Excess Attenuation Research Articles

Broadband attenuation-based measurements of bubble size distributions

Oceanic bubbles generated by breaking waves are a key mechanism for air-sea gas exchange. Dense bubble plumes can also interfere with acoustic propagation in shallow water due to their high scattering and attenuation. Most studies of oceanic bubbles have used narrow-band acoustical and optical techniques to quantify bubble size distributions under breaking waves in open water. To study bubble distributions at estuarine tidal fronts, where localized downwelling and advection can generate large bubbles plumes, we developed a measurement system for estimating bubble size distributions via broadband excess attenuation. The system consists of two transducers (3–30 kHz and 30–110 kHz) and two hydrophones mounted on a towable frame. Testing was performed in a laboratory wave tank to measure bubble distributions below a field-scale (1 + meter) breaking wave. This presentation will discuss the bubble size distributions observed at different locations along the breaking wave crest in the direction of propagation and their associated time scales and sound speed anomalies. We also compare these distributions with those previously observed in open water and will present preliminary results from a field deployment of the system in the Connecticut River estuary.

Modeling acoustic propagation on Mars

It is important to understand how the atmospheric conditions affect the propagation of sound waves on Mars, both for the study of the acoustic sources and of the atmosphere itself. As 3 microphones are already on Mars (2 on NASA/Perseverance and 1 on CNSA/Zhurong) and potentially more to come, a model of the propagation of sound in the Martian surface layer was needed. A first-principle acoustic attenuation model is used to quantify the excess attenuation of the Martian atmosphere. Thanks to inputs extracted from a global circulation model of Mars (the LMD Martian Climate Database), we are able to compare the magnitude of attenuation at different places and times, from 10 Hz to 20 kHz. Propagation effects are also considered by adapting a parabolic equation code to the Martian conditions. This accounts for strong temperature gradients near the surface, as well as gradients of wind speed. The acoustic reflection on the ground assumes a semi-porous medium. The turbulent fluctuations of temperature and wind speed are implemented using the frozen medium approach. The model shows that characteristics of sound waves propagation depend drastically on the local time. It provides a useful framework to interpret acoustic signal recorded on Mars. The model shows that characteristics of sound waves propagation depend drastically on the local time. It provides a useful framework to interpret acoustic signal recorded on Mars.

Measurement Trials and Modeling of Radio Propagation Through Small-Scale Fire Using Pinus pinaster Fuel Bed

This letter presents measurement results and initial physical modeling of the radiowave propagation phenomena in the presence of fire using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Pinus pinaster</i> fuel heaps. To this extent, this letter reports on small-scale measurement trials carried out at 700 MHz on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Pinus pinaster</i> fuel bed on fire and subsequent validation of simulation results of the propagation phenomena behavior based on the intertwined use of both the fire dynamics simulator and the cold plasma model. Excess attenuation of up to 1.52 dB was observed in measured results, which is thought to be critical considering it is a small-scale fire scenario composed of a 1 × 1 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> with 0.6 kg of pine needles

Experimental study on temperature attenuation of smoke flow driven by dual fire sources in a tunnel

A series of reduced-scale tunnel fire tests were carried out to investigate ceiling smoke temperature attenuation in a naturally ventilated tunnel under double fire sources of various sizes and distances. Experimental results showed that the interactions between the two flames affect excess gas temperature attenuation. Under a given fire size, the ceiling smoke temperature gradually decays more slowly when the spacing between the two fire sources is longer and then goes through a steady stage. Moreover, for different smoke spread regions (i.e., the radial ceiling jet region, the shooting flow region and the one-dimensional tranquil flow region), the ceiling smoke temperature attenuation trends are different. Models of non-dimensional excess ceiling smoke temperature attenuation in the radial ceiling jet and shooting flow regions were proposed using the plume radius at the ceiling level as the characteristic length scale. In the one-dimensional tranquil flow region, an exponential model was developed by theoretical analysis to predict non-dimensional ceiling smoke temperature. The lumped attenuation coefficient k was observed to decrease first and then approach a relatively stable value with an increasing fire spacing. This study is of great significance to the design and protection of tunnel structures under multiple fire sources.

