5,857 research outputs found
Nuclear Matter on a Lattice
We investigate nuclear matter on a cubic lattice. An exact thermal formalism
is applied to nucleons with a Hamiltonian that accommodates on-site and
next-neighbor parts of the central, spin- and isospin-exchange interactions. We
describe the nuclear matter Monte Carlo methods which contain elements from
shell model Monte Carlo methods and from numerical simulations of the Hubbard
model. We show that energy and basic saturation properties of nuclear matter
can be reproduced. Evidence of a first-order phase transition from an
uncorrelated Fermi gas to a clustered system is observed by computing
mechanical and thermodynamical quantities such as compressibility, heat
capacity, entropy and grand potential. We compare symmetry energy and first
sound velocities with literature and find reasonable agreement.Comment: 23 pages, 8 figures (some in color), to be submitted to Phys. Rev.
Quantum annealing with antiferromagnetic fluctuations
We introduce antiferromagnetic quantum fluctuations into quantum annealing in
addition to the conventional transverse-field term. We apply this method to the
infinite-range ferromagnetic p-spin model, for which the conventional quantum
annealing has been shown to have difficulties to find the ground state
efficiently due to a first-order transition. We study the phase diagram of this
system both analytically and numerically. Using the static approximation, we
find that there exists a quantum path to reach the final ground state from the
trivial initial state that avoids first-order transitions for intermediate
values of p. We also study numerically the energy gap between the ground state
and the first excited state and find evidence for intermediate values of p that
the time complexity scales polynomially with the system size at a second-order
transition point along the quantum path that avoids first-order transitions.
These results suggest that quantum annealing would be able to solve this
problem with intermediate values of p efficiently in contrast to the case with
only simple transverse-field fluctuations.Comment: 19 pages, 11 figures; Added references; To be published in Physical
Review
Magnetic-field induced competition of two multiferroic orders in a triangular-lattice helimagnet MnI2
Magnetic and dielectric properties with varying magnitude and direction of
magnetic field H have been investigated for a triangular lattice helimagnet
MnI2. The in-plane electric polarization P emerges in the proper screw magnetic
ground state below 3.5 K, showing the rearrangement of six possible
multiferroic domains as controlled by the in-plane H. With every 60-degree
rotation of H around the [001]-axis, discontinuous 120-degree flop of P-vector
is observed as a result of the flop of magnetic modulation vector q. With
increasing the in-plane H above 3 T, however, the stable q-direction changes
from q|| to q||, leading to a change of P-flop patterns under
rotating H. At the critical field region (~3 T), due to the phase competition
and resultant enhanced q-flexibility, P-vector smoothly rotates clockwise twice
while H-vector rotates counter-clockwise once.Comment: 4 pages, 3 figures. Accepted in Physical Review Letter
An automata characterisation for multiple context-free languages
We introduce tree stack automata as a new class of automata with storage and
identify a restricted form of tree stack automata that recognises exactly the
multiple context-free languages.Comment: This is an extended version of a paper with the same title accepted
at the 20th International Conference on Developments in Language Theory (DLT
2016
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