2,052 research outputs found
The ALICE electromagnetic calorimeter high level triggers
The ALICE (A Large Ion Collider Experiment) detector yields a huge sample of
data from different sub-detectors. On-line data processing is applied to select
and reduce the volume of the stored data. ALICE applies a multi-level hardware
trigger scheme where fast detectors are used to feed a three-level (L0, L1, and
L2) deep chain. The High-Level Trigger (HLT) is a fourth filtering stage
sitting logically between the L2 trigger and the data acquisition event
building. The EMCal detector comprises a large area electromagnetic calorimeter
that extends the momentum measurement of photons and neutral mesons up to
GeV/c, which improves the ALICE capability to perform jet
reconstruction with measurement of the neutral energy component of jets. An
online reconstruction and trigger chain has been developed within the HLT
framework to sharpen the EMCal hardware triggers, by combining the central
barrel tracking information with the shower reconstruction (clusters) in the
calorimeter. In the present report the status and the functionality of the
software components developed for the EMCal HLT online reconstruction and
trigger chain will be discussed, as well as preliminary results from their
commissioning performed during the 2011 LHC running period.Comment: Proceeding for the CHEP 2012 Conferenc
An empirical test for cellular automaton models of traffic flow
Based on a detailed microscopic test scenario motivated by recent empirical
studies of single-vehicle data, several cellular automaton models for traffic
flow are compared. We find three levels of agreement with the empirical data:
1) models that do not reproduce even qualitatively the most important empirical
observations,
2) models that are on a macroscopic level in reasonable agreement with the
empirics, and 3) models that reproduce the empirical data on a microscopic
level as well.
Our results are not only relevant for applications, but also shed new light
on the relevant interactions in traffic flow.Comment: 28 pages, 36 figures, accepted for publication in PR
Fullerene based devices for molecular electronics
We have investigated the electronic properties of a C_60 molecule in between
carbon nanotube leads. This problem has been tackled within a quantum chemical
treatment utilizing a density functional theory-based LCAO approach combined
with the Landauer formalism. Owing to low-dimensionality, electron transport is
very sensitive to the strength and geometry of interfacial bonds. Molecular
contact between interfacial atoms and electrodes gives rise to a complex
conductance dependence on the electron energy exhibiting spectral features of
both the molecule and electrodes. These are attributed to the electronic
structure of the C_60 molecule and to the local density of states of the leads,
respectively.Comment: 4 pages, 2 figures, to appear in Physica
Excitation and relaxation in atom-cluster collisions
Electronic and vibrational degrees of freedom in atom-cluster collisions are
treated simultaneously and self-consistently by combining time-dependent
density functional theory with classical molecular dynamics. The gradual change
of the excitation mechanisms (electronic and vibrational) as well as the
related relaxation phenomena (phase transitions and fragmentation) are studied
in a common framework as a function of the impact energy (eV...MeV). Cluster
"transparency" characterized by practically undisturbed atom-cluster
penetration is predicted to be an important reaction mechanism within a
particular window of impact energies.Comment: RevTeX (4 pages, 4 figures included with epsf
Cellular automata approach to three-phase traffic theory
The cellular automata (CA) approach to traffic modeling is extended to allow
for spatially homogeneous steady state solutions that cover a two dimensional
region in the flow-density plane. Hence these models fulfill a basic postulate
of a three-phase traffic theory proposed by Kerner. This is achieved by a
synchronization distance, within which a vehicle always tries to adjust its
speed to the one of the vehicle in front. In the CA models presented, the
modelling of the free and safe speeds, the slow-to-start rules as well as some
contributions to noise are based on the ideas of the Nagel-Schreckenberg type
modelling. It is shown that the proposed CA models can be very transparent and
still reproduce the two main types of congested patterns (the general pattern
and the synchronized flow pattern) as well as their dependence on the flows
near an on-ramp, in qualitative agreement with the recently developed continuum
version of the three-phase traffic theory [B. S. Kerner and S. L. Klenov. 2002.
