Improved Measurement of the Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay.

Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. In this Letter, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958 days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as the flux evolution with the ^{239}Pu isotopic fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted inverse-beta-decay spectrum from ^{239}Pu fission does not improve the agreement with the measurement for either model. The models can be brought into better agreement with the measurements if either the predicted spectrum due to ^{235}U fission is changed or the predicted ^{235}U, ^{238}U, ^{239}Pu, and ^{241}Pu spectra are changed in equal measure.

Precision Measurement of Reactor Antineutrino Oscillation at Kilometer-Scale Baselines by Daya Bay.

We present a new determination of the smallest neutrino mixing angle θ_{13} and the mass-squared difference Δm_{32}^{2} using a final sample of 5.55×10^{6} inverse beta-decay (IBD) candidates with the final-state neutron captured on gadolinium. This sample is selected from the complete dataset obtained by the Daya Bay reactor neutrino experiment in 3158 days of operation. Compared to the previous Daya Bay results, selection of IBD candidates has been optimized, energy calibration refined, and treatment of backgrounds further improved. The resulting oscillation parameters are sin^{2}2θ_{13}=0.0851±0.0024, Δm_{32}^{2}=(2.466±0.060)×10^{-3} eV^{2} for the normal mass ordering or Δm_{32}^{2}=-(2.571±0.060)×10^{-3} eV^{2} for the inverted mass ordering.

First Measurement of High-Energy Reactor Antineutrinos at Daya Bay.

This Letter reports the first measurement of high-energy reactor antineutrinos at Daya Bay, with nearly 9000 inverse beta decay candidates in the prompt energy region of 8-12 MeV observed over 1958 days of data collection. A multivariate analysis is used to separate 2500 signal events from background statistically. The hypothesis of no reactor antineutrinos with neutrino energy above 10 MeV is rejected with a significance of 6.2 standard deviations. A 29% antineutrino flux deficit in the prompt energy region of 8-11 MeV is observed compared to a recent model prediction. We provide the unfolded antineutrino spectrum above 7 MeV as a data-based reference for other experiments. This result provides the first direct observation of the production of antineutrinos from several high-Q_{ß} isotopes in commercial reactors.

[Clinical characteristics and death risk factors of severe COVID-19].

Objective: To analyze the clinical features and death-related risk factors of COVID-19. Methods: We enrolled 891 COVID-19 patients admitted to the Affiliated Hospital of Jianghan University from December 2019 to February 2020, including 427 men and 464 women. Of the 891 cases, 582 were severe or critical, including 423(73%)severe and 159 (27%) critical cases. We compared the demographics, laboratory findings, clinical characteristics, treatments and prognosis data of the 582 severe patients. Univariate and multivariate logistic regression analysis was conducted to explore the risk factors associated with death in COVID-19 patients. Results: The 582 severe patients included 293 males and 289 females, with a median age of 64(range 24 to 106). Sixty-three patients died, including 45 males and 18 females, with a median age of 71(range 37 to 90). The average onset time of the 582 patients was 8 days, of whom 461 (79%) had fever, 358 (62%) dry cough, 274 (47%) fatigue. There were 206 cases with shortness of breath (35%), 155 cases with expectoration (27%), 83 cases with muscle pain or joint pain (14%), 71 cases with diarrhea (12%), and 29 cases with headache (4%). Underlying diseases were present in 267 (46%) patients, most commonly hypertension (194, 33%), followed by diabetes (69, 12%), coronary atherosclerotic heart disease (37, 6%), tumor (18, 3%), and chronic obstructive pulmonary disease (5, 1%). Chest CT showed bilateral lung involvement in 505 patients (87%). Upon admission, the median lymphocyte count of the 582 patients was 0.8(IQR, 0.6-1.1)×10(9)/L, the median D-dimer was 0.5 (IQR, 0.4- 0.8) mg/L, the median N-terminal brain natriuretic peptide precursor (NT-proBNP) was 433 (IQR, 141- 806) pg/L, and the median creatinine was 70.3 (IQR, 56.9-87.9) µmol/L. The death group had a median lymphocyte count of 0.5 (0.4-0.8)×10(9)/L, D-dimer 1.1 (0.7-10.0)mg/L, N-terminal brain natriuretic peptide precursor 1479(893-5 087) pg/ml, and creatinine 89.9(67.1-125.3) µmol/L. Multivariate logistic analysis showed that increased D-dimer (OR: 1.095, 95% CI: 1.045-1.148, P<0.001), increased NT-proBNP (OR: 4.759, 95% CI: 2.437-9.291, P<0.001), and decreased lymphocyte count (OR: 0.180, 95% CI: 0.059-0.550, P=0.003) were the risk factors of death in COVID-19 patients. Conclusions: The average onset time of severe COVID-19 was 8 days, and the most common symptoms were fever, dry cough and fatigue. Comorbidities such as hypertension were common and mostly accompanied by impaired organ functions on admission. Higher D-dimer, higher NT-proBNP, and lower lymphocyte count were the independent risk factors of death in COVID-19 patients.

Extraction of the

This Letter reports the first extraction of individual antineutrino spectra from ^{235}U and ^{239}Pu fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses 3.5×10^{6} inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, ^{235}U and ^{239}Pu, are extracted using the evolution of the prompt spectrum as a function of the isotope fission fractions. In the energy window of 4-6 MeV, a 7% (9%) excess of events is observed for the ^{235}U (^{239}Pu) spectrum compared with the normalized Huber-Mueller model prediction. The significance of discrepancy is 4.0σ for ^{235}U spectral shape compared with the Huber-Mueller model prediction. The shape of the measured inverse beta-decay prompt energy spectrum disagrees with the prediction of the Huber-Mueller model at 5.3σ. In the energy range of 4-6 MeV, a maximal local discrepancy of 6.3σ is observed.

