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MicroRNA-196a-3p (miR-196a-3p) is known to increase in rat models subjected to middle cerebral artery occlusion (MCAO). In the present work, we aimed to investigate the effects of miR-196a-3p in cerebral ischemia/reperfusion (I/R) injury. Transient cerebral ischemia was induced in C57/BL6 mice subjected to MCAO. Mice were also administered miR-196a-3p antagomir by intracerebroventricular injection. MiR-196a-3p and its target ARF4 levels were quantified and cerebral infarct volume and neuronal apoptosis were evaluated. Primary neural stem cells (NSCs) were activated by oxygen–glucose deprivation/reoxygenation. NSCs were transfected with miR-196a-3p mimics, inhibitors, siARF4, or negative control using Lipofectamine 2000 reagent. ARF4, Ki-67, and Nestin expression levels were assessed using qRT-PCR and western blotting. The proliferation of NSCs was detected by CCK-8 assay and EdU staining. We found that levels of miR-196a-3p expression increased in vivo and in vitro when expression levels of its target ARF4 were decreased. We also found that miR-196a-3p aggravated cerebral I/R injury in vivo. We established that ARF4 is the target of miR-196a-3p using a dual-luciferase assay in vitro. Simultaneously, we observed that miR-196a-3p overexpression or the inhibition of ARF4 inhibited NSC proliferation. MiR-196a-3p inhibited NSC proliferation and aggravated cerebral I/R injury by targeting ARF4.

New classes of astronomical objects are often discovered serendipitously. The enormous data volumes produced by recent high-time resolution, radio-telescope surveys imply that efficient algorithms are required for a discovery. Such algorithms are usually tuned to detect specific, known sources. Existing data sets therefore likely contain unknown astronomical sources, which will remain undetected unless algorithms are developed that can detect a more diverse range of signals. We present the Single-dish PARKES data challenge for finding the uneXpected (SPARKESX), a compilation of real and simulated high-time resolution observations. SPARKESX comprises three mock surveys from the Parkes "Murriyang" radio telescope. A broad selection of simulated and injected expected signals (such as pulsars, fast radio bursts), poorly characterised signals (plausible flare star signatures) and unknown unknowns are generated for each survey. The goal of this challenge is to aid in the development of new algorithms that can detect a wide-range of source types. We show how successful a typical pipeline based on the standard pulsar search software, PRESTO, is at finding the injected signals. The dataset is publicly available at https://doi.org/10.25919/fd4f-0g20., Accepted for publication in MNRAS. 18 pages, 8 figures, 4 table

It is very computationally expensive to search for pulsars using time-domain observations, and the volume of data will be enormous with next-generation telescopes such as the Square Kilometre Array. We use artificial neural networks (ANNs), a machine learning method, for the efficient selection of pulsar candidates from radio continuum surveys; this is much cheaper than using time-domain observations. With observed quantities such as radio fluxes, sky position and compactness as inputs, our ANNs output the ‘score’ that indicates the degree of likeliness that an object is a pulsar. We demonstrate ANNs based on existing survey data by the Tata Institute for Fundamental Research (TIFR) Giant Metrewave Radio Telescope (GMRT) Sky Survey (TGSS) and the National Radio Astronomy Observatory (NRAO) Very Large Array (VLA) Sky Survey (NVSS) and we test their performance. The precision, which is the ratio of the number of pulsars classified correctly as pulsars to the number of any objects classified as pulsars, is about $96 {{\ \rm per\ cent}}$. Finally, we apply the trained ANNs to unidentified radio sources and our fiducial ANN with five inputs (the galactic longitude and latitude, the TGSS and NVSS fluxes and compactness) generates 2436 pulsar candidates from 456 866 unidentified radio sources. We need to confirm whether these candidates are truly pulsars by using time-domain observations. More information, such as polarization, will narrow the number of candidates down further.

