Microstructure Turbulence Measurement in the Northern South China Sea from a Long-Range Hybrid AUV.

This study describes the development of a long-range hybrid autonomous underwater vehicle (AUV) for ocean turbulence measurement. It is a unique instrument, combining the characteristics of the conventional AUV and the buoyancy-driven glider, with a variety of flexible motion modes, such as cruise mode, glider mode, drift mode, and combination of multiple motion modes. The hybrid AUV was used for continuous turbulence measurement in the continental slope of the northern South China Sea in 2020. A total of ten continuous profiles were completed covering a horizontal span of 25 Km and a depth of 200 m. The hybrid AUV was operated in the combined glider and cruise mode. The hybrid AUV's flight performance was stable and satisfied the requirement for turbulence observation. The measured velocity shears from both probes were in good agreement, and the noise-reduced shear spectra were in excellent agreement with the Nasmyth spectrum. The water column in the study area was highly stratified, with a thick thermocline. The dissipation rate (ε) varied from 1.41 × 10-10 to 4.18 × 10-7 W·kg-1. In the surface mixed layer, high values of ε (10-9∼10-8 W·kg-1) were observed toward the water surface. In the thermocline, ε was 10-9.5∼10-9 W·kg-1, which was smaller than the level of the surface mixed layer. This result was mainly because of the strong "barrier"-like thermocline, which damped the transmission of wind and heat energy from the surface mixed layer to the deep layer. Overall, this study demonstrates the utility of hybrid AUVs for collecting oceanic turbulence measurements. They are a powerful addition to traditional turbulence instruments, as they make it possible to survey large areas to obtain high-quality and high-resolution data in both vertical and horizontal directions over long durations.

Design and Motion Performance Analysis of Turbulent AUV Measuring Platform.

The use of a multi-functional autonomous underwater vehicle (AUV) as a platform for making turbulence measurements in the ocean is developed. The layout optimization of the turbulence package and platform motion performance are limitation problems in turbulent AUV design. In this study, the computational fluid dynamics (CFD) method has been used to determine the optimized layout position and distance of the shear probe integrated into an AUV. When placed 0.8 D ahead of the AUV nose along the axis, the shear probe is not influenced by flow distortion and can contact the water body first. To analyze the motion of the turbulence AUV, the dynamic model of turbulence AUV for planar flight is obtained. Then, the mathematical equations of speed and angle of attack under steady-state motion have also been obtained. By calculating the hydrodynamic coefficients of the turbulence AUV and given system parameters, the simulation analysis has been conducted. The simulation results demonstrated that the speed of turbulent AUV is 0.5-1 m/s, and the maximum angle of attack is less than 6.5°, which meets the observation requirements of the shear probe. In addition, turbulence AUV conducted a series of sea-trials in the northern South China Sea to illustrate the validity of the design and measurement. Two continuous profiles (1000 m) with a horizontal distance of 10 km were completed, and numerous high-quality spatiotemporal turbulence data were obtained. These profiles demonstrate the superior flight performance of turbulence AUV. Analysis shows that the measured data are of high quality, with the shear spectra being in very good agreement with the Nasmyth spectrum. Dissipation rates are consistent with background shear. When shear velocity is weak, the measurement of dissipation rate is 10-10 W Kg-1. All indications are that the turbulence AUV is suitable for long-term, contiguous ocean microstructure measurements, which will provide data needed to understand the temporal and spatial variability of the turbulent processes in the oceans.

A Nonlinear Circuit Analysis Technique for Time-Variant Inductor Systems.

Time-variant inductors exist in many industrial applications, including sensors and actuators. In some applications, this characteristic can be deleterious, for example, resulting in inductive loss through eddy currents in motors designed for high efficiency operation. Therefore, it is important to investigate the electrical dynamics of systems with time-variant inductors. However, circuit analysis with time-variant inductors is nonlinear, resulting in difficulties in obtaining a closed form solution. Typical numerical algorithms used to solve the nonlinear differential equations are time consuming and require powerful processors. This investigation proposes a nonlinear method to analyze a system model consisting of the time-variant inductor with a constraint that the circuit is powered by DC sources and the derivative of the inductor is known. In this method, the Norton equivalent circuit with the time-variant inductor is realized first. Then, an iterative solution using a small signal theorem is employed to obtain an approximate closed form solution. As a case study, a variable inductor, with a time-variant part stimulated by a sinusoidal mechanical excitation, is analyzed using this approach. Compared to conventional nonlinear differential equation solvers, this proposed solution shows both improved computation efficiency and numerical robustness. The results demonstrate that the proposed analysis method can achieve high accuracy.

