4,210 research outputs found
The experimental determination of tyre model parameters
SUMMARY
This report describes the analysis of a series of experiments on pneumatic tyres
which were designed to test the various hypotheses: regarding the deformed shape of a
tyre during the steering process.
The experiments consisted of several separate tests first described in Ref. 1 and 2.
a) The application of a point lateral force or a moment at one position on the tread band
which is restrained at the centre of the wheel, and the measurement of the resulting
lateral deflection of each point of the tyre perimeter.
b) The application of a uniform force around the tyre perimeter on a hollow cylindrical
former and applying a load at the centre of the wheel.
c) Direct determination of tread band tension by cutting the tread band and bridging the
cut by a dynamometer.
d) Estimation of the bending modulus of the tread band by test on sections cut from the
tread band.
The analysis of the experiments is carried out by first transforming the test results
into a Fourier series and determining the spectral content of the bending line with an
harmonic analysis. Transfer functions of beam and string models are derived and applied
to the test results. A method of considering a three parameter model is described
The GeV-TeV Connection in Galactic gamma-ray sources
Recent observations with atmospheric Cherenkov telescope systems such as
H.E.S.S. and MAGIC have revealed a large number of new sources of
very-high-energy (VHE) gamma-rays from 100 GeV - 100 TeV, mostly concentrated
along the Galactic plane. At lower energies (100 MeV - 10 GeV) the
satellite-based instrument EGRET revealed a population of sources clustering
along the Galactic Plane. Given their adjacent energy bands a systematic
correlation study between the two source catalogues seems appropriate. Here,
the populations of Galactic sources in both energy domains are characterised on
observational as well as on phenomenological grounds. Surprisingly few common
sources are found in terms of positional coincidence and spectral consistency.
These common sources and their potential counterparts and emission mechanisms
will be discussed in detail. In cases of detection only in one energy band, for
the first time consistent upper limits in the other energy band have been
derived. The EGRET upper limits are rather unconstraining due to the
sensitivity mismatch to current VHE instruments. The VHE upper limits put
strong constraints on simple power-law extrapolation of several of the EGRET
spectra and thus strongly suggest cutoffs in the unexplored energy range from
10 GeV - 100 GeV. Physical reasons for the existence of cutoffs and for
differences in the source population at GeV and TeV energies will be discussed.
Finally, predictions will be derived for common GeV - TeV sources for the
upcoming GLAST mission bridging for the first time the energy gap between
current GeV and TeV instruments.Comment: (1) Kavli Institute for Particle Astrophysics and Cosmology (KIPAC),
Stanford, USA (2) Stanford University, W.W. Hansen Experimental Physics Lab
(HEPL) and KIPAC, Stanford, USA (3) ICREA & Institut de Ciencies de l'Espai
(IEEC-CSIC) Campus UAB, Fac. de Ciencies, Barcelona, Spain. (4) School of
Physics and Astronomy, University of Leeds, UK. Paper Submitted to Ap
Monte Carlo Performance Studies of Candidate Sites for the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is the next-generation gamma-ray
observatory with sensitivity in the energy range from 20 GeV to beyond 300 TeV.
CTA is proposed to consist of two arrays of 40-100 imaging atmospheric
Cherenkov telescopes, with one site located in each of the Northern and
Southern Hemispheres. The evaluation process for the candidate sites for CTA is
supported by detailed Monte Carlo simulations, which take different attributes
like site altitude and geomagnetic field configuration into account. In this
contribution we present the comparison of the sensitivity and performance of
the different CTA site candidates for the measurement of very-high energy gamma
rays.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
EDGE: a code to calculate diffusion of cosmic-ray electrons and their gamma-ray emission
The positron excess measured by PAMELA and AMS can only be explained if there
is one or several sources injecting them. Moreover, at the highest energies, it
requires the presence of nearby (hundreds of parsecs) and middle age
(maximum of hundreds of kyr) source. Pulsars, as factories of electrons
and positrons, are one of the proposed candidates to explain the origin of this
excess. To calculate the contribution of these sources to the electron and
positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma
rays to the Earth), a code to treat diffusion of electrons and compute their
diffusion from a central source with a flexible injection spectrum. We can
derive the source's gamma-ray spectrum, spatial extension, the all-electron
density in space and the electron and positron flux reaching the Earth. We
present in this contribution the fundamentals of the code and study how
different parameters affect the gamma-ray spectrum of a source and the electron
flux measured at the Earth.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017),
Bexco, Busan, Kore
Second large-scale Monte Carlo study for the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) represents the next generation of ground
based instruments for Very High Energy gamma-ray astronomy. It is expected to
improve on the sensitivity of current instruments by an order of magnitude and
provide energy coverage from 20 GeV to more than 200 TeV. In order to achieve
these ambitious goals Monte Carlo (MC) simulations play a crucial role, guiding
the design of CTA. Here, results of the second large-scale MC production are
reported, providing a realistic estimation of feasible array candidates for
both Northern and Sourthern Hemisphere sites performance, placing CTA
capabilities into the context of the current generation of High Energy
-ray detectors.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
A Layer-Wise Information Reinforcement Approach to Improve Learning in Deep Belief Networks
With the advent of deep learning, the number of works proposing new methods
or improving existent ones has grown exponentially in the last years. In this
scenario, "very deep" models were emerging, once they were expected to extract
more intrinsic and abstract features while supporting a better performance.
However, such models suffer from the gradient vanishing problem, i.e.,
backpropagation values become too close to zero in their shallower layers,
ultimately causing learning to stagnate. Such an issue was overcome in the
context of convolution neural networks by creating "shortcut connections"
between layers, in a so-called deep residual learning framework. Nonetheless, a
very popular deep learning technique called Deep Belief Network still suffers
from gradient vanishing when dealing with discriminative tasks. Therefore, this
paper proposes the Residual Deep Belief Network, which considers the
information reinforcement layer-by-layer to improve the feature extraction and
knowledge retaining, that support better discriminative performance.
Experiments conducted over three public datasets demonstrate its robustness
concerning the task of binary image classification
Potential Neutrino Signals from Galactic Gamma-Ray Sources
The recent progress made in Galactic gamma-ray astronomy using the High
Energy Stereoskopic System (H.E.S.S.) instrument provides for the first time a
population of Galactic TeV gamma-rays, and hence potential neutrino sources,
for which the neutrino flux can be estimated. Using the energy spectra and
source morphologies measured by H.E.S.S., together with new parameterisations
of pion production and decay in hadronic interactions, we estimate the signal
and background rates expected for these sources in a first-generation water
Cherenkov detector (ANTARES) and a next-generation neutrino telescope in the
Mediterranean Sea, KM3NeT, with an instrumented volume of 1 km^3. We find that
the brightest gamma-ray sources produce neutrino rates above 1 TeV, comparable
to the background from atmospheric neutrinos. The expected event rates of the
brightest sources in the ANTARES detector make a detection unlikely. However,
for a 1 km^3 KM3NeT detector, event rates of a few neutrinos per year from
these sources are expected, and the detection of individual sources seems
possible. Although generally these estimates should be taken as flux upper
limits, we discuss the conditions and type of gamma-ray sources for which the
neutrino flux predictions can be considered robust.Comment: 20 pages, 4 figures; v2: ERROR in energy scale of KM3NeT effective
neutrino area corrected which resulted in event rates being about a factor 3
too low; v3: grammatical changes and update of references after receiving
proof
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