80 research outputs found
Stability of CFL cores in Hybrid Stars
We study the equation state of strongly interacting quark matter within a
NJL-like model in which the chiral condensates and the color superconducting
gaps are computed self-consistently as a function of the baryon density. A
vector interaction term is added to the Lagrangian in order to render the quark
matter equation of state stiffer. For the low density hadronic phase we use a
relativistic mean field model. The phase transition to quark matter is computed
by a Maxwell construction. We show that stable CFL cores in hybrid stars are
possible if the superconducting gap is sufficiently large. Moreover we find
stable stellar configurations in which two phase transitions occur, a first
transition from hadronic matter to 2SC quark matter and a second transition
from 2SC quark matter to CFL quark matter.Comment: 10 pages, 6 figure
`Similar' coordinate systems and the Roche geometry. Application
A new equivalence relation, named relation of 'similarity' is defined and
applied in the restricted three-body problem. Using this relation, a new class
of trajectories (named 'similar' trajectories) are obtained; they have the
theoretical role to give us new details in the restricted three-body problem.
The 'similar' coordinate systems allow us in addition to obtain a unitary and
an elegant demonstration of some analytical relations in the Roche geometry. As
an example, some analytical relations published in Astrophysical Journal by
Seidov in 2004 are demonstrated.Comment: 9 pages (preprint format), 9 figures, published in Astrophysics and
Space Scienc
Dynamical chaos in the problem of magnetic jet collimation
We investigate dynamics of a jet collimated by magneto-torsional
oscillations. The problem is reduced to an ordinary differential equation
containing a singularity and depending on a parameter. We find a parameter
range for which this system has stable periodic solutions and study
bifurcations of these solutions. We use Poincar\'e sections to demonstrate
existence of domains of regular and chaotic motions. We investigate transition
from periodic to chaotic solutions through a sequence of period doublings.Comment: 11 pages, 29 figures, 1 table, MNRAS (published online
Magnetic and vibrational properties of the covalent chain antiferromagnet RbFeS2
Ternary rubidium-iron sulfide, RbFeS2, belongs to a family of quasi-one-dimensional compounds with the general chemical composition AFeCh2 (where A – K, Rb, Cs, Tl; Ch – S, Se). Understanding the magnetic properties of these compounds is a challenge. The controversy concerning the spin-state of the iron ion needs to be resolved to build the proper model of magnetism. Single crystals of RbFeS2 were grown and characterized by powder x-ray diffraction. QD MPMS-5 SQUID magnetometry was used to measure the magnetic susceptibility, and specific heat was measured utilizing QD PPMS-9 setup. Above the transition to three-dimensional antiferromagnetic order at the Néel temperature of TN = 188 K, the susceptibility exhibits unusual quasi-linear increase up to the highest measured temperature of 500 K. The specific heat was measured in the temperature range 1.8 – 300 K. Ab initio phonon dispersion and density-of-states calculations were performed by means of density functional theory (DFT), and the calculated lattice specific heat was subtracted from the measured one giving the magnetic contribution to the specific heat. Our results suggest that the features of the magnetic specific heat are general for the whole family of the covalent chain ternary iron chalcogenides of the AFeCh2 structure and indicate an intermediate S = 3/2 spin state of the iron ion
Radiation measurements in the new tandem accelerator FEL
The measurements of both spontaneous and stimulated emissions of radiation in
the newly configured Israeli EA-FEL are made for the first time. The radiation
at the W-band was measured and characterized. The results match the predictions
of our earlier theoretical modeling and calculations.Comment: 4 pages, 3 figures, FEL 2003 Conference repor
Anisotropic exchange in LiCu2 O2
© 2017 American Physical Society. We investigate the magnetic properties of the multiferroic quantum-spin system LiCu2O2 by electron spin resonance (ESR) measurements at X- and Q-band frequencies in a wide temperature range (TN1≤T≤300 K). The observed anisotropies of the g tensor and the ESR linewidth in untwinned single crystals result from the crystal-electric field and from local exchange geometries acting on the magnetic Cu2+ ions in the zigzag-ladder-like structure of LiCu2O2. Supported by a microscopic analysis of the exchange paths involved, we show that both the symmetric anisotropic exchange interaction and the antisymmetric Dzyaloshinskii-Moriya interaction provide the dominant spin-spin relaxation channels in this material
Trapped and excited w modes of stars with a phase transition and R>=5M
The trapped -modes of stars with a first order phase transition (a density
discontinuity) are computed and the excitation of some of the modes of these
stars by a perturbing shell is investigated. Attention is restricted to odd
parity (``axial'') -modes. With the radius of the star, its mass,
the radius of the inner core and the mass of such core, it is
shown that stars with can have several trapped -modes, as long
as . Excitation of the least damped -mode is confirmed for
a few models. All of these stars can only exist however, for values of the
ratio between the densities of the two phases, greater than . We also
show that stars with a phase transition and a given value of can have far
more trapped modes than a homogeneous single density star with the same value
of , provided both and are smaller than 3. If the
phase transition is very fast, most of the stars with trapped modes are
unstable to radial oscillations. We compute the time of instability, and find
it to be comparable to the damping of the -mode excited in most cases where
-mode excitation is likely. If on the other hand the phase transition is
slow, all the stars are stable to radial oscillations.Comment: To appear in Physical Review
Scalar-Isovector Delta-Meson in the Relativistic Mean-Field Theory and the Structure of Neutron Stars with a Quark Core
In the framework of the relativistic mean-field theory, we have considered
the equation of state of superdense nuclear matter, taking into account an
effective scalar-isovector delta-meson field. The effect of the delta-meson
field on the characteristics of a Maxwell-type quark phase transition has been
studied. The quark phase is described with the aid of the improved version of
the MIT (Massachusetts Institute of Technology) bag model, in which
interactions between the u, d, s quarks inside the bag are taken into account
in the one-gluon exchange approximation. For different values of the bag
parameter B, series of neutron star models with a quark core have been built.
Stability problems for neutron stars with an infinitesimal quark core are
discussed. An estimate is obtained for the amount of energy released in a
catastrophic transformation of a critical neutron star to a star with a
finite-size quark core.Comment: 7 pages, 2 figures, Talk given at the International Conference
RUSGRAV-13, June 23-28, 2008, PFUR, Mosco
Magnetization of manganite thin films on ferroelectric substrates
© 2016 Elsevier B.V.Here we report the magnetic susceptibility measurements of magnetron sputtered orthorhombic manganite RMnO3 (R=Yb, Gd) thin films deposited on dielectric LaAlO3 and ferroelectric SrTiO3, LiNbO3 substrates. We observed that all of investigated o-RMnO3 films show a splitting in the temperature dependence of ZFC and FC magnetization curves. We found that the substrate can impact on the splitting temperature ZFC-FC curves and absolute value of the magnetization of thin films
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