March 16, 2009 - The Physics of Animals, Plants, and Materials Inspired by Nature
College Park, MD (March 9, 2009) -- Take a new look at nature through the eyes of physicists at next month's March Meeting of American Physical Society (APS), which takes place from March 16-20, 2009 at the David L. Lawrence Convention Center in Pittsburgh.
Many talks at the meeting will focus on animal locomotion and physiology: from the efficiency of trout swimming, to the wandering pattern of ants and the specially adapted ears of a lizard. Other talks look at the physical properties of new materials that are inspired by things in nature -- lotus leaf film, gecko tape, and fish-like sensors. Highlights of a few of these talks are described below.
Reporters are invited to cover this meeting remotely or in person. Information on how to register as press is contained at the bottom of this email.
HIGHLIGHTS OF TALKS ON ANIMALS AND PHYSICS
1) LOTUS LEAF INSPIRES NEW MATERIALS
In ancient eastern art, the Buddha is often depicted seated upon a lotus leaf -- a longstanding symbol of purity because these leaves always seem clean, even while floating atop murky waters. The physical basis of this "lotus effect," as it sometimes called, arises from microscopic ridges on the surface of the leaf. These ridges have their own, much smaller nanoscale ridges, and the overall effect is to repel water as well as anything in nature.
Prof. Spiros H. Anastasiadis and his colleagues, at the Foundation for Research and Technology-Hellas and the University of Crete in Greece, have been designing artificial surfaces that mimic the natural properties of lotus leaves. They use lasers to etch a silicon surface in ways that mimic the ridges of the lotus leaf, and they synthesize polymers on top of the silicon ridges that further enhance their lotus-like properties. Because they are using polymers, Anastasiadis and his colleagues can also chemically manipulate their artificial lotus surfaces in a number of novel ways. One surface they created has a lotus effect that is tunable with pH -- water droplets fully wet a surface that was exposed to an acidic environment whereas they bounce off a surface that was exposed to a basic one. They are now working on polymers that are tunable with light, electricity, and humidity. These artificial surfaces with responsive surfaces can have a wide range of applications, in the development of self-cleaning surfaces, low friction coatings, water proof and anti-rain textiles, molecular sensors, micro- and nano-fluidics, lab-on-chip devices, etc. (Talk Y19.13, http://meetings.aps.org/Meeting/MAR09/Event/100250).
2) THE PHYSICS OF SWIMMING TROUT
Fresh water trout can save energy when they swim by using the motion of the surrounding water. They can do this even if they are swimming upstream, by slaloming through the water and capturing energy from little local vortices. Ideally, a trout moves close to a vortex and sets the angle of its body just right so that it gains the maximal energy. But what is the best strategy a swimming trout should employ to accomplish this?
To answer this question, Silas Alben at the Georgia Institute of Technology has modeled a trout swimming through a series of vortices. Using this model, he has calculated the distribution of pressures a trout experiences as it swims and used this data to find swimming shapes that maximize its thrust and efficiency. He found that if fish are swimming through vortices that are close together, they should pass closely to each vortex. In a wide "vortex street" the fish should pass slightly upstream of each vortex.
The work will help scientists understand how fish swim in schools and how individual fish fine-tune their motion by using their various fins. Funded by the NSF. (Talk P15.1).
3) STARVATION AND THE ORIGINS OF COLLECTIVE LIFE
When some single-celled organisms are facing starvation, their response is to form spore-like "genomic lifeboats" that rescue the nuclei of tens of thousands of individual cells. In this way they can persist until food becomes plentiful again. Their survival is not guaranteed, however. At the outset of a hunger crisis, their survival depends not only on their ability to get together but how quickly they do so. Speed is achieved through long-range chemical signaling -- molecules released by the organisms that tell their brethren to stop wandering around as individuals and come together for the good of the whole.
Carl Franck and Kayvon Daie of Cornell University have been studying the starvation response in a common amoeba called Dictyostelium discoideum, which lives in damp soil. They and their colleagues B. Webster, R. Monaghan, E. Bodenschatz, A. Bae, and D. Loh have been looking at how easily the amoeba can find one another by altering the amount of water that covers them in a glass dish. They have found that this dramatically alters the speed with which the organisms respond to starvation, and they reconciled many of their observations with mathematical models that describe the behavior. Learning the factors that govern how fast cells can get together is also relevant to the formation of tissues, says Franck, and helps to understanding the transition from solitary to collective life. The effort has been supported by a gift from April and David Fellows, Cornell University, and the NIH. (Talk P39.6).
