48,743 research outputs found
Electrons in High-Tc Compounds: Ab-Initio Correlation Results
Electronic correlations in the ground state of an idealized infinite-layer
high-Tc compound are computed using the ab-initio method of local ansatz.
Comparisons are made with the local-density approximation (LDA) results, and
the correlation functions are analyzed in detail. These correlation functions
are used to determine the effective atomic-interaction parameters for model
Hamiltonians. On the resulting model, doping dependencies of the relevant
correlations are investigated. Aside from the expected strong atomic
correlations, particular spin correlations arise. The dominating contribution
is a strong nearest neighbor correlation that is Stoner-enhanced due to the
closeness of the ground state to the magnetic phase. This feature depends
moderately on doping, and is absent in a single-band Hubbard model. Our
calculated spin correlation function is in good qualitative agreement with that
determined from the neutron scattering experiments for a metal.Comment: 21pp, 5fig, Phys. Rev. B (Oct. 98
Study of charge-charge coupling effects on dipole emitter relaxation within a classical electron-ion plasma description
Studies of charge-charge (ion-ion, ion-electron, and electron-electron)
coupling properties for ion impurities in an electron gas and for a two
component plasma are carried out on the basis of a regularized electron-ion
potential without short-range Coulomb divergence. This work is motivated in
part by questions arising from recent spectroscopic measurements revealing
discrepancies with present theoretical descriptions. Many of the current
radiative property models for plasmas include only single electron-emitter
collisions and neglect some or all charge-charge interactions. A molecular
dynamics simulation of dipole relaxation is proposed here to allow proper
account of many electron-emitter interactions and all charge-charge couplings.
As illustrations, molecular dynamics simulations are reported for the cases of
a single ion imbedded in an electron plasma and for a two-component
ion-electron plasma. Ion-ion, electron-ion, and electron-electron coupling
effects are discussed for hydrogen-like Balmer alpha lines.Comment: 13 figures, submitted to Phys. Rev.
Challenges of Big Data Analysis
Big Data bring new opportunities to modern society and challenges to data
scientists. On one hand, Big Data hold great promises for discovering subtle
population patterns and heterogeneities that are not possible with small-scale
data. On the other hand, the massive sample size and high dimensionality of Big
Data introduce unique computational and statistical challenges, including
scalability and storage bottleneck, noise accumulation, spurious correlation,
incidental endogeneity, and measurement errors. These challenges are
distinguished and require new computational and statistical paradigm. This
article give overviews on the salient features of Big Data and how these
features impact on paradigm change on statistical and computational methods as
well as computing architectures. We also provide various new perspectives on
the Big Data analysis and computation. In particular, we emphasis on the
viability of the sparsest solution in high-confidence set and point out that
exogeneous assumptions in most statistical methods for Big Data can not be
validated due to incidental endogeneity. They can lead to wrong statistical
inferences and consequently wrong scientific conclusions
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