Detection and identification of oil spill species based on polarization information.

Aiming at the problem of poor oil identification accuracy in existing oil spill detection technologies, the polarization degree model of oil spill on rough sea surface under different azimuths and zenith angles was established based on Fresnel theory. The analytical expressions of visible light polarization degree in calm and fluctuating water surface were derived respectively, and the polarization degree model of oil spill in reflection space was constructed. The effectiveness of the method and its influence on the polarization distribution of oil spill were analyzed by simulation. A portable turntable was designed to test the polarization characteristics of the experiment, and the visible light polarization detection experiment was carried out. The visible light polarization images of five typical oil spills at different observation azimuth and zenth angles were obtained. The differences in the polarization degrees of different oil species were analyzed, and the correctness of the theoretical model was proved by experiments. The polarization detection experiment of visible light pBRDF was completed, which more intuitively showed the variation law of the polarization characteristics of light reflected by different oil spills in different spatial positions. Using polarization information to distinguish oil species is a useful supplement to the traditional oil spill detection method and has important significance to improve the marine pollution control ability.

Improvement of coated aluminum sheet pBRDF model based on scattering and phase function optimization.

The pBRDF model is able to relate the properties of target materials to the polarization information of incident and reflected light, and is an important basis for obtaining polarization information of targets in space. It is an important basis for obtaining target polarization information and polarization detection of space targets. P-G model is the first strictly pBRDF model officially released, but there are still deficiencies. In this paper, we first analyze the assumption framework of the P-G model, derive the imperfections in the framework through the analysis of the assumption framework, and add scattering and phase function to enhance the existing model. On the basis of the existing P-G model and parameter inversion, the output results of the model are compared with the experimental data through simulation, and the results show that the relative error of the target's linear polarizability is reduced under the improved model, which proves the accuracy and precision of the improved model.

Simplified analysis and suppression of polarization aberration in planar symmetric optical systems.

Polarized remote sensing imaging has attracted more attention in recent years due to its wider detection information dimension compared to traditional imaging methods. However, the inherent instrument errors in optical systems can lead to errors in the polarization state of the incident and outgoing light, which is the polarization aberration of the optical system, resulting in a decrease in polarization detection accuracy. We propose a polarization aberration simplification calculation method for planar symmetric optical systems, by what only three ray samples are needed to obtain the distribution of polarization aberrations within the pupil. This method has a calculation accuracy close to traditional methods, and the sampling rate is 0.003 times that of traditional methods. Based on this, we designed a merit function that optimizes both wavefront and polarization aberrations simultaneously. It is found that diattenuation and retardance of the optical system are 62% and 58% of the original, and the polarization crosstalk term is reduced by 37% when the polarization weight factor takes an appropriate value. And at the same time, the wavefront aberration has also been well optimized.

Compressive space-dimensional dual-coded hyperspectral polarimeter (CSDHP) and interactive design method.

A compressive space-dimensional dual-coded hyperspectral polarimeter (CSDHP) and interactive design method are introduced. A digital micromirror device (DMD), a micro polarizer array detector (MPA), and a prism grating prism (PGP) are combined to achieve single-shot hyperspectral polarization imaging. The longitudinal chromatic aberration (LCA) and spectral smile of the system are both eliminated to guarantee the matching accuracy of DMD and MPA pixels. A 4D data cube with 100 channels and 3 Stocks parameters is reconstructed in the experiment. The feasibility and fidelity are verified from the image and spectral reconstruction evaluations. It is demonstrated that the target material can be distinguished by CSDHP.

Polarization Super-Resolution Imaging Method Based on Deep Compressed Sensing.

The division of focal plane (DoFP) polarization imaging sensors, which can simultaneously acquire the target's two-dimensional spatial information and polarization information, improves the detection resolution and recognition capability by capturing the difference in polarization characteristics between the target and the background. In this paper, we propose a novel polarization imaging method based on deep compressed sensing (DCS) by adding digital micromirror devices (DMD) to an optical system and simulating the polarization transmission model of the optical system to reconstruct high-resolution images under low sampling rate conditions. By building a simulated dataset, training a polarization super-resolution imaging network, and showing excellent reconstructions on real shooting scenes, compared to current algorithms, our model has a higher peak signal-to-noise ratio (PSNR), which validates the feasibility of our approach.

Design and experimental study of a polarization imaging optical system for oil spills on sea surfaces.