Thermal physical property-based fusion of geostationary meteorological satellite visible and infrared channel images.

Geostationary meteorological satellite infrared (IR) channel data contain important spectral information for meteorological research and applications, but their spatial resolution is relatively low. The objective of this study is to obtain higher-resolution IR images. One common method of increasing resolution fuses the IR data with high-resolution visible (VIS) channel data. However, most existing image fusion methods focus only on visual performance, and often fail to take into account the thermal physical properties of the IR images. As a result, spectral distortion occurs frequently. To tackle this problem, we propose a thermal physical properties-based correction method for fusing geostationary meteorological satellite IR and VIS images. In our two-step process, the high-resolution structural features of the VIS image are first extracted and incorporated into the IR image using regular multi-resolution fusion approach, such as the multiwavelet analysis. This step significantly increases the visual details in the IR image, but fake thermal information may be included. Next, the Stefan-Boltzmann Law is applied to correct the distortion, to retain or recover the thermal infrared nature of the fused image. The results of both the qualitative and quantitative evaluation demonstrate that the proposed physical correction method both improves the spatial resolution and preserves the infrared thermal properties.

Transparent, Flexible, Responsive Switching "Delayed" Amphiphilic Coatings Designed on the Basis of the Full-Cycle Antifouling Strategy.

Marine fouling on the surface of ships and equipment not only creates problems of enhanced resistance to navigation and increased energy consumption but also leads to unclear vision and inaccurate data collection. Antifouling coatings to resist fouling are effective, but it is difficult to achieve long-lasting fouling protection with a single interface state. Switching the status of the interface by intelligent response is a reasonable way to achieve full-cycle efficient antifouling. In this study, the hydrophobic and active antifouling interface in the initial state was achieved by adopting the fluorine-containing group and the natural extract (citronellol) as the antifouling active site. The switching of the interface relies on silanes, which respond to the generation of zwitterions in a seawater environment. Eventually, the interface switched from the hydrophobic state to the amphiphilic state with delayed formation, which achieved continued antifouling. Based on the full-cycle antifouling concept, the combination of low surface energy and antifouling active ingredients in the initial state sustainably switched surfaces in the midterm (free radicals generated during the hydrolysis process), and amphiphilic interfaces formed by "delays" produced an antifouling effect from the initial stage to the subsequent stage. The excellent antifouling activity (bacterial and diatom attachment inhibition by over 90% and significantly reduced mussel adhesion force), optical transparency, and flexibility of these coatings indicate the potential for the application of antifouling coatings prepared from hyperbranched silicone-based resins; they can also be used for data extraction sensors, underwater probes, marine photovoltaics, and other areas where transparency is required.

Self-healing and corrosion-sensing multifunctional coatings containing pH-sensitive TiO2-based composites.

Polyelectrolyte-encapsulated nanocontainers can effectively respond to changes of pH and thus control the on-demand release of corrosion inhibitors. A pH-responsive release system (Phen-Tpp@MTNs-PDDA) was developed based on the cationic polyelectrolyte poly dimethyl diallyl ammonium chloride (PDDA) encapsulated mesoporous TiO2 nanocontainers (MTNs) loaded with 1,10-phenanthroline (Phen) and tripolyphosphate ions (Tpp) corrosion inhibitors. The epoxy coating (EP) embedded with Phen-Tpp@MTNs-PDDA (Phen-Tpp@MTNs-PDDA/EP) demonstrates superior self-healing properties and confers long-term protection on the metal substrate through the cooperative effect of Phen and Tpp. Simultaneously, this hybrid coating is endowed with corrosion sensing capability based on the color development originating from the interaction of Phen and carbon steel. This self-healing and corrosion-sensing multifunctional coating provides an effective strategy for the corrosion protection of metals.

Advanced MXene-based materials for efficient extraction of uranium from seawater and wastewater.

In order to realize the low-carbon development policy, the large-scale development and utilization of nuclear energy is very essential. Uranium is the key resource for nuclear industry. The extracting and recycling uranium from seawater and nuclear wastewater is necessary for secure uranium reserves, ensure energy security, control pollution and protect the environment. The novel nanomaterial MXene possesses the layered structure, high specific surface area, and modifiable surface terminal groups, which allowed it to enrich uranium. In addition, good photovoltaic and photothermal properties improves the ability to adsorb uranium. The excellent radiation resistance of the MAX phase strongly indicates the potential use of MXene as an effective uranium adsorbent. However, there are relatively few reviews on its application in uranium extraction and recovery. This review focuses on the recent advances in the use of MXene-based materials as highly efficient adsorbents for the recovery of uranium from seawater and nuclear wastewater. First, the structural, synthetic and characterization aspects of MXene materials are introduced. Subsequently, the adsorptive properties of MXene-based materials are evaluated in terms of uranium extraction recovery capability, selectivity, and reproducibility. Furthermore, the interaction mechanisms between uranium and MXene absorbers are discussed. Finally, the challenges for MXene materials in uranium adsorption applications are proposed for better design of new types of MXene-based adsorbents.

pH-Responsive Graphene Oxide-Based 2D/3D Composite for Enhancing Anti-Corrosion Properties of Epoxy Coating.

