A fiber-optic torsion sensor based on a helical two-core fiber (HTCF) is proposed and experimentally demonstrated for simultaneously measuring torsion angle and torsion direction. The sensor consists ...of a segment of HTCF and two single-mode fibers (SMFs) forming a Mach-Zehnder interferometer (MZI). The helical structure is implemented by pre-twisting a 1 cm long two-core fiber (TCF). The performance of the sensor with pre-twisted angles of 180°, 360°, and 540° is experimentally analyzed. The results show that the sensor can realize the angular measurement and effectively distinguish the torsion direction. It is worth noting that the sensor has maximum sensitivity when the pre-twist angle is 180 degrees. The obtained wavelength sensitivities of torsion and temperature are 0.242 nm/(rad/m) and 32 pm/°C, respectively. The sensor has the advantages of easy fabrication, low cost, compact structure, and high sensitivity, which is expected to yield potential applications in fields where both torsion angle and direction measurements are required.
Macro-tidal estuaries with mountain streams are typical estuarine systems in southeastern China. Suspended sediment transport and turbidity maxima are sensitive to changes in the tidal and fluvial ...regimes of estuaries. To improve our understanding of river-ocean interactions and thus improve estuarine forecasts for biogeochemical processes, we developed a high-resolution hydrodynamic and sediment transport coupled model to investigate the suspended sediment transport and estuarine turbidity maximum (ETM) in the Oujiang Estuary. This estuary is characterized as a macro-tidal estuarine system with a large tidal range and drastic fluctuations in freshwater and sediment discharge. The results led to the following conclusions: (1) the ETM occurred during spring tides due to strong tidal resuspension. In contrast, it was not formed during the neap tide because of weak bottom shear stress. The ETM moves upstream to Yanmen during low river discharge and migrates downstream to the river mouth during high river discharge, causing sediment deposition in the nearshore region. (2) Owing to the characteristics of mountain streams and upstream anthropogenic reservoirs, the ETM is strengthened during low river discharge (∼100 m3 s−1) even during the wet season, which supplements the fact that the ETM is more prevalent during the dry season and withers during the wet season. The suspended sediment forming the ETM mainly originates from shallow offshore shoals owing to tidal resuspension. Owing to the weak vertical exchange flow near the river mouth, the ETM is related to the exchange flow during the low water flow. (3) The ETM excursion shows semi-diurnal variability with different transport distance for high and low river discharges. Tidal pumping dominates the suspended sediment flux in the core of the ETM, which is mainly maintained by two components of the Euler and Stokes fluxes as the tidal energy depletes during the flood tide.
•Estuarine modeling was conducted to study suspended sediment dynamics.•ETM excursion occurs for high and low river.•Decomposing sediment fluxes reveals ETM mechanisms.•River discharge and tidal pumping play roles on ETM formations.
The instructional video is considered to be one of the most distinct and effective virtual learning tools. However, one of its biggest drawbacks is the lack of social interaction that occurs. This ...study tested the impact of participants sending zero danmaku (sending messages on the screen), three danmaku sending, and unlimited danmaku as an instructional video plays on learning performance.
We assessed learners' retention and transfer scores, as well as self-report scores for cognitive load and parasocial interaction. This study sample comprised 104 participants who were randomly assigned to learn from one of three instructional videos on the topic of the heart.
The results showed that sending danmaku improved learners' parasocial interaction, while significantly increasing their cognitive load and also hindering learning performance. The observed increase in cognitive load reported by learners was also caused by increased levels of parasocial interaction.
Our findings suggest that by sending danmaku, learners can promote interactive learning, but that this has a negative impact on learning performance and the process of video learning.
