Physics News off the Web compiled by John O’Connor, Past ...



Physics News off the Web compiled by John O’Connor, Past Federal President of AIP

Highlights:

• Lasers tackle radioactive waste

• Horizontal Brazil Nut Effect

• A single atom laser

• General Relativity passes Cassini test

Amino acid detected in space (Aug 11)

The idea that primitive life on Earth may have been seeded by a comet or asteroid impact is controversial. Since it was suggested more than 40 years ago, however, increasingly complex organic molecules have been discovered in space. Now astronomers have detected an amino acid - one of the building blocks of proteins - in interstellar dust clouds in our galaxy. The discovery of glycine in space suggests that interstellar molecules may have played a pivotal role in the prebiotic chemistry of the Earth (Y-J Kuan et al. 2003 Astrophys. J. 593 848).

Lasers tackle radioactive waste (Aug 13)

One of the biggest challenges facing the nuclear industry today is the storage and disposal of waste that will remain radioactive for millions of years. One approach to this problem involves bombarding the waste with neutrons to speed up the decay of long-lived isotopes into nuclei with much shorter half-lives. However, physicists in the UK and Germany have now demonstrated a new laser-driven approach to "transmutation" by converting iodine-129, which has a half-life of 15.7 million years, into iodine-128. The half-life of this lighter isotope is just 25 minutes (J. Phys. D to be published).

NANOTUBE VELCRO. 

Joining two or more nanochips, such as nano-electromechanical systems (NEMS), can be done by welding or gluing or with tiny nuts and bolts. But what if you could gently just fasten them the way fabrics are fastened, with velcro? Conventional velcro fastening works by pairing one patch of mm-scale hooked protuberances with a patch of looped protuberances.  In the microscopic version, both patches would bristle with carbon nanotubes, grown upright except for a hook on the top end.  David Tomanek and his colleagues at Michigan State (tomanek@pa.msu.edu, 517-355-9702) are studying how to make nano-velcro work (see movies as pa.msu.edu/cmp/csc/simulvelcro.html ). His calculations so far show that the nanotubes will remain in place on each separate substrate (they can be grown on selective pieces of surface geometry using lithographic-like patterning techniques) and will also remain locked together when mated with its counterpart on another substrate.  A typical application for nano-velcro would be to fasten a diamond coating onto specific parts of a metal surface.  (Berber et al., Physical Review Letters, upcoming article; co-authors, Savas Berber, berber@pa.msu.edu and Young-Kyun Kwon, ykkwon@ )

GOOD VIBRATIONS HELP A FROG LOCATE TASTY PREY. 

Living in southern Africa, the aquatic frog Xenopus catches insects by detecting critters' vibrations on the water surface.  Not able to see well in a liquid environment, the frog gets a wealth of information from the water waves that insects produce as they slosh around.  The waves tell Xenopus the direction in which the insect is located. They even give the frog a general idea of the type of insect that is making the waves.  To detect the water waves on its skin, the frog has about 180 receptors known as "lateral-line" organs, which are found on the skin along both sides of the body, around the eyes, and also on the head and neck.  Now, researchers in Germany (Leo van Hemmen, TU Munich, LvH@ph.tum.de, +49-89-289.12362) have developed a simple model that explains how the lateral-line organs enable Xenopus to locate and classify its prey.  Strikingly, the model suggests that the frog can reconstruct the shape of the water wave (its "waveform") from limited information, namely the movement of water recorded by the 180 simple sensory organs.  In the frog, water gets deflected by 4-8 flag-like structures (called "cupulae") in the lateral line organs. Each deflection stimulates nearby hair cells to generate electrical spikes that are synchronized in time with the deflection.  The timed electrical spikes from the 180 sensory organs, the researchers show, contain enough information for the frog to "estimate" the shape of the water wave pretty accurately. This is true even if some of the lateral-line organs are not functioning properly. Furthermore, they show how the frog can localize and distinguish between two different water waves coming simultaneously from two insects in different directions.  This model may also be applicable to the mechano-sensory systems of other animals, such as crocodiles (Soares, Nature, 16 May 2002), which have similar receptor organs (Franosch et al., Physical Review Letters, upcoming).

HORIZONTAL BRAZIL NUT EFFECT. 

