Just a few decades ago, some scientists doubted that snakes could hear at all. Snakes lack an outer ear and external ear openings, making it difficult to understand how the reptiles receive acoustic vibrations.
However, snakes do have an inner ear and a cochlea, and scientists have observed the animals react to auditory stimuli. But exactly how snakes hear without external ears is still unclear. In a new study, physicists Paul Friedel and J. Leo van Hemmen from the Technische Universitat Munchen in Germany and biologist Bruce Young from Washburn University in Kansas have presented a model of how the horned desert viper Cerastes cerastes hears ? with its jaws. While the jaw-hearing method is widely known, the new research uses naval engineering techniques to explain how vibrations from the jaw travel through the head and give rise to sounds in the animal?s brain. The scientists also explain one of the more intriguing parts of jaw-hearing, which is that the snake?s left and right sides of its jaw can move independently in order to localize a sound?s source, such as the location of a mouse?s footsteps. ?Up to now, no one has ever pondered the fact that snakes could use jaw-hearing in stereo,? Friedel told PhysOrg.com. ?This is, however, crucial, since stereo hearing is essential for locating a sound source. We have thus explained how jaw-hearing can actually be very informative for the snake, and not simply a system signifying that ?something is there.?? As a mouse skitters across the desert sand, its footsteps create surface waves (specifically, Raleigh waves) with a wavelength of about 15 centimeters and amplitude of the order of 1 micrometer. These surface waves are similar to water waves, in the sense that the sand particles (modeled as a continuous medium) carry out an elliptic motion. The wave velocity of the ripples is about 45 meters per second. The frequency of the waves peaks between 200 and 1000 Hz ? which falls squarely into the snake?s optimal sensitivity for frequencies of around 300 Hz. When the horned desert viper has its jaw resting on the sand, the vibrations from the mouse footsteps pass underneath both sides of the jaw. The vibrations travel through the snake?s head through two bones ? the quadrate and stapes ? and then stimulate the cochlea. The snake?s auditory system can sense jaw movement down to angstrom-sized motions (on the order of a single atom). The scientists determined that the lower jaw amplitude is about half that of the 1-micrometer incoming surface wave ? plenty large enough for the snake ear to detect with efficiency. From the cochlea, the auditory signals are relayed along axonal delay lines to a set of topographically organized map neurons in the brain. The researchers modeled this neuronal network, where every map neuron is tuned with microsecond accuracy to a specific ?interaural time difference,? or the time difference between signals received from the left and right sides of the jaw. When a map neuron fires, it corresponds to a specific input direction, enabling the snake to localize its prey with stereo precision. The hearing model gives strong support to snakes? unusual way of hearing, showing that the technique is not only possible, but is also a highly efficient survival mechanism. As Friedel explains, the jaw-hearing method offers some advantages compared with the conventional hearing method using outer ears.
Thursday, February 14, 2008
Perfect symmetry -- explaining the patterns in everyday life
The secrets of symmetry found in nature, art, music and architecture were the focus of a special lecture at Imperial College London this week, delivered by renowned Oxford mathematician, Dr Marcus du Sautoy.
Dr du Sautoy spoke to a large audience of all ages about the "magic trick moves" of symmetry which can be performed on a shape or object, leaving it looking untouched. As the audience discovered, there is a lot more to symmetry than mere mirror-images, and symmetry is found in the most unlikely of places. Dr du Sautoy began by revealing his childhood fascination with the language of mathematics: "A secret language, a coded language" is how he thought of maths as a child and, spurred on by his dreams of being a secret agent or spy like James Bond, he set about cracking this code. Going on to explain his current fascination with the area of mathematics concerned with symmetry, Dr du Sautoy explained that it has a language and code all of its own, which can perhaps be seen most clearly in the role it plays in the natural world. "Symmetry is the way that plants and animals communicate," he said. "It is an indication on meaning in the natural world." To illustrate this point, Dr du Sautoy cited the example of a bumble bee, which has very poor vision, but which can recognise symmetrical shapes ? which means bees are drawn to the symmetry of flowers, enabling them to carry out their key role in pollination and plant reproduction. Countless other examples of symmetry exist in nature. Dr du Sautoy highlighted the way in which it is a signal of "good genes," hence the reason people with more symmetrical faces are often perceived to be more attractive, and why eggs from free range hens tend to be symmetrical, whereas those from battery hens do not. Symmetrical shapes are also found at the molecular level, with viruses including AIDS and the herpes virus being symmetrical in shape, and in the arts, with music and architecture often drawing on the idea of symmetry for inspiration and design. The second half of Dr du Sautoy's lecture explored the complex study of symmetry that mathematicians have been carrying out since the pioneering work of a young Frenchman, Evariste Galois, who began to devise a "mathematical language" to explain symmetry before his untimely death in a dual in 1832. Dr du Sautoy's own work is focused on analysing different groups of symmetries, specialising in particular on their relationships with one another, building on a seminal book called 'Atlas,' published in the 1980s, which Dr du Sautoy described as being like a "periodical table," explaining how different types of symmetry interact and are related to each other. In his closing remarks, Dr du Sautoy emphasised the extent to which there is still lots to be learned in this fascinating field. "The fact that there are unsolved problems in maths keeps it a living subject," he said. The lecture was organised by the Royal Institution and Harper Collins, publishers of Dr du Sautoy's new book, 'Finding Moonshine: A Mathematician?s Journey Through Symmetry.'
