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We report the recent progress on diode-pumped high-power continuous-wave Pr:LiYF4 (YLF) green laser and deep ultraviolet (DUV) laser generation via intracavity frequency doubling. Using two InGaN blue diode lasers as pump source to form a double-end pumping geometry, in this work, we have demonstrated a green laser at 522 nm with a maximum output power of 3.42 W, which is believed to be the highest power ever achieved in all-solid-state Pr3+ lasers in this specific spectral region. Moreover, by intracavity frequency doubling of the achieved green laser, we have further obtained a DUV laser at about 261 nm with a maximum output power of 1.42 W, which is far higher than previous results. The watt-level 261-nm laser paves the way towards the realization of simple and compact DUV source for a variety of applications.

Over millions of years of evolution, nature has created organisms with overwhelming performances due to their unique materials and structures, providing us with valuable inspirations for the development of next-generation biomedical devices. As a promising new technology, 3D printing enables the fabrication of multiscale, multi-material, and multi-functional three-dimensional (3D) biomimetic materials and structures with high precision and great flexibility. The manufacturing challenges of biomedical devices with advanced biomimetic materials and structures for various applications were overcome with the flourishing development of 3D printing technologies. In this paper, the state-of-the-art additive manufacturing of biomimetic materials and structures in the field of biomedical engineering were overviewed. Various kinds of biomedical applications, including implants, lab-on-chip, medicine, microvascular network, and artificial organs and tissues, were respectively discussed. The technical challenges and limitations of biomimetic additive manufacturing in biomedical applications were further investigated, and the potential solutions and intriguing future technological developments of biomimetic 3D printing of biomedical devices were highlighted.

Flame-retardant and thermal management structures have attracted great attention due to the requirement of high-temperature exposure in industrial, aerospace, and thermal power fields, but the development of protective fire-retardant structures with complex shapes to fit arbitrary surfaces is still challenging. Herein, we reported a rotation-blade casting-assisted 3D printing process to fabricate nacre-inspired structures with exceptional mechanical and flame-retardant properties, and the related fundamental mechanisms are studied. 3-(Trimethoxysilyl)propyl methacrylate (TMSPMA) modified boron nitride nanoplatelets (BNs) were aligned by rotation-blade casting during the 3D printing process to build the “brick and mortar” architecture. The 3D printed structures are more lightweight, while having higher fracture toughness than the natural nacre, which is attributed to the crack deflection, aligned BN (a-BNs) bridging, and pull-outs reinforced structures by the covalent bonding between TMSPMA grafted a-BNs and polymer matrix. Thermal conductivity is enhanced by 25.5 times compared with pure polymer and 5.8 times of anisotropy due to the interconnection of a-BNs. 3D printed heat-exchange structures with vertically aligned BNs in complex shapes were demonstrated for efficient thermal control of high-power light-emitting diodes. 3D printed helmet and armor with a-BNs show exceptional mechanical and fire-retardant properties, demonstrating integrated mechanical and thermal protection.

Lightweight and cost-effective polymer matrix composites (PMCs) with extraordinary mechanical performance will be a key to the next generation of diverse industrial applications, such as aerospace, electric automobile, and biomedical devices. Limpet teeth made of mineral-polymer composites have been proved as nature’s strongest material due to the unique hierarchical architectures of mineral fiber alignment. Here, we present an approach to build limpet teeth inspired structural materials with precise control of geometric morphologies of microstructures by magnetic field-assisted 3D printing (MF-3DP). α-Iron (III) oxide-hydroxide nanoparticles (α-FeOOHs) are aligned by the magnetic field during 3D printing and aligned α-FeOOHs (aFeOOHs) bundles are further grown to aligned goethite-based bundles (aGBs) by rapid thermal treatment after printing. The mechanical reinforcement of aGBs in PMCs can be modulated by adjusting the geometric morphology and alignment of α-FeOOHs encapsulated inside the 3D printed PMCs. In order to identify the mechanical enhancement mechanism, physics-based modeling, simulation, and tests were conducted, and the results further guided the design of bioinspired goethite-based PMCs. The correlation of the geometric morphology of self-assembled α-FeOOHs, curing characteristics of α-FeOOHs/polymer composite, and process parameters were identified to establish the optimal design of goethite-based PMCs. The 3D printed PMCs with aGBs show promising mechanical reinforcement compared with PMCs without aGBs. This study opens intriguing perspectives for designing high strength 3D printed PMCs on the basis of bioinspired architectures with customized configurations.

