分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2019-07-02
摘要: P. W. Anderson raised an important question in 2007: Is There Glue in Cuprate Superconductors? The author believes that the change of the electron clouds of ions is the glue in cuprate superconductors. The change of the electron clouds of the ions in the parent structure of the layered high-temperature superconductors CaCuO2 has been studied by the first-principles calculations. The electron clouds of Cu2+ and O2- ions change obviously under electric fields. It is also found, for the first time, the characteristic frequencies of the change of the electron clouds are 250 meV, 360 meV, and 100 meV, respectively, for the modes observed. The frequencies are low and close to that of lattice vibrations, indicating the change of the electron cloud of ions can be the electron-pairing medium in cuprate superconductors.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2019-06-13
摘要: It is proposed that the electron-pairing medium of the iron-based superconductors may be the orbital fluctuation of the transition metal ions. But the characteristic frequency of the orbital fluctuation has not been given. For the first time, the author has calculated the real-time evolution of the electron clouds of transition metal ions in BaFe2As2 under excitations by the time-dependent density functional theory (TDDFT). There are different modes of fluctuations. The characteristic frequencies are 150 meV, 160 meV, 250 meV, and 200 meV, respectively, for the modes the author observed. The results are unexpected, because the general view is that the change of the electron density is very quick, and the frequency is much higher than the lattice vibration. The frequencies the author obtained are close to that of the lattice vibration in conventional superconductors at normal and high pressures, indicating the orbital (or electron cloud) fluctuation can by the electron pairing medium. Based on the calculation results, the author proposed a new electron pairing mechanism.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2019-04-24
摘要: The electron-pairing mechanism in unconventional high temperature superconductors (HTS) has not been resolved. The author proposed that the electron-pairing medium of unconventional HTS is the change of the electron clouds of transition metal ions, which is analogous to the lattice vibration in conventional superconductors. Real-time evolution of the electron clouds of transition metal ions under excitations in La2Fe2As2O2, FeSe sheet, Fe2KSe2, CaCuO2, and HgBa2Ca2Cu3O8 was calculated by the time-dependent density functional theory (TDDFT). The characteristic frequency is about 90-250 meV, which is equivalent to the lattice vibration frequencies, showing that the change of the electron clouds of the transition metal ions can be the electron-pairing medium in unconventional HTS.
分类: 生物学 >> 分子生物学 分类: 生物学 >> 动物学 提交时间: 2016-10-06
摘要: In this study, we introduced a general framework to use PacBio full-length transcriptome sequencing for the investigation of the fundamental problems in mitochondrial biology, e.g. genome arrangement, heteroplasmy, RNA processing and the regulation of transcription or replication. As a result, we produced the first full-length human mitochondrial transcriptome from the MCF7 cell line based on the PacBio platform and characterized the human mitochondrial transcriptome with more comprehensive and accurate information. The most important finding is two novel genes hsa-MDL1 and hsa-MDL1AS, which are encoded by the mitochondrial D-loop regions. We propose hsa-MDL1 and hsa-MDL1AS, as the precursors of transcription initiation RNAs (tiRNAs), belong to a novel class of long non-coding RNAs (lnRNAs), which is named as long tiRNAs (ltiRNAs). Based on the mitochondrial RNA processing model, the primary tiRNAs, precursors and mature tiRNAs could be discovered to completely reveal tiRNAs from their origins to functions. The ltiRNA/tiRNA system and their regulation mechanisms could exist ubiquitously in eukaryotes and prokaryotes. These findings will enrich the basic concepts in the field of mitochondrial biology, lnRNA functions and regulation of gene expression.
分类: 生物学 >> 植物学 提交时间: 2018-11-23 合作期刊: 《干旱区科学》
摘要: Plant phenotypic plasticity is a common feature that is crucial for explaining interspecific competition, dynamics and biological evolution of plant communities. In this study, we tested the effects of soil CaCO3 (calcium carbonate) on the phenotypic plasticity of a psammophyte, Artemisia ordosica, an important plant species on sandy lands in arid and semi-arid areas of China, by performing pot experiments under different CaCO3 contents with a two-factor randomized block design and two orthogonal designs. We analyzed the growth responses (including plant height, root length, shoot-leaf biomass and root biomass) of A. ordosica seedlings to different soil CaCO3 contents. The results revealed that, with a greater soil CaCO3 content, A. ordosica seedlings gradually grew more slowly, with their relative growth rates of plant height, root length, shoot-leaf biomass and root biomass all decreasing significantly. Root N/P ratios showed significant negative correlations with the relative growth rates of plant height, shoot-leaf biomass and root length of A. ordosica seedlings; however, the relative growth rate of root length increased significantly with the root P concentration increased, showing a positive correlation. These results demonstrate that soil CaCO3 reduces the local P availability in soil, which produces a non-adaptive phenotypic plasticity to A. ordosica seedlings. This study should prove useful for planning and promoting the restoration of damaged/degraded vegetation in arid and semi-arid areas of China.
分类: 计算机科学 >> 计算机科学的集成理论 提交时间: 2022-11-29 合作期刊: 《数据智能(英文)》
摘要: For many government departments, uncertainty aversion is a source of barriers in the advancement of data openness. A more active response to potential risks is needed and necessitates an in-depth examination of risks related to open government data (OGD). With a cross-case study in which three cases from the United Kingdom, the United States and China are examined, this study identifies potential risks that might emerge at different stages of the lifecycle of OGD programs and constructs a taxonomy model for them. The taxonomy model distinguishes the risks from OGD from the risks to OGD, which can help government departments make better responses. Finally, risk response strategies are suggested based on the research results.
