20,310 research outputs found
Mechanism of magnetism in stacked nanographite: Theoretical study
Nanographite systems, where graphene sheets of the orders of the nanometer
size are stacked, show novel magnetic properties, such as, spin-glass like
behaviors and the change of ESR line widths in the course of gas adsorptions.
We theoretically investigate stacking effects in the zigzag nanographite sheets
by using a tight binding model with the Hubbard-like onsite interactions. We
find a remarkable difference in the magnetic properties between the simple A-A
and A-B type stackings. For the simple stacking, there are not magnetic
solutions. For the A-B stacking, we find antiferromagnetic solutions for strong
onsite repulsions. The local magnetic moments tend to exist at the edge sites
in each layer due to the large amplitude of wavefunctions at these sites.
Relations with experiments are discussed.Comment: PACS numbers: 75.30.-m, 75.70.Cn, 75.10.Lp, 75.40.Mg; E-mail:
[email protected]; http://www.etl.go.jp/~harigaya/welcome_E.htm
A Nomographic Methodology for Use in Performance Trade-Off Studies of Parabolic Dish Solar Power Modules
A simple graphical method was developed to undertake technical design trade-off studies for individual parabolic dish models comprising a two-axis tracking parabolic dish with a cavity receiver and power conversion assembly at the focal point. The results of these technical studies are then used in performing the techno-economic analyses required for determining appropriate subsystem sizing. Selected graphs that characterize the performance of subsystems within the module were arranged in the form of a nomogram that would enable an investigator to carry out several design trade-off studies. Key performance parameters encompassed in the nomogram include receiver losses, intercept factor, engine rating, and engine efficiency. Design and operation parameters such as concentrator size, receiver type (open or windowed aperture), receiver aperture size, operating temperature of the receiver and engine, engine partial load characteristics, concentrator slope error, and the type of reflector surface, are also included in the graphical solution. Cost considerations are not included
Effect of disorder outside the CuO planes on of copper oxide superconductors
The effect of disorder on the superconducting transition temperature
of cuprate superconductors is examined. Disorder is introduced into the cation
sites in the plane adjacent to the CuO planes of two single-layer
systems, BiSrLnCuO and
LaNdSrCuO. Disorder is controlled by changing
rare earth (Ln) ions with different ionic radius in the former, and by varying
the Nd content in the latter with the doped carrier density kept constant. We
show that this type of disorder works as weak scatterers in contrast to the
in-plane disorder produced by Zn, but remarkably reduces suggesting
novel effects of disorder on high- superconductivity.Comment: 5 pages, 5 figures, to be published in Phys. Rev. Let
The X-ray Structure of A399 and A401: A Pre-Merging Cluster Pair
We present {\em ASCA} results of the pair clusters A399 and A401. The region
between the two clusters exhibits excess X-rays over the value expected with a
simple superposition of the two clusters. We see, however, no temperature rise
at the merging front; the temperature is near the average of those in the inner
regions of the two clusters. These indicate that the two clusters are really
interacting but it is not strong at present.
The inner regions of the two clusters show no radial variations of
temperature, abundance and absorption values. We set upper-limits of mass
deposition rate of cooling flow to be and
for A399 and A401, respectively. A hint of
azimuthal variation of the temperature is also found.Comment: 17 pages, 13 postscript figures, 2 external tables, accepted for
publication in PAS
The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks
We investigate the origin of the variation of the gas mass fraction in the
core of galaxy clusters, which was indicated by our work on the X-ray
fundamental plane. The adopted model supposes that the gas distribution
characterized by the slope parameter is related to the preheated temperature.
Comparison with observations of relatively hot (~> 3 keV) and low redshift
clusters suggests that the preheated temperature is about 0.5-2 keV, which is
higher than expected from the conventional galactic wind model and possibly
suggests the need for additional heating such as quasars or gravitational
heating on the largest scales at high redshift. The dispersion of the preheated
temperature may be attributed to the gravitational heating in subclusters. We
calculate the central gas fraction of a cluster from the gas distribution,
assuming that the global gas mass fraction is constant within a virial radius
at the time of the cluster collapse. We find that the central gas density thus
calculated is in good agreement with the observed one, which suggests that the
variation of gas mass fraction in cluster cores appears to be explained by
breaking the self-similarity in clusters due to preheated gas. We also find
that this model does not change major conclusions on the fundamental plane and
its cosmological implications obtained in previous papers, which strongly
suggests that not only for the dark halo but also for the intracluster gas the
core structure preserves information about the cluster formation.Comment: 17 pages, to be published in Ap
Direct Observation of Non-Monotonic dx2-y2-Wave Superconducting Gap in Electron-Doped High-Tc Superconductor Pr0.89LaCe0.11CuO4
We performed high-resolution angle-resolved photoemission spectroscopy on
electron-doped high-Tc superconductor Pr0.89LaCe0.11CuO4 to study the
anisotropy of the superconducting gap. The observed momentum dependence is
basically consistent with the dx2-y2-wave symmetry, but obviously deviates from
the monotonic dx2-y2 gap function. The maximum gap is observed not at the zone
boundary, but at the hot spot where the antiferromagnetic spin fluctuation
strongly couples to the electrons on the Fermi surface. The present
experimental results unambiguously indicate the spin-mediated pairing mechanism
in electron-doped high-Tc superconductors.Comment: 4 pages, 4 figure
Electronic phase diagram of LaBaSrCuO
We performed systematic measurements of magnetic susceptibility on single
crystals of LaBaSrCuO. The dependence of the
superconducting transition temperature on Sr-concentration demonstrates a
step-like pattern upon doping at {\it x}0.08 as the crystal structure
changes from low-temperature tetragonal (LTT) to low-temperature orthorhombic
(LTO) phase at low temperature. Upon cooling, an anomalous upturn in the
susceptibility was observed at the structural phase transition between the
LTT-LTO phases under the magnetic field parallel to {\it c}-axis.Comment: 6 pages, 4 figures, Proceeding paper of the Stripes2000 conference in
Roma, Ital
- …