Stories tagged Physical Science

Jul
20
2006

DNA directs nano-assembly: DNA used to direct nano-assembly. photo from wikimedia.
DNA directs nano-assembly: DNA used to direct nano-assembly. photo from wikimedia.

New nanoscale assembly technique

How can we assemble parts nearly a thousand times smaller than the width of a human hair? By using processes similar to those in Mother Nature, scientist are now constructing complex nanoassemblies. First we learned to produce nano-scaled parts like Buckyballs and carbon nanotubes(CNT). The next step in complexity is to connect some of these parts together in a particular way. Mother Nature does this using DNA. DNA contains code similar to a puzzle piece. It will only fit together with a correponding puzzle piece.

The Xu lab is the first in the world to make uniform arrays of carbon nanotubes. Lazareck and his collaborators at Brown and Boston College built on this platform to make their structures. They started with arrays of billions of carbon nanotubes of the same diameter and height evenly spaced on a base of aluminum oxide film. On the tips of the tubes, they introduced a tiny DNA snippet.
This synthetic snippet of DNA carries a sequence of 15 “letters” of genetic code. It was chosen because it attracts only one complement – another sequence made up of a different string of 15 “letters” of genetic code. This second sequence was coupled with a gold nanoparticle, which acted as a chemical delivery system of sorts, bringing the complementary sequences of DNA together. To make the wires, the team put the arrays in a furnace set at 600° C and added zinc arsenide. What grew: Zinc oxide wires measuring about 100-200 nanometers in length.
“We’re seeing the beginning of the next generation of nanomaterials,” said Xu, senior author of the article. Brown University Media Relations

The research team led by Brown University engineers has harnessed the coding power of DNA to create zinc oxide nanowires on top of carbon nanotube tips. The feat, detailed in the journal Nanotechnology, marks the first time that DNA has been used to direct the assembly and growth of complex nanowires. NanotechWire

Link to the paper published in the journal Nanotechnology

Jun
30
2006

It's all over the Internet. It's on David Letterman and the Today Show. It's on NPR, for Pete's sake. Across the country, people are caught up in a frenzy of extreme Diet Coke and Mentos experiments.

Want to try it at home?

Get permission, go outside, and have a hose handy. Things are gonna get messy...

  1. The simplest thing is to just drop a Mentos or two into a small bottle of Diet Coke.
  2. Not so satisfying? OK, now it's time to get serious.
  3. Make a "cartridge" of Mentos. Hold each candy with a pair of pliers, and carefully drill a small hole through the center. Then string five or six Mentos onto a straightened paper clip or a piece of fishing line.
  4. Hold the bottle cap with a pair of pliers and drill a hole through the top. (Start with a hole 1/4" in diameter.) Thread the paper clip or fishing line with the Mentos cartridge through the bottle cap so that the candy will hang down inside the bottle when you screw on the cap. Different sized holes in the cap will yield different effects.
  5. You can also carefully drill holes in the bottle, above the level of the soda. If you drill a ring of holes, you get a pretty neat effect. And you'll also make a super big mess.

Of course, you don't have to use Mentos and Diet Coke. The good folks at EepyBird.com have done many, many experiments, and it turns out that dropping just about anything into any kind of soda creates at least a little fizz. But Mentos and Diet Coke is an especially satisfying combination.

So how does it work?
The explosive effect is caused when the carbon dioxide that's been compressed in the soda escapes so quickly that the pressure pushes the soda out of the bottle. That's the easy part. But why do Mentos, in particular, cause such a good effect?

Part of the answer has to do with nucleation sites. "Huh?" you ask. Yeah, me, too. Soda is a liquid supersaturated with carbon dioxide gas, and nucleation sites are places where the carbon dioxide can make bubbles. A nucleation site can be a scratch on a surface, a speck of dust, or any place where you have a high surface area relative to volume.

Bubbles in soda: (Photo courtesy Spiff, Wikipedia Commons)
Bubbles in soda: (Photo courtesy Spiff, Wikipedia Commons)Courtesy Spiff

And Mentos have a lot of nucleation sites. There are lots of imperfections in their surfaces, and that allows lots and lots of bubbles to form. Plus, Mentos are heavy enough to sink when you drop them in, so they react to with the soda all the way to the bottom of the container. The sticky result is a fun, foaming mess.

But what happens if you drink Diet Coke and eat Mentos at the same time?
The EepyBird website has the answer, if you really must know...

May
17
2006


Keeper: Image courtesy various visual stuff.

