35,656 research outputs found
Forces between clustered stereocilia minimize friction in the ear on a subnanometre scale
The detection of sound begins when energy derived from acoustic stimuli
deflects the hair bundles atop hair cells. As hair bundles move, the viscous
friction between stereocilia and the surrounding liquid poses a fundamental
challenge to the ear's high sensitivity and sharp frequency selectivity. Part
of the solution to this problem lies in the active process that uses energy for
frequency-selective sound amplification. Here we demonstrate that a
complementary part involves the fluid-structure interaction between the liquid
within the hair bundle and the stereocilia. Using force measurement on a
dynamically scaled model, finite-element analysis, analytical estimation of
hydrodynamic forces, stochastic simulation and high-resolution interferometric
measurement of hair bundles, we characterize the origin and magnitude of the
forces between individual stereocilia during small hair-bundle deflections. We
find that the close apposition of stereocilia effectively immobilizes the
liquid between them, which reduces the drag and suppresses the relative
squeezing but not the sliding mode of stereociliary motion. The obliquely
oriented tip links couple the mechanotransduction channels to this least
dissipative coherent mode, whereas the elastic horizontal top connectors
stabilize the structure, further reducing the drag. As measured from the
distortion products associated with channel gating at physiological stimulation
amplitudes of tens of nanometres, the balance of forces in a hair bundle
permits a relative mode of motion between adjacent stereocilia that encompasses
only a fraction of a nanometre. A combination of high-resolution experiments
and detailed numerical modelling of fluid-structure interactions reveals the
physical principles behind the basic structural features of hair bundles and
shows quantitatively how these organelles are adapted to the needs of sensitive
mechanotransduction.Comment: 21 pages, including 3 figures. For supplementary information, please
see the online version of the article at http://www.nature.com/natur
Hair motion simulation
Hair motion simulation in computer graphics has been an attraction for many researchers. The application we have developed has been inspired by the related previous work as well as our own efforts in finding useful algorithms to handle this problem. The work we present uses a set of representations, including hair strands, clusters and strips, that are derived from the same underlying base skeleton, where this skeleton is animated by physical, i.e. spring, forces. © Springer-Verlag 2004
Art Directed Fire-Hair Simulation
Fire simulation and hair simulation can be used to create stylized characters and character animation in movies. In this research a system was created whereby fire simulation was guided by hair simulation, which this thesis refers to as Fire-Hair. This simulation system was built inside Houdini, a professional software package widely used in the visual effects industry. The goal of this research was to develop a workflow that utilized velocity field generated by the hair simulation to drive the fire simulation, and to let simulated fire represent the shape and animation of hair strands. This simulation approach is packaged as a digital asset for future use, with all requisite modifiable parameters exposed to artists.
About 20 hair strands were simulated to drive the fire simulation. Hair strand shapes were defined by curves created by the artist; these shapes remain modifiable after creation. Velocity fields which follow hair motion are used as a control field to affect the fire simulation. The final result shows both the physical appearance of fire as well as the shape and motion of hair. The approach was applied to several animated characters to verify reliability and ensure it was visually convincing and robust. The simulated results were rendered using the Houdini built-in render tool, Mantra
Chain Shape Matching for Simulating Complex Hairstyles
Animations of hair dynamics greatly enrich the visual attractiveness of human characters. Traditional simulation techniques handle hair as clumps or continuum for efficiency; however, the visual quality is limited because they cannot represent the fine-scale motion of individual hair strands. Although a recent mass-spring approach tackled the problem of simulating the dynamics of every strand of hair, it required a complicated setting of springs and suffered from high computational cost. In this paper, we base the animation of hair on such a fine-scale on Lattice Shape Matching (LSM), which has been successfully used for simulating deformable objects. Our method regards each strand of hair as a chain of particles, and computes geometrically derived forces for the chain based on shape matching. Each chain of particles is simulated as an individual strand of hair. Our method can easily handle complex hairstyles such as curly or afro styles in a numerically stable way. While our method is not physically based, our GPU-based simulator achieves visually plausible animations consisting of several tens of thousands of hair strands at interactive rates
Two adaptation processes in auditory hair cells together can provide an active amplifier
The hair cells of the vertebrate inner ear convert mechanical stimuli to
electrical signals. Two adaptation mechanisms are known to modify the ionic
current flowing through the transduction channels of the hair bundles: a rapid
process involves calcium ions binding to the channels; and a slower adaptation
is associated with the movement of myosin motors. We present a mathematical
model of the hair cell which demonstrates that the combination of these two
mechanisms can produce `self-tuned critical oscillations', i.e. maintain the
hair bundle at the threshold of an oscillatory instability. The characteristic
frequency depends on the geometry of the bundle and on the calcium dynamics,
but is independent of channel kinetics. Poised on the verge of vibrating, the
hair bundle acts as an active amplifier. However, if the hair cell is
sufficiently perturbed, other dynamical regimes can occur. These include slow
relaxation oscillations which resemble the hair bundle motion observed in some
experimental preparations.Comment: 13 pages, 6 figures,REVTeX 4, To appear in Biophysical Journa
Accretion of a Symmetry Breaking Scalar Field by a Schwarzschild Black Hole
We simulate the behaviour of a Higgs-like field in the vicinity of a
Schwarzschild black hole using a highly accurate numerical framework. We
consider both the limit of the zero-temperature Higgs potential, and a toy
model for the time-dependent evolution of the potential when immersed in a
slowly cooling radiation bath. Through these numerical investigations, we aim
to improve our understanding of the non-equilibrium dynamics of a symmetry
breaking field (such as the Higgs) in the vicinity of a compact object such as
a black hole. Understanding this dynamics may suggest new approaches for
studying properties of scalar fields using black holes as a laboratory.Comment: 16 pages, 5 figure
A Comprehensive Three-Dimensional Model of the Cochlea
The human cochlea is a remarkable device, able to discern extremely small
amplitude sound pressure waves, and discriminate between very close
frequencies. Simulation of the cochlea is computationally challenging due to
its complex geometry, intricate construction and small physical size. We have
developed, and are continuing to refine, a detailed three-dimensional
computational model based on an accurate cochlear geometry obtained from
physical measurements. In the model, the immersed boundary method is used to
calculate the fluid-structure interactions produced in response to incoming
sound waves. The model includes a detailed and realistic description of the
various elastic structures present.
In this paper, we describe the computational model and its performance on the
latest generation of shared memory servers from Hewlett Packard. Using compiler
generated threads and OpenMP directives, we have achieved a high degree of
parallelism in the executable, which has made possible several large scale
numerical simulation experiments that study the interesting features of the
cochlear system. We show several results from these simulations, reproducing
some of the basic known characteristics of cochlear mechanics.Comment: 22 pages, 5 figure
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