3,120 research outputs found
Cherenkov telescope array extragalactic survey discovery potential and the impact of axion-like particles and secondary gamma rays
The Cherenkov Telescope Array (CTA) is about to enter construction phase and
one of its main key science projects is to perform an unbiased survey in search
of extragalactic sources. We make use of both the latest blazar gamma--ray
luminosity function and spectral energy distribution to derive the expected
number of detectable sources for both the planned Northern and Southern arrays
of the CTA observatory. We find that a shallow, wide survey of about 0.5 hour
per field of view would lead to the highest number of blazar detections.
Furthermore, we investigate the effect of axion-like particles and secondary
gamma rays from propagating cosmic rays on the source count distribution, since
these processes predict different spectral shape from standard extragalactic
background light attenuation. We can generally expect more distant objects in
the secondary gamma-ray scenario, while axion-like particles do not
significantly alter the expected distribution. Yet, we find that, these results
strongly depend on the assumed magnetic field strength during the propagation.
We also provide source count predictions for the High Altitude Water Cherenkov
observatory (HAWC), the Large High Altitude Air Shower Observatory (LHAASO) and
a novel proposal of a hybrid detector.Comment: 16 pages, 4 figures, ApJ 2017 in pres
Unexpected Event Prediction in Wire Electrical Discharge Machining Using Deep Learning Techniques
Theoretical models of manufacturing processes provide a valuable insight into physical phenomena but their application to practical industrial situations is sometimes difficult. In the context of Industry 4.0, artificial intelligence techniques can provide efficient solutions to actual manufacturing problems when big data are available. Within the field of artificial intelligence, the use of deep learning is growing exponentially in solving many problems related to information and communication technologies (ICTs) but it still remains scarce or even rare in the field of manufacturing. In this work, deep learning is used to efficiently predict unexpected events in wire electrical discharge machining (WEDM), an advanced machining process largely used for aerospace components. The occurrence of an unexpected event, namely the change of thickness of the machined part, can be effectively predicted by recognizing hidden patterns from process signals. Based on WEDM experiments, different deep learning architectures were tested. By using a combination of a convolutional layer with gated recurrent units, thickness variation in the machined component could be predicted in 97.4% of cases, at least 2 mm in advance, which is extremely fast, acting before the process has degraded. New possibilities of deep learning for high-performance machine tools must be examined in the near future.The authors gratefully acknowledge the funding support received from the Spanish Ministry of Economy and Competitiveness and the FEDER operation program for funding the project "Scientific models and machine-tool advanced sensing techniques for efficient machining of precision components of Low Pressure Turbines" (DPI2017-82239-P) and UPV/EHU (UFI 11/29). The authors would also like to thank Euskampus and ONA-EDM for their support in this project
Axion searches with Fermi and IACTs
Axion Like Particles (ALPs), postulated to solve the strong-CP problem, are
predicted to couple with photons in the presence of magnetic fields, which may
lead to a significant change in the observed spectra of gamma-ray sources such
as AGNs. Here we simultaneously consider in the same framework both the
photon/axion mixing that takes place in the gamma-ray source and that one
expected to occur in the intergalactic magnetic fields. We show that
photon/axion mixing could explain recent puzzles regarding the observed spectra
of distant gamma-ray sources as well as the recently published lower limit to
the EBL intensity. We finally summarize the different signatures expected and
discuss the best strategy to search for ALPs with the Fermi satellite and
current Cherenkov telescopes like CANGAROO, HESS, MAGIC and VERITAS.Comment: 4 pages, 4 figures. To appear in the proceedings of the "2nd Roma
International Conference on Astroparticle Physics", Villa Mondragone, Rome,
Italy, May 13-15 200
Constraints to dark matter annihilation from high-latitude hawc unidentified sources
The ΛCDM cosmological framework predicts the existence of thousands of subhalos in
our own Galaxy not massive enough to retain baryons and become visible. Yet, some of them may
outshine in gamma rays provided that the dark matter is made of weakly interacting massive particles
(WIMPs), which would self-annihilate and would appear as unidentified gamma-ray sources (unIDs)
in gamma-ray catalogs. Indeed, unIDs have proven to be competitive targets for dark matter searches
with gamma rays. In this work, we focus on the three high-latitude (|b| ≥ 10) sources present
in the 2HWC catalog of the High Altitude Water Cherenkov (HAWC) observatory with no clear
associations at other wavelengths. Indeed, only one of these sources, 2HWC J1040+308, is found to
be above the HAWC detection threshold when considering 760 days of data, i.e., a factor 1.5 more
exposure time than in the original 2HWC catalog. Other gamma-ray instruments, such as Fermi-LAT
or VERITAS at lower energies, do not detect the source. Also, this unID is reported as spatially
extended, making it even more interesting in a dark matter search context. While waiting for more
data that may shed further light on the nature of this source, we set competitive upper limits on the
annihilation cross section by comparing this HAWC unID to expectations based on state-of-the-art
N-body cosmological simulations of the Galactic subhalo population. We find these constraints to be
particularly competitive for heavy WIMPs, i.e., masses above ∼25 (40) TeV in the case of the b
¯b (τ
+Ï„
−)
annihilation channel, reaching velocity-averaged cross section values of 2 × 10−25 (5 × 10−25) cm3
·s
−1
.
