3,519 research outputs found
Fragment Approach to Constrained Density Functional Theory Calculations using Daubechies Wavelets
In a recent paper we presented a linear scaling Kohn-Sham density functional
theory (DFT) code based on Daubechies wavelets, where a minimal set of
localized support functions is optimized in situ and therefore adapted to the
chemical properties of the molecular system. Thanks to the systematically
controllable accuracy of the underlying basis set, this approach is able to
provide an optimal contracted basis for a given system: accuracies for ground
state energies and atomic forces are of the same quality as an uncontracted,
cubic scaling approach. This basis set offers, by construction, a natural
subset where the density matrix of the system can be projected. In this paper
we demonstrate the flexibility of this minimal basis formalism in providing a
basis set that can be reused as-is, i.e. without reoptimization, for
charge-constrained DFT calculations within a fragment approach. Support
functions, represented in the underlying wavelet grid, of the template
fragments are roto-translated with high numerical precision to the required
positions and used as projectors for the charge weight function. We demonstrate
the interest of this approach to express highly precise and efficient
calculations for preparing diabatic states and for the computational setup of
systems in complex environments
The spatial distribution of coronae on Venus
Coronae on Venus are large, generally circular surface features that have distinctive tectonic, volcanic, and topographic expressions. They range in diameter from less than 200 km to at least 1000 km. Data from the Magellan spacecraft have now allowed complete global mapping of the spatial distribution of coronae on the planet. Unlike impact craters, which show a random (i.e., Poisson) spatial distribution, the distribution of coronae appears to be nonrandom. We investigate the distribution here in detail, and explore its implications in terms of mantle convection and surface modification processes
On the interpretation of removable interactions: A survey of the field 33Â years after Loftus
In a classic 1978 Memory &Cognition article, Geoff Loftus explained why noncrossover interactions are removable. These removable interactions are tied to the scale of measurement for the dependent variable and therefore do not allow unambiguous conclusions about latent psychological processes. In the present article, we present concrete examples of how this insight helps prevent experimental psychologists from drawing incorrect conclusions about the effects of forgetting and aging. In addition, we extend the Loftus classification scheme for interactions to include those on the cusp between removable and nonremovable. Finally, we use various methods (i.e., a study of citation histories, a questionnaire for psychology students and faculty members, an analysis of statistical textbooks, and a review of articles published in the 2008 issue of Psychology andAging) to show that experimental psychologists have remained generally unaware of the concept of removable interactions. We conclude that there is more to interactions in a 2 × 2 design than meets the eye
Optimization of a high work function solution processed vanadium oxide hole-extracting layer for small molecule and polymer organic photovoltaic cells
We report a method of fabricating a high work function, solution processable vanadium oxide (V2Ox(sol)) hole-extracting layer. The atmospheric processing conditions of film preparation have a critical influence on the electronic structure and stoichiometry of the V2Ox(sol), with a direct impact on organic photovoltaic (OPV) cell performance. Combined Kelvin probe (KP) and ultraviolet photoemission spectroscopy (UPS) measurements reveal a high work function, n-type character for the thin films, analogous to previously reported thermally evaporated transition metal oxides. Additional states within the band gap of V2Ox(sol) are observed in the UPS spectra and are demonstrated using X-ray photoelectron spectroscopy (XPS) to be due to the substoichiometric nature of V2Ox(sol). The optimized V2Ox(sol) layer performance is compared directly to bare indium–tin oxide (ITO), poly(ethyleneoxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and thermally evaporated molybdenum oxide (MoOx) interfaces in both small molecule/fullerene and polymer/fullerene structures. OPV cells incorporating V2Ox(sol) are reported to achieve favorable initial cell performance and cell stability attributes
Getting more from accuracy and response time data: Methods for fitting the linear ballistic accumulator
Buyer preferences for feeder calf traits
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Observation of a continuous phase transition in a shape-memory alloy
Elastic neutron-scattering, inelastic x-ray scattering, specific-heat, and
pressure-dependent electrical transport measurements have been made on single
crystals of AuZn and Au_{0.52}Zn_{0.48} above and below their martensitic
transition temperatures (T_M=64K and 45K, respectively). In each composition,
elastic neutron scattering detects new commensurate Bragg peaks (modulation)
appearing at Q = (1.33,0.67,0) at temperatures corresponding to each sample's
T_M. Although the new Bragg peaks appear in a discontinuous manner in the
Au_{0.52}Zn_{0.48} sample, they appear in a continuous manner in AuZn.
Surprising us, the temperature dependence of the AuZn Bragg peak intensity and
the specific-heat jump near the transition temperature are in favorable accord
with a mean-field approximation. A Landau-theory-based fit to the pressure
dependence of the transition temperature suggests the presence of a critical
endpoint in the AuZn phase diagram located at T_M*=2.7K and p*=3.1GPa, with a
quantum saturation temperature \theta_s=48.3 +/- 3.7K.Comment: 6 figure
Impacts of Mid-Level Biofuel Content In Gasoline on SIDI Engine-Out and Tailpipe Particulate Matter Emissions
In this work, the influences of ethanol and iso-butanol blended with gasoline on engine-out and post three-way catalyst (TWC) particle size distribution and number concentration were studied using a General Motors (GM) 2.0L turbocharged spark ignition direct injection (SIDI) engine. The engine was operated using the production engine control unit (ECU) with a dynamometer controlling the engine speed and the accelerator pedal position controlling the engine load. A TSI Fast Mobility Particle Sizer (FMPS) spectrometer was used to measure the particle size distribution in the range from 5.6 to 560 nm with a sampling rate of 1 Hz. U.S. federal certification gasoline (E0), two ethanol-blended fuels (E10 and E20), and 11.7% iso-butanol blended fuel (BU12) were tested. Measurements were conducted at 10 selected steady-state engine operation conditions.
Bi-modal particle size distributions were observed for all operating conditions with peak values at particle sizes of 10 nm and 70 nm. Idle and low-speed / low-load conditions emitted higher total particle numbers than other operating conditions. At idle, the engine-out particulate matter (PM) emissions were dominated by nucleation mode particles, and the production TWC reduced these nucleation mode particles by more than 50%, while leaving the accumulation mode particle distribution unchanged. At an engine load higher than 6 bar net mean effective pressure (NMEP), accumulation mode particles dominated the engine-out particle emissions, and the TWC had little effect. Compared to the baseline gasoline (E0), E10 does not significantly change PM emissions, while E20 and BU12 both reduce PM emissions under the conditions studied. Iso-butanol was observed to impact PM emissions more than ethanol, with up to 50% reductions at some conditions.
In this paper, issues related to PM measurement using the FMPS are also discussed. While some uncertainties are due to engine variation, the FMPS must be carefully maintained in order to achieve repeatable measurement results
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