The marine environment is complex and changeable. To meet the urgent needs of accurate detection and identification of oil spills, a visible/infrared dual-band common-aperture polarization imaging optical system based on a defocused plane polarization detector is designed. The optical system is evaluated by ZEMAX simulation software, and we carried out the polarization imaging oil species discrimination experiment based on the split focal plane polarization detector, which proved that for some oil species that cannot be distinguished by intensity information, the polarization information can be distinguished. It verifies the feasibility of polarization detection in the discrimination of marine oil spills, which is of great practical significance in the field of marine oil spill detection.

The Influence of Optical Alignment Error on Compression Coding Superresolution Imaging.

Superresolution (SR) imaging technology based on compression coding has always been considered as the key to break through the geometric resolution of the detector. In addition to factors such as the reconstruction algorithm and mounting platform vibrations, the impact of inherent errors in the optical system itself on the reconstruction results of SR imaging is also obvious. To address this issue, a study on the design of the SR optical system and the influence of optical alignment errors on SR imaging was conducted. The design of the SR optical system based on digital micro-mirror device (DMD) for long-wave infrared wavelength was completed, and an athermal analysis of the system was carried out. The design results showed that the SR optical system has good imaging quality in the operating temperature range. The imaging model of the DMD SR imaging optical system is established according to the designed SR optical system. We investigated the influence of various alignment errors, including decenter, tilt, lens interval error and defocus, on the imaging properties of the SR optical system. Various random combinations of alignment errors were introduced into the optical system, respectively, and the SR reconstructed image quality of the imaging system was analyzed using the inverse sensitivity method to obtain the tolerance limits when the system was assembled. Finally, the effectiveness of the method to obtain the alignment tolerance limit of the compression coding SR imaging optical system was verified through a desktop demonstration experiment.

Achieving stable Na metal cycling via polydopamine/multilayer graphene coating of a polypropylene separator.

Sodium metal batteries are considered one of the most promising low-cost high-energy-density electrochemical energy storage systems. However, the growth of unfavourable Na metal deposition and the limited cell cycle life hamper the application of this battery system at a large scale. Here, we propose the use of polypropylene separator coated with a composite material comprising polydopamine and multilayer graphene to tackle these issues. The oxygen- and nitrogen- containing moieties as well as the nano- and meso- porous network of the coating allow cycling of Na metal electrodes in symmetric cell configuration for over 2000 h with a stable 4 mV overpotential at 1 mA cm-2. When tested in full Na || Na3V2(PO4)3 coin cell, the coated separator enables the delivery of a stable capacity of about 100 mAh g-1 for 500 cycles (90% capacity retention) at a specific current of 235 mA g-1 and satisfactory rate capability performances (i.e., 75 mAh g-1 at 3.5 A g-1).

Scalable Production of Freestanding Few-Layer ß12-Borophene Single Crystalline Sheets as Efficient Electrocatalysts for Lithium-Sulfur Batteries.

Two-dimensional (2D) borophene has attracted tremendous interest due to its fascinating properties, which have potential applications in catalysts, energy storage devices, and high-speed transistors. In the past few years, borophene was theoretically predicted as an ideal electrode material for lithium-sulfur (Li-S) batteries because of its low-density, metallic conductivity, high Li-ion surface mobility, and strong interface bonding energy to polysulfide. But until now, borophene-based Li-S batteries have not yet been achieved in experiments due to the absence of a large-scale synthetic method of freestanding borophene nanostructures with a high enough structural stability, conductivity, and uniformity. Herein, we developed a low-temperature liquid exfoliation (LTLE) method to synthesize freestanding few-layer ß12-borophene single-crystalline sheets with a P6¯m2 symmetry in tens of milligrams. The as-synthesized 2D sheets were used as the polysulfide immobilizers and electrocatalysts of Li-S batteries. The resulting borophene-based Li-S battery delivered an extralarge areal capacity of 5.2 mAh cm-2 at a high sulfur loading of 7.8 mg cm-2, an excellent rate performance of 8 C (@721 mAh g-1), and an ultralow capacity fading rate of 0.039% in 1000 cycles, outperforming commercial Li-ion batteries and many other 2D material-based Li-S batteries. Based on the density functional theory model, the excellent electrochemical performances of the borophene-based Li-S batteries should originate from the enormous enhancement of ß12-borophene sheets for both the surface migration of the Li-ions and the adsorption energy of Li2Sn clusters. Our results thus demonstrate a great potential for scalable production of freestanding ß12-borophene single-crystalline sheets in future high-performance Li-S batteries.

