Fast radio bursts are a class of transient radio sources that are thought to originate from extragalactic sources since their dispersion measure greatly exceeds the highest dispersion measure that the Milky Way interstellar medium can provide. Host Galaxies of twenty-two fast radio bursts have already been identified. In this paper, the dispersion measurement of these fast radio bursts produced by the Milky Way interstellar medium, and the intergalactic medium is obtained through known physical models to yield the host galaxy dispersion measure. It is observed that the host galaxy dispersion measure increases with its redshift value. We also obtained that the host galaxy dispersion measure has different distribution between repeaters and non-repeaters. It is noted that the reason for the divergence of the host galaxy dispersion measures should be accounted for by the difference in their local environment.

Previous studies have identified two emission modes in PSR B1859+07: a normal mode that has three prominent components in the average profile, with the trailing one being the brightest, and an anomalous mode (i.e., the A mode) where emissions seem to be shifted to an earlier phase. Within the normal mode, further analysis has revealed the presence of two submodes, i.e., the cW mode and cB mode, where the central component can appear either weak or bright. As for the anomalous mode, a new bright component emerges in the advanced phase while the bright trailing component in the normal mode disappears. New observations of PSR B1859+07 using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) have revealed the existence of a previously unknown emission mode, dubbed the Af mode. In this mode, all emission components seen in the normal and anomalous modes are detected. Notably, the mean polarization profiles of both the A and Af modes exhibit a jump in the orthogonal polarization angle modes in the bright leading component. The polarization angles for the central component in the original normal mode follow two distinct orthogonal polarization modes in the A and Af modes respectively. The polarization angles for the trailing component show almost the same but a small systematic shift in the A and Af modes, roughly following the values for the cW and cB modes. Those polarization features of this newly detected emission mode imply that the anomalous mode A of PSR B1859+07 is not a result of “phase shift” or “swooshes” of normal components, but simply a result of the varying intensities of different profile components. Additionally, subpulse drifting has been detected in the leading component of the Af mode.

The segmentation of brain tissue by MRI not only contributes to the study of the function and anatomical structure of the brain, but it also offers a theoretical foundation for the diagnosis and treatment of brain illnesses. When discussing the anatomy of the brain in a clinical setting, the terms "white matter," "gray matter," and "cerebrospinal fluid" are the ones most frequently used (CSF). However, due to the fact that the human brain is highly complicated in its structure and that there are many different types of brain tissues, the human brain structure of each individual has its own set of distinctive qualities. Because of these several circumstances, the process of segmenting brain tissue will be challenging. In this article, several different clustering algorithms will be discussed, and their performance and effects will be compared to one another. The goal of this comparison is to determine which algorithm is most suited for segmenting MRI brain tissue. Based on the clustering method, the primary emphasis of this research is placed on the segmentation approach that is appropriate for medical brain imaging. The qualitative and quantitative findings of the experiment reveal that the FCM algorithm has more steady performance and better universality, but it is necessary to include the additional auxiliary conditions in order to achieve more ideal outcomes.

We present simultaneous broad-band radio observations on the abnormal emission mode from PSR B1859+07 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). This pulsar shows peculiar emission, which takes the form of occasional shifts of emission to an early rotational phase and mode change of emission at the normal phase. We confirm all these three emission modes with our data sets, including the B (burst) and Q (quiet) modes of the non-shifted pulses and the emission shift mode with a quasi-periodicity of 155 pulses. We also identify a new type of emission shift event, which has emission at the normal phase during the event. We studied polarization properties of these emission modes in detail, and found that they all have similar polarization angle curve, indicating the emissions of all these three modes are from the same emission height.

Observation of Interplanetary Scintillation (IPS) provides an important and effective way to study the solar wind and the space weather. A series of IPS observations were conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The extraordinary sensitivity and the wide frequency coverage make FAST an ideal platform for IPS studies. In this paper we present some first scientific results from FAST observations of IPS with the L-band receiver. Based on the solar wind velocity fitting values of FAST observations on September 26-28, 2020, we found that the velocity decreases with increasing frequency linearly, which has not yet been reported in literature. And we have also detected a variation of solar wind velocity on a timescale of 3-5 minutes, which imply the slow change of the background solar wind, a co-existence of high- and low-speed streams, or a reflect of the quasi-periodic electron-density fluctuations.