Phosphorus (P) is an essential element for crop production and a key source of nonpoint pollution in agroecosystems. In this study, we sought to analyze P levels and the factors affecting soil P ...availability, via P adsorption, in a typical field system that is characterized by the year-round cultivation of vegetables. A total of 190 sites were sampled from vegetable fields in Guangdong Province, South China. Within the research area, average concentrations of 124.49 mg P kg-1 and 1.55 g P kg-1 were recorded for available P (AP) and total P (TP), respectively, which are 8.53- and 1.78-fold higher, respectively, than the corresponding values recorded in 1980. The determined P adsorption maximum (Qm) averaged at 488.38 mg kg-1, which represents a reduction of 16% compared to the values obtained four decades ago. Accumulations of both TP and AP were found to be negatively correlated with the soil's maximum adsorption buffering capacity (MBC), although no significant correlations with the soil binding energies (k) and Qm, were seen. However, soil pH was found to be significantly correlated with k and Qm. Furthermore, both free Mn oxides (Mnd) and silt concentrations in the soil were found to contribute to explaining the variations in Qm. Collectively, the findings of this study provide evidence to indicate that there has been an excessive accumulation of P in the perennial vegetable fields of Guangdong Province over the past four decades, which may have had negative effects on the P supply potential of the soil by reducing the maximum adsorption buffering capacity.
The Oujiang River Estuary (ORE) is a macrotidal estuary with drastic variation of river discharge and large tidal range. Numerical simulations based on the unstructured grid, Finite-Volume, primitive ...equation Community Ocean Model (FVCOM) are conducted to investigate the intratidal and intertidal variations of salinity with an extremely upstream river boundary and large computational domain. The dynamic equation of potential energy anomaly is adopted to evaluate the stratification and mixing processes from model results. Meanwhile, the stability of estuarine stratification on different timescales and its spatial variation are studied using estuarine Richardson number and stratification parameter. The critical values of tidal range and river discharge that determine the stratification state are obtained. The critical values exhibit distinct spatial difference. The north branch of the ORE exhibits well-mixed conditions when the tidal range exceeds 3.8, 4.0 and 4.6 m at upper inlet, middle segment and the river mouth, respectively. When river discharge is below 280 m
3
/s or exceeds 510 m
3
/s, the upper part of the north branch is well-mixed sustainably. Near the river mouth, river discharge of 280 m
3
/s is a rough critical value that separates well-mixed and stratified states. It is also concluded that periodic stratification exists in the North Channel. The lower estuary appears to be partially stratified at early ebb or early flood tide, and well-mixed in other tidal stages. The stratification only develops during early ebb in the upper segment. The enhancement of stratification is mainly caused by longitudinal advection and lateral velocity shear, while turbulent mixing and longitudinal tidal strain are the main factors of stratification attenuation.
Nowadays, the online compulsive buying behavior of the young group is increasing, which has become a social problem that needs to be solved. This paper focuses on individual psychological factors and ...explores how social comparison orientation influences online compulsive buying. Through the research method of the questionnaire survey, this paper shows that different levels of the social comparison will lead to different buying preferences. And then we examined how mediating and moderating effects work on the influence path of the compulsive buying tendency. As a result, this study innovatively finds the mechanism of materialism values as a mediator and self-concept clarity as a moderator. It ultimately allows us to figure out a pathway that leads to the online compulsive buying tendency, and can provide new ideas for solving the problems caused by it.
Cascaded Brillouin random fiber lasers (BRFLs) with laser linewidth compression were theoretically and experimentally demonstrated. Thanks to photon-phonon coupled interplay as well as randomly ...distributed feedback along silica fibers, the coherent time of cascading BRFL radiation is significantly prolonged whilst the phase noise is further suppressed, albeit with a quantum-noise-induced linewidth narrowing limit. To validate it, the linewidth narrowing ratio in BRFLs, defined as the ratio of the Brillouin pump and its sequent order of Stokes linewidth, was carried out and exhibited a dependence on the Brillouin pump linewidth, which is in good agreement with theoretical predictions. Furthermore, the relative intensity noises of cascading BRFLs were also investigated and discussed.