Trends of epidemiological characteristics of traumatic spinal cord injury in China, 2009-2018.

OBJECTIVE: We focus on providing the first comprehensive national dataset on the incidence, injury aetiology and mortality of TSCI in China. METHODS: A multi-stage stratified cluster sampling method was used. We included TSCI cases from all hospitals in three regions, nine provinces and 27 cities in China via search of electronic medical records and retrospectively analysed the characteristics of TSCI in China from 2009 to 2018. We estimated the incidence of TSCI in the total population and subgroups. RESULTS: There were 5954 actual cases in 2009, corresponding to a total estimated TSCI incidence of 45.1 cases per million population (95% CI, 44.0-46.3). There were 10,074 actual cases in 2018, corresponding to a total estimated TSCI incidence of 66.5 cases per million population (95% CI, 65.2-67.8) (P < 0.001; annual average percentage change (AAPC), 4.4%). From 2009 to 2018, the incidence of almost all sex/age groups showed an increasing trend over time (P < 0.001; AAPC, 0.7-8.8%). The elderly population (aged 65-74) displayed the highest incidence of TSCI (with an average annual incidence of 127.1 cases per million [95% CI, 119.8-134.3]). CONCLUSIONS: The TSCI incidence increased significantly from 2009 to 2018. The incidence in the elderly populations was consistently high and continues to increase over time. The mortality of TSCI patients in hospitals is relatively low and continues to decrease each year, but elderly individuals remain at a high risk of hospital death.

Design of a superresolution large-aperture telescopic optical system with a wide field of view.

A pupil modulator is a useful tool to improve the resolution of an optical imaging system beyond the classical diffraction limit. However, when this technology is used in a large-aperture telescopic imaging system, the field of view (FOV) with good superresolution (SR) imaging quality is significantly smaller than the designed FOV of the baseline optical system. In this paper, we investigate the influence of various aberrations on the SR properties of a telescopic system using a low sidelobe five-ring pure phase pupil modulator. On this basis, we propose an optimal design method for a wide FOV and a large-aperture telescopic baseline optical system with uniform image quality and a particular residue of symmetric aberration. The design results show that when the optimized 4 m aperture baseline optical system and the modulator are combined as the imaging system, the imaging system has a round and very similar point spread function in the FOV range of 0.28°; the SR gain ratio is 1.234-1.254; and the highest sidelobe intensity is less than 0.1; thus, the system maintains a high resolution ratio and a low sidelobe energy throughout the entire FOV. Finally, a reasonable tolerance model of the baseline optical system is established. The central symmetry tolerances are observed to be loose in this model, thereby reducing the cost and manufacturing difficulty of the system.

3D Flexible, Conductive, and Recyclable Ti3C2Tx MXene-Melamine Foam for High-Areal-Capacity and Long-Lifetime Alkali-Metal Anode.

Alkali metals are ideal anodes for high-energy-density rechargeable batteries, while seriously hampered by limited cycle life and low areal capacities. To this end, rationally designed frameworks for dendrite-free and volume-changeless alkali-metal deposition at both high current densities and capacities are urgently required. Herein, a general 3D conductive Ti3C2TX MXene-melamine foam (MXene-MF) is demonstrated as an elastic scaffold for dendrite-free, high-areal-capacity alkali anodes (Li, Na, K). Owing to the lithiophilic nature of F-terminated MXene, conductive macroporous network, and excellent mechanical toughness, the constructed MXene-MF synchronously achieves a high current density of 50 mA cm-2 for Li plating, high areal capacity (50 mAh cm-2) with high Coulombic efficiency (99%), and long lifetime (3800 h), surpassing the Li anodes reported recently. Meanwhile, MXene-MF shows flat voltage profiles for 720 h at 10 mA cm-2 for the Na anode and 800 h at 5 mA cm-2 for the K anode, indicative of the wide applicability. Notably, the high current density of 20 mA cm-2 for 20 mAh cm-2 for the Na anode, accompanying good recyclability was rarely achieved before. When coupled with sulfur or Na3V2(PO4)3 cathodes, the assembled MXene-MF alkali (Li, Na)-based full batteries showcase enhanced rate capability and cycling stability, demonstrating the potential of MXene-MF for advanced alkali-metal batteries.

A Two-Dimensional Mesoporous Polypyrrole-Graphene Oxide Heterostructure as a Dual-Functional Ion Redistributor for Dendrite-Free Lithium Metal Anodes.

