Physics News Update no. 570
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The American Institute of Physics Bulletin of Physics News
Number 570 December 21, 2001
Published by the American Insitute of Physics.
THE BACTERIAL DIVIDE. Roughly once an hour, the rod-shaped bacterium E. coli multiplies by producing a copy of its DNA and then splitting into two daughter bacteria, each carrying a complete set of genetic information. It is vital that the division occur very close to the bacteria's midpoint to ensure the viability of the daughter cells, but it has long been a mystery as to how a bacteria locates its middle in preparation for division.
Researchers from Simon Fraser University (British Columbia) and Dalhousie University (Nova Scotia) believe they have solved the riddle by studying the interactions of three proteins that flow from end to end inside the bacteria.
(Martin Howard, 31-71-527-5515, mjhoward@lorentz.leidenuniv.nl; Andrew Rutenberg, 902-494-2952, adr@fizz.phys.dal.ca).
Biologists have known for several years that the proteins MinC, MinD, and MinE are important in cell division; the absence or incorrect distribution of any one of the three can corrupt cell division, or inhibit the process altogether. Experiments have shown that these Min proteins oscillate from end to end of the bacterium every minute or so. The effect of the oscillation is that MinC and MinD have the their highest concentration at the bacterial ends. Because MinC inhibits division, the bacterium will divide at the center, where MinC is minimized.
The nagging question concerns how these protein oscillations are driven. Jostling molecules in gases and liquids tend to spread concentrated substances around in a diffusion process; it's the reason a fragrance can drift across a room even in still air.
Diffusion is also the principle transport mechanism inside bacteria, but acting alone it should evenly distribute compounds throughout the cell. As the researchers' new model shows, however, it's when protein diffusion is combined with the binding and release of proteins from the cell membrane that oscillating patterns in E. Coli occur. The effect is closely related to the Turing model reaction-diffusion equations often championed as the mechanism behind complex patterns in nature, such as tiger stripes and ladybug spots (Update 558). In the case of E. Coli, oscillation of the Min protein self-organizing behavior causes the division site to be at the cell midpoint.
(M. Howard, A.D. Rutenberg, and S. de Vet, Physical Review Letters, 31 Dec 2001)
DENDRIMER LASERS have as their active medium fluorescing dye molecules lodged at the heart of hyper-structured, tree-shaped polymers. In most dye lasers the dye concentration cannot go above a millimole/liter without quenching the fluorescence process. But in a new experiment by scientists at the Communications Research Laboratory and PRESTO Japan Science and Technology Corporation, both in Japan, a dye concentration of 9 milli-mole/liter showed no diminution of laser output, but rather an increase. Furthermore, the spectral linewidth (the spread in wavelengths) is narrow, only 0.1 nm. The laser output was so potent that end mirrors were not used. This, combined with other organic-laser properties such as flexibility and tunability, will soon result in 100-nm-sized lasers. The researchers (Shiyoshi Yokoyama, 81-789-692-254, syoko@crl.go.jp) are now at work on extending their dendrimer structures in producing solid state waveguides, fibers, and photonic crystals.
(Yokoyama et al., Applied Physics Letters, 7 Jan 2002)
A TINY MICROPHONE DIAPHRAGM BASED ON FLY EARS
has been built by researchers (Ronald Miles, Binghamton University, 607-777-4038, miles@binghamton.edu), offering such possibilities as compact hearing aids that respond only to sound in front of the wearer. The diaphragm is the part of a microphone that vibrates in response to incoming sound waves; other components then convert the diaphragm's vibrations into electrical signals which can then be amplified or recorded. The researchers based their novel diaphragm on Ormia orchracea, a small parasitic fly that uses sound to track down its cricket host even in complete darkness. The fly can detect changes as small as two degrees in the direction of an incoming sound, as good as humans. This is remarkable since the fly's ears are just a couple hundred microns apart. Mammals, on the other hand, rely on the fact that their ears are well separated from one another, so that sound can arrive at each ear at sufficiently different times and with sufficiently different intensities. What's even more remarkable about the fly is that its hearing organs, a pair of rectangle-shaped membranes, are connected to each other. Specifically, they are "torsionally coupled" so that a sound wave that lands on one membrane can deflect the other membrane. The connection between the membranes enables them to vibrate in several different ways so that the fly can obtain both the average pressure of an incoming sound and its pressure gradient, the change in sound pressure as you move from one ear to the other. This provides lots of information with which to determine the direction of the sound.