Observations of Interplanetary Scintillation (IPS) are an efficient remote-sensing method to study the solar wind and inner heliosphere. From 2016 to 2018, some distinctive observations of IPS sources like 3C 286 and 3C 279 were accomplished with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single-dish telescope in the world. Due to the 270-1620 MHz wide frequency coverage of the Ultra-Wideband (UWB) receiver, one can use both single-frequency and dual-frequency analyses to determine the projected velocity of the solar wind. Moreover, based on the extraordinary sensitivity owing to the large collecting surface area of FAST, we can observe weak IPS signals. With the advantages of both the wider frequency coverage and high sensitivity, also with our radio frequency interference (RFI) mitigation strategy and an optimized model-fitting method developed, in this paper, we analyze the fitting confidence intervals of the solar wind velocity, and present some preliminary results achieved using FAST, which points to the current FAST system being highly capable of carrying out observations of IPS

In this paper, we present the Five-hundred-meter Aperture Spherical radio Telescope (FAST) observations of PSRs B1929+10 and B1842+14. Through analysis of the pulsars' scintillation pattern, we detected the known scintillation arc from PSR B1929+10 and two previously undetected scintillation arcs from B1842+14. We find that the B1929+10 arc's curvature scales with observing frequency as eta(-) proportional to nu(-2.1 +/- 0.1) and eta(+) proportional to nu(-1.8 +/- 0.2), consistent with Arecibo results and the theoretical expectations of eta proportional to nu(-2). From the arc curvature, we infer the scattering screen to be located at 0.20 +/- 0.02 kpc from the Earth, close to what was measured by RadioAstron at 324 MHz. From B1842+14, we find two scintillation arcs for the first time. The arcs' curvatures imply that they are caused by two scattering screens located at a distance of 0.3 +/- 0.2 kpc and 1.6 +/- 0.6 kpc from the Earth, respectively. The screen distance uncertainties mainly come from the uncertainty in pulsar's dispersion measure (DM)-derived distance. We present these FAST scintillation observations and discuss the future prospect of FAST pulsar scintillation study.

We report the discovery of a binary millisecond pulsar (namely PSR J1641+3627F or M13F) in the globular cluster (GC) M13 (NGC 6205) and timing solutions of M13A to F using observations made with the Five-hundred-meter Aperture Spherical radio Telescope. PSR J1641+3627F has a spin period of 3.00 ms and an orbital period of 1.4 days. The most likely companion mass is 0.13 M. M13A to E all have short spin periods and small period derivatives. We also confirm that the binary millisecond pulsar PSR J1641+3627E (also M13E) is a black widow with a companion mass around 0.02 M. We find that all the binary systems have low eccentricities compared to those typical for GC pulsars and that they decrease with distance from the cluster core. This is consistent with what is expected, as this cluster has a very low encounter rate per binary.

With the largest dish Five-hundred-meter Aperture Spherical radio Telescope (FAST), both the mean and single pulses of PSR B2016+28, especially including the single-pulse structure, are investigated in detail in this study. The mean pulse profiles at different frequencies can be well fitted in a conal model, and the peak separation of intensity-dependent pulse profiles increases with intensity. The integrated pulses are obviously frequency dependent (pulse width decreases by ~20% as frequency increases from 300 to 750 MHz), but the structure of single pulses changes slightly (the corresponding correlation scale decreases by only ~1%). This disparity between mean and single pulses provides independent evidence for the existence of the RS-type vacuum inner gap, indicating a strong bond between particles on the pulsar surface. Diffused drifting sub-pulses are analyzed. The results show that the modulation period along pulse series ( P 3 ) is positively correlated to the separation between two adjacent sub-pulses ( P 2 ). This correlation may hint a rough surface on the pulsar, eventually resulting in the irregular drift of sparks. All the observational results may have significant implications in the dynamics of pulsar magnetosphere and are discussed extensively in this paper.

The Square Kilometre Array (SKA) will be the world's largest synthesis radio telescope, which is designed to answer major scientific questions such as those relating to the cosmic origin and fundamental forces in the universe. With the SKA entering into the phase of pre-construction, more than 100 institutes in about 20 countries including China have been involved in the associated key technology development. The Dish Verification Antenna China (DVA-C) is a concept prototype which has been built to meet the requirements of the SKA's scientific goals. It utilizes a unique skin-and-rib structure with single-piece panel reflectors. This paper presents details on the design and measured performances of DVA-C, as well as the preliminary observational results. Current applications of the DVA-C are also introduced.

Rotating radio transients (RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation. In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively.

