Sound attenuation in high mach number oscillating bubble media.

We study theoretically and numerically sound attenuation in bubble-containing media when the bubbles are freely oscillating at high Mach numbers. This paper expands one of the main forms of bubble-related acoustic damping factors by extending the previous theories to higher Mach numbers, further improves the theories of nonlinear sound propagation in bubble-containing media. A nonlinear sound propagation model incorporating second-order liquid compression terms is developed, expressing the sound velocity and density in the medium as a function of the driving pressure, and taking into account the higher-order liquid compression effects on sound propagation. The correctness of the proposed model is verified by comparing with a linear model and a nonlinear model containing only low-order Mach number terms. When the bubble oscillates at a high Mach number, radiation damping, which is directly related to Mach number, becomes the main damping component affecting sound attenuation. The higher the driving amplitude, the stronger the nonlinear effect, and the greater the impact of high-order liquid compression effects on the sound attenuation, the more necessary it is to use the proposed model to calculate the sound attenuation. For high Mach numbers, varying the bubble radius and bubble number density, respectively, the difference between the proposed model and the model containing only low-order Mach number terms in capturing the pressure-dependent attenuation is calculated. Due to stronger radiation damping in smaller bubbles, the effect of compressibility becomes more important. The smaller the bubble radius, the greater the half-quality factor of the curve related to the difference in attenuation calculated by the two models, the more necessary it is to calculate the pressure-dependent attenuation using the proposed model. Here, the half-quality factor is defined as the corresponding frequency bandwidth when the curve falls from the maximum value to 22 times. Without considering the coupling effect between bubbles, the half-quality factor of the curve is not affected by the bubble number density.

Hydrogeochemical characteristics and recharge sources identification based on isotopic tracing of alpine rivers in the Tibetan Plateau.

Alpine rivers originating from the Tibetan Plateau (TP) contain large amounts of water resources with high environmental sensitivity and eco-fragility. To clarify the variability and controlling factors of hydrochemistry on the headwater of the Yarlung Tsangpo River (YTR), the large river basin with the highest altitude in the world, water samples from the Chaiqu watershed were collected in 2018, and major ions, δ2H and δ18O of river water were analyzed. The values of δ2H (mean: -141.4‰) and δ18O (mean: -18.6‰) were lower than those in most Tibetan rivers, which followed the relationship: δ2H = 4.79*δ18O-52.2. Most river deuterium excess (d-excess) values were lower than 10‰ and positively correlated with altitude controlled by regional evaporation. The SO42- in the upstream, the HCO3- in the downstream, and the Ca2+ and Mg2+ were the controlling ions (accounting for >50% of the total anions/cations) in the Chaiqu watershed. Stoichiometry and principal component analysis (PCA) results revealed that sulfuric acid stimulated the weathering of carbonates and silicates to produce riverine solutes. This study promotes understanding water source dynamics to inform water quality and environmental management in alpine regions.

Spatial patterns in water quality and source apportionment in a typical cascade development river southwestern China using PMF modeling and multivariate statistical techniques.

River cascade development is one of the human activities that have the most significant impact on the water environment. However, the mechanism of cascade development affecting river hydrochemical components still needs to be further studied. In this study, water quality index(WQI), positive matrix factorization(PMF) model and multivariate statistical techniques were used to identify the mechanism of cascade development affecting river hydrochemical components in an typical cascade development Rivers, Lancang River, China. The results showed that the water quality of Lancang River is relatively good due to less affected by human activity. The spatial variation of river hydrochemistry is affected by the development of cascade reservoirs, and shows three patterns: irregular variation (pH and DO), fluctuating decreasing (Na+, Cl-, SO42- and HCO3-) and multi-peak variation (TN, TDN, NO3--N and NH4+-N). It's worth noting that the concentration of the most hydrochemical parameters is higher in the upper reaches (less human activities) than that in the middle and lower reaches of river due to the retention effect of the reservoir on the chemical composition. The PMF model outputs revealed that the rock weathering and internal source, sewage and soil nitrogen, and chemical fertilizer were primary material sources of Lancang River. Compared with the natural channel zone (41.0%), the interaction of water-rock has more influence on chemical component in the reservoir area (56.3%), while the contribution of fertilizer (11.2%) to the river hydrochemistry is less. The sites of downstream of the reservoir dam were affected by the retention of the reservoir and the disturbance of the bottom drainage, which leads to the weakening of the influence of the sewage (44.7%) on the river material and the increase of the contribution of fertilizer (25.0%). These results could provide valuable information in controlling the eutrophication of cascade reservoirs and the scientific construction of river cascade reservoirs.

