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Search Results: 1 - 10 of 26364 matches for " Qian Zhong "
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Qian Yongfu,Zhong Zhong,

大气科学进展 , 1986,
Abstract: The atmospheric dynamic equations have been transformed from the z-coordinate system into a generalized vertical coordinate system by using a so-called DDD transformation method. Then the general-ized system is assumed being pressure, sigma or incorporated pressure-sigma coordinate system and corre-sponding equations are obtained with the second-order accuracy. It is pointed out that the usual equations are only of the first-order accuracy when their space-differential terms are approximated by central finite differences. Therefore the usual forms of the equations may result in quite large errors on steep slopes of mountains included in a model.
Diverse, massive-star-associated sources for elements heavier than Fe and the roles of neutrinos
Yong-Zhong Qian
Physics , 2013, DOI: 10.1088/0954-3899/41/4/044002
Abstract: Massive-star-associated models for production of elements heavier than Fe are reviewed. The important roles of neutrinos in many of these models are discussed along with uncertainties in the relevant neutrino physics. Data on elemental abundances in metal-poor stars are presented and their constraints on diverse sources for elements heavier than Fe are emphasized.
The Origin of the Heavy Elements: Recent Progress in the Understanding of the r-Process
Yong-Zhong Qian
Physics , 2003, DOI: 10.1016/S0146-6410(02)00178-3
Abstract: There has been significant progress in the understanding of the r-process over the last ten years. The conditions required for this process have been examined in terms of the parameters for adiabatic expansion from high temperature and density. There have been many developments regarding core-collapse supernova and neutron star merger models of the r-process. Meteoritic data and observations of metal-poor stars have demonstrated the diversity of r-process sources. Stellar observations have also found some regularity in r-process abundance patterns and large dispersions in r-process abundances at low metallicities. This review summarizes the recent results from parametric studies, astrophysical models, and observational studies of the r-process. The interplay between nuclear physics and astrophysics is emphasized. Some suggestions for future theoretical, experimental, and observational studies of the r-process are given.
Neutrino-induced neutron spallation and the site of the r-process
Yong-Zhong Qian
Physics , 1997,
Abstract: All of the actinides and roughly half the natural abundance of elements with mass number A > 70 come from the rapid neutron capture process, or the r-process. If the r-process, as suggested by many, occurs deep in a supernova, then it is under the influence of an intense neutrino flux. Here we discuss the effects of both charged-current and neutral-current neutrino interactions on the r-process. We show that the multiple-neutron emission induced by both kinds of neutrino interactions can affect the observed r-process abundance pattern significantly. In particular, we find that five nuclei below the r-process abundance peak at A = 195 may be entirely attributed to the neutrino-induced neutron spallation processes following the r-process freeze-out. Furthermore, the deduced neutrino fluence agrees with the conditions in the recent supernova r-process model. These results strongly argue that the r-process occurs in supernovae. They also provide a sensitive probe for the conditions at the supernova r-process site.
Neutrinos and the Supernova Origin of the Elements
Yong-Zhong Qian
Physics , 2000, DOI: 10.1016/S0920-5632(00)00961-0
Abstract: Intense fluxes of neutrinos are emitted by the hot neutron star produced in a supernova. The electron neutrino and antineutrino capture reactions on neutrons and protons, respectively, provide heating to drive a wind from the hot neutron star. The same reactions also determine the neutron-richness of the wind material. Nucleosynthesis via rapid neutron capture, the r-process, may occur in the wind material as it expands away from the neutron star. The neutron-richness of the wind material, and hence, the r-process nucleosynthesis therein, are sensitive to mixing between the muon (or tauon) neutrino/antineutrino and the electron (or sterile) neutrino/antineutrino. Indirect arguments and direct tests for the supernova origin of the r-process elements are discussed with a goal to establish supernova r-process nucleosynthesis as an important probe for neutrino mixing.
Recent Progress in Understanding Nucleosynthesis via Rapid Neutron Capture
Yong-Zhong Qian
Physics , 2000, DOI: 10.1063/1.1345358
Abstract: I discuss the recent progress in our understanding of nucleosynthesis via rapid neutron capture, the r-process, based on meteoritic data for the early solar system and observations of stars at low metallicities. At present, all data require that there be two distinct kinds of r-process events and suggest that supernovae are associated with these events. The diversity of supernova sources for the r-process may depend on whether a neutron star or black hole is formed in an individual supernova. This dependence, if substantiated by future observations discussed here, has important implications for properties of nuclear matter.
Astrophysical Models of r-Process Nucleosynthesis: An Update
Yong-Zhong Qian
Physics , 2012, DOI: 10.1063/1.4763396
Abstract: An update on astrophysical models for nucleosynthesis via rapid neutron capture, the r process, is given. A neutrino-induced r process in supernova helium shells may have operated up to metallicities of ~10^-3 times the solar value. Another r-process source, possibly neutron star mergers, is required for higher metallicities.
Some nuclear physics aspects of core-collapse supernovae
Yong-Zhong Qian
Physics , 1998,
Abstract: Here I review some nuclear physics aspects of core-collapse supernovae concerning neutrinos. Studies of neutrino emission and interactions in supernovae are crucial to our understanding of the explosion mechanism, the heavy element nucleosynthesis, and pulsar proper motions. I discuss the effects of reduced neutrino opacities in dense nuclear matter on supernova neutrino emission and their implications for the delayed supernova explosion mechanism and the synthesis of neutron-rich heavy elements. I also discuss the effects of parity violation in weak interactions on supernova neutrino emission and their implications for pulsar proper motions.
The r-Process: Current Understanding and Future Tests
Yong-Zhong Qian
Physics , 2005,
Abstract: Current understanding of the r-process is summarized in terms of the astrophysical sites, the yield patterns, and the role of neutrinos. The importance of observational and experimental tests is emphasized. A number of future tests regarding the above three aspects of the r-process are discussed.
Analysis and prediction of exon, intron, intergenic region and splice sites for A. thaliana and C. elegans genomes  [PDF]
Hao Lin, Qian-Zhong Li, Cui-Xia Chen
Journal of Biomedical Science and Engineering (JBiSE) , 2009, DOI: 10.4236/jbise.2009.26053
Abstract: Although a great deal of research has been undertaken in the area of the annotation of gene structure, predictive techniques are still not fully developed. In this paper, based on the characteristics of base composition of sequences and conservative of nucleotides at exon/intron splicing site, a least increment of diversity al-gorithm (LIDA) is developed for studying and predicting three kinds of coding exons, introns and intergenic regions. At first, by selecting the 64 trinucleotides composition and 120 position parameters of the four bases as informational parameters, coding exon, intron and intergenic sequence are predicted. The results show that overall predicted accuracies are 91.1% and 88.4%, respectively for A. thaliana and C. ele-gans genome. Subsequently, based on the po-sition frequencies of four kinds of bases in regions near intron/coding exon boundary, initia-tion and termination site of translation, 12 position parameters are selected as diversity source. And three kinds of the coding exons are predicted by use of the LIDA. The predicted successful rates are higher than 80%. These results can be used in sequence annotation.
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