A remark about possible unity of the neutron star and black hole high frequency QPOs

In a series of papers it was discussed,on the basis of phenomenological arguments, whether the high frequency quasiperiodic oscillations (kHz QPOs)observed in the neutron-star and black-hole X-ray sources originate in the same physical mechanism. Recently it was suggested that a general trend seen in neutron star kHz QPOs instead excludes such a uniform origin. Using the example of the atoll source 4U 1636-53 we illustrate that this is not neccesarily true.      

Underwater surf noise near sea coasts of different types

Data on underwater surf-generated noise measured near stony, rocky, and sandy coasts of the Black Sea and the Pacific Ocean are presented for a frequency band of 0.03–16 kHz and distances of 0.01–30 km from the coastline. The frequency-power spectra and the excess coefficients in the distributions of the instantaneous values of sound pressure in surf-generated noise are considered for coasts of different types. At surface wave heights of 0.5–0.8 m, the surf-generated acoustic noise near pebble-type coasts is higher than the noise of the open sea at a distance of 10 km from the coast, while the excess coefficients are positive at distances of up to 2.7 km from the coast.     

The underwater audiogram of the West Indian manatee (Trichechus manatus).

The hearing thresholds of two adult manatees were measured using a forced-choice two alternative paradigm and an up/down staircase psychometric method. This is the first behavioral audiogram measured for any Sirenian, as well as the first underwater infrasonic psychometric test with a marine mammal. Auditory thresholds were obtained from 0.4 to 46 kHz, and detection thresholds of possible vibrotactile origin were measured at 0.015-0.2 kHz. The U-shaped audiogram demonstrates an upper limit of functional hearing at 46 kHz with peak frequency sensitivity at 16 and 18 kHz (50 dB re: 1 microPa). The range of best hearing is 6-20 kHz (approximately 9 dB down from maximum sensitivity). Sensitivity falls 20 dB per octave below 0.8 kHz and approximately 40 dB per octave above 26 kHz. The audiogram demonstrates a wider range of hearing and greater sensitivity than was suggested from evoked potential and anatomical studies. High frequency sensitivity may be an adaptation to shallow water, where the propagation of low frequency sound is limited by physical boundary effects. Hearing abilities of manatees and other marine mammals may have also been shaped by ambient and thermal noise curves in the sea. Inadequate hearing sensitivity at low frequencies may be a contributing factor to the manatees' inability to effectively detect boat noise and avoid collisions with boats.     

Determination of acoustic attenuation in the Hudson River Estuary by means of ship noise observations

Analysis of sound propagation in a complex urban estuary has application to underwater threat detection systems, underwater communication, and acoustic tomography. One of the most important acoustic parameters, sound attenuation, was analyzed in the Hudson River near Manhattan using measurements of acoustic noise generated by passing ships and recorded by a fixed hydrophone. Analysis of the ship noise level for varying distances allowed estimation of the sound attenuation in the frequency band of 10-80 kHz. The effective attenuation coefficient representing the attenuation loss above cylindrical spreading loss had only slight frequency dependence and can be estimated by the frequency independent value of 0.058 dBm.     

水下隔声结构设计及评价方法

为使用混响法快捷地测量水下结构物的辐射噪声,需基于港口或海岸建造海上混响水池。针对内外都是水情况下的海上混响水池壁面隔声问题,设计了一种带梁空气夹层板水下隔声结构,通过仿真比较了不同参数的空气夹层板的隔声性能。为评价声波无规入射情况下水下大尺寸隔声结构隔声性能,提出了一种混响评价方法,通过隔声实验比较了混响法与脉冲法的不同。结果表明：带梁空气夹层板的水下隔声性能优异,声波无规入射情况下,面板厚度0.015 m、空气层厚度0.020 m的带梁空气夹层板在2～10 kHz频段插入损失大于20 dB;混响法可以有效评价大尺寸水下隔声结构的平均隔声性能,其反映的声波无规入射的平均隔声性能更接近于实际应用情况。     

Temporary threshold shifts in humans exposed to octave bands of noise for 16 to 24 hours.

