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  • 1
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 61 (1999), S. 809-834 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Mechanosensory hair cells of the vertebrate inner ear contribute to acoustic tuning through feedback processes involving voltage-gated channels in the basolateral membrane and mechanotransduction channels in the apical hair bundle. The specific number and kinetics of calcium-activated (BK) potassium channels determine the resonant frequency of electrically tuned hair cells. Kinetic variation among BK channels may arise through alternative splicing of slo gene mRNA and combination with modulatory beta subunits. The number of transduction channels and their rate of adaptation rise with hair cell response frequency along the cochlea's tonotopic axis. Calcium-dependent feedback onto transduction channels may underlie active hair bundle mechanics. The relative contributions of electrical and mechanical feedback to active tuning of hair cells may vary as a function of sound frequency.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 164 (1988), S. 151-163 
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Tall hair cells were isolated by enzymatic and mechanical dissociation from selected regions of the apical half of the alligator (A. mississippiensis) cochlea. Single cells were subjected to voltage-clamp and current-clamp using the tight-seal whole-cell recording technique. Most hair cells isolated from the apex of the cochlea produced slowly regenerative depolarizations or Na action potentials during current injection, whereas hair cells isolated from more basal regions usually produced voltage oscillations (ringing) in response to depolarizing current injection, an indication of electrical resonance. Resonant frequencies ranged from 50 to 157 Hz in different cells. The higher-frequency cells tended to have larger and more rapidly activating outward currents than did the lower-frequency cells. An inward Ca current and an outward Ca-activated K current were present in all hair cells. In addition, an inwardly rectifying current and a small, transient outward current were often seen. Thus, we conclude that an electrical tuning mechanism is present in alligator hair cells. The role of the ionic conductances in shaping hair cell responses to current injection, and the possible contributions of these electrical responses to cochlear function are discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 17 (1998), S. 141-152 
    ISSN: 1573-4862
    Keywords: Ultrasonic ; EMAT ; applied stress ; strain ; Rayleigh wave ; bridge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The measurement of applied stress on bridges can provide valuable information on the condition of the structure. The conventional technique for measuring applied stress is with a strain gage. However, strain gages can be time consuming to install because first the surface must usually be prepared. On a bridge, paint removal will most likely be necessary as part of this surface preparation. When dealing with lead-based paints, which are considered hazardous waste, many time consuming removal procedures are required. Because of these factors, a device that measures applied stress without requiring paint removal could be useful. While a “clamp-on” strain gage can also be used to measure applied stress without requiring paint removal, this type of strain gage can not be used on some bridge details, such as webs of I-beams and tops of box girders. An ultrasonic technique using non-contact electromagnetic transducers provides a possible method for applied stress measurement which is not limited by the same factors as those with conventional strain gages. The transducers operate through nonconductive and conductive (lead-based) paint and work on rusted, pitted surfaces. Our previous research developed a technique for measuring applied stresses on bridges with EMATs and included many laboratory tests. This paper describes field applications of the technique on actual bridge structures, as well as additional system testing and instrument calibration in the laboratory.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 17 (1998), S. 141-152 
    ISSN: 1573-4862
    Keywords: Ultrasonic ; EMAT ; applied stress ; strain ; Rayleigh wave ; bridge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The measurement of applied stress on bridges can provide valuable information on the condition of the structure. The conventional technique for measuring applied stress is with a strain gage. However, strain gages can be time consuming to install because first the surface must usually be prepared. On a bridge, paint removal will most likely be necessary as part of this surface preparation. When dealing with lead-based paints, which are considered hazardous waste, many time consuming removal procedures are required. Because of these factors, a device that measures applied stress without requiring paint removal could be useful. While a “clamp-on” strain gage can also be used to measure applied stress without requiring paint removal, this type of strain gage can not be used on some bridge details, such as webs of I-beams and tops of box girders. An ultrasonic technique using non-contact electromagnetic transducers provides a possible method for applied stress measurement which is not limited by the same factors as those with conventional strain gages. The transducers operate through nonconductive and conductive (lead-based) paint and work on rusted, pitted surfaces. Our previous research developed a technique for measuring applied stresses on bridges with EMATs and included many laboratory tests. This paper describes field applications of the technique on actual bridge structures, as well as additional system testing and instrument calibration in the laboratory.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 18 (1999), S. 103-113 
    ISSN: 1573-4862
    Keywords: acoustoelasticity ; stress ; EMATs ; bridges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Pin and hanger connections are used in bridges to suspend an interior span from the outer spans. The connections can sometimes lock up due to corrosion. If lockup occurs the stresses in the connection are cycled due to thermal expansion and contraction of the bridge; fatigue cracking and failure may occur. We constructed an apparatus to simulate a locked-up pin and hanger connection. We performed proof-of-concept tests of a method to detect stresses in pin and hanger connections. The method uses the stress-induced changes in sound velocity of shear waves polarized parallel and perpendicular to the hanger axis. The birefringence is the normalized difference in these shear wave velocities. We measured the birefringence at opposite sides of the hangers, at midsection. We simulated three scenarios: continuous monitoring of hanger status; intermittent monitoring from a known initial state; measurement with no a priori knowledge of hanger status. Good agreement with strain gauge data was obtained for all three scenarios.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 185 (1999), S. 455-462 
    ISSN: 1432-1351
    Keywords: Key words Apamin ; BK ; Charybdotoxin ; Cochlea ; SK ; AbbreviationsACh acetylcholine ; Chtx charybdotoxin ; IK(ACh) acetylcholine-evoked potassium current ; SHC short hair cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Acetylcholine released from efferent neurons in the cochlea causes inhibition of mechanosensory hair cells due to the activation of calcium-dependent potassium channels. Hair cells are known to have large-conductance, “BK”-type potassium channels associated with the afferent synapse, but these channels have different properties than those activated by acetylcholine. Whole-cell (tight-seal) and cell-attached patch-clamp recordings were made from short (outer) hair cells isolated from the chicken basilar papilla (cochlea equivalent). The peptides apamin and charybdotoxin were used to distinguish the calcium-activated potassium channels involved in the acetylcholine response from the BK-type channels associated with the afferent synapse. Differential toxin blockade of these potassium currents provides definitive evidence that ACh activates apamin-sensitive, “SK”-type potassium channels, but does not activate carybdotoxin-sensitive BK channels. This conclusion is supported by tentative identification of small-conductance, calcium-sensitive but voltage-insensitive potassium channels in cell-attached patches. The distinction between these channel types is important for understanding the segregation of opposing afferent and efferent synaptic activity in the hair cell, both of which depend on calcium influx. These different calcium-activated potassium channels serve as sensitive indicators for functionally significant calcium influx in the hair cell.
    Type of Medium: Electronic Resource
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