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Investigating the electric power generated by wave energy converters (WECs) has attracted increasing attention along with the developments of wave energy converting technologies in recent years. Electric power estimation currently depends on wave-to-wire model-based numerical analysis and experimental studies of scale-down prototypes. However, traditional numerical simulations are time-consuming and expensive for power orediction of a full-scale WECs operated in real sea. More importantly, they cannot accurately predict WECs' power performance in real time, thereby cannot be used for prediction-based real-time control. To address those problems, four machine learning techniques are employed as an alternative to traditional, complex physical modelling processes to evaluate and predict the generated electric power, based on historical experimental data of a two-body hinge-barge WEC. Comparative results of a Backpropagation (BP) Neural Network algorithm, a Long Short-Term Memory (LSTM) algorithm, a Support Vector Machine (SVM) algorithm and a Radial Basis Neural Network (RBFF) algorithm indicate that machine-learning-based approaches can accurately predict the electric performance of this complex multi-degree-of-freedom WEC, where the coefficient of determination (R 2) of the BP Neural Network on the test dataset is up to 0.9987. • Four machine learning techniques are employed to evaluate and predict the electric power. • The machine learning techniques can be used to predict WECs' power performance under new sea state. • The coefficient of determination (R2) of the BP Neural Network is up to 0.9987. [ABSTRACT FROM AUTHOR]

Wave energy is a practical option for the sustainable powering of the drifting buoy beyond solar energy. However, efficient harvesting of wave energy from a complex and dynamic ocean environment for a drifting buoy is significantly challenging, since the buoy's global location and orientation are always in spatiotemporal variation. Herein, we propose a novel multi-DOF wave energy harvesting mechanism that integrates three sets of frequency-tunable harvesting systems into an enclosed drifting buoy, which can greatly enhance the energy harvesting ability of a long-term working drifting buoy that encounters direction-varying and frequency-varying waves. A time-averaged electric power up to 9.18 mW was achieved by a prototype that has a diameter of 45 cm, which is 32.76 % higher than the single-DOF case in sea trials. Additionally, laboratory dry test results show that the prototype provided a power up to 288.76 mW in one direction. This work provides an effective strategy for sustainably generating electricity in the offshore environment for drifting buoys. • A built-in multi-DOF wave energy harvester for a drifting buoy was presented. • Two different-sized prototypes were designed, assembled and tested in the open sea. • A time-averaged electric power of up to 9.18 mW was achieved in real sea tests. • The prototype generated a power of up to 288.76 mW in one direction in laboratory dry test. [ABSTRACT FROM AUTHOR]

• A multifunctional coating was constructed on ZE21B alloy for biodegradable vascular stents. • MgF 2 layer and hydrophilic polymers in the functional coating could effectively protect ZE21B alloy from overfast degradation. • Anticoagulant ACH 11 peptides and ECs-selective REDV peptides in the functional coating could dramatically enhance the hemocompatibility and pro-endothelialization capacity of ZE21B alloy. • The functional coating systematically improved the corrosion resistance and biocompatibility of ZE21B alloy in vitro and in vivo. Biodegradable magnesium alloy stents (MAS) have great potential in the treatment of cardiovascular diseases. However, too fast degradation and the poor biocompatibility are still two key problems for the clinical utility of MAS. In the present work, a functional coating composed of hydrophilic polymers and bioactive peptides was constructed on magnesium alloy to improve its corrosion resistance and biocompatibility in vitro and in vivo. Mg-Zn-Y-Nd (ZE21B) alloy modified with the functional coating exhibited moderate surface hydrophilicity and enhanced corrosion resistance. The favourable hemocompatibility of ZE21B alloy with the functional coating was confirmed by the in vitro blood experiments. Moreover, the modified ZE21B alloy could selectively promote the adhesion, proliferation, and migration of endothelial cells (ECs), but suppress these behaviors of smooth muscle cells (SMCs). Furthermore, the modified ZE21B alloy wires could alleviate intimal hyperplasia, enhance corrosion resistance and re-endothelialization in vivo transplantation experiment. These results collectively demonstrated that the functional coating improved the corrosion resistance and biocompatibility of ZE21B alloy. This functional coating provides new insight into the design and development of novel biodegradable stents for biomedical engineering. [ABSTRACT FROM AUTHOR]

