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The last two decades have produced a great deal of evidence that in the mammalian organ of Corti outer hair cells undergo active shape changes that are part of a "cochlear amplifier" mechanism that increases sensitivity and freque...
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The last two decades have produced a great deal of evidence that in the mammalian organ of Corti outer hair cells undergo active shape changes that are part of a "cochlear amplifier" mechanism that increases sensitivity and frequency selectivity of the hearing epithelium. However, many signs of active processes have also been found in nonmammals, raising the question as to the ancestry and commonality of these mechanisms. Active movements would be advantageous in all kinds of sensory hair cells because they help signal detection at levels near those of thermal noise and also help to overcome fluid viscosity. Such active mechanisms therefore presumably arose in the earliest kinds of hair cells that were part of the lateral line system of fish. These cells were embedded in a firm epithelium and responded to relative motion between the hair bundle and the hair cell, making it highly likely that the first active motor mechanism was localized in the hair-cell bundle. In terrestrial nonmammals, there are many auditory phenomena that are best explained by the presence of a cochlear amplifier, indicating that in this respect the mammalian ear is not unique. The latest evidence supports siting the active process in nonmammals in the hair-cell bundle and in intimate association with the transduction process.
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Active processes in the inner ear of lizards can be monitored using spontaneous otoacoustic emissions (SOAE) measured outside the eardrum. In the Australian bobtail lizard, SOAE are generated by an active motility process in the h...
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Active processes in the inner ear of lizards can be monitored using spontaneous otoacoustic emissions (SOAE) measured outside the eardrum. In the Australian bobtail lizard, SOAE are generated by an active motility process in the hair-cell bundle. This mechanism has been shown to be sensitive to the calcium-chelating agent 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid and is presumed to be related to the calcium-sensitive transduction-channel motor implicated in other nonmammalian hair cell systems. In studies of frog saccular and turtle auditory papillar hair cells in vitro, the frequency and amplitude of bundle oscillations depend on the concentration of calcium in the bathing solutions. In the present study, the calcium concentration in the endolymph was changed in vivo in the Australian bobtail lizard Tiliqua rugosa, and SOAE were monitored. Glass pipettes with large tips and containing different calcium concentrations in their fluids were introduced into scala media, and their contents were allowed to passively flow into the endolymph. Low calcium concentrations resulted in a downward shift in the frequency of SOAE spectral peaks and generally an increase in their amplitudes. Calcium concentrations > 2 mM resulted in increases in frequency of SOAE peaks and generally a loss in amplitude. These frequency shifts were consistent with in vitro data on the frequencies and amplitudes of spontaneous oscillation of hair cell bundles and thus also implicate calcium ions in the generation of active motility in nonmammalian hair cells. The data also suggest that in this lizard species, the ionic calcium concentration in the cochlear endolymph is > or = 1 mM.
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Hair cells are the mechanoreceptive cells of the vertebrate lateral line and inner ear. In addition to their sensory function, hair cells display motility and thus themselves generate mechanical energy, which is thought to enhance...
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Hair cells are the mechanoreceptive cells of the vertebrate lateral line and inner ear. In addition to their sensory function, hair cells display motility and thus themselves generate mechanical energy, which is thought to enhance sensitivity. Two principal cellular mechanism are known that can mediate hair-cell motility in vitro. One of these is based on voltage-dependent changes of an intramembrane protein and has so far been demonstrated only in outer hair cells of the mammalian cochlea. Correlated with this, the cell membranes of outer hair cells carry an extreme density of embedded particles, as revealed by freeze fracturing. The present study explored the possibility of membrane-based motility in hair cells of nonmammals, by determining their density of intramembrane particles. Replicas of freeze-fractured membrane were prepared from auditory hair cells of a lizard, the Tokay gecko, and a bird, the barn owl. These species were chosen because of independent evidence for active cochlear mechanics, in the form of spontaneous otoacoustic emissions. For quantitative comparison, mammalian inner and outer hair cells, as well as vestibular hair, cells were reevaluated. Lizard and bird hair cells displayed median densities of 2,360 and 1,880 intramembrane particles/渭m(2), respectively. This was not significantly different from the densities in vestibular and mammalian inner hair cells; however, it was about half the density in of mammalian outer hair cells. This suggests that nonmammalian hair cells do not possess high densities of motor protein in their membranes and are thus unlikely to be capable of somatic motility. J. Comp. Neurol. 479:149-155, 2004. (c) 2004 Wiley-Liss, Inc.
