287 research outputs found
Reactor antineutrino spectra and their application to antineutrino-induced reactions. II
The antineutrino and electron spectra associated with various nuclear fuels are calculated. While there are substantial differences between the spectra of different uranium and plutonium isotopes, the dependence on the energy and flux of the fission-inducing neutrons is very weak. The resulting spectra can be used for the calculation of the antineutrino and electron spectra of an arbitrary nuclear reactor at various stages of its refueling cycle. The sources of uncertainties in the spectrum are identified and analyzed in detail. The exposure time dependence of the spectrum is also discussed. The averaged cross sections of the inverse neutron β decay, weak charged and neutral-current-induced deuteron disintegration, and the antineutrino-electron scattering are then evaluated using the resulting ν̅_e spectra.
[RADIOACTIVITY, FISSION 235U, 238U, (^239)Pu, (^240)Pu, (^241)Pu, antineutrino and electron spectra calculated. σ for ν̅ induced reactions analyzed.
Real single ion solvation free energies with quantum mechanical simulation
Single ion solvation free energies are one of the most important properties
of electrolyte solutions and yet there is ongoing debate about what these
values are. Only the values for neutral ion pairs are known. Here, we use DFT
interaction potentials with molecular dynamics simulation (DFT-MD) combined
with a modified version of the quasi-chemical theory (QCT) to calculate these
energies for the lithium and fluoride ions. A method to correct for the error
in the DFT functional is developed and very good agreement with the
experimental value for the lithium fluoride pair is obtained. Moreover, this
method partitions the energies into physically intuitive terms such as surface
potential, cavity and charging energies which are amenable to descriptions with
reduced models. Our research suggests that lithium's solvation free energy is
dominated by the free energetics of a charged hard sphere, whereas fluoride
exhibits significant quantum mechanical behavior that cannot be simply
described with a reduced model.Comment: 13 pages, 4 figure
Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions
Determining the solvation free energies of single ions in water is one of the
most fundamental problems in physical chemistry and yet many unresolved
questions remain. In particular, the ability to decompose the solvation free
energy into simple and intuitive contributions will have important implications
for models of electrolyte solution. Here, we provide definitions of the various
types of single ion solvation free energies based on different simulation
protocols. We calculate solvation free energies of charged hard spheres using
density functional theory interaction potentials with molecular dynamics
simulation (DFT-MD) and isolate the effects of charge and cavitation, comparing
to the Born (linear response) model. We show that using uncorrected Ewald
summation leads to unphysical values for the single ion solvation free energy
and that charging free energies for cations are approximately linear as a
function of charge but that there is a small non-linearity for small anions.
The charge hydration asymmetry (CHA) for hard spheres, determined with quantum
mechanics, is much larger than for the analogous real ions. This suggests that
real ions, particularly anions, are significantly more complex than simple
charged hard spheres, a commonly employed representation.Comment: 28 pages, 5 figure
Smoothed Dissipative Particle Dynamics model for mesoscopic multiphase flows in the presence of thermal fluctuations
Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly
nonlinear hydrodynamics in multiphase flows. In this work, we develop a novel
multiphase smoothed dissipative particle dynamics model. This model accounts
for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface
tension is modeled by imposing a pairwise force between SDPD particles. We show
that the relationship between the model parameters and surface tension,
previously derived under the assumption of zero thermal fluctuation, is
accurate for fluid systems at low temperature but overestimates the surface
tension for intermediate and large thermal fluctuations. To analyze the effect
of thermal fluctuations on surface tension, we construct a coarse-grained Euler
lattice model based on the mean field theory and derive a semi-analytical
formula to directly relate the surface tension to model parameters for a wide
range of temperatures and model resolutions. We demonstrate that the present
method correctly models the dynamic processes, such as bubble coalescence and
capillary spectra across the interface
Mass Density Fluctuations in Quantum and Classical descriptions of Liquid Water
First principles molecular dynamics simulation protocol is established using
revised functional of Perdew-Burke-Ernzerhof (revPBE) in conjunction with
Grimme's third generation of dispersion (D3) correction to describe properties
of water at ambient conditions. This study also demonstrates the consistency of
the structure of water across both isobaric (NpT) and isothermal (NVT)
ensembles. Going beyond the standard structural benchmarks for liquid water, we
compute properties that are connected to both local structure and mass density
uctuations that are related to concepts of solvation and hydrophobicity. We
directly compare our revPBE results to the Becke-Lee-Yang-Parr (BLYP) plus
Grimme dispersion corrections (D2) and both the empirical fixed charged model
(SPC/E) and many body interaction potential model (MB-pol) to further our
understanding of how the computed properties herein depend on the form of the
interaction potential
Reactor antineutrino spectra and their application to antineutrino-induced reactions
The knowledge of reactor antineutrino spectra is necessary for the interpretation of weak-interaction experiments located at nuclear reactors. We calculate the antineutrino and electron spectra accompanying thermal neutron fission of 235U and 239Pu for various irradiation times. It is stressed that the higher energy part (E≳4 MeV) of the spectra depends sensitively on the β-decay characteristics of fission products with experimentally unknown decay schemes. We also discuss the accuracy of a semiempirical conversion of the electron spectrum into the antineutrino spectrum. The resulting ν̅ e spectra are used to calculated cross sections and reaction rates for the inverse neutron β decay, weak charged and neutral current induced deuteron disintegration, and the antineutrino-electron scattering
Conductance Fluctuations of Generic Billiards: Fractal or Isolated?
We study the signatures of a classical mixed phase space for open quantum
systems. We find the scaling of the break time up to which quantum mechanics
mimics the classical staying probability and derive the distribution of
resonance widths. Based on these results we explain why for mixed systems two
types of conductance fluctuat ions were found: quantum mechanics divides the
hierarchically structured chaotic component of phase space into two parts - one
yields fractal conductance fluctuations while the other causes isolated
resonances. In general, both types appear together, but on different energy
scales.Comment: restructured and new figure
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