Thin-film technology: Sticky prospects for coats of diamond dust
J. Am. Chem. Soc. 127, 3712–3713 (2005)
A diamond coating can make a material robust and resistant to wear, and diamond-coated metal wires have been promoted as super-strong fibres for composites. Yu Liu et al. have begun to develop a ‘wet chemical’ technique for making diamond films under milder conditions than those previously used.
Coating a surface with diamond usually involves chemical-vapour deposition, in which the surface is exposed to carbon-rich vapour at temperatures above 1,000 K in a high vacuum. Liu and colleagues' approach entails chemically ‘gluing’ diamond nanoparticles to the substrate — in this case, glass — and could ultimately make diamond-coating not just more convenient and economical, but also possible with a wider range of substrates.
Nanoscale diamond powders are commercially available, and Liu et al. take advantage of their finding last year that the particles can be coated with fluorine atoms by simply heating them in a mixture of fluorine and hydrogen. The fluorinated diamond can then be covalently attached to the linking groups — amine-tipped alkoxysilanes — on the substrate. The silane group sticks to the glass, and the amine group bonds to the fluorinated diamond, creating a covering of tethered nanoparticles.
Nuclear physics: Absolutely smashing
Mendeleev Commun. 15, 1–4 (2005)
Superheavy element 115 of the periodic table, provisionally named ununpentium, was first produced in 2003 by smashing less weighty atoms together. But as the four atoms of the element that were created in the experiment survived for less than a second before decaying, study of the new element was always going to be tricky.
Sergey N. Dmitriev and colleagues seem to have confirmed the existence of element 115 through investigations of its decay chain. Ununpentium was produced by firing a beam of calcium-48 ions at a target made from americium-243. The element then underwent five radioactive decays, each ejecting an α-particle, which created a new isotope of element 105, dubnium-268. Its half-life, about a day, is unusually long for this part of the periodic table.
Dmitriev et al. therefore had enough time to separate the collision products from the target, and to isolate dubnium before it underwent spontaneous fission. These observations provide plausible confirmation that the initial collisions had indeed produced element 115.
Cell biology: Tug of war
PLoS Biol. doi: 10.1371/journal.pbio.0030100 (2005)
Neisseria gonorrhoeae, the bacterial cause of gonorrhoea, possesses a retractable appendage called a pilus that attaches to cell membranes in infected people. Heather L. Howie et al. show that the bacteria use their pili to alter the cells' genetic activity and, in the war with the human host, potentially help the infection to spread.
The team used microarrays to examine the genes that are switched on in human epithelial cells when they are infected with either normal N. gonorrhoeae or a strain of the bacterium that can latch on to cell membranes but cannot retract. They identified 52 genes whose activity is boosted by the pili tugging on the cell membrane.
Most of these genes are activated by a signalling protein called mitogen-activated protein kinase (MAPK). The bacterial yanks on the cell membrane seem to trigger MAPK and increase the cell's ability to withstand infection by averting programmed cell death.
The same pathway was activated when Howie et al. coated cell membranes with magnetic beads and mechanically tugged on the membranes with a magnet. The authors speculate that N. gonorrhoeae may use the pathway to keep the cells — and infected patients — alive long enough for the bacteria to spread to another host.
Optics: The hole story
Opt. Express 13, 1933–1938 (2005)
Put a pinprick in a sheet of aluminium foil, and light will shine through it. But if the light's wavelength is more than twice as long as the long edge of a rectangular aperture, it is stopped. This ‘Rayleigh cut-off condition’ seemed to have been contradicted by recent experimental results on light transmission through a rectangular hole in a metal — as the width of the aperture was reduced, the cut-off wavelength actually increased. Reuven Gordon and Alexandre G. Brolo have now developed a mathematical model to explain these effects.
The authors argue that light sets up a resonance motion — known as a ‘surface plasmon’ — in the electrons along the long edge of the hole. This changes the mode-shape of the light in the hole, leading to a cut-off that increases with decreasing hole width.
For a 15-nm-wide hole, Gordon and Brolo found the maximum transmittable wavelength to be 2.3 times that predicted by the Rayleigh condition for a ‘perfect metal’. They therefore advise caution in applying this model, especially as metal holes less than 20 nm across can now be created with nanofabrication techniques.
Auditory neuroscience: Sound connection
J. Exp. Biol. 208, 1209–1217 (2005)
If somebody calls your name across a room, you usually have no trouble working out where they are. This is because the difference between the sound detected by your two ears, in both intensity and time of arrival, provides information about where the sound is coming from.
For lizards it's a different story: their small head size, relative to the wavelengths of many sounds, means that they cannot rely on these principles. Yet experiments carried out by Jakob Christensen-Dalsgaard and Geoffrey A. Manley show, surprisingly, that the lizard ear shows the largest directionality of any land-vertebrate ear studied.
Laser measurements of eardrum motion in four lizard species show that the animals benefit from coupling of the two drums by virtue of a large cavity inside the head. This allows the two sound inputs to interact with each other and produces up to 50-fold differences between the motion of the two eardrums depending on the sound's direction. The directionality can largely be explained by a simple acoustical model, and would allow the brain to perform a simple subtraction calculation so that the lizard can respond accordingly.
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