A new twist on the Brazil-nut effect appears to be a good way to harvest large particles from a granular mixture, according to recent experiments and simulations performed at the University of Texas at Austin. The Brazil-nut effect is an odd but well-known phenomenon in agitated granular mixtures. Depending on the conditions, shaking containers filled with grains of various sizes will cause the larger grains to rise to the top of the mixture (Update 132), or sink to the bottom. The Texas researchers (contact: Sung Joon Moon, moon@Princeton.edu, 609-258-2977), however, showed that they could also control the horizontal distribution of large grains by using kinks that spontaneously arise in granular layers for sufficiently large container accelerations.  A kink separates two regions oscillating with opposite phase: the granular layer on one side of a kink is moving up while the layer on the other side is moving down.  Larger particles flow from the two oscillating regions and collect in the kink. The researchers can control the location of a kink by adjusting the driving signal, and harvest the large grains by sweeping the kink to one side of the container. The research shows that trapping results from avalanches that form at the kink as falling fluid-like regions move past rising, effectively solid, regions. The avalanches lead to internal convection rolls that carry the large particles toward a kink. The horizontal Brazil-nut effect may eventually lead to new commercial methods for segregating granular material by size. (S. J. Moon et al., Phys. Rev Lett.,date)

Carbon dating confirms origins of biblical tunnel (Sep 10)

Samples from the Siloam tunnel, which the books of Kings and Chronicles say was constructed in ancient Jerusalem during the reign of King Hezekiah, have been dated using radiometric techniques by researchers from Israel and the UK. Amos Frumkin at the Hebrew University of Jerusalem and colleagues at the Geological Survey of Israel and Reading University calculate that the tunnel was built in about 700 BC, and that the biblical text provides an accurate historical record of the tunnel's construction (A Frumkin et al. 2003 Nature 425 169).

Bose-Einstein condensates break temperature record (Sep 12)



Physicists have made another breakthrough in the field of Bose-Einstein condensation. Wolfgang Ketterle and colleagues at the Massachusetts Institute of Technology have succeeded in cooling a Bose condensate of sodium atoms down to below 500 pK. This is the lowest temperature ever recorded on Earth and is six times lower than the previous temperature record for Bose condensates . These ultracold samples could be important for spectroscopy, metrology and atomic optics applications (A Leanhardt et al. 2003 Science 301 1513).

A SINGLE-ATOM LASER, a device employing a single trapped atom to resonantly emit light back and forth between two reflective mirrors, has been created by Jeffrey Kimble at Caltech.  Although single-atom lasers have been demonstrated before ( ), Kimble's is the first to use a single atom nearly at rest, and not a parade of atoms in a dilute beam entering a reflective cavity one at a time.  The singleness of the source means that the number of photons emitted by the laser over a certain time interval is, while not exactly predictable (which would be outlawed by Heisenberg's uncertainty principle), much less jittery than emission from multi-atom lasers.  The emission is weak by laser standards---only about 100,000 photons per second---but this quiet, more controllable form of photons should aid future quantum information schemes. (McKeever et al., Nature, 18 September 2003.)

First light for one-atom laser (Sep 17)

Physicists in the US have built a laser with a single atom for the first time. Jeff Kimble and colleagues at the California Institute of Technology made the device by trapping a cold caesium atom in an optical cavity. The one-atom laser produces nonclassical light that could have applications in quantum information technology (J McKeever et al. 2003 Nature 425 268).

Hollow fibre carries megawatt pulses (Sep 19)

A US team has made an optical fibre that can support laser pulses with a peak power of several megawatts - several hundred times the power handling ability of conventional fibre. The hollow-core photonic band-gap fibre developed by Alexander Gaeta and colleagues at Cornell University and the optics company Corning could prove useful for applications in spectroscopy, biology and medicine where high-power pulses need to be delivered through a fibre (D G Ouzounov et al. 2003 Science 301 1702).

PROTON PULSE GIVES PLASMA POSSIBILITIES

It lurks in the dense interior of Jupiter and boils deep within the sun. Warm dense plasma, so common in the universe, is very difficult to manufacture on Earth's surface. In the 19 September PRL, a team describes their method of zapping aluminum foil with a proton beam to create a blob of warm dense plasma--a form of matter very different from other types of plasma. The technique may allow for previously impossible measurements that could lead to more accurate models of star and planetary interiors. (P. K. Patel et al., Phys. Rev. Lett. 91, 125004) Links to the papers: COMPLETE Focus story at

General relativity passes Cassini test (Sep 24)



Italian astrophysicists have confirmed the predictions of Einstein's general theory of relativity with a precision that is about 50 times better than previous measurements. Bruno Bertotti of the University of Pavia and colleagues in Rome and Bologna measured how radio waves sent from the Earth to the Cassini satellite and back again were deflected by the Sun (B Bertotti et al. 2003 Nature 425 374). Their results, which are accurate to 20 parts in a million, agree with the predictions of general relativity.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download