中川 誠司

Bone conduction hearing aids (BCHAs) offer an alternative solution for individuals with outer or middle ear issues who cannot benefit from traditional air conduction hearing aids. However, the phenomenon of "crosstalk," where sound intended for one ear is mistakenly transmitted to the other ear through bone conduction, presents a challenge. This unintended transmission may limit the benefits of binaural hearing that can be achieved using two BCHAs, such as accurately detecting a sound source's direction. In this article, we present a method to suppress "crosstalk" within the human head using an adaptive algorithm to control two audiometric bone transducers. •Our method involves positioning an error sensor at a location considered close to the cochlea, such as the ear canal or the mastoid, and utilizing an adaptive algorithm to estimate the crosstalk compensation filter. This filter generates an anti-signal, which is then transmitted to one of the two transducers, effectively cancelling the crosstalk.•To verify whether the crosstalk cancellation reaches the cochlea in the inner ear, we provide a procedure for measuring hearing thresholds with and without crosstalk cancellation. This acts as a subjective measure of the efficacy of our crosstalk cancellation method. By leveraging an adaptive algorithm, this approach provides personalized cancellation and has the potential to enhance the performance of binaural BCHAs.

This study aimed to address the issue of "crosstalk" in bone conduction hearing aids, where sound meant for one ear is mistakenly perceived by the other ear via bone conduction. We explored a potential solution by canceling the crosstalk sound at the cochlea. To achieve this, an accelerometer was placed on the mastoid to monitor the crosstalk sound produced by an audiometric bone transducer on the opposite side of the head, while a second transducer on the same side as the accelerometer was used to cancel it out. The filtered-x least mean square (FxLMS) algorithm was used to optimize the crosstalk compensation (CTC) filter for cancellation at the mastoid. Then, the subjects manually adjusted the filter coefficients through a lateralization task to achieve crosstalk cancellation at the cochlea. This task involved modifying phase and level differences between pure-tone sounds from the two transducers, making the sound seem to originate from the leftmost or rightmost side of the head. Our results indicated successful cancellation of crosstalk sound at the cochlea, as subjects' hearing thresholds under noise masking were lower with crosstalk cancellation.

The impressions of heating, ventilation, and air conditioning (HVAC) sounds are important for the comfort people experience in their living spaces. Revealing neural substrates of the impressions induced by HVAC sounds can help to develop neurophysiological indices of the comfort of HVAC sounds. There have been numerous studies on the brain activities associated with the pleasantness of sounds, but few on the brain activities associated with the thermal impressions of HVAC sounds. Seven time-varying HVAC sounds were synthesized as stimuli using amplitude modulation. Six participants took part in subjective evaluation tests and MEG measurements. Subjective coolness of the HVAC sounds was measured using the paired comparison method. Magnetoencephalographic (MEG) measurements were carried out while participants listened to and compared the time-varying HVAC sounds. Time-frequency analysis and cluster-based analysis were performed on the MEG data. The subjective evaluation tests showed that the subjective coolness of the amplitude-modulated HVAC sounds was affected by the modulation frequency, and that there was individual difference in subjective coolness. A cluster-based analysis of the MEG data revealed that the brain activities of two participants significantly differed when they listened to cooler or less cool HVAC sounds. The frontal low-theta (4–5 Hz) and the temporal alpha (8–13 Hz) activities were observed. The frontal low-theta and the temporal alpha activities may be associated with the coolness of HVAC sound. This result suggests that the comfort level of HVAC sound can be evaluated and individually designed using neurophysiological measurements.

Bone conduction hearing aids offer a unique solution for people with conductive hearing loss, providing a direct transmission of sound to the cochlea. However, a common issue called "crosstalk" can occur, where sound intended for one ear is received by the opposite ear via bone conduction, affecting the ability to localize sound sources and understand speech in noise. To address this issue, we investigated whether canceling "crosstalk" at an accelerometer located on the mastoid would create a "quiet zone" that reaches the cochlea in the inner ear. Our evaluation with individuals having normal hearing abilities showed that their hearing thresholds were improved with crosstalk cancellation than without. These results indicate that although designed to cancel "crosstalk" at the mastoid, the cancellation still reached the cochlea, making it perceptible and potentially beneficial for those with conductive hearing loss.

In conventional bone-conduction (BC) devices, a vibrator is typically attached to the mastoid process of the temporal bone or the condyle process of the mandible. However, BC-sound presentations to facial parts such as the nose and cheek have also been investigated recently. As the face is the among the most complex structures of the human body, transmission of sounds using BC on different facial parts are likely to show different perception and propagation characteristics than those presented to conventional parts. However, the characteristics of BC sound presented to different part of the face have not yet been studied in detail. To test the frequency discrimination ability, we measured difference limens for frequency (DLFs). We also conducted monosyllable articulation tests in Japanese to assess the speech-perception characteristics when BC sounds are presented to various facial (nasal, infraorbital region, zygomatic, jaw angle, and chin) and conventional (mastoid and condyle process) parts of a normal-hearing subject. The results suggest that, at least in the parts investigated in the current study, the frequency resolution and intelligibility of the facial parts were about the same as those of the conventional parts. These results indicate that practical frequency information and speech perception are possible with BC devices attached to different facial parts.

