1,663 research outputs found
Magnetic Excitations in the Quasi-1D Ising-like Antiferromagnet TlCoCl
Neutron inelastic scattering measurements have been performed in order to
investigate the magnetic excitations in the quasi-1D Ising-like antiferromagnet
TlCoCl. We observed the magnetic excitation, which corresponds to the
spin-wave excitation continuum corresponding to the domain-wall pair excitation
in the 1D Ising-like antiferromagnet. According to the Ishimura-Shiba theory,
we analyzed the observed spin-wave excitation, and the exchange constant
and the anistropy were estimated as 14.7 meV and 0.14 in TlCoCl,
respectively.Comment: 2 pages, 3 figures, jpsj2.cls, to be published in J. Phys. Soc. Jpn.
Vol.75 (2006) No.
Susceptibility of the one-dimensional, dimerized Hubbard model
We show that the zero temperature susceptibility of the one-dimensional,
dimerized Hubbard model at quarter-filling can be accurately determined on the
basis of exact diagonalization of small clusters. The best procedure is to
perform a finite-size scaling of the spin velocity , and to calculate
the susceptibility from the Luttinger liquid relation . We
show that these results are reliable by comparing them with the analytical
results that can be obtained in the weak and strong coupling limits. We have
also used quantum Monte Carlo simulations to calculate the temperature
dependence of the susceptibility for parameters that should be relevant to the
Bechgaard salts. This shows that, used together, these numerical techniques are
able to give precise estimates of the low temperature susceptibility of
realistic one-dimensional models of correlated electrons.Comment: 10 pages, latex, figures available from the authors. To appear in
Phys. Rev. B, Rapid Comm
Elastic Convection in Vibrated Viscoplastic Fluids
We observe a new type of behavior in a shear thinning yield stress fluid:
freestanding convection rolls driven by vertical oscillation. The convection
occurs without the constraint of container boundaries yet the diameter of the
rolls is spontaneously selected for a wide range of parameters. The transition
to the convecting state occurs without hysteresis when the amplitude of the
plate acceleration exceeds a critical value. We find that a non-dimensional
stress, the stress due to the inertia of the fluid normalized by the yield
stress, governs the onset of the convective motion.Comment: 4 pages, 6 figure
The calpastatin-derived calpain inhibitor CP1B reduces mRNA expression of matrix metalloproteinase-2 and-9 and invasion by leukemic THP-1 cells
The ubiquitous proteases μ- and m-calpain are Ca2+-dependent cysteine endopeptidases. Besides involvement in a variety of physio(patho)logical processes, recent studies suggest a pivotal role of calpains in differentiation of hematopoietic cells and tumor cell invasion. However, the precise actions of calpains and their endogenous inhibitor, calpastatin, in these processes are only partially understood. Here we have studied the role of the calpain/calpastatin system in the invasion of leukemic cells under basal and differentiationstimulating conditions. To further differentiate the human leukaemic cell line THP-1 (monocytic), the cells were treated for 24 hours with the differentiationstimulating reagents phorbol 12-myristate 13-acetate (PMA) and dimethyl sulfoxide (DMSO). Macrophage and granulocytelike differentiation was confirmed by induction of vimentin expression as well as by microscopic and fluorescence assisted cytometric analysis. Extracellular matrix (ECM) invasion of both the basal and differentiation stimulated cells in a Matrigel assay was inhibited by preincubation of the cells with the specific calpain inhibitor CP1B for 24 hours. Inhibition of invasiveness correlated with decreased mRNA expression and secretion of the matrix metalloproteinases MMP-2 and MMP-9. In contrast, addition of CP1B only during the invasion process did neither influence transmigration nor MMP release. This is the first report showing that the calpain/calpastatin system mediates MMPmRNA expression of the leukemic THP-1 cells and as a consequence their invasiveness
Polarized Neutron Inelastic Scattering Study of the Anisotropic Magnetic Fluctuations in the Quasi-1D Ising-like Antiferromagnet TlCoCl
Polarized neutron inelastic scattering experiments have been carried out in
the quasi-1D Ising-like antiferromagnet TlCoCl. We observed the
longitudinal magnetic fluctuation for the spin-wave
excitation continuum, which has not been observed in the unpolarized neutron
inelastic scattering experiments of the quasi-1D Ising-like antiferromagnets
CsCoCl and TlCoCl so far, together with the transverse magnetic
fluctuation . We compared both obtained intensities of
and with the perturbation theory from
the pure Ising limit by Ishimura and Shiba, and a semi-quantitative agreement
was found.Comment: 5 pages, 5 figures, jpsj2.cls, to be published in J. Phys. Soc. Jpn.
