13,953 research outputs found
Techniques, based on extremal subspaces, for improved reconstruction of signals from samples
Extremal subspaces techniques for reconstruction of signal from sample
Higher-order contributions and non-perturbative effects in the non-degenerate nonlinear optical absorption of direct-gap semiconductors
The semiconductor Bloch equations for a two-band model including inter- and
intraband excitation are used to study the nonlinear absorption of single and
multiple light pulses by direct-gap semiconductors. For a consistent analysis
the contributions to the absorption originating from both the interband
polarization and the intraband current need to be included. In the Bloch
equation approach theses contributions as well as different excitation pathways
in terms of sequences of inter- and intraband excitations can be evaluated
separately which allows for a transparent analysis, the identification of the
dominant terms, and analyzing their dependence on the excitation conditions. In
the perturbative regime, we obtain analytical expressions for the multi-photon
absorption coefficients for continuous-wave excitation. These results are shown
to agree well with numerical results for short pulses and/or finite dephasing
and relaxation times and we confirm the previously predicted strong enhancement
of two-photon absorption for non-degenerate conditions for pulsed excitation.
We discuss the dependencies on the light frequencies, initial band populations,
and the time delay between the pulses. The frequency dependence of the
two-photon absorption coefficient for non-degenerate excitation is evaluated
perturbatively in third-order. The higher-order contributions to the optical
absorption include three- and four-photon absorption and show a rich frequency
dependence including negative regions and dispersive lineshapes.
Non-perturbative solutions of the Bloch equations demonstrate a strongly
non-monotonous behavior of the intensity-dependent optical absorption for a
single incident pulse and in a pump-probe set-up
Building CMS Pixel Barrel Detectur Modules
For the barrel part of the CMS pixel tracker about 800 silicon pixel detector
modules are required. The modules are bump bonded, assembled and tested at the
Paul Scherrer Institute. This article describes the experience acquired during
the assembly of the first ~200 modules.Comment: 5 pages, 7 figures, Vertex200
Qualification Procedures of the CMS Pixel Barrel Modules
The CMS pixel barrel system will consist of three layers built of about 800
modules. One module contains 66560 readout channels and the full pixel barrel
system about 48 million channels. It is mandatory to test each channel for
functionality, noise level, trimming mechanism, and bump bonding quality.
Different methods to determine the bump bonding yield with electrical
measurements have been developed. Measurements of several operational
parameters are also included in the qualification procedure. Among them are
pixel noise, gains and pedestals. Test and qualification procedures of the
pixel barrel modules are described and some results are presented.Comment: 7 Pages, 7 Figures. Contribution to Pixel 2005, September 5-8, 2005,
Bonn, Germna
Nuclear magnetic resonance measurements reveal the origin of the Debye process in monohydroxy alcohols
Monohydroxy alcohols show a structural relaxation and at longer time scales a
Debye-type dielectric peak. From spin-lattice relaxation experiments using
different nuclear probes an intermediate, slower-than-structural dynamics is
identified for n-butanol. Based on these findings and on diffusion
measurements, a model of self-restructuring, transient chains is proposed. The
model is demonstrated to explain consistently the so far puzzling observations
made for this class of hydrogen-bonded glass forming liquids.Comment: 4 pages, 4 figure
A quasi-periodic oscillation in the blazar J1359+4011
The OVRO 40-m telescope has been monitoring the 15 GHz radio flux density of
over 1200 blazars since 2008. The 15 GHz light curve of the flat spectrum radio
quasar J1359+4011 shows a strong and persistent quasi-periodic oscillation. The
time-scale of the oscillation varies between 120 and 150 days over a
year time span. We interpret this as the active galactic nucleus mass-scaled
analog of low-frequency quasi-periodic oscillations from Galactic microquasars,
or as evidence of modulation of the accretion flow by thermal instabilites in
the "inner" accretion disc.Comment: 4 pages, 2 figures, 1 table. Accepted for publication in MNRAS
Letter
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