Study on the ground attenuation of engine run-up and APU noise for developing the airport noise model in Japan

The correction for ground effect around airports is modeled based on the results of numerical analysis in order to make it possible to estimate the propagation of noise caused by ground operations in airports such as engine run-ups and APU to the vicinity of airports. The excess attenuation due to ground effects on sound caused by engine run-ups and APU is calculated using a PE method for typical jet aircraft and propeller aircraft, respectively. On the assumption that the ground around an airport consists of asphalt-paved surface and grass-covered surface in a certain ratio, the excess attenuation for the mixed impedance ground is calculated with the Fresnel-zone method using the results of PE calculation. The composition ratio of ground surface is assumed based on the composition ratio of asphalt-paved surface and grass-covered surface along the propagation path from the engine run-up spot to the airport site boundary of six major airports in Japan. In this paper, we introduce the excess attenuation calculated with the PE method and the correction model for ground effects on noise of engine run-ups and APU is discussed to implement it in the airport noise prediction model used in Japan.

An investigation on source identification of very high frequency sounds radiated from home appliances around us.

We investigated the azimuth angle characteristics of head related transfer function (HRTF) at very high frequency region using two kinds of head and torso simulators (HATS). In the measurement of hearing thresholds, there are two ways using a headphone or a loudspeaker. In general, it will be carried out using a loudspeaker because sound pressure calibration and measurement are simple. However, the hearing threshold which measured using a loudspeaker at very high frequency region may contain some errors because sound pressure level (SPL) reaching the ear are seriously affected by a small movement of the head. Also, the SPL near the pinna seriously depends on both shapes of a pinna and a head because excess attenuation by diffraction of VHF sound is very large. To provide assurance for the accuracy measurement of hearing threshold, it is important to make clear the relationship between the SPL and shape of head and/or ear. In this paper, we reported the HRTFs calculated from the SPLs measured at three different positions of left ear - a tragus, an auricle and an eardrum and discussed the influence of head and/or ear of HATS from the azimuth angle characteristics of these HRTFs.

Audio-frequency surface waves over multiple width and depth grooves

Previous studies of airborne surface waves have been carried out at audio-frequencies over periodically rough surfaces formed by lighting lattices and bricks and at ultrasonic frequencies over mm scale compound gratings involving grooves of the same depth but different widths. In this paper, a modal model, which has been found to give comparable predictions to BEM while being much faster to run is used, together with BEM, to investigate audio-frequency sound propagation over grooves of varying widths and depths in the order of cm. Predictions of excess attenuation spectra, pressure contours and zeroes in the effective reflection coefficient over grooves with multiple widths and depths are used to indicate the nature of the surface waves which involve overlapping quarter wavelength resonances. Predictions are extended to multiple depth grooved surfaces without and with porous infills.

Outdoor mmWave Channel Modeling for Fixed Wireless Access at 60 GHz

AbstractThe large bandwidths that are available at millimeter wave (mmWave) frequency bands allow high‐throughput wireless communication systems that enable fixed wireless access (FWA) applications. In FWA networks, a stationary link is created between antennas installed at building facades or street furniture, such as lampposts. A Line‐of‐Sight (LOS) scenario is preferred, but to guarantee the quality of service to the user, communication should remain possible when the LOS path is obstructed. In this paper, outdoor channel models at 60 GHz are presented that can be used for the design and optimization of FWA networks, based on measurements with the Terragraph wireless system using IEEE Std. 802.11ad radios. LOS path loss measurement data is analyzed and building reflection loss, diffraction loss, and vegetation loss are measured. There is limited diffuse scattering, but reflections on the wall frame structure result in reflected paths with low losses. Existing vegetation models that are based on measurement campaigns at lower frequencies underestimate vegetation loss at mmWave frequencies, as measured excess attenuation values range from 15 to 25 dB for distances lower than 14 m. The presented channel models are used for link budget calculations for FWA networks.