Although far from testing the thermal relic cross section value, the obtained limits are independent
and nicely complementary to those from radically different DM analyses and targets, demonstrating
once again the high potential of this DM search approachJ.C.-B. and M.A.S.-C. are supported by the Atracción de Talento contract no. 2016-T1/TIC-1542
granted by the Comunidad de Madrid in Spain, by the Spanish Agencia Estatal de Investigación through
the grants PGC2018-095161-B-I00, IFT Centro de Excelencia Severo Ochoa SEV-2016-0597, and Red Consolider MultiDark FPA2017-90566-RED
The viability of low-mass subhaloes as targets for gamma-ray dark matter searches
In this work, we investigate the discovery potential of low-mass Galactic
dark matter (DM) subhaloes for indirect searches of DM. We use data from the
Via Lactea II (VL-II) N-body cosmological simulation, which resolves subhaloes
down to solar masses and it is thus ideal for this purpose.
First, we characterize the abundance, distribution and structural properties of
the VL-II subhalo population in terms of both subhalo masses and maximum
circular velocities. Then, we repopulate the original simulation with millions
of subhaloes of masses down to about five orders of magnitude below the minimum
VL-II subhalo mass (more than one order of magnitude in velocities). We compute
subhalo DM annihilation astrophysical "J-factors" and angular sizes for the
entire subhalo population, by placing the Earth at a random position but at the
right galactocentric distance in the simulation. Thousands of these
realizations are generated in order to obtain statistically meaningful results.
We find that some nearby low-mass Galactic subhaloes, not massive enough to
retain stars or gas, may indeed yield DM annihilation fluxes comparable to
those expected from other, more massive and acknowledgeable DM targets like
dwarf satellite galaxies. Typical angular sizes are of the order of the degree,
thus subhaloes potentially appearing as extended sources in gamma-ray
telescopes, depending on instrument angular resolution and sensitivity. Our
work shows that low-mass Galactic subhaloes with no visible counterparts are
expected to play a relevant role in current and future indirect DM search
searches and should indeed be considered as excellent DM targets.Comment: 15 pages, 15 figures. Submitted to MNRAS. Comments welcome
Evidence of spin disorder at the surface–core interface of oxygen passivated Fe nanoparticles
Hysteresis, thermal dependence of magnetization, and coercivity of oxide coated ultrafine Fe
particles prepared by inert gas condensation and oxygen passivation have been studied in the 5–300
K range. The results are found to be consistent with a spin-glasslike state of the oxide layer
inducing, through exchange interaction with the ferromagnetic core, a shift of the field cooled
hysteresis loops at temperatures below the freezing at approximately 50 K.Dirección General de Investigación y Desarrollo. Gobierno de España-CICYT MAT95- 1042-C02-02Dirección General de Investigación y Desarrollo. Gobierno de España-PB96-0863-C02-02.Comisión Europea-ERBFMBI-CT95-0534
Implementación del cà lculo de polinomios zonales y aplicaciones en análisis multivariante
En este trabajo se describe la implementación de un algoritmo para el cálculo de polinomios zonales, asà como dos aplicaciones explÃcitas de éstos en el ámbito del análisis multivariante. Concretamente, esta implementación permite obtener resultados de sumación aproximados para funciones hipergeométricas de argumento matricial que, a su vez, pueden utilizarse en la génesis de distribuciones multivariantes discretas con frecuencias simétricas. De igual forma, se pone en práctica un conocido resultado teórico que caracteriza la distribución de la menor raÃz caracterÃstica de una matriz aleatoria con distribución de Wishart
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