While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized (smaller than 100 μm) channels in the layer building direction. The considerable light penetration depth of transparent resin leads to over-curing that inevitably cures the residual resin inside flow channels, causing clogs. In this paper, a 3D printing process — in-situ transfer vat photopolymerization is reported to solve this critical over-curing issue in fabricating microfluidic devices. We demonstrate microchannels with high Z-resolution (within 10 μm level) and high accuracy (within 2 μm level) using a general method with no requirements on liquid resins such as reduced transparency nor leads to a reduced fabrication speed. Compared with all other vat photopolymerization-based techniques specialized for microfluidic channel fabrication, our universal approach is compatible with commonly used 405 nm light sources and commercial photocurable resins. The process has been verified by multifunctional devices, including 3D serpentine microfluidic channels, microfluidic valves, and particle sorting devices. This work solves a critical barrier in 3D printing microfluidic channels using the high-speed vat photopolymerization process and broadens the material options. It also significantly advances vat photopolymerization’s use in applications requiring small gaps with high accuracy in the Z-direction.

Lightweight and cost-effective polymer matrix composites (PMCs) with extraordinary mechanical performance will be a key to the next generation of diverse industrial applications such as aerospace, electric automobile, and biomedical devices. Limpet teeth made of mineral-polymer composites have been proved as nature’s strongest material due to the unique hierarchical architectures of mineral fiber alignment. Here, we present an approach to build limpet teeth inspired structural materials with precise control of geometric morphologies of microstructures by magnetic field-assisted 3D printing (MF-3DP). α-Iron (III) oxide-hydroxide nanoparticles (α-FeOOHs) are aligned by the magnetic field during 3D printing and aligned α-FeOOHs bundles are further grown to aligned goethite-based bundles (aGBs) by rapid thermal treatment after printing. The mechanical reinforcement of goethite-based fillers in PMCs can be modulated by adjusting the geometric morphology and alignment of mineral particles encapsulated inside the 3D printed PMCs. In order to identify the mechanical enhancement mechanism, physics-based modeling, simulation, and tests were conducted and the results further guided the design of bioinspired goethite-based PMCs. The correlation of the geometric morphology of self-assembled α-FeOOHs, curing characteristics of α-FeOOHs/polymer composite, and process parameters were identified to establish the optimal design of goethite-based PMCs. The 3D-printed PMCs with aGBs show promising mechanical reinforcement. This study opens intriguing perspectives for designing high strength 3D printed PMCs on the basis of bioinspired architectures with customized configurations.

The accuracy of heat transfer coefficient of internal cooling channel is directly related to the selection of the fluid bulk temperature called T b , and it is difficult to be directly measured in the test. As a result, a practical and precise method is needed to be developed for data processing. This paper investigates one theoretical derivation method and one practical experimental data processing method. The theoretical one is more precise but depends on much immeasurable flow field information. With some simplifications and corrections, the practical method is easy to calculate and the parameters involved are easy to measured. By dividing the channel into four kinds of segments, our methods are suitable for many kinds of channel. The energy balance method is used in the theoretical derivation method. The practical method is mainly based on local linear interpolation and the channel is divided into three parts that mainly influenced by mainstream flow, secondary flow or both two flows according to different mass flow ratios. The experimental data of the rotational turbine blade and corresponding numerical simulations show the superiority of this method in the aspect of accuracy, stability and applicability. In general, these two methods have their own characteristics and apply to different scenes, which makes them of great meaning and progressiveness.

For the bottom-up based stereolithography (SL) process, a separation process is required to detach the newly cured layer from the constrained surface in order to accomplish the fabrication of the current layer. Excessive separation force will cause damage to the built layers and the constrained surface. Different surface coatings, platform motions including tilting and sliding, and the utilization of oxygen-permeable films have been proposed to address the separation-related problems. Among these approaches, there is a limited study on the vibration-assisted (VA) separation method to reduce the separation force. The underlying mechanism of the VA-separation-based method remains unexplored for the SL-related additive manufacturing, and the best way to use VA separation in the bottom-up based SL process is still unclear. In this paper, a new VA separation design for the bottom-up SL process is presented. A prototype system has been built to study the VA separation mechanism in SL. Experiments on the separation performance under different parameters including vibration frequency, pre-stress level, and exposure area were conducted. Based on the collected separation force data, an analytical model based on the mechanics of fatigue fracture was built. The separation behaviors related to different shape sizes and topologies were also studied and compared. The results showed that the separation force in SL was significantly reduced using the VA-separation-based method. Furthermore, the relationship between the separation force and the separation time conforms to the stress-based fatigue model well. This study provides insights on how to choose process parameters by considering the trade-offs between separation force and building efficiency.