The effects of time variable fracture conductivity on gas production of horizontal well fracturing in natural gas hydrate reservoirs

AbstractHydrate reservoirs in the South China Sea belong to muddy silt‐type hydrate reservoirs with low permeability. Horizontal well fracturing is one of the main stimulation methods for low‐permeability oil and gas reservoirs. For muddy silt‐type hydrate reservoirs, the stability and effectiveness of hydraulic fractures may be a severe problem due to poor reservoir cementation, reservoir deformation, and sand production. In this paper, the time variability of fracture conductivity is considered for the first time. According to the geological data at offshore gas hydrate production test site in the South China Sea, a multilayer hydrate reservoir model was established, and the influence of the time variable fracture conductivity on the production behavior in the process of horizontal well fracturing was analyzed. The simulation results show that, compared with the case of constant fracture conductivity, the gas production rate with the case of time variable fracture conductivity is greatly reduced, and the 5‐year cumulative gas production is reduced by 49.9%. Sensitivity analysis shows that the larger the initial fracture conductivity, the higher the peak gas production rate; the larger the attenuation magnitude of the fracture conductivity, the lower the gas production rate in the late production period; the larger the decline rate coefficient of the fracture conductivity, the higher the gas production rate in the early production period. The analysis of the orthogonal experimental design shows that the influence of the attenuation magnitude of fracture conductivity, the initial conductivity of fracture, and the decline rate coefficient of fracture conductivity on the cumulative gas production decreases in order. The actual production process should try to avoid excessive attenuation magnitude of fracture conductivity, while improving the initial fracture conductivity as much as possible to ensure high cumulative gas production.

Male and female songs propagation in a duetting tropical bird species in its preferred and secondary habitat.

Acoustic signals produced by animals must transmit through the environment to reach potential receivers and change their behaviour. Both the environment (vegetation, air properties, other animals) and the form of the signal affect the propagation process. Here we investigated how the transmission of different song types of a duetting songbird species inhabiting an extreme environment within African montane forest, varies between males and females as well as different types of micro-habitats. We hypothesised that male and female songs would have different transmission properties, reflecting known differences in signal form and function. We analysed signal-to-noise ratio (SNR), excess attenuation (EA) and tail-to-signal ratio (TSR) of songs of male and female Yellow-breasted Boubous (Laniarius atroflavus) that were played and re-recorded in a range of sites representing the species-typical habitats. We found significant effects of distance, site (habitat) and sex reflected in all three measures of sound degradation. The clearest, primarily distance-dependent pattern was found for SNR of songs propagated in level forest site. EA was substantially higher in shrubs than in forest habitats, while TSR reflecting longer echoes appeared at longer distances in forest sites. Thus, Yellow-breasted Boubou songs are better propagated in forests than in disturbed sites covered with shrubs. We found that all male song types used for broadcast singing propagated farther than female songs, with significantly higher SNR at all distances. The different male song types which are known to have different functions, also demonstrated a differentiated pattern of propagation reflecting their functionality. All signals that were tested propagated the furthest in the ideal condition described as forest with a level terrain. Signals degraded much faster during transmission through shrubs regrowing after forest burning. On this site, the differences in the propagation of male and female songs, as well as the differences between male song types, were relatively least pronounced. Transmission in typical mountain forest among streams and with substantial terrain variation revealed that degradation pattern in such habitat could be perturbed in a non-linear way. Streams acting as a source of high noise level also negatively affected transmission and may strongly limit the perception of birds staying close to them. However, stream noise did not affect sex differences in song propagation as was found for the site located in shrubs. Male songs showed more efficient transmission through all habitats (least in the shrubs) than female song. These differences were the result of male songs having a whistle structure that is better adapted for long-range propagation than the atonal, wideband frequency female vocalisations. Results support the idea that signals of males of the Yellow-breasted Boubous evolved under the pressure of long-range communication both with rivals and females, while females of the species are much more focused on within-pair communication or signalling together with their partner. The consequence of deforestation resulting in pushing back territories to the forest remnants along streams may be a shortening of the song’s active range, in particular, in females.