Purpose: Our study aims to examine the clinicopathological features, disease progression, management, and outcomes of gallbladder sarcomatoid carcinoma (GBSC) patients.Methods: Between January 2000 and December 2020, 50 GBC patients received surgical treatment and pathologically verified as GBSC at our institution were enrolled. The clinical and pathological features and survival of these patients were retrospectively reviewed.Results: The median overall survival (OS) of GBSC patients was 14.5 months, and the 1-, 2- and 3-year OS rates were 68.0%, 32.0%, 10.0%, respectively. The median progression free survival (PFS) was 10.0 months, and the 1-, 2-, and 3-year PFS rates were 42.0%, 16.0%, and 2.0%, respectively. Patients who received radical resection had obviously better OS (18.0 vs. 7.0 months, PConclusion: GBSC patients always have aggressive biological behaviors and remarkably poor prognoses. Most GBSC patients are diagnosed in advanced stages, timely radical operation together with postoperative chemotherapy are significant important. S-1 based chemotherapy may be a selectively efficient plan to prolong the survival of GBSC patients.

We describe a new software package for simulating channelised, high-time resolution data streams from radio telescopes. The software simulates data from the telescope and observing system taking into account the observation strategy, receiver system and digitisation. The signatures of pulsars, fast radio bursts and flare stars are modelled, including frequency-dependent effects such as scattering and scintillation. We also simulate more generic signals using spline curves and images. Models of radio frequency interference include signals from satellites, terrestrial transmitters and impulsive, broadband signals. The simulated signals can also be injected into real data sets. Uses of this software include the production of machine learning training data sets, development and testing of new algorithms to search for anomalous patterns and to characterise processing pipelines., 12 pages, 11 figures, MNRAS in press

Making precise measurements of pulsar dispersion measures (DMs) and applying suitable corrections for them is amongst the major challenges in high-precision timing programmes such as pulsar timing arrays (PTAs). While the advent of wide-band pulsar instrumentation can enable more precise DM measurements and thence improved timing precision, it also necessitates doing careful assessments of frequency-dependent (chromatic) DMs that was theorised by Cordes et al. (2016). Here we report the detection of such an effect in broadband observations of the millisecond pulsar PSR J2241-5236, a high-priority target for current and future PTAs. The observations were made contemporaneously using the wide-band receivers and capabilities now available at the Murchison Widefield Array (MWA), the upgraded Giant Metrewave Radio Telescope (uGMRT) and the Parkes telescopes, thus providing an unprecedentedly large frequency coverage from 80 MHz to 4 GHz. Our analysis shows the measurable changes in DM that scale with the observing frequency ($\nu$) as $\rm \delta DM \sim \nu^{2.5 \pm 0.1}$. We discuss the potential implications of such a frequency dependence in the measured DMs, and the likely impact on the timing noise budget, and comment on the usefulness of low-frequency observations in advancing PTA efforts., Comment: 14 pages, 5 figures, 3 tables, Accepted for publication in The ApJ Letters

We present radio continuum observations of NGC 2082 using ASKAP, ATCA and Parkes telescopes frequencies from 888 MHz to 9000 MHz. Some 20 arc-sec from the centre of this nearby spiral galaxy, we discovered a bright and compact radio source, J054149.24–641813.7, of unknown origin. To constrain the nature of J054149.24–641813.7, we searched for transient events with the Ultra-Wideband-Low (UWL) Parkes receiver (704 MHz–4032 MHz coverage), and compare its luminosity and spectral index to various nearby supernova remnants (SNRs), and fast radio burst (FRB) local environments. Its radio spectral index is flat (α = 0.02 ± 0.09) which is unlikely to be either an SNR or pulsar. Also, we did not find a counterpart of this source at any other frequencies including HST, Spitzer and XMM-Newton X-rays. No transient events were detected with the Parkes telescope over three days of observations, and our calculations show J054149.24–641813.7 is two orders of magnitude less luminous than FRB 121102 & 190520Bs associated persistent radio sources — likely not bright enough to be a persistent radio source associated with an FRB. We conclude that the most likely origin for J054149.24–641813.7 is a background quasar or radio galaxy. Finally, we detect extended radio continuum emission that can be associated with the overall features of NGC 2082 itself. The spectral index of α = −0.15 ± 0.23 is somewhat unexpected for spiral galaxies, but consistent with thermal emission dominating across the galaxy. We explain that this rather flat radio spectral index is a consequence of NGC 2082’s radio quiet nucleus.

