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While seagrass meadows are perceived to be pertinent blue carbon reservoirs, they also potentially release methane (CH4) into the atmosphere. Seasonal and diurnal variations in CH4 emissions from a subtropical hypersaline lagoon dominated by Halodule wrightii in southern Texas, USA, on the northwest coast of the Gulf of Mexico were investigated. Dissolved CH4 concentrations decreased in the daytime and increased overnight during the diel observation period, which could be explained by photosynthesis and respiration of seagrasses. Photosynthetic oxygen was found to significantly reduce CH4 emissions from seagrass sediment. Diffusive transport contributed slightly to the release of CH4 from the sediment to the water column, while plant mediation might be the primary mechanism. The diffusive CH4 flux at the sea-air interface was 12.3–816.2 µmol/m2 d, over the range of the sea-air fluxes previously reported from other seagrass meadows. This was related to relatively higher dissolved CH4 concentrations (11.6–258.2 nmol/L) in a mostly closed lagoon with restricted water exchange. This study emphasizes seagrass meadows in the subtropical hypersaline lagoon as a source of atmospheric CH4, providing insights into the interactions between seagrass ecosystems and methane dynamics, with potential implications for seagrass meadow management and conservation efforts. [ABSTRACT FROM AUTHOR]

The high-intensity partial pressure of CO2 (pCO2) in karst underground rivers rapidly releases in open-flow sections. This is an important process affecting the global karst carbon cycle. This study focuses on the diurnal variation patterns and driving factors of CO2 exchange flux at the water–air interface in the open-flow sections of typical karst underground rivers in southwestern China. The inorganic carbon in water and water–air interface exchange fluxes are observed. Three representative survey stations, i.e., the outlet of the underground river (Q1), the river sections without submerged plants (H1), and the river sections with submerged plants (H2), are selected to study the CO2 exchange process and its influencing factors. The results show that the CO2 release flux at Q1 exhibits high pressure in the daytime and low pressure in the nighttime, while H1 and H2 exhibit the opposite pattern. The photosynthesis of submerged plants significantly inhibits the carbon release flux of the river, and in the river sections where submerged plants are distributed, their biological effects have inhibited approximately 0.131 Tg C/yr of carbon emissions. This study emphasizes the significant contribution of submerged plants in restraining the release of CO2, thereby promoting carbon sequestration and storage in karst water systems. [ABSTRACT FROM AUTHOR]

As a volatile organic compound, nitrobenzene has high vapor pressure and low boiling point, and it is very volatile when it enters the water body and enters the air. The mass transfer of VOCs at the water-air interface is a complex process of transboundary transport. In this paper, the effects of water temperature, interface turbulence, surfactant concentration, and humic acid concentration on the volatilization of nitrobenzene at the water-air interface were investigated. Under the influence of temperature, the volatilization of nitrobenzene accorded with the first-order kinetic equation. When the temperature increased from 5 ℃ to 25 ℃, the volatilization rate of nitrobenzene increased by 2.03 times. Temperature for volatilization rate constant was in accordance with the Arrhenius equation. The water-gas distribution of volatile organic compounds was in accordance with the Boltzman equation. Under the same temperature conditions, when the agitating intensity increased from 0 r/min to 250 r/min, the volatilization rate constant of nitrobenzene increased by 1.51 times. When the surfactant is greater than the critical micelle concentration, the volatilization rate constant of nitrobenzene decreases with the increase of surfactant. When the concentration of humic acid increased from 100 mg/L to 500 mg/L, the half-life increased by 1.14 h, and the volatilization rate decreased by 1.14 h, reduced by 17%. The results showed that the increase of temperature and the intensification of stirring had a significant promoting effect on the volatilization of nitrobenzene, while the surfactant and humic acid both played an inhibitory effect on the volatilization of nitrobenzene. [ABSTRACT FROM AUTHOR]

The significance of CO2 emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO2 emission flux in a catchment, little research has been carried out to investigate the spatio-temporal variations in CO2 emissions in view of a water continuum. Here, we systematically compared the differences and control factors of CO2 degassing across the water–air interface of a spring–river–lake continuum in the discharge area of Baotuquan Spring in July 2017, which is a typical temperate karst spring area in Jinan city, northern China, using hydrogeochemical parameters, stable carbon isotope values, and CO2 degassing flux. Affected by the pCO2 concentration gradient between the water and ambient air, the spring water showed a high CO2 degassing flux (166.19 ± 91.91 mmol/(m2 d)). After the spring outlet, the CO2 degassing flux in the spring-fed river showed a slight increase (181.05 ± 155.61 mmol/(m2 d)) due to river flow rate disturbance. The river flow rate was significantly reduced by the "blockage" of the lake, which promoted the survival and reproduction of phytoplankton and provided favorable conditions for aquatic plant photosynthesis, increasing the plankton biomass in the lake to 3383.79 × 104/L. In addition, the significant decrease in the dissolved inorganic carbon (DIC) concentration and the increase in the δ13CDIC values in the lake also indicated that the photosynthesis of the lake's aquatic plants resulted in a significant decrease in the pCO2 concentration, thus limiting the amount of CO2 off-gassing (90.56 ± 55.03 mmol/(m2 d)). [ABSTRACT FROM AUTHOR]