Bone conduction (BC) technology allows us to hear sounds without having anything blocking our ears and enables hearing even when wearing earplugs. However, optimizing this technology presents challenges, particularly in relation to the occlusion effect (OE), a phenomenon that takes place when the ear canal is occluded, causing low-frequency sounds to seem louder than their original intensity. While some facial regions exhibit greater OE than conventional areas, the impact of OE on speech perception in different facial regions has not been thoroughly investigated. This study explores the relationship between OE and speech perception in various facial regions to inform the functionality of BC technology. We conducted a quantitative analysis of monosyllable articulation in the mastoid process, condylar process, nasal bone, and infraorbital region using both female and male voices to assess OE's impact on speech perception. Our findings reveal that OE improves articulation, facilitating voice communication; however, the extent of articulation enhancement varies depending on the stimulus location and phoneme. By examining OE's role in speech perception, this research report contributes to the development and use of more effective BC technology applications.

In cartilage conduction (CC), a vibrator is presented onto the cartilage of the ear instead of the bony parts of the head used in ordinary bone conduction (BC). Because the auricle cartilage is softer and lighter than the bone, it doesn't require as much pressure as BC, which may cause discomfort (or pain) in the area where a BC transducer is being pressed. However, CC is a relatively new technology, and whether the less dense characteristics of cartilage, which varies from person to person, result in a better sound perception is still being studied. In this paper, we focused on investigating how the hardness and size of the auricle or pinna affect the effectiveness of CC. We used pure-tone hearing thresholds to evaluate this objectively. We also measured the thresholds of CC in subjects with auricular hematoma or "cauliflower ear" (misshapen ears commonly caused by close contact sports) to see if it affected CC differently. Our results indicate that the hardness and size of the auricle affect CC thresholds and that subjects with auricular hematoma have different perceptual characteristics compared to the normal ear group. These differences are believed to be caused by changes in hardness and mass.

In clinical practice, bowel sounds are often used to assess bowel motility. However, the mechanism of bowel-sound occurrence is unknown. Furthermore, there is no objective evidence indicating a relationship between bowel motility and bowel sounds, and diagnoses have been based on empirically established criteria. In this study, simultaneous X-ray fluoroscopy and bowel-sound measurements were used to reveal the mechanism of bowel-sound occurrence. The results indicate that the flow of luminal contents may cause bowel sounds. Additionally, on the basis of the hypothesis that bowel motility recovers with the postoperative course, bowel-sound features that reflect bowel motion were explored, revealing that the current diagnosis indices are appropriate.

Bone conduction (BC) is used in devices such as hearing aids and earphones. Audio devices using BC on the face have been developed; however, limited research has addressed the perception of BC sounds on the face. BC also entails an occlusion effect (OE), wherein the loudness of low-frequency sounds is enhanced when the ear canal is occluded. We evaluated the characteristics of OE by measuring hearing thresholds and ear canal sound pressure (ECSP) during BC stimulation of several facial parts. We compared them with those of conventionally used parts. OE, the difference in hearing thresholds between the open and occluded ears, was equal to or larger than that of conventionally used parts. The difference in ECSP was smaller than that in OE, indicating that BC components transmitted to the middle and inner ears affected OE in these facial parts. The complicated structure of the face may have affected the results.

In conventional bone conduction (BC) devices, a vibrator is typically applied to the mastoid or condyle processes. Recently, however, BC-sound presentations to facial parts such as the nose have also been investigated. As the face is among the most complex structures in the human body, BC sounds presented to facial parts are likely to show different perception and propagation characteristics from those presented to conventional parts. We measured hearing thresholds, ear canal sound pressures in both ears, and head vibrations at both mastoid processes when BC sounds were presented to the facial (nasal, infraorbital region, zygomatic, jaw angle, and chin) and conventional (mastoid and condyle processes and forehead) parts of normal-hearing subjects. The results indicated that the facial parts and mastoid process had similar threshold characteristics. By changing the stimulus parts on the face, the hearing thresholds did not change, whereas the amplitudes of each propagation component changed significantly.

The current worldwide energy supply is insufficient to meet the rising demand. As a result, the energy prices are expected to keep soaring despite the recent increases in a variety of renewable energy resources. Although not renewable, shale oil and gas-"unconventional" hydrocarbon resources are relatively clean forms of energy resources, which still hold a vast share of the energy market. For many oil and gas companies, meeting profitable production goals from shale reservoirs is sometimes challenging, due to the loss of fracture conductivity and premature declines in the production. In this paper we investigate the stress-dependent changes in the hydraulic conductivity of proppant-filled fractures and mechanical fracture-proppant interactions in Caney Shale, a calcareous, organicrich mudrock, through laboratory experiments and numerical modeling. American Petroleum Institute (API) fracture conductivity tests were conducted using 2% KCl on five locations within the Caney Shale that consisted of selecting three brittle (reservoir) zones and two ductile zones. Confining pressures ranged from 1,000 psi to 12,000 psi at 210 degrees F. Conductivity, permeability as well as embedment were measured during the test. Also, an additional, laboratory in-situ visualization test was conducted to examine the detailed proppant-shale matrix interaction under elevated stress (3,920 psi effective stress) and temperature (252 degrees F), with a synthetic reservoir fluid. Our experimental results have confirmed that improved fracture conductivity is attributed to proppant size, and that the increase in porosity of the proppant pack, closure pressure changes and the reduction in fracture conductivity are a function of many factors such as fracture closure stress.