Earlier I wrote a blog post where mathematicians had determined that soccer was the most exciting sport to watch because the probability for an upset was higher than in other sports. In recent soccer related science research, Ken Bray, a theoretical physicist from the University of bath in England has conducted research to show that the areas near the top corners of the net are what he calls an “unsaveable zone”. To find this zone, Bray studied games from the past 50 years and applied his knowledge of physics, biology, and psychology to calculate the reach of a goalkeeper attempting to save a penalty kick. His advice for the goalkeepers? Move before the ball is kicked…which I think is cheating, so that would not be my advice! Bray also says that in 85% of penalty kicks, the direction in which the plant foot is the direction of the shot.

Dr. Bray has written a book on the science of soccer titled, “How to Score”.

Feb
22
2006

The Science Museum's neighbor, the Xcel Energy High Bridge power plant, will be undergoing a significant construction project in the coming months. As part of a larger project called Metro Emissions Reduction Project (MERP) Xcel Energy has started working on a $1 billion program that will reduce emissions from three metro area plants (the High Bridge Plant being one) and increase power generating capacity.

Generator: Working principle of a combined cycle power plant.Courtesy Alureiter


Xcel - Current: Existing High Bridge plant. Image courtsey Xcel Energy.

The High Bridge power plant is being converted from a coal burning plant to a combined-cycle natural gas plant. Combined power plants generate electricity from two sources - a gas turbine generator that is powered by natural gas and a steam turbine generator that is powered by the heat exhaust from the gas turbine generator. This use of the gas to essentially power two different types of generators is a more efficient use of resources than the coal burning power plant. As a result of this change, air emissions from the High Bridge power plant will be significantly reduced. Sulfur dioxide emissions will be reduced 99.7%, nitrogen oxide 96.9% and particulate matter 91.5%, while mercury pollution will be completely eliminated.


Xcel - New: High Bridge plant after construction is complete - artist's rendition courtsey Xcel Energy.

My first thought after hearing this (and after having to put gas in my car and heat my home the past few months) was that switching to natural gas is not a very economical situation given current gas prices. However, Xcel says that:

Although natural gas prices have increased, this conversion makes sense for the long term. The gas market is subject to short-term volatility, but the plants will operate for another 30 years so it's the long-term projections that are most important.

If you are in the downtown area in the coming weeks you may hear construction noise from the site as the nearly 1,200 steel pilings for the new power plant are driven into the ground for the new plant's footings. Testing of the new power plant will begin around September 2007 and run through March 2008. The plant is expected to begin commercial operation in May 2008, and demolition of the old plant will start shortly thereafter.

For more information visit Xcel Energy's web pages on the conversion.

Feb
17
2006

U.S. and Canadian slalom skiers are wearing lightweight, flexible protective gear made from a new material (d3o) that hardens into armor when it's crashed into.


ski suits: A new material, d3o, means these racing suits are only hard when they need to be. (Photo courtesy Spyder)

Normally, skiers wear hard arm and leg guards to protect themselves from poles along the slalom run. But the Colorado-based skiwear company Spyder created racing suits with d3o along the shins and forearms, and the suits caught on.

The exact chemical composition of d3o is a trade secret, but it's made by combining a viscose fluid and a polymer, then pouring the liquid d3o into a mold that matches the shape of the body part needing protection.

According to a New Scientist article,

"The resulting material exhibits a material property called 'strain rate sensitivity'. Under normal conditions the molecules within the material are weakly bound and can move past each with ease, making the material flexible. But the shock of sudden deformation causes the chemical bonds to strengthen and the moving molecules to lock, turning the material into a more solid, protective shield.

Pretty cool.

Feb
16
2006

That's the promise of a new battery developed by researchers at MIT's Laboratory for Electromagnetic and Electronic Systems. They're using nanotechnology to improve an energy storage device called an ultracapacitor.


Nanotubes: (Photo courtesy Riccardo Signorelli, Laboratory for Electromagnetic and Electrical Studies, MIT)

Unlike regular batteries, which can generate electricity from a chemical reaction, capacitors store energy as an electrical field. Ultracapacitors can store lots of energy for a long time, but they need to be much bigger than regular batteries to hold the same amount of electricity. The new MIT technique, uses nanotechnology to improve the storage capacity of existing capacitors and may eventually help to make them smaller.

How does it work?