Extreme impedance mismatch causes sound insulation at water–air interfaces, limiting numerous cross‐media applications such as ocean‐air wireless acoustic communication. Although quarter‐wave impedance transformers can improve transmission, they are not readily available for acoustics and are restricted by the fixed phase shift at full transmission. Here, this limitation is broken through impedance‐matched hybrid metasurfaces assisted by topology optimization. Sound transmission enhancement and phase modulation across the water–air interface are achieved independently. Compared to the bare water–air interface, it is experimentally observed that the average transmitted amplitude through an impedance‐matched metasurface at the peak frequency is enhanced by ≈25.9 dB, close to the limit of the perfect transmission 30 dB. And nearly 42 dB amplitude enhancement is measured by the hybrid metasurfaces with axial focusing function. Various customized vortex beams are experimentally realized to promote applications in ocean‐air communication. The physical mechanisms of sound transmission enhancement for broadband and wide‐angle incidences are revealed. The proposed concept has potential applications in efficient transmission and free communication across dissimilar media. [ABSTRACT FROM AUTHOR]

Abstract Extreme impedance mismatch causes sound insulation at water–air interfaces, limiting numerous cross‐media applications such as ocean‐air wireless acoustic communication. Although quarter‐wave impedance transformers can improve transmission, they are not readily available for acoustics and are restricted by the fixed phase shift at full transmission. Here, this limitation is broken through impedance‐matched hybrid metasurfaces assisted by topology optimization. Sound transmission enhancement and phase modulation across the water–air interface are achieved independently. Compared to the bare water–air interface, it is experimentally observed that the average transmitted amplitude through an impedance‐matched metasurface at the peak frequency is enhanced by ≈25.9 dB, close to the limit of the perfect transmission 30 dB. And nearly 42 dB amplitude enhancement is measured by the hybrid metasurfaces with axial focusing function. Various customized vortex beams are experimentally realized to promote applications in ocean‐air communication. The physical mechanisms of sound transmission enhancement for broadband and wide‐angle incidences are revealed. The proposed concept has potential applications in efficient transmission and free communication across dissimilar media.

The high-intensity partial pressure of CO2 (pCO2) in karst underground rivers rapidly releases in open-flow sections. This is an important process affecting the global karst carbon cycle. This study focuses on the diurnal variation patterns and driving factors of CO2 exchange flux at the water–air interface in the open-flow sections of typical karst underground rivers in southwestern China. The inorganic carbon in water and water–air interface exchange fluxes are observed. Three representative survey stations, i.e., the outlet of the underground river (Q1), the river sections without submerged plants (H1), and the river sections with submerged plants (H2), are selected to study the CO2 exchange process and its influencing factors. The results show that the CO2 release flux at Q1 exhibits high pressure in the daytime and low pressure in the nighttime, while H1 and H2 exhibit the opposite pattern. The photosynthesis of submerged plants significantly inhibits the carbon release flux of the river, and in the river sections where submerged plants are distributed, their biological effects have inhibited approximately 0.131 Tg C/yr of carbon emissions. This study emphasizes the significant contribution of submerged plants in restraining the release of CO2, thereby promoting carbon sequestration and storage in karst water systems.

The temporal and spectral characteristics of nanosecond laser-induced underwater acoustic shockwave for varying input laser energies are obtained. The underwater acoustic shockwave results in reflection and transmission at the water-air interface due to enormous acoustic impedance mismatching between the water and air. With increasing input laser energies, the peak-to-peak overpressures of the reflected and transmitted signals increase linearly. The relationship between the reflected and transmitted acoustic energy coefficients across the water-air interface and the incident laser energy is studied. The advantage of power spectral density in classifying reflected and transmitted signals is based on their peak frequency and full width at half maximum (FWHM). With increasing incident laser energy, the FWHM decreases, and the area under the curve increases for reflected and transmitted signals. In addition to the experimental investigation, finite element analysis (FEA) was used to visualize underwater acoustic signal reflection and transmission at the interface. Experimental data is used as input for FEA in visualizing the acoustic signal in the spatio-temporal domain at the water-air interface. These studies could also be useful for understanding the blast wave evolution of underwater explosions and their interactions at the interfaces. [ABSTRACT FROM AUTHOR]

This paper presents the results of detailed studies of the processes of droplet formation and its characteristics under conditions of artificially induction of a bag-breakup fragmentation event. A shadow imaging method was used in combination with the high-speed video filming of the side-view fragmentation process. Trajectories and ejection velocity characteristics of the formed droplets are determined by identifying particles in consecutive frames with combined use of Particle Imaging Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). Based on the results of trajectory processing, the distributions of droplet velocities for the selected regions are obtained, and estimates of the ejection velocities at various heights are proposed. [ABSTRACT FROM AUTHOR]

Using a similar approach as Korteweg and de Vries, [19], we obtain periodic solutions expressed in terms of the Jacobi elliptic function cn, [3], for the self-focusing and defocusing one-dimensional cubic nonlinear Schrödinger equations. We will show that solitary wave solutions are recovered through a limiting process after the elliptic modulus of the Jacobi elliptic function cn that describes the periodic solutions for the self-focusing nonlinear Schrödinger model.

