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Abstract: This study comprehensively investigates the gamma-ray dim population of Fanaroff–Riley Type 0 (FR0) radio galaxies as potentially significant sources of ultra–high energy cosmic rays (UHECRs, E > 10[sup]18 eV) detected on Earth. While individual FR0 luminosities are relatively low compared to the more powerful Fanaroff–Riley Type 1 and Type 2 galaxies, FR0s are substantially more prevalent in the local universe, outnumbering the more energetic galaxies by a factor of ∼5 within a redshift of z ≤ 0.05. Employing CRPropa3 simulations, we estimate the mass composition and energy spectra of UHECRs originating from FR0 galaxies for energies above 10[sup]18.6 eV. This estimation fits data from the Pierre Auger Observatory (Auger) using three extensive air shower models; both constant and energy-dependent observed elemental fractions are considered. The simulation integrates an approximately isotropic distribution of FR0 galaxies, extrapolated from observed characteristics, with UHECR propagation in the intergalactic medium, incorporating various plausible configurations of extragalactic magnetic fields, both random and structured. We then compare the resulting emission spectral indices, rigidity cutoffs, and elemental fractions with recent Auger results. In total, 25 combined energy-spectrum and mass-composition fits are considered. Beyond the cosmic-ray fluxes emitted by FR0 galaxies, this study predicts the secondary photon and neutrino fluxes from UHECR interactions with intergalactic cosmic photon backgrounds. The multimessenger approach, encompassing observational data and theoretical models, helps elucidate the contribution of low-luminosity FR0 radio galaxies to the total cosmic-ray energy density.
Keywords: ultra-high-energy cosmic rays, UHECRs, UHECR energy spectrum, Pierre Auger Observatory, UHECR mass composition, UHECR sources, extragalactic magnetic fields, UHECR propagation, CRPropa tool
Published in RUNG: 06.01.2025; Views: 621; Downloads: 10
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Abstract: Waste management is a global problem, as waste production continues to rise, and the methods used today, such as landfilling and incineration, can cause many environmental issues. Waste gasification, among other technologies, is a promising alternative since waste is turned into useful energy resources and reduces emissions with the formation of syngas. Thus, this thesis investigated the potential of waste gasification systems in sustainable waste management and circular economy. Focusing on its energy and economic potential, modeling methods were used to recreate real-world systems, with the goal of properly estimating the true sustainability potential of the waste gasification systems. Biomass gasification was evaluated through thorough thermodynamics and economic analysis. Although the initial calculations failed to provide positive results by showing the energy of 54 MJ, instead of the expected energy release, further analysis with the optimized conditions and different assumptions, provided more accurate results. By increasing the share of oxidized CO from 10% to 25%, and reducing the wet material from 35% to 10%, total released heat was estimated to be −148.9 MJ. With the right assumptions, the gasification process was proved to provide good energy values necessary for the sustainability of such a process. Additionally, the financial analysis produced a high Net Present Value (NPV) of EUR 3,434,411.46, Internal Rate of Return (IRR) of 21.81%, and a short payback period (PP) of 4.48 years, hence proving the strong economic potential and financial strength of such technology. Therefore, biomass waste gasification was concluded to be a positive investment opportunity with valuable long-term economic benefits, while still providing good energy balance.
