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We report the properties of more than 800 bursts detected from the repeating fast radio burst (FRB) source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during an extremely active episode on UTC September 25-28, 2021 in a series of four papers. In this second paper of the series, we mainly focus on the energy distribution of the detected bursts. The event rate initially increased exponentially but the source activity stopped within 24 hours after the 4th day. The detection of 542 bursts in one hour during the fourth day marked the highest event rate detected from one single FRB source so far. The bursts have complex structures in the time-frequency space. We find a double-peak distribution of the waiting time, which can be modeled with two log-normal functions peaking at 51.22 ms and 10.05 s, respectively. Compared with the emission from a previous active episode of the source detected with FAST, the second distribution peak time is smaller, suggesting that this peak is defined by the activity level of the source. We calculate the isotropic energy of the bursts using both a partial bandwidth and a full bandwidth and find that the energy distribution is not significantly changed. We find that an exponentially connected broken-power-law function can fit the cumulative burst energy distribution well, with the lower and higher-energy indices being $-1.22\pm0.01$ and $-4.27\pm0.23$, respectively. Assuming a radio radiative efficiency of $\eta_r = 10^{-4}$, the total isotropic energy of the bursts released during the four days when the source was active is already $3.9\times10^{46}$ erg, exceeding $\sim 23\%$ of the available magnetar dipolar magnetic energy. This challenges the magnetar models invoking an inefficient radio emission (e.g. synchrotron maser models)., Comment: 26 pages, 7 figures, accepted for publication in Research in Astronomy and Astrophysics

As the third paper in the multiple-part series, we report the statistical properties of radio bursts detected from the repeating fast radio burst (FRB) source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio telescope (FAST) during an extremely active episode between the 25th and the 28th of September 2021 (UT). We focus on the polarisation properties of 536 bright bursts with $\mathrm{S/N}>50$. We found that the Faraday rotation measures (RMs) monotonically dropped from $-579 \ {\rm rad \ m^{-2}}$ to $-605 \ {\rm rad \ m^{-2}}$ in the 4-day window. The RM values were compatible with the values ($-300$ to $-900\ {\rm rad \ m^{-2}}$ ) reported 4 month ago (Xu et al. 2022). However, the RM evolution rate in the current observation window was at least an order of magnitude smaller than the one ($\sim 500\ {\rm rad \ m^{-2}\, day^{-1}}$) previously reported during the rapid RM-variation phase, but is still higher than the one ($\le 1\ {\rm rad \ m^{-2} day^{-1}}$ ) during the later RM no-evolution phase. The bursts of FRB 20201124A were highly polarised with the total degree of polarisation (circular plus linear) greater than 90% for more than 90\% of all bursts. The distribution of linear polarisation position angles (PAs), degree of linear polarisation ($L/I$), and degree of circular polarisation ($V/I$) can be characterised with unimodal distribution functions. During the observation window, the distributions became wider with time, i.e. with larger scatter, but the centroids of the distribution functions remained nearly constant. For individual bursts, significant PA variations (confidence level 5-$\sigma$) were observed in 33% of all bursts. The polarisation of single pulses seems to follow certain complex trajectories on the Poincar\'e sphere, which may shed light on the radiation mechanism at the source or the plasma properties along the path of FRB propagation., Comment: 25 pages, 16 figures. Accepted by Research in Astronomy and Astrophysics (RAA)

Fast radio bursts (FRBs) are brief, intense flashes of radio waves from unidentified extragalactic sources. Polarized FRBs originate in highly magnetized environments. We report observations of the repeating FRB 20190520B spanning seventeen months , which show its amount of Faraday rotation is highly variable and twice changes its sign. The FRB also depolarizes below radio frequencies around 1 to 3 GHz. We interpret these properties as due to change in the parallel component of the integrated magnetic field along the line-of-sight, including reversals. This could result from propagation through a turbulent, magnetized screen of plasma located between $10^{-5}$ to 100 parsecs of the FRB source. This is consistent with the bursts passing through the stellar wind of a binary companion of the FRB source., Comment: arXiv:2203.08151 has been merged into this

We report the properties of more than 800 bursts detected from the repeating fast radio burst (FRB) source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio telescope (FAST) during an extremely active episode on UTC September 25th-28th, 2021 in a series of four papers. In this fourth paper of the series, we present a systematic search of the spin period and linear acceleration of the source object from both 996 individual pulse peaks and the dedispersed time series. No credible spin period was found from this data set. We rule out the presence of significant periodicity in the range between 1 ms to 100 s with a pulse duty cycle $< 0.49\pm0.08$ (when the profile is defined by a von-Mises function, not a boxcar function) and linear acceleration up to $300$ m s$^{-2}$ in each of the four one-hour observing sessions, and up to $0.6$ m s$^{-2}$ in all 4 days. These searches contest theoretical scenarios involving a 1 ms to 100 s isolated magnetar/pulsar with surface magnetic field $10$ hours. We also perform a periodicity search of the fine structures and identify 53 unrelated millisecond-timescale "periods" in multi-components with the highest significance of 3.9 $\sigma$. The "periods" recovered from the fine structures are neither consistent nor harmonically related. Thus they are not likely to come from a spin period. We caution against claiming spin periodicity with significance below $\sim$ 4 $\sigma$ with multi-components from one-off FRBs. We discuss the implications of our results and the possible connections between FRB multi-components and pulsar micro-structures., Comment: Accepted by Research in Astronomy and Astrophysics (RAA)

