a bottle. Beats wooden boats any day.

About Scientific Discoveries

Usually, when we hear that someone a long long time ago made a very big discovery we tend to be skeptical. It’s understandable – I find it hard to see anyone getting along without a fast-paced computer, let alone working without an electron microscope, or a light bulb.

But the truth is, usually scientific discoveries don’t just “pop up” miraculously. We tend to remember the people who invented specific “gizmos”, or wrote a patent relating to a specific discovery (like Edison and the Light bulb, Bell’s telephone, and Morse’s telegraph), but they were rarely “the first”. The research started a long time before, and their discoveries were possible only due to past discoveries.

The same is true to DNA.

The 1869 Discovery

In 1962, James D. Watson, Francis Crick and Maurice Wilkins recieved the Nobel Prize for the discovery of the structure of DNA and its hereditary role. Because the Nobel Prize is a famous honor, we tend to remember them specifically, but their discovery was possible because of many prior researches, the first of which was done by a Swiss researcher called Friedrich Miescher in 1869.

Miescher researched the human cells, specifically white blood cells, by taking blood-stained bandages from a nearby hostpital. He noticed a microscopic substance inside the pus on the bandages – and identified the substance as coming from within a cell’s nucleus. He called this substance “Nuclein”.

The following dates mark the time line that lead to the famous discovery of the DNA structure in the 1950s:

• 1869 - Friedrich Miescher identifies a substance that came out of a cell’s nucleus and has a weak acidic properties. He calls it “Nuclein“.
• 1919 - Phoebus Levene identifies the base, sugar and phosphate nucleotide units. He suggests that DNA is made of strings of nucleotide units that are connected together through phosphate groups.
• 1928 – Frederick Griffith combined “smooth” and “rough” forms of Pneumococcus bacteria, showing that DNA plays a role in passing genetic information.
• 1937 - William Astbury produces an X-Ray diffraction pattern that shows DNA has a regular structure.
• 1943 – Oswald Avery, Colin MacLeod and Maclyn McCarty identify DNA as the transforming principle – showing that bacteria transfers genetic information through a process called “Transformation”.
• 1952 – Alfred Hershey and Martha Chase confirmed the heredity trait of DNA in an experiment.
• 1953 - The structure of DNA is suggested by James D. Watson and Francis Crick, based on X-Ray Diffraction images taken by Rosalind Franklin. This is the structure that is accepted today.
• 1957 - Crick lays out the “Central Dogma” of molecular biology, including RNA, DNA and proteins, and the relationships between them.
• 1963 - Watson, Crick and Wilkins receive the Nobel Prize in Physiology or Medicine.

Practical Applications

Wow. That’s going to be a huge huge list. The discovery of Genes, structure of DNA and Genetics in general has led to countless advancements in medicine and technology. From discovering diseases earlier to devising vaccines. The list is just too great, too big, and too important to summarize in a single post. If you look at the resources, however, you could find many places to start.

• Forensic Medicine.
• Interpol’s Attempt – DNA Profiling.
• The study of Human evolution (many more resources, including this one from National Geographic, and Berkley’s “DNA, the Language of Evolution“).

Resources:

• The Experiment Instructions can be found here: http://biology.about.com/c/ht/00/07/How_Extract_DNA_Human0962932481.htm
• Extracting DNA From Fruit:
  • http://www.funsci.com/fun3_en/dna/dna.htm
  • http://www.csiro.au/resources/ps1tp.html
• Great Clip about DNA Structure: http://www.youtube.com/watch?v=qy8dk5iS1f0
• Friedrich Miescher: http://en.wikipedia.org/wiki/Friedrich_Miescher
• Albrecht Kossel: http://en.wikipedia.org/wiki/Albrecht_Kossel
• History of Electricity Discoveries: http://www.code-electrical.com/historyofelectricity.html
• Griffith’s Experiment: http://en.wikipedia.org/wiki/Griffith%27s_experiment
• Hershey-Chase Experiment: http://en.wikipedia.org/wiki/Hershey-Chase_experiment

It’s Goo! It’s Solid! It’s Goo! It’s Solid! It’s— both???

My mom always told me never to play with my food, but in this case, I think even she will agree to make an exception. Not only am I going to play with this food, you should too. It’s way too fun to pass on.

This type of matter is called a “Non Newtonian Fluid”. Why? Well, because it is an exception to the rule Newton devised about the flow and viscosity of fluids.

Newton observed that fluids have a ‘tendency’ to resist flow; he called that tendency “viscosity”. If you have a water-pistol, for example, and you want to splash a target, the harder you press the trigger, the faster water come out. Pressure affects viscosity.

Ketchup is another example. It has very strong ‘resistance’ to flow – its viscosity is high. If you just tilt the ketchup bottle onto your fries plate, it takes a while for it to pour out of the bottle – and onto your plate. Honey is the same. You need to apply pressure on the bottle to force it out.

Newton’s theory was that the only way to change a liquid’s viscosity is to change its temperature. Honey, in that example, flows much more readily when it’s hot. I am not sure if Ketchup follows that example, but you’re welcome to try and let me know. I personally hate warm tomatoes; sauce or no.

Non Newtonian fluids, as their name suggest, are the exception of this rule. They, too, change their viscosity in different temperatures, but they also change viscosity when force is applied on them. And there lies the cool part.

Press down on a glop of honey, and your hands fill with honey. Press down on a glop of oobleck (corn starch and water, for example) and it’s solid.

So, when forces are applied to the glop of Non Newtonian liquid, the forces of attraction between the molecules of the liquid increases, and the liquid becomes solid-like. When the forces decrease, the attraction between the molecules decreases as well, and the glop is again fluid.

Woohoo!

Materials needed for the Experiment

• A Bowl
• Corn Starch
• Mop – it’s necessity is proportional to the amount of fun you have with the glop.
• Plastic Bag (to dispose of the mixture)

Warning!!! Do not dispose of the fluid down the drain. It’s going to clog up your pipes, and that’s bad. Put it in a plastic bag and throw it with the garbage, instead.

Practical Applications

• Fun. I mean.. c’mon now. It really is. And since corn starch can be found in any food store for cheap, and the preparations take less than 5 minutes to make, you simply must try it yourself. Must.
• “Walking on Water” is probably the most famous fun application of Non Newtonian fluids. You can have examples in YouTube, just by looking up “Non Newtonian Fluids”. Or by watching the MythBusters episode about Ninjas. If only to see the blue corn starch fluid.
• Fluid Armor: Yeah, it sounds weird, but technically, if a fluid turns to solid when force is applied to it, then it makes much more sense to ‘wear it’ as an armor. I wouldn’t recommend using corn starch and water to stop a speeding bullet, but there are other fluids out there that can help in the matter. In fact, in many of the Kevlar armor suits today, there is a few extra layers of special Non Newtonian liquids that react strongly when force is applied. That application makes Kevlar suits lighter, because less layers of fabric are required.

Extra Resources:

• Non Newtonian Fluids: http://www.madsci.org/posts/archives/mar97/856396884.Ph.r.html
• General Chemistry Online FAQ:
  http://antoine.frostburg.edu/chem/senese/101/liquids/faq/non-newtonian.shtml
• Oobleck: http://en.wikipedia.org/wiki/Oobleck
• Dr Seuss’ “Bartholomew and the Oobleck”: http://en.wikipedia.org/wiki/Bartholomew_and_the_Oobleck
• “How Stuff Works” on Liquid Body Armor: http://science.howstuffworks.com/liquid-body-armor.htm
• “Army scientists, engineers develop liquid body armor”: http://www4.army.mil/ocpa/read.php?story_id_key=5872