A battery has two electrodes, or terminals, one positive and one negative. Inside the battery are chemicals that react with each other to produce electrons. The electrons collect on the negative terminal of the battery. When you connect the terminals with a wire, you can use the flow of electrons to power things. A capacitor also has two electrodes-metal plates separated by a material that doesn't conduct electricity. A positive charge builds up on one plate, and a negative charge builds up on the other. When you connect the two electrodes, they discharge their energy. A battery can actually "create" energy by changing chemicals into electricity while a capacitor can only store energy it has been charged with.


Ultracapacitor in a hybrid engine: An ultracapacitor in a hybrid gas/electric engine for a car.

Today's ultracapacitors use electrodes made of activated carbon; the carbon is porous, so it has lots of surface area for the electrons to build up on. But the pores are irregular in size and shape, which reduces efficiency. That's why capacitors have to be big. But the MIT ultracapacitor has electrodes of vertically aligned carbon nanotubes, each one thirty-thousandth the width of a human hair. The regular shape and alignment of the nanotubes greatly increases the surface area, making the ultracapacitor very efficient at storing electrons.


Carbon nanotubes: Vertically aligned carbon nanotubes have lots of surface area to store electrons. (Photo courtesy Riccardo Signorelli, Laboratory for Electromagnetic and Electrical Systems, MIT)

Smaller is better

Ultracapacitors are long lasting and quick-charging. Storing energy at the atomic level with nanotubes means that they can finally be small, too, perhaps eventually powering everything from flashlights and cell phones to hybrid cars and missile-guidance systems.

Make it at the Museum

Stop by the Museum on Saturday, February 18th. You can make a pop can flashlight and test some conventional batteries. Experiment with electricity, circuits, and capacitors more at the AC/DC electricity bench in the Experiment Gallery.

Feb
14
2006

They fly through the air with the greatest of ease....and a bunch of science.


Ski jumper: Photo courtesy Morgan Goodwin, Calgary Canada.

When you're watching the ski jumpers fly off the huge hills at Torino during the Winter Olympics, you're not just seeing bravery and athleticism on display. You're also seeing some science.

While the forces of gravity eventually win out, the aerodynamics of lift play a big role in the outcome of the event. The way the jumpers position their skis and their bodies has will affect the air flows around them. The best jumpers will have mastered aerodynamics along with their physical training to get on to the medal stand.

The jumpers rely on scientific principles developed hundreds of years ago. The first is Isaac Newton's law that any action causes an equal and opposite reaction. In the case of ski jumping, the jumper's body and skis will push some air down. The reaction from that is that some air will actually then push the skier up.

The second scientific law in play is Daniel Bernouli's discovery that air pressure drops as air moves faster. Ski jumpers who know that will position their bodies so the air above them moves faster. The slower air beneath them will have more pressure, giving the skier another dimension of lift.

Another big change in ski jumping came in 1985 with the creation of the "V" position — holding their skies wide apart in front of them and crossed behind them. While the "V" was initially laughed at, jumpers discovered that it gave them a lot more distance. Jumpers were able to add up to 100 meters more distance to their jump with the change.

Dec
08
2005

Ever notice that uncooked spaghetti doesn't break neatly in two when you bend it? Instead, it shatters into several pieces of different lengths. Why?

Researchers recently solved the spaghetti mystery and improved scientists' understanding of how things shatter. Because strands of spaghetti are similar in some ways to lots of brittle objects—from industrial cutting tools to body armor—knowing why spaghetti breaks the way it does may help make those things stronger and safer.

Spaghetti catapult
The researchers clamped one end of a piece of spaghetti in place, and then bent the rod until it was just about to break. Then they let the unclamped end go, and filmed the results with a digital camera that took 1,000 images per second. The pictures showed that the spaghetti rod didn't spring back to its original position like a diving board would. Instead, the release caused ripples that ran down the rod's length and bounced back from the clamped end. The spaghetti snaps where the curvature is greatest—where the ripples from the free end meet the ripples bouncing back from the clamped end. And it happens again in the remaining piece of spaghetti each time the rod breaks. (See some movies of the breaking spaghetti.)

Just getting started
Now scientists know why spaghetti breaks into more than two pieces, but the new research opens up many more questions about how objects shatter.

MAKE IT at the Museum
The recent spaghetti discovery was made possible by an extremely high-speed camera that captured photos of how the pasta bent and broke. On Saturday, December 10, between 1:30 and 3:30, you can make a zoetrope and watch some spaghetti "filmstrips" for yourself. It's free, it's fun, it only takes a few minutes, and you can take your creation home with you when you're done.