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When the lubricant is not enough to maintain the ideal lubrication state of the bearing, the deep groove ball bearing will enter the starved lubrication state, which leads to the change of the vibration response of the deep groove ball bearing with localized defects. Previous bearing dynamics models mainly consider the lubrication state as an ideal lubrication condition, which may not reveal the effect of starved lubrication on the vibration characteristics of defective bearings. In this paper, the internal interaction of the system under starved condition is taken into account, and a dynamic model of defective deep groove ball bearings with insufficient lubricant is established to investigate the effects of different starved lubrication degrees on the contact force, friction force, cage speed, and system vibration characteristics. The results show that the lubricant insufficiency significantly changes the contact force inside the bearing, and the increase in friction caused by the increase in the degree of starved lubrication leads to the suppression of the degree of bearing slipping. The root mean square (RMS) value of the time-domain signal and the outer ring fault frequency both increase with the increase of the starved degree. The results of the study are helpful for fault diagnosis and condition monitoring of related equipment. [ABSTRACT FROM AUTHOR]

The current robot path planning methods only use global or local methods, which is difficult to meet the real-time and integrity requirements, and can not avoid dynamic obstacles. Based on this, this study will use the improved A-star global planning algorithm to design a hybrid robot obstacle avoidance path planning algorithm that integrates sliding window local planning methods to solve related problems. Specifically, A-star is optimized by evaluation function, sub node selection mode and path smoothness, and fuzzy control is introduced to optimize the sliding window algorithm. The study conducted algorithm validation on the TurtleBot3 mobile robot, with data sourced from experimental data from a certain college. The results showed that hybrid algorithm enabled the planned path to effectively navigate around dynamic obstacles and reach the target point accurately. When compared with traditional methods, path length reduced by 9.6%, path planning time decreased by 29% with an approximate 26.7% increase in the average speed of the robot. Compared with the traditional methods, the research algorithm has greatly improved in avoiding dynamic obstacles, path planning efficiency, model adaptability and so on, which has important value for relevant research. It can be seen that the algorithm proposed in the study has performance advantages, demonstrating the effectiveness and advantages of robot path planning, and can provide reference for robot obstacle avoidance optimization. Research can complete tasks for robots in practical environments, which has certain reference value for the research of robots in path planning and the development of path obstacle avoidance planning. [ABSTRACT FROM AUTHOR]

Three novel hexagonal Si–C–N structures, namely SiC3N3, SiC7N6, and SiC13N14, were constructed on the basis of the α-Si3N4 crystal structure. The stability of the three structures is demonstrated by analyzing their elastic constants and phonon dispersion spectra and by calculating their formation energies. The calculated band structures and partial densities of states suggest that the SiC3N3 and SiC7N6 structures possess hole conductivity. The electron orbital analyses indicate that the SiC3N3 and SiC7N6 crystals possess three-dimensional and one-dimensional conductivity, respectively. SiC13N14 is a semiconductor with a wide bandgap of 4.39 eV. Based on two different hardness models and indentation shear stress calculations, the Vickers hardness values of SiC3N3, SiC7N6, and SiC13N14 are estimated to be 28.04/28.45/16.18 GPa, 31.17/34.19/20.24 GPa, and 40.60/41.59/36.40 GPa. This result indicates that SiC3N3 and SiC7N6 are conductive hard materials while SiC13N14 is a quasi superhard material. [ABSTRACT FROM AUTHOR]

The relatively low-pressure layered hexagonal Li3B2 (h-Li3B2) phase under 20 GPa was identified on the basis of ab initio calculations. Inspired by the high-temperature superconductivity of metallic hydrogen, this study obtained a novel hexagonal Li2B2H (h-Li2B2H) structure by replacing Li2 with H. Contrast to h-Li3B2, h-Li2B2H may be directly synthesized by α-LiB and H2 under pressure. The two phases exhibited electronic features similar to those in MgB2 and were expected to be good superconductors. Electron–phonon coupling calculations illustrated that the layered h-Li3B2 structure is superconducting at 2 K with λ = 0.39 under 20 GPa. Moreover, h-Li2B2H was predicted to possess a large electron–phonon coupling parameter λ of approximately 0.81 and a resulting superconducting critical temperature about 28 K at 20 GPa. The introduced H in the h-Li2B2H structure had strong vibrational energy due to its light atomic mass and could enhance the energy of σ and π bonds by bonding with Li. Thus, the introduced H in the h-Li2B2H structure is important due to its enhanced electron–phonon coupling and superconducting property. [ABSTRACT FROM AUTHOR]

Ternary boron–carbon–nitrogen (B–C–N) compounds are considered to possess hardness comparable to diamond and thermal stability comparable to c-BN. Explorations for desirable B–C–N phases have been continuous. However, the nonconductive properties of most B–C–N compounds narrow the applications of these compounds. Herein, we propose a sp2–sp3 hybridized phase of t-B2C3N2, which consists of diamond-like BC blocks connected with single N–N bonds. Elastic constants and phonon dispersion curves confirm that t-B2C3N2 is mechanically and dynamically stable. The structure processes 2D metallicity in a strong 3D network. Furthermore, hardness and electron–phonon calculations reveal that t-B2C3N2 is superhard and superconductive with a superconducting critical temperature reaching 2.3 K. [ABSTRACT FROM AUTHOR]

Ternary boron-carbon-nitrogen (B-C-N) compounds are considered to possess hardness comparable to diamond and thermal stability comparable to c-BN. Explorations for desirable B-C-N phases have been continuous. However, the nonconductive properties of most B-C-N compounds narrow the applications of these compounds. Herein, we propose a sp2-sp3 hybridized phase of t-B2C3N2, which consists of diamond-like BC blocks connected with single N-N bonds. Elastic constants and phonon dispersion curves confirm that t-B2C3N2 is mechanically and dynamically stable. The structure processes 2D metallicity in a strong 3D network. Furthermore, hardness and electron-phonon calculations reveal that t-B2C3N2 is superhard and superconductive with a superconducting critical temperature reaching 2.3 K.

High-pressure phase transitions of AlB 2 -type transition-metal diborides (TMB 2 ; TM = Zr, Sc, Ti, Nb, and Y) were systematically investigated using first-principles calculations. Upon subjecting to pressure, these TMB 2 compounds underwent universal phase transitions from an AlB 2 -type to a new high-pressure phase tP6 structure. The analysis of the atomistic mechanism suggests that the tP6 phases result from atomic layer folds of the AlB 2 -type parent phases under pressure. Stability studies indicate that the tP6-structured ZrB 2 , ScB 2 , and NbB 2 are stable and may be observed under high pressure and the tP6-structured TiB 2 phase may be recovered at ambient pressure., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)