742 research outputs found
Vertex degree distribution and arc endpoints degree distribution of graphs with a linear rule of preferential attachment and Pennock graphs
The article deals with two classes of growing random graphs following the
preferential attachment rule with a linear weight function, L-graphs, and
hybrid Pennock graphs. We determine the exact final vertex degree distribution
and the exact final two-dimensional arcs degree distributions of graphs under
consideration. The study proves that each hybrid Pennock graph is isomorphic to
a certain L graph and that the converse does not hold since there are no
Pennock graphs isomorphic to L graphs with negative displacements in the
expression for the linear weight function. A formula is derived that makes it
possible to determine the weight functions, which are used to generate graphs
with the required asymptotic power-law vertex degree distribution. The
reliability of the obtained results is confirmed by calculations using accurate
numerical methods and simulation modeling, i.e. by direct generating of the
graphs. The practical value of the results is demonstrated by an example of
their effective application for accurate calibration of a growing graph that
simulates a network of Internet at the level of autonomous systems.Comment: 12 pages, 8 figures, the article is prepared for the conference
"Mechanical Science and Technology Update" (MSTU-2019
Role of the rho meson in the description of pion electroproduction experiments at JLab
We study the p(e,e' pi+)n reaction in the framework of an effective
Lagrangian approach including nucleon, pi and rho meson degrees of freedom and
show the importance of the rho-meson t-pole contribution to sigmaT, the
transverse part of cross section. We test two different field representations
of the rho meson, vector and tensor, and find that the tensor representation of
the rho meson is more reliable in the description of the existing data. In
particular, we show that the rho-meson t-pole contribution, including the
interference with an effective non-local contact term, sufficiently improves
the description of the recent JLab data at invariant mass W less 2.2 GeV and Q2
less 2.5 GeV2/c2. A ``soft'' variant of the strong piNN and rhoNN form factors
is also found to be compatible with these data. On the basis of the successful
description of both the sigmaL and sigmaT parts of the cross section we discuss
the importance of taking into account the sigmaT data when extracting the
charge pion form factor Fpi from sigmaL.Comment: 23 pages, 6 figures, accepted for publication in Phys. Rev.
Breit - Wigner parameters of nucleon resonance S11(1535)
The result of partial - wave analysis of angular distributions for the
process gamma+p -> eta +p at the energies upto 2 GeV are given. From the energy
dependence of the regression coefficient a0(W) the reliable estimates of Breit
- Wigner parameters of S11(1535) - resonance and energy dependence of real and
imagenery parts of electric dipol amplitude E0+ and its phase were obtainedComment: 12 pages, 11 figure
A generalized Ramsey excitation scheme with suppressed light shift
We experimentally investigate a recently proposed optical excitation scheme
[V.I. Yudin et al., Phys. Rev. A 82, 011804(R)(2010)] that is a generalization
of Ramsey's method of separated oscillatory fields and consists of a sequence
of three excitation pulses. The pulse sequence is tailored to produce a
resonance signal which is immune to the light shift and other shifts of the
transition frequency that are correlated with the interaction with the probe
field. We investigate the scheme using a single trapped 171Yb+ ion and excite
the highly forbidden 2S1/2-2F7/2 electric-octupole transition under conditions
where the light shift is much larger than the excitation linewidth, which is in
the Hertz range. The experiments demonstrate a suppression of the light shift
by four orders of magnitude and an immunity against its fluctuations.Comment: 5 pages, 4 figure
Polystyrene-based nanocomposites with different fillers: fabrication and mechanical properties
The paper presents a comprehensive analysis of elastic properties of
polystyrene-based nanocomposites filled with different types of inclusions:
small spherical particles (SiO2 and Al2O3), alumosilicates (montmorillonite,
halloysite natural tubules and Mica) and carbon nanofillers (carbon black and
multi-walled carbon nanotubes). Composites were fabricated by melt technology.
The analysis of composite melts showed that the introduction of
Montmorillonite, Multi-walled carbon nanotubes, and Al2O3 particles provided an
increase in melt viscosity by an average of 2 to 5 orders of magnitude over the
pure polystyrene. Block samples of composites with different filler
concentrations were prepared, and their linear and nonlinear elastic properties
were studied. The introduction of more rigid particles led to a more profound
increase in the elastic modulus of the composite, with the highest rise of
about 80% obtained with carbon fillers. Carbon black particles provided also an
enhanced strength at break of about 20% higher than that of pure polystyrene.
The nonlinear elastic moduli of composites were shown to be more sensitive to
addition of filler particles to the polymer matrix than the linear ones. The
nonlinearity coefficient comprising the combination of linear and
nonlinear elastic moduli of a material demonstrated considerable changes
correlating with changes of the Young's modulus. The absolute value of
showed rise in 1.5-1.6 times in the CB- and HNT-containing composites as
compared to that of pure PS. The changes in nonlinear elasticity of fabricated
composites were compared with measurements of the parameters of bulk nonlinear
strain waves in them. Variations of wave velocity and decay decrement
correlated with observed enhancement of materials nonlinearity
Measurements of vector magnetic field using multiple electromagnetically induced transparency resonances in Rb vapor
We study intensity distribution of transmission resonances under the
conditions of electromagnetically induced transparency (EIT) with lin||lin
configuration in 87Rb vapor. We demonstrate that for various orientations of
the external magnetic field all seven resolved EIT resonances exhibit maxima or
minima at certain directions of the linear polarization of the laser field.
This effect can be used for development of a high-precision vector EIT
magnetometer.Comment: 4 pages, 4 figure
- …