617 research outputs found
Classical Coulomb three-body problem in collinear eZe configuration
Classical dynamics of two-electron atom and ions H, He, Li,
Be,... in collinear eZe configuration is investigated. It is revealed
that the mass ratio between necleus and electron plays an important role
for dynamical behaviour of these systems. With the aid of analytical tool and
numeircal computation, it is shown that thanks to large mass ratio ,
classical dynamics of these systems is fully chaotic, probably hyperbolic.
Experimental manifestation of this finding is also proposed.Comment: Largely rewritten. 21 pages. All figures are available in
http://ace.phys.h.kyoto-u.ac.jp/~sano/3-body/index.htm
Fitting formulae for evolution tracks of massive stars under extreme metal poor environments for population synthesis calculations and star cluster simulations
We have devised fitting formulae for evolution tracks of massive stars with under extreme metal poor (EMP) environments for , and , where and are the solar mass and metallicity, respectively. Our fitting formulae are based on reference stellar models which we have newly obtained by simulating the time evolutions of EMP stars. Our fitting formulae take into account stars ending with blue supergiant (BSG) stars, and stars skipping Hertzsprung gap (HG) phases and blue loops, which are characteristics of massive EMP stars. In our fitting formulae, stars may remain BSG stars when they finish their core Helium burning (CHeB) phases. Our fitting formulae are in good agreement with our stellar evolution models. We can use these fitting formulae on the SSE, BSE, NBODY4, and NBODY6 codes, which are widely used for population synthesis calculations and star cluster simulations. These fitting formulae should be useful to make theoretical templates of binary black holes formed under EMP environments
Superconducting pi qubit with a ferromagnetic Josephson junction
Solid-state qubits have the potential for the large-scale integration and for
the flexibility of layout for quantum computing. However, their short
decoherence time due to the coupling to the environment remains an important
problem to be overcome. We propose a new superconducting qubit which
incorporates a spin-electronic device: the qubit consists of a superconducting
ring with a ferromagnetic pi junction which has a metallic contact and a normal
Josephson junction with an insulating barrier. Thus, a quantum coherent
two-level state is formed without an external magnetic field. This feature and
the simple structure of the qubit make it possible to reduce its size leading
to a long decoherence time.Comment: 4 pages, 3 figure
Tidal mass loss in star clusters and treatment of escapers in Fokker-Planck models
This paper presents a new scheme to treat escaping stars in the
orbit-averaged Fokker-Planck models of globular star clusters in a galactic
tidal field. The existence of a large number of potential escapers, which have
energies above the escape energy but are still within the tidal radius, is
taken into account in the models. The models allow potential escapers to
experience gravitational scatterings before they leave clusters and thus some
of them may lose enough energy to be bound again. It is shown that the mass
evolution of the Fokker-Planck models are in good agreement with that of N-body
models including the full tidal-force field. The mass-loss time does not simply
scale with the relaxation time due to the existence of potential escapers; it
increases with the number of stars more slowly than the relaxation time, though
it tends to be proportional to the relaxation time in the limit of a weak tidal
field. The Fokker-Planck models include two parameters, the coefficient gamma
in the Coulomb logarithm ln(gamma N) and the coefficient nu_e controlling the
efficiency of the mass loss. The values of these parameters are determined by
comparing the Fokker-Planck models with the N-body models. It is found that the
parameter set (gamma, nu_e)=(0.11, 7) works well for both single-mass and
multi-mass clusters, but that the parameter set (gamma, nu_e)=(0.02, 40) is
another possible choice for multi-mass clusters.Comment: 10 pages, 12 figures, accepted for publication in MNRAS; Corrected
typos in Table
Graphene as a buffer layer for silicon carbide-on-insulator structures
We report an innovative technique for growing the silicon carbide-on-insulator (SiCOI) structure by utilizing polycrystalline single layer graphene (SLG) as a buffer layer. The epitaxial growth was carried out using a hot-mesh chemical vapor deposition (HM-CVD) technique. Cubic SiC (3C-SiC) thin film in (111) domain was realized at relatively low substrate temperature of 750 °C. 3C-SiC energy bandgap of 2.2 eV was confirmed. The Si-O absorption band observed in the grown film can be caused by the out-diffusion of the oxygen atom from SiO2 substrate or oxygen doping during the cleaning process. Further experimental works by optimizing the cleaning process, growth parameters of the present growth method, or by using other growth methods, as well, are expected to realize a high quality SiCOI structure, thereby opening up the way for a breakthrough in the development of advanced ULSIs with multifunctionalities
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