4) THE SECRET OF WANDERING ANTS
How do ants look for food? Do they systematically search an area grid-by-grid, or do they randomly wander until they stumble upon their precious crumbs? A few years ago, G. William Baxter and his students at Penn State Erie were wondering exactly that and decided to put ants to the test. They did a controlled experiment, releasing one ant at a time into the middle of a flat, clean surface, and they recorded the movement of the ants on the plane. With enough data, they then began looking for the correct mathematical model that would represent the movement of the ants. What they discovered surprised them. Rather than searching systematically over the surface, as a foraging person might do, the ants all executed a non-reversing random walk once they were on the recording surface. The strategy may not be so bad, says Baxter. The random walk is a robust way to search a surface and no matter how complicated the foraging area, sooner or later you will always come home. (Talk H40.11).
5) BIOLOGICAL PHYSICS OF LIZARD EARS
The ability to localize sound is crucial for many animals. The barn owl, for instance, is a nocturnal hunter, and it depends on its sensitive hearing to catch small creatures in the night. Its brain localizes sound by taking into account time and spatial cues -- the distance between its two ears and the corresponding time difference between noises received in the right and left ear. This works well for barn owls and other predators with large interaural distance, but is less effective for small birds, lizards, and other potential prey eager to notice predators in time. For animals with smaller heads, the distance between the ears is smaller too, and they enjoy less of what is technically known as the "interaural time difference" between sounds hitting either ear. Furthermore, amplitude differences caused by shadowing effects of the head can help larger creatures localize sound, but in smaller animals, these effects are negligible and thus of no help at all.
According to Christine Vossen and her advisor J. Leo van Hemmen of TU Muenchen in Germany, lizards and many birds have adapted a solution to this problem by evolving eardrums that are physically coupled to one another via a channel passing through the head. Because of this channel, the vibration of one tympanic eardrum influences the vibration of the other and vice-versa. Vossen and van Hemmen, in collaboration with colleagues in biology, have both developed an exact mathematical model, performed numerical simulations of the cavity connection of a real lizard's ear, and found how by coupling its two eardrums the lizard creates a special "pressure-gradient receiver" that amplifies the difference in both sound arrival time and intensity received at each ear.
According to their calculations, the coupling effectively increases the incoming interaural time differences by a factor of three for low frequencies. For higher frequencies, the pressure-gradient receiver ear amplifies the arriving interaural intensity differences. Depending on sound frequency, an animal with pressure-gradient receiver ears can therefore either use time or amplitude information from the tympanic membranes. (Talk Y40.4).
6) A NEW MATERIAL INSPIRED BY BLIND CAVE FISH
Many fish have tiny hair-like cells on their bellies and other parts of their bodies that collect sensory information on their surroundings, helping them navigate their underwater environments. The blind cave fish (named for obvious reasons) has a large number of these receptors, which compensate for its degenerated non-functioning eyes. The blind cave fish further enhances its ability to sense its surroundings by covering its flow receptors with a gel-like material, called a cupula. The cupula couples the motion of its receptors to the surrounding waters, greatly increasing their sensitivity.
Graduate Student Mike McConney and his colleagues at the Georgia Institute of Technology have now designed an artificial polymer that mimics this effect. The work builds upon an earlier invention by their collaborators at Northwestern University who constructed tiny microfabricated sensors that mimic the blind cave fish receptor. Last year McConney and Vladimir Tsukruk studied the physical properties of the blind cave fish cupula and created a jelly-like material that approximates it. When applied to the microsensors, the artificial polymer improved their sensitivity 40 times. (Talk Y20.6).
The American Physical Society (www.aps.org) is a non-profit membership organization working to advance and diffuse the knowledge of physics through its outstanding research journals, scientific meetings, and education, outreach, advocacy and international activities. APS represents over 51,000 members, including physicists in academia, national laboratories and industry in the United States and throughout the world. Society offices are located in College Park, MD (Headquarters), Ridge, NY, and Washington, DC.