Daily Archives: March 5, 2013

It was so unexpected that we thought there was something wrong with the instrument

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I love it when scientists say that! And, so said scientist Daniel Baker, speaking of a newly observed feature of the famous and well known, or at least, we thought well known, Van Allen Belts.

First discovered in 1958, the Van Allen belts have been thought to comprise two reservoirs of high-speed, electrically charged particles, corralled into separate doughnut-shaped rings by Earth’s magnetic field. The outer ring orbits at a distance of some 10,000–60,000 kilometres above Earth, and encircles an inner band of even more energetic particles, roughly 100–10,000 kilometres above Earth. … that’s … the structure that NASA’s twin Van Allen Probes recorded when they began operation on 1 September 2012.

ResearchBlogging.orgBut just two days later, telescopes on the probes revealed the emergence of an additional, narrow belt of charged particles sandwiched between the inner ring and a now highly eroded outer ring….

This was apparently caused by a burst of solar wind which messed up the outer Van Allen Belt and led to the reconfiguration of orbiting electrically charged bits and pieces. A wave of solar wind in October then removed all of the remaining outer ring and also wiped out the new middle ring. Then, a third wave of solar wind restored the Van Allen Belts to what we had been thinking was the normal configuration.

From the original paper:

Since their discovery over 50 years ago, the Earth’s Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. The outer zone is comprised predominantly of mega-electron volt (MeV) electrons that wax and wane in intensity on time scales ranging from hours to days depending primarily on external forcing by the solar wind. The spatially separated inner zone is comprised of commingled high-energy electrons and very energetic positive ions (mostly protons), the latter being stable in intensity levels over years to decades. In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (E > 2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for over four weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage.

Here’s what it looks like:

Typical and Atypical Van Allen Belts
From Science: “Diagrams providing a cross-sectional view of the Earth’s radiation belt structure and relationship to the plasmasphere. (A) A schematic diagram showing the Earth, the outer and inner radiation belts and the normal plasmaspheric location. (B) Similar to (A) but showing a more highly distended plasmasphere and quite unexpected triple radiation belt properties during the September 2012 period. These diagrams show the highest electron fluxes as white and the lowest fluxes as blue. The radiation belts are really ‘doughnut’ or torus-shaped entities in three dimensions. The Earth is portrayed at the center. Also shown, as a translucent green overlay in each diagram, is the plasmasphere.”

Baker, D., Kanekal, S., Hoxie, V., Henderson, M., Li, X., Spence, H., Elkington, S., Friedel, R., Goldstein, J., Hudson, M., Reeves, G., Thorne, R., Kletzing, C., & Claudepierre, S. (2013). A Long-Lived Relativistic Electron Storage Ring Embedded in Earth’s Outer Van Allen Belt Science DOI: 10.1126/science.1233518

Insect Wings Can Shred Bacteria To Pieces

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The “clanger cicada” can physically kill bacteria by poking and shredding them with tiny pointy structures that seem to look a little like an old fashioned cheese grater. Keep in mind that this happens at a very small spacial scale, so the relationship between objects is different than in normal human experience. Essentially, the membrane of a bacterium spreads itself over the pointy nano-spikes of the insect wing. This is a little like a failed “laying on the bed of nails” attempt, but where the force involved with the bed of nails is gravity, gravity has nothing to do with the bacterium interacting with the nano spikes. Also, the bacterium does not shred because the nano spikes pierce it. Rather, the bacterial membrane is stretched to breaking point and falls apart that way. From the write-up in Nature News:

The clanger cicada (Psaltoda claripennis) is a locust-like insect whose wings are covered by a vast hexagonal array of ‘nanopillars’ — blunted spikes on a similar size scale to bacteria (see video, bottom). When a bacterium settles on the wing surface, its cellular membrane sticks to the surface of the nanopillars and stretches into the crevices between them, where it experiences the most strain. If the membrane is soft enough, it ruptures…

Here’s the model:

Not all bacteria are subject to this effect; it depends on the rigidity of the cell membrane.

Obviously, we want to make all doorknobs and toilet seats out of this stuff.

Pogodin, Et Al. 2013. Biophysical Model of Bacterial Cell Interactions with Nanopatterned Cicada Wing Surfaces. Biophysical Journal 104(4):835-840. The article was published on Feb. 19th in Biophysical Journal. Abstract:

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on their physical surface structure. The wings provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. We propose a biophysical model of the interactions between bacterial cells and cicada wing surface structures, and show that mechanical properties, in particular cell rigidity, are key factors in determining bacterial resistance/sensitivity to the bactericidal nature of the wing surface. We confirmed this experimentally by decreasing the rigidity of surface-resistant strains through microwave irradiation of the cells, which renders them susceptible to the wing effects. Our findings demonstrate the potential benefits of incorporating cicada wing nanopatterns into the design of antibacterial nanomaterials.