2,808 research outputs found

    Transformation of \u3cem\u3eTetrahymena thermophila\u3c/em\u3e with Hypermethylated rRNA Genes

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    The extrachromosomal rRNA genes (rDNA) of Tetrahymena thermophila contain 0.4% N6-methyladenine. C3 strain rDNA was isolated, hypermethylated in vitro, and microinjected into B strain host cells. Clonal cell lines were established, and transformants were selected on the basis of resistance to paromomycin, conferred by the injected rDNA. The effects of methylation by three enzymes which methylate the sequence 5\u27-NAT-3\u27, the dam, EcoRI, and ClaI methylases, were tested. Hypermethylation of the injected rDNA had no effect on transformation efficiency relative to mock-methylated controls. The injected C3 strain rDNA efficiently replaced host rDNA as the major constituent of the population of rDNA molecules. Hypermethylation of the injected DNA was not maintained through 20 to 25 cell generations

    Nonfactorizable Bχc0KB\to\chi_{c0}K decay and QCD factorization

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    We study the unexpectedly large rate for the factorization-forbidden decay Bχc0KB\to \chi_{c0}K within the QCD factorization approach. We use a non-zero gluon mass to regularize the infrared divergences in vertex corrections. The end-point singularities arising from spectator corrections are regularized and carefully estimated by the off-shellness of quarks. We find that the contributions arising from the vertex and leading-twist spectator corrections are numerically small, and the twist-3 spectator contribution with chiral enhancement and linear end-point singularity becomes dominant. With reasonable choices for the parameters, the branching ratio for Bχc0KB\to\chi_{c0}K decay is estimated to be in the range (24)×104(2-4)\times 10^{-4}, which is compatible with the Belle and BaBar data.Comment: Appendix added; it is emphasized that in the dominant twist-3 spectator corrections the end-point singularity contributions may be estimated by the off-shellness of the charm quark (by the binding energy in charmonium) and the gluon (by the transverse momentum of the light quark in the kaon

    Observational constraints on noncold dark matter and phenomenological emergent dark energy

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    It is well known that there are several long-standing problems implying the discordance of the Λ\LambdaCDM model. Although most of the models proposed to resolve these problems assume that dark matter is pressureless, it is still possible that dark matter is not cold, as current observations have not ruled out this possibility yet. Therefore, in this article, we treat the dark matter equation of state parameter as a free parameter, and apply observational data to investigate the non-coldness of dark matter. Impressing by the simplicity of the phenomenological emergent dark energy (PEDE) and its ability to relieve the Hubble tension, we propose the PEDE+wdmw_{\rm dm} model based on PEDE and non-cold dark matter. We then place constraints on this model in light of the Planck 2018 Cosmic Microwave Background (CMB) anisotropies, baryon acoustic oscillation (BAO) measurements, and the Pantheon compilation of Type Ia supernovae. The results indicate a preference for a negative dark matter equation of state parameter at 95%95\% CL for all data sets except CMB alone and CMB+BAO, which suggests that the non-coldness assumption of dark matter worth to be investigated further in order to understand the nature of dark matter. The Hubble tension is alleviated in this scenario compared to the Λ\LambdaCDM model, with a significance below 3σ\sigma level for all data sets except CMB+Pantheon. However, from the analysis based on Bayesian evidence, we clearly see that the data sets favor Λ\LambdaCDM over the PEDE+wdmw_{\rm dm} model.Comment: 8 pages, 2 figure, published on PR

    Few-Shot Knowledge Graph Completion

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    Knowledge graphs (KGs) serve as useful resources for various natural language processing applications. Previous KG completion approaches require a large number of training instances (i.e., head-tail entity pairs) for every relation. The real case is that for most of the relations, very few entity pairs are available. Existing work of one-shot learning limits method generalizability for few-shot scenarios and does not fully use the supervisory information; however, few-shot KG completion has not been well studied yet. In this work, we propose a novel few-shot relation learning model (FSRL) that aims at discovering facts of new relations with few-shot references. FSRL can effectively capture knowledge from heterogeneous graph structure, aggregate representations of few-shot references, and match similar entity pairs of reference set for every relation. Extensive experiments on two public datasets demonstrate that FSRL outperforms the state-of-the-art

    Comprehensive analysis of industrial-scale heating plants based on different biomass slow pyrolysis technologies:Product property, energy balance, and ecological impact

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    Slow pyrolysis poly-generation technology for rural heating using agroforest residues has reached the stage of industrial demonstration application in China. Comprehensive assessment of technical characteristics and technical adaptability is essential as further industrialization development requires related plants to be sustainable and replicable. In this study, three typical technical processes and application models are discussed; namely, poly-generation for syngas and char using a rotary kiln (SCRK), poly-generation for syngas and char using a vertical kiln (SCVK), and poly-generation for hot water and char using a chain grate furnace (HCCF). The technical characteristics, adaptability to raw materials, product property, energy balance, and ecological impact were systematically analyzed by an empirical analysis based on industrial-scale project data. The SCRK was advantageous in terms of product quality and yield of char; the low heating value (LHV) of syngas exceeded 17.3 MJ/m3, which was approximately thrice that of the other two technical processes. The energy conversion efficiency of the SCVK was 76.8%, that is, approximately 4.0–5.7 percentage points higher than that of the HCCF and SCRK. The emergy sustainability indices of SCRK, SCVK, and HCCF, as ecological indicators, were 31.2, 21.4, and 24.5, respectively. The above results indicate that the heating plants based on biomass slow pyrolysis have promising application prospects. The technology promotion path was discussed by matching production situations, market demands, and technical characteristics based on a technical evaluation radar chart. Some targeted suggestions were proposed for the industrial application of different biomass slow pyrolysis poly-generation technologies. This study provides a reference for industrialization development of biomass slow pyrolysis technologies for rural heating.</p
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