The researchers built a silicon nitride prototype microphone diaphragm that closely reproduces the characteristics of the fly ears. While the researchers face challenges in mass-producing such
a design, they hope that its unconventional approach to localizing sound will inspire lots of applications.
(Paper 2aEA1 at Acoustical Society of America meeting in Ft. Lauderdale, 3-7 Dec 2001.)
A QUANTUM COMPUTER HAS FACTORED THE NUMBER 15. This may sound like a trivial achievement, but it is actually a considerable physics milestone. It represents the most complex calculation yet performed in quantum computing, which offers a radically different means of information processing through the use of quantum mechanics. Even more noteworthy, it is the first experimental demonstration of Shor's algorithm, a quantum-computer program which can potentially factor large numbers in a fraction of the time needed for the world's currently fastest supercomputers. Such large numbers are used as the basis of encryption codes; the codes are broken by finding the prime-number factors of the large numbers. IBM-Almaden and Stanford University researchers (Isaac Chuang, now at MIT, ichuang@cba.mit.edu) built a quantum computer whose working substance was a liquid consisting of a billion billion molecules.
The molecules were specially designed to contain 7 nuclear "spins"--5 from fluorine nuclei and 2 from carbon-13 nuclei. Analogous to a bar magnet which could point north or south, each spin could represent the binary digits "0" or "1" (or both 0 and 1 at the same time through the subtleties of quantum mechanics) and could be controlled by magnetic fields and radio waves (i.e., nuclear magnetic resonance techniques). By manipulating the 7 qubits, the computer could take advantage of quantum computing's unique parallel processing capabilities to determine that the factors of 15 were 3 and 5. Enormous challenges must be surmounted to build larger-scale quantum computers which could factor very large numbers, and this is an early step forward.
(Vandersypen et al., Nature, 20/27 December 2001; also see IBM-Almaden news release at
http://www.research.ibm.com/resources/news/20011219_quantum.shtml)
Number 570 December 21, 2001
Published by the American Insitute of Physics.
THE BACTERIAL DIVIDE. Roughly once an hour, the rod-shaped bacterium E. coli multiplies by producing a copy of its DNA and then splitting into two daughter bacteria, each carrying a complete set of genetic information. It is vital that the division occur very close to the bacteria's midpoint to ensure the viability of the daughter cells, but it has long been a mystery as to how a bacteria locates its middle in preparation for division.
Researchers from Simon Fraser University (British Columbia) and Dalhousie University (Nova Scotia) believe they have solved the riddle by studying the interactions of three proteins that flow from end to end inside the bacteria.
(Martin Howard, 31-71-527-5515, mjhoward@lorentz.leidenuniv.nl; Andrew Rutenberg, 902-494-2952, adr@fizz.phys.dal.ca).
Biologists have known for several years that the proteins MinC, MinD, and MinE are important in cell division; the absence or incorrect distribution of any one of the three can corrupt cell division, or inhibit the process altogether. Experiments have shown that these Min proteins oscillate from end to end of the bacterium every minute or so. The effect of the oscillation is that MinC and MinD have the their highest concentration at the bacterial ends. Because MinC inhibits division, the bacterium will divide at the center, where MinC is minimized.
The nagging question concerns how these protein oscillations are driven. Jostling molecules in gases and liquids tend to spread concentrated substances around in a diffusion process; it's the reason a fragrance can drift across a room even in still air.
