Porcine Reproductive and Respiratory Syndrome in Hybrid Wild Boars, China

We conducted a serologic investigation of porcine reproductive and respiratory syndrome virus (PRRSV) in hybrid wild boar herds in China during 2008–2009. PRRSV isolates with novel genetic markers were recovered. Experimental infection of pigs indicated that hybrid wild boars are involved in the epidemiology of PRRSV

Effect of Annealing on Microstructures and Hardening of Helium-Hydrogen-Implanted Sequentially Vanadium Alloys

Abstract The effect of post-irradiation annealing on the microstructures and mechanical properties of V-4Cr-4Ti alloys was studied. Helium-hydrogen-irradiated sequentially V-4Cr-4Ti alloys at room temperature (RT) were undergone post-irradiation annealing at 450 °C over periods of up to 30 h. These samples were carried out by high-resolution transmission electron microscopy (HRTEM) observation and nanoindentation test. With the holding time, large amounts of point defects produced during irradiation at RT accumulated into large dislocation loops and then dislocation nets which promoted the irradiation hardening. Meanwhile, bubbles appeared. As annealing time extended, these bubbles grew up and merged, and finally broke up. In the process, the size of bubbles increased and the number density decreased. Microstructural changes due to post-irradiation annealing corresponded to the change of hardening. Dislocations and bubbles are co-contributed to irradiation hardening. With the holding time up to 30 h, the recovery of hardening is not obvious. The phenomenon was discussed by dispersed barrier hardening model and Friedel-Kroupa-Hirsch relationship

Study on irradiation hardening by He+ and subsequent V/self-ion irradiation in V-4Cr-4Ti under near-service conditions

V-4Cr-4Ti was irradiated by He+ and subsequent V/self-ions at 773 K to simulate the effect of the damages generated under near-service conditions on irradiation hardening. Microstructure observation and hardness test were carried out by transmission electron microscopy (TEM) and nanoindentation testing. Microstructure analysis showed that bubbles, dislocation loops and precipitates were produced whether samples were irradiated by He+ or He+/V+. Edge dislocation was observed by high-resolution images. The nanoindentation results showed that hardening appeared after irradiation, and hardness increment after He+ irradiation is 4.41 GPa, 6.2 GPa for He+/V+. Meanwhile, based on damage characterization, the irradiation hardening was also analyzed using the dispersion barrier hardening model (DBH), which showed that the main cause of hardening was dislocation loops. In addition, the deviation was discussed between the hardness increment obtained by nanoindentation testing and that calculated based on DBH

Experimental and numerical study on the effect of increasing frequency on the morphology and microstructure of aluminum alloy in laser wobbling welding

Laser wobbling welding is effective in reducing porosity and improving microstructure of aluminum welds. This work adopts the research form of experiment combined with numerical simulation to establish the relationship between different parameters and morphology and microstructure of the welds. The dynamic behavior of the molten pool and the keyhole, the thermal cycle process and the solidification parameters can be obtained through the numerical simulation considering the fluid flow and heat transfer. The research reveals that laser wobbling welding improves the weld formation by significantly weakening the molten pool eruption and stabilizing the welding process and also confirms that there is a special cross-regional flow field in the molten pool and the mushy zone which is different from ordinary laser welding. In addition, it is proved that the grain refinement at the weld boundary is the result of the combined effects of solidification parameters, dendrite remelting and flow field stirring, but the grain refinement at the center of the weld is mainly caused by the flow field stirring. These results explain the influence of the laser wobbling welding on the flow, heat transfer and solidification parameters of the welds and reveal the reasons for improving the weld formation and refining the microstructure

Experimental and numerical research on formation mechanism of intermetallic compounds in laser brazing welding for Ti/Al dissimilar alloy

Laser brazing is an esteemed technique for Ti/Al dissimilar alloy welding, yet the emergence of brittle intermetallic compounds (IMCs) restricts its broader application. In-depth knowledge of IMCs formation provides critical insights for process optimization targeting IMCs structural improvement, pivotal to high-performance of Ti/Al joint. Herein, we establish macroscopic heat transfer-fluid flow coupled model for laser brazing welding of Ti/Al dissimilar alloys firstly, followed by a comprehensive characterization of the types, distribution, and crystallographic features of IMCs, thereby elucidating the impact mechanism of laser offset on IMCs growth. Incremented laser offset prompts a conversion from transverse to tangential flow at the Ti/Al interface, attenuates peak temperatures and liquid phase duration, and significantly revises solidification parameters, thereby reducing the IMCs layer to 5 μm, augmenting solid-state transformation characteristic, and diversifying crystallographic orientations of IMCs. Ultimately, enhanced tensile strength in the Ti/Al joint is attributed to the presence of thinner IMCs with finer grains, produced by larger laser offset. This article constitutes a pivotal progression in modeling heat transfer-flow behaviors for Ti/Al laser brazing welding, revealing IMCs genesis with unparalleled granularity guided by crystal selective growth principles. It also lays a theoretical foundation for IMCs micro-structure improvement strategy via temperature-flow regulation

DV-Hop Algorithm Based on Multi-Objective Salp Swarm Algorithm Optimization

The localization of sensor nodes is an important problem in wireless sensor networks. The DV-Hop algorithm is a typical range-free algorithm, but the localization accuracy is not high. To further improve the localization accuracy, this paper designs a DV-Hop algorithm based on multi-objective salp swarm optimization. Firstly, hop counts in the DV-Hop algorithm are subdivided, and the average hop distance is corrected based on the minimum mean-square error criterion and weighting. Secondly, the traditional single-objective optimization model is transformed into a multi-objective optimization model. Then, in the third stage of DV-Hop, the improved multi-objective salp swarm algorithm is used to estimate the node coordinates. Finally, the proposed algorithm is compared with three improved DV-Hop algorithms in two topologies. Compared with DV-Hop, The localization errors of the proposed algorithm are reduced by 50.79% and 56.79% in the two topology environments with different communication radii. The localization errors of different node numbers are decreased by 38.27% and 56.79%. The maximum reductions in localization errors are 38.44% and 56.79% for different anchor node numbers. Based on different regions, the maximum reductions in localization errors are 56.75% and 56.79%. The simulation results show that the accuracy of the proposed algorithm is better than that of DV-Hop, GWO-DV-Hop, SSA-DV-Hop, and ISSA-DV-Hop algorithms