300 research outputs found
High sensitivity biomimetic accelerometer model using amplifying mechanism of stereocilia
No full textMechanical modelling of vestibular hair cell’s amplifying mechanism.
No full textINTRODUCTION: Vestibular hair cell is the basic sensory unit of nature’s inertia sensor. It has high sensitivity over broad dynamic range by combination of negative stiffness and adaptation mechanism.[1][2] To examine these biophysical mechanisms with a mechanical point of view[3], we developed a mechanical model of vestibular hair cell. We measure the system response and stiffness and observe similar characteristics with hair cell. This results help to better understanding of vestibular hair cell function.
METHODS: A mechanical model of stereocilia on hair cell consists of two inverted pendulums that demonstrate a pair of adjacent stereocilia. To make negative stiffness which induced by a transduction channels’ sudden opening, use pair of magnet which make repulsive force. Adaptation mechanism is mimicked by using stepping motor similar with molecular motor on stereocilia. Stiffness and temporal response was measured using force sensor and motion capture system.
RESULTS: Similar results from physiological stereocilia were observed. Negative stiffness region was observed near the origin and this region was shifted as motor made magnet moving side-to-side. And the spontaneous oscillation which known to induced by the interplay of the negative stiffness and the adaptation of the stereocilia also observed. Parameter study of the model well demonstrated the role of each system component.
CONCLUSIONS: Integration of adaptation and negative stiffness mechanism of hair cell was mechanically mimicked by two inverted pendulums and interacting moving magnet pair controlled by stepping motor and results is similar to the physiological measurement.
ACKNOWLEDGEMENTS: The work was supported by the Pioneer Research Program fund of the
Ministry of Education, Science and Technology.
Fig.1 Mechanical model of hair cell and force-displacement relation & time response of vestibular hair cell model.
REFERENCES
1. P.Martin. et al. PNAS. Vol.97, No.22, pp.12026-12031. 2000.
2. Peter G. Gillespie & Richard G. Walker. NATURE, Vol.413, 13. 2001.
3. Koeun Lim, Sukyung Park. Journal of Biomechanics. 42, 2158-2164. 2009
A biomimetic mechanical model of the negative stiffness and adaptation mechanism of stereocilia bundle
No full text
High sensitivity biomimetic accelerometer model using amplifying mechanism of stereocilia
No full textA mechanical mimicry of the negative stiffness and adaptation mechanism of stereocilia bundle.
No full textStereocilia is a mechanotransducer that change external mechanical stimuli into electrical signal and has high sensitivity over a broad dynamic range, which is design conflict of the conventional inertia sensor and accelerometer. The mechanism of the retained high sensitivity was hypothesized as an interplay between the negative stiffness and adaptation. The adaptation shifts the nonlinear high sensitivity region toward the operation region of the stereocilia bundle. In this study, we developed a biomimetic mechanical model of stereocilia to demonstrate the interplay between the negative stiffness and the adaptation mechanism. The model consists of an inverted pendulum supported by pivot spring and a fixed bar which represent a pair of adjacent stereocilia. The magnet pairs are attached to pendulum and fixed bar each other to emulate ion channel’s gating force. The magnet on the fixed bar connected to a stepping motor to move the magnet side-to-side which demonstrate readjustment of tip-link tension by slipping down and climbing up of adaptation molecular motors of stereocilia. A displacement clamping equipment which consists of a uniaxial force sensor and actuator was used to measure the mechanical stiffness of the model. Experimental data from mechanical model showed the negative stiffness region near the equilibrium position and shifted the high sensitivity region with the progress of adaptation. Spontaneous oscillation which produced by the interplay between negative stiffness and adaptation mechanism also observed. The results demonstrate that the negative stiffness and adaptation mechanism was mechanically produced by the combination of repulsive force and its continuous readjustment. The change of model parameters of biomimetic mechanical system such as spring stiffness, magnetic force, and adaptation motor speed provided us better understanding of nature’s inertia sensing mechanism
Z-curve: A computer program calculating DNA helical axis coordinates for three-dimensional graphic presentation of curvature
No full textIn order to predict curvature of DNA fragments, we previously developed a computer program for simply calculating a vectorial sum of all individual roll, tilt and twist wedge angles between the nearest base pairs for a given DNA fragment [Lee et al,, (1991)], Now a new program, called Z-curve, was developed to calculate three-dimensional coordinates of the helical center of each base pair along the DNA, using helical axis deviations from B-form DNA by wedge angles. The output file of the new program was designed to become an input file for a graphics program, Insight II. Thus, we were able to obtain three-dimensional graphic presentations of DNA helical axis curvatures of any length. It visualized spatial details of the DNA curvature, where and how much it curves, and to which direction, It also allowed calculation of the three-dimensional distance between two ends of a DNA fragment, which could provide a measure of its curvature, Here, three DNA fragments, both curved and straight, were subjected to the Z-curve and Insight II programs. The results showed that their curvature details could be visualized to the level of the base pair, whether the DNA fragments contained an oligo(A) track or not. Their estimated curvatures mere consistent with the experimental results of permutation gel mobility assay
Design and Assessment of Short-in-length Shape Transition Hypersonic Inlet with Circular Throat
No full textThis paper presents the design of an efficient, short-length shape transition inlet for hypersonic propulsion systems, operating at Mach 4 to 6. The inlet was shortened by approximately 24 % using a Busemann flow based on the median operating Mach number for streamline-tracing instead of the maximum operating Mach number. Additional upper circular arc of capture shape resulted in a compact compression surface that well preserves internal compression of the Busemann flow, and increased pressure rise by up to 31 % with higher total pressure recovery. The inlet was notched for maximum operating Mach number to minimize air spillage, and the range of operating Mach number and angle of attack was extended. Viscous effects were compensated by a proper truncation angle in order to maintain the exact circular throat shape for efficient manufacturing. The length-reduced inlet showed a wide operating range and high compression performance.
Z-curve: a Computer Program Calculating DNA Helical Axis Coordinates for Three-Dimensional Graphic Presentation of Curvature
No full text- …