Inland water ecosystems are unique, whereby water level changes can lead to variance in greenhouse gas (GHG) emissions. The GHG circulation intensity of inland waterbodies is high, so different water depths affect the temperature sensitivity of greenhouse gases, and have different cooling effects on CO 2 storage and warming effects on CH 4 emissions, being a typical GHG conversion channel. This study systematically reveals geographical GHG emission patterns from inland waterbodies and GHG impact mechanisms from regional waterbodies. Special emphasis is also paid to compounded environmental impact changes on GHG emissions under water level regulations. Additionally, we explore how increases in primary productivity can convert aquatic ecosystems from CO 2 sources to CO 2 sinks. However, GHG formation and emissions under ecological reservoir water level fluctuations in flood-ebb zones, intertidal tidal zones, wetlands, and lacustrine systems remain uncertain compared with those under natural hydrological conditions. Therefore, mechanisms that control GHG exchange and production processes under water level changes must first be determined, especially regarding post flood hydrological-based drying effects on GHG flux at the water-air interface. Finally, we recommend instituting environmental management and water-level control measures to reduce GHG emissions, which are favorable for minimizing GHG flux while protecting ecosystem functions and biodiversity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study addressed the challenges of cost and portability in synchronous monitoring water quality and greenhouse gas emissions in paddy-dominated regions by developing a novel Internet of Things (IoT)-based monitoring system (WG-IoT-MS). The system, equipped with low-cost sensors and integrated intelligent algorithms, enabled real-time monitoring of dissolved N 2 O concentrations. Combined with an air-water gas exchange model, the system achieved efficient monitoring and simulation of CO 2 and N 2 O emissions from agricultural water bodies while reducing monitoring costs by approximately 60 %. The proposed method was validated in paddy-dominated regions in Danyang, China. Results indicated the excellence of the dissolved N 2 O concentration model based on support vector regression, demonstrating accurate predictions within a concentration range of 2.003 to 13.247 μg/L. Notably, the model maintained acceptable predictive accuracy (R 2 > 0.70) even when some variables were partially absent (with the number of missing variables < 2 and the missing proportion (MP) ≤ 50 %), making up for the data loss caused by sensor malfunctions. Furthermore, the model performed well (R 2 > 0.80) when testing data sourced from paddy fields and lakes. Finally, CO 2 and N 2 O emissions were successfully monitored, with the results validated using a floating chamber method (R 2 > 0.70). The method provides crucial technical support for quantitative assessment of water quality and greenhouse gas emissions in paddy-dominated regions, laying a foundation for formulating effective emission reduction strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The significance of CO2 emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO2 emission flux in a catchment, little research has been carried out to investigate the spatio-temporal variations in CO2 emissions in view of a water continuum. Here, we systematically compared the differences and control factors of CO2 degassing across the water–air interface of a spring–river–lake continuum in the discharge area of Baotuquan Spring in July 2017, which is a typical temperate karst spring area in Jinan city, northern China, using hydrogeochemical parameters, stable carbon isotope values, and CO2 degassing flux. Affected by the pCO2 concentration gradient between the water and ambient air, the spring water showed a high CO2 degassing flux (166.19 ± 91.91 mmol/(m2 d)). After the spring outlet, the CO2 degassing flux in the spring-fed river showed a slight increase (181.05 ± 155.61 mmol/(m2 d)) due to river flow rate disturbance. The river flow rate was significantly reduced by the “blockage” of the lake, which promoted the survival and reproduction of phytoplankton and provided favorable conditions for aquatic plant photosynthesis, increasing the plankton biomass in the lake to 3383.79 × 104/L. In addition, the significant decrease in the dissolved inorganic carbon (DIC) concentration and the increase in the δ13CDIC values in the lake also indicated that the photosynthesis of the lake’s aquatic plants resulted in a significant decrease in the pCO2 concentration, thus limiting the amount of CO2 off-gassing (90.56 ± 55.03 mmol/(m2 d)).

The design of grouting engineering in practice is either based on conventional soil mechanics or empirical procedures ignoring the effect of degree of saturation (water content). In this study, a series of laboratory-pressurized grouting tests were conducted on unsaturated sand to reveal the influence of soil water content on the grouting characteristics. With combination of direct shear tests at constant water content, water retention tests as well as microscopy observations, the mechanisms that controlling the strength and in turn the grouting characteristics in unsaturated sand were interpreted from the perspective of water–air interface. It was found that the non-monotonic phenomena of grouting characteristics (injectability and diffusion characteristics) with increasing water content were strongly dependent on the shear strength, which is influenced by the apparent cohesion induced by capillary mechanisms relating to the water–air interface. The threshold value of the injectability and diffusion pattern is corresponding to the boundary of the two transition zones (two different desaturation mechanisms) in the water retention curve. In the primary transition zone, the water phase is interconnected with air bulbs entrapped. With the drainage of bulk water in the large pores, the amount of water menisci increases, generating larger and larger surface tension force between particles. Therefore, less and less grout was injected as the bearing capacity and shear strength increase. However, in the second transition zone, with the drainage of menisci water, the menisci area of each pores decreases, inducing less and less surface tension force. Thus, more and more grout was injected as the bearing capacity and shear strength decrease. It is hoped that the work in this study will facilitate researching the grouting mechanisms in unsaturated soil, thus optimizing the grouting parameters in engineering practice. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• We developed an underwater-to-air optical model using Monte Carlo (MC) numerical method to investigate the effects of calm sea and rough sea with wind-driven waves and bubbles on the OWC system. • The accuracy of ECKV model was verified by comparison of the modelled and measured data obtained through stereo imaging techniques under various sea and wind conditions. • The analysis of received power at the detector was done for the above scenarios at different wind speeds and time intervals and compared with another sets of results obtained for the calm sea and rough sea with gravity waves, statistically approximated by the Cox and Munk (CM) model. • The received power showed variations caused by surface waves using the ECKV method and remains nearly constant for the calm surface and CM model. • The analysis of the impacts of bubbles and water–air interface on an underwater-to-air OWC system showed that the received power decreased with bubble populations. • The current work provides significant guidance for the development and optimization of underwater-to-air optical communication systems in challenging marine environment conditions. Underwater-to-air Optical Wireless Communication (OWC) systems have emerged as a viable solution for transmitting data from Unmanned Underwater Vehicles (UUVs) to Unmanned Aerial Vehicles (UAVs) in order to meet the increasing demands of marine technology applications. However, the field of Underwater-to-air OWC poses significant challenges due to harsh marine environmental conditions and significant signal attenuation caused by particulates and bubbles in the water medium. Implementing an underwater-to-air OWC system in a marine environment is significantly challenged by the turbulent nature of gravity waves. In this paper, we developed an underwater-to-air optical model using the Monte Carlo (MC) numerical method to investigate the effects of calm sea and rough sea with wind-driven waves and bubbles on the OWC system. MC simulations were performed using the seawater optical properties obtained from field measurements in the Bay of Bengal and Southern Ocean waters. The optical properties of bubbles were derived from a popular Hall-Novarini (HN) model. A three-dimensional theoretical ECKV (Elfouhaily, Chapron, Katsaros, and Vandemark) wave model that employs the Fast Fourier Transform (FFT) technique was used. The accuracy of this model was verified by comparison of the modelled and publicly available measured data obtained through stereo imaging techniques under various sea and wind conditions. The results showed that the ECKV model accurately captured spatial and temporal distributions of waves at the water–air interface, which is crucial for understanding the laser beam propagation in the real oceanic medium. The analysis of received power at the detector was done for the above scenarios at different wind speeds and time intervals and compared with another set of results obtained for the calm sea and rough sea with gravity waves, statistically approximated by the Cox and Munk (CM) model. The surface waves significantly reduced the received power as compared to the calm sea. The received power showed variations caused by surface waves using the ECKV method and remains nearly constant for the calm surface and CM model. Further analysis of the impacts of bubbles and water–air interface on an underwater-to-air OWC system showed that the received power decreased with bubble populations. These results provide significant guidance for developing and optimising underwater-to-air optical communication systems in challenging marine environment conditions. [ABSTRACT FROM AUTHOR]