Groups of human subjects were exposed in a diffuse sound field for 16--24 h to an octave-band noise centered at 4, 2, 1, or 0.5 kHz. Sound-pressure levels were varied on different exposure occasions. At specified times during an exposure, the subject was removed from the noise, auditory sensitivity was measured, and the subject was returned to the noise. Temporary threshold shifts (TTS) increased for about 8 h and then reached a plateau or asymptote. The relation between TTS and exposure duration can be described by a simple exponential function with a time constant of 2.1 h. In the frequency region of greatest loss, threshold shifts at asymptote increased about 1.7 dB for every 1 dB increase in the level of the noise above a critical level. Critical levels were empirically estimated to be 74.0 dB SPL at 4 kHz. 78 dB at 2 kHz, and 82 dB at 1 and 0.5 kHz. Except for the noise centered at 4.0 kHz, threshold shifts were maximal about 1/2 octave above the center frequency of the noise. A smaller second maximum was observed also at 7.0 kHz for the noise centered at 2.0 kHz, at 6.0 kHz for the noise centered at 1.0 kHz, and at 5.5 kHz for the noise centered at 0.5 kHz. After termination of the exposure, recovery to within 5 dB of pre-exposure thresholds was achieved within 24 h or less. Recovery can be described by a simple exponential function with a time constant of 7.1 h. The frequency contour defined by critical levels matches almost exactly the frequency contour defined by the E-weighting network.     

What do evoked potentials tell us about the acoustic system of the harbor porpoise?

The evoked acoustic potentials of the brainstem (EAPB) were detected from the brain, the skull, and the surface of the head of the harbor porpoise (Phocaena phocaena). Experiments were performed at the Karadag biological station (Crimea). Clicks, noise, and tone bursts of different frequencies within 80–190 kHz were used as stimuli. The time and frequency selectivities of the auditory system were estimated by the simultaneous and direct forward masking methods. The minima of EAPB thresholds were usually observed in a frequency range of 120–140 kHz, which corresponded to the main spectral maximum of the species-specific echolocation signal. In addition to the regular EAPB, a pronounced off-EAPB was observed. In the aforementioned frequency range, a frequency selectivity (Q₁₀ of about 10) was revealed by the direct forward masking method. The EAPB could be measured up to a frequency of 190 kHz, but outside this high-resolution region (outside the ultrasonic “fovea”), the frequency selectivity was weak. A simultaneous masking of a click by a tone was strong only when the delay of the click with respect to the masker onset was smaller than 1.0 ms. In a continuous regime, the tone (unlike noise) produced only a weak masking. The response to a small intensity increment of 1–4 dB was rather strong. In the frequency range of 120–140 kHz, this response exhibited a nonmonotone dependence on the signal level. The time resolving power, which was measured by the EAPB recovery functions for double clicks of various levels, was rather high, even when the intensity of the test signal was 18 dB lower than the masker level. Experimental data show that the auditory system of the harbor porpoise is tuned to detecting ultrasonic echo signals in the frequency range within 120–140 kHz. A hypothesis is put forward that the acoustic system of the harbor porpoise allows the animal, from analyzing echo signals, to estimate not only the distance to the target and the target’s intrinsic properties but also the speed with which the target is approached, the latter estimate being presumably obtained on the basis of the Doppler effect.     

双层加肋球壳回波现象分析

双层加肋壳体是水下目标的典型结构。实验观测到双层加肋球壳回波的频率-角度谱在角度域呈现强烈的周期性振荡,在2 kHz～10 kHz频率范围内,这种振荡从低频到高频越来越明显。为了解释所观测到的现象,利用修正的板块元算法(Modified PEM)计算了不同入射角、不同频率下双层加肋球壳的回波,并与实验结果进行了对比分析。结果表明,目标强度随入射角的周期性剧烈起伏主要是由壳间肋板声散射导致的。     

Underwater psychophysical audiogram of a young male California sea lion (Zalophus californianus)

