205,452 research outputs found
Optical conductivity of one-dimensional narrow-gap semiconductors
The optical conductivities of two one-dimensional narrow-gap semiconductors,
anticrossing quantum Hall edge states and carbon nanotubes, are studied using
bosonization method. A lowest order renormalization group analysis indicates
that the bare band gap can be treated perturbatively at high
frequency/temperature. At very low energy scale the optical conductivity is
dominated by the excitonic contribution, while at temperature higher than a
crossover temperature the excitonic features are eliminated by thermal
fluctuations. In case of carbon nanotubes the crossover temperature scale is
estimated to be 300 K.Comment: RevTeX4 file, 6 pages, no figur
Determination of electron-nucleus collision geometry with forward neutrons
There are a large number of physics programs one can explore in
electron-nucleus collisions at a future electron-ion collider. Collision
geometry is very important in these studies, while the measurement for an
event-by-event geometric control is rarely discussed in the prior deep
inelastic scattering experiments off a nucleus. This paper seeks to provide
some detailed studies on the potential of tagging collision geometries through
forward neutron multiplicity measurements with a zero degree calorimeter. This
type of geometry handle, if achieved, can be extremely beneficial in
constraining nuclear effects for the electron-nucleus program at an
electron-ion collider
Reduction of blocking artifacts in both spatial domain and transformed domain
In this paper, we propose a bi-domain technique to reduce the blocking artifacts commonly incurred in image processing. Some pixels are sampled in the shifted image block and some high frequency components of the corresponding transformed block are discarded. By solving for the remaining unknown pixel values and the transformed coefficients, a less blocky image is obtained. Simulation results using the Discrete Cosine Transform and the Slant Transform show that the proposed algorithm gives a better quantitative result and image quality than that of the existing methods
Giant Shapiro Resonances in a Flux Driven Josephson Junction Necklace
We present a detailed study of the dynamic response of a ring of equally
spaced Josephson junctions to a time-periodic external flux, including
screening current effects. The dynamics are described by the resistively
shunted Josephson junction model, appropriate for proximity effect junctions,
and we include Faraday's law for the flux. We find that the time-averaged
characteristics show novel {\em subharmonic giant Shapiro voltage resonances},
which strongly depend on having phase slips or not, on , on the inductance
and on the external drive frequency. We include an estimate of the possible
experimental parameters needed to observe these quantized voltage spikes.Comment: 8 pages RevTeX, 3 figures available upon reques
Evidence for an incommensurate magnetic resonance in La(2-x)Sr(x)CuO(4)
We study the effect of a magnetic field (applied along the c-axis) on the
low-energy, incommensurate magnetic fluctuations in superconducting
La(1.82)Sr(0.18)CuO(4). The incommensurate peaks at 9 meV, which in zero-field
were previously shown to sharpen in q on cooling below T_c [T. E. Mason et al.,
Phys. Rev. Lett. 77, 1604 (1996)], are found to broaden in q when a field of 10
T is applied. The applied field also causes scattered intensity to shift into
the spin gap. We point out that the response at 9 meV, though occurring at
incommensurate wave vectors, is comparable to the commensurate magnetic
resonance observed at higher energies in other cuprate superconductors.Comment: 8 pages, including 4 figure
Charge-Density-Wave Ordering in the Metal-Insulator Transition Compound PrRu4P12
X-ray and electron diffraction measurements on the metal-insulator (M-I)
transition compound PrRuP have revealed the emergence of a periodic
ordering of charge density around the Pr atoms. It is found that the ordering
is associated with the onset of a low temperature insulator phase. These
conclusions are supported by the facts that the space group of the crystal
structure transforms from Im to Pm below the M-I transition
temperature and also that the temperature dependence of the superlattice peaks
in the insulator phase follows the squared BCS function. The M-I transition
could be originated from the perfect nesting of the Fermi surface and/or the
instability of the electrons.Comment: 4 pages, 5 figures, Phys. Rev. B (2004) (in press
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