8,949 research outputs found
Role of the plasma-electrode bias and the transverse magnetic field upon H- ion extraction in the negative ion source
Non peer reviewedPublisher PD
Spin melting and refreezing driven by uniaxial compression on a dipolar hexagonal plate
We investigate freezing characteristics of a finite dipolar hexagonal plate
by the Monte Carlo simulation. The hexagonal plate is cut out from a piled
triangular lattice of three layers with FCC-like (ABCABC) stacking structure.
In the present study an annealing simulation is performed for the dipolar plate
uniaxially compressed in the direction of layer-piling. We find spin melting
and refreezing driven by the uniaxial compression. Each of the melting and
refreezing corresponds one-to-one with a change of the ground states induced by
compression. The freezing temperatures of the ground-state orders differ
significantly from each other, which gives rise to the spin melting and
refreezing of the present interest. We argue that these phenomena are
originated by a finite size effect combined with peculiar anisotropic nature of
the dipole-dipole interaction.Comment: Proceedings of the Highly Frustrated Magnetism (HFM2006) conference.
To appear in a special issue of J. Phys. Condens. Matte
Ordered magnetic and quadrupolar states under hydrostatic pressure in orthorhombic PrCu2
We report magnetic susceptibility and electrical resistivity measurements on
single-crystalline PrCu2 under hydrostatic pressure, up to 2 GPa, which
pressure range covers the pressure-induced Van Vleck
paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in
the susceptibility shows that in the pressure-induced magnetic state the
ordered 4f-moments lie in the ac-plane. We propose that remarkable pressure
effects on the susceptibility and resistivity are due to changes in the
quadrupolar state of O22 and/or O20 under pressure. We present a simple
analysis in terms of the singlet-singlet model.Comment: 14 pages, 9 figures submitted to Phys. Rev.
SMA/PdBI multiple line observations of the nearby Seyfert2 galaxy NGC 1068: Shock related gas kinematics and heating in the central 100pc?
We present high angular resolution (0.5-2.0") observations of the mm
continuum and the 12CO(J=3-2), 13CO(J=3-2), 13CO(J=2-1), C18O(J=2-1),
HCN(J=3-2), HCO+(J=4-3) and HCO+(J=3-2) line emission in the circumnuclear disk
(r=100pc) of the proto-typical Seyfert type-2 galaxy NGC1068, carried out with
the Submillimeter Array. We further include in our analysis new 13CO(J=1-0) and
improved 12CO(J=2-1) observations of NGC1068 at high angular resolution
(1.0-2.0") and sensitivity, conducted with the IRAM Plateau de Bure
Interferometer. Based on the complex dynamics of the molecular gas emission
indicating non-circular motions in the central ~100pc, we propose a scenario in
which part of the molecular gas in the circumnuclear disk of NGC1068 is
radially blown outwards as a result of shocks. This shock scenario is further
supported by quite warm (Tkin>=200K) and dense (nH2=10^4cm^-3) gas constrained
from the observed molecular line ratios. The HCN abundance in the circumnuclear
disk is found to be [HCN]/[12CO]=10^-3.5. This is slightly higher than the
abundances derived for galactic and extragalactic starforming/starbursting
regions. This results lends further support to X-ray enhanced HCN formation in
the circumnuclear disk of NGC1068, as suggested by earlier studies. The HCO+
abundance ([HCO+]/[12CO]=10^-5) appears to be somewhat lower than that of
galactic and extragalactic starforming/starbursting regions. When trying to fit
the cm to mm continuum emission by different thermal and non-thermal processes,
it appears that electron-scattered synchrotron emission yields the best results
while thermal free-free emission seems to over-predict the mm continuum
emission.Comment: accepted for publication by ApJ; 35pages, 22 figures and 6 tables (at
the end of the file); 3 figures have been decreased in quality to match size
limi
Metal Abundances in the ICM as a Diagnostics of the Cluster History
Galaxy clusters with a dense cooling core exhibit a central increase in the
metallicity of the intracluster medium. Recent XMM-Newton studies with detailed
results on the relative abundances of several heavy elements show that the high
central abundances are mostly due to the contribution from supernovae type Ia.
The dominant source is the stellar population of the central cluster galaxy.
With this identification of the origin of heavy elements and the observed rates
of SN Ia in elliptical galaxies, the central abundance peak can be used as a
diagnostic for the history of the cluster core region. We find for four nearby
cooling core clusters that the enrichment times for the central peaks are
larger than 6 - 10 Gyrs even for a higher SN Ia rate in the past. This points
to an old age and a relatively quiet history of these cluster core regions. A
detailed analysis of the element abundance ratios provides evidence that the SN
Ia yields in the central cluster galaxies are more rich in intermediate mass
elements, like Si and S, compared to the SN Ia models used to explain the heavy
element enrichment in our Galaxy.Comment: Advances in Space Research in press (proceedings of the COSPAR 2004
Assembly, Paris), 9 pages, 5 figure
Implications of the central metal abundance peak in cooling core clusters of galaxies
Recent XMM-Newton observations of clusters of galaxies have provided detailed
information on the distribution of heavy elements in the central regions of
clusters with cooling cores providing strong evidence that most of these metals
come from recent SN type Ia. In this paper we compile information on the
cumulative mass profiles of iron, the most important metallicity tracer. We
find that long enrichment times (larger than 5 Gyr) are necessary to produce
the central abundance peaks. Classical cooling flows, a strongly convective
intracluster medium, and a complete metal mixing by cluster mergers would
destroy the observed abundance peaks too rapidly. Thus the observations set
strong constraints on cluster evolution models requiring that the cooling cores
in clusters are preserved over very long times. We further conclude from the
observations that the innermost part of the intracluster medium is most
probably dominated by gas originating predominantly from stellar mass loss of
the cD galaxy.Comment: 5 pages, 4 figures, A&A in press. Astronomy and Astrophysics Letters,
in pres
Superconductivity in charge Kondo systems
We present a theory of superconductivity in charge Kondo systems, materials
with resonant quantum valence fluctuations, in the regime where the transition
temperature is comparable to the charge Kondo resonance. We find
superconductivity induced by charge Kondo impurities, study how pairing of a
superconducting host is enhanced due to charge Kondo centers and investigate
the interplay between Kondo-scattering and inter-impurity Josephson coupling.
We discuss the implications of our theory for Tl-doped PbTe, which has recently
been identified as a candidate charge Kondo system.Comment: 4 pages, 4 figures; revised version; detailed discussion on the
physics of Tl-doped PbTe adde
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