3,267 research outputs found
Understanding and reducing errors in density functional calculations
We decompose the energy error of any variational DFT calculation into a
contribution due to the approximate functional and that due to the approximate
density. Typically, the functional error dominates, but in many interesting
situations, the density-driven error dominates. Examples range from
calculations of electron affinities to preferred geometries of ions and
radicals in solution. In these abnormal cases, the DFT error can be greatly
reduced by using a more accurate density. A small orbital gap often indicates a
substantial density-driven error
Avoiding Unbound Anions in Density Functional Calculations
Converged approximate density functional calculations usually do not bind
anions, due to large self-interaction error. But Hartree-Fock calculations have
no such prob- lem, producing negative HOMO energies. A recently proposed scheme
for calculating DFT energies on HF densities is shown to work very well for
molecules, better than the common practice of restricting the basis set, except
for cases like CN, where the HF density is too inaccurate due to spin
contamination
Can Sodium Abundances of A-Type Stars Be Reliably Determined from Na I 5890/5896 Lines?
An extensive non-LTE abundance analysis based on Na I 5890/5896 doublet lines
was carried out for a large unbiased sample of ~120 A-type main-sequence stars
(including 23 Hyades stars) covering a wide v_e sin i range of ~10--300 km/s,
with an aim to examine whether the Na abundances in such A dwarfs can be
reliably established from these strong Na I D lines. The resulting abundances
([Na/H]_{58}), which were obtained by applying the T_eff-dependent
microturbulent velocities of \xi ~2--4 km/s with a peak at T_eff ~ 8000 K
(typical for A stars), turned out generally negative with a large diversity
(from ~-1 to ~0), while showing a sign of v_e sin i-dependence (decreasing
toward higher rotation). However, the reality of this apparently subsolar trend
is very questionable, since these [Na/H]_{58} are systematically lower by
~0.3--0.6 dex than more reliable [Na/H]_{61} (derived from weak Na I 6154/6161
lines for sharp-line stars). Considering the large \xi-sensitivity of the
abundances derived from these saturated Na I D lines, we regard that
[Na/H]_{58} must have been erroneously underestimated, suspecting that the
conventional \xi values are improperly too large at least for such strong
high-forming Na I 5890/5896 lines, presumably due to the depth-dependence of
\xi decreasing with height. The nature of atmospheric turbulent velocity field
in mid-to-late A stars would have to be more investigated before we can
determine reliable sodium abundances from these strong resonance D lines.Comment: 14 pages, 8 figures, accepted for publication in Publ. Astron. Soc.
Japan, Vol. 61, No. 5 (2009
Determinants of user satisfaction and continuance intention of smartphones: Focus on interactivity perspective
The development and complexity of mobile and smart technologies continues to evolve with a greater speed, attention needs to be turned to the possibility of continuous development. It has become important to monitor users’ post-purchase behavior in order to understand their continued use of smartphones and other smart devices. This study posits interactivity as a key variable to describe customer satisfaction and continuance intention in using smartphones. We classify interactivity into five sub-dimensions: system quality, network quality, contents quality, customer support, and compatibility. The established model in this study was empirically examined through survey research. Structural equation modeling demonstrated several key findings: contents quality is the most influential factor in shaping satisfaction, followed by compatibility, system quality, and customer support. The results also showed that satisfaction has a positive effect on the continuance intention. In addition, network quality had a positive direct effect on the continuance intention. Users also exhibit significant differences in post-purchase behavior, depending on their operating systems. These results will be helpful for the practitioners to further deliver appropriate service strategies for strengthening ongoing relationship with their customers
Multi-Cell ECM compaction is predictable via superposition of nonlinear cell dynamics linearized in augmented state space
Cells interacting through an extracellular matrix (ECM) exhibit emergent behaviors resulting from collective intercellular interaction. In wound healing and tissue development, characteristic compaction of ECM gel is induced by multiple cells that generate tensions in the ECM fibers and coordinate their actions with other cells. Computational prediction of collective cell-ECM interaction based on first principles is highly complex especially as the number of cells increase. Here, we introduce a computationally-efficient method for predicting nonlinear behaviors of multiple cells interacting mechanically through a 3-D ECM fiber network. The key enabling technique is superposition of single cell computational models to predict multicellular behaviors. While cell-ECM interactions are highly nonlinear, they can be linearized accurately with a unique method, termed Dual-Faceted Linearization. This method recasts the original nonlinear dynamics in an augmented space where the system behaves more linearly. The independent state variables are augmented by combining auxiliary variables that inform nonlinear elements involved in the system. This computational method involves a) expressing the original nonlinear state equations with two sets of linear dynamic equations b) reducing the order of the augmented linear system via principal component analysis and c) superposing individual single cell-ECM dynamics to predict collective behaviors of multiple cells. The method is computationally efficient compared to original nonlinear dynamic simulation and accurate compared to traditional Taylor expansion linearization. Furthermore, we reproduce reported experimental results of multi-cell induced ECM compaction
Validation Test of Geant4 Simulation of Electron Backscattering
Backscattering is a sensitive probe of the accuracy of electron scattering
algorithms implemented in Monte Carlo codes. The capability of the Geant4
toolkit to describe realistically the fraction of electrons backscattered from
a target volume is extensively and quantitatively evaluated in comparison with
experimental data retrieved from the literature. The validation test covers the
energy range between approximately 100 eV and 20 MeV, and concerns a wide set
of target elements. Multiple and single electron scattering models implemented
in Geant4, as well as preassembled selections of physics models distributed
within Geant4, are analyzed with statistical methods. The evaluations concern
Geant4 versions from 9.1 to 10.1. Significant evolutions are observed over the
range of Geant4 versions, not always in the direction of better compatibility
with experiment. Goodness-of-fit tests complemented by categorical analysis
tests identify a configuration based on Geant4 Urban multiple scattering model
in Geant4 version 9.1 and a configuration based on single Coulomb scattering in
Geant4 10.0 as the physics options best reproducing experimental data above a
few tens of keV. At lower energies only single scattering demonstrates some
capability to reproduce data down to a few keV. Recommended preassembled
physics configurations appear incapable of describing electron backscattering
compatible with experiment. With the support of statistical methods, a
correlation is established between the validation of Geant4-based simulation of
backscattering and of energy deposition
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