Revealing the magnitude, dynamics, and influencing factors of CO 2 emissions across the water-air interface in karst water with high frequency is crucial for accurately assessing the carbon budget in a karst environment. Due to the limitations of observation methods, the current research is still very insufficient. To solve the above problems and clarify the main influencing factors of CO 2 emission in karst water, this study selected Dalongdong (DLD) Reservoir, located in the typical karst peak and valley area in southwest China, to carry out a multi-parameter high-frequency monitoring study from January to December 2021, and used the thin boundary model method to estimate the CO 2 flux across the water-air interface (CF). The average annual flux of DLD reservoir is 84.48 mmol·(m2·h)−1, which represents a CO 2 source overall. However, during the stratification period in August, there is a transient carbon sink due to negative CO 2 emission. The alteration of thermal stratification in water is crucial in regulating the seasonal variation of CF. Meanwhile, the diurnal variation is significantly influenced by changes in hydrochemical parameters during the thermal stratification stage. Compared to low wind speeds (<3 m/s), high wind speeds (≥3 m/s) have a greater impact on the CO 2 flux. Furthermore, high-frequency continuous data revealed that the reservoir triggered a CO 2 pulse emission during the turnover process, primarily at night, leading to unusually high CO 2 flux values. It is of great significance to monitor and reveal the process, flux, and control factors of CO 2 flux in land water at a high-frequency strategy. They will help improve the accuracy of regional or watershed carbon budgets and clarify the role of global land water in the global carbon budget. [Display omitted] • CO 2 emission flux shows seasonal and diurnal variations at hourly high resolution. • "Pulse" events are induced during the thermal stratification fading period. • CF changes are impacted by temperature, wind speed, and biogeochemical processes. • The total net CO 2 emission is about 2.43 Gg in 2021. [ABSTRACT FROM AUTHOR]

In this study, a pressurized, water-filled impedance tube (WFIT) was developed to measure the reflection coefficients of sound-absorbing materials under various hydrostatic pressures. The developed WFIT was calibrated using a two-microphone, three-parameter calibration method (3PCM). The accuracy and repeatability of the measured reflection coefficients for the water–air interface in the WFIT were determined by comparing these coefficients with corresponding theoretical reflection coefficients. The WFIT was then used to measure the acoustic reflection coefficient of a porous rubber specimen on three dates, and the corresponding measurement results exhibited satisfactory repeatability. The aforementioned impedance tube was also used to measure the reflection coefficient of a porous rubber specimen under a hydrostatic pressure of 4 Patm three times on the same day, and one time each on three days, using the same experimental setup and measurement procedure. The results obtained in the aforementioned tests also exhibited satisfactory repeatability. Finally, the WFIT was used to measure the reflection coefficients of porous rubber specimens with various thicknesses under different hydrostatic pressures. The results of this study indicate that the developed WFIT calibrated with the 3PCM can achieve suitable repeatability in the measurement of the reflection coefficients of sound-absorbing materials under various hydrostatic pressures. [ABSTRACT FROM AUTHOR]

This paper presents the results of detailed studies of the processes of droplet formation and its characteristics under conditions of artificially induction of a bag-breakup fragmentation event. A shadow imaging method was used in combination with the high-speed video filming of the side-view fragmentation process. Trajectories and ejection velocity characteristics of the formed droplets are determined by identifying particles in consecutive frames with combined use of Particle Imaging Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). Based on the results of trajectory processing, the distributions of droplet velocities for the selected regions are obtained, and estimates of the ejection velocities at various heights are proposed.

