In this paper, we report the recent progress in visible light positioning and communication systems using light-emitting diodes (LEDs). Due to the wide deployment of LEDs for indoor illumination, visible light positioning (VLP) and visible light communication (VLC) using existing LEDs fixtures have attracted great attention in recent years. Here, we review our recent works on visible light positioning and communication, including image sensor-based VLP, photodetector-based VLP, integrated VLC and VLP (VLCP) systems, and heterogeneous radio frequency (RF) and VLC (RF/VLC) systems. key words: visible light positioning, visible light communication.
The geometric precision of worm gears (WGs) determines the service performance and life of precision machine tools, indexing turntables and other equipment. The machining accuracy of worm gear machine tools (WGMTs) is the core to guarantee the geometric precision of WGs, and is greatly affected by the thermal and geometric errors. To improve the machining accuracy of WGMTs, the thermal and geometric errors should be controlled and compensated. But the control system has a poor real-time performance, and the synchronous control of the geometric and thermal errors cannot be currently achieved, and the thermal error model has a low prediction accuracy and low robustness. To make up for the above gap, a mist-edge-fog-cloud computing system is designed for the error prediction and compensation to relieve the bandwidth pressure of the industrial Internet. Moreover, a sensor network composed of multiple sensors is constructed to obtain the thermal information, and then the ordered neuron temporal-graph convolutional network (ONT-GCN) is proposed based on the ordered neuron-long short term memory network (ON-LSTMN) and graph convolutional network (GCN) for the first time to conduct the spatial and temporal modeling of the thermal error data. The interaction among multiple sensors is explicitly considered, and the dependence of the temporal information of the thermal error data on and spatial information of sensors is taken into account. Besides, to realize the error control, the mapping relationship between the tooth surface error and geometric-thermal errors is established. The error mapping model converts 51 geometric errors and 4 thermal errors into the spatial errors of the hob. Moreover, the sensitivity of errors is analyzed, and then the key error items that affect the geometric precision of the tooth surface are identified and compensated. The results show that the ONT-GCN is superior to traditional time-series modeling methods and that the mist-edge-fog-cloud computing system can effectively shorten the executing time compared with other system frameworks, and can improve the machining accuracy of WGMTs.
To address the challenge of global tourism resources being overloaded or underutilization, there requires an adequate method for assessing the tourism resource carrying capacity (TRCC). However, the majority of previous evaluation perspectives on TRCC are limited by thresholds. This paper develops an innovative approach for assessing TRCC from the “load-carrier” perspective. TRCC is assessed by exploring the interaction between the carriers and loads of tourism resources. Chongqing city in China is employed as the case city to demonstrate the application of the established TRCC method. The conclusions are as follows: 1) This study elaborates the new connotation of TRCC from the perspective of “load-carrier”, and establishes the TRCC evaluation system based on the dynamic relationship between the carrier and load of tourism resources. 2) The proposed TRCC evaluation method is proved effective through an empirical study of Chongqing. 3) Chongqing's case unveils that the overload performance of TRCC can be dynamically monitored and predicted. By applying the TRCC evaluation methodology developed in this study, tourism managers and policymakers can identify whether it is the load or the carrier of tourism resources that affect the performance of TRCC, thereby taking targeted policy measures to eliminate potential risks of overload or underutilization.
Due to the influence of gearbox structure complexity, vibration signals are always corrupted by heavy multiscale noise interference distributed in modulation frequency bands, which brings great challenge for early fault identification. However, conventional adaptive noise cancellation methods mainly focus on a comprehensive denoising effect while ignore improper reference induced by multiscale characteristics of noise interference. This will lead to two major problems. On one aspect, reference filtering at sensitive scales is not mutually independent, and it has a negative influence on each other. On the other aspect, improper reference may cause losses of fault-related information. These limitations greatly hinder the fault features identification, especially in an early fault stage of a fault. Aiming at these problems, this study proposes a novel variable-scale evolutionary adaptive mode denoising method (VEAMD) for weak feature enhancement of gearbox early fault diagnosis. First, to sense the multiscale distribution characteristics of a desired signal, an ergodic VMD process with a dual domain energy factor (DDEF) is presented, where a series of Wiener filters are adaptively designed. Secondly, the desired signal and a reference signal are input into these Wiener filters to generate multiple mode subsignals with wideband noise suppressed. Meanwhile, multiscale noise interferences are separated into different scales as reference bases for mode denoising. Third, via evolutionary digital filters (EDFs), a refined reference filtering is performed within mode scale to obtain multiple intrinsic mode subsignals (IMSs), namely mode denoising. Finally, the Pearson correlation coefficients between two parts of each subsignal pair is employed as a weight to synthesize a denoised signal. In this manner, VEAMD effectively tackles an improper reference at local scales by a series of adaptive mode denoising, achieving more significant noise cancellation capability and an effect of weak feature enhancement, which is conducive for a timely and accurate early gearbox fault diagnosis. Simulation and experiment prove the superiority of VEAMD over other four methods.
