4,497 research outputs found
Exotic solutions in string theory
Solutions of classical string theory, correspondent to the world sheets,
mapped in Minkowsky space with a fold, are considered. Typical processes for
them are creation of strings from vacuum, their recombination and annihilation.
These solutions violate positiveness of square of mass and Regge condition. In
quantum string theory these solutions correspond to physical states |DDF>+|sp>
with non-zero spurious component.Comment: accepted in Il Nuovo Cimento A for publication in 199
Relativistic Coulomb problem for particles with arbitrary half-integer spin
Using relativistic tensor-bispinorial equations proposed in hep-th/0412213 we
solve the Kepler problem for a charged particle with arbitrary half-integer
spin interacting with the Coulomb potential.Comment: Misprints are correcte
Convective plan-form two-scale dynamos in a plane layer
We study generation of magnetic fields, involving large spatial scales, by
convective plan-forms in a horizontal layer. Magnetic modes and their growth
rates are expanded in power series in the scale ratio, and the magnetic eddy
diffusivity (MED) tensor is derived for flows, symmetric about the vertical
axis in a layer. For convective rolls magnetic eddy correction is demonstrated
to be always positive. For rectangular cell patterns, the region in the
parameter space of negative MED coincides with that of small-scale magnetic
field generation. No instances of negative MED in hexagonal cells are found. A
family of plan-forms with a smaller symmetry group than that of rectangular
cell patterns has been found numerically, where MED is negative for molecular
magnetic diffusivity over the threshold for the onset of small-scale magnetic
field generation.Comment: Latex. 24 pages with 3 Postscript figures, 19 references. Final
version (expanded Appendix 2, 4 references added, notation changed to a more
"user-friendly"), accepted in Geophysical and Astrophysical Fluid Dynamic
Modification of the RLA model for presenting a cluster system of a composite material with a fractal filler structure
The paper proposes a modification of the diffusion-limited aggregation model to study the properties of a cluster system. A computational experiment to determine the mutual influence of the sticking probability and the volume concentration of particles on the formation of fractal clusters in a cluster system was carried out in accordance with the second-order orthogonal central compositional plan (OCCP). As a result of a computational experiment in accordance with the OCCP, an equation was obtained for the dependence of the mass fractal dimension of clusters on the volume of particle concentration and the probability of adhesion of diffusing particles and cluster particles in the adhesion zone. This dependence was obtained in a range of volume concentration of particles from 2 to 5 % and the probability of adhesion of diffusing particles and particles of clusters in the adhesion zone from 0.2 to 1.The paper proposes a modification of the diffusion-limited aggregation model to study the properties of a cluster system. A computational experiment to determine the mutual influence of the sticking probability and the volume concentration of particles on the formation of fractal clusters in a cluster system was carried out in accordance with the second-order orthogonal central compositional plan (OCCP). As a result of a computational experiment in accordance with the OCCP, an equation was obtained for the dependence of the mass fractal dimension of clusters on the volume of particle concentration and the probability of adhesion of diffusing particles and cluster particles in the adhesion zone. This dependence was obtained in a range of volume concentration of particles from 2 to 5 % and the probability of adhesion of diffusing particles and particles of clusters in the adhesion zone from 0.2 to 1
Experimental observation of magnetic dimers in diluted Yb:YAlO
We present a comprehensive experimental investigation of Yb magnetic dimers
in YbYAlO, an Yb-doped Yttrium Aluminum Perovskite (YAP)
YAlO by means of specific heat, magnetization and high-resolution inelastic
neutron scattering (INS) measurements. In our sample, the Yb ions are randomly
distributed over the lattice and \% of Yb ions form quantum dimers due
to nearest-neighbor antiferromagnetic coupling along the -axis. At zero
field, the dimer formation manifests itself in an appearance of an inelastic
peak at ~meV in the INS spectrum and a Schottky-like
anomaly in the specific heat. The structure factor of the INS peak exhibits a
cosine modulation along the direction, in agreement with the -axis
nearest-neighbor intra-dimer coupling. A careful fitting of the low-temperature
specific heat shows that the excited state is a degenerate triplet, which
indicates a surprisingly small anisotropy of the effective Yb-Yb exchange
interaction despite the low crystal symmetry and anisotropic magnetic dipole
contribution, in agreement with previous reports for the Yb parent compound,
YbAlO [arXiv:1904.11513, arXiv:1902.04112], and in contrast to
YbPtPb [arXiv:1606.01309, arXiv:1907.01067]. The obtained results are
precisely reproduced by analytical calculations for the Yb dimers.Comment: 9 pages, 5 figure
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