Numerical Simulation of Underwater Supersonic Jet of Vehicle with Shell-Shaped Flow Control Structure

When the underwater vehicle engine operates under the condition of over-expansion, the violent pulsation of the flow field pressure at the rear of the nozzle can cause violent fluctuations in engine thrust, leading to engine instability. In order to improve the engine's stability, this study drew inspiration from the wave attenuation characteristics of the shell-shaped surface texture structure and added a multi-layer shell-shaped texture structure to the rear wall to reduce pressure fluctuations in the flow field at the rear of the nozzle . Based on the numerical simulation method, the effects of different bionic shell-shaped structures on jet morphology, wall pressure and engine thrust were compared and analyzed. The results show that the multi-layer bionic shell-shaped texture structure can effectively inhibit the occurrence of periodic phenomena such as bulge, necking, and return stroke in the rear flow field, so as to effectively reduce the pressure fluctuation in the rear flow field of the nozzle. In addition, when the momentum thrust is almost unchanged, it is found through calculations that during the initial stage of the jet, the suppression of thrust is not significant. After 0.005 seconds, the oscillation amplitude of the combined force of pressure difference thrust and back pressure thrust decreased by 22%, and the oscillation amplitude of the total thrust decreased by 20%

Manipulating Multiple Order Parameters via Oxygen Vacancies: The case of Eu0.5Ba0.5TiO3-{\delta}

Controlling functionalities, such as magnetism or ferroelectricity, by means of oxygen vacancies (VO) is a key issue for the future development of transition metal oxides. Progress in this field is currently addressed through VO variations and their impact on mainly one order parameter. Here we reveal a new mechanism for tuning both magnetism and ferroelectricity simultaneously by using VO. Combined experimental and density-functional theory studies of Eu0.5Ba0.5TiO3-{\delta}, we demonstrate that oxygen vacancies create Ti3+ 3d1 defect states, mediating the ferromagnetic coupling between the localized Eu 4f7 spins, and increase an off-center displacement of Ti ions, enhancing the ferroelectric Curie temperature. The dual function of Ti sites also promises a magnetoelectric coupling in the Eu0.5Ba0.5TiO3-{\delta}.Comment: Accepted by Physical Review B, 201

The Linked Data Benchmark Council (LDBC): Driving competition and collaboration in the graph data management space

Graph data management is instrumental for several use cases such as recommendation, root cause analysis, financial fraud detection, and enterprise knowledge representation. Efficiently supporting these use cases yields a number of unique requirements, including the need for a concise query language and graph-aware query optimization techniques. The goal of the Linked Data Benchmark Council (LDBC) is to design a set of standard benchmarks that capture representative categories of graph data management problems, making the performance of systems comparable and facilitating competition among vendors. LDBC also conducts research on graph schemas and graph query languages. This paper introduces the LDBC organization and its work over the last decade

Friction and wear behavior of WS2/Zr self-lubricating soft coatings in dry sliding against 40Cr hardened steel balls

WS[subscript 2] and WS[subscript 2]/Zr self-lubricating soft coatings were produced by medium-frequency magnetron sputtering, multi-arc ion plating and ion beam assisted deposition technique on the cemented carbide YT15 (WC+15%TiC+6%Co) substrates. Microstructural and fundamental properties of these coatings were examined. Sliding wear tests against 40Cr hardened steel using a ball-on-disk tribometer method were carried out with these coated materials. The friction coefficient and wear rates were measured with various applied loads and sliding speeds. The wear surface features of the coatings were examined using SEM. The results showed that the WS-1 specimen (with WS[subscript 2]/Zr composite coating) has higher hardness and coating/substrate critical load compared with that of the WS-2 specimen (only with WS2 coating). The friction coefficient of WS-1 specimen increases with the increase in applied load, and is quite insensitive to the sliding speed. The wear rate of the WS-1 specimen is almost constant under different applied loads and sliding speeds. The WS-1 specimen shows the smallest friction coefficient and wear rate among all the specimens tested under the same conditions. The WS-1 specimen exhibits improved friction behavior to that of the WS-2 specimen, and the antiwear lifetime of the WS2 coatings can be prolonged through adding Zr additives. The self-lubricating and wear mechanism of the WS[subscript 2]/Zr coating was also found from the sliding wear tests