Auditory evoked potential (AEP) data are commonly obtained in air while sea lions are under gas anesthesia; a procedure that precludes the measurement of underwater hearing sensitivity. This is a substantial limitation considering the importance of underwater hearing data in designing criteria aimed at mitigating the effects of anthropogenic noise exposure. To determine if some aspects of underwater hearing sensitivity can be predicted using rapid aerial AEP methods, this study measured underwater psychophysical thresholds for a young male California sea lion (Zalophus californianus) for which previously published aerial AEP thresholds exist. Underwater thresholds were measured in an aboveground pool at frequencies between 1 and 38 kHz. The underwater audiogram was very similar to those previously published for California sea lions, suggesting that the current and previously obtained psychophysical data are representative for this species. The psychophysical and previously measured AEP audiograms were most similar in terms of high-frequency hearing limit (HFHL), although the underwater HFHL was sharper and occurred at a higher frequency. Aerial AEP methods are useful for predicting reductions in the HFHL that are potentially independent of the testing medium, such as those due to age-related sensorineural hearing loss.     

Frequency specific susceptibility to acoustic trauma in the budgerigar (Melopsittacus undulatus)

The effects of intense noise exposure on hearing in the budgerigar were examined by behavioral audiometry. After binaural exposure to an intense broadband noise, auditory threshold shifts (TS) of the birds were continuously measured at frequencies between 0.125 and 8 kHz using an avoidance conditioning technique. Temporary threshold shifts (TTS) were observed at frequencies higher than 1.5 kHz and considerable permanent threshold shifts (PTS) were observed at frequencies below 1 kHz. This pattern of threshold shifts is contrary to that observed in mammals.     

Sensitivity of a tucuxi (Sotalia fluviatilis guianensis) to airborne sound

Auditory systems of cetaceans are considered highly specialized for underwater sound processing, whereas the extent of their hearing capacity in air is still a point of issue. In this study, the sensitivity to airborne sound in a male tucuxi (Sotalia fluviatilis guianensis) was tested by means of a go/no go response paradigm. Auditory thresholds were obtained from 2 to 31.5 kHz. Compared to the hearing thresholds of other dolphins as well as of amphibian mammals, the sensitivity to airborne sound of the test subject is low from 2 to 8 kHz, with the highest threshold at 4 kHz. Thresholds at 16 and 31.5 kHz reveal a sharp increase in hearing sensitivity. Thus, although not obtained in this study, the upper aerial hearing limit is in the ultrasonic range. A comparison of the present data with the underwater audiogram of the same test subject referred to sound intensity indicates that the sensitivity of Sotalia to underwater sound is generally better than to airborne sound.     

Estimation and interpolation of underwater low frequency ambient noise spectrum using artificial neural networks

In this work, estimation of ambient noise spectrum influenced by wind speed and wave height carried out for the frequency range of 500 Hz to 5 kHz using Feed forward Neural Network (FNN) is presented. Ocean ambient noise measurements were made in the shallow waters of Bay of Bengal using a portable data acquisition system with a high sensitivity hydrophone at a depth of 5 m from the surface.100 sets of data covering a rage of wind speeds from 2.5 m/s to 8.5 m/s with approximately 15 sets of data falling within 1 m/s over the range of wind speed were used for training the FNN. The parameter wave height which contributes to the noise producing mechanism is also used for training along with wind speed. The results revealed that the proposed method is useful in the estimation and interpolation of underwater noise spectrum level and hence in simulation for the considered frequency range. These were confirmed by calculating the Mean Squared Error (MSE) between the experimental data and the simulation. As the measurements of the underwater ambient noise level are very difficult in remote oceanic regions, where conditions are often inhospitable, these studies seem to be relevant.     

