8,091 research outputs found
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
First Detection of A Sub-kpc Scale Molecular Outflow in the Starburst Galaxy NGC 3628
We successfully detected a molecular outflow with a scale of 370-450 pc in
the central region of the starburst galaxy NGC 3628 through deep CO(1-0)
observations by using the Nobeyama Millimeter Array (NMA). The mass of the
outflowing molecular gas is ~2.8x10^7 M_sun, and the outflow velocity is
~90(+/-10) km s^{-1}. The expansion timescale of the outflow is 3.3-6.8 Myr,
and the molecular gas mass flow rate is 4.1-8.5 M_sun yr^{-1}. It requires
mechanical energy of (1.8-2.8)x10^{54} erg to create this sub-kpc scale
molecular outflow. In order to understand the evolution of the molecular
outflow, we compare the physical properties between the molecular outflow
observed from our NMA CO(1-0) data and the plasma gas from the soft X-ray
emission of the Chandra X-ray Observatory (CXO) archival data. We found that
the distribution between the molecular outflow and the strong plasma outflow
seems to be in a similar region. In this region, the ram pressure and the
thermal pressure of the plasma outflow are 10^{-(8-10)} dyne cm^{-2}, and the
thermal pressure of molecular outflow is 10^{-(11-13)} dyne cm^{-2}. This
implies the molecular outflow is still expanding outward. The molecular gas
consumption timescale is estimated as 17-27 Myr, and the total starburst
timescale is 20-34 Myr. The evolutionary parameter is 0.11-0.25, suggesting
that the starburst activity in NGC 3628 is still in a young stage.Comment: 15 pages, 14 figures, accepted by Ap
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
Single crystal MgB2 with anisotropic superconducting properties
The discovery of superconductor in magnesium diboride MgB2 with high Tc (39
K) has raised some challenging issues; whether this new superconductor
resembles a high temperature cuprate superconductor(HTS) or a low temperature
metallic superconductor; which superconducting mechanism, a phonon- mediated
BCS or a hole superconducting mechanism or other new exotic mechanism may
account for this superconductivity; and how about its future for applications.
In order to clarify the above questions, experiments using the single crystal
sample are urgently required. Here we have first succeeded in obtaining the
single crystal of this new MgB2 superconductivity, and performed its electrical
resistance and magnetization measurements. Their experiments show that the
electronic and magnetic properties depend on the crystallographic direction.
Our results indicate that the single crystal MgB2 superconductor shows
anisotropic superconducting properties and thus can provide scientific basis
for the research of its superconducting mechanism and its applications.Comment: 7 pages pdf fil
ALMA Observations of the Gravitational Lens SDP.9
We present long-baseline ALMA observations of the strong gravitational lens
H-ATLAS J090740.0-004200 (SDP.9), which consists of an elliptical galaxy at
lensing a background submillimeter galaxy into two
extended arcs. The data include Band 6 continuum observations, as well as CO
=65 molecular line observations, from which we measure an updated source
redshift of . The image morphology in the ALMA data is
different from that of the HST data, indicating a spatial offset between the
stellar, gas, and dust component of the source galaxy. We model the lens as an
elliptical power law density profile with external shear using a combination of
archival HST data and conjugate points identified in the ALMA data. Our best
model has an Einstein radius of and a
slightly steeper than isothermal mass profile slope. We search for the central
image of the lens, which can be used constrain the inner mass distribution of
the lens galaxy including the central supermassive black hole, but do not
detect it in the integrated CO image at a 3 rms level of 0.0471 Jy km
s.Comment: Accepted for publication in ApJL; 6 pages, 2 figures, 3 table
Staggered magnetism in LiVO at low temperatures probed by the muon Knight shift
We report on the muon Knight shift measurement in single crystals of LiV2O4.
Contrary to what is anticipated for the heavy-fermion state based on the Kondo
mechanism, the presence of inhomogeneous local magnetic moments is demonstrated
by the broad distribution of the Knight shift at temperatures well below the
presumed "Kondo temperature" ( K). Moreover, a significant
fraction ( %) of the specimen gives rise to a second component which
is virtually non-magnetic. These observations strongly suggest that the
anomalous properties of LiV2O4 originates from frustration of local magnetic
moments.Comment: 11 pages, 5 figures, sbmitted to J. Phys.: Cond. Mat
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