Medescape

Skepticism, Medicine and Science News

Gravity Fingers Mathematically Explained

Since I have my math exam tomorrow, it seems only natural I should write about something math related. 

When water soaks down into the ground, it does not do so evenly, but rather forms spikes known as gravity fingers (see image below). Though it is a well known phenomenon in fluid mechanics, no one has been able to explain, mathematically, why it happens. In a recently published paper however, mathematicians at MIT give a both simple and elegant explanation. They got the idea when one of the researchers observed that gravity fingers looked very much like water flowing down a window (when you look at the picture it looks really obvious, it was definitely the first think I though of), which is a well understood phenomenon. Then it was just a matter of taking the equations describing that and apply it to water movement in soil. 

The short explanation to this phenomenon is that in order for water to flow down a window or in soil, the surface tension of the water has to be overcome. This will cause the water to flow in a finger-like pattern because as water builds up in the fingers, the weight overcomes the surface tension. My understanding of the phenomenon is that small indentations in the bottom flow line are bound to form no matter what because the soil/window is not perfectly uniform (and can never be), and when this happens the flow rate at the indentations increase because of the extra weight, leading to gravity fingers. 

Gravity fingers

December 14, 2008 Posted by | Math | , , , , , , , , , , , , | Leave a comment

Teddies In Space

It sounds like a bad sci-fi movie from the 80s, but it is actually a really, really cool science project. Students at the University of Cambrige recently managed to put four teddy bears in space by using a weather balloon. The maximum altitude reached was about 30km, and to prevent the bears from freezing solid the students designed and built space suits for them to wear. This was really the main part of the project, and was an excellent way of teaching the students the principles of insulation, convection, conduction, radiation, pressure and loads of other exciting physics. Oh, and the students in question were actually aged about 11-12, and I think this is a wonderful way of getting young kids excited about science. I really hope other schools follow Cambridge’s example on this one. 

I mean, how cool is that!

December 8, 2008 Posted by | Astronomy, General Science | , , , , , , , , , , , , , , , , , | Leave a comment

New Method for Creating Antimatter Developed

Antimatter consists of antiparticles in the same way matter consists of particles, and the antimatter equivalent of, for example, a proton found in normal matter would be an antiproton. When matter meets antimatter the result is total annihilation and radiation in the form of gamma rays. As a result, producing antimatter is not easy, but scientists have recently developed a new method that produces far more of it than previous methods. 

The research was done by a team led by physicist Hui Chen at Lawrence Livermore National Laboratory in Livermore, California. They managed to create an estimated 100 billion positrons, which is the antimatter equivalent of electrons, by modifying and perfecting earlier methods. Previously, the team created positrons by shooting a short, ultra-intense laser at a paper-thin sheet of gold, but recent computer simulations suggested that they would be able to produce far more positrons by using a thicker sheet. So, when the paper-thin foil was substituted for a millimetre-thick one, they were able to create an estimated 100 billion positrons. 1 million of these were physically measured by their detectors, and the final number was inferred from that. In comparison, when the laboratory first created positrons about 10 years ago, they were able to detect only 100 particles. 

The laser used in the experiment ionizes and accelerates electrons that are subsequently driven through the gold sample. Here, they interact with the gold nuclei to give off packets of energy that then decay into matter and antimatter. 

When the universe was created in the Big Bang, the theory goes that equal amounts of matter and antimatter were created. However, after some time, due to a not fully understood process called bayrogenesis, there was a small shift in the matter-antimatter equilibrium, resulting in the dominance of quarks and leptones over antiquarks and antileptones. Even though the dominance was only about 1 particle per 30 million, it led to the development of the matter-based universe we know today. This new method of creating positrons will thus perhaps enable physicist to conduct more research into antimatter, and maybe improve our understanding of the early development of the universe. 

A bubble chamber-photograph showing the movement of elementary particles, including positrons. For more information, go here. Credit: CERN

November 18, 2008 Posted by | Physics | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , | 1 Comment

Nobel Prize in Physics

The 2008 Nobel Prize in Physics is awarded to:

1/2 Yoichiro Nambu “for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics”

1/2 Makoto Kobayashi and Toshihide Maskawa “for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature”

Congrats!

Now, I was planning on writing something about what these discoveries actually imply, but I just found it so hard to wrap my mind around that I could not do it justice in just a couple of paragraphs. I therefore choose to give some links to sites that explains this better than I would be able to do:

New Scientists short overview of quantum physics. 

Wikipedias entry on spontaneous symmetry breaking.

And for the really daring, here‘s an article about the origins of families of quarks and leptons.

The original paper by Maskawa and Kobayashi is not free, as of yet, but can be bought here.

Edit: The major science websites have now had time to write their own articles about the science behind the award this year, and some examples can be found here and here.

October 7, 2008 Posted by | General Science, Physics | , , , , , , , , , , | Leave a comment

Carbon Nanotubes – What can’t they do?

Okey, so I’m not really going to write about what they can’t do. Instead, I’ll list some of the many possible applications of them, ranging from creating structural fibres to novel drug-delivery systems. 

Continue reading

October 1, 2008 Posted by | Other | , , , , , , , | Leave a comment