3,803 research outputs found
Constraining the properties of the magnetic turbulence in the Geminga region using HAWC -ray data
Observations of extended gamma-ray emission around Galactic cosmic-ray (CR)
sources can be used as novel probes of interstellar magnetic fields. Using
very-high-energy gamma-ray data from the HAWC Observatory, we place constraints
on the properties of the magnetic turbulence within pc from
Geminga. We inject and propagate individual CR electrons in 3D realizations of
turbulent magnetic fields, calculate the resulting gamma-ray emission, and
compare with HAWC measurements of this region. We find that HAWC data is
compatible with expectations for Kolmogorov or Kraichnan turbulence, and can be
well fitted for reasonable coherence lengths and strengths of the turbulence,
despite implying a CR diffusion coefficient significantly smaller than those
suggested by Galactic CR propagation codes. The best fit is found for a
coherence length pc and a magnetic field strength G, and the preferred value for increases with
. Moreover, the apparent lack of strong asymmetries in the
observed emission allows us to constrain the coherence length to pc in this region.Comment: submitted to MNRA
Constraints on the properties of the turbulent magnetic field around Geminga using HAWC measurements
We place constraints on the properties of the interstellar turbulence that
surrounds Geminga pulsar, using the recent measurements from the HAWC
Observatory in this region. We propagate very-high-energy electrons in
realizations of 3D isotropic Kolmogorov or Kraichnan turbulence, calculate
their gamma-ray emission, and compare with HAWC measurements. We show that the
measurements can be well fitted for both models of the turbulence and for
reasonable values of its strength, , and coherence length, . Our best fits are obtained for G and pc. Furthermore, the absence of strong asymmetries in the observed
emission favours pc.Comment: 6 pages, 3 figures. Submitted to Journal of Physics: Conference
Series. Talk presented at the 26th Extended European Cosmic Ray Symposium,
Barnaul, July 201
Existence of minimal and maximal solutions to first--order differential equations with state--dependent deviated arguments
We prove some new results on existence of solutions to first--order ordinary
differential equations with deviating arguments. Delay differential equations
are included in our general framework, which even allows deviations to depend
on the unknown solutions. Our existence results lean on new definitions of
lower and upper solutions introduced in this paper, and we show with an example
that similar results with the classical definitions are false. We also
introduce an example showing that the problems considered need not have the
least (or the greatest) solution between given lower and upper solutions, but
we can prove that they do have minimal and maximal solutions in the usual
set--theoretic sense. Sufficient conditions for the existence of lower and
upper solutions, with some examples of application, are provided too
A new countermeasure against side-channel attacks based on hardware-software co-design
This paper aims at presenting a new countermeasure against Side-Channel Analysis (SCA) attacks, whose implementation is based on a hardware-software co-design. The hardware architecture consists of a microprocessor, which executes the algorithm using a false key, and a coprocessor that performs several operations that are necessary to retrieve the original text that was encrypted with the real key. The coprocessor hardly affects the power consumption of the device, so that any classical attack based on such power consumption would reveal a false key. Additionally, as the operations carried out by the coprocessor are performed in parallel with the microprocessor, the execution time devoted for encrypting a specific text is not affected by the proposed countermeasure. In order to verify the correctness of our proposal, the system was implemented on a Virtex 5 FPGA. Different SCA attacks were performed on several functions of AES algorithm. Experimental results show in all cases that the system is effectively protected by revealing a false encryption key.Peer ReviewedPreprin
Hardware architecture implemented on FPGA for protecting cryptographic keys against side-channel attacks
This paper presents a new hardware architecture designed for protecting the key of cryptographic algorithms against attacks by side-channel analysis (SCA). Unlike previous approaches already published, the fortress of the proposed architecture is based on revealing a false key. Such a false key is obtained when the leakage information, related to either the power consumption or the electromagnetic radiation (EM) emitted by the hardware device, is analysed by means of a classical statistical method. In fact, the trace of power consumption (or the EM) does not reveal any significant sign of protection in its behaviour or shape. Experimental results were obtained by using a Virtex 5 FPGA, on which a 128-bit version of the standard AES encryption algorithm was implemented. The architecture could easily be extrapolated to an ASIC device based on standard cell libraries. The system is capable of concealing the real key when various attacks are performed on the AES algorithm, using two statistical methods which are based on correlation, the Welch’s t-test and the difference of means.Peer ReviewedPostprint (author's final draft
The retrieval of moving images at Spanish film archives: the oversight of content analysis
In the field of library and information science, content analysis is a crucial task for an effective retrieval of information by users at an archive. In this research, we analyse the current state of this task and the possibilities of retrieval of film information at six Spanish important film archives, interviewing their responsible librarians for film cataloguing and comparing the content fields inside their film cataloguing records used by each one of these six organizations
Baseline Design for a Next Generation Wide-Field-of-View Very-High-Energy Gamma-Ray Observatory
The TeV gamma ray sky is observable by recording footprints of extensive air
showers with an array of particle detectors. In the northern hemisphere there
are currently two projects employing this technique: The HAWC gamma ray
observatory which is currently operational in Mexico and LHAASO in the Sichuan
region in China which is currently under development. In the southern
hemisphere several efforts are currently ongoing to investigate the feasibility
of a similar observatory at very high altitude sites in the Andes. The science
case for such an observatory should be complementary to the science to be
performed by the future Cherenkov Telescope Array. There are two clear
directions in which such an observatory could optimize its performance.
Firstly, optimize the performance of sub-TeV energies. This is especially
important to provide an unbiased monitoring of a large fraction of the sky for
observations of transient and extended sources. Secondly, to obtain the largest
photon statistics above roughly 50 TeV, which requires a large collection area
with sufficient performance in angular and energy resolution. This would enable
to extend spectral measurements of Galactic sources and gives the opportunity
to search for dark matter and exotic physics in a new energy range. Using
simulated air showers and a generalized detector description the performance of
a conceptual observatory is studied and the ways to optimize it will be
discussed. With this approach the baseline design of such an observatory can be
obtained without the need of detailed simulations of the detector hardware.Comment: Proceeding if the 35th International Cosmic Ray Conferenc
Characteristics of extensive air showers around the energy threshold for ground-particle-based gamma-ray observatories
Very high energy gamma-ray astronomy based on the measurement of air shower
particles at ground-level has only recently been established as a viable
approach, complementing the well established air Cherenkov technique. This
approach requires high (mountain) altitudes and very high surface coverage
particle detectors. While in general the properties of air showers are well
established for many decades, the extreme situation of ground-level detection
of very small showers from low energy primaries has not yet been well
characterised for the purposes of gamma-ray astronomy. Here we attempt such a
characterisation, with the aim of supporting the optimisation of
next-generation gamma-ray observatories based on this technique. We address all
of the key ground level observables and provide parameterisations for use in
detector optimisation for shower energies around 1 TeV. We emphasise two
primary aspects: the need for large area detectors to effectively measure
low-energy showers, and the importance of muon identification for the purpose
of background rejection.Comment: This is a pre-print of an article published in EPJC. The final
authenticated version is available online at:
https://doi.org/10.1140/epjc/s10052-019-6942-
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