The functionalized graphene oxide (GO)-based composites as fillers added into organic coatings are desired for realizing the longstanding corrosion protection of carbon steel. Here, the pH-responsive two-dimensional/three-dimensional (2D/3D) GO-based composite (ZIF-90-AAP/GO) was developed by environmentally friendly corrosion inhibitor 4-aminoantipyrine (AAP) anchored on the in situ growth of zeolite imidazolate framework-90 (ZIF-90) on the GO surface (ZIF-90/GO) through the Schiff base reaction. The active filler (ZIF-90-AAP/GO) was incorporated into an epoxy coating (EP) to obtain a high-performance self-healing coating on the surface of carbon steel. ZIF-90-AAP can greatly improve dispersion and compatibility of GO in EP. The low-frequency impedance modulus of ZIF-90-AAP/GO-EP can still reach up to 1.35 × 1010 Ω⋅cm2 after 40 days, which is about three orders of magnitude higher than that of the EP containing GO (GO-EP) relying on its passive and active corrosion protection. Meanwhile, ZIF-90-AAP/GO-EP exhibits excellent self-healing performance. The self-healing rate of ZIF-90-AAP/GO changes from negative to positive after 24 h, which results from the effective corrosion inhibition activity of ZIF-90-AAP for carbon steel based on the pH-triggered controlled release of AAP. The developed pH-responsive 2D/3D GO-based composite coating is very attractive for the corrosion protection of carbon steel.

Underwater gliders linear trajectory tracking: The experience breeding actor-critic approach.

This paper studies the underwater glider trajectory tracking in currents field. The objective is to ensure that trajectories fit to the straight target track. The underwater glider model is introduced to demonstrate the vehicle dynamic properties. Considering currents disturbance as well as the uncertain status of the glider controlled by complicated roll policies, the trajectory tracking task can be classified into the model-free optimization. Such problem is difficult to solve with mathematical analysis. This work transfers the underwater glider trajectory tracking into a Markov Decision Process by specifying the actions and observations as well as rewards. On this basis, a neural network controls framework called experience breeding actor-critic is proposed to handle the trajectory tracking. The EBAC enhances the explorations to the potentially high reward area. And it steers glider heading meticulously so as to counteract the currents influence. Through simulation results, the EBAC shows a desired performance in controlling the gliders to accurately fit the target track.

Ionic liquid combined with NiCo2O4/rGO enhances electrochemical oxygen sensing.

Ionic liquids are promising electrolytes for electrochemical gas sensors that have unique physicochemical properties such as negligible vapor pressure and high thermal stability. The modification of ionic liquid (IL) by combining metal oxide with reduced graphene oxide (rGO) is an effective method to improve its gas-sensing properties. In this study, the mesoporous structure of NiCo2O4/rGO is synthesized by simple one-step method, and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) is mixed with it to form the composite material NiCo2O4/rGO/[BMIM][PF6]. Electrochemical test results indicate that the three electrolytes exhibit response current and long-term stability in the oxygen environment. The oxygen sensor based on NiCo2O4/rGO/[BMIM][PF6] significantly improves the response current and working stability of pure ionic liquid. The sensitivity of the sensor is 0.1087 µA/[%O2], and the linear regression coefficient of the reduction peak current calibration curve is 0.9995. After continuous cyclic voltammetry, the reduction peak current remains at 90% of the initial current value. The interaction of IL and NiCo2O4/rGO significantly enhances electrochemical oxygen sensing performance.

Three-dimensional heterostructured polypyrrole/nickel molybdate anchored on carbon cloth for high-performance flexible supercapacitors.

