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3. The distribution of ultrahigh-energy cosmic rays along the supergalactic plane measured at the Pierre Auger ObservatoryA. Abdul Halim, P. Abreu, M. Aglietta, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, izvirni znanstveni članek Opis: Ultrahigh-energy cosmic rays are known to be mainly of extragalactic origin, and their propagation is limited by energy losses, so their arrival directions are expected to correlate with the large-scale structure of the local Universe. In this work, we investigate the possible presence of intermediate-scale excesses in the flux of the most energetic cosmic rays from the direction of the supergalactic plane region using events with energies above 20 EeV recorded with the surface detector array of the Pierre Auger Observatory up to 2022 December 31, with a total exposure of 135,000 sq. km sr yr. The strongest indication for an excess that we find, with a posttrial significance of 3.1σ, is in the Centaurus region, as in our previous reports, and it extends down to lower energies than previously studied. We do not find any strong hints of excesses from any other region of the supergalactic plane at the same angular scale. In particular, our results do not confirm the reports by the Telescope Array Collaboration of excesses from two regions in the Northern Hemisphere at the edge of the field of view of the Pierre Auger Observatory. With a comparable integrated exposure over these regions, our results there are in good agreement with the expectations from an isotropic distribution.
Ključne besede: ultra-high-energy cosmic rays, UHECR propagation, large-scale structure, UHECR energy losses, UHECR deflections, supergalactic plane region, Centaurus region, Pierre Auger Observatory, Auger surface detector array
Objavljeno v RUNG: 06.05.2025; Ogledov: 547; Prenosov: 5
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4. Mass composition of ultrahigh energy cosmic rays from distribution of their arrival directions with the Telescope ArrayR. U. Abbasi, Y. Abe, T. Abu-Zayyad, M. Allen, Y. Arai, R. Arimura, E. Barcikowski, J. W. Belz, Douglas R. Bergman, Jon Paul Lundquist, 2024, izvirni znanstveni članek Opis: We use a new method to estimate the injected mass composition of ultrahigh cosmic rays (UHECRs) at energies higher than 10 EeV. The method is based on comparison of the energy-dependent distribution of cosmic ray arrival directions as measured by the Telescope Array (TA) experiment with that calculated in a given putative model of UHECR under the assumption that sources trace the large-scale structure (LSS) of the Universe. As we report in the companion Letter, the TA data show large deflections with respect to the LSS which can be explained, assuming small extragalactic magnetic fields (EGMF), by an intermediate composition changing to a heavy one (iron) in the highest energy bin. Here we show that these results are robust to uncertainties in UHECR injection spectra, the energy scale of the experiment and galactic magnetic fields. The assumption of weak EGMF, however, strongly affects this interpretation at all but the highest energies E > 100 EeV, where the remarkable isotropy of the data implies a heavy injected composition even in the case of strong EGMF. This result also holds if UHECR sources are as rare as 2 × 10[sup]−5 Mpc[sup]−3, that is the conservative lower limit for the source number density.
Ključne besede: ultrahigh energy cosmic rays, large-scale structure, extragalactic magnetic fields, UHECR propagation, Telescope Array, UHECR mass composition, UHECR arrival directions
Objavljeno v RUNG: 23.04.2025; Ogledov: 429; Prenosov: 4
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5. Isotropy of Cosmic Rays beyond 10[sup]20 eV Favors Their Heavy Mass CompositionR. U. Abbasi, Jon Paul Lundquist, 2024, izvirni znanstveni članek Opis: We report an estimation of the injected mass composition of ultrahigh energy cosmic rays (UHECRs) at energies higher than 10 EeV. The composition is inferred from an energy-dependent sky distribution of UHECR events observed by the Telescope Array surface detector by comparing it to the Large Scale Structure of the local Universe. In the case of negligible extragalactic magnetic fields (EGMFs), the results are consistent with a relatively heavy injected composition at E ∼ 10 EeV that becomes lighter up to E ∼ 100 EeV, while the composition at E > 100 EeV is very heavy. The latter is true even in the presence of highest experimentally allowed extragalactic magnetic fields, while the composition at lower energies can be light if a strong EGMF is present. The effect of the uncertainty in the galactic magnetic field on these results is subdominant.
Ključne besede: ultrahigh energy cosmic rays (UHECRs), Large Scale Structure, extragalactic magnetic fields, UHECR propagation, Telescope Array surface detector, UHECR mass composition, UHECR arrival directions
Objavljeno v RUNG: 23.04.2025; Ogledov: 448; Prenosov: 4
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6. Mastering the growth of antimonene on ▫$Bi_2Se_3$▫ : strategies and insightsRoberto Flammini, Conor Hogan, Stefano Colonna, Fabio Ronci, Mauro Satta, Marco Papagno, Ziya S. Aliev, Sergey V. Eremeev, Zipporah Rini Benher, Sandra Gardonio, 2025, izvirni znanstveni članek Opis: Antimonene, the two-dimensional phase of antimony, appears in two distinct allotropes when epitaxially grown on Bi2Se3: the puckered asymmetric washboard (α) and buckled honeycomb (β) bilayer structures. As-deposited antimony films exhibit varying proportions of single α and β structures. We identify the conditions necessary for ordered, pure-phase growth of single to triple β-antimonene bilayers. Additionally, we determine their electronic structure, work function, and characteristic core-level binding energies, offering an explanation for the relatively large chemical shifts observed among the different phases. This study not only establishes a protocol for achieving a single β phase of antimonene but also provides key signatures for distinguishing between the different allotropes using standard spectroscopic and microscopic techniques.
