46,519 research outputs found
Measurement of the Scaling Property of Factorial Moments in Hadronic Z Decay
Both three- and one-dimensional studies of local multiplicity fluctuations in
hadronic Z decay are performed using data of the L3 experiment at LEP. The
normalized factorial moments in three dimensions exhibit power-law scaling,
indicating that the fluctuations are isotropic, which correspends to a
self-similar fractal. A detailed study of the corresponding one-dimensional
moments confirms this conclusion. However, two-jet subsamples have anisotropic
fluctuations, correspending to a self-affine fractal. These features are, at
least qualitatively, reproduced by the Monte Carlo models \JETSET and \HERWIG.Comment: 4 pages, 4 figures in eps, talk given at XXXI International Symposium
on Multiparticle Dynamics, Sept 1-7, 2001, Datong China. see
http://ismd31.ccnu.edu.cn
Unconditionally secure one-way quantum key distribution using decoy pulses
We report here a complete experimental realization of one-way decoy-pulse
quantum key distribution, demonstrating an unconditionally secure key rate of
5.51 kbps for a 25.3 km fibre length. This is two orders of magnitudes higher
than the value that can be obtained with a non-decoy system. We introduce also
a simple test for detecting the photon number splitting attack and highlight
that it is essential for the security of the technique to fully characterize
the source and detectors used.Comment: 10 pages, 5 figure
A Simplified Scheme of Estimation and Cancellation of Companding Noise for Companded Multicarrier Transmission Systems
Nonlinear companding transform is an efficient method to reduce the high peak-to-average power ratio (PAPR) of multicarrier transmission systems. However, the introduced companding noise greatly degrades the bit-error-rate (BER) performance of the companded multicarrier systems. In this paper, a simplified but effective scheme of estimation and cancellation of companding noise for the companded multicarrier transmission system is proposed. By expressing the companded signals as the summation of original signals added with a companding noise component, and subtracting this estimated companding noise from the received signals, the BER performance of the overall system can be significantly improved. Simulation results well confirm the great advantages of the proposed scheme over other conventional decompanding or no decompanding schemes under various situations
X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?
We investigate the X-ray properties of the Parkes sample of flat-spectrum
radio sources using data from the ROSAT All-Sky Survey and archival pointed
PSPC observations. In total, 163 of the 323 sources are detected. For the
remaining 160 sources 2 sigma upper limits to the X-ray flux are derived. We
present power-law photon indices for 115 sources, which were either determined
with a hardness ratio technique or from direct fits to pointed PSPC data. For
quasars, the soft X-ray photon index is correlated with redshift and with radio
spectral index. Webster et al. (1995) discovered many sources with unusually
red optical continua among the quasars of this sample and interpreted this
result in terms of extinction by dust. Although the X-ray spectra in general do
not show excess absorption, we find that low-redshift optically red quasars
have significantly lower soft X-ray luminosities on average than objects with
blue optical continua. The difference disappears for higher redshifts, as is
expected for intrinsic absorption by cold gas associated with the dust.
Alternative explanations are briefly discussed. We conclude, however, that dust
does play an important role in some of the radio-loud quasars with red optical
continua.Comment: 21 pages, 13 figures, to appear in MNRA
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