1,600 research outputs found
The Recommendations Clause and the President’s Role in Legislation
Winner of the Law School\u27s 2020 Fred G Leebron Memorial Prize for the best student paper in the field of constitutional law
The structure of the hydrated electron. Part 2. A mixed quantum classical molecular dynamics - embedded cluster density functional theory: single-excitation configuration interaction study
Adiabatic mixed quantum/classical molecular dynamics simulations were used to
generate snapshots of the hydrated electron (e-) in liquid water at 300 K.
Water cluster anions that include two complete solvation shells centered on the
e- were extracted from these simulations and embedded in a matrix of fractional
point charges designed to represent the rest of the solvent. Density functional
theory and single-excitation configuration interaction methods were then
applied to these embedded clusters. The salient feature of these hybrid
calculations is significant transfer (ca. 0.18) of the excess electron's charge
density into the O 2p orbitals in OH groups forming the solvation cavity. We
used the results of these calculations to examine the structure of the
molecular orbitals, the density of states, the absorption spectra in the
visible and ultraviolet, the hyperfine coupling (hfc) tensors, and the IR and
Raman spectra of the e-. The calculated hfc tensors were used to compute the
EPR and ESEEM spectra for the e- that compared favorably to the experimental
spectra of trapped e- in alkaline ice. The calculated vibrational spectra of
the e- are consistent with the red-shifted bending and stretching frequencies
observed in resonance Raman experiments. The model also accounts for the VIS
and 190-nm absorption bands of the e-. Thus, our study suggests that to explain
several important experimentally observed properties of the e-, many-electron
effects must be accounted for.Comment: 68 pages, 12 figures + 16 more figures in the supplement (included)
submitted to J Phys Chem
Efficient real-space configuration-interaction method for the simulation of multielectron mixed quantum and classical nonadiabatic molecular dynamics in the condensed phase
We introduce an efficient configuration interaction (CI) method for the calculation of mixed quantum and classical nonadiabatic molecular dynamics for multiple electrons. For any given realization of the classical degrees of freedom (e.g., a solvent), the method uses a novel real-space quadrature to efficiently compute the Coulomb and exchange interactions between electrons. We also introduce an approximation whereby the classical molecular dynamics is propagated for several time steps on electronic potential energy surfaces generated using only a particularly important subset of the CI basis states. By only updating the important-states subset periodically, we achieve significant reductions in the computational cost of solving the multielectron quantum problem. We test the real-space quadrature for the cases of two electrons confined in a cubic box with infinitely repulsive walls and two electrons dissolved in liquid water that occupy a single cavity, so-called hydrated dielectrons. We then demonstrate how to perform mixed quantum and classical nonadiabatic dynamics by combining these computational techniques with the mean-field with surface hopping algorithm of Prezhdo and Rossky [J. Chem. Phys. 107, 825 (1997)]. Finally, we illustrate the practicality of the approach to multielectron nonadiabatic dynamics by examining the nonadiabatic relaxation dynamics of both spin singlet and spin triplet hydrated dielectrons following excitation from the ground to the first excited state. (C) 2003 American Institute of Physics
3.6 and 4.5 m Phase Curves of the Highly-Irradiated Hot Jupiters WASP-19b and HAT-P-7b
We analyze full-orbit phase curve observations of the transiting hot Jupiters
WASP-19b and HAT-P-7b at 3.6 and 4.5 m obtained using the Spitzer Space
Telescope. For WASP-19b, we measure secondary eclipse depths of and at 3.6 and 4.5 m, which are consistent
with a single blackbody with effective temperature K. The
measured 3.6 and 4.5 m secondary eclipse depths for HAT-P-7b are
and , which are well-described by a
single blackbody with effective temperature K. Comparing the phase
curves to the predictions of one-dimensional and three-dimensional atmospheric
models, we find that WASP-19b's dayside emission is consistent with a model
atmosphere with no dayside thermal inversion and moderately efficient day-night
circulation. We also detect an eastward-shifted hotspot, suggesting the
presence of a superrotating equatorial jet. In contrast, HAT-P-7b's dayside
emission suggests a dayside thermal inversion and relatively inefficient
day-night circulation; no hotspot shift is detected. For both planets, these
same models do not agree with the measured nightside emission. The
discrepancies in the model-data comparisons for WASP-19b might be explained by
high-altitude silicate clouds on the nightside and/or high atmospheric
metallicity, while the very low 3.6 m nightside planetary brightness for
HAT-P-7b may be indicative of an enhanced global C/O ratio. We compute Bond
albedos of 0 ( at ) and for WASP-19b and
HAT-P-7b, respectively. In the context of other planets with thermal phase
curve measurements, we show that WASP-19b and HAT-P-7b fit the general trend of
decreasing day-night heat recirculation with increasing irradiation.Comment: 22 pages, 29 figures, accepted by Ap
Phylogenetically independent behavior mediating geographic distributions suggests habitat is a strong driver of phenotype in crangonyctid amphipods
It is unclear if geographic distributions of animals are behaviorally mediated or simply maintained by ecologically-driven deleterious effects on fitness. Furthermore, it is not well known how behaviors that may affect geographic distributions and responses to environmental stressors evolve. To explore this, we examined behavioral and physiological reactions to light in six species of amphipods in the family Crangonyctidae collected from a variety of subterranean and epigean habitats. Stark differences between epigean and subterranean habitats occupied by different crangonyctid species allowed this clade to serve as an appropriate model system for studying the link between habitat and phenotype. We sampled habitats in or adjacent to the Edwards Aquifer in central Texas and collected two epigean and four stygobiontic species. We examined respiratory and behavioral responses to light in all study species. We found that similarities in behavioral and physiological responses to light between species were only weakly correlated with genetic relatedness but were correlated with habitat type. However, the breadth of variation in phenotype was found to be correlated with phylogenetic relationships, suggesting that population level trait evolution likely involves interactions between standing population level variation and strength of selection. Our findings suggest that natural selection via environmental conditions may outweigh history of common ancestry when predicting phenotypic similarities among species, and that behavioral and physiological phenotypes may mediate the evolution of biogeographic distributions
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