Site-Specific Radio Propagation Model for Macrocell Coverage at Sub-6 GHz Frequencies

This article presents a radio propagation model for macrocell coverage predictions in built-up areas for sub-6-GHz frequency band. The proposed two-ray model is a combination of various individual propagation models available in the literature, namely the discrete mixed Fourier transform split-step parabolic-equation (DMFT-SSPE) to characterize reflection and diffraction phenomena due to the presence of buildings and terrain irregularities, the building-transmission model (BTM) to account for the signal attenuation through the nearby buildings and the International Telecommunication Union of Radio-communications (ITU-R) model for attenuation in vegetation to weight the excess attenuation caused by the surrounding vegetation. The performance of the proposed modeling approach was assessed against measurement results obtained from an extensive measurement campaign conducted in Rio de Janeiro, Brazil. The receiver (RX) antenna was assembled on an automotive van, and it was made to travel around the city recording the received signal level. Several drive tests were conducted, including different transmitter (TX) locations and scenarios, and at various frequencies foreseen for 5G systems, namely 750 MHz, 2.5 GHz, and 3.5 GHz.

Ultrasonic propagation in high‐concentration TiO2 slurries for photocatalytic reactors

AbstractThis work reports measurements of the speed of sound and ultrasonic attenuation in high concentration (up to 3 g · L−1) aqueous TiO2 slurries close to neutral pH. Measurements were made at frequencies of 1675, 5545, and 9340 kHz using ultrasonic transducers submerged in the slurry. The experimental setup may be applied to slurries in practical reactors while in operation. Within an experimental uncertainty of ±0.5 m · s−1, the speed of sound in the slurry was the same as in pure water, at all the studied catalyst concentrations and frequencies. The excess ultrasonic attenuation with respect to pure water increases linearly with the catalyst concentration and is inversely proportional to the square of the excitation frequency. This indicates that viscous and thermal acoustic losses predominate over scattering. For TiO2 concentrations in the range of 0.15–3 g · L−1, the catalyst concentration in the slurry may be estimated as a linear function of the excess ultrasonic attenuation, with an uncertainty of 0.1 g · L−1.

Underwater Image Restoration via DCP and Yin–Yang Pair Optimization

Underwater image restoration is a challenging problem because light is attenuated by absorption and scattering in water, which can degrade the underwater image. To restore the underwater image and improve its contrast and color saturation, a novel algorithm based on the underwater dark channel prior is proposed in this paper. First of all, in order to reconstruct the transmission maps of the underwater image, the transmission maps of the blue and green channels are optimized by the proposed first-order and second-order total variational regularization. Then, an adaptive model is proposed to improve the first-order and second-order total variation. Finally, to solve the problem of the excessive attenuation of the red channel, the transmission map of the red channel is compensated by Yin–Yang pair optimization. The simulation results show that the proposed restored algorithm outperforms other approaches in terms of the visual effects, average gradient, spatial frequency, percentage of saturated pixels, underwater color image quality evaluation and evaluation metric.

Amycenone reduces excess body weight and attenuates hyperlipidaemia by inhibiting lipogenesis and promoting lipolysis and fatty acid β-oxidation in KK-Ay obese diabetic mice.