Guiding the lithium ion (Li-ion) transport for homogeneous, dispersive distribution is crucial for dendrite-free Li anodes with high current density and long-term cyclability, but remains challenging for the unavailable well-designed nanostructures. Herein, we propose a two-dimensional (2D) heterostructure composed of defective graphene oxide (GO) clipped on mesoporous polypyrrole (mPPy) as a dual-functional Li-ion redistributor to regulate the stepwise Li-ion distribution and Li deposition for extremely stable, dendrite-free Li anodes. Owing to the synergy between the Li-ion transport nanochannels of mPPy and the Li-ion nanosieves of defective GO, the 2D mPPy-GO heterostructure achieves ultralong cycling stability (1000 cycles), even tests at 0 and 50 °C, and an ultralow overpotential of 70 mV at a high current density of 10.0 mA cm-2 , outperforming most reported Li anodes. Furthermore, mPPy-GO-Li/LiCoO2 full batteries demonstrate remarkably enhanced performance with a capacity retention of >90 % after 450 cycles. Therefore, this work opens many opportunities for creating 2D heterostructures for high-energy-density Li metal batteries.

Three dimensional Ti3C2 MXene nanoribbon frameworks with uniform potassiophilic sites for the dendrite-free potassium metal anodes.

Potassium (K) metal batteries hold great promise as an advanced electrochemical energy storage system because of their high theoretical capacity and cost efficiency. However, the practical application of K metal anodes has been limited by their poor cycling life caused by dendrite growth and large volume changes during the plating/stripping process. Herein, three-dimensional (3D) alkalized Ti3C2 (a-Ti3C2) MXene nanoribbon frameworks were demonstrated as advanced scaffolds for dendrite-free K metal anodes. Benefiting from the 3D interconnected porous structure for sufficient K accommodation, improved surface area for low local current density, preintercalated K in expanded interlayer spacing, and abundant functional groups as potassiophilic nuleation sites for uniform K plating/stripping, the as-formed a-Ti3C2 frameworks successfully suppressed the K dendrites and volume changes at both high capacity and current density. As a result, the a-Ti3C2 based electrodes exhibited an ultrahigh coulombic efficiency of 99.4% at a current density of 3 mA cm-2 with long lifespan up to 300 cycles, and excellent stability for 700 h even at an ultrahigh plating capacity of 10 mA h cm-2. When matched with K2Ti4O9 cathodes, the resulting a-Ti3C2-K//K2Ti4O9 full batteries offered a greatly enhanced rate capacity of 82.9 mA h g-1 at 500 mA g-1 and an excellent cycling stability with high capacity retention (77.7% after 600 cycles) at 200 mA g-1, demonstrative of the great potential of a-Ti3C2 for advanced K-metal batteries.

Conducting and Lithiophilic MXene/Graphene Framework for High-Capacity, Dendrite-Free Lithium-Metal Anodes.

Li-metal anode is widely acknowledged as the ideal anode for high-energy-density batteries, but seriously hindered by the uncontrollable dendrite growth and infinite volume change. Toward this goal, suitable stable scaffolds for dendrite-free Li anodes with large current density (>5 mA cm-2) and high Li loading (>90%) are highly in demand. Herein, a conductive and lithiophilic three-dimensional (3D) MXene/graphene (MG) framework is demonstrated for a dendrite-free Li-metal anode. Benefiting from its high surface area (259 m2 g-1) and lightweight nature with uniformly dispersed lithiophilic MXene nanosheets as Li nucleation sites, the as-formed 3D MG scaffold showcases an ultrahigh Li content (∼92% of the theoretical capacity), as well as strong capabilities in suppressing the Li-dendrite formation and accommodating the volume changes. Consequently, the MG-based electrode exhibits high Coulombic efficiencies (∼99%) with a record lifespan up to 2700 h and is stable for 230 cycles at an ultrahigh current density of 20 mA cm-2. When coupled with Li4Ti5O12 or sulfur, the MG-Li/Li4Ti5O12 full-cell offers an enhanced capacity of 142 mAh g-1 after 450 cycles, while the MG-Li/sulfur cell delivers an improved rate performance, implying the great potential of this 3D MG framework for building long-lifetime, high-energy-density batteries.