PSR B0919+06 is known for its abnormal emission phenomenon, where the pulse emission window occasionally shifts progressively in longitude and returns afterwards. The physical mechanism behind this phenomenon is still under investigation. In this paper, we present our ultra-wideband observation of this pulsar using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), with simultaneous measurements in the frequency ranges 280–780 and 1250–1550 MHz. We have identified three abnormal events, each of which becomes less apparent as the frequency decreases. At 1400 MHz, the averaged profile slightly shifted after the first and third abnormal events, implying a relationship between abnormal event and profile variation. We also found a linear trend in the left-edge position of the averaged profiles between the first and third events as well as after the third event, suggesting the existence of a slow-drifting mode between the two major events. The second event has a comparatively small shift in phase and is thus categorized as a "small flare state". During the third event, a sequence of approximately nine pulses was seen to significantly weaken in all frequency bands, likely associated with the pseudo-nulling observed at 150 MHz. A three-component de-composition analysis of the normal averaged profiles shows that the trailing component is dominant at our observing frequencies, while the centre component has a comparatively steeper spectrum. We found the overall flux density in an abnormal event to slightly differ from that in an ordinary state, and the difference shows a frequency dependence. A comparison of the normal, abnormal and dimmed averaged profile indicates that the leading component is likely to be stable in all states.

Since 1993, astronomers and engineers from more than 100 institutions in 20 different countries including China, have engaged in the international mega-science project-the Square Kilometre Array (SKA), which will be the world's largest synthesis radio telescope. The SKA is currently in its pre-construction phase, and China has been playing a very active role. China has participated in 6 of the total of 10 SKA work packages, and carried out R&D in dish array, aperture array, wideband single pixel feeds, phased array feeds, signal and data transport, and science data processor. In the new SKA science book published in 2015, Chinese scholars have made their contributions in 20% of all the chapter proposals. After the SKA1 re-baselining, 20 Chinese astronomers participated in 11 out of the 13 SKA scientific working groups. The "2+1 Strategy" for China's SKA science priorities has been established, and some important progress has been made in cosmological re-ionization detection as well as in SKA data processing. In June 2015, the Chinese participation in SKA1 passed through the Chinese Academy of Sciences Panel Review. The Chinese Community is now deeply involved into the preparation of the SKA, with activities such as SKA science cases study, researching on high-precision light-weight antennas, developing the Chinese prototype array, as well as some efforts in building an SKA regional data center in China. This article gives a brief historical review of the SKA, overviews some international and domestic progress of the project during its preconstruction phase, and also discusses some future plans of the Chinese SKA.

PSR B0919+06 generally radiates radio pulses in a normal phase range. It has been known for its occasional perplexing abnormal emission events wherein individual pulses come to an earlier phase range for a few tens of periods and then returns to its usual phase. Heretofore, only a few such events have been available for study. We observed PSR B0919+06 for about 30 hours using the Jiamusi 66-m telescope at Jiamusi Deep Space Station at S-band, and detected 92 abnormal emission events. We identify four types of events based on the abrupted or gradual phase-shifting of individual pulses. The abnormal emission events are seen to occur randomly some every 1000 to 3000 periods, and they affect the leading edge of the mean profile by up to 2\% in amplitude. The abnormal emission events are probably related to gradual changes of emission processing in the pulsar magnetosphere.

Pointing accuracy is one of the most important characteristics for a large radio telescope;it is very fundamental for telescope running. To ensure good performance for measuring the flux density of a radio source, pointing accuracy must be kept within 10% of telescope beam size. In this paper we present results of large measurements of telescope points for Jiamusi 66m radio telescope, and show the basic-parameter model and the fitting residuals of pointing data. We find that even after the correction of a new best-fitting basic-parameter model, the pointing uncertainty data still have a systematic variations of concentration along with the azimuth and elevation, which we believe is caused by the high order variations of the angle between the azimuth axis and elevation axis as well as the gravity deformation. We improve the basic-parameter model for the pointing corrections, and we get much improved pointing accuracy for Jiamusi 66m radio telescope from 45″to less than 20″.

Directions of radio sources and the Galactic radio background map need to be known before or during practical radio-astronomy observing runs .We have developed a simple visualization software to display the radio sky and the distribution of radio sources .The visualization software , which should be helpful to observers , is developed using the C language and the PGPLOT subroutine library for graphic utilities .It can be run under a Linux environment .This software can be used to display the radio sky at any user-set time;particularly , it can display the real-time radio sky .It allows users to add or remove observational sites , to select desired data of the Galactic radio background , and to modify object entries in radio-source lists for display .This software has rather good expandability .The software together with its source codes will be made freely available to all astronomical institutes and amateur astronomers in China .