10,183 research outputs found
A search for energy-dependence of the Kes 73/1E 1841-045 morphology in GeV
While the Kes 73/1E 1841-045 system had been confirmed as an extended GeV
source, whether its morphology depends on the photon energy or not deserves our
further investigation. Adopting data collected by Fermi Large Area Telescope
(LAT) again, we look into the extensions of this source in three energy bands
individually: 0.3-1 GeV, 1-3 GeV and 3-200 GeV. We find that the 0.3-1 GeV
morphology is point-like and is quite different from those in the other two
bands, although we cannot robustly reject a unified morphology for the whole
LAT band.Comment: Approved for publication in PoS as a proceeding of the 7th
International Fermi Symposium (IFS2017
Investigation and prediction of slug flow characteristics in highly viscous liquid and gas flows in horizontal pipes
Slug flow characteristics in highly viscous liquid and gas flow are studied experimentally in a horizontal pipe with 0.074 m ID and 17 m length. Results of flow regime map, liquid holdup and pressure gradient are discussed and liquid viscosity effects are investigated. Applicable correlations which are developed to predict liquid holdup in slug body for low viscosity flow are assessed with high viscosity liquids. Furthermore, a mechanistic model is developed for predicting the characteristics of slug flows of highly viscous liquid in horizontal pipes. A control volume is drawn around the slug body and slug film in a slug unit. Momentum equations with a momentum source term representing the significant momentum exchange between film zone and slug body are applied. Liquid viscosity effects are considered in closure relations. The mechanistic model is validated by comparing available pressure gradient and mean slug liquid holdup data produced in the present study and those obtained from literature, showing satisfactory capabilities over a large range of liquid viscosity
Fermi Large Area Telescope Observations of the Fast-dimming Crab Nebula in 60-600 MeV
Context: The Crab pulsar and its nebula are the origin of relativistic
electrons which can be observed through their synchrotron and inverse Compton
emission. The transition between synchrotron-dominated and
inverse-Compton-dominated emissions takes place at eV. Aims: The
short-term (weeks to months) flux variability of the synchrotron emission from
the most energetic electrons is investigated with data from ten years of
observations with the Fermi Large Area Telescope (LAT) in the energy range from
60 MeV to 600 MeV. Methods: The off-pulse light-curve has been reconstructed
from phase-resolved data. The corresponding histogram of flux measurements is
used to identify distributions of flux-states and the statistical significance
of a lower-flux component is estimated with dedicated simulations of mock
light-curves. The energy spectra for different flux states are reconstructed.
Results: We confirm the presence of flaring-states which follow a log-normal
flux distribution. Additionally, we discover a low-flux state where the flux
drops to as low as 18.4% of the intermediate-state average flux and stays there
for several weeks. The transition time is observed to be as short as 2 days.
The energy spectrum during the low-flux state resembles the extrapolation of
the inverse-Compton spectrum measured at energies beyond several GeV energy,
implying that the high-energy part of the synchrotron emission is dramatically
depressed. Conclusions: The low-flux state found here and the transition time
of at most 10 days indicate that the bulk (%) of the synchrotron emission
above eV originates in a compact volume with apparent angular size of
. We tentatively infer that
the so-called inner knot feature is the origin of the bulk of the -ray
emission.Comment: Accepted by A&A on 05.05.2020; Original version submitted on
19.09.201
Self-Organization of Balanced Nodes in Random Networks with Transportation Bandwidths
We apply statistical physics to study the task of resource allocation in
random networks with limited bandwidths along the transportation links. The
mean-field approach is applicable when the connectivity is sufficiently high.
It allows us to derive the resource shortage of a node as a well-defined
function of its capacity. For networks with uniformly high connectivity, an
efficient profile of the allocated resources is obtained, which exhibits
features similar to the Maxwell construction. These results have good
agreements with simulations, where nodes self-organize to balance their
shortages, forming extensive clusters of nodes interconnected by unsaturated
links. The deviations from the mean-field analyses show that nodes are likely
to be rich in the locality of gifted neighbors. In scale-free networks, hubs
make sacrifice for enhanced balancing of nodes with low connectivity.Comment: 7 pages, 8 figure
Dynamics underlying Box-office: Movie Competition on Recommender Systems
We introduce a simple model to study movie competition in the recommender
systems. Movies of heterogeneous quality compete against each other through
viewers' reviews and generate interesting dynamics of box-office. By assuming
mean-field interactions between the competing movies, we show that run-away
effect of popularity spreading is triggered by defeating the average review
score, leading to hits in box-office. The average review score thus
characterizes the critical movie quality necessary for transition from
box-office bombs to blockbusters. The major factors affecting the critical
review score are examined. By iterating the mean-field dynamical equations, we
obtain qualitative agreements with simulations and real systems in the
dynamical forms of box-office, revealing the significant role of competition in
understanding box-office dynamics.Comment: 8 pages, 6 figure
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