The polarization of fast radio bursts (FRBs), which are bright astronomical transient phenomena, contains information about their environments. Using wide-band observations with two telescopes, we report polarization measurements of five repeating FRBs and find a trend of lower polarization at lower frequencies. This behavior is modeled as multipath scattering, characterized by a single parameter, σ RM , the rotation measure (RM) scatter. Sources with higher σ RM have higher RM magnitude and scattering time scales. The two sources with the highest σ RM , FRB 20121102A and FRB 20190520B, are associated with compact persistent radio sources. These properties indicate a complex environment near the repeating FRBs, such as a supernova remnant or a pulsar wind nebula, consistent with their having arisen from young stellar populations.

Pulsar timing array collaborations have recently reported evidence for a noise process with a common spectrum among the millisecond pulsars in the arrays. The spectral properties of this common-noise process are consistent with expectations for an isotropic gravitational-wave background (GWB) from inspiralling supermassive black-hole binaries. However, recent simulation analyses based on Parkes Pulsar Timing Array data indicate that such a detection may arise spuriously. In this paper, we use simulated pulsar timing array datasets to further test the robustness of the inference methods for spectral and spatial correlations from a GWB. Expanding on our previous results, we find strong support (Bayes factors exceeding $10^5$) for the presence of a common-spectrum noise process in datasets where no common process is present, under a wide range of timing noise prescriptions per pulsar. We show that these results are highly sensitive to the choice of Bayesian priors on timing noise parameters, with priors that more closely match the injected distributions of timing noise parameters resulting in diminished support for a common-spectrum noise process. These results emphasize shortcomings in current methods for inferring the presence of a common-spectrum process, and imply that the detection of a common process is not a reliable precursor to detection of the GWB. Future searches for the nanohertz GWB should remain focussed on detecting spatial correlations, and make use of more tailored specifications for a common-spectrum noise process., Comment: 12 pages, 12 figures. Accepted for publication in MNRAS

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

Wang, Y., et al., We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ∼20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cm-3, and rotation measure (RM) of +456 rad m-2 using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523-7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ∼1 mJy at 1400 MHz and ∼25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index α ≈ -3, where S ν ∝ ν α ) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds., Y.W. is supported by the China Scholarship Council. T.M. acknowledges the support of the Australian Research Council (ARC) through grant DP190100561. DK and AO are supported by NSF grant AST-1816492. V.G., N.R., and M.R. acknowledge support from the H2020 ERC Consolidator Grant "MAGNESIA" under grant agreement Nr. 817661 (PI: Rea), and grants SGR2017-1383 and PGC2018-095512-B-I00. R.M.S. acknowledges support through ARC Future Fellowship FT 190100155. A.R. gratefully acknowledges financial support by the research grant "iPeska" (PI: Andrea Possenti) funded under the INAF national call Prin-SKA/CTA approved with the Presidential Decree 70/2016 and continuing valuable support from the Max-Planck Society. AR also acknowledges support from the Ministero degli Affari Esteri e della Cooperazione Internazionale—Direzione Generale per la Promozione del Sistema Paese—Progetto di Grande Rilevanza ZA18GR02. G.R.S. is supported by NSERC Discovery Grants RGPIN-2016-06569 and RGPIN-2021-0400. This research was supported by the Sydney Informatics Hub (SIH), a core research facility at the University of Sydney.

In 2018 an ultra-wide-bandwidth low-frequency (UWL) receiver was installed on the 64-m Parkes Radio Telescope enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here, we present the analysis of a three-year data set of 35 millisecond pulsars observed with the UWL by the Parkes Pulsar Timing Array (PPTA), using wideband timing methods. The two key differences compared to typical narrow-band methods are, firstly, generation of two-dimensional templates accounting for pulse shape evolution with frequency and, secondly, simultaneous measurements of the pulse time-of-arrival (ToA) and dispersion measure (DM). This is the first time that wideband timing has been applied to a uniform data set collected with a single large-fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions including initial noise analysis. Precision of our ToA and DM measurements is in the range of 0.005 $-$ 2.08 $\mu$s and (0.043$-$14.24)$\times10^{-4}$ cm$^{-3}$ pc, respectively, with 94% of the pulsars achieving a median ToA uncertainty of less than 1 $\mu$s., Comment: 29 pages, 12 figures, Accepted for publication in ApJ

