In Nature this week

April 13, 2007

  1. Obituary to Knut Schmidt-Nielsen: McNeill Alexander recalls the man and his work; in the process he summarises the many important discoveries made by Schmidt-Nielsen:
    • Kangaroo rats minimise water loss by producing very concentrated urine, cooling the air that they exhale in the nasal cavity, which was cooled in the first place while inhaling, and living in burrows during day and venturing out only at night;
    • in contrast to kangaroo rats, dogs breathe in through the nose and breathe out through the mouth; thus, they let water vapour to evaporate helping them lose the extra heat generated by exercise;
    • camels avoid water loss by increasing their body temperature as the day progresses, and by drying the air that they exhale using the hygroscopic surfaces of their nasal cavities;
    • sea birds which drink sea water secrete droplets of concentrated salt solutions in their nostrils and shed them by the shake of their heads;
    • unlike mammalian lungs, in the lungs of birds the air-flow is one-way–it enters at one end and leaves another, and the counter current flow of blood and air helps in high rate of oxygen absorption in the blood to power their flight;
    • for a given body mass, swimming is cheaper than flight which is cheaper than running.
  2. Amazing indeed!

  3. Bending crystals by light: Michael McBride, in a news and views piece, writes about the recent experiments of Kobatake et al to use light induced chemical transformation to bend crystals–reversibly, so that they can be bent cyclically:

    The authors grew crystal needles (about 200 \mum long and 5 \mum in diameter) by sublimation so as to be attached at one end to a microscope slide. When illuminated from the side by an ultraviolet laser pulse, the needles bent within a millisecond, displacing the free end by 50 \mum. As a dramatic demonstration of this effect, the needles can launch a tiny gold sphere as if it were a tennis ball…The reversibility of this movement is particularly noteworthy — the needles can undergo 80 cycles of photochemical bending and straightening with no apparent damage to the crystal integrity, nor any diminution in displacement amplitude.

    You can see the movies of the crystal moving gold balls as well as other light induced mechanical movement at the supplementary information page. Wow! is all I can say.

  4. The quantum mechanical basis of photosynthesis: Roseanne Sension, in a News and Views piece, while commenting on the mapping of electronic states using two-dimensional Fourier transform spectroscopy in Fenna–Matthews–Olsen bacteriochlorophyll complex by Engel et al, indicates how energy transfer during photosynthesis is inherently quantum mechanical; she further feels that this discovery might be the key to designing artificial solar energy harvest systems. Considering the fact that

    In higher plants and certain bacterial systems, the initial steps of natural photosynthesis harness light energy with an efficiency of 95% or more,

    this certainly is a very important piece of information to have.

Have fun!

Title: Feynman’s wobbling plate

Authors: Slavomir Tuleja, Boris Gazovic, Alexander Tomori and Jozef Hanc

Source: American Journal of Physics, Vol. 75, No. 3, pp. 240–244, March 2007

Abstract: In the book Surely You Are Joking,Mr. Feynman! Richard Feynman tells a story of a Cornell cafeteria plate being tossed into the air. As the plate spun, it wobbled. Feynman noticed a relation between the two motions. He solved the motion of the plate by using the Lagrangian approach. This solution didn’t satisfy him. He wanted to understand the motion of the plate by analyzing the motion of its individual particles and the forces acting on them. He was successful, but he didn’t tell us how he did it. We provide an elementary explanation for the two-to-one ratio of wobble to spin frequencies, based on an analysis of the motion of the particles and the forces acting on them. We also demonstrate the power of numerical simulation and computer animation to provide insight into a physical phenomenon and guidance on how to do the analysis.

Internet resources: Java applets and supplementary information