In the eighth data release (DR8) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, more than 318,740 low-resolution stellar spectra with types from B to early F and signal-to-noise ratios >50 were released. With this large volume of the early-type stars, we tried machine-learning algorithms to search for class-one and class-two chemical peculiars (CP1 and CP2), and to detect spectral features to distinguish the two classes in low-resolution spectra. We selected the XGBoost algorithm after comparing the classification efficiency of three machine-learning ensemble algorithms. Using XGBoost followed by the visual investigation, we presented a catalog of 20,694 sources, including 17,986 CP1 and 2708 CP2, in which 6917 CP1 and 1652 CP2 are newly discovered. We also list the spectral features to separate CP1 from CP2 discovered through XGBoost. The stellar parameters (including effective temperature (T _eff), surface gravity (log g), metallicity [Fe/H]), the spatial distribution in Galactic coordinates, and the color magnitude were provided for all of the entries of the catalog. The T _eff for CP1 distributes from ∼6000 to ∼8500 K, while for CP2 it distributes from ∼7000 to ∼13,700 K. The log g of CP1 ranges from 2.8 to 4.8 dex, peaking at 4.5 dex, and of CP2 it ranges from 2.0 to 5.0 dex, peaking at 3.6 dex, respectively. The [Fe/H] of CP1 and CP2 are from −1.4 to 0.4 dex, and the [Fe/H] of CP1 are on average higher than that of CP2. Almost all of the targets in our sample locate around the Galactic plane.

The frequency evolution behavior of radio pulse profiles is an important clue for the radiation mechanism of a pulsar. Combined with the latest results of the European Pulsar Network and the Australia Telescope National Facility data, we systematically study the evolution of W ₅₀ (the full width of the pulse profile at 50% of the pulsar amplitude) for 74 pulsars with frequencies from tens to thousands of megahertz. We find that 71 pulsars show “absorption” features, which indicates that the absorption is an universal phenomenon in the pulsar population and independent of the type of pulsar profile. It is found that for most pulsars, the absorption features appear in the frequency range of 100–800 MHz, and the evolution trend of W ₅₀ at frequencies less than ∼100 MHz and larger than ∼800 MHz can be described as a power-law function.We quantify the absorption intensity and analyze the correlation between the absorption intensity and the pulsar parameters (such as the spin period, magnetic field, and age of the pulsar). It is found that there is no direct correlation between them. Our results will provide good samples and clues for the study of the physical mechanism of the absorption phenomenon.

The study of polarization and micro-structure is very important for understanding the radiation mechanism of Rotating Radio Transients (RRATs). Due to the limitations of telescope sensitivity and time resolution, studies of the polarization and micro-structure of RRATs have been rare in the past. In this work, we report on a high-time resolution and full polarization observation of RRAT J0139+3336 with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). A total of 96 burst pulses were detected in the 3-h observation. The degrees of linear and circular polarization and the shape of the polarization position angle (PPA) of the single pulses vary significantly. The average profile displays a small degree of linear and circular polarization, and the PPA exhibits a remarkably smooth and steep S-shaped curve, which are also characteristics of pulsars. The circular polarization in some single pulses demonstrates a clear sign change. We discuss the geometric structure of the emission beam based on the results from fitting the RVM model to the changes in the PPA. Using an autocorrelation analysis, the quasi-periodic micro-structure in the single pulse emission is detected with a median period of about 0.91 ms. We show that the position of RRAT J0139+3336 on the P–P_μ diagram falls in the normal pulsar (NP) region . The radio emission of RRAT J0139+3336 shows unique properties, such as the sign change in the circular polarization and quasi-periodicity in the micro-structure, which will provide important clues to the emission mechanism of RRATs.

The radio radiation mechanism is one of the open questions for pulsars. Multiband observations are very helpful to constrain pulsar radiation models. We observed PSR J1848-0123 at the 5 GHz band with the Shanghai Tianma 65 m radio telescope (TMRT). The 5 GHz observation together with the European Pulsar Network (EPN) and CSIRO ATNF Data Archives databases provides a broadband evolution property of the pulse profiles for this pulsar. We reprocessed these data sets to obtain the multiband pulse profiles. It was found that the pulse profile of PSR J1848-0123 narrows with increasing emission frequency. We separated the emission components of each pulse profile with a multi-Gaussian fitting method, and then calculated the beaming angle and emission radius of each component with the basic radiation geometry of pulsar. With the calculated beam angles and radiation radii, we simulated the radius-frequency mapping of this pulsar with an inverse Compton scatting model (ICS). It was found that the observed radio radiation could be generated in the core gap region above the polar cap of the pulsar. The beaming angle and emission radius versus frequency for PSR J1848-0123 can be explained well with the ICS model.

The multi-drifting subpulse behaviors in PSR J2007+0910 have been studied carefully with the high sensitivity observations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) at 1250 MHz. We found that there are at least six different single emission modes in PSR J2007+0910 are observed, four of which show significant subpulse drifting behaviors (modes A, B, C, and D), and the remaining two (modes E₁ and E₂) show stationary subpulse structures. The subpulse drifting periods of modes A, B, C, and D are P_{3, A} = 8.7 ± 1.6 P, P_{3, B} = 15.8 ± 1.2 P, P_{3, C} = 21.6 ± 1.3 P and P_{3, D} = 32.3 ± 0.9 P, respectively, where P represents the pulse period of this pulsar. The subpulse separation is almost the same for all modes P₂ = 6.01 ± 0.18^○. Deep analysis suggests that the appearance and significant changes in the drifting period of multi-drifting subpulse emission modes for a pulsar may originate from the aliasing effect. The observed non-drifting modes may be caused by the spark point move with a period ∼P₂. Our statistical analysis shows that the drift mode of this pulsar almost always switches from slower to faster drifts in the mode change. The interesting subpulse emission phenomenon of PSR J2007+0910 provides a unique opportunity to understand the switching mechanism of multi-drift mode.

Aiming at the problems of scarce datasets and the low identification accuracy faced in the field of weld-crack detection, this paper proposes an artificial-weld-crack preparation method based on the doping of dissimilar metal particles to augment the number of samples of weld-crack defects. Meanwhile, data augmentation methods such as random cropping, scaling and Mosaic are combined to further enhance the richness of the samples, so as to provide strong data support for the proposed weld-crack-defect detection model. Given the limitations of storage and computational resources in industrial application scenarios, this paper designs the lightweight detection network YOLOv6-NW. It is achieved by optimizing the YOLOv6-N model for width and depth compression to efficiently identify and locate weld-crack defects. The experimental results demonstrate that YOLOv6-NW significantly outperforms YOLOv5 in terms of both model detection performance and model size. Compared to YOLOv6-N, the number of model parameters in YOLOv6-NW is only 16% of that in YOLOv6-N, yet its model detection accuracy and recall rate remain on a comparable level with YOLOv6-N. Additionally, the precision of crack detection by YOLOv6-NW under low-resolution or low-illumination conditions remains above 0.9.