FAST Observations of an Extremely Active Episode of FRB 20201124A.Ⅱ.Energy Distribution

We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB20201124A with the Five-hundred-meter Aperture Spherical radio Telescope(FAST)during an extremely active episode on UTC 2021 September 25–28 in a series of four papers.In this second paper of the series,we study the energy distribution of 881 bursts(defined as significant signals separated by dips down to the noise level)detected in the first four days of our 19 hr observational campaign spanning 17 days.The event rate initially increased exponentially but the source activity stopped within 24 hr 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±0.01 and-4.27±0.23,respectively.Assuming a radio radiative efficiency ofη_(r)=10^(-4),the total isotropic energy of the bursts released during the four days when the source was active is already 3.9×10^(46)erg,exceeding~23%of the available magnetar dipolar magnetic energy.This challenges the magnetar models which invoke an inefficient radio emission(e.g.,synchrotron maser models).

The FAST Galactic Plane Pulsar Snapshot survey:I.Project design and pulsar discoveries

Discovery of pulsars is one of the main goals for large radio telescopes.The Five-hundredmeter Aperture Spherical radio Telescope(FAST),that incorporates an L-band 19-beam receiver with a system temperature of about 20 K,is the most sensitive radio telescope utilized for discovering pulsars.We designed the snapshot observation mode for a FAST key science project,the Galactic Plane Pulsar Snapshot(GPPS)survey,in which every four nearby pointings can observe a cover of a sky patch of 0.1575 square degrees through beam-switching of the L-band 19-beam receiver.The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes.The goal of the GPPS survey is to discover pulsars within the Galactic latitude of±10∘from the Galactic plane,and the highest priority is given to the inner Galaxy within±5∘.Up to now,the GPPS survey has discovered 201 pulsars,including currently the faintest pulsars which cannot be detected by other telescopes,pulsars with extremely high dispersion measures(DMs)which challenge the currently widely used models for the Galactic electron density distribution,pulsars coincident with supernova remnants,40 millisecond pulsars,16 binary pulsars,some nulling and mode-changing pulsars and rotating radio transients(RRATs).The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars.Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars.The GPPS survey discoveries are published and will be updated at http://zmtt.bao.ac.cn/GPPS/.

FAST Observations of an Extremely Active Episode of FRB 20201124A.Ⅳ.Spin Period Search

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 during an extremely active episode on UTC 2021 September 25th-28th 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 and 100 s with a pulse duty cycle<0.49±0.08(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–100 s isolated magnetar/pulsar with surface magnetic field<10^(15)G and a small duty cycle(such as in a polar-cap emission mode)or a pulsar with a companion star or black hole up to 100 M_(⊙)and P_(b)>10 hr.We also perform a periodicity search of the fine structures and identify 53 unrelated millisecond-timescale“periods”in multicomponents with the highest significance of 3.9σ.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~4σwith multi-components from one-off FRBs.We discuss the implications of our results and the possible connections between FRB multi-components and pulsar microstructures.

Ultrafast Electron Transfer in All-Small-Molecule Photovoltaic Blends Promoted by Intermolecular Interactions in Cyanided Donors

Cyano substitution has been established as a viable approach to optimize the performance of all-small-molecule organic solar cells.However,the effect of cyano substitution on the dynamics of photo-charge generation remains largely unexplored.Here,we report an ultrafast spectroscopic study showing that electron transfer is markedly promoted by enhanced intermolecular charge-transfer interaction in all-small-molecule blends with cyanided donors.The delocalized excitations,arising from intermolecular interaction in the moiety of cyano-substituted donor,undergo ultrafast electron transfer with a lifetime of∼3 ps in the blend.In contrast,some locally excited states,surviving in the film of donor without cyano substitution,are not actively involved in the charge separation.These findings well explain the performance improvement of devices with cyanided donors,suggesting that manipulating intermolecular interaction is an efficient strategy for device optimization.

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation is proposed in this paper to improve the efficiency and accuracy of electromagnetic calculation. An image boundary extraction algorithm is developed to map the image on the geometric domain. Identification algorithm for the location of nodes in polygon area is proposed to determine the state of the node. To promote the average quality of the mesh and the efficiency of mesh generation, a novel force-based mesh smoothing algorithm is proposed. One test case and a typical electromagnetic calculation are used to testify the effectiveness and efficiency of the proposed algorithm. The results demonstrate that the proposed algorithm can produce a high-quality mesh with less iteration.

