1,596 research outputs found
Real-Space Renormalization Group (RSRG) Approach to Quantum Spin Lattice Systems
The paper describes an explicit variational modification of the standard RSRG
method and its application to quantum spin lattice systems. The modified
approach is applied to exactly solvable ITF, XX and isotropic Heisenberg
models. Better upper bounds for the systems' ground state energy are obtained
as compared to the standard RSRG approach.Comment: http://www.mff.cuni.cz/veda/konference/wds/proc/proc-contents.php?year=2011#phy
Relationship between the Elemental Abundances and the Kinematics of Galactic-Field RR Lyrae Stars
Data of our compiled catalog containing the positions, velocities, and
metallicities of 415 RR~Lyrae variable stars and the relative abundances
[el/Fe] of 12~elements for 101 RR~Lyrae stars, including four ~elements
(Mg, Ca, Si, and Ti), are used to study the relationships between the chemical
and spatial--kinematic properties of these stars. In general, the dependences
of the relative abundances of ~elements on metallicity and velocity for
the RR~Lyrae stars are approximately the same as those for field dwarfs.
Despite the usual claim that these stars are old, among them are
representatives of the thin disk, which is the youngest subsystem of the
Galaxy. Attention is called to the problem of low-metallicity RR~Lyrae stars.
Most RR~Lyrae stars that have the kinematic properties of thick disk stars have
metallicities and high ratios [/Fe], whereas only about 10\,\% of field dwarfs belonging to the so-called
"low-metallicity tail" have this chemical composition. At the same time, there
is a sharp change in [/Fe] in RR~Lyrae stars belonging just to the
thick disk, providing evidence for a long period of formation of this
subsystem. The chemical compositions of SDSS J1707+58, V455 Oph, MACHO
176.18833.411, V456 Ser, and BPS CS 30339--046 do not correspond to their
kinematics. While the first three of these stars belong to the halo, according
to their kinematics, the last two belong to the thick disk. It is proposed that
they are all most likely extragalactic, but the possible appearance of some of
them in the solar neighborhood as a result of the gravitational action of the
bar on field stars cannot be ruled out.Comment: 16 pages, 3 figures, 1 tabl
The Chemical Composition of Globular Clusters of Different Nature in our Galaxy
A catalog of Galactic globular clusters has been compiled and used to analyze
relations between the chemical and kinematic parameters of the clusters. The
catalog contains positions, distances, luminosities, metallicites, and
horizontal-branch morphology indices for 157~globular clusters, as well as
space velocities for 72~globular clusters. For 69~globular clusters, these data
are suppleented with the relative abundances of 28~chemical elements produced
in various nuclear-synthesis processes, taken from 101~papers published between
1986 and 2018. The tendency for redder horizontal branches in low-metallicity
accreted globular clusters is discussed. The discrepancy between the criteria
for cluster membership in the thick-disk and halo subsystems based on chemical
and kinematic properties is considered. This is manifest through the fact that
all metal-rich () clusters are located close to the center
and plane of the Galaxy, regardless of their kinematic membership in particular
Galaxy subsystems. An exception is three accreted clusters lost by a dwarf
galaxy in Sagittarius. At the same time, the fraction of more distant clusters
is high among metal-poorer clusters in any kinematically selected Galactic
subsystem.Comment: 21 pages, 4 figures, 2 table
Destruction of the phase coherence by the magnetic field in the fluctuation region of thin superconducting film
It was shown as long ago as 1998 cond-mat/9811051 that the vortex lattice
melting theories are science fiction because the Abrikosov state is not the
vortex lattice with crystalline long-range order. Nevertheless this false
conception is used up to now in many works including the lecture notes
cond-mat/0111052 providing a pedagogical introduction. This false conception
has resulted from visual but incorrect ideas. In spite of outward appearances
only long-range order - long-range phase coherence exists in the Abrikosov
state. The phase transition interpreted erroneously as the vortex lattice
melting is in reality a disappearance of long-range phase coherence. The
investigation of the nonlocal resistivity made in this work is experimental
evidence that a state without phase coherence, differed qualitatively from
mythical vortex liquid, is observed above this transition.Comment: 4 pages, 3 figure
Peculiarities of {\alpha}-element abundances in Galactic open clusters
A catalog compiling the parameters of 346 open clusters, including their
metallicities, positions, ages, and velocities has been composed. The elements
of the Galactic orbits for 272 of the clusters have been calculated.
