6,679 research outputs found
Bifurcations in the Lozi map
We study the presence in the Lozi map of a type of abrupt order-to-order and
order-to-chaos transitions which are mediated by an attractor made of a
continuum of neutrally stable limit cycles, all with the same period.Comment: 17 pages, 12 figure
Heavy-to-light scalar form factors from Muskhelishvili-Omn\`es dispersion relations
By solving the Muskhelishvili-Omn\`es integral equations, the scalar form
factors of the semileptonic heavy meson decays ,
, and
are simultaneously studied. As input, we
employ unitarized heavy meson-Goldstone boson chiral coupled-channel amplitudes
for the energy regions not far from thresholds, while, at high energies,
adequate asymptotic conditions are imposed. The scalar form factors are
expressed in terms of Omn\`es matrices multiplied by vector polynomials, which
contain some undetermined dispersive subtraction constants. We make use of
heavy quark and chiral symmetries to constrain these constants, which are
fitted to lattice QCD results both in the charm and the bottom sectors, and in
this latter sector to the light-cone sum rule predictions close to as
well. We find a good simultaneous description of the scalar form factors for
the four semileptonic decay reactions. From this combined fit, and taking
advantage that scalar and vector form factors are equal at , we obtain
, and for the involved Cabibbo-Kobayashi-Maskawa (CKM) matrix
elements. In addition, we predict the following vector form factors at :
, ,
and , which might serve as alternatives to determine the CKM elements when
experimental measurements of the corresponding differential decay rates become
available. Finally, we predict the different form factors above the
regions accessible in the semileptonic decays, up to moderate energies
amenable to be described using the unitarized coupled-channel chiral approach.Comment: includes further discussions and references; matches the accepted
versio
Accuracy control in ultra-large-scale electronic structure calculation
Numerical aspects are investigated in ultra-large-scale electronic structure
calculation. Accuracy control methods in process (molecular-dynamics)
calculation are focused. Flexible control methods are proposed so as to control
variational freedoms, automatically at each time step, within the framework of
generalized Wannier state theory. The method is demonstrated in silicon
cleavage simulation with 10^2-10^5 atoms. The idea is of general importance
among process calculations and is also used in Krylov subspace theory, another
large-scale-calculation theory.Comment: 8 pages, 3 figures. To appear in J.Phys. Condens. Matter. A preprint
PDF file in better graphics is available at
http://fujimac.t.u-tokyo.ac.jp/lses/index_e.htm
Theoretical analysis of magnetic coupling in sandwich clusters V_n(C_6H_6)_{n+1}
The mechanism of ferromagnetism stability in sandwich clusters
V(CH) has been studied by first-principles calculation and
model analysis. It is found that each of the three types of bonds between V and
benzene (Bz) plays different roles. V 3d orbital, extending along the
molecular axis, is weakly hybridized with Bz's HOMO-1 orbital to form the
-bond. It is quite localized and singly occupied, which contributes
1 to the magnetic moment but little to the magnetic coupling of
neighboring V magnetic moments. The in-plane d, d orbitals
are hybridized with the LUMO of Bz and constitute the -bond. This
hybridization is medium and crucial to the magnetic coupling though the
states have no net contribution to the total magnetic moment.
d, d and HOMO of Bz form a quite strong -bond to hold the
molecular structure but they are inactive in magnetism because their energy
levels are far away from the Fermi level. Based on the results of
first-principles calculation, we point out that the ferromagnetism stability is
closely related with the mechanism proposed by Kanamori and Terakura [J.
Kanamori and K. Terakura, J. Phys. Soc. Jpn. 70, 1433 (2001)]. However, the
presence of edge Bz's in the cluster introduces an important modification. A
simple model is constructed to explain the essence of the physical picture.Comment: 16 pages, 7 figure
The Golden Channel at a Neutrino Factory revisited: improved sensitivities from a Magnetised Iron Neutrino Detector
This paper describes the performance and sensitivity to neutrino mixing
parameters of a Magnetised Iron Neutrino Detector (MIND) at a Neutrino Factory
with a neutrino beam created from the decay of 10 GeV muons. Specifically, it
is concerned with the ability of such a detector to detect muons of the
opposite sign to those stored (wrong-sign muons) while suppressing
contamination of the signal from the interactions of other neutrino species in
the beam. A new more realistic simulation and analysis, which improves the
efficiency of this detector at low energies, has been developed using the GENIE
neutrino event generator and the GEANT4 simulation toolkit. Low energy neutrino
events down to 1 GeV were selected, while reducing backgrounds to the
level. Signal efficiency plateaus of ~60% for and ~70% for
events were achieved starting at ~5 GeV. Contamination from the
oscillation channel was studied for the first
time and was found to be at the level between 1% and 4%. Full response matrices
are supplied for all the signal and background channels from 1 GeV to 10 GeV.
The sensitivity of an experiment involving a MIND detector of 100 ktonnes at
2000 km from the Neutrino Factory is calculated for the case of . For this value of , the accuracy in the
measurement of the CP violating phase is estimated to be , depending on the value of ,
the CP coverage at is 85% and the mass hierarchy would be determined
with better than level for all values of
Systematically improvable optimized atomic basis sets for {\it ab inito} calculations
We propose a unique scheme to construct fully optimized atomic basis sets for
density-functional calculations. The shapes of the radial functions are
optimized by minimizing the {\it spillage} of the wave functions between the
atomic orbital calculations and the converged plane wave calculations for dimer
systems. The quality of the bases can be systematically improved by increasing
the size of the bases within the same framework. The scheme is easy to
implement and very flexible. We have done extensive tests of this scheme for
wide variety of systems. The results show that the obtained atomic basis sets
are very satisfactory for both accuracy and transferability
Fast diffusion of a Lennard-Jones cluster on a crystalline surface
We present a Molecular Dynamics study of large Lennard-Jones clusters
evolving on a crystalline surface. The static and the dynamic properties of the
cluster are described. We find that large clusters can diffuse rapidly, as
experimentally observed. The role of the mismatch between the lattice
parameters of the cluster and the substrate is emphasized to explain the
diffusion of the cluster. This diffusion can be described as a Brownian motion
induced by the vibrationnal coupling to the substrate, a mechanism that has not
been previously considered for cluster diffusion.Comment: latex, 5 pages with figure
Large-scale electronic structure theory for simulating nanostructure process
Fundamental theories and practical methods for large-scale electronic
structure calculations are given, in which the computational cost is
proportional to the system size. Accuracy controlling methods for microscopic
freedoms are focused on two practical solver methods, Krylov-subspace method
and generalized-Wannier-state method. A general theory called the
'multi-solver' scheme is also formulated, as a hybrid between different solver
methods. Practical examples are carried out in several insulating and metallic
systems with 10^3-10^5 atoms. All the theories provide general guiding
principles of constructing an optimal calculation for simulating nanostructure
processes, since a nanostructured system consists of several competitive
regions, such as bulk and surface regions, and the simulation is designed to
reproduce the competition with an optimal computational cost.Comment: 19 pages, 6 figures. To appear in J. Phys. Cond. Matt. A preprint PDF
file in better graphics is available at
http://fujimac.t.u-tokyo.ac.jp/lses/index_e.htm
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