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排序方式: 共有87条查询结果,搜索用时 46 毫秒
51.
Abrams GS Adolphsen CE Averill D Ballam J Barish BC Barklow T Barnett BA Bartelt J Bethke S Blockus D Bonvicini G Boyarski A Brabson B Breakstone A Brom JM Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan DE Dorfan JM Drewer DC Elia R Feldman GJ Fernandes D Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Grindhammer G Grosse-Wiesmann P Hanson G Harr R Harral B Harris FA 《Physical review letters》1989,63(20):2173-2176
52.
Abrams GS Adolphsen CE Aleksan R Alexander JP Allen MA Atwood WB Averill D Ballam J Bambade P Barish BC Barklow T Barnett BA Bartelt J Bethke S Blockus D de Boer W Bonvicini G Boyarski A Brabson B Breakstone A Breidenbach M Brom JM Brown JL Brown KL Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Clendenin J Cords D Coupal DP Dauncey P Dean NR DeStaebler HC Dorfan DE Dorfan JM Drell PS Drewer DC Dydak F Ecklund S Elia R Erickson RA Fay J Feldman GJ Fernandes D Field RC Fieguth TH 《Physical review letters》1989,63(7):724-727
53.
Temporary threshold shift in a bottlenose dolphin (Tursiops truncatus) exposed to intermittent tones
Finneran JJ Carder DA Schlundt CE Dear RL 《The Journal of the Acoustical Society of America》2010,127(5):3267-3272
Temporary threshold shift (TTS) was measured in a bottlenose dolphin exposed to a sequence of four 3-kHz tones with durations of 16 s and sound pressure levels (SPLs) of 192 dB re 1 μPa. The tones were separated by 224 s of silence, resulting in duty cycle of approximately 7%. The resulting growth and recovery of TTS were compared to experimentally measured TTS in the same subject exposed to single, continuous tones with similar SPLs. The data confirm the potential for accumulation of TTS across multiple exposures and for recovery of hearing during the quiet intervals between exposures. The degree to which various models could predict the growth of TTS across multiple exposures was also examined. 相似文献
54.
The room-temperature rotational spectrum of anisole from 8.7 to 18.3 GHz was collected with a waveguide-based chirped-pulse Fourier transform microwave spectrometer whose operating principles are described. Three spectra were assigned, corresponding to the vibrational ground state and the first and second excited states of the lowest frequency torsional mode. Results for the ground state and first excited state are in agreement with prior millimeter wave studies of this molecule. Microwave–microwave double resonance measurements also confirm these assignments. 相似文献
55.
van der Klink JJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,148(1):147-154
It is shown that the NMR reciprocity theorem is a variant of a problem considered by Lorentz in 1895. This formulation is quite general and applies to electric-dipole-based as well as coil-based or resonator-based magnetic resonance probes. The reasoning is related to, but different from, the proof of the reciprocity theorem for radiofrequency networks and for transmit/receive antenna systems in telecommunications. The signal-to-noise ratio of the NMR experiment is also discussed in very general terms. 相似文献
56.
The acoustic environment of the bottlenose dolphin often consists of noise where energy across frequency regions is coherently modulated in time (e.g., ambient noise from snapping shrimp). However, most masking studies with dolphins have employed random Gaussian noise for estimating patterns of masked thresholds. The current study demonstrates a pattern of masking where temporally fluctuating comodulated noise produces lower masked thresholds (up to a 17 dB difference) compared to Gaussian noise of the same spectral density level. Noise possessing wide bandwidths, low temporal modulation rates, and across-frequency temporal envelope coherency resulted in lower masked thresholds, a phenomenon known as comodulation masking release. The results are consistent with a model where dolphins compare temporal envelope information across auditory filters to aid in signal detection. Furthermore, results suggest conventional models of masking derived from experiments using random Gaussian noise may not generalize well to environmental noise that dolphins actually encounter. 相似文献
57.