The urgent demands of energy storage for wearable electronics necessitates the development of flexible supercapacitors (FSCs). However, the service environment of portable/wearable devices requires supercapacitors to possess excellent mechanical properties to withstand harsh straining conditions, such as bending, rolling, and twisting. Hence, to develop a high-performance flexible supercapacitor (FSC) that possesses both superior electrochemical properties and remarkable mechanical capacities is still a formidable challenge. In this paper, we successfully fabricate a 3D heterostructured electrode with bulge structured polypyrrole (PPy) wrapped NiMoO4 nanowires on carbon cloth (CC). Benefiting from the 3D heterostructure and the synergistic effect between NiMoO4 and PPy, the PPy/NiMoO4/CC electrode shows a high areal capacitance of 3.4 F cm-2 and cyclic stability (94% capacitance retention). Moreover, the assembled PPy/NiMoO4/CC//activated carbon (AC)/CC device exhibits a high energy density (0.5 mW cm-2 at a power density of 3.7 mWh cm-2). Furthermore, the CV curves of PPy/NiMoO4/CC//AC/CC show no obvious change under miscellaneous deformation conditions, indicating good flexibility. This work demonstrates that the assembled PPy/NiMoO4/CC//AC/CC FSC possesses notable electrochemical properties and exhibits great potential for application in future wearable energy-storage devices.

Anti-Biofouling and Water-Stable Balanced Charged Metal Organic Framework-Based Polyelectrolyte Hydrogels for Extracting Uranium from Seawater.

Metal-organic frameworks (MOFs) are diffusely defined as a promising class of porous material for uranium extraction from seawater, but there are still challenges in their stability and anti-biofouling performance. Herein, a water-stable and anti-biofouling ZIF-67/SAP0.45 composite hydrogel was reported by the sequential processes of electrostatic interactions between the oppositely charged polymer, ionic gelation, and template growth of ZIF-67 crystals. Entanglement of positively charged polyethyleneimine (PEI) and negatively charged sodium alginate (SA) polymer chains provided external porosities, anti-biofouling properties, and mechanical support for the hydrogels and further reduced the possibility of ZIF-67 aggregation. The neutral composite hydrogel possessed the least Nitzschia on the surface after 7 days contact, which endows the adsorbent with a high uranium uptake capacity of 2107.87 ± 41.64 µg g-1 at 1 mg L-1 uranium-containing seawater with 8.6 × 105 mL-1 Nitzschia. Additionally, this adsorbent showed water stability with an uranium uptake capacity of 232.88 ± 8.02 mg g-1 even after five adsorption-desorption cycles because of the excellent preparation method. Benefitting from the distinctive hierarchical structure and large accessible surface area, the resultant adsorbent achieved a high uranium capacity of 6.99 ± 0.26 mg g-1 in real seawater. This flexible and scalable approach made the MOF/SAP composite hydrogel a highly desirable uranium adsorbent.

Layer-by-layer inkjet printing GO film and Ag nanoparticles supported nickel cobalt layered double hydroxide as a flexible and binder-free electrode for supercapacitors.

Inkjet printing is an attractive technique in the field of flexible electronics due to the direct writing, digital controls and non-contact operation process. In this work, we successfully printed graphite oxide and Ag nanoparticles on the substrate of flexible carbon cloth to form a flexible, conductive and hydrophilic layer, which could be used as a new substrate with an electron transport layer of large surface area. In addition, Ni-Co LDH nanosheets as the main active materials were synthesized for improving the electrochemical activity via a convenient electrochemical deposition method. The binder-free Ni-Co LDH/Ag/rGO@CC electrode exhibits outstanding electrochemical performance along with a high capacity of 173 mA h g-1 at 1 A g-1. Moreover, an asymmetric supercapacitor (ASC) was assembled with Ni-Co LDH/Ag/rGO@CC electrode as the positive electrode materials and activated carbon coated CC as the negative electrode materials, showing a high capacity of 95 mA h g-1 at 0.6 A g-1, and maximum energy density of 76 Wh kg-1 at a power density of 480 W kg-1.

Design and Performance Test of an Ocean Turbulent Kinetic Energy Dissipation Rate Measurement Probe.