Multiple Isotopes Reveal a Hydrology Dominated Control on the Nitrogen Cycling in the Nujiang River Basin, the Last Undammed Large River Basin on the Tibetan Plateau.

The Tibetan Plateau is sensitive to climate change, but the feedbacks of nitrogen (N) cycling to climate conditions on this plateau are not well-understood, especially under varying degrees of anthropogenic disturbances. The Nujiang River Basin, the last undammed large river basin on the Tibetan Plateau, provides an opportunity to reveal the feedbacks at a broad river basin scale. The isotopic compositions revealed that the conservative mixing of multiple sources controlled the nitrate (NO3-) loadings during the low-flow season, while biological removal processes (assimilation and denitrification) occurred in the high-flow season. During the high-flow season, soil sources, sewage, and atmospheric precipitation contributed 76.3%, 15.6%, and 8.1% to the riverine NO3-. In the low-flow season, the contribution of soil sources decreased while that of sewage increased. The relationship between d-excess and δ15N-NO3- suggests that the hydrological conditions largely controlled the N cycling dynamics in the basin, causing the high spatiotemporal heterogeneity of the riverine NO3- sources and transformation mechanisms. During the high-flow season, the precipitation and evaporation patterns controlled the in-soil processes and soil leaching. In contrast, in-stream nitrification became more evident during the low-flow season, which was related to the long water residence time. This study illustrates hydrology dominated control on N cycling over a large basin scale, which has implications for understanding the N cycling dynamics in the Tibetan Plateau.

Climatic and anthropogenic driving forces of the nitrogen cycling in a subtropical river basin.

To date, basin-scale understanding of nitrogen (N) cycling is lacking, which undermines riverine N pollution control efforts. Applying a multiple-isotopic approach, this study provided insights into the impacts of climate and anthropogenic activities on the N cycling at a basin scale. The isotopic compositions of the river water were regulated by a simple mixing process in winter, while unconservative processes (nitrification and denitrification) occurred in warm seasons. Denitrification dominated the N transformations in summer, while coupled nitrification-denitrification in soils after fertilization was responsible for the isotopic fractionations in spring and autumn. While at least 58.7% of the nitrate (NO3-) was removed from the basin, the NO3- loadings in the river remained high, suggesting that the ecosystem services could not balance the anthropogenic pollution. After correcting the isotopic fractionations, the sources of the riverine NO3- were quantified by a Markov chain Monte Carlo isotope mixing model. The contributions of point sources versus non-point sources changed dynamically with the precipitation and fertilization patterns. In summer and autumn, the soil organic N and chemical fertilizer dominated the riverine NO3-, with total contributions of 75.9% and 74.6%, respectively. The contributions from sewage and manure significantly increased during spring (47.9%) and winter (50.2%). Overall, the annual NO3- fluxes were from SON (28.7%), CF (28.1%), DS (18.2%), MA (23.9%), and AP (1.1%). In addition, we presented the large uncertainties in source apportionment that arose from the ignorance of isotope fractionations, highlighting the importance of considering the effect of isotopic fractionations in N source apportionment studies.

Spatiotemporal variations of nitrate sources and dynamics in a typical agricultural riverine system under monsoon climate.

