4,962 research outputs found
A Multifunctional Processing Board for the Fast Track Trigger of the H1 Experiment
The electron-proton collider HERA is being upgraded to provide higher
luminosity from the end of the year 2001. In order to enhance the selectivity
on exclusive processes a Fast Track Trigger (FTT) with high momentum resolution
is being built for the H1 Collaboration. The FTT will perform a 3-dimensional
reconstruction of curved tracks in a magnetic field of 1.1 Tesla down to 100
MeV in transverse momentum. It is able to reconstruct up to 48 tracks within 23
mus in a high track multiplicity environment. The FTT consists of two hardware
levels L1, L2 and a third software level. Analog signals of 450 wires are
digitized at the first level stage followed by a quick lookup of valid track
segment patterns.
For the main processing tasks at the second level such as linking, fitting
and deciding, a multifunctional processing board has been developed by the ETH
Zurich in collaboration with Supercomputing Systems (Zurich). It integrates a
high-density FPGA (Altera APEX 20K600E) and four floating point DSPs (Texas
Instruments TMS320C6701). This presentation will mainly concentrate on second
trigger level hardware aspects and on the implementation of the algorithms used
for linking and fitting. Emphasis is especially put on the integrated CAM
(content addressable memory) functionality of the FPGA, which is ideally suited
for implementing fast search tasks like track segment linking.Comment: 6 pages, 4 figures, submitted to TN
Evolution of a beam dynamics model for the transport lines in a proton therapy facility
Despite the fact that the first-order beam dynamics models allow an
approximated evaluation of the beam properties, their contribution is essential
during the conceptual design of an accelerator or beamline. However, during the
commissioning some of their limitations appear in the comparison against
measurements. The extension of the linear model to higher order effects is,
therefore, demanded. In this paper, the effects of particle-matter interaction
have been included in the model of the transport lines in the proton therapy
facility at the Paul Scherrer Institut (PSI) in Switzerland. To improve the
performance of the facility, a more precise model was required and has been
developed with the multi-particle open source beam dynamics code called OPAL
(Object oriented Particle Accelerator Library). In OPAL, the Monte Carlo
simulations of Coulomb scattering and energy loss are performed seamless with
the particle tracking. Beside the linear optics, the influence of the passive
elements (e.g. degrader, collimators, scattering foils and air gaps) on the
beam emittance and energy spread can be analysed in the new model. This allows
for a significantly improved precision in the prediction of beam transmission
and beam properties. The accuracy of the OPAL model has been confirmed by
numerous measurements.Comment: 17 pages, 19 figure
Hysteretic clustering in granular gas
Granular material is vibro-fluidized in N=2 and N=3 connected compartments,
respectively. For sufficiently strong shaking the granular gas is
equi-partitioned, but if the shaking intensity is lowered, the gas clusters in
one compartment. The phase transition towards the clustered state is of 2nd
order for N=2 and of 1st order for N=3. In particular, the latter is
hysteretic. The experimental findings are accounted for within a dynamical
model that exactly has the above properties
Kinetics of step bunching during growth: A minimal model
We study a minimal stochastic model of step bunching during growth on a
one-dimensional vicinal surface. The formation of bunches is controlled by the
preferential attachment of atoms to descending steps (inverse Ehrlich-Schwoebel
effect) and the ratio of the attachment rate to the terrace diffusion
coefficient. For generic parameters () the model exhibits a very slow
crossover to a nontrivial asymptotic coarsening exponent .
In the limit of infinitely fast terrace diffusion () linear coarsening
( = 1) is observed instead. The different coarsening behaviors are
related to the fact that bunches attain a finite speed in the limit of large
size when , whereas the speed vanishes with increasing size when .
For an analytic description of the speed and profile of stationary
bunches is developed.Comment: 8 pages, 10 figure
Potential impacts of genetic use restriction technologies (GURTs) on agrobiodiversity and agricultural production systems
Development and application of GURT as an appropriation mechanism may potentially have considerable impact on agriculture, the environment and the food security of rural areas in developing countries. Positive impacts may include increased investments in breeding as a result of increased intellectual property protection. Increased investments may contribute to higher yields and more advanced varieties, and thus to increased food production, a more sustainable production, and better consumer products. Potential negative impacts have been identified as well. These may require further discussion and close attention by regulatory authorities
Poincar\'{e} cycle of a multibox Ehrenfest urn model with directed transport
We propose a generalized Ehrenfest urn model of many urns arranged
periodically along a circle. The evolution of the urn model system is governed
by a directed stochastic operation. Method for solving an -ball, -urn
problem of this model is presented. The evolution of the system is studied in
detail. We find that the average number of balls in a certain urn oscillates
several times before it reaches a stationary value. This behavior seems to be a
peculiar feature of this directed urn model. We also calculate the Poincar\'{e}
cycle, i.e., the average time interval required for the system to return to its
initial configuration. The result can be easily understood by counting the
total number of all possible microstates of the system.Comment: 10 pages revtex file with 7 eps figure
The partially asymmetric zero range process with quenched disorder
We consider the one-dimensional partially asymmetric zero range process where
the hopping rates as well as the easy direction of hopping are random
variables. For this type of disorder there is a condensation phenomena in the
thermodynamic limit: the particles typically occupy one single site and the
fraction of particles outside the condensate is vanishing. We use extreme value
statistics and an asymptotically exact strong disorder renormalization group
method to explore the properties of the steady state. In a finite system of
sites the current vanishes as , where the dynamical exponent,
, is exactly calculated. For the transport is realized by active particles, which move with a constant velocity, whereas for
the transport is due to the anomalous diffusion of a single Brownian
particle. Inactive particles are localized at a second special site and their
number in rare realizations is macroscopic. The average density profile of
inactive particles has a width of, , in terms of the
asymmetry parameter, . In addition to this, we have investigated the
approach to the steady state of the system through a coarsening process and
found that the size of the condensate grows as for large
times. For the unbiased model is formally infinite and the coarsening is
logarithmically slow.Comment: 12 pages, 9 figure
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