352,703 research outputs found
Local Lattice Instability and Superconductivity in LaSrCuMO (M=Mn, Ni, and Co)
Local lattice structures of LaSrCuMO (M=Mn,
Ni, and Co) single crystals are investigated by polarized extended x-ray
absorption fine structure (EXAFS). The local lattice instability at low
temperature is described by in-plane Cu-O bond splitting. We find that
substitution of Mn for Cu causes little perturbation of local lattice
instability while Ni and Co substitution strongly suppresses the instability.
The suppression of superconductivity by Cu-site substitution is related to the
perturbation of lattice instability, indicating that local lattice instability
(polaron) plays an important role in superconductivity
Sustainability in design: now! Challenges and opportunities for design research, education and practice in the XXI century
Copyright @ 2010 Greenleaf PublicationsLeNS project funded by the Asia Link Programme, EuropeAid, European Commission
Comparison of Magnetic Flux Distribution between a Coronal Hole and a Quiet Region
Employing Big Bear Solar Observatory (BBSO) deep magnetograms and H
images in a quiet region and a coronal hole, observed on September 14 and 16,
2004, respectively, we have explored the magnetic flux emergence, disappearance
and distribution in the two regions. The following results are obtained: (1)
The evolution of magnetic flux in the quiet region is much faster than that in
the coronal hole, as the flux appeared in the form of ephemeral regions in the
quiet region is 4.3 times as large as that in the coronal hole, and the flux
disappeared in the form of flux cancellation, 2.9 times as fast as in the
coronal hole. (2) More magnetic elements with opposite polarities in the quiet
region are connected by arch filaments, estimating from magnetograms and
H images. (3) We measured the magnetic flux of about 1000 magnetic
elements in each observing region. The flux distribution of network and
intranetwork (IN) elements is similar in both polarities in the quiet region.
For network fields in the coronal hole, the number of negative elements is much
more than that of positive elements. However for the IN fields, the number of
positive elements is much more than that of negative elements. (4) In the
coronal hole, the fraction of negative flux change obviously with different
threshold flux density. 73% of the magnetic fields with flux density larger
than 2 Gauss is negative polarity, and 95% of the magnetic fields is negative,
if we only measure the fields with their flux density larger than 20 Gauss. Our
results display that in a coronal hole, stronger fields is occupied by one
predominant polarity; however the majority of weaker fields, occupied by the
other polarity
Observation of Terahertz Radiation via the Two-Color Laser Scheme with Uncommon Frequency Ratios
In the widely-studied two-color laser scheme for terahertz (THz) radiation
from a gas, the frequency ratio of the two lasers is usually fixed at
1:2. We investigate THz generation with uncommon frequency
ratios. Our experiments show, for the first time, efficient THz generation with
new ratios of 1:4 and 2:3. We observe that the THz
polarization can be adjusted by rotating the longer-wavelength laser
polarization and the polarization adjustment becomes inefficient by rotating
the other laser polarization; the THz energy shows similar scaling laws with
different frequency ratios. These observations are inconsistent with multi-wave
mixing theory, but support the gas-ionization model. This study pushes the
development of the two-color scheme and provides a new dimension to explore the
long-standing problem of the THz generation mechanism.Comment: 6 pages, 3 figure
Effective nucleon-nucleon interactions and nuclear matter equation of state
Nuclear matter equations of state based on Skyrme, Myers-Swiatecki and
Tondeur interactions are written as polynomials of the cubic root of density,
with coefficients that are functions of the relative neutron excess .
In the extrapolation toward states far away from the standard one, it is shown
that the asymmetry dependence of the critical point ()
depends on the model used. However, when the equations of state are fitted to
the same standard state, the value of is almost the same in Skyrme
and in Myers-Swiatecki interactions, while is much lower in Tondeur
interaction. Furthermore, does not depend sensitively on the choice
of the parameter in Skyrme interaction.Comment: 15 pages, 9 figure
- …