Multiband Omnidirectional Invisibility Cloak.

Transformation optics (TO) provides a powerful tool to manipulate electromagnetic waves, enabling the design of invisibility cloaks, which can render objects invisible. Despite many years of research, however, invisibility cloaks experimentally realized thus far can only operate at a single frequency. The narrow bandwidth significantly restricts the practical applications of invisibility cloaks and other TO devices. Here, a general design strategy is proposed to realize a multiband anisotropic metamaterial characterized by two principal permittivity components, i.e., one infinite and the other spatially gradient. Through a proper transformation and combination of such metamaterials, an omnidirectional invisibility cloak is experimentally implemented, which is impedance-matched to free space at multiple frequencies. Both far-field numerical simulations and near-field experimental mappings confirm that this cloak can successfully suppress scattering from multiple large-scale objects simultaneously at 5 and 10 GHz. The design strategy and corresponding practical realization bring multiband transformation optical devices one step closer to reality.

Eliminating the Scattering of Thin Film Structures.

Rendering invisibility in the wide application scenarios has seen a surge in interest in recent years. Though various approaches have been proposed to realize concealments under different conditions, achieving polarization-independent invisibility for large objects remains a big challenge. Here, we propose to attain invisibility of a large dielectric slab with polarization constraints being totally lifted. This is accomplished by employing an antiscattering coating made of anisotropic metamaterials. We show that by tailoring the electric resonance of a triangular mushroom structure, antiphase electric dipole moment can be induced, resulting in an antipolarization response of the whole metamaterial coatings. By putting the proposed coatings on both sides of a large dielectric slab, a neutralization effect of the total polarization is observed, leading to the peculiar phenomenon of full-polarization invisibility. Our results are validated through full-wave simulations and experimental measurements. Remarkably, the intrinsic null-polarization property of the coating-slab-coating structure guarantees the invisibility feature of a large-scale bulk made by simply stacking the sandwiched composites, which facilitates the application of invisibility in practical scenarios such as the invisibility cloaks and the reflectionless antenna radomes.

New insights into the process of intrinsic point defects in PuO2.

Intrinsic point defects are known to play a crucial role in determining the physical properties of solid-state materials. In this study, we systematically investigate the intrinsic point defects, including vacancies (VPu and VO), interstitials (Pui and Oi), and antisite atoms (PuO and OPu) in PuO2 using the first-principles plane wave pseudopotential method. Our calculations consider the whole charge state of these point defects, as well as the effect of oxygen partial pressure. This leads to a new perspective on the process of intrinsic point defects in PuO2. We find that the antisite atoms OPu and PuO are more likely to appear in O-rich and O-deficient environments, respectively. Interestingly, the most energetically favorable type of Schottky defect is {2VPu3-: 3VO2+} in an O-rich environment, while {4VO1+: VPu4-} is preferred in an O-deficient environment. These results differ from the commonly known {VPu4-: 2VO2+} type of Schottky defect. Moreover, under O-deficient conditions, we predict that the stable cation Frenkel defect is {VPu4+: Pui4+}, while the most stable anion Frenkel defect is {VO2+: Oi2-} under O-rich conditions. Lastly, we find that the only two types of antisite pairs that can appear are {OPu5-: PuO5+} and {OPu6-: PuO6+}, with the latter being the more stable configuration. These unconventional defect configurations provide a new viewpoint on the process of intrinsic point defects in PuO2 and lay theoretical foundations for future experiments.

Binocular stereo matching algorithm based on MST cost aggregation.

For common binocular stereo matching algorithms in computer vision, it is not easy to obtain high precision and high matching speed at the same time. In this paper, an improved binocular stereo matching algorithm based on Minimum Spanning Tree (MST) cost aggregation is proposed. Firstly, the performance of the parallel algorithm can be improved by reducing the height of the tree. Then, an improved Root to Leaf (L2R) cost aggregation algorithm is proposed. By combining stereo matching technology with parallel computing technology, the above method can realize synchronous parallel computing at the algorithm level. Experimental results show that the improved algorithm has high accuracy and high matching speed for binocular stereo vision.

Hybrid Path Planning Combining Potential Field with Sigmoid Curve for Autonomous Driving.