Finneran JJ Houser DS Blasko D Hicks C Hudson J Osborn M 《The Journal of the Acoustical Society of America》2008,123(1):542-551
Hearing thresholds were estimated in four bottlenose dolphins by measuring auditory evoked responses to single and multiple sinusoidal amplitude modulated tones. Subjects consisted of two males and two females with ages from 4 to 22 years. Testing was conducted in air using a "jawphone" transducer to couple sound into each subject's lower right jaw. Carrier frequencies ranged from 10 to 160 kHz in one-half octave steps. Amplitude modulated stimuli were presented individually and as the sum of four, five, and nine simultaneous tones with unique carrier and modulation frequencies. Evoked potentials were noninvasively recorded using surface electrodes embedded in silicon suction cups. The presence or absence of an evoked response at each modulation frequency was assessed by calculating the magnitude-squared coherence from the frequency spectra of the recorded sweeps. All subjects exhibited traditional "U-shaped" audiograms with upper cutoff frequencies above 113 kHz. The time required for threshold estimates ranged from 23 to 37 min for single stimuli to 5-9 min for nine simultaneous stimuli. Agreement between thresholds estimated from single stimuli and multiple, simultaneous stimuli was generally good, indicating that multiple stimuli may be used for quick hearing assessment when time is limited. 相似文献
58.
Finneran JJ 《The Journal of the Acoustical Society of America》2003,114(1):529-535
An acoustic backscatter technique was used to estimate in vivo whole-lung resonant frequencies in a bottlenose dolphin (Tursiops truncatus) and white whale (Delphinapterus leucas). Subjects were trained to submerge and position themselves near an underwater sound projector and a receiving hydrophone. Acoustic pressure measurements were made near the thorax while the subject was insonified with pure tones at frequencies from 16 to 100 Hz. Whole-lung resonant frequencies were estimated by comparing pressures measured near the subject's thorax to those measured from the same location without the subject present. Experimentally measured resonant frequencies for the white whale and dolphin lungs were 30 and 36 Hz, respectively. These values were significantly higher than those predicted using a free-spherical air bubble model. Experimentally measured damping ratios and quality factors at resonance were 0.20 and 2.5, respectively, for the white whale, and 0.16 and 3.1, respectively, for the dolphin. 相似文献
59.
Branstetter BK Moore PW Finneran JJ Tormey MN Aihara H 《The Journal of the Acoustical Society of America》2012,131(2):1613-1621
The directional properties of bottlenose dolphin clicks, burst-pulse, and whistle signals were measured using a five element array, at horizontal angles of 0°, 45°, 90°, 135°, and 180° relative to a dolphin stationed on an underwater biteplate. Clicks and burst-pulse signals were highly directional with directivity indices of ~11 dB for both signal types. Higher frequencies and higher amplitudes dominated the forward, on-axis sound field. A similar result was found with whistles, where higher frequency harmonics had greater directivity indices than lower frequency harmonics. The results suggest the directional properties of these signals not only provide enhanced information to the sound producer (as in echolocation) but can provide valuable information to conspecific listeners during group coordination and socialization. 相似文献
60.
Finneran JJ Mulsow J Schlundt CE Houser DS 《The Journal of the Acoustical Society of America》2011,130(2):1038-1048
Measurement of the auditory steady-state response (ASSR) is increasingly used to assess marine mammal hearing. These tests normally entail measuring the ASSR to a sequence of sinusoidally amplitude modulated tones, so that the ASSR amplitude function can be defined and the auditory threshold estimated. In this study, an alternative method was employed, where the ASSR was elicited by an amplitude modulated stimulus whose sound pressure level was slowly varied, or "swept," over a range of levels believed to bracket the threshold. The ASSR amplitude function was obtained by analyzing the resulting grand average evoked potential using a short-time Fourier transform. The suitability of this technique for hearing assessment of bottlenose dolphins and California sea lions was evaluated by comparing ASSR amplitude functions and thresholds obtained with swept amplitude and discrete, constant amplitude stimuli. When factors such as the number of simultaneous tones, the number of averages, and the frequency analysis window length were taken into account, the performance and time required for the swept-amplitude and discrete stimulus techniques were similar. The decision to use one technique over another depends on the relative importance of obtaining suprathreshold information versus the lowest possible thresholds. 相似文献