FAST Observations of an Extremely Active Episode of FRB 20201124A.Ⅲ.Polarimetry

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 during an extremely active episode between the 25th and 28th of September 2021(UT).We focus on the polarization properties of536 bright bursts with S/N>50.We found that the Faraday rotation measures(RMs)monotonically dropped from-579to-605 rad m^(-2)in the 4 day window.The RM values were compatible with the values(-300 to-900 rad m^(-2))reported 4 months ago.However,the RM evolution rate in the current observation window was at least an order of magnitude smaller than the one(~500 rad m^(-2)day^(-1))previously reported during the rapid RM-variation phase,but is still higher than the one(≤1 rad m^(-2)day^(-1))during the later RM no-evolution phase.The bursts of FRB 20201124A were highly polarized with the total degree of polarization(circular plus linear)greater than 90%for more than 90%of all bursts.The distribution of linear polarization position angles(PAs),degree of linear polarization(L/I)and degree of circular polarization(V/I)can be characterized 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 5σ)were observed in 33%of all bursts.The polarization of single pulses seems to follow certain complex trajectories on the Poincarésphere,which may shed light on the radiation mechanism at the source or the plasma properties along the path of FRB propagation.

Two-Dimensional Electronic Spectroscopy with Active Phase Management

Two-dimensional elec tronic spec troscopy(2DES)is a powerful met hod to probe the coherent electron dynamics in complicated systems.Stabilizing the phase difference of the incident ultrashort pulses is the mos t challenging par t for experimen tal demonstration of 2DES.Here,we present a tuto rial review on the 2DES proto cols based on active phase managements which are originally developed for quantum optics experiments.We introduce the 2DES techniques in box and pump-probe geometries with phase stabilization realized by interferometry,and outline the fully collinear 2DES approach with the frequency tagging by acoustic optical modulators and frequency combs.The combination of active phase managements,ultrashort pulses and other spectroscopic methods may open new opportunities to tackle essential challenges related to excited states.

Atlas of dynamic spectra of fast radio burst FRB 20201124A

Fast radio bursts(FRBs) are highly dispersed millisecond-duration radio bursts,[1,2]of which the physical origin is still not fully understood. FRB 20201124A is one of the most actively repeating FRBs. In this paper, we present the collection of 1863 burst dynamic spectra of FRB 20201124A measured with the Five-hundred-meter Aperture Spherical radio Telescope(FAST). The current collection, taken from the observation during the FRB active phase from April to June 2021, is the largest burst sample detected for any FRB so far. The standard PSRFITs format is adopted, including dynamic spectra of the burst, and the time information of the dynamic spectra, in addition, mask files help readers to identify the pulse positions are also provided. The dataset is available in Science Data Bank, with the link https://www.doi.org/10.57760/sciencedb.j00113.00076.

Current status and future prospects of mesenchymal stem cell therapy for liver fibrosis

Liver fibrosis is the end-stage of many chronic liver diseases and is a significant health threat. The only effective therapy is liver transplantation, which still has many problems, including the lack of donor sources, immu- nological rejection, and high surgery costs, among others. However, the use of cell therapy is becoming more prev- alent, and mesenchymal stem cells （MSCs） seem to be a promising cell type for the treatment of liver fibrosis. MSCs have multiple differentiation abilities, allowing them to migrate directly into injured tissue and differentiate into hepatocyte-like cells. Additionally, MSCs can release various growth factors and cytokines to increase hepatocyte regeneration, regress liver fibrosis, and regulate inflammation and immune responses. In this review, we summarize the current uses of MSC therapies for liver fibrosis and suggest potential future applications.

A Near-Infrared Polymer Acceptor Enables over 15%Efficiency for All-Polymer Solar Cells