This paper presents a numerical approach to perform large deformation simulation of spudcan penetration-consolidation-uplift process in soft soil. The coupled pore fluid flow and stress are simulated with large deformation finite element analysis, by using the remeshing and interpolation technology using small strand (RITSS) method in ABAQUS v2016. The surrounding soil is simulated by using modified Cam clay model. The simulation is validated by comparting with centrifuge test results. The calculation results show that the maximum uplift force of spudcan has a linear relationship with the penetration depth, and the negative excess pore pressure at the spudcan invert is almost equal to the hydrostatic pressure. By analyzing the soil velocity vector diagram at the corresponding position of the maximum uplift force at different penetration depths, three failure mechanisms of the soil at the position corresponding to the maximum uplift force are summarized.
Health indicator (HI) is an important metric to characterize a degradation process and detect the fault initiation time of rotating machineries as early as possible for condition monitoring. In recent years, many HIs are developed and reported, however, a constructed HI which is more sensitive to incipient defects, free of massive history degradation data and is able to quantitatively measure a degradation process is still remain to be studied. To address this issue, a novel HI constructed through canonical correlation analysis of dimension reduced degradation feature space is proposed. In the proposed method, the intrinsic low-dimensional degradation feature space is mined by a dimension reduction model based on auto-encoder from a high-dimensional statistical feature matrix. After that, the degradation state is measured by calculating the canonical correlation from the feature space of the baseline and the subsequent collected monitoring data. On this basis, a new HI is formed to quantitatively characterize a degradation process for condition monitoring. The performance of the proposed HI is investigated by comparing with some typical state-of-the-art HIs, such as L2/L1 norm, kurtosis, negative entropy, Gini index, smoothness index, Hoyer measure, etc., the experimental validation results demonstrate the proposed HI is able to detect incipient fault and is more sensitive to the early stage degradation process.
Reinforced concrete independent foundation has the advantages of simple structure, low economic cost and convenient design. In order to study the influence of buried depth on the stress mode of independent foundation in rock foundation, the stress and deformation characteristics of independent foundation in rock foundation under buried depth are analyzed through theoretical discussion and numerical simulation, and the differences of reaction force and internal stress field of foundation under different constraints are compared. The results show that the independent foundation is actually a stress model between the deep beam and the compression member under the constraints of the bottom and side walls; In addition, when the independent foundation is under different constraints, the mechanical properties are different, so the influence of various constraints on the independent foundation should be considered in the design.
The oxidation of cyclohexane is an important route in the chemical industries for producing cyclohexanol, cyclohexanone, plasticizers, surfactants and so on. However, it will be in danger of explosion once the concentration of cyclohexane in the mixture exceeds the explosion limit. Therefore, it is necessary to research the temperature distribution and flow characteristics in Rayleigh-Bénard (RB) convection of cyclohexane/oxygen mixture to avoid the potential hazard of deflagration. In this paper, a set of three-dimensional simulations were performed to understand RB flow characteristics of cyclohexane/oxygen mixture near the maximum density in a rectangular container with an aspect ratio of 2. Rayleigh (Ra) number ranges from 2 × 10³ to 6 × 10⁵. Results show that the density inversion has a notable influence on RB convection of cyclohexane/oxygen mixture. The critical Rayleigh numbers for the onset of stable flow and for the oscillatory flow show an upward tendency with increasing density inversion parameter (Θm). When Θm is small, the flow occurs in the whole cavity. When Θm is large, the fluid layer near the top wall is static in the region. Multiple flow states and their evolutions are obtained at various Θm. The heat transfer ability is enhanced with increasing Ra, while it weakens with increasing Θm.