Spectroscopic determinations of the relative abundances, [el/Fe], for 14
elements synthesized in various nuclear processes averaged over data from 109
publications are presented for 90 clusters. Since no systematic effects
distorting the relative abundances of the studied elements in these clusters
have been found, these difference suggest real differences between clusters
with high, elongated orbits and field stars. In particular, this supports the
earlier conclusion, based on an analysis of the elements of the Galactic
orbits, that some clusters formed as a result of interactions between
high-velocity, metal-poor clouds and the interstellar medium of the Galactic
thin disk. On average, clusterswith high, elongated orbits and metallicities
display lower relative abundances of the primary \'a
elements than do field stars. The low [O,Mg/Fe] ratios of these clusters can be
understood if the high-velocity clouds that gave rise to them were formed of
interstellar material from regions where the star-formation rate and/or the
masses of Type II supernovae were lower than near the Galactic plane. It is
also shown that, on average, the relative abundances of the primary
-elements are higher in relatively metal-rich clusters with high,
elongated orbits than in field stars. This can be understood if clusters with
formed as a result of interactions between metal-rich
clouds with intermediate velocities and the interstellar medium of the Galactic
disk; such clouds could form from returning gas in a so-called "Galactic
fountain".Comment: 23 pages, 5 figures, 2 table
Peculiarities of the abundances of neutron-capture elements in Galactic open clusters
The properties of the relative abundances of rapid and slow neutron-capture
elements are studied using a catalog containing spectroscopic abundance
determinations for 14~elements produced in various nuclear-synthesis processes
for 90~open clusters. The catalog also contains the positions, ages,
velocities, and elements of the Galactic orbits of the clusters. The relative
abundances of both -elements (Eu) and -elements (Y, Ba, La, and Ce) in
clusters with high, elongated orbits and in field stars of the Galactic thin
disk display different dependences on metallicity, age, Galactocentric
distance, and the elements of the Galactic orbits, supporting the view that
these objects have different natures. In young clusters, not only barium, but
also the three other studied -elements display significantly higher relative
abundances than field stars of the same metallicity. The relative abundances of
Eu are lower in high-metallicity clusters () with high,
elongated orbits than in field giants, on average, while the [Eu/Fe] ratios in
lower-metallicity clusters are the same as those in field stars, on average,
although with a large scatter. The metallicity dependence of the [O, Mg/Eu]
ratios in clusters with high, elongated orbits and in field stars are
substantially different. These and other described properties of the Eu
abundances, together with the properties of the abundances of primary
-elements, can be understood in a natural way if clusters with high,
elongated orbits with different metallicities formed as a result of
interactions of two types of high-velocity clouds with the interstellar medium
of the Galactic disk: low-metallicity high-velocity clouds that formed from
"primordial" gas, and high-metallicity clouds with intermediate velocities that
formed in "Galactic fountains".Comment: 14 pages, 3 figure
Annular Long Josephson Junctions in a Magnetic Field: Engineering and Probing the Fluxon Interaction Potential
The interaction of a Josephson fluxon with an external magnetic field-induced
potential in a long Josephson junction is investigated experimentally. The
thermal activation of the fluxon from a potential well is observed and
experiments probing its predicted quantum properties are discussed. A method
for engineering a magnetic double-well potential for a fluxon is proposed and
the use of the coupled fluxon states for quantum computation is suggested.Comment: 11 pages, 6 figure
Nonlocal electrodynamics of long ultra-narrow Josephson junctions: Experiment and theory
We experimentally and theoretically investigate electromagnetic cavity modes
in ultra-narrow Al-AlO-Al and Nb-AlO-Nb long Josephson junctions.
Experiments show that the voltage spacing between the Fiske steps on the
current-voltage characteristics of sub-m wide and several hundred m
long Al-AlO-Al and Nb-AlO-Nb Josephson junctions increases when
decreasing the width of a junction. This effect is explained by stray magnetic
fields, which become important for narrow junctions. Theoretical estimates of
the Fiske step voltage based on a nonlocal wave propagation equation are in
good agreement with our experimental data. Using the nonlocal model, we
determine the size and mass of a Josephson vortex by means of a variational
approach, and relate vortex size to the experimentally measured critical
magnetic field of the junction.Comment: Submitted to Phys. Rev.
On the scaling behaviour of the alternating spin chain
In this note we report the results of our study of a 1D integrable spin chain
whose critical behaviour is governed by a CFT possessing a continuous spectrum
of scaling dimensions. It is argued that the computation of the density of
Bethe states of the continuous theory can be reduced to the calculation of the
connection coefficients for a certain class of differential equations whose
monodromy properties are similar to those of the conventional confluent
hypergeometric equation. The finite size corrections to the scaling are also
discussed.Comment: 30 pages, 14 figure
Peculiarities of Abundances of Selected Elements in Metal-Rich Field RR Lyrae Stars
We use the data of our extended catalog of spectroscopic determinations of
elemental abundances in the atmospheres of Galactic-field RR Lyrae type
variables to show that metal-rich RR Lyraes () have
anomalous abundances of some elements. In particular, the relative abundances
of scandium, titanium, and yttrium in metal-rich RR Lyrae type variables are
lower than the corresponding abundances in field stars of similar metallicity
beyond the errors. We discuss the errors of the determination of the abundances
of the above elements and point out the fact that no europium, zirconium, and
lanthanum abundance determinations are available for metal-rich RR Lyrae type
variables. We also analyze various possible causes of the observed
peculiarities of the chemical composition of metal-rich RR Lyrae type
variables.Comment: 12 pages, 2 figures, 2 table
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