The Five-hundred-meter Aperture Spherical radio Telescope (FAST) was completed with its main structure installed on September 25, 2016, after which it entered the commissioning phase. This paper aims to introduce the commissioning progress of the FAST over the past two years. To improve its operational reliability and ensure effective observation time, FAST has been equipped with a real-time information system for the active reflector system and hierarchical commissioning scheme for the feed support system, which ultimately achieves safe operation of the two systems. For meeting the high-performance indices, a high-precision measurement system was set up based on the effective control methods that were implemented for the active reflector system and feed support system. Since the commissioning of the FAST, a low-frequency ultra-wideband receiver and 19-beam 1.05-1.45 GHz receiver have been mainly used. Telescope efficiency, pointing accuracy, and system noise temperature were completely tested and ultimately achieved the acceptance indices of the telescope. The FAST has been in the process of national acceptance preparations and has begun to search for pulsars. In the future, it will still strive to improve its capabilities and expand its application prospects. Keywords: Radio telescopes and instrumentation, astronomical observations, radio wave receivers, algorithms and implementation, control systems 95.55.Jz; 95.85.-e; 07.57.Kp; 07.05.Kf; 07.05.Dz Till date, several observation modes, such as tracking, drift scanning, andbasketweave scanning, have been realized, which means that the functional commissioning tasks have been completed. Now, the sensitivity of the FAST has reached 2,000 m 2 /K, the system noise temperature has been controlled below 20 K (19-beam 1.05-1.45 GHz receiver), and the pointing accuracy of the feed receivers has reached about 16″. The FAST has already begun to search for pulsars in batches.Several researches based on the FAST telescope have been reported. Qian et al. [3] reported their observation and basic parameters of the first pulsar discovered by the FAST, PSR J1900−0134. Zhang et al. [4] used FAST parameters obtained from the commissioning data to estimate the sensitivity of the CRAFTS extragalactic HI survey and predict its survey capacity in the future. Yu et al. [5] observed the abnormal emission shift event of PSR B0919+06 using the FAST with the ultra-wideband receive system. They found the potential existence of a slow-drifting mode between two major abnormal events. A sequence of dimmed pulses was observed during one of those events at all frequency bands. Lu, Peng et al. [6] reported the analysis of three rotating radio transients (RRATs), namely J1538+2345, J1854+0306, and J1913+1330, observed using the FAST. The derived burst rates of the three RRATs are higher than previous results owing to the high sensitivity of the FAST. Lu et al. [7] showed both the mean and single pulses of PSR B2016+28, observed in detail using the FAST. Wang, Zhu, Guo, et al. [8] developed a pulsa...
Glitch (sudden spinup) is a common phenomenon in pulsar observations. However, the physical mechanism of glitch is still a matter of debate because it depends on the puzzle of pulsar's inner structure, i.e., the equation of state of dense matter. Some pulsars (e.g., Vela-like) show large glitches (∆ν/ν ∼ 10 −6 ) but release negligible energy, whereas the large glitches of AXPs/SGRs (anomalous X-ray pulsars/soft gamma repeaters) are usually (but not always) accompanied with detectable energy releases manifesting as X-ray bursts or outbursts. We try to understand this aspect of glitches in a starquake model of solid quark stars. There are two kinds of glitches in this scenario: bulk-invariable (Type I) and bulk-variable (Type II) ones. The total stellar volume changes (and then energy releases) significantly for the latter but not for the former. Therefore, glitches accompanied with X-ray bursts (e.g., that of AXP/SGRs) could originate from Type II starquakes induced probably by accretion, while the others without evident energy release (e.g., that of Vela pulsar) would be the result of Type I starquakes due to, simply, a change of stellar ellipticity.
Hexagonal boron nitride (hBN) growth was carried out on (111) Si substrates at a temperature of 1350 C using a cold wall chemical vapor deposition system. The hBN phase of the deposited films was identified by the characteristic Raman peak at 1370 cm À1 with a full width at half maximum of 25 cm À1 , corresponding to the in-plane stretch of B and N atoms. Chemical bonding states and composition of the hBN films were analyzed by X-ray photoelectron spectroscopy; the extracted B/ N ratio was 1.03:1, which is 1:1 within the experimental error. The fabricated metal-hBN-metal devices demonstrate a strong deep UV (DUV) response. Further, the hBN growth on the vertical (111) surfaces of parallel trenches fabricated in (110) Si was explored to achieve a thermal neutron detector. These results demonstrate that hBN-based detectors represent a promising approach towards the development of DUV photodetectors and efficient solid-state thermal neutron detectors.
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