21,960 research outputs found
Shell and isospin effects in nuclear charge radii
The shell effect and isospin effect in nuclear charge radii are
systematically investigated and a four-parameter formula is proposed for the
description of the root-mean-square (rms) charge radii by combining the shell
corrections and deformations of nuclei obtained from the Weizs\"acker-Skyrme
mass model. The rms deviation with respect to the 885 measured charge radii
falls to 0.022 fm. The proposed formula is also applied for the study of the
charge radii of super-heavy nuclei and nuclear symmetry energy. The linear
relationship between the slope parameter L of the nuclear symmetry energy and
the rms charge radius difference of 30S - 30Si mirror pair is clearly observed.
The estimated slope parameter is about MeV from the coefficient
of the isospin term in the proposed charge radius formula.Comment: 7 figures, 1 table, accepted for publication as a Rapid Communication
in Physical Review
GPU-based Efficient Join Algorithms on Hadoop
The growing data has brought tremendous pressure for query processing and
storage, so there are many studies that focus on using GPU to accelerate join
operation, which is one of the most important operations in modern database
systems. However, existing GPU acceleration join operation researches are not
very suitable for the join operation on big data. Based on this, this paper
speeds up nested loop join, hash join and theta join, combining Hadoop with
GPU, which is also the first to use GPU to accelerate theta join. At the same
time, after the data pre-filtering and pre-processing, using Map-Reduce and
HDFS in Hadoop proposed in this paper, the larger data table can be handled,
compared to existing GPU acceleration methods. Also with Map-Reduce in Hadoop,
the algorithm proposed in this paper can estimate the number of results more
accurately and allocate the appropriate storage space without unnecessary
costs, making it more efficient. The rigorous experiments show that the
proposed method can obtain 1.5 to 2 times the speedup, compared to the
traditional GPU acceleration equi join algorithm. And in the synthetic data
set, the GPU version of the proposed method can get 1.3 to 2 times the speedup,
compared to CPU version.Comment: 39 page
Impurity effects and ferromagnetism in excitonic insulators
Both nonmagnetic and magnetic impurity effects in spin singlet and triplet
excitonic insulators were investigated. The bound state energies caused by
single impurity were given. The different compositions of the bound states can
be used to detect the symmetry of the excitonic insulators. In finite
concentration problems, nonmagnetic impurities showed same pair-breaking effect
in singlet and triplet excitonic insulators while magnetic impurities showed
weaker pair-breaking effect in triplet excitonic insulators than in singlet
ones. The pair-breaking effects suppressed the ferromagnetic range via doping
and gave a natural explaination for experimental results.Comment: 7 pages, 4 figure
Mechanism of production of light complex particles in nucleon-induced reactions
The Improved Quantum Molecular Dynamics (ImQMD) model incorporated with the
statistical decay model is successful in describing emission of nucleons in the
intermediate energy spallation reactions, but not good enough in describing
productions of light complex particles, i.e. , , He and He.
To improve the description on emission of light complex particles, a
phenomenological mechanism called surface coalescence and emission is
introduced into ImQMD model: nucleon ready to escape from the compound nuclei
can coalesce with the other nucleon(s) to form light complex particle and be
emitted. With updated ImQMD model, the description on the experimental data of
light complex particles produced in nucleon-induced reactions are great
improved.Comment: 17 pages, 6 figures. arXiv admin note: text overlap with
arXiv:nucl-th/0606004 by other author
Microscopic dynamics simulations of heavy-ion fusion reactions induced by neutron-rich nuclei
The heavy-ion fusion reactions induced by neutron-rich nuclei are
investigated with the improved quantum molecular dynamics (ImQMD) model. With a
subtle consideration of the neutron skin thickness of nuclei and the symmetry
potential, the stability of nuclei and the fusion excitation functions of
heavy-ion fusion reactions O+Ge, O+Sm,
Ca+Zr and Sn+Ca are systematically studied. The
fusion cross sections of these reactions at energies around the Coulomb barrier
can be well reproduced by using the ImQMD model. The corresponding slope
parameter of the symmetry energy adopted in the calculations is
MeV and the surface energy coefficient is MeVfm. In
addition, it is found that the surface-symmetry term significantly influences
the fusion cross sections of neutron-rich fusion systems. For sub-barrier
fusion, the dynamical fluctuations in the densities of the reaction partners
and the enhanced surface diffuseness at neck side result in the lowering of the
fusion barrier.Comment: 10 figures, the version published in PR
Improved Kelson-Garvey mass relations for proton-rich nuclei
The improved Kelson-Garvey (ImKG) mass relations are proposed from the mass
differences of mirror nuclei. The masses of 31 measured proton-rich nuclei with
and can be remarkably well reproduced by
using the proposed relations, with a root-mean-square deviation of 0.398 MeV,
which is much smaller than the results of Kelson-Garvey (0.502 MeV) and
Isobar-Mirror mass relations (0.647 MeV). This is because many more masses of
participating nuclei are involved in the ImKG mass relations for predicting the
masses of unknown proton-rich nuclei. The masses for 144 unknown proton-rich
nuclei with are predicted by using the ImKG mass relations. The
one- and two-proton separation energies for these proton-rich nuclei and the
diproton emission are investigated simultaneously.Comment: 23 Pages,7figures,to be published in Phys. Rev.