The white colour morph of the black bear (Ursus americanus kermodei) occurring on islands on the coast of British Columbia, western Canada, captures more salmon (Oncorhynchus spp.) than does the black morph and is hypothesized to have reduced contrast against the sky from the visual perspective of the salmon. We tested this hypothesis in a natural salmon stream by recording the number and proximity of chum salmon (Oncorhynchus keta) approaches (N = 1617 fish, 91 trials) towards life-size bear models differing in body and leg coloration under a mixed forest-sky canopy. Although salmon approached the white models at a much higher rate than black models, consistent with camouflage, we found greater abrupt evasions to the black models, largely independent of their contrast against the above-surface or below-surface backgrounds. Upward-facing sub-surface video-imaging through the rippled water-air interface indicated major visual fragmentation of the model's integrity. We suggest that increased evasiveness to black models reflects an evolutionary response due to 3+ million years of trophic interaction between salmon and bears, and that the major differences between calm vs. rippled conditions through the optical cone (Snell's window) at the water-air interface remains a largely unexplored theme in assessing foraging preferences and adaptive coloration within and among species using the water-air interface. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

While animals generally move through the aquatic environment by propelling themselves through the water or walking on submerged substrates, some have evolved the unique capacity to move along the water–air interface. This is because cohesive forces between water molecules cause the surface to be in tension, providing a physical substrate that can be used for support and pushed against for horizontal movement. Herein, we report on the use of the underside of the water's surface for locomotion in an unidentified Australian beetle (likely family: Hydrophilidae). Field observations revealed that the beetle was able to rest and move along the surface of an ephemeral pool inverted without penetrating the surface above. The beetle possessed a layer of trapped air along its abdomen and moved forward by walking, with deformations of the water's surface apparent each time a leg made contact. This appears to be the first visual evidence illustrating the ability of aquatic beetles to directly rest and walk on the underside of the water's surface. We propose that the air bubbles located on the abdomen and/or legs may be providing the upward force necessary for the beetle to be pushed against the underside of the water's surface. The water's surface seems to be acting as a support for the beetle, with the force needed for forward movement generated by the beetle's legs as each transition between the stance and swing phases of walking. Our work adds to the small number of observations of animals using the underside of the water's surface to move and highlights the likely importance of surface tension for locomotion on either side of the water–air interface. [ABSTRACT FROM AUTHOR]

• Discrete metasurface is proposed for water-air sound enhancement. • Excellent wide-angle transmission is observed for discrete units. • Influences of random immersion and bending effects are discussed. This study proposes a discrete metasurface for extreme sound transmission based on the impedance matching theory. The aim is to overcome the extreme mismatch of acoustic impedance at the water-air interface. By employing topology optimization, discrete unit cells with different aspect ratios are inversely designed with unitary sound transmission. The unit cell of continuous metasurface is also obtained for comparison. After analyzing the wide-angle performance of discrete unit cells, the enhancement of sound transmission of the samples at the water-air interface is experimentally measured. It is evident that the discrete metasurface significantly enhances sound transmission compared to the bare water-air interface. And the transmission amplitude is relatively larger than that of the continuous sample. Experimental results are generally agreement with numerical ones when the viscosity of the sample is considered. Furthermore, the resonate frequency shifts observed during the experiment are discussed. They can be primarily attributed to the random immersion of unit cells for discrete metasurface and the bending of continuous metasurface, respectively. The present work will greatly promote the practical application of acoustic metasurfaces in transmedia communication and sensing. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, a pressurized, water-filled impedance tube (WFIT) was developed to measure the reflection coefficients of sound-absorbing materials under various hydrostatic pressures. The developed WFIT was calibrated using a two-microphone, three-parameter calibration method (3PCM). The accuracy and repeatability of the measured reflection coefficients for the water–air interface in the WFIT were determined by comparing these coefficients with corresponding theoretical reflection coefficients. The WFIT was then used to measure the acoustic reflection coefficient of a porous rubber specimen on three dates, and the corresponding measurement results exhibited satisfactory repeatability. The aforementioned impedance tube was also used to measure the reflection coefficient of a porous rubber specimen under a hydrostatic pressure of 4 Patm three times on the same day, and one time each on three days, using the same experimental setup and measurement procedure. The results obtained in the aforementioned tests also exhibited satisfactory repeatability. Finally, the WFIT was used to measure the reflection coefficients of porous rubber specimens with various thicknesses under different hydrostatic pressures. The results of this study indicate that the developed WFIT calibrated with the 3PCM can achieve suitable repeatability in the measurement of the reflection coefficients of sound-absorbing materials under various hydrostatic pressures.

It was previously shown that hydrogen peroxide (H2O2) is spontaneously produced in micrometer-sized water droplets (microdroplets), which are generated by atomizing bulk water using nebulization without the application of an external electric field. Here we report that H2O2 is spontaneously produced in water microdroplets formed by dropwise condensation of water vapor on low-temperature substrates. Because peroxide formation is induced by a strong electric field formed at the water-air interface of microdroplets, no catalysts or external electrical bias, as well as precursor chemicals, are necessary. Time-course observations of the H2O2 production in condensate microdroplets showed that H2O2 was generated from microdroplets with sizes typically less than ∼10 μm. The spontaneous production of H2O2 was commonly observed on various different substrates, including silicon, plastic, glass, and metal. Studies with substrates with different surface conditions showed that the nucleation and the growth processes of condensate water microdroplets govern H2O2 generation. We also found that the H2O2 production yield strongly depends on environmental conditions, including relative humidity and substrate temperature. These results show that the production of H2O2 occurs in water microdroplets formed by not only atomizing bulk water but also condensing water vapor, suggesting that spontaneous water oxidation to form H2O2 from water microdroplets is a general phenomenon. These findings provide innovative opportunities for green chemistry at heterogeneous interfaces, self-cleaning of surfaces, and safe and effective disinfection. They also may have important implications for prebiotic chemistry. [ABSTRACT FROM AUTHOR]

