12,072 research outputs found
Preequilibrium particle emissions and in-medium effects on the pion production in heavy-ion collisions
Within the framework of the Lanzhou quantum molecular dynamics (LQMD)
transport model, pion dynamics in heavy-ion collisions near threshold energies
and the emission of preequilibrium particles (nucleons and light complex
fragments) have been investigated. A density, momentum and isospin dependent
pion-nucleon potential based on the -hole model is implemented in the
transport approach, which slightly leads to the increase of the
ratio, but reduces the total pion yields. It is found that a
bump structure of the ratio in the kinetic energy spectra
appears at the pion energy close to the (1232) resonance region. The
yield ratios of neutrons to protons from the squeeze-out particles
perpendicular to the reaction plane are sensitive to the stiffness of nuclear
symmetry energy, in particular at the high-momentum (kinetic energy) tails.Comment: 8 pages, 9 figures, submitted EPJA. arXiv admin note: text overlap
with arXiv:1509.0479
Momentum dependence of the symmetry potential and its influence on nuclear reactions
A Skyrme-type momentum-dependent nucleon-nucleon force distinguishing isospin
effect is parameterized and further implemented in the Lanzhou Quantum
Molecular Dynamics (LQMD) model for the first time, which leads to a splitting
of nucleon effective mass in nuclear matter. Based on the isospin- and
momentum-dependent transport model, we investigate the influence of
momentum-dependent symmetry potential on several isospin-sensitive observables
in heavy-ion collisions. It is found that symmetry potentials with and without
the momentum dependence but corresponding to the same density dependence of the
symmetry energy result in different distributions of the observables. The
mid-rapidity neutron/proton ratios at high transverse momenta and the
excitation functions of the total and yields
are particularly sensitive to the momentum dependence of the symmetry
potential.Comment: 12 pages, 5 figure
Cyclotomic Constructions of Skew Hadamard Difference Sets
We revisit the old idea of constructing difference sets from cyclotomic
classes. Two constructions of skew Hadamard difference sets are given in the
additive groups of finite fields using unions of cyclotomic classes of order
, where is a prime and a positive integer. Our main tools
are index 2 Gauss sums, instead of cyclotomic numbers.Comment: 15 pages; corrected a few typos; to appear in J. Combin. Theory (A
Strongly Regular Graphs From Unions of Cyclotomic Classes
We give two constructions of strongly regular Cayley graphs on finite fields
\F_q by using union of cyclotomic classes and index 2 Gauss sums. In
particular, we obtain twelve infinite families of strongly regular graphs with
new parameters.Comment: 17 pages; to appear in J. Combin. Theory (B
Semi-regular Relative Difference Sets with Large Forbidden Subgroups
Motivated by a connection between semi-regular relative difference sets and
mutually unbiased bases, we study relative difference sets with parameters
in groups of non-prime-power orders. Let be an odd prime. We
prove that there does not exist a relative difference set in any
group of order , and an abelian relative difference set can
only exist in the group . On the other hand, we
construct a family of non-abelian relative difference sets with parameters
, where is an odd prime power greater than 9 and
(mod 4). When is a prime, , and 1 (mod 4), the
non-abelian relative difference sets constructed here are
genuinely non-abelian in the sense that there does not exist an abelian
relative difference set with the same parameters
Josephson junction on one edge of a two dimensional topological insulator affected by magnetic impurity
Current-phase relation in a Josephson junction formed by putting two s-wave
superconductors on the same edge of a two dimensional topological insulator is
investigated. We consider the case that the junction length is finite and
magnetic impurity exists. The similarity and difference with conventional
Josephson junction is discussed. The current is calculated in the semiconductor
picture. Both the - and -period current-phase relations
() are studied. There is a sharp jump at
and for and respectively in the
clean junction. For , the sharp jump is robust against impurity
strength and distribution. However for , the impurity makes the jump
at smooth. The critical (maximum) current of is given
and we find it will be increased by asymmetrical distribution of impurity.Comment: 7 pages, 5 figure
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