Nitrogen pollution is a serious environmental issue in the Danjiangkou Reservoir region (DRR), the water source of the South-to-North Water Diversion Project of China. In this research, seasonal surveys and a bi-weekly time series survey were conducted in the Qihe River Basin, one of the most densely populated agricultural basins in the DRR. Hydrochemical compositions (NO3- and Cl-), dual isotopes (δD-H2O, δ18O-H2O, δ15N-NO3-, and δ18O-NO3-), and a Markov Chain Monte Carlo isotope mixing model were jointly applied to unravel the sources, migrations, and transformations of the nitrate (NO3-) in the basin. It was revealed that the mixing between different sources was the main process controlling the isotopic compositions of the riverine NO3- in the upper-middle reaches. In contrast, denitrification occurred in the lower reaches. For the first time, the sources of NO3- were quantified at a basin scale in the DRR. Overall, the river transported 484.2 tons/year of NO3-N to the reservoir, of which 32.6%, 36.4%, 28.0%, and 3.0% was from soil organic nitrogen, chemical fertilizer, residential sewage and atmospheric precipitation, respectively. The NO3-N fluxes of the different sources were regulated by the monsoon climate and anthropogenic activities. For example, high precipitation and intense fertilization resulted in severe nonpoint source pollution. Denitrification thrived in soils and reservoirs in wet seasons. Temperature could regulate the migration, nitrification and denitrification processes. Based on the results, we suggest that the management strategies dealing with nitrogen pollution issue in the DRR should follow the specific spatiotemporal characteristics of NO3- sources, migration and transformation mechanisms.

Fabricated Electrochemical Sensory Platform Based on the Boron Nitride Ternary Nanocomposite Film Electrode for Paraquat Detection.

Hexagonal boron nitride (BN), an effective diffusion material for mass transport, was functionalized with molybdenum disulfide (MoS2) and Au nanoparticles (Au NPs). Then, the working electrodes with developed nanomaterials were applied to construct an electrochemical paraquat sensor. BN was prepared using a solid-state synthesis method combined with solvent-cutting. The electrochemical properties of the BN/MoS2/Au NP-based glassy carbon electrode (GCE) were investigated using differential pulse voltammetry and cyclic voltammetry. An excellent response signal to paraquat was found from 0.1 to 100 µM with a limit of detection of 0.074 µM, and it had acceptable reproducibility (relative standard deviation = 2.99%, n = 5) and good anti-interference ability. The modified GCE showed superior performance owing to the synergistic effects among all three given nanomaterials. With the proposed method, paraquat in grass samples from an orchard was then investigated. The results of the electrochemical analysis agreed with those of experiments and obtained a 96.28% confidence level via high-performance liquid chromatography, exhibiting relatively high stability. Therefore, the fabricated sensor can be a candidate for the determination of paraquat.

Chemical composition of precipitation in Shenzhen, a coastal mega-city in South China: Influence of urbanization and anthropogenic activities on acidity and ionic composition.

Rainwater samples from Shenzhen in south China were collected over the period of a year, and the chemical compositions were measured with the main purpose of understanding the acidification of rainwater and the controlling factors. The pH value of precipitation ranged from 3.72 to 6.77, with a volume-weighted mean (VWM) value of 4.29, and the acid rain frequency was 97%. The VWM concentrations of anions and cations followed the order of SO42- > Cl- > NO3- and Na+ > Ca2+ > NH4+ > Mg2+ > K+, respectively. Air mass back-trajectory and positive matrix factorization analyses indicated that sources of ions in rainwater were mainly from sea salt, soil dust and anthropogenic activities. Compared with other areas in China, the rainwater of Shenzhen has the lowest values of the NP/AP, ∆pH and NF values of Ca2+ and NH4+, indicating that the lack of the capacity for neutralization could be the main reason for the severe acid rain problem. It is noteworthy that the rain acidification tendency is obvious, and the pH value has reduced by 1.0 units since the 1980s. Based on a comparison of the chemical compositions of the rainwater from different historical periods, the NO3- concentration was found to have increased consistently, whereas the NH4+ concentration maintained a decreasing trend since 1980. On the other hand, the nss-SO42- and nss-Ca2+ concentrations increased after 1980 and then decreased after 1994. Meanwhile, the decreasing pH was accompanied by a decreasing NP/AP ratio. These results suggest that the changes in human activities at different stages of urban development can lead to a synergistic change in the chemical characteristics of precipitation. Both an increase in the acidic species emissions (especially NOX) due to rapid economic development and a decrease in the alkaline ions concentration due to urbanization have resulted in the rain acidification tendency in Shenzhen.

Bright and gap solitons in membrane-type acoustic metamaterials.

We study analytically and numerically envelope solitons (bright and gap solitons) in a one-dimensional, nonlinear acoustic metamaterial, composed of an air-filled waveguide periodically loaded by clamped elastic plates. Based on the transmission line approach, we derive a nonlinear dynamical lattice model which, in the continuum approximation, leads to a nonlinear, dispersive, and dissipative wave equation. Applying the multiple scales perturbation method, we derive an effective lossy nonlinear Schrödinger equation and obtain analytical expressions for bright and gap solitons. We also perform direct numerical simulations to study the dissipation-induced dynamics of the bright and gap solitons. Numerical and analytical results, relying on the analytical approximations and perturbation theory for solions, are found to be in good agreement.