Researchers have a great interest in determining the characteristics of shock wave propagation by an underwater explosion. But it involves complex physical processes near boundaries during the underwater explosion. The major issues are explosions, fluid interactions, fluid–structure interactions, and shock wave propagation. In general, the underwater explosion leads to shock wave propagation and it moves toward two types of boundaries. The first one is the free surface of the water, and the second is fluid–structure interaction. The underwater explosion also deals with bulk cavitation behind shock waves. This paper deals with the shock wave propagation and bulk cavitation because of the underwater explosion near the free surface. The computation and analytical results of the underwater explosion were discussed and compared. Also, polynomial and Mie–Gruneisen (shock) equation of state (EOS) of water was implemented to determine the incompressible nature of water and to get realistic results. The results of both the EOS of water were compared against each other and validated against analytical results. These results show that the equation of state of water and water–air interface has a significant influence on the characteristics of the shock wave propagation and unsteady cavitation near the free surface. [ABSTRACT FROM AUTHOR]

The effect of anomalous transparency on the passage of sound from water to air is considered. A mathematical model is used to calculate the coefficient of pressure transmission through the water–air interface taking into account the influence of inhomogeneous plane waves. The features of the acoustic field in air are shown for an underwater source located at a distance from the media interface smaller than the wavelength. The theoretical dependences of the pressure transmission coefficient on the wave distance from the source to the interface are given. The conditions and methods for measuring the coefficient of transmission of spherical waves through a planar interface are described. The experimental dependences of the pressure transmission coefficient on the radiation frequency and depth of the source are presented. Oscillograms of acoustic signals transmitted from water to air are shown. [ABSTRACT FROM AUTHOR]

A storage tunnel system is the critical infrastructure of urban drainage systems, in which the rapid filling of water and release of trapped air can lead to the "geyser" phenomenon. This may cause serious damage, threatening both system operation and personal safety. In this paper, a detailed experimental study was carried out based on synchronous recorded video images and digital image processing technology. According to experimental observations, gas-flow geysers and surge-type geysers were analyzed deeply. The former is caused by high-speed gas flow and is accompanied by a pressure drop; the latter is caused by surge pressure and is accompanied by a pressure increase. The free surface velocity of the gas-flow geyser is mainly affected by the external pressure, the air volume, the diameter of the shaft, and the height of the water column, and the geyser phenomenon cannot occur when the air column is mainly dominated by buoyancy. Based on dimensional analysis and data fitting, this paper presents the empirical formula for the free surface velocity and the interface net velocity and puts forward the critical occurrence conditions for the gas-flow geyser. [ABSTRACT FROM AUTHOR]

Hydrophobins (HPs) are small secreted fungal proteins possibly involved in several processes such as formation of fungal aerial structures, attachment to hydrophobic surfaces, interaction with the environment and protection against the host defense system. The genome of the necrotrophic plant pathogen Fusarium graminearum contains five genes encoding for HPs (FgHyd1-5). Single and triple FgHyd mutants were produced and characterized. A reduced growth was observed when the ΔFghyd2 and the three triple mutants including the deletion of FgHyd2 were grown in complete or minimal medium. Surprisingly, the growth of these mutants was similar to wild-type when grown under ionic, osmotic or oxidative stress conditions. All the mutant strains confirmed the ability to develop conidia and perithecia, suggesting that the FgHyds are not involved in normal development of asexual and sexual structures. A reduction in the ability of hyphae to penetrate through the water-air interface was observed for the single mutants ΔFghyd2 and ΔFghyd3 as well as for the triple mutants including the deletion of FgHyd2 and FgHyd3. Besides, ΔFghyd3 and the triple mutant ΔFghyd234 were also affected in the attachment to hydrophobic surface. Indeed, wheat infection experiments showed a reduction of symptomatic spikelets for ΔFghyd2 and ΔFghyd3 and the triple mutants only when spray inoculation was performed. This result could be ascribed to the affected ability of mutants deleted of FgHyd2 and FgHyd3 to penetrate through the water-air interface and to attach to hydrophobic surfaces such as the spike tissue. This hypothesis is strengthened by a histological analysis, performed by fluorescence microscopy, showing no defects in the morphology of infection structures produced by mutant strains. Interestingly, triple hydrophobin mutants were significantly more inhibited than wild-type by the treatment with a systemic triazole fungicide, while no defects at the cell wall level were observed.

We have shown that, unlike bulk water, tiny water droplets (microdroplets) cause reduction of gold ions (1) as well as a number of organic compounds (2). Evidence has been presented that the source of electrons arises from hydroxyl anions (OH-) at or near the surface of the microdroplet (2). We report the formation of hydrogen peroxide (H2O2) in aqueous microdroplets and suggest that the observed H2O2 results from the recombination of hydroxyl radicals (OH) at or near the air- water interface of aqueous microdroplets sprayed into roomtemperature air. Hydrogen peroxide is a commodity chemical that has many different applications, such as chemical synthesis or as a disinfectant, in mining and metal processing, as well as pulp and textile bleaching (3). H2O2 has often been touted as a green oxidant because, upon decomposition, it generates oxygen and water (4). However, the most common industrial method (~95% worldwide) for 2O2 synthesis (5), the 2-step anthraquinone process, cannot be considered green (6) because organic wastes are generated from inefficient oxidation of the anthraquinone. Some advances in H2O2 synthesis have focused on catalytically combining 2 and 2 (7, 8). Other methods electrochemically generate H2O2 by electrolysis of O2 at the anode (9, 10), or photocatalytically generate reactive superoxo radicals (11). Recently, H2O2 was formed from a reaction between plasma and a water surface (12). However, these direct synthesis methods of H2O2 have limitations, including the use of precious metal catalysts, low yields, required 2 supply, and high energy consumption (13, 14). In what follows, we report the direct, spontaneous generation of H22 from aqueous microdroplets in the absence of applied voltage, catalyst, or any other added chemicals. We alsospeculate about the nature of the mechanism responsible for these observations. [ABSTRACT FROM AUTHOR]