Excess body weight and hyperlipidaemia cause severe health problems and have social implications. Amycenone is an active substance extracted from Yamabushitake mushrooms with no reports of its activity against excess body weight and hyperlipidaemia. This research clarifies the effects and mechanisms of action of amycenone on the inhibition of body weight excess and hyperlipidaemia attenuation using KK-Ay mice. Amycenone or water was administered to 8-week-old male KK-Ay mice by gavage for 8 weeks. Their body weight and food intake were recorded during the experiment. At the end of the experimental period, the mice were dissected, and blood samples, lipid metabolism-related organs and tissues were collected and stored for further analysis. Amycenone treatment suppressed body weight gain and improved serum levels of fasting blood glucose and non-esterified fatty acids. Additionally, serum and hepatic cholesterol and triacylglycerol levels were reduced after this treatment, whereas the phosphorylation levels of AMPK, PKA and HSL increased and the expression level of FAS decreased. The protein level of C/EBPβ and gene expression level of Cpt1 were higher in the perirenal adipose tissue of amycenone-treated KK-Ay mice. Furthermore, amycenone phosphorylated AMPK, PKA and ACC, and PPARγ expression was lower in the mesenteric adipose tissue. The phosphorylation levels of AMPK, LKB1, PKA and ACC were also induced, and FAS expression level was reduced in the liver of the amycenone-treated group. Amycenone could reduce excess body weight and attenuate hyperlipidaemia in KK-Ay mice by inhibiting lipogenesis and promoting lipolysis through lipid metabolism pathway stimulation and fatty acid β-oxidation acceleration.

Form and Function Predict Acoustic Transmission Properties of the Songs of Male and Female Canyon Wrens

To function effectively, animal signals must transmit through the environment to receivers, and signal transmission properties depend on signal form. Here we investigated how the transmission of multiple parts of a well-studied signal, bird song, varies between males and females of one species. We hypothesized that male and female songs would have different transmission properties, reflecting known differences in song form and function. We further hypothesized that two parts of male song used differentially in broadcast singing and aggressive contests would transmit differently. Analyses included male and female songs from 20 pairs of canyon wrens (Catherpes mexicanus) played and re-recorded in species-typical habitat. We found that male song cascades used in broadcast singing propagated farther than female songs, with higher signal-to-noise ratios at distance. In contrast, we demonstrated relatively restricted propagation of the two vocalization types typically used in short-distance aggressive signaling, female songs and male “cheet” notes. Of the three tested signals, male “cheet” notes had the shortest modeled propagation distances. Male and female signals blurred similarly, with variable patterns of excess attenuation. Both male song parts showed more consistent transmission across the duration of the signal than did female songs. Song transmission, thus, varied by sex and reflected signal form and use context. Results support the idea that males and females of the same species can show distinctly different signal evolution trajectories. Sexual and social selection pressures can shape sex-specific signal transmission, even when males and females are communicating in shared physical environments.

Observations of high-frequency acoustic attenuation due to bubble entrainment at estuarine fronts

Frontal boundary features with strong gradients in water properties and velocity are common features in coastal environments where fresh discharge meets ambient ocean waters. Convergence at these fronts results in two features that support the entrainment of bubbles. First, horizontal velocity gradients causes surface waves to steepen and break at these boundaries. Second, localized downwelling can further entrain and transport these bubbles. In experiments using broadband echosounders (45–420 kHz) at the Connecticut River ebb plume front and James River tidal intrusion front, bubble entrainment was observed to cause frequency-dependent excess attenuation. Seabed backscattering near fronts is used as a baseline, whereas a decrease in observed backscattering from the seabed under bubble plumes was attributed to excess attenuation due to bubble concentrations. Despite observing significant (>10 dB in some cases) excess attenuation in lower-frequency channels, we hypothesize that these fronts are unlikely to significantly affect propagation in the horizontal at these frequencies and that factors, such as refraction and three-dimension structure, are more operationally significant. [This work was funded by ONR.]

A study on variations in excess attenuation due to ground surface and meteorological conditions based on a long-term outdoor sound propagation experiment

From the winter of 2018, outdoor sound propagation experiments (maximum horizontal range: 300 m) have been repeatedly conducted three times a day on weekdays at a glider airfield in Hokkaido, Japan. The ground condition of the experimental field is grass-covered in summer and snow-covered in winter. In each experiment, impulse responses have been measured by time-stretched pulse method and excess attenuation has been obtained at receiving points. Meteorological data at the field has been also measured. Based on the data of excess attenuation collected under various meteorological conditions over a long period, variation in sound propagation characteristics due to the differences in ground surface condition and meteorological condition has been investigated. The numerical analysis based on the GFPE method has been also carried out with changing the parameter of meteorological condition and ground surface condition. By comparing the results with the experimental data, the prediction method of the variations in excess attenuation has been also investigated.

