Stories tagged Physical Science

Aug
08
2007

Bridge breaker?: An unusual factor that may have contributed to the I-35W bridge collapse is a build-up of pigeon poop in the box beams of the bridge. To keep pigeons from getting into the box beams, plastic covers were put over inspection holes on the bridge.
Bridge breaker?: An unusual factor that may have contributed to the I-35W bridge collapse is a build-up of pigeon poop in the box beams of the bridge. To keep pigeons from getting into the box beams, plastic covers were put over inspection holes on the bridge.
As the blame game starts to heat up in the aftermath of the I-35W bridge collapse, members of the animal kingdom are getting fingers pointed at them.

Tuesday’s Star Tribune carried a story about how problems with pigeons and spiders complicated bridge inspections over the past 13 years. How could those creatures play a part in a bridge going down? Read on.

Pigeon poop is a nuisance in all urban areas and was chronicled in this post to Science Buzz a few months ago. And evidently at the I-35W bridge, pigeon droppings were a big problem. Large numbers of pigeons were nesting in the box beam sections of the bridge structure from as far back as 1994. The box beam is vertical support beam between the bridge deck and the supporting floor beam below the bridge. The box beams had holes in them for inspectors to look inside, but that was also the access that pigeons were using to get inside and build nests.

With large numbers of pigeons in the bridge came heavy amounts of pigeon droppings. And the waste matter in those droppings can be very corrosive to metal. The solution taken in 1999 to solve that problem was to put plastic covers over the box beam holes. And those areas were some of the most critical areas for fatigue cracking that was occurring in the bridge. Some are now wondering if those plastic covers limited inspectors’ views of these critical areas of the bridge.

As for the spiders, inspectors said that the huge number of spider webs in and under the bridge could often be confused for bridge structure cracks.

The story also mentioned one other species that made inspections more challenging to engineers: humans. While the inspection work would be targeted to non-rush hour times from 9 a.m. to 3 p.m., inspectors said they still were often the targets of road rage from passing motorist who felt inconvenienced by having one lane of the bridge shut down during the inspection. Inspectors said they even had object thrown by passing drivers as they were trying to do an inspection.

Aug
02
2007

7 dead, 60 injured (as of 1am, Aug 2)

I-35W bridge
I-35W bridge
tangled roadwayAt 6:05 pm, during peak traffic, the 35-W bridge over the Mississippi river collapsed. All eight lanes, all the way across, just dropped straight down into the river along with more than 50 cars, trucks, and even a school bus. How could this happen? Here is what I have found so far.

The I -35W bridge.

What does it look like? How is it made? It was a steel arch deck truss bridge. Its longest span stretched 458 feet between supports. It was built in 1967. (Link to photos and more data about the I-35W bridge.)

What might have gone wrong?

"The state, whoever did the inspection, which was likely to be MnDOT, noticed and observed cracking in the structural steel members, the main girders that hold the bridge up in the air. What it means is that the bridge is no longer going to stay stable," Galarn said.

Link to early video with a safty engineer about what might have went wrong.

How safe are other bridges?

Transportation Commissioner Len Levine who served under Governor Rudy Perpich (said) "between 40 and 50 percent of the 20,000 bridges in Minnesota are deficient in some way."

What is going to happen to traffic?

There will be added bus services from North metro area.
Map of detour routes.(pdf)

Where are photos of this disaster?

KSTP has lots of photos and updates.
Detroit Free Press had 25 photos.
34 photos on Flickr by blogger s4xton Read his story here.

Please use our comments to add updates, photo links, or thoughts.

I could not sleep so I started this after midnight. This story will keep growing so stay tuned and share what you know.

May
07
2007

Ever since I first saw the action/horror film Predator I have had two objectives in life – one, to challenge Arnold Schwarzenegger in a battle of wits and physical strength, and two, to have my own invisibility suit*. Humble goals, I know, but I like to think that makes them more realistic.

While Governor Schwarzenegger has yet to return my calls, the recent work of some European scientists and mathematicians has brought my second dream one step closer to reality.Invisilibilty Cloak: A conceptual rendering of me wearing an invisibility cloak.
Invisilibilty Cloak: A conceptual rendering of me wearing an invisibility cloak.

Mathematical models and small-scale laboratory tests have shown that by surrounding objects with certain types of “metamaterials,” they could be rendered invisible.

Metamaterials are non-natural materials that gain properties through their structure instead of their composition. So, think of a metamaterial as something like a screen door, which you can see though because it was made with thousands of tiny holes in it, compared to something like plastic sandwich wrap (our “natural material”), which you can see through because the plastic itself is transparent. Maybe that’s not the best analogy, but it helps me get a grip on things.

Anyway, the idea with the invisibility cloak is that the metamaterial would bend electromagnetic radiation (like radar, microwaves, or visible light) around the object, sort of like, as one scientist put it, “river water flowing around a smooth rock.”