Author Correction: Three-Dimensional Printed Model-Assisted Screw Installation in Treating Posterior Atlantoaxial Internal Fixation.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Three-Dimensional Printed Model-Assisted Screw Installation in Treating Posterior Atlantoaxial Internal Fixation.

The aim of this study was to evaluate the efficacy and feasibility of a life-size 3-dimensional printing assisted posterior internal fixation. We performed a retrospective review of 138 patients who received posterior atlantoaxial internal fixation from October 2009 to March 2015 with a minimum follow-up period of 12 months. Group A included 76 patients who received the conventional free-hand technique. Group B included 62 patients who were treated with internal fixation assisted by 3D printing. The placement accuracy of the screw was evaluated in the computed tomography images according to the methods of Hojo and clinical outcomes were evaluated using the visual analogue scale, the Japanese Orthopedic Association Score, and the Neck Disability Index score. There were no significant differences in the clinical results at any of the follow-up time points regarding the JOA, VAS, or NDI scores between two group. However, compared to Group A, Group B had better results for screw installation (P = 0.003), shorter surgery time (P = 0.001), and less blood loss (P = 0.037). Compared to the conventional free-hand technique, 3D printed model-assisted is helpful to screw placement in atlantoaxial internal fixation, which can be used as a common tool to provides important guidance for upper cervical surgery.

All-MXene-Based Integrated Electrode Constructed by Ti3C2 Nanoribbon Framework Host and Nanosheet Interlayer for High-Energy-Density Li-S Batteries.

High-energy-density lithium-sulfur (Li-S) batteries hold promise for next-generation portable electronic devices, but are facing great challenges in rational construction of high-performance flexible electrodes and innovative cell configurations for actual applications. Here we demonstrated an all-MXene-based flexible and integrated sulfur cathode, enabled by three-dimensional alkalized Ti3C2 MXene nanoribbon (a-Ti3C2 MNR) frameworks as a S/polysulfides host (a-Ti3C2-S) and two-dimensional delaminated Ti3C2 MXene (d-Ti3C2) nanosheets as interlayer on a polypropylene (PP) separator, for high-energy and long-cycle Li-S batteries. Notably, an a-Ti3C2 MNR framework with open interconnected macropores and an exposed surface area guarantees high S loading and fast ionic diffusion for prompt lithiation/delithiation kinetics, and the 2D d-Ti3C2 MXene interlayer remarkably prevents the shuttle effect of lithium polysulfides via both chemical absorption and physical blocking. As a result, the integrated a-Ti3C2-S/d-Ti3C2/PP electrode was directly used for Li-S batteries, without the requirement of a metal current collector, and exhibited a high reversible capacity of 1062 mAh g-1 at 0.2 C and enhanced capacity of 632 mAh g-1 after 50 cycles at 0.5 C, outperforming the a-Ti3C2-S/PP electrode (547 mAh g-1) and conventional a-Ti3C2-S on an Al current collector (a-Ti3C2-S/Al) (597 mAh g-1). Furthermore, the all-MXene-based integrated cathode displayed outstanding rate capacity of 288 mAh g-1 at 10 C and long-life cyclability. Therefore, this proposed strategy of constructing an all-MXene-based cathode can be readily extended to assemble a large number of MXene-derived materials, from a group of 60+ MAX phases, for applications such as various batteries and supercapacitors.

Analysis of nodal aberration properties in off-axis freeform system design.

Freeform surfaces have the advantage of balancing off-axis aberration. In this paper, based on the framework of nodal aberration theory (NAT) applied to the coaxial system, the third-order astigmatism and coma wave aberration expressions of an off-axis system with Zernike polynomial surfaces are derived. The relationship between the off-axis and surface shape acting on the nodal distributions is revealed. The nodal aberration properties of the off-axis freeform system are analyzed and validated by using full-field displays (FFDs). It has been demonstrated that adding Zernike terms, up to nine, to the off-axis system modifies the nodal locations, but the field dependence of the third-order aberration does not change. On this basis, an off-axis two-mirror freeform system with 500 mm effective focal length (EFL) and 300 mm entrance pupil diameter (EPD) working in long-wave infrared is designed. The field constant aberrations induced by surface tilting are corrected by selecting specific Zernike terms. The design results show that the nodes of third-order astigmatism and coma move back into the field of view (FOV). The modulation transfer function (MTF) curves are above 0.4 at 20 line pairs per millimeter (lp/mm) which meets the infrared reconnaissance requirement. This work provides essential insight and guidance for aberration correction in off-axis freeform system design.