A comparison of the ground excess attenuation model in Harmonoise with finite-difference time-domain solutions under grounds with mixed types

Total noise exposure is calculated for the evaluation of health effects caused by environmental noise. For the calculation, computationally drawn noise maps are used. In the computation process, sound propagation over ground surface with mixed types should be calculated for better accuracy. One engineering model that allows such calculation is the ground excess attenuation model of the Harmonoise model. However, the applicability of the model to such complex grounds remains unclear. In this study, a 40m-length ground surface with a discontinuity in flow resistivity is defined. By moving the discontinuity position, sound propagation from a point source and a receiver at each end is calculated using the model and a numerical method. The numerical method is the finite-difference time-domain method with porous medium modeling that has been proven to be accurate. It is found from the numerical results that in higher frequencies the excess attenuations in terms of the discontinuity position have fluctuations. The fluctuations are found to correspond to the interference by diffraction path difference passing the discontinuity. In contrast, the model results exhibit smooth transition from an extremity of single flow resistivity surface to another. A simple model of such diffraction needs to be developed.

Postsecular rhetoric of the Pope: a discourse analysis of Pope Francis’ TED Talks

Pope Francis has gained a title as ‘the Pope of Surprises’ for his unprecedented and unconventional papal narratives, personal viewpoints, and equally electrifying mediatised public appearances. One of these surprises was his videotaped appearance on TED. By adopting postsecularism as a conceptual framework, this study examines the dominant discursive features in Pope Francis’ TED Talks. Three main types of narrative features were found: emphasis on the postsecular solidarity between the religious and the secular, negotiating religious doctrinal engagement in public spheres, and finally, de-emphasising the papal magisterial authority. While the surface language of the Pope’s TED Talks operates in a postsecular inclusive discursive spirit, its ontological roots are nevertheless cemented in a Catholic epistemology and a faith-motivated claim for moral theology. The similarities between Christian sermons and TED’s communicative norms and practices make the Pope’s new rhetoric possible without excessive attenuation of the Catholic vocabulary.

Key points of post-marketing evaluation of classic traditional Chinese medicine prescriptions based on combination of disease and syndrome

Classic prescriptions, hospital preparations and famous traditional Chinese medicine(TCM) experience prescriptions are the main sources of new drug development and innovation. The multi-components and multi-targets treatment characteristics of TCM are advantages, but at the same time, broad indications, unclear clinical positioning and lack of evidence-based evidence support are the key problems affecting the play of TCM efficacy and restricting its promotion and application. The hot in recent research was to how to break through the bottleneck, precise clinical positioning, highlight the advantages of the classic TCM prescriptions, and complete the transformation from clinical practice, clinical research to clinical evidence, but at the same time, it is also the difficulty. The clinical research model of the combination of disease and syndrome can fully reflect the ancient medical case evidence of classic TCM prescriptions, the historical experience of human used and the characteristics of syndrome differentiation and treatment, and highlight the advantages of Chinese medicine. At the same time, under the modern disease classification system and research mode, is conducive to established the standardized clinical evidence report and evaluation system, is conducive to promote the integration of clinical research evidence, and avoids excessive attenuation of information. Based on the previous work of our team, the intention of this study was to make a comment about the key points of the post-marketing evaluation of the classic TCM prescriptions under the combination of disease and syndrome and includes key points:(1)With the syndrome as the carrier, connected with the classical prescription and clinical diseases, focused on the clinical positioning on macroscopically.(2)The combination of syndrome visualization, standardization and pharmacological molecular basis, focus on clinical precise positioning in microscopic.(3)Innovating therapeutic effect evaluation methods, reflecting the curative effect characteristics based on syndrome differentiation.(4)The combination of &quot;randomized controlled evidence-based studies&quot; and &quot;real world evidence-based evaluation&quot;, focusing on clinical advantages, fully evidence-based evidence.(5)Make full use of clinical registration studies and pay attention to safety.