分类: 生物学 >> 生态学 提交时间: 2019-01-17 合作期刊: 《干旱区科学》
摘要: Intraspecific trait variation and heritability in different environmental conditions not only suggest a potential for an evolutionary response but also have important ecological consequences at the population, community, and ecosystem levels. However, the contribution of quantitative trait variation within a grassland species to evolutionary responses or ecological consequences is seldom documented. Leymus chinensis is an important dominant species in semi-arid grasslands of China, which has seriously suffered from drought and high temperature stresses in recent decades. In the present study, we measured variation and heritability of 10 quantitative traits, namely the number of tillers, maximum shoot height, number of rhizomes, maximum rhizome length, rhizome mass, aboveground mass, root mass, maximum net photosynthetic rate (Pmax), specific leaf area (SLA), and leaf length to leaf width ratio (LL/LW), for 10 genotypes of L. chinensis under one non-stress (Ck) condition and three environmental stress conditions (i.e., drought (Dr), high temperature (Ht), and both drought and high temperature (DrHt)). Result indicated that (1) the interaction of genotype and environmental condition (G×E) was significant for 6 traits but not significant for the other 4 traits as shown by two-way analysis of variance (ANOVA), suggesting that different selection forces were placed for different traits on the factors dominating phenotypic responses to different environmental conditions. Moreover, these significant G×E effects on traits indicated significantly different phenotypic adaptive responses among L. chinensis genotypes to different environmental conditions. Additionally, individuals could be grouped according to environmental condition rather than genotype as shown by canonical discriminant analysis, indicating that environmental condition played a more important role in affecting phenotypic variation than genotype; (2) by one-way ANOVA, significant differences among L. chinensis genotypes were found in all 10 traits under Ck and Dr conditions, in 8 traits under DrHt condition and only in 4 traits under Ht condition; and (3) all 10 traits showed relatively low or non-measurable broad-sense heritability (H2) under stress conditions. However, the lowest H2 value for most traits did not occur under DrHt condition, which supported the hypothesis of 'unfavorable conditions have unpredictable effects' rather than 'unfavorable conditions decrease heritability'. Results from our experiment might aid to improve predictions on the potential impacts of climate changes on L. chinensis and eventually species conservation and ecosystem restoration.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: Investigating the CKM matrix in different parametrization schemes, it is noticed that those schemes can be divided into a few groups where the sine values of the CP phase for each group are approximately equal. Using those relations, several approximate equalities among the elements of CKM matrix are established. Assuming them to be exact, there are infinite numbers of solutions and by choosing special values for the free parameters in those solutions, several textures presented in literature are obtained. The case can also be generalized to the PMNS matrix for the lepton sector. In parallel, several mixing textures are also derived by using presumed symmetries, amazingly, some of their forms are the same as what we obtained, but not all. It hints existence of a hidden symmetry which is broken in the practical world. The nature makes its own selection on the underlying symmetry and the way to break it, while we just guess what it is.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: The Jiangmen Underground Neutrino Observatory (JUNO) is an experiment proposed to determine the neutrino mass hierarchy and probe the fundamental properties of neutrino oscillation. The JUNO central detector is a spherical liquid scintillator detector with 20 kton fiducial mass. It is required to achieve a 3%/E(MeV)−−−−−−−√ energy resolution with very low radioactive background, which is a big challenge to the detector design. In order to ensure the detector performance can meet the physics requirements, reliable detector simulation is necessary to provide useful information for detector design. A simulation study of natural radioactivity backgrounds in the JUNO central detector has been performed to guide the detector design and set requirements to the radiopurity of detector materials.
分类: 生物学 >> 病毒学 提交时间: 2019-01-29
摘要: 本研究的主要目的是检测硬蜱携带的病毒。作为一个意外发现,检测到一个235 bp的来自非洲猪瘟病毒基因组的特异性片段。随后的测序发现,蜱和羊都具有这个片段,特别是共有一个特异性突变C38T,是目前已发布的非洲猪瘟病毒基因组上对应片段都没有的。
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: We present an evaluation of the background induced by�41Am-13C neutron calibration sources in the Daya Bay reactor neutrino experiment. As a significant background for electron-antineutrino detection at 0.26�.12 per detector per day on average, it has been estimated by a Monte Carlo simulation that was benchmarked by a special calibration data set. This dedicated data set also provided the energy spectrum of the background.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: Topological charge susceptibility χt for pure gauge SU(3) theory at finite temperature is studied using anisotropic lattices. The over-improved stout-link smoothing method is utilized to calculate the topological charge. Near the phase transition point we find a rapid declining behavior for χt with values decreasing from (188(1)MeV)4 to (67(3)MeV)4 as the temperature increased from zero temperature to 1.9Tc which demonstrates the existence of topological excitations far above Tc. The 4th order cumulant c4 of topological charge, as well as the ratio c4/χt are also investigated. Results of c4 show step-like behavior near Tc while the ratio at high temperature agrees with the value as predicted by the diluted instanton gas model.
分类: 物理学 >> 核物理学 提交时间: 2023-12-13
摘要: The reconstruction of the tracks of charged particles with high precision is crucial for HEP experiments toachieve their physics goals. The BESIII drift chamber, which is used as the tracking detector of the BESIIIexperiment, has suffered from aging effects resulting in degraded tracking performance after operation for ap-proximately 15 years. To preserve and enhance the tracking performance of BESIII, one of the proposals is toadd one layer of a thin cylindrical CMOS pixel sensor based on state-of-the-art stitching technology betweenthe beam pipe and the drift chamber. The improvement in the tracking performance of BESIII with such anadditional pixel detector compared to that with only the existing drift chamber was studied using the moderncommon tracking software ACTS , which provides a set of detector-agnostic and highly performant trackingalgorithms that h