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The article explores the vulnerability of social recommender systems to multi-agent adversarial attacks under a black-box scenario. Topics discussed include the application of Graph Neural Networks (GNNs) in social recommendations, the impact of untargeted attacks using fake user profiles and malicious social relations, and the introduction of a multi-agent reinforcement learning framework, MultiAttack, to coordinate these attacks effectively.

(TiZrHfNbTa)C high-entropy ceramics have wide range of application prospects due to their excellent performance, but their hardness and brittleness make them difficult to process. In this study, novel method based on nanosecond laser was used to cut (TiZrHfNbTa)C high-entropy ceramics. Results show that laser machining is efficient strategy for high-precision machining of (TiZrHfNbTa)C high-entropy ceramics. Slit width obtained via nanosecond-laser cutting is only 26.4 % of that obtained via mechanical cutting, and average roughness and maximum height difference of cut surface are 2.078 and 20.497 μm, respectively, which are smaller than those obtained through mechanical cutting (4.296 and 29.706 μm, respectively). Furthermore, removal mechanism under the action of nanosecond laser was investigated, and it was found that cut surface of (TiZrHfNbTa)C high-entropy ceramics formed thin oxide recast layer together with carbide underneath. This study provides important results for precision machining of (TiZrHfNbTa)C high-entropy ceramics. [ABSTRACT FROM AUTHOR]

Since it was first reported in 2013, the NADC30-like PRRSV has been epidemic in China. Hubei Province is known as China's key hog-exporting region. To understand the prevalence and genetic variation of PRRSV, herein, we detected and analyzed 317 lung tissue samples from pigs with respiratory disease in Hubei Province, and demonstrated that the NADC30-like strain was the second-most predominant strain during 2017–2018, following the highly pathogenic PRRSV (HP-PRRSV). Additionally, we isolated a new NADC30-like PRRSV strain, named CHN-HB-2018, which could be stably passaged in Marc-145 cells. Genetic characterization analysis showed that compared with the NADC30 strain, the CHN-HB-2018 strain had several amino acid variations in glycoprotein (GP) 3, GP5, and nonstructural protein 2 (NSP2). Moreover, the CHN-HB-2018 strain showed a unique 5-amino acid (aa) deletion in NSP2, which has not previously been reported. Gene recombination analysis identified the CHN-HB-2018 strain as a potentially recombinant PRRSV of the NADC30-like strain and HP-PRRSV. Animal experiments indicated that the CHN-HB-2018 strain has a mild pathogenicity, with no mortality and only mild fever observed in piglets. This study contributes to defining the evolutionary characteristics of PRRSV and its molecular epidemiology in Hubei Province, and provides a potential candidate strain for PRRSV vaccine development. [ABSTRACT FROM AUTHOR]

A remelted layer on the surface of a degradable Zn-1 Mg-0.2Fe alloy is prepared via laser remelted technology, and their microstructure, friction and wear performance, hardness, and corrosion behavior of the remelted layer are evaluated systematically by OM, SEM, XRD, high speed reciprocating friction tester, micro hardness tester, electrochemical workstation and immersion test. The results show that both the as cast and laser remelted samples are mainly composed of α-Zn matrix phase, Mg2Zn11, and FeZn13 . The laser remelted layer is denser than the substrate of Zn alloy, and the second phase of FeZn13 also tends to be round and thin. The friction and wear tests in Hank's solution revealed that the laser remelted sample shows a lower friction coefficient and wear loss than those of the as cast sample, with coefficient of friction of 0.821 and wear loss of 1.7 mg. The corrosion wear mechanism consists mainly of plowing and slight abrasive wear. The average micro hardness value of the laser remelted sample is 104.3 kg/mm², which is increase of 15.2% as compared to that of the as cast sample. Laser remelted sample exhibits more positive corrosion potential, lower values of corrosion current density and corrosion rate than their as cast alloy counterparts in Hank's solution, with corrosion potential of -- 1. 030 V vs. SCE, corrosion current density of 37. 4 µA/cm², and corrosion rate of 498.0 µm/a. The degradation rates of the laser remelted sample after immersing into Hank's solution are 39.2 µm/a for 30 days and 28. 7 µm/a for 90 days, which are 9. 4% and 3. 7% lower than those of the as cast sample, respectively, exhibiting better corrosion resistance. [ABSTRACT FROM AUTHOR]

A modified adaptive division beam tracing (MADBT) technique based on the localized kd-tree and the OpenMP-MPI parallel techniques is presented for the simulation of radio propagation in large-scale urban environments. Beams launched from a transmitter are recursively traced by applying the MADBT method and beam trees recorded the propagation path info are generated. By traversing the beam trees, all the valid propagation (transmitted, reflected and diffracted) paths are efficiently determined. Then the receiver power strength can be calculated based on geometrical optics (GO) and uniform theory of diffraction along the arrival paths. By tracing the continuous beams instead of a number of rays, the proposed method performs higher efficiency than the widely used ray tracing method. During the beam tracing procedure, several techniques are adopted to accelerate the calculation. Firstly, a localized kd-tree is built according to the coverage area of the transmitter, which is more efficient than the global kd-tree to do the beam-triangle intersection during the tracing procedure. Secondly, a virtual simulation face is generated to speed up the searching for ray paths. Lastly, the OpenMP and the MPI parallel technique are implemented to further enhance efficiency of the proposed method. As expected, the simulated results for the realistic Malaysia urban environment show good agreement with measured results and performance high efficiency. [ABSTRACT FROM AUTHOR]