6,556 research outputs found
Discussion on the progress and future of satellite communication (Japan)
The current status of communications satellite development in Japan is presented. It is shown that beginning with research on satellite communucations in the late 1950's, progress was made in the areas of communications, remote sensing, and technology experimentation. The current status of communication satellites is presented, stressing development in the areas of CFRP construction elements, the use of LSI and MIC circuits, advanced multibeam antenna systems, Ku and Ka band transmission systems, and the shift to small-scale earth stations. Methods for reducing costs and increasing transmission efficiency are shown. The technical specifications of all satellite projects currently under development are given. Users of Japanese communications satellite are presented
Origin of the Heavy Fermion Behavior in Ca_{2-x}Sr_{x}RuO_{4}: Roles of Coulomb Interaction and the Rotation of RuO_{6} octahedra
We study the electronic states for Ca_{2-x}Sr_{x}RuO_{4} in within the Gutzwiller approximation (GA) on the basis of the three-orbital
Hubbard model for the Ru t_{2g} orbitals. The main effects of the Ca
substitution are taken account as the changes of the hybridizations
between the Ru 4d and O 2p orbitals. Using the numerical minimization of the
energy obtained in the GA, we obtain the renormalization factor (RF) of the
kinetic energy and total RF, which estimates the inverse of the mass
enhancement, for three cases with the effective models of x=2 and 0.5 and a
special model. We find that the inverse of the total RF becomes the largest for
the case of x=0.5, and that the van Hove singularity, which is located on
(below) the Fermi level for the special model (the effective model of x=0.5),
plays a secondary role in enhancing the effective mass. Our calculation
suggests that the heavy fermion behavior around x=0.5 comes from the
cooperative effects between moderately strong Coulomb interaction compared to
the total bandwidth and the modification of the electronic structures due to
the rotation of RuO_{6} octahedra (i.e., the variation of the
hybridizations and the downward shift for the orbital). We propose
that moderately strong electron correlation and the orbital-dependent
modifications of the electronic structures due to the lattice distortions play
important roles in the electronic states for Ca_{2-x}Sr_{x}RuO_{4}.Comment: 16 pages, 13 figures, 1 table, accepted for publication in Physical
Review B; added the discussions both about the validity of the present
treatment and about Hund's metal in this allo
Quantum Melting of Charge Order due to Frustration in Two-Dimensional Quarter-Filled Systems
The effect of geometrical frustration in a two-dimensional 1/4-filled
strongly correlated electron system is studied theoretically, motivated by
layered organic molecular crystals. An extended Hubbard model on the square
lattice is considered, with competing nearest neighbor Coulomb interaction, V,
and that of next-nearest neighbor along one of the diagonals, V', which favor
different charge ordered states. Based on exact diagonalization calculations,
we find a metallic phase stabilized over a broad window at V' ~ V even for
large Coulomb repulsion strengths as a result of frustrating the charge ordered
states. Slightly modifying the lattice geometry relevant to the actual organic
compounds does not alter the results, suggesting that this `quantum melting' of
charge order is a robust feature of frustrated strongly correlated 1/4-filled
systems.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
Propagation of Correlations in Quantum Lattice Systems
We provide a simple proof of the Lieb-Robinson bound and use it to prove the
existence of the dynamics for interactions with polynomial decay. We then use
our results to demonstrate that there is an upper bound on the rate at which
correlations between observables with separated support can accumulate as a
consequence of the dynamics.Comment: 10 page
Experimental demonstration of four-party quantum secret sharing
Secret sharing is a multiparty cryptographic task in which some secret
information is splitted into several pieces which are distributed among the
participants such that only an authorized set of participants can reconstruct
the original secret. Similar to quantum key distribution, in quantum secret
sharing, the secrecy of the shared information relies not on computational
assumptions, but on laws of quantum physics. Here, we present an experimental
demonstration of four-party quantum secret sharing via the resource of
four-photon entanglement
A possible phase diagram of a t-J ladder model
We investigate a t-J ladder model by numerical diagonalization method. By
calculating correlation functions and assuming the Luttinger liquid relation,
we obtained a possible phase diagram of the ground state as a function of J/t
and electron density . We also found that behavior of correlation functions
seems to consist with the prediction of Luttinger liquid relation. The result
suggests that the superconducting phase appear in the region of for high electron density and for low electron density.Comment: Latex, 10 pages, figures available upon reques
Spin-Gap Phase in the One-Dimensional t-J-J' Model
The spin-gap phase of the one-dimensional t-J-J' model is studied by the
level-crossing of the singlet and the triplet excitation spectra.
The phase boundary obtained between the Tomonaga-Luttinger and the spin-gap
phases is remarkably consistent with the analytical results at the
and the low-density limits discussed by Ogata et al.
The spin-gap phase has a single domain in the phase diagram even if the spin
gap opens at half-filling.
The phase boundary coincides with the line where the
Tomonaga-Luttinger liquid behaves as free electrons, in the low-density region.
The relation between our method and the solution of the two-electron problem
is also discussed.Comment: 4 pages(JPSJ.sty), 5 figures(EPS), to appear in J. Phys. Soc. Jpn.
67, No.3 (1998
Recent developments in the eikonal description of the breakup of exotic nuclei
The study of exotic nuclear structures, such as halo nuclei, is usually
performed through nuclear reactions. An accurate reaction model coupled to a
realistic description of the projectile is needed to correctly interpret
experimental data. In this contribution, we briefly summarise the assumptions
made within the modelling of reactions involving halo nuclei. We describe
briefly the Continuum-Discretised Coupled Channel method (CDCC) and the
Dynamical Eikonal Approximation (DEA) in particular and present a comparison
between them for the breakup of 15C on Pb at 68AMeV. We show the problem faced
by the models based on the eikonal approximation at low energy and detail a
correction that enables their extension down to lower beam energies. A new
reaction observable is also presented. It consists of the ratio between angular
distributions for two different processes, such as elastic scattering and
breakup. This ratio is completely independent of the reaction mechanism and
hence is more sensitive to the projectile structure than usual reaction
observables, which makes it a very powerful tool to study exotic structures far
from stability.Comment: Contribution to the proceedings of the XXI International School on
Nuclear Physics and Applications & the International Symposium on Exotic
Nuclei, dedicated to the 60th Anniversary of the JINR (Dubna) (Varna,
Bulgaria, 6-12 September 2015), 7 pages, 4 figure
A temporal versioned object-oriented data schema model
AbstractThis paper describes in a formal way a data schema model which introduces temporal and versioning schema features in an object-oriented environment. In our model, the schema is time dependent and the history of the changes which occur on its elements are kept into version hierarchies. A fundamental assumption behind our approach is that a new schema specification should not define a new database, so that previous schema definitions are considered as alternative design specifications, and consequently, existing data can be accessed in a consistent way using any of the defined schemas
- …