With the increasingly stringent effluent requirement for phosphate worldwide, the demand for advanced phosphorus removal is rising. Although conventional flocculation-filtration is a reliable way for achieving low phosphorus concentrations, floc accumulation on the membrane will create additional resistance requiring greater operation pressure in practical applications. Here, we fabricated a layered double hydroxide (LDH) membrane for advanced removal of dissolved phosphate without pre-flocculation. The permeability of the LDH membrane can reach 32337.2 L/(m²·h·bar), which is 10–100 times higher than conventional adsorption membranes with embedded active sites. In addition, the LDH membrane yielded a strong phosphate retention capacity and could reduce the phosphate to <0.05 mg/L at a load of 1146.5 mg/(m²·h). And if 0.1 mg/L is selected as the target, the LDH membrane can treat 4400 bed volumes of wastewater at the above load. Moreover, actual wastewater experiments have demonstrated the advantage of LDH membranes in alleviating the rapid growth problem of transmembrane pressure. The intra-membrane kinetic analysis revealed the rate basis of LDH membranes to capture phosphate in an instant hydraulic residence time. Stoichiometric and characterization analyses indicated that the main phosphate retention mechanisms were ion exchange (56.7%), ligand exchange and electrostatic attraction. This study proposes new insight into the design and fabrication of membranes for advanced phosphate removal, which is enlightening for the development of tailored membranes with different functions.
Excessive discharge of nutrients from wastewater treatment plants (WWTPs) is an important pollutant source of eutrophic water bodies. In this work, three electrochemically integrated horizontal flow constructed wetlands (E-HFCWs) were developed for advanced nutrients removal from WWTPs effluent with different S/N ratios. In E-HFCWs, PO4³⁻-P, NO3⁻-N and TN removal percentages at current of 0.2 A and hydraulic retention time (HRT) of 24 h did not differ significantly as S/N ratios altered. When fed with low, middle and high concentrations of SO4²⁻-S wastewater during this period, PO4³⁻-P removal percentages respectively reached 99.3 %±0.9 %, 99.2 %±1.1 % and 99.0 %±1.4 %, NO3⁻-N removal percentages respectively reached 99.5 %±0.5 %, 99.6 %±0.4 % and 99.4 %±0.8 %, and TN removal percentages respectively reached 92.0 %±2.5 %, 90.8 %±3.4 % and 91.2 %±2.7 %. This work highlighted that sulfur cycle played crucial roles in improving nitrogen removal stability as current or HRT decreased in higher S/N ratio groups. The formed sulfur ferrites under higher current or HRT condition served as “electron reservoir”, and would resupply electron for denitrification when electron supplied by electrolysis was deficient. In addition, the higher S/N ratio groups allowed significantly lower N2O accumulation, which was accordance with the concept of carbon neutral. Based on metagenome results, the occurrence of more abundant sulfur-oxidizing denitrifying genes and bacteria (e.g., Thiobacillus) in higher S/N ratio groups under lower current or HRT further demonstrated the significant roles of sulfur cycle in stable autotrophic denitrification performance in E-HFCWs. Overall, this work provides perspective on the future practical application for the regulation of nitrogen removal stability enhancement and N2O emission reduction in electrochemically integrated bioreactors.
In this study, a model for describing both chain reactions and product growth for the explosions of methane/coal volatiles mixtures based on chemical reaction kinetics was established to calculate the impact of initial temperature and initial pressure on the deflagration features of the mixtures. The variation for the macroscopic explosion parameters and the microscopic reactions of methane/coal volatiles explosions under different conditions are investigated using reaction kinetics simulation. Results suggest that the Pmax increased by 64.496 %, 64.499 %, 64.502 %, and 64.504 % when the initial pressure changed from 0.8 to 1.3 atm. Whereas, under increasing initial temperature, the Pmax decreased by −18.167 %, −18.179 %, −18.190 %, and −18.200 % while the Tmax increased by 90.49 K, 90.07 K, 89.67 K, and 89.30 K, respectively. Meanwhile, the influence of initial temperature on the sensitivity of primary elementary reactions was more prominent than that of the initial pressure. The ROP of the key radicals H/O/OH unnecessarily presented an increasing tendency under the increasing initial temperature while the maximal molar fraction of each key radical increased. The increase in both initial pressure and initial temperature would greatly promote the growth of C(B), which in turn largely accelerated the formation of soot particles. This preliminary work would be beneficial for the preemptive precaution and effective control of the explosions in coal-derived industries.
