2,634 research outputs found
Transition Property For Cube-Free Words
We study cube-free words over arbitrary non-unary finite alphabets and prove
the following structural property: for every pair of -ary cube-free
words, if can be infinitely extended to the right and can be infinitely
extended to the left respecting the cube-freeness property, then there exists a
"transition" word over the same alphabet such that is cube free. The
crucial case is the case of the binary alphabet, analyzed in the central part
of the paper.
The obtained "transition property", together with the developed technique,
allowed us to solve cube-free versions of three old open problems by Restivo
and Salemi. Besides, it has some further implications for combinatorics on
words; e.g., it implies the existence of infinite cube-free words of very big
subword (factor) complexity.Comment: 14 pages, 5 figure
A Pulsational Model for the Orthogonal Polarization Modes in Radio Pulsars
In an earlier paper, we introduced a model for pulsars in which non-radial
oscillations of high spherical degree (\el) aligned to the magnetic axis of a
spinning neutron star were able to reproduce subpulses like those observed in
single-pulse measurements of pulsar intensity. The model did not address
polarization, which is an integral part of pulsar emission. Observations show
that many pulsars emit radio waves that appear to be the superposition of two
linearly polarized emission modes with orthogonal polarization angles. In this
paper, we extend our model to incorporate linear polarization. As before, we
propose that pulsational displacements of stellar material modulate the pulsar
emission, but now we apply this modulation to a linearly-polarized mode of
emission, as might be produced by curvature radiation. We further introduce a
second polarization mode, orthogonal to the first, that is modulated by
pulsational velocities. We combine these modes in superposition to model the
observed Stokes parameters in radio pulsars.Comment: 19 pages, 4 figures accepted Ap
INFLUENCE OF THE SEA-SIDE RESORT FACTORS UPON FIBRINOLYTIC ACTIVITY OF PATIENTS WITH HYPERTENSION
No abstrac
Ellipticity and Deviations from Orthogonality in the Polarization Modes of PSR B0329+54
We report on an analysis of the polarization of single pulses of PSR B0329+54
at 328 MHz. We find that the distribution of polarization orientations in the
central component diverges strongly from the standard picture of orthogonal
polarization modes (OPMs), making a remarkable partial annulus on the Poincare
sphere. A second, tightly clustered region of density appears in the opposite
hemisphere, at a point antipodal to the centre of the annulus. We argue that
this can be understood in terms of birefringent alterations in the relative
phase of two elliptically polarized propagation modes in the pulsar
magnetosphere (i.e. generalised Faraday rotation). The ellipticity of the modes
implies a significant charge density in the plasma, while the presence of both
senses of circular polarization, and the fact that only one mode shows the
effect, supports the view that refracted ordinary-mode rays are involved in the
production of the annulus. At other pulse longitudes the polarization
(including the circular component) is broadly consistent with an origin in
elliptical OPMs, shown here quantitatively for the first time, however
considerable non-orthogonal contributions serve to broaden the orientation
distribution in an isotropic manner.Comment: 13 pages, 5 figures, to appear in A&
Refraction in a pulsar magnetosphere - the effect of a variable emission height on pulse morphology
The Petrova (2000) model to calculate pulse profiles is extended to a
variable emission height model to make it physically self-consistent. In this
context variable means that the emission height is no longer considered to be
the same for different magnetic field lines. The pulse profiles calculated
using this new model seem to be less realistic due to a focusing effect and
cannot be used to fit (typical) multifrequency pulsar observations. Apart from
the focusing effect the general morphology of pulse profiles is not greatly
affected by introducing a variable emission height. Additional extensions of
the model will be needed to be able to fit observations, and several
suggestions are made.Comment: 7 pages, 5 figures, accepted to A&
Compositional stability of FePt nanoparticles on SiO2/Si during annealing
The loss of Fe due to oxidation or diffusion into the substrate can prevent the successful preparation of well-ordered, stoichiometric, FePt nanoparticles. In this work we report the composition changes during annealing observed for small ( \u3c 10 nm) FePt nanoparticles on thermally grown SiO2 layers on Si wafer substrates. Additionally, we describe the use of a controlled reducing gas mixture, Ar+H-2+H2O, to reduce the loss of Fe
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