Because of its simplicity and the ability to produce a stable, slow-propagating crack, the Double-Torsion (DT) method has been used widely for investigating the critical and subcritical propagation of a slow-propagating tensile (mode-I) crack. However, to determine the complex relationship between the crack velocity vc vs. the strain energy release rate G (or the stress intensity factor K) from laboratory measurements, several corrections must be made to account for the impact of sample and crack geometry. Particularly, DT test typically produces a crack with a curved edge profile instead of a straight line, causing the local vc and G vary along the crack front. The experimentally measured vc and G data merely reflect collective, averaged behavior of the crack. This makes inversion for the intrinsic, "true" crack growth kinetics necessary, based upon the knowledge of the crack geometry. Simple and effective correction methods have been proposed and validated for the slow, chemical-reaction-controlled part (Region I) of the vc-G curve. However, reliable methods for the highly nonlinear, transport-dominated part (Region II) and its sudden transition to the dynamic propagation part (Region III) are still lacking. In this paper, we propose a method for determining the intrinsic vc-G relationship across all three Regions based upon DT test data, using a simple model function and its numerical inversion. The performance of this approach is examined and demonstrated using both synthetic and laboratory data for subcritical crack growth in soda lime glass.

Fracture initiation and propagation in brittle materials is promoted in surface-reactive (sorptive) environments, a phenomenon known as subcritical crack growth (SCG). Laboratory measured crack-propagation velocity vs. stress intensity factor relationships typically exhibit highly nonlinear, multi-stage characteristics that are sensitive to environmental factors such as adsorbate concentration and temperature. For practical purposes, empirical relationships (e.g., a power law) have been used to describe this complex phenomenon. However, how the overall SCG behavior emerges from the underlying fundamental processes near the crack tip, such as the interaction of the crack surfaces separated by only a few nanometers and mass transport within the nano -confined space, is still not well understood. This paper develops a mechanistic, surface-force -based fracture theory (SFFT) which integrates surface force models, fluid transport models, and linear elastic fracture mechanics to quantitatively explain the multi-stage characteristics of SCG in brittle solids. A numerical model is developed based on SFFT and solved through an implicit partitioned scheme for efficiency and modularity. The results are validated by Wiederhorn's data on crack propagation in soda-lime glasses at a wide range of relative humidity levels. We show that, for the first time, the entire range of an SCG curve can be captured by a single physics-based model. The predicted SCG curves reveal that the development of repulsive disjoining pressure behind the crack tip can be responsible for the reduced apparent fracture toughness in a sorptive environment. The shape of the SCG curve, and its changes with respect to the environment, is found to critically depend on the assumed transport models.

The behavior of heated bentonite buffer is critical for the security and long-term performance of a geological repository for high-level radioactive waste (HLW). While laboratory column experiments have been conducted to investigate compacted bentonite and coupled THMC (thermal-hydro-mechanical and chemical) processes for a moderate temperature range of up to 100 degrees C, data for a higher temperature range are limited. Understanding bentonite behavior and coupled THMC processes under higher temperatures (e.g., up to 200 degrees C) could allow for a more economic repository design and would expand the data and knowledge base for more reliable modeling. In this study, a bench-scale experiment was conducted in a compacted bentonite column experiencing both heating up to 200 degrees C in the center and hydration from a sand-clay boundary surrounding the column. During the experiment run for 1.5 years, frequent X-ray computed tomography (CT) scanning of bentonite provided insights into the spatiotemporal evolution of (1) hydration/dehydration, (2) clay swelling/shrinkage, (3) displacement, and (4) mineral precipitation. After the experiment, a comprehensive post-dismantling characterization of bentonite samples was conducted. Results showed that the bentonite hydration was axi-symmetrical despite the initial heterogeneity due to packing, confirming the ability of bentonite to seal fast flow/transport paths. Compared to a non-heated control experiment, the heated column showed greater CT density variations along the radial distance, indicating that homogenization of bentonite might be more difficult if a temperature gradient is maintained in the repository. Precipitation of an anhydrite layer occurred in the inner hot zone, pointing to potential concerns about salt precipitation causing canister corrosion. Ultimately, the experiments provided a high-resolution window into the strongly dynamic and coupled behavior of bentonite exposed to heating, hydration and swelling, which will be valuable for improving modeling of coupled processes, especially for the early state of a HLW repository.