We report the independent discovery of PSR J0027-1956 with the Murchison Widefield Array (MWA) in the ongoing Southern-sky MWA Rapid Two-meter (SMART) pulsar survey. J0027-1956 has a period of ~1.306 s, a dispersion measure (DM) of ~20.869 pc cm^-3 , and a nulling fraction of ~77%. This pulsar highlights the advantages of the survey's long dwell times (~80 min), which, when fully searched, will be sensitive to the expected population of similarly bright, intermittent pulsars with long nulls. A single-pulse analysis in the MWA's 140-170 MHz band also reveals a complex sub-pulse drifting behavior, including both rapid changes of the drift rate characteristic of mode switching pulsars, as well as a slow, consistent evolution of the drift rate within modes. In some longer drift sequences, interruptions in the otherwise smooth drift rate evolution occur preferentially at a particular phase, typically lasting a few pulses. These properties make this pulsar an ideal test bed for prevailing models of drifting behavior such as the carousel model., Comment: Accepted for publication in ApJ

The environment of actively repeating fast radio bursts (FRBs) has been shown to be complex and varying. The recently localized FRB 20190520B is extremely active, has the largest confirmed host dispersion measure, and is only the second FRB source associated with a compact, persistent radio source (PRS). The main tracer of the magneto-ionic environments is the rotation measure (RM), a path-integral of the line-of-sight component of magnetic field strength (B) and electron density, which does not allow a direct probe of the B-field configuration. Here we report direct evidence for a B-field reversal based on the observed sign change and extreme variation of FRB 20190520B's RM, which changed from $\sim10000$ rad m$^{-2}$ to $\sim-16000$ rad m$^{-2}$ between June 2021 and January 2022. Such extreme RM reversal has never been observed before in any FRB nor in any astronomical object. The implied short-term change of the B-field configuration in or around the FRB could be due to the vicinity of massive black holes, or a magnetized companion star in binary systems, or a young supernova remnant along the line of sight., Comment: It was merged into arXiv:2202.11112. Science380,599-603(2023). DOI:10.1126/science.abo6526

As TeV gamma-ray astronomy progresses into the era of the Cherenkov Telescope Array (CTA), there is a desire for the capacity to instantaneously follow up on transient phenomena and continuously monitor gamma-ray flux at energies above $10^{12}$ eV. To this end, a worldwide network of Imaging Air Cherenkov Telescopes (IACTs) is required to provide triggers for CTA observations and complementary continuous monitoring. An IACT array sited in Australia would contribute significant coverage of the Southern Hemisphere sky. Here, we investigate the suitability of a small IACT array and how different design factors influence its performance. Monte Carlo simulations were produced based on the Small-Sized Telescope (SST) and Medium-Sized Telescope (MST) designs from CTA. Angular resolution improved with larger baseline distances up to 277m between telescopes, and energy thresholds were lower at 1000m altitude than at 0m. The $\sim$300 GeV energy threshold of MSTs proved more suitable for observing transients than the $\sim$1.2 TeV threshold of SSTs. An array of four MSTs at 1000m was estimated to give a 5.7$\sigma$ detection of an RS Ophiuchi-like nova eruption from a 4-hour observation. We conclude that an array of four MST-class IACTs at an Australian site would ideally complement the capabilities of CTA., Comment: 10 pages, 13 figures, 2 tables, accepted for publication in PASA

In this study, we developed an energy security evaluation model (ESEM) from three dimensions, energy supply-transport security, safety of energy utilization, and stability of political-socioeconomic environment, based on the integrated application of subjective and objective weight allocation technique. Then the spatial-temporal evolution of global energy security pattern and its driving mechanism was analyzed with the method above, and the results are shown as follows: (1) since the 1990s, the spatial patterns of global energy security have shown a deteriorating trend, with the growth of countries in at-risk type and relatively at-risk type. (2) The spatial distribution of countries with secure energy system shows a strong stability, and these countries are concentrated persistently in Western Europe and North America. The spatial evolution of countries with relatively secure energy system also presents a strong stability, which are mainly distributed in the periphery of the secure ones, namely Central and Southern Europe, South America and Eurasia, while countries with general energy system are mainly distributed in Asia, Africa and Southern Europe, and the spatial-temporal evolution of this type is the main cause for the deterioration of world energy security pattern. Countries with at-risk and relatively at-risk energy system are mainly concentrated in Africa, Asia, the Middle East and Eurasia, rendering spatial extension to the east and south. (3) In the past 20 years, the mechanism for world’s energy security pattern formation gradually transforms from the ‘unitary dimension dominated’ to the ‘binary dimension-dominated’, and the main factors influencing the global energy security pattern become more diverse. (4) In the pattern of world’s energy security, China’s performance on energy security has been the global average since the 1990s, which shows a decreasing trend in safety of energy utilization dimension. Findings in this study can provide a reference for the government in terms of formulating strategic responses and policy options.