Diffusion is also the principle transport mechanism inside bacteria, but acting alone it should evenly distribute compounds throughout the cell. As the researchers' new model shows, however, it's when protein diffusion is combined with the binding and release of proteins from the cell membrane that oscillating patterns in E. Coli occur. The effect is closely related to the Turing model reaction-diffusion equations often championed as the mechanism behind complex patterns in nature, such as tiger stripes and ladybug spots (Update 558). In the case of E. Coli, oscillation of the Min protein self-organizing behavior causes the division site to be at the cell midpoint.
(M. Howard, A.D. Rutenberg, and S. de Vet, Physical Review Letters, 31 Dec 2001)
 A large dendrimer polymer molecule (green) with a dye molecule lodged at its center. [link] |
(Yokoyama et al., Applied Physics Letters, 7 Jan 2002)
A TINY MICROPHONE DIAPHRAGM BASED ON FLY EARS
has been built by researchers (Ronald Miles, Binghamton University, 607-777-4038, miles@binghamton.edu), offering such possibilities as compact hearing aids that respond only to sound in front of the wearer. The diaphragm is the part of a microphone that vibrates in response to incoming sound waves; other components then convert the diaphragm's vibrations into electrical signals which can then be amplified or recorded. The researchers based their novel diaphragm on Ormia orchracea, a small parasitic fly that uses sound to track down its cricket host even in complete darkness. The fly can detect changes as small as two degrees in the direction of an incoming sound, as good as humans. This is remarkable since the fly's ears are just a couple hundred microns apart. Mammals, on the other hand, rely on the fact that their ears are well separated from one another, so that sound can arrive at each ear at sufficiently different times and with sufficiently different intensities. What's even more remarkable about the fly is that its hearing organs, a pair of rectangle-shaped membranes, are connected to each other. Specifically, they are "torsionally coupled" so that a sound wave that lands on one membrane can deflect the other membrane. The connection between the membranes enables them to vibrate in several different ways so that the fly can obtain both the average pressure of an incoming sound and its pressure gradient, the change in sound pressure as you move from one ear to the other. This provides lots of information with which to determine the direction of the sound.
The researchers built a silicon nitride prototype microphone diaphragm that closely reproduces the characteristics of the fly ears. While the researchers face challenges in mass-producing such
a design, they hope that its unconventional approach to localizing sound will inspire lots of applications.
(Paper 2aEA1 at Acoustical Society of America meeting in Ft. Lauderdale, 3-7 Dec 2001.)
A QUANTUM COMPUTER HAS FACTORED THE NUMBER 15. This may sound like a trivial achievement, but it is actually a considerable physics milestone. It represents the most complex calculation yet performed in quantum computing, which offers a radically different means of information processing through the use of quantum mechanics. Even more noteworthy, it is the first experimental demonstration of Shor's algorithm, a quantum-computer program which can potentially factor large numbers in a fraction of the time needed for the world's currently fastest supercomputers. Such large numbers are used as the basis of encryption codes; the codes are broken by finding the prime-number factors of the large numbers. IBM-Almaden and Stanford University researchers (Isaac Chuang, now at MIT, ichuang@cba.mit.edu) built a quantum computer whose working substance was a liquid consisting of a billion billion molecules.
The molecules were specially designed to contain 7 nuclear "spins"--5 from fluorine nuclei and 2 from carbon-13 nuclei. Analogous to a bar magnet which could point north or south, each spin could represent the binary digits "0" or "1" (or both 0 and 1 at the same time through the subtleties of quantum mechanics) and could be controlled by magnetic fields and radio waves (i.e., nuclear magnetic resonance techniques). By manipulating the 7 qubits, the computer could take advantage of quantum computing's unique parallel processing capabilities to determine that the factors of 15 were 3 and 5. Enormous challenges must be surmounted to build larger-scale quantum computers which could factor very large numbers, and this is an early step forward.
(Vandersypen et al., Nature, 20/27 December 2001; also see IBM-Almaden news release at
http://www.research.ibm.com/resources/news/20011219_quantum.shtml)
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