412 research outputs found
Effect of Umklapp Scattering on Magnetic Field Penetration Depth in High-Tc Cuprates
The renormalization of the magnetic field penetration depth owing
to the electron-electron correlation is discussed with its application to
high- cuprates. The formula for the current carried by quasiparticle
with the Umklapp scattering is derived, on the basis of which we investigate
how the value of deviates from that of where and
are the carrier density and the effective mass respectively. Although
this deviation is small in the case of weak momentum dependence of the vertex,
this is large and negative owing to the non-negligible value of the backflow in
the case of the strong antiferromagnetic spin fluctuation. The observed doping
dependence of in high- cuprates, specifically a peak
structure at the slightly overdoped region, is explained by the analytical
consideration and the numerical calculation based on the perturbation theory
and the spin fluctuation theory. The consistency between and
at absolute zero, which is the problem the
isotropic model fails to explain, is also obtained by our theory.Comment: 25 pages, 9 figures. Another version(11 pages longer) will appear in
J. Phys. Soc. Jpn (2002) No.
Electrical Conductivity of Fermi Liquids. II. Quasiparticle Transport
We develop a general theory of Fermi liquids to discuss the Kadowaki-Woods
relation . We derive a formula for the ratio
which is expressed as a product of two dimensionless parameters and
, where represents a coupling constant for quasiparticle scattering
and is a geometric factor determined by the shape of the Fermi surface.
Then we argue that the universal ratio observed in heavy fermion compounds is
reproduced under the conditions and . The former is
regarded as a universality of Fermi liquids in a strong coupling regime, and
the latter is corroborated by evaluating definitely in simple cases. It is
noted that the proportional relation is just an example of the universal
phenomena to be expected for the whole class of strong coupling Fermi liquids.Comment: 28 pages, 7 figures; J. Phys. Soc. Jpn. Vol.67, No.1
Electrical Conductivity of Fermi Liquids. I. Many-body Effect on the Drude Weight
On the basis of the Fermi liquid theory, we investigate the many-body effect
on the Drude weight. In a lattice system, the Drude weight is modified by
electron-electron interaction due to Umklapp processes, while it is not
renormalized in a Galilean invariant system. This is explained by showing that
the effective mass for is defined through the current, not
velocity, of quasiparticle. It is shown that the inequality is required
for the stability against the uniform shift of the Fermi surface. The result of
perturbation theory applied for the Hubbard model indicates that as a
function of the density is qualitatively modified around half filling
by Umklapp processes.Comment: 20 pages, 2 figures; J. Phys. Soc. Jpn. Vol.67, No.
A swollen phase observed between the liquid-crystalline phase and the interdigitated phase induced by pressure and/or adding ethanol in DPPC aqueous solution
A swollen phase, in which the mean repeat distance of lipid bilayers is
larger than the other phases, is found between the liquid-crystalline phase and
the interdigitated gel phase in DPPC aqueous solution. Temperature, pressure
and ethanol concentration dependences of the structure were investigated by
small-angle neutron scattering, and a bending rigidity of lipid bilayers was by
neutron spin echo. The nature of the swollen phase is similar to the anomalous
swelling reported previously. However, the temperature dependence of the mean
repeat distance and the bending rigidity of lipid bilayers are different. This
phase could be a precursor to the interdigitated gel phase induced by pressure
and/or adding ethanol.Comment: 7 pages, 6 figure
Neutron lifetime measurement with pulsed cold neutrons
The neutron lifetime has been measured by comparing the decay rate with the
reaction rate of He nuclei of a pulsed neutron beam from the spallation
neutron source at the Japan Proton Accelerator Research Complex (J-PARC). The
decay rate and the reaction rate were determined by simultaneously detecting
electrons from the neutron decay and protons from the He(n,p)H reaction
using a gas chamber of which working gas contains diluted He. The measured
neutron lifetime was 898\,\pm\,10\,_{\rm stat}\,^{+15}_{-18}\,_{\rm sys}\,s.Comment: 28 pages, 20 figures, will be submitted to PTE
Measurement of tau polarization in e+ e- annihilation at sqrt{s}=58 GeV
The polarization of tau leptons in the reaction e+ e- --> tau+ tau- has been
measured using a e+e- collider, TRISTAN, at the center-of-mass energy of 58
GeV. From the kinematical distributions of daughter particles in tau --> e nu
nu-bar, mu nu nu-bar, rho nu or pi(K) nu decays, the average polarization of
tau- and its forward-backward asymmetry have been evaluated to be 0.012 +-
0.058 and 0.029 +- 0.057, respectively.Comment: 18 pages, 5 figure
Effects of combined treatment with rapamycin and cotylenin A, a novel differentiation-inducing agent, on human breast carcinoma MCF-7 cells and xenografts