This paper proposes a novel neuronal current source localization method based on Deep Prior that represents a more complicated prior distribution of current source in the brain using convolutional neural networks. Deep Prior has been suggested as an unsupervised learning approach that does not require a large amount of training data, and randomly-initialized neural networks are used as implicit priors for solving inverse problems. In our previous work, a Deep-Prior-based current source localization method has been proposed but the performance was not almost the same as those of conventional approaches, such as standardized low-resolution brain electromagnetic tomography (sLORETA). In order to improve the Deep-Prior-based approach, in this paper, a depth weight of the current source is introduced for Deep Prior, where depth weighting amounts to assigning more penalty to the superficial currents. Its effectiveness is confirmed by experiments of current source estimation on simulated MEG data.

As a vibrator needs to be pressed onto the osseous parts of the head, bone conduction is often accompanied by pain and esthetic problems. To solve these problems, a "distant presentation" that involves presenting vibrators to the neck, trunk, or upper limb was proposed. Our previous studies focused on the perceptual and propagation characteristics of distantly presented bone-conducted sounds in the ultrasonic range. However, only a few studies have been conducted in the audible-frequency range. In this study, to examine the basic properties of distantly presented bone-conduction perception in the audible-frequency range, hearing thresholds, difference limens for frequency, and temporal modulation transfer functions were measured with insulated air-conducted sounds. The results indicate that the distance attenuation is much larger than that in the ultrasonic range, and the degradation of frequency and temporal information occurring in the propagation process of bone-conducted sounds is sufficiently small for the transmission of sound information.

High-frequency sounds above 20 kHz presented via bone conduction can be heard clearly and transmit speech information using amplitude modulation. Additionally, bone-conducted ultrasound (BCU) can be perceived even when the vibrator is presented to body parts distant from the head, such as the neck, arm, and trunk. To evaluate this previously presented BCU hearing, word intelligibility and monosyllable articulation tests were conducted in Japanese. The results suggested that a practical speech transmission, comparable to ordinary BCUs presented onto the head, can be obtained by distantly presented BCU.

Since bone conduction (BC) has the advantage that it does not cover the ear canal and can be easily heard even when earplugs are worn, it has been applied to various communication devices. Conventional BC is mainly applied to the mastoid process of the temporal bone (the osseous bulge behind the ear), however, some of recent BC devices, such as smart glasses, present stimuli to faces. The face has very complex structures in the human body; therefore, it is highly likely that the hearing and propagation characteristics of sound will change depending on the part to which sound is presented. However, the characteristics of BC presented to the face has not yet been studied in detail. In this study, we measured hearing threshold and ear canal sound pressure (ECSP) when BC stimuli were presented to various parts of the facial cranium (nasal, infraorbital region, zygomatic, jaw angle, and chin), and compared them with conventional placements of BC stimulus (the mastoid process, condyle process, and forehead). The facial parts such as the infraorbital region, zygomatic, and jaw angle had similar hearing thresholds and ECSPs to those of the mastoid process. The results suggested that these facial parts can be used as stimulus placements of BC devices.

Expectations concerning the timing of a stimulus enhance attention at the time at which the event occurs, which confers significant sensory and behavioral benefits. Herein, we show that temporal expectations modulate even the sensory transduction in the auditory periphery via the descending pathway. We measured the medial olivocochlear reflex (MOCR), a sound-activated efferent feedback that controls outer hair cell motility and optimizes the dynamic range of the sensory system. MOCR was noninvasively assessed using otoacoustic emissions. We found that the MOCR was enhanced by a visual cue presented at a fixed interval before a sound but was unaffected if the interval was changing between trials. The MOCR was also observed to be stronger when the learned timing expectation matched with the timing of the sound but remained unvaried when these two factors did not match. This implies that the MOCR can be voluntarily controlled in a stimulus- and goal-directed manner. Moreover, we found that the MOCR was enhanced by the expectation of a strong but not a weak, sound intensity. This asymmetrical enhancement could facilitate antimasking and noise protective effects without disrupting the detection of faint signals. Therefore, the descending pathway conveys temporal and intensity expectations to modulate auditory processing.

In bone-conducted sound reproduction, crosstalk is a phenomenon in which sound presented on either side of the head reaches the cochlea in the two ears. However, since the brain compares signals coming from each cochlea, crosstalk at high levels may limit the ability to hear with two ears, especially in patients with two bone-conduction hearing aids (BCHAs). In this study, we intended to suppress crosstalk sounds at the cochlea by canceling them at a sensor in the ear canal. Two sensors were evaluated here: (i) a probe microphone that can record the ear-canal sound pressure and (ii) an accelerometer that can capture the vibration of the inner wall of the ear canal. Since crosstalk cancellation was designed to occur at the sensor location, we used the tone reception threshold (TRT) as a subjective indicator to investigate which sensors contributed the most to the cancellation at the cochlea.

