788 research outputs found
Synthesis of as-grown superconducting MgB_2 thin films by molecular beam epitaxy in UHV conditions
As-grown superconducting MgB_2 thin films have been grown on SrTiO_3(001),
MgO(001), and Al_2O_3(0001) substrates by a molecular beam epitaxy (MBE) method
with novel co-evaporation conditions of low deposition rate in ultra-high
vacuum. The structural and physical properties of the films were studied by
RHEED, XRD, electrical resistivity measurements, and SQUID magnetometer. The
RHEED patterns indicate three-dimensional growth for MgB_2. The highest T_c
determined by resistivity measurement was about 36K in these samples. And a
clear Meissner effect below T_c was observed using magnetic susceptibility
measurement. We will discuss the influence of B buffer layer on the structural
and physical properties.Comment: 9 pages with 4 figures, ISS2003 proceedin
Superconducting Gap and Pseudogap in Iron-Based Layered Superconductor La(OF)FeAs
We report high-resolution photoemission spectroscopy of newly-discovered
iron-based layered superconductor La(OF)FeAs (Tc = 24 K). We
found that the superconducting gap shows a marked deviation from the isotropic
s-wave symmetry. The estimated gap size at 5 K is 3.6 meV in the s- or axial
p-wave case, while it is 4.1 meV in the polar p- or d-wave case. We also found
a pseudogap of 15-20 meV above Tc, which is gradually filled-in with increasing
temperature and closes at temperature far above Tc similarly to copper-oxide
high-temperature superconductors.Comment: 4 pages, 3 figures, J. Phys. Soc. Jpn. Vol. 77, No. 6 (2008), in
pres
Penetration Depth and Anisotropy in MgB2
The penetration depth lambda of MgB2 was deduced from both the ac
susceptibility chi and the magnetization M(H) of sorted powders. The good
agreement between the two sets of data without geometric correction for the
grain orientation suggests that MgB2 is an isotropic superconductor.Comment: 9 pages, 5 figures; submitted to Physical Review B (February 28,
2001; revised June 28, 2001); reference list update
Influence of Rb, Cs and Ba on Superconductivity of Magnesium Diboride
Magnesium diboride has been thermally treated in the presence of Rb, Cs, and
Ba. Magnetic susceptibility shows onsets of superconductivity in the resulting
samples at 52K (Rb), 58K (Cs) and 45K (Ba). Room-temperature 11B NMR indicates
to cubic symmetry of the electric field gradient at boron site for the samples
reacted with Rb and Cs, in contrast to the axial symmetry in the initial MgB2
and in the sample treated with Ba.Comment: 3 pages (twocolumn), 2 figure
Doping Effect of Nano-Diamond on Superconductivity and Flux Pinning in MgB2
Doping effect of diamond nanoparticles on the superconducting properties of
MgB2 bulk material has been studied. It is found that the superconducting
transition temperature Tc of MgB2 is suppressed by the diamond-doping, however,
the irreversibility field Hirr and the critical current density Jc are
systematically enhanced. Microstructural analysis shows that the diamond-doped
MgB2 superconductor consists of tightly-packed MgB2 nano-grains (~50-100 nm)
with highly-dispersed and uniformly-distributed diamond nanoparticles (~10-20
nm) inside the grains. High density of dislocations and diamond nanoparticles
may take the responsibility for the enhanced flux pinning in the diamond-doped
MgB2.Comment: 16 pages, 6 figure
Inhibition of eukaryotic elongation factor-2 confers to tumor suppression by a herbal formulation Huanglian-Jiedu decoction in human hepatocellular carcinoma
ETHNOPHARMACOLOGICAL RELEVANCE:
An oriental medicinal formulation, Huanglian Jiedu Decoction (HLJDD), has been well documented in few Traditional Chinese Medicine Classics 1300 years ago for treatment of heat and dampness-related diseases. Its effect is well accepted in Asian community, including China, Japan and Korea. Recent studies have postulated HLJDD as a regimen for cancer treatment, especially liver cancer, but the underlying mechanism is unknown. The aim of this study was to examine the suppressive effect of HLJDD on the growth of hepatocellular carcinoma (HCC) and its possible underlying mechanism.
METHODS:
Chemical composition of HLJDD was analyzed by high performance liquid chromatography. The tumor suppressive effect of HLJDD was determined on both HCC cells and xenograft model. Nascent protein synthesis was detected with Click-IT protein labeling technology; protein expression was determined by immunoblotting and imunnohistochemical analysis.
RESULTS:
Quality analysis revealed that HLJDD of different batches is consistent in both chemical composition and bioactivities. HLJDD inhibited HCC cell proliferation at its non-toxic doses, and suppressed growth and angiogenesis in xenografted murine model. HLJDD suppressed the synthesis of nascent protein via inactivation of eEF2 without deregulating the translation initiation factors. The major components in HLJDD, geniposide, berberine and baicalin, additively act on eEF2, and contributed to the responsible activity. HLJDD-activated eEF2 kinase (eEF2K) led to eEF2 inactivation, and activation of AMPK signaling may be responsible for the eEF2K induction. Blocked AMPK activity in HLJDD-treated HCC cells attenuated eEF2K activation as well as the inhibitory effect of the formula. In nutrient deprived HCC cells with inactivated eEF2, the inhibitory effect of HLJDD in tumor cell expansion was interfered.
CONCLUSION:
Our results indicate that HLJDD has potential in blocking HCC progression with involvement of eEF2 inhibition.
Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.postprin
Precise Tight-binding Description of the Band Structure of MgB2
We present a careful recasting of first-principles band structure
calculations for MgB2 in a non-orthogonal sp-tight-binding (TB) basis. Our TB
results almost exactly reproduce our full potential linearized augmented plane
wave results for the energy bands, the densities of states and the total
energies. Our procedure generates transferable Slater-Koster parameters which
should be useful for other studies of this important material.Comment: REVTEX, 2 Encapsulated PostScript Figure
Flux flow resistivity in the two-gap superconductivity
We investigate the flux flow state in a two-gap superconductor in which two
s-wave gaps with different amplitudes exist on two separate Fermi surfaces. The
flux flow resistivity is obtained on the basis of the Bardeen-Stephen relation
and the result agrees well with the anomalous field dependence of the flow
resistivity recently observed in the two-gap superconductor MgB2. Some typical
properties of the vortex in this system are also discussed.Comment: 5 pages, 1 figure. Some typos are corrected. Some comments are added.
To be published in J. Phys. Soc. Jp
Indication of Superconductivity at 35 K in Graphite-Sulfur Composites
We report magnetization measurements performed on graphite--sulfur composites
which demonstrate a clear superconducting behavior below the critical
temperature T = 35 K. The Meissner-Ochsenfeld effect, screening
supercurrents, and magnetization hysteresis loops characteristic of type-II
superconductors were measured. The results indicate that the superconductivity
occurs in a small sample fraction, possibly related to the sample surface.Comment: published versio
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