12,196 research outputs found
Quantum transport properties of two-dimensional systems in disordered magnetic fields with a fixed sign
Quantum transport in disordered magnetic fields is investigated numerically
in two-dimensional systems. In particular, the case where the mean and the
fluctuation of disordered magnetic fields are of the same order is considered.
It is found that in the limit of weak disorder the conductivity exhibits a
qualitatively different behavior from that in the conventional random magnetic
fields with zero mean. The conductivity is estimated by the equation of motion
method and by the two-terminal Landauer formula. It is demonstrated that the
conductance stays on the order of even in the weak disorder limit. The
present behavior can be interpreted in terms of the Drude formula. The
Shubnikov-de Haas oscillation is also observed in the weak disorder regime.Comment: 6 pages, 7 figures, to appear in Phys. Rev.
Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals
We report the magnetotransport properties of
Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+\delta} (Zn-doped BSLCO) single crystals
with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane
resistivity and the Hall angle, we demonstrate that the nature of the
low-temperature normal state in the Zn-doped samples is significantly altered
from that in the pristine samples under high magnetic fields. In particular, we
observe nearly-isotropic negative magnetoresistance as well as an increase in
the Hall coefficient at very low temperatures in non-superconducting Zn-doped
samples, which we propose to be caused by the Kondo scattering from the local
moments induced by Zn impurities.Comment: 4 pages, 4 figures, final version (one reference added), published in
Phys. Rev.
Determination of Caries Lesion Activity: Reflection and Roughness for Characterization of Caries Progression
Used by permission. © Operative Dentistry, Inc. Transmission or reproduction of protected items beyond that allowed by fair use requires the written permission of Operative Dentistry, Inc.Caries lesion progression is difficult to determine with visual and tactile examinations. The hypothesis of this study was that reflection and roughness measurements could determine caries progression. Ground/polished sound human enamel specimens were analyzed at baseline (sound) and after two four-day demineralization periods for reflection using optical reflectometry (ORef) and for roughness using optical surface profilometry (SPro). Specimens were demineralized using a microbial–Streptococcus mutans aries model. Comparisons among the periods for ORef and SPro were performed using repeated measures analysis of variance. Two-sample t-tests were used for differences in transverse microradiography. The integrated mineral loss and depth of the four-day demineralization period were significantly smaller than those for the eight-day demineralization period (p<0.01). With increased demineralization time, reflection was significantly decreased and roughness was significantly increased (p<0.01). Correlation between ORef and SPro was moderate (r=−0.63). Both reflection and roughness can be characterized for nondestructive longitudinal assessment of caries lesion progression
Twists of K-theory and TMF
We explore an approach to twisted generalized cohomology from the point of
view of stable homotopy theory and quasicategory theory provided by
arXiv:0810.4535. We explain the relationship to the twisted K-theory provided
by Fredholm bundles. We show how our approach allows us to twist elliptic
cohomology by degree four classes, and more generally by maps to the four-stage
Postnikov system BO. We also discuss Poincare duality and umkehr maps in
this setting
The Corporate Cost of Capital in Japan and the U.S.: A Comparison
This paper presents evidence about the coats of corporate capital in Japan and the US, for a sample of large companies, and evaluates a variety of hypotheses about why the cost might be lower in Japan.We find that the before-tax return to capital in Japan appears slightly lower than in the U.S. when corrected book measures of earnings are used, but that this result would be reversed if market returns to Japanese equity were used in place of corrected earningsto measure the cost of equity.To what ever extent the cost of capital may actually be lower in Japan, we show that this is unlikely to be due either to a lower overall corporate tax burden or the particular tax advantages of corporate borrowing.
Parity-violating asymmetry in with a pionless effective theory
Nuclear parity violation is studied with polarized neutrons in the
photodisintegration of the deuteron at low energies. A pionless effective field
theory with di-baryon fields is used for the investigation. Hadronic weak
interactions are treated by parity-violating di-baryon-nucleon-nucleon
vertices, which have undetermined coupling contants. A parity-violating
asymmetry in the process is calculated for the incident photon energy up to 30
MeV. If experimental data for the parity-violating asymmetry become available
in the future, we will be able to determine the unknown coupling contants in
the parity-violating vertices.Comment: 4 pages. A contribution to APFB2011, August 22-26, 2011, Seoul, Kore
Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta}
We measure the normal-state in-plane resistivity of La-doped Bi-2201 single
crystals at low temperatures by suppressing superconductivity with 60-T pulsed
magnetic fields. With decreasing hole doping, we observe a crossover from a
metallic to insulating behavior in the low-temperature normal state. This
crossover is estimated to occur near 1/8 doping, well inside the underdoped
regime, and not at optimum doping as reported for other cuprates. The
insulating regime is marked by a logarithmic temperature dependence of the
resistivity over two decades of temperature, suggesting that a peculiar charge
localization is common to the cuprates.Comment: 4 pages, 5 figures, accepted for publication in PR
Ando, Lavrov, and Segawa Reply
Authors' Reply to the Comment by Janossy et al. [cond-mat/0005275] on our
article, "Magnetoresistance Anomalies in Antiferromagnetic
YBa_{2}Cu_{3}O_{6+x}: Fingerprints of Charged Stripes" [cond-mat/9905071, Phys.
Rev. Lett. 83, 2813 (1999)].Comment: 1 page, 1 figure, accepted for publication in PR
Conductance plateau transitions in quantum Hall wires with spatially correlated random magnetic fields
Quantum transport properties in quantum Hall wires in the presence of
spatially correlated disordered magnetic fields are investigated numerically.
It is found that the correlation drastically changes the transport properties
associated with the edge state, in contrast to the naive expectation that the
correlation simply reduces the effect of disorder. In the presence of
correlation, the separation between the successive conductance plateau
transitions becomes larger than the bulk Landau level separation determined by
the mean value of the disordered magnetic fields. The transition energies
coincide with the Landau levels in an effective magnetic field stronger than
the mean value of the disordered magnetic field. For a long wire, the strength
of this effective magnetic field is of the order of the maximum value of the
magnetic fields in the system. It is shown that the effective field is
determined by a part where the stronger magnetic field region connects both
edges of the wire.Comment: 7 pages, 10 figure
Electron Interactions and Scaling Relations for Optical Excitations in Carbon Nanotubes
Recent fluorescence spectroscopy experiments on single wall carbon nanotubes
reveal substantial deviations of observed absorption and emission energies from
predictions of noninteracting models of the electronic structure. Nonetheless,
the data for nearly armchair nanotubes obey a nonlinear scaling relation as a
function the tube radius . We show that these effects can be understood in a
theory of large radius tubes, derived from the theory of two dimensional
graphene where the coulomb interaction leads to a logarithmic correction to the
electronic self energy and marginal Fermi liquid behavior. Interactions on
length scales larger than the tube circumference lead to strong self energy and
excitonic effects that compete and nearly cancel so that the observed optical
transitions are dominated by the graphene self energy effects.Comment: 4 page
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