A bone conduction (BC) sound presented on either side of the head will travel to the cochleae in both ears, and this crosstalk phenomenon is considered one factor limiting the benefits of binaural hearing with BC. Previous studies have demonstrated the feasibility of measuring the phase and level required for crosstalk cancellation at the cochlea; however, given a human subject's inability to consistently detect low frequencies, this method is limited to cancellations at frequencies above 1000 Hz. This study describes an alternative approach for implementing a crosstalk cancellation system for low frequencies by measuring ear-canal sound pressure (ECSP). Since the ear canal is close to the cochlea, we hypothesized that altering ECSP in response to a BC stimulation may be used to achieve crosstalk cancellation at the cochlea. Our approach relies on ECSP measurements to estimate impulse responses (IRs) from bone transducers to a probe microphone in the ear canal. The IRs are then used to predict the phase and level required for crosstalk cancellation at the probe microphone's location. To confirm the hypothesis, we measured tone reception threshold (TRT), the lowest tone level participants could detect, under two conditions: with and without crosstalk cancellation. Although crosstalk cancellation was designed to occur at the probe microphone and not at the cochlea, the TRT results showed that participants were still able to perceive cancellations at frequencies below 1000 Hz.

In clinical practice, bowel sounds are often used to assess bowel motility. However, the diagnosis differs depending on the literature because diagnoses have been based on empirically established criteria. To establish diagnostic criteria, researching the mechanism of bowel-sound occurrence is necessary. In this study, based on simultaneously measured X-ray fluoroscopy and bowel sounds, correlation and Granger causality among bowel movement, luminal content movement, and abdominal sound were estimated. The results supported our hypothesis that the bowel moves luminal contents and luminal contents generate abdominal sounds.

Since a vibrator needs to be pressed onto the osseous parts of the head, bone-conduction (BC) is often accompanied by pain and esthetic problems. In order to solve these problems, "distant presentation" has been proposed. In the distant presentation, vibrators are presented to the neck, upper limb or trunk. Our previous studies focused on the perception and propagation characteristics of distantly-presented BC sound in the ultrasonic range and an application to a novel audio-interface. On the other hand, a limited number of studies have been conducted on distantly-presented BC in the audible-frequency range. In this study, to examine the basic properties of the distantly-presented BC perception in the audible-frequency range, hearing thresholds, difference limens for frequency (DLFs) and temporal modulation transfer functions (TMTFs) were measured under the condition that AC sounds were insulated sufficiently. The results obtained indicated that BC sounds can be clearly perceived at distal parts of the body even in the audible-frequency range and no significant degradation of frequency and temporal information occurs in the propagation process in the body.

Bone-conduction microphones (BCMs) can detect speaker's voices with high signal-to-noise ratio even under extremely noisy environments. However, it is sometimes accompanied by discomfort and esthetic problems because BCMs are ordinarily attached to the front of the neck (larynx). In order to solve such problems, we have been developing a novel BCM systems built in a hard hat [2]. To develop this BCM system, characteristic of bone-conducted speech detected on the scalp need to be clarified. In this study, intelligibilities of bone-conducted speech detected at several locations on the head and neck were assessed by mono-syllable articulation tests and the speech transmission index (STI), objective measure of signal transmission quality. The results obtained indicated that the forehead and the vertex showed better articulation and STI than the mastoid process of the temporal bone, the mandibular condyle and occiput. Additionally, the larynx, commonly used in existing BCM systems, showed lower scores than others. These results suggest that attenuation of high-frequency components are smaller at the forehead and the vertex, and indicate the practicability of these locations as the BCM placement.

The Krauklis wave is a slow dispersive wave, generated in fluid-filled fractures. By analyzing the resonant frequency and quality factor of the Krauklis wave, the fracture dimension and fluid properties can be estimated. However, the accuracy of the estimation of fracture dimension and fluid properties depends on deciphering factors affecting the Krauklis wave such as fluid viscosity, fracture geometry, fracture compliance, and stiffness ratio, some of which have not been experimentally studied yet. We have developed an experimental apparatus to study the Krauklis wave within a trilayer model consisting of a pair of aluminum plates and a mediating viscous fluid layer. We utilize a piezoelectric source and miniature pressure transducers in our measurements. To evaluating the effects of the fracture aperture and fluid viscosity, we examine the impact of complex and realistic fracture geometry by introducing spatially varying aperture, surface roughness, and compliant partial surface contact provided by springs. The phase velocity, resonant frequencies, and quality factors (a) increase with the expansion of fracture aperture and (b) decrease with the increase of the fluid viscosity. Additionally, (c) phase velocity, resonant frequencies, and attenuation decrease with the increase of mechanical compliance. Furthermore, rough and wedge-shaped fracture surfaces tend to slow down the Krauklis wave. Since the Krauklis wave is used by different disciplines such as volcanology, glaciology, and the petroleum industry to characterize fracture dimensions and properties of the fluids involved, our experimental findings can be used as a benchmark to develop comprehensive theoretical models to better interpret the Krauklis waves.Plain Language Summary Fractures play an important role in fluid transports in geological settings (e.g., impermeable bedrock aquifers, volcanos, and petroleum reservoirs). To determine the scale of the fluid transport (e.g., the volume of gases that reaches the surface from magma), it is necessary to estimate the size of subsurface fractures. There is a specific seismic mode, called the Krauklis wave, that is generated from fractures when the fluid pressure within the fractures is disturbed. Since the Krauklis wave is initiated from fractures, it can be used to estimate their sizes and the fluids involved. However, an accurate interpretation of the Krauklis wave requires understanding the fundamental parameters that affect the Krauklis wave. These parameters include fracture aperture, fluid viscosity, fracture geometry, and fracture mechanical compliance. By conducting a comprehensive experimental study, we investigate the effects of the aforementioned parameters on the Krauklis wave. Our results can facilitate analyzing the Krauklis wave's dispersion, dissipation, and resonances properties to enhance fracture characterization.

