16,870 research outputs found
Microscopic study of induced fission dynamics of Th with covariant energy density functionals
Static and dynamic aspects of the fission process of Th are analyzed
in a self-consistent framework based on relativistic energy density
functionals. Constrained relativistic mean-field (RMF) calculations in the
collective space of axially symmetric quadrupole and octupole deformations,
based on the energy density functional PC-PK1 and a -force pairing, are
performed to determine the potential energy surface of the fissioning nucleus,
the scission line, the single-nucleon wave functions, energies and occupation
probabilities, as functions of deformation parameters. Induced fission dynamics
is described using the time-dependent generator coordinate method in the
Gaussian overlap approximation. A collective Schr\"odinger equation, determined
entirely by the microscopic single-nucleon degrees of freedom, propagates
adiabatically in time the initial wave packet built by boosting the
ground-state solution of the collective Hamiltonian for Th. The
position of the scission line and the microscopic input for the collective
Hamiltonian are analyzed as functions of the strength of the pairing
interaction. The effect of static pairing correlations on the pre-neutron
emission charge yields and total kinetic energy of fission fragments is
examined in comparison with available data, and the distribution of fission
fragments is analyzed for different values of the initial excitation energy.Comment: 25 pages, 14 figures, accepted for publication in Phys. Rev.
Spectroscopy of reflection-asymmetric nuclei with relativistic energy density functionals
Quadrupole and octupole deformation energy surfaces, low-energy excitation
spectra and transition rates in fourteen isotopic chains: Xe, Ba, Ce, Nd, Sm,
Gd, Rn, Ra, Th, U, Pu, Cm, Cf, and Fm, are systematically analyzed using a
theoretical framework based on a quadrupole-octupole collective Hamiltonian
(QOCH), with parameters determined by constrained reflection-asymmetric and
axially-symmetric relativistic mean-field calculations. The microscopic QOCH
model based on the PC-PK1 energy density functional and -interaction
pairing is shown to accurately describe the empirical trend of low-energy
quadrupole and octupole collective states, and predicted spectroscopic
properties are consistent with recent microscopic calculations based on both
relativistic and non-relativistic energy density functionals. Low-energy
negative-parity bands, average octupole deformations, and transition rates show
evidence for octupole collectivity in both mass regions, for which a
microscopic mechanism is discussed in terms of evolution of single-nucleon
orbitals with deformation.Comment: 36 pages, 21 figures, Accepted for Publication in Physical Review
Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear
We study the impact of catastrophic errors occurring in the photometric
redshifts of galaxies on cosmological parameter estimates with cosmic shear
tomography. We consider a fiducial survey with 9-filter set and perform photo-z
measurement simulations. It is found that a fraction of 1% galaxies at
z_{spec}~0.4 is misidentified to be at z_{phot}~3.5. We then employ both chi^2
fitting method and the extension of Fisher matrix formalism to evaluate the
bias on the equation of state parameters of dark energy, w_0 and w_a, induced
by those catastrophic outliers. By comparing the results from both methods, we
verify that the estimation of w_0 and w_a from the fiducial 5-bin tomographic
analyses can be significantly biased. To minimize the impact of this bias, two
strategies can be followed: (A) the cosmic shear analysis is restricted to
0.5<z<2.5 where catastrophic redshift errors are expected to be insignificant;
(B) a spectroscopic survey is conducted for galaxies with 3<z_{phot}<4. We find
that the number of spectroscopic redshifts needed scales as N_{spec} \propto
f_{cata}\times A where f_{cata}=1% is the fraction of catastrophic redshift
errors (assuming a 9-filter photometric survey) and A is the survey area. For
A=1000 {deg}^2, we find that N_{spec}>320 and 860 respectively in order to
reduce the joint bias in (w_0,w_a) to be smaller than 2\sigma and 1\sigma. This
spectroscopic survey (option B) will improve the Figure of Merit of option A by
a factor \times 1.5 thus making such a survey strongly desirable.Comment: 25 pages, 9 figures. Revised version, as accepted for publication in
Ap
Electron-Angular-Distribution Reshaping in Quantum Radiation-Dominated Regime
Dynamics of an electron beam head-on colliding with an ultraintense focused
ultrashort circularly-polarized laser pulse are investigated in the quantum
radiation-dominated regime. Generally, the ponderomotive force of the laser
fields may deflect the electrons transversely, to form a ring structure on the
cross-section of the electron beam. However, we find that when the Lorentz
factor of the electron is approximately one order of magnitude larger
than the invariant laser field parameter , the stochastic nature of the
photon emission leads to electron aggregation abnormally inwards to the
propagation axis of the laser pulse. Consequently, the electron angular
distribution after the interaction exhibits a peak structure in the beam
propagation direction, which is apparently distinguished from the
"ring"-structure of the distribution in the classical regime, and therefore,
can be recognized as a proof of the fundamental quantum stochastic nature of
radiation. The stochasticity signature is robust with respect to the laser and
electron parameters and observable with current experimental techniques
Catalytic efficiency and stability of cobalt hydroxide for decomposition of ozone and p-chloronitrobenzene in water
Cobalt hydroxide, a stable and efficient catalyst prepared in the laboratory, has been successfully used in the decomposition of ozone and trace quantities of p-chloronitrobenzene (pCNB) in water. The cobalt hydroxide was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the Brunauer-Emmet-Teller (BET) method. The decomposition rate of aqueous ozone was increased by 1.527 times in the presence of cobalt hydroxide. Increasing the catalyst loading from 0 to 500 mg/L increased the removal efficiency of pCNB from 59% to 99%. The catalyst morphology and its composition were found to be unaltered after the catalytic reaction. After five successive recycles, the catalyst remained stable in the catalytic ozonation of pCNB
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