We report the discovery of a highly-polarized, highly-variable, steep-spectrum radio source, ASKAP J173608.2-321635, located $\sim$4\,deg from the Galactic center in the Galactic plane. The source was detected six times between 2020 January and 2020 September as part of the Australian Square Kilometre Array Pathfinder Variables and Slow Transients (ASKAP VAST) survey at 888\,MHz. It exhibited a high degree ($\sim 25$\%) of circular polarization when it was visible. We monitored the source with the MeerKAT telescope from 2020 November to 2021 February on a 2--4 week cadence. The source was not detected with MeerKAT before 2021 February 07 when it appeared and reached a peak flux density of 5.6\,mJy. The source was still highly circularly polarized, but also showed up to 80\% linear polarization, and then faded rapidly with a timescale of one day. The rotation measure of the source varied significantly, from $-11.8\pm0.8$\,rad\,m$^{-2}$ to $-64.0\pm1.5$\,rad\,m$^{-2}$, over three days. No X-ray counterpart was found in follow-up \textit{Swift} or \textit{Chandra} observations about a week after the first MeerKAT detection, with upper limits of $\sim 5.0\times10^{31}$\,erg\,s$^{-1}$ (0.3--8\,keV, assuming a distance $\sim10$ kpc). No counterpart is seen in new or archival near-infrared observations down to $J=20.8$\,mag. We discuss possible identifications for ASKAP J173608.2-321635 including a low-mass star/substellar object with extremely low infrared luminosity, a pulsar with scatter-broadened pulses, a transient magnetar, or a Galactic Center Radio Transient: none of these fully explains the observations, which suggests that ASKAP J173608.2-321635 may represent part of a new class of objects being discovered through radio imaging surveys., Comment: 22 pages, 15 figures, Accepted by ApJ

The Variables and Slow Transients Survey (VAST) on the Australian Square Kilometre Array Pathfinder (ASKAP) is designed to detect highly variable and transient radio sources on timescales from 5 s to$\sim\!5$yr. In this paper, we present the survey description, observation strategy and initial results from the VAST Phase I Pilot Survey. This pilot survey consists of$\sim\!162$h of observations conducted at a central frequency of 888 MHz between 2019 August and 2020 August, with a typical rms sensitivity of$0.24\ \mathrm{mJy\ beam}^{-1}$and angular resolution of$12-20$arcseconds. There are 113 fields, each of which was observed for 12 min integration time, with between 5 and 13 repeats, with cadences between 1 day and 8 months. The total area of the pilot survey footprint is 5 131 square degrees, covering six distinct regions of the sky. An initial search of two of these regions, totalling 1 646 square degrees, revealed 28 highly variable and/or transient sources. Seven of these are known pulsars, including the millisecond pulsar J2039–5617. Another seven are stars, four of which have no previously reported radio detection (SCR J0533–4257, LEHPM 2-783, UCAC3 89–412162 and 2MASS J22414436–6119311). Of the remaining 14 sources, two are active galactic nuclei, six are associated with galaxies and the other six have no multi-wavelength counterparts and are yet to be identified.

We have searched for weak fast radio burst (FRB) events using a database containing 568,736,756 transient events detected using the Parkes radio telescope between 1997 and 2001. In order to classify these pulses, and to identify likely FRB candidates, we used a machine learning algorithm based on ResNet. We identified 81 new candidate FRBs and provide details of their positions, event times, and dispersion measures. These events were detected in only one beam of the Parkes multibeam receiver. We used a relatively low S/N cutoff threshold when selecting these bursts and some have dispersion measures only slightly exceeding the expected Galactic contribution. We therefore present these candidate FRBs as a guide for follow-up observations in the search for repeating FRBs., 8 pages, 5 figures, 2 tables, accepted by MNRAS