J. Phys. A: Math. Gen. 35, L31]. These features are qualitatively different
than in previously considered CA traffic models. The probability of the
breakdown phenomenon (i.e., of the phase transition from free flow to
synchronized flow) as function of the flow rate to the on-ramp and of the flow
rate on the road upstream of the on-ramp is investigated. The capacity drops at
the on-ramp which occur due to the formation of different congested patterns
are calculated.Comment: 55 pages, 24 figure
Calibration of the Particle Density in Cellular-Automaton Models for Traffic Flow
We introduce density dependence of the cell size in cellular-automaton models
for traffic flow, which allows a more precise correspondence between real-world
phenomena and what observed in simulation. Also, we give an explicit
calibration of the particle density particularly for the asymmetric simple
exclusion process with some update rules. We thus find that the present method
is valid in that it reproduces a realistic flow-density diagram.Comment: 2 pages, 2 figure
Intelligent Controlling Simulation of Traffic Flow in a Small City Network
We propose a two dimensional probabilistic cellular automata for the
description of traffic flow in a small city network composed of two
intersections. The traffic in the network is controlled by a set of traffic
lights which can be operated both in fixed-time and a traffic responsive
manner. Vehicular dynamics is simulated and the total delay experienced by the
traffic is evaluated within specified time intervals. We investigate both
decentralized and centralized traffic responsive schemes and in particular
discuss the implementation of the {\it green-wave} strategy. Our investigations
prove that the network delay strongly depends on the signalisation strategy. We
show that in some traffic conditions, the application of the green-wave scheme
may destructively lead to the increment of the global delay.Comment: 8 pages, 10 eps figures, Revte
Optimised Traffic Flow at a Single Intersection: Traffic Responsive signalisation
We propose a stochastic model for the intersection of two urban streets. The
vehicular traffic at the intersection is controlled by a set of traffic lights
which can be operated subject to fix-time as well as traffic adaptive schemes.
Vehicular dynamics is simulated within the framework of the probabilistic
cellular automata and the delay experienced by the traffic at each individual
street is evaluated for specified time intervals. Minimising the total delay of
both streets gives rise to the optimum signalisation of traffic lights. We
propose some traffic responsive signalisation algorithms which are based on the
concept of cut-off queue length and cut-off density.Comment: 10 pages, 11 eps figs, to appear in J. Phys.
Performance of prototypes for the ALICE electromagnetic calorimeter
The performance of prototypes for the ALICE electromagnetic sampling
calorimeter has been studied in test beam measurements at FNAL and CERN. A
array of final design modules showed an energy resolution of about
11% / 1.7 % with a uniformity of the response
to electrons of 1% and a good linearity in the energy range from 10 to 100 GeV.
The electromagnetic shower position resolution was found to be described by 1.5
mm 5.3 mm /. For an electron identification
efficiency of 90% a hadron rejection factor of was obtained.Comment: 10 pages, 10 figure
Criterion for traffic phases in single vehicle data and empirical test of a microscopic three-phase traffic theory
A microscopic criterion for distinguishing synchronized flow and wide moving
jam phases in single vehicle data measured at a single freeway location is
presented. Empirical local congested traffic states in single vehicle data
measured on different days are classified into synchronized flow states and
states consisting of synchronized flow and wide moving jam(s). Then empirical
microscopic characteristics for these different local congested traffic states
are studied. Using these characteristics and empirical spatiotemporal
macroscopic traffic phenomena, an empirical test of a microscopic three-phase
traffic flow theory is performed. Simulations show that the microscopic
criterion and macroscopic spatiotemporal objective criteria lead to the same
identification of the synchronized flow and wide moving jam phases in congested
traffic. It is found that microscopic three-phase traffic models can explain
both microscopic and macroscopic empirical congested pattern features. It is
obtained that microscopic distributions for vehicle speed difference as well as
fundamental diagrams and speed correlation functions can depend on the spatial
co-ordinate considerably. It turns out that microscopic optimal velocity (OV)
functions and time headway distributions are not necessarily qualitatively
different, even if local congested traffic states are qualitatively different.
The reason for this is that important spatiotemporal features of congested
traffic patterns are it lost in these as well as in many other macroscopic and
microscopic traffic characteristics, which are widely used as the empirical
basis for a test of traffic flow models, specifically, cellular automata
traffic flow models.Comment: 27 pages, 16 figure
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