105,770 research outputs found
Extended search for point sources of neutrinos below and above the horizon: Covering energies from TeV to EeV with IceCube
Point source searches with neutrino telescopes like IceCube are normally
restricted to one hemisphere, due to the selection of up-going events as a way
of rejecting the atmospheric muon background. In this work we show that the
down-going region above the horizon can be included in the search by
suppressing the background through energy-sensitive selection procedures. This
approach increases the reach to the EeV regime of the signal spectrum, which
was previously not accessible due to the absorption of neutrinos with energies
above a PeV inside the Earth. We present preliminary results of this analysis,
which for the first time includes up-going as well as down-going muon events in
a combined approach. We used data collected with IceCube in a configuration of
22 strings. No significant excess above the atmospheric background is observed.
While other analyses provided results for the Northern hemisphere, this new
approach extends the field of view to a large part of the Southern sky, which
was previously not covered with IceCube.Comment: 4 pages, 1 figure. To be published in the proceedings of the 2nd
Heidelberg workshop "High-Energy Gamma-rays and Neutrinos from Extra-Galactic
Sources", 2009 (Journal of Modern Physics D
Topic Similarity Networks: Visual Analytics for Large Document Sets
We investigate ways in which to improve the interpretability of LDA topic
models by better analyzing and visualizing their outputs. We focus on examining
what we refer to as topic similarity networks: graphs in which nodes represent
latent topics in text collections and links represent similarity among topics.
We describe efficient and effective approaches to both building and labeling
such networks. Visualizations of topic models based on these networks are shown
to be a powerful means of exploring, characterizing, and summarizing large
collections of unstructured text documents. They help to "tease out"
non-obvious connections among different sets of documents and provide insights
into how topics form larger themes. We demonstrate the efficacy and
practicality of these approaches through two case studies: 1) NSF grants for
basic research spanning a 14 year period and 2) the entire English portion of
Wikipedia.Comment: 9 pages; 2014 IEEE International Conference on Big Data (IEEE BigData
2014
Symmetry causes a huge conductance peak in double quantum dots
We predict a huge interference effect contributing to the conductance through
large ultra-clean quantum dots of chaotic shape. When a double-dot structure is
made such that the dots are the mirror-image of each other, constructive
interference can make a tunnel barrier located on the symmetry axis effectively
transparent. We show (via theoretical analysis and numerical simulation) that
this effect can be orders of magnitude larger than the well-known universal
conductance fluctuations and weak-localization (both less than a conductance
quantum). A small magnetic field destroys the effect, massively reducing the
double-dot conductance; thus a magnetic field detector is obtained, with a
similar sensitivity to a SQUID, but requiring no superconductors.Comment: 5pages 3 figures and an appendix ONLY in arXiv versio
- …