The rise in carbon emissions linked to the tourism industry has challenged its long-standing reputation as an eco-friendly sector. In parallel, the digital economy's evolution has introduced a series of transformations within tourism. This necessitates a thorough examination of the intricate interplay between the digital economy and carbon emissions in the tourism sector. With the help of Chinese provincial panel data, this study uncovers a compelling relationship marked by an inverted "U" curve through two-way fixed model, moderated effects model and threshold regression analysis. Intriguingly, an increase in road density shifts the inflection point of this curve to the lower left. As road density reaches a critical threshold of 0.361, it not only amplifies the elasticity of the inverted "U" curve but also accelerates the timeline to reach peak tourism-related carbon emissions. This study underscores a significant practical implication: while digital technology exacerbates carbon emissions from tourism at this stage, the dampening effect of digital technology is to be expected as the development of industrial manufacturing brings better transportation. However, the timing of the tipping point may be earlier or later for different regions, depending on whether the local level of industry is sufficiently developed. • The inverted "U" curve relationship between digital economy growth and tourism carbon emissions at the provincial level in China is validated. • Transportation accessibility is a key mechanism by which the digital economy affects carbon emissions from tourism. • This paper predicts the conditions for an inflection point in tourism carbon emissions within digital economy. [ABSTRACT FROM AUTHOR]

• Cryogenic throttle valves for superfluid helium system were developed and numerically simulated. • Influences of cone angle, unilateral minimum clearance, structure type and working medium type on flow field distribution and flow characteristics of valve are studied. • Increasing the cone angle and unilateral minimum clearance enhances valve flow capacity, with the cone angle having a more pronounced impact. • Altering the spool type significantly alters the flow characteristics, whereas changing the working fluid type only affects the velocity and pressure within the valve. As one of the important methods to obtain superfluid helium, throttling has been widely used due to its simple equipment. The cryogenic throttle valve, serving as a vital component in the throttling process, directly impacts the performance of the superfluid helium system. In this study, velocity and pressure field inside valve is numerically simulated by using computational fluid dynamics (CFD), and the flow characteristics of the valve are analyzed by theoretical calculations and experiments. Moreover, influences of cone angle, unilateral minimum clearance, structure type and working medium type on flow field distribution and flow characteristics of valve are studied by altering structural parameters of spool and working medium. The results demonstrate that increasing cone angle and unilateral minimum clearance can enhance flow capacity of valves, but influence of cone angle is more obvious. Changing the spool type will significantly alter the flow characteristics of the valve, while changing the working fluid type will only affect the velocity and pressure inside the valve. [ABSTRACT FROM AUTHOR]

Hard nitride coatings have the prospect of acting as protective layers for cutting tools because of their excellent mechanical properties and wear resistance. To enhance the mechanical, tribological, and high-temperature oxidation properties, the structural design of the coating is important. In this study, TiSiN, CrAlN/TiSiN bilayer and CrAlN/TiSiN multilayer coatings were deposited on the surface of high-speed steel by multi-arc ion plating technology. The microstructure, phase composition, mechanical properties and high-temperature tribological properties of prepared coatings were analyzed. Results indicated that the TiSiN and CrAlN/TiSiN bilayer coatings contain TiN phases and the CrAlN/TiSiN multilayer coating contains three main phases of TiN, AlN and CrN. The CrAlN/TiSiN multilayer coating possesses a denser microstructure than the other two coatings. The multilayer structure improves the cohesive and bonding strength of the coating by reducing the shear stress. The CrAlN/TiSiN multilayer coating exhibits a stable coefficient of friction and excellent wear resistance during high-temperature friction. The formation of TiO2 and Al2O3 oxide layers on the surface of the coating in a high-temperature environment contributes to the desired tribological properties of the coatings. [ABSTRACT FROM AUTHOR]

