900 research outputs found
Probing the Structure of Jet Driven Core-Collapse Supernova and Long Gamma Ray Burst Progenitors with High Energy Neutrinos
Times of arrival of high energy neutrinos encode information about their
sources. We demonstrate that the energy-dependence of the onset time of
neutrino emission in advancing relativistic jets can be used to extract
important information about the supernova/gamma-ray burst progenitor structure.
We examine this energy and time dependence for different supernova and
gamma-ray burst progenitors, including red and blue supergiants, helium cores,
Wolf-Rayet stars, and chemically homogeneous stars, with a variety of masses
and metallicities. For choked jets, we calculate the cutoff of observable
neutrino energies depending on the radius at which the jet is stalled. Further,
we exhibit how such energy and time dependence may be used to identify and
differentiate between progenitors, with as few as one or two observed events,
under favorable conditions
Quantum chaos in one dimension?
In this work we investigate the inverse of the celebrated
Bohigas-Giannoni-Schmit conjecture. Using two inversion methods we compute a
one-dimensional potential whose lowest N eigenvalues obey random matrix
statistics. Our numerical results indicate that in the asymptotic limit,
N->infinity, the solution is nowhere differentiable and most probably nowhere
continuous. Thus such a counterexample does not exist.Comment: 7 pages, 10 figures, minor correction, references extende
Embedded error estimation and adaptive step-size control for optimal explicit strong stability preserving Runge--Kutta methods
We construct a family of embedded pairs for optimal strong stability
preserving explicit Runge-Kutta methods of order to be used
to obtain numerical solution of spatially discretized hyperbolic PDEs. In this
construction, the goals include non-defective methods, large region of absolute
stability, and optimal error measurement as defined in [5,19]. The new family
of embedded pairs offer the ability for strong stability preserving (SSP)
methods to adapt by varying the step-size based on the local error estimation
while maintaining their inherent nonlinear stability properties. Through
several numerical experiments, we assess the overall effectiveness in terms of
precision versus work while also taking into consideration accuracy and
stability.Comment: 22 pages, 49 figure
Production of CO-free H2 from formic acid: a comparative study of the catalytic behavior of Pt metals on a carbon support
I detta examensarbete har fokusen varit pÄ att ta fram en design av en tidsaxel och implementera den. Tidsaxeln ska beskriva hÀndelseförloppet av en berÀttelse som anvÀndaren av programmet skrivit. Tidsperioderna sÀtts pÄ en berÀttelsenod, som anvÀndaren skapar i programmet. Programmet Àr ett program som Àr till för att skriva berÀttelser, som jag har skapat. Programmet kallar jag för tillfÀllet MapMyStory. Genom att införa en tidsaxel Àr det tÀnkt att anvÀndaren ska fÄ en bÀttre överblick av berÀttelsen. Och med hjÀlp utav tidsaxeln lÀttare förstÄ berÀttelsens hÀndelseförlopp. Jag beskriver hur designen av tidsaxel tagits fram och hur implementationen Àr gjord, och hur algoritmen för utplaceringen av tidslinjerna fungerar. I rapporten beskriver jag hur jag har arbetat med en nerskalad variant av Scrum. Jag beskriver ocksÄ hur jag har anvÀnt mig utav test driven utveckling för att bekrÀfta den kod som implementerats
Reverse engineering of linking preferences from network restructuring
We provide a method to deduce the preferences governing the restructuring
dynamics of a network from the observed rewiring of the edges. Our approach is
applicable for systems in which the preferences can be formulated in terms of a
single-vertex energy function with f(k) being the contribution of a node of
degree k to the total energy, and the dynamics obeys the detailed balance. The
method is first tested by Monte-Carlo simulations of restructuring graphs with
known energies, then it is used to study variations of real network systems
ranging from the co-authorship network of scientific publications to the asset
graphs of the New York Stock Exchange. The empirical energies obtained from the
restructuring can be described by a universal function f(k) -k ln(k), which is
consistent with and justifies the validity of the preferential attachment rule
proposed for growing networks.Comment: 7 pages, 6 figures, submitted to PR
Technologies for deposition of transition metal oxide thin films: application as functional layers in âSmart windowsâ and photocatalytic systems
Characterization of PLD grown WO3 thin films for gas sensing
Tungsten trioxide (WO3) thin films were grown by pulsed laser deposition (PLD) with the aim to be applied in gas sensors. The films were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and profilometry. To study the gas sensing behavior of these WO3 films, they were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was applied to analyze their gas sensitivity. Synthesis of tetragonal-WO3 films starting from a target with predominantly monoclinic WO3 phase was observed. The films deposited at 300 degrees C presented a surface topology favorable for the sorption properties, consisting of a film matrix with protruding craters/cavities. QCM prototype sensors with such films were tested for NO2 sensing. The PLD grown WO3 thin films show good sensitivity and fast reaction at room temperature, even in as-deposited state. With the presented technology, the manufacturing of QCM gas sensors is simple, fast and cost-effective, and it is also suitable for energy-effective portable equipment for on-line monitoring of environmental changes. (C) 2017 Elsevier B.V. All rights reserved
Directed network modules
A search technique locating network modules, i.e., internally densely
connected groups of nodes in directed networks is introduced by extending the
Clique Percolation Method originally proposed for undirected networks. After
giving a suitable definition for directed modules we investigate their
percolation transition in the Erdos-Renyi graph both analytically and
numerically. We also analyse four real-world directed networks, including
Google's own webpages, an email network, a word association graph and the
transcriptional regulatory network of the yeast Saccharomyces cerevisiae. The
obtained directed modules are validated by additional information available for
the nodes. We find that directed modules of real-world graphs inherently
overlap and the investigated networks can be classified into two major groups
in terms of the overlaps between the modules. Accordingly, in the
word-association network and among Google's webpages the overlaps are likely to
contain in-hubs, whereas the modules in the email and transcriptional
regulatory networks tend to overlap via out-hubs.Comment: 21 pages, 10 figures, version 2: added two paragaph
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