951 research outputs found
A fast, preconditioned conjugate gradient Toeplitz and Toeplitz-like solvers
AbstractFor a Toeplitz or Toeplitz-like matrix T, we define a preconditioning applied to the symmetrized matrix THT, which decreases the condition number compared to the one of THT and even the one of T. This enables us to accelerate the conjugate gradient algorithm for solving Toepiltz and Toeplitz-like linear systems, thus extending the previous results of [1], restricted to the Hermitian positive definite case. The extension relies on some recent formulae of Gohberg and Olshevsky for the inverses of Toeplitz-like matrices
Теоретичні аспекти процесу реструктуризації в умовах антикризового управління
У статті розкрито сутність поняття "реструктуризація", окреслено чинники, які викликають необхідність реструктуризаційних змін, визначено цілі та види реструктуризації, а також запропоновано ряд перспективних напрямів та відповідних заходів її проведення.Essence of concept "restructuring" is exposed in the article, outlined factors which cause the necessity of
restrukturizaciynikh changes, certainly aims and types of restructuring, and also the row of perspective directions
and proper measures of its leadthrough is offered
Charge ordering in charge-compensated by oxonium ions
Charge ordering behavior is observed in the crystal prepared through the
immersion of the crystal in distilled water. Discovery of the
charge ordering in the crystal with Na content less than 0.5 indicates that the
immersion in water brings about the reduction of the
. The formal valence of Co changes from +3.59 estimated from
the
Na content to +3.5, the same as that in . The charge
compensation is confirmed to arise from the intercalation of the oxonium ions
as occurred in the superconducting sodium cobalt oxide
bilayer-hydrate.\cite{takada1}
The charge ordering is the same as that observed in . It
suggests that the Co valence of +3.5 is necessary for the charge ordering.Comment: 5 pages, 4 figure
Magnetic phase diagram in EuLaFeAs single crystals
We have systematically measured resistivity, susceptibility and specific heat
under different magnetic fields (H) in EuLaFeAs single
crystals. It is found that a metamagnetic transition from A-type
antiferromagnetism to ferromagnetism occurs at a critical field for magnetic
sublattice of . The jump of specific heat is suppressed and shifts to
low temperature with increasing H up to the critical value, then shifts to high
temperature with further increasing H. Such behavior supports the metamagnetic
transition. Detailed H-T phase diagrams for x=0 and 0.15 crystals are given,
and possible magnetic structure is proposed. Magnetoresistance measurements
indicate that there exists a strong coupling between local moment of
and charge in Fe-As layer. These results are very significant to understand the
underlying physics of FeAs superconductors.Comment: 5 pages, 4 figure
Transition Form Factor up to within the Factorization Approach
In the paper, we apply the factorization approach to deal with the
transition form factor in the large recoil
regions. The B-meson wave functions and that include the
three-particle Fock states' contributions are adopted to give a consistent PQCD
analysis of the form factor up to . It has been found that
both the wave functions and can give sizable
contributions to the form factor and should be kept for a better understanding
of the meson decays. Then the contributions from different twist structures
of the kaon wavefunction are discussed, including the -breaking
effects. A sizable contribution from the twist-3 wave function is
found, whose model dependence is discussed by taking two group of parameters
that are determined by different distribution amplitude moments obtained in the
literature. It is also shown that and
, which are more
reasonable and consistent with the light-cone sum rule results in the large
recoil regions.Comment: 22 pages and 6 figure
A Dithienylbenzothiadiazole Pure Red Molecular Emitter with Electron Transport and Exciton Self-Confinement for Nondoped Organic Red-Light-Emitting Diodes
An amorphous photoluminescent material based on a dithienylbenzothiadiazole structure has been used for the fabrication of organic red-light-emitting diodes. The synergistic effects of the electron-transport ability and exciton confinement of the emitting material allow for the fabrication of efficient pure-red-light-emitting devices without a hole blocker
Three-Particle Correlations from Parton Cascades in Au+Au Collisions
We present a study of three-particle correlations among a trigger particle
and two associated particles in Au + Au collisions at = 200 GeV
using a multi-phase transport model (AMPT) with both partonic and hadronic
interactions. We found that three-particle correlation densities in different
angular directions with respect to the triggered particle (`center', `cone',
`deflected', `near' and `near-away') increase with the number of participants.
The ratio of `deflected' to `cone' density approaches to 1.0 with the
increasing of number of participants, which indicates that partonic Mach-like
shock waves can be produced by strong parton cascades in central Au+Au
collisions.Comment: 9 pages, 6 figures; Final version to appear in Physics Letters
Narrow width of a glueball decay into two mesons
The widths of a glueball decay to two pions or kaons are analyzed in the pQCD
framework. Our results show that the glueball ground state has small branching
ratio for two-meson decay mode, which is around . The predicted values
are consistent with the data of if particle is a
glueball. Applicability of pQCD to the glueball decay and comparison
with decay are also discussed.Comment: 12 pages, revtex, 2 ps figure
XUV digital in-line holography using high-order harmonics
A step towards a successful implementation of timeresolved digital in-line
holography with extreme ultraviolet radiation is presented. Ultrashort XUV
pulses are produced as high-order harmonics of a femtosecond laser and a
Schwarzschild objective is used to focus harmonic radiation at 38 nm and to
produce a strongly divergent reference beam for holographic recording.
Experimental holograms of thin wires are recorded and the objects
reconstructed. Descriptions of the simulation and reconstruction theory and
algorithms are also given. Spatial resolution of few hundreds of nm is
potentially achievable, and micrometer resolution range is demonstrated.Comment: 8 pages, 8 figure
Semileptonic decays and Charmonium distribution amplitude
In this paper we study the semileptonic decays of the meson in the
Light-Cone Sum Rule (LCSR) approach. The result for each channel depends on the
corresponding distribution amplitude of the final meson. For the case of
decaying into a pseudoscalar meson, to twist-3 accuracy only the leading twist
distribution amplitude (DA) is involved if we start from a chiral current. If
we choose a suitable chiral current in the vector meson case, the main twist-3
contributions are also eliminated and we can consider the leading twist
contribution only. The leading twist distribution amplitudes of the charmonium
and other heavy mesons are given by a model approach in the reasonable way.
Employing this charmonium distribution amplitude we find the cross section
which is consistent with Belle
and BaBar's data. Based on this model, we calculate the form factors for
various decay modes in the corresponding regions. Extrapolating the form
factors to the whole kinetic regions, we get the decay widths and branching
ratios for various decay modes including their modes when they are
kinematically accessible.Comment: Changed content partially, Added references, 16 pages,2 figure
- …