The measurements of the surface tension of aqueous solutions of 10 monoterpene alcohols, MAs: (−)-β-citronellol, geraniol, tetrahydrolinalool, linalool, (−)-menthol, (−)-terpinen-4-ol, p-cymene-8-ol, α-terpineol, isoborneol and (−)-borneol were made at T = 293 K. On the basis of the obtained results the values of the adsorption constant, the excluded area per molecule at the interface and the interaction parameter were determined by fitting the experimental data to various adsorption models. Next the adsorption free energy of studied MAs was determined and discussed in terms of the preferred orientation of studied MAs at the water–air interface and molecular structure of MAs. [ABSTRACT FROM AUTHOR]

CO 2 fluxes across water-air interfaces of river systems play important roles in regulating the regional and global carbon cycle. However, great uncertainty remains as to the contribution of these inland water bodies to the global carbon budget. Part of the uncertainty stems from limited understanding of the CO 2 fluxes at diurnal and seasonal frequencies caused by aquatic metabolism. Here, we measured surface water characteristics (temperature, pH, and DO, DIC, Ca 2 + concentrations) and CO 2 fluxes across the air-water interface at two transects of Guijiang River, southwest China to assess the seasonal and diurnal dynamics of fluvial carbon cycling and its potential role in regional and global carbon budgets. The two transects had differing bedrock; DM transect is underlain by carbonate and detrital rock and PY is underlain by pure carbonate. Our results show that the river water both degasses CO 2 to and absorbs CO 2 from the atmosphere in both summer and winter, but the degassing and absorption varied between the two transects. Further, CO 2 fluxes evolve through diurnal cycles. At DM, the river evaded CO 2 from early morning through noon and absorbed CO 2 from afternoon through early morning. At PY in summer, the CO 2 evasion decreased during the daytime and increased at night while in winter at night, CO 2 uptake increased in the morning and decreased in the afternoon but remained relatively stable at night. Although the river is a net source of carbon to the atmosphere (~ 15 mM m − 2 day − 1 ), the evasion rate is the smallest of all reported world's inland water bodies reflecting sequestration of atmospheric carbon through the carbonate dissolution and high primary productivity. These results emphasize the need of seasonal and diurnal monitoring of CO 2 fluxes across water-air interface, particularly in highly productive rivers, to reduce uncertainty in current estimates of global riverine CO 2 emission. [ABSTRACT FROM AUTHOR]

This paper presents an improved annular water-air jet pump concept design through integrating a self-induced oscillation mixing chamber with the conventional annular jet pump (AJP). The internal flow characteristics for both conventional and improved AJP were numerically investigated and compared by a validated computational fluid dynamics model. The numerical comparison demonstrated an approximately 10% pumping performance increase compared with the conventional pump, which is mostly attributed to the improved mass and energy transfer along the oscillating phase interface. Furthermore, transient flow analysis was conducted to resolve the unsteady self-introduced oscillation. The results revealed the self-introduced oscillation induces a continuous break-up and formation of fresh water-air interfaces, which exhibits a periodic feature with a dominant frequency of 147 Hz for the current design under given operational conditions. This study contributes toward a better understanding of the internal annular water-air jet pump flow patterns, and also demonstrates the feasibility of incorporating self-introduced oscillation chamber into AJP design. [ABSTRACT FROM AUTHOR]

An immersed-body method is developed here to model fluid–structure interaction for multiphase viscous flows. It does this by coupling a finite element multiphase fluid model and a combined finite–discrete element solid model. A coupling term containing the fluid stresses is introduced within a thin shell mesh surrounding the solid surface. The thin shell mesh acts as a numerical delta function in order to help apply the solid–fluid boundary conditions. When used with an advanced interface capturing method, the immersed-body method has the capability to solve problems with fluid–solid interfaces in the presence of multiphase fluid–fluid interfaces. Importantly, the solid–fluid coupling terms are treated implicitly to enable larger time steps to be used. This two-way coupling method has been validated by three numerical test cases: a free falling cylinder in a fluid at rest, elastic membrane and a collapsing column of water moving an initially stationary solid square. A fourth simulation example is of a water–air interface with a floating solid square being moved around by complex hydrodynamic flows including wave breaking. The results show that the immersed-body method is an effective approach for two-way solid–fluid coupling in multiphase viscous flows. [ABSTRACT FROM AUTHOR]

Tracy et al. (2015, doi: ) assumed in their recent paper that water velocity at the water-air interface is zero in their pore-scale simulations of water flow in 3-D soil images acquired using X-ray computed tomography. We comment that such a treatment is physically wrong, and explain that it is the water-velocity gradient in the direction normal to the water-air interface, rather than the water velocity, that should be assumed to be zero at the water-air interface if one needs to decouple the water flow and the air flow. We analyze the potential errors caused by incorrectly taking water velocity at the water-air interface zero based on two simple examples, and conclude that it is not physically sound to make such a presumption because its associated errors are unpredictable. [ABSTRACT FROM AUTHOR]

