1,764 research outputs found
Theoretical study of ionization profiles of molecular clouds near supernova remnants: Tracing the hadronic origin of GeV gamma radiation
Context: Since a few years, signatures of supernova remnants associated with
molecular clouds have been detected in gamma rays. Whether these gamma rays are
generated by cosmic ray electrons or by cosmic ray protons is usually not
known. The detection of hadronic ionization signatures in spatial coincidence
with gamma ray signatures can help to unambiguously identify supernova remnants
as sources of cosmic ray protons.
Methods: In order to calculate hadronic signatures from cosmic ray-induced
ionization for an examination of the origin of the observed gamma rays, the
transport equation for cosmic ray protons propagating in a molecular cloud,
including the relevant momentum loss processes, is solved analytically and the
proton flux at any position in the cloud is determined.
Results: Since the solution of the transport equation is obtained for
arbitrary source functions, it can be used for a variety of supernova remnants.
The corresponding theoretical ionization rate, as a function of the penetration
depth, is derived and compared to photoinduced ionization profiles in a case
study with four supernova remnants associated with molecular clouds. Three of
the remnants show a clear dominance of the hadronically induced ionization
rate, while for one remnant, X-ray emission seems to dominate by a factor of
10.
Conclusions: This is the first derivation of position-dependent profiles for
cosmic ray-induced ionization with an analytic solution for arbitrary cosmic
ray source spectra. The cosmic ray-induced ionization has to be compared to
X-ray ionization for strong X-ray sources. For sources dominated by cosmic
ray-induced ionization (e.g., W49B), the ionization profiles can be used in the
future to map the spatial structure of hadronic gamma rays and
rotation-vibrational lines induced by cosmic ray protons, helping to identify
sources of hadronic cosmic rays.Comment: published in Astronomy and Astrophysics, 20 pages, 17 figure
Which One is Me?: Identifying Oneself on Public Displays
While user representations are extensively used on public displays, it remains unclear how well users can recognize their own representation among those of surrounding users. We study the most widely used representations: abstract objects, skeletons, silhouettes and mirrors. In a prestudy (N=12), we identify five strategies that users follow to recognize themselves on public displays. In a second study (N=19), we quantify the users' recognition time and accuracy with respect to each representation type. Our findings suggest that there is a significant effect of (1) the representation type, (2) the strategies performed by users, and (3) the combination of both on recognition time and accuracy. We discuss the suitability of each representation for different settings and provide specific recommendations as to how user representations should be applied in multi-user scenarios. These recommendations guide practitioners and researchers in selecting the representation that optimizes the most for the deployment's requirements, and for the user strategies that are feasible in that environment
Semi-Supervised Manifold Learning for Hyperspectral Data
There are real world data sets where a linear approximation like the principalcomponents might not capture the intrinsic characteristics of the data. Nonlineardimensionality reduction ormanifoldlearning uses a graph-based approach tomodel the local structure of the data. Manifold learning algorithms assumethat the data resides on a low-dimensional manifold that is embedded in ahigher-dimensional space. For real world data sets this assumption might not beevident. However, using manifold learning for a classification task can reveal abetter performance than using a corresponding procedure that uses the principalcomponents of the data. We show that this is the case for our hyperspectral dataset using the two manifold learning algorithms Laplacian eigenmaps and locallylinear embedding
Ultracold Chemistry and its Reaction Kinetics
We study the reaction kinetics of chemical processes occurring in the
ultracold regime and systematically investigate their dynamics. Quantum
entanglement is found to play a key role in driving an ultracold reaction
towards a dynamical equilibrium. In case of multiple concurrent reactions
Hamiltonian chaos dominates the phase space dynamics in the mean field
approximation.Comment: 15 pages, 5 figure
Accelerating Parametric Probabilistic Verification
We present a novel method for computing reachability probabilities of
parametric discrete-time Markov chains whose transition probabilities are
fractions of polynomials over a set of parameters. Our algorithm is based on
two key ingredients: a graph decomposition into strongly connected subgraphs
combined with a novel factorization strategy for polynomials. Experimental
evaluations show that these approaches can lead to a speed-up of up to several
orders of magnitude in comparison to existing approache
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