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1. chinaXiv:201609.01035 [pdf]

Next-to-next-to-leading-order QCD corrections to $\chi_c0,2\rightarrow \gamma\gamma$

Wen-Long Sang; Feng Feng; Yu Jia; Shuang-Ran Liang
Subjects: Physics >> Nuclear Physics

We calculate the next-to-next-to-leading-order (NNLO) perturbative corrections to P-wave quarkonia annihilation decay to two photons, in the framework of nonrelativistic QCD (NRQCD) factorization. The order-α2s short-distance coefficients associated with each helicity amplitude are presented in a semi-analytic form, including the "light-by-light" contributions. With substantial NNLO corrections, we find disquieting discrepancy when confronting our state-of-the-art predictions with the latest \textsf{BESIII} measurements, especially fail to account for the measured χc2→γγwidth. Incorporating the effects of spin-dependent forces would even exacerbate the situation, since it lifts the degeneracy between the nonperturbative NRQCD matrix elements of χc0 and χc2 toward the wrong direction. We also present the order-α2s predictions to χb0,2→γγ, which await the future experimental test.

submitted time 2016-09-14 Hits630Downloads352 Comment 0

2. chinaXiv:201609.00930 [pdf]

Can NRQCD Explain the $\gamma\gamma^* \to \eta_c$ Transition Form Factor Data?

Feng Feng; Yu Jia; Wen-Long Sang
Subjects: Physics >> Nuclear Physics

Unlike the bewildering situation in the γγ∗→π form factor, a widespread view is that perturbative QCD can decently account for the recent \textsc{BaBar} measurement of γγ∗→ηc transition form factor. The next-to-next-to-leading order (NNLO) perturbative correction to the γγ∗→ηc,b form factor, is investigated in the NRQCD factorization framework for the first time. As a byproduct, we obtain by far the most precise order-α2s NRQCD matching coefficient for the ηc,b→γγ process. After including the substantial negative order-α2s correction, the good agreement between NRQCD prediction and the measured γγ∗→ηc form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of NRQCD approach to hard exclusive reactions involving charmonium.

submitted time 2016-09-13 Hits627Downloads353 Comment 0

3. chinaXiv:201608.00216 [pdf]

Performance of new 8-inch photomultiplier tube used for the Tibet muon-detector array

Ying Zhang; Jing Huang; Ding Chen; Liu-Ming Zhai; Xu Chen; Xiao-Bin Hu; Yu-Hui Lin; Hong-Bo Jin; Xue-Yao Zhang; Cun-Feng Feng: Huan-Yu Jia; Xun-Xiu Zhou; DANZENGLUOBU; Tian-Lu Chen; LABACIREN; Mao-Yuan Liu; Qi Gao; ZHAXICIREN
Subjects: Physics >> Nuclear Physics

A new hybrid experiment has been constructed to measure the chemical composition of cosmic rays around the "knee" in the wide energy range by the Tibet ASγ collaboration at Tibet, China, since 2014. They consist of a high-energy air-shower-core array (YAC-II), a high-density air-shower array (Tibet-III) and a large underground water-Cherenkov muon-detector array (MD). In order to obtain the primary proton, helium and iron spectra and their "knee" positions in the energy range lower than 1016 eV, each of PMTs equipped to the MD cell is required to measure the number of photons capable of covering a wide dynamic range of 100 - 106 photoelectrons (PEs) according to Monte Carlo simulations. In this paper, we firstly compare the characteristic features between R5912-PMT made by Japan Hamamatsu and CR365-PMT made by Beijing Hamamatsu. This is the first comparison between R5912-PMT and CR365-PMT. If there exists no serious difference, we will then add two 8-inch-in-diameter PMTs to meet our requirements in each MD cell, which are responsible for the range of 100 - 10000 PEs and 2000 - 1000000 PEs, respectively. That is, MD cell is expected to be able to measure the number of muons over 6 orders of magnitude.

submitted time 2016-08-31 Hits606Downloads373 Comment 0

4. chinaXiv:201605.01428 [pdf]

Cryo-EM Structure of Influenza Virus RNA Polymerase Complex at 4.3 angstrom Resolution

