Time-dependent generator coordinate method study of mass-asymmetric fission of actinides

Low-energy positive and negative parity collective states in the equilibrium minimum, and the dynamics of induced fission of actinide nuclei are investigated in a unified theoretical framework based on the generator coordinate method (GCM) with the Gaussian overlap approximation (GOA). The collective potential and inertia tensor, both at zero and finite temperature, are computed using the self-consistent multidimensionally constrained relativistic mean field (MDC-RMF) model, based on the energy density functional DD-PC1. Pairing correlations are treated in the BCS approximation with a separable pairing force of finite range. A collective quadrupole-octupole Hamiltonian characterized by zero-temperature axially-symmetric deformation energy surface and perturbative cranking inertia tensor, is used to model the low-lying excitation spectrum. The fission fragment charge distributions are obtained by propagating the initial collective states in time with the time-dependent GCM+GOA that uses the same quadrupole-octupole Hamiltonian, but with the collective potential and inertia tensor computed at finite temperature. The illustrative charge yields of $^{228}$Th, $^{234}$U, $^{240}$Pu, $^{244}$Cm, and $^{250}$Cf are in very good agreement with experiment, and the predicted mass asymmetry is consistent with the result of a recent microscopic study that has attributed the distribution (peak) of the heavier-fragment nuclei to shell-stabilized octupole deformations.Comment: 10 pages, 8 figures. arXiv admin note: text overlap with arXiv:1809.0614

Dynamics of Spontaneous Magnetization Reversal in Exchange Biased Heterostructures

The dependence of thermally induced spontaneous magnetization reversal on time-dependent cooling protocols was studied. Slower cooling and longer waiting close to the N\`{e}el temperature of the antiferromagnet ($T_N$) enhances the magnetization reversal. Cycling the temperature around $T_N$ leads to a thermal training effect under which the reversal magnitude increases with each cycle. These results suggest that spontaneous magnetization reversal is energetically favored, contrary to our present understanding of positive exchange bias

Key issues and development direction of petroleum geology research of source rock strata in China

After more than 20 years of technological advancements, the novel field of oil and gas production from source rock strata, which comprise tight and shale oil and gas reservoirs, has become the major contributor to the increase in unconventional oil and gas reserves in China. Accordingly, this field has gradually entered a new stage of revolutionary development. The oil and gas production in China from source rock strata will achieve sustainable development in the future. Different types of source rock strata present distinct challenges and require diverse development paths. Based on the geological conditions of source rock strata in China, this study focuses on identifying the “sweet areas” among hydrocarbon accumulations. It specifically analyzes the key development issues of tight oil, tight gas, shale oil, shale gas, and coal-bed methane, while proposing potential solutions and identifying the possible directions for future development. This study aims to provide a reference for scientists concerned with the development of unconventional oil and gas reserves in China.Cited as: Li, J., Yang, Z., Wu, S., Pan, S. Key issues and development direction of petroleum geology research on source rock strata in China. Advances in Geo-Energy Research, 2021, 5(2): 121-126, doi: 10.46690/ager.2021.02.0

Asymmetric Reversal in Inhomogeneous Magnetic Heterostructures

Asymmetric magnetization reversal is an unusual phenomenon in antiferromagnet / ferromagnet (AF/FM) exchange biased bilayers. We investigated this phenomenon in a simple model system experimentally and by simulation assuming inhomogeneously distributed interfacial AF moments. The results suggest that the observed asymmetry originates from the intrinsic broken symmetry of the system, which results in local incomplete domain walls parallel to the interface in reversal to negative saturation of the FM. Magneto-optic Kerr effect unambiguously confirms such an asymmetric reversal and a depth-dependent FM domain wall in accord with the magnetometry and simulations.Comment: 4 pages, 4 figure