Dynamical and statistical description of multifragmentation in heavy-ion collisions
To explore the roles of dynamical model and statistical model in the
description of multifragmentation in heavy-ion collisions at intermediate
energies, the fragments charge distributions of Au+Au at 35
MeV/u are analyzed by using the hybrid model of improved quantum molecular
dynamics (ImQMD) model plus the statistical model GEMINI. We find that, the
ImQMD model can well describe the charge distributions of fragments produced in
central and semi-central collisions. But for the peripheral collisions of Au+Au
at 35 MeV/u, the statistical model is required at the end of the ImQMD
simulations for the better description of the charge distribution of fragments.
By using the hybrid model of ImQMD+GEMINI, the fragment charge distribution of
Au+Au at 35 MeV/u can be reproduced reasonably well. The time evolution of the
excitation energies of primary fragments is simultaneously investigated.Comment: 6 pages, 3 figure
Fusion and quasi-fission dynamics in nearly-symmetric reactions
Some nearly-symmetric fusion reactions are systematically investigated with
the improved quantum molecular dynamics (ImQMD) model. By introducing two-body
inelastic scattering in the Fermi constraint procedure, the stability of an
individual nucleus and the description of fusion cross sections at energies
near the Coulomb barrier can be further improved. Simultaneously, the
quasi-fission process in Sm+Gd is also investigated with the
microscopic dynamics model for the first time. We find that at energies above
the Bass barrier, the fusion probability is smaller than for this
reaction, and the nuclear contact-time is generally smaller than fm/c.
From the central collisions of Sm+Gd, the neutron-rich fragments such as
Gd, W can be produced in the ImQMD simulations, which
implies that the quasi-fission reaction could be an alternative way to
synthesize new neutron-rich heavy nuclei.Comment: 11 figure
Search for possible way of producing super-heavy elements-Dynamic study on damped reactions of 244Pu+244Pu,238U and 197Au+197Au
By using the improved Quantum Molecular Dynamics model, the
Pu+Pu, U+U and Au+Au reactions
at the energy range of =800 to 2000 are studied. We find
that the production probability of superheavy fragments(SHF) with 114
is much higher for Pu+Pu reaction compared with that of
U+U reaction and no product of SHF is found for
Au+Au. The production probability of SHF is narrowly peaked in
incident energy dependence. The decay mechanism of the composite system of
projectile and target and the time scale of decay process are explored. The
binding energies of superheavy fragments are found to be broadly distributed
and their shapes turn out to be exotic form.Comment: 6 pages, 5 figures, 1 tabl
Determination of the nucleon-nucleon interaction in the ImQMD model by nuclear reaction at the Fermi energy region
The nucleon-nucleon interaction is investigated by using the ImQMD model with
the three sets of parameters IQ1, IQ2 and IQ3 in which the corresponding
incompressibility coefficients of nuclear matter are different. The charge
distribution of fragments for various reaction systems are calculated at
different incident energies. The parameters strongly affect the charge
distribution below the threshold energy of nuclear multifragmentation. The
fragment multiplicity spectrum for U+Au at 15 AMeV and the
charge distribution for Xe+Sn at 32 and 45 AMeV, and
Au+Au at 35 AMeV are reproduced by the ImQMD model with the set
of parameter IQ3. It is concluded that charge distribution of the fragments and
the fragment multiplicity spectrum are good observables for studying N-N
interaction, the Fermi energy region is a sensitive energy region to explore
the N-N interaction, and IQ3 is a suitable set of parameters for the ImQMD
model.Comment: 10pages,6figure
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