Vol. 75 (2006) No.
Resonant Impurity States in the D-Density-Wave Phase
We study the electronic structure near impurities in the d-density-wave (DDW)
state, a possible candidate phase for the pseudo-gap region of the
high-temperature superconductors. We show that the local DOS near a
non-magnetic impurity in the DDW state is {\it qualitatively} different from
that in a superconductor with -symmetry. Since this result is a
robust feature of the DDW phase, it can help to identify the nature of the two
different phases recently observed by scanning tunneling microscopy experiments
in the superconducting state of underdoped Bi-2212 compounds
Nearly universal crossing point of the specific heat curves of Hubbard models
A nearly universal feature of the specific heat curves C(T,U) vs. T for
different U of a general class of Hubbard models is observed. That is, the
value C_+ of the specific heat curves at their high-temperature crossing point
T_+ is almost independent of lattice structure and spatial dimension d, with
C_+/k_B \approx 0.34. This surprising feature is explained within second order
perturbation theory in U by identifying two small parameters controlling the
value of C_+: the integral over the deviation of the density of states
N(\epsilon) from a constant value, characterized by \delta N=\int d\epsilon
|N(\epsilon)-1/2|, and the inverse dimension, 1/d.Comment: Revtex, 9 pages, 6 figure
Nonequilibrium Current in the One Dimensional Hubbard Model at Half-Filling
Nonlinear transport in the one dimensional Hubbard model at half-filling
under a finite bias voltage is investigated by the adaptive time-dependent
density matrix renormalization group method. For repulsive on-site interaction,
dielectric breakdown of the Mott insulating ground state to a current-carrying
nonequilibrium steady state is clearly observed when the voltage exceeds the
charge gap. It is found that by increasing the voltage further the
current-voltage characteristics are scaled only by the charge gap and the
scaling curve exhibits almost linear dependence on the voltage whose slope is
suppressed by the electron correlation. In the case of attractive interaction
the linear conductance is the perfect one which agrees with the
prediction by the Luttinger liquid theory.Comment: 4 pages, 7 figure
Tail States in Disordered Superconductors with Magnetic Impurities: the Unitarity Limit
When subject to a weak magnetic impurity distribution, the order parameter
and quasi-particle energy gap of a weakly disordered bulk s-wave superconductor
are suppressed. In the Born scattering limit, recent investigations have shown
that `optimal fluctuations' of the random impurity potential can lead to the
nucleation of `domains' of localised states within the gap region predicted by
the conventional Abrikosov-Gor'kov mean-field theory, rendering the
superconducting system gapless at any finite impurity concentration. By
implementing a field theoretic scheme tailored to the weakly disordered system,
the aim of the present paper is to extend this analysis to the consideration of
magnetic impurities in the unitarity scattering limit. This investigation
reveals that the qualitative behaviour is maintained while the density of
states exhibits a rich structure.Comment: 18 pages AMSLaTeX (with LaTeX2e), 6 eps figure
Crossover from Spin-Density-Wave to Neel-like Ground state
The characterization and evolution of a Spin Density Wave into the Quantum
Neel ground state is considered in the context of a weak coupling theory of the
half-filled Hubbard model. Magnetic properties obtained from this weak coupling
approach in one dimension compare favorably with exact results from Bethe
ansatz (BA). A study of the evolution of several length scales from weak to
strong coupling is also presented.Comment: [email protected] Pages: 18 (REVTEX 3.0). 6 postscript figures
available upon reques
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