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The simulation of the aircraft dynamics and behavior of the open loop as well as the closed loop system is a central part in the development of controllers for real flight tests. This paper presents an approach for the systematic ...
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The simulation of the aircraft dynamics and behavior of the open loop as well as the closed loop system is a central part in the development of controllers for real flight tests. This paper presents an approach for the systematic development of a nonlinear simulation model in MATLAB/ Simulink for a high-agility model airplane, with a total of 16 different control inputs, together with the design of an appropriate rate command attitude hold (RCAH) controller. The simulation model is capable to represent the behavior of the aircraft, including the dynamics of the motors, the actuators and the sensors, for the nominal case as well as in the case of severe structural damage and failures. The highly sophisticated model of the aircraft is used subsequently for the design of a controller. Dynamic inversion (DI) uses the knowledge of the nonlinear plant dynamics to transform the nonlinear dynamics into a chain of integrators, and after this transformation, a controller can be designed using methods from classical or robust control. A relative degree 1 (RD1) rate command attitude hold controller, based on dynamic inversion, will be presented together with a semi-analytical approach to select and adjust the appropriate controller gains. The paper is completed by some simulation results encountering severe structural damage and failures. The derived controller can either serve as a stand-alone controller or as a baseline controller for more sophisticated control approaches.
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Following their origin during the early Cretaceous, the lizards radiated early into a number of families. This radiation was accompanied by a diversification in the structure of the inner ear. The morphology of the auditory basila...
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Following their origin during the early Cretaceous, the lizards radiated early into a number of families. This radiation was accompanied by a diversification in the structure of the inner ear. The morphology of the auditory basilar papilla is family-specific, with large variations in a number of parameters. At the physiologic level, this wide variation does not result in an equivalent range of physiologic parameters. This review considers the possible influence of various morphologic features on function, and correlates these features with physiologic response parameters. Anatomical variety that does not result in significant changes in the inputs to the brain is "neutral" with regard to selection pressures. This independence apparently removed evolutionary constraints and led to some of the great variety of auditory papillae seen. Other anatomical features are more important and do produce significant effects at the level of the auditory nerve. Copyright 2002 Wiley Periodicals, Inc. J Neurobiol 53: 202-211, 2002
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The efferent innervation of the auditory basilar papilla of birds and mammals is provided by a dedicated population of brainstem neurones that are separate from those supplying the vestibular organs. This study addresses the quest...
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The efferent innervation of the auditory basilar papilla of birds and mammals is provided by a dedicated population of brainstem neurones that are separate from those supplying the vestibular organs. This study addresses the question whether a population of bilaterally-projecting efferents, contacting hair cells in both basilar papillae, is consistently present in birds. The chicken and the barn owl were chosen, two species where the total number of efferents was already known and which represent two extremes of an auditory generalist and an auditory specialist, respectively. Fluorogold and Choleratoxin, two potent retrograde tracers, were injected into one cochlear duct each of all individuals. Labelled neurones were subsequently identified in the brainstem using standard fluorescence techniques. A small proportion (up to 2% of the total population) of double-labelled cells was found in both species. The great majority of those double-labelled neurones could be assigned to the ventrolateral group of efferents, which has previously been shown to project exclusively to the auditory basilar papilla. Thus, in birds, like in mammals, a small subgroup of auditory efferents innervates both basilar papillae.
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Synchronous envelope fluctuations in different frequency ranges of an acoustic background enhance the detection of signals in background noise. This effect, termed comodulation masking release (CMR), is attributed to both processi...