Unfortunately for me (and fortunately for Governor Schwarzenegger), the metamaterials required for this are a little more complex than a screen door, and the computer models that much of this research is based on use spherical, stationary objects as ideal candidates for invisibility cloaks. This could change as we are able to produce increasingly complex metamaterials, allowing things like submarines and airplanes** to be rendered invisible, but the days of something as oddly shaped and as mobile as I am having a personal invisibility suit are a long ways off. Shucks.

What do you think about the possibility of objects, vehicles, and maybe someday people being able to turn invisible? Awesome? Scary? Both?

*If you’re over seventeen, and not getting the Predator references, I highly recommend it. For younger invisibility fans, I suggest Harry Potter. For those of you who aren’t into invisibility, maybe Die Hard or Forest Gump would be more your speed – I don’t think there’s anything invisible in those movies.

**For more on invisible airplanes, see Wonder Woman .

Links to more info:
Invisibility at ScienceDaily
Invisibility Cloak Demonstration
Metamaterials

Apr
18
2007

Solar cells reduce your electric bill, but they are also very expensive to buy and install.  Are they worth it?: Photo by clownfish from www.flickr.com
Solar cells reduce your electric bill, but they are also very expensive to buy and install. Are they worth it?: Photo by clownfish from www.flickr.com

Some people are installing solar panels on their homes. These panels generate electricity from sunlight. Using the panels will lower your electric bill, and reduce demand from power plants (which often burn coal).
But, are they worth it?

On April 15, the San Francisco Chronicle said yes. They looked at the costs of buying and installing the panels, and weighed it against the benefits (which include getting a tax rebate). They found that, over 25 to 30 years, the average home would save about $33,000.

So, solar panels are a good idea, right? Not so fast! On April 14, the NY Times reported that solar panels never pay for themselves. Even accounting for electrical savings and tax rebates, they are so expensive that you never make your money back.

Well, the two articles can’t both be right. Right? Well, actually, they both seem correct -- but they are based on two very different scenarios:

  1. Different tax rebates in the two states.
  2. More sunshine in California, making the panels more useful.
  3. The panels are almost twice as expensive in NY than in SF.
  4. The NY Times assumed that, if you didn’t spend the money on panels, you’d put it in the bank or otherwise invest it, where it can earn money for you. The SF Chronicle did not take this into account.

So, whether or not solar panels are a good financial investment depends on a lot of factors. Whether they are good for the environment is much easier to answer – they produce electricity without pollution.

In the future, the debate may be moot – scientists are working on new types of solar cells that use nanotechnology, which may bring the costs way down.

Apr
18
2007

The amphitheater at Epidaurus has acoustics so good you can hear a pin drop, even when the seats are packed with 15,000 people: Photo by Randy Peters from flickr.com
The amphitheater at Epidaurus has acoustics so good you can hear a pin drop, even when the seats are packed with 15,000 people: Photo by Randy Peters from flickr.com

The ancient Greek amphitheater at Epidaurus has long been famous for its marvelous sound qualities. Audience members in the back row could hear every sound, even as soft as a match being struck.

Until recently, no one has unlocked the secrets of these perfect acoustics. The Greeks themselves thought it was the shape of the amphitheater. But other theaters built on the same model could not reproduce the sound quality of Epidaurus.

Now, researchers at the Georgia Institute of Technology have finally solved the problem. They found that the limestone seats work as a filter to dampen the sound of the crowd, while at the same time amplifying the sounds from the stage, . Other amphitheaters used the same design but different materials, and were never able to duplicate the results.

Mar
20
2007

Vibrations create cool patterns

Vibrating surfaces create sound waves. In the video below a plate of metal is vibrated with higher and higher frequencies. Salt spinkled on top of the plate can only stay where the surface is not vibrating. The nonvibrating areas are called nodes. Distance between nodes is shorter for higher frequencies.Standing waves
Standing waves
The patterns you see are known as standing waves. We have an apparatus like this at the Science Museum of Minnesota on the third floor. You might also try to make standing waves in a stretched slinky.

Try doing this yourself

I once stretched rubber from a large balloon over the front of a large car speaker. Using an amplifier and frequency generator, I was able to make similar patterns in salt sprinkled on top of the sheet of rubber. You could try an electric keyboard to produce the different frequencies of sound.

Want to see a longer video?

If you have time here is a link to part 1 of some extraordinary film clips of Hans Jenny experiments from the 1960's and early 70's(28 minutes).

Mar
20
2007

Eco Model Haus open meeting and Green Institute tour
Thursday, March 29th
Tour: 5:30-6:30; meeting to follow
The Green Institute, 2801 21st Ave S, Minneapolis

There are many green buildings built from the ground up, but there are not any options for showing what residents can do with their existing homes to live more sustainably. The Eco Model Haus will be an existing home that will be remodeled into a green model home. It will display ways that residents can make changes to their homes from very easy and affordable actions such as a display of fluorescent or LED lights and information on how they are more efficient and what they cost (i.e. Science Museum signage) to more expensive or technical actions such as solar panels. We are working towards finding a location off of the Greenway (bike trails) and/or Lightrail to make the connection to alternative transportation as well and easy to access. This will be a space for homeowners, apartment dwellers and students to tour with hands-on and interactive displays.

