From Physics Research Archive - Page 4

The Doppler Effect and Sonic Booms - Dec 1, 2010

This image of the shockwave made by a speeding bullet is a shadowgraph--simply a photograph of the shadow of the bullet and the shockwave. Variations in the density of air refract the light used to make the shadow and produce bright and dark regions.

- Note the little fragment that is moving just below the speed of sound (the disturbance is slightly ahead of it).
- To see animations of shockwaves made by objects moving at various speeds, visit The Doppler Effect and Sonic Booms (skip right to the animations).

image credit: Fatima Toor; image source; larger image

Quantum Cascade Lasers - Nov 1, 2010

The image above shows a quantum cascade laser captured by a camera that images infrared light. The laser light is the small dot in the middle of the round window. The laser itself--behind the window--is kept at a temperature of -193° C, just above the temperature of liquid nitrogen.

Quantum cascade lasers work like this:
- In a thin slice of a semiconductor, an electron can occupy discrete energy levels.
- When an electron moves from a higher level to a lower level, a photon is emitted.
- If many thin slices of semiconductor are stacked together, the electron can cascade from one to another, emitting a photon of the same frequency in each slice. These photons form the laser beam.
- To learn more, see Quantum Cascade Lasers.

image credit: A. Hildebrand, M. Pilkington, and M. Connors; image source; larger image

Do We Know What Killed the Dinosaurs? - Oct 16, 2010

In the image above (upper left) you can see two concentric circles. These mark the location of the Chicxulub crater, and the white line shows the coast of the Gulf of Mexico. See this Canadian site (scroll down to the third image) for a fuller explanation of how the image was made and for related images.

(This feature was updated on July 31, 2013.)

- The Chicxulub crater is a candidate for the asteroid impact that killed the dinosaurs, but not all scientists are convinced. Some believe the iridium layer (pictured at left) could also have been produced by volcanic eruptions at the same time as the layer was created.  

- For more about the Cretaceous extinction and the debate over what caused it, see these articles from the University of California Museum of Paleontology and the Geological Society of America.

(This feature was updated on July 13, 2012.)

Image credit: Michael Kelzenberg; image source; no larger image available

Caltech Researchers Create Highly Absorbing, Flexible Solar Cells - Oct 1, 2010

In a radical departure from the traditional design, a Caltech group has produced a flexible solar cell using an array of silicon wires. By packing light-scattering particles in among the wires, the researchers have achieved efficiencies up to 85%, despite the fact that the silicon wires take up only 2% of the volume, with significant cost reduction expected in a commercial version. To learn more, see this Caltech press release and this Scientific American article.

Image used with the consent of Agilent Laboratories; image source; larger image

The Physics Classroom: Total Internal Reflection - Sep 16, 2010

The optical fiber in the photo above doesn't just guide the beam--the fiber produces the beam. Instead of a tube of helium and neon gas, or a piece of ruby, the "active medium" of this laser is added to the glass in the fiber. Since the mirrors are just the polished ends of the fiber, there is nothing to go out of alignment, and maintenance is easy.

- Fiber lasers are using laser cutting.
- To find out how the fiber optic laser promises to fuse the technologies of transistors and fiber optics, see this Penn State page. Also, here's another image of a fiber laser.
- To see how the fiber contains a laser beam, visit The Physics Classroom: Total Internal Reflection.

Network Theory: A Key to Unraveling How Nature Works - Sep 1, 2010

You are looking at a network diagram that shows the interconnectedness of the world economy. To learn more about this network, visit Mapping the World Economy.

- To find out how networks are related to "Six Degrees of Kevin Bacon," visit Network Theory: A Key to Unraveling How Nature Works.
- To learn about a physicist who studies networks, see Physics Rules Network Dynamics.

Image credit: American Physical Society; Image source; Larger Image

Making a supersonic jet in your kitchen - Aug 16, 2010

What exactly happens when an object makes a splash in water? The disk shown above was pulled into water in a reproducible way to investigate the splash.

- The results were surprising... including a supersonic jet of air!
- To learn more, see Making a supersonic jet in your kitchen, and don't miss the video of the splash.

Image credit: Philippe Lijour; Image source; larger image

The Real Sea Monsters: On the Hunt for Rogue Waves - Aug 1, 2010

This "rogue wave" broke over the deck of an oil tanker, and was much taller than the other waves on the ocean at the time. See Freak Waves, Rogue Waves for graphs of rogue waves building up in the ocean, and for the measurement of one that struck an oil platform in the North Sea.

- To learn more about these waves, see The Real Sea Monsters: On the Hunt for Rogue Waves
- Also, check out this Discovery News article to find out about a cruise ship that was recently damaged by a huge wave.

From Soap Bubbles to Technology - Jul 16, 2010

The soap film you see here, made in between two metal rings, is called a catenoid, and it uses the minimum area to enclose a given volume. Click on the image to see another example of a "minimal surface" soap film.

- Minimizing area can reduce construction costs--see this catenoid-shaped cooling tower, from this Wikipedia page.
- To learn more, visit From Soap Bubbles to Technology.

About Dust - Jul 1, 2010

This satellite image shows a recent dust storm in China that was so large it spread out to neighboring countries. For more on this storm, see About Dust.

Also, for dust storms around the world, visit Earth Snapshot.

(This feature was updated on 8/31/2013.)

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