Dr du Sautoy spoke to a large audience of all ages about the "magic trick moves" of symmetry which can be performed on a shape or object, leaving it looking untouched. As the audience discovered, there is a lot more to symmetry than mere mirror-images, and symmetry is found in the most unlikely of places. Dr du Sautoy began by revealing his childhood fascination with the language of mathematics: "A secret language, a coded language" is how he thought of maths as a child and, spurred on by his dreams of being a secret agent or spy like James Bond, he set about cracking this code. Going on to explain his current fascination with the area of mathematics concerned with symmetry, Dr du Sautoy explained that it has a language and code all of its own, which can perhaps be seen most clearly in the role it plays in the natural world. "Symmetry is the way that plants and animals communicate," he said. "It is an indication on meaning in the natural world." To illustrate this point, Dr du Sautoy cited the example of a bumble bee, which has very poor vision, but which can recognise symmetrical shapes ? which means bees are drawn to the symmetry of flowers, enabling them to carry out their key role in pollination and plant reproduction. Countless other examples of symmetry exist in nature. Dr du Sautoy highlighted the way in which it is a signal of "good genes," hence the reason people with more symmetrical faces are often perceived to be more attractive, and why eggs from free range hens tend to be symmetrical, whereas those from battery hens do not. Symmetrical shapes are also found at the molecular level, with viruses including AIDS and the herpes virus being symmetrical in shape, and in the arts, with music and architecture often drawing on the idea of symmetry for inspiration and design. The second half of Dr du Sautoy's lecture explored the complex study of symmetry that mathematicians have been carrying out since the pioneering work of a young Frenchman, Evariste Galois, who began to devise a "mathematical language" to explain symmetry before his untimely death in a dual in 1832. Dr du Sautoy's own work is focused on analysing different groups of symmetries, specialising in particular on their relationships with one another, building on a seminal book called 'Atlas,' published in the 1980s, which Dr du Sautoy described as being like a "periodical table," explaining how different types of symmetry interact and are related to each other. In his closing remarks, Dr du Sautoy emphasised the extent to which there is still lots to be learned in this fascinating field. "The fact that there are unsolved problems in maths keeps it a living subject," he said. The lecture was organised by the Royal Institution and Harper Collins, publishers of Dr du Sautoy's new book, 'Finding Moonshine: A Mathematician?s Journey Through Symmetry.'
Graphene Holds Promise for Spintronics
Graphene is a nanomaterial which combines a very simple atomic structure with intriguingly complex and largely unexplored physics. Since its first isolation about four years ago, researchers suggest a large number of applications for this material in anticipation of future technological innovations. Specifically, graphene is considered as a potential candidate for replacing silicon in future electronic devices. Theoretical physicists from the Swiss Federal Institute of Technology in Lausanne (EPFL) and Radboud University of Nijmegen (The Netherlands) performed a virtual crash-test of graphene as a material for future spintronic devices. In particular, a possible components of future computers. The material successfully passed the test, albeit with some reservations. The results have been published in the February 1, 2008, issue of Physical Review Letters. Current technology uses the charge of electrons to operate information in electronic devices. As an alternative, one can use intrinsic spin of electrons for this purpose. Electronic devices making use of electron spin has acquired the term, spintronic devices. Several types of such devices have already found their way into the market-place in high-capacity hard drives. Recently it was introduced in a non-volatile magnetic random access memory (MRAM). Further, replacement of charge-based devices by the spintronic components promises faster computers and less energy consumption. While spintronics requires magnetic materials, graphene itself is non-magnetic. However, when a single graphene layer is cut properly, ( e.g. using lithographic techniques widely used in the current semiconductor technology), electron spins are theoretically predicted to align at the edges of graphene. This amazing property of graphene has attracted considerable attention by theoretical researchers giving rise to new designs of spintronic devices. However, there is a gap between the theoretical models and the actual prototypes of such devices. The problem lies in the fact that such edge spins form a truly one-dimensional system. It is known that one-dimensional systems are very sensitive to thermal disorder which destroys the perfect arrangement of spins. Strictly speaking, a one-dimensional magnet cannot maintain the perfect alignment of magnetism at a temperature above absolute zero. This entropy-driven behavior is in sharp contrast to bulk materials (such as iron), which is able to keep the perfect order of electron spins below certain temperatures, (Curie temperature). This factor allows using bulk materials as permanent magnets. An important component of modern technology. On graphene edges, the order on spins can exist only within a certain range which limits the dimensions of spintronic devices. Researchers from Switzerland and Netherlands performed, "computer-time-demanding first principles calculations," in order establish the range of magnetic order at graphene edges. At room temperature, the range or spin correlation length, was found to be around 1 nanometer which limits device dimensions to several nanometers. This result may first look rather disappointing. This is about one order of magnitude below the length scales of the present-day semiconductor manufacturing processes. Nevertheless, graphene performed better than any other material when it came to one-dimension and room temperature factors. In other words, graphene is the best performer on the nanoscale.
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