Enhanced geothermal systems (EGS) offer the potential for a much larger energy source than conventional hydrothermal systems. Hot, low-permeability rocks are prevalent at depth around the world, but the challenge of extracting thermal energy depends on the ability to create and sustain open fracture networks. Laboratory experiments were conducted using a suite of selected rock cores (granite, metasediment, rhyolite ash-flow tuff, and silicified rhyolitic tuff) at relevant pressures (uniaxial loading up to 20.7 MPa and fluid pressures up to 10.3 MPa) and temperatures (150-250 degrees C) to evaluate the potential impacts of circulating fluids through fractured rock by monitoring changes in fracture aperture, mineralogy, permeability, and fluid chemistry. Because a fluid in disequilibrium with the rocks (deionized water) was used for these experiments, there was net dissolution of the rock sample: this increased with increasing temperature and experiment duration. Thermal-hydrological-mechanical-chemical (THMC) modeling simulations were performed for the rhyolite ash-flow tuff experiment to test the ability to predict the observed changes. These simulations were performed in two steps: a thermal-hydrological-mechanical (THM) simulation to evaluate the effects of compression of the fracture, and a thermal-hydrological-chemical (THC) simulation to evaluate the effects of hydrothermal reactions on the fracture mineralogy, porosity, and permeability. These experiments and simulations point out how differences in rock mineralogy, fluid chemistry, and geomechanical properties influence how long asperity-propped fracture apertures may be sustained. Such core-scale experiments and simulations can be used to predict EGS reservoir behavior on the field scale.

The mixed-wet nature of reservoir formations imposes a wide range of rock wettability from strong resident-fluid wetting to strong invading-fluid wetting. The characteristics of two-phase flow in porous media composed of mixed-wetting surfaces remain poorly understood. In this study, we investigated the displacement of resident ethylene glycol (EG) by hexane in two mixed-wet micromodels of identical 2.5-D geometry heterogeneity, with uniformly or heterogeneously distributed patches strongly wetting to hexane. These patches are mixed among pores with unaltered EG-wetting surfaces. Along with control tests in the originally EG-wet micromodel, we show the classic fingering and transitions in flow regimes at logCa (capillary number) from -7.2 to -3.9. Moreover, pore-scale distributions of wettability and their spatial correlation influence displacement efficiency. In the two mixed-wet micromodels, we found (a) an increase of steady-state hexane saturation at the end of experiments by up to 0.12 in the capillary fingering regime and a decrease of at most by 0.06 in the viscous fingering regime, compared to the EG-wet micromodel, and (b) dispersed and fragmented hexane distribution after displacement. Brine drainage during supercritical CO2 (scCO(2)) injections in these micromodels occurs with lower wettability contrasts, and under similar viscosity ratios and interfacial tensions resulted in higher displacement efficiency relative to displacement of EG by hexane. While mixed-wettability can enhance displacement efficiency compared to uniform wettability, the dynamics of immiscible fluids in strong mixed-wet reservoirs are expected to be less pronounced in contributing to the efficiency of geological CO2 sequestration, oil recovery, and remediation of hydrocarbon-contaminated aquifers.

Bone-conduction microphones (BCMs) can detect speaker's voices with high signal-to-noise ratio even under extremely noisy environments like a machine factory or an engine room of a watercraft. BCMs are ordinarily attached to the front of the neck (the larynx), therefore, it is sometimes accompanied by discomfort and esthetic problems. In order to solve such problems, we have been developing a novel BCM system built in a hard hat [2]. To develop this BCM system, characteristics of bone-conducted speech detected on the scalp need to be clarified. In this study, mono-syllable articulations of bone-conducted speech detected at several locations on the head and neck were measured. Also, the speech transmission index (STI), objective measure of signal transmission quality, was calculated. The results obtained that the forehead and the vertex showed better articulation and STI than the mastoid process of the temporal bone, the mandibular condyle, and the occiput. In terms of the gender difference, the forehead and the vertex showed higher scores for the male voice, whereas the mandibular condyle showed the highest for the female voice. Additionally, the larynx, commonly used in existing BCM systems, showed lower scores than others. These results indicated that the attenuation of high-frequency components are smaller at the forehead and the vertex, and indicate the practicability of these locations as the BCM placement.