This paper presents a systematic methodology to optimise the geometry of a three-body hinge-barge wave energy converter, to maximise the energy extraction of the device in given sea states and in site-specific wave climates. To that end, a 5-degree-of-freedom mathematical model is proposed to describe the system dynamics in two-dimensional space and a two-layer optimisation is designed to find the optimal design and control variables. The inner-layer optimisation is used to find the optimal control parameters of the power take-off system and the outer-layer optimisation, which uses a genetic algorithm, is employed to find the optimal design parameters of barge lengths and of optimal ballast positioning. In the case study, this methodology is applied to a 1:20 scale prototype of the McCabe Wave Pump device. Numerical results indicate that the optimal dimensions of the device, under given sea states, can be found efficiently and accurately, and that there appears to be no obvious benefit in the use of three barges, over a two-barge system. • Geometric optimisation of a 3-barge hinge barge device (no comparable work to date). •Combined optimisation of geometry AND optimal positions for ballast masses. •2-level optimisation, updating the control for each geometry/ballast specification. •The analysis points to an optimal 2-barge configuration. [ABSTRACT FROM AUTHOR]

The co-production of ethylene glycol and methanol via ethylene carbonate hydrogenation derived from CO 2 has attracted great concerns because of the promising chemical utilization of CO 2 in large-scale. Copper-based catalysts are widely concerned in hydrogenation of ester due to the high catalytic efficiency and low cost, but the stability of copper-based catalyst is poor and needs to be further improved. In this study, the modification Cu–C@SiO 2 -R catalyst with graphite oxide was prepared by using Cu 3 (BTC) 2 as the precursor and ammonia evaporation method, and was applied in ethylene carbonate hydrogenation to synthesis ethylene glycol and methanol. Furthermore, the catalysts were characterized in detail. The results showed that the Cu–C@SiO 2 -R catalyst was modified with graphite oxide, the average size of Cu particles was 2.9 nm and Cu particles had good dispersion. In addition, both Cu–C@SiO 2 -R and Cu@SiO 2 -R catalysts had similar ratio of Cu+/(Cu0+Cu+). In a batch reactor, under 453 K, 5 MPa, 4 h, the catalytic efficiency was 80.0% EC conversion 92.2% EG and 70.8% MeOH selectivity showing excellent catalytic performance capability of Cu–C@SiO 2 -R catalyst. In long-term experiment, the Cu–C@SiO 2 -R catalyst showed excellent stability after using for 264 h. The activity was 0.63 g EC g cat −1 h−1, and 100.0% EC conversion 99.9% EG and 85.8% MeOH selectivity could be achieved in a fixed bed. After the long-term experiment, the Cu+/(Cu++Cu0) ratio in Cu–C@SiO 2 -R catalyst kept at around 0.48. In contrast, the Cu+/(Cu++Cu0) ratio in Cu@SiO 2 -R catalyst decreased sharply from 0.48 to 0.38. The stability of the structure and the balance of valence of Cu were considered to be responsible to the stability of Cu–C@SiO 2 -R catalyst, because the graphite oxide not only kept the Cu+/(Cu0+Cu+) ratio stability, but also restrained the aggregation of Cu particles and loss of copper. This work provides an in-depth understanding of the stabilization mechanism of Cu and can be a reference for the industrial application of ethylene carbonate hydrogenation. Graphite oxide modified Cu–C@SiO 2 -R catalyst was successfully prepared by using Cu 3 (BTC) 2 as the precursor and ammonia evaporation method, exhibited a high activity and stability for the hydrogenation of ethylene carbonate to co-produce methanol and ethylene glycol. [Display omitted] •The modification Cu–C@SiO 2 catalyst by graphite oxide was successfully prepared. •The Cu–C@SiO 2 catalyst shows superior catalytic performance. •Long-term experiment shows the Cu–C@SiO 2 catalyst has excellent catalytic stability. •The modification of graphite oxide is beneficial to keep the balance of copper species in the catalyst. [ABSTRACT FROM AUTHOR]

