19,675 research outputs found
Quantum transfer matrix method for one-dimensional disordered electronic systems
We develop a novel quantum transfer matrix method to study thermodynamic
properties of one-dimensional (1D) disordered electronic systems. It is shown
that the partition function can be expressed as a product of local
transfer matrices. We demonstrate this method by applying it to the 1D
disordered Anderson model. Thermodynamic quantities of this model are
calculated and discussed.Comment: 7 pages, 10 figure
Superposition of photon- and phonon- assisted tunneling in coupled quantum dots
We report on electron transport through an artificial molecule formed by two
tunnel coupled quantum dots, which are laterally confined in a two-dimensional
electron system of an AlGaAs/GaAs heterostructure. Coherent
molecular states in the coupled dots are probed by photon-assisted tunneling
(PAT). Above 10 GHz, we observe clear PAT as a result of the resonance between
the microwave photons and the molecular states. Below 8 GHz, a pronounced
superposition of phonon- and photon-assisted tunneling is observed. Coherent
superposition of molecular states persists under excitation of acoustic
phonons.Comment: 5 pages, 4 figure
Effect of collision dephasing on atomic evolutions in a high-Q cavity
The decoherence mechanism of a single atom inside a high-Q cavity is studied,
and the results are compared with experimental observations performed by M.
Brune et al. [Phys. Rev. Lett. 76, 1800 (1996)]. Collision dephasing and cavity
leakage are considered as the major sources giving rise to decoherence effect.
In particular, we show that the experimental data can be fitted very well by
assuming suitable values of collision Stark shifts and dark count rate in the
detector
XMM-Newton View of PKS 2155-304: Characterizing the X-ray Variability Properties with EPIC-PN
Starting from XMM-Newton EPIC-PN data, we present the X-ray variability
characteristics of PKS 2155-304 using a simple analysis of the excess variance,
\xs, and of the fractional rms variability amplitude, fvar. The scatter in \xs\
and \fvar, calculated using 500 s long segments of the light curves, is smaller
than the scatter expected for red noise variability. This alone does not imply
that the underlying process responsible for the variability of the source is
stationary, since the real changes of the individual variance estimates are
possibly smaller than the large scatters expected for a red noise process. In
fact the averaged \xs and \fvar, reducing the fluctuations of the individual
variances, chang e with time, indicating non-stationary variability. Moreover,
both the averaged \sqxs (absolute rms variability amplitude) and \fvar show
linear correlation with source flux but in an opposite sense: \sqxs correlates
with flux, but \fvar anti-correlates with flux. These correlations suggest that
the variability process of the source is strongly non-stationary as random
scatters of variances should not yield any correlation. \fvar spectra were
constructed to compare variability amplitudes in different energy bands. We
found that the fractional rms variability amplitude of the source, when
significant variability is observed, increases logarithmically with the photon
energy, indicating significant spectral variability. The point-to-point
variability amplitude may also track this trend, suggesting that the slopes of
the power spectral density of the source are energy-independent. Using the
normalized excess variance the black hole mass of \pks was estimated to be
about . This is compared and contrasted with the
estimates derived from measurements of the host galaxies.Comment: Accepted for publication in The Astrophysical Journa
Spectroscopy Measurement on an Afterglow Plasma Created by Pulsed Discharges in Liquid Helium
A case of implementing RFID-based real-time shop-floor material management for household electrical appliance manufacturers
Radio Frequency Identification (RFID) technologies provide automatic and accurate object data capturing capability and enable real-time object visibility and traceability. Potential benefits have been widely reported for improving manufacturing shop-floor management. However, reports on how such potentials come true in real-life shop-floor daily operations are very limited. As a result, skeptics overwhelm enthusiasm. This paper contributes to the re-vitalization of RFID efforts in manufacturing industries by presenting a real-life case study of applying RFID for managing material distribution in a complex assembly shop-floor at a large air conditioner manufacturer. The case study discusses how technical, social and organizational issues have been addressed throughout the project within the company. It is hoped that insights and lessons gained be generalized for future efforts across household electrical appliance manufacturers that share similar shop-floor. © 2010 The Author(s).published_or_final_versionSpringer Open Choice, 21 Feb 201
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