Characteristics of moisture and salinity of soil in Taklimakan Desert, China.

The Taklimakan desert is known as the largest dunefield in China and also as the world's second largest shifting sand desert. The Tarim Desert Highway, which is the first highway to cross the Taklimakan desert, was built for the purpose of oil and gas resources extraction in the Tarim area, as well as for the development of the southern area of the Xinjiang Uygur Autonomous Region. Shelterbelts have been planted along the highway to prevent shifting sand from burying the road. This paper analyzes the variations of moisture and salinity of the unirrigated desert soil under natural conditions in the center of Taklimakan Desert. A number of important findings indicating the moisture and salinity of the soil at capillary saturation zone were determined by the groundwater and related to the evaporation on the top. Salinity could be affected by vegetation, which was different from moisture in the soil. Meanwhile, clay layer played an important role in water preservation in the soil, which was also beneficial to the accumulation of salinity in soil. Compared with clay layer, vegetation was a decisive factor for the gathering of salinity. The findings were significant for reasonable adjustment of irrigation in the shelterbelts for the further development of the Tarim Desert Highway.

Reduction of acid effects on trace element determination in food samples by CH4 mixed plasma-DRC-MS.

A robust method for trace element determination in food samples by addition of methane to the plasma of a dynamic reaction cell mass spectrometer (CH(4) mixed plasma-DRC-MS) was developed. Addition of 3 mL min(-1) methane to Ar-plasma eliminates the signal suppressions of various elements (As, Se, Hg, etc.) due to the high concentration of nitric acid (10%, v/v). The CH(4)-Ar mixed plasma may compensate for the plasma cooling effects due to the highly concentrated nitric acid. The interfering polyatomic ions (40)Ar(12)C(+), (40)Ar(35)Cl(+) and (40)Ar(40)Ar(+) on (52)Cr(+), (75)As(+) and (80)Se(+) determination were removed effectively using the DRC with CH(4) as the reaction gas. The limits of quantification (LOQ, 10σ) were 0.35 ng g(-1), 0.07 ng g(-1), 0.35 ng g(-1), 0.07 ng g(-1), 0.15 ng g(-1), and 0.07 ng g(-1) for As, Cd, Cr, Hg, Pb and Se, respectively. The proposed method was applied to the determination of these trace elements in four food standard reference materials (NIST1577b, GBW10018, NIST1570a and GBW10016), and the results were in good agreement with the certified values.

Elimination of oxide interferences and determination of ultra-trace silver in soils by ICP-MS with ion-molecule reactions.

Silver is subject to significant spectral interferences caused by high concentrations of Zr, Nb, Mo and Y in inductively coupled plasma mass spectrometry (ICP-MS) analysis for soil or sediment samples. In this study, the Zr, Nb, and Mo based oxide and/or hydroxide polyatomic interferences were successfully eliminated by ion-molecule reactions in a dynamic reaction cell (DRC). These potentially interfering ions 9³Nb¹6O+, 9²Zr¹6OH+ and 9²Mo¹6OH+ on ¹°9Ag+ were rapidly oxidized to higher oxides 9³NbO2+, 9²ZrO2H+/9²ZrO2H+ and 9²MoO2H+ by O2 as the reaction gas in DRC. However, interfering ions 89Y¹8O+ and 9¹Zr¹6O+ on ¹°7Ag cannot be removed by this method, because the reaction rates of ZrO+ and YO+ to ZrO2+/ZrO3+ and YO2+/YO3+ were too low. Under the optimized O2 flow rate (2.4 mL min⁻¹) and DRC rejection parameter q (Rpq, 0.75), the background signal was reduced by up to 100-fold at m/z 109 and the limit of quantitation (LOQ, 10σ) for ¹°9Ag was 0.5 ng g⁻¹. The proposed method was used to determine the concentration of Ag in twenty-eight soil standard reference materials (SRMs). The accuracy of the results suggests that the method has great potential for the direct determination of trace or ultra-trace levels of Ag in various environmental samples.