77,469 research outputs found
Quantum Annealing Applied to De-Conflicting Optimal Trajectories for Air Traffic Management
We present the mapping of a class of simplified air traffic management (ATM)
problems (strategic conflict resolution) to quadratic unconstrained boolean
optimization (QUBO) problems. The mapping is performed through an original
representation of the conflict-resolution problem in terms of a conflict graph,
where nodes of the graph represent flights and edges represent a potential
conflict between flights. The representation allows a natural decomposition of
a real world instance related to wind-optimal trajectories over the Atlantic
ocean into smaller subproblems, that can be discretized and are amenable to be
programmed in quantum annealers. In the study, we tested the new programming
techniques and we benchmark the hardness of the instances using both classical
solvers and the D-Wave 2X and D-Wave 2000Q quantum chip. The preliminary
results show that for reasonable modeling choices the most challenging
subproblems which are programmable in the current devices are solved to
optimality with 99% of probability within a second of annealing time.Comment: Paper accepted for publication on: IEEE Transactions on Intelligent
Transportation System
Width and size of regular resolution proofs
This paper discusses the topic of the minimum width of a regular resolution
refutation of a set of clauses. The main result shows that there are examples
having small regular resolution refutations, for which any regular refutation
must contain a large clause. This forms a contrast with corresponding results
for general resolution refutations.Comment: The article was reformatted using the style file for Logical Methods
in Computer Scienc
Detecting filaments in the ultra-high energy cosmic ray distribution
We propose and test new statistical tools to study the distribution of cosmic
rays based on the use of the Minimal Spanning Tree. The method described is
particularly sensitive to filamentary structures, as those expected to arise
from strong sources of charged cosmic rays which get deflected by intervening
magnetic fields. We also test the method with data available from the AGASA and
SUGAR surface detector arrays.Comment: minor changes, matching the published version in Astroparticle
Physic
Mapping Topographic Structure in White Matter Pathways with Level Set Trees
Fiber tractography on diffusion imaging data offers rich potential for
describing white matter pathways in the human brain, but characterizing the
spatial organization in these large and complex data sets remains a challenge.
We show that level set trees---which provide a concise representation of the
hierarchical mode structure of probability density functions---offer a
statistically-principled framework for visualizing and analyzing topography in
fiber streamlines. Using diffusion spectrum imaging data collected on
neurologically healthy controls (N=30), we mapped white matter pathways from
the cortex into the striatum using a deterministic tractography algorithm that
estimates fiber bundles as dimensionless streamlines. Level set trees were used
for interactive exploration of patterns in the endpoint distributions of the
mapped fiber tracks and an efficient segmentation of the tracks that has
empirical accuracy comparable to standard nonparametric clustering methods. We
show that level set trees can also be generalized to model pseudo-density
functions in order to analyze a broader array of data types, including entire
fiber streamlines. Finally, resampling methods show the reliability of the
level set tree as a descriptive measure of topographic structure, illustrating
its potential as a statistical descriptor in brain imaging analysis. These
results highlight the broad applicability of level set trees for visualizing
and analyzing high-dimensional data like fiber tractography output
Scientific results of the Bryotrop expedition to Zaire and Rwanda : 3., photosynthetic gas exchange of bryophytes from different forest types in eastern Central Africa.
During the BRYOTROP-Expedition to Zaire and Rwanda bryophytes were collected from a rainforest habitat at 800 m a.s.l. and from bamboo forest and tree-heath environments between 2200 and 3200 m. The microclimates influencing the mosses are different at the altitudinally separated locations. Conditions are rather constant with 24 °C, 100 % rel. hum. and PAR below 100 μmol photons m-2 sec-1 at the lowland station, rather versatile in the mountains with six times higher daily sums of PAR, temperatures between 10 and 25 °C and relative humidities between 60 and 1oo %. In the bamboo forest epiphytic mosses dry out during the day to less than 70 % of their water content, but regain saturation from the vapor-saturated air during night. Bryophyte photosynthesis and respiration were studied by Warburg manometry with moisture saturated samples. Temperature curves of gas exchange peaked between 22 and 30 °C. Optima of the lowland species were somewhat higher than those from samples collected at the mountain sites. Habitat separation of characteristics of photosynthesis was more pronounced with respect to light responses. Saturation gas exchange rates were reached by all species still below 400 μmol photons m-2 sec-1. But the slopes of the curves in the low-light range were distinctly steeper, and the light compensation points smaller in the lowland than in the highland species (compensation points of the former: 3 - 12 μmol photons m-2 sec-1, of the latter: 8 - 20 μmol photons m-2 sec-1). It is emphasized that bryophytes in the rainforest understory experience extremely high ambient C02 concentrations near the floor. This, their low light requirements for photosynthesis, and the permanently optimal temperature and humidity conditions for maximal carbon gain enable them to live successfully, but with less biomass development in this dark and damp environment. By contrast, bryophytes from the bamboo forest and tree-heath environments can utilize light conditions combined with variable temperatures and humidities similarly as species from extratropical vegetation types
Casimir Meets Poisson: Improved Quark/Gluon Discrimination with Counting Observables
Charged track multiplicity is among the most powerful observables for
discriminating quark- from gluon-initiated jets. Despite its utility, it is not
infrared and collinear (IRC) safe, so perturbative calculations are limited to
studying the energy evolution of multiplicity moments. While IRC-safe
observables, like jet mass, are perturbatively calculable, their distributions
often exhibit Casimir scaling, such that their quark/gluon discrimination power
is limited by the ratio of quark to gluon color factors. In this paper, we
introduce new IRC-safe counting observables whose discrimination performance
exceeds that of jet mass and approaches that of track multiplicity. The key
observation is that track multiplicity is approximately Poisson distributed,
with more suppressed tails than the Sudakov peak structure from jet mass. By
using an iterated version of the soft drop jet grooming algorithm, we can
define a "soft drop multiplicity" which is Poisson distributed at
leading-logarithmic accuracy. In addition, we calculate the
next-to-leading-logarithmic corrections to this Poisson structure. If we allow
the soft drop groomer to proceed to the end of the jet branching history, we
can define a collinear-unsafe (but still infrared-safe) counting observable.
Exploiting the universality of the collinear limit, we define generalized
fragmentation functions to study the perturbative energy evolution of
collinear-unsafe multiplicity.Comment: 38+10 pages, 21 figures; v2: discussions added to match JHEP versio
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