水下强声频率对巴马小型猪肺脏病理损伤效应的观察

为探索大功率水声信号对入水哺乳动物肺脏的生物效应,以佩戴专用水下呼吸装置的巴马小型猪为实验对象,采用大功率连续声波为暴露手段,对水下正常体征状态的小型猪进行强声辐射,通过大体解剖、HE染色显微病理图像观察等方法,分析水下强声对哺乳动物肺脏器官的损伤效应。在300 Hz^10 kHz的正弦频段中,当声压级大于190 dB时,出现了不同程度的肺脏损伤。大功率水声信号对入水哺乳动物肺脏的生物效应显著,在相同声压级条件下,3 kHz水下连续波对实验动物肺脏病理损伤效应最大。      

Receiving beam patterns in the horizontal plane of a harbor porpoise (Phocoena phocoena)

Receiving beam patterns of a harbor porpoise were measured in the horizontal plane, using narrow-band frequency modulated signals with center frequencies of 16, 64, and 100 kHz. Total signal duration was 1000 ms, including a 200 ms rise time and 300 ms fall time. The harbor porpoise was trained to participate in a psychophysical test and stationed itself horizontally in a specific direction in the center of a 16-m-diameter circle consisting of 16 equally-spaced underwater transducers. The animal's head and the transducers were in the same horizontal plane, 1.5 m below the water surface. The go/no-go response paradigm was used; the animal left the listening station when it heard a sound signal. The method of constants was applied. For each transducer the 50% detection threshold amplitude was determined in 16 trials per amplitude, for each of the three frequencies. The beam patterns were not symmetrical with respect to the midline of the animal's body, but had a deflection of 3-7 degrees to the right. The receiving beam pattern narrowed with increasing frequency. Assuming that the pattern is rotation-symmetrical according to an average of the horizontal beam pattern halves, the receiving directivity indices are 4.3 at 16 kHz, 6.0 at 64 kHz, and 11.7 dB at 100 kHz. The receiving directivity indices of the porpoise were lower than those measured for bottlenose dolphins. This means that harbor porpoises have wider receiving beam patterns than bottlenose dolphins for the same frequencies. Directivity of hearing improves the signal-to-noise ratio and thus is a tool for a better detection of certain signals in a given ambient noise condition.     

海面干涉对船舶水下辐射噪声测量的影响及其消减方法

针对海面干涉对船舶辐射噪声测量的影响,进而导致声源级测量不准确的问题,文章给出了利用时间平均、深度平均、1/3倍频程谱级3种数据处理方法减弱海面干涉的影响,通过模型仿真验证了以上方法的有效性。根据船舶水下辐射噪声测量的国际标准,在浅海测量了某新型科考船不同航速下的水下辐射噪声,并采用前述方法进行了数据处理与分析。计算了不同航速下被测船舶辐射噪声1/3倍频程频带声压级,并与挪威船级社发布的辐射噪声衡准值进行了对比。结果表明被测船舶噪声低频控制较好,高频控制较差,高航速(13 kn)被测船舶的2 kHz以上辐射噪声大于衡准值。      

Echolocation signals of free-ranging killer whales (Orcinus orca) and modeling of foraging for chinook salmon (Oncorhynchus tshawytscha)

Fish-eating "resident"-type killer whales (Orcinus orca) that frequent the coastal waters off northeastern Vancouver Island, Canada have a strong preference for chinook salmon (Oncorhynchus tshawytscha). The whales in this region often forage along steep cliffs that extend into the water, echolocating their prey. Echolocation signals of resident killer whales were measured with a four-hydrophone symmetrical star array and the signals were simultaneously digitized at a sample rate of 500 kHz using a lunch-box PC. A portable VCR recorded the images from an underwater camera located adjacent to the array center. Only signals emanating from close to the beam axis (1185 total) were chosen for a detailed analysis. Killer whales project very broadband echolocation signals (Q equal 0.9 to 1.4) that tend to have bimodal frequency structure. Ninety-seven percent of the signals had center frequencies between 45 and 80 kHz with bandwidths between 35 and 50 kHz. The peak-to-peak source level of the echolocation signals decreased as a function of the one-way transmission loss to the array. Source levels varied between 195 and 224 dB re: 1 microPa. Using a model of target strength for chinook salmon, the echo levels from the echolocation signals are estimated for different horizontal ranges between a whale and a salmon. At a horizontal range of 100 m, the echo level should exceed an Orcinus hearing threshold at 50 kHz by over 29 dB and should be greater than sea state 4 noise by at least 9 dB. In moderately heavy rain conditions, the detection range will be reduced substantially and the echo level at a horizontal range of 40 m would be close to the level of the rain noise.     