CO2 mineral sequestration is one of the most promising strategies for combating global warming, which is composed of direct and indirect pathways. However, the high cost and heat consumption for recycling reagents used in the indirect carbonation process is the biggest obstacle for its widespread applications. In this study, a novel process by using a solid waste, copperas, as reagent to extract magnesium and nickel from laterite ore was proposed for simultaneous CO2 mineralization and recovery of nickel. In this process, the copperas was decomposed into SO2, which sulfated the laterite ore by in situ gas–solid reaction. The addition of Na2SO4 facilitated the formation of low melting point substances, converting the gas–solid reactions into a multiphase gas–liquid-solid reaction, thus the extraction was enhanced. Meanwhile, the heat of sulfation of laterite ore can compensate the heat of copperas decomposition, reducing the overall energy consumption. The maximum extraction efficiency of 94 % for Mg and 87 % for Ni was achieved at Na2SO4 dosage larger than 10 wt%. The carbonation of MgSO4-riched leachate experiments revealed the optimal CO2 storage capacity was approximately 291 kg·t⁻¹ laterite ore. Compared with the conventional acid-based Mg extracted process for CO2 mineralization, the cheap copperas avoided the recycle of reagent and obtained weak acidic leachate, reducing the amount of alkali used in the subsequent carbonation process.
The biogenic methane production experiment of FOG combined with lignite was performed to enhance the methane output of lignite anaerobic fermentation. Three-dimensional fluorescence, gas chromatography-mass spectrometry, volatile fatty acids and 16S rDNA tests were carried out to analyze the composition of the liquid substances at the biomethane peak production. The results showed that the yield of this compound in the combined fermentation of lignite and FOG could be increased by 380.25 %. Moreover, the degradable organic matter and acetic acid content increased, while the degree of humification decreased. In addition, the microbial activity was enhanced. In the combined substrate of the anaerobic fermentation process, both Acinetobacter and Methanosarcina were activated as the dominant bacteria and archaea, respectively, which improved the degradation efficiency of organic matter and the overall biomethane yield. This research showed that the combined anaerobic fermentation of FOG and lignite could promote the biomethane production efficiency in the context of anaerobic fermentation, which provided a new idea for the clean transformation of lignite and utilization of FOG.
Manganese carbonate ore is ascertained as the most abundant manganese ore in China, while its mining and beneficiation generated a large amount of manganese tailings which is regarded as a hazardous waste. Owing to great catalytic performance of manganese oxides, it is double-benefit to employ manganese tailings as catalyst to eliminate harmful nitrogen oxides from flue gas. In this study, the effects of calcination temperature on the low-temperature denitration performance and physicochemical properties of manganese tailings were systematically investigated via XRF, XRD, XPS, H2-TPR, NH3-TPD and DRIFTS, aiming at exploring the effective utilization of manganese tailings. The results revealed the best catalytic activity can be obtained at a calcination temperature of 500 °C with over 95 % NO conversion attained in the denitration temperature range of 75–225 °C. Lower calcination temperature led to the incomplete decomposition of MnCO3, while higher calcination temperature led to the decrease in specific surface area, surface acidity and oxidation performance. The denitration reaction was followed by Eley-Rideal pathway, in which the absorbed NH3 species was reacted with the gaseous NO and NO2. Based on the results in this study, the effective utilization of manganese tailings for NO emission reduction could promise for wide applications.
Solute segregation at the Si2Hf/Al interface of an Al-Si-Cu-Hf alloy was investigated by combining high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDS) and density functional theory (DFT) calculation. Density gradient segregation of Cu atoms was observed at the habit plane of the nanobelt-like Si2Hf phase, with the Cu concentrations gradually increasing to the Si2Hf/Al interface. This gradient segregation of Cu is found to be beneficial for decreasing both the strain and interfacial energies and thereby promoting the stabilization of the Si2Hf precipitates during heat treatment. This study provides an insight into the enhanced stability of Si2Hf precipitates in Al-Si-Cu-Hf alloy.