The traditional potential field-based path planning is likely to generate unexpected path by strictly following the minimum potential field, especially in the driving scenarios with multiple obstacles closely distributed. A hybrid path planning is proposed to avoid the unsatisfying path generation and to improve the performance of autonomous driving by combining the potential field with the sigmoid curve. The repulsive and attractive potential fields are redesigned by considering the safety and the feasibility. Based on the objective of the shortest path generation, the optimized trajectory is obtained to improve the vehicle stability and driving safety by considering the constraints of collision avoidance and vehicle dynamics. The effectiveness is examined by simulations in multiobstacle dynamic and static scenarios. The simulation results indicate that the proposed method shows better performance on vehicle stability and ride comfortability than that of the traditional potential field-based method in all the examined scenarios during the autonomous driving.

Fabrication of hydroxyapatite coatings on AZ31 Mg alloy by micro-arc oxidation coupled with sol-gel treatment.

Magnesium (Mg) alloys, can potentially be used as biodegradable orthopedic implants because of their biodegradability and good mechanical properties. However, a quick degradation rate and low bioactivity have prevented their clinical application. In order to enhance the corrosion resistance and the in vitro bioactivity of Mg alloys, protective composite coatings were prepared on AZ31 magnesium alloy followed by sol-gel sealing treatment under low-pressure conditions. The morphologies, crystalline structure and the composition of the samples were characterized by SEM, XRD, and XPS. Electrochemical corrosion test and the in vitro bioactivity were also studied. The results indicated that the composite coatings not only improved the corrosion resistance, but also enhanced the in vitro bioactivity of AZ31 Mg alloy. Therefore, Mg alloy treated with micro-arc oxidation and sol-gel offers a promising approach for biodegradable bone implants.

Thermo-responsive and compression properties of TEMPO-oxidized cellulose nanofiber-modified PNIPAm hydrogels.

In this study, TEMPO-oxidized bamboo cellulose nanofibers (TO-CNF) with anionic carboxylate groups on the surfaces were in-situ incorporated into poly(N-isopropylacrylamide) (PNIPAm) matrix to improve its thermo-responsive and mechanical properties during the polymerization. The microstructure, swelling behaviors, and compressive strength of resultant PNIPAm composite hydrogels with varying contents of TO-CNFs (0-10wt%) were then examined, respectively. Modified hydrogels exhibited the similar light transparency to pure PNIPAm one due to the formation of semi-IPN structure between PNIPAm and TO-CNF. FT-IR spectra demonstrated that the presence of TO-CNF did not alter the position of characteristic peaks associated with PNIPAm. SEM observation suggested that the pore size of PNIPAm hydrogels was markedly increased after the incorporation of TO-CNF. Also, the composite hydrogels showed superior swelling behavior and much improved compression properties with respect to pure PNIPAm one. Thus, TO-CNF appeared to be a "green" nanofiller that can simultaneously improve swelling and mechanical properties of PNIPAm hydrogel.

Fabrication of mesoporous metal oxide coated-nanocarbon hybrid materials via a polyol-mediated self-assembly process.

After clarifying the formation mechanism of a typical metal glycolate precipitate, Ti glycolate, in a polyol-mediated synthesis using acetone as a precipitation medium, we describe a simple template-free approach based on an ethylene glycol-mediated synthesis to fabricate mesoporous metal oxide coated-nanocarbon hybrid materials including TiO2 coated-carbon nanotube (CNT), SnO2 coated-CNT, Cu2O/CuO coated-CNT and TiO2 coated-graphene sheet (GS). In the approach, metal oxide precursors, metal glycolates, were first deposited on CNTs or GSs, and subsequently transformed to the metal oxide coatings by pyrolysis or hydrolysis. By a comparison between the characterization of two TiO2-CNT hybrid materials using carboxylated CNTs and pristine CNTs without carboxyl groups, the driving force for initiating the deposition of metal glycolates on the carboxylated CNTs is confirmed to be the hydrogen bonding between the carboxyl groups and the polymer chains in metal glycolate sols. The electrochemical performances of the mesoporous TiO2 coated-carboxylated CNTs and TiO2-pristine CNT hybrid materials were investigated. The results show that the mesoporous TiO2 coated-carboxylated CNT with a uniform core-shell nanostructure exhibits substantial improvement in the rate performance in comparison with its counterpart from 0.5 C to 100 C because of its higher electronic conductivity and shorter diffusion path for the lithium ion. At the extremely high rate of 100 C, the specific capacity of TiO2 of the former reaches 85 mA h g(-1), twice as high as that of the latter.