43,211 research outputs found
Hybrid Simulation between Molecular Dynamics and Binary Collision Approximation Codes for Hydrogen injection onto Carbon Materials
Molecular dynamics (MD) simulation with modified Brenner's reactive empirical
bond order (REBO) potential is a powerful tool to investigate plasma wall
interaction on divertor plates in a nuclear fusion device. However, MD
simulation box's size is less than several nm for the performance of a
computer. To extend the size of the MD simulation, we develop a hybrid
simulation code between MD code using REBO potential and binary collision
approximation (BCA) code. Using the BCA code instead of computing all particles
with a high kinetic energy for every step in the MD simulation, considerable
computation time is saved. By demonstrating a hydrogen atom injection on a
graphite by the hybrid simulation code, it is found that the hybrid simulation
code works efficiently in a large simulation box.Comment: 5 pages, 5 figure
Parity violating electron scattering on the proton and deuteron at backward angles
The parity violating asymmetry in quasielastic electron scattering from the deuteron at backward scattering angles has been recently measured for the first time. Combined with the previously performed similar measurement on the proton, this measurement provides a determination of both the proton's strange magnetic form factor G^(a)_(M) and the axial vector e-N form factor G^(a)_(A). A preliminary analysis indicates that G^(a)_(M) is slightly positive but consistent with zero and that G^(e)_(A)(T=1) is in substantial disagreement with the theoretical estimate
Mediation of Supersymmetry Breaking via Anti-Generation Fields
In the context of the weakly coupled heterotic string, we propose a new model
of mediating supersymmetry breaking. The breakdown of supersymmetry in the
hidden sector is transmitted to anti-generation fields via gravitational
interactions. Subsequent transmission of the breaking to the MSSM sector occurs
via gauge interactions. It is shown that the mass spectra of superparticles are
phenomenologically viable.Comment: 8pages, LaTeX, 1 figure, final version to appear in Prog. Theor.
Phys. Vol.103, No.6 (2000
Neutrino mass constraints on beta decay
Using the general connection between the upper limit on the neutrino mass and
the upper limits on certain types of non-Standard Model interaction that can
generate loop corrections to the neutrino mass, we derive constraints on some
non-Standard Model interactions. When cast into limits on
coupling constants, our results yield constraints on
scalar and tensor weak interactions improved by more than an order of magnitude
over the current experimental limits. When combined with the existing limits,
our results yield |C_S/C_V|\alt 5\times 10^{-3}, |C'_S/C_V|\alt 5\times
10^{-3}, |C_T/C_A| \alt 1.2\times 10^{-2} and |C'_T/C_A| \alt 1.2\times
10^{-2}.Comment: 4 pages, 3 figures; revised to reflect referee comments; accepted for
publication in Physical Review Letter
On the Magnetic Excitation Spectra of High Tc Cu Oxides up to the Energies far above the Resonance Energy
Magnetic excitation spectra c"(q,w) of YBa2Cu3Oy and La214 systems have been
studied. For La1.88Sr0.12CuO4, c"(q,w) have been measured up to ~30 meV and
existing data have been analyzed up to the energy w~150 meV by using the
phenomenological expression of the generalized magnetic susceptibility
c(q,w)=c0(q,w)/{1+J(q)c0(q,w)}, where c0(q,w) is the susceptibility of the
electrons without the exchange coupling J(q) among them. In the relatively low
energy region up to slightly above the resonance energy Er, it has been
reported by the authors' group that the expression can explain characteristics
of the q- and w-dependence of the spectra of YBa2Cu3Oy (YBCO or YBCOy). Here,
it is also pointed out that the expression can reproduce the rotation of four
incommensurate peaks of c"(q,w) within the a*-b* plane about (p/a, p/a) {or
so-called (p, p)} point by 45 degree, which occurs as w goes to the energy
region far above Er from E below Er. For La2-xSrxCuO4 and La2-xBaxCuO4,
agreements between the observed results and the calculations are less
satisfactory than for YBCO, indicating that we have to take account of the
existence of the "stripes" to consistently explain the observed c"(q,w) of
La214 system especially near x=1/8.Comment: 14 pages, 5 figure
A reconfigurations analogue of Brooks’ theorem.
Let G be a simple undirected graph on n vertices with maximum degree Δ. Brooks’ Theorem states that G has a Δ-colouring unless G is a complete graph, or a cycle with an odd number of vertices. To recolour G is to obtain a new proper colouring by changing the colour of one vertex. We show that from a k-colouring, k > Δ, a Δ-colouring of G can be obtained by a sequence of O(n 2) recolourings using only the original k colours unless
G is a complete graph or a cycle with an odd number of vertices, or
k = Δ + 1, G is Δ-regular and, for each vertex v in G, no two neighbours of v are coloured alike.
We use this result to study the reconfiguration graph R k (G) of the k-colourings of G. The vertex set of R k (G) is the set of all possible k-colourings of G and two colourings are adjacent if they differ on exactly one vertex. It is known that
if k ≤ Δ(G), then R k (G) might not be connected and it is possible that its connected components have superpolynomial diameter,
if k ≥ Δ(G) + 2, then R k (G) is connected and has diameter O(n 2).
We complete this structural classification by settling the missing case:
if k = Δ(G) + 1, then R k (G) consists of isolated vertices and at most one further component which has diameter O(n 2).
We also describe completely the computational complexity classification of the problem of deciding whether two k-colourings of a graph G of maximum degree Δ belong to the same component of R k (G) by settling the case k = Δ(G) + 1. The problem is
O(n 2) time solvable for k = 3,
PSPACE-complete for 4 ≤ k ≤ Δ(G),
O(n) time solvable for k = Δ(G) + 1,
O(1) time solvable for k ≥ Δ(G) + 2 (the answer is always yes)
Reconfiguration of Dominating Sets
We explore a reconfiguration version of the dominating set problem, where a
dominating set in a graph is a set of vertices such that each vertex is
either in or has a neighbour in . In a reconfiguration problem, the goal
is to determine whether there exists a sequence of feasible solutions
connecting given feasible solutions and such that each pair of
consecutive solutions is adjacent according to a specified adjacency relation.
Two dominating sets are adjacent if one can be formed from the other by the
addition or deletion of a single vertex.
For various values of , we consider properties of , the graph
consisting of a vertex for each dominating set of size at most and edges
specified by the adjacency relation. Addressing an open question posed by Haas
and Seyffarth, we demonstrate that is not necessarily
connected, for the maximum cardinality of a minimal dominating set
in . The result holds even when graphs are constrained to be planar, of
bounded tree-width, or -partite for . Moreover, we construct an
infinite family of graphs such that has exponential
diameter, for the minimum size of a dominating set. On the positive
side, we show that is connected and of linear diameter for any
graph on vertices having at least independent edges.Comment: 12 pages, 4 figure
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