Measurement of the Electron Antineutrino Oscillation with 1958 Days of Operation at Daya Bay.

We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor ν[over ¯]_{e} inverse ß decay candidates observed over 1958 days of data collection. The installation of a flash analog-to-digital converter readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic ^{9}Li and ^{8}He background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative ν[over ¯]_{e} rates and energy spectra among detectors yields sin^{2}2θ_{13}=0.0856±0.0029 and Δm_{32}^{2}=(2.471_{-0.070}^{+0.068})×10^{-3} eV^{2} assuming the normal hierarchy, and Δm_{32}^{2}=-(2.575_{-0.070}^{+0.068})×10^{-3} eV^{2} assuming the inverted hierarchy.

Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay.

The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW_{th} reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective ^{239}Pu fission fractions F_{239} from 0.25 to 0.35, Daya Bay measures an average IBD yield σ[over ¯]_{f} of (5.90±0.13)×10^{-43} cm^{2}/fission and a fuel-dependent variation in the IBD yield, dσ_{f}/dF_{239}, of (-1.86±0.18)×10^{-43} cm^{2}/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the ^{239}Pu fission fraction at 10 standard deviations. The variation in IBD yield is found to be energy dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1σ. This discrepancy indicates that an overall deficit in the measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes ^{235}U, ^{239}Pu, ^{238}U, and ^{241}Pu. Based on measured IBD yield variations, yields of (6.17±0.17) and (4.27±0.26)×10^{-43} cm^{2}/fission have been determined for the two dominant fission parent isotopes ^{235}U and ^{239}Pu. A 7.8% discrepancy between the observed and predicted ^{235}U yields suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.

Identification and expression analysis of 4-Coumarate: Coenzyme A ligase gene family in Dryopteris Fragrans.

4-Coumarate: coenzyme A ligase (4CL) catalyzes the conversion of hydroxycinnamates into corresponding CoA esters for biosynthesis of flavonoids and lignin. It has been widely studied in seed plants; however, it is poorly characterized in ferns. In this study, we identified 4CLs genes in ferns D. fragrans (L.) Schott (Df4CL gene) by rapid amplification of cDNA ends (RACE), and then investigated the expressions of the genes by real-time PCR, and determined total flavonoids and lignin contents. The results showed that four members of the 4CL genes were found from this species, which named Df4CL 1, 2, 3, and 4 genes. Their full-length cDNA was sequenced. Also, our analyses showed that the amino acid sequences derived from these cDNAs exhibited similar conserved regions (Box I and Box II), and substrate-binding regions compared to 4CLs isolated from seed plants.At the same time, the developmental and stress-induced gene expression patterns showed that the changes on the expression levels of Df4CL genes affected the levels of flavonoids and lignin. In conclusion, we identified 4CLs genes in ferns D. fragrans and analyzed the expressions of these genes, and finally explored the relationship between the expressions of 4CLs and syntheses of flavonoids and lignin.

Identification and characterisation of DfCHS, a chalcone synthase gene regulated by temperature and ultraviolet in Dryopteris fragrans.

Chalcone synthase (CHS) is an enzyme that catalyzes the first committed step in flavonoid biosynthesis, and its transcription level is regulated by light conditions. By using homology cloning and rapid amplification of cDNA ends, we cloned a chalcone synthase gene (DfCHS) from Dryopteris fragrans (L.) Schott. The full-length cDNA of DfCHS is 1,737 bp, with an open reading frame (ORF) of 1,122 bp (deposited in GenBank under Accession Number KF530802) encoding a predicted protein of 373 amino acids. The calculated molecular mass of DfCHS is 41.3 kDa. We studied the expression of DfCHS and total flavonoid contents in tissue culture seedlings cultured under the low temperature at 4ºC, high temperature at 35ºC and UV conditions, respectively. The results show that the expression of DfCHS are not the same, but all present rising trends, then flavonoid contents were increased. Overall, our results imply that the expression of DfCHS gene provide a certain theory basis in the status of evolution among ferns.

Overexpression of paralogues of the wheat expansin gene TaEXPA8 improves low-temperature tolerance in Arabidopsis.

Low temperature is one of the important factors limiting wheat yield in cold regions. Expansins are nonenzymatic proteins that loosen cell walls and play important roles in diverse biological processes related to cell wall modification, including development and stress tolerance. Many studies have shown that expansins are involved in resistance to various abiotic stresses, such as heat and drought. However, the role of expansins in response to low-temperature stress remains unclear. Based on our previous transcriptome data of a winter wheat cultivar Dongnongdongmai 2 (DN2), we found that one of the expansin genes, TaEXPA8, was significantly induced by low temperature, indicating a role for TaEXPA8 in cold resistance. In this study, the paralogous TaEXPA8 genes TaEXPA8-A, TaEXPA8-B and TaEXPA8-D were cloned by RT-PCR. These three genes were then transformed into Arabidopsis by the floral dip method. Expression patterns of TaEXPA8 genes in different tissues and in response to several abiotic stresses and hormones were detected by quantitative real-time PCR (qRT-PCR). The results showed that TaEXPA8-A and TaEXPA8-B were expressed mainly in roots, while TaEXPA8-D was expressed predominantly in flowers. TaEXPA8 genes were induced by low-temperature and drought. The overexpression of TaEXPA8-B and TaEXPA8-D enhanced low-temperature resistance and had increased superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity and soluble protein, MDA and proline content. In summary, our study suggested that the expansins TaEXPA8-B and TaEXPA8-D are involved in the response to low temperature and possibly play a role in cold resistance by activating the protective enzyme system.