Underwater localization of pure tones by harbor seals (Phoca vitulina)

The underwater sound localization acuity of harbor seals (Phoca vitulina) was measured in the horizontal plane. Minimum audible angles (MAAs) of pure tones were determined as a function of frequency from 0.2 to 16 kHz for two seals. Testing was conducted in a 10-m-diam underwater half circle using a right/left psychophysical procedure. The results indicate that for both harbor seals, MAAs were large at high frequencies (13.5 degrees and 17.4 degrees at 16 kHz), transitional at intermediate frequencies (9.6 degrees and 10.1 degrees at 4 kHz), and particularly small at low frequencies (3.2 degrees and 3.1 degrees at 0.2 kHz). Harbor seals seem to be able to utilize both binaural cues, interaural time differences (ITDs) and interaural intensity differences (IIDs), but a significant decrease in the sound localization acuity with increasing frequency suggests that IID cues may not be as robust as ITD cues under water. These results suggest that the harbor seal can be regarded as a low-frequency specialist. Additionally, to obtain a MAA more representative of the species, the horizontal underwater MAA of six adult harbor seals was measured at 2 kHz under identical conditions. The MAAs of the six animals ranged from 8.8 degrees to 11.7 degrees , resulting in a mean MAA of 10.3 degrees .     

Distribution of spectral density for underwater noise in the shelf zone of the Pacific Ocean

The results of measurements for the distribution of spectral density for underwater noise in the shelf zone of the Pacific Ocean 21 km from Shikotan Island at the depth of 130 m within the frequency range 1.9–11000 Hz at the wind speed 0–40 m/s are given. Measurements were conducted within the bands of 1/3- and 1/2-octave filters over six months. In the case of a realization length of 33 min and smaller, the distribution of the instant pressure values for underwater noise can be considered normal. The distribution of deep slow variations for the intensity of underwater noise at all frequencies differed from the normal one. The values for the asymmetry parameter and the coefficient of excess are given for the variation distribution of spectral density for underwater noise.     

舰船辐射噪声模拟发射系统的设计研究

本文依据典型舰船噪声的频谱特性规律,设计研制了一套舰船辐射噪声发射系统实验样机,包括信号结构设计、换能器选择配置、系统构成设计等,本噪声模拟发射系统具有100Hz～16kHz频带噪声的模拟发射功能,包括线谱、连续谱成分,频谱分配和谱线形式可调可控,信号总声源级动态范围达60dB。     

Temporary shift in masked hearing thresholds in odontocetes after exposure to single underwater impulses from a seismic watergun

A behavioral response paradigm was used to measure masked underwater hearing thresholds in a bottlenose dolphin (Tursiops truncatus) and a white whale (Delphinapterus leucas) before and after exposure to single underwater impulsive sounds produced from a seismic watergun. Pre- and postexposure thresholds were compared to determine if a temporary shift in masked hearing thresholds (MTTS), defined as a 6-dB or larger increase in postexposure thresholds, occurred. Hearing thresholds were measured at 0.4, 4, and 30 kHz. MTTSs of 7 and 6 dB were observed in the white whale at 0.4 and 30 kHz, respectively, approximately 2 min following exposure to single impulses with peak pressures of 160 kPa, peak-to-peak pressures of 226 dB re 1 microPa, and total energy fluxes of 186 dB re 1 microPa2 x s. Thresholds returned to within 2 dB of the preexposure value approximately 4 min after exposure. No MTTS was observed in the dolphin at the highest exposure conditions: 207 kPa peak pressure, 228 dB re 1 microPa peak-to-peak pressure, and 188 dB re 1 microPa2 x s total energy flux.