1,316 research outputs found
Coordinated design of coding and modulation systems
The joint optimization of the coding and modulation systems employed in telemetry systems was investigated. Emphasis was placed on formulating inner and outer coding standards used by the Goddard Spaceflight Center. Convolutional codes were found that are nearly optimum for use with Viterbi decoding in the inner coding of concatenated coding systems. A convolutional code, the unit-memory code, was discovered and is ideal for inner system usage because of its byte-oriented structure. Simulations of sequential decoding on the deep-space channel were carried out to compare directly various convolutional codes that are proposed for use in deep-space systems
Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction
We analyze the dynamics of the helical edge modes of a quantum spin Hall
state in the presence of a spatially non-uniform Rashba spin-orbit (SO)
interaction. A randomly fluctuating Rashba SO coupling is found to open a
scattering channel which causes localization of the edge modes for a weakly
screened electron-electron (e-e) interaction. A periodic modulation of the SO
coupling, with a wave number commensurate with the Fermi momentum, makes the
edge insulating already at intermediate strengths of the e-e interaction. We
discuss implications for experiments on edge state transport in a HgTe quantum
well.Comment: 4 pages, 2 figures; published versio
An upper bound on decoding bit-error probability with linear coding on extremely noisy channels
When concatenated coding schemes operate near channel capacity their component encoders may operate above capacity. The decoding bit-error performance of binary convolutional codes near and above capacity is investigate
Fermi-LAT Detection of a Break in the Gamma-Ray Spectrum of the Supernova Remnant Cassiopeia A
We report on observations of the supernova remnant Cassiopeia A in the energy
range from 100 MeV to 100 GeV using 44 months of observations from the Large
Area Telescope on board the Fermi Gamma-ray Space Telescope. We perform a
detailed spectral analysis of this source and report on a low-energy break in
the spectrum at GeV. By comparing the results with
models for the gamma-ray emission, we find that hadronic emission is preferred
for the GeV energy range.Comment: 18 pages, 5 figures, 2 tables, to be published in Ap
Description of a quantum convolutional code
We describe a quantum error correction scheme aimed at protecting a flow of
quantum information over long distance communication. It is largely inspired by
the theory of classical convolutional codes which are used in similar
circumstances in classical communication. The particular example shown here
uses the stabilizer formalism, which provides an explicit encoding circuit. An
associated error estimation algorithm is given explicitly and shown to provide
the most likely error over any memoryless quantum channel, while its complexity
grows only linearly with the number of encoded qubits.Comment: 4 pages, uses revtex4. Minor correction in the encoding and decoding
circuit
Local Spectral Weight of a Luttinger Liquid: Effects from Edges and Impurities
We calculate the finite-temperature local spectral weight (LSW) of a
Luttinger liquid with an "open" (hard wall) boundary. Close to the boundary the
LSW exhibits characteristic oscillations indicative of spin-charge separation.
The line shape of the LSW is also found to have a Fano-like asymmetry, a
feature originating from the interplay between electron-electron interaction
and scattering off the boundary. Our results can be used to predict how edges
and impurities influence scanning tunneling microscopy (STM) of one-dimensional
electron systems at low temperatures and voltage bias. Applications to STM on
single-walled carbon nanotubes are discussed.Comment: 15 pages, 10 figues, The latest version in pdf format is available at
http://www.physik.uni-kl.de/eggert/papers/LSW-LL.pd
Two-Species Reaction-Diffusion System with Equal Diffusion Constants: Anomalous Density Decay at Large Times
We study a two-species reaction-diffusion model where A+A->0, A+B->0 and
B+B->0, with annihilation rates lambda0, delta0 > lambda0 and lambda0,
respectively. The initial particle configuration is taken to be randomly mixed
with mean densities nA(0) > nB(0), and with the two species A and B diffusing
with the same diffusion constant. A field-theoretic renormalization group
analysis suggests that, contrary to expectation, the large-time density of the
minority species decays at the same rate as the majority when d<=2. Monte Carlo
data supports the field theory prediction in d=1, while in d=2 the
logarithmically slow convergence to the large-time asymptotics makes a
numerical test difficult.Comment: revised version (more figures, claim on exactnes of d=2 treatment
removed), 5 pages, 3 figures, RevTex, see related paper Phys. Rev. E, R3787,
(1999) or cond-mat/9901147, to appear in Phys. Rev.
Regional differences in health status in China : population health-related quality of life results from the National Health Services Survey 2008
Purpose: to measure, describe and analyse regional differences in health-related quality of life measured by EQ-5D in China. Data were obtained via face-to-face interviews on a national representative sample (n=120,703, 15-103 years). The EQ-5D instrument was used to measure health status.
Results: Rural areas had worse health status than urban areas. Health status was worst in western areas and best in eastern areas, and such disparities were profounder in rural areas. In urban areas, health status was best in middle-sized cities. In rural areas, health status increased with the economic development level of a county.
Conclusion: Our study enhances understanding of the urban-rural differences and east-middle-west differences in health and sheds light on inequalities in health status between different city categories in the urban areas and county categories in the rural areas.Swedish Research CouncilEuroQol Excutive OfficeAccepte
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