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Archive for category General Physics
Super cool atom thermometer
Posted by wideant in General Physics on March 4, 2010
As physicists strive to cool atoms down to ever more frigid temperatures, they face the daunting task of developing new, reliable ways of measuring these extreme lows. Now a team of physicists has devised a thermometer that can potentially measure temperatures as low as tens of trillionths of a degree above absolute zero. Their experiment is reported in the current issue of Physical Review Letters and highlighted with a Viewpoint in the December 7 issue of Physics.
Physicists can currently cool atoms to a few billionths of a degree, but even this is too hot for certain applications. For example, Richard Feynman dreamed of using ultracold atoms to simulate the complex quantum mechanical behavior of electrons in certain materials. This would require the atoms to be lowered to temperatures at least a hundred times colder than what has ever been achieved. Unfortunately, thermometers that can measure temperatures of a few billionths of a degree rely on physics that doesn’t apply at these extremely low temperatures. Read the rest of this entry »
Slipper-shaped blood cells
Posted by wideant in General Physics on March 4, 2010
Red blood cells, which make up 45 percent of blood, normally take the shape of circular cushions with a dimple on either side. But they can sometimes deform into an asymmetrical slipper shape. A team of physicists have used simulations to explore how fluid flow might be responsible for this deformation, as well as how the deformation in turn affects blood flow. The insights could help understand the mechanisms involved in arterial disease and other blood flow-related ailments. Their research is reported in Physical Review Letters and highlighted with a Viewpoint in the October 26 issue of Physics.
When a red blood cell flows through an artery, one face usually balloons out like a parachute, but sometimes the cell can deform to resemble a slipper. To find out why, Badr Kaoui at the Université Joseph Fourier in Grenoble, France and his colleagues modeled the cells as two-dimensional fluid-filled sacks flowing in a liquid. They found that when the cells weren’t sufficiently plump, the symmetric parachute collapsed into a slipper. They also found that this morphing helped the sacks catch up with the rest of the fluid, suggesting that the slipper shape achieves more efficient blood flow. Read the rest of this entry »
Spotting evidence of directed percolation
Posted by wideant in General Physics on March 2, 2010
A team of physicists has, for the first time, seen convincing experimental evidence for directed percolation, a phenomenon that turns up in computer models of the ways diseases spread through a population or how water soaks through loose soil. Their observation strengthens the case for directed percolation’s relevance to real systems, and lends new vigor to long-standing theories about how it works. Their experiment is reported in Physical Review E and highlighted with a Viewpoint in the November 16 issue of Physics.
While directed percolation models are handy for describing things as diverse as sand flow and calcium dynamics in cells, no one had managed to find clear, reproducible evidence of the phenomenon in a controlled experiment. Read the rest of this entry »