Disaster alerts are usually accompanied by auditory signals at the beginning. It is desirable that the auditory signal itself produces a sense of warning. The effects of (1) degree of consonance and (2) temporal pattern of the auditory signal on the auditory impression of warning were investigated using paired-comparison tests. In both tests, the sequences of three triads were used as stimuli. First, seven types of stimuli were generated by varying the degree of consonance of the triad (frequency ratio of sinusoids was varied systematically from 2:3:4, 4:5:6, 6:7:8, 8:9:10, 10:11:12, 12:13:14, and 14:15:16). Each subject showed changes in the auditory impression of warning depending on the degree of consonance however, variation among subjects was observed. Second, 21 types of stimuli were generated by changing several temporal parameters (duration of the triad, interval between the triads, and duty rate of the sequence). The results indicated that the auditory impression of warning increased as the triad duration increased, and the interval between the triads decreased.

Bone-conduction (BC) has been applied to hearing aids for the conductive hearing loss, however, also has some disadvantage especially in wearability of a sound transducer. Therefore, as a solution, "cartilage conduction (CC)" has been proposed and applied to devices such as a hearing aid and smartphones. In CC, a sound transducer is placed on the cartilage of the pinna, and the air-conduction (AC) and osseotympanic BC components are dominantly transmitted. However, even in CC, the vibrating surface often contacts not only with the aural cartilage but also with the osseous parts of/around the pinna, and effects of such transducer placement on perception characteristics and propagation mechanisms remain unclear. In this study, we measured hearing thresholds and vibrations of the head when the transducer was placed on (1) the pinna, (2) the mastoid process of the temporal bone, and (3) the ear-front point (middle of between the tragus and the mandibular condyle). The results suggested that the ratios of the inertial and compressional BC components increases when the transducer is placed on the osseous parts, particularly in high frequency range. These findings provide useful information to optimize CC devices and develop a calibration method of CC.

Noise induced by a heating, ventilation and air conditioning (HVAC) system is an important factor that affects the comfort of our living spaces. Much effort has been devoted to reduce HVAC-noise levels, however, the reduction of the noise levels beyond a certain level sometimes cause a relative rise of the secondary noise sources and/or a loss of operation feeling. Therefore, there is a need for a novel method to design “comfortable” HVAC noises. On the other hand, comfortable sounds sometimes elicit not only relaxation but also decrease of vigilance. Consequently, comfortable sounds may deteriorate the intellectual productivity. The present study investigated effects of some acoustical parameters (loudness, sharpness, and standout-frequency-peak amplitude) of HVAC noise on the preference and the intellectual productivity. First, effect of the parameters on the preference of each subject was measured using a paired comparison on a seven-point scale. The preference was improved as the loudness and dominant-frequency-peak amplitude decreased. Next, the intellectual productivity was measured using Kraepelin test during each subject listened to the most- and least-preferred HVAC noises. The intellectual productivity for the most-preferred noise was larger than that of the least preferred. These result provide useful information to design well-balanced or tailor-made HVAC noises.

The medial olivocochlear reflex (MOCR) is a feedback response that is activated by acoustic stimulation and suppresses the input to the auditory system. The MOCR is thought to play an important role in protecting the auditory periphery from damage caused by acoustic overexposure and to partly determine the risk of noise-induced hearing loss (HIHL). Although the sound-activated characteristics of the MOCR are well described, it is not clear whether the MOCR is flexibly controlled by cognitive processes. We investigate whether expectation about the intensity of upcoming sounds modulates the MOCR. The MOCR was evaluated by otoacoustic emissions (sounds generated by the inner ear). The appearance of a small or big cross cued participants to expect a loud or soft sound, respectively. The MOCR induced by the loud sound following a valid cue was stronger than following an invalid cue, in which the loud sound appears although the visual cue predicted the soft sound. The result implies that the protection provided by the MOCR does not work properly for loud sounds occurring unexpectedly, and the risk of NIHL would increase at the moment.

Geological carbon storage (GCS) involves unstable drainage processes, the formation of patterns in a morphologically unstable interface between two fluids in a porous medium during drainage. The unstable drainage processes affect CO(2)storage efficiency and plume distribution and can be greatly complicated by the mixed-wet nature of rock surfaces common in hydrocarbon reservoirs where supercritical CO2(scCO(2)) is used in enhanced oil recovery. We performed scCO(2)injection (brine drainage) experiments at 8.5 MPa and 45 degrees C in heterogeneous micromodels, two mixed-wet with varying water- and intermediate-wet patches, and one water-wet. The flow regime changes from capillary fingering through crossover to viscous fingering in the micromodels of the same pore geometry but different wetting surfaces at displacement rates withlogCa(capillary number) increasing from -8.1 to -4.4. While the mixed-wet micromodel with uniformly distributed intermediate-wet patches yields similar to 0.15 scCO(2)saturation increase at both capillary fingering and crossover flow regimes (-8.1 <= logCa <= - 6.1), the one heterogeneous wetting to scCO(2)results in similar to 0.09 saturation increase only at the crossover flow regime (-7.1 <= logCa <= - 6.1). The interconnected flow paths in the former are quantified and compared to the channelized scCO(2)flow through intermediate-wet patches in the latter by topological analysis. AtlogCa > - 6.1(near well), the effects of wettability and pore geometry are suppressed by strong viscous force. Both scCO(2)saturation and distribution suggest the importance of wettability on CO(2)storage efficiency and plume shape in reservoirs and capillary leakage through caprock at GCS conditions.