Finding effective molecular design strategies to enable efficient charge generation,high charge transport,and small energy loss is a longstanding challenge for developing high-performance all-polymer solar cells(all-PSCs).Here,we designed and synthesized a fused-aromatic-ring-constructed near-infrared(NIR)polymer acceptor(PA)PYT-Tz with fused-ring benzotriazole(BTz)-based A’-DAD-A’structure as electron-deficient-core,n-nonane as alkyl-side-chain and thiophene asπ-bridge,and achieved a power conversion efficiency(PCE)of 15.10%for the all-PSCs with PYT-Tz as acceptor and a wide-bandgap PBDB-T as donor.A control PA PYT reported by our lab recently was introduced for investigating the synergistic effect of the electron-deficient-core and alkyl-side-chain on the optoelectronic properties and photovoltaic performance of the n-type PAs.Compared with PYT,the designed PYT-Tz exhibits intense and red-shifted absorption,upshifted energy levels,high electron mobility and ordered molecular packing in the active layers,and,blended with PBDB-T,yields the efficient hole injection,ultrafast charge generation,and the decreased non-radiative recombination loss of 0.17 eV.Of note is that the PCE of 15.10%is one of the highest PCE values for an all-PSC reported to date.Our results indicate BTz-based fused-aromatic-ring-constructed PAs are promising NIR acceptors in the all-PSCs.

Slight Structural Disorder in Bithiophene-based Random Terpolymers with Improved Power Conversion Efficiency for Polymer Solar Cells

A series of random terpolymers P2-P5 were designed and synthesized by randomly embedding 5 mol%, 10 mol%, 15 mol% and 25 mol% feed ratios of low cost 2,2-bithiophene as the third monomer to the famous donor-acceptor （D-A） type copolymer PTBT-Th （P1）. All polymers showed similar molecular weight with number-average molecular weight （Mn） and weight-average molecular weight （Mw） in the range of （59-74） and （93-114） kg·mol-1, respectively, to ensure a fair comparison on the structure-property relationships. Compared with the control copolymer PTBT-Th, the random terpolymers exhibited enhanced absorption intensity in a wide range from 400 nm to 650 nm in both solution and film as well as in polymer/PC71BM blends. From grazing incident wide-angle X-ray diffraction （GIWAXS）, compared with the regularly alternated copolymer PTB7-Th, the random terpolymers demonstrated mild structural disorder with reduced （100） lamellar stacking and slightly weakened （010） π-π stacking for the polymers as well as slightly reduced PC71BM aggregation in polymer/PC71BM blends. However, the measured hole mobility for terpolymers （（1.20-3.73） × 10 -4 cm2·V-1·s-1） was evaluated to be comparable or even higher than 1.35 × 10 -4 cm2·V-1 ·s-1 of the alternative copolymer. Enhanced average power conversion efficiency （PCE） from 7.35% to 8.11% and 7.79% to 8.37% was observed in both conventional and inverted device architectures from copolymer P1 to terpolymers P4, while further increasing the 2,2-bithiophene feed ratio decreased the PCE.

Hsp90-associated DNA replication checkpoint protein and proteasome-subunit components are involved in the age-related macular degeneration

Background:Age-related macular degeneration(AMD)is the leading cause of vision loss worldwide.However,the mechanisms involved in the development and progression of AMD are poorly delineated.We aimed to explore the critical genes involved in the progression of AMD.Methods:The differentially expressed genes(DEGs)in AMD retinal pigment epithelial(RPE)/choroid tissues were identified using the microarray datasets GSE99248 and GSE125564,which were downloaded from the gene expression omnibus database.The overlapping DEGs from the two datasets were screened to identify DEG-related biological pathways using gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses.The hub genes were identified from these DEGs through protein-protein interaction network analyses.The expression levels of hub genes were evaluated by quantitative real-time polymerase chain reaction following the induction of senescence in ARPE-19 with FK866.Following the identification of AMD-related key genes,the potential small molecule compounds targeting the key genes were predicted by PharmacoDB.Finally,a microRNA-gene interaction network was constructed.Results:Microarray analyses identified 174 DEGs in the AMD RPE compared to the healthy RPE samples.These DEGs were primarily enriched in the pathways involved in the regulation of DNA replication,cell cycle,and proteasome-mediated protein polyubiquitination.Among the top ten hub genes,HSP90AA1,CHEK1,PSMA4,PSMD4,and PSMD8 were upregulated in the senescent ARPE-19 cells.Additionally,the drugs targeting HSP90AA1,CHEK1,and PSMA4 were identified.We hypothesize that Hsa-miR-16-5p might target four out of the five key DEGs in the AMD RPE.Conclusions:Based on our findings,HSP90AA1 is likely to be a central gene controlling the DNA replication and proteasome-mediated polyubiquitination during the RPE senescence observed in the progression of AMD.Targeting HSP90AA1,CHEK1,PSMA4,PSMD4,and/or PSMD8 genes through specific miRNAs or small molecules might potentially alleviate the progression of AMD through attenuating RPE senescence.