Faculty & Staff Research
http://hdl.handle.net/1911/75172
Sat, 18 Nov 2017 00:13:50 GMT2017-11-18T00:13:50ZAtmospheric species concentrations and reaction rates relevant to N2 chemistry derived from WACCM-X model used in Yeung et al., Extreme enrichment in atmospheric 15N15N. Sci. Adv. 3, eaao6741 (2017)
http://hdl.handle.net/1911/98842
Atmospheric species concentrations and reaction rates relevant to N2 chemistry derived from WACCM-X model used in Yeung et al., Extreme enrichment in atmospheric 15N15N. Sci. Adv. 3, eaao6741 (2017)
Data description: This dataset contains species concentrations and reaction rates relevant to N2 chemistry derived from the Whole Atmosphere Community Climate Model with thermospere and ionosphere extension (WACCM-X), data set f.e10.FWX.f19_f19.control.001, for model year 2001. Grid spacing and pressure levels are standard quantities used for the National Center for Atmospheric Research Community Earth System Models. Assumptions used when calculating reaction rates are detailed in the related paper (Yeung et al. 2017). Dataset format is netCDF.
http://hdl.handle.net/1911/98842Experimental and modeling data used in Yeung et al., Extreme enrichment in atmospheric 15N15N. Sci. Adv. 3, eaao6741 (2017)
http://hdl.handle.net/1911/98841
Experimental and modeling data used in Yeung et al., Extreme enrichment in atmospheric 15N15N. Sci. Adv. 3, eaao6741 (2017)
Data description: This dataset contains two types of data. The first is a set of isotopic data (d15N, d29, d30, and D30 values) collected on an ultrahigh resolution mass spectrometer. The second is a set of model parameters and results. Both were used to support the findings reported in L. Y. Yeung, S. Li, I. E. Kohl, J. A. Haslun, N. E. Ostrom, H. Hu, T. P. Fischer, E. A. Schauble, E. D. Young, Extreme enrichment in atmospheric 15N15N. Sci. Adv. 3, eaao6741 (2017). doi: 10.1126/sciadv.aao6741.
http://hdl.handle.net/1911/98841Two-Dimensional Massless Dirac Fermions in Antiferromagnetic AFe2As2 (A=Ba,Sr)
http://hdl.handle.net/1911/98837
Two-Dimensional Massless Dirac Fermions in Antiferromagnetic AFe2As2 (A=Ba,Sr)
Chen, Zhi-Guo; Wang, Luyang; Song, Yu; Lu, Xingye; Luo, Huiqian; Zhang, Chenglin; Dai, Pengcheng; Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel
We report infrared studies of AFe2As2 (A=Ba, Sr), two representative parent compounds of iron-arsenide superconductors, at magnetic fields (B) up to 17.5 T. Optical transitions between Landau levels (LLs) were observed in the antiferromagnetic states of these two parent compounds. Our observation of a √B dependence of the LL transition energies, the zero-energy intercepts at B=0 T under the linear extrapolations of the transition energies and the energy ratio (∼2.4) between the observed LL transitions, combined with the linear band dispersions in two-dimensional (2D) momentum space obtained by theoretical calculations, demonstrates the existence of massless Dirac fermions in the antiferromagnet BaFe2As2. More importantly, the observed dominance of the zeroth-LL-related absorption features and the calculated bands with extremely weak dispersions along the momentum direction kz indicate that massless Dirac fermions in BaFe2As2 are 2D. Furthermore, we find that the total substitution of the barium atoms in BaFe2As2 by strontium atoms not only maintains 2D massless Dirac fermions in this system, but also enhances their Fermi velocity, which supports that the Dirac points in iron-arsenide parent compounds are topologically protected.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/1911/988372017-01-01T00:00:00ZA Distributed-Memory Randomized Structured Multifrontal Method for Sparse Direct Solutions
http://hdl.handle.net/1911/98834
A Distributed-Memory Randomized Structured Multifrontal Method for Sparse Direct Solutions
Xin, Zixing; Xia, Jianlin; de Hoop, Maarten V.; Cauley, Stephen; Balakrishnan, Venkataramanan
We design a distributed-memory randomized structured multifrontal solver for large sparse matrices. Two layers of hierarchical tree parallelism are used. A sequence of innovative parallel methods are developed for randomized structured frontal matrix operations, structured update matrix computation, skinny extend-add operation, selected entry extraction from structured matrices, etc. Several strategies are proposed to reuse computations and reduce communications. Unlike an earlier parallel structured multifrontal method that still involves large dense intermediate matrices, our parallel solver performs the major operations in terms of skinny matrices and fully structured forms. It thus significantly enhances the efficiency and scalability. Systematic communication cost analysis shows that the numbers of words are reduced by factors of about $O(\sqrt{n}/r)$ in two dimensions and about $O(n^{2/3}/r)$ in three dimensions, where $n$ is the matrix size and $r$ is an off-diagonal numerical rank bound of the intermediate frontal matrices. The efficiency and parallel performance are demonstrated with the solution of some large discretized PDEs in two and three dimensions. Nice scalability and significant savings in the cost and memory can be observed from the weak and strong scaling tests, especially for some 3D problems discretized on unstructured meshes.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/1911/988342017-01-01T00:00:00Z