Rain barrel (top detail): Rain barrels like this one collect rain so you can use it to water your garden later. The screens keep children, pets, and mosquitos out, while letting water in. (Photo by chrisdigo)
Rain barrel (top detail): Rain barrels like this one collect rain so you can use it to water your garden later. The screens keep children, pets, and mosquitos out, while letting water in. (Photo by chrisdigo)

Other examples of what could be displayed in the Eco Model Haus include:

  • Permeable surface options
  • Compost bin displays with plexi glass showing the decomposition
  • Green rooftop with stairs to view it
  • Rain barrels and options for children to water a nearby garden with the rain barrel water
  • Hybrid (HOURCAR) parking spot
  • Rain garden and native plants
  • Recycling and composting set up inside the home
  • Non-toxic cleaning samples and station to make your own to take home with a recipe
  • The Sustainable Living Resource Center will offer a library, product sample displays, experts on hand, a meeting/workshop space and the Twin Cities Green Guide™'s office. The Eco Model Haus will offer a green model home to Minnesotans to tour, attend workshops, lectures, and do research.

    * For the next six months they will be offering open meetings to the public and professionals to offer opinions on what this space will look like and to assist in the planning and execution of the Eco Model Haus. They hope to obtain a space in 2007, begin planning and creating the space in 2008 and open to the public for tours in 2009 or 2010. And they anticipate a large portion of the project will be planned and installed by volunteers (community members and professionals in the field).

Mar
18
2007

Stradavarius sound from graphite and balsa

Violin engineering: image modified from TheViolinSite.com via wikipedia
Violin engineering: image modified from TheViolinSite.com via wikipedia
Can we make violins today that sound as sweet as those made by Antonio Stradivari? Joseph Curtin (Ann Arbor, Mich.),who received a 2005 MacArthur Foundation “genius award” for his violin designs, thinks so. In reference to violins made by Douglas Martin, Curtin stated that

“the traditional violin became obsolete in early July of 2005.”

One of Mr. Martin's prototype violins, Balsa 4, when passed around at a violin design workshop at Oberlin College, startled the participants with its punch and responsiveness. Using balsa for lightness and graphite for stiffness, Martin is breaking the traditional violin design rules.

New materials "sing"

Another violin maker to use modern materials like graphite fibers is Martin Schleske. Ingolf Turban, a touring concert violinist, compared Mr. Schleske’s latest violin, which has a top made of a mix of spruce and graphite, with a 1721 Stradivarius by recording passages from Mozart’s Violin Concerto in D Major with each. He told Mr. Schleske he preferred the new one.

I have never been playing any violin with such a singing E string,” Mr. Turban said in a testimonial. “It is no longer like playing violin but like singing.”

Violin acoustics analysed in physics laboratory

George Bissinger, a physicist at East Carolina University in Greenville, N.C., is using medical-imaging gear, laser scanners, arrays of microphones and computers to measure and model how the parts of a violin react once energy is introduced by a bow, fingertip, pick or, in the laboratory, the repeated taps of a tiny hammer.

Particularly important, Dr. Bissinger said, is determining which factors translate the side-to-side sawing of a bow on a string into vertical motions of the violin top. “Up and down is what matters,” he said.
Another important influence, particularly on low violin notes, is the movement of air in and out of the f-holes, Dr. Bissinger said. If the dimensions are right, the air sloshes forward and back like disturbed water in a bathtub (or air in an organ’s pipes) at rates that increase the instrument’s volume.

Want to learn more?

I recommend viewing the video and multimedia graphics found in the New York Times post, "String Theory: New Approaches to Instrument Design".

Mar
08
2007

Rural village in Bangladesh: How will nanotechnology benefit them in the coming years?  Courtesy adrenalin.
Rural village in Bangladesh: How will nanotechnology benefit them in the coming years? Courtesy adrenalin.
You may have heard about nanotechnology enhanced pants that keep that wine stay away or even a nanotech tennis racket. But if nanotechnology is truly set to revolutionize the world we live in what benefits can the poorest people of the world expect to see?

According to a 2005 study these are the areas we should focus on first:

  1. Energy storage, production and conversion
  2. Agricultural productivity enhancement
  3. Water treatment and remediation
  4. Disease diagnosis and screening
  5. Drug delivery systems
  6. Food processing and storage
  7. Air pollution and remediation
  8. Construction
  9. Health monitoring
  10. Vector and pest detection and control

The study was developed by the Canadian Program on Genomics and Global Health at the University of Toronto Joint Centre for Bioethics lead by Dr. Peter Singer. Read the full report

Not surprisingly energy tops the list. According to Singer easy access to cheap energy will lead to a great deal of economic growth in the developing world. Here at the Buzz we have covered several nanotechnology energy advances that might come to market in the future. super cheap solar cells, nano ultracapacitors from MIT, nano products now.

Look for more info on some exhibits we will be rolling out soon on nanotech's impact on energy and the environment.