Keywords: waste, gasification, energy, circular economy, emission
Published in RUNG: 18.12.2024; Views: 756; Downloads: 7
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Abstract: Abstract. Characterising the physico-chemical properties of dust-emitting sediments in arid regions is fundamental to understanding the effects of dust on climate and ecosystems. However, knowledge regarding high-latitude dust (HLD) remains limited. This study focuses on analysing the particle size distribution (PSD), mineralogy, cohesion, iron (Fe) mode of occurrence, and visible–near infrared (VNIR) reflectance spectra of dust-emitting sediments from dust hotspots in Iceland (HLD region). Extensive analysis was conducted on samples of top sediments, sediments, and aeolian ripples collected from seven dust sources, with particular emphasis on the Jökulsá basin, encompassing the desert of Dyngjunsandur. Both fully and minimally dispersed PSDs and their respective mass median particle diameters revealed remarkable similarities (56 ± 69 and 55 ± 62 µm, respectively). Mineralogical analyses indicated the prevalence of amorphous phases (68 ± 26 %), feldspars (17 ± 13 %), and pyroxenes (9.3 ± 7.2 %), consistent with thorough analyses of VNIR reflectance spectra. The Fe content reached 9.5 ± 0.40 wt %, predominantly within silicate structures (80 ± 6.3 %), complemented by magnetite (16 ± 5.5 %), hematite/goethite (4.5 ± 2.7 %), and readily exchangeable Fe ions or Fe nano-oxides (1.6 ± 0.63 %). Icelandic top sediments exhibited coarser PSDs compared to the high dust-emitting crusts from mid-latitude arid regions, distinctive mineralogy, and a 3-fold bulk Fe content, with a significant presence of magnetite. The congruence between fully and minimally dispersed PSDs underscores reduced particle aggregation and cohesion of Icelandic top sediments, suggesting that aerodynamic entrainment of dust could also play a role upon emission in this region, alongside saltation bombardment. The extensive analysis in Dyngjusandur enabled the development of a conceptual model to encapsulate Iceland's rapidly evolving high dust-emitting environments.
Keywords: mineral dust, high-latitude dust, Icelandic dust, aerosol particles
Published in RUNG: 29.11.2024; Views: 806; Downloads: 5
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Abstract: The Cherenkov Telescope Array (CTA) will be able to perform unprecedented observations of the transient very high-energy sky. An on-line science alert generation (SAG) pipeline, with a required 30 second latency, will allow the discovery or follow-up of gamma ray bursts (GRBs) and flaring emission from active galactic nuclei, galactic compact objects and electromagnetic counterparts of gravitational waves or neutrino messengers. The CTA sensitivity for very short exposures does not only depend on the technological performance of the array (e.g. effective area, background discrimination efficiency). The algorithms to evaluate the significance of the detection also define the sensitivity, together with their computational efficiency in order to satisfy the SAG latency requirements. We explore the aperture photometry and likelihood analysis techniques, and the associated parameters (e.g. on-source to off-source exposure ratio, minimum number of required signal events), defining the CTA ability to detect a significant signal at short exposures. The resulting CTA differential flux sensitivity as a function of the observing time, obtained using the latest Monte Carlo simulations, is compared to the sensitivities of Fermi–LAT and current-generation IACTs obtained in the overlapping energy ranges.
Keywords: very-high-energy gamma rays, Cherenkov Telescope Array (CTA) Observatory, transient astrophysical sources, gamma-ray bursts, active galactic nuclei
Published in RUNG: 15.11.2024; Views: 884; Downloads: 10
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Abstract: Two of the Key Science Projects of the Cherenkov Telescope Array (CTA) consist in performing a deep survey of the Galactic and Extragalactic sky, providing an unbiased view of the Universe at energies above tens of GeV. To optimize the time spent to perform the Extragalactic survey, a so-called “divergent mode” of the CTA was proposed as an alternative observation strategy to the traditional parallel pointing in order to increase its instantaneous field of view. The search for transient VHE sources would also benefit from an extended field of view. In the divergent mode, each telescope points to a position in the sky that is slightly offset, in the outward direction, from the center of the field of view. In this contribution, we present the first performance estimation from full Monte Carlo simulation of possible CTA divergent mode setups.
Keywords: very-high-energy gamma rays, Cherenkov Telescope Array (CTA) Observatory, CTAO Key Science Projects (KSPs), galactic survey KSP, extragalactic survey KSP
Published in RUNG: 15.11.2024; Views: 872; Downloads: 6
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