In order to enhance acidic sites in catalysts to improve conversion efficiency of microalgal lipids into biodiesel, an efficient bifunctional catalyst with synergetic Lewis and Brønsted acid sites was synthesized by modifying zeolitic imidazolate framework (ZIF-90) with sulfamic acid (SA). The sulfamic acid that combined with ZIF-90 through imine bond (CN) provided protons and destroyed coordinated Zn-N bonds in ZIF-90, thereby enhancing the number of Brønsted and Lewis acid sites. The total acidity of optimal catalyst increased from 0.478 to 0.848 mmol/g, while ratio of Brønsted acid to Lewis acid increased from 0.32 to 0.49. The Lewis acid sites in bifunctional catalysts exhibited higher activity towards transesterification reactions of triglycerides in microalgal lipids, while Brønsted acid sites exhibited higher activity towards esterification reactions of free fatty acids. Therefore, the optimal catalyst (weight ratio of SA to ZIF-90 was 0.05) promoted conversion efficiency of microalgal lipids into biodiesel from 80.6 % to 98.3 % at 200 °C, while conversion efficiency remained 91.7 % after 6 reusability cycles.
This paper proposes an optimal bidding strategy model of a virtual power plant (VPP) in the day-ahead market (DAM) that contains energy, reserve, and regulation markets. The VPP aggregates the wind farm (WF), photovoltaic power (PV), energy storage (ES), gas turbine (GT), and hydropower station (HS). Based on the uncertainty modeling for the output of uncontrollable power sources (UCPSs), such as the renewable energy in terms of WF and PV, this research develops countermeasures to reduce the penalty caused by the deviation between actual and predicted outputs of UCPSs. The other three controllable power sources (CPSs) are required to remain a certain reserve capacity for compensating the deviation to maximize the expected benefits of the whole VPP. By means of the quantile and superquantile theory, the proposed model considers the economic penalties beyond the reserve capacity and optimizes the allocation of reserve capacity to maximize the whole profit. With the construction of a mixed-integer nonlinear programming model, the best profits of the VPP in a variety of cases are reached and discussed. The experimental results demonstrate the effectiveness of diverse power sources integrated into a VPP, and the optimal bidding strategy of such renewable-based VPP in the DAM.
The enhancement of consumer well-being is critical for technology companies in building customer loyalty. Voice assistants (VAs), as the intelligent products launched by technology companies, are increasingly used by consumers in their daily lives. While many technology companies are striving to increase the intelligent attributes of VAs to improve product functionality, little is known about how such attributes affect consumer well-being. Drawing on the means-end chain theory, this study aims to explore the effect of VAs’ intelligent attributes (i.e., autonomy, interactivity) on consumer perceived consequences (i.e., psychological ownership, perceived intrusiveness) and subjective well-being, involving the moderating effect of technology readiness and brand credibility. The resulting relationships were tested by analyzing survey data collected from 412 valid samples in China through partial least squares-structural equation modeling (PLS-SEM) and fuzzy-set qualitative comparative analysis (fsQCA). PLS-SEM indicates that intelligent attributes have significant impacts on perceived consequences, thus affecting subjective well-being. Findings also reveal the moderating roles of technology readiness in the link between intelligent attributes and perceived consequences. Finally, brand credibility moderates the effect of perceived intrusiveness on subjective well-being. The fsQCA results reinforce the PLS-SEM findings and indicate five configurations leading to high subjective well-being. These findings can help technology companies develop novel strategies for improving consumer well-being.
Time-stretch tomography imaging with ultrahigh frame rate is a breathtaking optical imaging method for acquiring large data sets for detection and classification of rare events. However, mechanical scans of both x and y dimensions are required to obtain tomography imaging. Here we introduce an ultrafast multidimensional time-stretch imaging method, only by one-dimensional scan, a multidimensional imaging can be obtained. An entire row of surface and depth information for a reflective sample is encoded onto the amplitude and frequency of a spatially dispersed ultrafast chirped beam, respectively. The present multidimensional line-scan microscopy approaches an ultrafast imaging system with micron level positioning accuracy in depth, three-dimensional surface information acquisition and tomography capability, which aimed at emerging applications for optical coherence tomography (OCT), light detection and ranging (LIDAR) and hyperspectral imaging.
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