Ocean turbulent kinetic energy dissipation rate is an essential parameter in marine environmental monitoring. Numerous probes have been designed to measure the turbulent kinetic energy dissipation rate in the past, and most of them utilize piezoelectric ceramics as the sensing element. In this paper, an ocean turbulent kinetic energy dissipation rate measurement probe utilizing a microelectromechanical systems (MEMS) piezoresistor as the sensing element has been designed and tested. The triangle cantilever beam and piezoresistive sensor chip are the core components of the designed probe. The triangle cantilever beam acts as a velocity-force signal transfer element, the piezoresistive sensor chip acts as a force-electrical signal transfer element, and the piezoresistive sensor chip is bonded on the triangle cantilever beam. One end of the triangle cantilever beam is a nylon sensing head which contacts with fluid directly, and the other end of it is a printed circuit board which processes the electrical signal. A finite element method has been used to study the effect of the cantilever beam on probe performance. The Taguchi optimization methodology is applied to optimize the structure parameters of the cantilever beam. An orthogonal array, signal-to-noise ratio, and analysis of variance are studied to analyze the effect of these parameters. Through the use of the designed probe, we can acquire the fluid flow velocity, and to obtain the ocean turbulent dissipation rate, an attached signal processing system has been designed. To verify the performance of the designed probe, tests in the laboratory and in the Bohai Sea are designed and implemented. The test results show that the designed probe has a measurement range of 10-8⁻10-4 W/kg and a sensitivity of 3.91 × 10-4 (Vms²)/kg. The power spectrum calculated from the measured velocities shows good agreement with the Nasmyth spectrum. The comparative analysis between the designed probe in this paper and the commonly used PNS probe has also been completed. The designed probe can be a strong candidate in marine environmental monitoring.

Polypyrrole/cobalt ferrite/multiwalled carbon nanotubes as an adsorbent for removing uranium ions from aqueous solutions.

A novel rod-like, dual-shell structural adsorbent of polypyrrole/cobalt ferrite/multiwalled carbon nanotubes (PPy/CoFe2O4/MWCNTs) was successfully synthesized by a hydrothermal method, which could easily separate uranium(vi) ions with an external magnetic field. The structure and morphology of PPy/CoFe2O4/MWCNTs were characterized by VSM, XRD, XPS TEM and FT-IR. The results proved that the dual-shell structure was obtained in which a shell of cobalt ferrite and polypyrrole formed around the MWCNTs core. In batch adsorption experiments, including pH, equilibrium time and temperature on uranium adsorption, were investigated. The main results show that the PPy/CoFe2O4/MWCNTs composite has a higher affinity towards the uptake of uranium(vi) from aqueous solutions. The highest adsorption capacity reached was 148.8 mg U per g at pH 7. A kinetic analysis showed that the adsorption process was best described by a pseudo-second-order kinetic model. The uranium sorption equilibrium data correlated well with the Langmuir sorption isotherm model in the thermodynamic analysis. 0.5 mol per L NaHCO3 was used as the desorbent and good adsorption properties were shown after the desorption procedures were repeated three times. Thus, PPy/CoFe2O4/MWCNTs was an excellent adsorbent for removing uranium(vi) ions.

Synthesis, characterization and enhanced gas sensing performance of porous ZnCo2O4 nano/microspheres.

In recent years, spinel-type compounds have attracted great interest because of their gem-like qualities. However, little is known of their gas sensing properties. We report, in this paper, on a self-assembly method to prepare porous ZnCo2O4 (ZCO) nano/microspheres by a facile one-step solvothermal process and subsequent annealing. Abundant techniques were used to characterize the morphology and structure of the as-obtained compounds. Our data indicate that the hierarchical nano/microspheres are constructed from numerous nanoparticles primarily, which have a higher specific surface area (ca. 77.3 m(2) g(-1)) and are of uniform diameter (ca. 1 µm). To demonstrate their potential application, gas sensors based on the as-synthesized ZCO nano/microspheres were fabricated to test their sensing performance, whose sensing behaviours correspond to p-type semiconductors. The test results also indicate that porous spinel-type compounds have an excellent kinetic response to ethanol at an operating temperature of 175 °C and a superior selectivity. As such, hierarchical porous ZnCo2O4 nano/microspheres will hold promising potential in the gas sensor field.

Preparation of magnetic core-shell iron oxide@silica@nickel-ethylene glycol microspheres for highly efficient sorption of uranium(VI).

We report a facile approach for the formation of magnetic core-shell iron oxide@silica@nickel-ethylene glycol (Fe3O4@SiO2@Ni-L) microspheres. The structure and morphology of Fe3O4@SiO2@Ni-L are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen sorption isotherm. The composite possesses a high specific surface area of 382 m(2) g(-1). The obtained core/shell structure is composed of a superparamagnetic core with a strong response to external fields, which are recovered readily from aqueous solutions by magnetic separation. When used as the adsorbent for uranium(vi) in water, the as-prepared Fe3O4@SiO2@Ni-L multi-structural microspheres exhibit a high adsorption capacity, which is mainly attributed to the large specific surface area and typical mesoporous characteristics of Fe3O4@SiO2@Ni-L microspheres. This work provides a promising approach for the design and synthesis of multifunctional microspheres, which can be used for water treatment, as well as having other potential applications in a variety of biomedical fields including drug delivery and biosensors.