10,154 research outputs found
Comment on: "Transverse-Mass Dependence of Dilepton Emission from Preequilibrium and Quark-Gluon Plasma in High Energy Nucleus-Nucleus Collisions"
In a recent Letter, Geiger presents calculations of the dilepton emission
from the early stage of ultrarelativistic heavy ion collisions using the parton
cascade model (PCM). He shows that the scaling is not observed. In
this Comment, we point out that this is largely due to a defect in the PCM.Comment: 3 pages, LaTex, LBL-3526
Flash of photons from the early stage of heavy-ion collisions
The dynamics of partonic cascades may be an important aspect for particle
production in relativistic collisions of nuclei at CERN SPS and BNL RHIC
energies. Within the Parton-Cascade Model, we estimate the production of single
photons from such cascades due to scattering of quarks and gluons q g -> q
gamma, quark-antiquark annihilation q qbar -> g gamma, or gamma gamma, and from
electromagnetic brems-strahlung of quarks q -> q gamma. We find that the latter
QED branching process plays the dominant role for photon production, similarly
as the QCD branchings q -> q g and g -> g g play a crucial role for parton
multiplication. We conclude therefore that photons accompanying the parton
cascade evolution during the early stage of heavy-ion collisions shed light on
the formation of a partonic plasma.Comment: 4 pages including 3 postscript figure
Fibre DFB lasers in a 4x10 Gbit/s WDM link with a single sinc-sampled fibre grating dispersion compensator
WDM transmission and dispersion compensation at 40 Gbit/s over 200 km standard fibre is demonstrated on a 100 GHz grid using four high power single-polarisation single-sided output DFB fibre laser based transmitters and a single 4 channel WDM chirped fibre Bragg grating dispersion compensator
Parton cascade description of relativistic heavy-ion collisions at CERN SPS energies ?
We examine Pb+Pb collisions at CERN SPS energy 158 A GeV, by employing the
earlier developed and recently refined parton-cascade/cluster-hadronization
model and its Monte Carlo implementation. This space-time model involves the
dynamical interplay of perturbative QCD parton production and evolution, with
non-perturbative parton-cluster formation and hadron production through cluster
decays. Using computer simulations, we are able to follow the entwined
time-evolution of parton and hadron degrees of freedom in both position and
momentum space, from the instant of nuclear overlap to the final yield of
particles. We present and discuss results for the multiplicity distributions,
which agree well with the measured data from the CERN SPS, including those for
K mesons. The transverse momentum distributions of the produced hadrons are
also found to be in good agreement with the preliminary data measured by the
NA49 and the WA98 collaboration for the collision of lead nuclei at the CERN
SPS. The analysis of the time evolution of transverse energy deposited in the
collision zone and the energy density suggests an existence of partonic matter
for a time of more than 5 fm.Comment: 16 pages including 7 postscript figure
Deep Convolutional Neural Networks as strong gravitational lens detectors
Future large-scale surveys with high resolution imaging will provide us with
a few new strong galaxy-scale lenses. These strong lensing systems
however will be contained in large data amounts which are beyond the capacity
of human experts to visually classify in a unbiased way. We present a new
strong gravitational lens finder based on convolutional neural networks (CNNs).
The method was applied to the Strong Lensing challenge organised by the Bologna
Lens Factory. It achieved first and third place respectively on the space-based
data-set and the ground-based data-set. The goal was to find a fully automated
lens finder for ground-based and space-based surveys which minimizes human
inspect. We compare the results of our CNN architecture and three new
variations ("invariant" "views" and "residual") on the simulated data of the
challenge. Each method has been trained separately 5 times on 17 000 simulated
images, cross-validated using 3 000 images and then applied to a 100 000 image
test set. We used two different metrics for evaluation, the area under the
receiver operating characteristic curve (AUC) score and the recall with no
false positive (). For ground based data our
best method achieved an AUC score of and a
of . For space-based data our best
method achieved an AUC score of and a
of . On space-based data adding dihedral invariance to the CNN
architecture diminished the overall score but achieved a higher no
contamination recall. We found that using committees of 5 CNNs produce the best
recall at zero contamination and consistenly score better AUC than a single
CNN. We found that for every variation of our CNN lensfinder, we achieve AUC
scores close to within .Comment: 9 pages, accepted to A&
Stochastic Yield Catastrophes and Robustness in Self-Assembly
A guiding principle in self-assembly is that, for high production yield,
nucleation of structures must be significantly slower than their growth.
However, details of the mechanism that impedes nucleation are broadly
considered irrelevant. Here, we analyze self-assembly into finite-sized target
structures employing mathematical modeling. We investigate two key scenarios to
delay nucleation: (i) by introducing a slow activation step for the assembling
constituents and, (ii) by decreasing the dimerization rate. These scenarios
have widely different characteristics. While the dimerization scenario exhibits
robust behavior, the activation scenario is highly sensitive to demographic
fluctuations. These demographic fluctuations ultimately disfavor growth
compared to nucleation and can suppress yield completely. The occurrence of
this stochastic yield catastrophe does not depend on model details but is
generic as soon as number fluctuations between constituents are taken into
account. On a broader perspective, our results reveal that stochasticity is an
important limiting factor for self-assembly and that the specific
implementation of the nucleation process plays a significant role in
determining the yield
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