9,541 research outputs found
First Alignment of the Complete CMS Tracker
This conference proceeding presents the first results of the full CMS Tracker
alignment based on several million reconstructed tracks from the cosmic data
taken during the commissioning runs with the detector in its final position and
magnetic field present. The all-silicon design of the CMS Tracker poses new
challenges in aligning a complex system with 15\,148 silicon strip and 1440
silicon pixel modules. For optimal track-parameter resolution, the position and
orientation of its modules need to be determined with a precision of about one
micrometer. The modules, well illuminated by cosmic ray particles, were aligned
using two track-based alignment algorithms in sequence in combination with
survey measurements. The resolution in all five track parameters is controlled
with data-driven validation of the track parameter measurements near the
interaction region, and tested against prediction with detailed detector
simulation. An outlook for the expected tracking performance with the first
proton collisions is given.Comment: To appear in the Proceedings of the 7th International "Hiroshima"
Symposium on the Development and Application of Semiconductor Tracking
Detector
Three-dimensional structure and flexibility of a membrane-coating module of the nuclear pore complex.
The nuclear pore complex mediates nucleocytoplasmic transport in all eukaryotes and is among the largest cellular assemblies of proteins, collectively known as nucleoporins. Nucleoporins are organized into distinct subcomplexes. We optimized the isolation of a putative membrane-coating subcomplex of the nuclear pore complex, the heptameric Nup84 complex, and analyzed its structure by EM. Our data confirmed the previously reported 'Y' shape. We discerned additional structural details, including specific hinge regions at which the particle shows great flexibility. We determined the three-dimensional structures of two conformers, mapped the localization of two nucleoporins within the subcomplex and docked known crystal structures into the EM maps. The free ends of the Y-shaped particle are formed by beta-propellers; the connecting segments consist of alpha-solenoids. Notably, the same organizational principle is found in the clathrin triskelion, which may share a common evolutionary origin with the heptameric complex
Results from the commissioning of the ALICE Inner Tracking System with cosmics
The Inner Tracking System (ITS) is the detector of the ALICE central barrel
located closest to the beam axis and it is therefore a key detector for
tracking and vertexing performance. Here, the main results from the ITS
commissioning with atmospheric muons in 2008 are presented, focusing in
particular on the detector operation and calibration and on the methods
developed for the alignment of the ITS detectors using reconstructed tracks.Comment: 4 pages, 1 figure with 3 panels (=3 separate eps files) To appear in
the conference proceedings for Quark Matter 2009, March 30 - April 4,
Knoxville, Tennesse
Total Hadronic Cross-Section for Photon-Photon Interactions at LEP
The total hadronic cross-section for the interaction of real photons is
extracted from a measurement of the cross-section of the process e+e->e+e- +
hadrons using a luminosity function for the photon flux and form factors for
extrapolating to Q**2=0. The data was taken with the OPAL detector at LEP at
e+e- centre-of-mass energies of 161 GeV and 172 GeV. In the energy range 10 < W
< 110 GeV the total hadronic photon-photon cross-section is consistent with the
Regge behaviour of the total cross-section observed in \gamma p and
hadron-hadron interactions.Comment: 7 pages, 7 figues, needs espcrc2.sty, to be published in proceedings
of the XXVII INTERNATIONAL SYMPOSIUM ON MULTIPARTICLE DYNAMICS, INFN,
Frascati (Rome), Italy, 8-12 September 199
Anticipatory Buffer Control and Quality Selection for Wireless Video Streaming
Video streaming is in high demand by mobile users, as recent studies
indicate. In cellular networks, however, the unreliable wireless channel leads
to two major problems. Poor channel states degrade video quality and interrupt
the playback when a user cannot sufficiently fill its local playout buffer:
buffer underruns occur. In contrast to that, good channel conditions cause
common greedy buffering schemes to pile up very long buffers. Such
over-buffering wastes expensive wireless channel capacity.
To keep buffering in balance, we employ a novel approach. Assuming that we
can predict data rates, we plan the quality and download time of the video
segments ahead. This anticipatory scheduling avoids buffer underruns by
downloading a large number of segments before a channel outage occurs, without
wasting wireless capacity by excessive buffering. We formalize this approach as
an optimization problem and derive practical heuristics for segmented video
streaming protocols (e.g., HLS or MPEG DASH). Simulation results and testbed
measurements show that our solution essentially eliminates playback
interruptions without significantly decreasing video quality
SVD Approach to Data Unfolding
Distributions measured in high energy physics experiments are usually
distorted and/or transformed by various detector effects. A regularization
method for unfolding these distributions is re-formulated in terms of the
Singular Value Decomposition (SVD) of the response matrix. A relatively simple,
yet quite efficient unfolding procedure is explained in detail. The concise
linear algorithm results in a straightforward implementation with full error
propagation, including the complete covariance matrix and its inverse. Several
improvements upon widely used procedures are proposed, and recommendations are
given how to simplify the task by the proper choice of the matrix. Ways of
determining the optimal value of the regularization parameter are suggested and
discussed, and several examples illustrating the use of the method are
presented.Comment: 22 page
- …