Chang, Shenghai; Sun, Dapeng; Liang, Huanhuan; Li, Jun; Guo, Lu; Wang, Xiangli; Guan, Chengcheng; Boruah, Bhargavi M.; Yuan, Lingmin; Feng, Feng; Yang, Mingrui; Liu, Yingfang; Wang, Jia; Wang, Jiawei; Wang, Hong-Wei; Wojdyla, Justyna; Wang, Meitian; Li, Lanjuan; Liu, Yingfang; Wang, Lulan
Subjects: Biology >> Biophysics >> Biochemistry & Molecular Biology

Replication and transcription of influenza virus genome mainly depend on its RNA-dependent RNA polymerase (RdRP), composed of the PA, PB1, and PB2 subunits. Although extensively studied, the underlying mechanism of the RdRP complex is still unclear. Here we report the biochemical characterization of influenza RdRP subcomplex comprising PA, PB1, and N terminus of PB2, which exist as dimer in solution and can assemble into a tetramer state, regulated by vRNA promoter. Using single-particle cryo-electron microscopy, we have reconstructed the RdRP tetramer complex at 4.3 angstrom, highlighting the assembly and interfaces between monomers within the tetrameric structure. The individual RdRP subcomplex contains all the characterized motifs and appears as a cage-like structure. High-throughput mutagenesis profiling revealed that residues involved in the oligomer state formation are critical for viral life cycle. Our results lay a solid base for understanding the mechanism of replication of influenza and other negative-stranded RNA viruses.

submitted time 2016-05-12 Hits438Downloads288 Comment 0

5. chinaXiv:201605.01378 [pdf]

Interactome analysis identifies a new paralogue of XRCC4 in non-homologous end joining DNA repair pathway

Xing, Mengtan; Huo, Wei; Ning, Shaokai; Yan, Zhenxin; Li, Wen; Wang, Qingsong; Hou, Mei; Dong, Chunxia; Guo, Rong; Gao, Ge; Ji, Jianguo; Xu, Dongyi; Yang, Mingrui; Feng, Feng; Liang, Huanhuan; Yang, Mingrui; Wei, Leizhen; Lan, Li; Jiang, Wenxia; Zha, Shan
Subjects: Biology >> Biophysics

Non-homologous end joining (NHEJ) is a major pathway to repair DNA double-strand breaks (DSBs), which can display different types of broken ends. However, it is unclear how NHEJ factors organize to repair diverse types of DNA breaks. Here, through systematic analysis of the human NHEJ factor interactome, we identify PAXX as a direct interactor of Ku. The crystal structure of PAXX is similar to those of XRCC4 and XLF. Importantly, PAXX-deficient cells are sensitive to DSB-causing agents. Moreover, epistasis analysis demonstrates that PAXX functions together with XLF in response to ionizing radiation-induced complex DSBs, whereas they function redundantly in response to Topo2 inhibitor-induced simple DSBs. Consistently, PAXX and XLF coordinately promote the ligation of complex but not simple DNA ends in vitro. Altogether, our data identify PAXX as a new NHEJ factor and provide insight regarding the organization of NHEJ factors responding to diverse types of DSB ends.

submitted time 2016-05-12 Hits316Downloads211 Comment 0

6. chinaXiv:201605.01180 [pdf]

Structural and Functional Characterization of Acinetobacter baumannii Nucleoside Diphosphate Kinase

Hu Ying-Song; Feng Feng; Liu Ying-Fang; Hu Ying-Song
Subjects: Biology >> Biophysics >> Biochemistry & Molecular Biology

A cinetobacter baumannii is a new threat in intensive care units (ICUs) for its multiresistance to antibiotics, but little is known about this bacterium. Nucleoside diphosphate kinase (NDK) is an evolutionarily conserved enzyme that catalyzes phosphoryl transformation between nucleosides. In our study, the crystal structure of wild type A cinetobacter baumannii NDK along with its mutant generated through truncation of the C-terminal arginine-threonine-arginine (RTR) residues, were solved. In comparison with Myxococcus xanthus NDK structure, we speculated that A cinetobacter baumannii NDK shared a similar catalytic mechanism with Myxococcus xanthus. Activity assay and CD spectra analysis revealed that E28A mutant might interrupt the secondary structure of the protein leading to declined enzymatic activity. Truncation of the C-terminal RTR residues would lead to the instability of the tertiary structure resulting in reduced kinase activity. Lys33 was a key residue for maintaining dimer interaction when RTR residues were truncated but was not sufficient to keep efficient enzymatic reaction. The structural data can provide a potential target to develop novel therapeutic approaches to overcome multiresistance of the bacterium against antibiotics.

submitted time 2016-05-11 Hits153Downloads98 Comment 0

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