2,825 research outputs found
SU(3) symmetry breaking in decay constants and electromagnetic properties of pseudoscalar heavy mesons
In this paper, the decay constants and mean square radii of pseudoscalar
heavy mesons are studied in the SU(3) symmetry breaking. Within the light-front
framework, the ratios and are individually
estimated using the hyperfine splittings in the and
states and the light quark masses, (), to
extract the wave function parameter . The values and are obtained, which are not only
chiefly determined by the ratio of light quark masses , but also
insensitive to the heavy quark masses and the decay constants
. The dependence of on with the
varied charm quark masses is also shown. In addition, the mean square radii are
estimated as well. The values and are obtained, and the sensitivities of on
the heavy and light quark masses are similar to those of the decay constants.Comment: 21 pages, 5 figures, 4 tables, some typos are corrected, version to
be published in Phys. Rev.
Photon-meson transition form factors of light pseudoscalar mesons
The photon-meson transition form factors of light pseudoscalar mesons , , and are systematically calculated in a
light-cone framework, which is applicable as a light-cone quark model at low
and is also physically in accordance with the light-cone pQCD approach
at large . The calculated results agree with the available experimental
data at high energy scale. We also predict the low behaviors of the
photon-meson transition form factors of , and , which are measurable in process via Primakoff
effect at JLab and DESY.Comment: 22 Latex pages, 7 figures, Version to appear in PR
Conductivity Due to Classical Phase Fluctuations in a Model For High-T_c Superconductors
We consider the real part of the conductivity, \sigma_1(\omega), arising from
classical phase fluctuations in a model for high-T_c superconductors. We show
that the frequency integral of that conductivity, \int_0^\infty \sigma_1
d\omega, is non-zero below the superconducting transition temperature ,
provided there is some quenched disorder in the system. Furthermore, for a
fixed amount of quenched disorder, this integral at low temperatures is
proportional to the zero-temperature superfluid density, in agreement with
experiment. We calculate \sigma_1(\omega) explicitly for a model of overdamped
phase fluctuations.Comment: 4pages, 2figures, submitted to Phys.Rev.
Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+d
Identifying the mechanism of superconductivity in the high-temperature
cuprate superconductors is one of the major outstanding problems in physics. We
report local measurements of the onset of superconducting pairing in the
high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+d using a
lattice-tracking spectroscopy technique with a scanning tunneling microscope.
We can determine the temperature dependence of the pairing energy gaps, the
electronic excitations in the absence of pairing, and the effect of the local
coupling of electrons to bosonic excitations. Our measurements reveal that the
strength of pairing is determined by the unusual electronic excitations of the
normal state, suggesting that strong electron-electron interactions rather than
low-energy (<0.1 volts) electron-boson interactions are responsible for
superconductivity in the cuprates
Non-linear Characteristics of Luttinger Liquids and Gated Hall Bars
Non-linear current voltage characteristics of a disordered Luttinger liquid
are calculated using a perturbative formalism. One finds non-universal power
law characteristics of the form which is valid
both in the superfluid phase when is small and also in the insulator phase
when is large. Mesoscopic voltage fluctuations are also calculated. One
finds \Var(\Delta V) \sim I^{4\tilde{g}-3}. Both the characteristic
and the voltage fluctuations exhibit universal power law behavior at the
superfluid insulator transition where \tilde{g}=\tot. The possible
application of these results to the non-linear transport properties of gated
Hall bars is discussed.Comment: 8 pages. 4 uuencoded tiff figures available upon request to
[email protected]
Quasi-Fermi Distribution and Resonant Tunneling of Quasiparticles with Fractional Charges
We study the resonant tunneling of quasiparticles through an impurity between
the edges of a Fractional Quantum Hall sample. We show that the one-particle
momentum distribution of fractionally charged edge quasiparticles has a
quasi-Fermi character. The density of states near the quasi-Fermi energy at
zero temperature is singular due to the statistical interaction of
quasiparticles. Another effect of this interaction is a new selection rule for
the resonant tunneling of fractionally charged quasiparticles: the resonance is
suppressed unless an integer number of {\em electrons} occupies the impurity.
It allows a new explanation of the scaling behavior observed in the mesoscopic
fluctuations of the conductivity in the FQHE.Comment: 7 pages, REVTeX 3.0, Preprint SU-ITP-93-1
Local Thermometry of Neutral Modes on the Quantum Hall Edge
A system of electrons in two dimensions and strong magnetic fields can be
tuned to create a gapped 2D system with one dimensional channels along the
edge. Interactions among these edge modes can lead to independent transport of
charge and heat, even in opposite directions. Measuring the chirality and
transport properties of these charge and heat modes can reveal otherwise hidden
structure in the edge. Here, we heat the outer edge of such a quantum Hall
system using a quantum point contact. By placing quantum dots upstream and
downstream along the edge of the heater, we can measure both the chemical
potential and temperature of that edge to study charge and heat transport,
respectively. We find that charge is transported exclusively downstream, but
heat can be transported upstream when the edge has additional structure related
to fractional quantum Hall physics.Comment: 24 pages, 18 figure
On the security of arbitrated quantum signature schemes
Due to potential capability of providing unconditional security, arbitrated
quantum signature (AQS) schemes, whose implementation depends on the
participation of a trusted third party, received intense attention in the past
decade. Recently, some typical AQS schemes were cryptanalyzed and improved. In
this paper, we analyze security property of some AQS schemes and show that all
the previous AQS schemes, no matter original or improved, are still insecure in
the sense that the messages and the corresponding signatures can be exchanged
among different receivers, allowing the receivers to deny accepting the
signature of an appointed message. Some further improvement methods on the AQS
schemes are also discussed.Comment: 4 pages, no figure
MRI detection of hepatic n-acetylcysteine uptake in mice
This proof-of-concept study looked at the feasibility of using a thiol–water proton exchange (i.e., CEST) MRI contrast to detect in vivo hepatic N-acetylcysteine (NAC) uptake. The feasibility of detecting NAC-induced glutathione (GSH) biosynthesis using CEST MRI was also investigated. The detectability of the GSH amide and NAC thiol CEST effect at B0 = 7 T was determined in phantom experiments and simulations. C57BL/6 mice were injected intravenously (IV) with 50 g L−1 NAC in PBS (pH 7) during MRI acquisition. The dynamic magnetisation transfer ratio (MTR) and partial Z-spectral data were generated from the acquisition of measurements of the upfield NAC thiol and downfield GSH amide CEST effects in the liver. The 1H-NMR spectroscopy on aqueous mouse liver extracts, post-NAC-injection, was performed to verify hepatic NAC uptake. The dynamic MTR and partial Z-spectral data revealed a significant attenuation of the mouse liver MR signal when a saturation pulse was applied at −2.7 ppm (i.e., NAC thiol proton resonance) after the IV injection of the NAC solution. The 1H-NMR data revealed the presence of hepatic NAC, which coincided strongly with the increased upfield MTR in the dynamic CEST data, providing strong evidence that hepatic NAC uptake was detected. However, this MTR enhancement was attributed to a combination of NAC thiol CEST and some other upfield MT-generating mechanism(s) to be identified in future studies. The detection of hepatic GSH via its amide CEST MRI contrast was inconclusive based on the current results
Thermal-Fluid Flow Transport Phenomenon over Slot-Perforated Flat Plates Placed in Narrow Channel
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76151/1/AIAA-25872-119.pd
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