INTRODUCTION: Rapamycin, an inhibitor of the serine/threonine kinase target of rapamycin, induces G(1 )arrest and/or apoptosis. Although rapamycin and its analogues are attractive candidates for cancer therapy, their sensitivities with respect to growth inhibition differ markedly among various cancer cells. Using human breast carcinoma cell line MCF-7 as an experimental model system, we examined the growth-inhibitory effects of combinations of various agents and rapamycin to find the agent that most potently enhances the growth-inhibitory effect of rapamycin. METHOD: We evaluated the growth-inhibitory effect of rapamycin plus various agents, including cotylenin A (a novel inducer of differentiation of myeloid leukaemia cells) to MCF-7 cells, using either MTT assay or trypan blue dye exclusion test. The cell cycle was analyzed using propidium iodide-stained nuclei. Expressions of several genes in MCF-7 cells with rapamycin plus cotylenin A were studied using cDNA microarray analysis and RT-PCR. The in vitro results of MCF-7 cells treated with rapamycin plus cotylenin A were further confirmed in vivo in a mouse xenograft model. RESULTS: We found that the sensitivity of rapamycin to MCF-7 cells was markedly affected by cotylenin A. This treatment induced growth arrest of the cells at the G(1 )phase, rather than apoptosis, and induced senescence-associated β-galactosidase activity. We examined the gene expression profiles associated with exposure to rapamycin and cotylenin A using cDNA microarrays. We found that expressions of cyclin G(2), transforming growth factor-β-induced 68 kDa protein, BCL2-interacting killer, and growth factor receptor-bound 7 were markedly induced in MCF-7 cells treated with rapamycin plus cotylenin A. Furthermore, combined treatment with rapamycin and cotylenin A significantly inhibited the growth of MCF-7 cells as xenografts, without apparent adverse effects. CONCLUSION: Rapamycin and cotylenin A cooperatively induced growth arrest in breast carcinoma MCF-7 cells in vitro, and treatment with rapamycin and cotylenin A combined more strongly inhibited the growth of MCF-7 cells as xenografts in vivo than treatment with rapamycin or cotylenin A alone, suggesting that this combination may have therapeutic value in treating breast cancer. We also identified several genes that were markedly modulated in MCF-7 cells treated with rapamycin plus cotylenin A
Theory of Electric Transport in the Pseudogap State of High-Tc Cuprates
We theoretically investigate the electric transport in the pseudogap state of
High-Tc cuprates. Starting from the repulsive Hubbard model, we perform the
microscopic calculation to describe the pseudogap phenomena which are induced
by the superconducting fluctuations. The single particle Green function, spin
susceptibility and superconducting fluctuations are self-consistently
determined by the SC-FLEX+T-matrix approximation. The longitudinal and
transverse conductivities are calculated by using the Eliashberg and
Kohno-Yamada formalism. The effects of the spin fluctuations and
superconducting fluctuations are estimated, respectively. The vertex
corrections arising from the two fluctuations are also calculated. The
additional contribution from the Aslamazov-Larkin term is also estimated beyond
the Eliashberg formalism.
It is shown that the main effect of the superconducting fluctuations is the
feedback effect through the spin fluctuations. The correct results are obtained
by considering the superconducting fluctuations and the spin fluctuations
simultaneously. The temperature and doping dependences of the resistivity and
the Hall coefficient are well explained. We point out that the characteristic
momentum dependence of the systems plays an essential role in this explanation.Comment: To appear in J. Phys. Soc. Jpn. Vol.71 No.1 (2002
An inclusive measurement of the photon energy spectrum in b->s gamma decays
We report a fully inclusive measurement of the flavour changing neutral
current decay b->s gamma in the energy range 1.8 GeV < E* < 2.8 GeV, covering
95% of the total spectrum. Using 140 fb^-1 we obtain BF(b->s gamma)= 3.55 +/-
0.32 +0.30-0.31 +0.11-0.07, where the errors are statistical, systematic and
from theory corrections. We also measure the first and second moments of the
photon energy spectrum above 1.8 GeV and obtain = 2.292 +/- 0.026 +/- 0.034
GeV and -^2 = 0.0305 +/- 0.0074 +/- 0.0063 GeV^2, where the errors are
statistical and systematic.Comment: RevTex4, 6 pages, Submitted to Phys.Rev.Lett. Replaced: added table
of systematic errors. New results take into account radiative J/Psi decay
Measurement of K^+K^- production in two-photon collisions in the resonant-mass region
K^+K^- production in two-photon collisions has been studied using a large
data sample of 67 fb^{-1} accumulated with the Belle detector at the KEKB
asymmetric e^+e^- collider. We have measured the cross section for the process
gamma gamma -> K^+ K^- for center-of-mass energies between 1.4 and 2.4 GeV, and
found three new resonant structures in the energy region between 1.6 and 2.4
GeV. The angular differential cross sections have also been measured.Comment: 24 pages, 8 figures, to appear in Euro. Phys. Jour.
- …