We report three new FRBs discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), namely FRB 181017.J0036+11, FRB 181118 and FRB 181130, through the Commensal Radio Astronomy FAST Survey (CRAFTS). Together with FRB 181123 that was reported earlier, all four FAST-discovered FRBs share the same characteristics of low fluence ($\leq$0.2 Jy ms) and high dispersion measure (DM, $>1000$ \dmu), consistent with the anti-correlation between DM and fluence of the entire FRB population. FRB 181118 and FRB 181130 exhibit band-limited features. FRB 181130 is prominently scattered ($��_s\simeq8$ ms) at 1.25 GHz. FRB 181017.J0036+11 has full-bandwidth emission with a fluence of 0.042 Jy ms, which is one of the faintest FRB sources detected so far. CRAFTS starts to built a new sample of FRBs that fills the region for more distant and fainter FRBs in the fluence-$\rm DM_E$ diagram, previously out of reach of other surveys. The implied all sky event rate of FRBs is $1.24^{+1.94}_{-0.90} \times 10^5$ sky$^{-1}$ day$^{-1}$ at the $95\%$ confidence interval above 0.0146 Jy ms. We also demonstrate here that the probability density function of CRAFTS FRB detections is sensitive to the assumed intrinsic FRB luminosity function and cosmological evolution, which may be further constrained with more discoveries., 9 Pages, 4 Plots and 1 Table. The Astrophysical Journal Letter Accepted

Effects of chemical compositions, finish rolling temperature, isothermal temperature on runout table and coiling temperature on microstructure and mechanical properties of economical dual phase steel produced on CSP line were investigated. Experimental results showed that martensite volume fraction could be enhanced and banding microstructure could be reduced by controlling Mn, Si contents and applying proper finish rolling temperature. Optimized processing-parameters were obtained for DP580 production on CSP line of Wuhan Iron and Steel (group) Co (WISCO) in China. Optimal microstructure and mechanical properties could be achieved when the strip was finished rolling at the range of 790 to 830°C, isothermally holding at 680 to 740°C and coiling below 250 °C.

The dehydrationrate of Daqing crude oil was not stable and the amount of chemical demulsifier used too much, which caused serious environmental pollution and enlarged the difficulty of dealing with crude oil. Therefore, PRJ-1 bio-demulsifier was selected to combine with chemical demulsifiers SP-169 and GT-D01, respectively, to resolve the crude oil emulsion of Daqing. The results showed that PRJ-1 can combine with SP-169 efficiently. The demulsification efficiency was high and dehydrated water was clear. However, the demulsification efficiency increased a little with GD-D01. The study shows that efficient synergetic effect between PRJ-1 and SP-169 was confirmed. The suitable proportionality of combinational demulsifier is 1:1 and the demulsifying effect can meet requirement of oilfield demulsifiers currently.

Mechanical seal mechanism was applied to study block mechanism of gaswell microclearance block liquid for the first time, which explained block mechanism of microclearance block liquid. The paper has built a block physical model of microclearance block liquid and has got calculation formulas of the block liquid lifting height. Then the block liquid lifting heights were calculated and analyzed in different microclearance widths and pressures. The sealing effect of the block liquid was discussed. The analyzed results showed that sealing effect of the block liquid was very obvious when microclearance width was lesser than 12μm. The paper not only enriched the study on block mechanism of gaswell microclearance block liquid but also proposed theoretical guidance to solve radically gas migration problem of micro-annulus.

Bio-demulsifier has not been applied in industrial scale due to its production cost. In order to reduce the production cost and improve the efficiency of demulsification, cheap materials such as oilfield sludge, workshop waste oil and edible waste oil were used in experiments as carbon sources to culture PRJ-1 demulsifying bacteria. As a result, cell concentrations of 5.4g/L, 3.7g/L and 4.2g/L were gotten, which were higher than the concentration of 2.6g/L cultivated by using paraffin. PRJ-1 demulsifying bacteria were used to prepare the demulsifying solution with a concentration of 10g/L, which was used in the demulsification experiment on Liaohe crude oil with a water cut of 80%. With 100 ml/L being added into the crude oil, the demulsification efficiency at 12h reached 91%, which was higher than that of 100mg/L chemical demulsifier. Demulsification efficiency of 96% can be achieved by using the combination of 60ml/L demulsifying bacteria and 40mg/L chemical demulsifier, furthermore, the demulsifying speed was higher and dehydrated water was clearer.

To solve the problems which exist in Energy-aware Topology Control Protocol Based on Gradient(ETBG) algorithm, one strategy that considers a combination of factors to choose the cluster head is proposed based on Analytic Hierarchy Process(AHP). This way not only uses the comprehensive weight that composed of the residual energy, number of neighbor nodes, average distance to the neighbor nodes, distance to the center of gradient, but also utilizes mathematical methods to determine weight coefficients, to reduce the interference of human factors and make the elected nodes enough optimized to serve as cluster heads. Simulation results show that the elected cluster heads distribute more properly in space, so that the network lifetime can be further extended and the algorithm is suitable for large-scale sensor network.

Radiation noise of ship propeller model has been measured for investigating the influence of gas content in the water to propeller cavitation noise. The results of experimental investigations clearly show that if gas content is kept invariable, the total noise becomes loud as ship velocity increases; if ship velocity is a constant, the total noise decreases while gas content in water increases.