Ključne besede: density functional theory, electronic band structure, topological insulators, work functions, scanning tunneling microscopy, atomic structure, antimony, angle-resolved photoemission spectroscopy, core level shifts
Objavljeno v RUNG: 20.03.2025; Ogledov: 1142; Prenosov: 10
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7. Effect of shell thickness on the exchange bias blocking temperature and coercivity in Co-CoO core-shell nanoparticlesSenoy Thomas, K. Reethu, Thanveer Thajudheen, M. T. Z. Myint, S. H. Al-Harthi, 2017, izvirni znanstveni članek Opis: The exchange bias blocking temperature distribution of naturally oxidized Co-CoO core-shell nanoparticles exhibits two distinct signatures. These are associated with the existence of two magnetic entities which are responsible for the temperature dependence of an exchange bias field. One is from the CoO grains which undergo thermally activated magnetization reversal. The other is from the disordered spins at the Co-CoO interface which exhibits spin-glass-like behavior. We investigated the oxide shell thickness dependence of the exchange bias effect. For particles with a 3 nm thick CoO shell, the predominant contribution to the temperature dependence of exchange bias is the interfacial spin-glass layer. On increasing the shell thickness to 4 nm, the contribution from the spin-glass layer decreases, while upholding the antiferromagnetic grain contribution. For samples with a 4 nm CoO shell, the exchange bias training was minimal. On the other hand, 3 nm samples exhibited both the training effect and a peak in coercivity at an intermediate set temperature Ta. This is explained using a magnetic core-shell model including disordered spins at the interface.
Ključne besede: exchange interactions, magnetic ordering, ferromagnetic materials, magnetic materials, polycrystalline material, thin films, nanoparticle, nuclear structure models, oxides, transition metals
Objavljeno v RUNG: 13.12.2024; Ogledov: 1006; Prenosov: 6
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8. Single crystal synthesis and surface electronic structure of Bi_{1.993}Cr_{0.007}Se_{3}Sandra Gardonio, Zipporah Rini Benher, Mattia Fanetti, Paolo Moras, Polina M. Sheverdyaeva, Matjaž Valant, 2024, izvirni znanstveni članek Ključne besede: topological insulators, magnetic atoms, crystal synthesis, formation of clusters, surface electronic structure
Objavljeno v RUNG: 21.08.2024; Ogledov: 2002; Prenosov: 10
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9. From HX-groups to HX-polygroupsSeyed S. Mousavi, Morteza Jafarpour, Irina Elena Cristea, 2023, izvirni znanstveni članek Ključne besede: HX-group, hypercompositional structure, coset, polygroup, regularity, uniformity, essentiality, double coset
Objavljeno v RUNG: 22.12.2023; Ogledov: 3071; Prenosov: 8
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10. Spine-sheath jet model for low-luminosity AGNsMargot Boughelilba, Anita Reimer, Lukas Merten, Jon Paul Lundquist, 2023, objavljeni znanstveni prispevek na konferenci Opis: In several jetted AGNs, structured jets have been observed. In particular spine-sheath configurations
where the jet is radially divided into two or more zones of different flow velocities.
We present a model based on the particle and radiation transport code CR-ENTREES. Here,
interaction rates and secondary particle and photon yields are pre-calculated by Monte Carlo
event generators or semi-analytical approximations. These are then used to create transition
matrices, that describe how each particle spectrum evolves with time. This code allows for
arbitrary injection of primary particles, and the possibility to choose which interaction to include
(photo-meson production, Bethe-Heitler pair-production, inverse-Compton scattering, �-� pair
production, decay of all unstable particles, synchrotron radiation — from electrons, protons, and
all relevant secondaries before their respective decays — and particle escape).
In addition to the particle and radiation interactions taking place in each homogeneous zone, we
implement the feedback between the two zones having different bulk velocities. The main mechanism
at play when particles cross the boundary between the two zones is shear acceleration. We
follow a microscopic description of this acceleration process to create a corresponding transition
matrix and include it in our numerical setup. Furthermore, each zone’s radiation field can be
used as an external target photon field for the other zone’s particle interactions. We present here
the first results of the effect of a two-zone spine-sheath jet, by applying this model to typical
low-luminosity AGNs.
Ključne besede: active galactic nuclei, low-luminosity jetted AGN, spine-sheath jet structure
Objavljeno v RUNG: 24.08.2023; Ogledov: 2430; Prenosov: 5
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