709 research outputs found
Universality in a Class of Q-Ball Solutions: An Analytic Approach
The properties of Q-balls in the general case of a sixth order potential have
been studied using analytic methods. In particular, for a given potential, the
initial field value that leads to the soliton solution has been derived and the
corresponding energy and charge have been explicitly evaluated. The proposed
scheme is found to work reasonably well for all allowed values of the model
parameters.Comment: 9 Pages, 6 Figure
Kink-antikink interactions in the double sine-Gordon equation and the problem of resonance frequencies
We studied the kink-antikink collision process for the "double sine-Gordon"
(DSG) equation in 1+1 dimensions at different values of the potential parameter
. For small values of we discuss the problem of resonance frequencies.
We give qualitative explanation of the frequency shift in comparison with the
frequency of the discrete level in the potential well of isolated kink. We show
that in this region of the parameter the effective long-range interaction
between kink and antikink takes place.Comment: 9 pages, LaTeX, 4 figures (eps
Three-Dimensional Magnetohydrodynamics Simulations Of Counter-Helicity Spheromak Merging In The Swarthmore Spheromak Experiment
Recent counter-helicity spheromak merging experiments in the Swarthmore Spheromak Experiment (SSX) have produced a novel compact torus (CT) with unusual features. These include a persistent antisymmetric toroidal magnetic field profile and a slow, nonlinear emergence of the n = 1 tilt mode. Experimental measurements are inconclusive as to whether this unique CT is a fully merged field-reversed configuration (FRC) with strong toroidal field or a partially merged doublet CT configuration with both spheromak- and FRC-like characteristics. In this paper, the SSX merging process is studied in detail using three-dimensional resistive MHD simulations from the Hybrid Magnetohydrodynamics (HYM) code. These simulations show that merging plasmas in the SSX parameter regime only partially reconnect, leaving behind a doublet CT rather than an FRC. Through direct comparisons, we show that the magnetic structure in the simulations is highly consistent with the SSX experimental observations. We also find that the n = 1 tilt mode begins as a fast growing linear mode that evolves into a slower-growing nonlinear mode before being detected experimentally. A simulation parameter scan over resistivity, viscosity, and line-tying shows that these parameters can strongly affect the behavior of both the merging process and the tilt mode. In fact, merging in certain parameter regimes is found to produce a toroidal-field-free FRC rather than a doublet CT. (C) 2011 American Institute of Physics. [doi:10.1063/1.3660533
Metal-insulator transition induced by 16O -18O oxygen isotope exchange in colossal negative magnetoresistance manganites
The effect of 16O-18O isotope exchange on the electric resistivity was
studied for (La(1-y)Pr(y))0.7Ca0.3MnO3 ceramic samples. Depending on y, this
mixed perovskite exhibited different types of low-temperature behavior ranging
from ferromagnetic metal (FM) to charge ordered (CO) antiferromagnetic
insulator. It was found that at y=0.75, the substitution of 16O by 18O results
in the reversible transition from a FM to a CO insulator at zero magnetic
field. The applied magnetic field (H >= 2 T) transformed the sample with 18O
again to the metallic state and caused the increase in the FM transition
temperature Tc of the 16O sample. As a result, the isotope shift of Tc at H = 2
T was as high as 63 K. Such unique sensitivity of the system to oxygen isotope
exchange, giving rise even to the metal-insulator transition, is discussed in
terms of the isotope dependence of the effective electron bandwidth which
shifts the balance between the CO and FM phases.Comment: 5 pages (RevTeX), 2 eps figures included, to appear in J. Appl. Phys.
83, (1998
Spectroscopic Observation Of Simultaneous Bi-Directional Reconnection Outflows In A Laboratory Plasma
We report a precise, direct spectroscopic measurement of simultaneous bi-directional outflows from a reconnection event in a laboratory plasma. Outflow speeds are as Alfvenic and Abel analysis shows that the outflows are generated in the plasma core. A Sweet-Parker like analysis of outflow speed coupled with external measurements of reconnection electric field and assumption of Spitzer resistivity predict an aspect ratio of the reconnection layer and reconnection rate that are close to that measured in the experiment and in simulations. However, this analysis underestimates the absolute scale of the layer, indicating other than 2D resistive physics is at play. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4747345
Example of a self-consistent solution for a fermion on domain wall
We discuss a self-consistent solution for a fermion coupled to static scalar
field in the form of a kink (domain wall). In particular, we study the case
when the fermion occupies an excited non-zero frequency level in the presence
of the domain wall field. The effect of the domain wall profile distortion is
calculated analytically.Comment: 9 pages, no figures; minor corrections, one reference added, results
unchange
Superlattices Consisting of "Lines" of Adsorbed Hydrogen Atom Pairs on Graphene
The structures and electron properties of new superlattices formed on
graphene by adsorbed hydrogen molecules are theoretically described. It has
been shown that superlattices of the (n, 0) zigzag type with linearly arranged
pairs of H atoms have band structures similar to the spectra of (n, 0) carbon
nanotubes. At the same time, superlattices of the (n, n) type with a
"staircase" of adsorbed pairs of H atoms are substantially metallic with a high
density of electronic states at the Fermi level and this property distinguishes
their spectra from the spectra of the corresponding (n, n) nanotubes. The
features of the spectra have the Van Hove form, which is characteristic of each
individual superlattice. The possibility of using such planar structures with
nanometer thickness is discussed.Comment: 5 pages, 4 figure
Multiskyrmions and baryonic bags
Analytical treatment of skyrmions given by rational map (RM) ansaetze
proposed recently for the Skyrme model is extended to the model including the
6-th order term in chiral fields derivatives in the lagrangian (the SK6 variant
of the model) and used for calculation of different properties of
multiskyrmions. For special class of profile functions approximating the true
profile and the domain wall behaviour at the same time, the masses and other
static properties of multiskyrmions are expressed in terms of the Euler-type
integrals. An upper bound is obtained for the masses of RM multiskyrmions which
is close to the calculated masses, especially at large B. The gap between
rigorous upper bound and lower bound, obtained for the SK6 model as well, for
large B multiskyrmions is less than 9%, in comparison with about 4% for the SK4
(Skyrme) variant. The basic properties of such bubbles of matter are
investigated, some of them, e.g. the thickness of the bubbles envelope, being
of universal character, i.e. they do not depend on baryon number of
configuration, or reveal a simple and natural dependence. The dependence of
these properties on the number of flavours is absent or very weak in both
models. Qualitatively, the properties of the baryonic bags are the same for the
SK6 and SK4 variants of the model, although differ in some details.Comment: 16 pages, no figure
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