A mathematical model for describing the temperature distribution in the near-surface layer at the water-air interface is proposed. The model is composed based on the theory of contrast structures. Using numerical calculations, the temperature distribution in a 10-cm wide near-boundary layer has been obtained. The calculation results coincide well with the experimental data. [ABSTRACT FROM AUTHOR]

Water interfaces provide the platform for many important biological, chemical, and physical processes. The water-air interface is the most common and simple aqueous interface and serves as a model system for water at a hydrophobic surface. Unveiling the microscopic (<1 nm) structure and dynamics of interfacial water at the water-vapor interface is essential for understanding the processes occurring on the water surface. At the water interface the network of very strong intermolecular interactions, hydrogen-bonds, is interrupted and the density of water is reduced. A central question regarding water at interfaces is the extent to which the structure and dynamics of water molecules are influenced by the interruption of the hydrogen-bonded network and thus differ from those of bulk water. Herein, we discuss recent advances in the study of interfacial water at the water-air interface using laser-based surface-specific vibrational spectroscopy. [ABSTRACT FROM AUTHOR]

It was shown in recent experiments and molecular dynamics (MD) simulations that Schrage equation predicts evaporation and condensation rates of water in the absence of a non-condensable gas with good accuracy. However, it is not clear whether Schrage equation is still accurate or even valid for quantifying water evaporation and condensation rates in air. In this work, we carry out MD simulations to study steady-state evaporation and condensation of water at a planar water-air interface. The simulation results show that the evaporation and condensation fluxes of water in the presence of air are still in a good agreement with the predictions from Schrage equation. From Schrage equation and Stefan's law of mass diffusion, we derive an analytical expression for the effective thermal conductivity of a planar heat pipe. The analytical prediction of the dependence of effective thermal conductivity on heat pipe length and density of non-condensable gas is corroborated by our MD simulation results and recent experimental data. [ABSTRACT FROM AUTHOR]

The chamber method is widely used to measure CO 2 and CH 4 flux in inland water. However, the designs of chamber used in various studies are different and lack unified standards, which would affect the observation results. To clarify the impacts of chamber characteristics, including light transmittance, air pressure difference inside and outside the chamber, and gas mixing degree in the chamber, on CO 2 and CH 4 flux measurements at the water-air interface, we compared the effects of transparent/opaque chamber, the chamber with/without air pressure equalizing device and fan on CO 2 and CH 4 flux measurements in the aquaculture pond, based on the multi-channel closed dynamic chamber system. The results showed that, during the daytime in summer, compared with the transparent chamber which could measure the actual CO 2 flux, when CO 2 was emitted from the pond, the opaque chamber overestimated the CO 2 flux by 90%; when CO 2 was absorbed by the pond, the opaque chamber underestimated the CO 2 flux by 50%. The CH 4 diffusion flux measured by the opaque chamber was 40% lower than that measured by the transparent chamber. There was no significant difference between CO 2 and CH 4 flux measured by the chamber with and without air pressure equalizing device. CO 2 flux observed by the chamber without fan had poor representativeness, being 20% higher than that observed by the chamber with fan. Moreover, CH 4 flux emitted through different pathways could not be distinguished using the chamber without fan. Therefore, when the chamber method was used to observe the CO 2 and CH 4 flux at the water-air interface, the chamber shall be transparent and be installed with fan.

Plastic debris in the marine environment are the subject of an extensive literature. According to studies dedicated to the determination of plastic litter abundance and to the characterisation of degradation and fragmentation processes, models were used to estimate the global plastic debris abundance and to simulate their transfer and distribution. Despite these efforts, there is still missing plastic in the models used as areas exist where plastic abundance is less than that estimated. In parallel, microplastics presence in the atmosphere and in remote areas was confirmed suggesting long range atmospheric transport. Potentially addressing both these issues, recent literature suggests that microplastics (MPs) and nanoplastics (NPs) can be transferred from the marine environment to the atmosphere via the bursting of air bubbles at the sea surface. Nevertheless, to date there is no direct evidence of this transfer. In this study, we evaluate plastic particles transfer as a function of MPs/NPs characteristics and water composition by simulating the bubble bursting phenomenon in a laboratory reactor. Size distribution of transferred particles were recorded, and their plastic nature was confirmed using electron microscopy. Results show that under tested conditions, the transfer is possible but limited to particles smaller than 1 μm. The influence of the presence of proxies of components of the sea surface microlayer in the water was evaluated showing a higher particle transfer rate in the presence of a surfactant (sodium dodecyl sulfate) and no significant effect of polysaccharides (xanthan gum and dextran). The surface state of the particles can alter their behaviour in the aqueous phase and thus their transfer to the atmosphere. The effect of bubble size was also evaluated showing a higher transfer rate with the smaller bubble size. In addition, experiments performed with grounded polyethylene (PE) samples showed higher transfer for UV-aged PE than for pristine PE. [Display omitted] • Plastic particles are transferred by bubble bursting at the water-air interface. • The transfer is limited to particles smaller than 1 μm in tested conditions. • Under tested conditions, SDS surfactant promotes particle transfer. • Hydrophilic/hydrophobic particle transfer rate varies according to water composition. • UV-aged PE particles are transferred as opposed to pristine PE particles. Plastic particles are transferred by bubble bursting at the water-air interface according to their size, surface properties, and water composition. [ABSTRACT FROM AUTHOR]