584 research outputs found
Judicial Highlights of Civil Rights
Paper by Mr. C. M. Hudspeth, Lecturer in Governmen
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
Dynamic Response of Textile Material under Transverse Impact
Textile materials, such as Dyneema and Kevlar, are the major raw materials for state of the art military or personal security armor vests. However, in impact experiments, actual observed penetration speed is much lower than theoretically predicted penetration speed. Each armor vest is composed of high performance yarns which are woven together to form fabrics, which when stacked together form a vest. Understanding penetration behavior of yarns is essential to evaluate the performance of fabric, which will be useful for the design of better vests. The project is composed of three parts: static experiments, dynamic yarn experiments and dynamic fabric experiments. In the static experiments, several types of textile materials will be loaded onto MTS testing machine under slow and constant speed by different projectiles, such as Fragment Simulating Projectile, Hemispherical Nose Projectile and Blade Projectile. Secondly, a powder gun will be used to provide high speed impact conditions. Several yarns will be impacted at high velocities and imaged simultaneously using a high speed camera. Finally, aforementioned experimental conditions will be utilized for fabrics experiments. At this preliminary phase of the investigation, only expected results are being reviewed. In the yarn experiments, impact angle, between impacted region (shear wave propagation region) and impacting region (transvers wave propagation region), is expected to be approximately constant. In the fabric experiments, the goal is to acquire the range of the penetration speeds for different types of textile materials with different number of layers. The acquired data will yield a strong background database for further improvement and adjustment in personal vest design
Essential nonlinearities in hearing
Our hearing organ, the cochlea, evidently poises itself at a Hopf bifurcation
to maximize tuning and amplification. We show that in this condition several
effects are expected to be generic: compression of the dynamic range,
infinitely shrap tuning at zero input, and generation of combination tones.
These effects are "essentially" nonlinear in that they become more marked the
smaller the forcing: there is no audible sound soft enough not to evoke them.
All the well-documented nonlinear aspects of hearing therefore appear to be
consequences of the same underlying mechanism.Comment: 4 pages, 3 figure
Information Flow through a Chaotic Channel: Prediction and Postdiction at Finite Resolution
We reconsider the persistence of information under the dynamics of the
logistic map in order to discuss communication through a nonlinear channel
where the sender can set the initial state of the system with finite
resolution, and the recipient measures it with the same accuracy. We separate
out the contributions of global phase space shrinkage and local phase space
contraction and expansion to the uncertainty in predicting and postdicting the
state of the system. Thus, we determine how the amplification parameter, the
time lag, and the resolution influence the possibility for communication. A
novel representation for real numbers is introduced that allows for a
visualization of the flow of information between scales.Comment: 14 pages, 13 figure
Fast, Automated Implementation of Temporally Precise Blind Deconvolution of Multiphasic Excitatory Postsynaptic Currents
Records of excitatory postsynaptic currents (EPSCs) are often complex, with overlapping signals that display a large range of amplitudes. Statistical analysis of the kinetics and amplitudes of such complex EPSCs is nonetheless essential to the understanding of transmitter release. We therefore developed a maximum-likelihood blind deconvolution algorithm to detect exocytotic events in complex EPSC records. The algorithm is capable of characterizing the kinetics of the prototypical EPSC as well as delineating individual release events at higher temporal resolution than other extant methods. The approach also accommodates data with low signal-to-noise ratios and those with substantial overlaps between events. We demonstrated the algorithm’s efficacy on paired whole-cell electrode recordings and synthetic data of high complexity. Using the algorithm to align EPSCs, we characterized their kinetics in a parameter-free way. Combining this approach with maximum-entropy deconvolution, we were able to identify independent release events in complex records at a temporal resolution of less than 250 µs. We determined that the increase in total postsynaptic current associated with depolarization of the presynaptic cell stems primarily from an increase in the rate of EPSCs rather than an increase in their amplitude. Finally, we found that fluctuations owing to postsynaptic receptor kinetics and experimental noise, as well as the model dependence of the deconvolution process, explain our inability to observe quantized peaks in histograms of EPSC amplitudes from physiological recordings
Optimizing the vertebrate vestibular semicircular canal: could we balance any better?
The fluid-filled semicircular canals (SCCs) of the vestibular system are used
by all vertebrates to sense angular rotation. Despite masses spanning seven
decades, all mammalian SCCs are nearly the same size. We propose that the SCC
represents a sensory organ that evolution has `optimally designed'. Four
geometric parameters are used to characterize the SCC, and `building materials'
of given physical properties are assumed. Identifying physical and
physiological constraints on SCC operation, we find that the most sensitive SCC
has dimensions consistent with available data.Comment: 4 pages, 3 figure
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