20,755 research outputs found
Performance of prototype BTeV silicon pixel detectors in a high energy pion beam
The silicon pixel vertex detector is a key element of the BTeV spectrometer.
Sensors bump-bonded to prototype front-end devices were tested in a high energy
pion beam at Fermilab. The spatial resolution and occupancies as a function of
the pion incident angle were measured for various sensor-readout combinations.
The data are compared with predictions from our Monte Carlo simulation and very
good agreement is found.Comment: 24 pages, 20 figure
Performance of the LHCb vertex locator
The Vertex Locator (VELO) is a silicon microstrip detector that surrounds the proton-proton interaction region in the LHCb experiment. The performance of the detector during the first years of its physics operation is reviewed. The system is operated in vacuum, uses a bi-phase CO2 cooling system, and the sensors are moved to 7 mm from the LHC beam for physics data taking. The performance and stability of these characteristic features of the detector are described, and details of the material budget are given. The calibration of the timing and the data processing algorithms that are implemented in FPGAs are described. The system performance is fully characterised. The sensors have a signal to noise ratio of approximately 20 and a best hit resolution of 4 ÎĽm is achieved at the optimal track angle. The typical detector occupancy for minimum bias events in standard operating conditions in 2011 is around 0.5%, and the detector has less than 1% of faulty strips. The proximity of the detector to the beam means that the inner regions of the n+-on-n sensors have undergone space-charge sign inversion due to radiation damage. The VELO performance parameters that drive the experiment's physics sensitivity are also given. The track finding efficiency of the VELO is typically above 98% and the modules have been aligned to a precision of 1 ÎĽm for translations in the plane transverse to the beam. A primary vertex resolution of 13 ÎĽm in the transverse plane and 71 ÎĽm along the beam axis is achieved for vertices with 25 tracks. An impact parameter resolution of less than 35 ÎĽm is achieved for particles with transverse momentum greater than 1 GeV/c
HLOC: Hints-Based Geolocation Leveraging Multiple Measurement Frameworks
Geographically locating an IP address is of interest for many purposes. There
are two major ways to obtain the location of an IP address: querying commercial
databases or conducting latency measurements. For structural Internet nodes,
such as routers, commercial databases are limited by low accuracy, while
current measurement-based approaches overwhelm users with setup overhead and
scalability issues. In this work we present our system HLOC, aiming to combine
the ease of database use with the accuracy of latency measurements. We evaluate
HLOC on a comprehensive router data set of 1.4M IPv4 and 183k IPv6 routers.
HLOC first extracts location hints from rDNS names, and then conducts
multi-tier latency measurements. Configuration complexity is minimized by using
publicly available large-scale measurement frameworks such as RIPE Atlas. Using
this measurement, we can confirm or disprove the location hints found in domain
names. We publicly release HLOC's ready-to-use source code, enabling
researchers to easily increase geolocation accuracy with minimum overhead.Comment: As published in TMA'17 conference:
http://tma.ifip.org/main-conference
Final report on the evaluation of RRM/CRRM algorithms
Deliverable public del projecte EVERESTThis deliverable provides a definition and a complete evaluation of the RRM/CRRM algorithms selected in D11 and D15, and evolved and refined on an iterative process. The evaluation will be carried out by means of simulations using the simulators provided at D07, and D14.Preprin
Learning Analogies and Semantic Relations
We present an algorithm for learning from unlabeled text, based on the
Vector Space Model (VSM) of information retrieval, that can solve verbal
analogy questions of the kind found in the Scholastic Aptitude Test (SAT).
A verbal analogy has the form A:B::C:D, meaning "A is to B as C is to D";
for example, mason:stone::carpenter:wood. SAT analogy questions provide
a word pair, A:B, and the problem is to select the most analogous word
pair, C:D, from a set of five choices. The VSM algorithm correctly
answers 47% of a collection of 374 college-level analogy questions
(random guessing would yield 20% correct). We motivate this research by
relating it to work in cognitive science and linguistics, and by applying
it to a difficult problem in natural language processing, determining
semantic relations in noun-modifier pairs. The problem is to classify a
noun-modifier pair, such as "laser printer", according to the semantic
relation between the noun (printer) and the modifier (laser). We use a
supervised nearest-neighbour algorithm that assigns a class to a given
noun-modifier pair by finding the most analogous noun-modifier pair in
the training data. With 30 classes of semantic relations, on a collection
of 600 labeled noun-modifier pairs, the learning algorithm attains an F
value of 26.5% (random guessing: 3.3%). With 5 classes of semantic
relations, the F value is 43.2% (random: 20%). The performance is
state-of-the-art for these challenging problems
- …