In this study, we conducted numerical experiments to examine the effects of turbulence parameterization on temporal and spatial variations of suspended sediment dynamics. Then, we applied the ...numerical model to the Yamen Channel, one of the main eight outfalls in the Pearl River Delta. For the field application, we implemented the
k−ε
scheme with a reasonable stability function using the continuous deposition formula during the erosion process near the water-sediment interface. We further validated and analyzed the temporal-spatial suspended sediment concentrations (SSCs). The experimental results show that under specified initial and boundary conditions, turbulence parameterization with stability functions can lead to different vertical profiles of the velocity and SSC. The
k−ε
predicts stronger mixing with a maximum value of approximately twice the
k−kl.
The
k−kl
results in smaller SSCs near the surface layer and a larger vertical gradient than the
k−ε.
In the Yamen Channel, though the turbulent dissipation, turbulent viscosity and turbulence kinetic energy exhibit similar trends, SSCs differ significantly between those at low water and high water due to the tidal asymmetry and settling lag mechanisms. The results can provide significant insights into environmental protection and estuarine management in the Pearl River Delta.
Core Ideas
Vis‐NIR hyperspectral imaging can be used to predict the soil salt content (SSC) in soil profiles.
The least squares support vector machine (LS‐SVM) model predicted SSC more accurately ...than the partial least squares regression (PLSR) model in the field.
Hyperspectral imaging is an efficient and nondestructive method for mapping and characterizing the SSC distribution in soil profiles.
Recently, visible and near‐infrared (Vis‐NIR) hyperspectral imaging has shown great potential in fine mapping of soil properties in laboratory. Whether it could be used to predict soil salt content (SSC) in the soil profile under field conditions still remained to be determined. In this study, hyperspectral images were acquired in situ from a soil profile with a Vis‐NIR imaging spectrometer, and the optimum SSC prediction model was built to determine SSC of each pixel, and the fine SSC distribution maps were generated. The observed soil profile was located at an experimental station in Dongtai City, Jiangsu Province, China. Hyperspectral images with a spectral range of 397 to 1018 nm were obtained from 21 to 25 May 2015; a total of 140 soil samples were collected. Five spectral preprocessing methods, Daubechies wavelet (Db), LOG10(1/Db), Savitzky‐Golay (SG), multiplicative scatter correction (MSC), and standard normal variate (SNV) were applied, and partial least squares regression (PLSR) and least squares support vector machine (LS‐SVM) models were developed. Results showed that the LS‐SVM model predicted the SSC more accurately than the PLSR model, and the highest prediction accuracy was obtained with LOG10(1/Db) preprocessed spectra with R2p, RMSEp, RPIQ, and RPD values of 0.87, 0.58 g kg–1, 2.60 and 2.77, respectively. Based on the optimum prediction model, the fine distribution of SSC in soil profiles over 5 d were successfully obtained. This study indicated hyperspectral imaging is an efficient and nondestructive method for mapping SSC distribution in soil profiles and characterizing the vertical transportation of soil salt under field conditions with moderate soil moisture range.
We proposed and experimentally demonstrated a novel scheme of light group velocity control via a Mach-Zehnder fiber interferometer incorporated with Brillouin random lasing resonance in a half-open ...linear cavity. A theoretical model of the proposed Brillouin random lasing resonance-based Mach-Zehnder interferometer (BRLR-MZI) for the light group velocity manipulation was derived, predicting optical power-dependent transmittance spectrum shift as well as the enhancement of the temporal advancement. Thanks to Brillouin random lasing-induced fast light effect, the proposed scheme not only achieves a flexible all-optical manipulation of its transmittance spectrum but also overcomes the saturation effect for the light speed control based on a traditional MZI. In experimental validation, sinusoidally modulated signals with the modulation frequency of 160 kHz ultimately experienced a maximum advancement of 4031 ns (corresponding to the group index of 0.875), which exhibits an advancement improvement of 1364 ns compared with the traditional MZI-based scheme. It suggests a promising platform for exploring applications in fields of all-optical signal processing, microwave photonic, and ultra-sensitive fiber sensing.