The central engine of fast radio bursts (FRB) is not yet understood. Due to the interaction between the pulse and the intervening plasma, the dispersion sweep of FRBs provides a unique probe of its environment and the ionized baryon content of the intergalactic medium. Active repeaters has been shown to be associated with persistent radio source (PRS), and dense, energetic, magnetized plasmas. Here we report the discovery and localization of a new, extremely active repeater, FRB 190520, which is co-located with a compact PRS and identified with a dwarf host galaxy of high star formation at a redshift z=0.241. The estimated host galaxy contribution DMhost≈912+69−108pc cm−3 is nearly an order of magnitude higher than the average of FRB host galaxies and much larger than the contribution from the intergalactic medium, suggesting caution in inferring redshifts for FRBs without accurate host galaxy identifications. This represents the second source after FRB 121102 with confirmed association between FRB and compact PRS. The dense, complex host galaxy environment and the association with PRS may point to a distinctive origin or an earlier evolutionary stage for highly active repeating FRBs.

A nanohertz-frequency stochastic gravitational-wave background can potentially be detected through the precise timing of an array of millisecond pulsars. This background produces low-frequency noise in the pulse arrival times that would have a characteristic spectrum common to all pulsars and a well-defined spatial correlation. Recently the North American Nanohertz Observatory for Gravitational Waves collaboration (NANOGrav) found evidence for the common-spectrum component in their 12.5-year data set. Here we report on a search for the background using the second data release of the Parkes Pulsar Timing Array. If we are forced to choose between the two NANOGrav models $\unicode{x2014}$ one with a common-spectrum process and one without $\unicode{x2014}$ we find strong support for the common-spectrum process. However, in this paper, we consider the possibility that the analysis suffers from model misspecification. In particular, we present simulated data sets that contain noise with distinctive spectra but show strong evidence for a common-spectrum process under the standard assumptions. The Parkes data show no significant evidence for, or against, the spatially correlated Hellings-Downs signature of the gravitational-wave background. Assuming we did observe the process underlying the spatially uncorrelated component of the background, we infer its amplitude to be $A = 2.2^{+0.4}_{-0.3} \times 10^{-15}$ in units of gravitational-wave strain at a frequency of $1\, \text{yr}^{-1}$. Extensions and combinations of existing and new data sets will improve the prospects of identifying spatial correlations that are necessary to claim a detection of the gravitational-wave background., 10 pages, 5 figures

The event rate, energy distribution, and time-domain behaviour of repeating fast radio bursts (FRBs) contains essential information regarding their physical nature and central engine, which are as yet unknown. As the first precisely-localized source, FRB 121102 has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1652 independent bursts with a peak burst rate of 122~hr^{-1}, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be ~4.8 x 10^{37} erg at 1.25~GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allow sensitive periodicity searches between 1 ms and 1000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavoring emission mechanisms with large energy requirements or contrived triggering conditions., 69 pages, 14 figures, 2 tables; Updates for author correction

This paper presents the effects of manufacturing micro-structure on the elastic properties of FFF (fused filament fabrication) 3D printing material and the vibration characteristics of FFF 3D printing plates. According to the results of scanning electron microscopy, three different material directions are defined to describe the orthotropy of FFF 3D printing material including fibre direction, intra-layer direction, and inter-layer direction. Then, the constitutive model of the orthotropic elastic 3D printing material is established based on static experimental results and plane stress rotation formula. Static experimental results (totally 27 kinds of specimens) show that the largest difference of Young’s moduli in different material directions is 1104.684 MPa which is even larger than the Young’s modulus in the intra-layer direction. Finite element models of FFF 3D printing plates with six different printing directions ( α - 0 ° , α - 90 ° , β - 0 ° , β - 90 ° , λ - 0 ° , λ - 90 ° ) and three different layer thicknesses (0.2 mm, 0.25 mm, 0.3 mm) are built and their natural frequencies are determined. Simulation results show that the largest difference of the natural frequencies among plates with different printing directions are 10.645 Hz, 39.588 Hz, 66.710 Hz, 123.780 Hz, and 185.720 Hz when the mode of the plates changes from one to five. Meanwhile, these differences are relative large when compared with the first five out-of-plane natural frequencies of these plates. Additionally, vibration experiments of FFF 3D printing plates are carried out to verify the validity of the simulation process and all the relative errors of the natural frequencies between simulation and the experimental results are found to be very small. Therefore, the accuracy of the finite element models is good enough and one can confirm that the effects of manufacturing micro-structure on the vibration characteristics are significant.