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Synchronous envelope fluctuations in different frequency ranges of an acoustic background enhance the detection of signals in background noise. This effect, termed comodulation masking release (CMR), is attributed to both processing within one frequency channel of the auditory system and comparisons across separate frequency channels. Here we present data on CMR from a study in field L2 of the auditory forebrain of the European starling (Sturnus vulgaris) using two 25-Hz-wide bands of masking noise that provide the opportunity to distinguish between within-channel and across-channel effects. Acoustically evoked responses were recorded from unrestrained birds via radio telemetry. The signal was a 800 msec pure tone presented at the most sensitive frequency of the units in a previously determined frequency-tuning curve (FTC). One band of masking noise was centered on the signal frequency while the flanking band of noise was presented either within the limits of the excitatory FTC (i.e., within the same frequency channel as the on-frequency masker) or in the suppression area of the FTC (i.e., in a separate channel). For flanking bands inside the excitatory FTC, signal detection thresholds based on the rate code were lower in noise maskers with identical envelope fluctuations (comodulated) than in maskers with uncorrelated envelopes resulting in a neural CMR of approximately 4-7 dB. For flanking bands inside the suppression areas, the neural CMR was reduced. Although the average neural CMR was below the behaviorally determined CMR, a subsample of between 11 and 26% of the recording sites resembled the behavioral performance.
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For quantitative auditory determination of grasshopper population sizes, the diurnal song activity pattern must be known. This activity was quantified for 14 grassland species under optimal weather conditions. Six different patter...
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For quantitative auditory determination of grasshopper population sizes, the diurnal song activity pattern must be known. This activity was quantified for 14 grassland species under optimal weather conditions. Six different patterns were observed: (1) some species sang almost the whole day with a rather constant rate, (2) others increased activity towards noon followed by a decrease in the afternoon, the increase and decrease being rather symmetrical. (3) a third form showed a rapid increase in the morning, followed by a slow decrease from noon to the evening. (4) another type also showed a rather symmetrical curve with increase in the morning and decrease in the evening, with, however, a marked decrease around noon. The extremes were species which showed song activity (5) only in the morning or (6) from the evening into the night. The composition of the grasshopper community allows a rather detailed evaluation of grassland biotopes, taking the well-known ecological habitat-binding of the species into account.
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A derivation of density-functional response theory is presented which is based directly on the Runge-Gross theorem and does not invoke the action formalism and thus does not violate causality requirements in time. Working equation...
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A derivation of density-functional response theory is presented which is based directly on the Runge-Gross theorem and does not invoke the action formalism and thus does not violate causality requirements in time. Working equations to treat linear and nonlinear response properties of electronic systems by time-dependent density-functional theory in the frequency domain are given. Efficient noniterative methods to calculate dynamic hyperpolarizability tensors of molecules for arbitrary frequency combinations are presented. With the introduced methods, hyperpolarizabilities of benzene and stilbene derivatives are investigated. The results show that the influence of substituents on the frequency-dependent hyperpolarizability is well described by time-dependent density-functional theory at the adiabatic local density level. Inspection of the linear and nonlinear response of the electron density shows the importance of screening effects for the response properties of larger molecules on electric fields and electromagnetic radiation.
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The natural formation of the bioactive C_(17)-polyacetylenes (?)-(R)-panaxynol and panaxydol was analyzed by ~(13)C-labeling experiments. For this purpose, plants of Panax ginseng were supplied with ~(13)CO2 under field conditions...
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The natural formation of the bioactive C_(17)-polyacetylenes (?)-(R)-panaxynol and panaxydol was analyzed by ~(13)C-labeling experiments. For this purpose, plants of Panax ginseng were supplied with ~(13)CO2 under field conditions or, alternatively, sterile root cultures of P. ginseng were supplemented with [U-~(13)C6]glucose. The polyynes were isolated from the labeled roots or hairy root cultures, respectively, and analyzed by quantitative NMR spectroscopy. The same mixtures of eight doubly ~(13)C-labeled isotopologues and one single labeled isotopologue were observed in the C_(17)-polyacetylenes obtained from the two experiments. The polyketide-type labeling pattern is in line with the biosynthetic origin of the compounds via decarboxylation of fatty acids, probably of crepenynic acid. The ~(13)C-study now provides experimental evidence for the biosynthesis of panaxynol and related polyacetylenes in P. ginseng under in planta conditions as well as in root cultures. The data also show that ~(13)CO2 experiments under field conditions are useful to elucidate the biosynthetic pathways of metabolites, including those from roots.
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