With the growing worldwide attention to marine environment protection, marine resource exploration, and so on, unmanned surface vehicles (USVs) have become one of the critical mobile marine observation equipment. However, USVs generally rely on limited onboard batteries to provide electricity, and thus, they have low endurance and poor load capacity. The lack of a long-term power supply is currently a great challenge for the further application and development of USVs. Harvesting energy from the working environment of USVs is a promising solution to address that problem. To demonstrate the possibility of this scheme, a physical prototype of a novel USV with a built-in vibration energy harvester has been fabricated and tested in an open sea for the first time. Moreover, a full-coupled mathematical model is developed to further optimize the power performance of the USV based on the Taguchi method. Experimental results show that this prototype can generate a maximum instantaneous electric power of 277.71 mW , 112.95 mW and 101.27 mW when the USV is in a status of towage, propulsive and free-floating, respectively. Simulation results present that the optimized USV can achieve a mean electric power of 246.14 mW , which is improved by 49. 88 % compared with the unoptimized results of the developed prototype. • A novel USV with a built-in vibration energy harvester is developed. • A physical prototype is designed, fabricated and tested in an open sea. • A maximum instantaneous electric power of 277.71 mW is achieved in open sea tests. • The vibration energy harvester is numerically optimized based on the Taguchi method. [ABSTRACT FROM AUTHOR]

Unmanned surface vehicles (USVs) are playing a significant role in the marine science and engineering field, e.g., they have been widely used in measuring ocean waves and currents. However, their operation time and range are limited by the energy carried by internal batteries, and this challenge needs to be urgently addressed. In this study, a novel USV concept that can harvest vibration energy excited by ocean waves in the heaving and pitching direction is presented, which provides a sustainable and continuous power supply. A fully coupled wave-to-wire model that considers the viscous damping force is developed to investigate the dynamics and electric power performance of this novel device under site-specific realistic wave climates, with the external electric load optimally tuned for each sea state. Besides, the influence of the forward speed, geometric size, mass ratio and end-stop spring is studied. Numerical results show that the proposed USV in a freely floating situation can efficiently capture and convert harvested energy into electricity with a wave-to-wire efficiency of up to 20. 21 %. Additionally, it can generate an annual mean electric power of 29.73 W, under the wave climates of the national wave energy test site in China. • A novel wave-powered unmanned surface vehicle is designed. • A fully coupled wave-to-wire model is developed. • A high wave-to-wire efficiency up to 20.21% is obtained. • An annual mean electric power of 29.73 W is achieved by the USV. [ABSTRACT FROM AUTHOR]

Unmanned surface vehicles (USVs) have been widely used in various fields credited for their high flexibility and excellent manoeuvrability. However, the limited onboard electricity of USVs restricts their applications in long-term working tasks. A promising option to address that problem is employing a wave-powered USV, where a wave energy converter is integrated into the USV. For a wave-powered USV, it is challenging to achieve a precise estimation of its power generation under complex marine environments. Although there are physics-based models of WECs used for the estimation and prediction of power generation of USVs, they cannot achieve satisfactory accuracy in practice because of the linearization and simplification of those mathematical modelling. To fill up this gap, this paper proposes a data-driven modelling method utilizing feature engineering and ensemble learning to estimate the mean power generation of a wave-powered USV, relying on time-serial measurements obtained from real physical wave-flume experiments under regular waves. Results show that the estimation achieves promising performance, where the minimum RMSEs are 3.359 mW and 6.148 mW for a harvester-to-wire model and a wave-to-wire model, respectively. Additionally, the proposed method shows great potential for real-sea applications, such as online power prediction and control. • A data-driven method for power estimation of a wave-powered USV is proposed. • The robustness of the proposed method is verified with the presence of noise. • The proposed method possesses practical significance, such as data-driven control. [ABSTRACT FROM AUTHOR]