Bone-conducted ultrasound (BCU) can be clearly perceived and can transmit speech information using amplitude-modulation (AM). BCU can also be perceived when presented to body parts like the neck, trunk and arms. When AM-BCUs propagate in the biological tissues with nonlinearity, like the cartilage, modulator signals may be self-demodulated. This demodulated-sound may affect BCU hearing. To examine the availability of the demodulated-components, difference limens for frequency (DLFs) were measured with/without the low-pass-masking noises that masked the demodulated-components. Practical frequency-discrimination ability was obtained even at distant body parts, whereas DLFs increased when the demodulation components were masked. Additionally, to elucidate the demodulation mechanisms in the human body, vibrations were measured around the cartilage. Significant demodulated-components were generated at especially the cartilage near the outer ear canal. These results indicated the availability of demodulated-components to improve hearing of the distantly-presented BCU, and provide useful information to optimize the novel BCU devices. (C) 2020 The Japan Society of Applied Physics

Ultrasound can be clearly perceived by bone-conduction, and this "bone-conducted ultrasound (BCU)" can transmit speech information by using amplitude modulation (AM). Further, BCU can be perceived not only on the head but also on the distal parts of the body like the neck, trunk and arms. This "distantly-presented BCU" can be applied to the novel interface that can transmit sound information selectively to specific users who touches the vibrator. However, the ability to transmit sound information of distantly-presented BCU is unclear. First, to assess frequency discrimination ability, difference limens for frequency (DLFs) of the distantly-presented AM-BCU were measured with/without a low-pass masking noise that masked the self-demodulated components generated by the nonlinearity of biological tissues. DLFs comparable to that of air-conducted sounds were observed, whereas DLFs significantly increased above 1 kHz under the masking condition. These results suggest that practical frequency discrimination ability can be obtained even when BCUs were presented to distal body parts. Additionally, it is indicated that the demodulated components may contribute to transmitting frequency information above 1 kHz. Second, monosyllable articulation and word intelligibility tests were conducted in Japanese. The intelligibility and articulation at the neck were 55% and 38% respectively, whereas they decreased as the stimulus placement gets farther from the head. The results suggest the distantly-presented BCU device can be applied to transmission of speech information.

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf and has been applied to the development of a novel hearing aid. In the BCU hearing aid, the vibrator is pressed onto the mastoid process of the temporal bone (the osseous bulge behind the ear). However, BCU can be heard on distal parts of the body; e.g., the muscle of the neck, the clavicle and the upper limbs. Some studies have been carried out to develop other BCU hearing devices using this "distant presentation". However, the possibility of the localization of distantly-presented BCU has not been verified. In this study, we investigated whether listeners could use the interaural time differences (ITDs) and intensity differences (IIDs) as cues for lateralization (left/right discrimination) of distantly-presented BCU. The results showed that lateralization based on ITDs and IIDs is possible to some extent, even for the distant presentation, whereas lateralization become difficult as the stimulus placement gets further from the head. Lateralization based on IIDs was more accurate than that based on ITDs. IIDs seem to give more effective cues than ITDs in the lateralization of BCU.

Although the mechanisms involved remain unclear, several studies have reported that bone-conducted ultrasounds (BCUs) can be perceived even by those with profound sensorineural hearing impaired, who typically hardly sense sounds even with conventional hearing aids. We have identified both the psychological characteristics and the neurophysiological mechanisms underlying the perception of BCUs using psychophysical, electrophysiological, vibration measurements and computer simulations, and applied to a novel hearing aid for the profoundly hearing impaired. Also, mechanisms of perception and propagation of the BCU presented to distant parts of the body (neck, trunk, upper limb) were investigated.

While it has been recognized that a large amplitude incident wave upon a dry fracture can exhibit nonlinear seismic wave scattering due to its stress-dependent mechanical compliance, the impact of pore fluid in the fracture and a fluid-filled poroelastic background medium-features common for fractures in the Earth-are not well understood. As a first step toward an understanding of the nonlinear poroelastic response of elastic waves in fractured media, analytical approximate formulas are used for the amplitude and phase of a normally incident plane wave using a perturbation method, assuming a fluid-filled, highly compliant nonlinear interface embedded in a linear poroelastic solid. The stress-closure behavior of the fracture is modeled by nonlinear, poroelastic displacement-discontinuity boundary conditions (a linear-slip interface). The theory predicts that the static ("Direct current," or DC) and higher-order-harmonic waves produced by the nonlinear scattering can be greatly reduced by the presence of fluid in the fracture. This, however, depends upon a number of parameters, including fracture compliance, fluid properties (compressibility and viscosity), and the permeability of the background medium, as well as environmental parameters such as the initial fluid pressure and stress acting on the fracture. The static effect produces low-frequency fluid pressure pulses when a finite-duration wave is incident upon the fracture-behavior unique to fluid-filled fractures within a poroelastic medium.