The spiral corrugated aluminum sheath is most commonly used in HV XLPE land cables in China. In recent years, cable faults caused by discharge ablation of semi-conductive buffer layer below the aluminum sheath have been frequently reported, and a large scale of discharge traces on insulation screen surface have been found in the dismantled cables, which has aroused widespread concern. In this paper, after a brief summary of this kind of failure phenomena, the theoretical and experimental researches on the cause and mechanism of buffer layer failure are provided, with relevant conclusions listed. This is thought to be important for XLPE cables’ structure optimization and performance improvement. Several kinds of aluminum sheath structures commonly used in HV XLPE cables out of China are also introduced, with their advantages and disadvantages as well as their application scopes, which has reference value for the development of cable industry.

A study for heave compensation system of super capacitor energy storage devices, which uses the bidirectional DC/DC converter for connecting DC bus and super capacitor, and aims at solving problems of heave compensation feedback electricity use. The three-phase half bridge of isolated bidirectional DC/DC converter as the transmission circuit with the change of the DC bus voltage as reference is selected, the double closed loop control strategy of bidirectional DC/DC converter is designed, for achieving stability of bus bar voltage. As the DC bus voltage rises, super capacitor is charged, as the DC bus voltage reduces, the super capacitor is discharged. Experiments verify the effectiveness of the control strategy for the proposed bidirectional DC/DC converter based on DSP of super capacitor energy storage device.

Noble Metal-free catalysts attracted much attention as promising candidates for Pt-based catalyst replacement to advance applications related to oxygen reduction reaction (ORR), which is critical for large-scale renewable energy storage and conversion. Herein, this work focused on a synthesis of noble metal-free ORR electrocatalysts consisting of porous N-rich carbon/MXene, which was obtained using very conductive and reactive Ti3C2 MXene and polypyrrole (PPy) as a C and N source. The electrocatalyst exhibited excellent electrocatalytic activity and stability with an onset and a half-wave potentials equal to 0.85 and 0.71 V, respectively. Results obtained in this work demonstrate how to design efficient noble metal-free ORR electrocatalysts applicable to other chemical systems.

Offshore installations during harsh sea conditions results in rigorous requirements in terms of safety and efficiency for the floating crane. The forces resulting from the vertical motion of the vessel have an extensive effect on the overall crane structure and its lifetime. Moreover, vessel motion is proposed. Heave compensation is widely applied to decouple lifting loads from the ship motions due to wave excitation. The purpose of this paper is to compensate the vertical motion of the floating crane, analyzed the relationship between the floating crane and rope - hanging objects, establish the whole heave compensation system. Then use permanent magnet synchronous motor complete compensation for the hanging objects heave displacement in the system to achieve the movement. Finally, the static, rising and falling conditions of the actuator are analyzed, simulation results verify the effectiveness of the compensation system.

With the rapid development of new and high technology, such as the Internet of things (IoT), big data and intelligent equipment are becoming more and more mature. It provides important technical support for the transformation of China's major ports into intelligent ports. The application of wave compensation technology to port intelligent equipment will greatly improve the performance. The wave compensation system can reduce the movement of ships from wind, wave and current, thus safely and smoothly placing cargo on the deck of the replenished ship, make it possible to load and unload goods in bad conditions. In this paper, the dynamic modeling of wave compensation system of floating crane is carried out, and the analysis is carried out under different working conditions. Simulation results show that the model meets the corresponding requirements under the action of regular waves, which can provide a good reference for practical application.

Previous anti-spamming algorithms based on link structure suffer from either the weakness of the page value metric or the vagueness of the seed selection. In this paper, we propose two page value metrics, AVRank and HVRank. These two "values" of all the web pages can be well assessed by using the bidirectional links' information. Moreover, with the help of bidirectional links, it becomes easier to enlarge the propagation coverage of seed sets. We further discuss the effectiveness of the combination of these two metrics, such as the quadratic mean of them. Our experimental results show that with such two metrics, our method can filter out spam sites and identify reputable ones more effectively than previous algorithms such as TrustRank.

Seed selection is of significant importance for the biased PageRank algorithms such as TrustRank to combat link spamming. Previous work usually uses a small seed set, which has a big problem that the top ranking results have a strong bias towards seeds. In this paper, we analyze the relationship between the result bias and the number of seeds. Furthermore, we experimentally show that an automatically selected large seed set can work better than a carefully selected small seed set.

Recent studies show that the link-structure-based measures of Web page popularity prolong the procedure of new pages reaching their deserved ranking. In this paper we propose a promotional ranking scheme that offers an opportunity for newly-created pages to be recognized.We conduct a simulation to evaluate our method. Experimental results show that our method remarkably raises the probability for new pages to obtain user-awareness.