Pd catalysts supported on rGO-TiO_2 composites for direct synthesis of H_2O_2: Modification of Pd^(2+)/Pd^0 ratio and hydrophilic property

The use of nanostructured composites as catalyst supports is a promising route to prepare catalysts with high selectivity and productivity. In this work, reduced graphene oxide-TiO_2(rGP-x) composites with a variation of reduced graphene oxide(rGO) content were synthesized by hydrothermal method. Pd/rGP-x catalysts were prepared in incipient-wetness impregnation method for the direct synthesis of H_2O_2 from H2 and O_2. The morphology and electronic properties of catalysts were investigated by XPS, TEM, and Raman spectroscopy.The ratio of Pd^(2+)/Pd^0 and the hydrophobicity of the catalysts were increased with the rising content of rGO. As the amount of rGO in the catalysts varied in the range of 0.025 wt%–2 wt%, the selectivity of H_2O_2 exhibited a tendency of increasing firstly and then decreasing from 0.1 wt% to 2 wt%. It indicates that good catalytic performance for H_2O_2 synthesis can be achieved only when appropriate amount of rGO is introduced. The H_2O_2 selectivity and productivity of Pd/r GP-0.025 both improved remarkably compared with Pd/P25. This enhancement originated from the combined effects of the proper ratio of Pd^(2+)/Pd^0 and hydrophobicity of the catalyst.

An Identifier-Based Network Access Control Mechanism Based on Locator/Identifier Split

Legacy IP address-based access control has met many challenges, because the network nodes cannot be identified accurately based on their variable IP addresses. “Locator/Identifier Split” has made it possible to build a network access control mechanism based on the permanent identifier. With the support of “Locator/Identifier Split” routing and addressing concept, the Identifier-based Access Control (IBAC) makes net-work access control more accurate and efficient, and fits for mobile nodes’ access control quite well. Moreover, Self-verifying Identifier makes it possible for the receiver to verify the packet sender’s identity without the third part authentication, which greatly reduces the probability of “Identifier Spoofing”.

Chiral plasmonic nanostructure of twistedly stacked nanogaps

Nanogap plasmonic structures with strong coupling between separated components have different responses to orthogonal-polarized light, giving rise to giant optical chirality. Here, we proposed a three-dimensional(3D) nanostructure that consists of two vertically and twistedly aligned nanogaps, showing the hybridized charge distribution within 3D structures.It is discovered that the structure twisted by 60° exhibits plasmonic coupling behavior with/without gap modes for different circular-polarized plane waves, showing giant chiral response of 60% at the wavelength of 1550 nm. By controlling the disk radius and the insulator layer, the circular dichroism signal can be further tuned between 1538 and 1626 nm.

GNSS rapid precise point positioning enhanced by low Earth orbit satellites

The Low Earth Orbit(LEO)satellites can be used to efectively speed up Precise Point Positioning(PPP)convergence.In this study,180 LEO satellites with a global distribution are simulated to evaluate their contribution to the PPP convergence.LEO satellites can give more redundant observations and improve satellite geometric distributions,particularly for a single Global Navigation Satellite System(GNSS).The convergence speed of the PPP foat solution using the Global Positioning System(GPS,G)or BeiDou Navigation Satellite System(BDS,C)single system as well as the G/C/Galileo navigation satellite system(Galileo,E)/GLObal NAvigation Satellite System(GLONASS,R)combined system with LEO satellites added is improved by 90.0%,91.0%,and 90.7%,respectively,with respect to the system without LEO satellites added.We introduced LEO observations to assist GNSS in PPP-AR(Ambiguity Resolution)and PPP-RTK(Real Time Kinematic).The success fx rate of a single system is signifcantly improved,and the Time-To-First-Fix(TTFF)of G and G/C/E is reduced by 86.4%and 82.8%,respectively,for the PPP-AR solution.We analyzed the positioning performance of LEO satellite assisted G/C/E PPP-RTK in the reference networks of diferent scales,namely diferent atmospheric delay interpolation accuracies.The success fx rate of the G/C/E combined system is improved from 86.8 to 94.9%,and the TTFF is reduced by 36.8%,with the addition of LEO satellites in the 57 km reference network.In the 110 km reference network,the success fx rate of the G/C/E combined system is improved from 64.0 to 88.6%,and the TTFF is reduced by 32.1%.GNSS PPP-RTK with adding the LEO satellites in the reference networks of diferent scales shows obvious improvement because the atmospheric correlation decreases with increasing distance from the reference networks.

Morphologies of Al_4Sr Intermetallic Phase and Its Modification Property upon A356 Alloys

In general, the modification performance of AI-Sr master alloys is primarily dependent upon the morphologies and sizes of the AI4Sr intermetallic phase. In this paper, the crystal structure, morphologies, sizes, hardness and elastic modulus of AI4Sr in AI-Sr master alloys prepared from variant processes were studied by means of optical metallurgical microscope, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and nanoindentation system. The results revealed that the microstructures and modification performance of the AI4Sr phase were related to the preparation processes. That is to say, when a ＂direct reaction-hot extrusion＂ process was used, the AI4Sr phase exhibited a homogeneous distribution in the AI matrix with small size and roundish shapes, which ensured the AI-Sr master alloy wire advantages involving high recovery, good reproducibility, no delitescence of modification, no corrosion on equipments, and good workability. However, in the case of the traditional ＂direct reaction＂ process, the AI4Sr phase was in large size with shapes of rectangular stripe and plates, which limited the Sr content increasing due to the brittleness of the AI-Sr alloy. It was also found that the morphology and size of the AI4Sr phases changed during heat treatment at high temperature up to 600℃.

Recover the abnormal positioning,velocity and timing services caused by BDS satellite orbital maneuvers

The BeiDou Navigation Satellite System(BDS)provides global Positioning,Velocity,And Timing(PVT)services that are widely used in various areas.The BDS satellites frequently need the orbit maneuvers due to various perturbations to keep satellites in their designed positions.During these maneuvers,PVT services may be abnormal if the data from a maneuvering satellite is used.In this paper we developed an approach to recover the abnormal PVT services.By using BDS observations from multiple tracking stations,the orbital errors of a maneuvering satellite can be in real time obtained and corrected,thereby avoiding any influence on the performance of PVT services.The tests show that the average precision of position,velocity and timing services are improved by 0.8 m,0.1 mm/s and 0.16 ns,respectively,using the developed orbital maneuver recovery approach.In addition,the approach can also be used for the orbital maneuver detection and monitoring.