With the diversification of marine monitoring buoy functions, limited onboard batteries have been unable to meet the energy demand of multifarious carrying sensors. Finding a self-sustained power supply for marine monitoring buoys is an urgent problem, while wave energy is an ideal and promising option to address that problem. In this study, two wave-excited vibration energy harvesters (WVEHs) are proposed, which can be installed inside large buoys to provide a sustainable power supply. A full-coupled wave-to-wire model is developed to investigate the influence of blocks' mass, geometric size of buoys, mooring system and WVEH's quantity on the electric power performance of harvesters in realistic sea states. Parametric studies based on the Taguchi method imply that the sea state and the WVEH's quantity have a significant effect on the device's electric power performance. Numerical results indicate that the optimized two harvesters can produce a mean electric power of 777.50 W and 747.43 W , respectively, under a sea state with a peak wave period of 7 s and a significant wave height of 1.6 m. A high wave-to-wire efficiency of 2. 60 % is obtained for a specific system parameter combination. Furthermore, more electric power generation can be achieved by installing multiple harvesting units. • Two wave-excited vibration energy harvesters are proposed for large marine buoys. • A full-coupled wave-to-wire model is developed. • Harvesters are optimized based on the Taguchi method in realistic sea states. • A mean electric power of 777.50 W is achieved under a peak wave period of 7 s. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction (SCR) has been extensively employed in industries for the removal of NO x while it is still a challenge to develop novel low-temperature catalysts. The redox and acid sites on the catalyst are often preconditions that cooperate in the SCR reaction. In this study, a series of MnO x supported on MgAl 2 O 4 spinel catalysts (denoted as Mn/MAS) were successfully prepared by incipient wetness impregnation method for low-temperature SCR of NO x with ammonia. The effects of the calcination temperature of MAS support and Mn loading on catalyst structure and performance were examined. The Mn0.12/MAS-700 catalyst showed the best low-temperature denitrification performance, with more than 80% conversion of NO at 150–300 °C and higher than 60% N 2 selectivity. Moreover, the denitrification efficiency remained at nearly 90% in the presence of H 2 O. The physicochemical properties of the catalysts were determined using various characterization methods, and the corresponding results found that the higher concentration of Mn4+ and surface chemisorption oxygen enhanced the low-temperature activity of the catalysts. The addition of Mn species increased the surface acidity of weak acid centers which promoted the catalyst activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) revealed that the Eley-Rideal mechanism was introduced mainly at 100 °C on the Mn0.12/MAS-700 catalyst. This work provides new inspiration into the effect of Mn species, and the synergistic role of active components Mn and MAS support in the SCR reaction. [Display omitted] • The MnO x supported on Mg-Al spinel exhibited superior low-temperature activity and N 2 selectivity. • The optimal catalyst Mn0.12/MAS-700 showed excellent H 2 O resistance. • The balance of redox capacity and acid sites was considered as crucial factor. • The Eley-Rideal mechanism dominated in the SCR reaction. [ABSTRACT FROM AUTHOR]

Highlights • The fluctuation of the reflected intensity from a group of discrete particles in turbulence atmospheric model. • Log-amplitude covariance function of the reflected waves from two particles at different heights in turbulent atmosphere is deduced. • A fast algorithm to calculated the scintillation index of the received field is developed based on the Mote Carlo method. Abstract The intensity fluctuation of the reflected field from a group of discrete particles illuminated by a laser beam in turbulent atmosphere is investigated here. First, the expression of the correlation function of the received intensity is derived by dividing the illuminated space into a number of sub blocks. Then, the log-amplitude covariance function of the reflected waves from two particles at different heights in a turbulent atmosphere is deduced using the Rytov method. The dimensions of the sub blocks are discussed based on the 3D log-amplitude covariance function, and the normalized variance of the received intensity is calculated and discussed based on the sub blocks. Results show that the normalized variance is mainly affected by the cross section area of the illuminated space, whereas the latter is greatly influenced by the position of the received point and the width of the transmitting beam. [ABSTRACT FROM AUTHOR]